United States
Environmental Protection
Agency
Environmental Monitoring and Suppo
Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S4-86/024 June 1986
f/EPA Project Summary
Development of Standard
Methods for the Collection and
Analysis of Precipitation
Mark E. Peden
An analytical methods manual to be
used for acid deposition studies has
been developed to provide the scientific
community with a set of standardized
procedures for collecting and analyzing
wet precipitation samples. This manual
includes detailed methods documenta-
tion for the major inorganic constituents
of interest in wet deposition as well as
guidelines for collecting, preserving,
and processing samples. The impor-
tance of a comprehensive quality assur-
ance program is emphasized for all
aspects of a precipitation chemistry
measurement system. The analytical
methodologies include flame atomic
absorption spectrophotometry, ion se-
lective electrode, automated colori-
metry, ion chromatography, and titri-
metric procedures. These methods were
selected based on their sensitivities,
accuracy, and freedom from significant
chemical and physical interferences.
The instrumentation required for these
methods is available in most labora-
tories involved with water analyses so
that the procedures described will be
useful to as many researchers as pos-
sible. The adoption of standard test
procedures will lead to greater compar-
ability between laboratories reporting
precipitation chemistry data and will
improve the reliability of data interpre-
tation efforts.
This Project Summary was developed
by EPA's Environmental Monitoring and
Support Laboratory, Cincinnati. OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Heretofore, standard test procedures
for chemically analyzing wet deposition
were not available to the scientific com-
munity. As a result, different analytical
techniques have historically been used to
produce precipitation chemistry data.
These techniques often lacked the neces-
sary sensitivity and accuracy for measur-
ing the trace constituents characteristic
of wet deposition samples. Comparison of
these data for spatial and temporal trend
analyses is therefore difficult and may
lead to false conclusions.
An extensive literature review was
conducted at the onset of this project to
compile an inventory of recent and histor-
ical precipitation chemistry monitoring
programs. Information on study objec-
tives, sampling protocols, handling pro-
cedures, chemical constituents, analytical
methodologies, and quality assurance
practices was synthesized to develop an
overview of the current status of wet
deposition monitoring. This inventory
revealed that differences in sampling
periods were necessary depending on the
monitoring objectives. Weekly sampling
may be acceptable for assessing annual
deposition patterns while sequential
samples within a single event may be
important for obtaining information on
scavenging processes. The object, there-
fore, was to develop sampling 'guidelines'
that would meet as many study objectives
as possible. The sampler types and collec-
tion vessels commonly used were also
tabulated. A consensual standard is al-
ready in place since most of the monitor-
ing networks are already using similar
equipment and collection containers for
the analysis of the major inorganic spec-
ies in wet deposition. Efforts have focused
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on developing recommendations for se-
lecting, cleaning, and handling the col-
lection vessels.
The sample handling and processing
protocols used for wet deposition analy-
ses were also addressed. In this area the
primary focus was to minimize sample
contamination and ensure the integrity of
samples after collection. Guidelines for
recommended holding times for each of
the species detailed in the methods
documentation were developed based on
ion stability studies conducted by the
contract laboratory and by other research-
ers. Recommendations for storage con-
tainers and temperatures were also made.
Sample preservation by filtration was
included to stabilize constituents affected
by alkaline particulates or biological ac-
tivity or both. The guidelines are ion
specific since wet deposition samples are
characterized by both conservative and
nonconservative chemical species.
The first step in selecting candidate
procedures to include in this methods
manual was to tabulate methodologies
currently being used by major precipita-
tion chemistry laboratories. Usually, these
techniques were similar, although dif-
ferences were apparent in reporting units,
method detection limits, precision, and
bias. Quality assurance protocols were
extremely varied as were the procedures
for presenting quality control data. These
disparities emphasized the need for a set
of standardized procedures for both ana-
lytical determinations and quality assur-
ance data reporting.
The median concentration of dissolved
species in wet deposition samples from
the National Atmospheric Deposition
Program (NADP)/National Trends Net-
work (NTN) is about 90 microequivalents/
liter. Methods selection, therefore, must
take into consideration the fact that the
majority of analytes in wet deposition are
present at concentrations below one
milligram/liter. Analytical techniques
characterized by sufficiently low method
detection limits are crucial to the accurate
determination of these trace constituents.
Cumulative percentile concentration data
were tabulated from the 1984NADP/NTN
Program for use as a guide in both
methods selection and for recommending
appropriate calibration standards in the
methods documentation. This systematic
approach to method selection ensures
that the chemical data generated will be
of maximum utility to many users.
The documentation and formalization
of quality assurance protocols is an
integral component of the methods devel-
opment process. This includes quality
control at the sampling site, in the
laboratory and in data reporting. The
methods manual focuses on the specific
control procedures necessary to obtain
data with known bias and precision. The
use of blind audit solutions, internal
quality control check solutions, control
charts, analyte spikes, and performance
audits should atl be incorporated into the
standard operating procedures (SOP) for
laboratories engaged in wet deposition
measurements.
The methods in the full report are
comprehensive in coverage and include
detailed descriptions of the instrumenta-
tion, reagents, procedures, quality control
protocols, and data reporting require-
ments for each analyte. The documenta-
tion was prepared to meet the guidelines
set forth by the USEPA Environmental
Monitoring and Support Laboratory
(EMSL), Cincinnati, Ohio. These guide-
lines follow the format used by the
American Society for Testing and Mater-
ials, 1983 and are accepted as the
standard to be used in formalizing ana-
lytical test procedures.
Conclusions
Standard methods of documented bias
and precision are now available for the
major inorganic species in wet deposition.
The general methodologies described are
now being used by many precipitation
chemistry laboratories. By incorporating
these test methods as standard operating
procedures, laboratories involved with
wet deposition measurements will pro-
duce data of comparable quality, resulting
in easier interpretation of data by various
users and improving the reliability of wet
deposition measurements.
Methods contained in the manual
include:
1. Specific Conductance
2. pH.
3. Calcium, Magnesium, Potassium
and Sodium by Flame Atomic Ab-
sorption.
4. Chloride, Nitrate, Orthophosphate,
and Sulfate by Chemically Sup-
pressed Ion Chromatography.
5. Sodium, Ammonium, Potassium,
Magnesium and Calcium by Chem-
ically Suppressed Ion Chromatog-
raphy.
6. Acidity by Titrimetric Determina-
tion.
7. Chloride by Automated Determina-
tion using Thiocyanate.
8. Fluoride by Ion-Selective Electrode.
9. Ammonium by Ion-Selective Elec-
trode.
10. Ammonium by Automated Deter-
mination with Phenate.
11. Nitrate-Nitrite by Automated Deter-
mination with Cadmium Reduction.
12. Orthophosphate by Automated
Determination with Ascorbic Acid.
13. Sulfate by Automated Determina-
tion using Barium-Methylthymol
Blue.
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Mark E. Peden. Susan R. Bachman, Carla Jo Brennan, Brigita Demir. Kenni 0.
James, Brian W. Kaiser, Jacqueline M. Lockard, Jane E. Rothert, Jackie Sauer,
Loretta M. Skowron, and Michael J. Slater are with the Illinois State Water
Survey, Champaign. IL 61820.
John D. Pfaff is the EPA Project Officer (see below).
The complete report, entitled "Development of Standard Methods for the
Collection and Analysis of Precipitation," (Order No. PB 86-201 365/AS; Cost:
$22.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Cincinnati. OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S4-86/024
0000329
CHICG
STREET
60604
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