Reactive collisions in quadrupole cells. 3: H/D exchange reactions of protonated aromatic amines with ND3.

The H/D exchange reactions of a variety of protonated aromatic amines with ND3 m the collision cell of a hybrid BEqQ tandem mass spectrometer have been studied. The MH(+) ions were prepared by CH4, t-C4H10, and NH3 chemical ionization (CI) and, for some amines, by fast-atom bombardment (FAB). Evidence is presented that the kinetic energy of the incident ion as well as its internal energy must be dissipated by nonexchanging collisions before exchange occurs, once deactivated the MH(+) ions exchange efficiently, which leads, in most cases, to [MHJ(+) d x ions m which all active hydrogens have been exchanged. The MH(+) ion of 1,3-phenylenediamine formed by gas-phase CI exchanges only very slightly with ND3 whereas a significant fraction of the MH(+) ions formed by FAB exchange efficiently. This difference is rationalized in terms of dominant formation of the ring-protonated species in gas-phase CI reactions and significant formation of the N-protonated species by FAB with only the N-protonated species exchanging efficiently. Similar, although less pronounced, differences are observed for the MH(+) ion of m-anisidine. In a number of cases apparent exchange of aromatic hydrogens also is observed. Evidence is presented for the interchange of ring and amine hydrogens in protonated aromatic amines and it is suggested that only the N-protonated species undergoes significant exchange with ND3.