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Title: The nature and origin of mass spectral peaks
Author: Al-Mohammed, Maria Estela de Freita
ISNI:       0000 0001 3407 273X
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1975
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In Chapter one, a general review of mass spectrometry was made in which the history of mass spectrometry was traced from the discoveries of Goldstein and Wien to J. J. Thomson's first mass spectrograph and Aston's first mass spectrometer. The evolution and improvement in these early instruments was followed by reference to the work of Barber and Stephens, Nier, Herzog and Mattauch for the development of double-focusing instruments. Other types of instruments such as the dynamic instruments, have also been mentioned. Methods of ionisation and systems of sample introduction were described, as were the uses of mass spectrometry in analytical chemistry, both qualitatively and quantitatively, and in other branches of science. Automatic data acquisition, reduction and processing techniques, including precise mass measurement, were mentioned. Several theories useful in the interpretation of mass spectra were considered. The types of ions formed in the mass spectrometer were indicated and particular emphasis was placed on the use of metastable ions as a source of information to the organic mass spectroscopist. In addition, the relevance of thermochemical measurements, isotopic labelling, substituent effects, ion-molecule reactions and chemical ionisation to ion structure determination was discussed. In Chapter two, a new method of precise mass measurement of ions by mass spectrometry was described, and compared with methods used in the past by other workers. These ranged from the classical peak matching technique to the first semiautomatic process developed by Biemann and finally to ether more advanced automatic processes for both electrical and photographic recording, using on or off-line systems. The new mathematical method used, spline-fit interpolation was shown to yield results which were as accurate as the results obtained by the basic automatic method of Biemann; moreover, it had several advantages in its simplicity and applicability to both electrical and photographic recording systems. In Chapter three, the shape of the peaks in a double-focusing mass spectrometer in slow scans was studied. The mathematical treatment and the results showed that the peaks can be considered triangular. The calculation of the areas of the peaks accordingly became an easier task than if they were calculated using the planimeter, even in a digitisation treatment. In Chapter four, a review of ionisation phenomena was made. The definitions of ionisation and appearance potentials were given and methods for their calculation critically reviewed. Ways in which thermochemical data and structural details may be elucidated from these data were described. The ionisation and appearance potentials for the positive ions of methanol, deuterated methanol and ethylene glycol and their fragments were calculated from experimental data acquired by electron-impact on the neutral molecule. Thermochemical data and structural details derived from these observed values were discussed, and a compelling argument leading to the conclusion that the structure of the ion CH3O+ is in fact CH2OH+ was presented.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available