Tennessee
Valley
Authority
United States
Environmental Protection
Agency
Division of
Environmental Plannmq
Chattanooga. Tennessee 37401
Research and Development
Energy. Minerals and Industry
Washington DC <>04t>0
E EP 77 3
EPA-600'7-77-036
April 1977
TRACE ANALYSIS OF
ARSENIC BY COLORIMETRY,
ATOMIC ABSORPTION AND
POLAROGRAPHY
Interagency
Energy-Environment
Research and Development
Program Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
r
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
This document is-available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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E-EP-77-3
EPA-600/7-77-036
April 1977
TRACE ANALYSIS OF ARSENIC BY COLORIMETRY,
ATOMIC ABSORPTION, AND POLAROGRAPHY
by
Lyman H. Howe
Division of Environmental Planning
Tennessee Valley Authority
Chattanooga, Tennessee 37401
Interagency Agreement No. D5-E721
Project No. E-AP 78BDH
Program Element No. EHA 553
Project Officer
Gregory D'Alessio
Office of Energy, Minerals, and Industry
U.S. Environmental Protection Agency
Washington, D.C. 20460
This study was conducted
as part of the Federal
Interagency Energy/Environment
Research and Development Program.
Prepared for
OFFICE OF ENERGY, MINERALS, AND INDUSTRY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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DISCLAIMER
This report was prepared by the Tennessee Valley Authority
and has been reviewed by the Office of Energy, Minerals, and
Industry, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Tennessee
Valley Authority or the U.S. Environmental Protection Agency, nor
does mention of trade names or commercial products constitute
endorsement or recommendation for use.
ii
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ABSTRACT
A differential pulse polarographic method was developed for
determining total arsenic concentrations in water samples from
ash ponds at steam-electric generating plants. After digestion
of the sample and isolation of arsenic by solvent extraction, the
peak current for arsenic is measured and compared to a standard
curve. The effective range of concentrations for this method is
from 2 to 50 yg/1 of arsenic.
The precision and accuracy of this polarographic method for
determining concentrations of arsenic in water samples were
compared to two standard methods, atomic absorption and
colorimetry, for observations on replicate analyses of pure
standard solutions, split samples from ash ponds, standard
reference samples, and standard solutions spiked with potentially
interfering elements. The three methods compared favorably for
the split samples; however, results of the colorimetric method
for the replicate analyses were slightly negatively biased.
This report was submitted by the Tennessee Valley Authority,
Division of Environmental Planning, in partial fulfillment of
Energy Accomplishment Plan 78BDH under terms of Interagency
Energy Agreement D5-E721 with the Environmental Protection
Agency. Work was completed in September 1976.
111
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CONTENTS
Page
Abstract .........................
Figures ......................... vi
Tables .......................... vi
1 . Introduction .................. 1
2. Conclusions ................... 4
3. Recommendations ................. 5
4. Experimental .................. 6
Sample Preparation ............ ... 6
Colorimetric Determinations .......... 7
Atomic Absorption Determinations ........ 7
Polarographic Determinations .......... 8
5. Results and Discussion ............. 11
6. References ................... 15
Glossary ......................... 19
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FIGURES
No. Page
1 Typical Differential Pulse Polarograms for
Standard Arsenic Concentrations 23
2 Least-Squares Calibration Curve for Total
Arsenic by Differential Pulse Polarography 25
3 Two-Sample t Test Distribution and Values for
Polarographic and Colorimetric Determinations for
Total Arsenic in Solutions Spiked at 20 yg/1 .... 26
4 Two-Sample t Test Distribution and Values for
Polarographic and Colorimetric Determinations for
Total Arsenic in Solutions Spiked at 40 yg/1 .... 27
f
5 Paired-Sample t Tests Distribution and Values
for Total Arsenic in Split Samples from
Ash Ponds 28
TABLES
1 Effect of Reaction Time on Analysis
of 20 jUg/1 Arsenic Samples by
Atomic Absorption 31
2 Preliminary Test Results of Arsenic
Determinations for Split Samples
from Ash Ponds 31
3 Arsenic Determinations for Replicate
Spiked Surface Water Solutions 32
4 Precision and Accuracy of Arsenic Determinations
for Replicate Spiked Surface Water Solutions .... 33
5 Comparative Test Results of Arsenic
Determinations for Split Samples
from Ash Ponds 34
VI
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Concentrations of Elements other than Arsenic
in Split Samples from Ash Ponds 35
Comparative Test Results of Arsenic
Determinations for Standard Reference
and Synthetic Samples 36
Concentrations of Elements other than Arsenic
in Standard Reference Samples 37
vn
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SECTION 1
INTRODUCTION
Coal ash from steam-electric generating plants contains a
small amount of arsenic that probably exists in ash sluice water
and settling ponds as the anions arsenite (AsOa*3) and arsenate
(AsOi+~3) . Arsenic in these forms can be removed by
coprecipitation with ferric hydroxide1/ 2 and by precipitation
with thionalide;3 however, some arsenic may be leached into
surface or ground waters. The environmental effects of arsenic
have been discussed,*-' and the National Academy of Sciences
recommends that sources of public water supplies contain no more
than 0.1 mg/1 total arsenic.5
Methods for determining concentrations of arsenic in water
at trace levels (e.g., 0.1 mg/1) were reviewed in 1975.3'7
However, since that time, several new methods using atomic
absorption spectrometry have been devised.8"18 This study
evaluates those standard reference methods for determining
concentrations of arsenic in water that were not discussed or
referenced in the reviews in 1975.
For both standard reference methods now used for determining
concentrations of arsenic in water,19-21 the arsenic sample is
digested with nitric and sulfuric acid and arsine is generated by
adding potassium iodide, stannous chloride, and zinc dust to the
digestate. In both methods, arsenic is then isolated by
distillation of the gaseous arsine. These methods differ only in
the method of determining the concentration of arsenic in the
sample. The arsine is measured in one method2^ by colorimetry
with silver diethyldithiocarbamate and in the other method21 by
atomic absorption spectrometry with an argon-diluted, air-
entrained hydrogen flame.
Because of the similarities in sample preparation which make
possible a common bias in these reference methods,1*-21 a third
method,22 which includes a different sample preparation
procedure, was selected to confirm the results of analyses by the
first two methods. In this third method, the sample is digested
in a solution containing a molybdenum(VI) catalyst and nitric,
sulfuric, and perchloric acid. After digestion, the resulting
arsenate is reduced to arsenite by cuprous chloride in
concentrated hydrochloric acid. The resulting arsenic
trichloride is then isolated by solvent extraction with benzene.
