r/EPA
United Slates
Environmental Protection
Agency
Environmental Monisoring
Systems Laboratory
Research Triangle Park NC 27711
EPA/600/4-82-042b
Revised
July 1986
Research and Development
Operations and
Maintenance
Manual for
Precipitation
Measurement Systems
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EPA/600/4-82/042b
Revised
Julv 1986
Operations and Maintenance Manual
for
Precipitation Measurement Systems
By
I.E. Topol and S. Ozdemir
Environmental Monitoring and Services, Inc.
A Subsidiary of Combustion Engineering
Newbury Park, California 91320
Contract No 68-02-4125
July I 986
Berne I. Bennett, Project Officer
Performance Evaluation Branch
Quality Assurance Division
Research Triangle Park, North Carolina 27711
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Environmental Monitoring Systems Laboratory
Research Triangle Park, North Carolina 27711
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NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
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FOREWORD
Measurement and monitoring research efforts are designed to anticipate
potential environmental problems, to support regulatory actions by
developing an in-depth understanding of the nature and processes that
impact health and the ecology, to provide innovative means of monitoring
compliance with regulations and to evaluate the effectiveness of health
and environmental protection efforts through the monitoring of long-term
trends. The Environmental Monitoring Systems Laboratory, Research
Triangle Park, North Carolina, is responsible for development of:
environmental monitoring technology and systems; agency-wide quality
assurance programs for air pollution measurement systems; and technical
support to EPA's Office of Air, Noise and Radiation, Office of Toxic
Substances, and Office of Enforcement. This manual has been developed to
assist agencies which plan to make precipitation measurements. The
standard operating procedures in this manual currently are EPA's
recommended methods for precipitation monitoring. This manual, when used
with the Quality Assurance Manual for Precipitation Measurement Systems,
should be the basis for planning a precipitation monitoring effort.
John C. Puzak, Acting Director
Environmental Monitoring Systems Laboratory
Office of Research and Development
in
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ACKNOWLEDGMENT
This report was prepared for the Environmental Monitoring Systems
Laboratory, Research Triangle Park, North Carolina, under the direction
of the Project Officer, Berne I. Bennett. Material in this manual is
based on current EPA quality assurance procedures, air and water
monitoring methodology, and procedures employed in the Electric Power
Research Institute (EPRI) Acid Precipitation Study, the National
Atmospheric Deposition Program (NADP), and the Multi-State Atmospheric
Power Production Pollution Study (MAP3S). The authors wish to extend
grateful appreciation to the contributions of the staff at Environmental
Monitoring & Services, Inc. Newbury Park, California, and the many
reviewers of the drafts of this document.
IV
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ABSTRACT
This manual presents techniques and procedures for field and laboratory
operations associated with precipitation monitoring and analysis. The
analyses given are those approved by the U.S. Environmental Protection
Agency for acid precipitation. The methodology described will provid
guidance for personnel and will maximize the quality as well as the
quantity of data collected.
e
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CONTENTS
Section No. Contents
Revision No. 1
Date July 31, 1986
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Section
INTRODUCTION
1.1 COLLECTION SITES
1.2 PARAMETERS AND ANALYTES GENERALLY
MEASURED
1.3 SAMPLING PERIODS, DEFINITION OF EVENT
1.4 REFERENCES
FIELD OPERATIONS
2.1 EQUIPMENT AND SUPPLIES
2.1.1 Station Supplies
2.1.2 Spare Parts
2.1.3 Precipitation Collector
Description
2.1.4 Rain Gauge Description
2.2 INSTALLATION AND ACCEPTANCE TESTS
2.2.1 Precipitation Collector
2.2.1.1 Installation
2.2.1.2 Acceptance Tests
2.2.2 Rain Gauge
2.2.2.1 Installation
2.2.2.2 Acceptance Tests
2.3 EQUIPMENT CHECKS, MAINTENANCE AND
TROUBLESHOOTING
2.3.1 Precipitation Collector
2.3.1.1 Routine Checks
2.3.1.2 Special Calibration/
Maintenance
2.3.1.3 Winter Maintenance
2.3.2 Weighing Bucket Rain Gauge
2.3.2.1 Routine Checks
2.3.2.2 Calibrations
2.3.2.3 Winter Maintenance
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CONTENTS (Continued)
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2.4 SAMPLE COLLECTION AND HANDLING
2.4.1 Avoiding Contamination
2.4.2 Sampling Schedules
2.4.3 Collection and Handling
Procedures
2.4.3.1 Wet Buckets
2.4.3.2 Plastic Bag Liners
2.4.3.3 Bottles
2.5 FIELD MEASUREMENTS
2.5.1 Weighing Sample Containers
2.5.1.1 Balance Specifications
2.5.1.2 Procedure
2.5.2 Specific Conductance Measurement
2.5.2.1 Apparatus Requirements
2.5.2.2 Procedure
2.5.2.3 Conductivity Measurement
Problems and Tests
2.5.3 pH Measurement
2.5.3.1 Apparatus and Equipment
2.5.3.2 Procedure
2.5.3.3 Electrode Problems
and Tests
2.5.4 Temperature
2.5.4.1 Requirements
2.5.4.2 Procedure
2.6 SAMPLE IDENTIFICATION, PRESERVATION,
STORAGE, AND SHIPMENT
2.6.1 Background
2.6.2 Procedure
2.6.2.1 Weekly Cumulative
Samples
2.6.2.2 Daily, Event or
Sequential Samples
2..6. 3 Field Blanks
2.6.3.1 Buckets
2.6.3.2 Bottles
2.7 DOCUMENTATION
2.7.1 Logbook
2.7.2 Rain Gauge Charts
2.7.3 Field Data Forms
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CONTENTS (Continued)
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Date July 31, 1986
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Section
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2.8 QUALITY CONTROL
2.8.1 Unknown or Quality Control Test
Samples for the Field
2.8.2 Site Visits/Audits
2.8.3 Blind Samples for the Laboratory
2.9 FIELD PROCEDURE SUMMARY
2.10 REFERENCES
CENTRAL LABORATORY SUPPORT OPERATIONS
FOR THE FIELD
3.1 CLEANING AND SUPPLYING OF GLASSWARE
AND PLASTICWARE
3.1.1 Cleaning of New or Used
Plasticware
3.1.2 Cleaning of Glassware
3.1.2.1 Glassware Used for
Metal Analyses
3.1.2.2 Glassware Used for
Anions and NH,
3.1.3 Supplying Containers to the Field
3.2 PREPARATION OF STANDARDS FOR THE FIELD
3.2.1 Preparation and Measurement of
Conductivity Standards
3.2.2 Preparation and Measurement of
pH Reference Solution
3.2.3 Preparation of Quality Control
Samples
3.3 INITIAL EVALUATION OF FIELD EQUIPMENT
3.3.1 Evaluation of Conductivity
Meters and Cells
3.3.1.1 Evaluation of Accuracy
and Precision of Meter
3.3.1.2 Evaluation of Linearity
of Meter
3.3.2 Evaluation of pH Meters
3.3.3 Evaluation of pH Electrodes
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CONTENTS (Continued)
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Section
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3.3.4 Evaluation of Field Balance
and Thermometers
3.4 MONITORING OF FIELD OPERATION
3.4.1 Evaluation of Field Conductivity
and pH Measurement Systems
3.4.2 Evaluation of Field Precipita-
tion Collector, Rain Gauge, and
Balance
3.5 REPORT FORMS
3.6 REFERENCES
LABORATORY PROCEDURES
4.1 GRAVIMETRIC MEASUREMENTS
4.1.1 Apparatus
4.1.2 Calibration
4.1.3 Procedure
4.2 PH MEASUREMENT
4.3 CONDUCTANCE MEASUREMENT
4.4 SAMPLE FILTRATION
4.5 ACIDITY MEASUREMENTS
4.6 DETERMINATION OF SULFATE
4.7 DETERMINATION OF NITRATE
4.8 DETERMINATION OF CHLORIDE
4.9 DETERMINATION OF ORTHOPHOSPHATE
4.10 DETERMINATION OF FLUORIDE
4.11' DETERMINATION OF AMMONIUM
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CONTENTS (Continued)
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Revision No. 1
Date July 31, 1986
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Section
4.12 DETERMINATION OF SODIUM, POTASSIUM,
MAGNESIUM AND CALCIUM
4.13 REFERENCE
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APPENDICES
A. Aerochem Metrics Precipitation Collector A-l
Maintenance Manual
B. Instruction Book for Universal Recording Rain B-l
Gauge
C. Method 150.6 — pH of Wet Deposition by C-l
Electrometric Determination
D. Method 120.6 — Specific Conductance in Wet D-l
Deposition by Electrolytic Determination
E. Method 305.6 — Acidity in Wet Deposition by E-l
Titrimetric Determination
Method 305.2 — Acidity (Titrimetric)
F. Method 300.6 — Chloride, Orthophosphate, F-l
Nitrate and Sulfate in Wet Deposition by
Chemically Suppressed Ion Chromatography
Method 300.7 — Dissolved Sodium, Ammonium,
Potassium, Magnesium, and Calcium in Wet
Deposition by Chemically Suppressed Ion
Chromatography
G. Method 375.6 — Sulfate in Wet Deposition by G-l
Automated Colorimetric Determination Using
Barium-Methylthymol Blue
H. Method 353.6 — Nitrate-Nitrite in Wet Deposition H-l
by Automated Colorimetric Determination Using
Cadmium Reduction
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CONTENTS (Continued)
Section
APPENDICES
Section No. Contents
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Pa*
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I. Method 325.6 — Chloride in Wet Deposition by 1-1
Automated Colorimetric Determination Using
Thiocyanate
J. Method 365.6 — Orthophosphate in Wet Deposition J-l
by Automated Colorimetric Determination Using
Ascorbic Acid Reduction
K. Method 340.6 -- Fluoride in Wet Deposition by K-l
Potentiometric Determination Using an Ion-
Selective Electrode
L. Method 350.6 — Ammonium in Wet Deposition by L-l
Electrometric Determination Using Ion-Selective
Electrode
Method 350.7 — Ammonium in Wet Deposition by
Automated Colorimetric Determination with Phenate
M. Method 200.6 — Dissolved Calcium, Magnesium, M-l
Potassium, and Sodium in Wet Deposition by Flame
Atomic Absorption Spectrophototnetry
N. Method 200.6 — Dissolved Aluminum, Cadmium, N-l
Copper, Iron, Lead, Manganese, and Zinc in Wet
Deposition by Graphite Furnace Atomic Absorption
Spectrophotometry
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FIGURES
Section No. Contents
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Date July 31, 1986
Page 7 of 7
Number
2-1 Wet/Dry Precipitation Collector
2-2 Plastic Bag Liner Assembly
2-3 Field Data Form for State-Operated Network
age
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TABLES
Number
2-1
2-2
Field Equipment List for Each Station
Supplies List for a Network of 10 to 12
Stations
Page Rev. Date
2 1 7/31/86
5 1 7/31/86
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Section No. 1
Revision No. 1
Date July 31, 1986
Page 1 of 4
1.0 INTRODUCTION
The increasing national awareness of the harmful effects of acid
deposition on the ecology and materials has led to a significant increase
in the number of deposition monitoring networks and related effects
studies. It has become necessary to provide uniform, systematic and
approved precipitation monitoring procedures so that the acquired data
are accurate and comparable among all monitoring networks. The purpose
of this operations and maintenance (0 & M) manual is to describe in
detail the currently recommended procedures for conducting precipitation
monitoring. However, it is essential that these procedures be
supplemented by the quality assurance tasks which are presented in the
Quality Assurance Manual for Precipitation Measurement Systems (1). While
these two manuals contain the procedures recommended by the Environmental
Protection Agency, it must be emphasized that network protocols take
precedence if conflicts occur.
The basic goals of this manual are to instruct how to collect
representative samples without contamination and to preserve sample
integrity for analysis. The possibility of sample contamination,
degradation, or reaction must be minimized. The sample collector, the
first object that contacts the sample, must meet these basic goals and
must be reliable. The Department of Energy (DOE) Health and Safety
Laboratory (HASL) type automatic, wet/dry collector (2), (3), (4) has
been tested and accepted by most U.S. monitoring networks. Discussion
is limited to this type of collector. A reliable rain gauge, pH and
conductivity meter, a balance, and other accoutrements are also needed in
a monitoring station.
The material in this manual is based primarily on the procedures
used in the Electric Power Research Institute (EPRI) precipitation
network and the Utility Acid Precipitation Study Program (UAPSP) in the
Eastern United States, in the National Atmospheric Deposition Program
(NADP), and in the Multi-State Atmospheric Power Production Pollution
Study (MAP3S).
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Page 2 of 4
The EPA handbooks for air pollution measurements (5,6) and for vater
measurements (7) were used as guides for format and content. The
analytical procedures are based on those in the manual: Development of
Standard Methods for the Collection and Analysis of Precipitation (March,
1986) (7). To have this 0 & M manual stand alone without requiring
referrals to the other EPA handbooks, some duplication of material was
required; this material is referenced.
1.1 COLLECTION SITES
Collection sites must be located to meet the objectives of the
monitoring program—for example, baseline, regional or urban, and siting
criteria is given in Section 5.0 of the quality assurance manual (1).
The quality assurance manual also contains the general rules for the
placement of precipitation collectors, and the appropriate siting
documentation. In addition, siting characteristics may be quantified (8)
if desired. In essence, the site must yield representative samples—thus
must not have obstructions which may affect the results.
1.2 PARAMETERS AND ANALYTES GENERALLY MEASURED
The constituents and/or indicators commonly measured are listed
below. All are measured in the laboratory; items 8, 9, and 10 are also
measured in the field.
1. Sulfate (SO?) - Concentrations above the baseline values are caused
mainly by human activities, principally by the release of S0« during
the burning of fossil fuels and during refining processes; tne S02 is
oxidized to sulfate in the atmosphere.
2. Nitrogen Compounds (N0~, NHt and - NO - essentially NO + N02)
concentrationsabove thi baseline valuesxare caused primarily by tne
burning of fossil fuels, such as for transportation purposes; NH,
occurs chiefly from biochemical reactions.
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3. Chloride Ion (Cl~) - Originates chiefly from sea salt aerosols.
4. Phosphate (orthotribasic POT ) - Source is soil, rock, and
fertilizers; an important nutrient.
5. Metal Ions (Na"1", K+, Ca++, Mg++) - Na+ originates mainly from sea
salt aerosols, but all of these ions can originate from soil dust in
desert, semiarid and intensively cultivated areas.
6. Acidity - both S02 and N02 form the strong acids found in
precipitation; organic acids are frequently also present.
7' Alkalinity - Calcareous material (e.g., soil carbonate (CO,)), can
make precipitation alkaline, and can neutralize the effects of acids.
8. p_H - A quantitative measure of precipitation acidity or alkalinity.
In a theoretically clean atmosphere, a water sample in equilibrium
with atmospheric CO- would measure pH 5.6; the acidity increases as
the pH decreases from 5.6 to zero. Alkaline samples have pH 7 to 14.
9. Specific Conductance - The reciprocal of the resistance of a
solution; its magnitude depends on the concentrations and types of
dissolved salts.
10. Precipitation Amount - Value required both to calculate the weighted
mean values of theconstituents and to derive the total amount of
materials deposited over a time period.
1.3 SAMPLING PERIODS, DEFINITION OF EVENT
Precipitation sampling schedules that are commonly used include
weekly, daily, event, and subevent (sequential). An event can be defined
as a storm separated from a second storm by a dry interval, commonly at
least six hours in the winter or at least three hours in the summer. The
sampling schedule depends on the objectives of the program and on the
available funds. Aerometric and/or meteorological studies such as
transport modeling often require daily or hourly sampling. Studies of
long-term trends, and spatial and temporal variability generally use
longer sampling intervals. Sampling periods longer than one week are not
advisable because significant changes may occur to the sample while it
remains in the collector.
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1.4 REFERENCES
1. Quality Assurance Handbook for Air Pollution Measurement Systems,
Vol. V - Manual for Precipitation Measurement Systems, Part I -
Quality Assurance Manual.U.S. EnvironmentalProtectionAgency,
Research Triangle Park, NC. EPA-600/4-82-042a (January 1985).
2. Volchok, H.L., and R.T. Graveson, Proc. Second Fed. Conf. on Great
Lakes, pp. 259-264 (1976).
3. Galloway, J., Water, Air and Soil Pollution 6, p. 241 (1976).
4. Bogen, D.C., Water, Air and Soil Pollution 13, p. 453 (1980).
5. Quality Assurance Handbook for Air Pollution Measurement Systems -
Vol. I - Principles, U.S.Environmental Protection Agency,Research
Triangle Park, N.C., EPA-600/9-76-005 (December 1984).
6. Quality Assurance Handbook for Air Pollution Measurement Systems -
Vol. II - Ambient Air Specific MethoHFjU.S.Environmental
ProtectionAgency,Research Triangle Park,N.C., EPA-600/4-77-027a
(May 1977).
7. Development of Standard Methods for the Collection and Analysis of
Precipitation, U.S.EnvironmentalProtectionAgency, Environmental
Monitoring and Support Laboratory, Cincinnati, OH (March 1986).
8. Eaton, V.C. and E.L. Tew, "Site Evaluation Assistance to New and
Existing Acid Precipitation Collection Sites in the State-Operated
Network," Research Triangle Institute, RTP, NC, under EPA Contract
68-02-4125 (August 1985).
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2.0 FIELD OPERATIONS
Precipitation collection field operations are covered in the
following major areas:
1. Equipment operation and maintenance;
2. Sample collection, handling, measurement, preservation, storage,
and shipment;
3. Documentation of field activities;
4. Quality control procedures.
Precipitation samples are very dilute, thus large measurement errors can
occur due to contamination or degradation. Field procedures must be
accomplished in a way that ensures measurement accuracy.
2.1 EQUIPMENT AND SUPPLIES
This section contains a list of the field equipment required for
typical precipitation collection stations, followed by a list of spare
parts for support of these stations. The section concludes with detailed
descriptions of the precipitation collectors and rain gauges most
commonly in use. The rain gauge measures the amount of precipitation,
and the precipitation collector collects the sample for chemical
analysis. The two devices are not interchangeable.
2.1.1 Station Supplies
The equipment and supplies required depend upon sampling objectives.
Equipment and supplies for a weekly precipitation sampling station are
listed in Table 2-1. If plastic bag bucket liners are used, the number
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TABLE 2-1. FIELD EQUIPMENT LIST FOR EACH STATION
Equipment/Material Min. Quantity/Site
Automatic precipitation collector 1
Collection buckets (3.5 gal) for sampler and lids 5
Fuses for sampler 2
Recording rain gauge with event marker 1
Rain gauge mount 1
pH meter, electrode 1
Buffer, pH 4.0, and 7.0 (1 liter) 1
Conductivity meter and cell 1
Standard KCl solution, 74 nS/cm (500 mL) 1
Temperature probe 1
Pipette, syringe (20 mL capacity) 1
Tips, disposable (pkg. of 100) 1
Balance (20 kg capacity) or graduated cylinder (2 liter) 1
Set attachment weights for balance (1,2,2,5,10 kg) 1
Mailing cartons 3
Wash bottle 1
Test tubes, plastic (17x100 mm) disposable, or vials (35 mL) 375
Test tube rack 1
Rain gauge charts (package of 100) 1
Self-adhesive labels 300
Envelopes 300
Logbook (bound with perforated pages) 1
Data forms 300
Kimwipes or other tissues (boxes) 15
Shipping tape (rolls) 3
Mallet, rubber 1
Deionized water
Saran wrap (roll) 1
Bucket tie down 1
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TABLE 2-1. FIELD EQUIPMENT LIST FOR EACH STATION (cont.)
Equipment/Material Min. Quantity/Site
Additional Requirements for Bags:
Bucket modified for use with bags 2
Bucket lids 2
Plastic bucket liners (bags) 50
Strap with Velcro fasteners 2
Polyethylene gloves (box of 100) 1
500 mL polyethylene bottles 50
Indelible marking pen (black) 2
Scissors 1
Plastic cable ties (pkg. of 100) 1
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Page 4 of 49
of wet buckets required are reduced from five to two and a supply of
bucket liners, plastic gloves, plastic bottles, cable ties, two retaining
straps, and scissors vould be added to the list. Equipment required for
event or daily precipitation sampling is similar. Similar supplies as
listed in the table are also recommended for event or daily sampling. For
sequential sampling, the list in Table 2-1 should include a different
type of collector, a lower capacity (2.6 kg) more sensitive balance,
polyethylene bottles with caps, and possibly a means for storing and
shipping the sample in a cold state (insulated containers and freeze-gel
packs), and few, if any, buckets. If meteorological and/or aerometric
measurements are made, the appropriate instruments must be included in
the list; however, these instruments are not discussed in this manual.
All sites require deionized or distilled water. If this cannot be
produced at the site, it can be purchased locally. It is advisable to
use only water which has the analysis (or conductivity) printed on the
label. The specific conductance of the water should be 3 yS/cm or less
and should be measured before the water is used.
2-1.2 Spare Farts
Precipitation collector fuses should be kept at each station along
with spare parts and supplies. For larger networks, these items are more
conveniently supplied through the field manager or the central laboratory
when needed. Supplies for a network of 10 to 12 stations are listed in
Table 2-2. The polyethylene bottles are for special sampling studies
and/or for sample storage in the laboratory.
Electrodes in contact with solution have a limited life because the
wet glass membrane ages. Only electrodes that can be stored in a dry
state have a long shelf life. However, electrodes should not be emptied,
cleaned and filled with electrolyte solution by the station operators.
When an electrode breaks or becomes suspect (Section 2.5.3.3), it should
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TABLE 2-2. SUPPLIES LIST FOR A NETWORK OF 10 TO 12 STATIONS
EQUIPMENT/MATERIAL NO.
Precipitation collector fuses (12) 1
Precipitation collector sensor and motor box 2
Rain gauge clock 2
Rain gauge chart clip 3
Rain gauge chart paper (package of 100) 3
Rain gauge pens and ink (set) 1
pH meter 1
pH electrode 3
Buffer, pH 3.0, 4.0, 6.0, and 7.0 (1 gal) 2
Conductivity meter 1
Conductivity cell (cell constant ~1) 2
Standard KC1 solution, 74 yS/cm (a)
Syringe (20 mL) 20
Pipette, disposable tips 100
Shipping cartons and collection containers 36
Polyethylene sample bottles
16 oz (500 mL) 600
8 oz (250 mL) 600
4 oz (100 mL) 600
2 oz ( 50 mL) 200
Wash bottle 12
Temperature probe 3
Test tubes, plastic (17x100 mm) disposable, 35 mL vials 1000
Test tube racks 12
Self-adhesive labels 1000
Envelopes 1000
Logbooks 12
Data forms 300
Kimwipes or other tissues (boxes) 36
Shipping tape (rolls) 12
Plastic bucket liners (bags) 500
Polyethylene gloves (pkg. of 100) 12
Bucket modified (for use with plastic bucket liners if
network uses bags) 24
Collection buckets and lids (3.5 gal) 24
Saran wrap (roll) 12
Strap with fastener 24
Marking pen (black) 24
Scissors 12
Plastic cable ties (pkg. of 100) 12
Bucket tie down 24
(a) Make up as needed
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be replaced with a new tested electrode from the central laboratory.
Regardless whether the electrode is used or stored, it has a finite
useful life.
2.1.3 Precipitation Collector Description
The HASL-type precipitation collector (see Figure 2-1 and Appendix
A) has two containers and a common lid. The lid seals the wet sample
bucket when precipitation is not occurring, and thus minimizes
evaporation and contamination by dry deposition or dustfall. When
precipitation occurs, the lid moves off the wet bucket and covers the dry
deposition bucket. Two polyethylene buckets (1,2) are generally used to
collect wet and dry deposition, respectively, for inorganic species. For
organic constituents, glass or stainless steel containers should be used.
The common lid is driven by a motor that is controlled by a rain sensor.
The sensor contains a face plate with a grid closely spaced above it;
when the grid and plate are shorted by a drop of water (precipitation),
the motor is actuated to lift the lid from the collection bucket. The
sensor contains two heating circuits: one goes on when the temperature
falls below approximately 4°C to melt snow or ice on the sensor plate,
and the second goes on when the lid lifts off the sample bucket to heat
the sensor to about 55°C. Heating increases the rate of water
evaporation from the sensor, and hastens the closing of the wet bucket by
the lid after precipitation ceases to minimize the exposure time to dry
fallout. A seal between the bucket and the lid is achieved by a plastic
foam gasket under the lid and by a spring load; however, with strong
winds the lid may wobble, and some contamination may enter the wet
bucket. A bucket tie-down is useful in windy weather.
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Thermistor sensor —
plate activates
noveable lid when
wet precipitation
bucket to another.
Table
MoLor Box
(under table top)
Figure 2-1. Wet/Dry Precipitation Collector
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2.1.4 Rain Gauge Description
To reference all the precipitation amounts against a standard, a
recording rain gauge is used to measure the quantity of precipitation.
Recording rain gauges are of two basic designs (identified by the
principle on vhich they operate)—the weighing-type gauge and the tipping
bucket-type gauge. Recording rain gauges should be capable of measuring
precipitation to approximately 0.25 mm (0.01 in.), and be accurate to a
few percent. For the weighing gauges, the sensitivity is a few
hundredths of an inch (less than 1 mm), and the accuracy is independent
of precipitation rate and is about 1% of full scale. For the tipping
bucket gauges, the generally accepted accuracy is 1% for precipitation
rates of 25 mm/h (1 in./h) or less, 4% for rates of 75 mm/h (3 in./h),
and 6% for rates up to 150 mm/h (6 in./h). The precipitation rates are
either measured directly or derived from the cumulative precipitation
data. The weighing gauges generally have 8-day clocks and charts, and a
0 to 30 cm (0 to 12 in.) dual traverse weighing range. See Appendix B
for a typical weighing rain gauge manual.
The recording rain gauge should have an event marker pen to indicate
when the wet-side collector bucket is open or closed. The times can be
read off the 8-day chart. The Aerochem Metrics collector will interface
with the Belfort 5-780 series rain gauge. The event pen typically is
actuated, rising from its baseline, when the collector lid opens; and
remains actuated until the lid closes, whereupon the pen falls to its
baseline position again. To prevent the event marker pen from
interfering with the sample trace pen on the weighing gauge, the two are
offset on the time axis. Thus only one pen can be set at the correct
time. Care must be taken to use the correct event beginning or ending
time. Since the operator is seldom present to observe the collector
behavior during an event, the event marker pen is invaluable for
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indicating a collector malfunction. For precipitation collector
assembly, operation, installation, and servicing, see the manufacturer's
instructions.
2.2 INSTALLATION AND ACCEPTANCE TESTS
After a suitable site location is chosen, the precipitation
collector and rain gauge must be properly installed and system acceptance
tests performed before actual precipitation data can be collected.
2.2.1 Precipitation Collector
2.2.1.1 Installation—
The precipitation collector should be mounted on the ground so that
the rims of the buckets are level and at least 1 m above the ground. The
collector should be properly anchored against strong winds, and the
bucket should be secured to the precipitation collector by means of a
spring or elastic cord (bungee cord) hooked to the bucket handle and
collector iable edge. The precipitation collector may be shielded from
the wind, but it should not be put in an area where excessive turbulence
will be caused by the shield or where there are obstructions such as
trees and buildings (Reference 3, Section 5). For the placement of any
neighboring collectors and rain gauges of equal or smaller height, the
distance between rain gauge and collector, or between collector and
collector, should be at least equal to the height of the taller object.
Correct spacing should minimize interference as well as splash effects.
To ensure that the collector dry bucket does not act as an obstruction
for the wet bucket (or precipitation sample), the collector should be
aligned either perpendicularly to the prevailing winds or with the dry
bucket downwind of the wet bucket. The ground surface around the
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collector and rain gauge should consist of natural vegetation or gravel.
It should not be paved because a hard surface may cause contamination
from dust settling and water splashing into the collector or gauge.
2.2.1.2 Acceptance Tests—
Precipitation collector acceptance tests should be carried out
before the collector is used in the field. These tests include: (1)
sensor heating and actuating the lid when the sensor is shorted with
water drops, (2) sensor cooling and return of the lid to the wet-side
bucket upon removal of the shorting material (water may be wiped dry),
(3) sensor temperature attainment (50°-60°C) when the lid is off the wet
bucket, (4) sensor temperature (1°-2°C) when ambient temperature falls
below freezing and (5) lid cycling and sealing observation. The
procedures to be used for these acceptance tests are outlined below:
a) With the collector lid in its normal position over the wet
bucket, add several drops of water to the sensor. The lid should
move off the wet bucket within seconds, and should cover the dry
bucket. After the water evaporates, the lid should return to
cover the wet bucket. If there is no response, check to see that
the sensor is connected to the motor box and that the power is
on. If neither is the problem, the sensor or motor box is
probably faulty and should be replaced. To remove the box, see
the manufacturer's instructions.
b) Affix a temperature probe (thermistor, thermometer, or
thermocouple) to the sensor plate near the screw head in the
plate. Make sure good contact occurs, and cover the probe with
an insulating material. Short the grid and plate together with a
paper clip or coin. The temperature should start to climb in a
few minutes, and should level off at 50° to 60°C. If the
temperature setting is incorrect, it can be adjusted by turning
the potentiometer screw inside the sensor box. Directions are
given in the manufacturer's instructions, reprinted in Appendix
A.
c) Remove the shorting object. The lid should close within a few
seconds and the temperature should fall to ambient.
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d) During steps b and c, check that the lid does not cycle. Also
check the lid seals.
e) If the lid does not seal the wet bucket, check to see if the
plastic foam gasket is secured in the correct position. To
remove the seal, see the manufacturer's instructions and Section
2.3.1, step 5. If this is not the problem, contact the
manufacturer.
f) If the lid cycles while the sensor is shorted, the cause is
probably a bad magnetic svitch in the motor box or the lid arm
that actuates the svitch. The arm may be loose or may have moved
too far out (more than 1 mm (1/32 in.)) from the switch as it
passed the switch during lid movement. If the latter is the
case, the lid arm can be adjusted and secured by tightening the
1/4 x 20 head screw in the bronze collar that secures the arm and
the clutch to the motor shaft.
g) Check the sensor heating circuit at freezing temperatures. The
Aerochem Metrics collector has a standard heater/ammeter test
plug which connects the sensor and the table cannon plugs. When
the heater goes on, 0.6 to 0.7 A of current flows through the
heater. The sensor can be cooled at warm temperatures by
unscrewing the sensor probe from the collector table and by
placing it in a refrigerator freezer compartment. A temperature
probe on the sensor will give its temperature. Current should
flow when the temperature falls to 0° to 2°C. The temperature
setting of this circuit cannot be altered except by changing the
resistor in the circuit.
If any of the above tests indicate a malfunction, either the problem
must be remedied or the apparatus returned to the manufacturer. In
general, the problem can be rectified by the operator replacing the
sensor or the motor box. Do not replace any switches.
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2.2.2 Rain Gauge
2.2.2.1 Installation—
The rain gauge should be mounted on a firmly anchored support or
base so that its funnel rim is level and at about the same height as the
collector rim to enable comparisons of collection amounts between the
two. The Belfort gauge can be mounted with three bolts to a level
platform of 30.5 x 30.5 x 0.48 cm (12 x 12 x 3/16 in.) hot-rolled steel,
welded to a 5.1 cm (2 in.) diameter 1.0 m (3.5 ft.) pipe. The pipe is
sunk in cement for stability, and it should extend above ground about
0.53 m (21 in.) to bring the gauge to the same height as the
precipitation collector. Alternatively, the gauge can be mounted (bolted)
to cinder blocks. Holes can be drilled in the cinder block with a
masonry bit. The level of the gauge can be adjusted by the addition of
washers to the bolts. The gauge level can be checked with a carpenter's
level placed at two intersecting positions. The gauge mouth should be
high enough so that it will not be covered by snow.
In open, windy areas, a wind shield (e.g., swingleaf wind shields
such as the Alter used by the U.S. Weather Service) should be used with
the rain gauge.
For rain gauges which contain a clock (recorder), the access door to
the chart drive should be on the leeward side of the gauge and should be
kept closed to minimize dirt and moisture affecting the chart and the
clock mechanism. Never oil any part of the gauge except for the chart
drive, and oil this only when necessary with a light machine oil.
2.2.2.2 Acceptance Tests—
Rain gauge acceptance tests should include checks on the following:
1) sensitivity and accuracy, 2) clock function, 3) pen and recorder
function, and 4) event pen function. The procedures to be used for these
acceptance tests are outlined below.
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a) With the weighing rain gauge level and zeroed, add water
equivalent to several inches. For the Belfort rain gauge 5-780
series, 1 in. = 824 g.
b) If the rain gauge does not read correctly, adjust it according to
the manufacturer's instructions (Appendix B, Instruction Book for
Universal Recording Rain Gauge).
c) With the pens inked and a chart in place, turn the drum to
produce a zero-level trace; add water equivalent to 0.51 mm (0.02
in.), and measure the response. (For the Belfort recording rain
gauge 5-780 series, 0.51 mm = 16.4 g (0.02 in.). If there is no
response or if the response is more than 1.0 mm (0.04 in.),
contact the manufacturer. Check the turnover point on dual
traverse gauges. For tipping bucket gauges, add water in 0.25 mm
(0.01 in.) increments, and note when the bucket empties.
d) Wind the chart drive (or clock) until it is fully wound, and set
it for the correct time. Let the clock run for at least 24 h,
and check the pen traces and the clock time. The time should be
correct to within 0.5 h/24 h of running. If the clock does not
meet this specification, it should be replaced. If any other
problems are evident but are not addressed in the manufacturer's
instructions, call the manufacturer.
e) Note that the event and weight trace pens are offset about 4 h so
that they cannot interfere with each other. Set the weight pen
for the correct time. Make sure that the pens (weight and event)
are writing. If contact between the pen tips and the chart paper
is made but writing does not occur, draw some ink with a
toothpick down the pen tip to form a small pool at the contact
point.
f) Connect the wires to the proper terminals on the collector and
the rain gauge. Short the collector rain sensor, and observe if
the event pen moves up about 3 mm (1/8 in.) from its baseline.
Remove the short, and note if the event pen falls back to its
baseline position. If problems with the event pen occur, notify
the manufacturer.
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2.3 EQUIPMENT CHECKS, MAINTENANCE AND TROUBLESHOOTING
This section contains the checks or maintenance that should be
conducted on a routine basis on the precipitation collector and rain
gauge. In addition, equipment problems that commonly occur are
discussed, and troubleshooting remedies are presented. Records of all
equipment checks and maintenance should be clearly documented in the
station logbook. If malfunctions occur, attempt to diagnose and correct
the problem as soon as possible. If the problem cannot be corrected, ask
the field manager and/or the equipment manufacturer for advice and
direction. Record the diagnosis and corrective action taken in the
logbook.
2.3.1 Precipitation Collector
The precipitation collector does not require calibration, but to
ensure proper functioning of the collector the following checks and
maintenance should be conducted. The tasks are divided into routine
checks, special calibration/maintenance and winter maintenance.
2.3.1.1 Routine Checks—
These checks should be performed at daily or weekly intervals in
accordance wi'th network procedures.
1. Collector Sensor Test - Short the sensor with a piece of metal or some
water to check the lid opening and the sensor heating functions. When
the sensor short is removed, the lid should close within a few
seconds, and the sensor should cool. If an event pen is used, mark
its traces on the rain gauge chart for these tests. Clean the sensor
at monthly intervals or as needed.
2. Inspection of Dry Collector Bucket - If the collector has a dry bucket
(as the wet/dry collector has),check the bucket after an event or a
time period in which an event depositing more than 0.25 mm (0.01 in.)
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of precipitation has occurred. Ascertain if the dry bucket contains
or did contain any precipitation. Precipitation in the dry bucket is
possible evidence of a collector malfunction. Possible causes of such
a malfunction are (1) a dirty or faulty sensor, (2) a too high sensor
heating temperature and/or a low precipitation rate, (3) a defective
magnetic mercury switch in the motor box, or (4) the lid arm too far
out from the magnetic switch to actuate it. All of the above reasons,
except for the dirty or faulty sensor, can cause lid cycling.
3. Test of Vet-Side Bucket or Plastic Liner - At weekly intervals, if no
event has occurred, test the wet-side bucket for cleanliness. Add 250
mL of deionized or distilled water, swirl the bucket so that its
interior is washed, and measure the specific conductance of the
solution. If the conductance is over 3 yS/cm, rinse the bucket until
the rinse water conductance is less than 3 yS/cm. Conductivities
greater than 3 yS/cm indicate that the bucket is contaminated due to
poor initial cleaning, dry deposition and/or handling. If high
conductivities are frequent at a site, poor collector sealing and/or
an operator handling problem are probably present and must be
corrected.
4. Examination of the Event Pen Marker Trace - At weekly intervals,
inspect the event marker trace toseeTlthe lid cycled. The event
trace openings and closings should correspond to the beginning and end
of the event as indicated by the slopes of the sample weight trace.
Numerous up and down markings in short time intervals indicate lid
cycling. Some cycling traces may occur when no event is apparent;
this can occur during short, light rain events. Cycling during a
heavy rainfall is symptomatic of a collector problem. No lid movement
traces when the sample weight trace shows that an event occurred
indicates either a collector or sensor malfunction.
2.3.1.2 Special Calibration/Maintenance—
These special maintenance and troubleshooting tasks should be
undertaken as needed. Any other maintenance advised by the equipment
manufacturer should be carried out at the recommended time periods.
1. Minimizing Lid Lifting by Strong Winds - Where strong winds are
common, check the lid to be sureItdoes not wobble or is not lifted
off the bucket by the wind. If either is a common occurrence, replace
the springs on the collector with stronger ones, and readjust the lid
arm and the counterweight balance.
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2. Lid Cycling - As a common occurrence, lid cycling can be due to
several causes. First, cycling during low rainfall can take place if
the hot sensor plate dries the sensor rapidly. If this is a frequent
occurrence, lover the temperature by turning the potentiometer screw
(see manufacturer's instructions). Second, the lid arm can be loose
or too far out from the magnetic switch in the motor box. Third, the
switch may be defective. (For the last two, see Section 2.1.2.2, step
6).
3. Lid Halfunctioning - Another common source of collector problems is a
faultysensor.The lid may remain open, not open or open
intermittently. The lid staying open indicates a shorted rain sensor.
A short can be verified by unscrewing the sensor cannon connector at
the motor box. The lid should then close over the wet bucket; if the
lid does close, check if dirt is shorting the sensor plate and grid.
If so, clean with a toothbrush or by passing a card between the grid
and plate. For the other problems, the simplest remedy is to replace
the sensor.
4. Replacement of Collector Lid Seal - Replace the plastic foam underseal
onthe lid annually or as soon as needed. It will deteriorate with
time, especially in hot, dry climates. The collector lid seal is
removed using the following procedure:
a) With the collector power disconnected, place the collector lid in
the middle position.
b) Remove the two (2) screws on the edge of the lid.
c) Remove the two (2) L-brackets into which the screws were threaded.
d) Remove the lid pad by prying it gently along its edge with a coin
or a screwdriver.
5. Cleaning Techniques and Schedule - Wash the collector rain sensor
monthly with deionized water toremove dirt, salt, and film buildup.
If a film persists, clean the sensor grid and plate with detergent and
a toothbrush. Wipe the rim of the dry bucket weekly with clean tissues
(e.g., Kimwipes) to prevent carryover of dustfall to the sealing
gasket and then to the wet bucket.
6. Site Maintenance and Inspection for Obstacles - Periodically mow the
grassandinspect the siTe area for new obstacles (e.g., a growing
bush or tree) that may become an obstacle even though not one
initially.
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2.3.1.3 Winter Maintenance—
Check the sensor temperature if the ambient temperature falls below
freezing to ensure that the heater is working. This may be done by
adding snow to the sensor and observing if the snow melts (the lid will
open). If necessary, the following may be conducted to prevent the
freezing of equipment:
1. Prevent ion of Lid Freez ing—To prevent the lid from freezing to the
bucket, the followingT is; recommended (4):
a) Attach a peaked roof (available from Aerochem Metrics) to the lid
to prevent buildup of snow on the lid and to help insulate the lid.
b) Cut a small notch in one corner of the roof to insert a power cord.
c) Attach the power cord inside the roof to an air thermostat
(Honeywell or WRAP-ON) set for about 2°C (36°F); tape the cord to
the roof arms.
d) Use a 60-W or 75-W light bulb as a heater; set the bulb on a piece
of 9 mm (3/8 in.) Styrofoam on the lid top to prevent a hot spot.
e) Install a piece of 18 mm (3/4 in.) Styrofoam under the slope of the
roof to minimize heat loss.
f) To compensate for the additional weight on the lid, add two large
U-bolts to the counterweight shaft (approximately 200 gms).
2. Prevention of Lid Arms Freezing to Table—To prevent freezing of the
lid arms to the table,insulate one from the other.
a) Wrap and tape a plastic sheet around each lid arm to make a boot.
b) Tape one end of the boot to the table and the other end to the arm.
c) Check to see that the boot is secure and does not tear loose when
the lid arms move between the closed and the open bucket positions.
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2.3.2 Weighing Bucket Rain Gauge
The veighing bucket rain gauge must be calibrated upon installation
and at least at annual intervals thereafter. To ensure proper
functioning of the gauge, the following routine checks, calibrations and
maintenance should be conducted. Any other maintenance recommended by
the manufacturer should be carried out.
2.3.2.1 Routine Checks—
These checks should be performed at daily, weekly or monthly
intervals as appropriate.
1. Adjusting the Zero Setting - At daily or weekly intervals with no
precipitation in the rain gauge, adjust the zero setting if necessary
with the (red) fine adjust screw. The zero setting will fluctuate
with temperature, but generally not more than +0.75 mm (0.03 in.).
2. Checking the Pail Level - When the rain gauge pail is removed, be sure
it is replaced correctly so that it is level.
3. Adjusting and Winding the Clock - Weekly, for an eight day clock, wind
the clock (or chart drum) on the weighing gauge, and correct the time
setting if necessary. Be sure to correct for backlash and to set the
time correctly with respect to a.m. and p.m. Note the event pen
times are offset from the weighing pen by about 4 h; set the weighing
pen to the correct time.
4. Inspection of Pens and Ink - Weekly, inspect the pens to see if they
have ink and are writing.If they are not writing, clean the pens,
refill them, and be sure they are working. To help start the pens
writing, use a flat toothpick to make the ink from the pen reservoir
form a small pool at the point of contact between the pen and the
chart.
5. Chart Replacement - At the prescribed interval, generally weekly,
remove the old chart and replace it with a new one. Close the access
door to the chart.
6- Level Check - At bimonthly intervals, measure the gauge level to
ensure that it is still horizontal.
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2.3.2.2 Calibrations-
Two types of calibrations are recommended. A single point check to
be performed monthly and a multi-point calibration to be conducted at
least annually.
1. Rain Gauge Check - Once a month, add several known weights of tap
water to the rain gauge to see that it is measuring correctly. For
the Belfort weighing gauge, 25.4 mm = 1 in. = 824 g.
2. Rain Gauge Calibration - At 12-month intervals (unless test 1 shows it
is necessary sooner), calibrate and adjust the weighing bucket rain
gauge at each 25 mm (1 in.) level according to the manufacturer's
instructions. A set of weights and a linearity tool can be obtained
from the manufacturer for the calibration. Alternatively, weighed
quantities of tap water can be used. For the Belfort gauge, 25.4 mm =
1 in. = 824 g. With a dual traverse pen recorder such as the Belfort
(0 to 6 in. and 6 to 12 in. traverses), the range 127 to 178 mm (5 to
7 in.) has been found difficult to calibrate and to keep .calibrated.
To minimize use of this range interval, the rain gauge bucket can be
emptied after each event or week of events. In the winter, antifreeze
must be added to the weighing gauge bucket to help melt the captured
snow. Thus a severe or prolonged storm can bring the gauge to the 127
to 178 mm (5 to 7 in.) level. If it is found that a calibration
problem exists in the 127 to 178 mm (5 to 7 in.) range, it is
recommended that the bucket be emptied whenever the 127 mm (5 in.)
range is approached and that new antifreeze be added. If a tipping
bucket gauge is used, it can be calibrated by adding a measured volume
of water, using a slow drip technique, as specified in the
manufacturer's instructions.
2.3.2.3 Winter Maintenance—
In the winter, rain gauge problems can be caused by (1) snow filling
or drifting out of the gauge, (2) freezing of the collected precipitation
which can damage the gauge bucket, and (3) the cold affecting the clock
and/or ink.
Therefore, the following actions should be taken:
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a) Remove the funnel in the inlet mouth.
b) Add approximately 1600 g (2 in.) of an ethylene glycol-methyl
alcohol (40:60) antifreeze mixture (Belfort manual, Section 4.3).
To retard evaporation, add 180 mL (6 oz) of a 10V motor oil. Do
not adjust the gauge reading after adding the antifreeze. The
gauge vill indicate rainfall of approximately 50 mm (2 in.). The
ethylene glycol-methanol with precipitation added to yield 150 mm
(6 in.) of solution will freeze below -40°C (-40°F), For less
severe conditions, use approximately 50 mm (2 in.) of ethylene
glycol antifreeze alone. When enough precipitation has been
collected to yield 127 mm (5 in.), the mixture will be liquid at
-24°C (-12°F). Since the weighing gauge is most difficult to keep
in calibration in the 127 to 178 mm (5 to 7 in.) range, empty the
gauge when the 127 mm (5 in.) level is reached, and add new
antifreeze. The antifreeze will not only aid in melting the
snow, but will prevent freezing of collected precipitation and
resulting damage to the container.
c) In extremely cold periods, the clock (if not new) may run slowly,
and/or the ink may not flow. Low-temperature ink is available
from the rain gauge manufacturer. Use of a low-temperature
lubricant may be helpful if the clock runs too slowly.
2.4 SAMPLE COLLECTION AND HANDLING
2.4.1 Avoiding Contamination
Careful handling of equipment and samples to prevent contamination
is extremely important. The dissolved substances have very low
concentrations, so any contamination will result in large errors. Thus
all articles that contact the samples must be clean. All the buckets and
containers have been cleaned at the central laboratory. Only the
materials (e.g., sample buckets, electrodes, cells, and probes) that are
used and not returned to the laboratory must be rinsed. All rinses
should be done with deionized or distilled water.
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2.4.2 Sampling Schedules
Sampling schedules generally used include weekly, daily, event, and
subevent. Daily and weekly samples should be removed at the same time of
day for each sampling period unless precipitation is occurring at that
time; then a delay of up to 12 h for daily sampling and 24 h for weekly
is permissible. For event schedules, remove the sample immediately after
the event or at a set time daily.
For sequential schedules, treat the samples similarly to the event
samples. Since one event may produce several samples, it is important to
identify each sample in the chronological order of occurrence. For
sequential sampling it is important that the time corresponding to each
subevent specimen be known so that correlations with other data can be
made.
The samples are identified and measured for amount, pH, and
conductivity. They are then sealed in plastic bottles, if event or daily
samples, and stored in a refrigerator until shipment (Sections 2.5 and
2.6).
2.4.3 Collection and Handling Procedures
Precipitation samples are collected in wet buckets, plastic bag
bucket liners, or plastic bottles. The methodology for each is given
below.
The containers for the wet samples should have been cleaned prior to
shipment to the field and do not require rinsing in the field before use.
Never substitute a precipitation collector dry bucket for a wet bucket.
At all times, take care not to contact the inside wall of a container, a
lid or a cap with any object—especially one's finger which can leave a
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deposit of salt and oil. The container should be capped until
immediately before use, and must be resealed immediately after use.
Since human breath contains ammonia, do not exhale into a container.
2.4.3.1 Wet Buckets—
Immediately before use, label the new precipitation collector wet
bucket (or for sequential sampling, the capture bottles). Weigh the
bucket after the label is affixed. The label should contain the station
identification, the date placed in use, and the bucket weight (without
lid). After the sampling period, the final weight is added. Use a
pencil or ball point pen to inscribe the labels. Below are standard
operational procedures to be adopted when handling precipitation
collection buckets.
a) Do not remove a clean bucket from the plastic bag in which it is
shipped until it is to be placed in the collector.
b) Check the collector bucket for precipitation at the scheduled
times. Move the lid from the wet bucket by contacting a coin or
metal object to the sensor grid-plate to activate the motor and
move the lid to the dry sample bucket. The lid will remain open
until the metal object bridging the sensor is removed. NEVER TRY
TO FORCE THE LID OPEN BY HAND.
c) Remove the bucket from the collector at the scheduled time, and
replace it with a clean, weighed, labeled bucket.
d) Remove the lid from the new bucket after it has been placed in
the precipitation collector, and cover the removed sample bucket
with the new lid to minimize the chance of contamination. Fasten
lid on old bucket with masking tape.
e) If no sample is present, seal the empty bucket and return it to
the laboratory, or, depending on the protocol, rinse it at the
field station for reuse (see Section 2.6.3).
f) Remove and replace the rain gauge chart. Record readings (times
of start and end of precipitation) on data form. For the final
amount of precipitation reading, use the maximum value on the
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rain chart at end of event because loss of water by evaporation
will occur on standing.
g) If there is no antifreeze in the rain gauge, empty its bucket. If
there is antifreeze, do not empty the bucket until the reading is
127 mm (5.0 + 0.3 in.); then empty the bucket and add new
antifreeze.
h) Weigh bucket and sample (see Section 2.5.1).
2.4.3.2 Plastic Bag Liners—
When plastic bags are used for bucket liners, the buckets are
modified by drilling a vent hole near the bucket rim to allow air to
escape (5). A new bag is inserted in the bucket each week and removed at
the end of the weekly collection period. Avoid touching the inside of
the bucket or bag below its top except when wearing polyethylene gloves.
a) To insert the plastic bag (5), use a clean pair of plastic
disposable gloves. Open the bag to fill it with air.
b) About 4 to 5 in. down from the opening, squeeze the bag closed to
capture the air in the bag.
c) Push the inflated bag into the bucket until it touches the
bottom.
d) Fold the upper 4 or 5 in. of the bag over the bucket rim and
adjust to minimize creases on the rim.
e) Secure the bag flap to the outside of the bucket just above the
first ridge (and above the handle) with a retaining strap (see
Figure 2-2).
f) The bag can be opened more fully inside the bucket by smoothing
the bag against the inside wall. Always wear clean gloves while
doing this.
g) Weigh the bucket + bag assembly and record the weight.
h) Cover bucket with its lid until it is to be placed in the
precipitation collector.
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Ridga in
Molded Bucket
Vent Hole
Figure 2-2. Plastic Bag Liner Assembly
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To remove the sample (e), carry the covered bucket containing the
liner vith or without a sample to the site laboratory.
a) After the bucket containing the liner, retaining strap, and
sample is weighed, remove the retaining strap without passing it
over the open bucket (to avoid any contamination falling in).
b) Push up some of the liner flap outside the bucket to enable the
top of the liner to be grasped.
c) Lift the bag up out of the bucket several inches.
d) Holding the bag with one hand, squeeze the bag shut about one in.
below the bucket rim and close the bag with a cable tie. If
sample is frozen, allow it to melt completely before closing the
bag with the cable tie.
e) Remove the bag from the bucket, swirl to mix contents, and wash
one of its bottom corners with deionized water.
f) Elevate the cleaned, dried corner so that it is not in contact
with solution and cut off about 1/2 in. using cleaned scissors.
g) Lower the cut corner, carefully pouring an aliquot of the sample
into a clean, 500-mL, wide mouth plastic bottle. Label the
bottle with an indelible marking pen. Discard any collected
sample remaining in the bag.
2.4.3.3 Bottles—
For event or daily sampling, the number of buckets required, as well
as storage and shipment space, are minimized by transferring the sample
from the bucket after it is weighed (Section 2.5.1.2) to a 500-mL
labeled, wide-mouth polyethylene bottle. If frozen, the sample must be
completely melted and mixed before transferring. If sufficient sample is
present (e.g., more than 300 mL), use 50 mL to rinse the shipping bottle.
One 500-mL bottle per event is a sufficient sample for all measurements;
the rest of the sample may be discarded.
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For sequential samples, which are collected through a funnel
directly into prenumbered, prelabeled polyethylene bottles, seal the
bottles immediately after the samples are collected.
Wash the sample bucket or, for sequential precipitation collectors,
the funnel and tubing with deionized water until the rinse water has a
specific conductance below 2 yS/cm (step 3, Section 2.3.1).
The samples are now ready for field measurement; check that the
containers are correctly labeled.
2.5 FIELD MEASUREMENTS
The field measurement procedures for weighing, conductivity, pH, and
temperature should be identical to those used by the central laboratory.
Each bucket is weighed both before and after sampling. If sufficient
sample (more than 70 g) is available, its pH and conductivity are
measured both in the field laboratory and at the central laboratory.
These measurements are used as a check to detect sample changes. If less
than 70 g of sample are collected, the sample is sent to the central
laboratory without measuring conductivity and pH.
2.5.1 Weighing Sample Containers
2.5.1.1 Balance Specifications—
The balance should have a capacity of 20 kg and a precision of at
least +10 g. The mass of precipitation collected by the precipitation
collector is measured to determine the rain collector efficiency compared
to the rain gauge.
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2.5.1.2 Procedure—
a) Before each weighing, brush off the balance pan vith a soft
brush.
b) With the balance level, adjust to zero (see manufacturer's
instructions).
c) Before sampling, place a new bucket, or a bucket containing a new
plastic bag liner, without its lid (and/or bottle with its lid)
on the balance, and weigh to the nearest gram. Do not allow the
bucket lid's inner surface to contact any object. Record the
weight on the data form and on the container label (Section
2.7.3).
d) Before weighing the bucket containing a sample, tap the covered
bucket to knock any water drops off the inside lid surface into
the bucket, wipe off the outside of the bucket, remove the tape
and the lid from the bucket, and place lid with its outer surface
on the table.
e) After the balance has been zeroed, place the bucket without its
lid on the balance pan, cover the open bucket with Saran Wrap,
and weigh to the nearest gram.
f) Record the weight on the bucket label and on the field data form.
g) Subtract the initial weight of the empty container from the final
weight of container plus sample to obtain the sample weight.
Record on field data form.
h) Avoid breathing onto the sample to prevent ammonia contamination.
i) If sample is more than 70 g, remove an aliquot of about 20 g for
conductance and pH measurements. For this, a disposable syringe
can be used. If sample is frozen, allow it to melt completely in
its closed container, and swirl the container to assure
homogeneity before removing the aliquot. Reweigh sample plus
container to obtain aliquot weight by difference.
j) Seal container with lid; obtain and record total weight to be
shipped to the central laboratory. If sample is shipped in its
bucket, secure the lid with a rubber mallet.
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2.5.2 Specific Conductance Measurement
2.5.2.1 Apparatus Requirements—
The conductivity meter should permit selection of several different
measurement ranges between 0 to 10 and 0 to 1000 yS/cm, and have a
precision of +Q.5X of range and an accuracy of at least +1.0& full scale.
The range most frequently used is 0 to 100 yS/cm. A temperature-
compensated cell vith a cell constant of 1.0/cm is preferred.
For calibration, use a KCl solution of known specific conductance
and be sure the temperature of the KCl standard and the sample are the
same. For rain samples, a 0.0005M KCl solution which has a specific
conductance of 74 uS/cm at 25°C is appropriate.
The specific conductance of the sample can be measured on the same
aliquot as used for pH. If this is to be done, measure the specific
conductance before measuring the pH to avoid any possible error due to
electrolyte contamination from the pH electrode.
2.5.2.2 Procedure-
Measure the specific conductance for all samples over 70 g, using
the procedure in Method 120.1 (Specific conductance) (6).
1. Summary of Method
a) Measure the specific conductance of a sample by using a
self-contained conductivity meter, Wheatstone bridge-type or
equivalent.
b) Analyze samples preferably at 25°C. If not and if the meter does
not have automatic temperature compensation, measure at 20° to
28°C, and correct to 25°C.
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2. Sample Handling and Preservation
a) Perform analyses in the field laboratory and/or the central
laboratory.
b) If analysis is not completed within 24 h of sample collection,
store sample at 4°C for preservation. Wash the apparatus with high
quality distilled/deionized water, and prerinse with sample before
use.
c) Remove sample aliquot for measurement, and seal the bulk sample.
Allow sample aliquot to come to ambient temperature before
proceeding with conductance measurement.
3. Specific Conductance Meter Standardization
a) Follow the manufacturer's instructions for the operation of the
instrument.
b) Allow sample aliquot to come to room temperature <23<*-27°C), if
possible.
c) Use 74 yS/cm standard. For dip tube cell, rinse and shake test
tube or vial three times with deionized or distilled water.
d) Add 1.3 cm (0.5 in.) of 74 yS/cm solution to test tube; swirl to
coat walls; drain. Add 20 mL of solution or enough to cover
electrodes; insert rinsed conductivity cell. Remove and shake;
repeat two times.
e) Insert cell; set meter to conductivity, and control knob to read
74. Readjust after 1 min. Move cell up and down to remove
bubbles, readjust to 74 if required.
f) Discard solution; shake cell and tube dry. Put a second aliquot of
74 yS/cm solution in same tube; check reading. Readjust meter if
necessary. Discard solution.
g) For closed bottom type cell, use above instructions omitting the
test tube, and add sufficient water or solution to cover
electrodes.
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h) Determine the temperature of the sample to +0.5°C. If the
temperature of the sample is not 25°C, make the correction (as
shown below) to convert reading to 25°C. After measurement, either
discard the solution or save it for pH measurement; never pour the
solution back into its container. Record the data in logbook.
The following temperature corrections are based on the standard KCl
solution, and are used with instruments with no automatic temperature
compensation.
(1) If the temperature of the sample is below 25°C, add 27, of the
reading per degree.
(2) If the temperature is above 25°C, subtract 2% of the reading per
degree.
Report results as conductivity (yS/cm) at 25°C on the data form.
4. Conductance Test
a) For dip tube cell, rinse and shake a new test tube or vial five
times with deionized or distilled water. Rinse and shake
conductivity cell three times.
b) Pour deionized or distilled water into test tube or vial. Dip and
shake cell three times before reading. Let solution stand until
quiescent. If the conductance exceeds that of the deionized water,
repeat rinses until it is equal to that of the water. Record latter
of two readings on the field data form for conductivity of
distilled water.
c) Drain and shake tube; shake cell dry.
d) Rinse test tube or vial with sample. Pour sample into tube to
cover electrodes. Reseal bulk sample container. Dip and shake
cell three times, then, after solution has come to rest, measure
conductance and record.
e) For closed bottom type cell, use similar procedure, and add
sufficient deionized water or sample to cover electrodes.
f) Save this sample for pH test.
g) Rinse cell with deionized water; drain, shake, blot and store.
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2.5.2.3 Conductivity Measurement Problems and Tests—
The conductivity cell generally has few problems; store the cells as
recommended by the manufacturer. The working conductivity standard is
0.0005M KCl, which will slowly degrade and is easily contaminated. To
minimize errors due to changes in the calibration standard, replace the
74 pS/cm working solution at approximately quarterly intervals.
When a new working standard is received, correlate it against the
old working standard. Report the measured value of the old working
standard to the central laboratory, and always return enough of the old
standard to the central laboratory so that it can be remeasured. Never
return the old working standard before checking it against the new
solution.
Store the conductance standards in a refrigerator to minimize
changes but always bring them to room temperature before use. Changes of
less than 3% may be ignored. If the change is more than 3%, order a new
standard from the central laboratory.
If the conductance meter has an internal standardization circuit,
use it to check the KCl standard by following the manufacturer's
instructions. If the KCl standard has changed from its original value by
more than 5%, inform the central laboratory immediately. Since the
internal meter calibration is not a traceable standard, it must not be
substituted for the KCl solution.
Another means of evaluating the working conductance standard is to
compare it against the Q.A. samples received periodically from the
central laboratory. Return the test samples to the central labotatory
with the next sample shipment for remeasurement. If the laboratory finds
that the field conductance differs from the laboratory value by more than
10%, the central laboratory will replace the old conductance standard.
Store the cells as recommended by the manufacturer.
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2.5.3 pH Measurement
2.5.3.1 Apparatus and Equipment (7)—
LABORATORY pH METER — The meter may have either an analog or
digital display with a readability of 0.01 pH unit. A meter that has
separate calibration and slope adjustment features (8) and is
electrically shielded to avoid interferences from stray currents or
static charge is necessary. It may be powered by battery or 110 V AC
line; if battery povered, the meter must have a battery check feature. A
temperature compensator control to allow accurate measurements at
temperatures other than 25°C is desirable.
SENSING ELECTRODE — Select a sensing electrode constructed of
general-purpose glass. This electrode generates lower resistance, faster
response, and has a reliable range of 0-14 pH units. Refer to the manual
accompanying the probe for the manufacturer's recommendations on
electrode storage.
REFERENCE ELECTRODE — The reference electrode recommended for wet
deposition analysis is one equipped with a ceramic junction. The ceramic
construction minimizes differences in potential between high ionic
strength buffers and low ionic strength samples thus reducing errors from
residual junction potentials. A reference probe equipped with a ceramic
junction in an annular ring configuration generates a more stable
potential in less time due to a higher flow of internal electrolyte into
the solution. Single pore ceramic frit junctions also provide adequate
electrolyte flow.
COMBINATION ELECTRODE — The combination electrode combines the
indicating and reference elements in a single unit. Since sample volume
requirements are a consideration when analyzing wet deposition samples,
combination electrodes are more convenient than separate glass and
reference electrodes.
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-4
Before use, the electrode should be equilibrated in 1 x 10 mol/L
hydrochloric acid (7) and stored in the same solution. Refer also to
Appendix C.
THERMOMETER — The thermometer should be readable to 0.5°C in the
ambient range.
Stations may receive the required calibration buffer and storage
solutions from the central laboratory, according to network protocol.
The stations should notify the laboratory when the buffers need to be
replaced.
2.5.3.2 Procedure—
The pH is measured for all samples weighing over 70 g. If the
measurement is made on the same aliquot as that used for conductivity,
the pH must be measured after the conductivity (6). An alternate
procedure using dilute buffers is presented in Appendix C.
1. Scope and Application—This method is applicable to precipitation
samples.
2. Summary of Method—The pH of a sample is determined electrometrically
by using a glass electrode with a reference electrode.
3. Sample Handling and Preservation—
a) Perform the analyses on site immediately after sample collection.
b) After removal of a sample aliquot, seal the bulk sample container;
if the container is a bucket use a rubber mallet to secure the lid.
4. Reagents—Standard buffer solutions may be available from the central
laboratory, according to network protocol. Store buffer solutions at
room temperature.
5. pH Measurement—Always, determine the conductance first. Rinse water
should be the best grade of deionized or distilled water available. A
combination electrode is recommended. Rinse the pH electrode prior to
each measurement. Report the pH to the nearest 0.01 unit and the
temperature to the nearest 1.0°C on the data form.
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CALIBRATION FUNCTION:
a) Adjust the temperature control on the meter to room temperature.
Rinse the electrode(s) with three changes of water or with a
flowing stream from a wash bottle. Dispense two aliquots of the
buffer with the higher pH into separate, clean sample cups. Insert
the electrode(s) into one aliquot for 30 seconds.
b) Remove the electrode(s) from the first aliquot and insert directly
into the second. Allow either two minutes for equilibration or
allow sufficient time for the reading to remain steady within +0.01
pH unit for 30 seconds.
c) Adjust the calibration control until the reading corresponds to the
temperature corrected value of the reference buffer solution.
SLOPE FUNCTION:
a) Rinse the electrode(s) with three changes of water or with a
flowing stream from a wash bottle. Dispense two aliquots of the
second reference buffer solution into separate, clean sample cups.
Insert the electrode(s) into one aliquot for 30 seconds.
b) Remove the electrode(s) from the first aliquot and insert directly
into the second. Allow the system to equilibrate.
c) Adjust the slope function until the reading corresponds to the
temperature corrected value of the reference buffer solution.
CALIBRATION CHECK:
a) Remove the electrode(s), rinse thoroughly, and place into the first
reference buffer solution. If the pH does not read within +0.01
unit of the temperature corrected value, repeat the calibration
procedure until the buffers agree.
SAMPLE MEASUREMENT:
a) Again, remove the electrodes from the buffer and rinse them
thoroughly, using multiple rinsings (wash bottles are recommended).
Use 30 mL of water and be sure to rinse the tip. Gently blot the
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electrode tip dry. Determine the pH of the pH CHECK SAMPLE. Allow
the electrode to equilibrate without stirring for 2-4 minutes, or
allow sufficient time for the reading to remain steady within +0.01
pH unit for 30 seconds, and read and record the pH to the nearest
0.01 pH unit.
b) Repeat above step only using the same 20 mL aliquot used to measure
conductivity. Record the pH of the PRECIPITATION SAMPLE to the
nearest 0.01 pH unit.
c) Discard the 20 mL aliquot used for conductivity and pH measurements
(do not return the aliquot to the bucket) and rinse the electrodes
one last time. Store the pH electrode in the KC1-HC1 solution (see
Section 2.5.3.1). Change the storage solution weekly.
2.5.3.3 Electrode Problems and Tests—
Two diagnostic tests which indicate the aging of the electrode are
presented here.
The first test uses periodic test samples sent out to the field
stations by the central laboratory. The samples should have pH and
specific conductance values typical of precipitation. They rhould be
unknown to the site operator, and are measured for both variables. These
are measures of the station's accuracy if the laboratory value is assumed
to be correct and if no solution change occurs in shipment.
The test solution is poured into five test tubes and the
conductivity and then pH of each tube are measured as if they were five
different samples. That is, the conductivity cell and pH electrode are
rinsed before and after each tube is measured. The readings are
tabulated and the average value and standard deviation calculated. From
these results and from the time required to attain stable readings,
electrode performance and precision can be evaluated. The standard
deviation(s) is calculated from the relation:
1/2
- x)2/n 2-2
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vhere x. and x are the measured and the average pH readings of the series
and where n is the number of sample aliquots measured.
If the average of five field pH measurements differs from the
laboratory by more than +0.15 unit, or the standard deviation is greater
than 0.05 pH unit, the pH electrode may need replacing. The samples are
returned to the laboratory with the results for recheck and evaluation.
Consultation with the station operator on the technique may identify the
source of the problem.
The second test uses a reference solution, which has a known pH and
a conductivity similar to those of rain samples, to check the pH
electrode at the station at weekly intervals. The measurement procedure
is identical to that used for the rain sample. Store the solution in a
refrigerator, and replace it when needed or when the solution pH or
conductivity appears to have changed. For the reference solution, the pH
value should agree with the value assigned by the central laboratory to
better than +0.10 unit.
If the first measurement differs by more than +0.1 pH unit from the
others for the same solution, this value should be excluded. Thus, for
the test sample, a sixth sample tube should be measured. If this poor
first reading behavior is exhibited by an electrode, and if sufficient
precipitation sample exists, two tubes of each precipitation sample
should be measured for pH, and the second value entered on the data form.
The time to attain a stable reading, i.e., when pH is constant to +0.01
unit for 30 sec., should be no more than 2 minutes for a properly working
electrode. Results of these tests serve as guides for both the
measurement technique and the equilibration time to be used for
precipitation sample measurements. If an electrode consistently shows
behavior poorer than that given by the above time and pH difference
criteria, the electrode should be replaced. If the reference solution pH
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measurement has changed from the previous month's value by more than 0.10
unit, check the solution's conductivity. If the conductivity has changed
by more than 10% from its original value, the solution and not the
electrode has probably degraded and should be replaced. Always return
enough of the solution so that it can be checked by the central
laboratory.
2.5.4 Temperature
2.5.4.1 Requirements —
The temperature probe must display at least 0.5°C increments. A
thermistor, thermocouple, or thermometer can be used. The probe should be
calibrated by the central laboratory.
2.5.4.2 Procedure—
a) Before measuring a solution, rinse the temperature probe with
deionized water, and shake it dry.
b) To minimize contamination, do not insert the probe into any
solution until after the other measurements, i.e., conductivity
and pH, have been made.
c) Read and record the temperature to the nearest 0.5°C.
2.6 SAMPLE IDENTIFICATION, PRESERVATION, STORAGE, AND SHIPMENT
2.6.1 Background
Samples must be adequately identified so that they can be readily
and correctly matched up with their data forms. The sample label should
contain station identification, sampling date, and sample weight. Use a
pencil or a ball-point pen to mark the label so that it is still legible
if it gets wet.
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Sample degradation can be caused by chemical interactions—for
example, with particles or gases, or biochemical reactions. Preservation
of sample integrity after removal from the collector can be improved by
filtration, sealing the sample, and storage in the dark. Freezing is not
recommended. Refrigeration is typically used for daily or event samples
but not for weekly samples. To minimize contamination, sample filtration
is performed in the central laboratory.
In the case of duplicate (collocated) or sequential collectors,
treat each sample container as a separate sample. For duplicate
collectors, distinguish the samples by adding a -1 and -2 beside the
station identification space on the data form. For sequential samples,
add -11, -12, -13, and so forth to denote the chronological order of
collection for each event.
Sample shipments are made weekly to the central laboratory for
economic reasons for weekly, daily, event, or sequential samples.
Generally, the shipment should be made early in the week (preferably on
Mondays or Tuesdays) and shipped to the central lab by the U.S. Postal
Service first class mail, or by other carriers that will guarantee
delivery within three days. The method used should be prescribed by the
network protocol. All samples must be well-identified, and should be
accompanied by the appropriate data forms.
The central laboratory, upon receipt of the shipment, will replace
the used sample buckets or containers with clean ones by return mail or
other delivery mode.
2.6.2 Procedure
Label each sample with station identification, date of sampling
period, and sample weight (Section 2.4.3.1).
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2.6.2.1 Weekly Cumulative Samples—
a) Be sure the sample is sealed, identified, and accompanied by its
data form.
b) Pack the weekly sample collection bucket or plastic bottle (if a
liner is used) into a cardboard carton or other protective box.
c) Seal the carton, and ship it to the central laboratory by first
class mail or other method if prescribed in the program protocol.
2.6.2.2 Daily, Event or Sequential Samples—
Refrigerate event and sequential samples until they are shipped, and
keep them cold during shipment. Ship by first class mail or other method
if prescribed in the program protocol.
a) Be sure the samples are sealed, properly identified, and
accompanied by their data forms.
b) Pack the samples in cardboard-enclosed Styrofoam boxes with gel
freeze-packs. Keep the freeze-packs in the freezer compartment
of the refrigerator for about 24 h before shipping to ensure that
they are completely frozen. The gel packs are preferred because
they are less likely to leak when thawed. Generally, four packs
per box is sufficient to keep the samples cold for 4 or 5 days.
Seal the cartons, and ship to the central laboratory.
2.6.3 Field Blanks
Field blanks are used to determine the contamination of the sample
bucket or plastic bag bucket liner when there has been no measurable
precipitation for a week. The blanks levels are measured from a thorough
rinse of the bucket or its plastic liner and yield information on the
previous bucket cleaning, operator handling, contamination while in the
collector, and so forth.
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2.6.3.1 Buckets—
For weekly samples, when there has been no precipitation, the empty
wet-side bucket is removed from the precipitation collector. Depending on
network protocol, the bucket is either sealed and shipped to the central
laboratory or treated at the field lab as follows. At the field lab, 100
mL of deionized water is poured into the bucket, and the bucket is
swirled and tipped for the water to reach as much of the interior surface
as possible. Allow the water to stand for about 5 minutes and then
measure the conductance as in Section 2.9. Also measure the conductance
of the deionized water. Record both values in the site logbook and on
the field report form. Record under "Remarks" that the report is for a
field blank. Mail the field report form to the central laboratory.
Rinse out the bucket several more times using sufficient deionized
water (approximately 100 mL) to reach all the surfaces. Collect the
third rinse and measure the conductance. Continue the rinses until there
is no difference between the conductance of the deionized water and the
rinse sample. Cap the empty bucket securely and save for reuse on the
precipitation collector.
2.6.3.2 Bottles—
For daily or event samples which are shipped to the central
laboratory in plastic bottles, if no precipitation has been collected in
a week, prepare a field blank following the procedure described in
2.6.3.1. Perform the rinses that are required for buckets and record the
conductances on the field report form and note under "Remarks" that the
report is for a field blank. If the protocol calls for analysis of the
blank, the first rinse is shipped to the central laboratory in a labeled,
sealed plastic bottle using a similar procedure as for a sample.
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2.7 DOCUMENTATION
All data, observations, and changes or modifications must be
documented with dates on the proper data forms and/or in logbooks. The
data forms should be in duplicate (NCR paper) with one copy kept in the
station records and one shipped with the sample. The logbook entries are
made out in duplicate. One copy of the logbook entry is kept at the
station and the other is mailed with the data form and the rain chart to
the central laboratory.
2.7.1 Logbook
Use a bound logbook with perforated pages that can' be torn out
easily. Record all problems and actions; dates and times of visits;
equipment changes; procedural changes or modifications; standard solution
changes; electrode replacement; operator changes, and so forth, in the
logbook. Submit one copy to the central laboratory and keep the other at
the station.
2.7.2 Rain Gauge Charts
Mark the rain gauge chart with station identification, dates and
notations for tests, and any problems encountered, and submit weekly to
the central laboratory.
2.7.3 Field Data Forms
The field data form must contain all of the following information:
station, operator, date, sample weight, sampling times, field values of
pH and conductance, and any problems encountered.
-------
Section No. 2
Revision No. 2
Date July 31, 1986
Page 42 of 49
Start a new form when a clean bucket is installed in the collector.
(For daily, event or sequential sampling use a new form for each sample
collected.) Complete the form when the sample is removed from the
collector. An example of a data form used by the State-Operated Network
for weekly sampling is in Figure 2-3. The items below refer to Figure
2-3.
o STATION NAME and ID supplied by the project coordinator.
o OBSERVER'S signature and printed initials; person completing the
form even if substituting for regular observer.
o Enter DATE ON and OFF (mo/day/yr) and the local TIME when sample
buckets are installed and removed; specify 24-h time.
o Check appropriate boxes for the three SITE OPERATIONS. Diagnose
items 1 and 3 from the event pen trace on the rain chart. Add
evidence for item 1, for example, the lack or presence of
moisture in the dry bucket and the reasonableness between the
collector and rain gauge amounts in the PRECIPITATION RECORD
below. Be sure the weight trace is complete for the sampling time
period.
o SAMPLE CONDITION is a qualitative observation of precipitation
quality. Note any comment on obvious causes of the condition
under REMARKS.
o Complete the form for SAMPLE WEIGHT by entering weight of SAMPLE
BUCKET with BAG (if one is used). Include total weight of sealed
bucket, bag, and sample, beneath SAMPLE WEIGHT designation.
Start a new form for newly installed bucket by entering BUCKET
WEIGHT of bucket with a bag. Obtain the weight of precipitation
in exposed bucket by subtracting BUCKET WEIGHT + BAG from BUCKET
+ BAG + SAMPLE WEIGHT, and entering it as SAMPLE WEIGHT.
o The PRECIPITATION RECORD gives daily TYPE (if known) and the
AMOUNT (in.). Circle proper type (R,S,M, or U) under each day.
The M denotes a mixture of rain plus snow/sleet/hail. Obtain the
daily AMOUNT from recording rain gauge, and record it in the
squares. Trace (T) indicates precipitation of 0.25mm (0.01 in.)
or less. If rain gauge, chart, or pen malfunctioned and if no
amount can be observed, circle MM. For cumulative weekly
-------
ACID PRECIPITATION FIELD REPORT
Send Completed Form With Each Bottle To: CENTRAL LABORATORY
STATION Name
ID I I I I I
BUCKET
ON
BUCKET
DATE
TIME
MO
I
DAY
YR
1
DATE
MO
DAY
YR
SAMPLE WEIGHT • Grams
I I HI Buck«»B»9*
1_1—I—LJLU pie .
Sam-
I I I I H !•"*-•••
[•[ | Sample Weight
OBSERVER
SITE OPERATIONS
YES
YES
NO
NO
CHECK YES OR NO FOR EACH ITEM FOR WET- SIDE SAMPLES ONLY (If NO. Explain
in Remarks)
1. Collector appears to have operated properly and sampled all precipitation events during entire sampling period
2 Rain gauge appears to have operated properly during the week
3 Collector opened and. closed at least once during the week.
SAMPLE CONDITION
1. Bird droppings
2. Cloudy or discolored
3 Soot or dm
4. Insectfs) m sample
COMPLETE FOR ALL SAMPLES CONTAINING PRECIPITATION
(Describe All Else in Remarks)
PRECIPITATION RECORD
TYPE
Circle One For
Each Day of
Precipitation
AMOUNT
In Inches or
Circle One
R • Rain Only
Z - Zero
-BUCKET ON
S • Snow Only M - Mixture U - Unknown
T - Trace MM - Missing
TO BUCKET OFF-
TUES.
M
MM
WED
M
Z T MM
THURS
M
U
Z T MM
FBI
M
Z T MM
SAT
U
Z T MM
SUN.
M
U
Z T MM
Total Sampling Period Precipitation From Ram Gauge
Total Precipitation From Sampler - Sample Weight « OOOOS8 Inches, gram
SAMPLE CHEMISTRY
Only for Wet-Side Buckets
with Precipitation
Conductance I I 1*1 IpS/c
Distilled Water
;m
_LJ_] II I-1 M I I I. l-l l=rFTT~l
Aliquot Standard Certified Standard Measured Correction Factor
Removed
i i-i i i-rrr
Correction Factor
NTH 1111 i-i i
isured Sample Corrected
Sample Measured Sampl
REMARKS For Example: Contamination By Operator. Equipment Malfunction. Harvesting in Area
MON
M
Z T MM
pH
lll'lll
CALIBRATION SOLUTION
SAMPLE
TUES
M
Z T MM
Inches (gauge)
Inches (wt)
REFERENCE SOLUTIONS
PH
r i i-i i
CONDUCTIVITY
CORRECTED
ENCLOSE WHITE COPY WITH SAMPLE
SUPPUES
Circle if Needed
• FieM firms • FH Rt itroci SohtJon
• Bigs • CoMtuctmtr HchriKi Solution
• BoltltJ • Indiciu oftir nHid «uppfi«
in remarks
f» 0) fD (t>
oo rt (D H- rt
tn H-
Ł-i H- O
Ł~ C O P
oj M a
^ 2!
