United States
Environmental Protection
Agency
Environmental Research
Laboratory
Athens GA 30605
EPA-600'4-80-020
March 1980
Research and Development
Ion
Chromatography of
Anions
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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
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environme'ntal
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/4-80-020
March 1980
ION CHROMATOGRAPHY OF ANIONS
by
Thomas B. Hoover
and
George D. Yager
Analytical Chemistry Branch
Environmental Research Laboratory
Athens, Georgia 30605
ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ATHENS, GEORGIA 30605
-------
DISCLAIMER
This report has been reviewed by the Environmental Research
Laboratory, U.S. Environmental Protection Agency, Athens,
Georgia, and approved for publication. Mention of trade names
or commercial products does not constitute endorsement or
recommendation for use.
ii
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FOREWORD
Nearly every phase of environmental protection depends on a
capability to identify and measure chemical pollutants in the
environment. The Analytical Chemistry Branch of the Athens
Environmental Research Laboratory develops techniques for iden-
tifying and measuring chemical pollutants in water and soil.
This report evaluates a relatively new technique, ion chro-
matography, for the measurement of anionic species in water,
using commercial instrumentation. It will acquaint administra-
tors and researchers with the analytical capabilities of the
technique.
David W. Duttweiler
Director
Environmental Research Laboratory
Athens, Georgia
iii
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ABSTRACT
A Dionex Model 10 Ion Chromatograph was evaluated for the
measurement of anionic species in water. The theoretical
effect of hydrogen ion activity (pH) on the elution time of
phosphate and arsenate was tested and empirical selectivity
coefficients were determined for the major protolytic species
of these acids. Calibration curves were obtained for arsenate,
bromide, chloride, nitrate, nitrite, phosphate, selenate, sele-
nite, and sulfate by direct injection of 0.1 mL of standards
and, in most cases, by preconcentration of 5 to 50 mL of solu-
tion on the ion exchange concentrator columns available from
the instrument manufacturer. Detection limits for ions other
than chloride were approximately 0.2 yg independent of the
method of sample introduction. For chloride the detection
limit was 2 ngf by direct injection. The concentrator column
permitted determination of any of the above ions at concentra-
tions greater than 10 yg/L.
IV
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CONTENTS
Foreword ii:i-
Abstract iy
Figures vi
Tables vii
Abbreviations and Symbols viii
1. Introduction 1
2. Conclusions 3
3. Recommendations 4
4. Experimental 5
5. Results and Discussion 7
References 31
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FIGURES
Number Page
1. Calibration for arsenic (V) 10
2. Calibrations for nitrite and nitrate 12
3. Calibration for phosphate ...... 13
4. Calibrations for selenium (VI) 15
5. Calibrations for selenium (IV) by
direct injection 16
6. Calibration for selenium (IV) by
concentrator column 17
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TABLES
Number Page
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
pH effects on the retention time of phosphate
pH effects on the retention time of arsenate
Detection limits for phosphate ........
Calibration data for nitrate ,
Calibration data for phosphate
Calibration data for selenium (VI) on 500-mm
Calibration data for selenium (VI) on 150-mm
Calibration data for selenium (IV) by direct
Calibration data for selenium (IV) by
Summary of retention times and detection
. 18
. 18
9
. 19
. 20
. 21
. 22
. 23
. 24
. 25
, 26
, 27
, 28
, 29
, 30
vii
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LIST OF ABBREVIATIONS AND SYMBOLS
ABBREVIATIONS
min. - minute
mL - milliliter
mm - millimeter
mM - millimolar
ppb - parts per billion
yg - microgram
ym - micrometer
ymho/cm - micromhos per centimeter
SYMBOLS
A'2, A'3
As
1' 2' 3
E
H
H+
HPO 2
H2P04-
*!'
pH
4
Se
T
contributions of doubly- and triply-charged
species, respectively, to the retention time
of a tribasic acid
arsenic
selectivity coefficients of protonated species
having 1, 2, or 3 charges, respectively
molarity of eluent ion
recorder peak height
hydrogen ion activity
hydrogen phosphate anion
dihydrogen phosphate anion
successive protolysis constants of a tribasic
acid
negative logarithm of hydrogen ion activity
orthophosphate anion
selenium
retention time
viii
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SECTION 1
INTRODUCTION
Impr'oved analytical methods for inorganic anionic species
in water are needed both because the oxidation state, ioniza-
tion, and complexation of most of the heavy elements have a
critical influence on their distribution, cycling, and trans-
port in the environment and because the human health effects
of many elements seem to be most clearly related to specific
anionic species (1). Sawicki (2) has indicated that the
common atmospheric anions—arsenate, arsenite, chromate,
nitrate, nitrite, selenate, selenite, sulfate, and sulfite—
have all been implicated as carcinogenic, mutagenic, co- or
pre-carcinogenic. These ions may be equally significant as
water pollutants.
