EVIDENCE THAT GAS-PHASE ION MOLECULE REACTIONS ARE RESPONSIBLE FOR THE BEHAVIOR OF CROWN ETHERS UNDER FAST-ATOM-BOMBARDMENT CONDITIONS

The fast atom bombardment mass spectrometry of some crown ethers shows the formation of both [M + H]+ and [M - H]+ ions, paralleling behaviour already observed using electron impact ionization. The study of these oily samples with and without a glycerol matrix, trifluoroacetic acid or alkali metal salts, suggests that the ionization process does not occur in the condensed phase, but in the selvedge region by gas-phase ion-molecule reactions in accordance with the 'gas-phase explosion model'. Positive-ion chemical ionization experiments support this proposal.