gffi fU-
&EPA Method 1632: Determination of
Inorganic Arsenic in Water by
Hydride Generation Flame Atomic
Absorption
' Printed on Recycled Paper
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Method 1632
Acknowledgments
Method 1632 was prepared under the direction of William A. Telliard of the U.S. Environmental
Protection Agency's (EPA's) Office of Water (OW), Engineering and Analysis Division (BAD). The
method was prepared under EPA Contract 68-C3-0337 by the DynCorp Environmental Programs Division
with assistance from Quality Works, Inc. and Interface, Inc. The method is based on procedures
developed by Eric Crecelius of the Battelle Marine Sciences Laboratory in Sequim, Washington.
Disclaimer
This method has been reviewed and approved for publication by the Engineering and Analysis Division
of the U.S. Environmental Protection Agency. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
Questions concerning this method or its application should be addressed to:
W.A. Telliard
USEPA Office of Water
Analytical Methods Staff
Mail Code 4303
401 M Street, SW
Washington, DC 20460
Phone: 202/260-7120
Fax: 202/260-7185
Draft, April 1995
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Method 1632
Introduction
This analytical method was designed to support water quality monitoring programs authorized under the
Clean Water Act. Section 304(a) of the Clean Water Act requires EPA to publish water quality criteria
that reflect the latest scientific knowledge about the physical fate (e.g., concentration and dispersal) of
pollutants, the effects of pollutants on ecological and human health, and the effect of pollutants on
biological community diversity, productivity, and stability.
Section 303 of the Clean Water Act requires states to set a water quality standard for each body of water
within its boundaries. A state water quality standard consists of a designated use or uses of a waterbody
or a segment of a waterbody, the water quality criteria that are necessary to protect the designated use or
uses, and an antidegradation policy. These water quality standards serve two purposes: (1) they establish
the water quality goals for a specific waterbody, and (2) they are the basis for establishing water quality-
based treatment controls and strategies beyond the technology-based controls required by Sections 301(b)
and 306 of the Clean Water Act.
In defining water quality standards, the state may use narrative criteria, numeric criteria, or both.
However, the 1987 amendments to the Clean Water Act required states to adopt numeric criteria for toxic
pollutants (designated in Section 307(a) of the Act) based on EPA Section 304(a) criteria or other
scientific data, when the discharge or presence of those toxic pollutants could reasonably be expected to
interfere with designated uses.
In some cases, these water quality criteria are as much as 280 times lower than those achievable using
existing EPA methods and required to support technology-based permits. Therefore, EPA developed new
sampling and analysis methods to specifically address state needs for measuring toxic metals at water
quality criteria levels, when such measurements are necessary to protect designated uses in state water
quality standards. The latest criteria published by EPA are those listed in the National Toxics Rule (57
FR 60848). This rule includes water quality criteria for 13 metals, and it is these criteria on which the
new sampling and analysis methods are based. Method 1632 was specifically developed to provide
reliable measurements of inorganic arsenic at EPA WQC levels using hydride generation flame atomic
absorption techniques.
In developing these methods, EPA found that one of the greatest difficulties in measuring pollutants at
these levels was precluding sample contamination during collection, transport, and analysis. The degree
of difficulty, however, is highly dependent on the metal and site-specific conditions. This analytical
method, therefore, is designed to provide the level of protection necessary to preclude contamination in
nearly all situations. It is also designed to provide the procedures necessary to produce reliable results
at the lowest possible water quality criteria published by EPA. In recognition of the variety of situations
to which this method may be applied, and in recognition of continuing technological advances, the method
is performance based. Alternative procedures may be used, so long as those procedures are demonstrated
to yield reliable results.
Requests for additional copies should be directed to:
U.S. EPA NCEPI
11029 Kenwood Road
Cincinnati, OH 45242
513/489-8190
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Method 1632
Note: This method is intended to be performance based, and the laboratory is permitted to omit
any step or modify any procedure if all performance requirements set forth in this method are
met. The laboratory is not allowed to omit any quality control analyses. The terms "must,"
"may," and "should" are included throughout this method and are intended to illustrate the
importance of the procedures in producing verifiable data at water quality criteria levels. The
term "must" is used to indicate that researchers in trace metals analysis have found certain
procedures essential in successfully analyzing samples and avoiding contamination; however,
these procedures can be modified or omitted if the laboratory can demonstrate that data quality
is not affected.
IV
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Method 1632
Method 1632
Inorganic Arsenic in Water by
Hydride Generation Flame AA
1.0 Scope and Application
1.1 This method is for determination of total inorganic arsenic (As) in filtered and unfiltered water
by hydride generation and flame atomic absorption detection. The method is for use in EPA's
data gathering and monitoring programs associated with the Clean Water Act. The method is
based on a contractor-developed method (Reference 16.1) and on peer-reviewed, published
procedures for the determination of arsenic in aqueous samples (Reference 16.2).
1.2 This method is accompanied by Method 1669: Sampling Ambient Water for Determination of
Trace Metals at EPA Water Quality Criteria Levels (Sampling Method). The Sampling
Method is necessary to ensure that contamination will not compromise trace metals
determinations during the sampling process.
1.3 This method is designed for measurement of dissolved and total arsenic in the range of 10-200
ng/L. This method is not intended for determination of arsenic at concentrations normally
found in treated and untreated discharges from industrial facilities. Existing regulations (40
CFR Parts 400-500) typically limit concentrations in industrial discharges to the part-per-
billion (ppb) range, whereas ambient arsenic concentrations are normally in the low part-per-
trillion (ppt) range.
1.4 The detection limits and quantitation levels in this method are usually dependent on the level
of background elements rather than instrumental limitations. The method detection limit
(MDL; 40 CFR 136, Appendix B) for total inorganic arsenic has been determined to be 2 ng/L
when no background elements or interferences are present. The minimum level (ML) has been
established at 10 ng/L.
1.5 The ease of contaminating water samples with the metal(s) of interest and interfering
substances cannot be overemphasized. This method includes suggestions for improvements in
facilities and analytical techniques that should maximize the ability of the laboratory to make
reliable trace metals determinations and minimize contamination. Section 4.0 gives these
suggestions. Additional suggestions for improvement of existing facilities may be found in
EPA's Guidance for Establishing Trace Metals Clean Rooms in Existing Facilities, which is
available from the National Center for Environmental Publications and Information (NCEPI) at
the address listed in the introduction to this document.
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Method 1632
1.6 Clean and ultraclean—The terms "clean" and "ultraclean" have been applied to the techniques
needed to reduce or eliminate contamination in trace metals determinations. These terms are
not used in this method because they lack an exact definition. However, the information
provided in this method is consistent with EPA's summary guidance on clean and ultraclean
techniques.
1.7 This method follows the EPA Environmental Methods Management Council's "Format for
Method Documentation."
1.8 This method is "performance based." The analyst is permitted to modify the method to
overcome interferences or lower the cost of measurements if all performance criteria are met.
Section 9.1.2 gives the requirements for establishing method equivalency.
1.9 Any modification of this method, beyond those expressly permitted, shall be considered a
major modification subject to application and approval of alternate test procedures at 40 CFR
136.4 and 136.5.
