Molecular Ions of Ionic Liquids in the Gas Phase

Abstract

Ionic liquids form neutral ion pairs (CA) upon evaporation. The softness of the gas-phase ionization of field ionization has been used to generate "molecular ions," CA+•, of ionic liquids, most probably by neutralization of the anion. In detail, 1-ethyl-3-methylimidazolium-thiocyanate, [C6H11N2]+ [SCN]-, 1-butyl-3-methylimidazolium-tricyanomethide, [C8H15N2]+ [C4N3]-, N-butyl-3-methylpyridinium-dicyanamide, [C10H16N]+ [C2N3]-, and 1-butyl-1-methylpyrrolidinium-bis[(trifluormethyl)sulfonyl]amide, [C9H20N]+ [C2F6NO4S2]- were used. The assignment as CA+• ions, which has been confirmed by accurate mass measurements and misassignments due to thermal decomposition of the ionic liquids, has been ruled out by field desorption and electrospray ionization mass spectrometry of the residues. © 2008 American Society for Mass Spectrometry.