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The arsenic trichloride is back extracted into water, and then
the sample is analyzed in 1 molar (M) hydrochloric acid by
differential pulse polarography.23 Section 4 of this report
describes a method for the analysis of total arsenic by
differential pulse polarography with a sample preparation
procedure including digestion of the arsenic sample with a
molybdenum(VI) catalyst.22 Although the literature23 describes a
differential pulse polarographic method for determining trace
concentrations of arsenic (III) in water, that method does not
provide for the analysis of total arsenic that is made possible
by digesting the sample with the molybdenum(VI) catalyst.22
Although arsenic samples are conventionally digested with
nitric and sulfuric acid in the absence of a molybdenum
catalyst,20 such sample preparation procedures must include
extreme precautions to prevent the loss of arsenic.22 This loss
of arsenic may be caused by volatilization of arsenic
trichloride;2* however, the volatilization of arsenic in the
presence of chloride was not observed by Gorsuch2s for arsenic
samples digested with nitric and sulfuric acid even in the
presence of excess organic material.
At sufficiently high concentrations, Ag, Co, Cu, Cr, Hg, Mo,
Ni, Pt, and Sb may affect the evolution of arsine.'26' 27 Most
natural waters, however, do not contain such high concentrations
of these elements.28 These' elements may also interfere with
measurements by standard colorimetry and atomic absorption,19~21
but the concentrations at which interference occurs are not
known. A recent study29 evaluated the interference with these
measurements when arsine is generated by adding the reductant
sodium borohydride rather than potassium iodide, stannous
chloride, and zinc dust as in the standard reference
methods. 19-21 This study showed that (1) the cations Ag(I),
Al(III). Ba(II), Cd(II), Cr(II), Co (II), Cu(II), Fe (III) , Pb(II),
Mn(II) , Mo (III), Ni(II), Sr(II), Sn(II), V(II), and Zn (II) , at
concentrations of 0.3-33.3 mg/1, do not interfere with the
determination of arsenic at a concentration of 1 yg/1; (2) the
oxidizing anions CrzO?"2, MnOit-i, VOs"1, 8208~2, and MoOit-2, at
concentrations between 1.6 and 33.3 mg/1, do interfere,
presumably by consuming the reductant sodium borohydride; and (3)
the oxidizing anions N03-*, P04~3, and Si03~2, at concentrations
less than 33.3 mg/1, do not interfere.
The elements that may interfere with the polarographic
determination of arsenic are Cd, Cu, Mo, Pb, Sb(III), Sb (V) ,
Se(IV), Sn(II), Sn(IV), Ti (III) , and V(III).3<> Interference from
these elements other than copper, which is used to reduce
arsenate, is unlikely because of the selectivity in isolating
arsenic trichloride by solvent extraction22 before analysis by
differential pulse polarography.23
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This study evaluates and describes a polarographic
method22' " and evaluates the standard colorimetric20 and atomic
absorption19' 2t methods in (1) determining concentrations of
arsenic in effluents from coal-fired steam-electric power plants,
(2) assaying standard reference solutions, and (3) assaying for
arsenic in the presence of Ag, Cd, Cl, Co, Cu, Cr, Fe, Hg, Mo,
Ni, Pb, Sb, Se, Sn, Tl, Ti, and V.
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SECTION 2
CONCLUSIONS
A. method based on differential pulse polarography was used
to determine arsenic at concentrations between 2 and 50 yg/1 in
water samples collected from ash ponds at coal-fired steam-
electric power plants. Samples for arsenic analysis were
digested in an acidic solution containing a molybdenum(VI)
catalyst, and then the arsenic(V) was reduced to arsenic(III) by
cuprous chloride. Arsenic was then isolated by solvent
extraction with benzene, back-extracted into water, and
quantified in 1 M hydrochloric acid by measuring the differential
pulse polarographic current at about -0.4 volts versus a
saturated calomel electrode (V vs. see).
Seven replicate analyses at three concentrations showed that
concentrations of arsenic can be determined precisely 'by either
polarography, colorimetry, or atomic absorption. A two-sample t
test on the means of the polarographic and colorimetric
determinations showed at the 0.05 level of significance that the
colorimetric method gives results negatively biased by 1 yg/1 at
concentrations of 20 yg/1 and by 5 yg/1 at concentrations of 40
yg/1. Paired-sample t tests showed no significant difference at
the 0.05 level among the methods for split samples.
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SECTION 3
RECOMMENDATIONS
Colorimetry, atomic absorption, and polarography are
recommended methods for determining concentrations of arsenic in
ash ponds that receive effluents from steam-electric generating
plants. The atomic absorption and colorimetric methods are more
efficient, but the polarographic method is better suited for
confirmatory analysis.
Further studies should be conducted to determine the
applicability of these methods to other process waste streams.
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SECTION 4
EXPERIMENTAL
SAMPLE PREPARATION
Field Samples
Field samples were collected in January 1976 from ash ponds
at all Tennessee Valley Authority (TVA) coal-fired steam-electric
generating plants. These samples were analyzed for the presence
of arsenic, and samples containing representative concentrations
of arsenic were selected for use in this study.
Standard Reference Samples
Standard reference samples for trace metals were obtained
from the U.S. Environmental Protection Agency (EPA) and from the
U.S. Geological Survey (USGS). EPA standard reference samples,
which consisted of conceritrated trace metals in very pure
acidified water, were diluted to the desired concentrations
according to accompanying instructions. Standard reference
samples for trace metals were furnished in diluted form by USGS
and certified according to the average concentration as
determined by several laboratories (interlaboratory
certification).
Spiked Samples
Three solutions containing arsenic at a concentration of 50
yg/1 were prepared in the laboratory. The first arsenic solution
was spiked with Co, Cu, Cr, Fe^ Hg, Mo, Ni, Pb, Sb, Se, Sn, Tl,
Ti, and V to achieve a concentration of 500 yg/1 for each
element. The second arsenic solution was spiked with chloride to
achieve a chloride concentration of 50,000 yg/1. The third
arsenic solution was spiked with silver to achieve a silver
concentration of 50 yg/1. All solutions were preserved by
spiking with nitric acid to achieve a concentration of 0.2% (v/v,
volume expressed as a fraction of total volume). All elements
used to spike the arsenic solutions, except mercury, thallium,
and chloride were drawn from 1000-mg/l certified atomic-
absorption standards (Fisher Scientific Company, Fairlawn, New
Jersey). The mercury and chloride concentration used to spike
the arsenic solution were prepared according to procedures given
in the literature.*9/20 The 1000-mg/l thallium concentration
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used to spike the arsenic solution was prepared gravimetrically
from thallium chloride powder (1.1735 gram in 1000 ml of reagent
water) with weights checked against reference weights certified
at the U.S. National Bureau of Standards.