1.10 Each analyst who uses this method must demonstrate the ability to generate acceptable results
using the procedure in Section 9.2.
1.11 This method is accompanied by a data verification and validation guidance document,
Guidance on the Documentation and Evaluation of Trace Metals Data Collected for CWA
Compliance Monitoring. Before this method is used, data users should state data quality
objectives (DQOs) required for a project.
2.0 Summary of Method
2.1 A 100-2000 mL sample is collected directly into a specially cleaned, pretested, fluoropolymer,
conventional or linear polyethylene, polycarbonate, or polypropylene bottle using sample
handling techniques specially designed for collection of metals at trace levels (Reference 16.3).
2.2 The sample is either field or laboratory preserved by the addition of 5 mL of pretested 10%
HNO3 per liter of sample, depending on the time between sample collection and arrival at the
laboratory.
2.3 An aliquot of sample is removed and placed in a specially designed reaction vessel.
2.4 Before analysis, 6 M HC1 and 4% NaBH4 solution are added to convert organic and inorganic
arsenic to volatile arsines.
2.5 The arsines are purged from the sample onto a cooled glass trap packed with 15% OV-3 on
Chromasorb® WAW-DMCSO. or equivalent.
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Method 1632
2.6 The trapped arsines are thermally desorbed, in order of increasing boiling points, into an inert
gas stream that carries them into the flame of an atomic absorption spectrophotometer for
detection. The first arsine to be desorbed will be AsH3, which represents total inorganic
arsenic in the sample.
2.7 Quality is ensured through calibration and testing of the hydride generation, purging, and
detection systems.
3.0 Definitions
3.1 As defined by this method, total inorganic arsenic means all NaBH4-reducible inorganic arsenic
compounds found in aqueous solution. This method can be extended to measure organic
arsenic as well. Organic arsenic includes, but is not limited to, monomethylarsonate and
dimethylarsonate. In this context, "total" arsenic refers to the forms and species of arsenic, not
to the total recoverable or dissolved fraction normally determined in an unfiltered or filtered
sample, respectively. In this method, the total recoverable fraction will be referred to as "total
recoverable" or "unfiltered."
3.2 As defined by this method, dissolved inorganic arsenic means all NaBH4-reducible inorganic
arsenic compounds found in aqueous solution filtrate after passing the sample through a 0.45-
uM capsule filter.
3.3 Definitions of other terms used in this method are given in the glossary at the end of the
method.
4.0 Contamination and Interferences
4.1 Preventing ambient water samples from becoming contaminated during the sampling and
analytical process constitutes one of the greatest difficulties encountered in trace metals
determinations. Over the last two decades, marine chemists have come to recognize that much
of the historical data on the concentrations of dissolved trace metals in seawater are
erroneously high because the concentrations reflect contamination from sampling and analysis
rather than ambient levels. Therefore, it is imperative that extreme care be taken to avoid
contamination when collecting and analyzing ambient water samples for trace metals.
4.2 Samples may become contaminated by numerous routes. Potential sources of trace metals
contamination during sampling include: metallic or metal-containing labware (e.g., talc gloves
that contain high levels of zinc), containers, sampling equipment, reagents, and reagent water;
improperly cleaned and stored equipment, labware, and reagents; and atmospheric inputs such
as dirt and dust. Even human contact can be a source of trace metals contamination.
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Method 1632
4.3 Contamination Control
4.3.1 Philosophy—The philosophy behind contamination control is to ensure that any object
or substance that contacts the sample is metal free and free from any material that may
contain metals.
4.3.1.1 The integrity of the results produced cannot be compromised by contamination
of samples. This method and the Sampling Method give requirements and
suggestions for control of sample contamination.
4.3.1.2 Substances in a sample cannot be allowed to contaminate the laboratory work
area or instrumentation used for trace metals measurements. This method
gives requirements and suggestions for protecting the laboratory.
4.3.1.3 Although contamination control is essential, personnel health and safety remain
the highest priority. The Sampling Method and Section 5 of this method give
requirements and suggestions for personnel safety.
4.3.2 Avoiding contamination—The best way to control contamination is to completely
avoid exposure of the sample to contamination in the first place. Avoiding exposure
means performing operations in an area known to be free from contamination. Two of
the most important factors in avoiding/reducing sample contamination are (1) an
awareness of potential sources of contamination and (2) strict attention to work being
done. Therefore, it is imperative that the procedures described in this method be
carried out by well-trained, experienced personnel.
4.3.3 Use a clean environment—The ideal environment for processing samples is a class 100
clean room (Section 1.5). If a clean room is not available, all sample preparation
should be performed in a class 100 clean bench or a nonmetal glove box fed by
arsenic- and particle-free air or nitrogen. Digestions should be performed in a
nonmetal fume hood situated, ideally, in the clean room.
4.3.4 Minimize exposure—The apparatus that will contact samples, blanks, or standard
solutions should be opened or exposed only in a clean room, clean bench, or glove
box so that exposure to an uncontrolled atmosphere is minimized. When not being
used, the apparatus should be covered with clean plastic wrap, stored in the clean
bench or in a plastic box or glove box, or bagged in clean zip-type bags. Minimizing
the time between cleaning and use will also minimize contamination.
4.3.5 Clean work surfaces—Before a given batch of samples is processed, all work surfaces
in the hood, clean bench, or glove box in which the samples will be processed should
be cleaned by wiping with a lint-free cloth or wipe soaked with reagent water.
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Method 1632
4.3.6 Wear gloves—Sampling personnel must wear clean, nontalc gloves during all
operations involving handling of the apparatus, samples, and blanks. Only clean
gloves may touch the apparatus. If another object or substance is touched, the glove(s)
must be changed before again handling the apparatus. If it is even suspected that
gloves have become contaminated, work must be halted, the contaminated gloves
removed, and a new pair of clean gloves put on. Wearing multiple layers of clean
gloves will allow the old pair to be quickly stripped with minimal disruption to the
work activity.
4.3.7 Use metal-free apparatus—All apparatus used for determination of metals at ambient
water quality criteria levels must be nonmetallic, free of material that may contain
metals, or both.
4.3.7.1 Construction materials—Only fluoropolymer (FEP, PTFE), conventional or
linear polyethylene, polycarbonate, or polypropylene containers should be used
for samples that will be analyzed for arsenic. PTFE is less desirable than FEP
because the sintered material in PTFE may contain contaminants and is
susceptible to serious memory effects (Reference 16.4). All materials,
regardless of construction, that will directly or indirectly contact the sample
must be cleaned using the procedures given in this method and must be known
to be clean and metal free before proceeding.
4.3.7.2 Serialization—It is recommended that serial numbers be indelibly marked or
etched on each piece of apparatus so that contamination can be traced, and
logbooks should be maintained to track the sample from the container through
the labware to injection into the instrument. It may be useful to dedicate
separate sets of labware to different sample types; e.g., receiving waters vs.
effluents. However, the apparatus used for processing blanks and standards
must be mixed with the apparatus used to process samples so that
contamination of all labware can be detected.
