ASTM D5257-97
(Test Method)Standard Test Method for Dissolved Hexavalent Chromium in Water by Ion Chromatography
Standard Test Method for Dissolved Hexavalent Chromium in Water by Ion Chromatography
SCOPE
1.1 This test method covers procedures for the determination of dissolved hexavalent chromium in waste water, surface water, and drinking water.
1.2 The precision and bias of this test method has been tested in reagent water and industrial waste water and has been found suitable over the range of approximately 1 to 1000 [mu]g/L. See Table 1 for details. Higher levels can be determined by appropriate dilution.
1.3 Samples containing very high levels of anionic species (that is, chloride, sulfate, etc.) may cause column overload. Samples containing high levels of reducing species (that is, sulfides, sulfites, etc.) may cause reduction of Cr(VI) to Cr(III). This can be minimized by buffering the sample to a pH of 9 to 9.5, filtering it, storing it at 4°C and analyzing it within 24 h.
1.4 The values stated in SI units are to be regarded as the standard.
1.5 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
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Designation:D 5257–97
Standard Test Method for
Dissolved Hexavalent Chromium in Water by Ion
Chromatography
This standard is issued under the fixed designation D 5257; 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 (ϵ) indicates an editorial change since the last revision or reapproval.
TABLE 1 Determination of Precision and Bias for Hexavalent
1. Scope
Chromium
1.1 This test method covers procedures for the determina-
Amount Amount
Water Bias,
tion of dissolved hexavalent chromium in waste water, surface
A
Added, Found, S S
t o
Matrix %
water, and drinking water.
µg/L µg/L
1.2 The precision and bias of this test method has been
Reagent 1.2 1.40 0.16 0.15 + 16.6
tested in reagent water and industrial waste water and has been 1.6 1.87 0.65 . + 16.9
6.0 6.68 1.03 0.53 + 11.3
found suitable over the range of approximately 1 to 1000 µg/L.
8.0 8.64 1.10 . + 8.0
See Table 1 for details. Higher levels can be determined by
16.0 17.4 2.25 0.77 + 8.8
20.0 21.4 2.31 . + 7.0
appropriate dilution.
100 101 1.91 3.76 + 1.0
1.3 Samples containing very high levels of anionic species
140 143 5.52 . + 2.1
(that is, chloride, sulfate, etc.) may cause column overload.
800 819 24.3 12.7 + 2.4
960 966 18.5 . + 7.3
Samples containing high levels of reducing species (that is,
Waste 6.0 5.63 1.17 0.55 −6.2
sulfides,sulfites,etc.)maycausereductionofCr(VI)toCr(III).
8.0 7.31 1.91 . −8.6
This can be minimized by buffering the sample to a pH of 9 to
16.0 15.1 2.70 1.85 −5.6
20.0 19.8 1.01 . −1.0
9.5, filtering it, storing it at 4°C and analyzing it within 24 h.
100 98.9 4.36 3.31 −1.1
1.4 The values stated in SI units are to be regarded as the
140 138 8.39 . −1.4
standard.
800 796 60.6 27.1 −0.5
960 944 72.1 . −1.7
1.5 This standard does not purport to address all of the
A
Each Youden pair was used to calculate one lab data point, S .
safety concerns, if any, associated with its use. It is the
o
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
Chromium in DrinkingWater, Groundwater and Industrial
bility of regulatory limitations prior to use.
Wastewater Effluents by Ion Chromatography
2. Referenced Documents
3. Terminology
2.1 ASTM Standards:
3.1 Definitions—For definitions of terms used in this test
D 1066 Practice for Sampling Steam
method, refer to Terminology D 1129D 1129.
D 1129 Terminology Relating to Water
3.2 Definitions of Terms Specific to This Standard:
D 1192 Specification for Equipment for Sampling Water
3.2.1 eluant— the ionic mobile phase used to transport the
and Steam in Closed Conduits
sample through the ion exchange column.
D 1193 Specification for Reagent Water
3.2.2 resolution—the ability of a column to separate con-
D 2777 Practice for Determination of Precision and Bias of
stituents under specified test conditions.
Applicable Methods of Committee D-19 on Water
4. Summary of Test Method
D3370 Practices for Sampling Water from Closed Con-
duits
4.1 Afixedvolumeofbufferedandfilteredsample,typically
2.2 EPA Standard:
100 µL, is injected into the eluant flow path and separated by
EPA Method 218.6 Determination of Dissolved Hexavalent
anion exchange using an ammonium sulfate based eluant.
4.2 After separation, the sample is reacted with an acidic
solution of diphenylcarbohydrazide. Hexavalent chromium
reacts selectively with this reagent to form the characteristic
This test method is under the jurisdiction ofASTM Committee D-19 on Water
violet colored complex.
and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents
in Water.
Current edition approved Dec. 10, 1997. Published December 1998. Originally
published as D 5257 – 92. Last previous edition D 5257 – 93. Available from Superintendent of Documents, U.S. Government Printing
Annual Book of ASTM Standards, Vol 11.01. Office, Washington, DC 20402.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
D 5257–97
4.3 Theeluantstreampassesthroughaphotometricdetector
for detection of the chromium diphenylcarbohydrazide com-
plex by visible absorbance at 530 nm. Absorbance is propor-
tional to the hexavalent chromium concentration.
