Abundance and Impact of Doubly Charged Polyatomic Argon Interferences in ICPMS Spectra

Doubly charged molecular ions of alkaline earth metals and argon could be identified as spectral interferences in an inductively coupled plasma mass spectrometer. These molecular ions were found to occur at abundances reaching about 10–4 relative to the alkaline earth atomic ion abundances. They can thus substantially affect ultratrace analyses and, when present at similar concentration as the analyte elements, also isotope ratio measurements. For the case of Cu and Zn isotope ratio analyses, the same mass concentration of Sr was found to alter the measured 63Cu/65Cu and 64Zn/66Zn isotope ratios by −0.036‰ to −0.95‰ due to SrAr2+, appearing at m/Q 63 and 64. BaAr2+ can affect Sr isotope analyses, MgAr2+ may impair S isotope ratio measurements, while CaAr2+ may cause interference to Ca+ isotopes. The abundances of the doubly charged molecular ions were higher than those of the corresponding singly charged species, which is in accordance with their generally higher bond dissociation energies. The relative a...