Determination of Os and Re isotope ratios at subpicogram levels using MC-ICPMS with solution nebulization and multiple ion counting

A precise and accurate determination method of ¹⁸⁷Os/ ¹⁸⁸Os, ¹⁸⁹Os/¹⁸⁸Os, and ¹⁸⁵Re/ ¹⁸⁷Re ratios of down to 0.2 pg of Os and 0.08 pg of Re using multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) with multiple ion counting has been developed. Os and Re were introduced into MC-ICPMS as 0.5 mol L^-1 HF solutions through the desolvator, and ¹⁸⁵Re, ¹⁸⁷Os, ¹⁸⁸Os, and ¹⁸⁹Os ions were detected simultaneously by four channeltrons. The Os and Re ratios were determined by the standard bracketing method, in which channeltron yields and mass discrimination factors are corrected together. Os and Re memories after 800-s wash were <0.1% and negligible, typically 0.02 and 0.03%, respectively. Isotope ratios of ¹⁸⁷Os/¹⁸⁸Os, ¹⁸⁹Os/ ¹⁸⁸Os, and ¹⁸⁵Re/¹⁸⁷Re were constant within error in the concentration ranges of 1-100, 1-40, and 0.4-5 pg mL^-1 with reproducibility(1σ) of 2.7-0.14, 0.33-0.10, and 0.41-0.19%, respectively. For analysis of larger amounts of Os and Re, the Faraday cup measurement was employed. The precision and reproducibility obtained in this study are comparable to those of N-TIMS and better than MC-ICPMS achieved so far with a capability of higher sample throughput with simpler sample preparation.