2: o
o u> o •
VO
CO
CT\
-------
Section No. 2
Revision No, 2
Date July 31, 1986
Page 44 of 49
samples, add all daily rain gauge amounts, and record TOTAL
SAMPLING PERIOD PRECIPITATION (in.)- Do not merely subtract
initial reading for week from final reading because errors occur
due to evaporation. Convert TOTAL COLLECTOR PRECIPITATION amount
collected from grams to inches by multiplying SAMPLE WEIGHT by
0.00058 in./g, and record in appropriate boxes.
o Space is provided for ONE measurement of sample conductivity and
pH. Only one is necessary, but if the quality of the measurement
is suspect and if over 70 g of sample remain, repeat the
measurement, and record only the final value. Mention only
problems in the remarks section. (Instructions in Sections 2.5.2
and 2.5.3.) Enter DATE of determination as veil as volume in mL
of sample ALIQUOT REMOVED. Record CONDUCTANCE of DISTILLED (or
DEIONIZED) WATER used for rinses and SAMPLE MEASURED conductance
corrected to 25°C. If resistance bridge cannot be adjusted,
insert measured value of 74 yS/cm standard in STANDARD MEASURED
to calculate CORRECTION FACTOR; then calculate and record the
SAMPLE CORRECTED value. For conductivity meters adjusted to 74
yS/cm value using KCl standard, the correction factor is 1.0.
The sample aliquot used for the conductance measurement can also
be used for pH measurement. Never return any aliquot to the bulk
sample. Avoid contaminating bulk sample or aliquot. Measure pH
of SAMPLE aliquot (Section 2.5.3). After the measurement is
completed, recheck the pH 4 buffer value, and enter it if it
differs by less than +0.03 from 4.00. If the difference is more
than +0.03, repeat calibration, and remeasure the pH of the
sample aliquot and the pH 4 buffer.
o Obtain SUPPLIES by circling the appropriate material. If pH
standards are needed, write it in this section. To avoid running
out, request new material when about one-fourth of original
supply remains.
o The REMARKS space is provided for the observer to record any
unusual problems, weather, or other occurrences at the field site
or in the laboratory. Unusual occurrences in site area may
include contamination by the operator, moisture in the dry
bucket, plowing, harvesting, burning, increased atmospheric
pollution or dust, or power outage. The importance of the
information requested in the remarks section cannot be
overemphasized.Careful observation of the sample and occur-
rences in tEe surrounding environment can aid greatly in
evaluating the validity of the sample and in the interpretation
of the data collected.
-------
Section No. 2
Revision No. 2
Date July 31, 1986
Page 45 of 49
2.8 QUALITY CONTROL
Quality control procedures are used on a routine basis to help
assure the collection of high quality data. Complete documentation of
all observations and measurements, the use of known test solutions for pH
tests, and the recheck of the pH calibration after sample measurements
are examples of quality controls. In addition, these types of audits are
used to test the field operators and the central laboratory. The first
type, performance audits, uses blind samples made up by the Network
Quality Assurance Manager or central laboratory for pH and specific
conductance measurements to test the measurement capability at the sites.
The second type is field systems audits by an experienced observer. The
third type requires the field personnel to .forward a sample received from
quality assurance personnel to the central laboratory disguised as a
regular precipitation sample to test both field and laboratory sample
handling and analysis.
2.8.1 Unknown or Quality Control Test Samples for the Field
To evaluate the quality of each station's pH and conductivity
measurements as well as to detect problems with these measurements, test
samples of rain-type composition should be received from the central
laboratory on a regular (e.g., quarterly) basis.
1. Measure these samples for pH and conductance as soon as possible after
receipt. Use the same procedure as for precipitation samples
(Sections 2.5.2 and 2.5.3).
2. Fill out a data form; record the data and the results in SAMPLE
CHEMISTRY, and identify the sample in REMARKS.
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Section No. 2
Revision No. 2
Date July 31, 1986
Page 46 of 49
3. Return the results on a data form, and the remainder of the sample to
the central laboratory.
At the central laboratory, the sample is remeasured to be sure it
has not changed during shipment to and from the station. Comparisons
between the site and laboratory results will assist in the validation of
routine field data. If the comparison results are poor, the Network
Coordinator should initiate troubleshooting with the field operator to
determine the cause of the problem and take the appropriate corrective
action.
2.8.2 Site Visits/Audits
To review the quality of the measurement system and to evaluate each
station's performance firsthand, a site visit should be conducted once a
year or at least once every two years by experienced personnel. The
audit covers all aspects of site operation.
1. About 4 to 6 weeks before the audit, a questionnaire should be sent
from the Network Coordinator's office to the field personnel. They
fill in the questionnaire (Section 10.0, quality assurance handbook
(3)) and return it prior to the auditor's visit so that the auditor
can assess the operator's overall capabilities and prepare pertinent
questions.
2. The auditor will either add a test sample to a clean bucket at the
station, or give the sample to the operator for measurement. The
operator will weigh the sample, measure its pH and conductivity, and
record the data on a data form.
3. The auditor will inspect all equipment, check the calibration of the
rain gauge, offer advice, and ask questions while the operator goes
through the rounds and tests.
4. If there are any problems, the auditor attempts to correct them; and
failing to do so, the auditor will bring them to the attention of the
site supervisor.
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Section No. 2
Revision No. 2
Date July 31, 1986
Page 47 of 49
5. The site personnel will be informed of the results at the end of the
audit. A written audit report will be submitted to the site
supervisor, site sponsor, network coordinator and other officials who
are concerned with operation of the site. A follow-up on corrective
action will be made in 60 days. The follow-up can be by letter,
telephone or revisit.
2.8.3 Blind Samples for the Laboratory
Blind samples will be sent to each station at various times for
testing and forwarding to the central laboratory for analysis as part of
the quality assurance program. The following are instructions and
guidelines to be followed:
1. A reference sample can be shipped in a 500-mL polyethylene bot'tle with
two preaddressed postcards, a mailing label, and a set of data.
2. Refrigerate the sample at 4°C until it can be submitted to the central
laboratory during a week in which your site had no wet deposition.
3. If. your precipitation samples are submitted in buckets, pour the
contents of the bottle into a clean sample bucket (one which has not
been used in the field) when you are ready to submit the reference
sample; weigh, and record as usual on a data form.
If your precipitation samples are sent in bottles, transfer the sample
to one of your bottles, weigh, and record as usual on a data form.
4. Remove your normal aliquot and measure its pH and specific
conductance; record these values as usual on the data form,
5. Fill out the rest of the regular field report form, and ship it with
the sample to the central laboratory as a normal precipitation sample.
Make up the information for PRECIPITATION RECORD, and so forth, on the
data form.
6. Furnish the information requested on the two postcards which
accompanied the sample and mail the self-addressed cards.
7. Place a clean bucket in the collector, and proceed as usual.
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Section No. 2
Revision No. 2
Date July 31, 1986
Page 48 of 49
2.9 FIELD PROCEDURE SUMMARY
To serve as an outline, an operating procedure summary is given
belov. It includes the basic steps, but it is not complete. The
conductivity and pH procedures are those applicable to most of the
current instruments, but they may not pertain to a specific instrument
being used. Check the manufacturer's instructions, and adapt this
summary to your network as necessary.
Site Visits
a) Daily: check rain gauge for event occurrence. If an event
occurred, record its date and time, number of lid openings, and
amount of precipitation from gauge. Note the weather. Weekly:
change chart, fill pens, and wind clock. Monthly: check rain
gauge calibration, and clean collector sensor. Check the
condition of the lid pad.
b) Check dry side buckets for moisture and other unusual
occurrences. If not interested in the dry bucket analysis, wipe
off the rim and leave the dry bucket in place. The dry side
buckets should be cleaned weekly and replaced semi-annually.
c) If event occurred, replace wet bucket with a newly weighed one.
Put new weighed lid firmly on removed sample bucket. Record
observations on data form and in logbook. '
d) Check collector, sensor, and rain gauge for problems.
Sample Handling
a) Wipe outside of bucket dry; tap lid to knock off drops; remove,
weigh bucket (to nearest 1.0 g). Record on sample data form.
b) If sample is frozen, allow it to melt completely.
-------
Section No. 2
Revision No. 2
Date July 31, 1986
Page 49 of 49
c) If sample is sent to the laboratory in a bottle rather than
bucket, pour the sample into a 125, 250 or 500 mL sample bottle.
Discard any sample over bottle capacity. Mark total sample
weight on bottle.
d) Rinse sample bucket with deionized or distilled water, shake, and
drain.
e) For sample in sealed bucket or bottle, allow at least 1 h for
sample to reach room temperature before performing measurements.
2.10 REFERENCES
1. Galloway, J.N., and G.E. Likens, Water, Air and Soil Pollut. 6, 241
(1976).
2. Galloway, J.N., and G.E. Likens, Tellus 30, 71 (1978).
3. Quality Assurance Handbook for Air Pollution Measurement Systems, Vol.
V - Manual for Precipitation Measurement Systems, Part I - Quality
Assurance Manual". U.S. Environmental Protection Agency, Research
TrianglePark, NC. EPA-600/4-82-042a (January 1981). October 1984
Revision in print.
4. Martin, C.V. NADP Winter Operation of Sampler, Hubbard Brook
Experimental Forest, West Thornton, NH; letter to V.C. Bowersox, March
25, 1980.
5. Eaton, W.C., and E.D. Estes, "Use of Plastic Bags as Bucket Liners For
the Aerochem Metrics Precipitation Collector", Research Triangle
Institute, Research Triangle Park, NC, RTI-2474-86 (May 1984).
6. Methods for Chemical Analysis of Water and Wastes, U.S. Environmental
Protection Agency, Cincinnati, OH, EPA-600/4-79-020 (March 1979).
7. Koch, W.F., and G. Marinenko, Guidelines for the Measurement of pH in
Acidic Rainwater. National Bureau of Standards, for EPA.
8. Galloway, J.N., B.J. Cosby, G.E. Likens, and J. Limnol. Oceanogr.
24, 1161 (1979).
-------
Section No. 3
Revision No. 1
Date July 31, 1986
Page 1 of 20
3.0 CENTRAL LABORATORY SUPPORT OPERATIONS FOR THE FIELD
The central laboratory will supply clean containers to the field
sites, prepare reference standards to be used to calibrate field
instruments, and furnish quality control samples for use in the field.
This section discusses the care of glass and plasticware, the preparation
of reference solutions, and the evaluation of field equipment by the
central laboratory. The referred data forms are in Section 3.7.
The central laboratory vill serve as a focal point for solving field
operational problems involving equipment malfunctions. It will serve as
a central distributor of replacement parts for the collector, rain gauge,
pH meter, conductivity meter, balance, thermometers or thermistor probes,
and ancillary supplies. The central laboratory will provide consultation
service to field personnel on any technical question involving siting,
sample collection, analysis, data quality and transport of the collected
sample. The central laboratory will work with site personnel as
intensively as necessary to assure that data quality meets standards set
by the monitoring program.
3.1 CLEANING AND SUPPLYING OF GLASSWARE AND PLASTICWARE
3.1.1 Cleaning of New or Used Plasticware
a) Rinse with deionized water 6 to 10 times. NOTE: If the plastic
needs to be rubbed to remove a film, use a natural sponge.
b) Let stand, filled with deionized or distilled water for 48 h.
Empty and dry in an oven at 70°C.
c) After initial cleaning (steps I and 2), check a portion ("10%) of
the containers to ensure that rinsing has been adequate. To do
this, add 50 mL of deionized water to the cleaned container, seal
the container with a cap or with Parafilm, and slowly rotate it
so that the water touches all inner surfaces. DO NOT SHAKE.
Check the conductivity of the water (Section 4.3); it should be
less than 2.0 pS/cm. If any of the containers fail the check,
-------
Section No. 3
Revision No. 1
Date July 31, 1986
Page 2 of 20
rerinse all of the containers cleaned for the checked samples and
retest 10%.
d) After the plasticware is clean and dry, cap the containers and
place them in a plastic bag to be sealed for shipment or storage.
3.1.2 Cleaning of Glassvare
3.1.2.1 Glassware Used for Metal Analyses—
a) Rinse with deionized water twice and with 10% HNO-j once.
b) Rinse 6 to 10 times with deionized water.
3.1.2.2 Glassware Used for Anions and NH,—
a) Rinse with deionized water twice and with 10% KOH solution once.
b) Rinse 6 to 10 times with deionized water.
c) If water beads on the inner surface, the glassware needs to be
cleaned more thoroughly. Wash with detergent, and then clean
with 10% KOH solution. If water still beads, soak the glassware
overnight in 10% KOH, and rinse 6 to 10 times with deionized
water.
3.1.3 Supplying Containers to the Field
After a sample shipment has been logged in at the central
laboratory, replace the bucket or other sample container with a clean
one. The clean, sealed containers are shipped to the field site in
plastic bags and shipping cartons on an as-needed basis to maintain their
supply. If cold packs and insulated containers are used, these are
returned also. Check that the Styrofoam boxes are intact and not
cracked; if cracked, replace with a new one. The shipment can be made by
ground transport since each site should have a 3-week supply of these
materials on hand.
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Section No. 3
Revision No. 1
Date July 31, 1986
Page 3 of 20
3.2 PREPARATION OF STANDARDS FOR THE FIELD
3.2.1 Preparation and Measurement of Conductivity Standards
a) Weigh out 7.456 g of predried (2 h at 105°C) KC1 and dissolve it
in 1 liter of deionized water (0.10M KC1).
b) Dilute 20 mL of the 0.1M KCl to 4 liters with deionized water
(0.0005M KCl).
c) Fill washed 0.5-liter plastic bottles with the 0.0005M KCl
solution to be sent to the field. Label the bottles with the
preparation date and keep the solutions refrigerated.
d) Measure the conductivity of the solution in each bottle (Section
4.3).
e) Fill out the Field Conductivity Standard form and label the
bottle with the measured conductivity.
f) Send new standards to the field monthly. When old standards are
returned to the laboratory, reraeasure the conductivity. Complete
the Field Conductivity Standard form.
3.2.2 Preparation and Measurement of pH Reference Solution
a) Prepare 4 liters of a 10~4 to 10~5N H2SO, solution for the pH
reference solution by diluting 4 mL or 0.4 mL of commercially
available 0.100N sulfuric acid stock solution.
b) Fill washed 500-mL bottles with the pH reference solution. Label
the bottles with the preparation date. Keep the solutions
refrigerated.
c) Measure the pH of the solution in each bottle (Sections 4.2).
d) Fill out the Field pH Test Solution form, and label the bottle
with the measured pH.
e) Remeasure the pH of these solutions after they are returned from
the field. Complete the Field pH Test Solution form.
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Section No. 3
Revision No. 1
Date July 31, 1986
Page 4 of 20
3.2.3 Preparation of Quality Control Samples
a) Monthly, prepare a mixed solution of 10" to 10" N HjSO, from
commercially available 0.100N solution and 0.0001M to 0.0003M KCl
to be used as a quality control sample. A 0.10M KCl stock
solution is prepared by dissolving 7.456 g of predried (2 h at
105°C) KCl in 1 L of deionized water at 25°C. For 0.0001N KCl,
dilute 1 mL of the 0.10 M stock solution to 1000 mL with
deionized water.
b) Fill clean 60-mL polyethylene bottles with the mixed audit
sample, and send each site one sample. Three bottles should be
retained by the laboratory.
c) Immediately measure the three samples kept by the laboratory for
pH (Section 4.2) and conductivity (Section 4.3). Check the
laboratory electrode against another backup electrode for one
sample. Fill out the appropriate section of the Field Quality
Control Audit Sample Report (Section 3.6.). Refrigerate the
laboratory samples.
d) When the field quality control audit samples from all sites have
been returned to the laboratory, reanalyze the samples along with
the laboratory's three aliquots. Check the laboratory electrode
against another backup electrode for one sample. Complete the
Summary Field Quality Control Audit Sample Report.
3.3 INITIAL EVALUATION OF FIELD EQUIPMENT
All meters and electrodes should be tested before they are shipped
to the field. The meters have a serial number affixed, but the
electrodes do not. A unique identification number should therefore be
taped to each electrode.
3.3.1 Evaluation of Conductance Meters and Cells
3.3.1.1 Evaluation of Accuracy and Precision of Meter—
a) Prepare a 0.0003M KCl Test Solution—Dilute 3 mL of the stock
0.10M KCl solution (Section 3.2) to 1 liter with deionized water.
(Prepare daily.)
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Section No. 3
Revision No. 1
Date July 31, 1986
Page 5 of 20
b) Calibrate the Field Conductance Meter—Calibrate
the manufacturer or as described in Section A.3.
as indicated by
c) Fill 11 Vials or Plastic (17x100 mm) Tubes—Fill to a depth of
3 cm (or to cover the electrode) with the 0.0003M KC1. The first
tube is to be used as a rinse tube.
d) Measure the Conductance of the 10 Solutions—Between each
measurement, rinse the conductivity cell thoroughly with
distilled water, carefully shake it dry, and dip it in the rinse
solution three times.
e) Calculate an Average Value and the Standard Deviation—Use the
following relationships. Programmed calculators make this a
simple operation.
x =
10
Z
3-1
and
s =
10
Ł
i.l
1/2
3-2
where
x. s the measured value (in yS/cm or pH units),
x = the average value,
s = standard deviation, and
n = the number of values.
f) Record the Results—Record results on the Conductance Meter/Cell
Acceptance Test form and the Conductance Acceptance Test Summary
Form. The conductivity meter and cell are acceptable if the
average value is within 2% of the theoretical value of 44.6 yS/cm
(25°C) and if the relative standard deviation is less than 2%.
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Section No. 3
Revision No. 1
Date July 31, 1986
Page 6 of 20
3.3.1.2 Evaluation of Linearity of Meter—
a) Prepare three of the following standards so that each range of
the meter has at least one standard
Normality
Standard Preparation KC1
147.0 yS/cm Dilute 1 tnL of 0.1N 0.001
KC1 to 100 mL
75.0 yS/cm Dilute 500 yL of 0.1N 0.0005
KC1 to 100 mL
44.6 yS/cm Dilute 300 yL of 0.1N 0.0003
KC1 to 100 mL
14.9 yS/cm Dilute 100 yL of 0.1N 0.0001
KC1 to 100 mL
7.5 yS/cm Dilute 50 yL of 0.1N 0.00005
KC1 to 100 mL
b) Calibrate the field conductivity meter as indicated by the
manufacturer.
c) Measure the conductivity of each standard as described in Section
4.3.1.5.
d) Determine the linearity of the meter by performing a linear least
squares fit on the data. Record the results on the Conductance
Meter/Cell Acceptance Test Form and the Conductance Acceptance
Test Summary Form. The coefficient of correlation should be 0.999
or better. If it is less than 0.999, the meter should be
adjusted. Some manufacturers provide procedures for these
adjustments. Otherwise, the meter should be returned to the
manufacturer for calibration.
3.3.2 Evaluation of pH Meters
a) Calibrate the Field pH Meter—Calibrate as indicated by the
manufacturer or as described in Section 4.2.4. A laboratory pH
electrode of documented performance should be used.
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Section No. 3
Revision No. 1
Date July 31, 1986
Page 7 of 20
b) Fill 11 Vials or Plastic (17x100 mm) Tubes—Fill to a depth of
3 cm with fresh pH electrode reference solution (Section 3.2.2).
The first tube is to be used as a rinse tube.
c) Measure the pH of the 10 Solutions—Between each measurement,
rinse the pH electrode thoroughly with deionized or distilled
water, carefully drain or shake it dry, and dip it in the rinse
solution three times.
d) Calculate an Average Value and the Standard Deviation—See
Section 3.3.1.1, (e).
e) Record the Results—Record on the pH Meter/Electrode Acceptance
Test Form and the pH Acceptance Test Summary Form. The pH meter
is acceptable if the average pH is within 0.1 pH unit of the
calculated value and the standard deviation is less than 0.03
units. (Calculated pH = -log (Normality I^SO^).
3.3.3 Evaluation of pH Electrodes
a) Assign Each New pH Electrode an Identification Number—Allow it
to equilibrate overnight in 1 x 10" mol/L HC1.
b) Rinse the Electrode Carefully with Deionized Water—Prior to
testing, and then place it successively in deionized water in
different test tubes until a constant pH reading is achieved.
c) Calibrate the Laboratory pH Meter—Calibrate as indicated by the
manufacturer or as described in Section 4.2.
d) Measure the pH of 10 Tubes—Measure pH reference solution as
described in Section 3.3.2 and note drift, noise and response
time.
e) Calculate an Average Value and the Standard Deviation—See
Section 3.3.1.1, (e').
f) Record the Results—Record on the pH Meter/Electrode Acceptance
Test Form and the pH Acceptance Test Summary Form. The pH
electrode is acceptable if the average pH is within 0.1 pH unit
of the calculated value and if the standard deviation is less
than 0.03 pH unit.
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Section No. 3
Revision No. 1
Date July 31, 1986
Page 8 of 20
3.3.4 Evaluation of Field Balance and Thermometers
Reference weights traceable to NBS are necessary for balance
calibration. Each laboratory should purchase a set of NBS-traceable
weights to be used to certify a set of working weights used in the field
and laboratory. Semi-annual calibration checks are recommended. The
procedure used to certify weights is as follows:
a) zero the balance according to manufacturer's recommendations,
b) weigh the working certified 1.0 and 5.0 Kg weights,
c) weigh reference 1.0 and 5.0 Kg weights,
d) repeat this procedure five times, and
e) complete the Certification of Working Weights to NBS form.
Working reference weights should be certified by this procedure once
a year. The NBS-traceable weights are kept as primary standards. All
working reference weights should weigh within 0.1% of the NBS-traceable
weights.
Each laboratory should have an NBS-traceable thermometer. One
thermometer in the laboratory should be certified against the
NBS-traceable standard. Keep the NBS-traceable thermometer as a primary
standard. Assign all laboratory and field thermometers (or temperature
probes) identification numbers, and then calibrate them against the
(secondary) certified thermometer. Calibrate the temperature probes in a
circulating water bath in the 0° to 25°C range against the certified
thermometer, and complete the Thermometer Calibration Log Form. File one
copy in the laboratory, and send another to the field with the
temperature probe. If the water bath does not have a cooling coil, an
ice-water mixture can be used to achieve the low-temperature reading.
Calibration at two temperatures, near 0° and 25°C, is sufficient and a
linear temperature behavior may be assumed. Temperature differences
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Section No. 3
Revision No. 1
Date July 31, 1986
Page 9 of 20
between the certified thermometer and the test thermometer should be no
greater than 0.5 degree.
3.4 MONITORING OF FIELD OPERATION
It is the function of the central laboratory to monitor field
results to determine if a site is operating properly. The laboratory
receives a copy of the site log book and sample data sheets weekly. From
these and the results of the monthly Quality Control Sample (Section
3.2.3) the central laboratory can determine if the site is functioning
properly.
3.4.1 Evaluation of Field Conductivity and pH Measurement Systems
As needed, the central laboratory sends Quality Control (QC) samples
(Section 3.2.3) to each field site. After all samples have been measured
for conductivity and pH by the site operators, returned to the central
laboratory and remeasured by the central laboratory, the results are
recorded on the Monthly Field Audit Report (Section 9.1.2, QA Manual
(1)). Accuracy is estimated and the acceptance criteria are applied.
If a site's QC sample result is outside the pH acceptance criteria,
the pH reference solution (Section 3.2.2) values recorded by the site
operator on recent field sample data sheets' are checked. If these
results are also questionable, a new pH electrode which has been checked
by the central laboratory (Section 3.3.3) is sent to the field with a new
QC sample. If the pH system still does not function properly, the pH
meter is replaced.
If a QC conductance value measured by the site operator is outside
the conductivity acceptance criteria, a new conductance standard is sent
to the site. If this does not solve the problem, the conductivity meter
and cell are replaced. In all cases the central laboratory personnel
communicate with the site operator to determine if there is an outside
cause of malfunctioning.
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Section No. 3
Revision No. 1
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Page 10 of 20
3.4.2 Evaluation of Field Precipitation Collector, Rain Gauge and
Balance
All measurements in the field, including sample weight and rain
gauge reading, are recorded by the site operator on field data forms and
all observations are noted in a bound log book, with perforated second
copies that can be torn out easily. These pages are sent to the central
laboratory for review along with the data forms. Central laboratory
personnel evaluate the performance of the precipitation collector, rain
gauge, and balance from these sources, the weekly telephone call, and the
precipitation collector collection efficiency. In addition, the
performance of the rain gauge and balance are evaluated by reviewing the
field records when the site operators check the rain gauge and balance
with known weights. During field audits, the auditor evaluates all site
equipment.
3.5 REPORT FORMS
Blank data forms are included in this section for the convenience of
the manual user. Use of the forms is discussed throughout Section 3. The
forms included are listed below:
Title
Field Conductivity Standard Report
Field pH Reference Solution
Field Quality Control Audit Sample Report - Laboratory Data
Conductivity Meter/Cell Acceptance Test Report
Conductivity Acceptance Test Summary
pH Meter/Electrode Acceptance Test Report
pH Acceptance Test Summary
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Section No. 3
Revision No. 1
Date July 31, 1986
Page 11 of 20
Certification of Working Weights to NBS-Traceable Standards
Thermometer Calibration Log
3.6 REFERENCES
1. Quality Assurance Handbook for Air Pollution Measurement Systems, Vol.
V - Manual for Precipitation measurement Systems, Part I - Quality
Assurance ManualIU.S.EnvironmentalProtectionAgency,Research
TriangleParTTT NC. EPA-600/4-82-042a (January 1981). Revised
January 1985.
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Section No. 3 .
Revision No. 1
Date July 31, 1986
Page 12 of 20
FIELD CONDUCTIVITY STANDARD REPORT
DATE OF PREPARATION OF
0.1M KC1 STOCK SOLUTION:
DATE OF PREPARATION OF ___^
DILUTE FIELD STANDARD: (Analyst's Signature)
LABORATORY ANALYSIS BEFORE SHIPMENT TO THE FIELD (vS/cm)
Laboratory Values After Use In The Field:
Lab Value Date of Lab Analyst's
Field Site ft (yS/cm) Analysis Initials
Operations & Maintenance Manual for Precipitation Measurement Systems
-------
FIELD pH REFERENCE SOLUTION
Section No. 3
Revision No. 1
Date July 31, 1986
Page 13 of 20
DATE OF PREPARATION OF
0.1N H2S04 STOCK SOLUTION
VOLUME OF STOCK TAKEN
FINAL DILUTION VOLUME OF
FIELD pH ELECTRODE TEST SOLUTION
(Analyst's Signature)
DATE OF PREPARATION
OF TEST SOLUTION
LABORATORY ANALYSIS BEFORE SHIPMENT TO THE FIELD (pH)
pB-
LABORATORY ANALYSIS OF ALIQUOTS RETURNED FROM THE FIELD
Field
Site ft
Lab Values After Return
Date of Analysis
>H
Anal. Init.
Operations & Maintenance Manual for Precipitation Measurement Systems
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Page 14 of 20
FIELD QUALITY CONTROL AUDIT SAMPLE REPORT
SAMPLE
Date of Preparation of Field Audit Sample: .
Vol. of H^SO, Stock Used: mL; Normality of H9SO, Stock:
2 A *• H
Date of H2SO, Stock Preparation:
Vol. of KCl Stock Used: mL; Normality of KCl Stock:
Date of KCl Stock Preparation:
Final Dilution Volume of
Field Audit Samples: mL; (Analyst's Signature)
LABORATORY ANALYSIS BEFORE SHIPMENT*
TO THE FIELD
Conductivity p_H
Average and
Std. Dev.
LABORATORY ANALYSIS OF ALIQUOTS RETURNED FROM THE FIELD
DATE
OF LAB CONDUCTIVITY pH ANALYST'S
SITE # ANALYSIS VALUE VALUE INITIALS
* These data are for three laboratory aliquots which are analyzed before
shipment of samples, are then refrigerated, and are reanalyzed with the
• samples returned from the field.
Operations & Maintenance Manual for Precipitation Measurement Systems
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Section No. 3
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Page 15 of 20
CONDUCTIVITY METER/CELL ACCEPTANCE TEST REPORT
DATE OF TEST: ^
(Analyst's Signature)
PREPARATION DATE OF
KC1 REFERENCE SOLUTIONS:
METER TYPE/SERIAL NO. /
CONDUCTIVITY CELL TYPE/SERIAL NO.
INDICATE WHETHER TEST OF METER OR CELL
CONDUCTIVITY VALUES OBTAINED FOR PRECISION TEST (0.0003M KC1 SOLUTION)
(Section 3.5.1.1)
Aliquot 1: Aliquot 6:
Aliquot 2: . Aliquot 7:
Aliquot 3: Aliquot 8:
Aliquot 4: Aliquot 9:
Aliquot 5: Aliquot 10:
Average conductivity and
standard deviation:
CONDUCTIVITY VALUES OBTAINED FOR LINEARITY TEST (Section 3.5.1.2)
Normality Expected Found
KCl Conductivity (yS/cm) Conductivity (yS/cm)
Slope _
Intercept
Linearity
Accepted Rejected
Operations & Maintenance Manual for Precipitation Measurement Systems
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Section No. 3
Revision No. 1
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Page 16 of 20
CONDUCTIVITY ACCEPTANCE TEST SUMMARY
Meter Type/
Serial #
Cell Type/
Serial #
Date of
Check
Linearity
Conductivity Value
Average and Standard
Deviation(yS/cm)
Number
of
Values
Anal.
Initials
Operations & Maintenance Manual for Precipitation Measurement Systems
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Section No. 3
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Page 17 of 20
pH METER/ELECTRODE ACCEPTANCE TEST REPORT
DATE OF TEST:
(Analyst's Signature)
PREPARATION DATE OF
pH ELECTRODE REFERENCE SOLUTION:
NORMALITY OF pH ELECTRODE REFERENCE SOLUTION:
Meter Type/Serial No. /
pH Electrode Type/Serial No. /
Indicate whether test of meter or electrode
pH VALUES OBTAINED;
4.0(3.0) Buffer before:
7 n(6.0) Buffer before:
Aliquot Is
Aliquot 2:
Aliquot 3:
Aliquot 4:
Aliquot 5:
Aliquot 6:
Aliquot 7:
Aliquot 8:
Aliquot 9:
Aliquot 10:
4.0(3.0) Buffer after:
7.0(6.0) Buffer after:
pH ELECTRODE REFERENCE SOLUTION; (Section 3.5.2)
Calculated pH of reference solution:
Average pH and standard deviation:
Check One: Accepted Rejected
Operations & Maintenance Manual for Precipitation Measurement Systems
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Section No. 3
Revision No. 1
Date July 31, 1986
Page 18 of 20
pH ACCEPTANCE TEST SUMMARY
Meter Type/
Serial *
•
Electrode
Type/
Serial*
Date of Ref
Soln. Prep.
Date
of
Check
pH Value
Average and Standard
Deviation
Number
of
Values
Anal.
Initials
Operations & Maintenance Manual for Precipitation Measurement Systems
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Page 19 of 20
CERTIFICATION OF WORKING WEIGHTS TO NBS-TRACEABLE STANDARDS
DATE OF CERTIFICATION:
WEIGHT SET SERIAL #:
(Analyst's Signature)
BALANCE 0
NBS 1kg
NBS 5kg
TEST 1kg
TEST 5kg
BALANCE 0
NBS 1kg
NBS 5kg
TEST 1kg
TEST 5kg
BALANCE 0
NBS 1kg
NBS 5kg
TEST 1kg
TEST 5kg
* * *
* * *
BALANCE 0
NBS 1kg
NBS 5kg
TEST 1kg
TEST 5kg
BALANCE 0
NBS 1kg
NBS 5kg
TEST 1kg
TEST 5kg
BALANCE 0
NBS 1kg
NBS 5kg
TEST 1kg
TEST 5kg
* * *
* * *
SUMMARY: (Section 3.5.4)
Average and Standard Deviation
BALANCE 0
NBS 1kg
NBS 5kg
Check One:
Accepted
TEST 1kg
TEST 5kg
Rejected
Operation & Maintenance Manual for Precipitation Measurement Systems
-------
THERMOMETER CALIBRATION REPORT
Section No. 3
Revision No. 1
Date July 31, 1986
Page 20 of 20
DATE OF CALIBRATION:
IDENTIFICATION NUMBER:
(Analyst's Signature)
Certified Thermometer (°C) Test Thermometer (°C) Correction (°C)
— — (Section 3.3.4)
Check one: Accepted
Rejected
Operation & Maintenance Manual for Precipitation Measurement Systems
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Section No. 4
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Date July 31, 1986
Page 1 of 9
4.0 LABORATORY PROCEDURES
The laboratory procedures herein are for chemical measurements and
analyses of precipitation samples. Methods include analyses for pH,
specific conductance, acidity, NflJ, P0~3, SO'2, NO", Cl~, F~, Na+, K+,
Ca"1"1", Mg++, and dissolved Al, Cd, Cu, Pe, Pb, Mn and Zn. Detection
limits for these procedures will vary with instruments and conditions,
but representative detection limits, concentration ranges, precision and
bias are presented in each method. Brief discussions of the methods are
presented in this section with the full text of the procedures in the
appendices.
4.1 GRAVIMETRIC MEASUREMENTS
In both the field and the central laboratory the volume of rainwater
is determined by measuring the mass of the rain and multiplying the mass
3
by 1 g/cm to obtain the volume. The mass of rain is measured in the
field to determine the rain collector efficiency (compared to that of the
rain gauge), and the mass of the sample sent to the central laboratory is
measured as a check to determine if leakage occurred in shipment. The
sample should be sent to the central laboratory in plastic buckets or
plastic bottles. If sent in the bucket, the sample is weighed at the
field station and by the central laboratory. If transferred to
polyethylene bottles, the sample is weighed in the bucket at the field
station and the weight entered on the Field Data Form. The volume
received is estimated by the central laboratory. If collected in bottles,
the sample is weighed by both the field station and the central
laboratory.
4.1.1 Apparatus
The balance should have a capacity of 20 kg and a precision of at
least +10 g (for bucket weighing) or 1 kg with a precision of +0.5 g (for
bottle weighing).
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Section No. 4
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4.1.2 Calibration
Calibrate the balance monthly, using weights traceable to
NBS-traceable weights. Store the NBS-traceable weights (primary
references) in the laboratory, certify the working calibration weights
against these, and complete the Certification of Working Weights to NBS
report (Section 3.4). Recertify all working calibration weights against
the NBS-traceable weights every six months. The procedure for weight
certification is the same as for field balances (Section 3.3.4).
Calibrate each balance using weights close to those actually measured.
Calibrate high-capacity balances, using 1.0 and 5.0 kg weights.
4.1.3 Procedure
To obtain the weight of the sample received in the laboratory, use
the following procedure. During the procedure, avoid breathing on the
sample to avoid NH- contamination.
a) Be sure that the balance is level, and then adjust its zero knob
so that the balance zeroes (see manufacturer's instructions).
b) Place the bucket without its lid or the plastic bottle on the
balance pan, and weigh it to the nearest 10 grams or place the
bottle on the balance and weigh it to the nearest gram.
c) Record the weight on the bucket or bottle label and on a data
sheet.
d) Subtract the initial weight of the empty container (recorded on
the Field Data form) from the final weight of container plus the
sample to obtain the sample weight shipped.
4.2 pH MEASUREMENT
pH is measured in precipitation samples electrometrically by using
either a pH half cell with a reference electrode or a combination
electrode. The pH meter/electrode(s) measurement system is calibrated
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Section No. 4
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Date July 31, 1986
Page 3 of 9
with tvo reference buffer solutions that bracket the expected sample pH.
The acceptable method for the measurement of pH is presented in Appendix
C.
4.3 CONDUCTANCE MEASUREMENT
Specific conductance is measured in precipitation samples
electrolytically using a conductance cell. The conductance meter/cell
system is calibrated using potassium chloride solutions of known specific
conductances in the range of precipitation samples. The acceptable
method for the measurement of specific conductance can be found in
Appendix D.
4.4 SAMPLE FILTRATION
After measuring the pH and specific conductance, but before
measuring the other analytes, filter the rainwater sample. Use vacuum or
pressure filtration to minimize exposure of the sample to laboratory air.
The vacuum apparatus can be a bell jar (ground-glass plate) of sufficient
size to contain a 250-mL (8-oz) bottle, or it can be the apparatus used
by the Illinois State Water Survey for the National Atmospheric
Deposition Program (NADP). The recommended filter material is a 0.45- m
membrane filter (Millipore HA); the filter funnel should be plastic.
Before each filtration, thoroughly rinse the apparatus, including the,
filter, with 200 mL deionized water and a portion of sample if there is a
sufficient amount. Filter the sample as quickly as possible, and cap the
labeled sample bottle containing the filtrate to minimize contact with
laboratory air. If the filtered particulates are to be analyzed, they
should be oven-dried at 60°C for one hour and stored in glass vials.
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Page 4 of 9
4.5 ACIDITY MEASUREMENTS
Two methods for measuring acidity are acceptable. The first method
measures both strong and total acidity, while the second method only
measures total acidity.
In the first method, strong and total acidity are measured in the
precipitation samples by titrating the sample with dilute sodium
hydroxide solution and following the titration electrometrically with a
pH half cell and reference electrode or a combination electrode. The
titration is continued until a pH of 10.4 is reached. A method first
introduced by Gran (1) is used to calculate the strong and total acidity.
The Gran functions are plotted versus the volume of titrant added. The
total and strong acidity are obtained by extrapolating the linear
portions of the curve to zero. Weak acidity is obtained by subtracting
the strong acidity from the total acidity. This method can be found in
Appendix E.
In the second method, total acidity is measured by titrating the
sample electrometrically with a combination pH electrode to a pH of 8.3.
The total acidity is calculated from the volume and concentraiton of
titrant. This method is included with the above method in Appendix E.
4.6 DETERMINATION OF SULFATE
Sulfate is measured in the precipitation samples by one of two
methods; ion chromatography or automated colorimetry using barium-
methylthymol blue. The ion chromatographic method utilizes ion exchange
resins for separation and conductivity for detection. After a sample is
injected onto the separator column containing the ion exchange resin, an
eluent is used to pump the sample through the column. The anions are
separated depending on their radius and valence. After eluting from the
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Section No. 4
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Date July 31, 1986
Page 5 of 9
separator column, the ions are converted to the corresponding acids which
are detected in the conductance cell against a background of neutralized
eluent.
The automated colormetric method of analysis for sulfate uses the
blue colored barium-methylthymol blue complex to determine the
concentration of sulfate in the sample. After interfering cations are
removed by an ion exchange column, the sulfate in the sample reacts with
barium chloride to form barium sulfate. Excess barium ions react with
the methylthymol blue to form the chelate. Thus, '«;he concentration of
the sulfate in the sample is inversely proportional to the intensity of
the blue-colored chelate which is measured colorimetrically at 460 nm.
The ion chromatographic method is presented in Appendix F, while the
colorimetric method can be found in Appendix G.
4.7 DETERMINATION OF NITRATE
Nitrate is measured in the precipitation samples either by ion
chromatography or automated colorimetry using cadmium reduction. The ion
chromatographic method is identical to the method described in Section
4.6. It can be found in Appendix F.
The colorimetric method uses a color reagent made from NEDA
(n-(l-naphthyl)-ethylene-diaraine dihydrochloride), phosphoric acid and
sulfanilamide to develop a color that can be used to measure the nitrate
present in a sample. After mixing with ammonium chloride, the nitrate in
the sample is reduced in a copper-cadmium column to nitrite. The nitrite
is mixed with the color reagent and forms a reddish-purple complex which
is measured colorimetrically at a wavelength of 520 nm. The
concentration of the original nitrate in the sample is directly
proportional to the intensity of the color complex formed by the nitrite.
This method can be found in Appendix H.
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Section No. 4
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Date July 31, 1986
Page 6 of 9
4.8 DETERMINATION OF CHLORIDE
Chloride is measured in precipitation samples by chemically
suppressed ion chromatography or automated colorimetry using thiocyanate.
The ion chromatographic method is identical to the method described in
Section 4.6. It can be found in Appendix F.
The colorimetric method of analysis for chloride uses a colored
ferric thiocyanate complex to determine the concentration of chloride in
the sample. The chloride ions react with mercuric thiocyanate liberating
thiocyanate ions which reacts with ferric ions. The concentration of the
original chloride ions in the sample is directly proportional to the
intensity of the colored ferric thiocyanate complex. This method is
included with this manual as Appendix I.
4.9 DETERMINATION OF ORTHOPHOSPHATE
Orthophosphate is measured in the precipitation samples either by
ion chromatography or automated colorimetry using the phosphomolybdenum
blue complex. The ion chromatographic method is identical to the method
discussed in Section 4.6. It can be found in Appendix F.
The colorimetric method involves developing the phosphomolybdenum
blue complex by mixing the sample with an acidified solution of ammonium
molybdate, ascorbic acid and antimony potassium tartrate, and passing the
mixture through a 37°C temperature bath. The concentration of
orthophosphate is proportional to the intensity of the phosphomolybdenum
blue complex measured colorimetrically at 880 nm. This method is
presented in Appendix J.
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Section No. 4
Revision No. 1
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Page 7 of 9
4.10 DETERMINATION OP FLUORIDE
an
Fluoride is determined in the precipitation samples using
ion-selective electrode with a reference electrode. The meter/electrode
system is calibrated with fluoride solutions of known concentrations. The
specified method is presented in Appendix K.
4.11 DETERMINATION OF AMMONIUM
Ammonium is determined in the precipitation samples by one of three
methods; ion chromatography, ion-selective electrode or automated
colorimetry using the indophenol blue complex.
The ion chromatographic method utilizes ion exchange resins for
separation and conductance for detection. After a sample is injected
onto the separator column containing the ion exchange resin, an eluent is
used to pump the sample through the column. The cations are separated
depending on their radius and valence. After eluting from the separator
column, the ions are converted to the corresponding bases which are
detected in a conductance cell against a background of neutralized
eluent. This method can be found in Appendix F.
The second acceptable method for determining ammonium is to use a
gas sensing ion-selective electrode with a reference electrode. Ammonium
ion is converted to ammonia gas when the pH of the sample is adjusted to
pH 11-14. An electrode potential develops across the sensing membrane in
proportion to the ammonia concentration in solution. The meter/electrode
system is calibrated with ammonium solutions of known concentrations.
This method is included as Appendix L of this document.
The third method for determining ammonium in precipitation samples
is the automated colorimetric method using the indophenol blue complex.
After removing cations that could form hydroxide complexes, the sample is
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Section No. 4
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Date July 31, 1986
Page 8 of 9
mixed with alkaline phenol and hypochlorite to form the indophenol blue
complex. Sodium nitroprusside is added to precipitation samples to
intensify the color. The concentration of the ammonium is proportional
to the intensity of the indophenol blue complex measured colorimetrically
at 630 nm. This method can be found in Appendix L with the second method
described above.
4.12 DETERMINATION OF SODIUM, POTASSIUM, MAGNESIUM AND CALCIUM
Sodium, potassium, magnesium and calcium are measured in
precipitation samples either by chemically suppressed ion chromatography
or flame atomic absorption spectrophotometry. The ion chromatographic
procedure is identical to the one described in Section 4.11 for ammonium.
It can be found in Appendix F of this document.
The flame atomic absorption spectrophotometric method of analysis
for these metals involves aspirating the sample into a flame where the
cations are converted to ground state atoms. A light beam from a hollow
cathode lamp which emits light specific to the metal of interest is
passed through the flame, isolated by a monochromator and measured by a
photodetector. The ground state atoms of the metal of interest absorb
the light. The concentration of the metal in the sample is proportional
to the amount of light absorbed in the flame. This method is presented
in Appendix M.
4.13 DETERMINATION OF ALUMINUM, CADMIUM, COPPER, IRON, LEAD, MANGANESE
AND ZINC
Aluminum, cadmium, copper, iron, lead, manganese and zinc are measured in
precipitation samples by graphite furnace atomic absorption
spectrophotometry. Microliter quantities of sample are deposited into a
graphite tube where it is electrothermally dried, pyrolyzed and atomized.
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Section No. 4
Revision No. 1
Date July 31, 1986
Page 9 of 9
A light beam from a hollow cathode lamp which emits a spectrally pure
line source of light specific to the metal of interest is passed through
the atoms which are at ground state. The atmos of the specific metal
absorb the light. The concentration of the metal is proportinal to the
amount of light absorbed in the flame. This method can be found in
Appendix N.
4.14 REFERENCE
1. Gran, G., "Determination of the Equivalent Point in Potentiometric
Titrations," Acta Chemica Scandinavica, 4, 1950, p. 559.
-------
Appendix A
AEROCHEM METRICS PRECIPITATION COLLECTOR MAINTENANCE MANUAL
A-]
-------
Stote Water Survey Division
ATMOSPHERIC CHEMISTRY SECTION
AT THE
UNIVERSITY OF ILLINOIS
GSR
Illinois Department of
Energy and Natural Resources
SWS Contract Report 348
AEROCHEM METRICS
PRECIPITATION COLLECTOR
MAINTENANCE MANUAL
-------
SWS Contract Report 348
AEROCHEM METRICS
PRECIPITATION COLLECTOR
MAINTENANCE MAMJAL
Prepared By
Scott Dossett1
Central Analytical Laboratory
Atmospheric Chemistry Section
Illinois State Water Survey
605 E. Springfield Avenue
P.O. Box 5050, Station A
Champaign, IL 61820
September, 1984
Prepared under the contract with Colorado State University for the
National Atmospheric Deposition Program. This report has not yet been
reviewed and approved by NADP/NTN.
-------
Revision No. 0
Date: Sept. 5, 1984
TABLE OF CONTENTS
SECTION TITLE PAGE
1. INTRODUCTION 1-1
2. PARTS REFERENCE LIST 2-1
3. PICTORIAL GUIDE TO PARTS 3-1
4. TROUBLE SHOOTING 4-1
4.1. Sensor Unit 4-1
4.2. Motor Box Unit 4-2
4.3. Clutch Unit 4-4
4.4. Flow.Charts 4-7
5. COMPONENT REPLACEMENT AND ROUTINE SERVICING 5-1
-ii-
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Revision No. 0
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1. INTRODUCTION
The Aerochem Metrics wet/dry collector is a fairly simple device
which has proven to be reliable and efficient for capturing rainfall.
This guide is intended to address trouble shooting and repair of the
major collector components, namely the motor box, sensor, and clutch
units. Simple or site specific repairs such as battery checking, HOVAC
power supply, and instrument mounting are not discussed since they are
best diagnosed and corrected by site personnel.
Section 5 describes some routine maintenance procedures. .Part 2 of
that section prescribes weekly checks which are essential to obtain the
high quality wet-deposition only chemistry required by the modern
research community. PLEASE READ THIS SECTION.
IF YOU EXPERIENCE A COLLECTOR MALFUNCTION
(1) Please inform the CAL; call 217/333-0249, especially when
replacement parts are needed or if sample quality has been affected.
(2) Briefly describe the malfunction and indicate when it first occurred
on the Field Observer Report Form of the sample affected. Continue
to do this for each weekly sample until the malfunction is
eliminated. Pay particular attention to how the wet-side bucket was
exposed. Recall that when the sampler is operating correctly, the
wet-side bucket should only be open during rain, snow, etc.
Example: "Sensor heater went out on Thursday: wet-side bucket
remains open for several hours after the rain stops."
Refer to the NADP Instruction Manual for Site Operations for a
description of sample types.
1-1
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Revision No. 0
Date: Sept. 5,
1984
2. PARTS REFERENCE LIST
This list identifies parts by name and assigns part numbers that are
used in conjunction with the "Pictorial Guide to Parts" section which
follows. Also, all part numbers are cross-referenced to a corresponding
photo number.
Some part numbers are referenced in the "Trouble Shooting" section
of this text; others are included so that this additional detail can be
referenced in future communications. (These numbers are not
manufacturer's order or part numbers.)
Part Name
sensor unit
collector main frame
sensor screws
sampling bucket holder
sensor grid
sensor plate
motor box screws
sampling bucket holder screws
motor box unit
clutch arm unit
clutch arm machine bolt
counterweight(s)
Waldes ring
push rod
counter weight rod
lid drive arms
lid tension springs
110V AC power cord
event recorder terminal
sensor unit socket
12V DC power lugs
12V DC circuit fuse
110V AC circuit fuse
event recorder circuit fuse
motor box stop switches
event recorder/wet mode heater
switch
drive motor shaft
clutch tooth
thrust collar with set screw
clutch tooth tension plate
switching magnets
clutch tooth tension spring
Part No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
2
2
4
3
Photo No.
1
1
1
1
1
1
and
and
3
3 and 6
3
3
3
3
3
3
3
3 and 4
3 and 4
4
4
4
4
4
5
5
5
6
6
6
6
-------
3. PICTORIAL GUIDE TO PARTS
PHOTO #1
COLLECTOR MAINFRAME/SENSOR
3-1
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Revision No. 0
Date: Sept. 5, 1984
PHOTO #2
COLLECTOR MAINFRAME (TOP)
PHOTO # 3
COLLECTOR MAINFRAME (UNDERSIDE)
3-2
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Revision No. 0
Dace: Sept. 5, 1984
PHOTO #4
MOTOR BOX (FRONT)
3-3
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Date: Sept. 5, 1984
PHOTO #5
MOTOR BOX (SIDE)
PHOTO 46
CLUTCH ARM
3-4
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Revision No, 0
Date: Sept. 5, 1984
4. TROUBLE SHOOTING
4.1 Sensor Unit-"What Does It DO?"
The sensor unit has two functions: to signal the movement of the
collector lid by activating the motor box unit when the start and stop
of precipitation is detected, and to regulate two heating modes, the
ambient mode to melt snow and the wet collect mode to dry water from the
wetted sensor.
(1) Activating Motor Box Unit
When water fills the space between the sensor grid (5) and plate (6)
(rain begins), the sensor unit activates the motor box unit to move the
collector lid over the dry-side bucket. This leaves the wet-side bucket
exposed to capture precipitation. When water no longer fills this space
(the rain slows or stops), the motor box is once again activated to move
the collector lid over the wet-side bucket. This leaves the dry-side
bucket exposed. In serving this function the sensor unit is acting as a
simple on/off switch.
(2) Regulating Sensor Heating Modes
A heater fixed to the sensor plate in the sensor unit (1) is
activated when the ambient air temperature falls below 4°c (40°F) or
when the collector lid is covering the dry-side bucket due to a wetted
sensor.
The ambient heater mode is controlled by a temperature sensitive
electrical component called a thermistor, mounted to the sensor plate.
This component turns on the heater at a low power setting when the
sensor plate drops below 4°C (40°F) and turns it off again when the
plate warms above that temperature. In this fashion Che heater melts
snow and ice so that the resulting liquid can bridge the sensor grid and
plate, allowing the collector to open.
The wet collect mode of the sensor heater is activated when the
collector lid is covering the dry side bucket due to a wetted sensor.
In this position, the event recorder/wet mode heater switch on the left
side of the drive motor shaft (27) is tripped by the clutch unit
switching magnets (31). This turns on both the wet collect mode of the
sensor heater and energizes the event recorder terminal (19) with a 14 +
3 volt DC current. In this mode the thermistor attached to the sensor
plate budgets the current flow to the heater so that the plate
temperature is regulated to a 50°C maximum. Five to ten minutes
typically pass after the heater has been activated before it reaches
full heat.
4-1
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Revision No. 0
Date: Sept. 5, 1984
Sensor Units - "What Goes Wrong'
When the sensor unit is faulty, some of the following symptoms may
be observed:
Symptom See Flow Chart
Collector lid stays over the dry-side #1, page 4-8
bucket long after precipitation stops,
sensor dries slowly (more than 30
minutes for rain), motor not running.
(If motor is running, see Clutch Unit -
What Goes Wrong.)
Collector lid oscillates-non-stop #5, page 4-12
between buckets, sensor wet or dry
Collector lid stays over wet-side bucket, #6, page 4-13
sensor wet, motor not running. (If motor
is running, see Clutch Unit - "What Goes
Wrong".)
Collector lid stays over dry side bucket, /M, page 4-11
sensor dry, motor not running. (Again, if
motor is running, see Clutch Units - "What
Goes Wrong".)
Sensor plate (6) snow covered or iced up. 7/3, page 4-10
4«2 Motor Box Unit - "What It Does"
The motor box unit (9) houses a drive motor, power and control
circuitry, and fuses (22, 23, and 24). One visible side of the unit is
occupied by connectors, such as the sensor unit socket (20), event
recorder terminal (19), etc., (see Photo //4). The other side (see Photo
#5) is occupied by the drive motor shaft (27) and three switching
magnets (25 and 26).
The motor box has two main functions: to power the lid mechanism
between the wet and dry-side buckets, and to interact with the clutch
unit to control the lid position.
(1) Power Function
In order to move the lid mechanism from bucket to bucket, the
collector uses a small DC electric motor and gear cluster. These exit
the motor box at the drive motor shaft (27). This shaft is a steel
4-2
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Revision No. 0
Date: Sept. 5, 1984
half-round component to which the clutch arm unit (10) is fastened.
Force is then passed through the clutch arm and a long push rod (14) to
the lid drive arms (16). These lid drive arms, in turn, exit out the
top of the collector mainframe and attach to the lid or roof of the
collector.
(2) Motor Box/Clutch Interaction
As we have already mentioned, the sensor unit acts as the "on"
switch which tells the motor box to move the lid to the dry bucket (or
conversely the "off" switch which causes the collector to move the lid
to the wet bucket.) The motor box components responsible for this
interaction are the clutch arm switching magnets (31) and the motor box
stop switches (25).
When the motor box receives a "wet" signal the dry collect stop
switch, the one to the right of the motor shaft in Photo 5, releases.
The clutch arm then moves counterclockwise stopping at the wet collect
stop switch, which operates in tandem with the event recorder/wet mode
heater switch (see 25 and 26). The clutch arm should stay in this
position until the sensor signals "dry." This allows the wet collect
stop switch to "release" and the mechanism to power to the dry collect
stop switch, causing the wet collect bucket to be covered.
Motor Box Unit - "What Goes Wrong"
When the motor box unit is faulty, some of the following symptoms
may be observed:
. Symptom See Flow Chart
Collector lid stays over the dry-side #1, page 4-8
bucket long after precipitation stops,
sensor dries slowly (more than 30 minutes
for rain), motor not running. (If motor
running, see Clutch Unit - "What Goes Wrong".)
Collector lid stays over wet-side bucket, //6, page 4-13
sensor wet, motor not running. (If running,
see Clutch Unit - "What Goes Wrong".)
Collector lid stays over dry-side bucket, #4, page 4-11
sensor dry, motor not running. (If running,
see Clutch Unit - "What Goes Wrong".)
Collector lid oscillates non-stop between //5, page 4-12
buckets, sensor wet or dry.
4-3
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Revision No. 0
Date: Sept. 5, iy84
4.3 Clutch Unit - "What It Does'
The clutch unit (10) has two main functions: (1) to act as a
mechanical break or "fuse" in the drive system of the collector, and (2)
to signal to the motor box the position of the lid of the collector,
(i.e., the wet or dry mode).
(1) Fusing The Drive System
The clutch serves to protect the rest of the drive train from any
damage due to a stoppage in its motion. Such cases are generally either
caused by freeze downs, gross collector damage from blowover or tree
limbs, or snow mounding high on the flat lids or on unheated snow roofs.
In these cases the clutch works as follows (see Photo 5): from its
normal position with the clutch tooth (28) in the thrust collar indent
(29), one of the above cases causes the tooth to "pop out" of the
indent. After a full rotation of the thrust collar the tension spring
will again pull the tooth into the indent, beginning the cycle anew.
Since the thrust collar should be secured to the motor shaft by the set
screw (29) the thrust collar must turn with the motor shaft. For
efficient operation, the clutch tooth tension spring (32) is stretched
so as to hold the clutch tooth into the thrust collar indent. In this
way the force produced by the drive motor shaft is then transferred
through the clutch to the rest of the collector lid drive mechanism. In
addition the clutch locks this mechanism, keeping the lid tightly
secured over the appropriate sampling bucket.
(2) Signaling The Motor Box
As mentioned in the motor box unit description, the clutch interacts
with the motor box stop switches (25) to control the position of the lid
mechanism. In order to properly signal the stop switches, switching
magnets (31) are built into the clutch arm; their position reflects the
relative position of the lid mechanism. As the clutch arm and hence the
lid mechanism near their stop positions, the appropriate switch releases
or activates to fix the lid over either the wet or dry bucket (see
Photos 5 and 6).
Clutch Unit - What Goes Wrong
When the clutch unit is faulty or out of adjustment, some of the
following symptoms may be observed:
Symptom Cause .
Motor running, lid mechanism not moving. In this case the clutch
(Collector on wet side, dry side or in mechanism is probably worn of
between.) out Of adjustment. It should
be serviced using the follow-
ing steps:
4-4
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Symptom
NOTE: The clutch spring should
not be stretched so far as to
"freeze" the clutch. The drive
motor has a maximum torque rating
and can be damaged if the clutch
will not "pop out." After re-
setting the tension spring, be
certain the clutch can still be
popped out by the drive motor.
Revision No. 0
Date: Sept. 5, 1984
Cause
1. Remove the clutch arm
machine bolt (11), thus
separating the clutch unit
from the rest of the collector
lid mechanism.
2. Loosen the thrust collar
set screw (29) and gently pry
the clutch unit off the drive
motor shaft (27). NOTE: to
expose the set screw simply
start the motor running stop
the clutch arm with your hand
and unplug the collector when
the set screw becomes visible.
3. Examine the clutch unit:
if the thrust collar indent or
the clutch tooth (28) appear
severely rounded then the
clutch probably merits
replacement. (Call us here at
CAL.) If they do not .hen the
force with which the tooth is
held into the indent should be
increased.
4. ADJUSTING THE CLUTCH TOOTH
TENSION SPRING. The tooth/
indent pressure is adjusted
via the position of the clutch
tooth tension plate (30). The
further away from the thrust
collar the plate is pushed the
more tension is produced.
a) Mark the tension plate's
original position with a
pencil;
b) Loosen the tension plate
screw;
c) Move the plate out 1/4";
d) Test the clutch (see NOTE
aside);
4-S
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Symptom
Revision No. 0
Date: Sept. 5, 1984
Cause
e) slide clutch unit back into
the drive shaft and tighten
the set screw;
f) Plug in the collector and
hold the clutch unit to make
certain it will function as
described;
g) Reattach the machine bolt
and drive arm of the lid
mechanism.
Some trial and error may be necessary to reach an appropriate clutch
spring tension.
Symptom
Cause
Collector will not shut off,
continually recycling between buckets.
In this case the motor box has
malfunctioned (reference Flow
Chart #5) or the clutch unit
position is incorrect. In
order to properly signal the
motor box unit, the clutch
must be within 1/4 inch. This
is necessary so that the
switching magnets are close
enough to trigger the motor
box stop switches (25) and the
event recorder/wet mode heater
switch (26). To be certain
the clutch is on all the way,
loosen the set screw (29) and
gently tap the clutch with a
small hammer or screwdriver
handle, then retighten the
set screw.
The next section is a series of flow charts which should be useful
in diagnosing the problems with a malfunctioning collector.
4-6
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Revision No. 0
Date: Sept. 5, 1984
4.4 FLOW CHARTS
Below are listed the most common failure symptoms experienced with
the Aerochem Metrics wet/dry collector, at least those with which most
often come to our attention here at the CAL. Hopefully this list can
refer you to an appropriate flow chart so that you can begin the trouble
shooting steps necessary to get your collecor back into operation.
Symptom Flow Chart(s) No.
Collector stays open long after 1
precipitation event ends
Event recorder not working 1 and 2
Sensor ices up during cold weather 3
Collector stuck over dry-side bucket 4
Collector cycling continuously 5
Collector stays on wet-side bucket 6
although sensor grid and plate are
shorted
**Note; ALL OF THE FOLLOWING FLOWCHARTS ASSUME THAT THERE IS ADEQUATE
POWER TO THE UNIT. INCLUDING THAT THE FUSES ARE INTACT.
4-7
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Revision No. 0
Date: Scot. 5. 1984
FLOW CHART #1
COLLECTOR STAYS OPEN LONG AFTER
PRECIPITATION EVENT STOPS
WET COLLECT HEATER
IN SENSOR.NOT WORKING
CHECK THAT THE EVENT RECORDER (ER) IS OPERATIONAL AND/OR THAT
A 14± 3VDC CURRENT IS PRESENT AT THE EVENT RECORDER TERMINAL
(19). NOTE: THIS REQUIRES THAT THE COLLECTOR BE IN THE WET
COLLECT MODE.
ER OK OR
TERMINAL
CHARGED
THEN
1
SENSOR UNIT BAD
(CALL THE C.A.L.)
1)
ER NOT WORKING
AND INCORRECT
VOLTAGE FROM
TERMINAL
THEN
IF VOLTAGE OUTSIDE RANGE
THE MOTOR BOX IS BAD
(CALL THE C.A.L.)
2) IF NO VOLTAGE SEE
FLOWCHART #2
4-8
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Revision No. 0
Date: Sept, 5, 1984
FLOW CHART #2
EVENT RECORDER NOT WORKING
NOTE:
NO POWER TO ER TERMINAL (19)
DON'T FORGET TO CHECK ER TERMINAL FUSE AT 24
CHECK
CLUTCH UNIT TO MOTOR BOX
UNIT CLEARANCE
IF
CLUTCH UNIT LOOSE ON DRIVE
MOTOR SHAFT (27) OR MORE THAN
1/8-1/4 INCH AWAY FROM MOTOR
BOX
THEN
CLUTCH UNIT TIGHT ON DRIVE
MOTOR SHAFT (27) AND < 1/4
INCH FROM MOTOR UNIT ~
THEN
REPOSITION CLUTCH UNIT
(SEE A BELOW)
MOTOR BOX UNIT IS FAULT
(CALL THE C.A.L.)
A problem exists if the clutch unit is too far from the motor box unit.
The magnets in the clutch can only trip the switches in the motor box if
they are within ,1/4 inch. See the text of this guide, Section 4.3
page4-6 for more information on clutch position.
4-9
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Revision No. 0
Date: Sept. 5, 1984
FLOW CHART #3
SENSOR ICES UP IN COLD WEATHER AND SNOW
AMBIENT WEATHER
MODE MALFUNCTIONING
V
TEST BY PLACING SNOW
OR ICE ON SENSOR
SNOW OR ICE MELTS,
SENSOR IS OK
SNOW OR ICE DOESN'T
MELT, SENSOR IS BAD
(CALL THE C.A.L.)
4-10
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Revision No. 0
Date- Sept. 5, 1984,
FLOW CHART #4
COLLECTOR STUCK OVER DRY-SIDE BUCKET
LID MECHANISM COVERING DRY BUCKET, NO RAIN
MOTOR NOT. RUNNING
THEN
I
UNPLUG SENSOR AT (20)
LID MECHANISM MOVES TO
COVER WET-SIDE BUCKET
THEN
CHECK SENSOR GRID AND PLATE
(5 AND 6) FOR SHORT (e.g.,
BIRD FECES, PLANT PART)
LID MECHANISM STAYS OVER
DRY-SIDE BUCKET
THEN
MOTOR BOX UNIT BAD
(CALL THE C.A.L.)
IF
SHORT PRESENT, CLEAN
WITH OLD TOOTHBRUSH
AND D.I. WATER,
RETEST
NO SHORT.
SENSOR BAD
(CALL THE C.A.L.)
4-11
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Revision No. 0
Date: Sept. 5, 1984
FLOW CHART #5
COLLECTOR CYCLING CONTINUALLY
IF
WET/DRY LID CONTINUALLY MOVING
FROM WET TO DRY-SIDE
THEN
UNPLUG SENSOR UNIT AT (20)
WET/DRY SHUTS
OFF ON WET-SIDE
THEN
V
REPLACE SENSOR
(CALL THE C.A.L.)
WET/DRY CONTINUES
TO CYCLE
THEN
MOTOR BOX. PROBLEM
CHECK CLUTCH UNIT POSITION
(REF. FLOW CHART #2)
CLUTCH POSITION BAD, CLUTCH POSITION OK,
REPAIR, TEST MOTOR BOX BAD.
(CALL THE C.A.L.)
4-12
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Revision No. 0
Date: Sept. 5, 1934
FLOW CHART #6
COLLECTOR NOT OPENING TO EXPOSE WET-SIDE
IN HEAVY RAINFALL
SENSOR GRID AND PLATE (5 AND 6) SHORTED
BUT LID REMAINS ON WET-SIDE BUCKET
THEN
PUSH CLUTCH UNIT
COUNTERCLOCKWISE
~3 INCHES
IF
MOTOR BOX CYCLES
COLLECTOR LID
MOTOR BOX DOES NOT COME
ON TO CYCLE LID
THEN
THEM
SENSOR IS BAD
(CALL THE C.A.L.)
MOTOR BOX IS
BAD
(CALL THE C.A.L.)
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Revision No. 0
Date: Sept. 5, 1984
5. COMPONENT REPLACEMENT AND ROUTINE SERVICING
1. Component Replacement
a. Motor box - This component can be removed by separating the
sensor plug from the sensor socket (20), removing the clutch
arm machine bolt (11), and then removing the four motor box
attachments (7) from the collector main frame (2). Threaded
inserts are used in the motor box so there are no nuts to
replace.
WARNING: The motor box will literally fall out when the last of
the four screws are removed. Make plans to support it in some
fashion.
Last, with the box on the ground and in easy access, remove
the event recorder leads from their terminal (19).
b. Sensor unit - This component is easily removed by separating
the sensor socket (20) from the sensor plug in and removing the
four sensor attachments (3). Again, the main frame is equipped
with threaded inserts so there are no nuts to contend with.
c. Clutch unit - The clutch can be removed from the motor drive
shaft by choosing an appropriately sized Allen wrench and
loosening the set screw at (29). Then simply pry the clutch
assembly off using a sturdy screwdriver. Please reference page
10 of this manual for additional remarks concerning replacement
and maintenance.
Remember to return all used components to the manufacturer promptly.
2. Routine Servicing
In general, the Aerochem Metrics wet/dry collector is
maintenance free. The one routine service chore which all-sites
should perform is the testing of the sensor "switching" and heating
functions. It is recommended that these tests be incorporated into
weekly wet-side bucket changes using the steps listed below.
a) First, feel the sensor grid. Assuming it has not been raining,
it should be cool.
b) Short the sensor grid and plate with water (water is better than
metal for this test, due to its lower conductivity.)
5-1
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Revision No. 0
Dace: Sept. 5, 19b4
c) Allow the lid mechanism to move over and cover the dry-side
bucket.This step (1) checks Che switching function of che
sensor, (2) checks Che lid driving mechanism of the collector,
and (3) keeps the lid mechanism out of the way while you make
your bucket change.
d) Change buckets, (reference NADP Instruction Manual for Site
Operations).
e) After the collector has been open for at least 5 minutes.
feel the sensor grid. In all but very cold temperatures the
heater should be easy to feel.
f) Blow remaining water off the sensor, allowing the lid mechanism
to return to the wet-side bucket and the motor box to shut off.
Other Routine Servicing Suggestion:
a) Periodically clean the sensor grid so as to remove any
accumulation of minerals or contamination that could close the
circuit and thus present a false "wet" signal. To clean the space
between the grid and the plate, cut a strip of cardboard from a time
card or a manila folder to a width of about 1.8 inches (4.5 cm);
this can be passed between the Teflon washers which fix the
separation of the grid and plate, or simply use an old toothbrush
and deionized water or alcohol to remove accumulated material.
b) As needed, clean the lid, roof and arm mechanisms to remove any
residues (e.g., bird feces, dust, other organic material).
5-2
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- NOTES -
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Appendix B
INSTRUCTION BOOK FOR UNIVERSAL RECORDING RAIN GAUGE
B-l
-------
BELFORT INSTRUMENT COMPANY
INSTRUCTION MANUAL
CATALOG NUMBER 5-780 SERIES
UNIVERSAL RECORDING RAIN GAGE
727 SOUTH WOLFE STREET
BALTIMORE MARYLAND 21231-3513
301-342-2626
TELEX-87528 BELFORT BAL
MARCH 15,1986 INSTRUCTION MANUAL NUMBER 8777
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BELr-OHl INblhUhibHI COMPANY
FACTORY AND SALES • 727 S. Wolfe Street • Baltimore, Maryland 2 1231 • Telephone (301) 342-2626 • Telex B7528 (BELFORT BAL)
SALES AND SERVICE « 2620 Concord Avenue » 102 • Alhambra. California 91603 « Telephone (BIB) 282-4893 » Telex 6831 262 (BLFCA)
Belfort Warranty Statement
Belfort Instrument Company warrants that its manufactured equipment shall conform to
applicable specifications, as stated by Belfort Instrument Company, at the time of ship-
ment from a Belfort Instrument Company facility, and if used and maintained in normal
and proper manner in accordance with Belfort Instrument Company's instructions (in-
cluding without exception, Belfort Instrument Company's recommendations regarding
operating and maintenance procedures) shall remain free from defects in workmanship
and material for a period ending one (1) year (90 days for potentiometers, semiconductor
devices, batteries, fuses, relays, lamps and tubes) from the date of original shipment from
a Belfort Instrument Company facility.
Belfort Instrument Company's obligation under this Warranty shall be limited to repair at
either its main plant (727 S. Wolfe Street, Baltimore, MD 21231) or its Western Regional
facility (2620 Concord Avenue, #102, Alhambra, CA 91803) or, at its option, replacement of
the defective Product. In no event shall Belfort Instrument Company be responsible for in-
cidental or consequential damages, whether or not foreseeable or whether or not Belfort
Instrument Company has knowledge of the possibility of such damages. This Warranty
shall not apply to Products which have been altered, operated or maintained in a manner
not approved by Belfort Instrument Company, or which have been damaged through
negligence, accident, or misuse.
In order for any claim under this Warranty to be valid, such claim must be made in writing
to either facility mentioned above, Attention: Customer Services, within a reasonable
period of time, not to exceed 30 days after the defect is discovered, and all such claims are
subject to substantiation by Belfort Instrument Company's Inspection Department. Belfort
Instrument Company may require the return of the alleged defective Product or part to
establish a claim under this Warranty. Transportation charges to the factory shall be pre-
paid by the customer; transportation for the return of the repaired equipment to the
customer shall be paid by Belfort Instrument Company when legitimate claim to Warranty
has been established; else, Belfort Instrument Company will prepay shipment and bill the
customer. All shipments shall be accomplished best way surface freight. Should alter-
native shipment be required, Belfort Instrument Company shall be responsible only for that
portion of cost as would be applicable to best way surface freight. Belfort Instrument Com-
pany will not allow any credit for repairs or alterations to its Products, and Belfort Instru-
ment Company shall in no event assume any responsibility for repairs or alterations made
other than by Belfort Instrument Company. Any Products repaired or replaced under this
Warranty will be warranted for the balance of the warranty or warranted operating time re-
maining with respect to the original purchased Product.
BELFORT INSTRUMENT COMPANY HEREBY EXCLUDES ALL WARRANTIES OF
CHANTABILITY AND FITNESS FOR ANY PURPOSE, AND ALL OTHER WARRANTIES, EX-
PRESS OR IMPLIED, ON THE PRODUCTS, OTHER THAN THE WARRANTY STATED
ABOVE. Representations or warranties that are inconsistent with this Warranty made t>V
any person, including employees or representatives of Belfort Instrument Company, shall
not be binding on Belfort Instrument Company. The period of limitations for any cause of
action arising out of, based upon or relating to this Warranty is hereby reduced to and shaH
be a period of one year after such cause of action occurs.
-------
TABLE OF CONTENTS
SECTION DESCRIPTION PAGE
1. INTRODUCTION 1
2. DESCRIPTION
2.1 General 1
2.2 Weighing Mechanism 1
2.3 Single-traverse Gages 1
2.4. Dual-traverse Gages 1
2.5 Zero Adjustments 1
2.6 Technical Characteristics 3
2.7 Government Specifications 3
3. INSTALLATION
3.1 Unpacking 3
3.2 Gage Exposure 3
3.3 Mounting 3
3.4. Installation 4
4. OPERATION
4.1 Chart Changing 6
4.2 Chart Sets 7
4..3 Gage Winterizing 7
5. MAINTNENACE 7
6. CALIBRATION
6.1 General 10
6.2 Calibration Equipment 10
6.3 Pre-calibration 10
6.4. Single-traverse Calibration 10
6.5 Dual-traverse Calibration 11
7. REPLACEMENT PARTS LIST 13
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LIST OF ILLUSTRATIONS
FIG. NO. TITLE PAGE
1 Outline - Universal Recording Rain Gage 2
2 Removal of Dashpot 5
3 Linearity Setting, Dual-traverse Gages H
4. Universal Recording Rain Gage 16
5 Rain Gage Mechanism, Front View 18
6 Rain Gage Mechanism, Single-spring 22
7 Rain Gage Mechanism, Dual-spring 26
LIST OF TABLES
1 Gage Catch Freezing Temperatures 8
2 Available Rain Gage Charts 9
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1. Introduction
This instruction book contains all the
necessary information for the instal-
lation, operation, maintenance and
calibration of the Belfort Instrument
Company Cat. No. 5-780 Series Univer-
sal Recording Rain Gage.
2. Description
2.1 General. The Cat. No. 5-780
Series Universal Recording Rain Gages
are weighing-type gages in which a
weighing mechanism converts the weight
of the rainfall caught by a circular,
horizontal opening at the top of the
gage into the curvillinear movement of
a recording pen which makes an inked
trace on a rectangular paper chart.
The chart, graduated in inches, or
millimeters of rainfall, is wrapped
around a vertical cylinder which is
rotated either by an 8-day spring-
powered, or a long-term battery-pow-
ered, chart drive. In some gages of
this series the record capacity of the
gage is reached in a single traverse
of the pen across the chart; in others
it is reached after a double traverse
of the pen.
2.2 Weighing Mechanism. The rain-
fall falling through the 8"-diameter
collector (fig 4, #1) is caught in a
bucket (5) resting on a platform (6)
mounted to the vertical link of a 4-
bar linkage. The vertical link, or
movement bracket (Fig. 5, #15), is
supported from the mechanism frame by
a precision extension-spring assembly
(Fig 5, #9). The upper horizontal
link, or top lever (Fig 5, #6), of
the linkage is provided with an adj-
ustable extension (3) by which the
deflection of the spring is multiplied
and modified to fit the requirements
°f the recording mechanism. A second
horizontal link, or lower lever (ns),
Provides the additional constraint
needed to keep the movement bracket
vertical throughout its deflection.
^he top and lower levers turn in the
mechanism frame; the movement bracket
turns in the top and lower levers. A
Umit screw (Fig 6, #14) at the top
rear of the mechanism prevents the
ecording pen from striking the chart
Blinder flange when the catch bucket
18 removed from the gage by limiting
the upward movement of the top lever.
A second limit screw (Fig 4, #11),
attached to the movement bracket,
prevents the pen from falling off the
top of the chart cylinder in single-
traverse gages and from striking the
chart cylinder flange in dual traverse
gages. The bottom of the movement
bracket is linked to the piston of a
damping device, a dashpot (Fig 6, #2),
to reduce pen arm vibrations due to
wind gusts.
2.3 Single-Traverse Gages. In sin-
gle-traverse gages, only one link
(Fig 6, #8) and lever (5) is used to
transmit the motion of the top lever
to the pen arm shaft (33). For this
application, the lever extension (11)
is mounted to the rear finger of the
top lever.
2.4 Dual-Traverse Gages. In dual-
traverse gages, a second lever exten-
sion, and adjustable slotted link
(Fig 6, #7), and a counterweighted
lever (3) are added between the top
lever and the pen arm shaft. Addit-
ionally, a non-adjustable slotted linl
(8) and lever (5) replace the link
and lever used in the single-traverse
gages. In the first, upward traverse
of the pen arm (27), the counterweight
keeps the shorter rear lever (5) in
contact with the top of the slot in
the non-adjustable link (8) as the
top lever extension, link, and pen
arm move upwards, When the pen (28)
reaches the top of the chart, the
counterweighted lever (3) comes into
contact with the bottom of the slot
in the adjustable link. Continued
upward movement of the lever exten-
sion and link moves the pen arm down-
ward through its second traverse. The
slot in the nonadjustable link permits
the lever and the pen arm to move
downward even through the link is
moving upwards.
2.5 Zero Adjustments. All gages are
equipped with both coarse (Fig.6, #15)
and fine (20) zero adjustments with
which the pen may be set on the zero-
line of the chart. This setting must
always be made with an empty catch
bucket, or bucket-equivalent calib-
ration weight, on the weighing mech-
anism, In making continued zero ad-
-------
'/8 SCALE
DIMENSIONS IN INCHES
k- 8-3/32 O.DIA.
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5-3/8
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k 45°
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-7/16
1 I
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C
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I7/64D.HOLE,3PLCS
120° APART
3/8D.HOLE,3PLCS
120° APART
35-3/8
22-1/2*
5-3/8 R.
3-5/8 R.
Figure 1. Outline - Universal Recording Rain Gage
-------
justments, care should be taken to
make use of both adjustments so as to
keep the bar of the fine adjustment
(42) reasonably parallel to the top of
the mechanism frame.
2.6 Technical Characteristics.
Accuracy: 1/3 of 1% F.S. for single-
traverse gages, (-40 to +125 F.)
1/2 of 1% F.S. for dual-traverse gages,
(-40° to +120°F.)
Sensitivity: 0.01" of precipitation.
Collector Diameter: 8.00"
Chart Record: 6" wide x 11-1/2" long
Chart Periods: 6,12,24,48,96,168,
and 192 hours per revolution for 8-
day, spring-powered chart drives; any
of the preceding periods and 861 hours/
rev. for 3-volt battery-powered chart
drives.
Chart Timing Accuracy: within 14
minutes/week
Finish: aluminum lacquer
Gage Weight: 25 Ibs., empty
2.7 Government Specifications. The
Cat. No. 5-780 Series Universal Re-
cording Rain Gages are built to Nation-
al Weather Service Specifications
#450.2201 and 450.2203.
Ranges:
Range, 0- 6" ST 4.8" DT
Cat. No.
5-780
-6
04.8
12"DT
No Dash
No.
300mmDT
-300MM
20"DT
-20
SOOmmDT
-500MM
3. Installation
3.1 Unpacking. Unpack the gage
carefully. The chart set supplied
with the gage is to be found inside
the top insert of the carton. The
chart cylinder has been removed from
the chart drive and stowed in the
catch bucket along with the recording
ink and damping fluid. To get at
these items, cut the tie through the
collector padlock staples, rotate the
collector sufficiently to disengage
the bayonet lock, and lift the col-
lector up and off of the gage housing.
