Sample preparation and HPLC separation approaches to speciation analysis of selenium in yeast by ICP-MS

Eight solid-liquid extraction procedures were evaluated for the recovery of selenium species from yeast. Speciation of Se in the extracts was characte rized by different types of HPLC, including size-exclusion, anion-exchange and reversed-phase chromatography with ICP-MS detection. The results obtain ed depended critically on the sample preparation procedure used. Leaching w ith water and with methanol led only to 10-20% recoveries of Se, split into eight compounds, among which Se(rv) and selenomethionine could be identifi ed. Leaching with pectinolytic enzymes released an additional 20% of seleno methionine. Leaching with sodium dodecyl sulfate solution allowed the solub ilization of a selenoprotein that accounted for ca. 30% of the total Se pre sent. Leaching with proteolytic enzymes led to recoveries of Se above 85%, the majority as selenomethionine. Hydrolysis of the yeast with tetramethyla mmonium hydroxide solubilized the sample completely but the Se species pres ent were entirely degraded to selenomethionine and inorganic selenium. A se quential leaching procedure is proposed for the evaluation of selenium spec iation in yeast without the need for a coupled technique.