5. Significance and Use
5.1 Hexavalent chromium salts are used extensively in the
metal finishing and plating industries, in the leather industry as
a tanning agent, and in the manufacture of paints, dyes,
explosives, and ceramics. Trivalent chromium salts are used as
mordants in textile dying, in the ceramic and glass industry,
and in photography. Chromium, in either oxidation state, may
bepresentinwastewaterfromtheseindustriesandmayalsobe
discharged from chromate-treated cooling waters.
5.2 Hexavalent chromium is toxic to humans, animals, and
aquatic life. It can produce lung tumors when inhaled and
readily induces skin sensitization. It is not known whether
cancer will result from ingestion of chromium in any of its
valence states.
5.3 Ion chromatography provides a means of separating the
hexavalentchromiumfromotherspeciespresentinthesample,
many of which interfere with other detection methods. The
combination of this separation with a sensitive colorimetric
detection method provides a selective and sensitive analytical
method for hexavalent chromium with minimal sample prepa-
ration.
6. Interferences
6.1 By virtue of the chromatographic separation essentially
all interfering species are removed from the hexavalent chro-
mium before detection.
6.2 Interferences may result from overloading of the ana-
lytical column capacity with high concentrations of anionic
species in the sample. Concentrations of chloride ion or sulfate
ion up to the equivalent of 1 % NaCl and 3 % Na SO do not
2 4
FIG. 1 Diagram of an Ion Chromatograph Using Post-Column
affect the separation or detection when using an anion ex-
Reagent Addition and Photometric Detection
change column and a 100 µL sample loop.
6.3 The response of 1 mg/L of hexavalent chromium is not
7.1.3 Guard Column— A column placed before the separa-
affected by 1 g/L of chromic ion.
tor column to protect the separator column from fouling by
6.4 Reducing species may reduce hexavalent chromium in
particles or strongly absorbed organic constituents.
acidic matrices. Preservation at a pH 9 to 9.5 will minimize the
7.1.4 Analytical Column—A liquid chromatographic col-
effect of these species.
umn packed with a polymeric anion exchange resin capable of
6.5 Trace amounts of Cr are sometimes found in reagent
separating chromate from other anions in a sample containing
grade salts. Since a concentrated buffer solution is used in this
high total dissolved solids (for example 3 % Na SO ).
2 4
test method to adjust the pH of samples, reagent blanks should
7.1.5 Reagent Delivery Module—A device capable of de-
be analyzed to assess the potential for Cr(VI) contamination.
livering 0 to 2 mL/min of reagent against a backpressure of up
Contamination can also come from improperly cleaned glass-
to 60 psi.
ware or contact with caustic or acidic reagents with chromium
7.1.6 Mixing Tee and Reaction Coil—A device capable of
containing stainless steel or pigmented materials.
mixingtwoflowingstreamsprovidingasufficientreactiontime
for post column reaction with minimal band spreading.
7. Apparatus
7.1.7 Detector—A low-volume, flow-through UV-visible
7.1 Ion Chromatograph—An ion chromatograph having the absorbance detector with a non-metallic flow path. The recom-
following components configured as shown in Fig. 1. mended detection wavelength for hexavalent chromium is 530
7.1.1 Pump, capable of delivering a constant flow in the nm.
range of 1 to 5 mL/min at a pressure of 200 to 2000 psi. 7.2 Recorder, Integrator, Computer—A device compatible
7.1.2 Injection Valve— A high pressure, low dead volume with detector output, capable of recording detector response as
valve that allows introduction of 50 to 250 µL of sample into a function of time for the purpose of measuring peak height or
the eluant stream at up to 2000 psi. area.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
D 5257–97
7.3 Eluant Reservoir— A container suitable for storing for each column is described in 8.7.1 and 8.7.2. Eluants should
eluant. be filtered through a 0.45-µm filter and degassed.
7.4 Syringe—A syringe equipped with a male luer type 8.7.1 Eluant for IonPacAS7 Column (0.250 M(NH ) SO ,
4 2 4
fitting and a capacity of at least 1 mL. 0.1 M NH OH)—Add 100 mL of eluant concentrate (8.6)toa
7.5 Summary of Column Requirements: 1 L volumetric flask and dilute to volume with water.
7.5.1 Guard Column— A short liquid chromatographic 8.7.2 Eluant for IC Pac Anion HC Column (0.025 M (NH )
column capable of removing organics from the injected sample 2SO , 0.01 M NH OH)—Add 10 mL of eluant concentrate
4 4
so as to minimize organic fouling of the separator column. (8.6)toa1Lvolumetric flask and dilute to volume with water.
