Speciation analysis of selenium compounds in yeasts using pressurised liquid extraction and liquid chromatography–microwave-assisted digestion–hydride generation–atomic fluorescence spectrometry

Selenium species present in yeast samples were extracted using pressurised liquid extraction (PLE). Several experimental variables (dispersant agent, time, number of cycles, temperature, pressure and solvent) were evaluated for the extraction of selenocysteine, selenomethionine, selenoethionine, selenite, (Se(IV)) and selenate (Se (VI)) from spiked yeast. Only time, temperature and solvent had an influence on the recoveries. Subsequently, a central composite design was used to investigate the dependence of these operating variables on the recoveries from both spiked and native yeast. The results indicated that experimental conditions were different for spiked and native yeast. The optimum extraction conditions for the native yeast were 11 ml PLE cell, celatom as dispersant agent, 1:1 (v:v) H2O:MeOH, 1600 psi, 160 °C, 10 min static time, and 75 vol.% flush. The results obtained by PLE were compared to those obtained by mechanical agitation, sonication and Soxhlet extraction. The extracted selenium compounds were analysed by liquid chromatography (LC)–hydride generation (HG)–atomic fluorescence spectrometry (AFS).