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Title: Structural studies using ion mobility spectrometry
Author: Griffiths, John Robert
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2001
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The application of ion mobility spectrometry (IMS) to stractural studies of low molecular weight compounds and non-covalent complexes has been investigated using low pressure and atmospheric pressure drift cells. Cyclic and acyclic polyethers were analysed by atmospheric pressure ion mobility spectrometry with a ⁶³Ni ion source. The reduced mobilities of gas-phase cyclic polyether ions may be distinguished from their acyclic analogues as a consequence of differences in the collision cross-sections of their adopted conformations. Peaks attributed to polyether/protonated amine complexes are formed when polyethers are introduced in the presence of N-ethylmethylamine, npropylamine and benzylamine vapour. Variations in the reduced mobilities for the polyether complexes containing isomeric N-ethylmethylamine and n-propylamine guests are associated with small conformational differences for these ions. SYBYL™ molecular modelling software was used to confirm structural characteristics inferred from the experimental mobility data. A novel tandem quadrupole ion trap/ion mobility spectrometer (QIT/IMS) was used to conduct structural studies based on the gas phase mobilities of mass-selected ions. The in-house constructed instrument combining a quadrupole ion trap with a low-pressure (< 10 Torr) drift cell was assessed in terms of resolution, sensitivity and linearity. A membrane inlet was coupled to the QIT/IMS for the direct quantitative analysis of volatile compounds in aqueous samples. The gas-phase positive ion mobility spectra of aromatics, amines, amino acids and non-covalent inclusion complexes of amino acids and amines with polyethers were measured by QIT/IMS. Ion mobilities of isomeric amines in helium, determined relative to benzene at pressures in the range 1-2 Torr, vary with the structure of the amine. The ability of QIT/IMS to differentiate between a pharmacologically active substance and an associated isomeric amine is demonstrated. Non-covalent complexes of cyclic and acyclic polyethers with protonated amines were generated by ion/molecule reactions in the ion trap and analysed by ion mobility spectrometry. The ion mobilities in helium may be interpreted in terms of the preferred conformations for these complexes. The use of polyether hosts as shift compounds for enhancing the relative mobilities of small amine guest ions is proposed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Low molecular weight; Compounds; Non-covalent