Fundamental and applied studies in tandem mass spectrometry

Tapan Kanti Majumdar, Purdue University

Abstract

Tandem mass spectrometry is well established as an important analytical technique. This method can provide structural and fundamental information on impure samples with enhanced specificity and sensitivity. A kinetic method which is based on MS/MS of cluster ions is used to distinguish epimeric alcohols by their relative gas-phase acidity values. The high sensitivity of the method is reflected in its ability to distinguish isomers having gas-phase acidity differences of only 1 kcal/mol. Changes in the type of alcohol groups involved in hydrogen bonding to the proton have a discernible influence on the relative rates of competitive dissociation of the proton-bound dimers. Distinction of gas-phase isomers of (C$\sb2$H$\sb3$O) $\sp{+}$ and (C$\sb2$H$\sb3$S) $\sp{+}$ ions is achieved by structural characterization of the ion/molecule reaction products of these ions with neutral isoprene and methylanisoles using MS/MS/MS experiments. The acetyl cation forms a (4+2$\sp{+}$) Diels-Alder cycloaddition product with isoprene and an intact adduct with methylanisoles. The o- and m-methylanisoles both form methyl methoxytropylium ions by gas-phase reactive collisions with the oxiranyl cation, while p-methylanisole forms ionized 2,4-dimethylanisole. Ion/molecule reaction of (C$\sb2$H$\sb3$S) $\sp{+}$ with m-methylanisole allows distinction of the thioacetyl ion from the other (C$\sb2$H$\sb3$S) $\sp{+}$ isomers. Pyrolysis tandem mass spectrometric studies of poly(alkyl)isocyanates exhibit exclusive formation of cyclic trimers. Their fragmentation chemistry includes successive dealkylation of the ionized trimers to form protonated cyanuric acid, $\alpha$ and $\beta$ C-C bond cleavages and charge remote fragmentations. A new method is developed to examine the monomer distributions and it shows that some of these copolymers are random. Pyrolysis/tandem mass spectrometric analysis on poly(N-alkyl-4-vinyl-pyridinium) triflates shows the formation of five series of ions during pyrolysis. These are singly charged ions formed by the loss of only one triflate group from the pyrolyzed oligomer fragments. Formation of this type of ion during DEI, DCI and MS/MS of polysalts is unprecedented. Sequence distribution of the copolymers, elucidated using MS/MS and Bernoullian statistics, shows that the sequence of monomers is dependent on the methods of synthesis of the polymers.

Degree

Ph.D.

Advisors

Cooks, Purdue University.

Subject Area

Analytical chemistry

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