7.5.2 Analytical Column—An anion exchange column ca- 8.8 Diphenylcarbohydrazide Reagent—Dissolve 0.5 g of
pable of providing suitable retention and chromatographic 1,5-diphenylcarbohydrazidein100mLofreagentgrademetha-
efficiency for chromate ion even in the presence of high nol. Add to about 500 mL of water containing 28 mL of
amounts of dissolved solids that can occur in waste water concentrated sulfuric acid. Dilute with water, while stirring, to
samples. Note that high capacity columns will tolerate higher 1Linavolumetricflask.Filteranddegasifnecessarytoensure
dissolved solids before becoming overloaded. See Section 13 reliable delivery.
for details of the columns used in the collaborative test of this
test method.
9. Sampling
9.1 Collect the sample in accordance with the applicable
8. Reagents
ASTM Standards as follows: Practice D 1066D 1066, Specifi-
8.1 Purity of Reagents—Reagent grade chemicals shall be
cation D 1192D 1192, or Practices D 3370 D3370.
used in all tests. Unless otherwise indicated, it is intended that
9.2 Filter samples and adjust pH immediately upon sam-
all reagents shall conform to the specifications of the Commit-
pling to minimize any interconversion between Cr III and Cr
tee on Analytical Reagents of the American Chemical Society
VI species. Filter the sample through a 0.45 µm filter. Collect
where such specifications are available. Other grades may be
the filtrate and adjust its pH to 9 to 9.5 using the eluant
used, provided it is first ascertained that the reagent is of
concentrate (see 8.6). Ship and store samples at 4°C. Bring to
sufficiently high purity to permit its use without lessening the
ambient temperature prior to analysis. Analyze this stabilized
accuracy of the determination.
filtrate within 24 h. Adjust final calculations to account for
8.2 Purity of Water— Unless otherwise indicated, refer-
sample dilution.
ences to water shall be understood to mean reagent water
conforming to Specification D 1193D 1193, Type I. Other
10. Calibration
reagent water types may be used provided it is first ascertained
10.1 Prepare at least three levels of standards for each
that the water is of sufficiently high purity to permit its use
decade of the concentration range of interest. For standards of
without adversely affecting the bias and precision of the test
1 to 1000 µg/L, prepare by diluting measured volumes of the
method. Type II water was specified at the time of round robin
standard chromium solution (see 8.4) with water in separate
testing of this test method.
volumetric flasks.
8.3 Chromium Solution, Stock (1000 mg Cr/L)—Dissolve
10.2 Determine the chromium response for each of the
0.2828 g of potassium dichromate (K Cr O that has been
2 2 7
standards and blank using the procedure defined in Section 11.
dried at 105°C for 1 h) in water. Add 0.1 mL of eluant
10.3 Prepare a calibration curve by using a linear plot of the
concentrate (8.6) to ensure analyte stability. Dilute to 100 mL
peak height or area as a function of standard concentration. Do
in a volumetric flask.
not force the calibration curve through zero. The response of
8.4 Chromium Solution, Standard (1000 µg Cr/L)—Pipet
the reagent blank should be less than 0.1 µg/L hexavalent
1.00 mL of chromium stock solution (see 8.3)and1mLof
chromium.
eluantconcentrateintoa1Lvolumetricflask.Dilutetovolume
10.4 Prepare a new calibration curve when new reagents are
with water.
made or the hardware is altered.
8.5 Reagent Blank— Add 1 mL of eluant concentrate (8.6)
toa1L flask and dilute to volume with the water used to
11. Procedure
prepare the chromium standards.
11.1 Set up the ion chromatograph in accordance with the
8.6 Eluant Concentrate (2.5 M (NH ) SO , 1.0 M
4 2 4
manufacturer’s instructions.
NH OH)—Dissolve 330 g of ammonium sulfate (NH ) SO in
4 4 2 4
11.2 Adjust the eluant flow rate to 1.5 mL/min. Increase the
about500mLofwater.Add65mLofconcentratedammonium
flow of the post-column reagent until the flow rate from the
hydroxide (NH OH to sp gr 0.90). Mix well and dilute to 1 L
detector outlet line is 2.0 mL/min. so as to have a reagent flow
in a volumetric flask.
of 0.5 mL/min under operating conditions. Measure the pH of
8.7 Eluant—Two different analytical anion exchange col-
the detector effluent to confirm it is 2 or lower.
umns proved satisfactory in the collaborative test that is
11.3 After the flow rates are adjusted, allow the system to
summarized in Section 13.Accordingly, the eluant appropriate
equilibrate for about 15 min.
11.4 Ifusingafixedvolumesampleloop(typically100µL),
“Reagent Chemicals American Chemical Society Specifications” Am. Chemi-
load at least 1 mL of sample through the sample port using an
cal Soc., Washington, DC. For suggestions on the testing of reagents not listed by
appropriate syringe. Inject the sample into the eluant stream
theAmerican Chemical Society, see “Analar Standards for Laboratory Chemicals,”
BDH Ltd., Poole, Dorset, U.K., and the “United States Pharmacopeia.” and record the chromatogram (see Fig. 2). If using a variable
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
D 5257–97
C = µg Cr(VI)/L read from the calibration curve,
F = volume o
...
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