Fast atom bombardment induced reduction of aromatic oximes

Aromatic oximes and β-hydroxyoximes are reduced to their corresponding imines by interaction of their solutions in glycerol solvent with a 7-keV argon atom beam. Evidence that the reduction occurs for the protonated oximes comes from fast atom bombardment (FAB) mass spectrometry, tandem mass spectrometry, and time-resolved FAB studies. The requirement that the oxime be in solution was established by comparing the FAB results with those obtained by electron ionization, chemical ionization, and laser desorption. The time-dependent studies of the concentration of the protonated oxime and the reduced product, a protonated imine, were made with and without added anionic surfactant. The abundance of the reduced species depends on the concentration of the protonated oxime at the matrix surface, thus showing that the first step of the reduction mechanism is the protonation of the analyte, followed by reduction and eventual desorption of the reduced species. Surface reduction occurs for all the compounds containing an oxime group that were studied and Is a useful characteristic for identifying oximes by fast atom bombardment mass spectrometry.