COLORIMETRIC DETERMINATIONS
Arsenic samples for colorimetric determination were digested
with nitric and sulfuric acid to yield sulfur trioxide fumes.
The digestate was diluted with 25 ml of reagent water, and then
the following reagents were added: 5 ml of 12 M hydrochloric
acid, 2 ml of 15% (w/w, weight expressed as a fraction of total
weight) potassium iodide, and 0.40 ml of 40X (w/v, weight
expressed as a fraction of total volume) stannous chloride
dihydrate in 12 M hydrochloric acid. .After 15 minutes, allowed
for reduction of arsenic (V) to arsenic(III), arsine was generated
by adding 3 grams of granular zinc (8.5 mm - 12.7 mm pore size).
The arsine was reacted with silver diethyldithiocarbamate to
yield the red complex for colorimetric measurement.20 The lead
acetate scrubber20 Was not used because sulfide is destroyed by
strong oxidizing conditions in the digestion. Colorimetric
measurements were made with either a Beckman Model B
photoelectric spectrophotometer or a Beckman DB-GT grating
spectrophotometer.
ATOMIC ABSORPTION DETERMINATIONS
The samples were digested by the same procedure described
for colorimetric analysis.20 After dilution of the digestate
with 50 ml of reagent water, the following reagents were added:
8 ml of 12 M hydrochloric acid, 4 ml of 15% (w/w) potassium
iodide, and 1 ml of 40% (w/v) stannous chloride dihydrate in 12 M
hydrochloric acid. After 15 minutes, allowed for reduction of
arsenic(V) to arsenic (III), arsine was generated by injecting 2
ml of a suspension of 33% (w/w) powdered zinc in reagent water.
These reagent concentrations31 were different from those employed
by Caldwell et al.z*
The arsine gas was formed in a 200-ml Berzelius beaker. The
zinc slurry was injected through a rubber serum stopper that had
been inserted into a glass sleeve fabricated from a test tube and
forced through a hole in the rubber stopper for the beaker. The
arsine gas was forced from the beaker by sparging with nitrogen
through a sintered glass frit into a nitrogen-diluted, air-
entrained, hydrogen flame. This apparatus31 differs from the one
described in the literature.2* Absorbance measurements were made
with a Varian Techtron AA-5 atomic absorption spectrometer.
A study was conducted to determine if reaction time would
affect the results of analysis of arsenic samples by atomic
absorption. After the reagents were added and 15 minutes had
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been allowed for reduction of arsenic (V) to arsenic (III) , 10
observations were made at 10-minute intervals for a series of
20-yg/l arsenic standards (Table 1). Reappearance of arsenic(V)
as a result of reoxidation of arsenic(III) by iodine formed by
air oxidation of iodide in the acidic solution was not evidenced
by decreasing absorbance measurements.
POLAROGRAPHIC DETERMINATIONS
All measurements were made with the Princeton Applied
Research (PAR) Model 174 Polarographic Analyzer with mechanical
drop timer and Houston Omnigraphic X-Y Recorder Model 2200-3-3.
The dropping mercury electrode was a 2-to-5-second capillary from
Sargent-Welch Company with Part No. S-29419. The spectroscopic-
grade carbon counter electrode, saturated calomel electrode,
outgassing tube, cell holder, cell, and other electrochemical
accessories32 were obtained from PAR.
Nitrogen gas used to deaerate solutions for polarographic
analysis was purged of oxygen. Zero-grade nitrogen gas was
passed through a furnace containing a special catalytic converter
(Model 02-2315 Gas Purifier purchased from Supelco, Beliefonte,
Pennsylvania) and heated to 600 degrees Celsius (centrigrade,
°C). The gaseous effluent from the furnace was successively
passed through a Hydro-Purge unit and a Dow gas purifier
(available from Applied Science Laboratories, State College,
Pennsylvania) . The gas was then passed through sintered glass
frits in three scrubbing towers: two of the scrubbing towers
contained 100 ml of 0.1 M chromous chloride in 2.4 M hydrochloric
acid with amalgamated zinc, and the other contained 100 ml of
reagent water. The amalgamated zinc was from 0.8-3.2 mm in pore
size for a Jones reductor (Fisher Scientific Company, Fairlawn,
New Jersey). Details for preparing the chromous chloride
scrubbers are given by Meites.33
Reagent-grade chemicals were used to prepare all solutions
with the exception of the hydrochloric acid that was added to the
water extracts for polarographic analysis. This acid was the
high-purity "Ultrex" grade from Baker Chemical Company,
Phillipsburg, New Jersey. The stock, intermediate, and standard
arsenic solutions were prepared from reagent grade arsenic
trioxide.zo The cuprous chloride reagent, 2 N (normal) CU2C12
in concentrated hydrochloric acid was prepared by adding 150 ml
of concentrated hydrochloric acid, 30 g of copper powder, and 30
g of cuprous chloride powder to a pint bottle containing a
teflon-coated stirring bar. The bottle was immediately stoppered
with a Polyseal cap and stirred for 2 hours. After the
insolubles had settled, the clear supernatant was siphoned into
15-ml centrifuge tubes containing 0.5 ml of copper powder, and
the tubes were immediately sealed with Teflon-lined caps. Just
before use, the tubes were centrifuged for 1 minute to produce a
8
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colorless or amber solution. The digestion reagent was prepared
by dissolving 2.0 g of sodium molybdate dihydrate (Na2Mo04-2H?0)
in HO ml of water, adding 50 ml concentrated sulfuric acid,
allowing the solution to cool, and then adding 10 ml of 70*
perchloric acid.
The samples were digested" by adding 1.0 ml of concentrated
nitric acid, 2.0-ml of digestion reagent, and four glass beads to
100-ml of the sample in a 500-ml Erlenmeyer flask. The solution
was digested at full heat until the solution boiled vigorously,
red fumes appeared and dissipated, and white fumes of sulfur
trioxide were evolved for 1 or 2 minutes.
CAUTION
Do not evaporate S03 fumes longer than
specified because the perchloric acid may
concentrate to explosive levels. With
samples containing excessive organic matter,
the amount of nitric acid may be increased or
the amount of sample reduced to assure
complete digestion and prevent possible
explosion.
