How is the molecular ion of α‐tocopherol formed under fast atom bombardment conditions?

Abstract

AbstractThe mechanism for the formation of the M+· ion of α‐tocopherol, a viscous oily material, under fast atom bombardment (FAB) conditions without a liquid matrix was investigated by using positive‐ and/or negative‐ion electron impact, gas‐phase FAB, gas‐phase fast molecule bombardment and charge‐exchange reaction techniques. The results obtained could not be explained by the charge exchange alone, and they also suggested that M+· ion formation under FAB conditions is not due to direct collisions between analytes and fast atoms but to collision interactions between analyte molecules in a dense gas‐like phase formed immediately after the collision cascade caused by particle bombardment and/or in the collision cascade itself. It is argued that the formation of M+· ions under matrix FAB conditions is essentially due to collision interactions between analyte and matrix molecules. In order to understand the M+· ion fromation, the energetics are discussed from the standpoint of the chargeexchange ionization reaction.