Dried-droplet laser ablation ICP-MS of HPLC fractions for the determination of selenomethionine in yeast

Offline coupling of high performance liquid chromatography ( HPLC) to dried droplet laser ablation ( LA) ICP-MS detection is described. The method is based on the offline spotting of HPLC fractions onto a substrate followed by LA introduction of the dried sample residues to an ICP-MS for elemental analysis. Quantitation of selenomethionine ( SeMet) in yeast using species specific isotope dilution ( ID) was achieved following digestion of samples in 4 M methanesulfonic acid and HPLC separation of species. Chromatographic fractions having retention times of 180-210 seconds were collected for each sample. Dried micro-droplets from each fraction were ablated from a polystyrene substrate and quantitated for SeMet. Concentrations of 3301 +/- 18 and 3309 +/- 24 mu g g(-1) (one standard deviation, n = 4) with RSDs of 0.55% and 0.73% were obtained based on measured Se-78/Se-74 and Se-82/Se-74 ratios, in good agreement with the values of 3309 +/- 19 and 3305 +/- 26 mu g g(-1) (one standard deviation, n = 4, RSDs of 0.58% and 0.79%), respectively, obtained by direct HPLC-ICP-MS analysis. The proposed method provides a satisfactory alternative technique for the quantitation of SeMet in yeast.