The method described by Simon et al.22 was used to reduce
arsenate to arsenite with cuprous chloride and to isolate arsenic
trichloride by solvent extraction with the following exceptions:
the combined benzene extracts were washed by back-extraction with
two 3-ml portions and one 4-ml portion of concentrated
hydrochloric acid instead of three 4-ml portions, and the arsenic
trichloride was isolated by back-extraction into exactly 15.0 ml
of reagent water instead of by successive extractions with 9.0 pH
buffers.
The isolated arsenic was measured by differential pulse
polarography." A 4.0-ml aliquot of the aqueous extract was
dispensed into a suitable polarographic cell, and 0.4 ml of high-
purity hydrochloric acid was added. After the solution was
deaerated for 7 minutes with nitrogen gas treated to remove
oxygen, a differential pulse polarographic scan was made between
-0.240 and -0.590 V vs. see under suitable conditions. The peak
for arsenic appeared at about -0.4 V. Typical conditions were
(1) the mercury head above the capillary (Sargent-Welch
Scientific Co., Part No. S-29419) was adjusted to about 45 cm to
produce a natural drop time of about 3 seconds in 1 M
hydrochloric acid and (2) the PAR Model 174 polarographic
analyzer was adjusted as follows: DROP TIME - 2 seconds, SCAN
RATE - 2 mV/sec, DISPLAY DIRECTION - positive, SCAN DIRECTION -
negative, INITIAL POTENTIAL - (-0.240 V), RANGE - (0.75 V),
SENSITIVITY - 1 yA full-scale deflection for 0-2 yg of arsenic
and 2 yA for 2-5 yg of arsenic, MODULATION AMPLITUDE - 100 mV,
OPERATION MODE - differential pulse, OUTPUT OFFSET - negative
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settings between 0 and -45%, RECORDER - (Houston Omnigraphic X-Y
Model 2200-3-3), Y-AXIS - equal to 0.039 V/mm (1 V/in.) and
X-AXIS - equal to 3.9U mV/mm (100 mV/in.). To calculate unknown
arsenic concentrations in samples, a comparison method was used.
The amplitude of electric current was extrapolated from values
occurring just before and just after the electrical current peak
for arsenic. The extrapolations were compared to a standard
curve prepared from analyses of arsenic standards of 0 yg/1,
1.0 ug/1, 2.0 vg/1, 3.0 yg/1, and 4.0 yg/1, and 5.0 yg/1.
Standards were analyzed by the same methods used to analyze
unknown concentrations of arsenic in samples.
10
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SECTION 5
RESULTS AND DISCUSSION
A sensitive differential pulse polarographic method for
determining concentrations of total arsenic in water was
developed. This method involves digesting a 100-ml sample with
nitric, sulfuric, and perchloric acid containing a molybdenum(VI)
catalyst; reduction of arsenic(V) to arsenic (III) with cuprous
chloride; solvent extraction with benzene to isolate arsenic(III)
chloride; back-extraction of the arsenic (III) chloride into
water; and measurement of arsenic (III) by differential pulse
polarography in 1 M hydrochloric acid. This new method combines
the sample preparation for total arsenic described by Simon et
al.22 with the sensitive differential pulse polarographic method
described by Meyers and Oysteryoung.23
Figure 1 shows typical differential pulse polarograms for
standard arsenic concentrations of 0, 10, 20, 30, 40, and
50 yg/1. These concentrations produced peak current readings of
55, 189, 392, 627, 702, and 932 nA, respectively, as determined
by extrapolating current values just before and after the peak.
A typical least-squares calibration curve prepared from these
peak currents is shown in Figure 2, where the least-squares
equation is Y = 17.6X «• 42.9, Y is the current in nA, and X is
the arsenic concentration in yg/1.
The sensitivity of this differential pulse polarographic
method for determining concentrations of arsenic is limited by
the current produced by the sample blank. If the lowest
quantifiable concentration produces a peak current twice that of
the least squares sample blank given by the intercept in Figure 2
(85.8 nA), the least-squares equation yields a lowest
quantifiable concentration of 2.4 ug/1 arsenic. This method
using differential pulse polarographic determination is about 20
times more sensitive than coulometric determination with the same
sample preparation procedure.22 This pulse polarographic method
for determining concentrations of total arsenic is also about
8 times more sensitive than the 20-yg/l sensitivity reported for
differential pulse polarography with raw, undigested samples in 1
M hydrochloric acid and interfering elements present.23 Meyers
and Oysteryoung23 have achieved sensitivities of 0.2 yg/1 with
differential pulse polarography in determining concentrations of
arsenic in undigested samples with no interfering elements.
11
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The selectivity of the polarographic procedure for total
arsenic was demonstrated by quantitatively recovering 20 yg/1 (2
yg in a 100 ml sample) of arsenic in the presence of 200 yg/1 (20
yg in a 100 ml sample) of. selenium(IV), cadmium(II) , and
lead(II). The latter elements are polarographically active in 1
M hydrochloric acid at voltages sufficiently close to arsenic to
interfere.3°
Copper, which is added in the form of cuprous chloride to
reduce the arsenic(V), causes interference if it is not
sufficiently removed from the aqueous extract used for
polarographic analysis. If present, copper will cause a cathodic
charging background that is difficult to offset when scanning for
the arsenic(III) peak. Atomic absorption analysis has revealed
that most of the extracts for polarographic analysis contained
about 0.05 mg/1 copper. As much as 0.40 mg/1 can be tolerated
without affecting recovery of the arsenic, but when the
concentration of copper is 0.80 mg/1, only 7056 of the arsenic is
recovered at 10 yg/1 arsenic.
Other digestions were tried unsuccessfully with this
polarographic method. Digestion of an arsenic sample with nitric
and sulfuric acid20 was compared to digestion with a
molybdenum(VI) catalyst for a standard 50-yg/l arsenic sample.
The former method of digestion recovered only 28% of that
recovered by digestion with the molybdenum(VI) catalyst. Also,
digestion of 100 ml of a standard 50-yg/l arsenic sample with
3 ml of 25% (w/v) potassium persulfate in concentrated sulfuric
acid recovered only 14X of that recovered by digestion with a
molybdenum(VI) catalyst.
