| Electrospray ionization (ESI) is one of the most widely deployed techniques for generating gaseous ions under atmospheric-pressure conditions for mass spectrometry (MS). The combined ESI-MS technique is widely used for characterization, and qualitative and quantitative analysis of organic and inorganic analytes. All research results presented herein are based on ESI-MS methods.;In one structural study, the utility of CO2 as a reagent for ion-molecule reactions was explored. We found that gas-phase anilide anions generated under negative-mode ESI conditions undergo facile addition to CO 2 in the collision cell of a triple-quadrupole mass spectrometer. The presence of electron-donating substituents on the anilide ring facilitates the addition process by increasing the electron density on the nitrogen atom. Computational results showed that the adduct is not formed if the Gibbs free energy released during the reaction is less than 10 kcal/mol.;A detailed investigation on collision-induced dissociation CID pathways of deprotonated diamide derivatives of p-phenylenediamine demonstrated the formation of an unexpected m/z 159 ion. For example, the anion from N,N-ditrifluoroacetyl- p-phenylenediamine fragments by two consecutive CHF3 eliminations via an ion-neutral-complex intermediate.;Upon activation, deprotonated N,N'-diphenylacetyldapsone fragments primarily by two competing pathways: a phenylketene or a toluene loss by the intermediacy of an ion-neutral complex. The first pathway is favored in the fragmentation process that deprotonated N,N'-di- p-methoxyphenylacetyldapsone undergoes upon activation. However, with deprotonated N,N'-di-p-nitrophenylacetyldapsone, the second fragmentation pathway is dominant.;Moreover, fragmentation studies on deprotonated sulfonamides showed that the m/z 92 ion generated under our experimental conditions from N-butylbenzenesulfonamide is a composite of an anilide anion and an ion of formula CH2NSO2-. Mechanistic studies revealed that other competing fragmentation pathways, such as the formation of the m/z 136 ion by a benzyne loss from deprotonated N-butylbenzenesulfonamide, also exist.;Our investigations on synthetic hexadecanamide demonstrated that a unique protonated butyramide m/z 88 fragment-ion is generated from protonated carboxamides, via an ion-neutral complex, by a non-specific hydrogen transfer from virtually any position of the alkyl cation. A broader investigation on a variety of carboxamides enabled us to make generalizations on the formation of a-, b-, y"-, c"- and z-type ions. |
