Price, Sarah Ellen (2010)
Ph.D. thesis, University of Birmingham.
A commercial Ion Mobility Spectrometer that is designed to detect Chemical Warfare Agents (CWAs), is modified by the addition of a second ion gate, and connected to a commercial Ion Trap Mass Spectrometer (ITMS). The addition of the second gate allows selection of individual ion mobility peaks for m/z analysis in the ITMS. This was demonstrated with the organophosphorus ester ions (CWA nerve gas simulants). The ITMS was used to perform isolation and fragmentation of the CWA simulants ions produced in the IMS. For the organophosphates dimethyl methylphosphonate, diethyl methylphosphonate and diisopropyl methylphosphonate, two ion mobility peaks were observed, which are shown to be the ammoniated monomer and ammoniated dimer ions. Using an ElectroSpray Ionisation (ESI) - ITMS, the fragmentation pathway of dimethyl ethylphosphonate (DMEP) is investigated. The isotopomers of DMEP have unusual fragmentations, and density functional theory calculations are used to aid in the interpretation of the mechanisms involved in these fragmentations. Of note, it is shown that entropy must be taken into consideration, and hence the free energy of the final transition involved in the mechanism, so that the true rate-limiting steps can be determined. Preliminary fragmentations using ESI-ITMS of eighteen other organophosphorus esters have been undertaken. These give an insight as to which fragmentations will require further investigations involving Density Functional Theory (DFT) calculations and deuterated isotopomers to fully understand the mechanisms involved.
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