THERMAL-DEGRADATION OF O-ACYL GRIMES UNDER ELECTRON-IMPACT IONIZATION CONDITIONS

Thermal 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.