ASTM: D5257: Chromium, Hexavalent, in Water by Ion Chromatography

Summary
Analytes
Revision
Data and Sites

Official Method Name

Standard Test Method for Dissolved Hexavalent Chromium in Water by Ion Chromatography

Current Revision

Current edition approved Dec. 10, 1997. Published December 1998. Originally published as D 5257 ? 92

Media

WATER

Instrumentation

Ion Chromatography

Method Subcategory

Inorganic

Method Source

ASTM

Citation

Annual Book of ASTM Standards, Section 11, Water and Environmental Technology, Volume 11.01, Water (I)

Brief Method Summary

A fixed volume of buffered and filtered sample, typically 100 mL, is injected into the eluant flow path and separated by anion exchange using an ammonium sulfate based eluant. After separation, the sample is reacted with an acidic solution of diphenylcarbohydrazide. Hexavalent chromium reacts selectively with this reagent to form the characteristic violet colored complex. The eluant stream passes through a photometric detector for detection of the chromium diphenylcarbohydrazide complex by visible absorbance at 530 nm. Absorbance is proportional to the hexavalent chromium concentration.

Scope and Application

This test method covers procedures for the determination of dissolved hexavalent chromium in waste water, surface water, and drinking water.

Applicable Concentration Range

1-1000 ug/L

Interferences

By virtue of the chromatographic separation essentially all interfering species are removed from the hexavalent chromium before detection. Interferences may result from overloading of the analytical 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 % Na₂SO₄ do not affect the separation or detection when using an anion exchange column and a 100 mL sample loop.
The response of 1 mg/L of hexavalent chromium is not affected by 1 g/L of chromic ion.
Reducing species may reduce hexavalent chromium in acidic matrices. Preservation at a pH 9 to 9.5 will minimize the effect of these species.
Trace amounts of Cr are sometimes found in reagent grade salts. Since a concentrated buffer solution is used in this test method to adjust the pH of samples, reagent blanks should be analyzed to assess the potential for Cr(VI) contamination. Contamination can also come from improperly cleaned glassware or contact with caustic or acidic reagents with chromium containing stainless steel or pigmented materials.

Quality Control Requirements

Sample Handling

Collect the sample in accordance with the applicable ASTM Standards as follows: Practice D 1066, Specification D 1192, or Practices D 3370.
Filter samples and adjust pH immediately upon sampling to minimize any interconversion between Cr III and Cr VI species. Filter the sample through a 0.45 um filter. Collect the filtrate and adjust its pH to 9 to 9.5 using the eluant concentrate (see Section 8.6). Ship and store samples at 4^oC. Bring to ambient temperature prior to analysis. Analyze this stabilized filtrate within 24 h. Adjust final calculations to account for sample dilution.

Maximum Holding Time

24 hours

Relative Cost

Unknown

Sample Preparation Methods

This method has 1 analyte associated with it.

Analyte	Detection Level	Bias	Precision	Pct False Positive	Pct False Negative	Spiking Level
Hexavalent chromium(18540-29-9) Chrome(VI) Chromium (+6) Chromium (VI) Chromium hexavalent ion Chromium(VI) Chromium, hexavalent Hexavalent chrome Hexavalent chromium	1.000 ug/L	108% Rec (ML)	13.70 % RSD (ML)			8.00 ug/L

Precision Descriptor Notes:	The following separator columns were used in the collaborative test: high capacity separator column and low capacity separator column. NOTE: The collaborative test of this test method was performed in reagent water and waste water by fifteen laboratories using one operator each. For reagent water the test used ten levels of concentration comprised of five Youden pairs ranging from 1.2 to 960 mg/L of hexavalent chromium. For waste water the test used eight levels of concentration comprised of four Youden pairs ranging from 6 to 960 mg/L of hexavalent chromium.
Detection Level Note:	None.

Precision Descriptor Notes:

The following separator columns were used in the collaborative test: high capacity separator column and low capacity separator column. NOTE: The collaborative test of this test method was performed in reagent water and waste water by fifteen laboratories using one operator each. For reagent water the test used ten levels of concentration comprised of five Youden pairs ranging from 1.2 to 960 mg/L of hexavalent chromium. For waste water the test used eight levels of concentration comprised of four Youden pairs ranging from 6 to 960 mg/L of hexavalent chromium.

Detection Level Note:

None.

Revision	PDF/Link
Current edition approved Dec. 10, 1997. Published December 1998. Originally published as D 5257 ? 92

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ASTM: D5257: Chromium, Hexavalent, in Water by Ion Chromatography

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