Detection and identification of cations and anions of ionic liquids by means of electrospray ionization mass spectrometry and tandem mass spectrometry

Electrospray ionization (ESI) and collision-induced dissociation (CID) spectra of nine ionic liquids have been measured. The main fragmentations of most of these ionic liquid cations were due to the loss of a butene molecule. In contrast to tetraalkylammonium ions, CID spectra of aromatic cations may represent insufficient information for unambiguous identification due to their only partial fragmentation. CID spectra of ionic liquid anions, however, allowed their reliable recognition, since isomers/isobars of such inorganic species are rare. Detection limits of cations and anions in a mixture of different ionic liquids seemed to depend on their surface activity as determined by the hydrophobicity of these species.