No description available.

Peripheral steroids and oxycholesterols are important lipid compounds controlling various functions in the human body. Steroid analysis of biological samples is routinely employed in the clinical environment as an essential source of information on endocrine and metabolic disorders. It has been reported that stress related neurosteroids have been implicated in the development and prognoses of neurodegenerative disorders such as Alzheimer’s disease (AD). These compounds have been identified as possible biomarkers in the diagnosis of AD and other neurodegenerative disorders. Therefore, methods for the simultaneous analysis of steroids from the four major classes (estrogens, androgens, progestogens and corticosteroids) are vital in providing useful and more comprehensive data. Homeostasis of cholesterol in the brain is maintained primarily by metabolism to oxysterols, including oxycholesterols. These oxycholesterols act as a transport form of cholesterol as it readily navigates the blood-brain barrier. Oxycholesterols are generally more bioactive than cholesterol and is of interest in pathophysiology. Moreover, if their production in cells and tissues and/or their introduction with dietary animal fat are excessive, oxycholesterols could indeed contribute to the pathogenesis of various disease processes. The first study in this thesis focuses on a novel supercritical fluid chromatography–tandem mass spectrometry method for targeted analysis of eighteen peripheral steroids. The method is simple and fast. It has sufficient sensitivity for quantification of 18 different steroids in small volume human plasma. Therefore, this novel method can be applied for screening many steroids within 5 minutes providing the possibility to use for routine healthcare practice. The second study involves the quantification of three adrenal steroids in plasma from domesticated White Leghorn (WL) chickens and Red Junglefowl (RJF) birds. The domestication effects on stress induced steroid secretion and adrenal gene expression in chickens are evaluated. The third study focuses on determination of more than ten oxycholesterols in biological samples with a gas chromatography–mass spectrometry method and a supercritical fluid–tandem mass spectrometry method.

Thesis (M. Sc.)(Chemistry)--University of Pretoria, 2006. / Summaries in English and Afrikaans. Includes bibliographical references. Available on the Internet via the World Wide Web.

No description available.

Thesis (doctoral)--University of Helsinki, 2008. / Includes bibliographical references. Also available on the World Wide Web.

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.

The analysis of polar compounds has been studied by SFC using 100% CO₂ or methanol modified CO₂ as the mobile phase. Both microbore packed and capillary columns are employed to separate the mixtures of steroids and agricultural compounds of various chemical classes such as amides, sulfonamides and ureas. The highly deactivated and crosslinked stationary phases used for both packed and capillary columns afford the elution of polar analytes with 100% CO₂ which in turn makes the on-line FT-IR detection of these analytes feasible. The flow cell interface is employed which provides very low detection limits. Spectra with high signal to noise ratio are obtained for the analytes with real time data acquisition. Some polar and structurally similar triazine herbicides are separated using a gradient mobile phase and a rapid separation of all the components with complete resolution is achieved. The effect of flow rate, column outlet pressure and the temperature on resolution is also studied for these analytes. The performance of microbore packed and capillary columns is compared using polar and nonvolatile solutes and the retention and resolution offered by both the columns are also compared. Several van Deemter plots are generated at various constant operating densities and temperatures. Also, the effect of density and temperature on efficiency and resolution is studied for capillary column with split and splitless injection techniques. Several conclusions regarding the favorable operating conditions in each case can be drawn based on the results obtained here. / Ph. D.

Alkylphenol ethoxylates (APEOs), alcohol ethoxylates (AEOs), and alcohol propoxylates (APOs) are non-ionic surfactants used in daily care products and detergents. They are formed as an oligomeric series with a varying distribution, which determines their commercial application. The goal of the research performed was the development of sample characterization methods for non-ionic surfactants utilizing supercritical fluid chromatography (SFC) under mild instrument operating conditions. The aryl group present in APEOs allowed ultraviolet (UV) detection, with an equal molar response for oligomers, allowing average molar oligomer values to be calculated. APEOs were separated by ethoxylate unit via SFC-UV as well as normal phase HPLC-UV employing packed columns. Stationary phase and column length were varied in the SFC setup to produce the most favorable separation conditions. Fractions from SFC runs of APEOs were collected and analyzed by flow injection analysis electrospray ionization mass spectrometry (FIA-ESI-MS) to identify fraction composition. SFC provided shorter retention times with similar resolution as HPLC for separation of APEOs and consumed a smaller amount of organic solvent. AEOs and APOs lack functionality capable of absorbing UV light outside the UV cut-off of normal organic solvents. SFC was able to separate AEOs and APOs derivatized as trimethylsilyl ethers (TMS) with pure CO2 with detection at 195 nm. The instrumental conditions, however, needed for separation necessitated high temperature and high CO2 pressure. Derivatization of alcohol polyether samples with an UV absorbing agent was achieved with phenylated disilazane-chlorosilane mixtures forming phenylsilylethers detected at 215 nm. Use of an organic solvent-modified CO2 mobile phase afforded lower pressure and temperature conditions for oligomer separation. The use of polar embedded alkyl phases combined with use of organic modified CO2 produced good resolution between oligomers. Better peak shape and shorter retention times were realized with methanol-modified CO2 than acetonitrile-modified CO2. Peak assignments were made via SFC coupled with ESI-MS detection in the positive ion mode. SFC-UV and SFC-ESI-MS data were jointly used for calculation of average molar oligomer values. Proton nuclear magnetic resonance (1H-NMR) analysis of non-derivatized samples was performed to determine average molar oligomer values and was used for comparison with values calculated from SFC-UV data. / Ph. D.