3,2 Gage Exposure. The exposure of
a rain gage is of primary importance
to the accuracy of precipitation mea-
surements. An ideal exposure for the
8age would eliminate all air turbu-
lence near the gage tending to carry
Precipitation away from the gage.
Loss of precipitation in this manner
lncreases with increase in wind speed.
Selection of the rain gage site should
be based on the following considera-
"• The extensive presence of objects
which individually or in small groups
would constitute obstructions may
Prove beneficial in reducing prevail-
In8 wind speed, and subsequent air
turbulence, in the vicinity of the
gage. As a general rule for those
areas where the height of the objects
and their distance from the gage are
generally uniform, their height above
the gage should not exceed twice their
distance froa the gage.
B. In open areas, serious air turbu-
lence may be created near individual
or small isolated groups of objects.
As a general rule, the height of such
objects above the gage should not ex-
ceed half their distance from the gage.
C. Wind shields of the Alter type may
be employed to minimize losses in the
precipitation catch.
D. In areas where heavy snowfall oc-
curs, the gage should be mounted on a
support (tower) at a height well above
the level of average snowfall accumul-
ation.
E. Good exposures are not always per-
manent. The growth of vegetation,
trees, and shrubbery, as well as man-
made alterations about the site, may
change an excellent exposure into a
poor one in a relatively short time.
3.3 Mounting. A sturdy wooden, or
concrete, foundation should be pre-
pared for mounting the gage at the
-------
required height above ground level.
It is essential that the edge of the
collector opening be horizontal as
determined by a carpenter's level.
The gage design is such that this con-
dition will be satisfied if provision
is made to insure that the surface
to which the gage is mounted is hori-
zontal, whether it be the foundation
or the accessory support base (Fig 4,
#4). The support base can be bolted
to either type of foundation or im-
bedded in the concrete foundation.
3.4 Installation. The rain gage is
installed on its foundation as fol-
lows :
A. Remove the collector (Fig 4, #1)
by rotating it sufficiently clockwise
to disengage the bayonet lock and pul-
ling it up and off of the gage housing.
Use extreme care not to distort the
area of the collector opening.
B. Remove the catch bucket. The
chart cylinder, recording ink, and
damping fluid have been packed and
shipped in the bucket.
C. Remove the screw (Fig 6, #19),
washer (18), and bucket platform (17).
D. Remove five screws and washers
(Fig. 4, #3), and remove gage housing
(2) from the base (9). Note the lo-
cation of the sliding access door rel-
ative to the chart drive and pen arm.
E. Three 3/8"-diameter holes, 120°
apart on a 10-3/4"-diameter circle,
are provided in the mechanism base for
mounting it to the support base or
foundation. Exercise extreme care in
mounting the mechanism base: the
machined gage housing shoulder must
be horizontal, and the bolting-up
must not distort the base. Hardware
for mounting the mechanism base is not
supplied with the gage, however, hard-
ware is supplied with the support base
for mounting it to the mechanism base.
Additionally, hardware is supplied
with the support base for mounting it
to the foundation, or to assist in
imbedding it in the concrete foun-
dation.
F. Remove the shipping tie holding
the pen arm to the pen shifter (Fig 5.
#13).
G. Loosen the mechanism locking screw
(Fig 6, #21), and nut, and back out
the screw until the top lever is stop-
ped by limit screw (14). Retract the
locking screw a turn or two farther;
lock in position with its nut. Remove
the stop sleeve (Fig. 4, #8) from
about the movement bracket limit
screw (7). Do not discard the sleeve;
it will be needed for reshipment of
the gage. Do not disturb the setting
of the limit screws (Section 2.2);
their positions are a part of the
gage's calibration.
H. Remove the wrapping from the
chart drive mechanism, and unscrew
mechanism from the base.
I. The dashpot (Fig. 2, #3) is mount-
ed to the mechanism base with two
identical thumbscrews (1,2). Remove
thumbscrew (2), loosen thumbscrew (1),
push up the dashpot cover (4), and
pull dashpot out from between the
mechanism frame as shown in Fig. 2 (a)
and (b).
J. From the bottle of damping fluid
shipped in the catch bucket, fill the
dashpot cylinder to within an 1/8" of
its rim, and replace the dashpot bet-
ween the mechanism frame. Empty the
catch bucket, setting aside the re-
cording ink and discarding all packing
materials, and set the bucket on its
platform. If the gage is equipped
with an overflow attachment, the over-
flow tube is placed in the round hole
in the platform centering the tube
over the overflow funnel mounted in
the mechanism base.
K. Replace the chart drive mechanism.
The mounting stud of the chart drive
mechansim has been adjusted so that
the winding key of the spring-powered
chart drive and the movement viewing
part of the battery-powered chart
drive are accessible from the sliding •
access door of the gage housing. Make
certain that the stud flange is firm-
ly seated against its mounting surface,
but do not overtighten the mechanism
and disturb the stud setting.
L. Remove thumbnut from chart drive
mechanism spindle. Mount chart
cylinder (with chart clip), supplied
in the catch bucket, on the spindle,
making certain that the mechanism
-------
rxxxxxx xxxx XXX XX X x x
(a)
jxxxxxx xx x xxx
xx xxx x x
Figure and
Index Number
2-1
-2
-3
-4
-5
(b)
Figure 2. Removal of Dashpot
Manufacturer's
Part Number Description
7207
7207
8621
928
8623
Screw, Mounting - Dashpot
Screw, Mounting - Dashpot
Dashpot Cylinder Assembly
Cap, Dashpot
Piston, Dashpot
-------
pinion and the cylinder gear are
meshed, and replace the thumbnut.
M. Replace the gage housing, posi-
tioning it on the mechanism base so
that the chart drive and pen arm are
accessible from the sliding access
door. If the gage is equipped with
overflow protection, make certain that
the overflow-clearance hole in the
dust shield, which rests on an interior
bead of the gage housing, is centered
over the overflow funnel in the base.
Fasten the housing in place with five
screws and washers (Fig. 4, #3).
N. Replace the bucket platform (Fig
6, #17) on the movement bracket (16),
and fasten it in place with the wash-
er (18) and screw (19). If the gage
is equipped with an overflow attach-
ment, make certain the round hole in
the bucket platform is over the over-
flow funnel (Fig. V, #6) mounted in
the mechanism base.
0. Replace the collector on the gage
housing, reversing the procedure of
par. A of this section. The collector
can be padlocked to the gage housing
through the staples provided on each.
P. The gage housing and its sliding
access door are equipped with a slid-
ing-bolt and staple so that the door
can be padlocked shut.
Q. Using the large zero and fine
adjustment screws, (Fig 6, #20,15),
re-zero the pen.
R. The gage is now ready to be put
into operation.
4. Operation
4.1 Chart Changing. The chart drive
and pen arm are accessible from the
sliding access door in the gage
housing. The following procedure
should be followed when changing
charts:
A. Open the sliding access door, and
make a short vertical mark (time-
check) on the chart by lightly touch-
ing the bucket platform. If the
chart drive has stopped, turn the
chart cylinder slightly in both dir-
ections to mark the existing pen po-
sition. If the pen is not making a
trace, indicate the pen position by
a dot enclosed in a circle.
B. Lift the pen off of the chart by
moving the pen shifter (Fig. 5, #13)
outward.
C. Remove the collector, and empty
the catch bucket except during the
winter when the bucket may be changed
with an anti-freeze solution (par. 4.
3,B) or when oil has been added to the
catch to retard evaporation.
D. Remove the chart cylinder thumb-
nut, and remove the cylinder by lift-
ing it up and off of its spindle.
Take care not to smear the pen trace.
Release the chart clip holding the
chart, and remove the chart. Do not
store the chart until the pen trace
his dried.
E. Wind the chart drive if it is
spring-powered. The battery-powered
chart drive will need no preparation
for a new recording period unless the
time has arrived for a battery change.
Refer to the chart drive instructions
for deta-ils of the chart operation.
F. Clean the pen if necessary: refer
to instruction book #12049, included
with these instructions, for proper
care of the recording pen.
G. Mount new chart to the cylinder
as follows:
1. If chart is the double-tab
type, fold righthand tab under back
of chart, and wrap chart snugly around
cylinder so that a) time is read from
left to right, b) corresponding rain-
fall graduations meet, c) the bottom
edge of the chart is against the
cylinder flange, d) the folded end of
the chart overlaps the opposite end,
and e) the crease in the fold is at
the right-hand edge of both the notch
in the upper edge of the cylinder and
the slot in the cylinder flange.
2. Clamp the chart to the cylin-
der by placing the clip inside the
fold at the overlapping end of the
chart, placing the straight end of the
clip in the slot in the cylinder, and
seating the formed end of the clip in
the notch in the upper edge of the
cylinder.
3. If the chart is the single-
edge type, wrap it snugly around the
cylinder so that a) time is read
to right, b) corresponding rainfall
-------
graduations meet, c) the bottom edge
of the chart is against the cylinder
flange, d) the untabbed end is at the
right-hand edge of both the notch in
the upper edge of the cylinder and
the slot in the cylinder flange.
4. Clamp the chart to the cylin-
der by placing the clip over the un-
tabbed end of the chart, inserting
the straight end of the clip into the
slot in the cylinder flange, and
seating the formed end of the clip
in the notch in the upper edge of the
cylinder.
H. Replace the chart cylinder and
thumbnut on the chart drive mechanism
spindle making certain that the
mechanism pinion and cylinder gear
mesh.
I. Refill the pen, and push in pen
shifter to return the pen almost to
the chart surface. If the catch
bucket is empty, and the pen does not
indicate zero within the gage toler-
ance, set the pen to the zero line
with the coarse (Fig. 6, #15) and fine
(20) adjustment screws. Set chart to
time by first turning the cylinder
clockwise past the correct time and
then returning it counterclockwise to
the correct time. Be sure the time is
correctly set with respect to a.m. or
p.m.
J. Push the pen shifter all the way
in to put the pen on the chart. Light-
ly touch the bucket platform to make
a time check on the chart. The gage
is now ready for a new recording
Period. Close and padlock the access
door.
4.2 Chart Sets. Charts available
for use with the 5-780 Series Rain
Gages are listed in Table 2. Chart
sets of the 6 through 192-hour period
charts contain 100 charts; sets of
the 861-hour charts contain 25 charts.
4.3 Gage Winterizing. During the
winter months the gage should be
Protected against possible damage
**om snow, ice pellets, and freezing
temperatures by taking the following
8teps:
Remove the funnel fixed to the
of the collector (Fig. 4,
*°tate the funnel until its bead
clears the pens in the collector tube,
and lift it off.
B. Empty the catch bucket, replace it
in the gage, and add to it an anti-
freeze solution composed of two pints
of ethylene glycol and three pints of
methyl alcohol (methanol). Add six.
ounces of a 10W motor oil to the
solution to retard evaporation.
C. Do not make any adjustment to the
gage after adding the anti-freeze and
oil to the bucket: the gage will
indicate a rainfall level of approxi-
mately 2-3/4".
D. The anti-freeze solution and oil
are self-mixing with respect to the
snow and ice added to it. Table 1
gives the approximate freezing temp-
eratures of the anti-freeze solution
when diluted by additional water-
content to the gage levels indicated.
The catch bucket should be emptied
and recharged with fresh anti-freeze
and oil whenever the gage level and
the prevailing temperatures indicate
that freezing of catch is probable.
5. Maintenance
The frequency with which the gage is
serviced will depend on the environ-
ment of the gage: as frequent as once
every three months in dusty climates;
as infrequent as once a year in mild
climates. The appearance of the gage
at regular operational visits will
make apparent the need for servicing.
The following procedures and recom-
mendations should be made part of the
gage service schedule:
A. Clean all moving parts with a soft
brush moistened with varsol. Solvents
that attack paint must never be used
for this purpose.
B. Except as required in the chart.
drive mechanism, never oil any part
of the gage: corrosion-resistant
materials have been used throughout
the gage's construction, and oil will,
in time, become gummy and cause slug-
gishness in the gage's operation.
C. Examine the weighing mechanism
linkage for evidence of excessive
friction. If corrections for this
fault require significant disassembly
or part replacement, recalibrate as
described in Section VI.
-------
D. Clean the bucket thoroughly. Suf-
ficient foreign matter accumulating
in or on the bucket, adding to its
weight, can cause depletion of avail-
able zero-adjustment.
E. Inspect the dash pot: add sili-
cone fluid, if necessary, to cover
the piston when it is in its upper-
most position (gage zero.)
F. Clean the pen:
book #12049.
see instruction
G. Inspect the chart drive, and if
necessary, service it. See instruc-
tion book #12049 for details of chart
drive maintenance.
H. If recalibration of the gage is
necessary, it may be returned to the
factory for this purpose. However,
for the do-it-yourself gage owner,
complete calibration instructions are
given in Section 6. Additionally,
calibration-weight sets of various
capacities are listed in Section 7.
TABLE 1
GAGE CATCH FREEZING TEMPERATURE
(Glycol-Methanol-Water Mixture)
GAGE LEVEL, INCHES
FREEZING TEMPERATURE, °C
6
-40
7
-30
8
-23
10
-13
12
-4
-------
TABLE 2
AVAILABLE RAIN GAGE CHARTS
CHART
NUMBER
5-400 3-B
5-4006-MM
5-404 1-B
5-4042-B
5-4044-B
5-4045-B
5-4046-B
5-4046-MM
5-4047-B
5-4047-MM
5-4048-B
5-4049-B
5-4050-B
5-4068
15620
15668
15669
RANGE
0 to 6", ST
0 to 150mm, ST
0 to 12", DT
0 to 12", DT
0 to 12", DT
0 to 12", DT
0 to 12", DT
0 to 300mm, DT
0 to 12", DT
0 to 300mm, DT
0 to 4.8", DT
0 to 4.8", DT
0 to 4.8", DT
0 to 20", DT
0 to 300mm, DT
0 to 12", DT
0 to 20", DT
CHART
PERIOD
HRS/REV
24
192
6
12
48
96
192
192
24
24
6
24
192
168
861 (1)
861 (1)
861 (1)
GRID SIZE
WIDTH
6"
6"
6"
6"
6"
6"
6"
6"
6"
6"
6"
6"
6"
6"
6"
6"
6"
LENGTH
11.52"
11.30"
11.52"
11.52"
11.52"
11.52"
11.52"
11.30"
11.52"
11.30"
11.52"
11.52"
11.52"
11.52"
11.52"
11.52"
11.52"
LEAST DIVISION
RANGE
.05"
1 mm
.05"
.05"
.05"
.05"
.05"
1 mm
.05"
1 mm
.02"
.02"
.02"
.10"
1 mm
.05"
.10"
TIME
20 min
2 hrs.
5 min.
10 min
15 min
1 hr
2 hrs.
2 hrs.
15 min
15 min
5 min.
15 min
2 hrs.
2 hrs.
6 hrs .
6 hrs .
6 hrs .
-------
6. CALIBRATION PROCEEDURES
6.1 General
Calibration of the gages described
herein is based on the assumption that
822.7 grams is the weight of a volume
of water 1" high with an area equal to
the area of the 8" diameter collector
opening of the gage. It also assumes
that the weight of the bucket used in
the 12" (300mm) gage is one kilogram
and 2.1 kg for the 20" (500mm) gages,
and that the gage zero-adjustment
range is sufficient to accomodate nor-
mal variations in bucket weight.
6.2 Equipment
Calibration of the gages requires one
of the calibration weight sets as
listed in Section 7, Parts List, and a
small machinist's level (approximately
2" long). Each set consists of an
equivalent-bucket weight, a number of
calibration weights, and a linearity
setting tool (Figure 3, #4). Inch
weights are finished in aluminum lac-
quer; mm weights in gold.
6.3 Pre-Calibration
Calibration of all gage mechanisms re-
quires the mechanism base to be level
and the following preliminary adjust-
ments to be made:
A, Loosen the Limit Screws (Figure* 4,
#7; Figure 6, #14 and 21) suffi-
ciently enough so that endplay is
not restricted on the Back Shaft
(22), the Movement Bracket (16),
the Top Lever (19), the Extension
Levers (12), the Lower Casting
(ns), and the Pen Arm Shaft (38),
within the range of the calibra-
tion.
B. Center the screws and nuts (12) in
the slot lengths of the Lever Ex-
tension (11).
6.4 Single Traverse Calibration
A. Center the equivalent-bucket
weight in the bucket platform, and
place a number of calibration
weights equal to one-half of the
gage capacity on the bucket weight.
B. Place the machinist's level across
the two pads'in front finger of
the Top Lever (23), and rotate the
linkage with the zero-adjustment
thumbscrews (15 and 20) so as to
make the pads level. In making
continued zero-adjustments, care
should be taken to make use of botl
the Fine and Large Adjustment Screws
so as to keep the Fine-Adjustment
setting bar reasonably parallel to
the top of the mechanism frame.
C. Loosen the Set Screw (6) fastening
the Lever (5) to the Pen Arm Shaft
(33), and rotate the Pen Arm Shaft
to put the recording pen in the
center of the chart; retighten the
set screw.
D. Remove the calibration weights from
the bucket weight. Set the pen to
the zero-line of the chart; rotate
the thumbscrews (15 and 20) clock-
wise to lower the pen and counter-
clockwise to raise it.
E. Place all calibration weights on the
bucket weight, one at a time. Check
the pen position after the addition
of each weight to determine if the
pen position is within the accuracy
tolerance of Section 2.6.
F. If the pen movement is linear but
the pen positions are not suffi-
ciently accurate, it will be neces-
sary to change the Lever Extension
(11) length. Moving the link pivot
(10) away from the top lever will
raise the pen position. Remove the
calibration weights, loosen the
nuts (12) fastening the extension
sufficiently to move the extension
with the screw (13), and make the
adjustment with the screw - one
turn of the screw will move the pen
about one chart division; retighten
the nuts. If an outward adjustment
is required, back out the screw
sufficiently to allow an over-ad-
justment of the extension, and re-
turn to the required adjustment by
use of the screw. Rezero the pen,
and repeat the procedure of Para-
graph E. Repeat the procedures of
Paragraph E and this paragraph un-
til the pen positions are within
tolerance.
G. If the pen movement is unlinear as
well as inaccurate, it will also be
necessary to rotate the pen shaft
(33) relative to the Lever (5).
Viewed from the pen arm side of the
gage, rotation of the pen arm shaft
in a counter-clockwise sense rela-
tive to the lever will increase the
pen movement per calibration weight
in the upper-half of the chart;
-------
Figure and
Index Number
6-14
-15
-16
Manufacturer's
Part Number
8471
-17
-18
-19
-20
-21
-22
-23
-24
-25
952
8713
985
8586
3279
953
16471
908
8319
8317-1
8306
16072
16072-1
16472
8471
8597
8292
10504
993
8717
7204
8741
8722
934
8886
8586
3279
16252
16250
Description
Screw, Adjustment (limit)
10-32 Hex Nut, ST, ST
Thumb Nut (Coarse Zero Adjust)
.Bracket Movement
Shaft, Plain
2-56 x 5/6" Fil. Hd. Screw, ST, ST
Shaft (Connector) Dashpot Piston
Retainer Clip, Shaft
Platform Bucket
Platform Bucket with overflow option
Washer, Bucket Platform
V-20 x 7/8" Flat Hd. Screw, ST, ST
Zero Setting Assembly (Fine)
Setting Bar Assembly
Screw, Setting
Zero Setting Assembly (for 20" and 500MM
Gages)
Setting Bar Assembly (for 20" and 500MM
Gages)
Screw, Setting (for 20" and 500MM Gages)
Screw, Adjustment (Limit)
10-32 Hex Nut, ST, ST
Mechanism Frame
Front Sideplate Assembly
Plate, Top
Plate, Top (for 20" and 500MM Gages)
Pen Shaft Bracket Assembly
Angle Bracket Base
Sideplate, Rear
Bracket, Stop (Limit)
6-32 x 3/16" Bd. Hd. Screw, ST, ST
8-32 x 5/16" Bd. Hd. Screw, ST, ST
Lever, Top
Shaft (Long), Lever
Washer, Flat
Shaft, Dash Pot Pivot (Spring Link)
Retainer Clip, Shaft
Bracket, Zero Adjust
Stud, Pen Arm
-------
Co Che proper reading, (k turn
is approximately one division.)
3. Once adjusted to the proper
reading, retighten the nuts (12).
4. Remove all the weights.
5. Using the Large Zero Adjust
Knob (15), adjust the pen (28)
to zero if necessary.
6. One at a time, place the weights
back into the bucket, taking
note of the readings.
7. Continue to repeat this entire
process, steps 1 through 6 until
the pen reads correctly.
NOTE: If weights 1 thru 4 read cor-
rectly, it can expected that
both weights 5 and 6 will read
slightly higher than the correct
mark. This is attributed to
the springs and should not be
adjusted for.
0. If the pen is reading slow, i.e.
lower than the expected increments,
adjust the gage as follows:
1. Using the First Traverse Lever
Link (8), loosen the two nuts
(12) on the top of the link.
2. Turn the Adjusting Screw (13)
counter-clockwise until the pen
adjusts to the proper reading.
3. Once adjusted to the proper
reading, retighten the nuts (12).
4. Remove all the weights.
5. Using the Large Zero Adjustment
Knob (15), adjust the pen (28)
to zero, if necessary.
6. One at a time, place the weights
back onto the bucket weight,
noting the reading for each
weight.
7. Continue to repeat the entire
process, steps 1 thru 6, until
the pen reads correctly.
NOTE: If weights 1 thru 4 read cor-
rectly, it can be expected that
both weights 5 and 6 will read
slightly higher than expected.
This can be attributed to the
springs and should not be ad-
justed for.
P. When the pen (28) reads correctly
with all the weights on the bucket
weight, this signifies that the
First Traverse is zeroed. (Zero to
six inches for a 12" DT Gage.)
Q. Next, proceed to the Second Traverse
Lever Link. Turn the screw (34)
down until the pen (28) is exactly
at the top of the chart and will go
no higher than the top measurement
line, 6 inches.
R. Place the second set of weights onto
the bucket weight, noting the read-
ings as the pen descends down the
chart.
S. If the pen is reading fast or slow,
the same procedures are used on the
Second Traverse as on the First.
1. On the Second Traverse Lever Link
loosen the two nuts on the top of
the link.
2. Turn the Adjusting Screw (34)
clockwise to slow the reading
down, or counter-clockwise to
speed it up, until the pen ad-
justs to the proper reading.
3. Once adjusted to the proper read-
ing, retighten the nuts.
4. Remove the second set of weights.
5. Using the Large Zero Adjustment
Knob (15), adjust the pen to zero
if necessary.
6. One at a time, place the weights
back onto the bucket weight, a-
gain marking down the readings.
7. Continue to repeat the entire
process, steps 1 through 6 until
the pen reads correctly.
T. Once the pen is zeroed, place some
extra weight (anything) onto the
bucket weight. Using the Back Screv
(ns) directly behind the Movement
Bracket (16), turn it clockwise to
bring the pen up, stopping immedi-
ately before the pen reaches the
bottom of the flange (30). Tighten
the nut on the back screw once this
has been done.
U. Remove all weights and the bucket
weight from the gage.
V. Turn the Front Screw (14) clockwise
bringing the pen to rest slightly
above the flange (30). Tighten the
nut on the screw.
W. Replace the bucket weight on the
gage.
X. Using either Zero Adjustment Kno
(15 or 20), adjust the pen to
zero.
-------
7. Replacement Parts List
The Parts Lists given in this section
are applicable to the Belfort Model
5-780 Series Universal Recording Rain
Gage, manufactured by Belfort Instru-
ment Company, 727 South Wolfe Street,
Baltimore, Maryland 21231. Parts may
be ordered from the Belfort Sales Cen-
ter listed at the end of this manual.
Prices will be furnished upon request.
-------
Set pen four
divisions below
chart centerline
(a)
Set pen four
divisions above
chart centerline
Figure and
Index Number
3-1
-2
-3
-4
-5
-6
-7
Figure 3. Linearity Setting, Dual Traverse Gages
Manufacturer's
Part Number
16246-1
16246-4
917
10503
16453
991
16246-2
914
10502
909
Description
Link, Non-adjustable
Link (for 6" ST Gage)
3-56 x 3/16" Fil HD Screw, ST, ST
Lever, Short
Lever, Short (for 20" and 500MM Gages)
Tool, Linearity-Setting (for DT Gages)
Screw, Shoulder
Link, Adjustable
2-64 x 5/8" Oval HD Screw, ST, ST
Lever, Long
Lever, Long (for 20" and 500MM Gages)
Counterweight
-------
Figure 4. Universal Recording Rain Gage
-------
Figure and
Index Number
4-1
ns
-2
ns
ns
-3
-4
-5
-6
-7
-8
-9
Manufacturer's
Part Number
957
8711
8648
8463
16472
978
6121
16470
7042
953
16471
8471
8517
16461
8598
16473
Description
Collector Assembly
Funnel, Collector
Case Assembly (Gage Housing)
Dust Shield
Dust Shield (with Overflow option)
8-32 x 5/16" Bd. Hd. Screw ST, ST
#8 Flat Washer, ST, ST
Base Support (optional)
5/15-18 x 3/4" Hex Hd. Capscrew, ST, ST
5/16" Flat Washer, ST, ST
#12 x 1" Rd. Hd. Wood Screw, ST, ST
Bucket, 12 Quart Galvanized
Bucket, 12 Quart Galvanized with Overflow
Tube
Bucket, 20-inch
Platform, Bucket
Platform, Bucket with overflow option
Screw, Adjustment (Stop)
10-32 Hex Nut ST, ST
Shipping Stop
Shipping Stop (for 6" ST Gage)
Base, Mechanism
Base, with overflow option
-------
27
26
Figure 5. Rain Gage Mechanism, Front View
-------
Figure and
Index Number
5-1
-2
-3
-4
-5
-6
-8
-9
-10
-11
-12
-13
-14
-14
Manufacturer's
Part Number
6121
16470
7042
953
16471
943
16246-1
16246-4
16246-2
-15
8722
934
8886
914
10502
909
16252
16250
3279
992
918
8598
16473
559
933
14253-4
11460
8572-4
8570-4
16474-4
15349
8572-4
8570-4
8713
985
Description
Bucket, 12 Quart Galvanized
Bucket, 12 Quart Galvanized with overflow
tube
Bucket, 20 inch
Platform, Bucket
Platform, Bucket with overflow option
Lever Extension
Link, Non-adjustable
Link, for 6" ST Gage
Link, Adjustable
2-64 x 5/8" Oval Hd. Screw ST, ST
Lever, Top
Shaft (Long) Lever
Flat Washer
Lever, Long
Lever, Long (for 20" and 500MM Gages)
Counterweight
Bracket, Zero Adjust
Stud, Pen Arm
3-56 x 5/8" Fil. Hd. Screw ST, ST
2-64 x 3/8" Oval Hd. Screw ST, ST
Retainer Clip, Shaft
Pen Arm Assembly
Bearing (screw), Pen Arm
Base, Mechanism
Base, with overflow option
Pen, #3LS
Pen Shifter
Chart Drive Assembly, 8-Day Spring Powered
Chart Drive Mechanism
Chart Cylinder
Chart Clip
Chart Drive Assembly, 3V Battery-Powered
Chart Drive Mechanism
Chart Cylinder
Chart Clip
Bracket, Movement
Shaft, Plain
-------
Figure and Manufacturer's
Index Number Part Number Description
2-56 x 5/16" Fil. Hd. Screw ST, ST
8586 Shaft (Connector), Dashpot Piston
3279 Retainer Clip, Shaft
-------
Figure 7. Rain Gage Mechanism, Dual-Spring
-------
Figure and
Index Number
6-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
-11
-13
Manufacturer's
Part Number
7207
8621
914
10502
909
906
917
10503
16246-2
16246-1
16246-4
8197-1
6123
9885
8197-2
6122
8197-5
16339
14831-1
14831-1
5287
8197-6
5243
5270
5246
3279
5269
1000
943
Description
Screw, Mounting - Dashpot
Dashpot Cylinder Assembly
Lever, Long
Lever, Long (for 20" and 500MM Gages)
Counterweight
Pivot, Pen Arm Shaft
3-56 x 3/16" Fil. Hd. Screw, ST, ST
Lever, Short
Lever, Short (for 20" and 500MM Gages)
3-56 x 3/16" Fil. Hd. Screw, ST, ST
Link, Adjustable
2-64 x 5/8" Oval Hd. Screw ST, ST
Link, Non-adjustable
Link (for 6" ST Gage)
Spring Assembly (for 4.8" Gage)
Screw, Link
Link, Spring (for 4.8" Gage)
Spring Assembly (for 6" ST Gage)
Link, Spring
Spring Assembly
Spring Assembly, Dual (for'20" and 500MM
Gages
Bar, Spring Mounting (for 20" and 500MM Gages)
Guide, Spring (for 20" and 500MM Gages)
2-56 x 5/16 Bd. Hd. Screw, ST, ST (for
20" and 500MM Gages)
Spring Assembly (for 20" and 500MM Gages)
Nut, Spring Mtg. (for 20" and 500MM Gages)
Bar (Lower), Spring Mtg. (for 20" and
500MM Gages)
Pin, Coupling (for 20" and 500MM Gages)
Retainer Clip (Pin) (for 20" and 500MM
Gages.)
Coupling, Spring (for 20" and 500 MM Gages)
Pin, Link
Lever Extension
6-32 Hex Nut, ST, ST
6-32 x 7/16" Bd. Hd. Screw, ST, ST
6-32 x *s Bd. Hd. Screw, ST, ST
-------
clockwise rotation will decrease it.
The magnitude of the adjustment will
be in the order of three chart divi-
sions. Loosen the Setscrew (6)
fastening the lever to the pen arm
shaft, and rotate the pen arm shaft
to reposition the pen on the chart.
Re tighten the setscrew. Remove the
calibration weights, re-zero the
pen, and repeat the procedures of
Paragraph E.
H. Repeat the procedures of Paragraphs
E, F, and G until the calibration of
the gage meets the accuracy require-
ments of Section 2.6.
I. Calibration of the gage is now com-
plete. It remains only to reset the
Limit Screws (Figure 4, #7; Figure
6, #14) as required by Paragraph 2.2.
J. The pen arm adjustment (25) is not a
calibration tool: it's sole, intended
purpose is to rezero the pen, if
necessary, when changing charts and
chart drives.
6.5 Dual Traverse Calibration
A. Using the Red Fine Adjustment Screw
(20), level the Zero Set Assembly
Plate (35), and tighten the four
side screws.
B. Place the bucket weight onto the
Bucket Platform (18), and put half
the gage's capacity of weights onto
the bucket weight.
C. Line up the Pen Arm Bracket (32) so
that the screws line up straight a-
cross with the First and Second
Traverse levers.
D. While holding the Pen Arm Bracket
(32) steadily in place, insert the
Linearity Setting Tool (Figure 4,
#4) onto the First Traverse Link
(this process is shown in Figure 3A).
Line the link up straight, and
tighten the screw (2). The link
must be perpendicular to the base
before the screw is tightened.
E. The same process is repeated on the
Second Traverse link, as shown .in
Figure 3B. Continue to hold the Pen
Arm Bracket steady while inserting
the Linearity Setting Tool (4) onto
the Second Traverse link. Line the
link up perpendicular to the base,
and tighten the screw (2).
F. Continue to hold the Pen Arm Brac-
ket (Figure 6, #32) straight and
steady. Place the complete Pen Arm
(25, 27, and 28) onto the bracket.
Line the pen up to the three inch or
center line of the chart and tighten
the screw (36). The Lever Screw (6)
on each traverse should be straight
across.
G. Release the Pen Arm Bracket (32).
The Pen Arm should rise above the
center line. Using the Large Zero
Adjustment Knob (15), adjust the pen
down to the center line. (The screw
should be turned clockwise to adjust
the pen down into place.)
H. Place the linearity setting tool
back onto the First Traverse Link.
Make sure the tool fits easily,
without bending the link. Loosen
the screw (Figure 3, #2). While
holding the First Traverse Link and
tool steady, move the pen down four
division, and retighten the screw
(2). (If a linearity setting tool is
not available, make all adjustments
while keeping the First Traverse
Link Perfectly straight (perpendic-
ular to the base).
I. Place the linearity setting tool in-
to the Second Traverse Link. The
tool should once again fit easily
into the slot without bending the
link. Loosen the screw (Figure 3B,
#2). While holding all parts steady
move the pen up four divisions on
the chart, and retighten the screw
(2).
J. Remove all the weights from the
bucket weight.
K. Use the Large Zero Adjustment Knob
(Figure 6, #15) to position the pen
at zero. Tap the base of the gage
to make sure the pen is not sticking
and that it returns to zero.
L. Place the first weight onto the buc-
ket weight and tap the base to check
for sticking. DO NOT ADJUST IF THE
PEN IS OFF THE DESIRED MARK.
M. One by one, place the remaining
weights onto the bucket weight, tap'
ping the gage each time to ensure
non-sticking of the pen. Again, do
not adjust if the pen is not exactly
correct.
N. If the pen reads fast, i.e. higher
than the expected increment, use tb*
following steps to correct the prob"
lem:
1. Using the First Traverse Lever
Link (8), loosen the two nuts ae
the top of the link (12).
2. Turn the Adjusting Screw (13)
clockwise until the pen adjusts
-------
Figure and
Index Number
6-25
-26
Manufacturer's
Part Number
-27
-28
-29
-30
-31
-32
-33
-34
14253-4
11460
16474-4
15348
8572-4
8570-4
992
918
559
8598
16473
933
903
905
Description
3-56 x 5/8" Fil. Hd. Screw, ST, ST
2-64 x 3/8" Oval Hd. Screw, ST, ST
Chart Drive Assembly, 8-day Spring Powered
Chart Drive Mechanism
Chart Drive Assembly, 3V Battery Powered
Chart Drive Mechanism
Chart Cylinder
Chart Clip
Pen Arm Assembly
Bearing (screw), Pen Arm
Pen, #3LS
Base, Mechanism
Base, with overflow option
Chart Cylinder Flange
Pen Shifter
Bracket, Pen Arm (Stud)
3-56 x 3/16" Fil. Hd. Screw, ST, ST
Shaft, Pen Arm Pivot
2-64 x 3/8" Oval Hd. Screw, M/S
-------
15
B
30
Figure 6. Rain Gage Mechanism, Single-Spring
-------
Figure and
Index Number
7-1
-2
-3
-4
-5
-6
-7
-8
Manufacturer's
Part Number
8319
8317-1
8306
16072
16072-1
16472
8586
3279
908
953
16471
8728
5898
16473
Description
Zero Setting Assembly (Fine)
Setting Bar Assembly
Screw, Setting
Zero Setting Assembly (for 20" and 500MM
Gages)
Setting Bar Assembly (for 20" and 500MM
Gages)
Screw, Setting (for 20" and 500MM Gages)
Shaft, Dash Pot Pivot
Retainer Clip, Shaft
k-2Q x 7/8" Flat Hd. Screw, ST, ST
Washer, Bucket Platform
Platform Bucket
Platform, Bucket with overflow option
Funnel, Overflow
Spring Assembly (See Figure 6, Index
Number 9 for Parts Breakdown)
Base, Mechanism
Base, Mechanism with overflow option
-------
For further information, contact one of the following
Sales offices.
BELFORT INSTRUMENT COMPANY
Factory and Sales
727 South Wolfe Street
Baltimore, Maryland 21231
(301) 342-2626
Telex: 87528 (BELFORT BAL)
Sales and Service
2620 Concord Avenue #102
Alhambra, California 91803
(818) 282-4893
Telex: 6831262 (BLF-CA)
-------
Appendix C
METHOD 150.6 ~ pH OF WET DEPOSITION
BY ELECTROMETRIC DETERMINATION
C-l
-------
Method 150.6 — pH of Wet Deposition by
Electrometric Determination
March 1986
Performing Laboratory:
Jackie Sauer
Jacqueline M. Lockard
Carla Jo Brennan
Mark E. Peden
Illinois State Water Survey
Analytical Chemistry Unit
2204 Griffith Drive
Champaign, Illinois 61820
Sponsoring Agency:
John D. Pfaff, Project Officer
Inorganic Analysis Section
Physical and Chemical Methods Branch
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
150.6-1
-------
INDEX
Section
Number Subject
1 Scope and Application
2 Summary of Method
3 Definitions
4 Interferences
5 Safety
6 Apparatus and Equipment
7 Reagents and Consumable Materials
8 Sample Collection, Preservation, and Storage
9 Calibration and Standardization
10 Quality Control
11 Procedure
12 Calculations
13 Precision and Bias
14 References
TABLES
1. Values for F/(2.3026 RT) at Different Temperatures.
2. Suitable pH Reference Electrodes for the Analysis of Wet Deposition
Samples.
3. National Bureau of Standards (NBS) Salts for Reference Buffer
Solutions.
4. Single-Operator Bias and Precision of pH Measurements Determined from
Quality Control Check Samples.
FIGURES
1. Percentile pH Values Obtained from Wet Deposition Samples.
2. Time Required to Obtain Stable pH Response in Wet Deposition Samples,
150.6-2
-------
1. SCOPE AND APPLICATION
1.1 This method is applicable to the determination of pH in wet
deposition samples by electrometric measurement using either a pH
half cell with a reference probe or a combination electrode as the
sensor.
1.2 The term "wet deposition" is used in this method to designate rain,
snow, dew, sleet, and hail.
1.3 Figure 1 represents a cumulative frequency percentile pH plot
obtained from analyses of over five thousand wet deposition samples.
These data may be used as an aid in the selection of appropriate
calibration buffers.
2. SUMMARY OF METHOD
2.1 Electrodes approximate the pH of a solution by the Nernst equation
that relates the potential measured by the pH electrode in a standard
buffer solution to that measured in an unknown sample:
(E - E )F
pH « pH H-
2.3026 RT
where: pHg » pH of the standard buffer solution
E » potential measured in an unknown sample
Eg » potential met
F * Faraday's cor
R a gas constant
T » absolute temperature (T(°C) + 273)
Values of the factor F/(2.3026 RT) at different temperatures are
provided in Table 1. The pH meter and the associated electrode(s)
are calibrated with two reference buffer solutions that bracket
the anticipated sample pH. The pH of the wet deposition sample is
determined from this calibration.
3. DEFINITIONS
3.1 pH — the negative logarithm to the base ten of the conventional
hydrogen ion activity (14.1):
pH - -log[H+]
3.2 For definitions of other terms used in this method, refer to the
glossary. For an explanation of the metric system including units,
symbols, and conversion factors see American Society for Testing and
Materials (ASTM) Standard E 380, "Metric Practices" (14.2).
Eg » potential measured in the buffer solution
F * Faraday's constant
150.6-3
-------
4. INTERFERENCES
4.1 The pH meter and the associated electrode(s) reliably measure pH in
nearly all aqueous solutions and in general are not subject to
solution interferences from color, turbidity, oxidants, or
reductants.
4.2 The true pH of an aqueous solution is affected by the temperature.
The electromotive force between the glass and the reference electrode
is a function of temperature as well as pH. Temperature effects
caused by a change in electrode output can be compensated for
automatically or manually depending on the pH meter selected.
4.3 Organic materials dispersed in water appear to poison the glass
electrode, particularly when analyzing low ionic strength solutions.
Difficulty encountered when standardizing the electrode(s), erratic
readings, or slow response times may be an indication of
contamination of the glass bulb. To remove these coatings, refer to
the manual accompanying the probe for the manufacturer's
recommendations.
4.4 When analyzing samples that have low ionic strengths, such as wet
deposition, an effect known as "residual junction potential" can lead
to errors as large as 0.1 pH units (14.3). This error occurs when
the junction potential of the sample differs greatly from that of the
standard. These conditions are frequently met in wet deposition
analyses when the pH electrode(s) is calibrated with high ionic
strength standard reference buffers. This error is reduced by using
a reference electrode with a ceramic junction.
4.5 When measuring the pH of wet deposition, the sample may be agitated
to speed electrode response. Care must be taken, however, to avoid
introducing a source of error known as "residual streaming potential"
that can result in a significant difference between the stirred and
unstirred pH of the sample (14.4). The magnitude of the streaming
potential is dependent on the electrode(s) and on the stirring rate.
Differences in pH for stirred and unstirred wet deposition samples
when the electrode assembly has been calibrated only with quiescent
reference standards average 0.05 pH units at a stirring rate of
4 revolutions per second.
4.5.1 Eliminate the errors associated with residual streaming
potentials by agitating all calibration standards and wet
deposition samples thoroughly to speed electrode response and
then allowing each aliquot to become quiescent before taking
a pH reading.
4.5.2 If magnetic stirring is used, take care not to contaminate
the sample when inserting the stirring bar. Maintain an air
space between the surface of the stirring motor and the sample
container to prevent heating the wet deposition sample.
150.6-4
-------
5. SAFETY
5.1 The reference buffer solutions, sample types, and most reagents used
in this method pose no hazard to the analyst. Use a fume hood,
protective clothing, and safety glasses when handling concentrated
nitric (Sect. 7.4) and hydrochloric acids (Sect. 7.5.1) and sodium
hydroxide (Sect. 7.5.3-7.5.4).
5.2 Follow American Chemical Society guidelines regarding the safe
handling of chemicals used in this method (14.5).
6. APPARATUS AND EQUIPMENT
6.1 LABORATORY pH METER — The meter may have either an analog or
digital display with a readability of 0.01 pH units. A meter that
has separate calibration and slope adjustment features and is
electrically shielded to avoid interferences from stray currents or
static charge is necessary. It may be powered by battery or 110 V AC
line; if battery powered, the meter must have a battery check
feature. A temperature compensator control to allow accurate
measurements at temperatures other than 25 C is desirable.
6.2 SENSING ELECTRODE — Select a sensing electrode constructed of
general purpose glass. This electrode type is characterized by
low resistance, quick response, and has a reliable range of 0-14 pH
units. Refer to the manual accompanying the probe for the
manufacturer's recommendations on electrode storage.
6.3 REFERENCE ELECTRODE — The reference electrode recommended for wet
deposition analysis is one equipped with a ceramic junction. The
ceramic construction minimizes differences in potential between high
ionic strength buffers and low ionic strength samples thus reducing
errors from residual junction potential (14.3). A reference probe
equipped with a ceramic junction in an annular ring configuration
generates a more stable potential in less time due to a higher flow
of internal electrolyte into the solution. Single pore ceramic frit
junctions also provide adequate electrolyte flow. Table 2 lists
suitable reference electrodes that have been found to be
satisfactory. Other electrodes having similar characteristics are
also suitable. Refer to the manual accompanying the probe for the
manufacturer's recommendations on electrode storage.
6.4 COMBINATION ELECTRODE — The combination electrode combines the
indicating and reference elements in a single unit. Since sample
volume requirements are a consideration when analyzing wet deposition
samples, combination electrodes are more convenient than separate
glass and reference electrodes. Refer to the manual accompanying
the probe for the manufacturer's recommendations on electrode
storage.
150.6-5
-------
6.5 TEMPERATURE CONTROL — To ensure accurate results, use either a
constant temperature water bath, a temperature compensator, or a
thermometer to verify that all standards and samples are maintained
at temperatures within _+! C of one another. If a thermometer is
used, select one capable of being read to the nearest 1 C and
covering the range 0 -40 C.
6.6 STIRRING DEVICE (optional) — electric or water-driven. If an
electric stirrer is selected, leave an air gap or place an insulating
pad between the stirrer surface and the solution container to
minimize heating of the sample. Use a TFE-fluorocarbon-coated
stirring bar.
6.7 LABORATORY FACILITIES — Laboratories used for the analysis of wet
deposition samples should be free from external sources of
contamination. The use of laminar flow clean air workstations is
recommended for sample processing and preparation to avoid the
introduction of airborne contaminants. Samples should always be
capped or covered prior to analysis. A positive pressure
environment within the laboratory is also recommended to minimize
the introduction of external sources of contaminant gases and
particulates. Windows within the laboratory should be kept closed
at all times and sealed if air leaks are apparent. The use of
disposable tacky floor mats at the entrance to the laboratory is
helpful in reducing the particulate loading within the room.
7. REAGENTS AND CONSUMABLE MATERIALS
7.1 PURITY OF REAGENTS ~ Use reagent grade chemicals for all solutions.
All reagents shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society (ACS) where such
specifications are available.
7.2 PURITY OF WATER — Use water conforming to ASTM Specification D
1193, Type II (14.6). Point of use 0.2 micrometer filters are
recommended for all faucets supplying ASTM Type II water to prevent
the introduction of bacteria and/or ion exchange resins into
reagents, standard solutions, and internally formulated quality
control check solutions.
7.3 QUALITY CONTROL CHECK SAMPLE (QCS) (5.0 x 10~ N HNO ) — Dilute
1.0 mL of concentrated, nitric acid (HNO , sp gr 1.42) to 1 L with
water (Sect 7.2). Dilute 3.2 mL of this stock solution to 1 L with
water (Sect 7.2). The resulting solution has a pH of 4.30 +_ 0.10
at 25 C. Store at room temperature in a high density polyethylene
or polypropylene container. This solution is stable for one year.
150.6-6
-------
7.4 REFERENCE BUFFER SOLUTIONS — Table 3 identifies each buffer salt by
its National Bureau of Standards (NBS) number and provides a
recommended drying procedure prior to use. Store the reference
buffer solutions in polyethylene or chemical-resistant glass bottles
and replace after one year or sooner if a visible change
such as the development of colloidal or particulate materials is
observed.
7.4.1 Phthalate Reference Buffer Solution (0.02 N HC1, 0.05 N
KHC HO ) — Add 83.0 mL of concentrated hydrochloric
acid (HC1, sp gr 1.19) to water (Sect. 7.2) and dilute to
1 L. Dissolve 10.20 g of potassium hydrogen phthalate
(KHC HO ) in 22.3 mL of the hydrochloric acid solution
and dilute to 1 L with water (Sect. 7.2). This solution has
a pH of 3.00 at 25°C.
7.4.2 Phthalate Reference Buffer Solution (0.05 N KHCQH40 ) —
Dissolve 10.12 g of potassium hydrogen phthalate
(KHC HO ) in water (Sect. 7.2) and dilute to 1 L. This
solution has a pH of 4.00 at 25 C.
7.4.3 Phosphate Reference Buffer Solution (0.005 N NaOH, 0.05 N
KH PO ) — Dissolve 4.00 g of sodium hydroxide (NaOH) in
water (Sect. 7.2) and dilute to 1 L. Dissolve '6.80 g of
potassium dihydrogen phosphate (KH PO ) in 56.0 mL of the
hydroxide solution and dilute to 1 L with water (Sect. 7.2).
This solution has a pH of 6.00 at 25°C.
7.4.4 Phosphate Reference Buffer Solution (0.03 N NaOH, 0.05 N
KH PO ) — Dissolve 40.0 g of sodium hydroxide (NaOH) in
water4(Sect. 7.2) and dilute to 1 L. Dissolve 6.80 g of
potassium dihydrogen phosphate (KH PO ) in 29.1 mL of the
hydroxide solution and dilute to 1 L with water (Sect. 7.2).
This solution has a pH of 7.00 at 25 C.
7.4.5 Commercial Buffer Solutions — Commercially available buffer
solutions traceable to NBS buffers are adequate for
standardization. These commercial buffer solutions usually
have pH values near 3, 4, 6, and 7, the exact pH and use
temperature being provided by the supplier of the specific
buffer.
7.5 SAMPLE CONTAINERS — Use glass or polyolefin sample cups that have
been thoroughly rinsed with water (Sect. 7.2) before use.
8. SAMPLE COLLECTION, PRESERVATION AND STORAGE
8.1 Collect samples in high density polyethylene (HOPE) containers that
have been thoroughly rinsed with water (Sect. 7.2). Do not use
strong mineral acids or alkaline detergent solutions for cleaning
collection vessels. Residual acids may remain in the polyethylene
matrix and slowly leach back into the sample. Alkaline detergents
may also leave residues that may affect the sample chemistry, cap
collection bottles after cleaning to prevent contamination from
150.6-7
-------
airborne contaminants. Air dry collection buckets in a laminar flow
clean air workstation and wrap in polyethylene bags prior to use. If
a laminar flow workstation is not available, pour out any residual
rinse water and bag the buckets immediately. Do not dry the bucket
interior by any method other than air drying in a laminar flow clean
air workstation.
8.2 The frequency of sample collection and the choice of sampler design
are dependent on the monitoring objectives. In general, the use of
wet-only samplers is recommended to exclude dry deposition
contributions, minimize sample contamination, retard evaporation,
and enhance sample stability. Sample collection frequency may vary
from sequential sampling within a wet deposition event to weekly
sampling periods. Collection periods of more than one week are not
recommended since sample integrity may be compromised by longer
exposure periods.
8.3 The dissolution of particulate materials and the presence of
microbial activity will affect the stability of hydrogen ions (pH)
in wet deposition samples (14.7, 14.8). This instability generally
results in a decrease in hydrogen ions (higher pH). Measurements of
pH should be made immediately after sample collection and thermal
equilibration with calibration buffers. Refrigeration of samples at
4 C will minimize but not prevent a decrease in the hydrogen ion
content.
8.3.1 Filtration of samples through a 0.45 micrometer membrane
leached with water (Sect. 7.2) is effective at stabilizing pH
values that are influenced by the dissolution of alkaline
particulate matter (14.7). Monitoring of the filtration
procedure is necessary to ensure that samples are not
contaminated by the membrane or filtration apparatus.
8.3.2 A biocide such as chloroform (CHC1 ) may be used to
stabilize the organic acid component of the measured pH
and to prevent pH changes due to biological reactions on
other sample constituents (14.8). Add the chloroform (0.5 mL
per 250 mL sample) to a separate sample aliquot that will be
used only for "the measurement of pH.
9. CALIBRATION AND STANDARDIZATION
9.1 Turn on the meter and allow it to warm up according to manufacturer's
instructions.
9.2 If necessary, add filling solution to the electrode before using.
Maintain the filling solution level at least one inch above the level
of the sample surface to ensure proper electrolyte flow rate.
9.3 Determine the temperature of the wet deposition sample. Allow
sample, buffers, and QCS solutions to reach room temperature before
making pH measurements or bring the temperature of all solutions to
within +1 C of each other.
150.6-0
-------
9.4 Select two reference buffer solutions that bracket the anticipated
pH of the wet deposition sample. The difference between the
nominal pH values of the two buffers should not exceed three pH
units. Buffer solutions with pH's of 7.00 and 4.00 are recommended
for wet deposition samples.
9.5 CALIBRATION FUNCTION
9.5.1 Rinse the electrode(s) with three changes of water (Sect. 7.2)
or with a flowing stream from a wash bottle. Dispense two
aliquots of the buffer with the higher pH into separate, clean
sample cups. Insert the electrode(s) into one aliquot for
30 seconds.
9.5.2 Remove the electrode(s) from the first aliquot and insert
directly into the second. Allow either two minutes for
equilibration or allow sufficient time for the reading to
remain steady within +Q.Q1 pH units for 30 seconds.
9.5.3 Adjust the calibration control until the reading corresponds
to the temperature corrected value of the reference buffer
solution.
9.6 SLOPE FUNCTION
9.6.1 Rinse the electrode(s) with three changes of water (Sect. 7.2)
or with a flowing stream from a wash bottle. Dispense two
aliquots of the second reference buffer solution into
separate, clean sample cups. Insert the electrode(s) into one
aliquot for 30 seconds.
9.6.2 Remove the electrode(s) from the first aliquot and insert
directly into the second. Allow the system to equilibrate as
directed in Sect. 9.5.2.
9.6.3 Adjust the slope function until the reading corresponds to
the temperature corrected value of the reference buffer
solution.
9-7 CALIBRATION CHECK
9.7.1 Remove the electrode(s), rinse thoroughly, and place into the
first reference buffer solution. If the pH does not read
within ^0.01 units of the temperature corrected value,
repeat the calibration procedure until the buffers agree.
150.6-9
-------
10. QUALITY CONTROL
10.1 Each laboratory using this method should develop formalized quality
control protocols to continually monitor the bias and precision of
all measurements. These protocols are required to ensure that the
measurement system is in a state of statistical control. Estimates
of bias and precision for wet deposition analyses cannot be made
unless these control procedures are followed. Detailed guidelines
for the development of quality assurance and quality control
protocols for precipitation measurement systems are published in a
manual available from the United States Environmental Protection
Agency, Research Triangle Park, NC 27711 (14.9). Included in this
manual are procedures for the development of statistical control
charts for use in monitoring bias and precision as well as
recommendations for the introduction of reagent blanks, laboratory
duplicates, field duplicates, spike samples, and performance
evaluation samples. These guidelines are to be used by all
laboratories involved with wet deposition measurements.
10.2 .ESTABLISHMENT OF WARNING AND CONTROL LIMITS — Warning and control
limits are used to monitor the analyses of quality control check
samples (QCS).
10.2.1 Quality Control Check Samples (QCS) — Calculate warning
and control limits for QCS solutions from a minimum of ten
analyses performed on ten days to provide a realistic
estimate of method variability. Calculate a standard
deviation (s) for the pH measurements for each QCS
solution. Use the certified or NBS traceable pH value as
the mean (target) value (x) for determining the control
limits. A warning limit of _+2s and a control limit of
+3s should be used. Constant positive or negative
measurements with respect to the true value are indicative
of a method or procedural bias. If the pH measurements for
the QCS solutions fall outside of the +2s limits,
recalibrate the system and reanalyze all samples from the
last time the system was in control. If two successive QCS
pH measurements are outside of the jf2s limits, verify the_
meter calibration according to Sect. 10.5 before continuing
with sample measurements. The standard deviations used to
generate the QCS control limits should be comparable to the
single operator precision reported in Table 4. Reestablish
new warning and control limits whenever instrumental
operating conditions are varied or QCS concentrations are
changed.
10.2.2 All warning and control limits should be reevaluated on a
continual basis as additional data are collected during
routine analyses. The limits should be broadened or
-.arrowed if a recalculated standard deviation under similar
operating conditions provides a different estimate of the
procedure variability.
150.6-10
-------
10.3 Monitor the cleaning procedure by pouring a volume of water (Sect.
7.2) that approximates the median sample size into the collection
vessel. Allow the water to remain in the'sealed or capped
collection container for at least 24 hours and determine the
solution pH. If the measured pH is not within the range of
5.4-6.0, a contamination problem is indicated in the cleaning
procedure. Corrective action should be taken before the sampling
containers are used for the collection of wet deposition.
10.4 Electrodes used for the measurement of wet deposition samples
should not be used for other sample types. Strongly acidic or
basic solutions may cause electrode degradation and result in
biased measurements and/or slow response in precipitation samples.
Similarly, samples characterized by high concentrations of organic
matter may leave a residue on the glass sensing bulb resulting in
slow electrode response.
10.5 Verify the meter calibration after every ten samples and at the end
of each day's analyses using both reference buffer solutions. The
pH measured for the calibration buffers must agree within +O.02 '
of the temperature corrected value reported for each buffer. If
the measured pH of either buffer falls outside of these limits,
recalibrate the electrode/meter assembly and reanalyze those
samples analyzed since the last time the system was•in control.
10.6 Determine the pH of a quality control check sample (QCS) after the
meter and electrode assembly have been calibrated. This sample may
be formulated in the laboratory, obtained from the National Bureau
of Standards (NBS Standard Reference Material 2694, Simulated
Rainwater), or the United States Environmental Protection Agency
(NBS Traceable Reference Material). Verify the accuracy of
internally formulated QCS solutions with an NBS traceable standard
before acceptance as a quality control check. The check sample
selected must be within the range of the. calibration buffers and _
should approximate the pH ranqe of the samples to be analyzed. If
the measured value for the QCS is not within the specified limits
of the control solution, measure a second aliquot. Failure to
obtain acceptable results on the second aliquot indicates a problem
with the electrode or meter. Check the pH meter according to the
manufacturer's guidelines. If an electrode problem is indicated,
replace the electrode and repeat the calibration procedure before
measuring the QCS again. Plot the data obtained from the QCS
checks on a control chart for routine assessments of bias and
precision.
10.6.1 QCS measurements should be made after every ten samples
or after completion of a batch of samples consisting of
less than ten. If the QCS measurement is out of the
predetermined control limits, check the calibration buffers
and recalibrate if any one of the buffer values has shifted
by more than 0.02 pH units. Recheck the QCS and reanalyze
all samples from the last time, the measurement system was
in control.
150.6-11
-------
10.7 Submit a Field Blank (FB) to the laboratory for every 20 samples.
The FB may consist of a water sample (Sect. 7.2) or a known
reference solution that approximates the concentration levels
characteristic of wet deposition. The FB is poured into the
sampling vessel at the field site and undergoes identical
processing and analytical protocols as the wet deposition
sample(s). Use the analytical data obtained from the FB to
determine any contamination introduced in the field and laboratory
handling procedures. The data from the known reference solution
can be used to calculate a system precision and bias.
10.8 Participation in performance evaluation studies is recommended for
precipitation chemistry laboratories. The samples used for these
performance audits should contain the analytes of interest at
concentrations within the normal working range of the method. The
true values are unknown to the analyst. Performance evaluation
studies for precipitation chemistry laboratories are conducted
semiannually by the USEPA Performance Evaluation Branch, Quality
Assurance Division, Research Triangle Park, NC 27711.
11. PROCEDURE
11.1 Bring all buffers, solutions, and samples to ambient temperature
making sure any necessary compensation is .made for deviations in
temperature (Sect. 6.5).
11.2 Calibrate the electrode assembly with two reference buffer
solutions as described in Sect. 9.1-9.7.
11.3 After the electrode(s) and meter are calibrated, analyze a QCS
sample. If the measured value for the QCS is not within the
specified limits (Sect. 10.2.1), refer to Sect. 10.6.
11.4 SAMPLE ANALYSIS
11.4.1 Rinse the electrode(s) with three changes of water (Sect.
7.2) or with a flowing stream from a wash bottle. Dispense
two aliquots of wet deposition sample into 'separate, clean
sample cups. Insert the electrode(s) into one aliquot for
30 seconds.
11.4.2 Remove the electrode(s) from the first aliquot and insert
directly into the second, once again allowing the system
time to stabilize. Record the pH measurements when
readings differ by no more than +0.01 pH units within a
30 second period. Record the pH and the temperature of the
sample.
Note: The time necessary for the system response to
stabilize depends on the pH of the sample. As Figure 2
illustrates, the pH electrode response time is usually
three to five minutes for samples with a pH<5.5. For
samples with pH>5.5, a stable response is usually generated
in five to seven minutes.
150.6-12
-------
12. CALCULATIONS
12.1 Most pH meters are calibrated in pH units and the pH of the sample
is obtained directly by reading the meter scale. Record pH
measurements to the nearest hundredth of a pH unit and sample
temperature to the nearest degree.
13. PRECISION AND BIAS
13.1 Single-operator precision and bias data were obtained using three
quality control check samples. The results are tabulated in
Table 4.
14. REFERENCES
14.1 Annual Book of ASTM Standards, Part 31, "Definitions of Terms
% Relating to Water," Standard D 1129-82b, 1982, p. 5.
14.2 Annual Book of ASTM Standards, Part 31, "Excerpts from Standard
for Metric Practice," Standard E 380-79, 1982, pp. 679-694.
14.3 Koch, W. G., Marinenko, G. , and Stolz, J. W., "Simulated
Precipitation Reference Materials, IV," National Bureau of
Standards (U.S.), NBSIR 82-2581, June 1982, p. 14.
14.4 McQuaker, N. R., Kluckner, P. D., and Sandberg, D. K., "Chemical
Analysis of Acid Precipitation: pH and Acidity Determinations,"
Environ. Sci. Technol., Vol. 17, No. 7, 1983, pp. 431-435.
14.5 "Safety in Academic Chemistry Laboratories," American Chemical
Society Publication, Committee on Chemical Safety, 3rd Edition,
1979.
14.6 Annual Book of ASTM Standards, Part 31, "Standard Specification
for Reagent Water," Standard D 1193-77, 1982, D. 39.
.•
14.7 Peden, M. E. and Skowron, L. M., "Ionic Stability of Precipitation
Samples," Atmos. Environ. 12, 1978, p. 2343-2349.
14.8 Keene, W. C. and Galloway, J. N., "Organic Acidity in Precipitation
of North America," Atmos. Environ. 18, 1984, p. 2491-2497.
14.9 Topol, L. E., Lev-On, M., Flanagan, J., Schwall, R. J., Jackson, A.
E., Quality Assurance Manual for Precipitation Measurement
Systems, 1985, U.S. Environmental Protection Agency,
Environmental Monitoring Systems Laboratory, Research Triangle
Park, NC 27711.
150.5-13
-------
Table 1. Values for F/(2.3026 RT) at Different
Temperatures.
Temperature,
°C
F/(2.3026 RT),
V"1
0
5
10
15
20
25
30
35
40
45
18.4512
18.1195
17.7996
17.4907
17.1924
16.9041
16.6253
16.3555
16.0944
15.8414
The above data were calculated using
a precise value of the logarithmic
conversion factor (2.302585) and values
of the fundamental constants.
F = 96,487.0 C/eq
R » 8.31433 J/K mol
T - 273.15 + °C
150.6-14
-------
Table 2. Suitable pH Reference Electrodes for the
Analysis of Wet Deposition Samples.
Manufacturer
Model
Number
Electrode Type
Beckman
Corning
Orion (Ross)
39417
476109
800500
glass bodied with ceramic
junction (calomel)
glass bodied with ceramic
junction (calomel)
glass bodied reference half
cell
150.6-15
-------
Table 3. National Bureau of Standards (NBS) Salts for
Reference Buffer Solutions.
NBS Standard Sample Drying
Designation Buffer Salt Procedure
186-1-c potassium dihydrogen phosphate 2 h in oven at
130°C
185-f potassium hydrogen phthalate 2 h in oven at
110°C
The buffer salts listed above can be purchased from the Office of
Standard Reference Materials, National Bureau of Standards, Washington, D. C.
20234.
150.6-16
-------
Table 4. Single-Operator Bias and Precision of pH Measurements
Determined from Quality Control Check Samples.
Precision,
Theoretical Mean Bias, s, RSD
pH Measured pH n pH % pH %
3.61 3.63 15 0.02 0.6 0.01 0.3
4.30 4.32 72 0.02 0.5 0.01 0.2
5.60 5.42 80 -0.18 -3.2 0.04 0.7
The above data were obtained from records of pH measurements made under
the direction of the NADP quality assurance program. The solutions used were
a National Bureau of Standard (NBS) simulated rainwater sample (Research
Material #8409-11, pH = 3.61), a 5.01 x 10" N nitric acid solution
(pH = 4.30), and a 0.0005 M potassium chloride solution (pH = 5.60).
a. Number of replicates.
b. Calculations of bias and precision data were made using hydrogen ion
concentrations.
150 fi-17
-------
Figure 1. Percentile Concentration Values Obtained from
Wet Deposition Samples: pH
100
90 ••
80 ••
~ 70 ..
u
z
Cd
a
M
3
60
50
40
30
20
10
4.00
5.00
6.00
7.00
150.6-18
-------
Figure 2. Time Required to Obtain Stable pH Response in Wet
Deposition Samples.
10
SAMPLE pH
150.6-19
-------
Appendix D
METHOD 120.6 — SPECIFIC CONDUCTANCE IN WET DEPOSITION
BY ELECTROLYTIC DETERMINATION
D-l
-------
Method 120.6 — Specific Conductance in Wet Deposition by
Electrolytic Determination
March 1986
Performing Laboratory:
Carla Jo Brennan
Jackie Sauer
Mark E. Peden
Illinois State Water Survey
Analytical Chemistry Unit
2204 Griffith Drive
Champaign, Illinois 61820
Sponsoring Agency:
John D. Pfaff, Project Officer
Inorganic Analysis Section
Physical and Chemical Methods Branch
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
120.6-1
-------
INDEX
Section
Number Subject
1 Scope and Application
2 Summary of Method
3 Definitions
4 Interferences
5 Safety
6 Apparatus and Equipment
7 Reagents and Consumable Materials
8 Sample Collection, Preservation, and Storage
9 Calibration and Standardization
10 Quality Control
11 Procedure
12 Calculations
13 Precision and Bias
14 References
TABLES
1. Single-Operator Bias and Precision for Specific Conductance Measurements
Determined from Quality Control Check Samples.
2. Specific Conductance of KC1 Solutions at 25°C as a Function of the Molar
Concentration.
FIGURES
1. Percentile Conductance Values Obtained from Wet Deposition Samples.
120.6-2
-------
1. SCOPE AND APPLICATION
1.1 This method is applicable to the determination of specific
conductance in wet deposition samples by electrolytic measurement
using a conductance cell as the sensor.
1.2 The term "wet deposition" is used in this method to designate rain,
snow, dew, sleet, and hail.
1.3 Figure 1 represents a cumulative frequency percentile specific
conductance plot obtained from analyses of over five thousand wet
deposition samples. These data may be used as an aid in the
selection of calibration standards. The operating range of this
method is 0.10-1000 us/cm. Most wet deposition samples have
a specific conductance in the range of 5 to 50 uS/cm.
2. SUMMARY OF METHOD
2.1 Specific conductance is a numerical expression of the ability of an
aqueous solution to carry an electric current. This ability depends
on the presence of ions, their total concentration, mobility, and
valence. Conductance is also a function of the relative
concentrations of the ions in solution and of the solution
temperature. The physical measurement made in a laboratory
determination of specific conductance is resistance, expressed as:
R » K (I/a)
where: a * cross section of conductor (cm )
1 » length of conductor (cm)
Measured Resistance
K = cell constant *
Specific Resistance
Specific resistance is the resistance of a cube 1 cm on an edge.
Since commercially available conductance cells measure a given
fraction of the specific resistance, it is necessary to include the
cell constant when determining specific conductance. The conductance
meter and the associated cell are calibrated using potassium chloride
solutions of known specific conductances comparable "to that found in
wet deposition samples.
3< DEFINITIONS
3.1 ELECTRICAL CONDUCTANCE — the reciprocal of the resistance in ohms
measured between opposite faces of a centimeter cube of an aqueous
solution at a specified temperature (14.1).
3.2 For definitions of other terms used in this method, refer to the
glossary. For an explanation of the metric system including units,
symbols, and conversion factors see American Society for Testing and
Materials (ASTM) Standard E 380, "Metric Practices" (14.2).
120.6-3
-------
4. INTERFERENCES
4.1 The conductance cell reliably measures specific conductance in
nearly all aqueous solutions and in general is not subject to
solution interferences from color, turbidity, oxidants, or
reductants.
4.2 Exposure of samples to laboratory atmosphere can result in the
absorption of carbon dioxide, ammonia, and other gases by the
solution being analyzed, with this absorption of additional
electrolytes, the measured conductance of the sample is elevated. To
minimize errors, keep all sample aliquots tightly covered prior to
analysis.
4.3 Organic materials dispersed in water will affect the cell constant
and the accuracy of measurements by coating the electrode surface.
To remove these coatings, refer to the manual accompanying the
conductance cell for the manufacturer's recommendations for
cleaning the cell.
5. SAFETY
5.1 The calibration standards, sample types, and most reagents used in
this method pose no hazard to the analyst. Use a fume hood,
protective clothing, and safety glasses when handling concentrated
nitric acid (Sect. 7.4).
5.2 Follow American chemical Society guidelines regarding the safe
handling of chemicals used in this method (14.3).
6. APPARATUS AND EQUIPMENT
6.1 SPECIFIC CONDUCTANCE METER — Select an instrument equipped with a
manual or electrically balanced conductance bridge, powered by
battery or 110 V AC line. If battery powered, however, the meter
must have a battery check feature. Select an instrument capable of
measuring conductance with an error not exceeding 1% or 1 uS/ctn,
whichever is greater. The meter used must have a range of
0.1-1000 uS/cm and readability to 0.1 uS/cm sensitivity.
6.1.1 Check the electronic calibration of the meter monthly and
adjust when necessary. This may be accomplished either through
use of an internal calibration feature or an external
calibration set.
6.3 SPECIFIC CONDUCTANCE CELL ~ Conductance cells are available in
pipette, flow-through, cup, or immersion form. Select a cell having
a constant of 1.0 or 0.1. A sample volume requirement of 10 mL or
less is desirable.
120.6-4
-------
6.3.1 When not in use, rinse the cell thoroughly with water (Sect.
7.2} and store according to manufacturer's guidelines.
6.3.2 If readings become erratic, refer to the manual accompanying
the cell for the manufacturer's recommendations.
6.4 THERMOMETER— Select a thermometer capable of being read to the
nearest 0.1°C and covering the range 0 -40°C.
6.5 LABORATORY FACILITIES — Laboratories used for the analysis of
wet deposition samples should be free from external sources of
contamination. The use of laminar flow clean air workstations is
recommended for sample processing and preparation to avoid the
introduction of airborne contaminants. Samples should always be
capped or covered prior to analysis. A positive pressure
environment within the laboratory is also recommended to minimize
the introduction of external sources of contaminant gases and
particulates. Windows within the laboratory should be kept closed
at all times and sealed if air leaks are apparent. The use of
disposable tacky floor mats at the entrance to the laboratory is
helpful in reducing the particulate loading within the room.
Maintain laboratory temperature within _+3°C.
7'• REAGENTS AND CONSUMABLE MATERIALS
7.1 PURITY OF REAGENTS — Use reagent grade chemicals for all solutions.
All reagents shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society, where such
specifications are available.
7-2 PURITY pp WATER — Use water conforming to ASTM Specification D
1193, Type II (14.4). Point of use 0.2 micrometer filters are
recommended for all faucets supplying ASTM Type II water to prevent
the introduction of bacteria and/or ion exchange resins into
reagents, standard solutions, and internally formulated quality
control check solutions.
7.3 POTASSIUM CHLORIDE REFERENCE SOLUTION (5.0 X 10~4 N) — Dissolve
37.28 mg anhydrous potassium chloride (KCl), dried at 105 C for one
hour, in water (Sect. 7.2) and dilute to 1 L. This solution has a
specific conductance of 73.9 uS/cm at 25°C. Store the reference
solution at room temperature in a tightly sealed high density
polyethylene or polypropylene container for a period not exceeding
one year.
7.3.1 Determine if the meter reading is linear throughout all range
settings using the reference solution described above. If
not, recalibrate the meter at higher and/or lower settings as
needed with different concentrations of KCl reference solution
prepared according to Table 2.
120.6-5
-------
7.4 QUALITY CONTROL CHECK SAMPLE (5.0 x 10 N HNO ) — Dilute 1.0 mL
of concentrated nitric acid (HNO,, sp gr 1.42) to 1 L with water
(Sect. 7.2). Dilute 3.2 mL of this stock solution to 1 L with water.
The resulting solution has a conductance of 21.8 uS/cm at 25°C.
Store at room temperature in a high density polyethylene or
polypropylene container for a period not exceeding one year.
7.5 SAMPLE CONTAINERS — Use glass or disposable polyolefin sample cups
if the conductance cell selected requires a sample container. Rinse
the sample cups a minimum of three times with water (Sect. 7.2)
before use.
8. SAMPLE COLLECTION, PRESERVATION AND STORAGE
8.1 Collect samples in high density polyethylene (HOPE) containers that
have been thoroughly rinsed with ASTM Type II water (7.2). Do not
use strong mineral acids or alkaline detergent solutions for cleaning
collection vessels. Residual acids may remain in the polyethylene
matrix and slowly leach back into the sample. Alkaline detergents
may also leave residues that may affect the sample chemistry. Cap
collection bottles after cleaning to prevent contamination from
airborne contaminants. Air dry collection buckets in a laminar flow
clean air workstation and wrap in polyethylene bags prior to use. If
a laminar flow workstation is not available, pour out any residual
rinse water and bag the buckets immediately. Do not dry the bucket
interior by any method other than air drying in a laminar flow clean
air workstation.
8.2 The frequency of sample collection and the choice of sampler design
are dependent on the monitoring objectives. In general, the use of
wet-only samplers is recommended to exclude dry deposition
contributions, minimize sample contamination, retard evaporation,
and enhance sample stability. Sample collection frequency may vary
from sequential sampling within a wet deposition event to weekly
sampling periods. Collection periods of more than one week are not
recommended since sample integrity may be compromised by longer
exposure periods.
8.3 The dissolution of particulate materials and the presence of
microbial activity will affect the stability of the ions in wet
deposition samples (14.5). This instability can result in either an
increase or a decrease in specific conductance of the solution.
Measurements of conductance should be made immediately after sample
collection and thermal equilibration with calibration standard(s).
Refrigeration of samples at 4°C will minimize but not prevent
changes in specific conductance.
8.3.1 Filtration of samples through a 0.45 micrometer membrane
leached with water (Sect. 7.2) is effective at stabilizing
changes in conductance that result from the dissolution of
alkaline particulate matter (14.5). Monitoring of the
filtration procedure is necessary to ensure that samples are
not contaminated by the membrane or filtration apparatus.
120.6-6
-------
9. CALIBRATION AND STANDARDIZATION
9.1 Bring all standards and samples to ambient temperature, (_+l°C) .
9.2 Rinse the specific conductance cell at least three times with the
same volume of KCl standard as the aliquot to be measured. Measure
the conductance of a fourth portion of the KCl standard. The
conductance measured for the calibration solution must agree within
+2 uS/cm of the nominal value.
9.3 CELL CONSTANT
9.3.1 If the meter selected requires that a cell constant be
calculated, use the equations provided in Sect. 12.2.
9.3.2 If the specific conductance of the reference solution is
incorporated into the meter for direct readout of conductance,
follow the manufacturer's guidelines for calibration.
10. QUALITY CONTROL
10.1 Each laboratory using this method should develop formalized quality
control protocols to continually monitor the bias and precision of
all measurements. These protocols are required to ensure that the
measurement system is in a state of statistical control. Estimates
of bias and precision for wet deposition analyses cannot be made
unless these control procedures are followed. Detailed guidelines
for the development of quality assurance and quality control
protocols for wet deposition measurement systems are published in a
manual available from the United States Environmental Protection
Agency, Research Triangle Park, NC 27711 (14.6). Included in this
manual are procedures for the development of statistical control
charts for use in monitoring bias and precision as well as
recommendations for the introduction of reagent blanks, laboratory
duplicates, field duplicates, spike samples, and performance
evaluation samples. These guidelines are to be used by all
laboratories involved with wet deposition measurements.
10.2 ESTABLISHMENT OF WARNING AND CONTROL LIMITS — Warning and control
limits are used to monitor the analyses of quality control check
samples (QCS).
10.2.1 Quality Control Check Samples (QCS) ~ Calculate warning
and control limits for QCS solutions from a minimum of ten
analyses performed on ten days to provide a realistic
estimate of the method variability. Calculate a standard
deviation (s) for the measured conductance of each QCS
solution. Use the certified or NBS traceable specific
conductance as the mean (target) value (5?) for determining
control limits. A warning limit of x + 2s and a control
limit of * + 3s should be used. Constant positive or
negative measurements with respect to the true value are
indicative of a method or procedural bias. If the measured
conductance for the QCS solutions fall outside of the + 3s
120.6-7
-------
limits, recalibrate the system and reanalyze all samples
from the last time the system was in control. if two
successive QCS conductance measurements are outside of the
+2s limits, verify the meter calibration according to
Sect. 10.5 before continuing with sample measurements. The
standard deviations used to generate the QCS control limits
should be comparable to the single operator precision
reported in Table 1. Reestablish new warning and control
limits whenever instrumental operating conditions are
varied or QCS concentrations are changed.
10.2.2 All warning and control limits should be reevaluated on a
continual basis as additional data are collected during
routine analyses. The limits should be broadened or
narrowed if a recalculated standard deviation under similar
operating conditions provides a different estimate of the
procedure variability.
10.3 Monitor the cleaning procedure by pouring a volume of water (Sect.
7.2) that approximates the median sample size into the collection
vessel. Allow the water to remain in the sealed or capped
collection container for at least 24 hours and determine the
specific conductance of the solution. If the measured conductance
is greater than 3 uS/cm, a contamination problem is indicated in
the cleaning procedure. Corrective action should be taken before
the sampling containers are used for the collection of wet
deposition.
10.4 Conductance cells used foj the measurement of wet deposition
samples should not be used for other sample types. Strongly acidic
or basic solutions may cause cell degradation and result in biased
measurements. Similarly, samples characterized by high
concentrations of organic matter may leave a residue on the cell
resulting in inaccurate measurements.
10.5 Verify the meter calibration after every ten samples and at the end
of each day's analyses. If the measured conductance falls outside
of the limits described in Sect. 9.2, recalibrate the conductance
meter assembly and reanalyze those samples analyzed since the last
calibration.
10.6 Determine the conductance of a quality control check sample (QCS)
after the meter and cell assembly have been calibrated. This
sample may be formulated in the laboratory, obtained from the
National Bureau of Standards (NBS Standard Reference Material 2694,
Simulated Rainwater), or the United States Environmental Protection
Agency (NBS Traceable Reference Material). Verify the accuracy of
internally formulated QCS solutions with an NBS traceable standard
before acceptance as a quality control check. The check sample
selected should approximate the conductance of the samples to be
analyzed. If the measured value for the QCS is not within the
specified limits of the control solution, measure a second aliquot.
Failure to obtain acceptable results on the second aliquot
indicates a problem with the cell or meter. Check the conductance
120.6-8
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meter according to the manufacturer's guidelines. If a cell
problem is indicated, replace the cell and repeat the calibration
procedure before measuring the QCS again. Plot the data obtained
from the QCS checks on a control chart for routine assessments of
bias and precision.
10.6.1 The conductance of the QCS should be measured after every
ten samples or after completion of a batch of samples
consisting of less than ten. If the QCS measurement is out
of the predetermined control limits, check the calibration
and recalibrate if it has shifted by more than 2 uS/cm.
Recheck the QCS and reanalyze all samples from the last
time the measurement system was in control.
10.7 Submit a Field Blank (FB) to the laboratory for every 20 samples.
The FB may consist of a water sample (Sect. 7.2) or a known
reference solution that approximates the concentration levels
characteristic of wet deposition. The FB is poured into the
sampling vessel at the field site and undergoes identical
processing and analytical protocols as the wet deposition
sample (s). Use the analytical data obtained from the FB to
determine any contamination introduced in the field and laboratory
handling procedures. The data from the known reference solution
can be used to calculate a system precision' and bias.
