Speciation of chromium by solid-phase extraction coupled to reversed-phase liquid chromatography with UV detection

A method for the on-line pre-concentration and chromatographic separation of chromium(III) and chromium(VI) was investigated. Therefore the different complexes which chromium(III) and chromium(VI) form with ammonium pyrrolidine dithiocarbamate (APDC) were enriched by reversed-phase solid-phase extraction (SPE) using an automated solid phase extractor, and determined by reversed-phase liquid chromatography (RP-LC) using UV detection. The automated SPE system has been optimised with respect to the conditioning of the SPE material, the adsorption of the chromium complexes onto the solid phase (73.0±0.4 mg of LiChrospher 100 RP-8® and 113±3 mg of LiChrospher 60 RP-18®), the washing step, and also the on-line elution of the chromium complexes into the LC system. The detection limits achieved were 0.2 μg l−1 for chromium(III) and 0.1 μg l−1 for chromium(VI) with LiChrospher 100 RP-8® and 0.2 μg l−1 for chromium(III) and 0.06 μg l−1 for chromium(VI) with LiChrospher 60 RP-18® as solid phase extraction material. Relative standard deviations at the 50 μg l−1 level were between 2% and 5% (n=10). The method was applied to the determination of 25 μg l−1 chromium(III) and 15 μg l−1 chromium(VI) in a standard reference water sample.