EPA Method 7199

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EPA Method 7199:
Chromium in Water by Ion Chromatography. Official Name: Determination of Hexavalent Chromium in Drinking Water, Groundwater and Industrial Wastewater Effluents by Ion Chromatography

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.

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).

SW-846 Online: Test Methods for Evaluating Solid Waste, Physical/Chemical Methods

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.

QC Requirements:
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.

Maximum Holding Time:
24 hours after collection.



This method was tested by 21 volunteer laboratories in a joint study by USEPA and the American Society for Testing and Materials (ASTM). Mean recovery and accuracy for Cr(VI) (as CrO4 2-) was determined from the retained data of 13 laboratories in reagent water, drinking water, groundwater, and various industrial wastewaters. For reagent water, the mean recovery and the overall and single-analyst relative standard deviations were 105%, 7.8%, and 3.9%, respectively.

The MDLs were calculated for drinking water, groundwater, and wastewater.

Revision Number:
December 1996, Revision 0.

Test Description:
Hexavalent Chromium

Report Number:
SW-846 Ch 3.3

Instrument used for this test: