Determination of 187Os in molybdenite by ICP-MS with neutron-induced 186Os and 188Os spikes

The article describes a method for the determination of 187Os in molybdenite by isotope dilution inductively coupled plasma-mass spectrometry (ID-ICP-MS) with neutron-induced 186Os and 188Os spike. The spike used in the present work was prepared in line with the principle by which artificial nuclides are produced in a nuclear reaction. The concentration and isotopic composition of osmium in the prepared spike were evaluated accurately with the isotope dilution method, using negative thermal ion mass spectrometry (N-TIMS). The advantage of this method is that using 186Os and 188Os double spikes can effectively compensate for the mass discrimination effects of ICP-MS. Thus, the common correction practice for mass bias in the isotope dilution method with a single spike is unnecessary. In addition, the method enables one to reduce the determined error arising from instrumental instability. The precision for the 187Os/(186Os+188Os) ratio was ≈2% (2σ, RSD), but in the case of 187Os/186Os, 187Os/188Os and 186Os/188Os, precision ranged from 2.0 to 8% (2σ, RSD). The results for 187Os concentration in a molybdenite sample determined with this method showed good agreement with reference values.