Designation: E1787 − 08

Standard Test Method for

Anions in Caustic Soda and Caustic Potash (Sodium
Hydroxide and Potassium Hydroxide) by Ion
Chromatography1
This standard is issued under the fixed designation E1787; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.

1. Scope* 2. Referenced Documents

1.1 This test method covers the determination of anionic 2.1 ASTM Standards:2
impurities in 50 % caustic soda (sodium hydroxide) and 50 % D1193 Specification for Reagent Water
caustic potash (potassium hydroxide) solutions using ion E180 Practice for Determining the Precision of ASTM
chromatography (IC). Anions that can be determined at con- Methods for Analysis and Testing of Industrial and Spe-
centrations of approximately 0.1–1000 ug/g (ppm) include: cialty Chemicals (Withdrawn 2009)3
bromide, chlorate, chloride, fluoride, nitrate, phosphate, and E291 Test Methods for Chemical Analysis of Caustic Soda
sulfate. and Caustic Potash (Sodium Hydroxide and Potassium
1.2 By varying the sample size, this test method can be used Hydroxide)
for anhydrous caustic soda and caustic potash products, as well 3. Summary of Test Method
as other concentrations of liquid products.
3.1 Bromide, chlorate, chloride, fluoride, nitrate, phosphate
1.3 This test method is not intended to be used to quantify and sulfate are measured in NaOH or KOH by ion chromatog-
chloride in caustic soda where the sodium chloride concentra- raphy. The sample solution is diluted and injected onto a
tion is approximately 1 %. For the most accurate sample loop of an automated neutralization module. The
determinations, it is recommended that high concentrations of sample in the loop is pumped to a suppression device which
chloride be analyzed using a potentiometric titration procedure, uses electrolysis to neutralize the hydroxide ions. The sample
such as the one described in Test Methods E291. then is circulated through this device several times until it is
1.4 The values stated in SI units are to be regarded as completely neutralized. Anionic constituents of the neutralized
standard. The values given in parentheses are for information sample are concentrated on an anion concentrator column.
only. After the concentration they are separated into individual
elution bands in the eluent on a separator column. The
1.5 Review the current appropriate Material Safety Data
conductivity of the eluent is reduced with an anion suppression
Sheets (MSDS) for detailed information concerning toxicity,
device, and the anions of interest are detected using a conduc-
first aid procedures, and safety precautions.
tivity detector. Quantitation of the anions in the sample
1.6 This standard does not purport to address all of the solution is achieved by calibrating the IC with a series of
safety concerns, if any, associated with its use. It is the standards containing known amounts of the anions. These
responsibility of the user of this standard to establish appro- standards are also passed through the neutralization device.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. Specific hazards 4. Significance and Use
statements are given in Section 8. 4.1 Anion impurities in caustic soda and caustic potash are
monitored by manufacturers and users for quality control of the

1 2
This test method is under the jurisdiction of ASTM Committee E15 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Industrial and Specialty Chemicals and is the direct responsibility of Subcommittee contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
E15.01 on General Standards. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved April 1, 2008. Published May 2008. Originally the ASTM website.
3
published in 1996. Last previous edition approved in 2002 as E1787-02. DOI: The last approved version of this historical standard is referenced on
10.1520/E1787-08. www.astm.org.

