A Calibration Strategy of 87Sr/86Sr Ratio for Rocks with High Rb/Sr Measured by Multiple Collector-Inductively Coupled Plasma-Mass Spectrometry

The presence of 87Rb causes isobaric interference of 87Sr for Multiple Collector-Inductively Coupled Plasma-Mass Spectrometric (MC-ICPMS) measurements. 87Sr/86Sr isotopic composition of rocks with Rb/Sr≤0.0005 after chromatography separation can be effectively corrected by using a traditional Rb-interference calibration. However, the traditional calibration method is not valid for solutions with high Rb/Sr ratio which cannot completely remove isobaric interference of 87Rb to obtain an accurate 87Sr/86Sr ratio. The two curves of the 87Sr/86Sr isotope ratio and Rb/Sr element content ratio were obtained by two sets of experiments to calibrate Rb interference in this work. Based on theoretical analysis, a new calibration method is reported, including an isotope fractionation calibration. The method yields an accurate 87Sr/86Sr ratio for geology samples with Rb/Sr0.2 after chemical separation was significantly lower due to mass fractionation and memory effect, which can not be calibrated to obtain an accurate Sr isotopic composition by any kind of calibration method.