Evaluation of methods for total selenium determination in yeast.

The selenium determination in biological materials by the classical fluorometric method (FM) is time-consuming and also hazardous, as it requires the destruction of the organic matrix samples with hot HNO3/HClO4 mixtures prior to analysis. Accordingly, commercial analytical laboratories are increasingly using faster instrumental methods; for sample digestion, avoid using HClO4. Because of these procedural changes, the results obtained by commercial laboratories may be unreliable, especially for samples containing Se in organic forms. One such "difficult" substrate is Se yeast, which contains most of its Se as selenomethionine. To establish which methods for Se analysis and sample digestion are applicable, samples of Se yeast and of selenomethionine standards were sent to laboratories employing either flame atomic absorption spectrometry (FAAS), inductively coupled plasma-mass spectrometry (ICP-MS), or hydride generation atomic absorption spectrometry (HGAAS). The results were compared with those obtained by FM and non-destructive instrumental neutron activation analysis (INAA). ICP-MS, after microwave digestion of sample with HNO3/H2O2, produced results within 5% of the expected values, as did those obtained by FM and INAA. With FAAS, acceptable results were obtained after digestion with HNO3/HCl. With HGAAS, sample digestion with HNO3/H2O2 produced values that were systematically elevated by about 10% and exhibited standard deviations of > or = 10%. Thus, current methods of sample digestion are applicable for Se yeast analysis by ICP-MS and FAAS, but not by HGAAS.