THE DETERMINATION OF ARSENIC, ANTIMONY,
SELENIUM AND TELLURIUM IN ENVIRONMENTAL WATER
SAMPLES BY FLAMELESS ATOMIC ABSORPTION
By
G. C. KUNSELMAN AND E. A. HUFF
U.S. ENVIRONMENTAL PROTECTION AGENCY
CENTRAL REGIONAL LABORATORY
1819 WEST PERSHING ROAD
CHICAGO, ILLINOIS 60609
Ouly 1, 1975
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BRIEF
Total arsenic, antimony, selenium and tellurium have been determined
in environmental samples without the need for prior digestion. The
method of standard additions was required in order to correct analytical
results for observed interferences. Recoveries ranged from 90% to 110%
at a concentration of 10pg/l for individual metals.
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ABSTRACT
A method has been developed for the direct determination of arsenic, antimony,
selenium, and tellurium in surface waters and industrial effluents using the
graphite furnace. Optimization of instrumental variables is discussed.
Representative inorganic acids enhanced the analytical signal of arsenic,
antimony, and tellurium, and suppressed the response of selenium. The effect
of alkali and alkaline earth elements, commonly present in environmental
samples, on the determinations have been studied and their interferences
documented. These investigations showed that for valid analytical results
experimental variables must be closely controlled, and the method of standard
additions is required. The results of the developed procedure were compared
to the hydried generation technique for arsenic and selenium on real samples.
Recoveries ranged from 90% to 110% at a concentration of 10yg/l for individual
metals.
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INTRODUCTION
Currently, flame atomic absorption spectrophotometry is usually the method
of choice in characterizing environmental samples for trace metals. The
proposed interim drinking water standards (1) set maximum permissible
concentrations of 50yg/l and 10yg/l for arsenic and selenium, respectively,
and the United States Public Health Service (2) recommends an acceptable
arsenic level of lOug/1. The United States Environmental Protection Agency
(U.S.EPA) approved procedure for total metals (3) requires acid digestion
of samples prior to the analytical measurements. Since direct flame atomic
absorption procedures fall short of the required sensitivities for the
above metals, the U.S. EPA is promulgating the hydride generation - atomic
absorption method. However, this technique also requires wet oxidation
of samples prior to analytical measurements and can thus be slow and sub-
ject to volatilization losses of the elements of interest.
Flameless atomic absorption spectrophotometry has the capability to determine
total metals without chemical pretreatment, provided the aqueous phase can be
sampled in a reproducible manner. Electrically heated furnace units, commer-
cially available from several manufacturers, are finding wider acceptance in
the characterization of environmental samples for trace elements (4-9). Their
application to filtered (5) and relatively clean (4, 7, 8) waters have been
reported.
This study was undertaken to demonstrate the applicability of flame!ess atomi-
zation methods to the determination of total arsenic, antimony, selenium, and
tellurium in surface waters and industrial effluents without prior digestion.
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Well mixed samples are injected directly into the furnace. Although inter-
ferences, i.e., suppression or enhancement of a spike signal by a matrix
compared to the corresponding response in a matrix-free standard, are
observed, the application of the standard additions method provides valid
analytical data for all metals investigated.
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EXPERIMENTAL
Apparatus. A Perkin-Elmer Model 503 atomic absorption spectrophotometer
equipped with a deuterium background corrector, an HGA-2100 or HGA-2000
heated graphite atomizer, electrodeless discharge lamps (EDLs), and a
strip chart recorder was used for all analytical measurements. Table I
lists the instrumental settings. The auto-interrupt gas flow mode was
applied for all determinations.
Eppendorf pi pets were used for all volume measurements and furnace sample
injections. Polystyrene cups were procured commercially (Instrumentation
Laboratory, Inc.).
Reagents. Arsenic, antimony, selenium and tellurium certified atomic
absorption standards (1000 yg/ml) were obtained commercially (Fisher
Scientific Co. and Varian Instrument Div.). Working standards were
prepared by serial dilutions of the concentrates using distilled,
deionized water and reagent grade acids. Prepurified grade argon was
used as the purge gas during sample analysis.
Procedure. All reported data were obtained by the method of standard
additions. In general, equal volumes of a well mixed sample and a
working standard or blank were prepared in 1 ounce polystyrene cups.
A 100 pi-aliquot of each of the series of solutions was injected into
the furnace to generate a linear working curve. Metal concentrations
were derived from either graphical extrapolations or linear regression
calculation routines. The standards employed ranged in concentration from
0 to 10wg/l.
