Chromium ions, viz., chromic (Cr+3 = III) and chromate (Cr+6 = VI), can be reliably, conveniently, reproducibly, and quickly separated and detected by the use of conventional paired-ion, reversed phase (RP) high performance liquid chromatography (HPLC) together with refractive index (RI) and/or inductively coupled plasma emission spectroscopic (ICP) detection. A number of novel paired-ion approaches have now been developed, using PIC A (tetrabutylammonium hydroxide) or PIC B (sodium n-alkyl sulfonate) separately in the mobile phase. This allows for the retention of each Cr species depending on the particular ion pairing reagent being used, while the remaining Cr ion elutes in the solvent front. Changing the ion pairing reagent reverses the overall situation. The total time for each HPLC analysis is about 10 mins. ICP detection provides for a complete, overall method of speciation for both Cr (III) and Cr (VI) via two seperate injections, together with quatitation for both species. This method of using paired-ion RP-HPLC can easily be applied to other mixtured of inorganic cations and anions, presumably with equally successful results. Minimum limits of detection are computed for chromate via direct-IPC and HPLC-ICP, using at least two basic methods for such computations. It is suggested that virtually all chromatographic detection limits can be significantly improved by the application of newer, spectroscopic based methods of automated computation of detection limits.
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