Liquid Injection Field Desorption/Ionization-Mass Spectrometry of Ionic Liquids

Ten ionic liquids based on four types of organic cations, C+ (imidazolium, pyrrolidinium, pyridinium, and phosphonium), combined with various types of anions, A−, were analyzed by liquid injection field desorption/ionization- (LIFDI) mass spectrometry. For the purpose of LIFDI analysis the ionic liquids were dissolved in methanol, acetonitrile or tetrahydrofuran at concentrations of 0.01-0.1 μl mL−1. The measurements were performed on a double-focusing magnetic sector instrument. In all ionic liquid LIFDI spectra, the intact cation of the compound yielded the base peak accompanied by cluster ions of the general formula [C2A]+ and occasionally [C3A2]+. Tandem mass spectrometry and reconstructed ion chromatograms were employed to reveal the identity of the observed ions. Although limited to positive-ion mode, LIFDI also provided analytical information on the anions due to cluster ion formation. Depending on actual emitter condition and ionic liquid the limit of detection in survey scans was determined to 5-50 pg of ionic liquid.