EPA-EAD: 1636: Hexavalent Chromium by Ion Chromatography
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Official Method Name
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Determination of Hexavalent Chromium by Ion Chromatography. |
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Current Revision
| January 1996 |
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Media
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WATER |
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Instrumentation
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Ion Chromatography |
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Method Subcategory
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Inorganic |
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Method Source
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Citation
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Brief Method Summary
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An aqueous sample is filtered through a 0.45 um filter and the filtrate is adjusted to a pH of 9-9.5 with a concentrated buffer solution. A measured volume of the sample is introduced into the ion chromatograph. A guard column removes organics from the sample before the Cr(VI), as CrO42-, is separated on a high capacity anion exchange separator column. Postcolumn derivatization of the Cr(VI) with diphenylcarbazide is followed by detection of the colored complex using an in-series spectrophometer. |
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Scope and Application
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This method determines dissolved hexavalent chromium as (CrO42-) in ambient waters at EPA water quality criteria (WQC) levels using ion chromatography (IC). |
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Applicable Concentration Range
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Not Available. |
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Interferences
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(A) Contamination by carryover: Contamination may occur when a sample containing low concentrations of metals is processed immediately after a sample containing relatively high concentrations of these metals. To reduce carryover, the sample introduction system may be rinsed between samples with dilute acid and reagent water. (B) Contamination by samples: Significant laboratory or instrument contamination may result when untreated effluents, in-process waters, landfill leachates, and other samples containing high concentrations of inorganic substances are processed and analyzed. (C) Contamination by indirect contact: Apparatus that may not directly come in contact with the samples may still be a source of contamination. It is imperative that every piece of the apparatus that is directly or indirectly used in the collection, processing, and analysis of ambient water samples be cleaned. (D) Contamination by airborne particulate matter: Samples may be contaminated by airborne dust, dirt, particles, or vapors from unfiltered air supplies; nearby corroded or rusted pipes, wires, or other fixtures; or metal-containing paint. (E) Reduction: Reduction of Cr(VI) to Cr(III) can occur in the presence of reducing species in an acidic medium. At pH 6.5 or greater, however, CrO42-, which is less reactive than HCrO42-, is the predominant species. (F) Overloading: Overloading of the analytical column capacity with high concentrations of anionic species, especially chloride and sulphate, will cause a loss of Cr(VI). |
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Quality Control Requirements
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The minimum requirements consist of an initial demonstration of laboratory capability, analysis of samples spiked with metals of interest to evaluate and document data quality, and analysis of standards and blanks as tests of continued performance. |
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Sample Handling
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Collect samples as described in EPA Method 1669. For dissolved Cr(VI), samples and field blanks are filtered through a 0.45 um capsule filter at the field site. Field preservation is advised for hexavalent chromium to provide sample stability for up to 30 days. Samples should be stored in polyethylene bags at 0-4oC until analysis. |
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Maximum Holding Time
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30 days (with preservation). 24 hours (without preservation). |
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Relative Cost
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$51 to $200 |
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Sample Preparation Methods
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None. |
