Analytical Chemistry and Spectroscopy
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
The ion [C3H5]+ generated in a chemical ionization source by a variety of methods, including protonation and charge exchange, exhibits a metastable peak for H2 loss which is two orders of magnitude weaker than that formed in an electron impact source. The stable [C3H5]+ ions generated by electron impact and chemical ionization undergo collision-induced dissociation to a comparable extent, both losing H2 by only one of the two competitive mechanisms observed for metastable ions. In contrast to the behavior of [C3H5]+, the molecular ions of p-substituted nitrobenzene, generated by charge exchange at high source pressure, yield composite metastable peaks for NO loss which are very similar in shape and intensity to those generated by electron impact. The contrasting behavior of the metastable ions extracted from high pressure ion sources in the two systems may be due to differences in the efficiencies of quenching of the ionic states responsible for fragmentation as metastable ions. It is noteworthy that the NO loss reactions require considerably lower activation energies than does the H2 loss reaction.
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