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The secret life of small alcohols: the discovery and exploitation of fragmentation, adduct formation and auto-modification phenomena in differential ion mobility spectrometry leading to next-generation toxicity screening
The research presented in this thesis started with the idea to study alcohols as modifiers and dopants in differential ion mobility spectrometry (d-IMS) to produce complicated chemical signatures to explore a concept of chemical labels for product security application. D-IMS is a gas phase atmospheric pressure separation and detection technique which distinguishes compounds based on differences in their ions mobility as their travel under a low and high electric field. The hypothesis was that alcohols will form typical d-IMS products such as protonated monomers and proton bound cluster ions. However, the very first experiments revealed unexpected phenomena which included changes in the mobility of ions over a narrow range of concentrations that could not be explained by existing theory. Another observation was the apparent regeneration of reactant ions. It became evident that the observed phenomena had not been described in the open literature and that addressing the research-questions that were being raised would be essential for the determination of alcohols by d-IMS and its use in medical applications for toxicity screening and monitoring of alcohols. The above discovery shifted the research objective towards a fundamental and comprehensive study on the behaviour of alcohols in d-IMS.
This thesis describes designed experiments and constructed systems allowing the efficient study of effect of concentration, electric field and temperature on the d-IMS responses of alcohols. The results of those studies demonstate: extensive fragmentation of alcohols, including previously undescribed fragmentation patterns with regeneration of the hydrated proton; new phenomena of adduct ion formation within the d-IMS drift tube, observed in the case of methanol within a narrow range of concentration; and self-modification of the alpha function of alcohols. This knowledge was exploited by developing an non-invasive analytical method for recovery, separation and detection of toxins from human saliva (including alcohols, diols and GHB) using TD-GC-d-IMS (thermal desorption - gas chromatography d-IMS) within a full range of toxicological concentration levels.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.