EPA-RCA: 7199: Chromium in Water by Ion Chromatography
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Official Method Name
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Determination of Hexavalent Chromium in Drinking Water, Groundwater and Industrial Wastewater Effluents by Ion Chromatography |
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Current Revision
| December 1996, Revision 0. |
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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 ?m filter and the filtrate is adjusted to a pH of 9 to 9.5 with a buffer solution. A measured volume of the sample (50-250 ?L) is introduced into the ion chromatograph. A guard column removes organics from the sample before the Cr(VI) as CrO4 2- is separated on an anion exchange separator column. Post-column derivatization of the Cr(VI) with diphenylcarbazide is followed by detection of the colored complex at 530 nm. |
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Scope and Application
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This method provides procedures for the determination of hexavalent chromium in drinking water, groundwater, and industrial wastewater effluents. Samples containing high levels of anionic species such as sulfate and chloride may cause column overload. Samples containing high levels of organics or sulfides cause rapid reduction of soluble Cr(VI) to Cr(III). |
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Applicable Concentration Range
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Interferences
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Interferences which affect the accurate determination of Cr(VI) may come contaminated reagents or glassware. Reduction of Cr(VI) to Cr(III) can occur in the presence of reducing species in an acidic medium. However, at a pH of 6.5 or greater, CrO4 2- which is less reactive than the HCrO-, is the predominant species. Overloading of the analytical column capacity with high concentrations of anionic species, especially chloride and sulfate, will cause a loss of Cr(VI). The column specified in this method can handle samples containing up to 5% sodium sulfate or 2% sodium chloride. Poor recoveries from fortified samples and tailing peaks are typical manifestations of column overload. |
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Quality Control Requirements
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Calibration curves should be composed of a minimum of a blank and three standards. Samples exceeding the highest calibration standard must be diluted and re-analyzed. A minimum of one method blank sample per sample batch must be analyzed to check for contamination. A method blank is reagent water prepared by adjusting the pH to between 9 and 9.5 with the same volume of buffer as used for the samples. A minimum of one duplicate sample and one matrix spike sample per sample batch must be analyzed for each analytical batch to check for duplicate precision and matrix-spike recovery. A quality control sample (QCS) must be analyzed at the beginning of each analytical run to validate the instrument calibration. |
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Sample Handling
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Prior to the collection of the sample, consideration should be given to the type of data required so that appropriate preservation and pretreatment steps can be taken. Filtration and pH adjustment should be performed at the time of sample collection or as soon thereafter as practically possible. For the determination of dissolved Cr(VI), the sample should be filtered through a 0.45-um filter. Use a portion of the sample to rinse the syringe filtration unit and filter and then collect the required volume of filtrate. Adjust the pH of the sample to 9-9.5 by dropwise addition of buffer solution (Section 5.7), periodically checking the pH with the pH meter or narrow pH-range pH paper. If salts are formed as a result of the pH adjustment, the filtrate must be filtered again prior to analysis. Approximately 10 mL of sample are sufficient for three IC analyses. Ship and store the samples at 4EC in 125-mL narrow-mouth, high-density polypropylene containers, or equivalent. Bring to ambient temperature prior to analysis. Samples should be analyzed within 24 hours of collection. |
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Maximum Holding Time
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24 hours after collection. |
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Relative Cost
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$51 to $200 |
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Sample Preparation Methods
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