Elucidating the structures of molecules, mixture components and reactive intermediates by gas-phase ion -molecule reactions in a mass spectrometer

Michael Alan Watkins, Purdue University


High-resolution and accurate mass spectrometric instrumentation is often employed to mass resolve unknown mixture components and to provide their molecular formulas. Tandem mass spectrometric (MSn) collision-activated dissociation (CAD) is commonly used to aid in structure elucidation. However, since the elemental connectivity can only be inferred by using these techniques, the identities of the functional groups in the analytes often remain unknown. The first three studies presented in this thesis address this issue by using the chemical specificity of ion-molecule reactions to provide functional group information. The first study demonstrates the concept of ion-molecule reaction-assisted structure elucidation by introducing methods that can be used to identify the functional group present in a series of simple monofunctional analytes. The second study extends this method to encompass a series of polyols commonly employed as drug tablet excipients. This method was shown to be useful for counting the number of functional groups in the polyol analytes. The third study describes the development of a functional group-selective ion-molecule reaction for the screening of compounds with a nitrogen oxide functional group. This method is of particular interest since these species are commonly formed during the metabolism and degradation of pharmaceuticals, and they are typically considered to be genotoxic. The fourth, and final, study in this thesis describes the rapid interconversion of phenylcarbene radical cation to dehydrotropylium cation. Thermochemistry and computations suggest that the major pathway to rearrangement is through a solvation mediated mechanism. Ion-molecule reactions revealed that phenylcarbene radical cation and dehydrotropylium cation represent 20% and 80% of the total C7H6 ion population, respectively.




Kenttamaa, Purdue University.

Subject Area

Analytical chemistry

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