4.3.7.3 The laboratory or cleaning facility is responsible for cleaning the apparatus
used by the sampling team. If there are any indications that the apparatus is
not clean when received by the sampling team (e.g., ripped storage bags), an
assessment of the likelihood of contamination must be made. Sampling must
not proceed if it is possible that the apparatus is contaminated. If the
apparatus is contaminated, it must be returned to the laboratory or cleaning
facility for proper cleaning before any sampling activity resumes.
4.3.8 Avoid sources of contamination—Avoid contamination by being aware of potential
sources and routes of contamination.
4.3.8.1 Contamination by carryover—Contamination may occur when a sample
containing low concentrations of metals is processed immediately after a
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Method 1632
sample containing relatively high concentrations of these metals. To reduce
carryover, the sample introduction system may be rinsed between samples with
dilute acid and reagent water. When an unusually concentrated sample is
encountered, it is followed by analysis of a laboratory blank to check for
carryover. Samples known or suspected to contain the lowest concentration of
metals should be analyzed first followed by samples containing higher levels.
4.3.8.2 Contamination by samples—Significant laboratory or instrument contamination
may result when untreated effluents, in-process waters, landfill leachates, and
other samples containing high concentrations of inorganic substances are
processed and analyzed. This method is not intended for application to these
samples, and samples containing high concentrations should not be permitted
into the clean room and laboratory dedicated for processing trace metals
samples.
4.3.8.3 Contamination by indirect contact—Apparatus that may not directly come in
contact with the samples may still be a source of contamination. For example,
clean tubing placed in a dirty plastic bag may pick up contamination from the
bag and subsequently transfer the contamination to the sample. Therefore, it is
imperative that every piece of the Apparatus that is directly or indirectly used
in the collection, processing, and analysis of ambient water samples be cleaned
as specified in Section 11.
4.3.8.4 Contamination by airborne paniculate matter—Less obvious substances capable
of contaminating samples include airborne particles. Samples may be
contaminated by airborne dust, dirt, particles, or vapors from unfiltered air
supplies; nearby corroded or rusted pipes, wires, or other fixtures; or metal-
containing paint. Whenever possible, sample processing and analysis should
occur as far as possible from sources of airborne contamination.
4.4 Interferences
4.4.1 If the transfer line between the cold trap and the atomizer is not well heated, water vapor may
condense in the line. Such condensation can interfere with the determination of
dimethylarsine.
4.4.2 High concentrations of cobalt, copper, iron, mercury, or nickel can cause interferences through
precipitation as reduced metals and blockage of transfer lines and fittings
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Method 1632
5.0 Safety
5.1 The toxicity or carcinogenicity of each chemical used in this method has not been precisely
determined; however, each compound should be treated as a potential health hazard. Exposure
to these compounds should be reduced to the lowest possible level. It is recommended that
the laboratory purchase a dilute standard solution of the As in this method. If primary
solutions are prepared, they shall be prepared in a hood, and a NIOSH/MESA-approved toxic
gas respirator shall be worn when high concentrations are handled.
5.2 This method does not address all safety issues associated with its use. The laboratory is
responsible for maintaining a current awareness file of OSHA regulations for the safe handling
of the chemicals specified in this method. A reference file of material safety data sheets
(MSDSs) should also be made available to all personnel involved in these analyses. It is also
suggested that the laboratory perform personal hygiene monitoring of each analyst who uses
this method and that the results of this monitoring be made available to the analyst. Additional
information on laboratory safety can be found in References 16.5-16.8. The references and
bibliography at the end of Reference 16.8 are particularly comprehensive in dealing with the
general subject of laboratory safety.
5.3 Samples suspected to contain high concentrations of As are handled using essentially the same
techniques used in handling radioactive or infectious materials. Well-ventilated, controlled
access laboratories are required. Assistance in evaluating the health hazards of particular
laboratory conditions may be obtained from certain consulting laboratories and from State
Departments of Health or Labor, many of which have an industrial health service. Each
laboratory must develop a strict safety program for handling As.
5.3.1 Facility—When samples known or suspected of containing high concentrations of
arsenic are handled, all operations (including removal of samples from sample
containers, weighing, transferring, and mixing) should be performed in a glove box
demonstrated to be leaktight or in a fume hood demonstrated to have adequate air
flow. Gross losses to the laboratory ventilation system must not be allowed. Handling
of the dilute solutions normally used in analytical and animal work presents no
inhalation hazards except in an accident.
5.3.2 Protective equipment—Disposable plastic gloves, apron or laboratory coat, safety
glasses or mask, and a glove box or fume hood adequate for radioactive work should
be used. During analytical operations that may give rise to aerosols or dusts, personnel
should wear respirators equipped with activated carbon filters.
5.3.3 Training—Workers must be trained in the proper method of removing contaminated
gloves and clothing without contacting the exterior surfaces.
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Method 1632
5.3.4 Personal hygiene—Hands and forearms should be washed thoroughly after each
manipulation and before breaks (coffee, lunch, and shift).
5.3.5 Confinement—Isolated work areas posted with signs, segregated glassware and tools,
and plastic absorbent paper on bench tops will aid in confining contamination.
5.3.6 Effluent vapors—The effluent from the AAS should pass through either a column of
activated charcoal or a trap designed to remove As.
5.3.7 Waste handling—Good technique includes minimizing contaminated waste. Plastic
bag liners should be used in waste cans. Janitors and other personnel must be trained
in the safe handling of waste.
5.3.8 Decontamination
5.3.8.1 Decontamination of personnel—Use any mild soap with plenty of scrubbing
action.
5.3.8.2 Glassware, tools, and surfaces—Satisfactory cleaning may be accomplished by
washing with any detergent and water.
5.3.9 Laundry—Clothing known to be contaminated should be collected in plastic bags.
Persons who convey the bags and launder the clothing should be advised of the hazard
and trained in proper handling. If the launderer knows of the potential problem, the
clothing may be put into a washer without contact. The washer should be run through
a cycle before being used again for other clothing.
5.3.10 Wipe tests—A useful method of determining cleanliness of work surfaces and tools is
to wipe the surface with a piece of filter paper. Extraction and analysis by this method
can achieve a limit of detection of less than 1 ng per wipe. Less than 0.1 pg per wipe
indicates acceptable cleanliness; anything higher warrants further cleaning. More than
10 pg on a wipe constitutes an acute hazard and requires prompt cleaning before
further use of the equipment or work space, and indicates that unacceptable work
practices have been employed.
6.0 Apparatus and Materials
Note: Brand names, suppliers, and part numbers are for illustration purposes only
and no endorsement is implied. Equivalent performance may be achieved using
apparatus and materials other than those specified here. The laboratory is responsible
for meeting the performance requirements of this method.
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Method 1632
6.1 Sampling equipment
6.1.1 Sample collection bottles-Fluoropolymer, conventional or linear polyethylene,
polycarbonate, or polypropylene, 500-1000 mL
6.1.2 Cleaning—Bottles are cleaned with liquid detergent and thoroughly rinsed with reagent
water. They are then heated to 50-60°C in concentrated reagent grade HNO3 for at
least 2 h. The bottles are rinsed with reagent water, then immersed in a hot (50-60°)
bath of IN trace metal grade HC1 for at least 48 h. The bottles are then thoroughly
rinsed with reagent water and filled with 0.1 % (v/v) ultrapure HC1 and double-bagged
in new polyethylene zip-type bags until needed.
