Precise determination of rhenium isotope composition by multi-collector inductively-coupled plasma mass spectrometry

Abstract

We present rhenium (Re) isotope data for commercially available Re reference materials SRM 989, SRM 3143, and Alfa Aesar Specpure^®Re, as well as two Re solutions made in-house from perrhenic acid and zone-refined flattened-wire ribbon from H. Cross Company. Data were generated by MC-ICPMS (Thermo Fisher Scientific NEPTUNE) using standard-bracketing combined with a tungsten (W) external correction. Intermediate measurement precision (i.e. the precision for similar analytical procedures and measurement conditions on the same instrument over time) is ±0.05‰ (2s) for analyte solution concentrations of 20 ng g⁻¹Re and 70 ng g⁻¹W; intermediate precision decreases to ±0.1‰ (2s) when respective analyte concentrations are halved to 10 ng g⁻¹ and 35 ng g⁻¹. The five Re solutions exhibit an isotopic range of 0.29‰, providing the first evidence for stable isotope fractionation of Re. Data are also presented for the Devonian Ohio Shale standard USGS SDO-1; intermediate precision for this natural material (±0.13‰, 2s) is comparable to solution standard precisions at equivalent concentrations (10 ng g⁻¹Re, 35 ng g⁻¹W). Analysis of geochemical materials introduces additional concerns. The low concentration of Re in most materials limits these analyses to Re-rich substrates. Isotopic fractionation occurring during chromatographic purification is nullified by quantitative recovery, and the sample matrix does not introduce fractionation artifacts. Isobaric interference from radiogenic ¹⁸⁷Os can be effectively removed by sparging sample solutions prior to analysis.