*A Summary of Changes section appears at the end of this standard

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States

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 E1787 − 08
products. Anions of primary interest are chloride, chlorate, and vided it is first ascertained that the reagent is of sufficiently
sulfate. This test method has determined precision estimates high purity to permit its use without lessening the accuracy of
only for these three impurities. the determination.
5. Interferences 7.2 Purity of Water—References to water means Type 1 (18
MΩ-cm deionized water) conforming to Specification D1193.
5.1 Substances that coelute with the anions of interest will
interfere. A high concentration of one anion can interfere with 7.3 Anion Stock Standards, 1000 ug/g (ppm):
accurate quantitation of another anion if their retention times 7.3.1 Bromide Stock Solution (1.00 mL = 1.00 mg
are close and resolution is affected. For example, caustic soda Bromide)—Dry sodium bromide (NaBr) for 6 h at 150°C and
samples containing large concentrations of chloride can inter- cool in a desiccator. Dissolve 1.288 g of the dried NaBr in
fere with the quantitation of small amounts of fluoride. water, dilute to 1 L with water, and mix well.
Selection of a high capacity anion separator column will 7.3.2 Chlorate Stock Solution (1.00 mL = 1.00 mg
minimize this problem. Chlorate)—Dissolve 1.275 g of sodium chlorate (NaClO3) in
5.2 Organic acids, surfactants, dyes, metals, etc., can cause water, dilute to 1 L with water, and mix well.
fouling of the columns and membranes used in this test 7.3.3 Chloride Stock Solution (1.00 mL = 1.00 mg
method, resulting in interferences and decreased sensitivity. It Chloride)—Dry sodium chloride (NaCl) for 1 h at 100°C and
is very important to follow the manufacturer’s recommenda- cool in a desiccator. Dissolve 1.648 g of the dried NaCl in
tions for cleaning and maintaining the various parts of the IC water, dilute to 1 L with water, and mix well.
system. 7.3.4 Fluoride Stock Solution (1.00 mL = 1.00 mg
5.3 The anion concentrator column in the neutralization Fluoride)—Dry sodium fluoride (NaF) at 105°C for at least 8
module has a finite capacity for trapping anions, approximately h and cool in a desiccator. Dissolve 2.210 g of the dried NaF
25 micro-equivalents per column. When the capacity of the in 500 mL of water, dilute to 1 L with water, and mix well.
column is exceeded, the stripping of anions will not be 7.3.5 Nitrate Stock Solution (1.00 mL = 1.00 mg Nitrate)—
quantitative. Dry sodium nitrate (NaNO3) at 105°C for 48 h and cool in a
desiccator. Dissolve 1.371 g of the dried NaNO3 in water,
6. Apparatus dilute to 1 L with water, and mix well.
6.1 Ion Chromatograph, equipped with: 7.3.6 Phosphate Stock Solution (1.00 mL = 1.00 mg
6.1.1 Conductivity Detector, Phosphate)—Dissolve 1.433 g of potassium dihydrogen phos-
6.1.2 Anion Separator Column, phate (KH2PO4) in water, dilute to 1 L with water, and mix
6.1.3 Guard Column, well.
6.1.4 100-µL Sample Loop, 7.3.7 Sulfate Stock Solution (1.00 mL = 1.00 mg Sulfate)—
6.1.5 Autoneutralization Device, capable of neutralizing the Dry sodium sulfate (Na2SO4) for 1 h at 105°C and cool in a
caustic sample prior to being directed through the separator desiccator. Dissolve 1.479 g of the Na2SO4 in water, dilute to
column, 1 L with water, and mix well.
6.1.6 Post-Column Chemical Suppression Device, capable 7.4 Eluent—The eluent used for the anion analysis will
of reducing background conductivity due to the eluent, and depend on the choice of separator column selected. The eluent
6.1.7 Data Acquisition System, such as an integrator or described below is used with the Dionex AS-12A separator
computer system. column.
6.2 100-mL Volumetric Flasks, for preparing sample solu- 7.4.1 Eluent Concentrate, 0.27 mol/L (M) Sodium
tions. Carbonate/0.03 mol/L (M) Sodium Bicarbonate (100×
6.3 Disposable 10-mL Syringes, for injecting solution into Concentrate)—Dissolve 28.6 g of sodium carbonate and 2.52 g
the IC. of sodium bicarbonate in a 1- L volumetric flask containing
6.3.1 IC Autosampler (optional), can be used as an alterna- 800 mL of water. Dilute to volume with water and mix. Store
tive to manually injecting samples. in a tightly capped polypropylene bottle.
7.4.2 Eluent, 2.7 mmol/L (mM) Sodium Carbonate/0.3
7. Reagents mmol/L (mM) Sodium Bicarbonate Eluent—Pipet 20.0 mL of
7.1 Purity of Reagents—Reagent grade chemicals should be the eluent concentrate into a 2-L volumetric flask, dilute to the
used in all tests. Unless otherwise indicated, all reagents must mark with water, and mix.
conform to the specifications of the Committee on Analytical
Reagents of the American Chemical Society, where such 8. Hazards
specifications are available.4 Other grades may be used pro- 8.1 Sodium and potassium hydroxides are caustic alkalies,
which in their anhydrous or strong solution form, are hazard-
4
Reagent Chemicals, American Chemical Society Specifications , American ous materials. In contact with the skin they produce burns that
Chemical Society, Washington, DC. For suggestions on the testing of reagents not may be quite serious unless promptly treated. Their action is
listed by the American Chemical Society, see Analar Standards for Laboratory
insidious since they produce no immediate stinging or burning
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, sensation, and damage may result before their presence is
MD. realized.

