EPA-OW: 218.7: Hexavalent Chromium in Water by Ion Chromatography
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Official Method Name
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Method 218.7: Determination of Hexavalent Chromium in Drinking Water by Ion Chromatography with Post-Column Derivatization and UV–Visible Spectroscopic Detection |
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Current Revision
| Version 1.0, November 2011 |
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Media
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WATER |
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Instrumentation
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Ion Chromatography with Post-Column Derivatization and UV–Visible Spectroscopic Detection |
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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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Samples are preserved with a combined buffer/dechlorinating reagent which complexes free chlorine and increases the pH to a value greater than eight. A measured volume (usually 1 mL) of the sample is introduced into an ion chromatograph. CrO42- is separated from other matrix components on an anion exchange column. CrO42- is derivatized with 1,5-diphenylcarbazide in a post-column reactor and is detected spectrophotometrically at a wavelength of 530 nm. Cr(VI) is qualitatively identified via retention time, and the concentration of CrO42- in the sample is calculated using the integrated peak area and the external standard technique. Results are reported in units of ug/L of Cr(VI). |
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Scope and Application
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Method 218.7 provides procedures for the determination of hexavalent chromium Cr(VI) as the chromate anion CrO42- in finished drinking water using ion chromatography. Samples are analyzed by direct injection. This method is intended for use by analysts skilled in the operation of ion chromatographic instrumentation and in the interpretation of the associated data. |
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Applicable Concentration Range
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0.012 to 0.036 |
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Interferences
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Use high-density polyethylene (HDPE) or polypropylene copolymer sample bottles. Reagents and the ion chromatographic system must be routinely demonstrated to be free from interferences. To ensure sample integrity, Cr(VI) must be protected from reduction, and Cr(III), if present, must not oxidize to Cr(VI) during sample storage. |
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Quality Control Requirements
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QC criteria discussed in the following sections are summarized in Section 17, Tables 8 and 9. |
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Sample Handling
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Samples are stable for at least 14 days at both ambient temperature 25oC and chilled temperature 6oC. |
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Maximum Holding Time
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14 days |
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Relative Cost
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Unknown |
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Sample Preparation Methods
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The samples are preserved with a combined buffer/dechlorinating reagent. Either the liquid formulation or the solid formulation of the preservative described in the following sections may be used. Open the tap and allow the system to flush for approximately 5 minutes. Fill sample bottles with 100-mL of sample, taking care not to flush out the preservative. Invert the bottle several times to mix the sample with the preservative. |
