The work described in this thesis is concerned with the development and application of laser desorption laser photoionisation time-of-flight mass spectrometry (L<SUP>2</SUP>TOFMS). This technique has been used to enable photoionisation mass spectra of a very wide variety of involatile and thermally labile molecules to be recorded. The instrument used for this work is described along with an overview of the fundamental principles behind this methodology. A number of specific classes of molecules have been studied using the L<SUP>2</SUP>TOFMS. These include polyaromatic hydrocarbons, porphyrins, dyestuffs and a variety of analytically important staining agents. The advantages of this approach for analysing complex mixtures, which yield relatively simple mass spectra, have been demonstrated for both environmental systems and commercially important mixtures. It has also been shown that L<SUP>2</SUP>TOFMS can be used for the direct interrogation of target systems adsorbed onto organic substrates. L<SUP>2</SUP>TOFMS has been used to probe the photophysics of both porphyrin molecules and a series of azo dyes. Ionising wavelength dependent fragmentation was observed for a number of metallotetraphenylprophyrins and metallo- octaethylporphyrins. Using 193 nm laser photoionisation, molecular dissociation, involving loss of the macrocycle side groups, was shown to be similar to that obtained by electron impact ionisation. Whereas, at 266 nm, fragmentation via a neutral intermediate state, resulting in the loss of the metal from the macrocycle, competes with further photon absorption. Characteristic azo-bond photoreductive cleavage has been observed for azo molecules when using 266 nm laser photoionisation. This behaviour is linked to the cis-trans photoiosomerisation of the azo bond.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:649077 |
| Date | January 1994 |
| Creators | Dale, Michael John |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13547 |
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