Ion chromatography is a relatively recent analytical
development that appears especially promising for the determi-
nation of aqueous anions. It has already become established
for the analysis of airborne particulates (3,4). This devel-
opment depends on the successful application of the conduc-
tivity detector to ion exchange chromatography. The princi-
ple, described by Small, Stevens, and Bauman (5) utilizes a
so-called suppressor column following the ion exchange sepa-
rator column to convert the eluent ions to a form that makes
little contribution to the specific conductance of the final
discharge. Although the principle has been applied to a
variety of systems, it has been most successful with a
carbonate-bicarbonate reagent used to elute selectively a
series of anions. In the cationic exchange suppressor column
the eluent is converted to carbonic acid, which makes a
consistent, small contribution to the background conductance.
Analyte anions, as they come through the system individually,
are converted to the corresponding acids and are registered as
sharp increases in conductance.
Ion chromatography offers several major advantages for
water analysis.
• It is especially applicable to the determination of
the anions of strong acids, for which there are few
alternate, general, sensitive methods.
-------
• The non-specific nature of conductometrie detection
allows several ions to be determined in the same
sample and permits extension of the procedure to many
ionic species.
• Conductometric detection is highly sensitive and
relatively free of interferences.
• The technique permits the determination of different
stable valence states of the same element.
On the other hand, some limitations need to be considered
in any application of ion chromatography.
• Because of the non-specific nature of the detector *
the chromatographic peaks are identified only by
their retention times.
* In common with other column chromatographic techni-
ques, the system gives peaks that broaden appreciably
with increasing retention time. At present, ion
chromatography has no compensatory techniques, such
as temperature programming or gradient elution.
• To provide a practicable working life for the
suppressor column between regenerations, the
separator column has a very small exchange capacity.
Sample injections are limited to a few microequiva-
lents of exchangeable ions and a volume usually less
than one mL.
This report presents a preliminary evaluation of ion chro-
matography and gives calibration data for nine anions both by
direct injection of aqueous standards and by preconcentration
on small ion exchange columns.
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SECTION 2
CONCLUSIONS
Ion chroraatography is a convenient and dependable instru-
mental technique for the separation and measurement of several
anions in water samples.
The detection limit for the ions studied in this report
(arsenate, bromide, nitrate, nitrite, phosphate, selenate,
selenite, and sulfate) is about 0.2 ug.
Concentrator columns provide the reproducible collection
of trace anions from 50 mL or more of water, permitting the
measurement of concentrations greater than 10 ppb.
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SECTION 3
RECOMMENDATIONS
Further work needs to be done with environmental samples
to assess the extent and impact of interferences in complex
samples. Because peak identification in ion chromatography is
made by retention time, a reliable means of detecting co-
eluting peaks is needed, and rapid, simple methods of con-
firming peaks are desirable.
For trace analysis and speciation of environmental
samples, lower detection limits are needed. This probably
entails improved precision through closer temperature control
of the separator and detector, reduction of dead volume, and
more reproducible loading of concentrator columns.
Improved analytical methods should be developed for the
anions of weak acids, which are not sensitively measured by
conductance.
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SECTION 4
EXPERIMENTAL PROCEDURES
EQUIPMENT
A Dionex Corporation Model 10 Ion Chroraatograph was used.
This model requires manual sample injection and has a single
analytical train of separator and suppressor columns. Ion
exchangers used in various combinations were: Anion Precolumn
(3 x 150 mm), Anion Separator (3 x 150 and 3 x 500 mm),
Suppressor (6 x 250 mm), and several Anion Concentrators (3 x
50 mm).
Flow rate was usually recorded as percentage of full output
of the eluent pump (30% in most cases). During the study, the
control knob on the eluent pump became loose and had to be
reset. The pump was calibrated with eluent flowing through a
500-mm separator and the suppressor columns.
The original 0.1 mL sample injection loop was used as
supplied, without calibration. Sample volumes loaded onto the
concentrator columns were measured by the markings on 25- and
50-mL disposable syringes driven by a Harvard Apparatus
infusion pump (Model 975) at 0.5-1.0 mL/min. In later runs,
the effluents from the concentrator columns were collected in
volumetric flasks.
The suppressor column was regenerated, usually daily,
according to the manufacturer's recommendation. The semi-
automatic schedule used a 15-min. regeneration cycle followed
by a 30-min. rinse.
MATERIALS
Laboratory reverse-osmosis water was deionized in a three-
column Illinois Water Treatment system and used for all solu-
tions. Reagent solutions (eluents, regenerant, and standards)
were filtered through 0.45-ym Millipore cellulose acetate-
nitrate membranes. Stock solutions of anions (1000 mg/L) were
prepared from reagent-grade chemicals and were not purified or
independently Assayed, except for sodium nitrite. The nitrite
stock solution was titrated into standard potassium perman-
ganate-sulfur ic acid as recommended by Kolthoff and Belcher
(6). The indicated assay of the nitrite (80.5%) was used in
subsequent calculations.