Preliminary test results for arseni'c in split samples from
ash ponds as analyzed by the colorimetric method2o and the
polarographic method described in Section H compare favorably
(Table 2). The precision and accuracy of the polarographic,22>23
colorimetric,2° and atomic absorption methods19'21 for
determining trace levels of arsenic in seven replicate spiked
solutions were determined by comparing test results (Table 3) to
a calibration curve prepared by analyzing a series of standard
solutions. Table 4 contains the standard deviations, relative
standard deviations, means, and percentage accuracies (of the
means) for each concentration and method.34 In addition to these
single laboratory tests, the precision of the polarographic
method was determined for concentrations of arsenic of 7, 16, 30,
and 150 yg/1 by a round-robin test with three laboratories with
single operators on three days.", 36 The precision of this
method for arsenic in reagent water is given by
St = 0.108X + 2.37 and Sp = 0.053X * 1.87, where St is overall
precision in yg/1, So is single operator precision in yg/1, and
X is concentration of arsenic in yg/1. The percentage accuracies
of the means are -8.6, -0.6, +8.0, and -9.3, respectively.3* A
12
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version of this polarographic method has been approved by
committee ballot as a proposed standard in the American Society
for Testing and Materials.36
A two-sample t test" was performed on some of the data in
Table 3 to test the significance of the difference between the
means, A, assuming that the variances are equal. Figure 3 shows
the results of this test for the polarographic and colorimetrie
methods at 20 yg/1. The t distribution and two-sample t test
values shown in Figure 3 were calculated by means of readily
available programs.38 For a A of 0, the t value is 3.29. This
value is greater than the 2.18 for t0.025 for 12 degrees of
freedom; therefore, the methods are different at the 0.05 level
significance. For a A of 1, the t value is 1.37 and the methods
agree at the 0.05 level of significance when biased by this
amount. Figure 4 shows the t distribution and two-sample t test
values for the polarographic and colorimetric methods at 40 yg/1.
These data illustrate that the bias of the methods increased to 5
yg/1. The lower results by colorimetry probably were caused by
the absence of careful fuming in the digestion.22 For the
polarographic and atomic absorption methods at 10 yg/1, the t
value for a A of 0 was 0.86, and the methods did not differ
significantly at the 0.05 level.
In addition to replicate analyses, the polarographic,
colorimetric, and atomic absorption methods for arsenic described
in Section 4 were compared for split samples from ash ponds in
the Tennessee and Ohio River valleys (Table 5). Background
concentration for Ag, Cdr Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb,
Se, Sn, Tir V, Zn, Cl, and suspended solids (SS) are given in
Table 6. The results of analyses reported in Table 6 were
performed by standard techniques.19 The metals were analyzed by
digesting the suspended material concentrated onto a 0.45 ym
membrane filter and adding this to the value for the dissolved
element. The detection limit for the suspended material is
lowered by the volume ratio of raw sample to digested material.
Because of this, some of the measured values reported for the
suspended material are below the detection limit for the
dissolved elements.
A paired-sample t test37 was performed on the split-sample
data in Table 5 to determine whether the atomic absorption,
colorimetric, and polarographic methods compare favorably at the
0.05 level of significance. For the t test computation,
concentrations indicated as less than some value (<) were taken
to be zero, and duplicate values were averaged. Figure 5 shows
the t distribution for 13 degrees of freedom and t values38 for
the three possible comparisons: (1) polarography vs. atomic
absorption, (2) atomic absorption vs. colorimetry, and (3)
polarography vs. colorimetry. The calculated t values are much
less than 2.16, the t value for 0.025 and 13 degrees of
13
-------
freedom;37 therefore, there is no significant difference at the
0.05 level among the three methods.
Comparative tests by colorimetry, atomic absorption, and
polarography were made for arsenic in standard reference and
synthetic water samples. Test results are given in Table 7.
Table 8 includes data for elements other than arsenic in the
standard reference samples. Data for arsenic and percentage
accuracies3* by the three methods compare reasonably well with
the certified analyses. The same is true for results for the
three synthetic samples with potentially interfering
elements.2*/26-30
-------
SECTION 6
REFERENCES
1. Skripach, T., V. Kagan, M. Romanov, L. Kamen, and A. Semina.
Removal of Fluorine and Arsenic from the Wastewater of the
Rare-Earth Industry. The State Research Institute for Rare
Metals, Moscow, U.S.S.R. (Presented at Fifth International
Water Pollution Research Conference. July-August 1970.)
pp. Ill - 34/1-7.
2. Elenkova, N. G. and R. A. Tsoneva. Polarographic
Determination of Arsenic in Industrial and Drainage Waters.
Zh. Analit. Khim. 29 (2); 289-293, 1974. In: Anal. Ab.
29(2); 176, August 1975.
3. Talmi, Y. and C. Feldman. The Determination of Traces of
Arsenic: A Review. In: Arsenical Pesticides. ACS
Symposium Series, Number 7. American Chemical Society,
Washington, D.C. Reprint No. 2. 1975. pp. 13-34.
4. Great Lakes Laboratory. Chromium, Cadmium, Arsenic,
Selenium, Mercury and Aquatic Life: A Brief Literature
Review. Great Lakes Laboratory, State University College at
Buffalo. Special Report No. 9. November 1971. pp. 10-12.
5. Committee on Water Quality Criteria. Water Quality Criteria
1972. Environmental Studies Board, National Academy of
Sciences, Washington, D.C., 1972. p. 56.
6. Editors. Arsenic Doesn't Bioaccumulate. Chem. and Eng.
News. 49, September 23, 1974.
7. Talmi, Y. and D. T. Bostick. The Determination of Arsenic
and Arsenicals. J. Chrom. Sci. 13: 231-237, May 1975.
8. Florino, J. A., J. W. Jones and S. G. Capar. Sequential
Determination of Arsenic, Selenium, Antimony, and Tellurium
in Foods Via Rapid Hydride Evolution and Atomic Absorption
Spectrometry. Anal. Chem. 48; 120-125, January 1976.
9. Pierce, F. D., T. C. Lamoreaux, H. R. Brown and R. S.
Fraser. An Automated Technique for the Sub-microgram
Determination of Selenium and Arsenic in Surface Waters by
15
-------
Atomic Absorption Spectroscopy. Appl. Spectry. 30(1); 38-
40, 1976.
10. Wauchope, R. D. Atomic Absorption Determination of Trace
Quantities of Arsenic: Application of a Rapid Arsine
Generation Technique to Soil, Water and Plant Samples.
Atomic Absorption Newsletter 15(3); 64-67, May-June 1976.
11. Vijan, P. N., A. C. Rayner and G. R. Wood. A Semi-Automated
Method for the Determination of Arsenic in Soil and
Vegetation by Gas-Phase Sampling and Atomic Absorption
Spectrometry. Anal. Chim. Acta 82; 329-336, 1976.
12. Mesman, B. B. and T. C. Thomas. A study of Two Atomic
Absorption Methods for the Determination of Sub-Microgram
Amounts of Arsenic and Selenium. Anal. Letters 8(7); 449-
459, 1973.