6.2 Equipment for bottle and glassware cleaning
6.2.1 Vats, up to 200-L capacity, constructed of high-density polyethylene (HOPE) or other
nonmetallic, noncontaminating material suitable for holding concentrated HNO3 and
dilute HC1
6.2.2 Panel immersion heater, all-fluoropolymer coated, capable of maintaining a
temperature of 60-75°C in a vat of the size used
6.2.3 Laboratory sink in class 100 clean area, with high-flow reagent water for rinsing
6.2.4 Clean bench, class 100, for drying rinsed bottles.
6.3 Atomic absorption spectrophotometer (AAS)—Any atomic absorption spectrophotometer may
serve as a detector. A bracket is required to hold the quartz atomizer in the optical path of the
instrument. Table 1 gives typical conditions for the spectrophotometer.
6.3.1 Electrodeless discharge lamp for measuring arsenic at 193.7 nm
6.3.2 Quartz cuvette burner tube (Reference 16.2), 70 mm long and 9 mm in diameter with
two 6-mm o.d. side tubes, each 25 mm long. Figure la shows a schematic of the tube
and bracket.
6.4 Equipment for reaction vessel—Figure Ib shows the schematic diagram for the vessel used for
the reaction of the sample with sodium borohydride. The system consists of the following:
6.4.1 125-mL gas wash bottle (Corning # 1760-125 or equivalent) onto which an 8-mm o.d.
sidearm inlet tube 2 cm long has been grafted
6.4.2 Silicone rubber stopper septum (Ace Glass #9096-32 or equivalent)
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Method 1632
6.4.3 Four-way Teflon stopcock valve capable of switching of the helium from the purge to
the analysis mode of operation
6.4.4 Flow meter/needle valve capable of controlling and measuring gas flow rate to the
reaction vessel at 150 (± 30) mL/min
6.4.5 Silicone tubing—All glass-to-glass connections are made with silicone rubber sleeves.
6.5 Equipment for cryogenic trap—Figure Ic shows the schematic diagram for the trap. It consists
of the following:
6.5.1 Nichrome wire (22-gauge)
6.5.2 Variacs for controlling Nichrome wire
6.5.3 A 6-mm o.d. borosilicate glass U-tube about 30 cm long with a 2-cm radius of bend
(or similar dimensions to fit into a tall widemouth Dewar flask), which has been
silanized and half-packed with 15% OV-3 on Chromasorb® WAW-DMCS (45-60
mesh), and the ends of which have been packed with silanized glass wool.
6.5.3.1 Conditioning the trap—The input side of the trap (the side that is not packed)
is connected with silicone rubber tubing to He at a flow rate of 40 mL/min,
and the trap is placed in an oven at 175°C for 2 h. At the end of this time,
inject two 25-uL aliquots of GC column conditioner (Silyl-8®, Supelco, Inc., or
equivalent) through the silicone tubing into the glass trap. Return the trap to
the oven, with the He still flowing, for 24 h.
6.5.3.2 After conditioning, the trap is wrapped with approximately 1.8 m of 22-gauge
Nichrome wire, the ends of which are affixed to crimp-on electrical contacts.
The wire-wrapped column is coated with approximately 2 mm of silicon
rubber caulking compound.
6.5.3.3 The trap is connected by silicone rubber tubing to the output of the reaction
vessel. The output side of the trap is connected by 6-mm diameter borosilicate
tubing that has been wrapped by Nichrome wire to the input of the flame
atomizer.
6.5.4 Dewar flask capable of containing the trap described in Section 6.5.3.
6.6 Recorder/integrator—Any integrator with a range compatible with the AAS is acceptable.
6.7 Pipettors—All-plastic pneumatic fixed volume and variable pipettors in the range of 10 uL to
5.0 mL.
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Method 1632
6.8 Analytical balance capable of weighing to the nearest 0.01 gram
7.0 Reagents and Standards
7.1 Reagent water—Water demonstrated to be free from As and potentially interfering substances
at the MDL. Prepared by distillation, deionization, reverse osmosis, anodic/cathodic stripping
voltammetry, or other technique that removes As and potential interferant(s).
7.2 Hydrochloric acid—Trace-metal purified reagent HC1.
7.3 6M hydrochloric acid—Equal volumes of trace metal grade concentrated HC1 (Section 7.2) and
reagent water (Section 7.1) are combined to give a solution approximately 6M in HC1.
7.4 Nitric acid—Trace-metal purified reagent HNO3
7.5 10% nitric acid—Nitric acid (HNO3): 10% wt, Seastar, or equivalent.
7.6 Sodium borohydride solution-4 g of >98% NaBH4 (previously analyzed and shown to be free
of measurable arsenic) are dissolved in 100 mL of 0.02 M NaOH solution. This solution is
stable for only 8-10 h, and must be made fresh daily.
7.7 Liquid nitrogen for cooling the cryogenic trap
7.8 Helium—Grade 4.5 (standard laboratory grade) helium.
7.9 Hydrogen—Grade 4.5 (standard laboratory grade) hydrogen.
7.10 Air—Grade 4.5 (standard laboratory grade) air.
7.11 QC sample concentrate—From a source different than the one used to prepare calibration
standards, prepare a QC sample concentrate containing 1.50 ug/L As in reagent water (Section
7.1) preserved with sufficient HNO3 to bring the pH to <2.
7.12 Arsenic Standards
7.12.1 Stock standard solution (1000 mg/L)—Either procure A2LA-certified aqueous
standards from a supplier and verify by comparison to a second standard from a
separate source, or dissolve 1.320 g of arsenic trioxide (As2O3) in 100 mL of reagent
water (Section 7.1) containing 4 g NaOH. Acidify the solution with 20 mL
concentrated HNO3 and dilute to 1.0 liter.
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Method 1632
9.1.2.2.2 A listing of metal measured (As), by name and CAS Registry
number
9.1.2.2.3 A narrative stating reason(s) for the modification(s)
9.1.2.2.4 Results from all quality control (QC) tests comparing the
modified method to this method, including:
(a) Calibration
(b) Calibration verification
(c) Initial precision and recovery (Section 9.2)
(d) Analysis of blanks
(e) Accuracy assessment
9.1.2.2.5 Data that will allow an independent reviewer to validate each
determination by tracing the instrument output (peak height,
area, or other signal) to the final result. These data are to
include, where possible:
(a) Sample numbers and other identifiers
(b) Preparation dates
(c) Analysis dates and times
(d) Analysis sequence/run chronology
(e) Sample volume
(f) Volume before each preparation step
(g) Volume after each preparation step
(h) Final volume before analysis
(i) Dilution data
(j) Instrument and operating conditions (make, model,
revision, modifications)
(k) Sample introduction system (ultrasonic nebulizer, hydride
generator, flow injection system, etc.)
