Precise determination of triple Sr isotopes (δ87Sr and δ88Sr) using MC-ICP-MS

The non-traditional stable strontium (Sr) isotopes have received increasing attention recently as new geochemical tracers for studying Sr isotopic fractionation and source identification. This has been attributed to the advancement in multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), allows to determine precisely and simultaneously of the triple Sr isotopes. In this study, we applied a modified empirical external normalization (EEN) MC-ICPMS procedure for mass bias correction in Sr isotopic measurement using Zr-92/Zr-90. High-purity Zr Standard was spiked into sample solutions and the degree of fractionation was calculated off-line using an exponential law. The long-term external reproducibility for NIST SRM 987 delta Sr-87 and delta Sr-88 was better than 0.040 parts per thousand. and 0.018 parts per thousand. (2SD), respectively. The IAPSO standard seawater was used as a secondary standard to validate the analytical protocol and the absolute ratios measured were 0.709161 +/- 0.000018 for Sr-87/Sr-86, 0.177 +/- 0.021 parts per thousand for delta Sr-87, and 0.370 +/- 0.026 parts per thousand. for delta Sr-88 (2SD, n = 7). These values are in good agreement with the literature data analyzed by thermal ionization mass spectrometry (TIMS) double spike technique. Rock standards, BHVO-2, BCR-2 and AGV-2 were also analyzed to validate the robustness of the methodology and showed identical results with literature data. Compared to previous Zr-91/Zr-90 correction, we obtained improved results based on Zr-92/Zr-90, probably due to similar mass difference between Zr-92/Zr-90 and measured Sr isotopes. The new analytical protocol presented in this study not only improves the analytical precision but also increases sample efficiency by omitting the use of the standard-sample bracketing (SSB) procedure. (C) 2011 Elsevier B.V. All rights reserved.