10.8 Participation in performance evaluation studies is recommended for
wet deposition chemistry laboratories. The samples used for these
performance audits should contain the analytes of interest at
concentrations within the normal working range of the method. The
true values are unknown to the analyst. Performance evaluation
studies for wet deposition chemistry laboratories are conducted
semiannually by the USEPA Performance Evaluation Branch, Quality
Assurance Division, Research Triangle Park, NC 27711.
PROCEDURE
11.1 Determine the temperature of the wet deposition sample to be tested
and bring all standards and samples to ambient temperature,
11.2 Calibrate the conductance assembly as described in Sect. 9.
11.3 After the cell and meter are calibrated, measure the QCS. If the
measured value for the QCS is not within the specified limits
(Sect. 10.2.1), refer to Sect. 10.6.
11.4 Rinse the cell at least three times with the same volume of water
(Sect. 7.2) as the sample aliquot to be measured, discarding each
rinse. Determine the specific conductance of a fourth portion of
the water to the nearest 0.1 uS/cm. If the corrected specific
conductance exceeds 1.0 uS/cm, the water is not suitable for use in
specific conductance measurements. Discard the water and any
standard solutions or quality control check samples that have been
prepared using that water.
120.6-9
-------
11.5 Rinse the cell at least three times with the same volume of water
(Sect. 7.2) as the sample aliquot to be measured, discarding each
rinse. Rinse the cell with an aliquot of the wet deposition sample
to be measured. Discard the rinse solution. Determine the
specific conductance of a second portion of the sample.
Note: When the same sample aliquot must be. used for further
analyses, measure the specific conductance prior to all other
determinations. Measurement of pH especially must be postponed.
Leakage of reference solution from a pH reference cell will alter
the measured value of the specific conductance of the solution
(14.7).
12. CALCULATIONS
12.1 If the meter selected has a feature that allows adjustment of the
direct readout of the specific conductance standard to the
theoretical value, no calculations are required.
12.2 CELL CONSTANT — If the meter selected requires that a cell
constant be calculated, follow the instructions provided below:
12.2.1 Compute the corrected cell constant, K , that includes
the calculation for the cell constant, K, and temperature
correction to 25 C, using the conductance value obtained
in Sect. 9.2 and the following equation:
74 uS/cm
KC
KC1M
where: KCl = conductance value measured for the KC1
standard (uS/cm)
12.2.2 Determine the corrected specific conductance for the
water (Sect. 7.2) using the corrected cell constant, the
conductance value measured in Sect. .11.4, and the following
equation:
where: W = Corrected specific conductance value for the
water sample (uS/cm)
Specific conductance
water sample (uS/cm)
W * Specific conductance value measured for the
120.6-10
-------
12.2.3 Determine the corrected sample conductance using the
following equation, the corrected cell constant, and the
conductance value measured in Sect. 11.5.
SC = KC X SM
where: S = Corrected specific conductance value for the
wet deposition sample (uS/cm)
S = Specific conductance value measured for the
wet deposition sample (uS/cm)
12.3 Report specific conductance to the nearest tenth in units of uS/cm.
13. PRECISION AND BIAS
13.1 Single operator precision and bias were determined from
measurements of quality control check samples that approximated the
conductance range of wet deposition samples. The results are
tabulated in Table 1.
14. REFERENCES
14.1 Annual Book of ASTM Standards, Part 31, "Definitions of Terms
Related to Water," Standard D 1129-82b, 1982, p. 4.'
14.2 Annual Book of ASTM Standards, Part 31, "Excerpts from Standard
for Metric Practice," Standard E 380-79, 1982, pp. 679-694.
14.3 "Safety in Academic Chemical Laboratories," American Chemical
Society Publication, Committee on Chemical Safety, 3rd Edition,
1979.
14.4 Annual Book of ASTM Standards, Part 31, "Standard Specification
for Reagent Water," Standard D 1193-77, 1982, p. 39.
14.5 Peden, M. E. and Skowron, L. M., "Ionic Stability of Precipitation
Samples," Atmos. Environ. 12, 1978, pp. 2343-2349.
14.6 Topol, L. E., Lev-On, M., Flanagan, J., Schwall, R. J., Jackson, A.
E., Quality Assurance Manual for Precipitation Measurement
Systems, 1985 U.S. Environmental Protection Agency,
Environmental Monitoring Systems Laboratory, Research Triangle
Park, NC 27711.
14.7 Koch, W. G., Marinenko, G., and Stolz, J. W., "Simulated
Precipitation Reference Materials, IV," National Bureau of
Standards (U.S.), NBSIR 82-2581, June 1982, p. 3.
120.6-11
-------
Table 1. Single-Operator Bias and Precision of Specific
Conductance Measurements Determined from
Quality Control Check Samples.
Theoretical Mean Measured Precision
Conductance, Conductance, Bias, s, RSD,
uS/cm uS/cm na uS/cm % us/cm %
21.8 22.0 80 0.2 1.0 0.3 1.4
128.0 128.2 9 0.2 0.1 2.0 1.6
The above data were obtained from the records of conductance measurements
made under the direction of the NADP quality assurance program. The quality
control solutions used were a 5.01 x 10 N nitric acid solution having a
calculated specific conductance of 21.8 uS/cm at 25°C and a simulated
rainwater solution (Research Material #8409-11) provided by the National
Bureau of Standards.
a. Number of replicates.
120.6-12
-------
Table 2. Specific Conductance of KC1 Solutions at 25 C
as a Function of the Molar Concentration.
Specific
Concentration, Conductance,
moles of KCl/L uS/cm
0.0001 14.89
0.0002 29.71
0.0003 44.47
0.0004 59.20
0.0005 73.89
0.0006 88.55
0.0007 103.19
0.0008 117.80
0.0009 132.38
0.0010 146.95
120.6-13
-------
Figure 1. Percentile Concentration Values Obtained from
Wet Deposition Samples: Specific Conductance
100 ••
90 ••
80 ••
~ 70 ••
o
z
Cd
i
sat
Ed
>
h- I
H
<
60
50
40
30
20
10
i t
i i i
i i i
i i
20 40 60 80
SPECIFIC CONDUCTANCE (uS/cm)
100
120.6-14
-------
Appendix E
METHOD 305.6 — ACIDITY IN WET DEPOSITION BY
TITRIMETRIC DETERMINATION
METHOD 305.2 — ACIDITY (TITRIMETRIC)
-------
Method 305.6 — Acidity in Wet Deposition by
Titrimetric Determination
March 1986
Performing Laboratory:
Jacqueline M. Lockard
Kenni 0. James
Carla Jo Brennan
Mark E. Peden
Illinois State Water Survey
Analytical Chemistry Unit
2204 Griffith Drive
Champaign, Illinois 61820
Sponsoring Agency:
John D. Pfaff, Project Officer
Inorganic Analysis Section
Physical and Chemical Methods Branch
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
305.6-1
-------
INDEX
Section
Number Subject
1 Scope and Application
2 Summary of Method
3 Definitions
4 Interferences
5 Safety
6 Apparatus and Equipment
7 Reagents and Consumable Materials
8 Sample Collection, Preservation, and Storage
9 Calibration and Standardization
10 Quality Control
11 Procedure
12 Calculations
13 Precision and Bias
14 References
TABLES
1. National Bureau of Standards (NBS) Salts for Reference Buffer
Solutions.
2. Single-Operator Bias and Precision from Acidity Titrations of Quality
Control Check Samples.
FIGURES
1. Sample Vessel Used for an Acidity Titration.
2. A Standard Titration Curve with Gran's Plot for an Equimolar Mixture of
Dilute Nitric Acid and Acetic Acid.
3. A Standard Titration Curve with Gran's Plot for a Dilute Nitric Acid
Solution.
305.6-2
-------
1. SCOPE AND APPLICATION
1.1 This method is applicable to the titrimetric determination of strong
and total acidity by electrometric measurement using either a pH half
cell with a reference probe or a combination electrode as the sensor.
The concentration of weak acids present is determined from the
difference between the measured total and strong acidities. These
guidelines outline the procedure by which titration to an end point
pH is to be made on wet deposition samples.
1.2 The term "wet deposition" is used in this method to designate rain,
snow, dew, sleet, and hail.
1.3 The method detection limit (MDL) determined from replicate analyses
of a 5.0 x 10 N nitric acid solution is 5 ueq/L.
2. SUMMARY OF METHOD
2.1 The pH meter and the associated electrode(s) are calibrated against
two reference buffer solutions that bracket the anticipated sample
pH. Small increments of a sodium hydroxide solution are added to an
unfiltered wet deposition sample. The course of the titration is
followed by measuring the pH and the amount of titrant added as the
titration progresses to a pH of 10.3. The strong acid equivalence
point lies at the inflection point of the curve, i.e., at the point
of maximum slope. The presence of dissociated weak acids in the
sample will make the accurate determination of this equivalence point
difficult. To reduce the potential for error when graphically
determining the equivalence point, a method developed by Gran (14.1)
is used. A plot of Gran's function versus volume .of titrant added to
the sample is constructed, from which strong, weak, and total
acidities are derived.
DEFINITIONS
3.1 pH — the negative logarithm to the base ten of the conventional
hydrogen ion activity (14.2):
pH = -log[H+]
*
3.2 ACIDITY — the quantitative capacity of aqueous media to react with
hydroxyl ions.
3.3 TITRATION — a method for determining the concentration of a
dissolved substance in terms of the amount of a reagent of known
concentration required to quantitatively react with a measured
volume of the test solution.
305.6-3
-------
3.4 EQUIVALENCE POINT — the point in the process of a titration at
which the titrated species and titrant are present in equivalent
amounts.
3.5 For definitions of other terms used in this method, refer to the
glossary. For an explanation of the metric system including units,
symbols, and conversion factors see American Society for Testing and
Materials (ASTM) Standard E 380, "Metric Practices" (14.3).
4. INTERFERENCES
4.1 The pH meter and the associated electrode(s) reliably measure pH in
nearly all aqueous solutions and in general are not subject to
solution interference from color, turbidity, oxidants, or reductants.
4.2 The true pH of an aqueous solution is affected by the temperature.
The electromotive force between the glass and the reference electrode
is a function of temperature as well as pH. Temperature effects
caused by a change in electrode output can be compensated for
automatically or manually depending on the pH meter selected.
4.3 Organic humic materials present in wet deposition samples degrade the
glass electrode performance by coating the sensing bulb. Difficulty
encountered when standardizing the electrode(s), erratic readings, or
slow response times may be an indication of contamination of the
glass bulb. To remove these coatings, refer to the manual
accompanying the probe for the manufacturer's recommendations.
4.4 As discussed in Sect. 4.5 of Method 150.6 of this manual, measuring
pH in solutions while stirring can result in errors due to residual
streaming potentials. These errors are minimized by maintaining a
constant stirring' rate during both meter calibration and sample
titration. The effect of streaming potentials is less important
during titrimetric procedures since the relative, and not the
absolute, change in pH values with added titrant is used to calculate
acidity. Stirring the sample throughout the titration ensures
complete mixing of titrant and sample and reduces the time necessary
to complete the procedure.
Note: When magnetic stirring is used, avoid sample contamination
when inserting the stirring bar. Maintain an air space between the
surface of the stirring motor and the sample container to prevent
heating the sample.
4.5 Dissolved gases affecting sample acidity, such as carbon dioxide or
ammonia, may be gained or lost during- sampling, storage, or
titration. Minimize these effects by titrating to the end point
promptly after opening the sample container. Purge the sample of
CO. with a nitrogen stream and maintain a nitrogen atmosphere
within the vessel throughout the titration.
305.6-4
-------
4.6 The important assumption in Gran's method is that only strong acids
contribute to the free acidity of a solution. The presence of weak
acids (formic acid, acetic acid, and the ammonium ion) and
hydrolyzable metal salts (Al(H 0)g) can lead to an overestimate
of both the strong and the total acidity when using this technique.
In the absence of complete chemical characterization of the wet
deposition sample to correct for this overestimation, the usefulness
of the data obtained by this method becomes limited (14.4).
5. SAFETY
5.1 The reference buffer solutions, sample types, and most reagents
used in this method pose no hazard to the analyst. Use a fume hood,
protective clothing, and safety glasses when handling concentrated
nitric acid (Sect. 7.6) and sodium hydroxide (Sect. 7.8).
5.2 Follow American Chemical Society guidelines regarding the safe
handling of chemicals used in this method (14.5).
6. APPARATUS AND EQUIPMENT
6.1 LABORATORY pH METER — The meter may have either an analog or
digital display but must have a 0.01 pH unit sensitivity. A meter
that has separate calibration and slope adjustment features and is
electrically shielded to avoid interferences from stray currents or
static charge is necessary. It may be powered by battery or 110 VAC;
if battery powered, the meter must have a battery check feature. A
temperature compensator control to allow accurate measurements at
temperatures other than 25°C is desirable.
6.2 SENSING ELECTRODE — Select a sensing electrode constructed of
general purpose glass. This electrode type generates lower
resistance, faster response, and has a reliable range of 0-14 pH
units. Refer to the manual accompanying the probe for the
manufacturer's recommendations on electrode storage.
6.3 REFERENCE ELECTRODE — Select a reference probe compatible with the
sensing electrode used. Refer to the manual accompanying the probe
for the manufacturer's recommendations on electrode storage.
6.4 COMBINATION ELECTRODE — The combination electrode combines the
indicating and reference elements in a single unit. Since sample
volume requirements are a consideration when analyzing wet deposition
samples, combination electrodes are more convenient than separate
glass and reference electrodes. Refer to the manual accompanying
the probe for the manufacturer's recommendations on electrode
storage.
6.5 TEMPERATURE CONTROL — To ensure accurate results, use either a
constant temperature water bath, a temperature compensator, or a
thermometer to verify that all standards and samples are maintained
at temperatures within _+l°C of one another. If a thermometer is
used, select one capable of being read to the nearest 1 C and
covering the range 0° to 40 C.
305.6-5
-------
6.6 MICROBURET — For the addition of titrant, select a microburet or
an autoburet assembly. Alternatively, a micropipette capable of
reproducibly delivering 5 uL of solution may be used.
6.7 STIRRING DEVICE — electric or water-driven. If an electric stirrer
is selected, leave an air gap or place an insulating pad between the
stirrer surface and the solution container to minimize heating of the
sample. Use a TFE-fluorocarbon-coated stirring bar.
6.8 TITRATION VESSEL — Use a borosilicate glass or polyolefin vessel
with a 75-mL capacity. Equip.the vessel with a lid having openings
to accommodate the pH electrode(s), a nitrogen purge line, buret, and
exhaust (to prevent pressure build-up as N is pumped into the
chamber). A suitable titration vessel is illustrated in Figure 1.
6.9 LABORATORY FACILITIES — Laboratories used for the analysis of
wet deposition samples should be free from external sources of
contamination. The use of laminar flow clean air workstations is
recommended for sample processing and preparation to avoid the
introduction of airborne contaminants. Samples should always be
capped or covered prior to analysis. A positive pressure
environment within the laboratory is also recommended to minimize
the introduction of external sources of contaminant gases and
particulates. Windows within the laboratory should be kept closed
at all times and sealed if air leaks are apparent. The use of
disposable tacky floor mats at the entrance to the laboratory is
helpful in reducing the particulate loading within the room.
7. REAGENTS AND CONSUMABLE MATERIALS
7.1 PURITY OF REAGENTS — Use reagent grade chemicals for all solutions.
All reagents shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society (ACS) where such
specifications are available.
7.2 PURITY OF WATER — Use carbon dioxide-free water prepared by boiling
ASTM Type II water (14.6) in a conical flask for 20 minutes. Stopper
the flask with a 1-hole rubber stopper fitted to a soda lime-ascarite
drying tube and allow the water to cool. Point of use 0.2 micrometer
filters are recommended for all faucets supplying water to prevent
the introduction of bacteria and/or ion exchange resins into
reagents, standard solutions, and internally formulated quality
control check solutions.
7.3 NITROGEN, GAS — Use pre-purified nitrogen gas (N , 99.995%)
to purge the sample of carbon dioxide and maintain a N atmosphere
above the sample during titration.
7.4 POTASSIUM HYDROGEN PHTHALATE SOLUTION (0.02 N) — Dissolve 4.00 g of
potassium hydrogen phthalate (KHC-H .0.), dried at 105 C for
one hour, in water (Sect. 7.2) and dilute to 1 L.
305.6-6
-------
7.5 QUALITY CONTROL CHECK SAMPLES (QCS) ~ Prepare the following
solutions and analyze according to Sect. 11.3-11.4 to verify the
titration procedure.
7.5.1 Strong Acid — Nitric Acid (5.0 x 10 N) — Dilute 1.0 mL
of concentrated nitric acid (HNO , sp gr 1.42) to 1 L with
water (Sect. 7.2). Dilute 3.2 mL of this stock solution to
1 L with water (Sect. 7.2). The resulting solution has a pH
of 4.30 +_ 0.10 and a total acidity of 50.1 +_ 10. 0 uea./L at
25 C. Store at room temperature in a high density
polyethylene or polypropylene container.
7.5.2 Mixed Strong/Weak Acid — NiŁric Acid : Acetic Acid
(2.5 x 10 N : 2.5 x 10 N) — Dilute 1.0 mL of
concentrated nitric acid to 1 L with water (Sect. 7.2).
Dilute 1.0 mL of concentrated acetic acid (HC H 0 ,
sp gr 1.05) to 1 L with water (Sect. 7.2). Combine 1.60 mL
of HNO solution with 1.45 mL of HC2H3°2 solution
and dilute to 1 L with water (Sect. 7.27. The resulting
solution has a pH of 4.60 ± 0.10 and a total acidity of
50.6 +; 5.0 ueq/L at 25 C. Store at room temperature in
a high density polyethylene or polypropylene container.
7.6 REFERENCE BUFFER SOLUTIONS — Table 1 identifies each buffer salt by
its National Bureau of Standard (NBS) number and provides a
recommended drying procedure prior to use. Store the reference
buffer solutions in polyethylene or chemical-resistant glass bottles
and replace yearly or sooner if a visible change such as the
development of colloidal or particulate materials is observed.
7.6.1 Phthalate Reference Buffer Solution (0.02 N HC1, 0.05 N
KHC HO ) — Add 83.0 mL of concentrated hydrochloric
acid (HCl, sp gr 1.19) to water (Sect. 7.2) and dilute to 1 L.
Dissolve 10.20 g of "potassium hydrogen phthalate
(KHC HO ) in 22.3 mL of the hydrochloric acid solution
and dilute to 1 L with water (Sect. 7.2). This solution has a
pH of 3.00 at 25°C.
7.6.2 Phthalate Reference Buffer Solution (0.05 N
Dissolve 10.12 g of potassium hydrogen phthalate
(KHCgH 0 ) in water (Sect. 7.2) and dilute to 1 L. This
solution has a pH of 4.00 at 25°C.
7.6.3 Phosphate Reference Buffer Solution (0.005 N NaOH, 0.05 N
KH PO ) — Dissolve 4.00 g of sodium hydroxide (NaOH) in
water4(Sect. 7.2) and dilute to 1 L. Dissolve 6.80 g of
potassium dihydrogen phosphate (KH PO ) in 56.0 mL of the
hydroxide solution and dilute to 1 L with water (Sect. 7.2).
This solution has a pH of 6.00 at 25 C.
305.6-7
-------
7.6.4 Phosphate Reference Buffer Solution (0.03 N NaOH, 0.05 N
KH PO ) — Dissolve 40.0 g of sodium-hydroxide (NaOH) in
water (Sect. 7.2) and dilute to 1 L. Dissolve 6.80 g of
potassium dihydrogen phosphate (KH PO ) in 29.1 mL of the
hydroxide solution and dilute to 1 L with water (Sect. 7.2).
This solution has a pH of 7.00 at 25 C.
7.6.5 Commercial Buffer Solutions — Commercially available buffer
solutions traceable to NBS buffers are adequate for
standardization. These buffer solutions have pH values near
3, 4, 6, or 7. The exact pH and use temperature are provided
by the supplier of the specific buffer.
7.7 SODIUM HYDROXIDE SOLUTION, TITRANT (0.02 N) -- Use commercially
available 0.02 N sodium hydroxide solution or prepare from ACS
reagent grade materials. Dissolve 1.0 g of sodium hydroxide (NaOH)
in 10 mL of water (Sect. 7.2), cool, and filter through hardened
filter paper. Dilute the filtrate to 1 L with water (Sect. 7.2).
Standardize with potassium hydrogen phthalate (Sect. 7.5) according
to Sect. 9.2. Calculate the normality using the equation in Sect.
12.2. Refrigerate the solution at 4 C in a high density
polyethylene or polypropylene container.
8. SAMPLE COLLECTION, PRESERVATION, AND STORAGE
B.I Collect samples in high density polyethylene (HOPE) containers that
have been thoroughly rinsed with ASTM Type II water (7.2). Do not
use strong mineral acids or alkaline detergent solutions for cleaning
collection vessels. Residual acids may remain in the polyethylene
matrix and slowly leach back into the sample. Alkaline detergents
may also leave residues that may affect the sample chemistry. Cap
collection bottles after cleaning to prevent contamination from
airborne contaminants; air dry collection buckets in a laminar flow
clean air workstation and wrap in polyethylene bags prior to use. If
a laminar flow workstation is not available, pour out any residual
rinse water and bag the buckets immediately. Do not dry the bucket
interior by any method other than air drying in a laminar flow clean
air workstation.
8.2 The frequency of sample collection and the choice of sampler design
are dependent on the monitoring objectives. In general, the use of
wet-only samplers is recommended to exclude dry deposition
contributions, minimize sample contamination, retard evaporation,
and enhance sample stability. Sample collection frequency may vary
from sequential sampling within a wet deposition event to total event
samples. In addition to the replacement of sampling containers at
the cessation of each wet deposition event, a routine weekly
container change is recommended. This replacement protocol ensures
sample integrity which may be compromised by long term container
exposure.
305.6-8
-------
8.3 The dissolution of particulate materials and the presence of
microbial activity will affect the stability of both the strong and
the weak acid components of wet deposition samples (14.7, 14.8).
This instability generally results in a decrease in measured
acidity. Titrations should be made immediately after sample
collection and thermal equilibration with calibration buffers.
Refrigeration of samples at 4 C will minimize but not prevent a
decrease in the hydrogen ion content.
8.3.1 Filtration of samples through a deionized water leached
0.45 micrometer membrane is effective at stabilizing the
acidic components of the wet deposition sample that are
influenced by the dissolution of alkaline particulate matter
(14.7). Monitoring of the filtration procedure is necessary
to ensure that sample acidities are not affected by the
membrane or filtration apparatus.
8.3.2 A biocide such as chloroform (CHC1 ) may be used to
stabilize the organic acid component of the sample and to
prevent changes in acid content due to biological actions on
other sample constituents (14.8). Add the chloroform (0.5 mL
per 250 mL sample) to a separate sample aliquot that will be
used only for the determination of strong and total acid
components.
9. CALIBRATION AND STANDARDIZATION
9.1 Turn on the meter and allow it to warm up according to manufacturer's
instructions.
9.2 If necessary, add filling solution to the electrode before using.
Maintain the filling solution level at least one inch above the level
of the sample surface to ensure proper electrolyte flow rate.
9.3 Determine the temperature of the wet deposition sample. Allow
sample, buffers, and QCS solutions to reach room temperature
(^1 C) before using for calibration or titration.
9.4 Select two reference buffer solutions that bracket the anticipated
pH of the wet deposition sample. The difference between the nominal
pH of each buffer solution should not exceed three units. A pH
7.00 and a pH 4.00 buffer are most frequently used for wet deposition
studies.
9.5 CALIBRATION FUNCTION
9.5.1 Rinse the electrode(s) with three changes of water (Sect. 7.2)
or with a flowing stream from a wash bottle. Dispense
20-40 mL of the buffer with the higher pH into the titration
vessel (Fig. 1). Insert the stirring bar and continue
stirring throughout the calibration procedure at a rate of
4 revolutions per second (rps). Maintain a nitrogen
atmosphere within the titration chamber during measurement as
in Sect. 11.4.1.
305.6-9
-------
9.5.2 Insert the electrode (s) into the buffer and allow tine for the
reading to remain stable within +0.01 pH units over a
30 second period.
9.5.3 Adjust the calibration function until the reading corresponds
to the temperature corrected value of the reference buffer
solution.
9.6 SLOPE FUNCTION
9.6.1 Rinse the electrode(s) with three changes of water (Sect. 7.2)
or with a flowing stream from a wash bottle. Dispense
20-40 mL of the second reference buffer solution into the
titration vessel. Insert the stirring bar and continue
stirring throughout the calibration procedure. Maintain a
nitrogen atmosphere within the titration chamber during
measurement as in Sect. 11.4.1.
•
9.6.2 Insert the electrode(s) into the buffer and allow the system
to equilibrate as directed in Sect. 9.5.2.
9.6,3 Adjust the slope function until the reading corresponds to
the temperature corrected value of the second reference buffer
solution.
9.7 CALIBRATION CHECK
9.7.1 Remove the electrode(s), rinse thoroughly, and place into the
first reference buffer solution following the procedure in
Sect. 9.5. If the pH does not read within _+0.01 units of
the temperature corrected value, repeat the calibration
procedure until the buffers agree.
9.8 To standardize the NaOH titrant prepared in Sect. 7.8, fill a 25-mL
buret with 0.02 N KHC HO (Sect. 7.5). Pipette 20 mL of
0.02 N NaOH into a beaker and immerse a calibrated pH electrode into
the solution. Add KHC HO solution to the dilute NaOH in
small increments until the pH of the solution reads 8.70. Calculate
the normality of the NaOH using the equation provided in Sect. 12.2.
13. QUALITY CONTROL
10.1 ' Each laboratory using this method should develop formalized quality
control protocols to continually monitor the bias and precision of
all measurements. These protocols are required to ensure that the
measurement system is in a state of statistical control. Estimates
of bias and precision for wet deposition analyses cannot be made
unless these control procedures are followed. Detailed guidelines
for the development of quality assurance and quality control
protocols for wet deposition measurement systems are published in a
manual available from the United States Environmental Protection
Agency, Research Triangle Park, NC 27711 (14.9). Included in this
manual are procedures for the development of statistical control
charts for use in monitoring bias and precision as well as
305.6-10
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recommendations for the introduction of reagent blanks, laboratory
duplicates, field duplicates, spike samples, and performance
evaluation samples. These guidelines are to be used by all
laboratories involved with wet deposition measurements.
10.2 ESTABLISHMENT OF WARNING AND CONTROL LIMITS — Warning and control
limits are used to monitor the analyses of quality control check
samples (QCS).
10.2.1 Quality Control Check Samples (QCS) — Calculate warning
and control limits for QCS solutions from a minimum of ten
analyses performed on ten days to provide a realistic
estimate of the method variability. Calculate a standard
deviation (s) for the measured acidity of each QCS
titrated. Use the certified or NBS traceable acidity as
the mean (target) value (x) . A warning limit of x +_ 2s
and a control limit of 1? +_ 3s should be used. Constant
positive or negative measurements with respect to the true
value are indicative of a method or procedural bias. If
the measured acidity found by titration of the QCS solution
falls outside of the +2s limits, recalibrate the system
and reanalyze all samples from the last time the system was
in control. If two successive QCS acidity measurements ar^e
outside of the _+2s limits, verify the meter calibration
according to Sect. 10.5 before continuing with titrations.
The standard deviations used to generate the QCS control
limits should be comparable to the single operator
precision reported in Table. 2. Reestablish new warning and
control limits whenever instrumental operating conditions
are varied or QCS concentrations are changed.
10.2.2 All warning and control limits should be reevaluated on a
continual basis as additional data are collected during
routine analyses. The limits should be broadened or
narrowed if a recalculated standard deviation under similar
operating conditions provides a different estimate of the
procedure variability.
10.3 Monitor the cleaning procedure by pouring a volume of water (Sect.
7.2) that approximates the median sample size into the collection
vessel. Allow the water to remain in the sealed or capped
collection container for at least 24 hours and determine the
solution pH. If the measured pH is not within the range of
5.4-6.0, a contamination problem is indicated in the cleaning
procedure. Corrective action should be taken before the sampling
containers are used for the collection of wet deposition.
10.4 Electrodes used for the measurement of wet deposition samples
should not be used for other sample types. Strongly acidic or
basic solutions may cause electrode degradation and result in
biased measurements and/or slow response in wet deposition samples.
Similarly, samples characterized by high concentrations of organic
matter may leave a residue on the glass sensing bulb resulting in
slow electrode response.
305.6-11
-------
10.5 Verify the meter calibration after every ten samoles and at the end
of each day's analyses using both reference buffar solutions. The
pH measured for the calibration buffers must agree within +Q.Q2
of the nominal value reported for each buffer. If the measured pH
of either buffer falls outside of these limits, recalibrate the
electrode/meter assembly and reanalyze those samples measured since
the last time the system was in control.
10.6 Determine the pH and titrated acidity of a quality control check
sample (QCS) after the meter and electrode assembly have been
calibrated. This sample may be formulated in the laboratory or
obtained from the National Bureau of Standards (NBS Standard
Reference Material 2694, Simulated Rainwater). Verify the accuracy
of internally formulated QCS solutions with an NBS traceable
standard before acceptance as a quality control check. The check
sample selected muse have a pH within the range of the calibration
buffers and should approximate the acidity range of the samples to
be analyzed. The use of two QCS samples, one a dilute strong acid
solution and the other a dilute equimolar mixture of a strong and a
weak acid, is recommended. If the measured acidity found by
titration of the QCS is not within the specified limits of the
control solution, recheck the meter calibration and recalibrate if
necessary. Titrate a second aliquot. If acceptable results on the
second aliquot cannot be obtained, systematically replace titrant,
electrode, and then the meter. Titrate a separate aliquot of QCS
after each change to determine if the problem was corrected. When
the system is in control, titrate the QCS solutions as directed in
Sect. 11. Plot the data obtained from the QCS checks on a control
chart for routine assessments of bias and precision.
10.6.1 The pH and titrated acidity of the QCS should be measured
at the start and completion of each batch of samples. If
the QCS measurement is out of the predetermined control
limits, check the calibration buffers and recalibrate if
any one of the buffer values has shifted by more than
0.02 pH units. Recheck the QCS and reanalyze all samples
from the last time the measurement system was in control.
10.7 Submit a Field Blank (FB) to the laboratory for every 20 samples.
The FB may consist of a water sample (Sect. 7.2) or a known
reference solution that approximates the concentration levels
characteristic of wet deposition. The FB is poured into the
sampling vessel at the field site and undergoes identical
processing and analytical protocols as the wet deposition
sample(s). Use the analytical data obtained from the FB to
determine any contamination introduced in the field and laboratory
handling procedures. The data from the known reference solution
can be used to calculate a system precision and bias.
305.6-12
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10.8 Participation in performance evaluation studies is recommended
for wet deposition chemistry laboratories. The samples used for
these performance audits should contain the analytes of interest at
concentrations within the normal working range of the method. The
true values are unknown to the analyst. Performance evaluation
studies for wet deposition chemistry laboratories are conducted
semiannually by the USEPA Performance Evaluation Branch, Quality
Assurance Division, Research Triangle Park, NC 27711.
11. PROCEDURE
11.1 Bring all buffers and solutions to ambient temperature making sure
any necessary compensation is made for deviations in temperature
(Sect. 6.5).
11.2 Calibrate the electrode assembly with two reference buffer
solutions as described in Sect. 9.1-7.
11.3 After the electrode(s) and meter are calibrated, titrate the QCS
according to Sect. 11.4. If the pH and acidity measured for the
QCS is not within the specified limits (Sect. 10.2.1), refer to
Sect. 10.6.
11.4 SAMPLE ANALYSIS
11.4.1 Rinse the electrode(s) with three changes of water (Sect.
7.2) or with a flowing stream from a wash bottle. Pipette
20-40 mL of sample into the titration vessel. Record the
volume of sample used and begin stirring the sample. Record
the pH after the meter has stabilized to within jKJ.Ol
units. Sparge the sample with N for 10-15 minutes to
remove dissolved CO . Raise the N line to rest above
the level of the solution to maintain a nitrogen atmosphere
of <5 psi (3.5 g/m ) within the titration chamber.
11.4.2 Record the pH of the sample after sparging. The difference
in pH before and after sparging is a measure of the
volatile weak acidity present. Carbon dioxide is the
predominant volatile weak acid found in wet deposition
samples. The contribution of dissolved CO2 to lowering
pH is generally negligible below pH 4.50. Add the 0.02 N
NaOH titrant to the sample in increments of 1-10 uL.
Determine the size of the increment of titrant added by the
change in pH that results from each addition. When the
change in pH is very small (<0.01), increase the volume of
titrant added to 10 uL. Record both the volume of titrant
added and the pH once the meter has become stable.
Continue titrating the sample until a pH of approximately
10.4 is reached, recording pH and volume after each titrant
addition.
305.6-13
-------
11.4.3 Stir the sample throughout the titration. Rinse the
titration assembly and vessel between each titration with
at least three changes of water (Sect. 7.2) or with a
flowing stream from a wash bottle for a minimum of 30
seconds.
11.5 To perform the Gran's analysis on the results of the titration,
refer to Sect. 12.3.
12. CALCULATIONS
12.1 Record pH measurements to the nearest hundredth of a pH unit and
sample temperature to the nearest degree.
12.2 Calculate the normality (N) of the solutions standardized according
to Sect. 9.9 as follows:
4.0 x B
——— eq/L
204.2 x C
where: A = amount of KHC H.O in grams weighed into 1 L.
B = volume of KHC HO used in titration in mL.
EW = equivalent weight of KHC HO (204.2).
C = volume of NaOH titrated in mL*.
12.3 To calculate total and strong acidity, a Gran's plot can be
constructed using the volume and pH data from the titration.
Calculate the Gran function for each point as follows (14.10):
i -DH
«A= (VQ + VT)10 P T
function will be altered by the dissociation of the
weak acids. This produces nonlinearity in the curve ij/ vs. VT<
The linear portion of the curve can be extrapolated to obtain the
equivalence point V for strong acidity. The intersection of the
V axis of «^'vs. V is the equivalence point for total acidity.
See Figures 2 and 3.
305.6-14
-------
Strong acidity = 10~ C_(V /V ) ueq H /L
B Ł 0
Total acidity = 10~6C(V'_/V ) ueq H+/L
B E u
where: C = Normality of titrant
V = volume of titrant added at the equivalence point
in mL (strong acidity)
V = volume of titrant added at the equivalence point
in mL (total acidity)
V = initial volume of sample in mL
The concentration of weak acid is obtained from the following
relationship:
Weak Acidity = Total Acidity - Strong Acidity
13. PRECISION AND BIAS
13.1 Single-operator precision and bias data were obtained using two
quality control check samples. The results are tabulated in
Table 2.
14. REFERENCES
14.1 Gran, G., "Determination of the Equivalent Point in Potentiometric
Titrations," Acta Chemica Scandinavica, 4, 1950, p. 559.
14.2 Annual Book of ASTM Standards, Part 31, "Definitions of Terms
Relating to Water," Standard D 1129-82b, 1982, pp. 3-5.
14.3 Annual Book of ASTM Standards, Part 31, "Excerpts from Standard
for Metric Practice," Standard E 380-79, 1982, pp. 679-694.
14.4 Keene, W. C. and Galloway, J. N., "Gran's Titrations: Inherent
Errors in Measuring the Acidity of Precipitation," Atmos. Environ.
19, 1985, pp. 199-202.
14.5 "Safety in Academic Chemistry Laboratories," American Chemical
Society Publication, Committee on Chemical Safety, 3rd Edition,
1979.
14.6 Annual Book of ASTM Standards, Part 31, "Standard Specification
for Reagent Water," Standard D 1193-77, 1982, p. 39.
14.7 Peden, M. E. and Skowron, L. M., "Ionic Stability of Precipitation
Samples," Atmos. Environ. 12, 1978, pp. 2343-2349.
14.8 Keene, W. C. and Galloway, J. N., "Organic Acidity in
Precipitation of North America," Atmos. Environ. 18, 1984,
pp. 2491-2497.
305.6-15
-------
14.9 Topol, L. E., Lev-On, M., Flanagan, J., Schwall, R. J., Jackson,
A. E., Quality Assurance Manual for Precipitation^ Measurement
Systems, 1985 U.S. Environmental Protection Agency, Environmental
Monitoring Systems Laboratory, Research Triangle Park, NC 27711.
14.10 McQuaker, N. R., Kluckner, P. D. and Sandberg, D. K., "Chemical
Analysis of Acid Precipitation: pH and Acidity Determinations,"
Environ. Sci. & Tech., 17, 1983, pp. 431-435.
305.6-16
-------
Table 1. National Bureau of Standards (MBS) Salts for
Reference Buffer Solutions.
NBS Standard Sample
Designation
Buffer Salt
Drying
Procedure
186-1-c
potassium dihydrogen phosphate
2 h in oven at
130°C
185-f
potassium hydrogen phthalate
2 h in oven at
110°C
The buffer salts listed above can be purchased from the Office of
Standard Reference Materials, National Bureau of Standards, Washington,
D. C. 20234.
305.6-17
-------
Table 2. Single-Operator Bias and Precision from Acidity
Titrations of Quality Control Check Samples.
Theoretical
Mean Measured
Precision,
Total Acidity,
ueq/L
50.1
50.5
Total Acidity,
ueq/L n
50.1 10
47.8 7
Bias, s, RSD,
ueq/L % ueq/L %
0 0 1.8 3.6
-2.7 -5.4 2.4 5.0
The solutions used were a 5.01 x 10 N nitric acid solution (pH = 4.30) and a
5.05 x 10~ N equimolar mixture of nitric acid and acetic acid (pH = 4.60).
a. Number of replicates
305.6-18
-------
Figure 1. Sample Vessel Used for an Acidity
Titration.
pH ELECTRODE
MAGNETIC STIRRER
305.6-19
-------
Figure 2. A Standard Titration Curve with Gran's
Plot for an Equimolar Mixture of Dilute
Nitric Acid and Acetic Acid,
STRONG ACID/WEAK ACID STANDARD
0.05 0.10 0.15 0.20
TITRANT VOLUME, ml
0.25
Calculated Acidities
strong acidity - 25.3 Meq/L (pH « 4.60) - 50.1%
total acidity = 50.6 /ueq/L = 100%
weak acidity » 25.2 Ateq/L » 49.9%
Measured Acidities
mean strong acidity « 22.9 (±1.6) Meq/L (pH 4.64)
mean total acidity » 47.8 (±2.3)
weak acidity a 24.9 Mep/L * 52.1%
47.9%
305.6-20
-------
Figure 3. A Standard Titration Curve with Gran's
Plot for a Dilute Nitric Acid Solution.
STRONG ACID STANDARD
0.05 0.10 0.15 0.20
TITRANT VOLUME, mL
0.25
Calculated Acidity
strong acidity - 50.4 Meq/L (pH 4.30) = 100%
Measured Acidities
mean strong acidity - 51.1 (±3.5) jueq/L (pH 4.29) - 99%
mean total acidity - 51.6 (±3.6)
weak acidity - 0.5 M«q/L - 1%
305.5-21
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Method 305.2 — Acidity (Titrimetric)
December 1982
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
305.2-1
-------
SCOPE AND APPLICATION
1.1 This method is applicable to rain, surface and other waters of pH
less than 8.3.
1.2 This method is a measure of the concentration of strong and weak
acids that react with hydroxyl ions. This includes the dissolved
gases that are present.
1.3 The range of this method depends on the volume of sample titrated
and upon the precision that the increments of titrant can be
measured. If only 10 ml of sample is available for analysis, it
is necessary to use a 50 uL syringe for dispensing the titrant in
order to achieve a precision of less than 10 ueq/L.
SUMMARY OF METHOD
2.1 Samples are titrated with 0.02 N carbonate-free NaOH solution.
The end point is determined with a pH meter. Results are
reported as microequivalents (ueq) per liter.
SAMPLING HANDLING AND STORAGE
3.1 The sample container must be filled completely, sealed and stored
at 4°C. Care must be taken to minimize exposure of the sample to
the atmosphere. Open the sample container immediately before
analysis.
3.2 Analysis should be performed as soon as possible after
collection.
COMMENTS
4.1 Samples with an initial pH between 4.3 and 8.3 are subject to
error due to the loss or gain of dissolved gases during sampling,
storage and analyses.
APPARATUS
5.1 pH meter and electrode(s), see Method 150.1 or 150.2.
5.2 Microburet or microsyringe.
5.3 Teflon or glass magnetic stirring bar.
5.4 Magnetic stirrer.
5.5 Beakers or flasks.
305.2-2
-------
6. REAGENTS
6.1 Standard sodium hydroxide solution, 1 N: Dissolve 40g NaOH in 250
mL distilled water. Cool and dilute to 1 liter with CO^-free
distilled water. Store in a polyolefin bottle and fitted with a
soda lime tube or tight cap to protect from atmospheric COj.
6.2 Standard sodium hydroxide titrant, 0.02 N: Dilute 20.0 mL of 1 N
NaOH with C02-free distilled water to 1 liter. Store in rubber
stoppered bottle. Protect from atmospheric C0« by using a soda
lime tube. Standardize against an 0.02 N potassium acid
phthalate solution prepared by dissolving 4.085 g of anhydrous
O in C0~free distilled water and diluted to 1:1.
7. PROCEDURE
7.1 Pipet an appropriate aliquot of sample into beaker or flask
containing a small Teflon on glass stirring bar. Use extreme
care to minimize the sample surface disturbance.
7.2
7.3
Immerse pH electrode(s) into sample and stir at a rate that does
not cause sample surface disturbance.
Titrate with 0.02 N NaOH (6.2) to pH 8.3. Titration should be
made as quickly as possible to prevent absorption of atmospheric
CO
,,.
Record volume of titrant.
8. CALCULATION
8.1 Acidity, ueq/L =
x Nnxl0
mLS B
ueq/L = microequivalents per liter
mL_ = mL of NaOH titrant
mL_ = mL of sample
o
N
B
normality of titrant
9. PRECISION AND ACCURACY
9.1 Precision and accuracy data are not available.
10. REFERENCES
1. Seymour, M.D., S.A. Schubert, J.W. Clayton, Q. Fernando,
"Variation in the Acid Content of Rain Water in the Course of a
Single Precipitation," Water, Air and Soil Pollution, 10, 1978,
pp. 147-161.
305.2-3
-------
2. Peden, M.E. and L. Skowron, "Ionic Stability of Precipitation
Samples," Atmosph. Environ. 12, 1978, pp. 2343-2349.
3. USGS, "Methods for Collection and Analysis of Water Samples for
Dissolved Minerals and Gases," 1970, p. 39.
4. Annual Book of ASTM Standards, part 31, "Water," 1978, D1067, p.
TUT;
5. Standard Methods for the Examination of Water and Wastevater,
14th Edition, 1975, Method 402, p. 273.
305.2-4
-------
Appendix F
METHOD 300.6 — CHLORIDE, ORTHOPHOSPHATE, NITRATE AND SULFATE
IN WET DEPOSITION BY CHEMICALLY SUPPRESSED ION CHROMATOGRAPHY
METHOD 300.7 — DISSOLVED SODIUM, AMMONIUM, POTASSIUM, MAGNESIUM,
AND CALCIUM IN WET DEPOSITION BY CHEMICALLY SUPPRESSED ION CHROMATOGRAPHY
F-l
-------
Method 300.6 — Chloride, Orthophosphate, Nitrate and
Sulfate in Wet Deposition by Chemically
Suppressed Ion Chromatography
March 1986
Performing Laboratory:
Susan R. Bachman
Carla Jo Brennan
Jane E. Rothert
Mark E. Peden
Illinois State Water Survey
Analytical Chemistry Unit
2204 Griffith Drive
Champaign, Illinois 61820
Sponsoring Agency:
John D. Pfaff, Project Officer
Inorganic Analysis Section
Physical and Chemical Methods Branch
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
300.6-1
-------
INDEX
Section
Number Subject
1 Scope and Application
2 Summary of Method
3 Definitions
4 Interferences
5 Safety
6 Apparatus and Equipment
7 Reagents and Consumable Materials
8 Sample Collection, Preservation, and Storage
9 Calibration and Standardization
10 Quality Control
11 Procedure
12 Calculations
13 Precision and Bias
14 References
TABLES
Method Detection Limits and Concentration Ranges for the Determination of
Anions in Wet Deposition.
Compatibility of Separator and Suppressor Columns with Suggested
Regeneration and Eluent Solutions for the Analysis of Wet Deposition.
Retention Times and Suggested Calibration Standard Concentrations
for the Determination of Anions in Wet Deposition Samples.
Single-Operator Precision and Bias for Chloride, Orthophosphate, Nitrate,
and Sulfate Determined from Analyte Spikes of Wet Deposition Samples.
Single-Operator Precision and Bias for Chloride, Orthophosphate, Nitrate,
and Sulfate Determined from Quality Control Check Samples.
FIGURES
1. Percentile Concentration Values Obtained from Wet Deposition Samples.
2. Chromatogram of a Wet Deposition Sample Containing Chloride,
Orthophosphate, Nitrate, and Sulfate, (a) Without and (b) With Eluent
Matching.
300.6-2
-------
1. SCOPE AND APPLICATION
1.1 This method is applicable to the determination of chloride,
orthophosphate, nitrate, and sulfate in wet deposition by chemically
suppressed ion chromatography.
1.2 The term "wet deposition" is used in this method to designate rain,
snow, dew, sleet, and hail.
1.3 The method detection limits (MDL) for the above analytes were
determined from replicate analyses of calibration solutions containing
0.05 mg/L of each analyte. The measured MDL's for chloride, nitrate,
and sulfate are 0.03 mg/L as Cl~, NO ", and SO " . The MDL for
orthophosphate is 0.02 mg/L as PO ~ . The analyte concentration
range of this method is outlined in Table 1.
1.4 Figure 1 represents cumulative frequency percentile concentration
plots of chloride, nitrate, orthophosphate, and sulfate obtained from
analyses of over five thousand wet deposition samples. These data
may be used as an aid in the selection of appropriate calibration
standard concentrations.
2. SUMMARY OF METHOD
2.1 Ion chromatography combines conductimetric detection with the
separation capabilities of ion exchange resins. A filtered aliquot
of sample, ranging in size from 100 to 250 uL, is pumped through an
ion exchange column where the anions of interest are separated. Each
ion's affinity for the exchange sites, known as its selectivity
quotient, is largely determined by its radius and valence. Because
different ions have different migration rates, the sample ions elute
from the column as discrete bands. Each ion is identified by its
retention time within the exchange column. The sample ions are
selectively eluted off the separator column and onto a suppressor
column. The eluent ions are neutralized and the sample ions are
converted to their corresponding strong acids which are detected in a
conductance cell. The chromatograms produced are displayed on a
strip chart recorder or other data acquisition device for measurement
of peak height or area. The ion chromatograph is calibrated with
standard solutions containing known concentrations of the anion(s) of
interest. Calibration curves are constructed from which the
concentration of each analyte in the unknown sample is determined.
3. DEFINITIONS
3.1 ION EXCHANGE — a reversible process by which ions are interchanged
between an insoluble material and a liquid with no substantial
structural changes of the material (14.1).
3.2 ELUENT — the ionic liquid mobile phase used to transport the sample
through the exchange columns.
3.3 REGENERANT — a solution that converts and maintains an active form
of the suppressor.
300.6-3
-------
3.4 RESOLUTION — the ability of a column to separate constituents under
specified test conditions. Peak resolution is a function of column
efficiency, selectivity, and capacity.
3.5 RETENTION TIME — the interval measured from the point of sample
injection to the point of maximum peak height or area.
3.6 For definitions of other terms used in this method, refer to the
glossary. For an explanation of the metric system including units,
symbols, and conversion factors see American Society for Testing and
Materials (ASTM) Standard E 380, "Metric Practices" (14.2).
4. INTERFERENCES
4.1 Unresolved peaks will result when the concentration of one of the
sample components is 10 to 20 times higher than another component
that appears in the chromatogram as an adjacent peak. Decreasing
the eluent concentration or the flow rate may correct this problem.
4.2 Interferences can be caused by ions with retention times that are
similar to and thus overlap those of the anion of interest. This
type of positive interference is rare in wet deposition samples. If
this interference occurs, decreasing the eluent concentration or the
flow rate may result in improved peak resolution.
4.3 Water from the sample injection will cause a negative peak or dip
in the chromatogram when it elutes because its conductance is less
than that of the suppressed eluent. Any ion of interest eluting near
the water dip must be sufficiently resolved from the dip to be
accurately quantified. This can be achieved by changing the eluent
concentration or decreasing the flow rate. Alternatively, the
negative peak can be reduced by adding an equivalent of 100 uL of
a prepared eluent concentrate (solution that is 100 times more
concentrated than the eluent used for analysis) per 10.0 mL of
sample. Proportionate eluent additions must also be included in
calibration and quality control solutions.
4.4 Deterioration in column performance can result from the buildup of
contaminants on the exchange resin. Losses in retention and
resolution are symptoms of column deterioration. Refer to the
manufacturer's guidelines for instructions en cleaning the column
resin.
4.5 The presence of air bubbles in the columns, tubing, or conductivity
detector cell will cause baseline and peak variability. Avoid
introducing air into the system when injecting samples and standards.
Using degassed eluents and regenerants will help to minimize the
introduction of air.
100.fi-4
-------
5. SAFETY
5.1 The calibration standards, sample types, and most reagents used in
this method pose no hazard to the analyst. Use a fume hood,
protective clothing, and safety glasses when handling concentrated
sulfuric acid (Sect. 7.4).
5.2 Keep the doors of the instrument column compartment closed at all
times when pumps and columns are in use to prevent injury to the
operator from column explosion if the pump pressure or column
backpressure increases.
5.3 Follow American Chemical Society guidelines regarding the safe
handling of chemicals used in this method (14.3).
6. APPARATUS AND EQUIPMENT
6.1 ION CHROMATOGRAPH — Select an instrument equipped with an injection
valve, sample loop, a sampling system, analytical columns, compressed
gas, pumps, detector, and strip chart recorder or other data
acquisition device. All tubing that comes in contact with samples
and standards must be manufactured from inert material such as
polyethylene or tetrafluoroethylene (TFE). Refer to Table 2 for
details on column compatibility.
6.1.1 Anion Guard Column — Place before the separator column.
This contains the same resin as the separator column and
is used to protect the ion exchange column from being
fouled by particulates or organic constituents. Using an
anion guard column will prolong the life of the separator
column (4 x 50 mm, Dionex P/N 030986, AG3, or equivalent).
6.1.2 Anion Separator Column — This is a column packed with a
pellicular low-capacity anion exchange resin constructed of
polystyrene-divinylbenzene beads coated with ammonium active
sites (4 x 250 mm, Dionex P/N 030985, AS3, or equivalent).
6.1.3 Anion Suppressor Column — Place after the separator column.
This may be in the form of a packed bed, fiber or
micro-membrane suppressor. The first type of suppressor is
packed with a .high-capacity anion exchange resin in the
protonated form capable of converting the eluent to a low or
negligible background conductance and converting the sample
anions to their corresponding strong acids (Dionex P/N 030828,
ASC2, or equivalent). The second two types of suppressors
utilize a semipermeable membrane containing anion exchange
sites to suppress eluent conductance. Both the fiber and
micro-membrane suppressors are under continuous regeneration.
(Dionex P/N 35350, AFS, fiber; Dionex P/N 38019, AMMS,
micro-membrane, or equivalent).
300.6-5
-------
6.1.4 Compressed Gas (Nitrogen or Air) — Use ultra-high purity,
99.999% (v/v) compressed gas conforming to the recommendations
of the manufacturer of the ion chromatograph.
6.1.5 Detector — Select a flow-through, temperature-compensated,
electrical conductance cell with a volume of approximately
6 uL coupled with a meter capable of reading from 0 to
1000 uS/cm on an analog or digital scale.
6.1.6 Pump — Use a pump capable both of delivering an accurate
flow rate and of tolerating the optimal pressure as suggested
by the instruction manual accompanying the ion chromatograph
and columns selected. A constant pressure, constant flow pump
is recommended for enhanced baseline stability. All interior
pump surfaces that will be in contact with samples and
standards should be manufactured from inert materials.
6.1.7 Recorder — This should be compatible with the maximum
conductance detector output with a full-scale response time of
0.5 sec or less.
6.1.8 Sample Loop — Select a sample loop compatible with the column
system having a capacity of 100-250 uL.
6.1.9 Sampling System — Select one of the following for sampling.
6.1.9.1 Syringe — Use a syringe equipped with a male fitting
with a minimum capacity of 2 mL.
6.1.9.2 Autosampler — Use an autosampling system capable of
precise delivery, equipped with a dust cover to
prevent airborne contamination.
6.2 ELUENT AND REGENERANT RESERVOIRS — Select containers with a 4-20 L
capacity that are designed to minimize introduction of air into the
flow system. The regenerant reservoirs may be pressurized with
nitrogen or air (5-10 psi) to ensure constant delivery to the
suppressor column.
6.3 INTEGRATOR (optional) — Select an instrument compatible with the
detector output to quantitate the peak height or area. A system such
as the Spectra Physics 4270 Integrator or a personal computer with a
chromatographic software package such as furnished by Nelson
Analytical, may be used to provide a direct readout of the
concentration of the analyte of interest. If an integrator is used,
the maximum peak height or area measurement must be within the linear
range of the integrator.
300.6-6
-------
6.4 LABORATORY FACILITIES — Laboratories used for the analysis of
wet deposition samples should be free from external sources of
contamination. The use of laminar flow clean air workstations is
recommended for sample processing and preparation to avoid the
introduction of airborne contaminants. Samples should always be
capped or covered prior to analysis. A positive pressure
environment within the laboratory is also recommended to minimize
the introduction of external sources of contaminant gases and
particulates. Room temperature fluctuations should be controlled to
within ^3 C to prevent baseline drift and changes in detector
response. Windows within the laboratory should be kept closed
at all times and sealed if air leaks are apparent. The use of
disposable tacky floor mats at the entrance to the laboratory is
helpful in reducing the particulate loading within the room.
7. REAGENTS AND CONSUMABLE MATERIALS
7.1 PURITY OF REAGENTS — Use reagent grade chemicals for all solutions.
All reagents shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society (ACS) where such
specifications are available.
7.2 PURITY OF WATER — Use water conforming to ASTM Specification D 1193,
Type II (14.4). Point of use 0.2 micrometer filters are recommended
for all faucets supplying water to prevent the introduction of
bacteria and/or ion exchange resins into reagents, standard
solutions, and internally formulated quality control check solutions.
Degas the water prior to use by placing in a glass container,
agitating vigorously, and aspirating off the liberated gases.
7.3 ELUENT SOLUTION ~ Sodium bicarbonate 0.0056 N, sodium carbonate
0.0044 N (eluent strength recommended for wet deposition analysis
using an AS3 or AS4 separator column). Dissolve 0.941 g sodium
bicarbonate (NaHCO-) and 0.933 g of sodium carbonate (Na2CO3)
in water (Sect. 7.2) and dilute to 4 L. Mix the solution well and
degas before use. Refer to Table 2 for a list of suitable eluent
solutions for other separator columns.
7.4 REGENERATION SOLUTION — Dilute concentrated sulfuric acid
(H SO , sp gr 1.84) to one of the following concentrations for
use with packed bed, fiber, or micro-membrane suppressors.
7.4.1 Sulfuric Acid (1.0 N) — (regenerant for a packed bed column)
Add 111 mL of concentrated H-SO, to 2 L of water (Sect.
7.2) and dilute to 4 L.
7.4.2 Sulfuric Acid (0.025 N) — (regenerant for a fiber suppressor)
Add 2.8 mL of concentrated H-SO. to 2 L of water (Sect.
7.2) and dilute to 4 L.
7.4.3 Sulfuric Acid (0.018 N) — (regenerant for a micro-membrane
suppressor) Add 2.0 mL of concentrated H-SO. to 2 L of
water (Sect. 7.2) and dilute to 4 L.
300.6-7
-------
7.5 STOCK STANDARD SOLUTIONS -- Stock standard solutions may be
purchased as certified solutions or prepared from ACS reagent grade
materials as listed below. Store the solutions at room temperature
in high density polyethylene or polypropylene containers.
7.5.1 Chloride Solution, Stock (1.0 mL = 1.0 mg CD — Dissolve
1.6484 g of sodium chloride (NaCl), dried at 105°C for on
hour, in water (Sect. 7.2) and dilute to 1 L.
7.5.2 Nitrate Solution, Stock (1.0 mL = 1.0 mg NO.)— Dissolve
1.3707 g sodium nitrate (NaNO ) in water (Sect. 7.2) and
dilute to 1 L.
7.5.3 Orthophosphate Solution, Stock (1.0 mL = 1.0 mg PO ) —
Dissolve 1.4328 g anhydrous potassium phosphate (KH PO )
in water (Sect. 7.2) and dilute to 1 L.
7.5.4 Sulfate Solution, Stock (1.0 mL = 1.0 mg SO ) — Dissolve
1.8142 g anhydrous potassium sulfate (K SO.) in water
(Sect. 7,2) and dilute to 1 L.
7.6 SAMPLE CONTAINERS — Use polyolefin or glass sample cups that have
been rinsed thoroughly with.water (Sect. 7.2) before use.
8. SAMPLE COLLECTION, PRESERVATION AND STORAGE
8.1 Collect samples in high density polyethylene (HOPE) containers that
have been thoroughly rinsed with ASTM Type II water (7.2). Do not
use strong mineral acids or alkaline detergent solutions for cleaning
collection vessels. Residual acids may remain in the polyethylene
matrix and slowly leach back into the sample. Alkaline detergents
may also leave residues that may affect the sample chemistry. Cap
collection bottles after cleaning to prevent contamination from
airborne contaminants; air dry collection buckets in a laminar flow
clean air workstation and wrap in polyethylene bags prior to use. If
a laminar flow workstation is not available, pour out any residual
rinse water and bag the buckets immediately. Do not dry the bucket
interior by any method other than air drying in a laminar flow clean
air workstation.
8.2 The frequency of sample collection and the choice of sampler design
are dependent on the monitoring objectives. In general, the use of
wet-only samplers is recommended to exclude dry deposition
contributions, minimize sample contamination, retard evaporation,
and enhance sample stability. Sample collection frequency may vary
from subevent to monthly sampling periods. Collection periods of
more than one week are not recommended since sample integrity may be
compromised by longer exposure periods.
300.6-8
-------
8.3 Chloride is the only anion in this method that is stable in
solution (14.5). Nitrate and orthophosphate concentrations are
affected by biological activity within wet deposition samples. The
oxidation of nitrite and sulfite after sample collection will result
in increased concentrations of nitrate and sulfate, respectively.
Sample measurements for sulfate, nitrate, and orthophosphate ions
should be made immediately after collection if possible.
Refrigeration of samples at 4 C will minimize, but not eliminate,
concentration changes prior to chemical analysis (14.5).
8.3.1 Filtration of samples through a 0.45 micrometer membrane
leached with water (Sect. 7.2) is partially effective at
stabilizing nitrate and orthophosphate by removal of
biologically active species. Refrigeration after immediate
filtration is the most reliable method to ensure sample
integrity for these two parameters. Sample storage time
should not exceed one week. Chloride and sulfate
determinations should be made within two weeks of sample
collection.
9. CALIBRATION AND STANDARDIZATION
9.1 Assemble the ion chromatograph according to the manufacturer's
instructions. Recommended operating conditions for the apparatus are
listed in Table 1. Included in Table 3 are retention times
characteristic of this method. Other columns, chromatographic
conditions, or detectors may be used provided the requirements
detailed in Sect. 6 are met.
9.2 Bring all standards, samples, eluents, and regenerants to ambient
temperature before beginning any analyses. Maintain laboratory
temperature conditions within +3 C while conducting analyses.
9.3 Use the eluent strength in Sect. 7.3 for wet deposition analyses.
If peak resolution is not adequate, it may be necessary to decrease
the eluent strength. Befer to the manufacturer's recommendations Cor
guidelines on optimizing eluent strength.
9.4 Adjust the instrument flow rate for optimal peak resolution.
Decreasing the flow rate may provide improved peak resolution but
will lengthen retention times. Increasing the flow rate decreases
peak resolution and shortens retention times. Refer to the
manufacturer's recommendations for guidelines on optimizing flow
rate.
9.5 Equilibrate the system by pumping eluent through all the columns and
the detector until a stable baseline is obtained.
300 6-9
-------
9.6 CALIBRATION SOLUTIONS
9.6.1 Five calibration solutions and one zero standard are needed to
generate a suitable calibration curve. The lowest calibration
solution should contain the analyte(s) of interest at a
concentration greater than or equal to the method detection
limit. The highest solution should approach the expected
upper limit of concentration of the analyte in wet deposition.
Prepare the remaining solutions such that they are evenly
distributed throughout the concentration range, if a second
detector sensitivity scale setting is used to increase the
instrument's concentration range, calibrate at the two
sensitivity levels. Suggested calibration standards for each
analyte are listed in Table 3.
9.6.2 Prepare all calibration standards by diluting the stock
standards (Sect. 7.5). Use glass (Class A) or plastic
pipettes that are within the bias and precision tolerances
specified by the manufacturer. Standards with a concentration
greater than 0.10 mg/L of each anion are stable for one week
when stored at room temperature in high density polyethylene
or polypropylene containers. Prepare standards with 0.10 mg/L
or less of each anion fresh every day and store at room
temperature in high density.polyethylene or polypropylene
containers.
9.6.3 Chloride, orthophosphate, nitrate, and sulfate can be combined
into a single solution at each of the five standard
concentration levels.
9.7 CALIBRATION CURVE
9.7.1 Flush the sampling system with the calibration standard using
at least ten times the injection loop volume. Inject the
standard and record the peak height or area response. Repeat
this step for each calibration standard. Construct
calibration curves for each of the four analytes according to
Sect. 12.
9.7.2 Record the retention times for each analyte. Measure
retention time from an initial starting point on the
chromatogram.
9.7.3 Verify the calibration curve after every ten samples and at
the end of each day's analyses according to Sect. 10.5.
9.7.4 Whenever a new eluent or regenerant solution is made,
reestablish the calibration curve.
300.6-10
-------
10. QUALITY CONTROL
10.1 Each laboratory using this method should develop formalized quality
control protocols to continually monitor the bias and precision of
all measurements. These protocols are required to ensure that the
measurement system is in a state of statistical control. Estimates
of bias and precision for wet deposition analyses cannot be made
unless these control procedures are followed. Detailed guidelines
for the development of quality assurance and quality control
protocols for wet deposition measurement systems are published in a
manual available from the United States Environmental Protection
Agency, Research Triangle Park, NC 27711 (14.6). Included in this
manual are procedures for the development of statistical control
charts for use in monitoring bias and precision as well as
recommendations for the introduction of reagent blanks, laboratory
duplicates, field duplicates, spike samples, and performance
evaluation samples. These guidelines are to be used by all
laboratories involved with wet deposition measurements.
10.2 ESTABLISHMENT OF WARNING AND CONTROL LIMITS — Warning and control
limits are used to monitor drift in the calibration curve, analyses
of quality control check samples (QCS), and measured recoveries
from laboratory spikes.
10.2.1 Calibration Curve — After a calibration curve has been
constructed according to Sect. 12, reanalyze additional
aliquots of the low and high concentration standards.
Calculate the concentrations using the previously derived
calibration curve. Repeat this procedure until at least
ten determinations at each concentration level have been
made. These data should be collected on ten different days
to provide a realistic estimate of the method variability.
Calculate a standard deviation (s) at each concentration
level. Use the nominal standard concentration as the mean
value (x) for determining the control limits. A warning
limit of x ;f 2s and a control limit of x ^ 3s should be
used. Reestablish these limits whenever instrumental
operating conditions change.
10.2.2 Quality Control Check Samples (QCS) -- Calculate warning
and control limits for QCS solutions from a minimum of 10
analyses performed on 10 days. Use the calculated standard
deviation (s) at each QCS concentration level to develop
the limits as described in Sect. 10.2.1. Use the certified
or NBS traceable concentration as the mean (target) value.
Constant positive or negative measurements with respect to
the true value are indicative of a method or procedural
bias. Utilize the data obtained from QCS measurements
as in Sect. 10.4 to determine when the measurement system
is out of statistical control. The standard deviations
300.6-11
-------
used to generate the QCS control limits should be
comparable to the single operator precision reported in
Table 5. Reestablish new warning and control limits
whenever instrumental operating conditions are varied or
QCS concentrations are changed.
10.2.3 Laboratory Spike Solutions — A minimum of 10 analyte
spikes of wet deposition samples is required to develop a
preliminary data base for the calculation of warning and
control limits for spike recovery data. Select the spike
concentration such that the working range of the method
will not be exceeded. Samples selected for the initial
spike recovery study should represent the concentration
range common to wet deposition samples in order to reliably
estimate the method accuracy. Calculate a mean and
standard deviation of the percent recovery data using the
formulas provided in the glossary. Determine warning and
control limits using +2s and _+3s, respectively. If
the data indicate that no significant method bias exists
(14.7), the 100 percent recovery is used as the mean
percent recovery. Where a significant bias is determined
at the 95% confidence level, the control limits are
centered around the bias estimate. Routine spiked sample
analyses that yield percent recovery data outside of the
control limits are an indication of matrix interferences
that should be resolved before routine analyses are
continued.
10.2.4 All warning and control limits should be reevaluated on a
continual basis as additional data are collected during
routine analyses. The limits should be broadened or
narrowed if a recalculated standard deviation under similar
operating conditions provides a different estimate of the
procedure variabilitv.
10.3 Monitor the cleaning procedure by pouring a volume of water (Sect.
7.2) that approximates the median sample size into the collection
vessel. Allow the water to remain in the sealed or capped
collection container for at least 24 hours and determine the
concentrations of the anions that will be measured in wet
deposition. If any of the analyte concentrations exceed the MDL,
a contamination problem is indicated in the cleaning procedure.
Take corrective action before the sampling containers are used for
the collection of wet deposition.
10.4 Analyze a quality control check sample (QCS) after the ion
chromatograph has been calibrated. This sample may be formulated
in the laboratory or obtained from the National Bureau of Standards
(MBS Standard Reference Material 2694, Simulated Rainwater).
Verify the accuracy of internally formulated QCS solutions with an
NBS traceable standard before acceptance as a quality control
check. The check sample(s) selected must be within the range of
the calibration standards. If the measured value for the QCS falls
outside of the +3s limits (Sect. 10.2.2), or if two successive
300.6-12
-------
QCS checks are outside of the +2s limits, a problem is indicated
with the ion chromatograph or calibration curve. Corrective action
should be initiated to bring the results of the QCS within the
established control limits. Plot the data obtained from the QCS
checks on a control chart for routine assessments of bias and
precision.
10.5 Verify the calibration curve after a maximum of ten samples and at
the end of each day's analyses. Analyze calibration standards at
the low and high ends of the working range. If the routine
calibration checks do not meet the criteria described in Sect.
10.4, recalibrate the system and reanalyze all samples from the
last time the system was in control. Verify the new calibration
curve with the QCS according to Sect. 10.4 and reanalyze all
samples measured since the last time the system was in control.
10.6 Submit a Field Blank (FB) to the laboratory for every 20 samples.
The FB may consist of a water sample (Sect. 7.2) or a known
reference solution that approximates the concentration levels
characteristic of wet deposition. The FB is poured into the
sampling vessel at the field site and undergoes identical
processing and analytical protocols as the wet deposition
sample(s). Use the analytical data obtained from the FB to
determine any contamination introduced in the field and laboratory
handling procedures. The data from the known reference solution
can be used to calculate a system precision and bias.
10.7 Prepare and analyze a laboratory spike of a wet deposition sample
according to the guidelines provided in "Quality Assurance Manual
for Precipitation Measurement Systems" (14.6). Compare the results
obtained from spiked samples to those obtained from identical
samples to which no spikes were added. Use these data to monitor
the method percent recovery as described in Sect. 10.2.3.
10.8 Participation in performance evaluation studies is recommended for
wet deposition chemistry laboratories. The samples used for these
performance audits should contain the analytes ot interest at
concentrations within the normal working range of the method. The
true values are unknown to the analyst. Performance evaluation
studies for wet deposition chemistry laboratories are conducted
semiannually by the USEPA Performance Evaluation Branch, Quality
Assurance Division, Research Triangle Park, NC 27711.
11. PROCEDURE
11.1 Check the instrumental operating parameters each day according to
Sect. 9 and Table 1.
11.2 Prepare all standards and construct calibration curves according
to Sect. 9.6 and 9.7.
11.3 After the calibration curve-is established, analyze the QCS. If
the measured value for the QCS is not within the specified limits
(Sect. 10.2.2), refer to Sect. 10.4.
300.6-13
-------
11.4 SAMPLE INJECTION
11.4.1 Use the same size injection loop for both standards and
samples. Samples may be injected manually with a syringe
or with an autosampler.
11.4.2 Plush the sampling system thoroughly with each new sample
using a rinse volume of at- least ten times the loop size.
Inject the sample, avoiding the introduction of air
bubbles into the system.
11.4.3 Record the resulting peak heights or areas.
11.5 If the peak height or area response exceeds the working range of
the system, dilute the sample with zero standard and reanalyze.
11.6 A sample chromatogram is provided in Figure 2.
12. CALCULATIONS
12.1 For each analyte of interest, calculate a linear least squares fit
of the standard concentrations as a function of the measured peak
height or area. The linear least squares equation is expressed as
follows:
y = BQ + BIX
where: y = standard concentration in mg/L
x = peak height or area measured
B = y-intercept calculated from: y - B.x
B = slope calculated from:
n n
2 (xi - x) (y - y)/ 2 (x - xr
i=l i=l
where: x = mean of peak heights or areas measured
y = mean of standard concentrations
n = number of samples
The correlation coefficient should be 0.9990 or greater. Determine
the concentration of the analyte of interest from the calibration
curve.
12.2 If the relationship between standard concentration and measured peak
height or area is nonlinear, use a second degree polynomial least
squares equation to derive a curve with a correlation j>0.9990.
The second degree polynomial equation is expressed as follows:
y = B x + B x + BQ
A computer program is necessary for the derivation of this
function. Determine the concentration of the analyte of interest
from the calibration curve.
300.6-14
-------
12.3 An integration system may also be used to provide a direct readout
of the concentration of the analyte of interest.
12.4 Report data in mg/L as Cl~, N03~, PO " , or SO ~ . Do
not report data lower than the lowest calibration standard.
13. PRECISION AND BIAS
13.1 The mean percent recovery and mean bias of this method were
determined from the analysis of spiked wet deposition samples
according to ASTM Standard Practice D4210, Annex A4 (14.7). The
results are summarized in Table 4. No statistically significant
biases were found for any of the four inorganic anions.
13.2 Single-operator precision and bias were obtained from the analysis
of quality control check samples that approximated the levels
common to wet deposition samples. These results reflect the
accuracy that can be expected when the method is used by a
competent operator. These data are presented in Table 5.
L REFERENCES
14.1 Annual Book of ASTM Standards, Section 11, Vol. 11.01 (1),
"Definitions of Terms Related to Water," Standard D 1129-82b,
1983, p. 4.
14.2 Annual Book of ASTM Standards, Part 31, "Excerpts from Standard
for Metric Practice," Standard E 380-79, 1982, pp. 679-694.
14.3 "Safety in Academic Chemistry Laboratories," American Chemical
Society Publication, Committee on Chemical Safety, 3rd Edition,
1979.
14.4 Annual Book of ASTM Standards, Part 31, "Standard Specification
for Reagent Water," Standard D 1193-77, 1982, p. 39.
14.5 Peden, M. E. and Skowron, L. M., "Ionic Stability of Precipitation
Samples," Atmos. Environ. 12, 1978, pp. 2343-2349.
14.6 Topol, L. E., Lev-On, M., Flanagan, J., Schwall, R. J., Jackson, A.
E., Quality Assurance Manual for Precipitation Measurement
Systems, 1985, U.S. Environmental Protection Agency,
Environmental Monitoring Systems Laboratory, Research Triangle
Park, NC 27711.
14.7 Annual Book of ASTM Standards, Section 11, Vol. 11.01 (1),
"Practice for Intralaboratory Quality Control Procedures and a
Discussion of Reporting Low-Level Data," Standard D4210 Annex A4,
1983, pp. 15-16.
300.6-15
-------
Table 1. Method Detection Limits and Concentration
Ranges for the Determination of Anions in Wet
Deposition.
Method Detection Concentration
Limit, Range,
Analyte mg/L mg/L
Chloride 0.03 0.03-2.00
Orthophosphate 0.02 0.02-0.25
Nitrate 0.03 0.03 - 5.00
Sulfate 0.03 0.03 - 8.00
a. Chromatographic Conditions:
Guard Column — Dionex AG3
Separator Column — Dionex AS3
Fiber Suppressor — Dionex AFS
Detector — As specified in 6.1.5
Eluent — As specified in 7.3
Sample Loop — 250 uL
Flow Rate — 3 mL/min
Detector Sensitivity — 10 uS/cm
300.6-16
-------
Table 2. Compatibility of Separator and Suppressor Columns
with Suggested Regeneration and Eluent Solutions for
the Analysis of Wet Deposition.
Anion Separator
Column
Eluent
Solution
Anion Suppressors
Packed Bed Fiber Micro-membrane
Dionex AS1
0.003 M NaHCO
0.0024 M Na
compatible compatible
not
recommended
Dionex AS3
Dionex AS4
0.0028 M NaHCO.
0.0022 M Na2CO:
0.0028 M NaHCO.
0.0022 M Na,CO:
compatible compatible
compatible compatible
not
recommended6
compatible
Dionex AS4A 0.00075 M NaHCO.
0.0022 M Na_CO,"
compatible compatible compatible
a. The increased back-pressure created by the micro-membrane suppressor
may reduce column efficiency when this type of separator column is used.
Refer to the manufacturer's guidelines for recommendations of minor
adjustments necessary to make this system work properly.
Regeneration Solutions:
Packed Bed -- 0.1 N HC1 or 1.0 N H.SO.
Fiber — 0.025 N H2S04
Micro-membrane — 0.018 N H.SO.
300.6-17
-------
Table 3. Retention Times and Suggested Calibration
Standard Concentrations for the Determination
of Anions in Wet Deposition Samples.
Analyte
Approximate Retention
Time Range,
sec
Calibration
Standards,
mg/L
Chloride
84 - 120
zero
0.03
0.40
0.75
1.10
1.50
Orthophosphate
144 - 180
zero
0.02
0.10
0.15
0.20
0.25
Nitrate
240 - 300
zero
0.03
1.00
2.00
3.00
4.00
Sulfate
336 - 396
zero
0.03
,25
,50
,75
5.00
Based on the MDL and 95th percentile concentrations of each
analyte obtained from analyses of over five thousand wet deposition
samples from the NADP/NTN precipitation network.
The retention time was measured from the time of injection. For
chromatographic conditions, refer to Table 1.
300.6-18
-------
Table 4. Single-Operator Precision and Bias for Chloride,
Orthophosphate, Nitrate, and Sulfate Determined
from Analyte Spikes of Wet Deposition Samples.
Analyte
Amount
Added ,
f*)
mg/L n
Mean
Percent
Recovery
Mean
Bias,
mg/L
Standard
Deviation,
mg/L
Statistically
Significant
Bias?
Chloride
0.10
0.32
10
9
102.0
101.8
0.00
0.01
0.01
0.02
No
No
Ortho- 0.11
phosphate
10
98.3
0.00
0.01
No
Nitrate
0.44
1.10
10
10
99.8
96.0
0.00
-0.04
0.03
0.07
NO
No
Sulfate
0.46
1.10
10
10
101.3
98.7
0.01
•0.01
0.04
0.05
No
No
b.
c.
Chromatographic Conditions:
Guard Column — Dionex AG3
Separator Column — Dionex AS3
Packed Bed Suppressor Column — Dionex ASC2
Detector — As specified in 6.1.5
Eluent — As specified in 7.3
Sample Loop — 250 uL
Flow Rate — 3 mL/min
Detector Sensitivity — 10 uS/cm
Number of replicates
95% Confidence Level
300.6-19
-------
Table 5. Single-Operator Precision and Bias for Chloride,
Orthophosphate, Nitrate, and Sulfata Determined
from Quality Control Check Samples.a
Theoretical Measured
Concentration, Concentration,
Analyte mg/L mg/L n
Chloride
Orthophosphate
Nitrate
Sulfate
0.18
0.85
1.78
0.05
0.15
0.80
3.54
0.72
0.94
3.60
The above data were obtained from
direction of the NADP/NTN quality
0.
0.
1.
0.
0.
0.
3.
0.
0.
3.
19
87
88
05
15
81
64
72
92
69
132
479
255
10
10
485
415
340
482
122
Bias,
mg/L %
0
0
0
0
0
0
0
0
-0
0
.01
.02
.10
.00
.00
.01
.10
.00
.02
.09
records of measurements
assurance program.
a. For chromatographic conditions,
b. Number of replicates
refer
to Table
1.
5.
2.
5.
0.
0.
1.
2.
0.
-2.
2.
6
4
6
0
0
2
8
0
1
5
made
Precision,
s , RSD ,
mg/L %
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
under
02
03
05
00
01
02
12
03
03
11
the
10.5
3.4
2.7
0.0
6.7
2.5
3.3
4.2
3.3
3.0
300.6-20
-------
Figure 1. Percentile Concentration Values Obtained from Wet
Deposition Samples: Chloride, Orthophosphate,
Nitrate, and Sulfate.
u>
o
o
O
§
a
100
90
SO
70
to
50
40
30
20
10
1.00
I.DO
chloride
j.oo
5.0O
7.00
nitrate
3.00
5-. 00
7.00
100
90
80
70
60
50
(.0
10
20
10
CONCENTRATION (mg/L)
orthophosphate
O.OO5
O.UIO
<—I—
0.015
2.50
5.00
7.50
10.00
-------
Figure 2. Chromatogram of a Wet Deposition Sample Containing
Chloride, Orthophosphate, Nitrate, and Sulfate,
(a) Without and (b) With Eluent Matching.
8
u
§E 5
UJ
I
ID
Q.
