Ion-chromatography of inorganic selenium species with a preliminary preconcentration step

The essential as well as toxic character of selenium is related to its chemical forms and oxidation states. This study presents a method for the determination of Se(IV) and Se(VI) in aqueous solution by ion chromatography with UV detection. Several chromatographic parameters, including mobile phase concentration, pH and methanol content were optimised. The influence of other anions commonly present in water samples was also tested. The best results were obtained on a Hamilton PRRX-100 column with a 1 mM phthalate eluent at pH 6 with 2.5% methanol. The linear calibration range was from 0.5 to 20 mg L-1. LOD were 60 and 40 mug L-1 for Se(IV) and Se(VI), respectively Because this range was not sufficient for the determination of selenium in natural samples, a preconcentration step using solid-phase extraction with an Al2O3 microcolumn was added for the enrichment of the analytes. To improve the sensitivity and selectivity of the measurements, electrothermal AAS was also used as a detection method. This method was applied to the determination of selenium in thermal waters and extracts of pharmaceutical supplements.