Determination of 87Rb/86Sr and 87Sr/86Sr ratios and Rb-Sr contents on the same filament loading for geological samples by isotope dilution thermal ionization mass spectrometry

Abstract

Isotope dilution thermal ionization mass spectrometry (ID-TIMS) is considered the "gold standard" for obtaining precise ⁸⁷Rb/⁸⁶Sr and ⁸⁷Sr/⁸⁶Sr isotope ratios and accurate elemental concentrations of Rb-Sr. However, the classical ID-TIMS technique is laborious and time-consuming because the purified Rb and Sr fractions must be individually loaded onto different independent filaments due to severe ⁸⁷Rb isobaric interference on ⁸⁷Sr. To overcome this issue, we developed a new method whereby Rb and Sr were sequentially measured by TIMS on the same filament, without venting, to obtain both ratios of ⁸⁷Rb/⁸⁶Sr and ⁸⁷Sr/⁸⁶Sr and concentrations of Rb and Sr. Results obtained from six silicate powders of certified reference materials are in good agreement with recommended values within ±0.002% for the ⁸⁷Sr/⁸⁶Sr ratio, ±2% for the ⁸⁷Rb/⁸⁶Sr ratio and the Rb and Sr elemental contents. The only exception is JG-1a, with slightly higher ⁸⁷Rb/⁸⁶Sr and slightly lower ⁸⁷Sr/⁸⁶Sr. This new method improved the analytical efficiency and sample throughput without compromising the analytical accuracy and precision. The filament consumption is reduced by 50% compared with conventional methods and therefore significantly reduces operation costs.

Keywords: (87)Rb/(86)Sr; (87)Sr/(86)Sr; ID-TIMS; Rb–Sr isotopes.