Intrinsic Mobility of Gaseous Cationic and Anionic Aggregates of Ionic Liquids

Travelling-wave ion mobility mass spectrometry was used to measure the intrinsic mobility of a series of gaseous supra-cation and supra-anion aggregates of several ionic liquids. Close mobilities were observed in a T-wave cell filled with helium at ca. 0.8 mbar for [(DAI)n+1(X)n]+ (DAI is the 1,3-dialkylimidazolium cation and X is the anion) as compared to the respective anions [(DAI)n(X)n+1]− for n=0 to 9. The anomalous behavior reported before in the condensed phase seems therefore to be related to the unique structural organization of pure ionic liquids that provides both polar and non-polar regions with directionality in which the anionic species are more retained than the cationic species in the salt network.