Simultaneous multiple collector-ICP-MS measurement of Nd isotopic composition and Sm/Nd ratio in geological reference materials by interference corrections and external calibration using matrix-matched standards

摘要

This study introduces an improved multiple collector- ICP-MS protocol to simultaneously determine the Nd isotopic composition and Sm/Nd ratio of geological samples without isotope dilution. Our pretreatment procedure simply consists of sample digestion and single-step group separation of Sm and Nd. The Nd isotopic composition was conventionally corrected for Sm isobaric interference by using the exponential mass fractionation law and selected Sm isotopic compositions, and the Sm/Nd ratio was externally corrected by the standard-sample bracketing method. This protocol yielded the corrected ~(143)Nd/~(144)Nd ratios of the USGS GRMs (BHVO-2, BCR-2, AGV-2, and RGM-1) mostly in good agreement with previously recommended values. By contrast, their Sm/Nd ratios were consistently higher (up to 3.4%) than the recommended values when the measured ratios were corrected simply using data of an aqueous standard solution. Further calibration using a matrixmatched GRM as a secondary standard significantly reduced the discrepancies with previous ratios to within a 0.3% difference. Therefore, we recommend that the matrix of calibration standard should be matched with that of the samples as closely as possible in the inter-elemental ratio measurement of geological samples.