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The hydride generation results were obtained by standard U.S. EPA approved
procedures (3).
Results and Discussion
Furnace Optimi zation. Preliminary HGA furnace operating parameters provided
by Perkin-Elmer Corp. (10) appeared to be less than optimum according to
our observations and those of others (5,6). As a consequence, experiments
were performed to generate charring temperature - absorbance relationships
for the elements under study. These results are presented for inorganic
standards in Figure 1. The data show that in a 1% nitric acid medium ashing
temperatures of 700°C for tellurium and 1000°C for arsenic, antimony and
selenium can be used without a significant loss of signal. The use of
maximum permissible charring temperatures is of advantage in flameless
atomization techniques for minimizing non-specific absorption interferences
due to incomplete volitilization of organic components. Figure 2 presents
ashing temperature - absorbance profiles for three organoarsenic compounds.
No losses were observed up to 1400°C.
Sensitivities were found to be independent of atomization temperature
for the above metals. Therefore, all elements but antimony were analyzed
at the maximum furnace temperature of 2700°C in order to insure the removal
of less volatile components that may show a cumulative interference during
sample analyses. An atomization temperature of 2200°C was chosen for
antimony, since at higher settings non-specific furnace peaks were observed.
Interferences. Figures 3, 4 and 5 show absorbances of 10 yg/1 standards
as a function of acidity for hydrochloric, nitric, and sulfuric acids,
respectively. All acids exert a positive and concentration dependent
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Interference for arsenic, antimony, and tellurium, while a suppression
effect is observed for selenium. Selenium could in fact not be success-
fully recovered from any of the sulfuric acid standards due to severe
background absorptions that exceeded the background correction capabilities
of the instrument. While the theoretical aspects of this behavior are as
yet unknown, the results indicate that for valid and reproducible data
close control over acidities must be exercised. As a consequence, the
proposed analytical procedure incorporates mixing of samples and standards
prior to furnace injection.
Matrix interferences due to cations at concentrations normally found
in surface waters and industrial effluents were also studied. Table II
summarizes the data for the alkali and the alkaline earth metals. Selenium
was not investigated in detail, since our experience coincides with matrix
effects reported in the literature (6) for this element. These results
show that suppression and enhancement effects are observed, which are in
general a function of interferant concentration and element determined.
No interferences were observed for cobalt, copper, lead and manganese up
to 1 mg/1 and iron up to 10 mg/1. Several investigators have used matrix
separation by either ion exchange (6) or liquid-liquid extraction (9) prior
to analysis. These procedures are lengthy and are subject to incomplete
recoveries, considerations that are of importance to high-volume environ-
mental laboratories.
Comparability and Recovery Studies. Table III lists comparative data for
arsenic and selenium on representative water samples by the graphite furnace
and the hydride generation methods. The results show a satisfactory
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agreement and indicate the applicability of the furnace technique for total
metal determinations without prior digestion in most cases. However, some
samples may contain a matrix that would significantly suppress the analytical
signal of the metal at the concentration of interest. As a general rule,
if this suppression exceeds approximately 75% of the original spike standard,
a wet oxidation step prior to analysis becomes mandatory for valid results.
Table IV assesses the precision of the method at two concentration levels.
This data was obtained by repetitive injections of unspiked and spiked
samples, and reflects the reproducibility that can be expected on actual
samples. Results on recoveries are summarized in Table V. Standard addition
procedures were used throughout, and the data are representative of results
routinely obtained on surface waters and industrial effluents. Low level
determinations of the metals under study were of primary interest; higher
concentrations can be readily determined by appropriate adjustments of
instrumental variables, i.e. wavelength, gas flow mode, or sample dilutions.
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ACKNOWLEDGMENT
The authors express their appreciation to B. J. Fairless for the encouragement
he provided during the course of this work.
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LITERATURE CITED
1. Federal Register, Vol. 40, No. 51, pp. 11990, 1975.
2. United States Public Health Service, "Drinking Water Standards", U.S.
Department of Health, Education and Welfare, Washington, D.C., 1962.
3. United States Environmental Protection Agency, Cincinnati, Ohio,
"Methods for Chemical Analysis of Water and Wastes", 1974.
4. W. M. Bernard and M. J. Fishman, At. Absorption Newsletter, 12,
118 (1973).