(1) Operating conditions (ashing temperature, temperature
program, flow rates, etc.)
(m) Detector (type, operating conditions, etc.)
(n) Printer tapes and other recordings of raw data
(o) Quantitation reports, data system outputs, and other data to
link the raw data to the results reported
9.1.3 Analyses of blanks are required to demonstrate freedom from contamination. Section
9.5 describes the required types, procedures, and criteria for analysis of blanks.
9.1.4 The laboratory shall spike at least 10% of the samples with As to monitor method
performance. Section 9.3 describes this test. When results of these spikes indicate
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Method 1632
atypical method performance for samples, an alternative extraction or cleanup
technique must be used to bring method performance within acceptable limits. If
method performance for spikes cannot be brought within the limits given in this
method, the result may not be reported for regulatory compliance purposes.
9.1.5 The laboratory shall, on an ongoing basis, demonstrate through calibration verification
and through analysis of the ongoing precision and recovery aliquot that the analytical
system is in control. Sections 9.6 and 10.2 describe these procedures,
9.1.6 The laboratory shall maintain records to define the quality of data that are generated.
Section 9.3.4 describes the development of accuracy statements.
9.2 Initial demonstration of laboratory capability
9.2.1 Method detection limit—To establish the ability to detect As, the analyst shall
determine the MDL per the procedure in 40 CFR 136, Appendix B using the
apparatus, reagents, and standards that will be used in the practice of this method. The
laboratory must produce an MDL that is no more than one-tenth the regulatory
compliance level or that is less than the MDL listed in Table 1, whichever is greater.
9.2.2 Initial precision and recovery (IPR)—To establish the ability to generate acceptable
precision and recovery, the analyst shall perform the following operations.
9.2.2.1 Analyze four aliquots of reagent water spiked with As at 0.015 ug/L according
to the procedures in this method. Prepare these by diluting each of four 1.0-
mL aliquots of the QC Sample Concentrate to 100 mL. All digestion,
extraction, and concentration steps, and the containers, labware, and reagents
that will be used with samples must be used in this test.
9.2.2.2 Using results of the set of four analyses, compute the average percent recovery
(X) in each aliquot and the standard deviation(s) of the recovery.
9.2.2.3 Compare s and X with the corresponding limits for initial precision and
recovery in Table 2. If s and X meet the acceptance criteria, system
performance is acceptable and analysis of blanks and samples may begin. If,
however, s exceeds the precision limit or X falls outside the range for
accuracy, system performance is unacceptable for As. Correct the problem and
repeat the test (Section 9.2.2.1).
9.3 Method accuracy—To assess the performance of the method on a given sample matrix, the
laboratory must perform matrix spike (MS) and matrix spike duplicate (MSD) sample analyses
on 10% of the samples from each site being monitored, or at least one MS sample analysis
and one MSD sample analysis must be performed for each sample set (samples collected from
the same site at the same time, to a maximum of 10 samples), whichever is more frequent.
Draft, April 1995 75
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Method 1632
9.3.1 The concentration of the MS and MSD is determined as follows:
9.3.1.1 If, as in compliance monitoring, the concentration of As in the sample is being
checked against a regulatory concentration limit, the spike must be at that limit
or at five times the background concentration, whichever is greater.
9.3.1.2 If the concentration is not being checked against a regulatory limit, the
concentration must be at five times the background concentration or at five
times the ML in Table 1, whichever is greater.
9.3.2 Assessing spike recovery
9.3.2.1 Determine the background concentration (B) of As by analyzing one sample
aliquot according to the procedures specified in this method.
9.3.2.2 If necessary, prepare a matrix spiking concentrate that will produce the
appropriate level (Section 9.3.1) in the sample when the concentrate is added.
9.3.2.3 Spike a second sample aliquot with the QC check sample concentrate (or, if
necessary, with the matrix spiking concentrate) and analyze it to determine the
concentration after spiking (A).
9.3.2.4 Calculate each percent recovery (P) as 100(A - B)/T, where T is the known
true value of the spike.
9.3.3 Compare the percent recovery (P) with the corresponding QC acceptance criteria in
Table 2. If P falls outside the designated range for recovery, As has failed the
acceptance criteria.
9.3.3.1 If As has failed the acceptance criteria, analyze the ongoing precision and
recovery standard (Section 9.6). If the OPR is within its respective limit
(Table 2), the analytical system is in control and the problem can be attributed
to the sample matrix.
9.3.3.2 For samples that exhibit matrix problems, further isolate As from the sample
matrix using chelation, extraction, concentration, hydride generation, or other
means, and repeat the accuracy test (Section 9.3.2).
9.3.3.3 If the recovery for As remains outside the acceptance criteria, the analytical
result in the unspiked sample is suspect and may not be reported for regulatory
compliance purposes.
9.3.4 Recovery for samples should be assessed and records maintained.
16 Draft, April 1995
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Method 1632
9.3.4.1 After the analysis of five samples of a given matrix type (river water, lake
water, etc.) for which As passes the tests in Section 9.3.3, compute the average
percent recovery (R) and the standard deviation of the percent recovery (SR).
Express the accuracy assessment as a percent recovery interval from R - 2SR
to R + 2SR for each matrix. For example, if R - 90% and SR - 10% for five
analyses of river water, the accuracy interval is expressed as 70-110%.
9.3.4.2 Update the accuracy assessment in each matrix regularly (e.g., after each five
to ten new measurements).
9.4 Precision of matrix spike duplicates
9.4.1 Calculate the relative percent difference (RPD) between the MS and MSD according to
the equation below using the concentrations found in the MS and MSD. Do not use
the recoveries calculated in Section 9.3.2.4 for this calculation because the RPD of
recoveries is inflated when the background concentration is near the spike
concentration.
RPD -
(Dl+D2)/2
Where:
Dl = concentration of the analyte in the MS sample
Dl = concentration of the analyte in the MSD sample
9.4.2 Compare the RPD with the limits in Table 2. If the criteria are not met, the analytical
system is judged to be out of control. Correct the problem and reanalyze all samples
in the sample set associated with the MS/MSD that failed the RPD test.
9.5 Blanks—Blanks are analyzed to demonstrate freedom from contamination.
9.5.1 Laboratory (method) blank
9.5.1.1 Prepare a method blank with each sample batch (samples of the same matrix
started through the preparation process on the same 12-hour shift, to a
maximum of 10 samples). Analyze the blank immediately after analysis of the
OPR (Section 9.6) to demonstrate freedom from contamination.
9.5.1.2 If As or any potentially interfering substance is found in the blank at a
concentration equal to or greater than the MDL (Table 1), sample analysis
must be halted, the source of the contamination determined, the problem
corrected, and the sample batch and fresh method blank reanalyzed.
Draft, April 1995 17
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Method 1632
9.5.1.3 Alternatively, if a sufficient number of blanks (three minimum) are analyzed to
characterize the nature of a blank, the average concentration plus two standard
deviations must be less than the regulatory compliance level.
