Evaluation of slurry preparation procedures for the simultaneous determination of Hg and Se in biological samples by axial view ICP OES using on-line chemical vapor generation

Seven slurry preparation procedures were evaluated concerning the simultaneous determination of Hg and Se by on-line chemical vapor generation coupled to axial view ICP OES, using: (1) aqua regia and sonication; (2) HCl, sonication and heating at 90 °C; (3) tetramethylammonium hydroxide (TMAH); (4) H2O2, sonication, addition of HCl and heating at 90 °C; (5) K2S2O8, sonication, addition of HCl and heating at 90 °C (6) TMAH, sonication, ozonation, addition of HCl and heating at 90 °C; (7) Triton X-100, sonication, ozonation, addition of HCl and heating at 90 °C. The concentrations of HCl and NaBH4, used in the chemical vapor generation, in the different slurry media and in the slurry blanks, were optimized by factorial analysis. The calibrations were carried out using aqueous solutions in the same medium as the slurry, containing the analytes, Hg(II) and Se(IV), in the concentration range of 0.5-10 μg L−1. The procedures were applied initially to the certified material TORT-2 (Lobster Hepatopancreas) and all of them produced results for Hg in agreement with the certified value, according to the t-test for a 95% confidence level. However, for Se, results in agreement with the certified value were obtained only when Procedures 4 and 5 were used, indicating that either H2O2 or K2S2O8 is required, most probably to break the Se bonds efficiently. Procedure 5, with detection limits (3 s, n = 10) of 0.08 μg g−1 for Hg and 0.10 μg g−1 for Se, for a sample mass of 20 mg in a final volume of 15 mL, was adopted and applied to the analysis of five certified reference biological materials and the tissues of six real oyster samples grown in the Santa Catarina Island coast. The obtained Hg and Se concentrations were in agreement with the certified values. The recommended procedure is simple, rapid and robust.