The reliable analysis of highly toxic hexavalent chromium, Cr(VI), at safe environmental levels is still challenging given its labile equilibrium with non-toxic trivalent chromium. This work successfully applied direct isotope dilution (DID) quantification method to samples with low ng/L concentration levels. Ion chromatography tandem mass spectrometry (IC-MS/MS) was used for the analysis of Cr(VI) as H52CrO4- → 52CrO3-. A method detection limit (MDL) of 7 ng /L Cr(VI) was obtained using a classical linear multipoint calibration curve with Cl18O4- as an internal standard. The DID mass spectrometry (DIDMS) approach described in U.S. EPA 6800 allowed for the quantification of Cr(VI) with an MDL of 2 ng/L and provided results corrected for Cr(VI) loss that can occur after sample collection. The DIDMS method was applied for the analysis of surface and ground water samples from the Ring of Fire region in Northern Ontario. Preservation at pH values &gt; 8.5 was required only for ground water samples containing high level of organic matter and caused little to no oxidation of environmental Cr(III). Drinking water samples were also analyzed, obtaining unbiased Cr(VI) values even for samples below the Public Health Goal of 20 ng/L proposed by the state of California in 2011.

Direct isotope dilution measurement of trace level Cr(VI)  using ion chromatography tandem mass spectrometry

251st National Meeting (2016)

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