REFINEMENTS OF MASS SPECTROMETRY/MASS SPECTROMETRY AND APPLICATIONS TO ORGANIC ANALYSIS
Abstract
As a part of the development of mass spectrometry/mass spectrometry (MS/MS) for metastable ion analysis, the addition of collision-induced dissociation (CID) capabilities has permitted various novel applications of the technique. This work deals with applications of the CID MS/MS technique; characterizing its usage for analytical questions. The basic experiment involves kinetic energy analysis of fragments produced upon collisional excitation of a mass-analyzed ion generated in a chemical ionization source. The applications presented here include characterization of fragmentation chemistry, isomer analysis, quantitative direct analysis of mixtures, studies of doubly-charged negative ions, and utilization of dual collision phenomena. As a prelude to applications of the CID MS/MS technique the fragmentation chemistry must be well characterized. Studies of the dissociation processes of positive and negative ions formed in a chemical ionization source show systematic fragmentations indicative of the original ion structure. Protonated molecules can undergo functional group specific fragmentations; ketones lose water, ethers exhibit alcohol loss, amines undergo ammonia and amine loss, and esters produce carboxylic acid and alcohol neutral fragments. Deprotonated molecules, viz. the molecular anions of carboxylic acids, generate negative and positive ion fragments upon collision. The negative ion fragmentations are generally limited to decarboxylation reactions while the positive ion fragmentations show numerous dissociations diagnostic of the hydrocarbon backbone. Analytical questions often center around isomer structure differentiation; the CID MS/MS technique is shown to have capabilities for differentiation of structural isomers, geometric isomers, and optical isomers. Structural isomers can typically be characterized by unique fragmentation processes. To magnify the subtle differences in the spectra of geometric isomers, adduct ions are generated which undergo unique dissociations. The requirement of a chiral reagent for optical isomer resolution can be met through generation of an enantiomer adduct ion in a chemical ionization source. In this thesis, application of CID MS/MS to direct mixture analysis shows the quantitative properties of the technique. Analysis of individual isomeric urinary acids without pretreatment of urine samples exemplifies the degree of mixture complexity directly analyzable with CID MS/MS. Questions surrounding the existence of long-lived doubly-charged negative ions in the gas phase are addressed using the CID MS/MS technique. Additional questions arise from the results of this study. Refinements of the CID MS/MS technique allow sequential collision-induced decompositions to be monitored. This investigation initiates the characterization of dual collision processes and their use in organic mass spectrometry.
Degree
Ph.D.
Subject Area
Analytical chemistry
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