Barium isotopic analysis of geological reference materials by MC-ICP-MS

Abstract

Barium (Ba) isotopes have been developed as a valuable tracer for chemical weathering, marine biogeochemical processes, and riverine Ba input to the ocean. To facilitate inter-laboratory data comparisons, it is essential to measure Ba isotope ratios of widely available reference materials. We presented 21 geological reference materials, most of which are new stream sediment Ba isotope reference materials in this study. Purification of synthetic solutions and rock samples with different Ba concentrations and matrix compositions, showed similar elution curves with recoveries close to 100 %. The long-term reproducibility for δ^138/134Ba measurements was ≤0.07 ‰ (2SD). The results indicated that the Ba isotope ratios of AGV-2, BCR-2, BHVO-2, GSP-2, RGM-2, GSS-2, GSR-1, GSR-2 and GSR-5 were in good agreement within analytical uncertainties with previously published data. The δ^138/134Ba values of sediment materials ranged from −0.31 ± 0.06 ‰ to 0.03 ± 0.07 ‰.With the exception of one stream sediment from a carbonate tributary, all analyzed sediment reference materials exhibited significant homogeneity in Ba isotopic composition, with an average δ^138/134Ba of 0.01 ± 0.06 ‰, which was in excellent agreement with the upper continental crust (0.00 ± 0.05 ‰) and the bulk silicate earth (0.07 ± 0.08 ‰). This dataset of reference materials in this study provides the basis for data quality assurance and later inter-laboratory comparison of Ba isotope analyses.