9.5.1.4 If the result for a single blank remains above the MDL or if the result for the
average concentration plus two standard deviations of three or more blanks
exceeds the regulatory compliance level, results for samples associated with
those blanks may not be reported for regulatory compliance purposes. Stated
another way, results for all initial precision and recovery tests (Section 9.2)
and all samples must be associated with an uncontaminated method blank
before these results may be reported for regulatory compliance purposes.
9.5.2 Field blank
9.5.2.1 Analyze the field blank(s) shipped with each set of samples (samples collected
from the same site at the same time, to a maximum of 10 samples). If the
samples are filtered for the determination of dissolved As, the field blank shall
be filtered as well. Analyze the blank immediately before analyzing the
samples in the batch.
9.5.2.2 If As or any potentially interfering substance is found in the field blank at a
concentration equal to or greater than the MDL (Table 1), or greater than one-
fifth the level in the associated sample, whichever is greater, results for
associated samples may be the result of contamination and may not be reported
for regulatory compliance purposes.
9.5.2.3 Alternatively, if a sufficient number of field blanks (three minimum) are
analyzed to characterize the nature of the field blank, the average concentration
plus two standard deviations must be less than the regulatory compliance level
or less than one-half the level in the associated sample, whichever is greater.
9.5.2.4 If contamination of the field blanks and associated samples is known or
suspected, the laboratory should communicate this to the sampling team so that
the source of contamination can be identified and corrective measures taken
before the next sampling event.
9.5.3 Equipment blanks—Before any sampling equipment is used at a given site, the
laboratory or cleaning facility is required to generate equipment blanks to demonstrate
that the sampling equipment is free from contamination. Two types of equipment
blanks are required: bottle blanks and sampler check blanks.
9.5.3.1 Bottle blanks—After undergoing appropriate cleaning procedures (Section
11.4), bottles should be subjected to conditions of use to verify the
effectiveness of the cleaning procedures. A representative set of sample bottles
10
0 Draft, April 1995
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Method 1632
should be filled with reagent water acidified to pH < 2 and allowed to stand
for a minimum of 24 h. Ideally, the time that the bottles are allowed to stand
should be as close as possible to the actual time that sample will be in contact
with the bottle. After standing, the water should be analyzed for any signs of
contamination. If any bottle shows signs of contamination, the problem must
be identified, the cleaning procedures corrected or cleaning solutions changed,
and all affected bottles recleaned.
9.5.3.2 Sampler check blanks—Sampler check blanks are generated in the laboratory
or at the equipment cleaning contractor's facility by processing reagent water
through the sampling devices using the same procedures that are used in the
field (see Sampling Method). Therefore, the "clean hands/dirty hands"
technique used during field sampling should be followed when preparing
sampler check blanks at the laboratory or cleaning facility.
9.5.3.2.1 Sampler check blanks are generated by filling a large carboy or
other container with reagent water (Section 7.2) and processing
the reagent water through the equipment using the same
procedures that are used in the field (see Sampling Method).
For example, manual grab sampler check blanks are collected
by directly submerging a sample bottle into the water, filling
the bottle, and capping. Subsurface sampler check blanks are
collected by immersing the sampler into the water and
pumping water into a sample container. "Clean hands/dirty
hands" techniques must be used.
9.5.3.2.2 The sampler check blank must be analyzed using the
procedures in this method. If As or any potentially interfering
substance is detected in the blank, the source of contamination
or interference must be identified and the problem corrected.
The equipment must be demonstrated to be free from As
before the equipment may be used in the field.
9.5.3.2.3 Sampler check blanks must be run on all equipment that will
be used in the field. If, for example, samples are to be
collected using both a grab sampling device and a subsurface
sampling device, a sampler check blank must be run on both
pieces of equipment.
9.6 Ongoing precision and recovery
9.6.1 Prepare a precision and recovery sample (laboratory-fortified method blank) identical
to the initial precision and recovery aliquots (Section 9.2) with each sample batch
(samples of the same matrix started through the extraction process on the same 12-
Draft, April 1995 19
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Method 1632
hour shift, to a maximum of 10 samples) by diluting a 1.0-mL aliquot of QC check
sample concentrate to 100 mL with reagent water.
9.6.2 Analyze the OPR aliquot before analyzing the method blank and samples from the
same batch.
9.6.3 Compute the percent recovery of As in the OPR aliquot using the procedure given in
this method.
9.6.4 Compare the concentration to the limits for ongoing recovery in Table 2. If the
acceptance criteria are met, system performance is acceptable and analysis of blanks
and samples may proceed. If, however, recovery falls outside of the range given, the
analytical processes are not being performed properly. Correct the problem, reprepare
the sample batch, and repeat the OPR test (Section 9.6).
9.6.5 Add results that pass the specifications in Section 9.6.4 to initial and previous ongoing
data for As in each matrix. Update QC charts to form a graphic representation of
continued laboratory performance. Develop a statement of laboratory accuracy in each
matrix type by calculating the average percent recovery (R) and the standard deviation
of percent recovery (SR). Express the accuracy as a recovery interval from R - 2SR to
R + 2SR. For example, if R = 95% and SR - 5%, the accuracy is 85-105%.
9.7 The specifications in this method can be met if the instrument used is calibrated properly and
then maintained in a calibrated state. A given instrument will provide the most reproducible
results if dedicated to the settings and conditions required for the analyses of As by this
method.
9.8 Depending on specific program requirements, field duplicates may be collected to determine
the precision of the sampling technique. The relative percent difference (RPD) between field
duplicates should be less than 20%.
10.0 Calibration and Standardization
10.1 Calibration—Calibrate at a minimum of three points, one of which must be the ML (Table 1),
and another that must be near the upper end of the linear dynamic range. Calibration is
required before any samples or blanks are analyzed.
10.1.1 External standard calibration
10.1.1.1 Calculate the response factor (RF) for As in each CAL solution using
the following equation and the height or area produced.
20 Draft, April 1995
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Method 1632
(RJ
RF = — Z-
Where.
Rx = height or area of the signal for As
Cx = concentration of compound injected (\ig/L)
10.1.1.2 Calculate the mean RF (M), the standard deviation of the RF (SD), and
the relative standard deviation (RSD) of the mean, where RSD = 100 x
SD/M.
10.1.1.3 Linearity—If the RSD of the mean RF is less than 25% over the
calibration range, an averaged response factor may be used.
Otherwise, a calibration curve must be used over the calibration range.
Note: The reagents used in the hydride generation process are likely to cause some
absorbance in the absence of As. Using a mean RF to quantitate samples will
therefore result in decreasing accuracy with decreasing concentrations of As. To
avoid this, it is recommended that a calibration curve that is not forced through the
origin be used in lieu of a mean RF, even if the %RSD of the Rfs is less than 25%.
10.2 Calibration verification—Immediately after calibration, an initial calibration verification should
be performed. Adjustment of the instrument is performed until verification criteria are met.
Only after these criteria are met may blanks and samples be analyzed.
10.2.1 Verify the specificity of the instrument for As and adjust the wavelength or tuning
until the resolving power specified in this method is met.
10.2.2 Inject the mid-point calibration standard (Section 10.1) or a dilution of the QC check
sample concentrate with a concentration near the midpoint of the calibration range.