-------
The Dionex recommended eluent of 2.4 mM sodium carbonate -
3.0 mM sodium bicarbonate is referred to as the "standard
eluent11 in this report. Other eluent compositions are defined
as they are referred to.
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SECTION 5
RESULTS AND DISCUSSION
pH EFFECTS
It is well recognized (5) that polybasic acids elute as a
single component in anion exchange chromatography, even though
the less protonated and more highly charged species are more
strongly held by the exchanger. This is true because the
dynamic hydrolysis process maintains the equilibrium distribu-
tion of species at the pH of the eluent in opposition to the
ion exchange tendency to separate the hydrolytic species.
Consequently, the retention time of an acid such as phosphoric
can be shifted by changing the pH of the eluent. A higher pH
increases the proportion of highly charged (deprotonated)
species and increases the retention time. The effect is
described quantitatively by the following equation, adapted
from Rieman and Walton (7) for a doubly-charged eluting ion
(carbonate).
[C1K1(H+)2/E1/2] + [C2K1K2(H+)/E]
Toe i-± -j-3- +"2" * -1" - " (1)
In equation 1 T is the retention time of a tribasic acid having
protolysis constants K^, K2, and 1(3. E is the molar
concentration (strictly, activity) of the doubly charged eluent
ion and H+ is the hydrogen ion activity of the eluent. C]_,
C2r and C3 are the respective ion exchange selectivity
constants for the singly-, doubly-, and triply-charged hydro-
lytic species.
The relation of equation 1 was tested using a series of
carbonate-bicarbonate eluents of varying pH and carbonate
concentration. Table 2 summarizes the data for ortho-phos-
phate. The column headed E (mM) gives the analytical concen-
tration of carbonate ion in the eluent, in millimoles per
liter. The effect of the singly charged bicarbonate ion on the
elution was neglected. The third and fourth columns give the
calculated contributions of the doubly- (HPO^" ) and triply-
charged (PO£3~) species to the overall retention time of_ the
component. The contribution of the singly-charged H-PO/" ion
was too small to estimate from these data. The selectivity
-------
constants, C2 and €3, shown at the bottom of Table 2, were
calculated by a least-squares multivariate fit to the last two
terms of Equation 1. The quantities A~2 and A~3 in the
table were then calculated from these selectivity constants.
The third row of the table shows anomalously poor agreement
between the calculated and observed retention times. This same
eluent, however, gave consistent results with arsenate and the
phosphate retention time measured with it was included in the
least-squares fitting of the constants. Although at pH 11 the
ionization constants indicate that 96% of the phosphate is in
the doubly-charged form, HP042~, Table 2 indicates that the
triply-charged species, A~3, determines the retention time.
Corresponding results are shown for arsenate in Table 3.
The selectivity constants are not directly comparable to those
for phosphate because the latter data were obtained with a
500-mm separator column whereas the arsenate results were
obtained with the 150-mm column to keep the retention times
conveniently short. Although phosphate and arsenate have very
similar ionization constants, the pH effect on retention time
is appreciably less for arsenate and only the selectivity
constant for the triply-charged species could be reliably esti-
mated from these data.
CALIBRATIONS
General Observations
Instrumental response was measured by the peak height on
the recorder chart but converted to specific conductance in
this report by use of the nominal cell constant of one mho/cm.
Some workers (8,9) have measured peak area, which is more
directly related to the quantity of analyte passing through the
detector. We compared calibration curves for nitrite, nitrate,
sulfate, and arsenate using peak heights, on one hand, and peak
areas determined by hand planimetry of the charts, on the
other. No significant improvement in detection limits could be
ascribed to the areal measurements.
Calibrations for several ions were made both on a concen-
tration basis, using the standard 0.1 mL injection loop, and on
a weight basis, collecting the analyte on concentrator columns
(10) from varying volumes and concentrations of sample. Table
4 compares some results for phosphate, showing that the ulti-
mate sensitivity is essentially the same on either basis.
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TAflLE 3. ION CHROMATOGRAPHY DETECTION LIMITS FOR PHOSPHATE
Full-Scale Direct Injection Accumulator
ymho/cm (0.1 mL) (5-25 mL)
(yg) (yg)
1 0.067 0.040
2 0.016 0.039
10 - 0.24
30 0.86 0.80
The different full-scale sensitivities of the instrument
appeared to be fully consistent and interconvertible in terms
of the specific conductance. Nearly all calibration data were
pooled over several sensitivity ranges. Detection limits are
given as the quantity of analyte distinguishable from the blank
with 95% confidence (11).
Arsenate
The arsenic (V) anion is strongly retained on the separator
column, having a long retention time. Hansen et al (12) have
recommended a strongly alkaline eluent for arsenate (3.5 mM
sodium carbonate plus 2.6 mM sodium hydroxide) that provides
good resolution of the arsenate peak from other common anions.