The thesis outlines an investigative study of the supercritical fluid extraction (SFE) of organic natural products from two Meliaceae species. Extractions from ground wood, bark and seeds of the selected species were studied. Qualitative and quantitative studies were performed using a number of techniques. In the qualitative study, both off-line and on-line combination of micro-SFE with capillary gas chromatography (SFE-GC) were performed on the wood and bark of Cedrela toona to show the applicability of the technique in the analysis of semi-volatile components from plant matrices. Results for the on-line and off-line SFE-GC were comparable and indicated that the on-line studies could be used to predict results obtainable from large scale SFE. Dynamic SFE of the limonoid (cedrelone) from the wood of Cedrela toona using pure and modified carbon dioxide was studied on the basis of a theoretically-derived dynamic extraction model. Extracts were collected for different lengths of time in order to investigate the extraction kinetics of this compound. The theoretically-derived model which involved extrapolating data obtained from shorter extraction times was used to estimate the amount of the compound present in the wood. The estimated quantitative results were found to be comparable to exhaustive extractions using liquid hexane as well as methanol-modified carbon dioxide. Further, data from the SFE extractions were fitted into the model to produce a characteristic kinetic curve from which factors controlling the extraction of the specific compound could be predicted. Following the dynamic extraction study, a statistical optimisation strategy was used to propose a model equation for the extraction of cedrelone from the wood of Cedrela toona. As the preliminary step, a screening design utilising a two level, three-factor full factorial analysis was used to study the effects of the variables pressure, temperature and the length of extraction time on the yields of cedrelone from the wood of Cedrela toona. By a statistical analysis of variance (ANOVA) at the 95% confidence level on the preliminary data collected, pressure and temperature were found to be the significant variables influencing the yields of the compound. Finally response surface methodology using the central composite design was used in an attempt to determine the maximum response space for the pressure and temperature effects by plotting a 3-dimensional response surface graph. An ANOVA study at the 99% confidence level was then employed to establish the true model equation for the extraction. / Thesis (M.Sc.)-University of Natal, 1995.

Supercritical fluid chromatography has recently been coupled to an ICPMS detector. The method has been shown to be suitable for the speciation and analysis of organometallic compounds at trace levels. This study has attempted to further the research initiated by other groups in this field by developing a new interface for coupling these two instruments. The new interface makes use of a modified join between the nebuliser and the torch in the ICP unit. The effect of the mobile phase on the plasma with time has been investigated and little spectral background interference has been observed. The chromatographic conditions were optimised using a flame ionisation detector and a series of tin, arsenic, iron, and mercury compounds were analysed using SFC-ICPMS. Mter focusing the ICP-MS on the element of interest, each compound was evaluated in terms of the change in peak intensity with change in concentration and the theoretical detection limits were compared to the practical detection limit. The restrictor temperature was determined using a rough calibration procedure with bench top experiments. The effect of the restrictor temperature on the peak intensity of each compound was then studied. All results were plotted and a theory for the observed trends and observations is proposed. The results obtained and the interface used have been compared to the results and interfaces of other groups and differences have been explained. Attempts to extract relevant compounds from topsoil using supercritical fluid extraction were made. Finally, sediment samples were collected from relevant points in Durban Bay and an attempt was made to extract these samples using supercritical fluid extraction. The extracted samples were analysed using SFC-ICPMS although little success was obtained. Reasons for the failure of this method on the real samples have been proposed. In the concluding section of this study SFC~ICPMS has been evaluated in terms of its future applicability and use as a viable analytical method. / Thesis (M.Sc.-)-University of Natal, Durban, 1994.