The metastable ion fragmentation reactions of protonated α‐amino acids were recorded. In addition, the low‐energy collision‐induced dissociation (CID) reactions were studied as a function of collision energy and breakdown graphs, expressing the energy dependence of the fragmentation reactions, were established for a variety of protonated amino acids. The fragmentation reactions observed depend strongly on the identity of the R group in H2NCH(R)COOH. Protonated amino acids containing only alkyl groups in the side‐chain fragment primarily by elimination of (H2O+CO) in both metastable and CID reactions. Hydroxylic and acidic amino acids show loss of H2O and loss of (H2O+CO) from MH+ with the H2O loss occurring from the side‐chain and (H2O+CO) loss occurring from the α‐carbohydroxy group. Amidic amino acids show NH3 loss from the side‐chain and (H2O+CO) loss from the carbohydroxy group. Aromatic and sulfur‐containing amino acids show loss of NH3 from MH+, as does lysine. Protonated arginine shows a variety of fragmentation pathways, including elimination of NH3, elimination of neutral guanidine and formation of protonated guanidine. The energy‐dependent breakdown graphs elucidate a variety of secondary fragmentation reactions of the primary fragment ions.

Secondary ion mass spectra and images were obtained from spikes of choline chloride, acetylcholine chloride, and methylphenylpyridinium iodide deposited onto specimens of porcine brain tissue. Samples were subsequently subjected to a dose of 10-keV Cs(+) sufficient to suppress secondary ion emission characteristic of the targeted analytes. Following ablation of the samples by massive glycerol clusters generated by electrohydrodynamic emission, secondary ion mass spectra and images could be obtained that reflected the identity and location of the spiked analytes. The absolute intensity of secondary ion emission that followed ablation was found to be between 30 and 100% of the intensity obtained prior to exposure to the high dose of Cs'. Not all chemical noise is removed by ablation, however, so that the signal-to-noise ratios after ablation correspond to between 10 and 85% of their values observed under conditions of low primary ion dose.

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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.

A focused Cs+ beam was used to obtain secondary ion mass spectra and images from samples of stearic acid on gold before and after ablation by a beam of massive cluster ions. Ablation appears to have two effects on secondary ion emission. First, the number and intensity of peaks reflecting contamination are substantially reduced. Secondly, the absolute intensity of secondary ion current characteristic of the analyte increases. These features simplify mass spectra and improve contrast in the images obtained.