This eluent, even on a 250-mm separator column gives a reten-
tion time of 22 to 27 minutes. When separation from other
interferents is not a problem, the sensitivity of detection can
be improved and the retention time shortened by working at a
lower pH. (See the section on pH effects.) A calibration
curve for As (V) by direct injection of 0.1 mL portions is
shown in Figure 1. The eluent was 3 mM sodium carbonate and 3
mM sodium bicarbonate and gave a retention time of 8.7 to 9.0
minutes on the 150-mm separator column. The calibration data
are summarized in Table 5.
Bromide
Table 6 presents calibration data for bromide by direct
injection on the 500-mm separator column, with standard eluent.
Chloride
Calibration data for the direct injection of chloride
standards are summarized in Table 7. Data were pooled for the
calculation of -the least-squares equation although variances at
the different full-scale ranges were not strictly homogeneous.
-------
8
K-
-------
The negative water peak immediately preceding the elution of
the chloride may account for the inhomogeneity, as the standard
solutions were not adjusted to the same carbonate strength as
the eluent (10).
Nitrate
The nitrate calibration was made by collecting 5 to 40 mL
samples of 0.1 to 1000 ppb solutions of nitrate on the concen-
trator column. A blank correction of 1 yg/L nitrate was esti-
mated from eight runs with 5 to 90 mL of deionized water
treated in the same manner as the standards. Even after
correction for the blank, the calibration curve had an appar-
ently significant positive intercept. This result may denote a
small but consistent source of contamination that was not iden-
tified. The results are presented in Table 8 and Figure 2.
Nitrite
The nitrite calibration, summarized in Table 9 and Figure
2, was made with the concentrator column, using 5 to 25-mL
volumes of standard solutions containing 6 to 160 yg/L. A peak
appearing immediately after the water peak was assumed to be
chloride impurity at the time the runs were made. Koch (13)
has recently presented evidence that this peak represents
oxidation to nitrate in the suppressor column. The data were
recalculated in Table 9 using the sums of the two peaks as an
approximation to the total response to injected nitrite ion.
The correction for the oxidation product varied from 0.2 to 7
pmhos/cm. In Figure 2, the curve for nitrite is much steeper
than that for nitrate because the nitrite, eluting sooner, has
a much sharper peak and, therefore, provides a higher concen-
tration in the detector cell for the same quantity injected.
Phosphate
The phosphate calibration was made with the concentrator
column, collecting 5 to 25 mL of 10 to 100 ppb solutions. The
data, presented in Table 10 and Figure 3, reveal a small but
significant curvature but negligible intercept.
Selenate
When separated with the standard eluent and a 500-mm
separator column the Se (VI) anion has an inconveniently long
retention time of 29.2 minutes. A calibration for direct
injection via the 0.1 mL sample loop and these analytical
conditions is presented in Table 11 and the lower curve of
Figure 4. A calibration was also made with the 150-mm
separator column and an eluent of 1 mM sodium carbonate and 10
mM sodium bicarbonate, providing a retention time of 14.7
11
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§ Nitrite & Nitrate Calibrations
0.00 0.81 1.63 2.44 3.25 4.06 4.88
NOi & NOi (/xg)
Figure 2. Calibrations for nitrite and nitrate.
12
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Phosphate Calibration
0.00 0.44 0.88 1.31 1.75 2.19 2.63 3.06 3.50
P04
Figure 3. Calibration for phosphate.
13
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minutes. The result, shown as the upper curve of Figure 4, had
significant curvature in the range of 0.5 to 25 ppm. The data
are summarized in Table 12.
Selenite
A calibration for selenium (IV) anion, made in January
1979, by direct injection of 0.1 mL of standards showed
remarkably little scatter and a highly significant curvature
over the range 0.1 to 40 ppm. These data are shown as the
upper curve of Figure 5 and in Table 13. Five months later,
five additional points, presumably run under the same condi-
tions, showed an appreciably longer retention time (7.4 minutes
vs. 5.9 minutes) and more random error. The latter points were
linear over the range of 8 to 27 ppm and extrapolated approxi-
mately to the original calibration at lower concentrations. No
explanation for the discrepancy has been found.
A calibration using 5 to 50 mL samples collected on the
concentrator column and analyzed by the same conditions used
previously yielded the same retention time as the first
calibration by direct injection and was linear in the range 0
to 2.5 yg. The slope of the latter was slighty less (1.9
ymho/yg vs. 2.2 ymho/yg) and the detection limit was higher
(0.1 yg vs. 0.01 yg) . This calibration is presented in Figure
6 and Table 14.
Sulfate
A calibration for sulfate by direct injection is summarized
in Table 15. The negative intercept is statistically signifi-
cant.
