Determination of selenium at sub-mu g/g-levels in biological materials by MIP-MS

Determination of Se in biological materials was attempted by microwave-indu ced plasma mass spectrometry (MIP-MS). (1) Serum samples were available aft er 10 times dilution with 0.5% nitric acid solution containing 0.1% Triton X-100. When oxygen gas was inserted into the plasma gas (nitrogen) in order to improve the combustion, the sensitivity was reduced to 45%. The detecti on limit of this method was 0.5 ng/mL. (2) Standard reference materials on commercial base were used to evaluate the accuracy of the Se determination by MIP-MS after microwave digestion. In samples like bovine liver and human hair with Se concentrations of more than 0.7 mu g/g, the standard curve me thod after internal standard (IS) correction was acceptable. This procedure was unsuitable for samples with low Se concentrations such as milk powder (certified value of Se 0.11 mu g/g), or plant leaf samples. (3) Instead of IS correction, the peak height of the spectrum was used for calculations fr om the matrix matched calibration curve. The results of all materials were close to the certified values, even at 25 ng/g. The detection limit of the MIP-MS with microwave digestion and IS correction was 0.05 ng/mL in standar d solutions. The detection limit of the peak height method was 0.1 ng/mL an d was estimated to be < 20 ng/g in plant materials.