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 E1787 − 08
TABLE 1 Ion Chromatograph—Typical Analytical Conditions
Anion separator column: AS-12A
Guard column: AG-12A
Eluent: 2.7 mmol/L Na2CO3/0.3 mmol/L NaHCO3
Eluent flow rate: 1.5 mL/min
Sample loop: 100 µL
Eluent suppression: ASRS, recycle mode
Neutralization cycles: 2

the elution order of various anions from the Dionex AS-12A

separator column using the carbonate/bicarbonate eluent.
9.2 Calibrate the ion chromatograph using a series of
calibration standards. Each standard should contain all the
anions of interest. The concentration of anions in this series of
standards should be prepared so they bracket the expected
concentration of anions in the diluted sample. After the
standards have been analyzed by IC, the “best-fit” straight line
is determined for each anion using the concentration versus IC
area counts. If the IC is equipped with a computer operated
software or an integrator, calibration should be done according
to manufacturer’s instructions for multi-level external standard
Peak # Retention Time (min) Component
1 1.90 Fluoride
calibrations. If an integrator or computer is not used, calibra-
2 2.44 Chlorite tion curves can be created on graph paper by plotting concen-
3 2.94 Bromate tration versus peak area for each anion of interest and drawing
4 3.30 Chloride
5 4.15 Nitrite the “best-fit” straight line through the points.
6 6.61 Bromide 9.2.1 A typical calibration would include a series of four to
7 7.08 Chlorate five standards containing the anions of interest from 0.1–10
8 7.82 Nitrate
9 9.03 Phosphate µg/mL (ppm).
10 11.02 Sulfate
10. Procedure
FIG. 1 Typical Chromatogram of Anions Eluting from a AS-12A
Separator Column Using Na2CO3/NaHCO3 Eluent 10.1 Set up the ion chromatograph and the automated
neutralization device according to the manufacturer’s instruc-
tions. The IC system can be set up to accommodate the use of
an autosampler or manual injection with a syringe. The
8.2 Eyes are particularly vulnerable to severe damage from detector ranges are variable. The range setting required for the
these alkalies. analysis will depend on the concentration of anions in the
8.3 Use safety goggles or face shields and rubber gloves sample and should be chosen accordingly. Table 1 lists typical
when handling these alkalies, and avoid spillage on clothing. analytical conditions for the anion analysis by IC.
These materials rapidly attack wool and leather. NOTE 1—Styrene-based strong acid resin in the H+ form and commer-
8.4 Flush away spilled caustic with water where possible, or cially available neutralization cartridges containing this resin have been
used to neutralize caustic samples prior to introduction into an IC. Their
cover with absorbent material (such as sawdust, vermiculite, or use can eliminate the need for sophisticated on-line neutralization devices.
baking soda), and sweep up and discard in accordance with all Even when rinsed thoroughly, however, they introduce contaminants
federal, state, and local health and environmental regulations. (especially chloride and sulfate) to the sample solution and are not
Last traces may be neutralized with dilute acetic acid and the recommended for determining anions with concentrations less than 50
ug/g (ppm) in caustic soda or caustic potash.
area washed with water. NOTE 2—A chemical suppression device or commercially available
8.5 Consult Material Safety Data Sheets (MSDS) for chemi- neutralization cartridge installed in the IC system before the separator
cals listed in this test method for further information. column, has been successfully used as a replacement for the automated
neutralization module to neutralize caustic soda and caustic potash
samples. By using this approach, however, the 50 % solutions of caustic
9. Calibration soda and caustic potash must be diluted by a ratio of 100:1. The
9.1 The retention time for each anion is determined by quantitation limits using this modified technique, therefore, are corre-
spondingly higher. Details of the modification are not given in this test
injecting a series of standard solutions, each containing only method.
one anion of interest, into the IC and recording the time
required for a peak to appear on the chromatogram. Retention 10.2 Equilibrate the system by pumping eluent through the
times vary with operating conditions. The standards, therefore, columns and the detector until a stable baseline is obtained
must be chromatographed in the same manner as the sample (approximately 15 to 20 min).
solutions, which includes passing them through the autoneu- 10.3 Sample solutions are prepared by transferring a known
tralization module. Fig. 1 is a typical chromatogram that shows weight of sample (weighed to the nearest 0.01 g) to a 100-mL