Summary
All anions discussed in this report except arsenate were
run at the conditions recommended by Dionex: 500-mm separator
column, 30% flow (2.56 mL/min.), and "standard" eluent of 2.4
mM sodium carbonate plus 3 mM sodium bicarbonate. The reten-
tion times and detection limits observed at these uniform
conditions are summarized in Table 16. At retention times
greater than 4 minutes, the detection limits were generally in
the range 0.1 to 0.2 yg. No distinction in detection limit
could be drawn between the direct injection procedure and the
use of the concentrator column although the latter permits
relatively large samples of much more dilute solutions to be
analyzed.
14
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8
Selenate Calibration
8
o-l
I
8,
«1
0.00 6.25 12.50 18.75 25.00 31.25 37.50 43.75 50.00
Se(VI) (ppm)
Figure.4. Calibrations for selenium (VI)
15
-------
8
m
8
0.
Selenite Calibration
r
I
o
g
Cj S
10'
*
8k*
d^i3
0.00 6.25 12.50 18.75 25.00 31.25 37.50 43.75 50.00
Se(IV) (ppm)
Figure 5. Calibrations for selenium (IV) by direct injection.
16
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R
^^^
1
10
Is
I 81
Selenite Calibration
000 0.34 0.69 1.03 1.37 1.72 2.06 2.41 2.75
Se(IV)
Figure 6. Calibration for selenium (IV) by concentrator column.
17
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TABLE 1. EFFECT OF pH ON RETENTION TIME OF PROTONATED
SPECIES OF ORTHOPHOSPHATE
PH
11.5
11.5
(11.2
9.9
9.7
9.6
9.6
9.4
E(mM)
6.00
1.50
3.10
2.55
2.29
0.73
0.39
1.00
A-2
0.6
2.4
1.2
1.6
1.8
5.6
10.4
4.1
A-3
10.1
81.1
14.9
1.1
0.8
3.0
9.1
.2
Retention Time
Calc. Meas.
10.7
83.5
16.2
2.7
2.6
8.6
19.5
5.3
15.7
83
33.6
10
4.6
8.4
17.6
6.6
Diff.
5.0
-0.5
17.4)
7.3
2.0
-0.2
-1.9
1.3
C2 = (4.1 + 1.4) x ID"3
C3 = (4.04 + 0.22) x ID"2
TABLE 2. EFFECT OF pH ON RETENTION TIME OF PROTONATED
SPECIES OF ARSENATE
PH
11.5
11.3
11.2
11.2
10.0
9.7
9.6
9.4
E(mM)
6.00
3.93
3.10
3.10
1.94
2.29
0.73
1.00
A-2
0.2
0.1
0.4
0.4
0.4
0.5
1.6
1.2
A-3
13.7
7.7
20.1
20.1
1.6
1.1
4.1
1.6
Retention Time
Calc. Meas.
13.8
7.8
20.5
20.5
2.0
1.6
5.7
2.8
9.9
14
23
18.6
3.5
2.6
4.4
3.4
Diff.
-3.9
6.2
2.5
-1.9
1.5
1.0
-1.3
0.6
C2 = (8 + 14) x lO-4
Ca = (4.9 + 0.5) x 10-3
18
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TABLE 4. ARSENATE CALIBRATION
0.1 mL injection, 150-mm Precolumn + 150-mm Anion Separator,
Eluent: 3 mM Na^COs, 3 mM NaHCC>3, pH 10.0.
Flow: 1.25 mL/min. Retention time: 8.7 to 9.0 min.
Range
Full-Scale
ymho/cm
1
1
1
1
1
1
1
1
3
3
3
10
10
10
10
10
10
As(V)
Concentration
(ppm)
1
1
2
2
2
4
4
4
8
8
12
16
16
16
20
25
30
Peak
Height
(ymho/cm)
0.19
.20
.35
.35
.38
.79
.80
.82
1.57
1.61
2.52
3.39
3.39
3.50
4.25
5.51
6.77
H(ymho/cm) = (-0.108 + 0.029) + (0.2236 + 0.0022) C (ppm)
19
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TABLE 5. BROMIDE CALIBRATION
0.1
Range
mL injection, 500-mm
Standard Eluent, Plow
Bromide
Full-Scale Concentration
Umho/cm
1
1
1
1
3
3
3
3
3
10
10
10
10
30
30
30
30
30
(ppm)
1
2
3
4
1
2
4
8
16
8
16
32
64
16
32
64
128
200
Anion Separator
2.56 mL/min.
