Thermal degradation of O‐acyl oximes under electron impact ionization conditions

Abstract

AbstractThermal degradation of O‐acyl oximes under electron impact ionization (EI) conditions has been examined. The EI mass spectra gave fragment ions originating from thermal degradation, as well as molecular ions M+· and normal fragment ions due to unimolecular decomposition of the M+· ions. The fragment ions due to thermal degradation of O‐acyl oximes were identified by using fast‐atom bombardment (FAB) mass spectrometry with a liquid matrix together with the collision‐induced dissociation (CID) technique. While the FAB mass spectra of O‐acyl oximes gave, preferentially, M+· ions together with some characteristic fragment ions, as well as the molecular related ions [M+H]+ and [M−H]+, the spectra showed little evidence of the fragment ions which may originate from thermal degradation, under EI conditions. The CID spectra of selected M+· ions formed by electron impact also showed little of such fragment ions. The thermal degradation was directly confirmed by measuring the FAB mass spectra of O‐acyl oximes that had been heated in a sealed sample tube.