Nonchromatographic Speciation of Selenium in Edible Oils Using Dispersive Liquid-Liquid Microextraction and Electrothermal Atomic Absorption Spectrometry

A methodology for the nonchromatographic separation of the main selenium species present in edible oils is presented. Dispersive liquid-liquid microextraction is used to extract inorganic selenium (iSe), seleno-L-cystine (SeCys(2)), seleno-L-methionine (Se Met), and selenocystamine (SeCM) into a slightly acidic aqueous medium. The selenium total (tSe) content is measured in the extracts by electrothermal atomic absorption spectrometry. By repeating the microextraction stage using an ionic liquid instead of water, the sum of SeCys(2), SeMet, and SeCM is obtained and iSe is calculated by difference. The detection limit is 0.03 ng of Se per gram of oil. The fractionation of the edible oils by solid phase extraction followed by dispersive liquid-liquid extraction and atomic absorption measurement also permits speciation of iSe to be carried out. Data for tSe and iSe levels of 15 samples of different origin are given.