5. J. C. Guillaumin, At. Absorption Newsletter, 13, 135 (1974).
6. Earl L. Henn, Anal. Chem., 47, 428 (1975).
7. Anthony RAltonelti, Anal. Chem., 46_, 739 (1974).
8. Arthur W. Struempler, Anal. Chenr., 45_, 2251 (1973).
9. Kai C. Tarn, Environ. Sci. Techno!., 8_, 734 (1974).
10. Perkin-Elmer Corp., Norwalk, Conn., "Analytical Methods for Atomic
Absorption Spectroscopy Using the HGA Graphite Furnace", Rev. April, 1974,
p. 33.
11. W. J. Youden, "Statistical Techniques for Collaboration Tests",
The Association of Official Anal. Chem., Washington, D.C., 1973, p. 18.
The use of trade names or commercial products does not constitute endorsement
nor recommendation by the United State Environmental Protection Agency.
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TABLE I
INSTRUMENTAL SETTINGS FOR THE DETERMINATION OF
ARSENIC, ANTIMONY, SELENIUM AND TELLURIUM
Wavelength, nm
Bandpath, nm
JEDL Power, w
Drying Temp. ,0C(Time, sec)
Charring Temp. ,
°C (Time, sec)
Atomize Temp. ,
°C(Time,sec)
Argon Gas Flow, ml/min
As
193.7
0.7
8
125(60)
1000(40)
2700 (5)
50
Sb
217.6
0.2
8
125(60)
1000(40)
2200 (5)
50
Se
196.0
0.7
6
125(60)
1000(40)
2700 (3)
50
Te
214.3
0.7
9
125(60)
700(40)
2700 (5)
50
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TABLE II
Effect of the Alkali and the Alkaline
Earth Metals On 10 yg/1 of As, Sb, and Te
% enhancement (+) or suppression (-) on the
absorbance of a lOyg/1 solution containing As, Sb &
Element
As
Sb
Te
As
Sb
Te
As
Sb
Te
As
Sb
Te
As
Sb
Te
As
Sb
Te
Cone, of interfering
metal , mg/1 '
50
100
250
500
750
1000
Ca ,
0
+9
-19
-5
+4
-13
+5
+5
-22
+6
-3
-18
+7
+2
-14
4-9
-2
-17
K
-5
-10
+5
-10
-3
+15
-11
-6
+3
-10
+8
0
-11
+4
-20
-15
+5
-30
Mg
+23
+ 5
-7
+21
+3
-23
+17
+2
-26
+20
+11
-26
+15
0
-33
+22
+4
-35 •
Na
-6
+7
0
0
-7
+10
+8
+2
0
+7
+2
-12
+13
0
-14
+4
0
-17
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TABLE III
Comparison of the Furnace and the Hydride Generation Methods
In the Analysis of Environmental Samples for Arsenic and Selenium
Type of Sample
Metals Industry
Power Plant
Sewage Treatment Plant
S. D. of Diff., yg/1 (11)
As, yg/1
Furnace
16
12
24
16
13
20
14
14
14
14
10
10
11
11
10
10
Hydride
14
12
28
13
12
20
10
12
12
12
12
14
12
10
12
12
1.7
Se, ug/1
Furnace
13
14
13
14
13
13
12
11
12
15
13
15
10
11
12
11
Hydride
14
14
16
14
12
11
11
12
13
13
13
12
13
12
13
13
1.2
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TABLE IV
Precision of the Flameless Atomization Method
As a Function of Concentration
Element
As
Sb
Se
Te
Concentration, yg/1
2.5
10.0
2.5
10.0
3.0
10.0
2.5
10.0
n
12
16
15
15
8
13
15
15
S.D.,yg/l
0.2
0.3
0.1
0.3
0.2
0.5
0.1
0.4
Rel.S.D., %
8.0
3.0
4.0
3.0
6.7
5,0
4.0
4.0
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FIGURE CAPTIONS
Figure 1 - Absorbance as a function of charring temperature for
inorganic compounds (lOyg/1). A temperature of 1000°C
is optimum for arsenic, antimony, selenium and 700°C
for tellurium.
Figure 2 - Absorbance as a function of charring temperature for
organoarsenic compounds (10pg/l). A temperature up to
1400°C provides for quantitative recovery.
Figure 3 - Absorbance as a function of hydrochloric acid concentra-
tion. Arsenic, antimony and tellurium are enhanced,
selenium is suppressed.
Figure 4 - Absorbance as a function of nitric acid concentration.
Arsenic, antimony and tellurium are enhanced, selenium
is suppressed.
Figure 5 - Absorbance as a function of sulfuric acid concentration.
Arsenic, antimony and tellurium are enhanced, selenium
is totally suppressed.
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