Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (M.S.)--University of Missouri-Columbia, 2008. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 12, 2009) Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 243-252). Available also in a digital version from Dissertation Abstracts.

Thesis (M. Sc.)--University of Alberta, 2010. / Title from pdf file main screen (viewed on June 30, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Environmental Engineering, Department of Civil and Environmental Engineering, University of Alberta. Includes bibliographical references.

The use and supply of various organic solvents for analytical chemistry is coming under scrutiny due to their environmental impact. International legislation now prevents the supply of "ozone depleting" solvents for laboratory purposes. Consequently alternative analytical methods to those which had previously relied upon the use of a range of organic solvents need to be developed. Supercritical fluids exhibit some properties associated with gases and liquids, and in particular their solvating characteristics are equivalent to a wide range of conventional organic solvents. Environmentally benign carbon dioxide in its supercritical fluid state can be utilised to imitate the solvating power of a range of organic solvents from non polar pentane through to more polar pyridine. There are many reports detailing the use of supercritical fluid extraction for the isolation of target compounds from a very wide range of solid matrices. The objective of these studies was to develop direct liquid supercritical fluid extraction procedures using carbon dioxide to isolate, concentrate and quantify target analytes from aqueous media. These investigations involved using off-line and on-line supercritical fluid extraction procedures with final analytical detection and quantification being accomplished using a range of chromatographic, spectroscopic and mass spectrometric methods. Within chapters 2 and 3, an alternative infrared method for determining the quantity of oil in process and discharge waters is described. The results of quantification studies involving various oils and hydrocarbons indicate that the custom built supercritical fluid extraction system developed for these investigations directly coupled with an infrared spectrometer provide an alternative method to traditional liquid-liquid extraction procedures that involve the use of ozone depleting and/or toxic organic solvents. Chapter 4 describes how direct aqueous supercritical fluid extraction was used to continuously isolate free testosterone as it was liberated during the enzymic digest of a testosterone-/3-D-glucuronide solution incubated with Helix pomatia glucuronidase. Other studies described within this chapter that also involved the use of direct aqueous supercritical fluid extraction with off-line gas chromatography-mass spectrometry describe procedures for determining trace levels of organophosphate pesticides and polyaromatic hydrocarbons in aqueous samples. The development and use of on-line direct aqueous supercritical fluid extraction coupled with supercritical fluid chromatography-mass spectrometry using atmospheric pressure chemical ionisation for the analysis of phenols at the ppb level is described in Chapter 5. Chapter 6 describes the use of direct aqueous supercritical fluid extraction coupled online with liquid chromatography-mass spectrometry using ammonia chemical ionization for the analysis of three veterinary drugs at the ppb level. Results of off-line and on-line studies involving electrospray tandem mass spectrometry with high pressure liquid chromatography for the analysis of a range of ionophores at the low ppb level following their isolation using direct aqueous supercritical fluid extraction are also presented.

A third of adults in the UK admit to using controlled substances at least once hi their lives and the most commonly abused drug was found to be cannabis, followed by the opiates and ecognine derivatives. Forensic laboratories are continually trying to reduce the turnaround time for samples submitted for analysis, to less than the current time of four days. One of the main aims of this work was to reduce the time taken to prepare, extract and analyse hair for target analytes. A new method combining supercritical fluid extraction and solid phase micro-extraction (SFE/SPME) is introduced. This coupled procedure utilises the advantages of using supercritical carbon dioxide as an extraction solvent and collecting the extract on a selected SPME fibre. Together the combined techniques provide a method that is solvent-free and highly selective, whilst reducing sample preparation to a minimum. Digested hair samples are examined by SEM to find the best method. Alkali hydrolysis and enzyme digestion using proteinase K were found to be the most effective pre-extraction methods. Solid hair samples with the addition of a derivatization reagent (BSTFA) gave the best results using the coupled technique. After optimisation and validation, the extraction from both real and spiked samples resulted in recoveries between 60% to 80% for the target analytes A9 -tetrahydrocannabinol (A9- THC) , cannabinol (CBN) and cannabidiol (CBD). Other forensic applications such as the extraction of polycyclic aromatic hydrocarbons and pesticides from environmental and food samples and the examination of fire debris for the presence of accelerants are also carried out. PAH could easily be extracted from complex matrices to give recoveries of up to 97% for some analytes at the optimized conditions of 90°C at 4500 psi over a 10 minute dynamic extraction period. Pesticide extraction gave recoveries of 60 - 80% while the extraction of accelerants from fire debris clearly showed that accelerants such as diesel can be identified over the coincidental PAH and hydrocarbon peaks found in burnt debris. The coupling of SFE to SPME provides an exciting technique that has a wide range of applications and creates potential for a fully automated on-line system.

