Precise and accurate determination of Sm, Nd concentrations and Nd isotopic compositions in geological samples by MC-ICP-MS

Abstract

In this work, we established a highly reproducible analysis of Sm, Nd concentrations and Nd isotopic compositions in geological samples by isotope dilution analysis with MC-ICP-MS. This technique is superior in terms of the analytical reproducibility or rapidity of analysis compared with quadrupole ICP-MS or with thermal ionization mass spectrometry (TIMS) isotope dilution techniques. Samples were spiked with ¹⁴⁹Sm–¹⁵⁰Nd enriched tracer and then digested by a commonly used HF, HNO₃ and HClO₄ acid protocol. The bulk rare earth elements (REEs) were separated from the sample on a standard cation exchange resin, and further purified on Eichrom Technologies Ln Resin, to obtain Sm and Nd fractions prior to mass spectrometric measurements. Replicate analyses of international certified reference materials (CRMs) demonstrate that our obtained ¹⁴⁷Sm/¹⁴⁴Nd and ¹⁴³Nd/¹⁴⁴Nd isotopic ratios are in good agreement with previously published values from isotope dilution methods. In addition to determining the concentrations of Sm and Nd, the Nd isotopic composition can be measured simultaneously during Nd isotope dilution run. Additionally, a mineral Sm-Nd isochronal age that is identical to, within error, a U-Th-Pb zircon age for the same rock is further measured and validates the robustness of the present protocol. Therefore, the high actual sample throughput inherent to the MC-ICP-MS can be fully exploited for the determination of Sm and Nd concentrations and Nd isotopic compositions.