Matrix effects and mass bias caused by inorganic acids on boron isotope determination by multi-collector ICP-MS

Abstract

The influence of inorganic acids (HCl, HNO₃, and HF) on boron isotope measurement by using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has been investigated. The acid concentration is in the range of 0–0.2 M. Generally, acids can enhance B signal intensities and reduce isotopic mass bias compared to that of the same B concentration in a H₂O matrix. The signal enhancement in each acid matrix differs slightly, while B isotopic mass bias is significantly different among them, with the highest ¹¹B/¹⁰B ratio in the HF matrix and the lowest in the HCl matrix. In HCl and HNO₃ matrices, boron isotopic mass bias reduces when the acid concentration goes up. However, such a scenario is not observed in the HF matrix. Furthermore, the ¹¹B/¹⁰B ratio in the HF matrix is the same as that in the H₂O matrix within the studied acid concentration (up to 0.2 M). This implies that changes in mass bias and the B signal cannot be related to the same process in ICP-MS. We suggest that B signal enhancement in inorganic acids can mainly be attributed to Coulomb fission during aerosol transport towards plasma, while boron ion redistributions in the plasma caused by matrix element (e.g. Cl, N) ionization lead to changes in isotopic mass bias. As acids can cause considerable matrix effects and mass bias for boron, acidity match between samples and standard solutions is imperative for accurate and precise B isotope measurement by MC-ICP-MS.