Chemical ionization and collision induced dissociation mass spectrometry

• Main Author: Wright, Andrew David
• Published: University of Warwick 1989
• Subjects: 541; QD Chemistry
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.237823

The work contained in this thesis covers two aspects of mass spectrometry, namely chemical ionization (CI) and collision induced dissociation (CIO). Chapter 2 deals with an investigation into the CI mass spectra of tetraisopropyl methylenebisphosphonate recorded using mixtures of argon and dimethylamine as the reagent gas. Comparison of the mixed gas spectra with those obtained using the individual gases revealed additional fragmentation in the case of the mixed gases. The conclusion drawn from the study is that the dilution of dimethylarnine with argon causes the formation of additional protonating species of lower proton affinity than dimethylamine which can undergo more exothermic proton transfer reactions with the sample. Chapter 3 reports a comprehensive study of the chemical ionization mass spectra of urethanes. Four main classes of fragment ions are found in the spectra and the mechanisms for their formation are postulated. Evidence for these mechanisms is obtained from parallel studies of methyl carbamates and from a CIO study. A study of the effects of the collision gas on the CIO mass spectra of leucine-enkephalin is presented in chapter 4. The collision gases used were helium, argon, krypton and carbon tetrafluoride The monatomic gases used cause more fragmentation of the peptide ion as the mass of the collision gas is increased. Conversely, when a poly atomic species is used, the CIO spectra resemble those acquired using a much less heavy target gas. Two possible explanations are proposed. Either the additional internal energy which would be expected to be transferred to the incident ion is absorbed by vibrational modes of the target molecule, or that the amount of energy transferred during the collision is dependent on the particular atoms of the colliding species rather than their overall masses. The final chapter of this thesis is a report of the development of new linked-scan equations for the detection of fragment ions resulting from CID in the first field-free region of a forward geometry mass spectrometer. These scan laws and terms relating to the size of the translational energy losses are incorporated into the calibration software for use with a commercial mass spectrometer.