2 -
1 -
T
Point of
Injection
t
I I
I
cr
1.01 mg/L Cl~
0.25 mg/L P0~3 '
0.69 mg/L N0~
1.60 mg/L S0~2 -1
I I
cr
I I 1 I I
Point of
Injection
1.01 mg/L Cl"
0.25 mg/L P0~3
0.69 mg/L N0~
1.60 mg/L S0~2
I
I I
468 02
RETENTION TIME, minutes
Chromatographic Conditions:
Guard Column — Dionex AG3
Separator Column — Dionex AS3
Fiber Suppressor — Dionex AFS
Detector — As specified in 6.1.5
Eluent — As specified in 7.3
Sample Loop — 250 uL
Flow Rate — 3 raL/min
Detector Sensitivity — 10 uS/cm
8
300.6-22
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Method 300.7 — Dissolved Sodium, Ammonium, Potassium,
Magnesium, and Calcium in Wet Deposition by
Chemically Suppressed Ion Chromatography
March 1986
Performing Laboratory:
Susan R. Bachman
Jane E. Rothert
Brian Kaiser
Carla Jo Brennan
Mark E. Peden
Illinois State Water Survey
Analytical Chemistry Unit
2204 Griffith Drive
Champaign, Illinois 61820
Sponsoring Agency:
John D. Pfaff, Project Officer
Inorganic Analysis Section
Physical and Chemical Methods Branch
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
300.7-1
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INDEX
Section
Number Subject
1 Scope and Application
2 Summary of Method
3 Definitions
4 Interferences
5 Safety
6 Apparatus and Equipment
7 Reagents and Consumable Materials
8 Sample Collection, Preservation, and Storage
9 Calibration and Standardization
10 Quality Control
11 Procedure
12 Calculations
13 Precision and Bias
14 ' References
TABLES
Method Detection Limits and Concentration Ranges for Chemically Suppressed
Ion Chromatographic Determination of Cations in Wet Deposition.
Retention Times and Suggested Calibration Standard Concentrations for the
Determination of Cations in Wet Deposition.
Single-Operator Precision and Bias for Sodium, Ammonium, Potassium,
Magnesium, and Calcium Determined from Analyte Spikes of Wet Deposition
Samples.
Single-Operator Precision and Bias for Sodium, Ammonium, Potassium,
Magnesium, and Calcium Determined from Quality Control Check Samples.
FIGURES
1. Percentile Concentration Values Obtained from Wet Deposition Samples.
2. Chromatogram of a Calibration Standard Containing Sodium, Ammonium, and
Potassium.
3. Chromatogram of a Calibration Standard Containing Magnesium and Calcium.
300.7-2
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1. SCOPE AND APPLICATION
1.1 This method is applicable to the determination of sodium, ammonium,
potassium, magnesium, and calcium in wet deposition by chemically
suppressed ion chromatography.
1.2 The term "wet deposition" is used in this method to designate rain,
snow, dew, sleet, and hail.
1.3 The method detection limits (MDL) for the above analytes determined
from replicate analyses of quality control check solutions are
0.02 mg/L for magnesium and calcium, 0.03 mg/L for sodium and
ammonium, and 0.01 mg/L for potassium. The concentration of analyte
in each check sample is detailed in Table 4. The applicable analyte
concentration range of this method is outlined in Table 1.
1.4 Figure 1 represents cumulative frequency percentile concentration
plots of sodium, ammonium, potassium, magnesium, and calcium obtained
from analyses of over five thousand wet deposition samples. These
data may be used as an aid in the selection of appropriate
calibration standard concentrations.
2. SUMMARY OF METHOD
2.1 Ion chromatography combines conductimetric detection with the
separation capabilities of ion exchange resins. A filtered 100 uL
aliquot of sample is pumped through an ion exchange column where the
cations of interest are separated. .Each ion's affinity for the
exchange sites, known as its selectivity quotient, is largely
determined by its radius and valence. Because different ions have
different migration rates, the sample ions elute from the column as
discrete bands. Each ion is identified by its retention time within
the exchange column. The sample ions are selectively eluted off the
separator column and onto a suppressor column. The eluent ions are
neutralized and the sample ions are converted to their corresponding
strong bases which are detected in a conductance cell. The
chromatograms produced are displayed on a strip chart recorder or
other data acquisition device for measurement of peak height or area.
The ion chromatograph is calibrated with standard solutions
containing known concentrations of the cation(s) of interest.
Calibration curves are constructed from which the concentration of
each analyte in the unknown sample is determined.
3. DEFINITIONS
3.1 ION EXCHANGE — a reversible process by which ions are interchanged
between an insoluble material and a liquid with no substantial
structural changes of the material (14.1).
3.2 ELUENT — the ionic liquid mobile phase used to transport the sample
through the exchange columns.
3.3 REGENERANT — a solution that converts and maintains an active form
of the suppressor.
300.7-3
-------
3.4 RESOLUTION — the ability of a column to separate constituents under
specified test conditions. Peak resolution is a function of column
efficiency, selectivity, and capacity.
3.5 RETENTION TIME — the interval measured from the point of sample
injection to the point of maximum peak height or area.
3.6 For definitions of other terms used in this method, refer to the
glossary. For an explanation of the metric system including units,
symbols, and conversion factors see American Society for Testing and
Materials (ASTM) Standard E 380, "Metric" Practices" (14.2).
4. INTERFERENCES
4.1 Unresolved peaks will result when the concentration of one of the
sample components is 10 to 20 times higher than another component
that appears in the chromatogram as an adjacent peak. Decreasing the
eluent concentration or the flow rate may correct this problem.
4.2 Interferences may be caused by ions with retention times that are
similar to and thus overlap those of the cation of interest. This
type of positive interference is rare in wet deposition samples. If
this type of interference occurs, decreasing the eluent concentration
or the flow rate may improve peak resolution.
4.3 The divalent cations, present in solution, which are not eluted with
the monovalent cation eluent, will cause a loss of retention and
resolution of the monovalent species, as they accumulate on the
separator column. When this occurs, clean the monovalent column
with 20 mL of 1.0 N HCl for 15 minutes and then equilibrate by
rinsing the column with eluent until a stable baseline is obtained.
4.4 Deterioration in column performance may result from the buildup of
contaminants on the exchange resin. Losses in retention and
resolution are symptoms of column deterioration. Refer to the
manufacturer's guidelines for instructions on cleaning the column
resin.
4.5 The presence of air bubbles in the columns, tubing, or conductivity
detector cell will cause baseline and peak variability. Avoid
introducing air into the system when injecting samples and standards.
Using degassed eluents and regenerants will help to minimize the
introduction of air.
5. SAFETY
5.1 The calibration standards, sample types, and most reagents used in
this method pose no hazard to the analyst. Use a fume hood,
protective clothing, and safety glasses when handling concentrated
hydrochloric acid (Sect. 7.3-7.4).
300.7-4
-------
5.2 Keep the doors of the instrument column compartment closed at ail
times when pumps and columns are in use to prevent injury to the
operator from column explosion if the pump pressure or column
backpressure increases.
5.3 Follow American Chemical Society guidelines regarding the safe
handling of chemicals used in this method (14.3).
6. APPARATUS AND EQUIPMENT
6.1 ION CHROMATOGRAPH — Select a chromatograph equipped as detailed in
Sects. 6.1.1-6.1.9. To determine monovalent and divalent cations
simultaneously, select a dual channel chromatograph equipped with two
separator and two suppressor columns. If the sample ions are to be
determined sequentially by analyzing the sample twice, the same
suppressor column may be used for both determinations. The divalent
eluent solution is strongly retained on the guard and separator
columns, making the determination of monovalent ions after divalent
ions with the same guard and separator columns impractical.
Therefore, use two different sets of cation guard and separator
columns; one set should be dedicated to the determination of
monovalent and the other to divalent cations.
6.1.1 Cation Guard Column — Place before the separator column.
This contains the same resin as the separator column and
is used to protect the ion exchange column from being
fouled by particulates or organic constituents (4 x 50 mm,
Dionex P/N 30830, CGI, or equivalent). Using a cation guard
column will prolong the life of the separator column.
6.1.2 Cation Separator Column — This is a column packed with a
pellicular low-capacity cation exchange resin containing
polystyrene-divinylbenzene beads coated with sulfate active
sites (4 x 250 mm, Dionex P/N 30831, CS1, or equivalent).
6.1.3 Cation Suppressor Column — Place after the separator column.
This may be in the form of a packed bed, a fiber, or a
micro-membrane suppressor. The first type of suppressor is
packed with a high-capacity cation exchange resin in the
unprotonated form capable of converting the eluent to a low or
negligible background conductance and converting the sample
cations to their corresponding strong bases (Dionex P/N 30834,
CSC2, or equivalent). The second two types of suppressors
utilize a semipermeable membrane containing cation exchange
sites to suppress eluent conductance {Dionex P/N 35352, CFS,
fiber; Dionex P/N 37076, CMMS, micro-membrane; or equivalent).
Both the fiber and micro-membrane suppressors are under
continuous regeneration.
300.7-5
-------
6.1.4 Compressed Gas (Nitrogen or Air) — Use ultra-high purity
99.999% (v/v) compressed gas conforming to the recommendations
of the manufacturer of the ion chromatograph.
6.1.5 Detector — Select a flow-through, temperature-compensated,
electrical conductance cell with a volume of approximately
6 uL coupled with a meter capable of reading from 0 to
1000 us/cm on an analog or digital scale.
6.1.6 Pump — Use a pump capable both of delivering an accurate flow
rate and of tolerating the optimal pressure suggested by
the instruction manual accompanying the ion chromatograph and
columns selected. A constant pressure, constant flow pump is
recommended for enhanced baseline stability.
6.1.7 Recorder — This should be compatible with the maximum
detector output with a full-scale response time in
0.5 sec or less.
6.1.8 Sample Loop — Select a sample loop compatible with the column
system having a capacity of 100 uL for optimal sensitivity in
wet deposition analyses.
6.1.9 Sampling System — Select one of the following for sampling.
6.1.9.1 Syringe — Use a syringe equipped with a male fitting
having a minimum capacity of 2 mL.
6.1.9.2 Autosampler — Use an autosampling system capable of
precise delivery, equipped with a dust cover to
prevent airborne contamination.
6.2 ELUENT AND REGENERANT RESERVOIRS — Select containers with a 4-20 L
capacity that are designed to minimize introduction of air into the
flow system. The regenerant reservoirs may be pressurized with
nitrogen or air (5-10 psi) to ensure constant delivery to the
suppressor column.
6.3 INTEGRATOR (optional) — Select an instrument compatible with the
detector output to quantitate the peak height or area. A system such
as the Spectra Physics 4270 Integrator or a personal computer with a
chromatographic software package such as furnished by Nelson
Analytical, may be used to provide a direct readout of the
concentration of the analyte of interest. If an integrator is used,
the maximum height or area measurement must be within the linear
range of the integrator.
300.7-6
-------
6.4 LABORATORY FACILITIES — Laboratories used for the analysis of
wet deposition samples should be free from external sources of
contamination. The use of laminar flow clean air workstations is
recommended for sample processing and preparation to avoid the
introduction of airborne contaminants. Samples should always be
capped or covered prior to analysis. A positive pressure
environment within the laboratory is also recommended to minimize
the introduction of external sources of contaminant gases and
particulates. Windows within the laboratory should be kept closed
at all times and sealed if air leaks are apparent. The use of
disposable tacky floor mats at the entrance to the laboratory is
helpful in reducing the particulate loading within the room.
Maintain laboratory temperature within +2°C to minimize baseline
drift and changes in detector response.
7. REAGENTS AND CONSUMABLE MATERIALS
7.1 PURITY OF REAGENTS — Use reagent grade chemicals for all solutions.
All reagents shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society (ACS), where
such specifications are available.
7.2 PURITY OF WATER — Use water conforming to ASTM Specification D 1193,
Type II (14.4). Point of use 0.2 micrometer filters are recommended
for all faucets supplying water to prevent the introduction of
bacteria and/or ion exchange resins into reagents, standard
solutions, and internally formulated quality control check solutions.
Degas the water prior to use by placing in a glass container,
agitating vigorously, and aspirating off the liberated gases.
7.3 ELUENT SOLUTION — For the determination of monovalent cations
(sodium, ammonium, and potassium), use a dilute (0.005 N)
hydrochloric acid (HC1) eluent. For the determination of divalent
cations (magnesium and calcium), use a solution of 0.002 N HC1 and
0.004 N meta phenylenediamine Dihydrochloride (mPDA 2HC1).
7.3.1 Hydrochloric Acid (0.005 N) — (eluent solution for monovalent
cations) Add 1.65 mL of concentrated HC1 (sp gr 1.19) to
500 mL of water (Sect. 7.2) and dilute to 4 L.
7.3.2 Hydrochloric Acid : meta Phenylenediamine Dihydrochloride
(0.0015 N : 0.0030 N) — (eluent solution for divalent
cations) Add 1.087 g of mPDA 2HC1 and 0.50 mL of concentrated
HC1 to about 500 mL of water (Sect. 7.2). Mix well and dilute
to 4 L with water (Sect. 7.2).
7.4 HYDROCHLORIC ACID (1.0 N) — Add 83.0 mL of concentrated HCl (sp gr
1.19) to 900 mL of water (Sect. 7.2) and dilute to 1 L.
300.7-7
-------
7.5 REGENERATION SOLUTION ~ Prepare the following solutions for use with
packed bed, fiber, or micromembrane suppressors.
7.5.1 Sodium Hydroxide (0.5 N) — (regenerant for a packed bed
column) Dissolve 80 g of sodium hydroxide (NaOH) in water
(Sect. 7.2) and dilute to 4 L.
7.5.2 Tetramethylammonium hydroxide (0.04 N) — (regenerant for a
fiber or micro-membrane suppressor) Dissolve 29.976 g of
tetramethylammonium hydroxide pentahydrate (TMAOH 5H O)
in water (Sect. 7.2) and dilute to 4 L. Alternatively, add
58.4 mL of a 25% solution of TMAOH to water (Sect. 7.2) and
dilute to 4 L.
7.5.3 Barium Hydroxide (0.08 N) — (regenerant for a fiber or
micro-membrane suppressor) Dissolve 50.45 g of barium
hydroxide octahydrate (Ba(OH) 8H 0) in water (Sect. 7.2)
and dilute to 4 L. Carbon dioxide present in the air and
water will form barium carbonate (BaCO.) that must be
filtered out of the regenerant before it enters the
micro-membrane suppressor. To prevent the intake of BaCO-
precipitate into the suppressor, install a filter over the
inlet end of the regenerant line, Agitate the regenerant
thoroughly before use to ensure that the barium hydroxide is
completely in solution.
7.6 STOCK STANDARD SOLUTIONS — Stock standard solutions may be purchased
as certified solutions or prepared from ACS reagent grade materials
as listed below. Store the solutions at room temperature in high
density polyethylene or polypropylene containers.
7.6.1 Ammonium Solution, Stock (1.0 mL = 1.0 mg NH ) — Dissolve
2.9654 g of ammonium chloride (NH CD, dried at 105 C for
1 hour, in water (Sect. 7.2) and dilute to 1 L.
7.6.2 Calcium Solution, Stock (1.0 mL = 1.0 mgQCa) — Add 2.497 g of
calcium carbonate (CaCO ), dried at 180 C for one hour, to
approximately 600 mL of water (Sect. 7.2). Add concentrated
hydrochloric acid (HCl, sp gr 1.19) slowly until all the solid
has dissolved. Dilute to 1 L with water (Sect. 7.2).
7.6.3 Magnesium Solution, Stock (1.0 mL = 1.0 mg Mg) — Dissolve
1.000 g of magnesium ribbon in a minimal volume of 6 N HCl
and dilute to' 1 L with water (Sect. 7.2).
7.6.4 Potassium Solution, Stock (1.0 mL - 1.0 mg K) — Dissolve
1.9067 g of potassium chloride (KCl), dried at 105 C for 1
hour, in water (Sect. 7.2) and dilute to 1 L.
7.6.5 Sodium Solution, Stock (1.0 mL » 1.0 mg Na) — Dissolve
2.5420 g of sodium chloride (NaCl), dried at 105 C for 1
hour, in water (Sect. 7.2) and dilute to 1 L.
300.7-8
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7.7 SAMPLE CONTAINERS — Use polyolefin or glass sample holders that have
been rinsed thoroughly with water (Sect. 7.2) before use.
8. SAMPLE COLLECTION, PRESERVATION AND STORAGE
8.1 Collect samples in high density polyethylene (HOPE) containers that
have been thoroughly rinsed with ASTM Type II water (7.2). Do not
use strong mineral acids or alkaline detergent solutions for cleaning
collection vessels. Residual acids may remain in the polyethylene
matrix and slowly leach back into the sample. Alkaline detergents
may also leave residues that may affect the sample chemistry. Cap
collection bottles after cleaning to prevent contamination from
airborne contaminants; air dry collection buckets in a laminar flow
clean air workstation and wrap in polyethylene bags prior to use. If
a laminar flow workstation is not available, pour out any residual
rinse water and bag the buckets immediately. Do not dry the bucket
interior by any method other than air drying in a laminar flow clean
air workstation.
8.2 The frequency of sample collection and the choice of sampler design
are dependent on the monitoring objectives. In general, the use of
wet-only samplers is recommended to exclude dry deposition
contributions, minimize sample contamination, retard evaporation,
and enhance sample stability. Sample collection frequency may vary
from subevent to monthly sampling periods. Collection periods of
more than one week are not recommended since sample integrity may be
compromised by longer exposure periods.
8.3 The dissolution of particulate materials and the presence of
microbial activity will affect the stability of all of the cations in
this method. This instability generally results in increased
concentrations of magnesium, calcium, sodium, and potassium and
decreased ammonium concentrations. Ion chromatographic measurements
should be. made immediately after sample collection when possible.
Refrigeration of samples at 4 C will retard but not prevent changes
in the concentration of these species (14.5).
8.3.1 Filtration of samples through a 0.45 micrometer membrane
leached with water "(Sect. 7.2) is effective at stabilizing
magnesium, calcium, sodium, and potassium concentrations that
are influenced by the dissolution of alkaline particulate
matter (14.5). Monitoring of the filtration procedure is
necessary to ensure that samples are not contaminated by the
membrane or filtration apparatus. Filtered samples are stable
for a period of six weeks.
300.7-9
-------
8.3.2 Filtration followed by refrigeration at 4°C is the
recommended preservation technique for ammonium ion.
Holding times should not exceed seven days.
9. CALIBRATION AND STANDARDIZATION
9.1 Assemble the ion chromatograph according to the manufacturer's
instructions. Recommended operating conditions for the apparatus are
listed in Table 1. Included in Table 2 are retention times
characteristic of this method. Other columns, chromatographic
conditions, or detectors may be used provided the requirements in
Sect. 6 are met.
9.2 Bring all standards, samples, eluents, and regenerants to ambient
temperature before beginning any analyses. Maintain laboratory
temperature conditions within +3 C while conducting analyses.
9.3 Use the eluent strength in Sect. 7.3 for wet deposition analyses. If
peak resolution is not adequate, it may be necessary to decrease the
eluent strength. Refer to the manufacturer's recommendations for
guidelines on optimizing eluent strength.
9.4 Adjust the instrument flow rate for optimal peak resolution.
Decreasing the flow rate may provide greater peak resolution but
will lengthen retention times. Increasing the flow rate decreases
peak resolution and shortens retention times. Refer to the
manufacturer's recommendations for guidelines on optimizing flow
rate.
9.5 Equilibrate the system by pumping eluent through all the columns and
the detector until a stable baseline is obtained.
9.6 CALIBRATION SOLUTIONS
9.6.1 Five calibration solutions and one zero standard are needed to
generate a suitable calibration curve. The lowest calibration
solution should contain the analyte(s) of interest at a
concentration greater than or equal to the method detection
limit. The highest solution should approach the expected
upper limit of concentration of the analyte in wet deposition.
Prepare the remaining solutions such that they are evenly
distributed throughout the concentration range. If a second
detector sensitivity scale setting is used to increase the
instrument's concentration range, calibrate at the two
sensitivity levels. Suggested calibration standards for each
analyte are listed in Table 2.
9.6.2 Prepare all calibration standards by diluting the stock
standards (Sect. 7.6). Use glass (Class A) or plastic
pipettes that are within the bias and precision tolerances
specified by the manufacturer. The calibration standards are
stable for one week when stored at 4°C in high density
polyethylene containers.
30C.7-10
-------
9.6.3 Sodium, ammonium, potassium, magnesium, and calcium can be
combined into a single solution at each of the five standard
concentration levels.
9.7 CALIBRATION CURVE
9.7.1 Flush the sampling system with the calibration standard using
at least ten times the injection loop volume. Inject the
standard and record the peak height or area response. Repeat
this procedure for the remaining standards. Construct
calibration curves for each of the five analytes according to
Sect. 12.
9.7.2 Record the retention times for each analyte. Measure
retention time from an initial starting point on the
chromatogram.
9.7.3 Verify the calibration curve after every ten samples and at
the end of each day's analyses according to Sect. 10.5.
9.7.4 Whenever a new eluent or regenerant solution is made,
reestablish the calibration curve.
10. QUALITY CONTROL
10.1 Each laboratory using this method should develop formalized quality
control protocols to continually monitor the bias and precision of
all measurements. These protocols are required to ensure that the
measurement system is in a state of statistical control. Estimates
of bias and precision for wet deposition analyses cannot be made
unless these control procedures are followed. Detailed guidelines
for the development of quality assurance and quality control
protocols for wet deposition measurement systems are published in a
manual available from the United States Environmental Protection
Agency, Research Triangle Park, NC 27711 (14.6). Included in this
manual are procedures for the development of .statistical control
charts for use in monitoring bias and precision as well as
recommendations for the introduction of reagent blanks, laboratory
duplicates, field duplicates, spike samples, and performance
evaluation samples. These guidelines are to be used by all
laboratories involved with wet deposition measurements.
10.2 ESTABLISHMENT OF WARNING AND CONTROL LIMITS — Warning and control
limits are used to monitor drift in the calibration curve, analyses
of quality control check samples (QCS), and measured recoveries
from laboratory spikes.
300.7-11
-------
10.2.1 Calibration Curve — After a calibration curve has been
constructed according to Sect. 12, reanalyze additional
aliquots of the low and high concentration standards.
Calculate the concentrations using the previously derived
calibration curve. Repeat this procedure until at least
ten determinations at each concentration level have been
made. These data should be collected on ten different days
to provide a realistic estimate of the method variability.
Calculate a standard deviation (s) at each concentration
level. Use the nominal standard concentration as the mean
value (X) for determining the control limits. A warning
limit of x" Ł 2s and a control limit of x +_ 3s should be
used. Reestablish these limits whenever instrumental
operating conditions change.
10.2.2 Quality Control Check Samples (QCS) — Calculate warning
and control limits for QCS solutions from a minimum of ten
analyses performed on ten days. Use the calculated
standard deviation (s) at each QCS concentration level to
develop the limits as described in Sect. 10.2.1. Use the
certified or NBS traceable concentration as the mean
(target) value. Constant positive or negative measurements
with respect to the true value are indicative of a method
or procedural bias. Utilize the data obtained from QCS
measurements as in Sect. 10.4 to determine when the
measurement system is out of statistical control. The
standard deviations used to generate the QCS control limits
should be comparable to the single operator precision
reported in Table 4. Reestablish new warning and control
limits whenever instrumental operating conditions are
varied or QCS concentrations are changed.
10.2.3 Laboratory Spike Solutions — A minimum of ten analyte
spikes of wet deposition samples is required to develop a
preliminary data base for the calculation of warning and
control limits for spike recovery data. Select the spike
concentration such that the working range of the method
will not be exceeded. Samples selected for the initial
spike recovery study should represent the concentration
range common to wet deposition samples in order to reliably
estimate the method accuracy. Calculate a mean and
standard deviation of the percent recovery data using the
formulas provided in the glossary. Determine warning and
control limits using +2s and ^3s, respectively. If
the data indicate that no significant method bias exists
(14.7), the 100 percent recovery is used as the mean
percent recovery. Where a significant bias is determined
at the 95% confidence level, the control limits are
centered around the bias estimate. Routine spiked sample
analyses that yield percent recovery data outside of the
control limits are an indication of matrix interferences
that should be resolved before routine analyses are
continued.
300.7-12
-------
10.2.4 All warning and control limits should be reevaluated on a
continual basis as additional data are collected during
routine analyses. The limits should be broadened or
narrowed if a recalculated standard deviation under similar
operating conditions provides a different estimate of the
procedure variability.
10.3 Monitor the cleaning procedure by pouring a volume of water (Sect.
7.2) that approximates the median sample size into the collection
vessel. Allow-the water to remain in the sealed or capped
collection container for at least 24 hours and determine the
concentrations of the cations of interest. If the solution
concentrations exceed the MDL, a contamination problem is indicated
in the cleaning procedure. Take corrective action before the
sampling containers are used for the collection of wet deposition.
10.4 Analyze a quality control check sample after the ion chromatograph
has been calibrated. This sample may be formulated in the
laboratory, or obtained from the National Bureau of Standards (NBS
Standard Reference Material 2694, Simulated Rainwater). Verify the
accuracy of internally formulated QCS solutions with an NBS
traceable standard before acceptance as a quality control check.
The check sample(s) selected must be within the range of the
calibration standards. If the measured value for the QCS falls
outside of the ±3s limits (Sect. 10.2.2), or if two successive
QCS checks are outside of the +2s limits, a problem is indicated
with the ion chromatograph or calibration curve. Corrective action
should be initiated to bring the results of the QCS within the ,
established control limits. Plot the data obtained from the QCS
checks on a control chart for routine assessments of bias and
precision.
10.5 Verify the calibration curve after a maximum of ten samples and at
the end of each day's analyses. Analyze calibration standards at
the low and high ends of the working range. If the routine
calibration checks do not meet the criteria described in Sect.
10.4, recalibrate the system and reanalyze all samples from the
last time the system was in control. Verify the new calibration
curve with the QCS according to Sect. 10.4 and reanalyze all
samples measured since the last time the system was in control.
10.6 Submit a Field Blank (FB) to the laboratory for every 20 samples.
The FB may consist of a water sample (Sect. 7.2) or a known
reference solution that approximates the concentration levels
characteristic of wet deposition. The FB is poured into the
sampling vessel at the field site and undergoes identical
processing and analytical protocols as the wet deposition
sample(s). Use the analytical data obtained from the FB to
determine any biases introduced in the field and laboratory
handling procedures, the data from the known reference solution
can be used to calculate a system precision and bias.
300.7-13
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10.7 Prepare and analyze a laboratory spike of a wet deposition sample
according to the guidelines provided in "Quality Assurance Manual
for Precipitation Measurement Systems" (14.6). Compare the results
obtained from spiked samples to those obtained from identical
samples to which no spikes were added. Use these data to monitor
the method percent recovery as described in Sect. 10.2.3.
10.8 Participation in performance evaluation studies is recommended for
wet deposition chemistry laboratories. The samples used for these
performance audits should contain the analytes of interest at
concentrations within the normal working range of the method. The
true values are unknown to the analyst. Performance evaluation
studies for wet deposition chemistry laboratories are conducted
semiannually by the USEPA Performance Evaluation Branch, Quality
Assurance Division, Research Triangle Park, NC 27711.
11. PROCEDURE
11.1 Check the instrumental operating parameters each day according to
Sect. 9 and Table 1.
11.2 Prepare all standards and construct calibration curves according to
Sect. 9.6 and 9.7.
11.3 After the calibration curve is established, analyze the QCS. If
the measured value for the QCS is not within the specified limits
(Sect. 10.2.2), refer to Sect. 10.4.
11.4 SAMPLE INJECTION
11.4.1 Use the same size injection loop for both standards and
samples. Samples may be injected manually with a syringe
or with an autosampler.
11.4.2 Flush the sampling system thoroughly with each new sample
using a rinse volume of at least ten times the loop size.
Inject the sample, avoiding the introduction of air bubbles
into the system.
11.4.3 Record the resulting peak heights or areas.
11.5 If the peak height or area response exceeds the working range of
the system, dilute the sample with zero standard and reanalyze.
11.6 Sample chromatograms are provided in Figures 2 and 3.
300.7-14
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12. CALCULATIONS
12.1 For each analyte of interest, calculate a linear least squares fit
of the standard concentrations as a function of the measured peak
height or area. The linear least squares equation is expressed as
follows:
where: y = standard concentration in mg/L
x = peak height or area measured
B = y-intercept calculated from: y - B x
B = slope calculated from:
n n
2 (x - x) (y - y)/ 2 (x. - *)
i=l i=l
where: 3? = mean of peak height or area measured
y » mean of standard concentrations
n * number of samples
The correlation coefficient should be 0.9990 or greater. Determine
the concentration of analyte of interest from the calibration
curve.
12.2 If the relationship between standard concentration and measured peak
height or area is nonlinear, use a second degree polynomial least
squares equation to derive a curve with a correlation >0.99BO.
The second degree polynomial equation is expressed as follows:
y =• B x + B x + B
A computer is necessary for the derivation of this function.
Determine the concentration of analyte of interest from the
calibration curve.
12.3 An integration system may also be used to provide a direct readout
of the concentration of the analyte of interest.
12.4 Report data in mg/L as Na , NH , K , Mg , and Ca
Do not report data lower than the lowest calibration standard.
13. PRECISION AND BIAS
13.1 The mean percent recovery and mean bias of this method were
determined from the analysis of spiked wet deposition samples
according to ASTM Standard Practice D4210, Annex A4 (14.7). The
results are summarized in Table 3. No statistically significant
biases were found for any of the five inorganic cations.
300.7-15
-------
13.2 Single-operator precision and bias were obtained from the analysis
of quality control check samples that' approximated the levels
common to wet deposition samples. These results reflect the
accuracy that can be expected when the method is used by a
competent operator. These data are presented in Table 4.
14. REFERENCES
14.1 Annual Book of ASTM Standards, Part 31, "Definitions of Terms
Related to Water," Standard D 1129-82b, 1982, p. 4.
14.2 Annual Book of ASTM Standards, Part 31, "Excerpts from Standard
for Metric Practice," Standard E 380-79, 1982, pp. 679-694.
14.3 "Safety in Academic Chemistry Laboratories," American Chemical
Society Publication, Committee on Chemical Safety, 3rd Edition,
1979.
14.4 Annual Book of ASTM Standards, Part 31, "Standard Specification
for Reagent Water," Standard D 1193-77, 1982, p. 39.
14.5 Peden, M. E. and Skowron, L. M., "Ionic Stability of Precipitation
Samples," Atmos..Environ. 12, 1978, pp. 2343-2349.
14.6 Topol, L. E.-, Lev-On, M., Flanagan, J., Schwall, R. J., Jackson, A.
E., Quality Assurance Manual for Precipitation Measurement
Systems, 1985, U.S. Environmental Protection Agency,
Environmental Monitoring Systems Laboratory, Research Triangle
Park, NC 27711.
14.7 Annual Book of ASTM Standards, Section 11, Vol. 11.01 (1),
"Practice for Interlaboratory Quality Control Procedures and a
Discussion of Reporting Low-Level Data," Standard D4210 Annex A4,
1983, pp. 15-16.
300.7-16
-------
Table 1. Method Detection Limits and Concentration Ranges
for Chemically Suppressed- Ion Chromatographic
Determination of Cations in Wet Deposition.
Method Detection Concentration
Limit,a Range,
Analyte mg/L mg/L
Sodium 0.03 0.03 - 1.00
Ammonium (as NH "*") 0.03 0.03-2.00
Potassium 0.01 0.01-1.00
Magnesium 0.02 0.02-1.00
Calcium 0.02 0.02-3.00
a. Chromatographic Conditions:
Guard Column — Dionex CGI
Separator Column — Dionex CS1
Fiber Suppressor Column — Dionex CFS
Detector — As specified in 6.1.5
Eluent — As specified in 7.3
Sample Loop — 100 uL
Flow Rate — 2.3 mL/min
Detector Sensitivity — 10 uS/cm
300.7-17
-------
Table 2. Retention Times and Suggested Calibration
Standard Concentrations for the Determination
of Cations in Wet Deposition.3
Analyte
Approximate Retention
Time Range,
sec
Calibration
Standards,
mg/L
Sodium
276 - 336
zero
0.03
0.25
0.50
0.75
1.00
Ammonium
(as NH4 )
432 - 512
zero
0.03
0.25
0.50
0-.75
1.00
Potassium
528 - 636
zero
0.01
0.05
0.10
0.20
0.25
Magnesium
144 - 204
zero
0.02
0.10
0.15
0.20
0.30
Calcium
252 - 324
zero
0.02
,40
0.
0.
1.
75
10
1.50
a. Based on the MDL and 95th percentile concentrations of each
analyte obtained from analyses of over five thousand wet deposition
samples from the NADP/NTN precipitation network.
b. The retention time was measured from the time of injection. For
chromatographic conditions, refer to Table 1.
300.7-18
-------
Table 3. Single-Operator Precision and Bias for
Sodium, Ammonium, Potassium, Magnesium,
and Calcium Determined from Analyte
Spikes of Wet Deposition Samples.3
Analyte
Amount
Added,
mg/L
n
Mean
Percent
Recovery
Mean
Bias,
mg/L
Standard
Deviation,
mg/L
Statistically
Significant
Bias?0
Sodium
0.108
0.273
10
9
95.3
94.4
-0.001
•0.015
0.010
0.010
No
No
Ammonium
0.188
0.473
10
9
113.8
107.5
0.026
0.035
0.030
0.025
No
No
Potassium
0.014
0.034
8
8
157.1
132.4
0.008
0.011
0.009
0.016
No
No
Magnesium
Calcium
0.018
0.044
0.079
0.199
9
9
10
10
E9.
92.
93.9
97.1
-0.002
•0.003
•0.005
•0.008
0.004
0.002
0.008
0.014
No
No
No
No
a. Concentrations are significant to two decimal places.
conditions, refer to Table 1.
b. Number of replicates
c. 95% Confidence Level
For chromatographic
300.7-19
-------
Table 4. Single-Operator Precision and Bias for
Sodium, Ammonium, Potassium, Magnesium,
and Calcium Determined from Quality
Control Check Samples. a
Theoretical
Concentration,
Analyte mg/L
Sodium
Ammonium
Potassium
Magnesium
Calcium
0.082
0.465
0.063
0.400
0.021
0.098
0.018
0.084
0.053
0.406
Measured
Concentration,
mg/L n
0.090
0.454
0.067
0.400
0.024
0.098
0.026
0.085
0.058
0.405
7
7
7
7
7
7
7
7
7
7
Bias,
mg/L %
0.008
-0.011
0.004
0.000
0.003
0.000
0.008
0.001
0.005
-0.001
9.8
-2.4
6.4
0.0
14.3
0.0
44.4
1.2
9.4 '
-0.2
Precision,
s, RSD,
mg/L %
0.009
0.019
0.011
0.032
0.004
0.005
0.008
0.018
0.006
0.045
10.0
4.2
16.4
8.0
16.7
5.1
30.8
21.2
10.3
11.1
a. Concentrations are significant to two decimal places. For chromatographic
conditions, refer to Table 1.
b. Number of replicates.
300.7-20
-------
0.50
Figure 1. Percentile Concentration Values Obtained
from Wet Deposition Samples: Sodium,
Ammonium* Potassium, Magnesium, and Calcium.
1.50
2.10
sodium
3.50
100 <
»0'
to •
ro
60
50
40
10
20
10
ammonium
0.50
i.oo
1.30
2.00
I
«
fa
Cd
>
•1.40 0.50
too- •
so.
70.
60'
50
40
JO
20
10
0.20
magnesium
o.-o
0.60
CONCENTRATION (mg/L)
i.oo
300.7-21
-------
Figure 2. Chrotnatogram of a Calibration Standard
Containing Sodium, Ammonium, and Potassium,
10
6
I I
I I I I
0.25 mg/L Na+ _
0.25 mg/L NH*
0.25 mg/L K+
Na1
246 8 10
RETENTION TIME, minutes
Chromatographic Conditions:
Guard Column — Dionex CGI
Separator Column — Dionex CS1
Fiber Suppressor Column — Dionex CFS
Detector — As specified in 6.1.5
Eluent — As specified in 7.3
Sample Loop — 100 uL
Flow Rate — 2.3 mL/min
Detector Sensitivity — 10 uS/cm
300.7-22
-------
Figure 3. Chromatogram of a Calibration Standard
Containing Magnesium and Calcium,
10
9
8
7
E
. 6
H
oi 5
X
01 4
Q.
0.50 mg/L Mg
1.50 mg/L Ca"1
02468
RETENTION TIME, minutes
Chromacographic Conditions:
Guard Column — Dionex CGI
Separator Column — Dionex CS1
Fiber Suppressor Column — Dionex CFS
Detector — As specified in 6.1.5
Eluent — As specified in 7.3
Sample Loop — 100 uL
Flow Rate ~ 2.3 mL/min
Detector Sensitivity — 10 uS/cm
300.7-?3
-------
Appendix G
METHOD 375.6 — SULFATE IN WET DEPOSITION BY AUTOMATED COLORIMETRIC
DETERMINATION USING BARIUM-METHYLTHYMOL BLUE
G-l
-------
Method 375.6 — Sulfate in Wet Deposition by Automated
Colorimetric Determination Using
Barium-Methylthymol Blue
March 1986
Performing Laboratory:
Susan R. Bachman
Michael J. Slater
Carla Jo Brennan
Mark E. Peden
Illinois State Water Survey
Analytical Chemistry Unit
2204 Griffith Drive
Champaign, Illinois 61820
Sponsoring Agency:
John D. Pfaff, Project Officer
Inorganic Analysis Section
Physical and Chemical Methods Branch
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
375.6-1
-------
INDEX
Section
Number Subject
1 Scope and Application
2 Summary of Method
3 Definitions
4 Interferences
5 Safety
6 Apparatus and Equipment
7 Reagents and Consumable Materials
8 Sample Collection, Preservation, and Storage
9 Calibration and Standardization
10 Quality Control
11 Procedure
12 Calculations
13 Precision and Bias
14 References
TABLES
1. Single-Operator Precision and Bias for Sulfate Determined from Analyte
Spikes of Wet Deposition Samples.
2. Single-Operator Bias and Precision for Sulfate Determined from Quality
Control Check Samples.
FIGURES
1. Percentile Concentration Values Obtained from Wet Deposition Samples:
Sulfate.
2. Sulfate Sampling and Analytical System — Segmented Flow.
375.6-2
-------
1. SCOPE AND APPLICATION
1.1 This method is applicable to the automated colorimetric determination
of sulfate in wet deposition samples by barium-methylthymol blue
reaction.
1.2 The term "wet deposition" is -used in this method to designate rain,
snow, dew, sleet, and hail.
1.3 The method detection limit (MDL) determined from replicate analyses
of a quality control check solution containing 0.36 mg/L sulfate is
0.05 mg/L. The concentration range of this method is 0.05-6.00 mg/L
as SO ~
4
1.4 Figure 1 represents a cumulative frequency percentile sulfate
concentration plot obtained from analyses of over five thousand wet
deposition samples. These data may be used as an aid in the
selection of calibration standard concentrations.
2. SUMMARY OF METHOD
2.1 A sample is pumped through an ion exchange column for the removal of
interfering cations, and then reacted with barium chloride at pH
2.5-3.0 to form barium sulfate. To enhance the complexation of
barium with methylthymol blue (MTB), sodium hydroxide is added to
increase the pH to approximately 12.5. Excess barium ions react with
an equivalent concentration of MTB to form a blue-colored chelate.
The concentration of unchelated MTB ions is related to the initial
sulfate ion concentration. Therefore, the intensity of the
blue-colored chelate is inversely proportional to the concentration
of sulfate in solution. After color reduction, a flowcell receives
the stream for measurement. A light beam of a wavelength
characteristic of the blue-colored chelate is passed through the
solution. The light energy measured by a photodetector is inversely
related to the concentration of sulfate in the sample. A calibration
curve is constructed using standard solutions containing known
concentrations of sulfate. From this curve, the concentration of
sulfate in a wet deposition sample is determined.
3. DEFINITIONS
3.1 COLORIMETRY — the measurement of light transmitted by a colored
complex as a function of concentration.
3.2 ION EXCHANGE — a reversible process by which ions are interchanged
between an insoluble material and a liquid with no substantial
structural changes of the material (14.1).
3.3 For definitions of other terms used in these methods, refer to the
glossary. For an explanation of the metric system including units,
symbols, and conversion factors see American Society for Testing and
Materials (ASTM) Standard E 380, "Metric Practices" (14.2).
375.6-3
-------
4. INTERFERENCES
4.1 Sample color absorbing in the wavelength range of 450-470 nm will
reduce the measured concentration of sulfate in the sample. Wet
deposition samples are generally colorless, therefore, this type of
interference is rare.
4.2 Phosphate at concentrations as low as 0.01 mg/L will complex with the
methylthymol blue reagent to result in a positive bias. Sulfite may
be oxidized to sulfate to yield a positive bias.
4.3 Cations such as calcium, aluminum, and iron that may also interfere
by complexing with the methylthymol blue reagent are removed by the
ion exchange column. If the ion exchange column capacity is
exceeded, the interfering cations are not completely removed and a
new column must be prepared.
4.4 The presence of air bubbles in the ion exchange column results in
incomplete removal of the interfering cations and is evidenced by an
unstable baseline. Eliminate this interference by preparing the .
column carefully in accordance with the details provided in Sect.
11.1.
5. SAFETY
5.1 The calibration standards, sample types, and most reagents used in
this method pose no hazard to the analyst. Use a fume hood,
protective clothing, and safety glasses when handling concentrated
hydrochloric acid (Sect. 7.5) and sodium hydroxide (Sect. 7.9).
5.2 Follow American Chemical Society guidelines regarding the safe
handling of chemicals used in this method (14.3).
6. APPARATUS AND EQUIPMENT
6.1 AUTOMATED COLORIMETRIC INSTRUMENT ~ Select and assemble an
analytical system consisting of the following:
6.1.1 Sampler.
6.1.2 Proportioning Pump.
6.1.3 Analytical Cartridge.
6.1.3.1 Ion Exchange Column — Flexible polyolefin tubing or
glass tubing having a length of 15 to 20 cm with an
inside diameter equal to the tubing in the rest of
the system. Prepare the ion exchange column
according to the procedure in Sect. 11.1.
375.6-4
-------
6.1.4 Colorimeter with a 460 run wavelength setting. Ensure that the
colorimeter is equipped with photodetectors having maximum
sensitivity at this wavelength setting. A 15 mm flow cell is
adequate to achieve the MDL stated in Sect. 1.3. A 50 mm flow
cell may be selected to increase sensitivity.
6.1.5 Strip Chart Recorder (or other data acquisition device).
6.1.6 Printer (optional).
6.2 Wherever possible, use glass transmission lines with an inside
diameter of 1.85 mm (0.073 inches) in the analytical cartridge and
colorimeter. Glass yields a more uniform sample flow and does not
degrade as quickly as other tubing materials. When connecting two
glass lines, ensure that the ends are abutted. To minimize pulsing
of the analytical stream, maintain uniform inside diameter throughout
all transmission tubing. Minimize the length of all transmission
tubing to optimize the performance of the hydraulic system.
6.4 Enclose the sampler with a dust cover to prevent contamination.
6.5 To prevent the intake of any precipitates from the reagents, install
intake filters at the end of the transmission lines that are used to
transport the reagents from their respective containers to the
proportioning pump.
6.6 LABORATORY FACILITIES — Laboratories used for the analysis of
wet deposition samples should be free from external sources of
contamination. The use of laminar flow clean air workstations is
recommended for sample processing and preparation to avoid the
introduction of airborne contaminants. Samples should always be
capped or covered prior to analysis. A positive pressure
environment within the laboratory is also recommended to minimize
the introduction of external sources of contaminant gases and
particulates. Windows within the laboratory should be kept closed
at all times and sealed if air leaks are apparent. The use of
disposable tacky floor mats at the entrance to the laboratory is
helpful in reducing the particulate loading within the room.
7• REAGENTS AND CONSUMABLE MATERIALS
7.1 PURITY OF REAGENTS — Use reagent 'grade chemicals for all solutions.
All reagents shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society (ACS), where
such specifications are available.
7.2 PURITY OF WATER — Use water conforming to ASTM Specification D
1193,- Type II (14.4). Point of use 0.2 micrometer filters are
recommended for all faucets supplying water to prevent the
introduction of bacteria and/or ion exchange resins into reagents,
standard solutions, and internally formulated quality control check
solutions.
375.6-5
-------
7.3 BARIUM CHLORIDE SOLUTION — Dissolve 1.526 g of barium chloride
(BaCl «H 0) in water (Sect. 7.2) and dilute to 1 L. Store at
room temperature in an amber high density polyethylene or
polypropylene container.
7.4 ETHANOL (C H-OH, Et-OH) — 95% volume/volume.
7.5 HYDROCHLORIC ACID (1.0 N) — Add 83.0 mL of concentrated hydrochloric
acid (HC1, sp gr 1.19) to 900 mL of water (Sect. 7.2) and dilute to
1 L.
7.6 ION EXCHANGE RESIN — Analytical grade carboxylic cation exchange
resin with a 20 to 50 mesh; sodium form.
7.7 METHYLTHYMOL BLUE REAGENT (MTB) — Add 25 mL of the barium chloride
solution to 0.1182 g of methylthymol blue (3'3"-Bis-N, N-bis
(carboxymethyl)- amino methylthymolsulfonephthalein pentasodium
salt). Add 4 mL of 1 N HCl to the solution, mix well, add 71 mL
of water (Sect. 7.2) , and 0.5 mL of Brij-35 or a similar wetting
agent. Mix and dilute to 500 mL with 95% EtOH. Prepare daily.
7.8 SAMPLER RINSE WATER ~ Add 0.5 mL Brij-35 or a similar wetting agent
to 1 L of water (Sect. 7.2).
7.9 SODIUM HYDROXIDE SOLUTION (0.18 N) — Dissolve 7.2 g of sodium
hydroxide (NaOH) in 900 mL of water (sect. 7.2), add 0.5 mL of
Brij-35 or a similar wetting agent and dilute to 1 L. Store at room
temperature in a high density polyethylene or polypropylene
container.
7.10 SULFATE SOLUTION, STOCK (1.0 mL = 1.0 mg SO ) — The stock
solution may be purchased as a certified solution or prepared from
ACS reagent grade materials. To prepare, dissolve 1.4789 g of
sodium sulfate (Na SO.), dried at 105°C for one hour, in water
(Sect. 7.2) and dilute to 1 L. This solutions is stable for one
year when stored in a high density polyethylene or polypropylene
container at 4 C.
7.11 SAMPLE CONTAINERS — Use polyolefin sample cups or glass test tubes
that have been rinsed thoroughly with water (Sect. 7.2) before use.
8. SAMPLE COLLECTION, PRESERVATION AND STORAGE
8.1 Collect samples in high density polyethylene (HOPE) containers that
have been thoroughly rinsed with ASTM Type II water (7.2). Do not
use strong mineral acids or alkaline detergent solutions for cleaning
collection vessels. Residual acids may remain in the polyethylene
matrix and slowly leach back into the sample. Alkaline detergents
may also leave residues that may affect the sample chemistry. Cap
collection bottles after cleaning to prevent contamination from
airborne contaminants; air dry collection buckets in a laminar flow
375.6-6
-------
clean air workstation and wrap in polyethylene bags prior to use. If
a laminar flow workstation is not available, pour out any residual
rinse water and bag the buckets immediately. Do not dry the bucket
interior by any method other than air drying in a laminar flow clean
air workstation.
8.2 The frequency of sample collection and the choice of sampler design
are dependent on the monitoring objectives. In general, the use of
wet-only samplers is recommended to exclude dry deposition
contributions, minimize sample contamination, retard evaporation,
and enhance sample stability. Sample collection frequency may vary
from subevent to monthly sampling periods. Collection periods of
more than one week are not recommended since sample integrity may be
compromised by longer exposure periods.
8.3 The oxidation of sulfite to sulfate after sample collection will
increase the concentration of SO in stored samples. Sample
measurements should be made immediately after collection if possible.
Refrigeration of samples at 4 C will minimize, but not eliminate
concentration changes prior to chemical analysis.
9. CALIBRATION AND STANDARDIZATION
9.1 INSTRUMENT OPTIMIZATION
9.1.1 For a segmented flow system with a concentration range from
0.05-6.00 mg/L as sulfate, assemble the sampling and
analytical system as shown in Figure 2.
9.1.2 Prepare the ion exchange column according to Sect. 11.1.
9.1.3 Silicone is more resistant to the effects of ethanol,
therefore, use flow rated silicone transmission and pump
tubing to transport the methylthymol blue reagent from-the
reagent source to the analytical stream. Use silicone
tubing to transport the sample from the flow cell through the
pump and to waste. Elsewhere, use flow rated polyvinyl chloride
or polyethylene pump and transmission tubing throughout the
sampling and analytical system. Check the tubing for chemical
buildup, splits, cracks, and deformations before beginning
each day's analysis. Change pump tubes after 50 hours of
operation. Change transmission tubing after 100 hours of
operation or when uneven flow patterns are observed.
9.1.4 Optimize the tension of pump tubes according to manufacturer's
recommendations.
9.1.5 Set the wavelength of the colorimeter to 460 ran. Allow the
colorimeter to warm up for 30 minutes while pumping sampler
rinse water and reagents through the system. After a stable
baseline has been obtained, adjust the recorder to maximize
the full-scale response.
375.6-7
-------
9.1.6 Sample at a rate of 30 samples/hour with a 1:4 sample to rinse
ratio. This sampling rate provides good peak separation.
Adjust the colorimeter to maximize sensitivity while
minimizing instrument noise. Refer to the manufacturer's
recommendations.
9.2 CALIBRATION SOLUTIONS
9.2.1 Five calibration solutions and one zero standard are needed to
generate a suitable calibration curve. The lowest calibration
solution should contain sulfate at a concentration greater
than or equal to the method detection limit. The highest
solution should approach the expected upper limit of
concentration of sulfate in wet deposition. Prepare the
remaining solutions such that they are evenly distributed
throughout the concentration range. Suggested calibration
standards for sulfate are as follows: zero, 0.05, 1.50, 3.00,
4.50, and 6.00 mg/L as SO ~ .
9.2.2 Prepare all calibration standards by diluting the stock
standard (Sect. 7.10) with water (Sect. 7.2). Use glass
(Class A) or plastic pipettes that are within the bias and '
precision tolerances specified by the manufacturer. The
standards are stable for one month if stored at room
temperature in high density polyethylene or polypropylene
containers.
9.3 CALIBRATION CURVE
9.3.1 Analyze the standard containing the highest concentration of
sulfate and adjust the colorimeter calibration control to
achieve full-scale deflection on the recorder. Use the zero
standard to establish a baseline. If a printer is used,
adjust it to read the correct concentration. Analyze all the
standards and construct a calibration curve according to
Sect. 12. After every 30 samples and at the end of the day's
analyses, reconstruct the entire calibration curve.
9.3.2 Verify the calibration curve after every ten samples and at
the end of each day's analyses according to Sect. 10.5.
10. QUALITY CONTROL
10.1 Each laboratory using this method should develop formalized quality
control protocols to continually monitor the bias and precision of
all measurements. These protocols are required to ensure that the
measurement system is in a state of statistical control. Estimates
of bias and precision for wet deposition analyses cannot be made
unless these control procedures are followed. Detailed guidelines
for the development of quality assurance and quality control
protocols for wet deposition measurement systems are published in a
manual available from the United States Environmental Protection
Agency, Research Triangle Park, NC 27711 (14.5). Included in this
manual are procedures for the development of statistical control
375.6-8
-------
charts for use in monitoring bias and precision as well as
recommendations for the introduction of reagent blanks, laboratory
duplicates, field duplicates, spike samples, and performance
evaluation samples. These guidelines are to be used by all
laboratories involved with wet deposition measurements.
10.2 ESTABLISHMENT OF WARNING AND CONTROL LIMITS — Warning and control
limits are used to monitor drift in the calibration curve, analyses
of quality control check samples (QCS), and measured recoveries
from laboratory spikes.
10.2.1 Calibration Curve — After a calibration curve has been
constructed according to Sect. 12, reanalyze additional
aliquots of the low and high concentration standards.
Calculate the concentrations using the previously derived
calibration curve. Repeat this procedure until at least
ten determinations at each concentration level have been
made. These data should be collected on ten different days
to provide a realistic estimate of the method variability.
Calculate a standard deviation (s) at each concentration
level. Use the nominal standard concentration as the mean
value (x) for_determining the control limits. A warning
limit of x _+ 2s and a control limit of x _+ 3s should be
used.- Reestablish these limits whenever instrumental
operating conditions change.
10.2.2 Quality Control Check Samples (QCS) — Calculate warning
and control limits for QCS solutions from a minimum of ten
analyses performed on ten days. Use the calculated
standard deviation (s) at each QCS concentration level to
develop the limits as described in Sect. 10.2.1. Use the
certified or NBS traceable concentration as the mean
(target) value. Constant positive or negative measurements
with respect to the true value are indicative of a method
or procedural bias. Utilize the data obtained from QCS
measurements as in Sect. 10.4 to determine when the
measurement system is out of statistical control. The
standard deviations used to generate the QCS control limits
should be comparable to the single operator precision
reported in Table 2. Reestablish new warning and control
limits whenever instrumental operating conditions are
varied or QCS concentrations are changed.
10.2.3 Laboratory Spike Solutions — A minimum of ten analyte
spiJces of wet deposition samples is required to develop a
preliminary data base for the calculation of warning and
control limits for spike recovery data. Select the spike
concentration such that the working range of the method
will not be exceeded. Samples selected for the initial
spike recovery study should represent the concentration
range common to wet deposition samples in order to reliably
estimate the method accuracy. Calculate a mean and
standard deviation of the percent recovery data using the
formulas provided in the glossary. Determine warning and
37J.6-9
-------
control limits using +_2s and _+3s, respectively, if
the data indicate that no significant method bias exists.
(14.6), the 100 percent recovery is used as the mean
percent recovery. Where a significant bias is determined
at the 95% confidence level, the control limits are
centered around the bias estimate. Routine spiked sample
analyses that yield percent recovery data outside of the
control limits are an indication of matrix interferences
that should be resolved before routine analyses are
continued.
10.2.4 All warning and control limits should be reevaluated on a
continual basis as additional data are collected during
routine analyses. The limits should be broadened or
narrowed if a recalculated standard deviation under similar
operating conditions provides a different estimate of the
procedure variability.
10.3 Monitor the cleaning procedure by pouring a volume of water (Sect.
7.2) that approximates the median sample size into the collection
vessel. Allow the water to remain in the sealed or capped
collection container for at least 24 hours and determine the
sulfate concentration. If the solution concentration exceeds the
MDL, a contamination problem is indicated in the cleaning
procedure. Take corrective action before the sampling containers
are used for the collection of wet deposition.
10.4 Analyze a quality control check sample (QCS) after the calibration
curve has been established. This sample may be formulated in the
laboratory or obtained from the National Bureau of Standards (NBS
Standard Reference Material 2694, Simulated Rainwater). Verify the
accuracy of internally formulated QCS solutions with an NBS traceabl6
standard before acceptance as a quality control check. The check
sample(s) selected must be within the range of the calibration
standards. If the measured value for the QCS falls outside of the
_*3s limits (Sect, 10.2.2), or if two successive QCS checks are
outside of the _+2s limits, a problem is indicated with the system
or the calibration procedure. Corrective action should be initiated
to bring the results of the QCS within the established control
limits. Plot the data obtained from the QCS checks on a control
chart for routine assessments of bias and precision.
10.5 Verify the calibration curve after a maximum of ten samples and at
the end of each day's analyses. Analyze calibration standards at
the low and high ends of the working range. If the routine
calibration checks do not meet the criteria described in Sect.
10.4, recalibrate the system and reanalyze all samples from the
last time the system was in control. Verify the new calibration
curve with the QCS according to Sect. 10.4 and reanalyze all
samples measured since the last time the system was in control.
375.6-10
-------
10.6 Submit a Field Blank (FB) to the laboratory for every 20 samples.
The FB may consist of a water sample (Sect. 7.2) or a known
reference solution that approximates the concentration levels
characteristic of wet deposition. The FB is poured into the
sampling vessel at the field site and undergoes identical
processing and analytical protocols as the wet deposition
sample(s). Use the analytical data obtained from the FB to
determine any contamination introduced in the field and laboratory
handling procedures. The data from the known reference solution
can be used to calculate a system precision and bias.
10.7 Prepare and analyze a laboratory spike of a wet deposition sample
according to the guidelines provided in "Quality Assurance Manual
for Precipitation Measurement Systems" (14.5). Compare the results
obtained from spiked samples to those obtained from identical
samples to which no spikes were added. Use these data to monitor
the method percent recovery as described in Sect. 10.2.3.
10.8 Participation in performance evaluation studies is recommended for
wet deposition chemistry laboratories. The samples used for these
performance audits should contain the analytes of interest at
concentrations within the normal working range of the method. The
true values are unknown to the analyst. Performance evaluation
studies for wet deposition chemistry laboratories are conducted
semiannually by the USEPA Performance Evaluation Branch, Quality
Assurance Division, Research Triangle Park, NC 27711.
11. PROCEDURE
11.1 ION EXCHANGE COLUMN
11.1.1 Soak the ion exchange resin overnight in water (Sect.
7.2). Stir the slurry and decant particles smaller than 50
mesh. Store the resin in water (Sect. 7.2) in a glass or
polyolefin container until the column is prepared.
11.1.2 Insert a small plug of teflon screen in one end of the
column tube. To prevent the entrapment of air bubbles,
fill the column with resin using a syringe or pipette
attached to the same tube end and draw the resin and
water mixture into the tube.
11.1.3 Do not allow air to enter the column. Do not let the resin
dehydrate. Air bubbles entering the analytical stream will
result in an unstable baseline. If air enters the column,
repeat the procedure from Sect. 11.1.2.
11.1.4 To prevent the introduction of air, insert the column in
the analytical stream while the system is pumping.
11.1.5 Prepare the column daily or whenever air enters the column.
11.2 Optimize the instrument each day according to Sect. 9.1.
375.6-11
-------
11.3 Prepare all standards and construct a calibration curve according
to Sect. 9.2 and 9.3.
11.4 After the calibration curve is established, analyze the QCS. If
the measured value for the QCS is not within the specified limits
(Sect. 10.2.2), refer to Sect. 10.4.
11.5 Load the sampler tray and begin analysis.
11.6 If the peak height response exceeds the working range of the
system, dilute the sample with zero standard and reanalyze.
11.7 When analysis is complete, rinse the system with sampler rinse
water (Sect. 7.8) for 15 minutes. Before changing the pump tubes,
rinse a dilute concentration of HC1 (1.0 N) through the system for
15 minutes to clean the mixing coils and flow cell. If the
baseline appears unstable or sensitivity decreases it may be
necessary to repeat this procedure more often than after 50 hours
of operation.
12. CALCULATIONS
12.1 The relationship betv/een standard concentration and measured
peak height for sulfate deviates from Beer's Law. Use a second-
degree polynomial least squares equation to derive a curve with a
correlation _>0-9990. The second degree polynomial .equation is
expressed as follows:
y = B2x + BLX + BQ
A computer is necessary for the derivation of this function.
Determine the concentration of sulfate from the calibration curve.
12.2 An integration system may also be used to provide a direct readout
of the concentration of sulfate.
12.3 Report data in mg/L as SO . Do not report data lower than the
lowest calibration standard.
13. PRECISION AND BIAS
13.1 The mean percent recovery and mean bias of this method were
determined from the analysis of spiked wet deposition samples
according tc ASTM Standard Practice D4210, Annex A4 (14.6). The
results are summarized in Table 1. No statistically significant
biases were found.
13.2 Single-operator precision and bias were obtained from the analysis
of quality control check samples that approximated the levels
common to wet deposition samples. These results reflect the
accuracy that can be expected when the method is used by a
competent operator. These data are presented in Table 2.
375.6-12
-------
14. REFERENCES
14.1 Annual Book of ASTM Standards, Part 31, "Definitions of Terms
Relating to Water," Standard D 1129-82b, 1982, p. 5.
14.2 Annual Book of ASTM Standards, Part 31, "Excerpts from Standard
for Metric Practice," Standard E 380-79, 1982, pp. 679-694.
14.3 "Safety in Academic Chemistry Laboratories," American Chemical
Society Publication, Committee on Chemical Safety, 3rd Edition,
1979.
14.4 Annual Book of ASTM Standards, Part 31, "Standard Specification
for Reagent Water," Standard D 1193-77, 1982, p. 39.
14.5 Topol, L. E., Lev-On, M., Flanagan, J., Schwall, R. J., Jackson, A.
E., Quality Assurance Manual for Precipitation Measurement
Systems, 1985, U.S. Environmental Protection Agency, Environmental
Monitoring Systems Laboratory, Research Triangle Park, NC 27711.
14.6 Annual Book of ASTM Standards, Section 11, Vol. 11.01 (1),
"Practice for Intralaboratory Quality Control Procedures and a.
Discussion of Reporting Low-Level Data," Standard D4210 Annex A4,
1983, pp. 15-16.
37S.6-13
-------
Table 1. Single-Operator Precision and Bias for Sulfate
Determined from Analyte Spikes of Wet Deposition Samples.
Analyte
Sulfate
Amount
Added,
mg/L n
1.0 10
2.6 9
Mean
Percent
Recovery
100.1
107.3
Mean
Bias,
mg/L
0.0
0.2
Standard
Deviation,
mg/L
0.1
0.1
Statistically
Significant
Bias?
No
NO
a. Number of replicates
b. 95% Confidence Level
375.6-14
-------
Table 2. Single-Operator Bias and Precision for Sulfate
Determined from Quality Control Check Samples.
Theoretical Measured Precision,
Concentration, Concentration,
mg/L mg/L n
0.94 0.90 170
7.20 7.13 172
Bias,
mg/L %
-0.04 -4.2
-0.07 -0.97
s,
mg/L
0.06
0.11
RSD,
%
6.7
1.5
The above data were obtained from records of measurements made under the
direction of the NADP/NTN quality assurance program.
a. Number of replicates
375.6-15
-------
Figure 1. Percentile Concentration Values Obtained from
Wet Deposition Samples: Sulfate
9-
U
8
s,
3
100
90
80
70
60
50
40
30
20
10
I i i i i I i i i i I -i
2,50 5.00 7.50
CONCENTRATION (mg/L)
10.00
375.6-16
-------
Figure 2. Sulfate Sampling and Analytical
System — Segmented Flow.
D20
Turn
Mixing
Coil
20
Turn
Mixing
'Coil
5T
f
urn Coil
— •— \
e_
:J
ION
EXCHANGE
COLUMN
(WASTE)
v3<
^i^M^PMK^
>
(
I
J
Pump Tube
Colors
Wht Wht
Blu Yel
Pur 81k
Blu Blu
Blk Blk
Wht Wht
Orn Orn
PROPORTIONING
PUMP
Flow Rate
(mL/min)
0.60
waste
1.40 from
' " flov
cell
2-90 Mm
rins
wat
1.60
°'32 lir
^
pier
*
er
le •'"—
methyl-
0,60 thymol
blue
reage
0.42 J.
hydr
t
COLORIMETER
460 nm
_ f
IECORDER
mt
jm
oxide
^^ i ^^
f SAMPLER I
H^
Sampling Rate:
30/hr
Sampling Volume:
0.6 mL
Sample to Rinse Ratio
1:4
(24 second sample,
96 second rinse)
375.6-17
-------
Appendix H
METHOD 353.6 — NITRATE-NITRITE IN WET DEPOSITION BY AUTOMATED
COLORIMETRIC DETERMINATION USING CADMIUM REDUCTION
H-l .
-------
Method 353.6 — Nitrate-Nitrite in Wet Deposition by
Automated Colorimetric Determination
using Cadmium Reduction
March 1986 s
Performing Laboratory:
Brigita Demir
Susan R. Bachman
Carla Jo Brennan
Mark E. Peden
Illinois State Water Survey
Analytical Chemistry Unit
2204 Griffith Drive
Champaign, Illinois 61820
Sponsoring Agency:
John D. Pfaff, Project Officer
Inorganic Analysis Section
Physical and Chemical Methods Branch
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
353.6-1
-------
INDEX
Section
Number Subject
1 Scope and Application
2 Summary of Method
3 Definitions
4 Interferences
5 Safety
6 Apparatus and Equipment
7 Reagents and Consumable Materials
8 Sample Collection, Preservation, and Storage
9 Calibration and Standardization
10 Quality Control
11 Procedure
12 Calculations
13 Precision and Bias
14 References
TABLES
Single-Operator Bias and Precision for Nitrate-Nitrite Determined from
Analyte Spikes of Wet Deposition Samples.
Single-Operator Bias and Precision for Nitrate Determined from Quality
Control Check Samples.
FIGURES
1. Percentile Nitrate-Nitrite Concentration Values Obtained from Wet
Deposition Samples.
2. Nitrate-Nitrite Sampling and Analytical System — Segmented Flow.
353.6-2
-------
1. SCOPE AND APPLICATION
1.1 This method is applicable to the automated colorimetric measurement
of nitrate-nitrite in wet deposition samples by cadmium reduction.
1.2 The term "wet deposition" is used in this method to designate rain,
snow, dew, sleet, and hail.
1.3 The method detection limit (MDL) determined from replicate analyses
of a calibration standard containing 0.10 mg/L nitrate is 0.02 mg/L.
The analyte concentration range of this method is 0.02-5.00 mg/L as
NO ~
1.4 Figure 1 represents a cumulative frequency percentile nitrate-nitrite
concentration plot obtained from analyses of over five thousand wet
deposition samples. These data may be used as an aid in the
selection of appropriate calibration standard concentrations.
2. SUMMARY OF METHOD
2.1 A filtered sample is mixed with ammonium chloride and introduced
into a copper-cadmium reduction column. Nitrate ions are reduced to
nitrite ions and mixed with a color reagent to form a reddish-purple
complex. Determination of nitrite alone can be conducted by
eliminating the reduction column. The intensity of the color complex
is proportional to the concentration of nitrite in solution. After
color development, a flowcell receives the stream for measurement. A
light beam of a wavelength characteristic of the color complex is
passed through the solution. The light energy measured by a
photodetector is a function of the concentration of nitrite ion in
the sample. Beer's Law is used to relate the measured transmittance
to concentration:
log(l/T) = abc
where: T * transmittance
a * absorptivity
b a length of light path
c » concentration of absorbing species (mg/L)
A calibration curve is constructed using standard solutions
containing known concentrations of nitrate. From this curve, the
concentration of nitrate-nitrite in a wet deposition sample is
determined.
353.6-3
-------
3. DEFINITIONS
3.1 COLORIMETRY — the measurement of light transmitted by a colored
complex as a function of concentration.
3.2 For definitions of other terms used in this method, refer to the
glossary. For an explanation of the metric system including units,
symbols, and conversion factors see American Society for Testing and
Materials (ASTM) Standard E 380, "Metric Practices" (14.1).
4. INTERFERENCES
4.1 Sample color absorbing in the wavelength range of 510-530 nm will
increase the measured concentration of nitrate-nitrite in the sample.
Wet deposition samples are generally colorless; therefore, this type
of interference is rare. If color does cause a problem, however, a
sample not containing N-(l-naphthyl)ethylenediamine Dihydrochloride
can be analyzed and the measured concentration subtracted.
4.2 In this method, the volume of alkaline solution (NH.C1) used is 3.8
times that of the sample. This ensures that wet deposition samples
with pH's as low as 3.5 are easily neutralized by the alkaline
reagent and reduced properly in the cadmium column.
5. SAFETY
5.1 The calibration standards, sample types, and most reagents used in
this method pose no hazard to the analyst. Use a fume hood,
protective clothing, and safety glasses when handling concentrated
hydrochloric acid (Sect. 7.8).
5.2 Use a fume hood when preparing the alkaline water (Sect. 7.3).
Vapors produced by this reagent are extremely irritating.
5.3 When preparing the cadmium reduction column (Sect. 11.1), use gloves,
safety glasses, protective clothing, and a fume hood. Cadmium
produces nephrotoxic effects; therefore, avoid all skin and
respiratory contact (14.2).
CAUTION: When discarding cadmium waste, store in a tightly sealed
container for later disposal at a hazardous waste treatment/storage
facility.
5.4 Follow American Chemical Society guidelines regarding safe handling
of chemicals used in this method (14.3).
353.6-4
-------
6. APPARATUS AND EQUIPMENT
6.1 AUTOMATED COLORIMETRIC INSTRUMENT ~ Select and assemble an
analytical system consisting of the following:
6.1.1 Sampler.
6.1.2 Proportioning Pump.
6.1.3 Analytical Cartridge.
6.1.3.1 Reduction column — Use glass or flexible polyolefin
tubing having a length of 36 cm with an inside
diameter of 2.29 mm (0.09 inches). Prepare the
reduction column according to the procedure in
Sect. 11.1.
6.1.4 Colorimeter with a 520 nm wavelength setting. Ensure that the
colorimeter is equipped with photodetectors having maximum
sensitivity at this wavelength setting. A 15 mm flow cell is
adequate to achieve the MDL stated in Sect. 1.3.
6.1.5 Strip Chart Recorder (or other data acquisiton device).
6.1.6 Printer (optional).
6.3 Wherever possible, use glass transmission lines with an inside
diameter of 1.85 mm (0.073 inches) in the analytical cartridge and
colorimeter. Glass yields a more uniform sample flow and does not
degrade as quickly as other tubing materials. When connecting two
glass lines, ensure that the lines are abutted. To minimize sample
pulsing, maintain uniform inside diameter throughout-all transmission
tubing. Minimize the length of all transmission tubing to optimize
the performance of the hydraulic system.
6.4 Enclose the sampler with a dust cover to prevent contamination.
6.5 To prevent the intake of any precipitates from the reagents, install
intake filters at the end of the transmission lines that are used to
transport the reagents from their respective containers to the
proportioning pump.
6.6 LABORATORY FACILITIES — Laboratories used for the analysis of
wet deposition samples should be free from external sources of
contamination. The use of laminar flow clean air workstations is
recommended for sample processing and preparation to avoid the
introduction of airborne contaminants. Samples should always be
capped or covered prior to analysis. A positive pressure
environment within the laboratory is also recommended to minimize
the introduction of external sources of contaminant gases and
particulates. Windows within the laboratory should be kept closed .
at all times and sealed if air leaks are apparent. The use of
disposable tacky floor mats at the entrance to the laboratory is
helpful in reducing the particulate loading within the room.
353.6-5
-------
7. REAGENTS AND CONSUMABLE MATERIALS
7.1 PURITY OF REAGENTS — Use reagent grade chemicals for all solutions.
All reagents shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society (ACS), where
such specifications are available.
7.2 PURITY OF WATER — Use water conforming to ASTM Specification D
1193, Type II (14.4). Point of use 0.2 micrometer filters are
recommended for all faucets supplying water to prevent the
introduction of bacteria and/or ion exchange resins into reagents,
standard solutions, and internally formulated quality control check
solutions.
7.3 ALKALINE WATER (pH 10.0) — Add 1.8 mL of ammonium hydroxide
(NH OH) to water (Sect. 7.2) and dilute to 1 L. Store at room
temperature in a polyolefin container.
CAUTION: Refer to Sect. 5.2 for precautions when preparing this
reagent since it produces irritating vapors.
7.4 AMMONIUM CHLORIDE REAGENT (pH 8.5) — Dissolve 10 g of ammonium
chloride (NH CD in alkaline water (Sect. 7.3) and dilute to 1 L.
Add 0.5 mL of a wetting agent that does not contain nitrate-nitrite,
such as Brij-35.
7.5 CADMIUM — 40 mesh, coarse granules, 99% pure.
CAUTION: Follow the precautions in Sect. 5.3 to avoid all skin and
respiratory contact with the granules.
7.6 COLOR REAGENT — Add 100 mL of concentrated phosphoric acid
(H PO sp gr 1.71), 10 g of sulfanilamide (C-H.N.O-S), and 0.50 g of
N-fl-Naphthyl)-ethylenediamine Dihydrochloride (C..H..N-'2HC1)
to 800 mL of water (Sect. 7.2) and dilute to 1 L. Add 0.5 mL
of a wetting agent that does not contain nitrate-nitrite, such
as Brij-35. This solution is stable for one month when refrigerated
at 4°C in an amber glass or polyolefin container. Allow the
color reagent to reach ambient temperature before use.
7.7 COPPER SULFATE SOLUTION (4.00 g/L) — Dissolve 2.00 g of copper
sulfate pentahydrate (CuSO »5H 0) in water (Sect. 7.2) and
dilute to 500 mL. This solution is stable for two months when
stored at room temperature in a glass or polyolefin container.
7.8 HYDROCHLORIC ACID (1.0 N) — Add 83.0 mL of concentrated hydrochloric
acid (HC1, sp gr 1.19) to 900 mL of water (Sect. 7.2) and dilute to
1 L.
7.9 NITRATE SOLUTION, STOCK (1.0 mL = 1.0 mg NO.) — Dissolve 1.3707 g
'of sodium nitrate (NaNO,), dried at 105 C for one hour, in water
(Sect. 7.2) and dilute to 1 L. This solution is stable for one year
when stored at room temperature in a glass or polyolefin container.
353.6-6
-------
7.10 SAMPLER RINSE WATER — Add 0.5 mL of a wetting agent that does not
contain nitrate-nitrite, such as Brij-35, to 1 L of water (Sect.
7.2).
7.11 SAMPLE CONTAINERS — Use polyolefin sample cups or glass test tubes
that have been rinsed thoroughly with water (Sect. 7.2) before use.
8. SAMPLE COLLECTION, PRESERVATION AND STORAGE
8.1 Collect samples in high density polyethylene (HOPE) containers that
have been thoroughly rinsed with ASTM Type II water (7.2). Do not
use strong mineral acids or alkaline detergent solutions for cleaning
collection vessels. Residual acids may remain in the polyethylene
matrix and slowly leach back into the sample. Alkaline detergents
may also leave residues that may,jiffeet the sample chemistry. Cap
collection bottles after cleaning to prevent contamination from
airborne contaminants; air dry collection buckets in a laminar flow
clean air workstation and wrap in polyethylene bags prior to use. If
a laminar flow workstation is not available, pour out any residual
rinse water and bag th« buckets immediately. Do not dry the bucket
interior by any method other than air drying in a laminar flow clean
air workstation.
8.2 The frequency of sample collection and the choice of sampler design
are dependent on the monitoring objectives. In general, the' use of
wet-only samplers is recommended to exclude dry deposition
contributions, minimize sample contamination, retard evaporation,
and enhance sample stability. Sample collection frequency may vary
from subevent to monthly sampling periods. Collection periods of
more than one week are not recommended since sample integrity may be
compromised by longer exposure periods.
8.3 The presence of microbial activity will affect the stability of
nitrate concentrations in wet deposition samples. Sample
measurements should be made immediately after collection whenever
possible. The biological conversion of'NH and nitrite (NO ) to
nitrate after sample collection can be minimized by storing samples
at 4 C prior to analysis.
8.3.1 Filtration of samples through a 0.45 micrometer membrane
leached with water (Sect. 7.2) is partially effective at
stabilizing nitrate by removal of biological species.
Refrigeration after immediate filtration is the most reliable
method to ensure sample integrity (14.5). Sample storage
time should not exceed one week.
353.6-7
-------
9. CALIBRATION AND STANDARDIZATION
9.1 INSTRUMENT OPTIMIZATION
9.1.1 For a segmented flow system with a concentration range from
0.02-5.00 mg/L as nitrate-nitrite, assemble the sampling and
analytical system as shown in Figure 2.
9.1.2 Prepare and activate the reduction column according to Sect.
11.1.
9.1.3 Use flow rated polyvinyl chloride (PVC) or polyethylene pump
and transmission tubing throughout the sampling and analytical
system. Check the tubing for chemical buildup, splits,
cracks, and deformations before beginning each day's analysis.
Change pump tubes after 50 hours of operation. Change
transmission tubes after 100 hours of operation or when uneven
flow patterns are observed.
9.1.4 Optimize the tension of the pump tubes according to the
manufacturer's recommendations.
9.1.5 Set the wavelength of the colorimeter to 520 nm. Allow the
colorimeter to warm up for 30 minutes while pumping sampler
rinse water (Sect. 7.10) and reagents through the system.
After a stable baseline has been obtained, adjust the recorder
to maximize the full-scale response.
9.1.6 Sample at a rate of 40 samples/hour with a 1:4 sample to rinse
ratio. This sampling rate provides good peak separation.
Adjust the colorimeter to maximize sensitivity while
minimizing instrument noise. Refer to the manufacturer's
recommendations.
9.2 CALIBRATION SOLUTIONS
9.2.1 Five calibration solutions and one zero standard are needed to
generate a suitable calibration curve. The lowest calibration
solution should contain nitrate at a concentration greater
than or equal to the method detection limit. The highest
solution should approach the expected upper limit of
concentration of nitrate-nitrite in wet deposition. Prepare
the remaining solutions such that they are evenly distributed
throughout the concentration range.* Suggested calibration
standards for nitrate-nitrite are as follows: zero, 0.02,
1.25, 2.50, 3.75, and 5.00 mg/L as NO ".
353.6-8
-------
9.2.2 Prepare all calibration standards by diluting the stock
standard (Sect. 7.9) with water (Sect. 7.2). Use glass
(Class A) or plastic pipettes that are within the bias and
precision tolerances specified by the manufacturer. Standards
with nitrate concentrations greater than 0.25 mg/L are stable
for one week when stored at room temperature in glass or
polyolefin containers. Prepare standards with 0.25 mg/L or
less of nitrate every day and store at room temperature in
glass or polyolefin containers.
9.3 CALIBRATION CURVE
9.3.1 Analyze the standard containing the highest concentration of
nitrate and adjust the colorimeter calibration control to
obtain full-scale deflection on the recorder. Use the zero
standard to adjust the baseline. If a printer is used, adjust
it to read the correct concentration. Analyze all the
standards and construct a calibration curve according to
Sect. 12. After every 30 samples and at the end of each day's
analyses, reconstruct the entire calibration curve.
9.3.2 Verify the calibration curve after every ten samples and at
the end of each day's analyses according to Sect. 10.5.