Peak
Height
(y mho/cm)
0.10
.20
.33
.43
.11
.21
.44
1.00
2.09
.83
1.83
3.90
8.07
1.71
3.84
7.85
15.83
25.69
H(umho/cm) = (-0.118 + 0.046) + (0.1274 + 0.0007) C (ppm)
20
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TABLE 6. CHLORIDE CALIBRATION
0.1 mL
injection, 500 mm
Anion Separator,
Flow 2.56 mL/min, Std. Eluent
Range
Pull-Scale
ymho/cm
1
1
1
1
1
3
3
3
3
10
10
10
10
30
30
30
Chloride
Concentration
(ppm)
0.01
.02
.03
.04
.05
.04
.10
.16
.24
.16
.24
.32
.40
.32
.4
.8
Peak
Height
(ymho/cm)
0.126
.185
.242
.323
.435
.378
.880
1.470
2.285
1.319
1.929
2.657
3.366
2.480
3.189
6.732
H(ymho/cm) = (0.024 + 0.039) + (8.29 + 0.13) C (ppm)
21
-------
TABLE 7. NITRATE CALIBRATION
10
to
Range
Full-Scale
( ymho/cm)
30
10
10
10
10
30
10
10
10
10
10
10
3
3
3.x
Volume
(mL)
5
5
10
10
10
10
10
10
10
10
10
10
10
10
50 mm Concentrator Column, 500 mm Anion Separator
Standard Eluent; Flow 2.56 mL/min.
Nitrate
(ug)
5.0
5.0
2.0
5.0
1.0
6.0
6.0
0.1
0.2
0.4
0.8
1.0
1.0
0.1
Peakd)
Height
( ymho/cm)
5.42
5.48
2.28
5.71
1.46
7.24
7.32
0.02
0.28
0.79
1.04
1.54
1.57
0.40
Range
Full-Scale
( ymho/cm)
3
3
3
3
3
3
3
3
3
3
1
1
1
1
1
1
1
Volume
(mL)
20
9
10
10
10
10
10
20
15
15
30
15
10
40
40
20
40
Nitrate
(ug)
0.2
0.09
0.1
0.4
0.1
0.1
0.1
0.2
0.15
0.15
0.03
0.015
0.01
0.04
0.02
0.01
0.004
Peak
Height
(ymho/cm)
0.59
0.21
0.41
0.91
0.26
0.25
0.26
0.60
0.38
0.37
0.35
0.18
0.09
0.39
0.10
0.02
0.18
H(ymho/cm) = (0.207 + 0.040) + (1.124 + 0.018) C (yg)
(1) Peak heights corrected for water blank. See text.
-------
TABLE 8. NITRITE CALIBRATION
3 x 50
mm Concentrator
Column, 500 mm Anion
Separator ,
Standard Eluent, Flow 2.56 mL/min.
Range
Full-Scale
ymho/cm
30
30
30
30
30
30
30
30
30
30
10
10
10
3
3
3
3
3
3
3
1
1
1
1
1
1
1
1
Volume
(mL)
25
20
20
15
15
15
10
10
5
5
20
15
10
20
20
15
10
10
5
5
20
20
20
i 20
15
10
10
5
Nitrite
Ion Injected
(ug)
4.0
3.2
3.2
2.4
2.4
2.4
1.6
1.6
0.8
0.8
0.96
0.72
0.48
0.32
0.32
0.24
0.16
0.16
0.08
0.08
0.13
0.13
0.16
0.13
0.10
0.06
0.06
0.03
Peak
Height*
(ymho/cm)
31.00
24.71
25.47
15.74
17.83
18.07
11.25
10.67
6.58
4.69
5.99
4.28
4.28
5.2
2.38
4.54
2.96
1.22
1.22
0.60
1.8
2.0
1.8
1.7
1.5
1.2
1.40
.76
Sum of two peaks, assuming the first is nitrate resulting
from oxidation on the suppressor column.
H(ymho/cm) = (0.57+0.28) + (7.29+0.19) C (yg)
23
-------
TABLE 9. PHOSPHATE CALIBRATION
3 x 50
Range
Full-Scale
u mho/cm
1
1
1
1
1
1
1
1
3
3
3
3
3
10
10
10
10
10
10
10
mm Concentrator Column, 500 mm Anion
Standard Eluent,
Volume
(mL)
5
10
15
20
5
10
15
25
5
15
10
25
20
5
10
5
10
15
20
25
Flow 2.56 mL/min
Phosphate
Ion Injected
(ug)
0.05
0.10
0.15
0.20
0.05
0.10
0.15
0.25
0.15
0.45
0.30
0.75
0.60
1.5
3.0
0.5
1.0
1.5
2.0
2.5
Separator.
•
Peak
Height
(y mho/cm)
^ 0.07
0.14
0.22
0.26
0.06
0.12
0.19
0.28
0.18
0.67
0.45
1.15
0.90
2.09
4.86
0.63
1.46
2.28
3.23
4.17
H(ymho/cm) = (-0.017*+0.
(0.084 + 0.
029) + (1.406 + 0
025) (ug)2
.071) yg +
24
-------
TABLE 10. SELENATE CALIBRATION
0.1 mL injection, Precolumn plus 500-mm Anion Separator;
Standard Eluent; Flow 2.56 mL/min.