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 E1787 − 08
TABLE 2 Recommended Sample Amount for IC Analysis where:
Anion Concentration, µg/mL Sample Dilution, g/100 mL 20 000 000 = A, area counts of Cl peak from
<1 50 chromatogram,
1–10 20–50
10–100 10–20
1 × 10−7 = R, the Cl response factor from calibration,
100–1000 1–10 (µg/mL)/area count,
>1000 <1 100 = B, final volume of sample solution, mL,
10.00 = G, sample size, g,
58.44 = molecular wt. of NaCl, and
35.45 = molecular wt. of Cl.
12. Report
volumetric flask and diluting to volume with water. The
amount of dilution is dependent on levels of anions in the 12.1 Report the concentration of each anion of interest in
sample. In many cases, when both high level and lower levels ug/g (wt./wt.) basis as follows:
of anions are to be quantified in the same sample, two or more Anion, ug/g Report to nearest, ug/g
sample solutions of different dilutions may have to be ana- $10 1
$1 & <10 0.5
lyzed. The neutralization module is capable of neutralizing <1 0.1
solutions containing 25 % sodium hydroxide when the solution
is cycled through the neutralizer at least twice. Sample solu- 13. Precision and Bias
tions containing up to 50 g of 50 % product or 25 g of 13.1 The following criteria should be used for judging the
anhydrous, therefore, can be neutralized effectively. Table 2 acceptability of results (see Note 3).
can be used as a general guideline of sample dilutions based on 13.1.1 Repeatability (Single Analyst)—The standard devia-
expected concentrations of individual anions. An IC calibration tion for a single determination has been estimated to be the
covering the range of 0.1 to 10 µg/mL has been assumed. value shown in Table 3 at the indicated degrees of freedom.
The 95 % limit for the difference between two such runs is
10.4 Inject the sample into the ion chromatograph and
given also in the table.
record the ion chromatogram of anions in caustic. Fig. 2 shows
13.1.2 Laboratory Precision (Within-Laboratory, Between-
an IC chromatogram of 45 % caustic potash that was diluted 20
Days Variability)—The standard deviation of results (each the
g/100 mL.
average of duplicates) obtained by the same analyst on
different days, has been estimated to be the value shown in
11. Calculation
Table 3 at the indicated degrees of freedom. The 95 % limit of
11.1 Calculate the concentration of each anion of interest the difference between two such averages is given also in the
using the peak area of that anion from the sample chromato- table.
gram and response factor derived from “best-fit” linear equa- 13.1.3 Reproducibility (Multilaboratory)—The standard de-
tion obtained during the calibration procedure. viation of results (each the average of duplicates), obtained by
A 3R 3B analysts in different laboratories, has been estimated to be the
Anion, ppm ~ wt./wt. basis! 5 (1) value shown in Table 3 at the indicated degrees of freedom.
G
The 95 % limit for the difference between two such averages is
where: given also in the table.
A = area of anion peak from the chromatogram of the
NOTE 3—The precision estimates are based on an interlaboratory study
diluted sample, area counts, conducted in 1995 on one sample of 50 % caustic soda and one sample of
B = final volume of diluted sample, mL, 45 % caustic potash. The samples were analyzed for chloride, chlorate,
R = response factor from “best-fit” calibration line, (µg/ and sulfate. One analyst in each of six laboratories performed duplicate
mL)/area counts, and determinations on each of two days. Practice E180 was used in developing
G = sample weight, g. these precision estimates.5