10. QUALITY CONTROL
10.1 Each laboratory using this method should develop formalized quality
control protocols to continually monitor the bias and precision of
all measurements. These protocols are required to ensure that the
measurement system is in a state of statistical control. Estimates
of bias and precision for wet deposition analyses cannot be made
unless these control procedures are followed. Detailed guidelines
for the development of quality assurance and quality control
protocols for wet deposition measurement systems are published in a
manual available from the United States Environmental Protection
Agency, Research Triangle Park, NC 27711 (14.6). Included in this
manual are procedures for the development of statistical control
charts for use in monitoring bias and precision as well as
recommendations for the introduction of reagent blanks, laboratory
duplicates, field duplicates, spike samples, and performance
evaluation samples. These guidelines are to be used by all
laboratories involved with wet deposition measurements.
10.2 ESTABLISHMENT OF WARNING AND CONTROL LIMITS — Warning and control
limits are used to monitor drift in the calibration curve, analyses
of quality control check samples (QCS), and measured recoveries
from laboratory spikes.
351 6-9
-------
10.2.1 Calibration Curve — After a calibration curve has been
constructed according to Sect. 12, reanalyze additional
aliquots of the low and high concentration standards.
Calculate the concentrations using the previously derived
calibration curve. Repeat this procedure until at least
ten determinations at each concentration level have been
made. These data should be collected on ten different days
to provide a realistic estimate of the method variability.
Calculate a standard deviation (s) at each concentration
level. Use the nominal standard concentration as the mean
value (x) for determining the control limits. A warning
limit of x ^ 2s and a control limit of x ^ 3s should be
used. Reestablish these limits whenever instrumental
operating conditions change.
10.2.2 Quality Control Check Samples (QCS) — Calculate warning
and control limits for QCS solutions from a minimum of ten
analyses performed on ten days. Use the calculated
standard deviation (s) at each QCS concentration level to
develop the limits as described in Sect. 10.2.1. Use the
certified or MBS traceable concentration as the mean
(target) value. Constant positive or negative measurements
with respect to the true value are indicative of a method
or procedural bias. Utilize the data obtained from QCS
measurements as in Sect. 10.4 to determine when the
measurement system is out of statistical control. The
standard deviations used to generate the QCS control limits
should be comparable to the single operator precision
reported in Table 2. Reestablish new warning and control
limits whenever instrumental operating conditions are
varied or QCS concentrations are changed.
10.2.3 Laboratory Spike Solutions — A minimum of ten analyte
spikes of wet deposition samples is required to develop a
preliminary data base for the calculation of warning and
control limits for spike recovery data. Select the spike
concentration such that the working range of the method
will not be exceeded. Samples selected for the initial
spike recovery study should represent the concentration
range common to wet deposition samples in order to reliably
estimate the method accuracy. Calculate a mean and
standard deviation of the percent recovery data using the
formulas provided in the glossary. Determine warning and
control limits using ^2s and ^3s, respectively. If
the data indicate that no significant method bias exists
(14.7), the 100 percent recovery is used as the mean
percent recovery. Where a significant bias is determined
at the 95% confidence level, the control limits are
centered around the bias estimate. Routine spiked sample
analyses that yield percent recovery data outside of the
control limits are an indication of matrix interferences
that should be resolved before routine analyses are
continued.
353.6-10
-------
10.2.4 All warning and control limits should be reevaluated on a
continual basis as additional data are collected during
routine analyses. The limits should be broadened or
narrowed if a recalculated standard deviation under similar
operating conditions provides a different estimate of the
procedure variability.
10.3 Monitor the cleaning procedure by pouring a volume of water (Sect.
7.2) that approximates the median sample size into the collection
vessel. Allow the water to remain in the sealed or capped
collection container for at least 24 hours and determine the
nitrate concentration. If the solution concentration exceeds the
MDL, a contamination problem is indicated in the cleaning
procedure. Take corrective action before the sampling containers
are used for the collection of wet deposition.
10.4 Analyze a quality control check sample (QCS) after the calibration
curve has been established. «This sample may be formulated in the
laboratory or obtained from the National Bureau of Standards (NBS
Standard Reference Material 2694, Simulated Rainwater). Verify the
accuracy of internally formulated QCS solutions with an NBS
traceable standard before acceptance as a quality control check.
The check sample(s) selected must be within the range of the
calibration standards. If the measured value for the QCS falls
outside of the _+3s limits (Sect. 10.2.2), or if two successive
QCS checks are outside of the +2s limits, a problem is indicated
with the system or the calibration procedure. Corrective action
should be initiated to bring the results of the QCS within the
established control limits. Plot the data obtained from the QCS
checks on a control chart for routine assessments of bias and
precision.
10.5 Verify the calibration curve after a maximum of ten samples and at
the end of each day's analyses. Analyze calibration standards at
the low and high ends of the working range. If the routine
calibration checks do not meet the criteria described in Sect.
10.4, recalibrate the system and reanalyze all samples from the
last time the system was in control. Verify the new calibration
curve with the QCS according to Sect. 10.4 and reanalyze all
samples measured since the last time the system was in control.
10.6 Submit a Field Blank (FB) to the laboratory for every 20 samples.
The FB may consist of a water sample (Sect. 7.2) or a known
reference solution that approximates the concentration levels
characteristic of wet deposition. The FB is poured into the
sampling vessel at the field site and undergoes identical
processing and analytical protocols as the wet deposition
sample(s). Use the analytical data obtained from the FB to
determine any contamination introduced in the field and laboratory
handling procedures. The data from the known reference solution
can be used to calculate a system precision and bias.
353.6-11
-------
10.7 Prepare and analyze a laboratory spike of a wet deposition sample
according to the guidelines provided in "Quality Assurance Manual
for Precipitation Measurement Systems" (14.6). Compare the results
obtained from spiked samples to those obtained from identical
samples to which no spikes were added. Use these data to monitor
the method percent recovery as described in Sect. 10.2.3.
10.8 Participation in performance evaluation studies is recommended for
wet deposition chemistry laboratories. The samples used for these
performance audits should contain the analytes of interest at
concentrations within the normal working range of the method. The
true values are unknown to the analyst. Performance evaluation
studies for wet deposition chemistry laboratories are conducted
semiannually by the USEPA Performance Evaluation Branch, Quality
Assurance Division, Research Triangle Park, NC 27711.
11. PROCEDURE
11.1 REDUCTION COLUMN
11.1.1 Wash about 5 g of cadmium granules with five 10 mL aliquots
of 1.0 N HC1. Rinse with equal volumes of water (Sect.
7.2). The cadmium should be a silver color after cleaning.
11.1.2 Wash the cadmium with five 10 mL aliquots of CuSO4 until
colloidal copper particles form and no blue color remains.
Wash the granules thoroughly with equal portions of water
(Sect. 7.2) to remove the colloidal copper. The cadmium
should appear black after cleaning.
11.1.3 Fill the column with water (Sect. 7.2). Add the prepared
cadmium to the column and .plug the open ends with 80 mesh
teflon screen or glass wool.
Note: Do not allow air to enter the column or let the
cadmium become dry. The presence of air bubbles reduces
column efficiency. If air enters the column, repeat the
above procedure.
11.1.4 Fill all pump tubes with reagents before inserting the
column in the analytical stream to prevent the introduction
of air bubbles. Make sure no air is present in any of the
transmission lines leading to the column.
11.1.5 For initial activation of the column, continuously sample a
100 mg/L nitrate standard for five minutes. Rinse with
sampler rinse water (sect. 7.10) for at least ten minutes.
11.2 A reduction column prepared according to Sect. 11.1 should last fbr
300-400 samples. The cadmium in the column can be reactivated and
' used again to prepare a new column by repeating the procedure
outlined in Sect. 11.1.
*
11.3 Optimize the instrument each day according to Sect. 9.1.
353.6-12
-------
11.4 Prepare all standards and construct a calibration curve according
to Sects. 9.2 and 9.3.
11.5 After the calibration curve is established, analyze the QCS. If
the measured value for the .QCS is not within the specified limits
(Sect. 10.2.2), refer to Sect. 10.4.
11.6 Load the sampler tray and begin analysis.
11.7 If the peak height response exceeds the working range of the
system, dilute the sample with zero standard and reanalyze.
11.8 When analysis is complete, rinse the cadmium reduction column with
NH Cl for one minute, remove the reduction column, and seal each
end of the column tubing to avoid exposure of the cadmium to air.
Alternatively, the system can be equipped with a switching valve to
allow the operator to take the column off-line. Rinse the
remainder of the system with sampler rinse water (Sect. 7.10) for
30 minutes.
12. CALCULATIONS
12.1 Calculate a linear least squares fit of the standard concentration
as a function of the measured peak height. The linear least
squares equation is expressed as follows:
where: y - standard concentration in mg/L
x * peak height measured
BO » y-intercept calculated from: y - B.x
B- * slope calculated from:
n n
2 (x - x) (y - 7)/ Ł (xi - x)
i=»l i=l
where: x = mean of peak heights measured
y » mean of standard concentrations
n = number of samples
The correlation coefficient should be 0.9990 or greater. Determine
the concentration of nitrate-nitrite from the calibration curve.
12.2 If the relationship between standard concentration and measured
peak height is nonlinear, use a second degree polynomial least
squares equation to derive a curve with a correlation _>0.9990.
The second degree polynomial equation is expressed as follows:
A computer is necessary for the derivation of this function.
Determine the concentration of nitrate-nitrite from the calibration
curve .
353.6-13
-------
12.3 An integration system may also be used to provide a direct readout
of the concentration of nitrate-nitrite.
12.4 If the concentration of nitrate alone is desired, determine the
content of nitrite in the samples by eliminating the reduction
column from the system. Subtract the nitrite from the total
nitrate-nitrite concentration.
12.5 Report data in mg/L as NO ~. Do not report data lower than the
lowest calibration standard.
13. PRECISION AND BIAS
13.1 The mean percent recovery and mean bias of this method were
determined from the analysis of spiked wet deposition samples
according to ASTM Standard Practice D4210, Annex A4 (14.7). The
results are summarized in Table 1. No statistically significant
biases were found.
13.2 Single-operator precision and bias were obtained from the analysis
of quality control check samples that approximated the levels
common to wet deposition samples. These results reflect the
accuracy that can be expected when the method is used by a
competent operator. These data are presented in Table 2.
14. REFERENCES
14.1 Annual Book of ASTM Standards, Part 31, "Excerpts from Standard
for Metric Practice," Standard E 380-79, 1982, pp. 679-694.
14.2 "Trace Metals in Water Supplies: Occurrence, Significance, and
Control," American Water Works Association, Illinois Environmental
Protection Agency, Vol. 71, No. 108, April 29, 1974.
14.3 "Safety in Academic Chemistry Laboratories," American Chemical
Society Publication, Committee on Chemical Safety, 3rd Edition,
1979.
14.4 Annual Book of ASTM Standards, Part 31, "Standard Specification
for Reagent Water," Standard D 1193-77, 1982, p. 39.
14.5 Peden, M. E. and Skowron, L. M., "Ionic Stability of Precipitation
Samples," Atmos. Environ. 12, 1978, pp. 2343-2349.
14.6 Topol, L. E., Lev-On, M., Flanagan, J., Schwall, R. J., Jackson, A.
E., Quality Assurance Manual for Precipitation Measurement
Systems, 1985, U.S. Environmental Protection Agency, Environmental
Monitoring Systems Laboratory, Research Triangle Park, NC 27711.
14.7 Annual Book of ASTM Standards, Section 11, Vol. 11.01 (1),
"Practice for Intralaboratory Quality Control Procedures and a
Discussion of Reporting Low-Level Data," Standard D4210 Annex A4,
1983, pp. 15-16.
353.6-14
-------
Table 1. Single-Operator Precision and Bias for Nitrate-Nitrite
Determined from Analyte Spikes of Wet Deposition Samples.
Analyte
Amount
Added,
mg/L
Mean
Percent
Recovery
Mean
Bias,
mg/L
Standard
Deviation,
mg/L
Statistically
Significant
Bias?
Nitrate
0.56
1.21
9
10
94.5
96.3
-0.03
-0.04
0.03
0.03
No
No
a. Number of replicates
b. 95% Confidence Level
353.6-15
-------
Table 2. Single-Operator Precision and Bias for Nitrate
Determined from Quality Control Check Samples.
Theoretical Measured Precision,
Concentration, Concentration, Bias, s, RSD,
mg/L mg/L n mg/L % mg/L %
0.62 0.63 88 0.01 1.6 0.02 3.2
0.80 0.78 24 -0.02 -2.5 0.01 1.3
3.17 3.11 88 -0.06 -1.9 0.07 2.2
3.54 3.44 23 -0.10 -2.8 0.05 1.4
The above data were obtained from records of measurements made under the
direction of the NADP/NTN quality assurance program.
a. Number of replicates
353.6-1G
-------
Figure 1. Percentile Concentration Values Obtained from
Wet Deposition Samples: Nitrate-Nitrite
I
Cd
M
s
100
90
80
70
60
50
40
30
20
10
0
1.00
3.00 5.00
CONCENTRATION (mg/L)
7.00
353.6-17
-------
Figure 2. Nitrate-Nitrite Sampling and Analytical
System — Segmented Flow.
5
Turn
Mixing
Coil
Pump Tube
Colors
Red
Red
Red
Red
Grn
Grn
Orn
Orn
Blu
Blu
Orn
Wht
Orn
Wht
Orn
Orn
PROPORTIONING
PUMP
Flow Rate
(mL/min)
0.80
•debubbler
waste
0.80 from
flow
cell
2-°0 sampler
rinse
/"A
,.,„„ . y
water \ /
sample^ • ' j X^^**—
1.80 ammonium
~~~" chloride
0.23
•air
0.23
• air
0.42 color
reagent
COLORIMETER
520 nm
Rate:
40/hr
Sampling Volume:
0.13 mL
Sample to Rinse Ratio:
1:4
(18 second sample,
72 second rinse)
353.6-18
-------
Appendix I
METHOD 325.6 — CHLORIDE IN VET DEPOSITION BY AUTOMATED COLORIMETRIC
DETERMINATION USING THIOCYANATE
1-1
-------
Method 325.6 — Chloride in Wet Deposition by Automated
Colorimetric Determination Using Thiocyanate
March 1986
Performing Laboratory:
Brigita Demir
Susan R. Bachman
Carla Jo Brennan
Mark E. Peden
Illinois State Water Survey
Analytical Chemistry Unit
2204 Griffith Drive
Champaign, Illinois 61820
Sponsoring Agency:
John D. Pfaff, Project Officer
Inorganic Analysis Section
Physical and Chemical Methods Branch
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
325.6-1
-------
INDEX
Section
Number Subject
1 Scope and Application
2 Summary of Method
3 Definitions
4 Interferences
5 Safety
6 Apparatus and Equipment
7 Reagents and Consumable Materials
8 Sample Collection, Preservation, and Storage
9 Calibration and Standardization
10 Quality Control
11 Procedure
12 Calculations
13 Precision and Bias
14 References
TABLES
1. Single-Operator Precision and Bias for Chloride Determined from Analyte
Spikes of Wet Deposition Samples.
2. Single-Operator Precision and Bias for Chloride Determined from Quality
Control Check Samples.
FIGURES
1. Percentile Concentration Values Obtained from Wet Deposition Samples:
Chloride.
2. Chloride Sampling and Analytical System — Segmented Flow.
325.6-2
-------
1. SCOPE AND APPLICATION
1.1 This method is applicable to the automated colorimetric determination
of chloride in wet deposition samples by reaction with thiocyanate.
1.2 The term "wet deposition" is used in this method to designate rain,
snow, dew, sleet, and hail,
1.3 The method detection limit (MDL) determined from replicate analyses
of a calibration standard containing 0.10 mg/L chloride is 0.03 mg/L.
The concentration range of this method is 0.03-2.00 mg/L as-Cl~.
1.4 Figure 1 represents a cumulative frequency percentile chloride
concentration plot obtained from analyses of over five thousand wet
deposition samples. These data may be used as an aid in the
selection of appropriate calibration standard concentrations.
2. SUMMARY OF METHOD
2.1 A sample is mixed with a solution of saturated mercuric thiocyanate
and ferric ammonium sulfate. Mercuric thiocyanate reacts with
chloride ions in the sample to form mercuric chloride. The liberated
thiocyanate ions then react with ferric ions to form a colored ferric
thiocyanate complex. The intensity of the color of this complex
is proportional to the concentration of chloride in solution. After
color development, a flowcell receives the stream for measurement. A
light beam of a wavelength characteristic of the ferric thiocyanate
complex is passed through the solution. The light energy measured by
photodetectors is a function of the concentration of chloride ion in
the sample. Beer's Law is used to relate the measured transmittance
to concentration:
log(l/T) = abc
where: T =* transmittance
a = absorptivity
b » length of light path
c » concentration of absorbing species (mg/L)
A calibration curve is constructed using standard solutions
containing known concentrations of chloride. From this curve, the
concentration of chloride in a wet deposition sample is determined.
3. DEFINITIONS
3.1 COLORIMETRY — the measurement of light transmitted by a colored
complex as a function of concentration.
3.2 For definitions of other terms used in these methods, refer to the
glossary. For an explanation of the metric system including units,
symbols, and conversion factors see American Society for Testing and
Materials (ASTM) Standard E 380, "Metric Practices" (14.1).
325.6-3
-------
4. INTERFERENCES
4.1 Sample color absorbing in the wavelength range of 470-490 nm will
increase the measured concentration of chloride in the sample. Wet
deposition samples are generally colorless, therefore, this type of
interference is rare.
4.2 Other halogens such as bromide and fluoride present in the sample
will compete with chloride ions to complex the mercury from the
mercuric thiocyanate reagent. The excess thiocyanate ions liberated
form the colored ferric thiocyanate complex, resulting in an elevated
concentration of chloride determined in the sample.
5. SAFETY
5.1 The calibration standards and sample types used in this method pose
no hazard to the analyst. Many of the reagents, however, require
special precautions as detailed below. Use a fume hood, protective
clothing, and safety glasses when handling concentrated nitric 'Sect.
7.4) and sulfuric acids (Sect. 7.7).
5.2 Use a fume hood and protective gloves when preparing the ferric
ammonium sulfate solution (Sect. 7.4). Vapors produced by the
reaction between ferric ammonium sulfate and nitric acid are
hazardous.
5.3 Anytime the mercuric thiocyanate solution (Sect. 7.5) is prepared,
wear gloves and avoid all skin contact with this poisonous reagent.
CAUTION: When discarding the mercuric sulfide waste, follow the
precautions detailed in Sect. 11.7.
5.4 Follow American Chemical Society guidelines regarding the safe
handling of chemicals user* in this method (14.2).
6. APPARATUS AND EQUIPMENT
6.1 AUTOMATED COLORIMETRIC INSTRUMENT — Select and assemble an
analytical system consisting of the following:
6.1.1 Sampler.
6.1.2 Proportioning Pump.
6.1.3 Analytical Cartridge.
6.1.4 Colorimeter with a 480 nm wavelength setting. Ensure that the
colorimeter is equipped with photodetectors having maximum
sensitivity at this wavelength setting. A 15 mm flow cell is
adequate to achieve the MDL stated in Sect. 1.3.
6.1.5 Strip Chart Recorder (or other data acquisition device).
6.1.6 Printer (optional).
325.6-4
-------
6.2 Wherever possible, use glass transmission lines with an inside
diameter of 1.86 mm (0.073 inches) in the analytical cartridge and
colorimeter. Glass yields a more uniform sample flow and does not
degrade as quickly as other tubing materials. When connecting two
glass lines, ensure that the ends are abutted. To minimize pulsing
of the analytical stream, maintain uniform inside diameter throughout
all transmission tubing. Minimize the length of all transmission
tubing to optimize the performance of the hydraulic system.
6.3 Enclose the sampler with a dust cover to prevent contamination.
6.4 To prevent the intake of any precipitates from the reagents, install
intake filters at the end of the transmission lines that are used to
transport the reagents from their respective containers to the
proportioning pump.
6.5 LABORATORY FACILITIES — Laboratories used for the analysis of
wet deposition samples should be free from external sources of
contamination. The use of laminar flow clean air workstations is
recommended for sample processing and preparation to avoid the
introduction of airborne contaminants. Samples should always be
capped or covered prior to analysis. A positive pressure
environment within the laboratory is also recommended to minimize
the introduction of external sources of contaminant gases and
particulates. Windows within the laboratory should be kept closed
at all times and sealed if air leaks are apparent. The use of
disposable tacky floor mats at the entrance to the laboratory is
helpful in reducing the particulate loading within the room.
7. REAGENTS AND CONSUMABLE MATERIALS
7.1 PURITY OF REAGENTS — Use reagent grade chemicals for all solutions.
All reagents shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society (ACS), where
such specifications are available.
7.2 PURITY OF WATER — Use water conforming to ASTM Specification D
1193, Type II (14.3). Point of use 0.2 micrometer filters are
recommended for all faucets supplying water to prevent the
introduction of bacteria and/or ion exchange resins into reagents,
standard solutions, and internally formulated quality control check
solutions.
7.3 CHLORIDE SOLUTION, STOCK (1.0 mL = 1.0 mg CD — Dissolve 1.6485 g
of sodium chloride (NaCl), dried at 105 C for one hour, in water
(Sect. 7.2) and dilute to 1 L. Store at room temperature in a high
density polyethylene or polypropylene container.
* fi-
-------
7.4 FERRIC AMMONIUM SULFATE SOLUTION -- Dissolve 60 g of ferric ammonium
sulfate (FeNH4(S04),•12(H20) in approximately 500 mL of water
(Sect. 7.2). Add 355 mL of concentrated nitric acid (HNO-, sp gr
1.42) and dilute to 1 L with water (Sect. 7.2). Filter the solution
and add 0.5 mL Brij-35 or a similar wetting agent. This solution is
stable for one year when stored at room temperature in an amber glass
container.
CAUTION: The vapors produced when ferric ammonium sulfate is
dissolved in acid are hazardous. Refer to Sect. 5.2 for an
explanation of necessary safety precautions.
7.5 MERCURIC THIOCYANATE SOLUTION (Saturated) — Add 5 g of mercuric
thiocyanate (Hg(SCN)-) to water (Sect. 7.2) and dilute to 1 L.
Decant and filter a 200 mL portion of the saturated supernatant
liquid to use as the reagent. Store the solution at room temperature
in a high density polyethylene or polypropylene container.
CAUTION: Mercuric thiocyanate solution is a poisonous reagent.
Avoid all skin contact with this solution. Refer to Sect. 5.3 for
an explanation of necessary safety precautions.
7.6 SAMPLER RINSE WATER -- Add 0.5 mL Brij-35 or another suitable wetting
agent to 1 L of water (Sect. 7.2).
7.7 SULFURIC ACID (7.2 N) — Add 200 mL of sulfuric acid (H2S04, sp
gr 1.84) to water (Sect. 7.2) and dilute to 1 L. Store at room
temperature in a glass container.
7.8 THIOACETAMIDE SOLUTION (13% w/v) — Dissolve 130 g of thioacetamide
(CH SCNH ) in water (Sect. 7.2) and dilute to 1 L. This solution
is stable for one year when stored at room temperature in a glass
container.
7.9 SAMPLE CONTAINERS — Use pol'yolefin sample cups or glass test tubes
that have been thoroughly rinsed with water (Sect. 7.2) before use.
8. SAMPLE COLLECTION, PRESERVATION AND STORAGE
8.1 Collect samples in high density polyethylene (HDPE) containers that
have been thoroughly rinsed with ASTM Type II water (7.2). Do not
use strong mineral acids or alkaline detergent solutions for cleaning
collection vessels. Residual acids may remain in the polyethylene
matrix and slowly leach back into the sample. Alkaline detergents
may also leave residues that may affect the sample chemistry. Cap
collection bottles after cleaning to prevent contamination from
airborne contaminants; air dry collection buckets in a laminar flow
clean air workstation and wrap in polyethylene bags prior to use. If
a laminar flow workstation is not available, pour out any residual
.rinse water and bag the buckets immediately. Do not dry the bucket
interior by any method other than air drying in a laminar flow clean
air workstation.
325.6-6
-------
8.2 The frequency of sample collection and the choice of sampler design
are dependent on the monitoring objectives. In general, the use of
wet-only samplers is recommended to exclude dry deposition
contributions, minimize sample contamination, retard evaporation,
and enhance sample stability. Sample collection frequency may vary
from subevent to monthly sampling periods. Collection periods of
more than one week are not recommended since sample integrity may be
compromised by longer exposure periods.
8.3 Chloride ion has been found to be stable in HOPE bottles for six
weeks without special preservation techniques such as filtration or
refrigeration (14.4).
9. CALIBRATION AND STANDARDIZATION
9.1 INSTRUMENT OPTIMIZATION
9.1.1 For a flow segmented system with a concentration range .from
0.03-2.00 mg/L as chloride, assemble the sampling and
analytical system as shown in Figure 2.
9.1.2 Use flow rated polyvinyl chloride (PVC) or polyethylene pump
and transmission tubing throughout the sampling and analytical
system. Use polyethylene tubing to transport the ferric
ammonium sulfate reagent. This solution will degrade PVC
tubing quickly. Check the tubing for chemical buildup,
splits, cracks, and deformations before beginning each day's
analysis. Change pump tubes' after 50 hours of operation.
Change transmission tubing after 100 hours of operation or
when uneven flow patterns are observed. Replace the tubing
used to transport the ferric ammonium sulfate reagent daily.
9.1.3 Optimize the tension of the pump tubes according to
manufacturer's recommendations.
9.1.4 Set the wavelength of the colorimeter to 480 nm. Allow the
colorimeter to warm up for 30 minutes while pumping sampler
rinse water (Sect.' 7.6) and reagents through the system.
After a stable baseline has been obtained, adjust the recorder
to maximize the full-scale response.
9.1.5 Sample at a rate of 40 samples/hour with a 1:4 sample to
rinse ratio. This sampling rate provides good peak
separation. Adjust the colorimeter to maximize sensitivity
while minimizing instrument noise. Refer to the
manufacturer's recommendations.
325.6-7
-------
9.2 CALIBRATION SOLUTIONS
9.2.1 Five calibration solutions and one zero standard are needed to
generate a suitable calibration curve. The lowest calibration
solution should contain chloride at a concentration greater
than or equal to the method detection limit. The highest
solution should approach the expected upper limit of
concentration of chloride in wet deposition. Prepare the
remaining solutions such that they are evenly distributed
throughout the concentration range. Suggested calibration
standards for chloride are as follows: zero, 0.03, 0.50,
1.00, 1.50, and 2.00 mg/L as Cl".
9.2.2 Prepare all calibration standards by diluting the stock
standard (Sect. 7.3) with water (Sect. 7.2). Use glass
(Class A) or plastic pipettes that are within the bias and
precision tolerances specified by the manufacturer. The
standards are stable for one month when stored at room
temperature in high density polyethylene or polypropylene
containers,
9.3 CALIBRATION CURVE
9.3.1 Analyze the standard containing the highest, concentration of
chloride and adjust the colorimeter calibration control to
obtain full-scale deflection on the recorder. Use the zero
standard to set the instrument baseline. If a printer is
used, adjust it to read the correct concentration. Analyze
all the standards and construct a calibration curve according
to Sect. 12. After every 30 samples and at the end of the
day's analyses, reconstruct the entire calibration curve.
9.3.2 Verify the calibration curve after every ten samples and at
the end of each day's analyses according to Sect. 10.5.
10. QUALITY CONTROL
10.1 Each laboratory using this method should develop formalized quality
control protocols to continually monitor the bias and precision of
all measurements. These protocols are required to ensure that the
measurement system is in a state of statistical control. Estimates
of bias and precision for wet deposition analyses cannot be made
unless these control procedures are followed. Detailed guidelines
for the development of quality assurance and quality control
protocols for wet deposition measurement systems are published in a
manual available from the United States Environmental Protection
Agency, Research Triangle Park, NC 27711 (14.5). Included in this
manual are procedures for the development of statistical control
charts for use in monitoring bias and precision as well as
recommendations for the introduction of reagent blanks, laboratory
duplicates, field duplicates, spike samples, and performance
evaluation samples. These guidelines are to be used by all
laboratories involved with wet deposition measurements.
325.6-8
-------
10.2 ESTABLISHMENT OF WARNING AND CONTROL LIMITS — Warning and control
limits are used to monitor drift in the calibration curve, analyses
of quality control check samples (QCS), and measured recoveries
from laboratory spikes.
10.2.1 Calibration Curve — After a calibration curve has been
constructed according to Sect. 12, reanalyze additional
aliquots of the low and high concentration standards.
Calculate the concentrations using the previously derived
calibration curve. Repeat this procedure until at least
ten determinations at each concentration level have been
made. These data should be collected on ten different days
to provide a realistic estimate of the method variability.
Calculate a standard deviation (s) at each concentration
level. Use the nominal standard concentration as the mean
value (x) for determining the control limits. A warning
limit of x _* 2s and a control limit of x _+ 3s should be
used. Reestablish these limits whenever instrumental
operating conditions change.
10.2.2 Quality Control Check Samples (QCS) — Calculate warning
and control limits for QCS solutions from a minimum of ten
analyses performed on ten days. Use the calculated
standard deviation (s) at each QCS concentration level to
develop the limits as described in Sect. 10.2.1. Use the
certified or NBS traceable concentration as the mean
(target) value. Constant positive or negative measurements
with respect to the true value are indicative of a method
or procedural bias. Utilize the data obtained from QCS
measurements as in Sect. 10.4 to determine when the
measurement system is out of statistical control. The
standard deviations used to generate the QCS control limits
should be comparable to the single operator precision
reported in Table 2. Reestablish new warning and control
limits whenever instrumental operating conditions are
varied or QCS concentrations are changed.
10.2.3 Laboratory Spike Solutions — A minimum of ten analyte
spikes of wet deposition samples is required to develop a
preliminary data base for the calculation of warning and
control limits for spike recovery data. Select the spike
concentration such that the working range of the method
will not be exceeded. Samples selected for the initial
spike recovery study should represent the concentration
range common to wet deposition samples in.order to reliably
estimate the method accuracy. Calculate a mean and
standard deviation of the percent recovery data using the
formulas provided in the glossary. Determine warning and
control limits using ^2s and jOs, respectively. If
the data indicate that no significant method bias exists
(14.6), the 100 percent recovery is used as the mean
percent recovery. Where a significant bias is determined
325.6-9
-------
at the 95% confidence level, the control limits are
centered around the bias estimate. Routine spiked sample
analyses that yield percent recovery data outside of the
control limits are an indication of matrix interferences
that should be resolved before routine analyses are
continued.
10.2.4 All warning and control limits should be reevaluated on a
continual basis as additional data are collected during
routine analyses. The limits should be broadened or
narrowed if a recalculated standard deviation under similar
operating conditions provides a different estimate of the
procedure variability.
10.3 Monitor the cleaning procedure by pouring a volume of water (Sect.
7.2) that approximates the median sample size into the collection
vessel. Allow the water to remain in the sealed or capped
collection container for at least 24 hours and determine the
chloride concentration. If the solution concentration exceeds the
MDL, a contamination problem is indicated in the cleaning
procedure. Take corrective action before the sampling containers
are used for the collection of wet deposition.
10.4 Analyze a quality control check sample (QCS) after the calibration
curve has been established. This sample may be formulated in the
laboratory or obtained from the National Bureau of Standards (NBS
Standard Reference Material 2694, Simulated Rainwater). Verify the
accuracy of internally formulated QCS solutions with an NBS
traceable standard before acceptance as a quality control check.
The check sample(s) selected must be within the range of the
calibration standards. If the measured value for the QCS falls
outside of the ^3s limits (Sect. 10.2.2), or if two successive
QCS checks are outside of the +2s limits, a problem is indicated
with the system or the calibration procedure. Corrective action
should be initiated to bring the results of the QCS within the
established control limits. Plot the data obtained from the QCS
checks on a control chart for routine assessments of bias and
precision.
10.5 Verify the calibration curve after a maximum of ten samples and at
the end of each day's analyses. Analyze calibration standards at
the low and high ends of the working range. If the routine
calibration checks do not meet the criteria described in Sect.
10.4, recalibrate the system and reanalyze all samples from the
last time the system was in control. Verify the new calibration
curve with the QCS according to Sect. 10.4 and reanalyze all
samples measured since the last time the system was in control.
325.6-10
-------
10.6 Submit a Field Blank (FB) to the laboratory for every 20 samples.
The FB may consist of a water sample (Sect. 7.2) or a known
reference solution that approximates the concentration levels
characteristic of wet deposition. The FB is poured into the
sampling vessel at the field site and undergoes identical
processing and analytical protocols as the wet deposition
sample(s). Use the analytical data obtained from the FB to
determine any contamination introduced in the field and laboratory
handling procedures. The data from the known reference solution
can be used to calculate a system precision and bias.
10.7 Prepare and analyze a laboratory spike of a wet deposition sample
according to the guidelines provided in "Quality Assurance Manual
for Precipitation Measurement Systems" (14.5). Compare the results
obtained from spiked samples to those obtained from identical
samples to which no spikes were added. Use these data to monitor
the method percent recovery as described in Sect. 10.2.3.
10.8 Participation in performance evaluation studies is recommended for
wet deposition chemistry laboratories. The samples used for these
performance audits should contain the analytes of interest at
concentrations within the normal working range of the method. The
true values are unknown to the analyst. Performance evaluation
studies for wet deposition chemistry laboratories are conducted
semiannually by the USEPA Performance Evaluation Branch, Quality"
Assurance Division, Research Triangle Park, NC 27711.
11. PROCEDURE
11.1 Optimize the instrument each day according to Sect. 9.1.
11.2 Prepare all standards and construct a calibration curve according
to Sect. 9.2 and 9.3.
11.3 After the calibration curve is established, analyze the QCS. If
the measured value for the QCS is not within the specified limits
(Sect. 10.2.2), refer to Sect. 10.4.
11.4 Load the sampler tray and begin analysis.
11.5 If the peak height response exceeds the working range of the
system, dilute the sample with zero standard and reanalyze.
11.6 When analysis is complete, rinse the system with sampler rinse
water (Sect. 7.6) for 15 minutes. Rinse with 7.2 N sulfuric acid
(Sect. 7.7) for 15 minutes, and repeat the water rinse for 15
minutes.
325.6-11
-------
11.7 Collect chloride waste from the flowcell, place in a fume hood, and
add 20 mL of 13% thioacetamide solution per liter of chloride
waste. Cap the container and mix well. A precipitate, of mercuric
sulfide will form. After 24 hours, filter the solution in a fume
hood. Discard the filtrate and store the residue of mercuric
sulfide in a closed glass container for later disposal at a
hazardous waste treatment/storage facility.
12. CALCULATIONS
12.1 Calculate a linear least squares fit of the standard
concentrations as a function of the measured peak height. The
linear least squares equation is expressed as follows:
y = BQ * BLX
where: y = standard concentration in mg/L
x = peak height measured
B = y-intercept calculated from: 7 - B x
B- = slope calculated from:
n n
2 (x - x) (y - y)/ Ł (x. - x)
i=l i-1 L
where: x = mean of peak heights measured
y = mean of standard concentrations
n = number of samples
The correlation coefficient should be 0.9990 or greater. Determine
the concentration of chloride from the calibration curve.
12.2 If the relationship between standard concentration and measured
peak height is nonlinear, use a second degree polynomial least
squares equation to derive a curve with a correlation _>0-9990.
The second degree polynomial equation is expressed as follows:
y = B x + B x + B
A computer is necessary for the derivation of this function.
Determine the concentration of chloride from the calibration curve.
12.3 An integration system may also be used to provide a direct readout
of the concentration of chloride.
12.4 Report data in mg/L as Cl. Do not report data lower than the
lowest calibration standard.
325.6-12
-------
13. PRECISION AND BIAS
13.1 The mean percent recovery and mean bias of this method were
determined from the analysis of spiked wet deposition samples
according to ASTM Standard Practice D4210, Annex A4 (14.6). The
results are summarized in Table 1. A small but statistically
significant bias of 0.04 mg/L was determined at a spike
concentration of 0.41 mg/L. No statistically significant bias was
present at a spike concentration of 0.14 mg/L.
13.2 Single-operator precision and bias were obtained from the analysis
of quality control check samples that approximated the levels
common to wet deposition samples. These results reflect the
accuracy that can be expected when the method is used by a
competent operator. These data are presented in Table 2.
14. REFERENCES
14.1 Annual Book of ASTM Standards, Part 31, "Excerpts from Standard
for Metric Practice," Standard E 380-79, 1982, pp. 679-694.
14.2 "Safety in Academic Chemistry Laboratories," American Chemical
Society Publication, Committee on Chemical Safety, 3rd Edition,
1979.
14.3 Annual Book of ASTM Standards, Part 31, "Standard Specification
for Reagent Water," Standard D 1193-77, 1982, p. 39.
14.4 Peden, M. E. and Skowron, L. M., "Ionic Stability of Precipitation
Samples," Atmos. Environ. 12, 1978, pp. 2343-2349.
14.5 Topol, L. E., Lev-On, M., Flanagan, J., Schwall, R. J., Jackson, A.
E., Quality Assurance Manual for Precipitation Measurement
Systems, 1985, U.S. Environmental Protection Agency, Environmental
Monitoring Systems Laboratory, Research Triangle Park, NC 27711.
14.6 Annual Book of ASTM Standards, Section 11, Vol. 11.01 (1),
"Practice for Intralaboratory Quality Control Procedures and a
Discussion of Reporting Low-Level Data," Standard D4210 Annex A4,
1983, pp. 15-16.
325.6-13
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Table 1. Single-Operator Precision and Bias for Chloride
Determined from Analyte Spikes of Wet Deposition Samples.
Analyte
Chloride
Amount
Added,
mg/L n
0.14 10
0.41 10
Mean
Percent
Recovery
107.1
109.5
Mean
Bias,
mg/L
0.01
0.04
Standard
Deviation,
mg/L
0.01
0.01
Statistically
Significant
Bias?
No
Yes
a. Number of replicates
b. 95% Confidence Level
325.6-14
-------
Table 2. Single-Operator Precision and Bias for Chloride
Determined from Quality Control Check Samples.
Theoretical Measured Precision,
Concentration, Concentration, Bias, s, RSD,
mg/L mg/L n mg/L % mg/L %
0.85 0.88 105 0.03 3.5 0.02 2.3
1.78 1.87 105 0.09 5.1 0.03 1.6
The above data were obtained from records of measurements made under the
direction of the NADP/NTN quality assurance program.
a. Number of replicates
325.6-15
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Appendix J
METHOD 365.6 — ORTHOPHOSPHATE IN WET DEPOSITION BY AUTOMATED
COLORIMETRIC DETERMINATION USING ASCORBIC ACID REDUCTION
J-l
-------
Method 365.6 — Orthophosphate in Wet Deposition by
Automated Colorimetric Determination
Using Ascorbic Acid Reduction
March 1986
Performing Laboratory:
Susan R. Bachman
Michael J. Slater
Carla Jo Brennan
Mark E. Peden
Illinois State Water Survey
Analytical Chemistry Unit
2204 Griffith Drive
Champaign, Illinois 61820
Sponsoring Agency:
John D. Pfaff, Project Officer
Inorganic Analysis Section
Physical and Chemical Methods Branch
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
365.6-1
-------
INDEX
Section
Number Subject
1 Scope and Application
2 Summary of Method
3 Definitions
4 Interferences
5 Safety
6 Apparatus and Equipment
7 Reagents and Consumable Materials
8 Sample Collection, Preservation, and Storage
9 Calibration and Standardization
10 Quality Control
11 Procedure
12 Calculations
13 Precision and Bias
14 References
TABLES
Single-Operator Precision and Bias for Orthophosphate Determined from
Analyte Spikes of Wet Deposition Samples.
Single-Operator Bias and Precision for Orthophosphate Determined from
Quality Control Check Samples.
FIGURES
1. Orthophosphate Sampling and Analytical System — Segmented Flow,
365.6-2
-------
1. SCOPE AND APPLICATION
1.1 This method is applicable to the automated colorimetric determination
of orthophosphate in wet deposition samples by ascorbic acid
reduction.
1.2 The term "wet deposition" is used in this method to designate rain,
snow, dew, sleet, and hail.
1.3 The method detection limit (MDL) determined from replicate analyses
of a calibration standard containing 0.03 mg/L orthophosphate is
0.02 mg/L. The concentration range of this method is 0.02-0.25 mg/L
as P04'J.
1.4 The maximum concentration of phosphate observed from analyses of over
five thousand wet deposition samples was 12.60 mg/L. Over 90% of the
samples, however, had phosphate concentrations below the MDL.
2. SUMMARY OF METHOD
2.1 A filtered sample is mixed with an acidified solution of ammonium
molybdate containing ascorbic acid and antimony to form a
phosphomolybdenum blue complex. The intensity of the color complex
is proportional to the concentration of orthophosphafce in solution.
The solution is pumped through a 37 C controlled temperature
heating bath. After color development, a flowcell receives the
stream for measurement. A light beam of a wavelength characteristic
of the phosphomolybdenum blue complex is passed through the solution.
The light energy measured by a photodetector is a function of the
concentration of orthophosphate ion in the sample. Beer's Law is
used to relate the measured transmittance to concentration:
log(l/T) = abc
where: T » transmittance
a = absorptivity
b = length of light path
c » concentration of absorbing species (mg/L)
A calibration curve is constructed using standard solutions
containing known concentrations of orthophosphate. From this curve,
the concentration of orthophosphate in a wet deposition sample is
determined.
3. DEFINITIONS
3.1 COLORIMETRY — the measurement of light transmitted by a colored
complex as a function of concentration.
3.2 For definitions of other terms used in these methods, refer to the
glossary. For an explanation of the metric system including units,
symbols, and conversion factors see American Society for Testing and
Materials (ASTM) Standard E 380, "Metric Practices" (14.1).
365.6-3
-------
4. INTERFERENCES
4.1 Sample color absorbing in the wavelength range of 870-890 nm will
increase the measured concentration of orthophosphate in the sample.
Wet deposition samples are generally colorless, therefore, this type
of interference is rare.
5. SAFETY
5.1 The calibration standards, sample types, and most reagents used in
this method pose no hazard to the analyst. Use a fume hood,
protective clothing, and safety glasses when handling concentrated
hydrochloric acid (Sect. 7.6) and sulfuric acid (Sect. 7.8).
5.2 Follow American Chemical Society guidelines regarding the safe
handling of chemicals used in this method (14.2).
6. APPARATUS AND EQUIPMENT
6.1 AUTOMATED COLORIMETRIC INSTRUMENT ~ Select and assemble an
analytical system consisting of the following:
6.1.1 Sampler.
6.1.2 Proportioning Pump.
6.1.3 Analytical Cartridge.
6.1.4 Heating Bath (37 C) equipped with an 8 mL capacity glass
heating coil.
6.1.5 Colorimeter with an 880 nm wavelength setting. Ensure that
the colorimeter is equipped with photodetectors having maximum
sensitivity at this wavelength setting. A 50 mm flow cell is
required to achieve the MDL stated in Sect. 1.3.
6.1.6 Strip Chart Recorder (or other data acquisition device).
6.1.7 Printer (optional).
6.2 Wherever possible, use glass transmission lines in the analytical
cartridge and colorimeter. Glass yields a more uniform sample flow
and does not degrade as quickly as -other tubing materials. When
connecting two glass lines, ensure that the ends are abutted. To
minimize pulsing of the analytical stream, maintain uniform inside
diameter throughout all transmission tubing. Flexible transmission
tubing should have an inside diameter of 1.3 mm (0.051 inches).
Minimize the length of all transmission tubing to optimize the
performance of the hydraulic system.
365.6-4
-------
6.3 Enclose the sampler with a dust cover to prevent contamination.
6.4 To prevent the intake of any precipitates from the reagents, install
intake filters at the end of the transmission lines that are used to
transport the reagents from their respective containers to the
proportioning pump.
6.5 LABORATORY FACILITIES — Laboratories used for the analysis of
wet deposition samples should be free from external sources of
contamination. The use of laminar flow clean air workstations is
recommended for sample processing and preparation to avoid the
introduction of airborne contaminants. Samples should always be
capped or covered prior to analysis. A positive pressure
environment within the laboratory is also recommended to minimize
the introduction of external sources of contaminant gases and
particulates. Windows within the laboratory should be kept closed
at all times and sealed if air leaks are apparent. The use of
disposable tacky floor mats at the entrance to the laboratory is
helpful in reducing the particulate loading within the room.
7. REAGENTS AND CONSUMABLE MATERIALS
7.1 PURITY OF REAGENTS — Use reagent grade chemicals for all solutions.
All reagents shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society (ACS), where
such specifications are available.
7.2 PURITY OF WATER — Use water conforming to ASTM Specification D
1193, Type II (14.3). Point of use 0.2 micrometer filters are
recommended for all faucets supplying water to prevent the
introduction of bacteria and/or ion exchange resins into reagents,
standard solutions, and internally formulated quality control check
solutions.
7.3 AMMONIUM MOLYBDATE SOLUTION -- Dissolve 40 g of ammonium molybdate
((NH4)6Mo?024'4H20) in water (Sect. 7.2) and dilute to 1 L.
Store at room temperature in a high density polyethylene or
polypropylene container.
7.4 ANTIMONY POTASSIUM TARTRATE SOLUTION — Dissolve 3 g of antimony
potassium tartrate (K(SbO)C4H4Og'1/2H20) in water (Sect. 7.2)
and dilute to 1 L. Store at room temperature in a high density
polyethylene or polypropylene container.
7.5 ASCORBIC ACID SOLUTION — Dissolve 9.0 g of ascorbic acid
(CgHgOg) in water (Sect. 7.2) and dilute to 500 mL. This
solution is stable for two weeks when refrigerated at 4 C in a high
density polyethylene or polypropylene container.
7.6 HYDROCHLORIC ACID (1.0 N) ~ Add 83.0 mL of concentrated hydrochloric
acid (HC1, sp gr 1.19) to 900 mL of water (Sect. 7.2) and dilute to
1 L.
365.6-5
-------
7.7 ORTHOPHOSPHATE SOLUTION, STOCK (1.0 mL = 0.1 mg P04) —^Dissolve
143.47 mg of potassium phosphate (KH PO ), dried at 105 C
for one hour, in water (Sect. 7.2). Add 1 mL of chloroform
(CHC1-) and dilute to 1 L with water* (Sect. 7.2). This solution is
stable for one year when stored in a glass or a high density
polyethylene or polypropylene container at 4 C.
7.8 SULFURIC ACID (4.9 N) — Add 136 mL of concentrated sulfuric acid
(H SO sp gr 1.84) to 800 mL of water (Sect. 7.2). Allow the
solution to cool and dilute to 1 L.
7.9 COLOR REAGENT — Allow all solutions to reach room temperature before
combining as follows: to 50 mL of sulfuric acid add 15 mL of
ammonium molybdate solution, 30 mL of ascorbic acid solution, and
5 mL of antimony potassium tartrate solution. Add approximately
50 uL of Levor V or a similar wetting agent that does not contain
orthophosphate. The color reagent will remain relatively stable in a
high density polyethylene or polypropylene container for eight hours.
This reagent does, however, slowly degrade over an eight hour period
resulting in decreased sensitivity. To better preserve the reagent,
place the container in an ice water bath while analyzing samples.
7.10 SAMPLE CONTAINERS — Use polyolefin sample cups or glass test tubes
that have been rinsed thoroughly with water (Sect. 7.2) before use.
8. SAMPLE COLLECTION, PRESERVATION AND STORAGE
8.1 Collect samples in high density polyethylene (HOPE) containers that
have been thoroughly rinsed with ASTM Type II water (7.2). Do not
use strong mineral acids or alkaline detergent solutions for cleaning
collection vessels. Residual acids may remain in the polyethylene
matrix and slowly leach back into the sample. Alkaline detergents
may also leave residues that may affect the sample chemistry. Cap
collection bottles after cleaning to prevent contamination from
airborne-contaminants; air dry collection buckets in a laminar flow
clean air workstation and wrap in polyethylene bags prior to use. If
a laminar flow workstation is not available, pour out any residual
rinse water and bag the buckets immediately. Do not dry the bucket
interior by any method other than air drying in a laminar flow clean
air workstation.
8.2 The frequency of sample collection and the choice of sampler design
are dependent on the monitoring objectives. In general, the use of
wet-only samplers is recommended to exclude dry deposition
contributions, minimize sample contamination, retard evaporation,
and enhance sample stability. Sample collection frequency may vary
from subevent to monthly sampling periods. Collection periods of
more than one week are not recommended since sample integrity may be
compromised by longer exposure periods.
8.3 ' The presence of microbial activity will affect the stability of
orthophosphate concentrations in wet deposition samples. Sample
measurements should be made immediately after collection whenever
possible.
365.6-6
-------
8.3.1 Filtration of samples through a 0.45 micrometer membrane
leached with water (Sect. 7.2) is partially effective
at stabilizing orthophosphate by removal of biological
species. Refrigeration after immediate filtration is the most
reliable method to ensure sample integrity (14.4). Sample
storage time should not exceed one week.
9. CALIBRATION AND STANDARDIZATION
9.1 INSTRUMENT OPTIMIZATION
9.1.1 For a flow segmented system with a concentration range from
0.02-0.25 mg/L as orthophosphate, assemble the sampling and
analytical system as shown in Figure 1.
9.1.2 Use flow rated polyvinyl chloride or polyethylene pump and
transmission tubing throughout the sampling and analytical
system. Check the tubing for chemical buildup, splits,
cracks, and deformations before beginning each day's
analysis. Change pump tubes after 25 hours of operation.
Change transmission tubing after 50 hours of operation or when
uneven flow patterns are observed.
9.1.3 Optimize the tension of the pump tubes according to
manufacturer's recommendations.
9.1.4 Set the heating bath to 37°C. Set the wavelength of the
colorimeter to 880 run. Allow the colorimeter and heating bath
to warm up for 30 minutes while pumping water (Sect. 7.2) and
color reagent through the system. After a a stable baseline
has been obtained, adjust the recorder to maximize the
full-scale response.
9.1.5 Sample at a rate of 30 samples/hour with a 1:4 sample to rinse
ratio. This sampling rate provides good peak separation.
Adjust the colorimeter to maximize sensitivity while
minimizing instrument noise. Refer to the manufacturer's
recommendations.
9.2 CALIBRATION SOLUTIONS
9.2.1 Five calibration solutions and one zero standard are needed to
generate a suitable calibration curve. The lowest calibration
solution should contain orthophosphate at a concentration
greater than or equal to the method detection limit. The
highest solution should approach the expected upper limit of
concentration of orthophosphate in wet deposition. Prepare
the remaining solutions such that they are evenly distributed
throughout the concentration range. Suggested calibration
standards for orthophosphate are as follows: zero, 0.02,
0.04, 0.06, 0.08, and 0.10 mg/L as P0~ .
365.6-7
-------
9.2.2 Prepare all calibration standards by diluting the stock
solution (Sect. 7.7) with water (Sect. 7.2). Use glass
(Class A) or plastic pipettes that are within the bias and
precision tolerances specified by the manufacturer. Standards
with a concentration greater than 0.04 mg/L orthophosphate are
stable for one week if stored at room temperature in high
density polyethylene or polypropylene containers. Prepare
standards with 0.04 mg/L or less orthophosphate every day and
store at room temperature in high density polyethylene or
polypropylene containers.
9.3 CALIBRATION CURVE
9.3.1 Analyze the standard containing the highest concentration
of orthophosphate and adjust the colorimeter calibration
control to obtain full-scale deflection on the recorder. If a
printer is used, adjust it to read the correct concentration.
Analyze all the standards and construct a calibration curve
according to Sect. 12. After every 30 samples and at the end
of the day's analyses, reconstruct the entire calibration
curve.
9.3.2 Verify the calibration curve after every ten samples and at
the end of each day's analyses according to Sect. 10.5.
10. QUALITY CONTROL
10.1 Each laboratory using this method should develop formalized quality
control protocols to continually monitor the bias and precision of
all measurements. These protocols are required to ensure that the
measurement system is in a state of statistical control. Estimates
of bias and precision for wet deposition analyses cannot be made
unless these control procedures are followed. Detailed guidelines
for the development of quality assurance and quality control
protocols for wet deposition measurement sys-tems are published in a
manual available from the United States Environmental Protection
Agency, Research Triangle Park, NC 27711 (14.5). Included in this
manual are procedures for the development of statistical control
charts for use in monitoring bias and precision as well as
recommendations for the introduction of reagent blanks, laboratory
duplicates, field duplicates, spike samples, and performance
evaluation samples. These guidelines are to be used by all
laboratories involved with wet deposition measurements.
10.2 ESTABLISHMENT OF WARNING AND CONTROL LIMITS — Warning and control
limits are used to monitor drift in the calibration curve, analyses
of quality control check samples (QCS), and measured recoveries
from laboratory spikes.
365.6-8
-------
10.2.1 Calibration Curve ~ After a calibration curve has been
constructed according to Sect. 12, reanalyze additional
aliquots of the low and high concentration standards.
Calculate the concentrations using the previously derived
calibration curve. Repeat this procedure until at least
ten determinations at each concentration level have been
made. These data should be collected on ten different days
to provide a realistic estimate of the method variability.
Calculate a standard deviation (s) at each concentration
level. Use the nominal standard concentration as the mean
value (3<) for determining the control limits. A warning
limit of x n^ 2s and a control limit of x jf 3s should be
used. Reestablish these limits whenever instrumental
operating conditions change.
10.2.2 Quality Control Check Samples (QCS) — Calculate warning
and control limits for QCS solutions from a minimum of ten
analyses performed on ten days. Use the calculated
standard deviation (s) at each QCS concentration level to
develop the limits as described in Sect. 10.2.1. Use the
certified or NBS traceable concentration as the mean
(target) value. Constant positive or negative measurements
with respect to the true value are indicative of a method
or procedural bias. Utilize the data obtained from QCS
measurements as in Sect. 10.4 to determine when the
measurement system is out of statistical control. The
standard deviations used to generate the QCS control limits
should be comparable to the single operator precision
reported in Table 2. Reestablish new warning and control
limits whenever instrumental operating conditions are
varied or QCS concentrations are changed.
10.2.3 Laboratory Spike Solutions — A minimum of ten analyte
spikes of wet deposition samples is required to develop a
preliminary data base for the calculation of warning and
control limits for spike recovery data. Select the spike
concentration such that the working range of the method
will not be exceeded. Samples selected for the initial
spike recovery study should represent the concentration
range common to wet deposition samples in order to reliably
estimate the method accuracy. Calculate a mean and
standard deviation of the percent recovery data using the
formulas provided in the glossary. Determine warning and
control limits using jf2s and jOs, respectively. If
the data indicate thatf no significant method bias exists
(14.6), the 100 percent recovery is used as the mean
percent recovery. Where a significant bias is determined
at the 95% confidence level, the control limits are
centered around the bias estimate. Routine spiked sample
analyses that yield percent recovery data outside of the
control limits are an indication of matrix interferences
that should be resolved before routine analyses are
continued.
365.6-9
-------
10.2.4 All warning and control limits should be reevaluated on a
continual basis as additional data are collected during
routine analyses. The limits should be broadened or
narrowed if a recalculated standard deviation under similar
operating conditions provides a different estimate of the
procedure variability.
10.3 Monitor the cleaning procedure by pouring a volume of water (Sect.
7.2) that approximates the median sample size into the collection
vessel. Allow the water to remain in the sealed or capped
collection container for at least 24 hours and determine the
orthophosphate concentration. If the solution concentration
exceeds the MDL, a contamination problem is indicated in the
cleaning procedure. Take corrective action before the sampling
containers are used for the collection of wet deposition.
10.4 Analyze a quality control check sample (QCS) after the calibration
curve has been established. This sample may be formulated in the
laboratory or obtained from the National Bureau of Standards (NBS
Standard Reference Material 2694, Simulated Rainwater). Verify the
accuracy of internally formulated QCS solutions with an NBS
traceable standard before acceptance as a quality control check.
The check sample(s) selected must be within the range of the
calibration standards. If the measured value for the QCS falls
outside of the +2s limits (Sect. 10.2.2), or if two successive
QCS checks are outside of the jf2s limits, a problem is indicated
with the system or the calibration procedure. Corrective action
should be initiated to bring the results of the QCS within the
established control limits. Plot the data obtained from the QCS
checks on a control chart for routine assessments of bias and
precision.
10.5 Verify the calibration curve after a maximum of ten samples and at
the end of each day's analyses. Analyze calibration standards at
the low and high ends of the working range. If the routine
calibration checks do not meet the criteria described in Sect.
10.4, recalibrate the system and reanalyze all samples from the
last time the system was in control. Verify the new calibration
curve with the QCS according to Sect. 10.4 and reanalyze all
samples measured since the last time the system was in control.
10.6 Submit a Field Blank (FB) to the laboratory for every 20 samples.
The FB may consist of a water sample (Sect. 7.2) or a known
reference solution that approximates the concentration levels
characteristic of wet deposition. The FB is poured into the
sampling vessel at the field site and undergoes identical
processing and analytical protocols as the wet deposition
sample(s). Use the analytical data obtained from the FB to
determine any contamination introduced in the field and laboratory
handling procedures. The data from the known reference solution
. can be used to calculate a system precision and bias.
365.6-10
-------
10.7 Prepare and analyze a laboratory spike of a wet deposition sample
' according to the guidelines provided in "Quality Assurance Manual
for Precipitation Measurement Systems" (14.5). Compare the results
obtained from spiked samples to those obtained from identical
samples to which no spikes were added. Use these data to monitor
the method percent recovery as described in Sect. 10.2.3.
10.8 Participation in performance evaluation studies is recommended for
wet deposition chemistry laboratories. The samples used for these
performance audits should contain the analytes of interest at
concentrations within the normal working range of the method. The
true values are unknown to the analyst. Performance evaluation
studies for wet deposition chemistry laboratories are conducted
semiannually by the USEPA Performance Evaluation Branch, Quality
Assurance Division, Research Triangle Park, NC 27711.
11. PROCEDURE
11.1 Optimize the instrument each day according to Sect. 9.1.
11.2 Prepare all standards and construct a calibration curve according
to Sect. 9.2 and 9.3.
11.3 After the calibration curve is established, analyze the QCS. If_
the measured value for the QCS is not within the specified limits
(Sect. 10.2.2), refer to Sect. 10.4.
11.4 Load the sampler tray and begin analysis.
11.5 If the peak height response exceeds the working range of the
system, dilute the sample with zero standard and reanalyze.
11.6 When analysis is complete, turn off the heating bath and rinse the
system with 1 N HC1 for 15 minutes. Rinse the system with water
(Sect. 7.2) for an additional 15 minutes.
12. CALCULATIONS
12.1 Calculate a linear least squares fit of the standard concentration
as a function of the measured peak height. The linear least
squares equation is expressed as follows:
y = BQ + BIX'
where: y » standard concentration in mg/L
x - peak height measured
B * y-intercept calculated from: 7 ~ Bi*
B. « slope calculated from:
365.6-31
-------
n n
Ł (x. - x) (y. - y)/ 2 (x. - *)
i-1 i=l
where: x » mean of peak heights measured
7 = mean of standard concentrations
n - number of samples
The correlation coefficient should be 0.9990 or greater. Determine
the concentration of analyte of interest from the calibration
curve.
12.2 If the relationship between standard concentration and measured
peak height is nonlinear, use a second degree polynomial least
squares equation to derive a curve with a correlation >Q.999Q.
The second degree polynomial equation is expressed as follows:
y = B2x -»• B:X + BQ
A computer is necessary for the derivation of ohis function.
Determine the concentration of orthophosphate from the calibration
curve.
12.3 An integration system may also be used to provide a direct readout
of the concentration of orthophosphate.
12.4 Report data in mg/L as PO . Do not report data lower than
the lowest calibration standard.
13. PRECISION AND BIAS
13.1 The mean percent recovery and mean bias of this method were
determined from the analysis of spiked wet deposition samples
according to ASTM Standard Practice D4210, Annex A4 (14.6). The
results are summarized in Table 1. A small but statistically
significant bias of -0.01 mg/L was found at both spike
concentration levels.
13.2 Single-operator precision and bias were obtained from the analysis
of quality control check samples. These results reflect the
accuracy that can be expected when the method is used by a
competent operator. These data are presented in Table 2.
14. REFERENCES
14.1 Annual Book of ASTM Standards, Part 31, "Excerpts from Standard
for Metric Practice," Standard E 380-79, 1982, pp. 679-694.
14.2 "Safety in Academic Chemistry Laboratories," American Chemical
Society Publication, Committee on Chemical Safety, 3rd Edition,
1979.
365.6-12
-------
14.3 Annual Book of ASTM Standards, Part 31, "Standard Specification
for Reagent Water," Standard D 1193-77, 1982, p. 39.
14.4 Peden, M. E. and Skowron, L. M., "Ionic Stability of Precipitation
Samples," Atmos. Environ. 12, 1978, pp. 2343-2349.
14.5 Topol, L. E., Lev-On, M., Flanagan, J., Schwall, R. J., Jackson, A.
E., Quality Assurance Manual for Precipitation Measurement
Systems, 1985, U.S. Environmental Protection Agency, Environmental
Monitoring Systems Laboratory, Research Triangle Park, NC 27711.
14.6 Annual Book of ASTM Standards, Section 11, Vol. 11.01 (1),
"Practice for Intralaboratory Quality Control Procedures and a
Discussion of Reporting Low-Level Data," Standard D4210 Annex A4,
1983, pp. 15-16.
365.6-13
-------
Table 1. Single-Operator Precision and Bias for Orthophosphate
Determined from Analyte Spikes of Wet Deposition
Samples.a
Analyte
Amount
Added,
mg/L
n
Mean
Percent
Recovery
Mean
Bias,
mg/L
Standard
Deviation,
mg/L
Statistically
Significant
Bias?C
Ortho- 0.061 10 81.0 -0.012
phosphate 0.159 9 92.7 -0.012
0.002
0.004
Yes
Yes
a. Concentration values are significant to two decimal places.
b. Number of replicates
c. 95% Confidence Level
365.6-14
-------
Table 2. Single-Operator Bias and Precision for Orthophosphate
Determined from Quality Control Check Samples.3
Theoretical Measured Precision,
Concentration,
mg/L
0.031
0.062
0.123
0.215
Concentration, , Bias, s, RSD,
mg/L n mg/L % mg/L %
0.026 151 -0.005 -16.1 0.007 26.9
0.055 161 -0.007 -11.3 0.008 14.5
0.117 84 -0.006 -4.9 0.006 5.1
0.205 74 -0.010 -4.6 0.010 4.9
The above data were obtained from records of measurements made under the
direction of the NADP/NTN quality assurance program.
a. Concentration values are significant to two decimal places;
b. Number of replicates
365.6-15
-------
Figure 1. Orthophosphate Sampling and Analytical
System — Segmented Flow.
0
5
Turn
Mixing
Coil
Pump Tube
Colors
31k
Blk
'
Ł
^
/
Ł
/
',
\
Pur Blk
Wht Wht
Orn Grn
Grn Orn
PROPORTIONING
PUMP
Ł
Ł
/
'*,
;
\
tlOW
cell
2,90 sampler
water
°'60 5amplff •
0.10
0.10 color
reagent
Plow Rate
(mL/min)
waste
0.32 from
Sampling Rate:
30/hr
Sampling Volume:
0.3 mL
Sample to Rinse Ratio:
1:4
(24 second sample,
96 second rinse)
365.6-16
-------
Appendix K
METHOD 340.6 ~ FLUORIDE IN WET DEPOSITION BY POTENTIOMETRIC
DETERMINATION USING AN ION-SELECTIVE ELECTRODE
K-l
-------
Method 340.6 — Fluoride in Wet Deposition by
Potentiometric Determination Using ah
Ion-Selective Electrode
March 1986
Performing Laboratory:
Kenni 0. James
Carla Jo Brennan
Mark E. Peden
Illinois State Water Survey
Analytical Chemistry Unit
2204 Griffith Drive
Champaign, Illinois 61820
Sponsoring Agency:
John D. Pfaff, Project Officer
Inorganic Analysis Section
Physical and Chemical Methods Branch
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
340.6-1
-------
INDEX
Section
Number Subject
1 Scope and Application
2 Summary of Method
3 Definitions
4 Interferences
5 Safety
6 Apparatus and Equipment
7 Reagents and Consumable Materials
8 Sample Collection, Preservation, and Storage
9 Calibration and Standardization
10 Quality Control
11 Procedure
12 Calculations
13 Precision and Bias
14 References
TABLES
1. Values for 2.3026 RT/F at Different Temperatures.
2. Single-Operator Precision and Bias for Fluoride Determined from Analyte
Spikes of Wet Deposition Samples.
3. Single-Operator Precision and Bias for Fluoride Determined from Quality
Control Check Samples.
340.6-2
-------
1. SCOPE AND APPLICATION
1.1 This method is applicable to the potentiometric determination of
fluoride in wet deposition samples using an ion-selective electrode
as the sensor.
1.2 The term "wet deposition" is used in this method to designate rain,
snow, dew, sleet, and hail.
1.3 The method detection limit (MDL) determined from replicate analyses
of a quality control check solution containing 0.011 mg/L fluoride is
0.003 mg/L. The concentration range over which this method is
applicable is 0.003-0.10 mg/L as F~.
1.4 Fluoride concentrations in wet deposition samples range from
0.003-1.00 mg/L. Average concentrations are in the range of
0.01-0.10 mg/L. Fluoride concentrations as high as 10.00 mg/L
have been reported in wet deposition samples collected near
industrial sources (14.1).
2. SUMMARY OF METHOD
2.1 Ion-selective electrodes approximate the concentration of specific
ions in solution according to the electrode potential that develops
across the sensing membrane. In the case of the fluoride electrode,
this potential, which depends on the level of free fluoride ion in
solution, is measured against a constant reference potential. The
measured potential corresponding to the level of fluoride ion in
solution is described by the Nernst equation:
2.3026 RT
E - E log [F]
nF
where: E » measured electrode potential
E » reference potential (a constant)
R = gas constant
T » absolute temperature [T(°O + 273]
F « Faraday's constant
n " number of electrons transferred
[F] » molar concentration of fluoride in solution
Values of the factor 2.3026 RT/F at different temperatures are
provided in Table 1. The meter and the associated fluoride and
reference electrode are calibrated with standard fluoride solutions.
A calibration curve is constructed from which the concentration of
fluoride in a wet deposition sample is determined.
3. DEFINITIONS
3.1 For definitions of terms used in this method, refer to the glossary.
For an explanation of the metric system including units, symbols, and
conversion factors see American Society for Testing and Materials
(ASTM) Standard E 380, "Metric Practices" (14.2).
340.6-3
-------
4. INTERFERENCES
4.1 The sample pH must be >5 to avoid complexation by hydrogen ions and
<7 to avoid hydroxide interference. The addition of total ionic
strength adjustment buffer (TISAB II) to samples will eliminate this
potential source of error as well as eliminate possible interferences
from aluminum and iron complexation.
5. SAFETY
5.1 The calibration standards, sample types, and most of the reagents
used in this method pose no hazard to the analyst. Use a fume hood,
protective clothing, and safety glasses when handling sodium
hydroxide (Sect. 7.4) and glacial acetic acid (Sect. 7.5).
5.2 Follow American Chemical Society guidelines regarding the safe
handling of chemicals used in this method (14.3).
6. APPARATUS AND EQUIPMENT
6.1 SPECIFIC ION OR mV METER — The meter must have a readability of
0.1 mV with an analog or digital display. A meter that has separate
calibration and slope adjustment features and is electrically
shielded to avoid interferences from stray currents or static charge
is necessary. It may be powered by battery or by 110 VAC. If
battery powered, the meter must have a battery check feature. A
temperature compensator control to provide accurate measurements at
temperatures other than 25 C is desirable.
6.2 SENSING ELECTRODE — The most commonly used fluoride electrode
consists of a single-crystal lanthanum fluoride membrane which is an
ionic conductor in which only fluoride ions are mobile. Select an
electrode with a concentration range of 0.01 to 1.00 mg/L, a
temperature range of 20°-30°C, and a reproducibility of +2%.
Store the electrode according to manufacturer's guidelines.
6.3 REFERENCE ELECTRODE — Select a single junction Ag/AgCl sleeve type
reference electrode for analysis. Store the electrode according to
manufacturer's guidelines.
6.4 COMBINATION FLUORIDE ION-SELECTIVE ELECTRODE — Due to sample volume
limitations in wet deposition samples, a combination fluoride
electrode that contains both the sensing and the reference elements
in one probe is recommended over using two separate electrodes. Use
a combination electrode with a single junction Ag/AgCl sleeve type
reference element (Orion #96-09 or equivalent). When not in use,
store the combination fluoride electrode according to manufacturer's.
guidelines.
6,5- STIRRING DEVICE (electric or water-driven) — If an electric
stirrer is selected, place an air gap or insulating pad between the
stirrer surface and the solution container to minimize heating, of the
sample. Use a Teflon-coated stirring bar.
310.6-4
-------
6,6 THERMOMETER — Select a thermometer capable of being read
nearest 1°C and covering the range 0 -40°C.
to the
6.7 LABORATORY FACILITIES — Laboratories used for the analysis of wet
deposition samples should be free from external sources of
contamination. The use of laminar flow clean air workstations is
recommended for sample processing and preparation to avoid the
introduction of airborne contaminants. Samples should always be
capped or covered prior to analysis. A positive pressure environment
within the laboratory is also recommended to minimize the
introduction of external sources of contaminant gases and
particulates. Windows within the laboratory should be kept closed at
all times and sealed if air leaks are apparent. The use of
disposable tacky floor mats at the entrance to the laboratory is
helpful in reducing the particulate loading within the room.
7. REAGENTS AND CONSUMABLE MATERIALS
7.1 PURITY OF REAGENTS — Use reagent grade chemicals for all solutions.
All reagents shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society (ACS), where
such specifications are available.
7.2 PURITY OF WATER — Use water conforming to ASTM Specification D 1193
Type II (14.4). Point of use 0.2 micrometer filters are recommended
for all faucets supplying water to prevent the introduction of
bacteria and/or ion exchange resins into reagents, standard
solutions, and internally formulated quality control check solutions.
7.3 FLUORIDE SOLUTION, STOCK (1.0 mL » 1.0 mg F) — The stock solution
may be purchased as a certified solution or prepared from ACS reagent
grade materials. To prepare, dissolve 0.221 g of anhydrous sodium
fluoride (NaF) in water (Sect. 7.2) and dilute to 1 L. Store at room
temperature in a high density polyethylene or polypropylene
container.
7.4 SODIUM HYDROXIDE SOLUTION (5.0 N) — Dissolve 200.0 g of sodium
hydroxide (NaOH) slowly in 500 mL of water (Sect. 7.2). Cool to
room temperature and dilute to 1 L with water (Sect. 7.2).
7.5 TOTAL IONIC STRENGTH ADJUSTMENT BUFFER (TISAB II for low level
measurements) —- Add 57.0 mL of glacial acetic acid (CH..COOH) ,
4.0 g of cyclohexylene dinitrilo tetraacetic acid (CDTAJ, and
58.0 g.of sodium chloride (NaCl) to 500 mL of water (Sect. 7.2).
Stir to dissolve and cool to room temperature. Add 150 mL of 5 N
NaOH. Cool to room temperature and dilute to 1 L with water (Sect.
7.2). Store at room temperature in a polyolefin container. Add to
standards and samples as directed in Sect. 9.5.2 and Sect. 11.4 to
provide a constant background ionic strength and to maintain the pH
of the solution between 5.0 and 5.5.
7.5 SAMPLE CONTAINERS — Use polyolefin sample cups that have been rinsed
thoroughly with water (Sect. 7.2) before use.
340.6-5
-------
8. SAMPLE COLLECTION, PRESERVATION AND STORAGE
8.1 Collect samples in high density polyethylene (HOPE) containers that
have been thoroughly rinsed with ASTM Type II water (7.2). Do not
use strong mineral acids or alkaline detergent solutions for cleaning
collection vessels. Residual acids may remain in the polyethylene
matrix and slowly leach back into the sample. Alkaline detergents
may also leave residues that may affect the sample chemistry. Cap
collection bottles after cleaning to prevent contamination from
airborne contaminants; air dry collection buckets in a laminar flow
clean air workstation and wrap in polyethylene bags prior to use. If
a laminar flow workstation is not available, pour out any residual
rinse water and bag the buckets immediately. Do not dry the bucket
interior by any method other than air drying in a laminar flow clean
air workstation.
8.2 The frequency of sample collection and the choice of sampler design
are dependent on the monitoring objectives. In general, the use of
wet-only samplers is recommended to exclude dry deposition
contributions, minimize sample contamination, retard evaporation',
and enhance sample stability. Sample collection frequency may vary
from subevent to monthly sampling periods.
8.3 Fluoride concentrations are stable in natural waters' for 28 days when
stored at 25 C in high density polyethylene or polypropylene
containers (14.5). No data are available for the stability of fluoride
in wet deposition samples.
9. CALIBRATION AND STANDARDIZATION
9.1 Turn on the meter and allow it to warm up according to manufacturer's
instructions. If an ion selective meter is used, set the function
switch to detect monovalent anions.
9.2 If necessary, add filling solution supplied by the manufacturer to
the electrode before using. Maintain the filling solution level at
least one inch above the level of the sample surface to ensure proper
electrolyte flow rate.
9.3 Bring all standards and samples to ambient temperature before
beginning any analyses. Maintain samples and standard solutions
within +1 C of each other and maintain operating temperatures of
25 _+ 2<*C (14.6) . The absolute potential of the reference electrode
changes slowly with temperature because of the solubility equilibrium
upon which the- electrode depends. The slope of the fluoride
electrode also varies with temperature as indicated in the Nernst
equation in Sect. 2.1.
340.6-6
-------
9.4 CALIBRATION SOLUTIONS
9.4.1 Five calibration solutions and one zero standard are needed to
generate a suitable calibration curve. The lowest calibration
solution should contain fluoride at a concentration greater
than or equal-to the method detection limit. The highest
solution should approach the expected upper limit of
concentration of fluoride in wet deposition. Prepare the
remaining solutions such that they are evenly distributed
throughout the concentration range. Suggested calibration
standards for fluoride are as follows: zero, 0.01, 0.03,
0.05, 0.07, and 0.10 mg/L as F~.
9.4.2 Prepare all calibration standatv diluting the stock
standard (Sect. 7.3) with water (Ł>«. . 7.2). Use glass
(Class A) or plastic pipettes that are within the bias and
precision tolerances specified by the manufacturer. The
standards are stable for one month when stored at room
temperature in high density polyethylene or polypropylene
containers.
9.5 ELECTRODE SLOPE — Check the electrode slope daily before any
analyses are performed. Use two fluoride solutions that differ from
one another in concentration by a factor of ten and are within the
working concentration range. Suitable solutions to be used for this
procedure are the 0.01 and 0.10 mg/L calibration standards prepared
in Sect. 9.4.1.
9.5.1 Rinse the sample cup with three changes of water (Sect. 7.2).
Pipette a minimum of 5 mL of 0.01 mg/L calibration standard
"into the sample cup. Add TISAB II in a 1:1 volumetric ratio
and equilibrate for at least 15 minutes for complete Al
and Fe complexation. Rinse the electrode(s) with three
changes of water (Sect. 7.2) or with a flowing stream from a
wash bottle. Blot the electrode(s) dry with a clean
laboratory tissue and immerse into the 0.01 mg/L standard to
which TISAB II has been added. Stir the solution and maintain
a stirring rate of approximately 4 revolutions per second
(rps) throughout the analysis. Allow the electrode about
three minutes to stabilize. Adjust the calibration control
until the display reads "1" if a specific ion meter is used or
until the display reads 0.0 if a mV meter is used.
9.5.2 Dispense an aliquot of 0.10 mg/L calibration -standard into a
second clean sample cup, add TISAB II, and allow to
equilibrate as directed in Sect. 9.5.1. Rinse the
electrode(s), blot dry, immerse in the solution, and stir as
directed in Sect 9.5.1. Allow the electrode about three
minutes to stabilize. If a mV meter is used, correct
electrode performance is indicated by a reading of -57^3 mV.
If a specific ion meter is used, use the slope adjustment
feature to set the display to read "10".
340.6-7
-------
9.5.3 If the slope is not within the acceptable range indicated in
Sect. 9.5.2, refer to the electrode instruction manual for
corrective action.
9.6 CALIBRATION CURVE
9.6.1 Rinse the sample cup with three changes of water (Sect. 7.2).
Pipette an aliquot of zero standard into the sample cup. Add
TISAB II in a 1:1 volumetric ratio and equilibrate for at
least 15 minutes for complete Al and Fe complexation.
Rinse the electrode(s) with three changes of water (Sect. 7.2)
or with a flowing stream from a wash bottle. Blot the
electrode(s) dry with a clean laboratory tissue and immerse
into the zero standard to which TISAB II has been added. Stir
the solution and maintain a stirring rate of approximately
4 rps throughout the analysis. Allow sufficient time for the
reading to remain steady within _+0.01 mg/L or 0.1 mV
(depending on the type of meter used) for 30 seconds. When
the meter reading is stable, record the measurement.
9.6.2 Analyze the remaining standards in order of increasing
fluoride concentration, measuring the most concentrated
standard last. Rinse the electrode(s) between standards.
Construct a calibration curve according to Sect. 12.
9.6.3 Verify the calibration curve after every ten samples and at
the end of each day's analyses according to Sect. 10.6.
10. QUALITY CONTROL
10.1 Each laboratory using this method should develop formalized quality
control protocols to continually monitor the bias and precision of
all measurements. These protocols are required to ensure that the
measurement system is in a state of statistical control. Estimates
of bias and precision for wet deposition analyses cannot be made
unless these control procedures are followed. Detailed guidelines
for the development of quality assurance and quality control
protocols for wet deposition measurement systems are published in a
manual available from the United States Environmental Protection
Agency, Research Triangle Park, NC 27711 (14.7). Included in this
manual are procedures for the development of statistical control
charts for use in monitoring bias and precision as well as
recommendations for the introduction of reagent blanks, laboratory
duplicates, field duplicates, spike samples, and performance
evaluation samples. These guidelines are to be used by all
laboratories involved with wet deposition measurements.
340.6-8
-------
10.2 ESTABLISHMENT OF WARNING AND CONTROL LIMITS — Warning and control
limits are used to monitor drift in the calibration curve, analyses
of quality control check samples (QCS), and measured recoveries
from laboratory spikes.
10.2.1 Calibration Curve — After a calibration curve has been
constructed according to Sect. 12, reanalyze additional
aliquots of the low and high concentration standards.
