FI-HG-AFS Determination of Selenium in Tea

0.5g of dried and powdered tea sample was digested with 10 mL of HNO3-HClO4(4+1) mixed acid by heating on an electric hot-plate to obtain a transparent and clear solution, and then fumed to have a residual solution of ca. 2 mL. 5 mL of 6 mol·L-1 HCl were added and heated to reduce Se(Ⅵ) to Se(Ⅳ). Repeated evaporations (thrice) with additions of 2 mL portions of water to expel acid from the solution, and the solution was finally made up to 25.0 mL with HCl(4+96). The solution was introduced into the FI-system with the carrier HCl(4+96) and 10 g·L-1 KBH4 solution (dissolved in 5 g·L-1 KOH solution) was introduced as reductant. Linear relationship between values of fluorescence intensity and mass concentration of Se(Ⅳ) was kept in the range within 80 μg·L-1. Detection limit (3s/k) found was 0.034 μg·L-1. Samples of 3 kinds of tea were analyzed by this method. Recovery was tested by adding standard Se(Ⅳ) solution to the 3 tea samples as matrixes, values of recovery were found in the range from 97.8% to 103.0%, with RSD′s (n=6) less than 1.5%.