13. Woidich, H. and W. Pfannhauser. Bestimmung von Arsen in
biologischen Material mittels Atomabsorptions
spektralphotometrie. (Determination of Arsenic in
Biological Material Using Flame Atomic Absorption
Spectroscopy.) Z. Anal. Chem. (New York) 276; 61-66, 1975.
C
14. Kunselman, G. C. and E. A. Huff. The Determination of
Arsenic, Antimony, Selenium, and Tellurium in Environmental
Samples by Flameless Atomic Absorption. Atomic Absorption
Newsletter. 15(2); 29-32, March-April 1976.
15. Owens, J. W. and E. S. Gladney. The Determination of
Arsenic in Natural Waters by Flameless Atomic Absorption.
Atomic Absorption Newsletter. 15(2); 47-48, March-April
1976.
16. Freeman, H. and J. F- Uthe and B. Flemming. A Rapid and
Precise Method for the Determination of Inorganic and
Organic Arsenic With and Without Wet Ashing Using a Graphite
Furnace. Atomic Absorption Newsletter. 15 (2): 49-50,
March-April 1976.
17. Ediger, R. D. Atomic Absorption Analysis with the Graphite
Furnace Using Matrix Modification. Atomic Absorption
Newsletter. 14 (5); 127-130, September-October 1975.
18. Rozenblum, V. Successive Determination of Picogram Amounts
of Phosphorus and Arsenic in Pure Water by Indirect
Flameless Atomic Absorption- (Mo) Spectroscopy. Anal.
Letters 8(8); 549-557, 1975.
19. U.S. Environmental Protection Agency. Methods for Chemical
Analysis of Water and Wastes. U.S. Environmental Protection
16
-------
Agency, Cincinnati, Ohio. Publication Number
EPA-625-/6-74-003. 1974. pp. 9-10, 29, 82, 92-155, 268.
20. American Public Health Assoc. Standard Methods for the
Examination of Water and Waste Water. 13th Edition. New
York, American Public Health Association, Publishers, 1971.
pp. 62-67, 96.
21. Caldwell, J. S., R. J. Raymond and E. F. McFarren.
Evaluation of a Low-Cost Arsenic and Selenium Determination
at Microgram-per-Liter Levels. J. Am. Water Works Assoc.
731-735, November 1973.
22. Simon, R. K., G. D. Christian and W. C. Purdy- Coulometric
Determination of Arsenic in Urine. Am. J. Clin. Pathol.
49 (2); 207-215, 1968.
23. Myers, D. J. and J. Osteryoung. Determination of Arsenic
(III) at the Parts-per-Billion Level by Differential Pulse
Polarography. Anal. Chem. 45(2); 267-271, February 1973.
24. Farkas, E. J., R. C. Griesbach, D. Schachter, and M. Hutton.
Concentration of Arsenic from Water Samples by Distillation.
Environ. Sci. Technol. 13 (6); 1116-1117, December 1972.
25 Gorsuch, T. Radiochemical Investigations on the Recovery
for Analysis of Trace Elements in Organic and Biological
Materials. Analyst 84, 135-173, March 1959.
26. Stratton, G. and H. C. Whitehead. Colorimetric
Determination of Arsenic in Water with Silver
Diethyldithiocarbamate. J. Am. Water Works Assoc. 54, 861-
864, 1962.
27. Liederman, D., J. E. Bowen and O. I. Milner. Determination
of Arsenic in Petroleum Stocks and Catalysts by Evolution as
Arsine. Anal. Chem. 31: 2052-2055, December 1959.
28. Ballinger, D. C., R. J. Lishka and M. E. Gales. Application
of Silver Diethyldithiocarbamate Method to Determination of
Arsenic. J. Am. Water Works Assoc. 54; 1424-1428, 1962.
29. Pierce, F. D. and H. R. Brown. Inorganic Interference Study
of Automated Arsenic and Selenium Determination With Atomic
Absorption Spectrometry. Anal. Chem. 48; 693-695, April
1976.
30. Meites, L. (Ed.). Handbook of Analytical Chemistry. First
Edition. New York, McGraw-Hill Publishers, 1963. pp. 5-59-
5-62.
17
-------
31. Fishman, M. J. Personal Communication on Prescriptive
Methods for Arsenic. USGS Analytical Methods Research,
Denver Federal Center, Denver, Colorado. July 15, 1975.
32. Princeton Applied Research Corp. Electroanalytical
Instrumentation. Princeton Applied Research Corp., P.O. Box
2565, Princeton, N.J. Publication No. T359-10M-3/76-CP.
pp. 7-11. 1976.
33. Meites, L. Polarographic Techniques. Second Edition. New
York, Interscience Publishers, January 1967. pp. 87-90,
411.
34. Editors, Anal. Chem. 47: 2527, 1975.
35. Standard Recommended Practice for Determination of Precision
of Methods of Committee D-19 on Water. IN: 1976 Annual
Book of ASTM Standards. Part 31. Philadelphia, American
Society for Testing and Materials, Publishers, 1976. p. 11-
20.
36. Howe, L. H. Personal Communication on Method for Arsenic
Under Jurisdiction of ASTM Task Group on Voltammetry. TVA
Laboratory Branch, Chattanooga, Tennessee. December 1976.
37. Miller, I. and J. E. Freund. Probability and Statistics for
Engineers. Prentice-Hall, Inc., Publishers, 1965. pp. 167-
170, 399.
38. Texas Instruments. Program Manual ST1 Statistics Library.
Dallas, Texas Instruments, Inc., Publishers, 1975. pp. 26-
33, 76-79.
18
-------
GLOSSARY
A - Ampere.
c^ - Centi-, X10-2 (as a prefix, e.g., cm).
°c - Degrees Celsius (centigrade).
^ - Difference between the means.
EDTA - Ethylenediaminetetraacetic acid.
cj - Grams.
hr - Hour.
in - Inch.
1 - Liter.
m - Meter.
jj£ - Micro-, X10-6 (as a prefix, e.g., yl) .
m^ - Milli-, X10-3 (as a prefix, e.g., mm).
min - Minute.
M - Molar, mole per liter.
n- - Nano-, X10~9 (as a prefix, e.g., ng).
N - Normal, equivalent per liter.
% - Percent.
Polaroqraphy - Voltammetry at the dropping mercury electrode.
PAR - Princeton Applied Research
sec - Second.
t - Student t statistic.
TVA - Tennessee Valley Authority.
19
-------
V - Volt.
v/v - Volume expressed as a fraction of total volume.
