Barium Isotopic Compositions in Thirty-Four Geological Reference Materials Analysed by MC-ICP-MS

Measurement of Ba isotope ratios of widely available reference materials is required for interlaboratory comparison of data. Here, we present new Ba isotope data for thirty-four geological reference materials, including silicates, carbonates, river/marine sediments and soils. These reference materials (RMs) cover a wide range of compositions, with Ba mass fractions ranging from 6.4 to 1900 mu g g(-1), SiO2 from 0.62% to 90.36% m/m and MgO from 0.08% to 41.03% m/m. Accuracy and precision of our data were assessed by the analyses of duplicate samples and USGS rock RMs. Barium isotopic compositions for all RMs were in agreement with each other within uncertainty. The variation of delta Ba-138/134 in these RMs was up to 0.7 parts per thousand. The shale reference sample, affected by a high degree of chemical weathering, had the highest delta Ba-138/134 (0.37 +/- 0.03 parts per thousand), while the stream sediment obtained from a tributary draining carbonate rocks was characterised by the lowest delta Ba-138/134 (-0.30 +/- 0.05 parts per thousand). Geochemical RMs play a fundamental role in the high-precision and accurate determination of Ba isotopic compositions for natural samples with similar matrices. Analyses of these RMs could provide universal comparability for Ba isotope data and enable assessment of accuracy for interlaboratory data.