Calculate the concentrations using the previously derived
calibration curve. Repeat this procedure until at least
ten determinations at each concentration level have been
made. These data should be collected on ten different days
to provide a realistic estimate of the method variability.
Calculate a standard deviation (s) at each concentration
level. Use the nominal standard concentration as the mean
value (x) for determining the control limits. A warning
limit of x HH 2s and a control limit of x +_ 3s should be
used. Reestablish these limits whenever instrumental
operating conditions change.
10.2.2 Quality Control Check Samples (QCS) —- Calculate warning
and control limits for QCS solutions from a minimum of ten
analyses performed on ten days. Use the calculated
standard deviation (s) to develop the limits as described
in Sect. 10.2.1. Use the certified or NBS traceable
concentration as the mean (target) value. Constant
positive or negative measurements with respect to the true
value are indicative of a method or procedural bias.
Utilize the data obtained from QCS measurements as in Sect.
10.5 to determine when the measurement system is out of
statistical control. The standard deviations used to
generate the QCS control limits should be comparable to the
single operator precision reported in Table 3. Reestablish
new warning and control limits whenever instrumental
operating conditions are varied or QCS concentrations are
changed.
10.2.3 Laboratory Spike Solutions — A minimum of ten analyte
spikes of wet deposition samples is required to develop a
preliminary data base for the calculation of warning and
control limits for spike recovery data. Select the spike
concentration such that the working range of the method
will not be exceeded. Samples selected for the initial
spike recovery study should represent the concentration
range common to wet deposition samples in order to reliably
estimate the method accuracy. Calculate a mean and
standard deviation of the percent recovery data using the
formulas provided in the glossary. Determine warning and
control limits using ^2s and ^3s, respectively. If
the data indicate that no significant method bias exists
(14.8), the 100 percent recovery is used as the mean
percent recovery. Where a significant bias is determined
340.6-9
-------
at the 95% confidence level, the control limits are
centered around the bias estimate. Routi'ne spiked sample
analyses that yield percent recovery data outside of the
control limits are an indication of matrix interferences
that should be resolved before routine analyses are
continued.
10.2.4 All warning and control limits should be reevaluated on a
continual basis as additional data are collected during
routine analyses. The limits should be broadened or
narrowed if a recalculated standard deviation under similar
operating conditions provides a different estimate of the
procedure variability.
10.3 Monitor the cleaning procedure by pouring a volume of water (Sect.
7.2) that approximates the median sample size into the collection
vessel. Allow the water (Sect. 7.2) to remain in the sealed or
capped collection container for at least 24 hours and determine the
fluoride concentration. If the solution concentration exceeds the
MDL, a contamination problem is indicated in the cleaning
procedure. Take corrective action before the sampling containers
are used for the collection of wet deposition.
10.4 Electrodes used for the measurement of wet deposition samples
should not be used for other sample types. Solutions with high
concentrations of fluoride may cause electrode degradation and
result in biased measurements and/or slow response in wet
deposition samples. If the sensing element of the electrode
becomes coated with organic deposits, longer response times in
dilute fluoride solutions will result. Refer to the manufacturer's
guidelines for instructions on how to clean the electrode of
organic deposits.
10.5 Analyze a quality control check sample (QCS) after the meter and
electrode assembly have been calibrated. This sample may be
formulated in the laboratory or obtained from the National Bureau
of Standards (NBS Standard Reference Material 2694, Simulated
Rainwater). Verify the accuracy of internally formulated QCS
solutions with an NBS traceable standard before acceptance as a
quality control check. The check sample(s) selected must be within
the range of the calibration standards and should approximate the
range of the samples to be analyzed. If the measured value for the
QCS falls outside of the +3s limits (Sect. 10.2.2), or if two
successive QCS checks are outside of the Ł2s limits, a problem is
indicated with the calibration procedure or the electrode/meter
assembly. Check the meter according to the manufacturer's
guidelines. If an electrode problem is indicated, replace the
electrode. Plot the data obtained from the QCS checks on. a control
chart for routine assessments of bias and precision.
340.6-10
-------
10.6 Verify the calibration curve after a maximum of ten samples and at
the end of each day's analyses. Analyze calibration standards at
the low and high ends of the working range. If the routine
calibration checks do not meet the.criteria described in Sect.
10.5, recalibrate the system and reanalyze all samples from the
last time the system was in control. Verify the new calibration
curve with the QCS according to Sect. 10.5 and reanalyze all
samples analyzed since the last time the system was in control.
10.7 Submit a Field Blank (FB) to the laboratory for every 20 samples.
The FB may consist of a water sample (Sect. 7.2) or a known
reference solution that approximates the concentration levels
characteristic of wet deposition. The FB is poured into the
sampling vessel at the field site and undergoes identical
processing and analytical protocols as the wet deposition
sample(s). Use the analytical data obtained from the FB to
determine any contamination introduced in the field and laboratory
handling^procedures. The data from the known reference solution
can be used to calculate a system precision and bias.
10.8 Prepare and analyze a laboratory spike of a wet deposition sample
according to the guidelines provided in "Quality Assurance Manual
for Precipitation .Measurement Systems" (14.7). Compare the results
obtained from the spiked sample to that obtained from an identical
sample to which no spike was added. Use these data to determine
percent recovery as described in Sect. 10.2.3.
10.9 Participation in performance evaluation studies is recommended for
wet deposition chemistry laboratories. The samples used for these
performance audits should contain the analytes of interest at
concentrations within the normal working range of the method. The
true values are unknown to the analyst. Performance evaluation
studies for wet deposition chemistry laboratories are conducted
semiannually by the USEPA Performance Evaluation Branch, Quality
Assurance Division, Research Triangle Park, NC 27711.
11. PROCEDURE
11.1 Prepare all standards and bring solutions and samples to ambient
temperature (+1°C).
11.2 Check electrode slope each day according to Sect. 9.5 and construct
a calibration curve according to Sect. 9.6.
11.3 After the calibration curve is established, analyze the QCS. If
the measured value for the QCS is not within the specified limits
(Sect. 10.2.2), refer to Sect. 10.5.
340.6-11
-------
11.4 SAMPLE ANALYSIS
11.4.1 Rinse the sample cup with three changes of water (Sect.
7.2). Dispense an aliquot of sample equivalent to that
used for the calibration standards. Add TISAB II in a 1:1
volumetric ratio and allow the solution to equilibrate for
at least 15 minutes.
11.4.2 Rinse the electrode(s) with three changes of water (Sect.
7.2) or with a flowing stream from a wash bottle. Blot dry
with a clean, absorbent laboratory tissue. Immerse the
clean electrode(s) into the sample and observe the meter
reading while mixing. When the reading is steady within
_+0.01 mg/L or 0.1 mV (depending on the type of meter
used) for 30 seconds, record the measurement.
11.5 TISAB to sample volume ratios of 1:10 have been used successfully
for the determination of fluoride in wet deposition samples (14.9).
The smaller volume of TISAB used in this procedure provides
increased method sensitivity for low level analyses.
11.6 Response times for the electrode assembly may be shortened by
preconditioning the electrode(s) (14.10). Immerse the clean
electrode(s) into a portion of the wet deposition sample to be
analyzed, allow the system to equilibrate for approximately three
minutes, and remove the electrode. Insert the electrode(s)
directly into a second portion of sample and record the reading
when the system is stabilized according to Sect. 11.4.2. This
procedure, however, is limited by the amount of wet deposition
sample available.
11.7 If the concentration of fluoride in a sample exceeds the working
range of the system, dilute the sample with zero standard and
reanalyze.
12. CALCULATIONS
12.1 Calculate a linear least squares fit of the standard concentration
as a function of the measured concentration. The linear least
squares equation is expressed as follows:
y = BQ + B:X
where: y = standard concentration in mg/L
x » concentration measured
B- » y-intercept calculated from: y - B.x
B « slope calculated from:
340.6-12
-------
2
2, (x. - ZHy - y)/ 2 (x - x)
i=l i=l
where: x - mean of concentration measured
y = mean of standard concentrations
n = number of samples
The correlation coefficient should be 0.9990 or greater. Determine
the concentration of fluoride from the calibration curve.
12.2 If the relationship between standard and measured concentration is
nonlinear, a second degree polynomial least squares equation can be
used to derive an acceptable curve with a correlation _>0.9990.
The second degree polynomial equation is expressed as follows:
y = B_x + B x + B
A computer is necessary for the derivation of this function.
Determine the concentration of fluoride from the calibration curve.
12.3 An integration system may also be used to provide a direct readout
of the concentration of fluoride.
12.4 Report data in mg/L as F . Do not report data lower than the
lowest calibration standard.
13. PRECISION AND BIAS
13.1 The mean percent recovery and mean bias of this method were
determined from the analysis of. spiked wet deposition samples
according to ASTM Standard Practice D4210, Annex A4 (14.8). The
results are summarized in Table 2. A small but statistically
significant bias of -0.004 was determined at a spike concentration
of 0.027 mg/L. No statistically significant bias was present at a
spike concentration of 0.082 mg/L.
13.2 Single-operator precision and bias were obtained from the analysis
of quality control check samples that approximated the levels
common to wet deposition samples. These results reflect the
accuracy that can be expected when the method is used by a
competent operator. These data are presented in Table 3.
14. REFERENCES
14.1 Smith, F. A. and Hodge, H. C., "Airborne Fluorides and Man:
Part 1," CRC Grit Rev. Envir. Control, 8, 1979, pp. 293-372.
14.2 Annual Book of ASTM Standards, Part 31, "Excerpts from Standard
for Metric Practice," Standard E 380-79, 1982, pp. 679-694.
14.3 "Safety in Academic Chemistry Laboratories," American Chemical
Society Publication, Committee on Chemical Safety, 3rd Edition,
1979.
340.S-13
-------
14.4 Annual Book of ASTM Standards, Part 31, "Standard Specification
for Reagent Water," Standard D 1193-77, 1982, p. .39.
14.5 Handbook for Sampling and Sample Preservation of Water and
Wastewater, 1982, U.S. Environmental Protection Agency,
Environmental Monitoring and Support Laboratory, EPA-600/4-82-029,
Cincinnati, OH 45268.
14.6 Nicholson, K., and Duff, E. J., "Fluoride Determination in Water:
An Optimum Buffer System for Use with the Fluoride Selective
Electrode," Analytical Letters, 14(A12), 1981, pp. 887-912.
14.7 Topol, L. E., Lev-On, M., Flanagan, J., Schwall, R. J., Jackson, A.
E., Quality Assurance Manual for Precipitation Measurement
Systems, 1985, U.S. Environmental Protection Agency, Environmental
Monitoring Systems Laboratory, Research Triangle Park, NC 27711.
14.8 Annual Book of ASTM Standards, Section 11, Vol. 11.01 (1),
"Practice for Intralaboratory Quality Control Procedures and a
Discussion of Reporting Low-Level Data," Standard D4210 Annex A4,
1983, pp. 15-16.
14.9 Barnard, Willian R. and Nordstrom, D. Kirk, "Fluoride in
Precipitation - I. Methodology with the Fluoride-Selective
Electrode," Atmos. Environ., 16, 1982, pp. 99-103.'
14.10 Kissa, Erik, "Determination of Fluoride at Low Concentrations with
the Ion-Selective Electrode," Analytical Chemistry, 55, 1983,
pp. 1445-1448.
340.6-14
-------
Table 1. Values for 2.3026 RT/F at Different
Temperatures
Temperature, 2.3026 RT/F,
C V
0 0.054
5 0.055
10 0.056
15 0.057
20 0.058
25 0.059
30 0.060
35 0.061
40 0.062
45 0.063
•The above data were calculated using
a precise value of the logarithmic
conversion factor (2.302585) and values
of the fundamental constants.
F - 96,487.0 C/eq
:R - 8.31433 J/K mol
T - 273.15 + °C
340.6-15
-------
Table 2. Single-Operator Precision and Bias for Fluoride
Determined from Analyte Spikes of Wet Deposition
Samples.
Analyte
Amount
Added ,
mg/L na
Mean
Percent
Recovery
Mean
Bias,
mg/L
Standard
Deviation,
mg/L
Statistically
Significant
Bias?
Fluoride
0.027
0.082
10
10
87.1
98.3
-0.004
-0.001
0.003
0.003
Yes
No
b.
Number of replicates
95% Confidence Level
340.6-16
-------
Table 3. Single-Operator Precision and Bias for Fluoride
Determined from Quality Control Check Samples.
Theoretical Measured Precision,
:oncentration, Concentration, Bias, s, RSD,
mg/L mg/L n mg/L % mg/L %
0.0112 0.0108 6 -0.0004 -3.6 0.0010 9.2
0.0560 0.0558 7 -0.0001 -0.2 0.0010 1.8
a. Concentration values are significant to three decimal places.
b. Number of replicates
340.C-17
-------
Appendix L
METHOD 350.6 — AMMONIUM IN WET DEPOSITION BY ELECTROMETRIC
DETERMINATION USING ION-SELECTIVE ELECTRODE
METHOD 350.7 — AMMONIUM IN WET DEPOSITION BY AUTOMATED
COLORIMETRIC DETERMINATION WITH PHENATE
L-l
-------
Method 350.6 — Ammonium in Wet Deposition by
Electrometric Determination Using an
Ion-Selective Electrode
March 1986
Performing Laboratory:
Carla Jo Brennan
Mark E. Peden
Illinois State Water Survey
Analytical Chemistry Unit
2204 Griffith Drive
Champaign, Illinois 61820
Sponsoring Agency:
John D. Pfaff, Project Officer
Inorganic Analysis Section
Physical and Chemical Methods Branch
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
350.6-1
-------
INDEX
Section
Number Subject
1 Scope and Application
2 Summary of Method
3 Definitions
4 Interferences
5 Safety
6 Apparatus and Equipment
7 Reagents and Consumable Materials
8 Sample Collection, Preservation, and Storage
9 Calibration and Standardization
10 Quality Control
11 Procedure
12 Calculations
13 Precision and Bias
14 References
TABLES
1. Values for 2.3026 RT/F at Different Temperatures.
2. Single-Operator Bias and Precision for Ammonium Determined from Analyte
Spikes of Wet Deposition Samples.
3. Single-Operator Bias and Precision for Ammonium Determined from Quality
Control Check Samples.
FIGURES
1. Percentile Concentration Values Obtained from Wet Deposition Samples:
Ammonium.
350.6-2
-------
1. SCOPE AND APPLICATION
1.1 This method is applicable to the measurement of ammonium in wet
deposition samples using an ion-selective electrode as the sensor.
1.2 The term "wet deposition" is used in this method to designate rain,
snow, dew, sleet, and hail.
1.3 The method detection limit (MDL) determined from replicate analyses
of a quality control check solution containing 0.17 mg/L ammonium is
0.05 mg/L. The analyte concentration range over which this method is
applicable is 0.05-2.00. mg/L as NH .
1.4 Figure 1 represents a cumulative frequency percentile ammonium
concentration plot obtained from analyses of over five thousand wet
deposition samples. These values may be used as an aid in the
selection of appropriate calibration standard concentrations.
2. SUMMARY OF METHOD
2.1 The pH of a solution is adjusted to between 11 and 14 to convert
ammonium ion to ammonia gas. A gas sensing ion-selective electrode
approximates the concentration of ammonia in solution according to
the electrode potential that develops across the sensing membrane.
This, potential is measured against a constant reference potential
according to the Nernst equation:
2.3026 RT
E = E - log (NH,]
o _ J
nF
where: E * measured electrode potential
E * reference potential (a constant)
R * gas constant
T - absolute temperature [T( C) + 273]
F * Faraday's constant
n * number of electrons transferred
• [NH ] * molar concentration of ammonia in solution
Values of the factor 2.3026 RT/F at different temperatures are
provided in Table 1. The meter and the ammonia electrode are
calibrated with standard ammonium solutions. A calibration curve is
constructed from which the concentration of ammonium ion in a wet
deposition sample is determined.
350.6-3
-------
3. DEFINITIONS
3.1 For definitions of terms used in this method, refer to the glossary.
For an explanation of the metric system including units, symbols, and
conversion factors see American Society for Testing and Materials
(ASTM) Standard E 380, "Metric Practices" (14.1).
4. INTERFERENCES
4.1 Stirring rates that form a vortex will result in ammonia loss. A
stirring rate of approximately two revolutions per second is
recommended. Maintain a constant stirring rate throughout analyses
of all standards and samples.
5. SAFETY
5.1 The calibration standards, sample types, and most reagents used in
this method pose no hazard to the analyst. Use a fume hood,
protective clothing, and safety glasses when handling sodium
hydroxide (Sect. 7.4).
5.2 Follow American Chemical Society guidelines regarding the safe
handling of chemicals used in this method (14.2).
6. APPARATUS AND EQUIPMENT
6.1 SPECIFIC ION OR mV METER — The meter must have a readability of
0.1 mV with an analog or digital display. A meter that has separate
calibration and slope adjustment features and is electrically
shielded to avoid interferences from stray currents or static charge
is necessary. It may be powered by battery or by 110 VAC; if battery
powered, the meter must have a battery check feature.
6.2 AMMONIA ION-SELECTIVE ELECTRODE — Select a gas-sensing ammonia
electrode containing a reference element with a liquid internal filling
solution in contact with a hydrophobic gas-permeable membrane. Select
an electrode that has a concentration range of 0.05 to 2.00 mg/L
ammonium and a temperature range of 20 -30 C with a reproducibility
of _*2%. When not in use, store the electrode according to
manufacturer's guidelines.
6.3 STIRRING DEVICE (electric or water-driven) — If an electric stirrer
is selected, leave an air gap or place an insulating pad between the
stirrer surface and the solution container to prevent heating of the
sample. Use a tetrafluoroethylene (TFE)-coated stirring bar.
6.4 THERMOMETER — Select a thermometer capable of being read to the
nearest 1 C and covering the range 0°-40°C.
350.6-4
-------
6.5 LABORATORY FACILITIES — Laboratories used for the analysis of wet
deposition samples should be free from external sources of
contamination. The use of laminar flow clean air workstations is
recommended for sample processing and preparation to avoid the
introduction of airborne contaminants. Samples should always
be capped or covered prior to analysis. A positive pressure
environment within the laboratory is also recommended to minimize the
introduction of external sources of contaminant gases and
particulates. Windows within the laboratory should be kept closed .at
all times and sealed if air leaks are apparent. The use of
disposable tacky floor mats at the entrance to the laboratory is
helpful in reducing the particulate loading within the room.
7. REAGENTS AND CONSUMABLE MATERIALS
7.1 PURITY OF REAGENTS — Use reagent grade chemicals for all solutions.
All reagents shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society (ACS), where
such specifications are available.
7.2 PURITY OF WATER — Use water conforming to ASTM Specification D 1193,
Type II (14.3). Point of use 0.2 micrometer filters are recommended
for all faucets supplying water to prevent the introduction of
bacteria and/or ion exchange resins into reagents, standard solutions
and internally formulated quality control check solutions.
7.3 AMMONIUM SOLUTION, STOCK (1.0 mL = 1.0 mg NH4> — The stock
solution may be purchased as a certified solution or prepared from
ACS reagent grade materials. To prepare, dissolve 2.9654 g of
ammonium chloride (NH CD, dried at 105°C for 1 hour, in water
(Sect. 7.2) and dilute to 1 L. The stock solution is stable for one
year when refrigerated at 4°C in a high density polyethylene or
polypropylene container.
7.4 SODIUM HYDROXIDE SOLUTION (2.0 N) — Prepare a dilute sodium
hydroxide (NaOH) solution by dissolving 80.0 g of reagent grade
sodium hydroxide (NaOH) in water (Sect. 7.2) and diluting to 1 L.
Store at room temperature in a high density polyethylene or
polypropylene container for a period not exceeding one year.
7.5 SAMPLE CONTAINERS — Use glass or polyolefin sample cups that have
been rinsed thoroughly with water (Sect. 7.2) before use. To reduce
the opportunity for ammonia loss to the ambient atmosphere, select
sample containers designed to minimize the ratio of surface area to
sample volume.
350.6-5
-------
8. SAMPLE COLLECTION, PRESERVATION AND STORAGE
8.1 Collect samples in high density polyethylene (HOPE) containers that
have been thoroughly rinsed with ASTM Type II water (7.2). Do not
use strong mineral acids or alkaline detergent solutions for cleaning
collection vessels. Residual acids may remain in the polyethylene
matrix and slowly leach back into the sample. Alkaline detergents
may also leave residues that may affect the sample chemistry. Cap
collection bottles after cleaning to prevent contamination from
airborne contaminants; air dry collection buckets in a laminar flow
clean air workstation and wrap in polyethylene bags prior to use. If
a laminar flow workstation is not available, pour out any residual
rinse water and bag the buckets immediately. Do not dry the bucket
interior by any method other than air drying in a laminar flow clean
air workstation.
8.2 The frequency of sample collection and the choice of sampler design
are dependent on the monitoring objectives. In general, the use of
wet-only samplers is recommended to exclude dry deposition
contributions, minimize sample contamination, retard evaporation,
and enhance sample stability. Sample collection frequency may vary
from subevent to monthly sampling periods. Collection periods of
more than one week are not recommended since sample integrity may be
compromised by longer exposure periods.
8.3 The presence of microbial activity will affect the stability of
ammonium concentrations in wet deposition samples. Chemical
determinations should be made immediately after collection whenever
possible.
8.3.1 Filtration of samples through a 0.45 micrometer membrane
leached with water (Sect. 7.2) is partially effective at
stabilizing ammonium by removal of biologically active
species. Refrigeration after immediate filtration is the most
reliable method to ensure sample integrity (14.4). Sample
storage time should not exceed one week.
9. CALIBRATION AND STANDARDIZATION
9.1 Turn on the meter and allow it to warm up thoroughly according to the
manufacturer's instructions. If an ion selective meter is used, set
the function switch to detect monovalent anions.
9.2 If necessary, add filling solution to the electrode before using. To
improve electrode response at low concentrations, prepare a 1:10
dilution of the internal filling solution by adding 1 mL of solution
to 10 mL of water (Sect. 7.2) (14.5). Maintain the filling solution
level at least one inch above the level of the sample surface to
ensure proper electrolyte flow rate.
350.6-6
-------
9.3 Bring all standards and samples to ambient temperature before
beginning any analyses. Maintain samples and standard solutions
within +1°C of each other and maintain operating temperatures of
25 + 2°C during analyses to minimize ammonia loss from solutions.
The~absolute potential of the reference element changes slowly with
temperature because of the solubility equilibrium upon which the
electrode depends. The slope of the ammonia electrode also varies
with temperature as indicated in the Nernst equation in Sect. 2.1.
9.4 CALIBRATION SOLUTIONS
9.4.1 Five calibration solutions and one zero standard are needed to
generate a suitable calibration curve. The lowest calibration
solution should contain ammonium at a concentration greater
than or equal to the method detection limit. The highest
solution should approach the expected upper limit of
concentration of ammonium in wet deposition. Prepare the
remaining solutions such that they evenly encompass the
concentration range. Suggested calibration standards for
ammonium are as follows: zero, 0.05, 0.50, 1.00, 1.50, and
2.00 mg/L as NH/".
9.4.2 Prepare all calibration standards by diluting the stock
standard (Sect. 7.3) with water (Sect. 7.2). Use glass
(Class A) or plastic pipettes that are within the bias and
precision tolerances specified by the manufacturer. TheQ
standards are stable for one week when refrigerated at 4 C
in high density polyethylene or polypropylene containers.
9.5 ELECTRODE SLOPE — Check the electrode slope daily before any
analyses are performed. Use two ammonium solutions that differ from
one another in concentration by a factor of ten and are within the
range of subsequent ammonium analyses. Suitable solutions to be used
for this procedure are the 0.20 and 2.00 mg/L calibration standards
prepared in Sect. 9.4.1.
9.5.1 Rinse the electrode and the sample cup with three changes of
water (Sect. 7.2) or with a flowing stream from a wash bottle.
Immerse the electrode into the 0.20 mg/L calibration standard.
Add 1 mL of NaOH solution to 15 mL of standard solution. Stir
the solution while maintaining a stirring rate of
approximately 2 rps throughout the analysis. Allow the
electrode to stabilize for two minutes. Adjust the
calibration control until the display reads "1" if a specific
ion meter is used or until the display reads 000.0 if a mV
meter is used.
350.6-7
-------
9.5.2 Rinse the electrode, add an equal volume aliquot of 2.00 mg/L
standard to the sample cup, add 1 mL of NaOH, and stir as
directed in Sect. 9.5.1. Allow the electrode to equilibrate
for two minutes. If a mV meter is used, correct electrode
operation is indicated by a reading of -57 +_ 3 mV. If a
specific ion meter is used, use the slope adjustment feature to
set the display to read "10".
9.5.3 If the slope is not within the acceptable range indicated in
Sect. 9.5.2, refer to the electrode instruction manual for
corrective action.
9.6 CALIBRATION CURVE
9.6.1 Rinse the electrode and the sample cup with three changes of
water (Sect. 7.2) or with a flowing stream from a wash bottle.
Immerse the electrode into the zero standard. Add the NaOH
solution (1 mL of NaOH:15 mL standard) to adjust the pH of the
solution to between 11 and 14. Stir the solution and maintain
a stirring rate of approximately 2 rps throughout the
analysis. Allow sufficient time for the reading to remain
steady within +0.01 mg/L or 0.1 mV (depending on the meter
used) for 30 seconds. When the meter reading is stable,
record the measurement.
9.6.2 Rinse the electrode. Analyze the remaining standards in order
of increasing ammonium concentration, measuring the most
concentrated standard last. Rinse the electrode between
standards. Construct a calibration curve according to
Sect. 12.
9.6.3 Verify the calibration curve after every ten samples and at
the end of each day's analyses according to Sect. 10.6.
10. QUALITY CONTROL
10.1 Each laboratory using this method should develop formalized quality
control protocols to continually monitor the bias and precision of
all measurements. These protocols are required to ensure that the
measurement system is in a state of statistical control. Estimates
of bias and precision for wet deposition analyses cannot be made
unless these control procedures are followed. Detailed guidelines
for the development of quality assurance and quality control
protocols for wet deposition measurement systems are published in a
manual available from the United States Environmental Protection
Agency, Research Triangle Park, NC 27711 (14.6). Included in this
manual are procedures for the development of statistical control
charts for use in monitoring bias and precision as well as .
recommendations for the introduction of reagent blanks, laboratory
.duplicates, field duplicates, spike samples, and performance
evaluation samples. These guidelines are to be used by all
laboratories involved with wet deposition measurements.
350.6-9
-------
10.2 ESTABLISHMENT OF WARNING AND CONTROL LIMITS -- -Warning and control
limits are used to monitor drift in the calibration curve, analyses
of quality control check samples (QCS), and measured recoveries
from laboratory spikes.
10.2.1 Calibration Curve — After a calibration curve has been
constructed according to Sect. 12, reanalyze additional
aliquots of the low and high concentration standards.
Calculate the concentrations using the previously derived
calibration curve. Repeat this procedure until at least
ten determinations at each concentration level have been
made. These data should be collected on ten different days
to provide a realistic estimate of the method variability.
Calculate a standard deviation (s) at each concentration
level. Use the nominal standard concentration as the mean
value (x) for determining the control limits. A warning
limit of 3? Ł 2s and a control limit of x jf 3s should be
used. Reestablish these limits whenever instrumental
operating conditions change.
10.2.2 Quality Control Check Samples {QCS) — Calculate warning
and control limits for QCS solutions from a minimum of ten
analyses performed on ten days. Use the calculated
standard deviation (s) to develop the limits as described
in Sect. 10.2.1. Use the certified or NBS traceable
concentration as the mean (target) value. Constant
positive or negative measurements with respect to the true
value are indicative of a method or procedural bias.
Utilize the data obtained from QCS measurements as in Sect.
10.5 to determine when the measurement system is out of
statistical control. The standard deviations used to
generate the QCS control limits should be comparable to the
single operator precision reported in Table 3- Reestablish
new warning and control limits whenever instrumental
operating conditions are varied or QCS concentrations are
changed.
10.2.3 Laboratory Spike Solutions — A minimum of ten analyte
spikes of wet deposition samples is required to develop a
preliminary data base for the calculation of warning and
control limits for spike recovery data. Select the spike
concentration such that the working range of the method
will not be exceeded. Samples selected for the initial
spike recovery study should represent the concentration
range common to wet deposition samples in order to reliably
estimate the method accuracy. Calculate a mean and
standard deviation of the percent recovery data using the
formulas provided in the glossary. Determine warning and
control limits using ^2s and +;3s, respectively. If
the data indicate that no significant method bias exists
(14.7), the 100 percent recovery is used as the mean
percent recovery. Where a significant bias is determined
350,6-9
-------
at the 95% confidence level, the control limits are
centered around the bias estimate. Routine spiked sample
analyses that yield percent recovery data outside of the
control limits are an indication of matrix interferences
that should be resolved before routine analyses are
continued.
10.2.4 All warning and control limits should be reevaluated on a
continual basis as additional data are collected during
routine analyses. The limits should be broadened or
narrowed if a recalculated standard deviation under similar
operating conditions provides a different estimate of the
procedure variability.
10.3 Monitor the cleaning procedure by pouring a volume of deionized
water that approximates the median sample size into the collection
vessel. Allow the water to remain in the sealed or capped
collection container for at least 24 hours and determine the
ammonium concentration. If the solution concentration exceeds the
MDL, a contamination problem is indicated in the cleaning
procedure. Take corrective action before the sampling containers
are used for the collection of wet deposition.
10.4 Electrodes used for the measurement of wet deposition samples
should not be used for other sample types.
10.5 Analyze a quality control check sample (QCS) after the meter and
electrode assembly have been calibrated. This sample may be
formulated in the laboratory or obtained from the National Bureau
of Standards (NBS Standard Reference Material 2694, Simulated
Rainwater). Verify the accuracy of internally formulated QCS
solutions with an NBS traceable standard before acceptance as a
quality control check. The check sample(s) selected must be within
the range of the calibration standards and should approximate the
range of the samples to be analyzed. If the measured value for the
QCS falls outside of the _+3s limits (Sect. 10.2.2), or if two
successive QCS checks are outside of the _+2s limits, a problem is
indicated with the calibration procedure or the electrode/meter
assembly. Check the meter according to the manufacturer's
guidelines. If an electrode problem is indicated, replace the
electrode. Plot the data obtained from the QCS checks on a control
chart for routine assessments of bias and precision.
10.6 Verify the calibration curve after a maximum of ten samples and at
the end of each day's analyses. Analyze calibration standards at
the low and high ends of the working range. If the routine
calibration checks do not meet the criteria described in Sect.
10.5, recalibrate the system and reanalyze all samples from the
last time the system was in control. Verify the new calibration
curve with the QCS according to Sect. 10.5 and reanalyze all
samples analyzed since the last time the system was in control.
350.6-10
-------
10.7 Submit a Field Blank (FB) to the laboratory for every 20 samples.
The FB may consist of a water sample (Sect. 7.2) or a known
reference solution that approximates the concentration levels
characteristic of wet deposition. The FB is poured into the
sampling vessel at the field site and undergoes identical
processing and analytical protocols as the wet deposition
sample(s). Use the analytical data obtained from the FB to
determine any contamination introduced in the field and laboratory
handling procedures. The data from the known reference solution
can be used to calculate a system precision and bias.
10.8 Prepare and analyze a laboratory spike of a wet deposition sample
standard according to the guidelines provided in "Quality Assurance
Manual for Precipitation Measurement Systems" (14.6). Compare the
results obtained from the spiked sample to that obtained from an
identical sample to which no spike was added. Use these data to
determine percent recovery as described in Sect. 10.2.3.
10.9 Participation in performance evaluation studies is recommended for
wet deposition chemistry laboratories. The samples used for these
performance audits should contain the analytes of interest at
concentrations within the normal working range of the method. The
true values are unknown to the analyst. Performance evaluation
studies for wet deposition chemistry laboratories are conducted
semiannually by the USEPA Performance Evaluation Branch, Quality
Assurance Division, Research Triangle Park, NC 27711.
11. PROCEDURE
11.1 Prepare all standards and bring solutions and samples to ambient
temperature (+1 C).
11.2 Check electrode slope each day according to Sect. 9.5 and construct
a calibration curve according to Sect. 9.6.
11.3 To minimize the loss of ammonia from the sample to the ambient
atmosphere, do not dispense the samples or standards until
immediately before measurement. Do not adjust the pH of the
solutions until the electrode is immersed in the sample.
11.4 After the calibration curve is established, analyze the QCS. If
the measured value for the QCS is not within the specified limits
(Sect. 10.2.2), refer to Sect. 10.5.
350.6-11
-------
11.5 SAMPLE ANALYSIS
11.5.1 Rinse the electrode and the sample cup with three changes
of water (Sect. 7.2) or with a flowing stream from a wash
bottle.
11.5.2 Measure an aliquot of sample equivalent to that used for
the calibration standards. Immerse the clean electrode
into the sample and add NaOH (1 mL NaOH:15 mL sample).
Stir the solution while maintaining a stirring rate of
approximately 2 rps throughout the analysis. Allow
sufficient time for the reading to remain steady within
_+0.01 mg/L or 0.1 mV (depending on the meter used)
for 30 seconds. When the meter reading is stable, record
the measurement.
11.6 If the concentration of ammonium in a sample exceeds the working
range of the system, dilute the sample with zero standard and
reanalyze.
12. CALCULATIONS
12.1 Calculate a linear least squares fit of the standard concentration
as a function of the measured concentration. The linear least
squares equation is expressed as follows:
y a BO + BLX
where: y » standard concentration in mg/L
x = concentration measured
B = y-intercept calculated from: y - B x
B = slope calculated from:
n n
2 (x._ - x) (y - y)/ I (x - x)
i=l i=l
where: x = mean of concentrations measured
y = mean of standard concentrations
n = number of samples
The correlation coefficient should be 0.9990 or greater. Determine
the concentration of ammonium from the calibration curve.
12.2 An integration system may also be used to provide a direct readout
of the concentration of ammonium.
12.3 Report data in mg/L as NH . Do not report data lower than the
lowest calibration standard.
350.6-12
-------
13. PRECISION AND BIAS
13.1 The mean percent recovery and mean bias of this method were
determined from the analysis of spiked wet deposition samples
according to ASTM Standard Practice D4210, Annex A4 (14.7). The
results are summarized in Table 2. A small but statistically
significant bias of 0.05 mg/L was determined at a spike
concentration of 0.25 mg/L. No statistically significant bias was
present at a spike concentration of 0.10 mg/L.
13.2 Single-operator precision and bias were obtained from the analysis
of quality control check samples that approximated the levels
common to wet deposition samples. These results reflect the
accuracy that can be expected when the method is used by a
competent operator. These data are presented in Table 3.
14. REFERENCES
14.1 Annual Book of ASTM Standards, Part 31, "Excerpts from Standard
for Metric Practice," Standard E 380-79, 1982, pp. 679-694.
14.2 "Safety in Academic Chemistry Laboratories," American Chemical
Society Publication, Committee on Chemical Safety, 3rd Edition,
1979.
14.3 Annual Book of ASTM Standards, Part 31, "Standard Specification
for Reagent Water," Standard D 1193-77, 1982, p. 39.
14.4 Peden, M. E. and Skowron, L. M., "Ionic Stability of Precipitation
Samples," Atmos. Environ. 12, 1978, pp. 2343-2349.
14.5 Orion Research, Inc.', "Instruction Manual — Ammonia Electrode,
Model 95-12," Orion Research, Inc., Cambridge, Massachusetts, 1982,
pp. 1-17.
14.6 Topol, L. E., Lev-On, M., Flanagan, J., Schwall, R. J., Jackson, A.
E., Quality Assurance Manual for Precipitation Measurement
Systems, U.S. Environmental Protection Agency, Environmental
Monitoring Systems Laboratory, Research Triangle Park, NC 27711.
14.7 Annual Book of ASTM Standards, Section 11, Vol. 11.01 (1),
"Practice for rntralaboratory Quality Control Procedures and a
Discussion of Reporting Low-Level Data," Standard D4210 Annex A4,
1983, pp. 15-16.
350.6-13
-------
Table 1. Values for 2.3026 RT/F at Different
Temperatures.
Temperature, 2.3026 RT/F,
°C V
0 0.054
5 0.055
10 0.056
15 0.057
20 0.058
25 0.059
30 0.060
35 0.061
40 0.062
45 0.063
The above data were calculated using
a precise value of the logarithmic
conversion factor (2.302585) and values
of the fundamental constants.
F = 96,487.0 C/eq
R = 8.31433 J/K mol
T = 273.15 + °C
350.6-14
-------
Table 2. Single-Operator Precision and Bias for Ammonium
Determined from Anal/te Spikes of Wet Deposition Samples,
Analyte
Amount
Added,
mg/L na
Mean
Percent
Recovery
Mean
Bias,
mg/L
Standard
Deviation,
mg/L
Statistically
Significant
Bias?
Ammonium
0.10 10
0.25 8
125.0
119.0
0.02
0.05
0.02
0.01
No
Yes
a. Number of replicates
b. 95% Confidence Level
350.6-15
-------
Table 3. Single-Operator Bias and Precision for Ammonium
Determined from Quality Control Check Samples.
Theoretical Measured Precision,
Concentration,
mg/L
0.18
0.39
Concentration, Bias, s, RSD,
mg/L n mg/L % mg/L %
0.17 12 -0.01 -5.6 0,018 10.6
0.38 12 -0.01 -2.6 0.025 6.6
a. Number of replicates
350.6-16
-------
Figure 1. Percentile Concentration Values Obtained from
Wet Deposition Samples: Ammonium
w
H
3
100
90
80
70
60
50
40
30
20
10
0.50 1.00 1.50
CONCENTRATION (mg/L)
2.00
350.6-17
-------
Method 350.7 — Ammonium in Wet Deposition by Automated
Colorimetric Determination with Phenate
March 1986
Performing Laboratory:
Brigita Demir
Susan R. Bachman
Carla Jo Brennan
Mark E. Peden
Illinois State Water Survey
Analytical Chemistry Unit
2204 Griffith Drive
Champaign, Illinois 61820
Sponsoring Agency:
John D. Pfaff, Project Officer
Inorganic Analysis Section
Physical and Chemical Methods Branch
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
350.7-1
-------
INDEX
Section
Number Subject
1 Scope and Application
2 Summary of Method
3 Definitions
4 Interferences
5 Safety
6 Apparatus and Equipment
7 Reagents and Consumable Materials
8 Sample Collection, Preservation, and Storage
9 Calibration and Standardization
10 Quality Control
11 Procedure
12 Calculations
13 Precision and Bias
14 References
TABLES
1. Single-Operator Precision and Bias for Ammonium Determined from Analyte
Spikes of Wet Deposition Samples.
2. Single-'Operator Precision and Bias for Ammonium Determined from Quality
Control Check Samples.
FIGURES
1. Percentile Concentration Values Obtained from Wet Deposition Samples:
Ammoniunu
2. Ammonium Sampling and Analytical System ~ Segmented Flow.
350.7-2
-------
1. SCOPE AND APPLICATION
1.1 This method is applicable to the automated colorimetric determination
of ammonium in wet deposition samples by reaction with phenate.
1.2 The term "wet deposition" is used in this method to designate rain,
snow, dew, sleet, and hail.
1.3 The method detection limit (MDL) determined from replicate analyses
of a calibration standard containing 0.10 mg/L ammonium is 0.03 mg/L.
The concentration range of this method is 0.03-2.00 mg/L as NH +
4
1.4 Figure 1 represents a cumulative frequency percentile ammonium
concentration plot obtained from analyses of over five thousand wet
deposition samples. These data may be used as an aid in the
selection of appropriate calibration standard concentrations.
2. SUMMARY OF METHOD
2.1 A sample is introduced into the automated analyzer and mixed with a
complexing reagent to prevent the formation of hydroxide
precipitates. This solution is then mixed with alkaline phenol and
hypochlorite to form an indophenol blue complex. The blue color is
intensified with the addition of sodium nitroprusside. A 50°C
controlled temperature heating bath is used to increase the rate of
color formation. After color development, a flowcell receives the
solution for measurement of the color intensity. A light beam of the
wavelength characteristic of the indophenol complex is passed through
the solution. The transmitted light energy measured by a photodetectoi
is a function of the concentration of ammonium ion in the sample.
Beer's Law is used to relate the measured transmittance to
concentration:
log(l/T) » abc
where: T * transmittance
a - absorptivity
b • length of light path
c » concentration of absorbing species (mg/L)
A calibration curve is constructed using standard solutions
containing known concentrations of ammonium. From this curve, the
concentration of ammonium in a wet deposition sample is determined.
3. DEFINITIONS
3.1 COLORIMETRY — the measurement of light transmitted by a colored
complex as a function of concentration.
3.2 For definitions of other terms used in these methods, refer to the
glossary. For an explanation of the metric system including units,
symbols, and conversion factors see American Society for Testing and
Materials (ASTM) Standard t 380, "Metric Practices" (14.1).
-------
4. INTERFERENCES
4.1 Sample color absorbing in the wavelength range of 620-640 nm will
increase the measured concentration of ammonium in the sample. Wet
deposition samples are generally colorless, therefore, this type of
interference is rare.
4.2 Elevated concentrations of ammonia in the laboratory will result in
a positive interference.
5. SAFETY
5.1 The calibration standards, sample types and most reagents used in
this method pose no hazard to the analyst. Use a fume hood,
protective clothing, and safety glasses when handling concentrated
sulfuric acid (Sect. 7.5).
5.2 Use a fume hood when preparing the alkaline phenol (Sect. 7.3).
Vapors produced by this reagent are hazardous. Anytime this solution
is handled, wear gloves and safety goggles and ovoid all skin contact
with the phenol.
5.3 Follow American Chemical Society guidelines regarding the safe
handling of chemicals used in this method (14.2).
6. APPARATUS AND EQUIPMENT
6.1 AUTOMATED COLORIMETRIC INSTRUMENT — Select and assemble an
analytical system consisting of the following:
6.1.1 Sampler.
6.1.2 Proportioning Pump.
6.1.3 Analytical Cartridge.
6.1.4 Heating Bath -(50°C) equipped with an 8 mL capacity glass
heating coil.
6.1.5 Colorimeter "with a 630 nm wavelength setting. Ensure that the
colorimeter is equipped with photodetectors having maximum
sensitivity at this wavelength setting. A 15 mm flow cell is
adequate to achieve the MDL stated in Sect. 1.3.
6.1.6 Strip Chart Recorder (or other data acquisition device).
6.1.7 Printer (optional).
350.7-4
-------
6.2 Wherever possible, use glass transmission lines with an inside
diameter of 1.85 mm (0.073 inches) in the analytical cartridge and
colorimeter. Glass yields a more uniform sample flow and does not
degrade as quickly as other tubing materials. When connecting two
glass lines, ensure that the ends are abutted. To minimize pulsing
of the analytical stream, maintain uniform inside diameter throughout
all transmission tubing. Minimize the length of all transmission
tubing to optimize the performance of the hydraulic system.
6.3 Enclose the sampler with a dust cover to prevent contamination.
6.4 To prevent the intake of any precipitates from the reagents, install
intake filters at the end of the transmission lines that are used to
transport the reagents from their respective containers to the
proportioning pump.
6.5 LABORATORY FACILITIES — Laboratories used for the analysis of
wet deposition samples should be free from external sources of
contamination. The use of laminar flow clean air workstations is
recommended for sample processing and preparation to avoid the
introduction of airborne contaminants. Samples should always be
capped or covered prior to analysis. A positive pressure
environment within the laboratory is also recommended to minimize
the introduction of external sources of contaminant gases and
particulates. Windows within the laboratory should be kept closed
at all times and sealed if air leaks are apparent. The use of
disposable tacky floor mats at the entrance to the laboratory is
helpful in reducing the particulate loading within the room.
7. REAGENTS AND CONSUMABLE MATERIALS
7.1 PURITY OF REAGENTS — Use reagent grade chemicals for all solutions.
All reagents shaJ1 conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society (ACS), where
such specifications are available.
7.2 PURITY OF WATER ~ Use water conforming to ASTM Specification D
1193, Type II (14.3). Point of use 0.2 micrometer filters are
recommended for all faucets supplying water to prevent the
introduction of bacteria and/or ion exchange resins into reagents,
standard solutions, and internally formulated quality control check
solutions.
7.3 ALKALINE PHENOL — Add 35 g of sodium hydroxide (NaOH) to 250 mL of
water (Sect. 7.2). Stir and cool. Slowly add 85 mL of 88% (w/w)
phenol solution. Dilute to 500 mL with water (Sect. 7.2) and add
0.25 mL Brij-35 or another suitable wetting agent that is free from
ammonium. Refrigerate the solution at 4°C in an amber glass
container for a period not exceeding one week.
CAUTION: The vapors produced by the alkaline phenol solution are
hazardous. Avoid all respiratory and skin contact with this reagent.
Refer to Sect. 5.2 for an explanation of necessary safety
precautions.
350.7-5
-------
7.4 AMMONIUM SOLUTION, STOCK (1.0 mL = 1.0 mg NH ) — Dissolve 2.9654 g
of anhydrous ammonium chloride (NH Cl) , dried at 1C! C for one
hour, in water (Sect. 7.2) and dilute to 1 L. The stock solution is
stable for one year when stored at room temperature in a high density
polyethylene or polypropylene container.
7.5 COMPLEXING REAGENT — Dissolve 33 g of potassium sodium tartrate
(KNaC H.06-4H20) and 24 g of sodium citrate ( (HOC (COONa)CH2COONa) 2« 2H20)
in 950 mL of water (Sect. 7.2). Add 2.5 mL of concentrated sulfuric
acid (H SO , sp gr 1.84). Dilute to 1 L with water (Sect. 7.2)
and refrigerate at 4°C in a glass container.
7.6 SAMPLER RINSE WATER — Add 0 . 5 mL Brij-35 or another suitable wetting
agent that is free from ammonium to 1 L of water (Sect. 7.2).
7.7 SODIUM HYPOCHLORITE SOLUTION (1.75% w/v) — Dilute 100 mL of 5.25%
sodium hypochlorite (NaOCl) solution to 300 mL with water (Sect. 7.2).
Prepare this solution fresh daily and store at room temperature in a
high density polyethylene or polypropylene container. Commercial
bleach products containing about 5.25% (w/v) sodium hypochlorite may be
used. Due to the instability of commercial bleaches, avoid storage
periods longer than six months.
7.8 SODIUM NITROPRUSSIDE SOLUTION (500 mg/L) — Dissolve 0.5 g of sodium
nitroprusside (Na.Fe (CN) -NO'H.O) in water (Sect. 7.2) and
dilute to 1 L. Store at room temperature away from light in an amber
glass container.
7.9 SAMPLE CONTAINERS — Use polyolefin sample cups or glass test tubes
that have been rinsed thoroughly with water (Sect. 7.2) before use.
8. SAMPLE COLLECTION, PRESERVATION AND STORAGE
8.1 Collect samples in high density polyethylene (HDPE) containers that
have been thoroughly rinsed with ASTM Type II water (7.2). Do not
use strong mineral acids or alkaline detergent solutions for cleaning
collection vessels. Residual acids may remain in the polyethylene
matrix and slowly leach back into the sample. Alkaline detergents
may also leave residues that may affect the sample chemistry. Cap
collection bottles after cleaning to prevent contamination from
airborne contaminants; air dry collection buckets in a laminar flow
clean air workstation and wrap in polyethylene bags prior to use. If
a laminar flow workstation is not available, pour out any residual
rinse water and bag the buckets immediately. Do not dry the bucket
interior by any method other than air drying in a laminar flow clean
air workstation.
350.7-6
-------
8.2 The frequency of sample collection and the choice of sampler design
are dependent on the monitoring objectives. In general, the use of
wet-only samplers is recommended to exclude dry deposition
contributions, minimize sample contamination, retard evaporation,
and enhance sample stability. Sample collection frequency may vary
from subevent to monthly sampling periods. Collection periods of
more than one week are not recommended since sample integrity may be
compromised by longer exposure periods.
8.3 The presence of microbial activity will affect the stability of
ammonium ion in wet deposition samples. This instability generally
results in a decrease in ammonium concentration. Measurements of
NH should be made immediately after sample collection.
Refrigeration of samples at 4 C will minimize but not prevent a
decrease in the ammonium ion concentration.
8.3.1 Filtration of samples through a 0.45 micrometer membrane
leached with water (Sect. 7.2) followed by refrigeration at
4°C is the recommended preservation technique for ammonium
ion. Holding times should not exceed seven days. Monitoring
of the filtration procedure is necessary to ensure that
samples are not contaminated by the membrane or filtration
apparatus.
9. CALIBRATION AND STANDARDIZATION
9.1 INSTRUMENT OPTIMIZATION
9.1.1 For a flow segmented system with a concentration range from
0.03-2.00 mg/L as ammonium, assemble the sampling and
analytical system as shown in Figure 2.
9.1.2 Use flow rated polyvinyl xrhloride (PVC) or polyethylene pump
and transmission tubing throughout -the sampling and analytical
system. Check the tubing for chemical buildup, splits,
cracks, and deformations before beginning each day's analysis.
Change pump tubes after 50 hours of operation. Change
transmission tubing after 100 hours of operation or when
uneven flow patterns are observed.
9.1.3 Optimize the tension of the pump tubes according to
manufacturer's recommendations.
9.1.4 Set the heating bath to 50°C. Set the wavelength of the
colorimeter to 630 nm. Allow the colorimeter and heating
bath to warm up for 30 minutes while pumping sampler rinse
water and reagents through the system. After a stable
baseline has been obtained, adjust the recorder to maximize
the full-scale response.
350.7-7
-------
9.1.5 Sample at a rate of 40 samples/hour with a 1:4 sample to
rinse ratio. This sampling rate provides good peak
separation. Adjust the colorimeter to maximize sensitivity .
while minimizing instrument noise. Refer to the
manufacturer's recommendations.
9.2 CALIBRATION SOLUTIONS
9.2.1 Five calibration solutions and one zero standard are needed to
generate a suitable calibration curve. The lowest calibration
solution should contain ammonium at a concentration greater
than or equal to the method detection limit. The highest
solution should approach the expected upper limit of
concentration of ammonium in wet deposition. Prepare the
remaining solutions such that they are evenly distributed
throughout the concentration range. Suggested calibration
standards for ammonium are as follows: zero, 0.03, 0.40,
0.75, 1.00, and 1.50 mg/L as NH4+.
9.2.2 Prepare all calibration standards by diluting the stock
standard (Sect. 7.4) with water (Sect. 7.2). Use glass
(Class A) or plastic pipettes that are within the bias and
precision tolerances specified by the manufacturer. Standards
with a concentration greater than 0.10 mg/L ammonium are
stable for one week if stored at room temperature in high
density polyethylene or polypropylene containers. Prepare
standards with 0.10 mg/L or less ammonium every day and store
at room temperature in high density polyethylene or
polypropylene containers.
9.3 CALIBRATION CURVE
9.3.1 Analyze the standard containing the highest concentration of
ammonium and adjust the colorimeter calibration control to
obtain full-scale deflection on the recorder. Use the zero
standard to set the* instrument baseline. If 'a printer is
used, adjust it to read the correct concentration. Analyze
all the standards and construct a calibration curve according
to Sect. 12. After every 30 samples and at the end of each
day's analyses, reconstruct the entire calibration curve.
9.3.2 Verify the calibration curve after every ten samples and at
the end of each day's analyses according to Sect. 10.5.
10. QUALITY CONTROL
10.1 Each laboratory using this method should develop formalized quality
control protocols to continually monitor the bias and precision of
all measurements. These protocols are required to ensure that the
measurement system is in a state of statistical control. Estimates
of bias and precision for wet deposition analyses cannot be made
unless these control procedures are followed. Detailed guidelines
for the development of quality assurance and quality control
protocols for wet deposition measurement systems are published in a
350.7-8
-------
manual available from the United States Environmental Protection
Agency, Research Triangle Park, NC 27711 (14.4). Included in this
manual are procedures for the development of statistical control
charts for use in monitoring bias and precision as well as
recommendations for the introduction of reagent blanks, laboratory
duplicates, field duplicates, spike samples, and performance
evaluation samples. These guidelines are to be used by all
laboratories involved with wet deposition measurements.
10.2 ESTABLISHMENT OF WARNING AND CONTROL LIMITS — Warning and control
limits are used to monitor drift in the calibration curve, analyses
of quality control check samples (QCS), and measured recoveries
from laboratory spikes.
10.2.1 Calibration Curve — After a calibration curve has been
constructed according to Sect. 12, reanalyze additional
aliquots of the low and high concentration standards.
Calculate the concentrations using the previously derived
calibration curve. Repeat this procedure until at least
ten determinations at each concentration level have been
made. These data should be collected on ten different days
to provide a realistic estimate of the method variability.
Calculate a standard deviation (s) at each concentration
level. Use the nominal standard concentration as the mean
value (x) for determining the control limits. A warning
limit of X j* 2s and a control limit of x Ł 3s should be
used. Reestablish these limits whenever instrumental
operating conditions change.
10.2.2 Quality Control Check Samples (QCS) — Calculate warning
and control limits for QCS solutions from a minimum of ten
analyses performed on ten days. Use the calculated
standard deviation (s) at each QCS concentration level to
develop the limits as described in Sect. 10.2.1. Use the
certified or NBS traceable concentration as the mean
(target) value. Constant positive or negative measurements
with respect to the true value are indicative of a method
or procedural bias. Utilize the data obtained from QCS
measurements as in Sect. 10.4 to determine when the
measurement system is out of statistical control. The
standard deviations used to generate the QCS control limits
should be comparable to the single operator precision
reported in Table 2. Reestablish new warning and control
limits whenever instrumental operating conditions are
varied or QCS concentrations are changed.
10.2.3 Laboratory Spike Solutions — A minimum of ten analyte
spikes of wet deposition samples is required to develop a
preliminary data base for the calculation of warning and
control limits for spike recovery data. Select the spike
concentration such that the working range of the method
will not be exceeded. Samples selected for the initial
spike recovery study should represent the concentration
range common to wet deposition samples in order to reliably
350.7-9
-------
estimate the method accuracy. Calculate a mean and
standard deviation of the percent recovery data using the
formulas provided in the glossary. Determine warning and
control limits using +2s and +3s, respectively. If
the data indicate that no significant method bias exists
(14.5), the 100 percent recovery is used as the mean
percent recovery. Where a significant bias is determined
at the 95% confidence level, the control limits are
centered around the bias estimate. Routine spiked sample
analyses that yield percent recovery data outside of the
control limits are an indication of matrix interferences
that should be resolved before routine analyses are
continued.
10.2.4 All warning and control limits should be reevaluated on a
continual basis as additional data are collected during
routine analyses. The limits should be broadened or
narrowed if a recalculated standard deviation under similar
operating conditions provides a different estimate of the
procedure variability.
10.3 Monitor the cleaning procedure by pouring a volume of water (Sect.
7.2) that approximates the median sample size into the collection
vessel. Allow the water to remain in the sealed or capped
collection container for at least 24 hours and determine the
ammonium concentration. If the solution concentration "exceeds the
MDL, a contamination problem is indicated in the cleaning
procedure. Take corrective action before the sampling containers
are used for the collection of wet deposition.
10.4 Analyze a quality control check sample (QCS) after the calibration
curve has been established. This sample may be formulated in the
laboratory or obtained from the National Bureau of Standards (NBS
Standard Reference Material 2694, Simulated Rainwater). Verify the
accuracy of internally formulated QCS solutions with an NBS
traceable standard before acceptance as a quality control check.
The check sample(s) selected must be within the range of the
calibration standards. If the measured value for the QC1 falls
outside of the _+3s'limits (Sect. 10.2.2), or if two successive
QCS checks are outside of the ^2s limits, a problem is indicated
with the system or the calibration procedure. Corrective action
should be initiated to bring the results of the QCS within the
established control -limits. Plot the data obtained from the QCS
checks on a control chart for routine assessments of bias and
precision.
10.5 Verify the calibration curve after a maximum of ten samples, and at
the end of each day's analyses. Analyze calibration standards at
the low and high ends of the working range. If the routine
.calibration checks do not meet the criteria described in Sect.
10.4, recalibrate the system and reanalyze all samples from the
last time the system was in control. Verify the new calibration
curve with the QCS according to Sect. 10.4 and reanalyze all
samples measured since the last time the system was in control.
350.7-10
-------
10.6 Submit a Field Blank (FB) to the laboratory for every 20 samples.
The FB may consist of a water sample (Sect. 7.2) or a known
reference solution that approximates the concentration levels
characteristic of wet deposition. The FB is poured into the
sampling vessel at the field site and undergoes identical
processing and analytical protocols as the wet deposition
sample(s). Use the analytical data obtained from the FB to
determine any contamination introduced in the field and laboratory
handling procedures. The data from the known reference solution
can be used to calculate a system precision and bias.
10.7 Prepare and analyze a laboratory spike of a wet deposition sample
according to the guidelines provided in "Quality Assurance Manual
for Precipitation Measurement Systems" (14.4). Compare the results
obtained from spiked samples to those obtained from identical
samples to which no spikes were added. Use these data to monitor
the method percent recovery as described in Sect. 10.2.3.
10.8 Participation in performance evaluation studies is recommended for
wet deposition chemistry laboratories. The samples used for these
performance audits should contain the analytes of interest at
concentrations within the normal working range of the method. The
true values are unknown to the analyst. Performance evaluation
studies for wet deposition chemistry laboratories are conducted
semiannually by the USEPA Performance Evaluation Branch, Quality
Assurance Division, Research Triangle Park, NC 27711.
11. PROCEDURE
11.1 Optimize the instrument each day according to Sect. 9.1.
11.2 Prepare all standards and construct a calibration curve according
to Sect. 9.2 and 9.3.
11.3 After the calibration curve is established, analyze the QCS. If
the measured value for the QCS is not within the specified limits
(Sect. 10.2.2), refer to Sect. 10.4.
11.4 Load the sampler tray and begin analysis.
11.5 If the peak height response exceeds the working range of the
system, dilute the sample with zero standard and reanalyze.
11.6 When analysis is complete, turn off the heating bath and rinse the
system with sampler rinse water (Sect. 7.6) for 15 minutes.
350 7-11
-------
12. CALCULATIONS
12.1 Calculate a linear least squares fit of the standard concentration
as a function of the measured peak height. The linear least
squares equation is expressed as follows:
where: y = standard concentration in mg/L
x = peak height measured
BO = y-intercept calculated from: y - B.x
B » slope calculated from:
n n
Ł (x. - x) (y. - y)/ Ł (x. - x)
i»l 1 1 i=l
where: 3? = mean of peak heights measured
y = mean of standard concentrations
n = number of samples
The correlation coefficient should be 0.9990 or greater. Determine
the concentration of ammonium from the calibration curve.
12.2 If the relationship between standard concentration and measured
peak height is nonlinear, use a second degree polynomial least
squares equation to derive a curve with a correlation 2.0-9990.
The second degree polynomial equation is expressed as follows:
y = B2x •»• BXX +• BQ
A computer is necessary for the derivation of this function.
Determine the concentration of ammonium from the calibration curve.
12.3 An integration system may also be used to provide a direct readout
of the concentration of ammonium.
12.4 Report data in mg/L as NH . Do not report data lov/er than the
lowest calibration standard.
13. PRECISION AND BIAS
13.1 The mean percent recovery and mean bias of this method were
determined from the analysis of spiked wet deposition samples
according to ASTM Standard Practice D4210, Annex A4 (14.5). The
results are summarized in Table 1. No statistically significant
biases were found.
13.2 Single-operator precision and bias were obtained from the analysis
of quality control check samples that approximated the levels
common to wet deposition samples. These results reflect the
accuracy that can be expected when the method is used by a
competent operator. These data are presented in Table 2.
350.7-12
-------
14. REFERENCES
14.1 Annual Book of ASTM Standards, Part 31, "Excerpts from Standard
for Metric Practice," Standard E 380-79, 1982, pp. 679-694.
14.2 "Safety in Academic Chemistry Laboratories," American Chemical
Society Publication, Committee on Chemical Safety, 3rd Edition,
1979.
14.3 Annual Book of ASTM Standards, Part 31, "Standard Specification
for Reagent Water," Standard D 1193-77, 1982, p. 39.
14.4 Topol, L. E., Lev-On, M., Flanagan, J., Schwall, R. J., Jackson, A.
E., Quality Assurance Manual for Precipitation Measurement
Systems, 1985, U.S. Environmental Protection Agency, Environmental
Monitoring Systems Laboratory, Research Triangle Park, NC 27711.
14.5 Annual Book of ASTM Standards, Section 11, Vol. 11.01 (1),
"Practice for Intralaboratory Quality Control Procedures and a
Discussion of Reporting Low-Level Data," Standard D4210 Annex A4,
1983, pp. 15-16.
350.7-13
-------
Table 1. Single-Operator Precision and Bias for Ammonium
Determined from Analyte Spikes of Wet Deposition Samples,
Analyte
Amount
Added,
mg/L
Mean
Percent
Recovery
Mean
Bias,
mg/L
Standard
Deviation,
mg/L
Statistically
Significant
Bias?
Ammonium
0.17 8
0.74 10
100.0
103.4
-0.01
0.02
0.01
0.03
No
No
a. Number of replicates
b. 95% Confidence Level
350.7-14
-------
Table 2. Single-Operator Bias and Precision for Ammonium
Determined from Quality Control Check Samples.
Theoretical Measured Precision,
Concentration, Concentration, Bias, s, RSD,
mg/L mg/L na mg/L % mg/L %
0.19 0.18 215 -0.01 -5.3 0.02 11.1
0.36 0.36 82 0.00 0.0 0.02 5.6
0.98 0.92 224 -0.06 -6.1 0.05 5.4
1.22 1.24 81 0.02 1.6 0.03 2.4
The above data were obtained from records of measurements made under the
direction of the NADP/NTN quality assurance program.
a. Number of replicates
350.7-15
-------
Figure 1. Percentile Concentration Values Obtained from
Wet Deposition Samples: Ammonium
I
s
til
M
3
100
90
80
70
60
50
40
30
20
10
0.50 1.00 1.50
CONCENTRATION (mg/L)
2.00
350.7-16
-------
Figure 2. Ammonium Sampling and Analytical
System — Segmented Flow.
Pump Tube Flow Rate
**• •>
V S
(
I
•»« . •*
20 Turn
| Mixing Coil
i
20
Turn
| Mixing Coil
HEATER
50° C
,
Colors
Blu Biu
Grn Grn
Om Qrn
Red Red
Blk 81k
Orn Orn
Blk Blk
Orn Orn
'A (mL/min)
' , cn waste
? flow
' cell
^
'" 2.00$arT|P|er
^ water
' 0.42
reagent
0.32
0.42 alk
phc
aline
nol
0.32 sodium
nypochiome
!0.42 sodium
nitroprussiae
PROPORTIONING
PUMP
t
COLORIMETER
630 nm
R
ECORDER
f*
[ SAMPLE
v
LX-x
r^
Sampling Ran
40/hr
Sampling Voli
0.13mL
Sample to Rin
1:4
(IS second a
7 2 second n
350.7-17
-------
Appendix M
METHOD 200.6 — DISSOLVED CALCIUM, MAGNESIUM, POTASSIUM, AND SODIUM
IN WET DEPOSITION BY FLAME ATOMIC ABSORPTION SPECTROPHOTOMETRY
M-l
-------
Method 200.6 — Dissolved Calcium, Magnesium, Potassium,
and Sodium in Wet Deposition by Flame Atomic
Absorption Spectrophotometry
March 1986
Performing Laboratory:
Loretta M. Skowron
Carla Jo Brennan
Mark E. Peden
Illinois State Water Survey
Analytical Chemistry Unit
2204 Griffith Drive
Champaign, Illinois 61820
Sponsoring Agency:
John D. Pfaff, Project Officer
Inorganic Analysis Section
Physical and Chemical Methods Branch
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
200.6-1
-------
INDEX
Section
Number Subject
1 Scope and Application
2 Summary of Method
3 Definitions
4 Interferences
5 Safety
6 Apparatus and Equipment
7 Reagents and Consumable Materials
8 Sample Collection, Preservation, and Storage
9 Calibration and Standardization
10 Quality Control
11 Procedure
12 Calculations
13 Precision and Bias
14 References
TABLES
Method Detection Limits and Concentration Ranges for Flame Atomic
Absorption Spectrophotometric Analysis of Wet Deposition.
Operating Conditions and Suggested Calibration Standard Concentrations
for the Determination of Calcium, Magnesium, Potassium, and Sodium in Wet
Deposition Samples.
Single-Operator Precision and Bias for Calcium, Magnesium, Potassium, and
Sodium.Determined from Analyte Spikes of Wet Deposition Samples.
Single-Operator Precision and Bias for Calcium, Magnesium, Potassium, and
Sodium Determined from Quality Control Check Samples.
FIGURES
1. Percentile Concentration Values Obtained from Wet Deposition Samples:
Calcium, Magnesium, Potassium, and Sodium.
200.6-2
-------
7. REAGENTS AND CONSUMABLE MATERIALS
7.1 PURITY OF REAGENTS — Use chemicals of reagent grade or better for
all solutions. All reagents shall conform to the specifications of
the Committee on Analytical Reagents of the American Chemical Society
(ACS) where such specifications are available.
7.2 PURITY OF WATER — Use water conforming to ASTM Specification D
1193, Type II (14.9).
7.3 ARGON — Use standard, welder's grade compressed argon. A line
filter or trap is recommended to ensure particle and moisture
free gas. Nitrogen is not recommended because of its tendency to
form stable nitrides with aluminum at high temperatures.
7.4 HYDROCHLORIC ACID — Use concentrated hydrochloric acid (HC1, sp gr
1.19) that meets specification for trace metal analysis «0.05 mg/L
Al, <0.02 mg/L Fe, and <0.005 mg/L Cd, Cu, Pb, Mn, and Zn).
7.5 HYDROCHLORIC ACID (6.0 N) — Add 1 volume of concentrated
hydrochloric acid (HC1, sp gr 1.19) to an equal volume of water
(Sect. 7.2).
7.6 NITRIC ACID -- Use concentrated nitric acid (HN03, sp gr 1.43)
that meets specification for trace metal analysis (Sect. 7.4).
7.7 NITRIC ACID (8.0 N) — Add 1 volume of concentrated nitric acid
(HNO , sp gr 1.43) to an equal volume of water (Sect. 7.2).
7.8 NITRIC ACID (3.2 N) — Add 1 volume of concentrated nitric acid
(HNO-, sp gr 1.43) to 4 volumes of water (Sect. 7.2).
7.9 STOCK STANDARD SOLUTIONS — Stock standard solutions may be
purchased as certified solutions or prepared from ACS reagent grade
materials as detailed below. Store the solutions at room temperature
in polyethylene containers.
7.9.1 Aluminum Solution, Stock (1.0 mL = 1.0 mg Al) — Dissolve
1.000 g of pure aluminum wire in 50 mL of concentrated HC1
(Sect. 7.4) over low heat. Cool and dilute to 1 L with water
(Sect. 7.2).
7.9.2 Cadmium Solution, Stock (1.0 mL = 1.0 mg Cd) — Dissolve
1.000 g of pure metallic cadmium in 50 mL of 6.0 N HC1
(Sect. 7.5) and dilute to 1 L with water (Sect. 7.2).
7.9.3 Copper Solution, Stock (1.0 mL » 1.0 mg Cu) — Dissolve
1.000 g of electrolytic copper in 50 mL of 8.0 N HNO
(Sect. 7.7) and dilute to 1 L with water (Sect. 7.2).
7.9.4 Iron Solution, Stock (1.0 mL « 1.0 mg Fe) — Dissolve
1.000 g of pure metallic iron in 50 mL of 6.0 N HC1
200.6-8
-------
(Sect. 7.5) and dilute to 1 L with water (Sect. 7.2).
7.9.5 Lead Solution, Stock (1.0 mL = 1.0 mg Pb) — Dissolve
1.000 g of pure metallic lead or 1.598 g of lead nitrite
(Pb(NO ) ) in 50 mL of 8.0 N HNO (Sect. 7.7) and
dilute to 1 L with water (Sect. 7.2).
7.9.6 Manganese Solution, Stock (1.0 mL = 1.0 mg Mn) — Dissolve
1.000 g of pure metallic manganese in 50 mL of 8.0 N HNO
(Sect. 7.7) and dilute to 1 L with water (Sect. 7.2).
7.9.7 Zinc Solution, Stock (1.0 mL = 1.0 mg Zn) — Dissolve
1.000 g of pure metallic zinc in 50 mL of 6.0 N HC1
(Sect. 7.5) and dilute to 1 L with water (Sect. 7.2).
7.10 GRAPHITE FURNACE TUBES
7.10.1 Pyrolytically coated graphite tubes will improve
sensitivity, reduce memory effects, and decrease carbide
formation by reducing sample penetration into the tube-wall,
Note: The samples are acidic (Sect. 8.4) and will degrade
the coating and rapidly decrease the signal to noise ratio.
7.10.2 Platforms or graphite tubes with walls thicker in the
center are recommended as a method of decreasing
interferences (Sect. 4.1.1.1) (14.4).
7.11 BOTTLES FOR SAMPLES AND STANDARDS — Use polyethlene containers.
7.11.1. Rinse thoroughly with water (Sect. 7.2).
7.11.2 Fill with 3.2 N HNO (Sect. 7.8) and leach for 48 hours.
7.11.3 Discard leachate and rinse thoroughly with water
(Sect. 7.2).
7.11.4 Refill with water (Sect. 7.2) and leach for 24 hours.
7.11.5 Discard leachate and rinse thoroughly with water
(Sect. 7.2) .
7.11.6 Refill with water (Sect. 7.2) and store.
7.11.7 Rinse thoroughly with water (Sect. 7.2) before use.
7.12 SAMPLE CONTAINERS — Use disposable polystyrene sample cups that
have been thoroughly rinsed with water (Sect. 7.2) before use. Do
not reuse.
7.12.1. Check sample cups for contamination. If contamination
is a problem, clean the sample cups as directed in
Sect. 7.11.
200.6-9
-------
8. SAMPLE COLLECTION, PRESERVATION, AND STORAGE
8.1 Collect samples in a funnel connected to a sample bottle. All
components should be constructed of polyethylene (14.10) or
fluorohydrocarbon plastic. Clean according to Section 7.11 (14.11).
Cap collection bottles after cleaning. Air dry funnels and tubing
in a laminar flow clean air work station and store in new
polyethylene bags.
8.1.1. Evaluate the cleaning procedure according to Section 10.3.
and check for desorption and/or adsorption of trace metals
(14.10) .
8.2 The use of wet-only samplers is recommended to exclude dry
deposition contributions, minimize sample contamination, retard
evaporation, and enhance sample stability. Sample collection
frequency may vary from subevent to event sampling periods.
Collection periods of more than one day are not recommended since
sample integrity may be compromised by longer exposure periods.
8.3 Immediately after collection, filter the samples through a 0.4um
polycarbonate membrane which has been leached with 300 mL of water
(Sect. 7.2). A polysulfone filtration apparatus is recommended. Do
not use glass. Monitoring of the filtration procedure is necessary
to ensure that metals are neither adsorbed nor desorbed on the
membrane or filtration apparatus.
8.4 Immediately after filtration, acidify the filtrate to pH 1.8
(1.0 mL = 1 uL HN03 (Sect. 7.6)). This will stabilize and
preserve the metals in solution. Filtered and acidified samples
are stable for up to six months.
9. CALIBRATION AND STANDARDIZATION
9.1 CALIBRATION SOLUTIONS
9.1.1 Five calibration standards and one zero standard are
required. The lowest calibration standard should contain the
analyte of interest at a concentration of one to five times
the method detection limit. The highest standard
concentration is determined by curve linearity, sensitivity,
and expected analyte concentrations. The remaining standards
are uniformly distributed between the low and high standards.
Suggested calibration standard concentrations are listed in
Table 3.
9.1.2 Prepare calibration standards by diluting stock standards
with water (Sect. 7.2). Acidify the solution to pH 1.8
(1.0 mL = luL HNO3 (Sect. 7.6)) for Cd, Cu, Fe, Pb,. Mn,
and Zn. Acidify aluminum standards to pH 1.1
(1.0 mL = 5 uL HNO (Sect. 7.6)). Use plastic tipped
pipettes that are within the precision and tolerances
specified in Sect. 6.3.1.
200.6-1.0
-------
9.1.3 The calibration standards for Al, Cu, Fe, Mn, and Pb are
stable for six months if stored at room temperature in nitric
acid leached (Sect. 7.11) high density polyethylene (HOPE)
bottles. Standards for Cd and Zn are stable for three months.
NOTE: If bottles are used that are made of a plastic other
than HOPE, the cleaning procedure must be evaluated according
to Sect. 10.2.1 and 10.3.
9.2 CALIBRATION
9.2.1 A calibration curve must be constructed every day. If the
instrument is turned off or if there is an interruption in
the heating cycle, verify the calibration curve.
9.2.2 Clean any residue from the graphite tube by heating to
atomization temperature until there is no absorbance signal.
Analyze the zero standard and check for peaks in the
atomization stage. If a peak is apparent, analyze another
zero standard. An atomization peak indicates a memory
effect (Sect. 4.2), zero standard contamination, or
contamination in the furnace components. Refer to
Appendix A for corrective action. When atomization of the
zero standard results in no absorbance peaks, continue.
9.2.3 Analyze the calibration standards and record their
absorbances. Duplicates of each standard should agree
within Ł 5% RSD for Cd, Cu, Fe, Mn, and Zn and Ł 10%
RSD for Al and Pb.
NOTE: The lowest calibration standard will usually have
higher RSD's. Duplicate agreements of Ł 15% are accept-
able for the lowest standards, since they are at the MDL.
9.2.4 Construct calibration curves for each analyte according
to Sect. 12.
200.6-11
-------
10. QUALITY CONTROL
10.1 Each laboratory using this method should develop formalized
quality control protocols to continually monitor the bias and
precision of all measurements. These protocols are required to
ensure that the measurement system is in a state of statistical
control. Estimates of bias and precision for wet deposition
analyses cannot be made unless these control procedures are
followed. Detailed guidelines for the development of quality
assurance and quality control protocols for precipitation
measurement systems are published in a manual available from the
United States Environmental Protection Agency, Research Triangle
Park, NC 27711 (14.12). Included in this manual are procedures
for the development of statistical control charts for use in
monitoring bias and precision as well as recommendations for the
introduction of reagent blanks, laboratory duplicates, field
duplicates, spike samples, and performance evaluation samples.
These guidelines are to be used by all laboratories involved with
wet deposition measurements.
10.2 ESTABLISHMENT OF WARNING AND CONTROL LIMITS — Warning and control
limits are used to monitor drift in the calibration curve, analyses
of quality control check samples (QCS), and measured recoveries
from laboratory spikes.
10.2.1 Calibration Curve — After a calibration curve has been
constructed according to Sect. 12, reanalyze additional
aliquots of all the standards. Calculate the
concentrations using the previously derived calibration
curve. Repeat this procedure until at least ten
determinations at each concentration level have been made.
These data should be collected on ten different days to
provide a realistic estimate of the method variability.
Calculate a standard deviation (s) at each concentration
level. Use the nominal standard concentration as the mean
value (x) for determining the control limits. A warning
limit of x + 2s and a control limit of x ^ 3s should be
used. Reestablish these limits whenever instrumental
operating conditions change.
10.2.2 Quality Control Check Samples (QCS) — Calculate warning
and control limits for QCS solutions from a minimum of ten
analyses performed on ten days. Use the calculated
standard deviation (s) at each QCS concentration level to
develop the limits as described in Sect. 10.2.1. Use the
certified concentration as the mean (target) value.
Constant positive or negative measurements with respect to
the true value are indicative of a method or procedural
bias. Utilize the data obtained from QCS measurements as
in Sect. 10.5 to determine when the measurement system is
out of statistical control. The standard deviations used
to generate the QCS control limits should be comparable to
20n *-
-------
the single operator precision reported in Table 4.
Reestablish new warning and control limits whenever
instrumental operating conditions are varied or QCS
concentrations are changed.
10.2.3 Laboratory Spike Solutions — A minimum of ten analyte
spikes of wet deposition samples is required to develop a
preliminary data base for the calculation of warning and
control limits for spike recovery data. Select the spike
concentration such that the working range of the method
will not be exceeded. Samples selected for the initial
spike recovery study should represent the concentration
range common to wet deposition samples in order to reliably
estimate the method accuracy. Calculate a mean and
standard deviation of the percent recovery data using the
formulas provided in the glossary. Determine warning and
control limits using ^f2s and ^3s, respectively. If
the data indicate that no significant method bias exists
(14.13), the 100 percent recovery is used as the mean
percent recovery. Where a significant bias is determined
at the 95% confidence level, the control limits are
centered around the bias estimate. Routine spiked sample
analyses that yield percent recovery data outside of the
control limits are an indication of matrix interferences
that should be resolved before routine analyses are
continued.
10.2.4 All warning and control limits should be reevaluated on a
continual basis as additional data are collected during
routine analyses. The limits should be broadened or
narrowed if a recalculated standard deviation under similar
operating conditions provides a different estimate of the
procedure variability.
10.3 Monitor the cleaning procedure by pouring a volume of water (Sect.
7.2) that approximates the median sample size into the collection
vessel. Allow the water to remain in the sealed or capped
collection container for at least 24 hours and determine the
concentration of the analytes of interest. If any of the measured
concentrations exceed the MDL, a contamination problem is indicated
in the cleaning procedure. Take corrective action before the
sampling containers are used for the collection of wet deposition.
10.4 Keep daily records of calibration data and the instrument
operating parameters. Use these historical data as general
performance indicators. Gross changes in sensitivity, curve
linearity, or photomultiplier tube voltage are indicative of a
problem. Possibilities include instrument malfunction, defective
graphite tube, arcing in the furnace, improper optimization,
faulty hollow cathode lamp, contamination, and inaccurate standard
solutions.
200.6-13
-------
10.5 Analyze a quality control check sample (QCS) after a calibration
curve has been established. This sample may be formulated in the
laboratory or obtained from the U.S. Environmental Protection
Agency (USEPA), Environmental Monitoring and Support Laboratory
in Cincinnati,Ohio. The check sample selected must be within the
range of the calibration standards, and it must be prepared at
the same acid concentration. Prepare according to Sect. 11.6.