V vs. see - Volts versus a calomel electrode filled with
saturated potassium chloride.
w/v - Weight expressed as a fraction of total volume.
w/w - Weight expressed as a fraction of total weight.
20
-------
FIGURES
21
-------
1
I
30ug/l ARSENIC
20ug/l ARSENIC
IOug/1 ARSENIC
'
Oug/l ARSENIC
I
-0.240
-0.340 , -0.440
VOLTS vs. S.C.E.
-0.540
-0.640
Figure 1. Typical differential pulse polarograms
for standard arsenic concentrations
23
-------
200nA
50ug/l ARSENIC
40ug/l ARSENIC
-0.240
-0.340 -0.440
VOLTS vs. S.C.E.
-0.540
Figure 1. Typical differential pulse polarograms
for standard arsenic concentrations
(Continued)
0.640
24
-------
LU
cn
ce
1000
900-
800-
700-
600 -
500 -
400 -
300 -
200 -
10
20 30 40
ARSENIC, Ug/l
50 60
Figure 2.
Least-squares calibration curve for total
arsenic by differential pulse polarography
25
-------
CTl
A IS MEAN (ug/l) BY POLAROGRAPHY
MINUS MEAN BY COLORIMETRY
r-t = 2.l8ATt0025>|2
r- = 0,t = 3.29
-3-2-10 I 23
t VALUES FOR 12 DEGREES OF FREEDOM
Figure 3. Two-sample t test distribution and values for
polarographic and colorimetric determinations for
total arsenic in solutions spiked at 20 yg/1
-------
i r
A=5,t = l.60
1 I \ T
A IS MEAN («g/l) BY POLAR06RAPHY
MINUS MEAN BY COLORIMETRY
= 2-l8AT'0.025,12
M
a- V, 1 -3. OO
1 1 1 1 1
'-6 -5-4-3-2-10123456
t VALUES FOR 12 DEGREES OF FREEDOM
Figure 4. Two-sample t test distribution and values for
polarographic and colorimetric determinations for
total arsenic in solutions spiked at 40 yg/1
-------
to
00
t VALUES FOR 13 DEGREES OF FREEDOM
Figure 5. Paired-sample t tests distribution and values
for total arsenic in split samples from ash ponds
-------
TABLES
29
-------
Table 1. EFFECT OF REACTION TIME ON THE ANALYSES
OF 20 yg/1 ARSENIC SAMPLES BY ATOMIC ABSORPTION
Reaction Time
Absorbance (Minutes)
0.494 10
0.992 20
0.774 30
0.792 40
0.613 50
0.691 60
0.772 70
0.718 80
0.761 90
0.716 100
Time after allowing 15 minutes for reduction of Arsenic(V)
to Arsenic (III) .
TABLE 2. PRELIMINARY TEST RESULTS OF ARSENIC
DETERMINATIONS FOR SPLIT SAMPLES FROM ASH PONDS
Polarography Colorimetry
Ash Pond (yg/1) (ug/1)
1 323 296
2 38 49
3 99 88
4 88 84
5 68 66
31
-------
TABLE 3. ARSENIC DETERMINATIONS FOR REPLICATE SPIKED
SURFACE WATER SOLUTIONS
Arsenic Concentration Arsenic Determination
(yg/i)
0
10
20
40
0
10
20
40
0
2.0
5.0
10.0
Polarography
<2
10
20
39
<2
7
20
42
<2
11
18
42
<2
9
19
41
<2
8
21
42
<2
10
20
37
<2
9
20
41
Colorimetry
<5
10
18
27
1.5
4.4
9.0
<5
10
17
34
1.6
3.7
9.2
<5
10
18
33
1.6
6.2
11.0
<5
10
18
35
Atomic
1.6
4.4
8.8
<5
10
20
34
<5
10
17
35
<5
10
18
36
Absorption
2.0
4.3
9.9
1.9
4.5
9.9
1.0
4.4
9.7
32
-------
TABLE 4,
Arsenic
Added
(ug/i)
10
20
40
PRECISION AND ACCURACY OF ARSENIC DETERMINATIONS FOR
REPLICATE SPIKED SURFACE WATER SOLUTIONS
Standard
Deviation
1.4
1.0
1.9
Relative
Standard
Deviation Mean
(*) (yg/D
Polarography
14.8 9.1
4.8 19.7
4.8 40.6
Percentage
Accuracy
<*)
-9.0
-1.5
+ 1.5
10
20
40
0.0
1.0
3.0
Colorimetry
0.0
5.6
8.9
10.0
18.0
33.4
0.0
10.0
16.4
2.0
5.0
10.0
Atomic Absorption
0.3 20.0 1.6
0.8 16.9 4.6
0.7 7.7 9.6
-20.0
-8.8
-3.6
33
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TABLE 5. COMPARATIVE TEST RESULTS OF ARSENIC DETERMINATIONS
FOR SPLIT SAMPLES FROM ASH PONDS
Location
Allen
Bull Run
Colbert
Cumberland
Gallatin
John Sevier
John Sevier
Johnsonville
Kingston
Paradise
Paradise
Shawnee
watts Bar
Widows Creek
Atomic
Polarographic Colorimetric Absorption
(yg/1)
0
40
<5
<5
44
237, 280
157
145
143
4
2
179
215
2
aSamples of water from the fly ash pond were collected at
these locations.
Samples of water from the bottom ash pond were collected at
these locations.
