Differentiation of N from CProtonated Aniline by NeutralizationReionization

Amino- and ring-protonated aniline are distinguished in the gas phase by neutralization–reionization mass spectrometry. This method takes advantage of the dramatically different stabilities and reactivities of the neutralized forms of N- and C-protonated aniline, to ascertain thereby the specific protonation site(s). Fast atom bombardment ionization of aniline is found to yield primarily the anilinium cation (N-protonated tautomer). In contrast, chemical ionization with a variety of reagent gases is shown to generate mixtures in which the ring-protonated species predominates.