Abstract
Advanced extraction methods have been developed for direct speciation of dissolved inorganic and organic selenium (Se) species in aqueous extracts of medicinal plants (MPs). The inorganic species of Se (Se-IV and Se-VI) were separated from organic forms by adsorbing inorganic Se on alumina, while the organic Se was not retained. The retained inorganic Se species was eluted with 10 mL 0.2 M HCI. The total inorganic Se species was determined after prereduction of Se-VI into Se-IV with concentrated HCI. The Se-IV in the eluent and total inorganic Se species were then complexed with diethyldithiocarbamate. The resultant complexes were entrapped in the nonionic surfactant Triton X-114. The total Se, organic Se, total inorganic Se, and Se-IV species were determined by electrothermal atomic absorption spectrometry with a modifier. The Se-VI concentration was obtained by subtracting Se-IV from total inorganic Se contents. The main factors affecting the methodologies were investigated in detail. Under the optimized experimental conditions, the LOD for Se-IV was 50 mu g/L. Among dissolved inorganic and organic Se species in aqueous extracts of MPs, organic Se species were present in the range of 74-84%, Se-IV 3.62-7.47%, and Se-VI 12.4-18.57% of total Se contents.