11.2 Concentration of the sodium or potassium salt of the 13.2 Bias—The bias of this test method has not been
anion can be calculated as follows: determined because of the lack of acceptable reference mate-
rial.
molecular wt. of anion salt
Salt concentration 5 anion conc. 3 (2) 14. Keywords
molecular wt. of anion
11.3 Example Calculations: 14.1 bromide; caustic potash; caustic soda; chlorate; chlo-
ride; chromatography; fluoride; ion chromatography; nitrate;
20 000 000 3 1 3 1027 3 100
Cl, ppm 5 5 20 (3) phosphate; potassium hydroxide; sodium hydroxide; sulfate
10.00
20 3 58.44 5
Supporting data have been filed at ASTM International Headquarters and may
NaCl, ppm 5 5 33 (4)
35.45 be obtained by requesting Research Report RR:E15-1060.

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 E1787 − 08

Retention
Time, min Component Conc., ug/g Area
3.96 Chloride 6.7 38 702 776
8.05 Chlorate 5.3 9 926 832
11.79 Sulfate 0.8 3 537 308

FIG. 2 Typical Chromatogram of 45 % Caustic Potash (Diluted 20 g/100 mL) Using AS-12A Separator Column and 2.7 mmol/L Na2CO3/
0.3 mmol/L NaHCO3 Eluent

TABLE 3 Precision for Anions by IC Method

Repeatability Laboratory Precision Reproducibility
Average 95 %
Material Anion Concentration, 95 % Range 95 % Range
Standard Degrees of Standard Degrees of Standard Degrees of Range
ug/g ug/g, ug/g,
Deviation Freedom Deviation Freedom Deviation Freedom ug/g,
absolute absolute
absolute
50 % NaOH Cl 90 1.95 10 5.4 2.33 5 6.5 4.62 4 12.9
ClO3 11 0.341 12 0.95 0.470 6 1.3 2.02 5 5.6
SO4 291 3.74 8 10.5 1.79 4 5.0 11 3 30.8
45 % KOH Cl 7.9 0.254 12 0.71 0.273 6 0.76 1.21 5 3.4
ClO3 4.9 0.070 12 0.19 0.133 6 0.37 0.862 5 2.4
SO4 0.8 0.110 8 0.31 0.147 4 0.41 0.30 3 0.84

SUMMARY OF CHANGES

Committee E15 has identified the location of selected changes to this standard since the last issue (E1787–02)
that may impact the use of this standard.

(1) Updated units of measure to comply with the International (3) Added 1.5 stating to review the current appropriate Mate-
System of Units (SI). rial Safety Data Sheets (MSDS) for detailed information
(2) Added 1.4 stating that the SI units are to be considered concerning toxicity, first aid procedures and safety precautions.
standard. (4) Added Summary of Changes.

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 E1787 − 08

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