Fractionation studies of selenium compounds from oysters, and their determination by high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry

A procedure is described for the fractionation of selenium species in oyster samples by aqueous extraction. Several parameters were tested in order to evaluate the efficiency or the aqueous extraction: nature, concentration, pH and temperature of the solvent used, The Soluble fraction ill the aqueous Solvent Contains 35+/-3% of the total selenium content (1.22+/-0.03 mug g(-1)). The subsequent enzymatic hydrolysis of both the liquid extract and the solid residue allows the determination of selenium species by high-performance liquid chromatography in conjunction with inductively coupled plasma mass spectrometry. The chromatographic analyses were carried out in two chromatographic modes (anionic and cationic exchange) for the identification of selenium species in the samples. The species found in oyster tissues under the proposed treatment were trimethylselenonium ion (9.8+/-0.8%) and selenomethionine (46+/-6%). By Using Mass cut-off filters it was possible to determine the percentage of selenium remaining in chemical forms with a molecular weight higher than 10 kDa, and therefore to conclude that enzymatic hydrolysis is more efficient in the soluble fraction than in the non-soluble one.