Evidence that gas‐phase ion‐molecule reactions are responsible for the behaviour 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.