10.2.3 Compute the percent recovery of As using the mean response or calibration curve
obtained in the initial calibration.
10.2.4 Compare the recovery with the corresponding limit for calibration verification in Table
2. If acceptance criteria are met, system performance is acceptable and analysis of
blanks and samples may continue using the response from the initial calibration. If
acceptance criteria are not met, system performance is unacceptable. Locate and
correct the problem and/or prepare a new calibration check standard and repeat the test
(Sections 10.2.2-10.2.4), or recalibrate the system according to this method and
Section 10.1.
Draft, April 1995 21
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Method 1632
10.2.5 Calibration should be verified following every ten samples by analyzing the mid-point
calibration standard. If the recovery does not meet the acceptance criteria specified in
Table 2, analysis must be halted, the problem corrected, and the instrument
recalibrated. All samples after the last acceptable calibration verification must be
reanalyzed.
11.0 Procedure
11.1 Set the AA system up according to manufacturer's instructions. The settings in Tables 3 and 4
can be used as a guide. Calibrate the instrument according to Section 10.
Note: Precision and sensitivity are affected by gas flow rates and these must be
individually optimized for each system, using the figures in Table 4 as an initial guide.
11.2 To light the flame, turn on all gases and expose the end of the quartz cuvette to a flame. At
this point, a flame will be burning out the ends of the tube. Allow the tube to heat for
approximately 5 min, then place a flat metal spatula over each end of the tube in sequence.
An invisible air/hydrogen flame should now be burning in the center of the cuvette. To check
for the flame, place a mirror near the end of the tube.
11.3 Place a known volume of aqueous sample (up to 70 mL) into the reaction vessel. If less than
70 mL of sample is used, add sufficient reagent water to result in a total volume of 70 mL.
Add 5.0 mL of 6M HC1. Set the four-way valve on the reaction vessel to pass the flow of He
through the sample and onto the trap and begin purging the vessel with He.
11.4 Lower the trap into a Dewar flask containing liquid nitrogen (LN2) and top the flask off with
LN2 to a constant level.
11.5 Add 10 mL of NaBH4 solution slowly (over a period of approximately 2 min) through the
rubber septum with a disposable hypodermic syringe and begin timing the reaction. After 7
min, turn the stopcock on the four-way valve to bypass the reaction vessel and pass helium
directly to the trap.
11.6 Quickly remove the trap from the LN2, activate the heating coils to heat the trap and transfer
line to 80°C, and begin recording output from the AA system.
11.7 To ensure that all organic reduction products have been desorbed from the trap, maintain the
trap temperature at 80°C and keep He flowing through the trap for at least 3 min between
samples.
22 Draft, April 1995
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Method 1632
12.0 Data Analysis and Calculations
12.1 Compute the concentration of As in ng/L (parts-per-trillion; ppt) using the calibration data
(Section 10.1) according to the following equation:
where the terms are defined in Section 10.1.1
12.2 If the concentration exceeds the linear dynamic range of the instrument, dilute the sample by
successive factors of 10 lu until the concentration is within the linear dynamic range.
12.3 Report results at or above the ML for As found in samples and determined in standards.
Report all results for As found in blanks, regardless of level.
12.4 Report results to one significant figure at or below the MDL, two significant figures between
the MDL and ML, and three significant figures at or above the ML.
12.5 Do not perform blank subtraction on the sample results.
13.0 Method Performance
Before this method was documented, an MDL study was conducted using the techniques
described in the method. Additional method performance studies will be conducted in 1995,
and the method will be revised as needed to reflect the results of those studies.
14.0 Pollution Prevention
14.1 Pollution prevention encompasses any technique that reduces or eliminates the quantity or
toxicity of waste at the point of generation. Many opportunities for pollution prevention exist
in laboratory operation. EPA has established a preferred hierarchy of environmental
management techniques that places pollution prevention as the management option of first
choice. Whenever feasible, laboratory personnel should use pollution prevention techniques to
address their waste generation. When wastes cannot be feasibly reduced at the source, the
Agency recommends recycling as the next best option. The acids used in this method should
be reused as practicable by purifying by electrochemical techniques. The only other chemicals
used in this method are the neat materials used in preparing standards. These standards are
used in extremely small amounts and pose little threat to the environment when managed
Draft, April 1995 23
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Method 1632
properly. Standards should be prepared in volumes consistent with laboratory use to minimize
the disposal of excess volumes of expired standards.
14.2 For information about pollution prevention that may be applied to laboratories and research
institutions, consult Less is Better: Laboratory Chemical Management for Waste Reduction,
available from the American Chemical Society's Department of Governmental Relations and
Science Policy, 1155 16th Street NW, Washington DC 20036, 202/872-4477.
15.0 Waste Management
15.1 The laboratory is responsible for complying with all federal, state, and local regulations
governing waste management, particularly hazardous waste identification rules and land
disposal restrictions, and for protecting the air, water, and land by minimizing and controlling
all releases from fume hoods and bench operations. Compliance with all sewage discharge
permits and regulations is also required.
15.2 Acids and samples at pH < 2 must be neutralized before being disposed, or must be handled as
hazardous waste.
15.3 For further information on waste management, consult The Waste Management Manual for
Laboratory Personnel and Less is Better: Laboratory Chemical Management for Waste
Reduction, both available from the American Chemical Society's Department of Government
Relations and Science Policy, 1155 16th Street NW, Washington, DC 20036.
16.0 References
16.1 Crecelius, E.A.; Bloom, N.S.; Cowan, C.E.; Jenne, E.A. Speciation of Selenium and Arsenic in
Natural Waters and Sediments, Volume 2: Arsenic Speciation. Final Report. Prepared for
Electric Power Research Institute, Palo Alto, CA by Battelle, Pacific Northwest Laboratories,
Richland, WA. 1986.
16.2 Andreae, M.O. "Determination of Arsenic Species in Natural Waters," Anal. Chem. 1977, 49,
820.
16.3 Method 1669, "Method for Sampling Ambient Water for Determination of Metals at EPA
Ambient Criteria Levels," U.S. Environmental Protection Agency, Office of Water, Office of
Science and Technology, Engineering and Analysis Division (4303), 401 M St SW,
Washington, DC 20460 (1995).
24 Draft, April 1995
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Method 1632
16.4 Patterson, C.C.; Settle, D.M. "Accuracy in Trace Analysis"; In National Bureau of Standards
Special Publication 422; LaFleur, P.D., Ed., U.S. Government Printing Office, Washington,
DC, 1976.
16.5 "Working with Carcinogens," Department of Health, Education, and Welfare, Public Health
Service, Centers for Disease Control, NIOSH, Publication 77-206, Aug. 1977, NTIS PB-
277256.
16.6 "OSHA Safety and Health Standards, General Industry," OSHA 2206, 29 CFR 1910.
16.7 "Safety in Academic Chemistry Laboratories," ACS Committee on Chemical Safety, 1979.
16.8 "Standard Methods for the Examination of Water and Wastewater," 18th ed. and later
revisions, American Public Health Association, 1015 15th Street NW, Washington DC 20005,
1-35: Section 1090 (Safety), 1992.
