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

Isotope dilution thermal ionization mass spectrometry (ID-TIMS) is considered the "gold standard" for obtaining precise Rb-87/Sr-86 and Sr-87/Sr-86 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 Rb-87 isobaric interference on Sr-87. 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 Rb-87/Sr-86 and Sr-87/Sr-86 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 Sr-87/Sr-86 ratio, +/- 2% for the Rb-87/Sr-86 ratio and the Rb and Sr elemental contents. The only exception is JG-1a, with slightly higher Rb-87/Sr-86 and slightly lower Sr-87/Sr-86. 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.