Common analyte internal standardization as a tool for correction for mass discrimination in multi-collector inductively coupled plasma-mass spectrometry

It is well known that to achieve accurate isotope ratio data using multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS), mass discrimination needs to be adequately corrected for. In this work, the capabilities and limitations of common analyte internal standardization (CAIS) as a method for correction for mass discrimination were assessed for two target elements, one in the low mass region (boron) and another in the medium mass region (antimony). CAIS has already been used in the context of element determination and, more recently, also in isotope ratio measurements with quadrupole-based ICP-MS, but it has, to the best of the authorsʹ knowledge, never been applied to isotope ratio determination via MC-ICP-MS so far. Results obtained relying on CAIS were compared with those obtained via more established correction models, i.e. external correction in a standard-sample bracketing approach (SSB) and internal correction based on both the Russellʹs law (original and empirical) and the revised Russellʹs law. To the best of the authorsʹ knowledge, such comparison has not been done before, especially not for low mass elements. Also the robustness of these approaches with respect to concomitant matrix elements was assessed using synthetic solutions, containing various concentrations of the matrix elements Be, Cs, Be + Cs or Fe. Whereas for B, the isotope ratio result did not seem to be significantly affected by the matrix, thus suggesting that complete separation of B from a matrix might not be necessary, at least in the cases studied, the mass discrimination observed for Sb was influenced by the presence of Cs. The experiments carried out demonstrate that the CAIS technique can be successfully applied for mass bias correction in MC-ICP-MS, providing data of the same quality as the revised Russellʹs law, while being more transparent and accessible. While for B, all mass bias correction approaches tested provided similar data quality (external correction with SSB gives slightly better precision), for Sb, CAIS and the revised Russellʹs law provide better precision and accuracy.