(yg/D
10
45
<1
<1
50
190
140
160
140
10
5
220
190
<5
(yg/D
4.2
35
2
3
47
290
140
120
140
9
6.8
180, 170
210
2.6
34
-------
TABLE 6. CONCENTRATIONS OF ELEMENTS OTHER THAN ARSENIC
IN SPLIT SAMPLES FROM ASH PONDS
Location
Allen
Bull Run
Colbert
Cumberland
Gallatin
John Sevier
Fly Ash
OJ
ui John Sevier
Bottom Ash
Johnsonville
Kingston
Paradise
Fly Ash
Paradise
Bottom Ash
Shawnee
watts Bar
Widows creek
Ag
00
<10
<10
<10
<10
<10
<10
<10
<10
<10
<10
<10
<10
<10
Cd
12
0
o
<1
o
7
2
32
0
0
3
3
O
Co Cr Cu Fe
8 6 31 1400
3 <5 2 330
2 <5 9 660
1 <5 <10 20
3 35 <10 290
Hg Mn Mo Ni
<0.2 138 100 <50
<0.2 60 160 <50
<0.2 36 <100 <50
<0.2 2 480 <50
<0.2 17 380 <50
Pb Sb Se
<10 <100 <2
<10 <100 10
<10 <100 <2
<10 <100 7
11 <100 8
Sn Ti V Zn Cl
<1000 0000 <500 299 13
<1000 OOOO <500 10 4
<1000 OOOO <500 <10 6
<1000 OOOO <500 <10 5
<1000 OOOO <500 <10 4
9 20 120 970 <0.2 83 200 <50 OO <100 4 OOOO OOOO <500 72 11
<1 <5 6 1100
<1 7 4 920
7 <5 50 2650
<0.2 38 180 <50
<0.2 6 170 <50
<0.2 232 <100 <50
<10 <100 3
<10 <100 3
<100 <2
<1000 OOOO <500 41 11
<1000 OOOO <500 <10 b
<1000 OOOO <500 50 3
18 116 283 4790 <0.2 493 <100 <50 34 <100 <2 OOOO OOOO <500 794
3 5 33 4000
4 6 00 1290
10 10 42 5100
1 12 <10 20
<0.2 108 <100 <50
<0.2 4 200 <50
<0.2 371 <100 <50
<0.2 6 180 <50
<100 <2
<10 <100 2
00 000 <2
<10 <100 2
SS
15
13
20
7
32
34
29
34
23
24
OOOO OOOO <500 61 5 40
OOOO OOOO <500 4 8 37
OOOO OOOO <500 200 8 20
OOOO OOOO <500 <10 6 4
Concentrations are in vg/1, except Cl and SS (suspended solids) are in mg/1.
-------
TABLE 7. COMPARATIVE TEST RESULTS OF ARSENIC DETERMINATIONS
FOR STANDARD REFERENCE AND SYNTHETIC SAMPLES
Certified
Arsenic Polarography Colorimetry Atomic Absorption
Concentration Concentration Accuracy concentration Accuracy Concentration Accuracy
Description
EPA Trace Metals Reference
Sample 1171 (No. 1)
EPA Trace Metals Reference
Sample 1171 (No. 2)
u> EPA Trace Metals Reference
a\ Sample 1171 (No. 3)
USGS standard Reference
Sample No. 44
USGS standard Reference
Sample No. 49
500 Ug/1 each: Cd, Co,
Cu, Cr, Fe, Hg, Mo, Ni,
Pb, Sb, Se, Sn, Tl, Ti, V
50 ug/1 Ag
50 mg/1 Cl
ug/D
22
73
278
4.9
18.1
50
50
50
(ug/D (») (ug/D
20 -9.1 22, 20
70 -4.1 62, 70
282 1.4 296, 288
<5
- 20
31, 52 -16.0 40, 48
49, 47 -4.0 52, 51
46, 43 -12.0 52, 56
(»)
-4.5
-9.6
5.0
-
10.5
-12.0
4.0
8.0
(ug/D
24
74
305
4.4
19
51, 55
55, 54
55, 61
(%)
9.1
1.4
9.7
-10.2
5.0
6.0
8.0
16.0
-------
TABLE 8. CONCENTRATIONS3 OF ELEMENTS OTHER THAN ARSENIC IN
STANDARD REFERENCE SAMPLES
Description Ag Al Be Cd Co Cr Cu Fe Hg Li Mn Mo Ni Pb Se Zn
EPA Trace Metals
Reference Sample
1171 (No. 1) 25 1.8 - 9.2 9.0 18 13 28 5.0 10
EPA Trace Metals
Reference Sample
1171 (No. 2) - 575 16 83 67 402 96 92 16 79
EPA Trace Metals
Reference sample
1171 (NO. 3) - 1100 73 406 314 769 - 449 - 350 48 367
OSGS Standard
Reference Sample
No. 44 - 229 14 6.4 6.0 8.5 101 498 0.42 - 115 1.6 5.5 8.8 6.3 42
USSS Standard
Reference Sample
No. 49 6.3 84 - 4.6 5.1 14.9 385 87 0.68 110 162 56.6 7.8 24.1 15.5 345
a
Concentrations are in pg/1.
-------
TECHNICAL REPORT DATA
(['lease read Inslnictiuni on the reverse before completing)
REPORT NO.
EPA-6QQ/7-77-0.%
3. RECIPIENT'S ACCESSION NO.
TITLE AND SUBTITLE
Trace Analysis of Arsenic by Colorimetry,
Atomic Absorption, and Polarography
6. REPORT DATE
April 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Lyman H. Howe
8. PERFORMING ORGANIZATION REPORT NO.
E-EP-77-3
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Division of Environmental Planning
Tennessee Valley Authority
Chattanooga, Tennessee 3/401
10. PROGRAM ELEMENT NO.
EHE-625C
11. CONTRACT/GRANT NO.
78 BPH
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Research & Development
Office of Energy, Minerals & Industry
Washinoton^ D_C_ 2046Q
13. TYPE OF REPORT AND PERIOD COVERED
Technical FY-76
14. SPONSORING AGENCY CODE
EPA/fiOO/17
15. SUPPLEMENTARY NOTES
This project is part of the EPA-planned and coordinated Federal Interagency
Energy/Environment R&D Program.
16. ABSTRACT
A differential pulse polarographic method was developed for determining total
arsenic concentrations in water samples from ash ponds at steam-electric
generating plants. After digestion of the sample and isolation of arsenic
by solvent extraction, the peak current for arsenic is measured and compared
to a standard curve. The effective range of concentrations for this method
is from 2 to 50 wg/1 of arsenic.
The precision and accuracy of this polarographic method for determining con-
centrations of arsenic in water samples were compared to tv/o standard methods,
atomic absorption and colorimetry, for observations on replicate analyses of
pure standard solutions, split samples from ash ponds, standard reference
samples, and standard solutions spiked with potentially interfering elements.
The three methods compared favorably for the split samples; however, results
of the colorimetric method for the replicate analyses were slightly negatively
biased.
17.
KEY WORDS AND DOCUMENT ANALYSIS
(circle one or more)
a.
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Ecology
Environments
Earth Atmosphere
Environmental Engineering
Gcjgraphy
Hydrology. Limnology
Biochemistry
Earth Hydrosphere
Combustion
Refining
Energy Conversion
Physical Chemistry
Malrrlals Handling
tnurgantc Chemistry ^
Organic Chemistry
Chemical Engineering
forirH Tytoot.-^tf-
Cnw«V teiouxr CxtltCtltM
fllM C»« Clf*ltP«
Dtraci CoMbuiKoo
lyiMhttte1 fu^lf
vtnrfrf trftrmn
wl.i nt ttlrrt:
fiipi" rti»wM«i
6F 8A 8F
8H 10A 10B
7C 13B
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