Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references. Available also in a digital version from Dissertation Abstracts.

Thesis (M.S.)--University of North Texas, Dec., 2008. / Title from title page display. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains vii, 75 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 74-75).

Thesis (Ph.D.)--York University, 2009. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references. Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR51666

Thesis (Ph. D.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xiv, 152 p. : ill. (some col.). Includes abstract. Includes bibliographical references.

Electrospray ionization (ESI) facilitates the transfer of ions in solution into the gas-phase for analysis by mass spectrometry. The ionization process is intricate and required further investigation, especially because of the lack of in-depth literature on the subject. Furthermore, investigations into the ESI process will serve to assist development of real-time reaction monitoring. To do this, a cationic ionic liquid, butyl methylimidazolium, [BMIM]+, was paired with several counterions and mixed in various solvents. This was analyzed by ESI mass spectrometry to determine the relative response ratio between two observable aggregates. The findings assisted in the elucidation of differential surface activity of chemically distinct ions in ESI, with respect to changes in solvent. Furthermore, the results obtained suggested acetonitrile is an optimal solvent for the analysis of ions of this type due to a reduction in differential effects, whereas other common ESI solvents prove to enhance the surface activity of specific aggregate ions. Further investigations into ESI-MS involved effects of spray head geometry relative to the inlet to the mass spectrometer. The position of the spray-head, the solvent, and additional instrumental parameters were independently adjusted during the analysis of an equimolar mixture of two different ions. It was found that these parameters have dramatic effects on the distribution of signal intensity from one ion to another, and therefore the resulting usefulness of acquired spectra. The sharp contrast in ion intensity, and even differential ion activity, with relatively minor instrument changes (such as temperature programming, gas flow rates and solvent choice) demonstrated the importance of finding the optimal spot for the ESI spray head, especially when signal intensity and a quality analysis is key. Additional ESI-MS work involved working with an industry partner to develop selective charge-tagging reagents for the characterization of petroleum fractions by ESI-MS. A simple chemical derivatization technique was developed in which thiols and disulfides may be selectively analyzed in a complex matrix and easily characterized. These reagents enhanced detection of thiols and disulfides solely due to the nature of the charged tag derivatization agent. The charged disulfides readily and exclusively react with thiols in a complex matrix in a short amount of time. The synthesis of these reagents was simple and resulted in a pure and stable reagent. The efficacy of the reaction was demonstrated using on-line monitoring, while the scope and usefulness of the reaction was demonstrated in petroleum fractions. A combination of UV-Vis spectroscopy and electrospray ionization mass spectrometry was used for real-time monitoring of Pd2(dba)3 activation with sulfonated versions of PPh3 and a Buchwald-type ligand. This provides insight into the effect of ligand and preparation conditions on activation and allows for establishment of rational activation protocols. It is expected that this reaction monitoring technique will be enhanced through the use of tandem mass spectrometry. Finally, an experimental method of visualizing atomic orbitals was developed as a demonstration intended for first year chemistry students. This demonstration involved the examination of nodal and anti-nodal regions of Chladni figures which students could then connect to the concept of quantum mechanical parameters and their relationship to atomic orbital shape. / Graduate

No description available.

The use of femtosecond (fs) laser pulses in laser-induced breakdown spectroscopy (LIBS) and for chemical analysis using mass spectrometry is explored. A comparison of fs-LIBS and remote filament-induced breakdown spectroscopy (R-FIBS) in the analysis of graphite composites yielded more accurate results with filaments due to intensity clamping within the filament. The investigation of fs-LIBS and R-FIBS in the detection of explosives led to the discovery of femtosecond vaporization of intact molecules under ambient conditions. This knowledge was then used in the development of a new ambient laser-based mass analysis technique. The combination of nonresonant femtosecond laser vaporization with electrospray post-ionization called laser electrospray mass spectrometry (LEMS) was investigated as a universal detection method of pharmaceuticals, biological macromolecules and plant tissues. We show the capability of femtosecond lasers to desorb sample without any sample preparation or resonant transition in the sample or substrate. Ambient mass spectral imaging and tissue type classification is also demonstrated. / Chemistry

Pseudo-molecular ion formation is an artifact common to most analyses performed by electrospray ionization mass spectrometry. These species are non-covalent complexes formed between an analyte of interest and any other components (such as mobile phase, additives, and impurities) present in the ionized sample band. Published literature addresses pseudo-molecular ion formation in routine analyses as well as in complicated molecular recognition processes. The majority of these works are directed towards the formation of complexes in the positive ionization mode. Consequently, investigation of pseudo-molecular ion formation in the negative ionization mode is a logical extension of work in this area. Experiments presented here detail the work performed on elucidation of factors controlling ionization efficiency of aromatic acid pseudo-molecular ions by electrospray ionization in the negative ionization mode. Sets of tested acidic analytes, including ibuprofen derivatives and benzoic acid derivatives, were analyzed in the presence of various solution systems by flow injection analysis to determine the effect of pH, concentration, injection volume, and instrumental parameters on dominant ion forms observed in the mass spectra. These ion forms correspond to a deprotonated molecular ion ([M-H]-), a hydrogen-bound dimer ion ([2M-H]-), and a sodium-bridged dimer ion ([2M-2H+Na]-). Report of the latter ion form is unique to this work. Response of these ion forms were found to vary greatly with changing solution parameters, particularly in the presence of common LC-MS modifiers, such as triethylamine, acetic acid, formic acid, and ammonium formate. Results point to the formation of the sodium-bridged dimer ion during gas-phase processes following the release of ions from disintegrated droplets. Ab initio theoretical calculations and correlations with calculated solution phenomena (such as pKa and log P) were used to elucidate structural arrangements and dominant factors controlling pseudo-molecular ion formation by aromatic acids in the negative ionization mode. / Ph. D.

Analysis of low-abundance components in small samples remains a challenge within bioanalytical chemistry, and new techniques for sample pretreatments followed by sensitive and informative detection are required. In this thesis, procedures for preconcentration and separation of proteins and peptides in open microchannels fabricated on silicon microchips are presented. Analyte electromigration was induced by applying a voltage along the channel length, and detection was performed either by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) within the open channel, or by sampling a nL fraction containing the preconcentrated analytes from the channel for subsequent nano-electrospray ionization- (nESI-) or MALDI-MS. Utilizing solvent evaporation from the open system during sample supply, sample volumes exceeding the 25-75 nL channel volume could be analyzed. For preconcentration/separation of components in the discrete channel volume a lid of inert fluorocarbon liquid was used for evaporation control. In Papers I and II, aqueous, carrier-free solutions of proteins and peptides were analyzed, and the method was successfully applied for fast and simple preconcentration of amyloid beta (Aβ) peptides, related to Alzheimer’s disease. The impact of possible impurities in the analysis of carrier-free solutions was investigated in Paper III with the 1D simulation software GENTRANS, and a method for open-channel isoelectric focusing in a tailor-made pH gradient was developed. The latter approach was used in Paper IV for preconcentration and purification of Aβ peptides after immunoprecipitation from cerebrospinal fluid and blood plasma, followed by MALDI-MS from a micropillar chip. Paper V includes simulations of an isotachophoretic strategy for selective enrichment of Aβ peptides. GENTRANS simulations were used to select the electrolyte composition, and 2D simulations in a geometry suitable for on-chip implementation were performed using COMSOL Multiphysics. / <p>QC 20160930</p>