Molecular Detection and Identification Using Laser Mass Spectrometry

Sander, Joseph (1994) Molecular Detection and Identification Using Laser Mass Spectrometry. PhD thesis, University of Glasgow.

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Chapter 1 gives a brief review of the advent of laser based techniques for atomic and thereafter molecular detection. The laser based techniques have been used in conjunction with mass spectrometers and other spectroscopic instruments, with the system based on a Time-of-flight mass spectrometer. The essence of the thesis is to show results pertaining to detection of explosive type molecules and currently deployed techniques in this area are discussed in this chapter. Chapter 2 gives detailed insight into the laser interaction with matter and the fragmentation mechanisms which result in the production of atomic and molecular species. The pros and cons of some ionisation schemes are put forward and a discussion of those deployed in our experiments is carried out. Chapter 3 is an exposition of the various components of the apparatus used. Chapter 4 highlights the presence of an impurity, viz., benzene in our nitrobenzene sample and also demonstrates the potency of our technique as a sensitive analytical instrument. A number of different techniques were used by the author in order to show the presence of the contaminant. These techniques provided inconclusive evidence to support our prediction, unlike the information provided by the TOF system. This system has shown both the presence and further the unambiguous identification of the contaminant. Chapter 5 deals with nitrobenzene and o-nitrotoluene which are the simplest compounds of the nitroaromatic group. It describes the typical fragmentation patterns observed and a thorough discussion of the most prominent fragment, namely, the NO ion. Also a computer program written by the author is used to compare the experimental with theoretical results. The origins and significance of this ion for sensitivity and selectivity purposes is investigated. Measurements from the nitrobenzene sample have demonstrated that parts per billion sensitivity levels can be attained. Chapter 6 pursues the investigation of the fragments concentrating on the atomic species of oxygen & hydrogen which are analysed by Dr Marshall and the author. An analysis of the possible pathways leading to the oxygen ion formation are discussed. The second half this chapter looks at the various higher mass fragments obtained from nitrobenzene. From the presence of the higher mass fragments, interpretations of the possible fragmentation pathways has been elucidated by Dr Kosmidis. Of primary significance in this analysis was the first recorded presence of the nitrobenzene parent ion in a laser photolysis experiment. Chapter 7 discusses results from a variety of commonly used explosive compounds obtained by Dr Marshall and the author. Their analysis is undertaken using the modified sample entry system. This allows the variation in signal heights against temperature to be recorded which were subsequently plotted. The identification of the individual species is sought from the mass spectra obtained which were also used to determine sensitivity levels.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Kenneth Ledingham
Keywords: Applied physics, Molecular physics, Optics
Date of Award: 1994
Depositing User: Enlighten Team
Unique ID: glathesis:1994-75009
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 27 Sep 2019 14:38
Last Modified: 27 Sep 2019 14:38

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