EPA Method 218.7 hexavalent chromium analysisThis second post on the continuing challenges of monitoring hexavalent chromium(OSHA site) compare results from two types of eluent systems: ammonium sulfate and carbonate, and demonstrates that the ammonium sulfate eluent provides a two-fold improved detection limit as compared to the carbonate-based eluent system!

As our readers are aware, hexavalent chromium [Cr(VI)] is highly toxic at low concentrations and difficult to remove from water sources and, therefore, continues to be a major area of concern in drinking water analysis across the United States.

We are pleased to report that, recently, the U.S. EPA used Thermo Scientific Dionex ion chromatography (IC) technology to develop the newly approved EPA Method 218.7 (downloadable PDF) for the determination of Cr(VI) in drinking water. Findings recently released by the EPA show that the use of ammonium sulfate eluent and our anion-exchange column (Thermo Scientific Dionex IonPac™ AS7 column) provided a two-fold better detection limit compared to the carbonate-based eluent systems. This easily attains the California Public Health Goal (PHG) of 0.02 μg/L Cr(VI). A review of the two methods in Figure 1 below illustrates how detection limits for the ammonium hydroxide/ammonium sulfate eluent system (our preferred method) is approximately twice as favorable. This is important since effective implementation of this method is dependent upon obtaining the lowest possible detection. This also means that for California, the Public Health Goal (PHG) of 0.02 ug/L the method will not be usable using carbonate eluent.

hexavalent chromium detection limits

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In addition, the run times for Cr(VI) analysis using this method are 4 to 5 minutes faster than the carbonate-based method thus resulting in the analysis of a much larger numbers of samples in the same time as shown in Figure 2 below!

hexavalent chromium traces

For further details on the method, check out Application Update 179, Sensitive Determination of Hexavalent Chromium in Drinking Water, (downloadable PDF).

Do not forget to comment below if you found this application helpful in your work. Our experts look forward to hearing from you!