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(R) and 1131+/-3 mg of LiChrospher 60 RP-18(R)), the washing step, and also the on-line elution of the chromium complexes into the LC system. The detection limits achieved were 0.2 mu gl(-1) for chromium(III) and 0.1 mu gl(-1) for chromium(VI) with LiChrospher 100 RP-8(R) and 0.2 mu gl(-1) for chromium(III) and 0.06 mu gl(-1) for chromium(VI) with LiChrospher 60 RP-18(R) as solid phase extraction material. Relative standard deviations at the 50 mu gl(-1) level were between 2% and 5% (n=10). The method was applied to the determination of 25 mu gl(-1) chromium(III) and 15 mu gl(-1) chromium(VI) in a standard reference water sample. (C) 1998 Elsevier Science B.V.