A method for Se isotope analysis of low ng-level geological samples via double spike and hydride generation MC-ICP-MS

The isotopic signature of the chalcophile, redox-sensitive and moderately volatile element Se in geological materials may offer valuable new insights into the origin and evolution of volatiles in planetary systems. Here, we report a new method for Se isotope determination of low Se containing samples relevant to the Earth's mantle reservoir. We present a method that combines a double spike and hydride generation sample introduction system with a ThermoFisher Scientific® NeptunePlus™ MC-ICP-MS. The measurement routine takes advantage of methane injection in the instrument source during measurement, resulting in enhanced Se signals and suppression of polyatomic interferences. Purification of Se from natural samples was simplified by employing conventional ion exchange chromatography procedures. An external reproducibility of 0.15‰ (2σ) on δ82/76Se values for measurements performed on natural samples with Se abundances down to ~5 ng is obtained. We demonstrate that our technique allows the determination of Se isotope signatures of low Se-bearing geological materials with complex matrices such as mafic igneous rocks, which is essential to extend the Se isotopic investigation to Se-depleted planetary reservoirs such as the Earth's mantle.