Range Se(VI) Peak
Full-Scale Concentration Height
ymho/cm (ppm) (u mho/cm)
3 8 0.69
3 15 1.37
3 20 1.77
3 22 1.98
3 27 2.49
Hfymho/cm) = (-0.058 + 0.045) + (0.0934 + 0.0023) C (ppm)
25
-------
TABLE 11. SELENATE CALIBRATION
0.1 mL injection, 150-mm Precolumn plus 150-mm Anion Separator
Eluent: 1 mM Na2CO3, 10 mM NaHCOa, pH 9.75
Flow: 1.25 mL/min; Retention time: 14.7 min.
Range
Full-Scale
ymho/cm
Se(VI)
Concentration
(ppm)
Peak
Height
(umho/cm)
30
30
30
10
10
10
3
3
3
1
1
1
1
1
1
1
1
1
25
25
25
10
10
10
5
5
5
2
2
2
1
1
1
0.5
0.5
0.5
7.09*
7.20
7.32*
2.60
2.64
2.68
1.31
1.45*
1.28
0.57
0.58
0.56
0.29
0.30
0.32
0.16
0.22
0.19
H(umho/cm) = (0.072 + 0.010) + 0.2376 + 0.0030) C +
(0.0019 + 0.0012) C2
* Outliers omitted (> 2 standard deviations)
26
-------
TABLE 12. SELENITE CALIBRATION
0.1 mL injection, 3 x 150-mm Precolumn plus 500-mm Anion Separator.
Standard Eluent, Flow 2.56 mL/min.
ro
-j
17 Jan 79
Retention time 5.9 min
Range Se(IV) Peak
Full-Scale Concentration Height
ymho/cm (ppm) (y mho/cm)
12 June 1979
Retention time 7.4 min
Range Se(IV) Peak
Full-Scale Concentration Height
y mho/cm (ppm) (y mho/cm)
1
1
1
1
1
1
1
1
3
3
3
3
10
10
10
10
30
30
30
0.1
.2
.3
.4
.5
.8
1.6
3.2
.8
1.6
3.2
6.4
3.2
6.4
10.0
20.0
10.0
20.0
40.0
0.03
.04
.07
.09
.11
.18
.35
.71
.17
.35
.71
1.45
.69
1.44
2.32
5.04
2.30
5.02
10.98
3
10
10
10
10
H(y mho/cm)
8.0
15.0
20.0
22.0
27.0
= (-3.2
(4.93
1.42
2.82
3.78
4.06
5.16
+ 2.1) +
+0.22) C (ppm)
H(ymho/cm) = 0.0088 + 0.2069 C + 0.00272 C2
0.000026 C3
-------
TABLE 13. SELENITE CALIBRATION
3 x 50 nun
500-rnm Anion
Range
Full-Scale
ymho/cm
1
1
1
1
1
1
1
1
3
3
3
3
1
1
1
3
3
10
3
1
Concentrator Column
Separator. Standard
Volume Ion
(mL)
25
50
5
10
25
10
5
10
25
5
10
25
50
10
25
25
10
50
50
25
/ 150-mm
Eluent,
Se ( IV)
Injected
(yg)
0.05
.10
.05
.10
.25
.02
.10
.20
.50
.25
.50
1.25
.10
.02
.05
1.25
.50
2.50
.50
.25
Precolumn and
Flow 2.56 mL/min.
Peak
Height
(y mho/cm)
.09
.23
.07
.16
.39
.05
.20
.37
.90
.51
.98
2.56
.16
.07
.14
2.35
.64
4.80
1.52
.59
H(ymho/cm) = (0.014 + 0.044) + (1.932 + 0.061) C (yg)
28
-------
TABLE 14. SULFATE CALIBRATION
0.1
Range
mL injection, 500-mm Anion
Standard Eluent, Flow 2.56
Sulfate
Full-Scale Concentration
umho/cm
1
1
1
3
3
3
3
10
10
10
10
30
30
30
30
30
30
(ppm)
1
2
4
2
4
8
12
8
12
16
20
16
20
50
100
100
150
Separator,
mL/min.
Peak
Height
(ymho/cm)
.10
.22
.42
.18
.42
.87
1.38
.85
1.34
1.89
2.36
1.71
2.24
6.38
13.82
14'. 06
20.26
H(ymho/cm) = (-0.247 + 0.066) + (0.1384 + 0.0013) C (ppm)
29
-------
TABLE 15. RETENTION TIMES AND DETECTION LIMITS OF ANIONS
Eluent: 2.4 mM Na2CO3 plus 3 mM
Flow: 2.56 mL/min.
3 x 500-mm Anion Separator Column
Ion
Cl
NO 2
SeO3
PO4
Br
NO3
SO4
SeO4
Retention
Time
(Min.)
3.5
4.5-5.0
5.9
7.0-7.6
9.5
11.1
15.5-16.7
29.2
Detection
Limit
(yg)
0.002
0.15 *
0.10 *
.008
0.07 *
0.15
0.14 *
0.20
0.011
* Determined on concentrator column; others, by direct
injection of 0.1 mL.
