Trace Analysis and Speciation for Cr(VI) and Cr(III) via HPLC-Direct Current Plasma Emission Spectroscopy (HPLC-DCP)

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Abstract
High performance liquid chromatography (HPLC) can be rapidly, easily, and inexpensively interfaced with a commercial direct current plasma (DCP) emission spectrometer in order to obtain overall instrumentation useful for the trace analysis and speciation of at least two chromium species via HPLC-DCP, viz., Cr(III) and Cr(VI) ions are soluble in aqueous media compatible with HPLC injection/separation methods. The HPLC separations of the two chromium (Cr) ions are readily accomplished using paired-ion, reversed-phase conditions, with either a tetrabutylammonium counter-ion or a camphor sulfonate counter-ion in solution. The order of elution of the two Cr ions is completely reversed in going from one counter-ion to the other in the mobile phase. These HPLC conditions are interfaced with a conventional DCP spectrometer utilizing nothing more than a short length of narrow-bore plastic tubing between the end of the HPLC column and the sample introduction orifice on the DCP spray chamber. It is possible using this HPLC-DCP approach to obtain detection limits for both Cr species in the range of 5 to 10 ppb, with at least 3 to 4 orders of magnitude linearity in the calibration plots. This was demonstrated with both retained and unretained HPLC conditions for both Cr species. These overall methods of analysis and speciation were applied to a number of spiked water samples, an NBS chromium water standard, several environmental water samples, various biological samples from the Atlantic Ocean, and two Maine tannery samples. It is suggested that these particular HPLC-DCP methods of speciation are uniquely appropriate and applicable for most environmental, biological, toxicological, and/or consumer product samples, wherein chromium contamination may be a suspected or known problem.