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MS: Fachverband Massenspektrometrie

MS 1: New Mass Spectrometric Methods and Technical Developments

MS 1.7: Vortrag

Montag, 17. März 2014, 12:15–12:30, DO24 1.205

Unexpected Ions in the ICPMS: Abundance and Impact of Doubly Charged Molecular Argide (MAr²⁺) Ions — •Bodo Hattendorf, Bianca Gusmini, Ladina Dorta, Markus Reiher, and Detlef Günther — ETH Zurich, Laboratory of Inorganic Chemistry, Wolfgang Pauli Str. 10, 8093 Zurich, Switzerland

Doubly charged molecular ions containing argon in mass spectra from an inductively coupled plasma mass spectrometer were recently detected using a highly sensitive sector field instrument (NU Plasma HR). Their presence was previously unexpected as only molecular ions with high binding energies were suspected to survive the high temperature, high density atmospheric ICP ion source. Quantum mechanical calculations indicate that such species can be formed via association of a doubly charged elemental ion to a neutral argon atom and their bond energy can reach values of up to 0.3 eV. Doubly charged atomic ions are present in the ICP at varying degree for elements with low 2nd ionization energy as alkaline earth or rare earth elements amongst others. Due to the fact that formation rates are in the 10⁻⁵ range, relative to the corresponding elemental ions, their influence on quantification should remain small. Significant impact can, however, occur in isotope ratio analyses, when aiming at accuracy in the 10 ppm range. Critical contributions may be observed for Sr isotope ratios, where ⁸⁶Sr⁺, ⁸⁷Sr⁺ and ⁸⁸Sr⁺ cannot be resolved from ¹³²Ba⁴⁰Ar²⁺, ¹³⁴Ba⁴⁰Ar²⁺ and ¹³⁶Ba⁴⁰Ar²⁺ respectively or S isotopes where ³²S⁺ and ³³S⁺ cannot be distinguished from ²⁴Mg⁴⁰Ar²⁺ and ²⁶Mg⁴⁰Ar²⁺. Additionally interesting was the fact that the corresponding singly charged molecular ions are by about 10 times less abundant, despite the more than 10 times higher concentration of the atomic ions within the ICP source.