No description available.

Supercritical fluids (SF)s have several physicochemical properties that can often make them superior to conventional liquid solvents. These characteristics include relatively high densities, low viscosities, zero surface tension and high diffusivities. This unique combination of properties allows them to have solvating strengths that can approach those of pure liquids while maintaining many of the advantageous transport qualities of gases. In the past decade SFs have seen increased use as solvents for both extraction (SFE) and chromatography (SFC). A particularly exciting area of applications has been in the field of polymeric materials. Since polymers are not discrete molecules, but, rather broad distributions of very similar compounds (oligomers), they can pose interesting challenges for the separation chemist. SFs are uniquely suited to meet these challenges. The goal of the work done in this laboratory over the past few years has been to use SFs to extract and characterize both oligomers and additives from polymeric materials. A method for the post-polymerization fractionation of a low molecular weight, high density polyethylene wax using analytical scale SFE equipment was developed. Supercritical CO₂ was used to separate very narrow molecular weight distributions (MWD)s from the polyethylene feedstock. The resulting MWDs were characterized by SFC and high temperature gel permeation chromatography (GPC) and found to have polydispersities and molecular weights much lower than the parent wax. Supercritical propane was used to fractionate higher MWDs from the feedstock, however its greater solvating strength for the polyethylene oligomers resulted in larger polydispersities. A dual pump SFE system was used to deliver a dynamic mixture of propane in CO₂. The resulting fractions were very similar to those achieved by pure CO₂, but the recoveries were much higher. Increasing the temperature appeared to have both a kinetic and thermodynamic contribution to oligomer extraction. Supercritical CO₂ was also used to extract additives from an insoluble polymeric nitrocellulose (NC). The primary stabilizer additive (diphenylamine) and its nitrated derivatives were extracted from the propellant. The SF extracted stabilizer profile was characterized using liquid chromatography (LC), gas chromatography (GC) and SFC. SFC was shown to provide separations of propellant additives that were superior to the existing LC method while maintaining lower temperatures than GC. Extracts from propellants stored at elevated surveillance temperatures contained more highly nitrated stabilizer derivatives. However, some question was raised as to the actual validity of elevated temperature programs for propellant screening due to potential differences in reaction mechanisms. A LC-thermospray mass spectrometry (MS) interface was modified for use wtih packed column SFC. The system was used as a chemical ionization (CI) source for the high CO₂ flow rates emanating from packed columns. Methane was used as a reagent gas (RG) for positive chemical ionization (PCI). The resulting CO₂ + CH₄ mixed RG was studied at CO₂ pump pressures typical of SFC pressure programming. The background ions varied widely with CO₂ partial pressure and source temperature, however, spectra of a propellant test mixture were relatively unaffected by changing RG. The system was also used to perform negative CI (NCI) using the mobile phase CO₂ as a RG. This method was found to be very useful for nitrated derivatives of diphenylamine. SFC-CH₄-PCI-MS confirmed the intact elution of thermally labile N-nitroso compounds thought to exist in propellants. SFC-CI-MS, both NCI and PCI, was used to characterize the SF extracts of polymeric nitrocellulose and was demonstrated to have potential for the analysis of a wide range of compounds found in the propellant industry. SFC-CH₄-PCI was also determined to be compatible with methanol modified mobile phases. The mobile phases in this case were delivered from premixed cylinders. However, severe limitations regarding the reliability of premixed mobile phases in SFC were shown to exist. / Ph. D.

