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.

Automated summary

The new method of measuring Rb and Sr on the same filament using TIMS improves analytical efficiency, reduces sample processing time, while maintaining high accuracy and precision.