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

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 216-234).

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Thesis (Honors)--College of William and Mary, 2009. / Includes bibliographical references (leaves 53-54). Also available via the World Wide Web.

Thesis (Ph. D.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xvi, 193 p. : ill. Vita. Includes abstract. Includes bibliographical references.

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 16, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Dong Xu. Vita. Includes bibliographical references.

This thesis begins with an examination of the feasibility of using the Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) method, and its variants, for the co-extraction of nonpolar and polar pesticides, including highly polar quaternary ammonium salts (QA) and organophosphates (OP). QuEChERS was performed on a mixture of nine different chemical classes of pesticides, with triphenyl phosphate (TPP) as the internal standard, on aqueous Chinese lettuce samples, at 0.1 and 1.0 μg/mL levels. QuEChERS provided superior sample recovery and precision (RSD) for nonpolar pesticides than it did for its polar variants, including most of the polar pesticides and several carbamates, as judged from quintuplicate analyses. A modification of the extraction buffer and cleanup reagent significantly enhanced the recovery of highly polar QA and carbamates at sub–microgram-per-milliliter levels, while maintaining the performance of the other nonpolar pesticides. Thus, QuEChERS is a versatile and convenient methodology for multi-residue analyses, although unambiguous confirmation and quantification of some polar pesticides, namely chlormequat, mepiquat, and glyphosate, required separate analyses using tedious and time-consuming single-residue methods. Liquid chromatography/tandem mass spectrometry (LC-MS/MS) provides the potential advantages of low detection limits, simple sample preparation procedures, and high selectivities for multi-residue analyses of organic toxics in food. In this study, a novel methodology based on LC-MS/MS was developed for the simultaneous analyses of both polar and nonpolar pesticides; an online-coupled hydrophilic-interaction chromatography/reversed-phase (HILIC-RP) separation platform, featuring a HILIC column for online sample enrichment and a downstream high-flow injector for solvent mixing and reconditioning, was constructed to allow efficient, concomitant analyses of both hydrophilic and hydrophobic pesticides from a single sample injection event. The performance of the HILIC-RP system, verified using a standard pesticide mixture, was satisfactory. 6 out the 7 polar pesticides were successfully retained on the HILIC column and 11 out of the 15 nonpolar pesticides were transferred to and separated by the RP column; the remaining compounds were determined as flow-through prior to the HILIC separation. No sensitivity loss of the polar pesticides was observed when using this hyphenated system. The calibration curves for 20 out of the 22 standard pesticides exhibited excellent linear responses (R2 > 0.995) over a typical working concentration range. The performance of the HILIC-RP platform was comparable with those of individual one-dimensional HILIC and RP analyses, thereby potentially eliminating redundant quantification procedures and allowing highthroughput multi-residue analyses of toxic organic compounds. / published_or_final_version / Chemistry / Master / Master of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

A binary mixture of copper (II) chloride and gold (III) chloride solutions were introduced into a FT-ICR Mass Spectrometer through electrospray ionization techniques to produce ion clusters in the gaseous state. A series of families of ion clusters were detected across a range of different concentrations and they were identified as heterometallic mono-cationic clusters with possible hydrated and ligated species present as well. Ab initio calculations on the first member of the family of hetero-metallic monocationic species detected in the mass spectra were carried out using density function theory (DFT) methods and correlation consistent (cc) basis sets. Equilibrium bond lengths and vibrational frequencies were computed and resulting values compared with published literature values. / published_or_final_version / Applied Geosciences / Master / Master of Science