The 87Rb-87Sr dating system is staple in geo- and cosmochemistry. With a half-life of ~ 49 Gyr for 87Rb, the system allows for dating of objects nearly as old as the solar system. However, the accuracy and precision of an age derived from an isochron diagram is limited by several factors.

In situ isotopic measurements by LA-MC-ICP-MS are challenging: isotopic and elemental fractionation induced by the laser, combined with the presence of molecular interferences (e.g., Fe/Zn/Ga oxides, Ca dimers and Ca argides in the mass region 84-88), often limit the precision on the Rb-Sr age determination. Moreover, the 87Rb-87Sr radiochronometer is characterized by a beta decay producing a daughter nuclide (87Sr) that isobarically interferes with the parent nuclide (87Rb) during isotopic analyses. However, these interferences can be avoided by MS/MS analysis, allowing for mass filtering around the masses of interest and mass shifting using the collision/reaction cell (CRC) of an instrument.

In this study, we present the first Rb-Sr data using in solution mode measured on a Nu Instrument Sapphire XD Dual Path MC-ICP-MS/MS. This new system had been tested stepwise to build up to Rb-Sr. We present data that demonstrates the stepwise validation of the Rb-SrF technique on Sapphire XD using the various analytical modes to ensure accuracy and the absence of any analytical artifacts. Before laser ablation analysis, rigorous doping experiments with Rb, Pd, and Cd in solution mode were performed to investigate the effect CRC-based oxide formation and evaluate different measures to suppress or minimise said oxides for absolute isotope ratio precision.