Applicability of high sensitivity cone combination for precise measurement of 87Sr/86Sr and δ88/86Sr using MC-ICP-MS

Abstract

The applicability of a high sensitivity cone combination (Jet sample and X skimmer cones; hereafter “Jet/X”) for high-precision measurements of Sr isotope ratios was evaluated via a Neptune Plus multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) system (Thermo Fisher Scientific Inc.) under wet plasma conditions. Although Jet/X has effectively achieved highly precise and sensitive measurements of isotope ratios for various elements (e.g., Li, B, Cu, Hf, and U), its applicability for Sr has not been adequately evaluated. In this study, the sensitivity, accuracy, and precision of measurements, the extent of mass fractionation that occurs in MC-ICP-MS, and the behavior of spectral interference from a concomitant element (i.e., Ca) in ⁸⁷Sr/⁸⁶Sr and δ⁸⁸/⁸⁶Sr measurements using Jet/X were compared with those of a conventional cone combination (standard sample and H skimmer cones; hereafter “Standard/H”). Jet/X improved the signal sensitivity of ⁸⁸Sr by a factor of four, which enabled measurements at lower Sr concentrations (i.e., 50 μg kg⁻¹) with comparable reproducibility to that of measurements of 200 μg kg⁻¹ Sr using Standard/H. Measured ⁸⁷Sr/⁸⁶Sr and δ⁸⁸/⁸⁶Sr of the Sr isotopic standard (i.e., NIST SRM 987) using Jet/X were consistent with those using Standard/H, literature data, and theoretical values. With Jet/X, the magnitude of mass-dependent fractionation within MC-ICP-MS was smaller than that with Standard/H. No significant difference in the magnitude of Ca-induced spectral interference was observed between Jet/X and Standard/H at Ca/Sr concentration ratios of ≤10. Finally, the applicability of Jet/X to matrix-type samples was confirmed by measuring the ⁸⁷Sr/⁸⁶Sr and δ⁸⁸/⁸⁶Sr of standard reference materials, JCp-1 and FEBS-1.