If the measured value for the QCS falls outside of the +^s limits
(Sect. 10.2.2), or if two successive QCS checks are outside of the
+2s limits, a problem is indicated with the spectrophotometer or
calibration curve. Reestablish the baseline with the zero standard
and/or recalibrate. If the QCS analysis is still beyond control
limits, inaccurate working standards might be the problem. Prepare
new standards. Plot the data obtained from the QCS checks on a
control chart for routine assessments of bias and precision.
10.6 Reestablish the baseline with the zero standard after every ten
samples. Verify the calibration curve after a maximum of twenty
samples and at the end of each day's analyses by analyzing
calibration standards at the low and high ends of the working
range. If the routine calibration checks do not meet the criteria
described in Sect. 10.2.1, recalibrate the system and reanalyze
all samples from the last time the system was in control. Verify
the new calibration curve with the QCS according to Sect. 10.5 and
reanalyze all samples from the last time the measurement system
was in control.
10.7 Submit a Field Blank (FB) to the laboratory for every 20 samples.
The FB may consist of a water sample (Sect. 7.2) or a known
reference solution that approximates the concentration levels
characteristic of wet deposition. The FB is poured into the
sampling vessel at the field site and undergoes identical
processing and analytical protocols as the wet deposition
sample(s). Use the analytical data obtained from the FB to
determine any contamination introduced in the field and laboratory
handling procedures. The data from the known reference solution
can be used to calculate a system precision and bias.
10.8 Prepare and analyze a laboratory spike of a wet deposition sample
according to the guidelines provided in "Quality Assurance Manual
for Precipitation Measurement Systems" (14.12). Compare the
results obtained from the spiked samples to those obtained from
identical samples to which no spikes were added. Use these data
to monitor the method percent recovery as described in Sect.
10.2.3.
10.9 Participation in performance evaluation studies is recommended
for precipitation chemistry laboratories. The samples used for
these performance audits should contain the analytes of interest
at concentrations within the normal working range of the method.
The true values are unknown to the analyst. Performance
evaluation studies for precipitation chemistry laboratories are
conducted semiannually by the USEPA Performance Evaluation Branch,
Quality Assurance Division, Research Triangle Park, NC 27711.
200.6-14
-------
10.10 INSTRUMENT MAINTENANCE — Strictly adhere to manufacturer's
maintenance schedule.
10.10.1 Exposed optical mirrors should be replaced yearly to
maintain optimal sensitivity and precision.
10.10.2 Clean all exposed lenses weekly. Use methanol and
lint-free laboratory wipes.
10.10.3 Each time the graphite tube is changed, thoroughly clean
the furnace parts and electrodes with methanol. Check
all parts for wear and replace if necessary.
11. PROCEDURE
11.1 SET AAS PARAMETERS
11.1.1 Lamp Current — Refer to manufacturer's guidelines for
optimization of this parameter. The use of excessively
high currents will shorten lamp life. High currents also
cause line broadening, resulting in a reduction in
sensitivity and calibration curve linearity. The use
of currents that are too low will cause, lamp instability
and insufficient throughput of energy through the
instrument's optical system. The result is increased
signal noise due to excess electrical gain applied to
the photodetector.
11.1.2 Light Beam — Focus the light beam in the center of the
graphite tube according to the manufacturer's guide-
lines. Rotate the lamp within its holder for maximum
energy output readings.
11.1.3 Furnace Alignment — Position the atomizer cell so that
the light beam passes through the center of the graphite
furnace allowing optimum light transmission.
11.1.4 Wavelength — Set the wavelength according to Table 2
following manufacturer's guidelines.
11.1.5 Spectral Bandwidth — Select the appropriate bandwidth
according to Table 2.
11.2 When a new graphite tube is installed, condition and clean the
tube by the following procedure:
11.2.1 Dry stage — 500°C for 15 sec.
11.2.2 Pyrolyze stage — 1500 C for 10 sec.
11.2.3 Atomize stage — 2500°C for 10 sec.
200.6-15
-------
11.3 SET FURNACE PARAMETERS
11.3.1 Gas Settings — Follow manufacturer's guidelines.
11.3.2 Cooling Water — Follow manufacturer's guidelines for
water flow. Tap water may be used if filtered to remove
particulates.
11.3.3 Set furnace parameters according to manufacturer's guide-
lines or those presented in Table 2.
11.3.4 Adjustments to the settings in Sect. 11.3.3 will be
necessary in order to establish optimal furnace settings
specific to the instrument in use. Use a strip chart
recorder or video graphics to monitor drying,
pyrolyzation, and atomization.
11.3.4.1 Inject the highest concentration calibration
standard into the furnace and initiate the dry
cycle. Refer to Table-2 for guidelines in
selecting appropriate sample volume. The sample
will block the light path (shown with an
absorbance increase). The solvent should
evaporate slowly and evenly with no sputtering,
so that the signal decreases steadily to the
baseline before entering the pyrolyzation
stage (Fig. 1).
11.3.4.2 Adjust the pyrolyzation stage temperature so
that it is high enough and long enough to
decompose and volatilize the matrix components
without losing any of the analyte. The nonatomic
absorption signals should return to the base-
line before the atomizatior. stage begins
(Fig. 2).
NOTE: The nitric acid in the matrix (Sect 8.4)
may cause nonatomic absorption signals in the
pyrolyze stage.
11.3.4.3 Adjust the atomization stage temperature so that
it is high enough to volatilize all of the
analyte. The use of too high a temperature will
result in premature deterioration of the graphite
tube, black body emission, and/or poor precision.
The absorbance signal should be returning to
baseline before the end of the atomization stage
(Fig. 2).
NOTE: To determine whether all o? the analyte
has been atomized, analyze a zero standard. If
there is an atomic absorption sigi il during
atomization, the atomization temperature is too
low (Fiy. 3). Adjust accordingly.
200.6-16
-------
11.3.4.4 Analyze the standard at the final settings.
11.3.4.5 Repeat the steps in Sect. 11.3.4.1-4, if
necessary, making the necessary temperature and
time adjustments to achieve optimal atomization.
11.3.4.6 Turn on the background corrector, and adjust
according to manufacturer's guidelines. Analyze
the same calibration standard at the settings
determined in Sect. 11.3.4.1-5.
11.3.4.7 Compare the traces of Sect. 11.3.4.5 and
11.3.4.6. The background correction trace
should have no peaks in the pyrolyzation stage.
The peaks in the atomization stage should be
similar on the two traces. If the settings are
correct, almost all of the nonatomic absorption
will be in the pyrolyzation stage and all of the
atomic absorption will be in the atomization
stage (Fig. 4).
11.3.4.8 If premature analyte vaporization is apparent
on the background corrected trace, readjust the
temperature settings. If any adjustments are
made, repeat steps 11.3.4.1-7. Continue until
the conditions in Sect. 11.3.4.7 are met.
11.3.4.9 Record the final settings for each analyte.
Once the settings are established, they can be
used routinely in the analysis of wet
deposition.
11.3.4.10 Typical atomization profiles for each metal are
shown in Fig. 5. Typical absorbances for the
sample volumes reccomended are listed in
Table 6.
11.4 Calibrate according to Section 9.2.
11.5 Verify the calibration curve according to Section 10.5.
11.6 For aluminum determinations, increase the nitric acid
concentration of the sample (Sect. 4.1.1.3). Pour the sample
into the sample cup containing the acid.
11.7 Analyze duplicates of all samples. The duplicates must agree
within Ł 10% RSD. The reported value is the mean of the
' duplicates. If precision is poor, refer to Appendix A.
11.8 If the absorbance (or concentration) for a given sample exceeds the
calibration range, dilute a separate sample with the zero standard.
200.6-17
-------
11.9 When analysis is complete, follow the manufacture's instructions
for instrument shut-down.
12. CALCULATIONS
12.1 For each analyte of interest, calculate a linear least squares fit
of the standard concentration as a function of the measured
absorbance. The linear least squares equation is expressed as
follows:
y = BQ + BIX
where: y = standard concentration in ug/L
x = absorbance measured
BQ = y-intercept calculated from: y - B.x
B. » slope calculated from:
n n
(X - x) (y. - y)/ (x.. - x)
where: x = mean of absorbances measured
y = mean of standard concentrations
n = number of samples
The correlation coefficient should be 0.9990 or greater.
Determine the concentration of the analyte of interest from the
calibration curve.
12.2 If the relationship between concentration and absorbance is
nonlinear, use a second degree polynomial least squares equation to
derive a curve with a correlation _>0.9990. The second degree
polynomial equation is expressed as follows:
y = B x + B x + B
Determine the concentration of analyte of interest from the
calibration curve.
12.3 An integration system or internal calibration software may be used
to provide a direct readout of the concentration of the analyte of
interest.
12.4 Report concentrations in ug/L. Do not report data lower than the
lowest calibration standard.
13. PRECISION AND BIAS
13.1 The percent recovery and mean bias of this method were
determined from the analysis of spiked wet deposition samples
according to ASTM Standard Practice D4210, Annex A4 (14.13). The
results are summarized in Table 5.
200.6-18
-------
13.2 Single-operator precision and bias were obtained from the analysis
of quality control check samples that approximated the levels
common to wet deposition samples. These results reflect the
accuracy that can be expected when the method is used by a
competent operator. These data are presented in Table 4.
14. REFERENCES
14.1 Annual Book of ASTM Standards, Part 42, "Standard Definitions of
Terms and Symbols Relating to Molecular Spectroscopy," Standard E
131-81, 1981, p. 66.
14.2 Annual Book of ASTM Standards, Section 11, Vol. 11.01 (1),
"Excerpts from Standard for Metric Practice," Standard E 380-79,
1983, pp. 679-694.
14.3 Sotera, J.J., Bancraft, M.F., Smith, S.B.,Jr., and Corum, T.L.,
Atomic Absorption Methods Manual, Vol. 2 "Flameless Operations",
Instrumentation Laboratory, Inc, Wilmington, Massachusetts, 1981,
pp. 2-22, 23.
14.4 Murphy, L.C., Almeida, M.C., Dulude, G.R., and Sotera, J.J.,
"Minimizing Matrix Interferences in Furnace Atomic Absorption
Spectrometry," Spectroscopy, 1986, Vol. 1 (3), pp. 39-43.
14.5 Friedman, L.C. and Erdmann, D.E. "Quality Assurance Practices
for the Chemical and Biological Analyses of Water and Fluvial
Sediments", Techniques of Water-Resources Investigations of the
United States Geological Survey, Book 5, Chapter A6, 1982,
p. 31.
14.6 Prudent Practices for Disposal of Chemicals from Laboratories,
National Research Council, Committee on Hazardous Substances in
the Laboratory, Commission of Physical Sciences, Mathematics and
Resources. National Academy Press, Washington D,C, 1983.
14.7 "Safety in Academic Chemistry Laboratories", American Chemical
Society Publication, Committee on chemical Safety, 4th Edition,
1985.
14.8 Annual Book of ASTM Standards, Section 14, Vol. 14.02
"Specification for Volumetric Ware", Standard E 694-83.
14.9 Annual Book of ASTM Standards, Section 11, Vol. 11.01 (1)
"Standard Specification for Reagent Water", Standard D 1193-77,
1983, pp. 39-41.
14.10 Moody, J.R. and Lindstrom, R.M., "Selection and Cleaning of
Plastic Containers for Storage of Trace Element Samples", 1977
Anal. Chetn. 49 (14), pp 2264-2267.
14.11 Laxen, D.P.H. and Harrison, R.M. "Cleaning Methods for
Polyethylene Containers Prior to the Determination of Trace
Metals in Freshwater Samples," Anal. Chem. 1981 53, pp. 345-350.
200.6-19
-------
14.12 Topol, L.E., Lev-On, M., Flanagan, J., Schwall, R.J., Jackson,
A.E., Quality Assurance Manual for Precipitation Measurement
Systems, 1985, U.S. Environmental Protection Agency,
Environmental Monitoring Systems Laboratory, Research Triangle
Park, NC 27711.
14.13 Annual Book of ASTM Standards, Section 11, Vol, 11.01 (1)
"Practice for Intralaboratory Quality Control Procedures and a
Discussion of Reporting Low-Level Data", Standard D4210 Annex A4,
1983, pp. 15-16.
200.6-20
-------
Table 1. Method Detection Limits and Concentration Ranges for
Graphite Furnace Atomic Absorption (GFAA) Trace Metal
Analysis of Wet Deposition.
Analyte
Aluminum
Cadmium
Copper
Iron
Lead
Manganese
Zinc
Method Detection
Limit,
ug/L
3.5
0.05
0.9
1.1
1.1
0.8
0.5
Concentr
Rang
ug/
3.5 -
0.05 -
0.9 -
1.1 -
1.1 -
0.8 -
0.5 -
ation
e,
L
60.0
2.00
40.0
50.0
50.0
20.0
30.0
-------
Table 2.
Operating Conditions for GFAA Determination
of Trace Metals in Wet Deposition Samples.
Metal
Al
Cd
Cu
Fe
Pb
Mn
Zn
wavelength Spectral Integration
Setting, Bandwidth, Mode
run nm
309.3 1.0 Peak Area
228.8 l.o Peak Height
324-7 1.0 Peak Height
248.3 0.3 Peak Height
283.3 1.0 Peak Height
279.5 0.3 Peak Height
213.9 1.0 Peak Area
Graphite
Tube
Coating
pyrolytic
uncoated
uncoated
pyrolytic
uncoated
uncoated
pyrolytic
Sample
Size,
uL
Dry
35 70/5
35 70/5
100 80/15
15 70/5
35 70/5
25 70/5
3 70/5
110/45
110/45
110/45
110/35
110/45
110/45
110/20
Furnace Setting,3
Temp, °c / Time, sec
Pyrolyze Atomize
900/20
225/10
550/15
650/15
350/15
400/20
325/15
1100/35
300/10
750/15
900/15
550/15
600/20
425/15
2700/0
1900/0
2600/0
2300/0
2000/0
2500/0
1900/10
2700/5
1900/10
2600/5
2300/5
2000/5
2500/5
1900/0
a. These settings are specific for the Instrumentation Laboratory Model 655 Furnace Atomizer.
They are to be used as guidelines.
-------
Table 3. Suggested Calibration Standard Concentrations for
GFAA Determination of Trace Metals in Wet Deposition.
Al
ug/L
zero
3.5
15.0
30.0
45.0
60.0
Cd
ug/L
zero
0.05
0.50
1.00
1.50
2.00
Cu
ug/L
zero
1.0
10.0
20.0
30.0
40.0
Fe
ug/L
zero
1.0
12.5
25.0
37.5
50.0
Mn
ug/L
zero
1.0
5.0
10.0
15.0
20.0
Pb
ug/L
zero
1.0
12.5
25.0
37.5
50.0
Zn
ug/L
zero
0.5
7.5
15.0
22.5
30.0
-------
Table 4. Single-Operator Precision and Bias for Trace Metals
Determined from USEPA Quality Control Check Samples.
Theoretical
Metal Concentration,
ug/L
Aluminum 36.5
Cadmium 1.56
Copper 17.0
Iron 39.8
Manganese 13.0
Lead 21.8
Zinc 20.9
Measured Precision,
Concentration n Bias, s, RSD,
ug/L ug/L % ug/L %
35.8 34 -0.7 -1.9 3.4 9.6
1.55 49 -0.01 -0.6 0.09 6.0
17.2 65 0.2 1.2 0.8 4.6
39.4 52 -0.4 -1.0 2.3 5.9
13.4 32 0.4 3.1 0.6 4.2
20.9 51 -0.8 -3.7 1.0 5.0
20.1 71 -0.8 -3.8 1.1 5.3
a. Number of replicates
-------
Table 5. Single-Operator Precision and Bias for Trace
Metals Determined from Analyte Spikes of Wet
Deposition Samples.
Amount Mean Percent Mean
Added, Recovery, Bias,
Metal ug/L n % ug/L
Al
Cd
Cu
Fe
Pb
Mn
Zn
18. 5d 12 95.7
30. 96 12 102.4
6.11d 13 109.2
1.99e 12 95.7
11. Od 13 100.0
16. 5e 12 101.4
11. ld 12 89.2
38. 26 12 90.6
20. 8d 13 101.9
20. 56 12 89.6
10. ld 13 107.9
17. O6 12 98.9
21. 9d 13 107.8
20. 26 12 115.8
a. Samples were spiked prior
b. Number of replicates (each
readings)
c. 95% confidence level
-0.8
0.7
0.56
-0.08
0.0
0.2
-1.2
-3.7
0.4
.-2.1
0.8
-0.2
1.7
3.2
to filtration.
replicate is
d. In situ filtration collector (funnel and
e. Filtered in lab
Standard Statistically
Deviation, Significant
ug/L Bias?
2.1
4.1
0.73
0.26
0.6
0.5
0.9
1.3
1.5
2.1
0.5
0.4
4.7
1.4
the mean of two
bottle)
yes
no
yes
no
no
yes
yes
yes
no
yes
yes
yes
yes
yes
-------
Table 6. Typical Absorbance Values for Trace Metal GFAA Analyses.
Analyte
Aluminum
Cadmium
Copper
Iron
Lead
Manganese
Zinc
Concentration
ug/L
60.0
2.00
40.0
50.0
50.0
20.0
30.0
Sample
Volume
uL
35
35
100
15
35
25
3
Absorbc
0.150 -
0.250 -
0.250 -
0.400 -
0.250 -
0.400 -
0.500 -
mce
0,250
0.300
0.300
0.500
0.350
0.500
0.700
-------
a.
TIME, seconds
30-60
b.
(A
0 5-10
TIME, seconds
w
o
o
V)
Pyrolyze
30-60
TIME, seconds
Figure 1. Recorder Traces for Drying Cycles in GFAA Analyses.
a. Correct Drying Cycle.
b. Drying Too Fast (analyte loss in dry cycle).
c. Drying Too Slow (analyte loss in pyrolyze cycle)
-------
w
u
5
i
en
PQ
DRY
|PYROLYZE| ATOMIZE
TIME, seconds.
Figure 2. Ideal GFAA Recorder Trace Without Background Correction.
w
u
o
en
i I r
3 03
TIME, seconds
b.
JlJU
JL
i i
0 3
TIME, seconds
Figure 3, GFAA Atomization Cycle.
a. Ideal Atomize (zero signal on subsequent zero
standard analysis).
b. Poor Atomize (sample carry-over on subsequent
zero standard analysis).
-------
ULJ
U
z
m
oc
CD
I
DRY
PYROLYZE ATOMIZE
TIME (SECONDS)
I
DRY PYROLYZE ATOMIZE
TIME (SECONDS)
Figure 4. Typical GFAA Recorder Tracings (14.3).
a. Signal Plus Background.
b. Background Corrected Signal.
-------
LU
U
<
CO
ec
o
V)
CO
I I I
Aluminum
i I r
Copper
Manganese
i r
u
<
CD
CC
i i I
Cadmium
Lead
l i
Zinc
Ill
I L
UJ
O
<
CO
CC
o
CO
CO
I I
Iron
4 6
TIME, seconds
10
2 3
TIME, seconds
Figure 5. Trace Metal Atoraization Profiles in GFAA Analyses.
-------
w
o
o
en
TIME, seconds
Figure 6. Multiple Atomization Peaks in GFAA Analyses (14.3)
-------
APPENDIX A. Troubleshooting in GFAA Analysis
of Wet Deposition.
Problem
Possible Cause
Possible Solution
Decrease in
Sensitivity
Analyte loss in dry
cycle (Fig. Ib)
Analyte loss in
pyrolyze cycle
(Fig. Ic)
Degraded graphite
Dirty optical lenses
Incomplete atomization
of analyte
Calibration standard
changes
Reduce dry temperature.
Increase dry temperature
or time.
Change graphite tube.
Clean exposed lenses
with methanol.
Increase atomization
temperature.
Make new calibration
standards.
Poor Precision
Arcing in furnace
Change graphite tube.
Clean electrodes with
methanol.
Changes in line voltage
Cooling water flow rate
too slow
Tighten contacts between
graphite and electrodes.
Put furnaces on an
isolated circuit.
Install a line surge
supressor.
Increase flow rate.
Clean water-cooling
system.
-------
Problem
APPENDIX A. (cont.)
Possible Cause
Possible Solution
Multiple Atomization
Peaks (Fig. 6)
Degraded graphite
Spattering of sample
within tube
Analyte in multiple
valence states
Blackbody emission
from graphite tube
Install new graphite
tube.
Reduce dry temperature.
Increase pyrolysis time
and/or temperature.
Realign furnace.
Reduce slit height.
Increase lamp current and
decrease photomultiplier
voltage.
Decrease atomization
temperature.
Memory Effects
Sample carry over
(Fig. 3b)
Contamination
Cycle a series of zero
standards until there are
no atomzation peaks.
Increase atomization
temperature and time.
Change graphite tube.
Clean furnace with
methanol.
Check zero standard for
contamination.
Check sample cups for
contamination
(Sect. 7.12.1) .
-------
GLOSSARY
Item
Abbreviation
Definition
Accuracy
Bias
The difference between the mean value and
the true value when the latter is known or
assumed. The concept of accuracy includes
both bias (systematic error) and precision
(random error).
A persistent positive or negative deviation
of the measured value from the true value,
due to the experimental method. In practice,
it is expressed as the difference between the
mean value obtained from repetitive testing of
a homogenous sample and the accepted true
value:
Black Body Emission
Control Limits
CL
Field Blank
FB
Fluorohydrocarbon
Plastics
Laboratory Spike
Bias = measured value - true value
A wide spectrum of electromagnetic radiation
emitted from a black body. Graphite is
close to being a black body and will emit
at high wavelengths and temperatures. The
emission is reflected from the window of the
hollow cathode lamp.
Statistically derived values that limit the
range of acceptable random error in a
measurement process. They consist of an
upper and lower range of acceptable values
that are defined as 3s from the mean.
An aliquot of reagent water or equivalent
neutral reference material treated as a
sample in all aspects, including exposure
to a collection vessel, holding time,
preservatives, and all other sample
processing and analysis protocols.
Plastics formed from polymers made only
with fluorine, hydrogen, and carbon.
A known volume of method analyte that is
added to a sample. The concentration of
analyte spiked into the sample usually
approximates the expected concentration
of that analyte in the unspiked sample.
The difference in concentration between the
spiked and the unspiked sample is used to
calculate a method percent recovery.
-------
Mean Bias
Mean Percent Recovery
Method Detection
Limit
MDL
_. bias for each sample
total number of replicates (n)
. percent recovery for each sample
total number of replicates (n)
The minimum concentration of an analyte
that can be reported with 99% confidence
that the value is above zero. The MDL is
operationally defined as:
MDL
st
(n-1,1- = 0.99)
(1)
where:
s = standard deviation of
repetitive
measurements (>1) of
a solution containing
the analyte at a
concentration near the
MDL.
'(n-1,1-
0.99)
student's t value
for a one-tailed test
appropriate for a 99%
confidence level and a
standard deviation
estimate with n-1
degrees of freedom.
Percent Bias
The difference between the mean value
obtained by repeated testing of a
homogenous sample and the accepted true
value expressed as a percentage of the true
value:
% Bias = 100 x [(V - VJ/V 1
m t t
where: V = measured value
V = true value
(1) Glaser, J.A., D.L. Foerst, G.D. McKee, S.A. Quave, and W.L. Budde. "Trace
Analyses for Wastewaters". Environmental Science and Technology, 1981,
Vol. 15', No. 12. pp. 1426-1435.
-------
Percent Recovery
Polyethylene
Polystyrene
Precision
Pyrolytic Coating
Quality Control
Check Sample
QCS
Refractory
An estimate of the bias of an analytical
method determined from analyte spikes of
natural samples. The percent recovery is
calculated as:
% Recovery = 100 x [(a - b)/c]
where: a = measured concentration of
spiked sample
b = measured concentration of
unspiked sample
c = calculated spike
concentration
A branched chain high molecular weight
hydrocarbon, resulting from the polymer-
ization of ethylene.
High density polyethylene
branching.
(HOPE) has miminal
A plastic formed from the polymerization
of styrene (a synthetic resin made from vinyl
benzene).
The degree of agreement of repeated
measurements of a homogenous sample by a
specific procedure, expressed in terms of
dispersion of the value obtained about the
mean value. It is often reported as a
sample standard deviation (s).
A thin surface layer of carbon produced by
heat without oxygen.
A sample containing known concentrations of
analytes prepared by the analyst or a
laboratory other than the laboratory
performing the analysis. The performing
laboratory uses this sample to demonstrate
that it can obtain acceptable results with
procedures to be used to analyze wet
deposition samples. Analyte true values
are known by the analyst.
Resistant to decomposition at high
temperatures.
-------
Relative Standard
Deviation
RSD
The standard deviation expressed as a
percentage.
RSD = 100 x (s/x)
where: s = sample standard deviation
x = mean value
Sensitivity
The method signal response per unit of
analyte.
Standard Deviation
A number that represents the dispersion of
values around their mean, calculated as:
2
(x. - x)
.s =
n - 1
Statistical Control
where: x. = each individual value
x = average of all values
n = number of values
The description of a measurement process that
is characterized solely by random errors.
Warning Limits
WL
Zero Standard
Limits used in quality control charts to
indicate that the analytical procedure is
close to being out of statistical control.
They consist of an upper and lower range of
values that are defined as +^s from the mean
value.
A calibration standard used to set the
instrument response to zero. It contains
all of the matrix components of the
remaining calibrants except the method
analyte.
-------
1. SCOPE AND APPLICATION
1.1 This method is applicable to the determination of calcium,
magnesium, potassium, and sodium in wet deposition by flame atomic
absorption spectrophotometry (FAAS).
1.2 The term "wet deposition" is used in this method to designate rain,
snow, dew, sleet, and hail.
1.3 The method detection limits (MDL) for the above analytes determined
from replicate analyses of quality control check solutions containing
0.053 mg/L calcium, 0.018 mg/L magnesium, 0.012 mg/L sodium, and
0.013 mg/L potassium are 0.007, 0.002, 0.003, and 0.003 mg/L,
respectively. The concentration range of this method is outlined in
Table 1.
1.4 Figure 1 represents cumulative frequency percentile concentration
plots of calcium, magnesium, potassium, and sodium obtained from the
analysis of over five thousand wet deposition samples. These data
should be considered during the selection of appropriate calibration
standard concentrations.
2. SUMMARY OF METHOD
2.1 A solution containing the element(s) of interest is aspirated as a
fine mist into a flame where it is converted to an atomic vapor
consisting of ground state atoms. These ground state atoms are
capable of absorbing electromagnetic radiation over a series of
very narrow, sharply' defined wavelengths. A distinct line source of
light, usually a hollow cathode lamp specific to the metal.of
interest, is used to pass a beam through the flame. Light from the
source beam, less whatever intensity was absorbed'by the atoms of the
metal of interest, is isolated by the monochromator and measured by
the photodetector. The amount of light absorbed by the analyte is
quantified by comparing the light transmitted through the flame to
light transmitted by a reference beam. The amount of light absorbed
in the flame is proportional to the concentration of the metal in
solution. The relationship between absorption and concentration is
expressed by Beer's Law:
log(I /I) * abc = A
where: I » incident radiant power
I * transmitted radiant power
a » absorptivity (constant for a given system)
b » sample path length
c » concentration of absorbing species (mg/L)
A » absorbance
The atomic absorption spectrophotometer is calibrated with standard
solutions containing known concentrations of the element(s) of
interest. Calibration curves are constructed from which the
concentration of each analyte in the unknown sample is determined.
200.6-3
-------
3. DEFINITIONS
3.1 ABSORBANCE (A) — the logarithm to the base ten of the reciprocal
of the transmittance, (T):
A = log(l/T)
0.0044 A = the absorption of 1% of
the transmitted light.
The absorbance is related to the analyte concentration by Beer's Law
(Sect. 2.1) where 1/T =1/1
o
3.2 ATOMIC ABSORPTION — the absorption of electromagnetic radiation by
an atom resulting in the elevation of electrons from their ground
states to excited states. Atomic absorption spectrophotometry
involves the measurement of light absorbed by atoms of interest as a
function of the concentration of those atoms in a solution.
3.3 SPECTRAL BANDWIDTH ~ the wavelength or frequency interval of
radiation leaving the exit slit of a monochromator between limits set
at a radiant power level half way between the continuous background
and the peak of an emission line or an absorption band of negligible
intrinsic width (14.1).
3.4 SPECTROPHOTOMETER — an instrument that provides the ratio, or a
function of the ratio, of the radiant power of two light beams as a
function of spectral wavelength. These two beams may be separated
in time and/or space.
3.5 For definitions of other terms used in this method, refer to the
glossary. For an explanation of the metric system including units,
symbols, and conversion factors see American Society for Testing and
Materials (ASTM) Standard E 380, "Metric Practices" (14.2).
4. INTERFERENCES
4.1 Chemical interference is the most frequently encountered
interference in atomic absorption spectrophotometry. A chemical
interference may prevent, enhance, or suppress the formation of
ground state atoms in the flame. For example, in the case of
calcium determinations, the presence of phosphate or sulfate can
result in the formation of a salt that hinders proper atomization of
the solution when it is aspirated into the flame. This decreases the
number of free, ground state atoms in the flame, resulting in lowered
absorbance values. Aluminum can cause a similar interference when
measuring magnesium. The addition of appropriate complexing 'agents
to the sample solution reduces or eliminates chemical interferences
and may increase the sensitivity of the method.
200.6-4
-------
4.2 Alkali metals such as sodium and potassium may undergo ionization in
an air-acetylene flame resulting in a decrease in ground state atoms
available for measurement by atomic absorption. Addition of a large
excess of an easily ionizable element such as cesium will eliminate
this problem, since cesium will be preferentially ionized. The
preferential ionization of the cesium solution results in an enhanced
atomic absorption signal for both potassium and sodium (14.3).
4.3 If a sample containing low concentrations of the metal being
measured is analyzed immediately after a sample having a
concentration exceeding the highest calibration standard, sample
carry-over will result in elevated readings. To prevent this
interference, routinely aspirate water (Sect. 7.2) for about 15
seconds after a high concentration sample. Depending on the
concentration of metal in the last sample analyzed, it may be
necessary to rinse for longer time periods. Complete purging of the
system is ascertained by aspirating water until the absorbance
readout returns to the baseline.
4.4 Wet deposition samples are characterized by low ionic strength and
rarely contain enough salts to cause interferences due to
nonspecific background absorbance. The use of background correction
techniques is not necessary and will decrease the signal to noise
ratio and lessen precision.
5. SAFETY
5.1 The calibration standards, sample types, and most reagents used in
this method pose no hazard to the analyst. Use a fume hood,
protective clothing, and safety glasses when handling concentrated
hydrochloric acid (Sect. 7.5-6).
5.2 Use a fume hood, protective clothing, and safety glasses when
preparing the lanthanum solution. The reaction between the lanthanum
oxide and acid (Sect. 7.7) is extremely exothermic.
5.3 A permanent ventilation system is required to eliminate the large
quantity of hot exhaust gases produced during instrument operation.
Since acetylene is a flammable gas, take precautions when using it.
To avoid explosions, never pass acetylene through copper or
high-copper alloy (brass, bronze) fittings or piping.
5.4 The operator must wear safety glasses to avoid eye damage from the
ultraviolet light emitted by the flame.
5.5 To avoid in-line explosions, do not allow the pressure of acetylene
being delivered to the instrument to exceed 15 psig (10.6 g/m ).
In the event of a flashback, turn off the gas control switch, the
instrument power, and the gas tanks.
5.6 Follow manufacturer's operating guidelines carefully when optimizing
gas flow rates. Too low gas flow rates can result in a combustion •
within the gas mixing chamber and therefore a flashback.
200.6-5
-------
5.7 Check that the drain tube from the gas mixing chamber, fitted with a
safety trap, is filled with water before igniting the flame. Keep
the drain tube filled to prevent explosion in the chamber. The
safety trap may be either looped or valved.
5.8 Avoid any contact with a hot burner head. Serious tissue burns will
result.
5.9 Follow American Chemical Society guidelines regarding safe handling
of chemicals used in this method (14.4).
6. APPARATUS AND EQUIPMENT
6.1 ATOMIC ABSORPTION SPECTROPHOTOMETER — Select a double-beam
instrument having a dual grating monochromator, photodetector,
pressure-reducing valves, adjustable spectral bandwith, wavelength
range of 190-800 nm, and provisions for interfacing with a strip
chart recorder or a suitable data system.
6.1.1 Burner — Use a long path, single slot air-acetylene burner
head supplied by the manufacturer of the spectrophotometer.
6.1.2 Hollow Cathode Lamps — Single element lamps are recommended.
Multi-element lamps are available but are not recommended.
They generally have a shorter lifespan, are less sensitive,
require a higher operating current, and increase the chances
of spectral interferences. When available, electrodeless
discharge lamps (EDL) may also be used.
6.1.3 Monochromator — To increase sensitivity of calcium and
potassium determinations, use a monochromator equipped with a
blaze grating in the range of 500-600 nm (14.5). For the
analysis of sodium and magnesium, a blaze grating in the range
of 200-250 nm is adequate.
6.1.4 Photomultiplier Tube — A wide spectral range (160-900 nm)
phototube is recommended. Select a red-sensitive phototube to
detect potassium at 766.5 nm and to increase sensitivity to
calcium at 422.7 nm.
6.2 The first time any glassware is used for making stock solutions and
standards, clean with 0.6 N HC1 and- rinse thoroughly with water
(Sect. 7.2) before use. Maintain a set of Class A volumetric flasks
to be used only when making dilute working standards for the analysis
of wet deposition samples. Store filled with water (Sect. 7.2} and
covered.
200.6-6
-------
6.3 LABORATORY FACILITIES — Laboratories used for the analysis of
wet deposition samples should be free from external sources of
contamination. The use of laminar flow clean air workstations is
recommended for sample processing and preparation to avoid the
introduction of airborne contaminants. If a clean air bench is
unavailable, samples must be capped or covered prior to analysis. A
positive pressure environment within the laboratory is also
recommended to minimize the introduction of external sources of
contaminant gases and particulates. Windows within the laboratory
should be kept closed at all times and sealed if air leaks are
apparent. The use of disposable tacky floor mats at the entrance to
the laboratory is helpful in reducing the particulate loading within
the room.
7. REAGENTS AND CONSUMABLE MATERIALS
7.1 PURITY OF REAGENTS — Use chemicals of reagent grade or better for
all solutions. All reagents shall conform to the specifications of
the Committee on Analytical Reagents of the American Chemical Society
(ACS) where such specifications are available.
7.2 PURITY OF WATER — Use water conforming to ASTM Specification D
1193, Type II (14.6). Point of use 0.2 micrometer filters are
recommended for all faucets supplying water to prevent' the
introduction of bacteria and/or ion exchange resins into reagents,
standard solutions, and internally formulated quality control check
solutions.
7.3 ACETYLENE (C H ) — Fuel — Minimum acceptable acetylene purity
is 99.5% (v/v) . Change the cylinder when the pressure reaches
75 psig (53 g/m ) if the acetylene is packed in acetone.
Pre-purified grades that contain a proprietary solvent can be used to
30 psig (21 g/m ) before replacement. Avoid introducing these
solvents into the instrument. Damage to the instrument's plumbing
system can result. Solvent in the system is indicated by abnormally
high pulsating background noise. To prevent solvent carryover, allow
acetylene cylinders to stand for at least 24 hours before use.
CAUTION: Acetylene is a highly flammable gas. Follow the
precautions in Sect. 5.3-6 regarding safe operating pressures,
suitable plumbing, and operator safety.
7.4 CESIUM SOLUTION (1.0 mL » 100.0 mg Cs) — lonization Suppressant —
Dissolve 126.7 g of cesium chloride (CsCl), dried at 105 C for one
hour, in water (Sect. 7.2) and dilute to 1 L. Store at room
temperature in a high density polyethylene or polypropylene
container. Add to samples and standards as directed in Sect. 9.4 and
11.4 for the determination of potassium and sodium.
7.5 HYDROCHLORIC ACID (6.0 N) — Carefully add 1 volume of concentrated
hydrochloric acid (HCl, sp gr 1.19) to an equal volume of water
(Sect. 7.2).
200,6-7
-------
7.6 HYDROCHLORIC ACID (0.6 N) — Add 50 mL of concentrated hydrochloric
acid (HC1, sp gr 1.19) to 900 mL of water (Sect. 7.2) and dilute to
1 L.
7.7 LANTHANUM SOLUTION (1.0 mL = 100.0 mg La) ~ Releasing Agent — In a
glass 1 L volumetric flask, place 117.0 g of lanthanum oxide
(La 0 ), dried at 105°C for one hour. Add 6 N HC1 very
carefully to the solid in increments of about 0.5 mL. Cool the
solution between additions. Continue adding the acid solution to the
flask in increasing increments until a total of 500 mL of 6 N HCl has
been added. Dilute to 1 L with water (Sect. 7.2). Store at room
temperature in a high density polyethylene or polypropylene
container. Add to samples and standards as directed in Sect. 9.4.3
and 11.4 for the determination of calcium and magnesium.
CAUTION: Dissolving lanthanum oxide in hydrochloric acid is a
violently exothermic reaction; use extreme caution when dissolving
the reagent. Refer to Sect. 5.2 for proper safety precautions when
preparing this solution.
7.8 OXIDANT (air) — The air may be provided by a compressor or
commercially bottled gas supply. Remove oil, water, and other
foreign matter from the air using a filter recommended by the
manufacturer. Refer to the manufacturer's guidelines for recommended
delivery pressure.
7.9 STOCK STANDARD SOLUTIONS — Stock standard solutions may be
purchased as certified solutions or prepared from ACS reagent grade
materials as detailed below. Store the solutions at room temperature
in high density polyethylene or polypropylene containers.
7.9.1 Calcium Solution, Stock (1.0 mL = 1.0 mg Ca) — Add 2.497 g
of calcium carbonate (CaCO ), dried at 180°C for one
hour, to approximately 600 mL of water (Sect. 7.2). Add
concentrated hydrochloric acid (HCl, sp.gr 1.19) slowly until
all the solid has dissolved. Dilute to 1 L with water (Sect.
7.2) .
7.9.2 Magnesium Solution, Stock (1.0 mL = 1.0 mg Mg) — Dissolve
1.000 g of magnesium ribbon in a minimal volume of 6 N HCl and
dilute to 1 L with water (Sect. 7.2).
7.9.3 Potassium Solution, Stock (1.0 mL = 1.0 mg K) — Dissolve
1.907 g of potassium chloride (KC1), dried at 105 C for one
hour, in water (Sect. 7.2) and dilute to 1 L.
7.9.4 Sodium Solution, Stock (1.0 mL - 1.0 mg Na) — Dissolve
2.542 g of sodium chloride (NaCl), dried at 105°C for one
hour, in water (Sect. 7.2) and dilute to 1 L.
7.10 SAMPLE CONTAINERS — Use polyolefin sample cups that have been
thoroughly rinsed with water (Sect. 7.2) before use.
200.6-8
-------
8. SAMPLE COLLECTION, PRESERVATION, AND STORAGE
8.1 Collect samples in high density polyethylene (HDPE) containers that
have been thoroughly rinsed with ASTM Type II water (7.2). Do not
use strong mineral acids or alkaline detergent solutions for cleaning
collection vessels. Residual acids may remain in the polyethylene
matrix and slowly leach back into the sample. Alkaline detergents
may also leave residues that may affect the sample chemistry. Cap
collection bottles after cleaning to prevent contamination from
airborne contaminants; air dry collection buckets in a laminar flow
clean air workstation and wrap in polyethylene bags prior to use. If
a laminar flow workstation is not available, pour out any residual
rinse water and bag the buckets immediately. Do not dry the bucket
interior by any method other than air drying in a laminar flow clean
air workstation.
8.2 The frequency of sample collection and the choice of sampler design
are dependent on the monitoring objectives. In general, the use of
wet-only samplers is recommended to exclude dry deposition
contributions, minimize sample contamination, retard evaporation,
and enhance .sample stability. Sample collection frequency may vary
from subevent to monthly sampling periods. Collection periods of
more than one week are not recommended since sample integrity may be
compromised by longer exposure periods.
8.3 The dissolution of particulate materials can affect the stability of
calcium, magnesium, sodium, and potassium in wet deposition samples
(14.7). This instability generally results in a concentration
increase for these constituents. Measurements should be made
immediately after sample collection to obtain representative data.
Refrigeration of samples at 4 C will minimize but not eliminate
concentration changes.
8.3.1 Filtration of samples through a 0.45 micrometer membrane leached
with wate"r (Sect. 7.2) is effective at stabilizing samples that
are influenced by the dissolution of alkaline particulate matrer
(14.7). Monitoring of the filtration procedure is necessary to
ensure that samples are not contaminated by the membrane or
filtration apparatus. Filtered samples are stable for six weeks
when stored at room temperature.
9. CALIBRATION AND STANDARDIZATION
9.1 SETTING INSTRUMENT PARAMETERS
9.1.1 Lamp Current — Refer to manufacturer's guidelines for
optimization of this parameter. The use of excessively high
currents will shorten lamp life. High currents also cause
line broadening, resulting in a reduction in sensitivity and
calibration curve linearity, especially in the determination of
magnesium. The use of currents that are too low will cause lamp
instability and insufficient throughput of energy through the
instrument's optical system. The result is increased signal
noise due to excess electrical gain applied to the photodetector,
20* 6-9
-------
9.1.2 Light Beam — Position ajsmall card over the burner slot to
intercept the light beam from the hollow cathode lamp. Check
that the beam is focused 'midway along the slot and, if
necessary, focus according to the manufacturer's guidelines.
Rotate the lamp within its holder for maximum energy output
readings.
9.1.3 Burner/Beam Alignment — Position a small card over the burner
slot to intercept the light beam from the hollow cathode lamp.
For optimal sensitivity when analyzing calcium, magnesium,
potassium, and sodium, adjust the burner height so that the
center of the light beam is approximately 6 mm above the
surface of the burner slot. By adjusting the burner alignment
and rotation, set the light beam to coincide with the burner
slot. While observing from above, move the card along the
full length of the burner slot to ensure that the beam is
centered over the slot for the entire length of the burner.
Optimize this parameter for maximum instrumental sensitivity
as directed in Sect. 9.2.
9.1.4 Wavelength — Set the wavelength of the spectrophotometer for
each analyte according to Table 2 by following the
manufacturer's operating guidelines. After the instrument has
warmed up with the flame burning (about 30 minutes), check the
wavelength and readjust if necessary.
Note: The sodium spectrum is characterized by a doublet at
589.0 nm and 589.5 run. The wavelength chosen for sodium
determinations depends on the degree of analytical sensitivity
desired by the operator. A setting of 589.0 nm will provide
maximum sensitivity in the concentration range of most wet
deposition samples. For those samples with higher sodium
concentrations, a less sensitive setting of 589.5 nm is more
appropriate. Refer to Tables 1 and 2 for information
regarding working ranges, standards, and detection limits for
sodium at each wavelength setting.
9.1.5 Spectral Bandwidth — The selection of optimum bandwidth
depends upon the spectrum of the particular element being
analyzed. For the determination of calcium, magnesium, and
potassium, a relatively wide (1.0 nm) bandwidth is
appropriate. Because the sodium spectrum is characterized by
a doublet, use a smaller bandwidth of 0.5 nm.
9.1.6 External Gas Settings — Follow manufacturer's recommended
delivery pressures for air and acetylene. Never allow
acetylene pressure to exceed 15 psig (10.6 g/m ).
200.6-10
-------
9.1.7 Nebulization Rate — Set the acetylene and air flow rates as
recommended by the manufacturer. Adjust the nebulizer sample
uptake rate to approximately 5 mL/min. If an adjustable glass
bead nebulizer is used, adjust it according to manufacturer's
guidelines. Exact placement of the glass bead is critical to
ensure that a uniform vapor of the smallest size particles is
introduced into the flame. Improper spacing of the bead from
the nebulizer end will result in poor precision and
sensitivity. Optimize the sample uptake rate for maximum
sensitivity as directed in Sect. 9.2.
Note: The nebulizer can clog easily if particulates are
present in the samples. Symptoms of this are decreased
sensitivity and/or dramatically increased signal noise,
especially noticeable at the higher concentration levels.
A thorough cleaning with a small diameter wire is usually
sufficient to unclog the nebulizer.
9.1.8 Flame Conditions — If the flame temperature is too low,
compounds containing the analyte will not be completely
dissociated. Alternatively, too high a flame temperature may
result in ionization. In both cases, a decrease in the
apparent concentration of the analyte will result. In
general, calcium exhibits maximum sensitivity at'higher fuel-
and oxidant flow rates. Maximum sensitivity for potassium is
obtained with minimal gas flow rates, resulting in lower flame
temperature and allowing longer residence time of the atomic
vapor in the flame. The MDLs stated in Sect. 1.3 for
magnesium and sodium are obtained over a wide range of flame
conditions. Optimize this parameter for maximum instrumental
sensitivity as directed in Sect. 9.2.
CAUTION: Follow manufacturer's operating guidelines
carefully when setting gas flow rates since combustion within
the gas mixing chamber can occur if caution is not exercised.
9.2 Optimization — Allow the instrument to warm up for 30 minutes before
beginning the optimization. Set the instrument readout to absorbance
units and set the integration time to <0.5 seconds. Use either a
strip chart recorder or set the display in a continuous read mode to
monitor absorbance readings. Aspirate a calibration standard at a
concentration near the midpoint of the working range (Sect. 9.4).
While watching the absorbance readings, adjust the instrument
parameters with small, discrete changes until maximum values are
obtained. Parameters such as. flame conditions, nebulization rate,
and the region of maximum atom concentration in the flame are
interrelated. Adjustment of any of these three parameters usually
requires adjustment of the other two.
200.6-11
-------
9.3 Instrument Response Time — Determine the minimum sample uptake time
before taking a reading on a sample or standard solution. Use either
a strip chart recorder or set the display in a continuous read mode
to monitor absorbance readings. After purging the system with water
(Sect. 7.2), aspirate the highest calibration standard (Sect. 9.4)
and measure the length of time necessary to obtain a stable reading.
Aspirate water (Sect. 7.2) and measure the time it takes for the
baseline to return to zero.
Note: If the time necessary for the baseline to return to zero is
longer than 15 seconds, a clogged nebulizer may be suspect. If
purging time begins to increase during sample analysis, this may also
be an indication of nebulizer clogging.
9.4 CALIBRATION SOLUTIONS
9.4.1 Five calibration solutions and one zero standard are needed to
generate a suitable calibration curve. The lowest calibration
solution should contain the analyte of interest at a
concentration greater than or equal to the method detection
limit. The highest solution should approach the expected
upper limit of concentration of the analyte in wet deposition.
Prepare the remaining solutions such that they are evenly
distributed throughout the concentration range. Suggested
calibration standards for each analyte are listed in Table 2.
9.4.2 Prepare all calibration standards by diluting the stock
standards (Sect. 7.9) with water (Sect. 7.2). Use glass
(Class A) or plastic pipettes that are within the bias and
precision tolerances specified by the manufacturer. The
calibration standards are stable for three months if stored at
room temperature in high density polyethylene or polypropylene
containers.
9.4.3 After preparing the calibration standards to volume, add the
lanthanum solution (Sect. 7.7) to the calcium and magnesium
standards to yield 1000 mg/L La. Add the cesium solution
(Sect. 7.4) to the potassium and sodium standards for
1000 mg/L Cs. Mix well. Use the same stock of ionization
suppressant or releasing agent for the samples and the
calibration standards.
Note: The final volume of each working standard solution
exceeds the nominal volume by 1%. This adjustment is
necessary to maintain consistency when the appropriate volume
of suppressor solution is added to the wet deposition samples.
200.5-12
-------
9.5 CALIBRATION
9.5.1 To establish a baseline, aspirate the zero standard and set
the absorbance readout to 0.000. Aspirate the calibration
standards, allowing time for each standard to equilibrate in
the flame and gas mixing chamber before measuring the
absorbance (Sect. 9.3). Construct calibration curves for each
of the four analytes according to Sect. 12.
9.5.2 Analyze all the calibration standard solutions. The apparent
concentration values must agree with the nominal
concentrations within the predetermined control limits (Sect.
10.2.1) of three times the standard deviation (^3s) . If
results fall outside of these limits, recalibrate the
instrument. If there is a consistent bias greater than
x _+ 2s and less than x +_ 3s, for all of the concentration
values measured, reestablish the baseline with the zero
standard and reanalyze the calibration standards.
9.5.3 Verify the calibration curve after every ten samples and at
the end of each day's analyses according to Sect. 10.7.
10. QUALITY CONTROL
10.1 Each laboratory using this method should develop formalized quality
control protocols to continually monitor the bias and precision of
all measurements. These protocols are required to ensure that the
measurement system is in a state of statistical control. Estimates
of bias and precision for wet deposition analyses cannot be
made unless these control procedures are followed. Detailed
guidelines for the development of quality assurance and quality
control protocols for precipitation measurement systems are
published in a manual available from the United States
Environmental Protection Agency, Research Triangle Park, NC 27711
(14.8). Included in this manual are procedures for the development
of statistical control charts for use in monitoring bias and
precision as well as recommendations for. the introduction of
reagent blanks, laboratory duplicates, field duplicates, spike
samples, and performance evaluation samples. These guidelines are
to be used by all laboratories involved with wet deposition
measurements.
10.2 ESTABLISHMENT OF WARNING AND CONTROL LIMITS ~ Warning and control
limits are used to monitor drift in the calibration curve, analyses
of quality control check samples (QCS), and measured recoveries
from laboratory spikes.
10.2.1 Calibration Curve — After a calibration curve has been
constructed according to Sect. 12, reanalyze additional
aliquots of'all the standards. Calculate the
concentrations using the previously derived calibration
curve. Repeat this procedure until at least ten
200.6-13
-------
determinations at each concentration level have been made.
These data should be collected on ten different days to
provide a realistic estimate of the method variability.
Calculate a standard deviation (s) at each concentration
level. Use the nominal standard concentration as the mean
value (x) for determining the control limits. A warning
limit of x" _+ 2s and a control limit of x +_ 3s should be
used. Reestablish these limits whenever instrumental
operating conditions change.
10.2.2 Quality Control Check Samples (QCS) ~ Calculate warning
and control limits for QCS solutions from a minimum of ten
analyses performed on ten days. Use the calculated
standard deviation (s) at each QCS concentration level to
develop the limits as described in Sect. 10.2.1. Use the
certified or NBS traceable concentration as the mean
(target) value. Constant positive or negative measurements
*ith respect to the true value are indicative of a method
or procedural bias. Utilize the data obtained from QCS
measurements as in Sect. 10.6 to determine when the
measurement system is out of statistical control. The
standard deviations used to generate the QCS control limits
should be comparable to the single operator precision
reported in Table 4. Reestablish new warning and control
limits whenever instrumental operating conditions are
varied or QCS concentrations are changed.
10.2.3 Laboratory Spike Solutions — A minimum of ten analyte
spikes of wet deposition samples is required to develop a
preliminary data base for the calculation of warning and
control limits for spike recovery data. Select the spike
concentration such that the working range of the method
will not be exceeded. Samples selected for the initial
spike recovery study should represent the concentration
range common to wet deposition samples in order to reliably
estimate the method accuracy. Calculate a mean and
standard deviation of the percent recovery data using the
formulas provided in the glossary. Determine warning and
control limits using +2s and jv3s, respectively. If
the data indicate that no significant method bias exists
(14.9), the 100 percent recovery is used as the mean
percent recovery. Where a significant bias is determined
at the 95% confidence level, the control limits are
centered around the bias estimate. Routine spiked sample
analyses that yield percent recovery data outside of the
control limits are an indication of matrix interferences
that should be resolved before routine analyses are
continued.
200.6-14
-------
10.2.4 All warning and control limits should be reevaluated on a
continual basis as additional data are collected during
routine analyses. The limits should be broadened or
narrowed if a recalculated standard deviation under similar
operating conditions provides a different estimate of the
procedure variability.
10.3 Monitor the cleaning procedure by pouring a volume of water (Sect.
7.2) that approximates the median sample size into the collection
vessel. Allow the water to remain in the sealed or capped
collection container for at least 24 hours and determine the
concentration of the analytes of interest. If any of the measured
concentrations exceed the MDL, a contamination problem is indicated
in the cleaning procedure. Take corrective action before the
sampling containers are used for the collection of wet deposition.
10.4 Keep daily records of calibration data and the instrument operating
parameters used at the time of data acquisition. Use these
historical data as general performance indicators. Gross changes
in sensitivity, curve linearity, or photomultiplier tube voltage
are indicative of a problem. Possibilities include instrument
malfunction, clogged nebulizer, incomplete optimization, bad hollow
cathode lamp, contamination, and inaccurate standard solutions.
10.5 Precision will vary over the andlyte concentration range. Standard
deviation (s) increases as concentration increases while relative
standard deviation (RSD) decreases. At approximately 100 times the
MDL, the RSD should remain less than 1%.
10.6 Analyze a quality control check sample (QCS) after a calibration
curve has been established. This sample may be formulated in the
laboratory or obtained from the National Bureau of Standards (NBS
Standard Reference Material 2694, Simulated Rainwater). The check
sample(s) selected must be within the range of the calibration
standards. Prepare according to Sect. 11.4. If the measured value
for the QCS falls outside of the +2s limits (Sect. 10.2.2), or if
two successive QCS checks are outs'ide of the ^2s limits, a
problem is indicated with the spectrophotometer or calibration
curve. Reestablish the baseline with the zero standard and/or
recalibrate. If the QCS analysis is still beyond control limits,
inaccurate working standards might be the problem. Prepare new
standards. Plot the data obtained from the QCS checks on a control
chart for routine assessments of bias and precision.
10.7 Verify the calibration curve after a maximum of ten samples and at
the end of each day's analyses. Analyze a zero standard and
calibration standards at the low and high ends of the working
range. If the routine calibration checks do not meet the criteria
described in Sect. 10.6, recalibrate the system and reanalyze all
samples from the last time the system was in control. Verify the
new calibration curve with the QCS according to Sect. 10.6 and
'reanalyze all samples from the last time the measurement system was
in control.
200.6-15
-------
10.8 Submit a Field Blank (FB) to the laboratory for every 20 samples.
The FB may consist of a water sample (Sect. 7.2) or a known
reference solution that approximates the concentration levels
characteristic of wet deposition. The FB is poured into the
sampling vessel at the field site and undergoes identical
processing and analytical protocols as the wet deposition
sample(s). Use the analytical data obtained from the FB to
determine any contamination introduced in the field and laboratory
handling procedures. The data from the known reference solution
can be used to calculate a system precision and bias.
10.9 Prepare and analyze a laboratory spike of a wet deposition sample
according to the guidelines provided in "Quality Assurance Manual
for Precipitation Measurement Systems" (14.8). Compare the
results obtained from the spiked samples to those obtained from
identical samples to which no spikes were added. Use these data
to monitor the method percent recovery as described in Sect.
10.2.3.
10.10 Participation in performance evaluation studies is recommended for
precipitation chemistry laboratories. The samples used for these
performance audits should contain the analytes of interest at
concentrations within the normal working range of the method. -The
true values are unknown to the analyst. Performance evaluation
studies for precipitation chemistry laboratories are conducted
semiannually by the USEPA Performance Evaluation Branch, Quality
Assurance Division, Research Triangle Park, NC 27711.
10.11 INSTRUMENT MAINTENANCE — Strictly adhere to manufacturer's
maintenance schedule.
10.11.1 Exposed optical mirrors should be replaced yearly to
maintain optimal sensitivity and precision.
10.11.2 If the instrument is used for other sample types that
have high analyte concentrations it may be necessary to
disassemble the entire burner-nebulizer system for
cleaning before analyzing wet deposition samples. This
is best accomplished by placing the components in a water
(Sect. 7.2) bath in an ultrasonic cleaner for a half
hour. Rinse with water (Sect. 7.2) after cleaning and
allow to air dry in a dust-free environment before
reassembly. Check o-rings for wear and replace if
necessary.
200.6-16
-------
11. PROCEDURE
11.1 Set instrument parameters and optimize the instrument each day
according to Sect. 9.1-2.
11.2 Prepare all standards and construct calibration curves according
to Sect. 9.4-5.
11.3 After the calibration curve is established, analyze the QCS. If
the measured value for the QCS is not within the specified limits
(Sect. 10.2.2), refer to Sect. 10.7.
11.4 Pipette the appropriate cesium or lanthanum solution into the
empty sample cup (Cs or La:Sample = 1:100). For the determination
of calcium and magnesium, use the lanthanum solution described in
Sect. 7.7. For potassium and sodium determinations, add cesium
solution (Sect. 7.4). Pour the sample into the sample cup
containing Cs or La; 3 mL of sample for 30 uL of Cs or La is
suggested. Mix well, aspirate, wait for equilibration in the flame
(Sect. 9.3), and record the measured absorbance (or concentration).
11.5 If the absorbance (or concentration) for a given sample exceeds
the working range of the system, dilute a separate sample with •
water (Sect. 7.2). Prepare and analyze according to Sect. 11.4.
11.6 When analysis is complete, rinse the system by aspirating water
(Sect. 7.2) for ten minutes. Follow the manufacturer's guidelines
for instrument shut-down.
12. CALCULATIONS
12.1 For each analyte of interest, calculate a linear least squares fit
of the standard concentration as a function of the measured
absorbance. The linear least squares equation is* expressed as
follows:
where: y = standard concentration in mg/L
x = absorbance measured
B. » y-intercept calculated from: 7
B » slope calculated from:
• \f\t\r ^ (V ^5?^
A / \ y . V / / ^^ \ « > A /
where: x * mean of absorbances measured
y « mean of standard concentrations
n =• number of samples
Ttva correlation coefficient should be 0.9995 or greater. Determine
the concentration of analyte of interest from the calibration
curve.
POO.6-17
-------
12.2 If the relationship between concentration and absorbance is
nonlinear, use a second degree polynomial least squares equation to
derive a curve with a correlation _>0.9995. The second degree
polynomial equation is expressed as follows:
y = B x + B x + B
A computer is necessary for the derivation of this function.
Determine the concentration of analyte of interest from the
calibration curve.
12.3 An integration system or internal calibration software may also
be used to provide a direct readout of the concentration of the
analyte of interest.
12.4 Report concentrations in mg/L as Ca , Mg , Na , and K .
Do not report data lower than the lowest calibration standard.
13. PRECISION AND BIAS
13.1 The mean percent recovery and mean bias of this method were
determined from the analysis of spiked wet deposition samples
according to ASTM Standard Practice D4210, Annex A4 (14.9). The.
results are summarized in Table 3. No statistically significant
biases were found for any of the metal cations.
13.2 Single-operator precision and bias were obtained from the analysis
of quality control check samples that approximated the levels
common to wet deposition samples. These results reflect the
accuracy that can be expected when the method is used by a
competent operator. These data are presented in Table 4.
14. REFERENCES
14.1 Annual Book of ASTM Standards, Part 42, "Standard Definitions of
Terms and Symbols Relating to Molecular Spectroscopy," Standard E
131-81, 1981, p. 66.
14.2 Annual Book of ASTM Standards, Section 11, Vol. 11.01 (1),
"Excerpts from Standard for Metric Practice," Standard E 380-79,
1983, pp. 679-694.
14.3 Van Loon, J. C., Analytical Atomic Absorption Spectroscopy,
Selected Methods Academic Press, Inc., New York, N. Y., 1980,
p. 42.
14.4 "Safety in Academic Chemistry Laboratories," American Chemical
Society Publication, Committee on Chemical Safety, 3rd Edition,
1979.
200.6-18
-------
14.5 Instrumentation Laboratory, Inc., Operator's Manual Model IL951,
AA/AE Spectrophotometer, Instrumentation Laboratory, Inc.,
Wilmington, Massachusetts, 1982, pp. 3-4.
14.6 Annual Book of ASTM Standards, Section 11, Vol. 11.01 (1),
"Standard Specification for Reagent Water," Standard D 1193-77,
1983, pp. 39-41.
14.7 Peden, M. E. and Skowron, L. M., "Ionic Stability of Precipitation
Samples," Atmps. Environ. 12, 1978, .pp. 2343-2349.
14.8 Topol, L. E., Lev-On, M., Flanagan, J., Schwall, R. J., Jackson, A.
E., Quality Assurance Manual for Precipitation Measurement
Systems, 1985, U.S. Environmental Protection Agency,
Environmental Monitoring Systems Laboratory, Research Triangle
Park, NC 27711.
14.9 Annua^ Book of ASTM Standards, Section 11, Vol. 11.01 (1),
"Practice for Intralaboratory Quality Control Procedures and a
Discussion of Reporting Low-Level Data," Standard D4210 Annex A4;
1983, pp. 15-16.
200.6-19
-------
Table 1. Method Detection Limits and Concentration Ranges for
Flame Atomic Absorption Spectrophotometric Analysis
of Wet Deposition.
Method Detection Concentration
Limit, Range,
Analyte mg/L mg/L
Calcium 0.007 0.030 - 3.00
Magnesium 0.002 0.010 - 1.00
Potassium 0.003 0.010 - 1.00
Sodium 0.003a 0.010 - 1.00a
0.007b 0.020 - 2.00b
a. 589.0 run wavelength setting
b. 589.5 run wavelength setting
200.6-20
-------
Table 2. Operating Conditions and Suggested Calibration
Standard Concentrations for the Determination of
Calcium, Magnesium, Potassium, and Sodium in Wet
Deposition Samples.
Analyte
Wavelength
Setting,
nm
Spectral
Bandwidth,
nm
Working
Standards,
mg/L
Calcium
422.7
1.0
zero
0.03
0.75
1.50
2.25-
3.00
Magnesium
285.2
1.0
zero
0.01
0.25
0.50
0.75
1.00
Potassium
766.5
1.0
zero
0.01
0.25
0.50
0.75
1.00
Sodium
589.0
0.5
zero
0.01
0.25
0.50
0.75
1.00
589.5
0.5
zero
0.02
0.50
1.00
1.50
2.00
Based on the MDL and 95th percentile concentration of each analyte
obtained from analyses of over five thousand wet deposition samples
from the NADP/NTN precipitation network.
Refer to Sect. 9.1.2 for details on wavelength selection
200.6-21
-------
Table 3. Single-Operator Precision and Bias for Calcium,
Magnesium, Potassium, and Sodium Determined from Analyte
Spikes of Wet Deposition Samples.
Analyte
Amount
Added,
mg/L n
Mean
Percent
Recovery
Mean
Bias,
mg/L
Standard
Deviation,
mg/L
Statistically
Significant
Bias?5
Calcium 0.037 20 101.5
0.221 20 98.3
0.001
-0.003
0.010
0.011
No
No
Magnesium 0.018 20 97.2
0.045 20 96.6
-0.001
-0.002
0.001
0.002
No
No
Potassium 0.021 18 145.2
0.052 13 108.1
0.010
0.004
0,
0,
006
002
No
No
Sodium
0.099
0.249
19
20
107.1
100.2
0.007
0.000
0.011
0.008
No
No
a. Number of replicates
b. 95% Confidence Level
c. 589.0 nm wavelength
200.6-22
-------
Table 4. Single-Operator precision and Bias for Calcium,
Magnesium, Potassium, and Sodium Determined
from Quality Control Check Samples.
Theoretical Measured
Concentration, Concentration,
Analyte mg/L mg/L na
Calcium
Magnesium
Potassium
,, ,, b
Sodium
0.
0.
0.
0.
0.
0.
0.
0.
053
406
018
084
021
098
082
465
0
0
0
0
0
0
0
0
.051
.413
.017
.083
.020
.095
.084
.479
145
145
145
145
127
122
123
122 '
Bias,
mg/L %
-0
0
-0
-0
-0
-0
0
0
.002
.007
.001
.001
.001
.003
.002
.014
-3.8
1.7
-5.6
-1.2
-4.8
-3.1
2.4
3.0
Precision,
s , RSD ,
mg/L %
0.
0.
0.
0'.
0.
0.
0.
0.
002
003
001
001
001
001
001
003
3.9
0.7
5.9
1.2
5.0
1.0
1.2
0.6
The above data were obtained from records of measurements made under the
direction of the NADP quality assurance program.
a. Number of replicates
b. 589.0 nm wavelength
200.6-23
-------
r-o
O
o
K»
or
t-t
H
CJ
Figure 10 Percentile Concentration Values Obtained from
Wet Deposition Samples: Calcium, Magnesium,
Potassium, and Sodium.
calcium
1.00
2.00
*-*-
3.00
potassium
100
90
80
70
60
iO
40
JO
20.
10
magnesium
0.20
H-
0.40
H-
0.60
sodium
0.10 0.20 O.JO 0.40 O.SO ° °*5°
CONCENTRATION (mg/L)
1.50
2.50
3. SO
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Appendix N
METHOD 200.6 — DISSOLVED ALUMINUM, CADMIUM, COPPER, IRON, LEAD,
MANGANESE, AND ZINC IN WET DEPOSITION BY GRAPHITE FURNACE
ATOMIC ABSORPTION SPECTROPHOTOMETRY
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Method 200.6 — Dissolved Aluminum, Cadir.ium, Copper,
Iron, Lead, Manganese, and Zinc in Wet
Deposition by Graphite Furnace
Atomic Absorption Spectrophotometry
July 1986
Performing Laboratory:
Barbara J. Keller
Loretta M. Skowron
Mark E. Peden
Illinois State Water Survey
Analytical Chemistry Unit
2204 Griffith Drive
Champaign, Illinois 61820
Sponsoring Agency:
John D. Pfaff, Project Officer
Inorganic Analysis Section
Physical and Chemical Methods Branch
United States Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
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INDEX
Section
Number Subject
1 Scope and Application
2 Summary of Method
3 Definitions
4 Interferences
5 Safety
6 Apparatus and Equipment
7 Reagents and Consumable Materials
8 Sample Collection, Preservation and Storage
9 Calibration and Standardization
10 Quality Control
11 Procedure
12 Calculations
13 Precision and Bias
14 References
TABLES
Method Detection Limits and Concentration Ranges for Graphite Furnace
Atomic Absorption (GFAA) Trace Metal Analysis of Wet Deposition.
Operating Conditions for GFAA Determination of Trace Metals in Wet
Deposition Samples.
Suggested Calibration Standards for GFAA Determination of Trace
Metals in Wet Deposition.
Single-Operator Precision and Bias for Trace Metals Determined from
USEPA Quality Control Check Samples.
Single-Operator Precision and Bias for Trace Metals Determined from
Analyte Spikes of Wet Deposition Samples.
Typical Absorbance Values for Trace Metals.
FIGURES
1. Recorder Traces for Drying Cycles in GFAA Analyses.
2. Ideal GFAA Recorder Trace, Without Background Correction.
3. GFAA Atomization Cycle.
4. Typical GFAA Recorder Tracings, Signal Plus Background versus Background
Corrected Signal.
5. Trace Metal Atomization Profiles in GFAA Analyses.
6. Multiple Atomization Peaks in GFAA Analyses.
200.6-1
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1. SCOPE AND APPLICATION
1.1 This method is applicable to the determination of aluminum, cadmium,
copper, iron, lead, manganese, and zinc in wet deposition by graphite
furnace atomic absorption spectrophotometry (GFAAS).
1.2 The term "wet deposition" is used in this method to designate rain,
snow, dew, sleet, and hail.
1.3 The method detection limits (MDL) for the above analytes were
determined from replicate analyses of calibration standards
containing 10 ug/L Al, 0.25 ug/L Cd, 5.0 ug/L Cu, 5.0 ug/L Fe,
2.5 ug/L Pb, 5.0 ug/L Mn, and 2.5 ug/L Zn. The MDL's and
concentration ranges of this method are presented in Table 1.
1.4 GFAAS is recommended when minimal MDLs are needed or when sample
size is limited.
2. SUMMARY OF METHOD
2.1 A discrete volume of solution containing the element of interest is
deposited into a graphite furnace where it is electrothermally dried,
pyrolyzed, and atomized. The dense population of ground state atoms
is confined in the graphite tube. Conversion of nearly all the
analyte into atoms and increased atom residence times in the light
path improve method detection limits up to three orders of magnitude
over flame atomic absorption spectrophotometry (FAAS) methods. These
ground state atoms absorb electromagnetic radiation over a series of
narrow, sharply defined wavelengths. A spectrally pure line source
of light, usually a hollow cathode lamp specific to the metal of
interest, is used to pass a beam through the tubular graphite
furnace. Light from the source beam, less whatever intensity was
absorbed by the ground-state atoms of the analyte, is isolated by the
monochromator and measured by the photodetector. The amount of light
absorbed by the atoms is proportional to the concentration of the
metal in solution. The relationship between absorption and
concentration is expressed by Beer's Law:
log U0/I) = abc = A
where: I = incident radiant power
I « transmitted radiant power
a * absorptivity (constant for a given system)
b « sample path length
c « concentration of absorbing species (ug/L)
A = absorbance
The atomic absorption spectrophotometer is calibrated with standard
solutions containing known concentrations of the element(s) of
interest. Calibration curves are constructed from which the
concentration of each analyte in the unknown sample is determined.
200.6-2
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3. DEFINITIONS
3.1 ABSORBANCE — the logarithm to the base ten of the reciprocal of the
transmittance (T):
A = log (1/T)
0.0044 Absorbance = the absorption of 1% of
the transmitted light.
The absorbance is related to the analyte concentration by Beer's Law
where 1/T = IQ/I.
3.2 ATOMIC ABSORPTION — the absorption of electromagnetic radiation by
an atom resulting in the elevation of electrons from their ground
states to excited states. Atomic absorption spectrophotometry
involves the measurement of light absorbed by atoms of interest as a
function of the concentration of those atoms in a solution.
3.3 SPECTRAL BANDWIDTH — the wavelength or frequency interval of
radiation leaving the exit slit of a monochromator between limits set
at a radiant power level half way between the continuous background
and the peak of an emission line or an absorption band of negligible
intrinsic width (14.1).
3.4 SPECTROPHOTOMETER — an instrument that provides the ratio, or a
function of the ratio, of the radiant power of two beams as a
function of spectral wavelength. These two beams may be separated
in time and/or space.
3.5 GRAPHITE TUBE FURNACE — an electrothermal atomizer consisting of a
tubular graphite furnace connected to a power unit. The furnace is
contained in a water-cooled housing and is purged with inert gas.
Voltage is passed directly through the graphite tube via electrodes,
producing furnace temperatures over 3000 C.
3.6 PLATFORM — a thin graphite plate which is inserted into the
graphite tube. The sample is deposited directly onto the platform,
which heats more slowly than the surrounding tube. Atomization is
delayed, and it occurs in a higher temperature environment.
3.7 HEATING CYCLES
3.7.1 Dry — the sample is heated to uniformly evaporate the
solvent.
3.7.2 Pyrolyze (Char/Ash) — the residue is heated to a
temperature selected for decomposition and volatilization of
the matrix components. The temperature must be controlled to
prevent vaporization of the analyte.
3.7.3 Atomize — the furnace temperature is increased to
completely convert the analyte into ground state atoms.
200.6-3
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3.8 For definitions of other terms used in this method, refer to the
glossary. For an explanation of the metric system including units,
symbols, and conversion factors see American Society for Testing and
Materials (ASTM) Standard E 380, "Metric Practices". (14.2)
4. INTERFERENCES
4.1 Matrix interferences are common in GFAAS, causing enhancement or
suppression of the formation of ground state atoms.
4.1.1 Chemical Interferences — If the sample contains a compound
that does not dissociate in the pyrolyzation stage of the
furnace program it may alter atomization rates, allow
molecular analyte loss, or cause the analyte to remain
involatile.
4.1.1.1 Aluminum has a tendency to form highly refractory
carbides on the furnace surface. The carbide is
difficult to dissociate completely. The use of
pyrolytically coated graphite and a platform will
reduce this interference. Since the platform heats
primarily by radiation, its temperature increase is
slower than that of the tube walls. Sample
deposition onto the platform allows the sample to be
atomized into a higher temperature environment,
reducing the effect of the sample matrix. The
pyrolytic coating minimizes sample penetration into
the graphite, reducing carbide formation.
4.1.1.2 Aluminum forms stable nitrides at high temperatures
in the presence of nitrogen. To avoid this inter-
ference, use argon as the purge gas. (14.3)
4.1.1.3 Acidifying standards and samples to 0.5% (v/v)
nitric acid (ImL = 5 uL HNCO will prevent
hydrolysis of aluminum
(Al + HO H + A10H ).
4.1.1.4 Volatile halide interferences can be prevented by
avoiding the use of halide acids as preservatives.
Nitric acid is recommended.
4.1.1.5 Nitric acid concentrations in samples and standards
must be closely matched. Different concentrations
result in changes in the decomposition and
volatilization of the acid and other matrix
components in the pyrolyzation stage of the furnace
program. This difference will also affect
vaporization of the analvte.
200.6-4
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4.1.2 Physical interferences may occur with nonuniform distribu-
tion of samples on the tube surface, resulting in varied
atomization rates and/or crystal formation. This problem can
be abated by an automatic sample injection system that uses a
nebulizer to deposit the sample in aerosol form. (14.4)
4.1.3 Nonspecific background absorption is due to light scattering
and/or molecular absorption by the matrix components. Highly
volatile elements tend to vaporize before the matrix
components'can be completely decomposed and volatilized.
Various background correction systems are available.
4.1.3.1 Zeemah — An external magnetic field splits the
atomic spectral line into polarized components.
When the magnetic field is applied, only background
absorbance is measured. When the magnetic field is
off, the absorbance of the sample and background are
both measured. The difference between the two
measurements is the background corrected value.
4.1.3.2 Continuum Source — Light from a continuum
(broad-band) source and from the analyte spectral
source are monitored separately. The light from
the analyte source is absorbed by the analyte and
the background, while light from the continuum
source is absorbed only by the background. Their
difference is the background corrected value.
4.1.3.3 Smith-Hieftje — The line source is cycled at low
and high currents. At low current, light is
absorbed by both the analyte and the background.
At high current, the emission line is broadened
since unexcited atoms in the analyte line source
absorb radiation and emit light at different wave-
lengths (self-reversal). At the high current
pulses, the light is absorbed only by the background.
The difference between the two measurements is the
background corrected value.
4.1.4 Although wet deposition samples are characterized by low
ionic strength, the use of background correction is
recommended.
4.1.4.1 The nitric acid matrix of the samples may be a
source of nonspecific background absorption.
4.1.4.2 The salts present in coastal wet deposition samples
may cause chemical interferences (e.g. halides).
4.1.4.3 Wet deposition samples from urban areas will have
a more complex matrix. These samples may require
the standard addition technique (14.5).
200.6-5
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4.1.4.4 Cadmium, lead, and zinc are highly volatile. They
tend to vaporize before the matrix components can be
completely decomposed and volatilized.
4.2 Memory effects can occur when analyte from a previous sample is
not completely atomized. These effects will result in elevated
concentration readings. To check for this interference,
analyze a zero standard immediately after a high concentration
sample. If an atomization peak is observed, refer to Appendix A.
5. SAFETY
5.1 Use a fume hood, protective clothing, and safety glasses when
handling concentrated acids and metallic cadmium, lead, and
manganese (Sect. 7.4, 7.6, 7.9.2, 7.9.5, and 7.9.6).
5.2 The operator must wear eye protection (welder's goggles) to avoid
eye damage from the ultraviolet light emitted by the furnance
during atomization.
5.3 To avoid severe skin burns, do not touch the furnace until it has
returned to ambient temperature.
5.4 The GPAA operates at high voltages. Check furnace and electrode
alignment and connections before applying power.
5.5 Metallic cadmium, lead, manganese, their stock standard solutions,
and spent hollow cathode lamps are hazardous wastes. Dispose of
them appropriately (14.6).
5.6 Follow American Chemical Society guidelines regarding safe handling
of chemicals used in this method (14.7).
6. APPARATUS AND EQUIPMENT
6.1 ATOMIC ABSORPTION SPECTROPHOTOMETER (AAS) — Select a single-
beam or double-beam instrument with adjustable spectral
bandwidth, wavelength range of 190-400 nm, background correction
capabilities, zero and calibration controls.
6.1.1 Spectral Line Source — Use single element lamps. Hollow
cathode lamps or electrodeless discharge lamps (EDL) may
be used.
6.1.2 Photomultiplier Tube — Select a photomultiplier tube with
optimal quantum efficiency in the wavelength range of
190-400 nm.
200.6-6
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6.2 GRAPHITE FURNACE — Select a furnace with preciste temperature
control to 2800°C, variable gas flow rates, and a cooling system.
6.3 SAMPLE INTRODUCTION SYSTEM
6.3.1 Pipette — For manual introduction of the sample into the
furnace, select a microliter pipette with disposable
polypropylene tips. Precision requirements are Ł1.0%
relative standard deviation (RSD) at volumes less than
10 uL and <0.7% RSD at volumes greater than 10 uL.
6.3.2 Autosampler — An autosampler, although not required, is
recommended for improved precision. It should be equipped
with a dust cover to prevent airborne contamination.
NOTE: An autosampler that uses a nebulizer to deposit the
sample as an aerosol will abate some interferences
(Sect. 4.1.2).
6.4 DATA AQUISITION SYSTEM
6.4.1 Strip Chart Recorder — Select a recorder with a full scale
response of 0.25 seconds or better and a variable chart
speed.
6.4.2 Printer — A printer may be used to document data. Either
a graphics option or a strip chart recorder in tandem with
the printer is required to establish furnace parameters.
(Sect. 11.3).
6.5 Maintain a set of Class A (14.8) volumetric flasks to be used
only when making dilute working standards for the analysis of wet
deposition samples. New glassware should be cleaned according to
Sect. 7.11 before use. Store filled with water (Sect. 7.2) and
covered.
6.6 LABORATORY FACILITIES — Laboratories used for the analysis of
wet deposition samples should be free from external sources of
contamination. The use of laminar flow clean air work stations is
recommended for sample processing and preparation to avoid the
introduction of airborne contaminants. If a clean air work station
is unavailable, samples must be capped or covered prior to analysis.
A positive pressure environment within the laboratory is also
recommended to minimize the introduction of external sources of
contaminant gases and particulates. Windows within the laboratory
should be kept closed at all times and sealed if air leaks are
apparent. The use of disposable tacky floor mats at the entrance to
the laboratory is helpful in reducing the particulate loading within
the room. Point of use 0.2 urn filters are recommended for all
faucets supplying water (Sect. 7.2) to prevent the introduction of
bacteria and/or ion exchange resins into reagents, standard
solutions, and internally formulated quality control check solutions.
The circulation and delivery systems for water (Sect. 7.2) must be
constructed entirely of non-metal components.
200.6-7
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