Supercritical extraction (SFE) has most often been linked to the use of modified or unmodified CO₂ for the recovery of relatively non-polar analytes from solid matrices. The objective of this research was to expand current supercritical fluid (SF) techniques to the recovery of analytes from non-traditional matrices. SFE with three unique matrices was completed. Small mammals are often used in drug toxicity studies. Pharmaceutical dosage verification in the animal feed is a requirement in these studies. Atovaquone, a drug used in the treatment of aids related pneumonia, was successfully recovered from rat feed with supercritical CO₂. Drug recoveries of ≥ 90% were achieved with a range of drug concentrations from 0.03% to 1.1% in the feed. The second phase of the investigation studied the recovery of acyclovir, an antiviral agent, from Zovirax® 5% ointment. This recovery required a radically different approach from all previous SFE techniques, as the analyte was completely insoluble in the supercritical fluid. This unique situation led to the development of "Inverse SFE", where the ointment matrix was extracted and the drug analyte was retained in the extraction vessel. Included in the investigation were the effects of temperature, modifier, drug recovery techniques and length of extraction. Employing a 20 minute inverse SFE, 99% of the acyclovir was recovered from the ointment. Increasing regulation, disposal costs and environmental issues have fueled concerns over the use of chlorinated organic solvents. Currently, over 50% of the samples regulated by the EPA have liquid matrices that have been traditionally analyzed using these solvents. The implementation of solid phase extraction (SPE) has significantly reduced the amount of organic solvent utilized for the extraction of liquid matrices; however, further reduction is desired. The third phase of this work concerned the elution of a SPE disk with SF wherein the disk had been used to concentrate pollutants from fresh and brackish water. Initially, this research focused on the quantitation of polyaromatic hydrocarbons (PAHs) from distilled water. The analytes were deposited onto a solid phase extraction disk and eluted with a SF. The proper method of quantitation, relative versus absolute, was also investigated. Optimization of the SF elution in relation to time, temperature, flow rate, and pressure while maintaining quantitative recoveries was performed. A three step, 27 minute SF elution method resulted from this effort. Recoveries were ≥ 90% for all the 16 PAHs studied. A chamber temperature of 80°C with liquid flow rate of 2 mL/minute was employed. The study was expanded to 39 EPA Method 525.1 analytes in distilled water. Although system contamination proved to be a problem, all but four analytes were quantitatively recovered according to EPA criteria. SF elution studies of brackish water matrices from the Chesapeake Bay indicated suspended sediment was responsible for water retention on the surface of the SPE disk. The retained water interfered with analyte recovery. More thorough drying techniques resulted in the recovery all but five analytes meeting EPA criteria. / Ph. D.

Supercritical fluid extraction (SFE) is becoming an attractive alternative to conventional solvent extraction for many reasons. These reasons include advantages of speed, the ability to be automated more easily than conventional solvent extractions and the lack of solvent disposal after the extraction has been performed. At this date SFE is performed in a multitude of ways with no one method out performing the others. The different ways in which SFE is performed is reviewed. Supercritical fluid extraction of analytes from aqueous solution has not received much attention. The design of a system which allows for the extraction of analytes from aqueous solution has been explored in this thesis. Several related areas (injection techniques for supercritical fluid chromatography and on-line SFE) were also developed. The injection port of a supercritical fluid chromatograph was modified to provide better ( more reproducible) sample introduction. For a 100 ppm 3,5-nitrobenzamide solution in methylene chloride the area reproducibility was increased from 3.2% RSD for the unmodified valve to 0.74% RSD for the modified valve. The method also resulted in a more narrow solvent front as well as an increase of 10% in the number of theoretical plates of the system. On-line SFE\SFC was explored as one possible configuration for the extraction of analytes from aqueous solution. Solvent elimination injection (SEI), was developed for SFC. The difference in vapor pressure between the analytes and solvent allowed for the solvent to evaporate and be transported form the system while the analytes were collected on various traps. After evaporation of the injection solvent the analytes were flushed onto a chromatographic column. SEI allowed for the reproducible injection of larger volumes of sample (solvent and analyte) into the system. SEI allowed for different hardware configurations to be tested without performing an actual supercritical fluid extraction. An off-line solid phase trapping system for SFE was developed. The system trapped the analytes from the SFE effluent onto a solid phase extraction cartridge. The cartridge could then be rinsed in a normal fashion to elute the analytes of interest. Trapping in this way was found to allow for faster extraction rates than liquid trapping. The efficiency of the trapping mechanism was found to be dependent upon the temperature of the trap, the chemical functionality of the phase bonded io the silica and the nature of the analytes. A system which allowed for the extraction of moderate volumes (3-5 mL) of aqueous solution was developed. A test solution of phenols was used to evaluate the system. The extractability of the phenols was found to be a function of pressure of the system and the chemical nature of the phenol. A decrease in extractability of the phenols was found to take place at pressures greater than 250 atm. The distribution coefficient of phenol was found to increase steadily through 400 atm. A decrease in surface area of the supercritica1 fluid passing through the aqueous solution was thought to be responsible for the apparent contradiction in behavior. / Ph. D.