Simultaneous Determination of Selenium and Mercury in Tea and Auricularia Auricula Judae by HG-AFS with Double Channels

The washed, dried and pulverized sample was soaked in HNO3 overnight, then digested in HNO3-HClO4 mixed acid, and evaporated to fumes of HClO4 and further to near dryness. Definite amount of HCl was added to dissolve the residue and boiled gently for 1-2 min to reduce Se(Ⅵ) to Se(Ⅳ). The solution was made up to 50 mL with HCl(5+95), which was carried over by the carrier solution of HCl(5+95) and mixed with the reductant, 10 g·L-1 KBH4 solution in the hydride generator. Selenium hydride together with the atomic mercury vapour was introduced into the atomizer by the carrier gas and fluorescence intensity of Se and Hg were measured under the optimized instrumental conditions. Since the concentration ratio of Se to Hg was less than 10 in substantial samples, no interference was found between Se and Hg in co-existence. Under the optimized conditions, linear relationships between values of fluorescence intensity and mass concentration of Se and Hg were found in the same range of 1.0-5.0 μg·L-1, with detection limits (3s/k) of 0.077, 0.009 8 μg·L-1 respectively. Precision of the instrument was tested and values of RSD′s (n=7) found were 1.98% (for Se) and 1.31% (for Hg).