Study on imidazolium-based ionic liquids with scanning atom probe and Knudsen effusion mass spectrometry

Scanning atom probe (SAP) and Knudsen effusion mass spectrometry (KEMS) were used to investigate several imidazolium-based ionic liquids (ILs) of the form [R][Tf2N], where [R] can be one of the three cations - [emim], [bmim], and [hmim], and [Tf2N] is the anion of N(SO2CF3)(2). In the case of SAP, it was found that only a cupola-shaped tip allows measuring the proper mass spectra. The dominant peak at m/q of 69 was identified mainly with CF3+ ions generated via decomposition of the [Tf2N] anions. Neither parent molecular ions nor intact anions were detected in our experiments with both techniques applied. At the same time, the peaks of the complete cations were found to be the most intense mass species via thermal evaporation of ILs. It is very likely that in KEMS the fragmentation of evaporated molecules occurred under the electron impact (EI) ionization while in the SAP experiments ILs dissociated into the fragments directly during the pulsed field evaporation/ionization. Copyright (C) 2008 John Wiley & Sons, Ltd.