30
-------
REFERENCES
1. Hoove-r, T. B. Inorganic Species in Water: Ecological
Significance and Analytical Needs. EPA-600/3-78-064.
U.S. Environmental Protection Agency, Athens, QA (July
1978). 108 pp.
2. Sawicki, E. Potential of Ion Chromatography. In: Ion
Chromatographic Analysis of Environmental Pollutants, E.
Sawicki, J. D. Mulik, and E. Wittgenstein, eds. Ann Arbor
Science Publishers, Ann Arbor, MI (1978). pp. 1-9.
3. Ion Chromatographic Analysis of Environmental Pollutants.
Vol. 1. Sawicki, E., J.* D. Mulik, and E. Wittgenstein
(eds.). Ann Arbor Science Publishers, Ann Arbor, MI
(1978). 210 pp.
4. Mulik, J. D. and E. Sawicki. Ion Chromatography.
Environ. Sci. Technol. 13 (7), 804-809 (1979).
5. Small, H., T. S. Stevens, and W. C. Bauman. Novel Ion
Exchange Chromatographic Method Using Conductimetric
Detection. Anal. Chem. £7(11), 1801-1809 (Sept. 1975).
6. Kolthoff, I. M. and R. Belcher. Volumetric Analysis.
Vol. 3. Titration Methods: Oxidation-Reduction
Reactions. Interscience Publishers, New York (1957). p.
70.
7. Rieman, W. and H. F. Walton. Ion Exchange in Analytical
Chemistry. Pergamon Press, Oxford (1970). p. 100.
8. Colaruotolo, J. F. Organic Elemental Microanalysis by Ion
Chromatography. In: Ion Chromatographic Analysis of
Environmental Pollutants, E. Sawicki, J. D. Mulik, and E.
Wittgenstein, (eds.). Ann Arbor Science Publishers, Ann
Arbor, MI (1978). pp. 149-167.
9. Lathouse, J. and R. W. Coutant. Determination of Anions
in Filter Catch Samples. In: Ion Chromatographic
Analysis of Environmental Pollutants, E. Sawicki, J. D.
Mulik, and E. Wittgenstein, (eds.). Ann Arbor Science
Publishers, Ann Arbor, MI (1978). pp. 53-64.
31
-------
10. Wetzel, R. A., C. L. Anderson, H. Schleicher, and G. D.
Cook. Determination of Trace Level Ions by Ion Chromato-
graphy with Concentrator Columns. Anal. Chem. 5_1(9) ,
1532-1535 (Aug. 1979).
11. Natrella, M. G. Experimental Statistics. National Bureau
of Standards Handbook 91. U.S. Department of Commerce,
Washington, DC (1963). 5.18.
12. Hansen, L. D., B. E. Richter, D. K. Rollins, J. D. Lamb,
and D. J. Eatough. Determination of Arsenic and Sulfur
Species in Environmental Samples by Ion Chromatography-
Anal. Chem. 51(6), 633-637 (May 1979).
13. Koch, W. F. Complication in the Determination of Nitrite
by Ion Chromatography. Anal. Chem. 5_1(9) , 1571-1573
(August 1979).
32
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/4-80-020
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Ion Chromatography of Anions
5. REPORT DATE
March 1980 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Thomas B. Hoover and George D. Yager
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORG \NIZATION NAME AND ADDRESS
Environmental Research Laboratory
U.S. Environmental Protection Agency
Athens, Georgia 30605
10. PROGRAM ELEMENT NO.
A37B1D
11. CONTRACT/GRANT NO.
In-house
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Research Laboratory-Athens, GA
Office of Research and Development
U.S. Environmental Protection Agency
Athens, Georgia 30605
13. TYPE OF REPORT AND PERIOD COVERED
Interim, 7/78-7/79
14. SPONSORING AGENCY CODE
EPA/600/01
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A Dionex Model 10 Ion Chromatograph was evaluated for the
measurement of anionic species in water. The theoretical effect of
hydrogen ion activity (pH) on the elution time of phosphate and
arsenate was tested and empirical selectivity coefficients were
determined for the major protolytic species of these acids.
Calibration curves were obtained for arsenate, bromide, chloride,
nitrate, nitrite, phosphate, selenate, selenite, and sulfate by
direct injection of 0.1 mL of standards and, in most cases, by
preconcentration of 5 to 50 mL of solution on the ion exchange
concentrator columns available from the instrument manufacturer.
Detection limits for ions other than chloride were approximately 0.2
Ug independent of the method of sample introduction. For chloride
the detection limit was 2 ng, by direct injection. The concentrator
column permitted determination of any of the above ions at
concentrations greater than 10 yg/L.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COS AT I Field/Group
Chemical analysis
Water analysis
Anions
Concentrators
Ion Chromatography
07B
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)'
Unclassified
21. NO. OF PAGES
41
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
33
* U.S. GOVERNMENT MINTING OFFICE: 1980 -657-146/5625
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