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Title: In situ molecular analysis using two-step laser mass spectrometry
Author: Wright, Scott Jason
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1997
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The work described in this thesis is concerned with the development of laser desorption laser photoionisation mass spectrometry (L2MS) towards spatially resolved analysis of real complex molecular systems. A broad overview of the main elements of the technique is presented. In addition, the experimental procedures and equipment used to carry out this work are described in some detail. Photoionisation mass spectra recorded for a series of azo dyes and porphyrin pigments revealed a marked wavelength dependence in their ionisation and fragmentation channels. The relationship between this behaviour and the known photochemical and photophysical properties of these molecules is discussed. The photochemistry of these molecules has been exploited to aid the differentiation between isomeric species. The selectivity inherent in the L2MS technique has been exploited for in situ studies of a number of real systems. Polymer additives, such as antioxidants and ultraviolet stabilisers, have been successfully detected directly from their host polymer matrices without recourse to extraction, separation or pre-concentration. The technique has been shown to be surface specific, suggesting that the long-term goal of spatially resolved analysis to monitor, for example, additive aggregation and migration to the surface are feasible. In further in situ studies, polycyclic aromatic hydrocarbons, an important class of priority pollutants, adsorbed onto aerosol particulates have been detected. Electrochemically polymerised indoles, known to form conducting films, have also been identified directly from the electrode surface. Finally, current limitations of the L2MS technique are discussed. It is suggested that many of the problems identified are inextricably linked to the laser desorption process. It is shown that energy imparted to neutral molecules during the desorption event can lead to fragmentation. This has implications for both the ionisation of high mass molecules and for quantitative studies. Possible ways of circumventing these problems are discussed. The future outlook for the technique, both for fundamental studies, and as an analytical tool, is also discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available