NEMI Method Summary

Method Summary Information

Method Number: D5257 Media: WATER
Revision: Current edition approved Dec. 10, 1997. Published December 1998. Originally published as D 5257 ? 92
Method Source: ASTM International
Subcategory: INORGANIC Analytes in this method
Official Name: Standard Test Method for Dissolved Hexavalent Chromium in Water by Ion Chromatography
Descriptive Name Chromium, Hexavalent, in Water by Ion Chromatography
Source Info: ASTM International
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Citation: ASTM Volume 11.01
 
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
Conc 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.
QC 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 4oC. Bring to ambient temperature prior to analysis. Analyze this stabilized filtrate within 24 h. Adjust final calculations to account for sample dilution.
Max Holding Time:
 24 hours
 
Relative Cost: Unknown
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