17.0 Glossary
The definitions and purposes below are specific to this method, but have been conformed to common
usage as much as possible.
17.1 Ambient Water—Waters in the natural environment (e.g., rivers, lakes, streams, and other
receiving waters), as opposed to effluent discharges.
17.2 Analytical Shift—All the 12-hour periods during which analyses are performed. The period
begins with the purging of the OPR standard and ends exactly 12 hours later. All analyses
both started and completed within this 12-hour period are valid.
17.3 Calibration Standard (CAL)—A solution prepared from a dilute mixed standard and/or stock
solutions and used to calibrate the response of the instrument with respect to analyte
concentration.
17.4 Equipment Blank—An aliquot of reagent water that is subjected in the laboratory to all
aspects of sample collection and analysis, including contact with all sampling devices and
apparatus. The purpose of the equipment blank is to determine if the sampling devices and
apparatus for sample collection have been adequately cleaned before shipment to the field site.
An acceptable equipment blank must be achieved before the sampling devices and apparatus
are used for sample collection. In addition, equipment blanks should be run on random,
representative sets of gloves, storage bags, and plastic wrap for each lot to determine if these
materials are free from contamination before use.
Draft, April 1995 25
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Method 1632
17.5 Field Blank—An aliquot of reagent water that is placed in a sample container in the
laboratory, shipped to the field, and treated as a sample in all respects, including contact with
the sampling devices and exposure to sampling site conditions, storage, preservation, and all
analytical procedures, which may include filtration. The purpose of the field blank is to
determine if the field or sample transporting procedures and environments have contaminated
the sample.
17.6 Field Duplicates (FD1 and FD2)—Two separate samples collected in separate sample bottles
at the same time and place under identical circumstances and treated exactly the same
throughout field and laboratory procedures, Analyses of FD1 and FD2 give a measure of the
precision associated with sample collection, preservation, and storage, as well as with
laboratory procedures.
17.7 Initial Precision and Recovery (IPR)—Four aliquots of the ongoing precision and recovery
standard analyzed to establish the ability to generate acceptable precision and accuracy. IPRs
are performed before a method is used for the first time and any time the method or
instrumentation is modified.
17.8 Intercomparison Study—An exercise in which samples are prepared and split by a reference
laboratory, then analyzed by one or more testing laboratories and the reference laboratory.
The intercomparison, with a reputable laboratory as the reference laboratory, serves as the best
test of the precision and accuracy of the analyses at natural environmental levels.
17.9 Laboratory Blank—An aliquot of reagent water that is treated exactly as a sample including
exposure to all glassware, equipment, solvents, reagents, internal standards, and surrogates that
are used with samples. The laboratory blank is used to determine if analytes or interferences
are present in the laboratory environment, the reagents, or the apparatus.
17.10 Laboratory Control Sample (LCS)—See Ongoing Precision and Recovery (OPR) Standard.
17.11 Laboratory Duplicates (LD1 and LD2)—Two aliquots of the same sample taken in the
laboratory from the same sample bottle and analyzed separately using the referenced method.
Analyses of LD1 and LD2 indicate precision associated with laboratory procedures, but not
with sample collection, preservation, transportation, or storage procedures.
17.12 Laboratory Fortified Blank—See Ongoing Precision and Recovery (OPR) Standard.
17.13 Laboratory Fortified Sample Matrix—See Matrix Spike (MS) and Matrix Spike Duplicate
(MSD).
17.14 Laboratory Reagent Blank—See Laboratory Blank.
17.15 Matrix Spike (MS) and Matrix Spike Duplicate (MSD)—Aliquots of an environmental
sample to which known quantities of the analytes are added in the laboratory. The MS and
26 Draft, April 1995
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Method 1632
MSD are analyzed exactly like a sample. Their purpose is to quantify the bias and precision
caused by the sample matrix. The background concentrations of the analytes in the sample
matrix must be determined in a separate aliquot and the measured values in the MS and MSD
corrected for background concentrations.
17.16 May—This action, activity, or procedural step is optional.
17.17 May Not—This action, activity, or procedural step is prohibited.
17.18 Method Blank—See Laboratory Blank.
17.19 Minimum Level (ML)—The lowest level at which the entire analytical system gives a
recognizable signal and acceptable calibration point.
17.20 Must—This action, activity, or procedural step is required.
17.21 Ongoing Precision and Recovery (OPR) Standard - A laboratory blank spiked with known
quantities of analytes. The OPR is analyzed exactly like a sample. Its purpose is to assure
that the results produced by the laboratory remain within the limits specified in the referenced
methods for precision and accuracy.
17.22 Preparation Blank—See Laboratory Blank.
17.23 Primary Dilution Standard—A solution containing the analytes that is purchased or prepared
from stock solutions and diluted as needed to prepare calibration solutions and other solutions.
17.24 Quality Control Sample (QCS)—A sample containing all or a subset of the analytes at
known concentrations. The QCS is obtained from a source external to the laboratory or is
prepared from a source of standards different from the source of calibration standards. It is
used to check laboratory performance with test materials prepared external to the normal
preparation process.
17.25 Reagent Water—Water demonstrated to be free from the metal(s) of interest and potentially
interfering substances at the MDL for that metal in the referenced method.
17.26 Should—This action, activity, or procedural step is suggested but not required.
17.27 Stock Solution—A solution containing an analyte that is prepared using a reference material
traceable to EPA, the National Institute of Science and Technology (NIST), or a source that
will attest to the purity and authenticity of the reference material.
Draft, April 1995 27
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Method 1632
TABLE 1: METHOD DETECTION LIMIT
(MDL) AND MINIMUM LEVEL (ML)
Method Detection Limit (MDL):
Minimum Level (ML):
0.002 ug/L
0.01000 ug/L
TABLE 2: METHOD QC CRITERIA
IPR Average Recovery (X)
IPR Standard Deviation(s)
Matrix Spike Recovery (P)1
OPR Recovery (P)1
MS/MSD RPD
Calibration Verification
59-143%
<42%
55-146%
55-146%
<20%
76-116%
OPR recovery required only it matrix spike recovery ooes not meet criteria
28
Draft, April 1995
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Method 1632
TABLE 3: TYPICAL SPECTROPHOTOMETER
SETTINGS
Parameter
EDL energy
EDL power
Wavelength
Slit width
Typical Setting
59
8 W
193.7 nm
0.7 nm
TABLE 4: TYPICAL FLOWS AND PRESSURES FOR GASES IN THE HYDRIDE
GENERATION SYSTEM
Gas
Flow Rate (mlVmin)
Pressure (lb/in2)
He
H2
Air
150
350
180
10
20
20
Draft, April 1995
29
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Method 1632
Figure 1. Arsenic Speciation Apparatus: (a) Quartz Cuvette Burner Tube, (b) Reaction Vessel, and
(c) Schematic Diagram
Light Path
Hi Input
From Trap
1C
SCHEMATIC DIAGRAM
Wiie-wound
Pyrex U-Tob«
Hall-packed with
15% OV-3oo
Crwomanxti "W"
Chart FiecorOer Output
30
Draft, April 1995
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