Determination of Selenium Speciation in Tea Samples by HPLC-DRC-ICP-MS

The purpose of this work was to develop a method for the determination of selenium speciation in tea samples. The contents of selenium in extracts as well as in original tea samples were determined by inductively coupled plasma mass spectrometry (ICP-MS). Separation of Se(IV), Se(VI) and SeMet was achieved by a Hamilton PRP-X100 anion exchange column with the mobile phase of 40 mM (NH₄)₂HPO₄ (pH 6.0), 2% CH₃OH. Dynamic reaction cell (DRC) technology was used to reduce isobaric interferences and the optimized Rpq value was 0.4, the reaction gas flow rate was 0.4 mL min^-1. The detection limits for Se(IV), SeMet and Se(VI) were 0.307 μg-L^-1, 0.286 μg-L^-1 and 0.189 μg-L^-1, respectively, and their corresponding RSD were 1.01%, 0.953% and 0.629% respectively. In the extracts of 95°C water, Se(IV) was found at the retention time of 2.27 min, as well as an unknown selenium speciation at the retention time of 1.97 min. In the extracts of black tea, an unidentified peak at the retention time of 2.45 min was also observed.