High-precision direct determination of the Sr/Sr isotope ratio of bottled Sr-rich natural mineral drinking water using multiple collector inductively coupled plasma mass spectrometry

We describe a precise and accurate method for the direct determination of the ⁸⁷Sr/⁸⁶Sr isotope ratio of bottled Sr-rich natural mineral drinking water using multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The method is validated by the comparative analysis of the same water with and without cation-exchange resin purification. The work indicates that isobarically interfering elements can be corrected for when ⁸⁷Rb/⁸⁶Sr < 0.05 (Rb/Sr < 0.015), and that the matrix elements (Ca, Mg, K and Na) have no significant effect on the accuracy of the Sr isotope data. The method is simple, rapid, eliminates sample preparation time, and avoids potential contamination during complicated sample-preparation procedures. Therefore, the high sample throughput inherent to the MC-ICP-MS can be fully exploited.