High-Mass Capabilities of Positive-Ion and Negative-Ion Direct Analysis in Real Time Mass Spectrometry

Abstract

Of the ionic liquid 1-butyl-3-methylimidazolium (C+) tricyanomethide (A−) high-mass cluster ions of both positive ([C nA n–1]+) and negative ([C n–1A n]−) charge were generated and detected by direct analysis in real time (DART) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS). After optimization of the settings of the DART ionization source and of the mass analyser, ions of m/ z values unprecedented in DART-MS were detected. Thus, the upper m/ z limits of positive-ion and negative-ion DART-MS were substantially expanded. Negative-ion DART-MS delivered cluster ions up to [C15A16]−, m/ z 3527 (nominal mass of monoisotopic ion), while positive-ion DART-MS even yielded ions up to [C30A29]+, m/ z 6784. The identification of the cluster ions is supported by their accurate mass and exact mass differences corresponding to CA between adjacent cluster ion peaks.