Thesis (MTech. degree in Environmental management.)-Tshwane University of Technology, 2008. / Aims to determine the presence and levels of DDT and its metabolites in human breast milk samples using supercritical fluid extraction and liquid-liquid extraction techniques.

A novel strategy to investigate interfaces relevant to chromatographic separations is presented. The strategy in this dissertation relies on three key ideas: 1) design and fabrication of appropriate model of chromatographic interface, 2) use of forced dewetting to separate interfacial constituent of mobile phase from its bulk component yet preserves the interface, and 3) use of IR spectroscopy and ellipsometry to investigate the structure and thickness of isolated interface.Stratified structures of ultrathin (< 10 nm thick) silica films on gold using gold oxide as adhesive layer and wetting control agent are used as model solid phase. Such design provides chemical environment of bulk silica surface, does not introduce significant spectral background, is suitable for reflection-based spectroscopies, and allow for easy modification to mimic wide range of silica - solvent interfaces. Bare silica-water models capillary electrophoresis interfaces; water-methanol mixture at octadecylsilane-modified silica represents reversed phase liquid chromatography interfaces.Forced dewetting is used to decouple interfacial constituent of mobile phase from its bulk component; yet, the integrity of interface is preserved. This approach, combined with the use of IR spectroscopy and ellipsometry, allowed for ambient atmosphere characterization of these interfacial layers in terms of their structure, composition, and thickness for water at bare silica. Hydrogen bonding was probed in case of complex water-methanol binary mixture at octadecylsilane-modified silica surface.The analysis of residual water layers formed by forced dewetting at bare silica as a function of bulk solution pH shows that the structure of the interfacial layer is highly ordered compared to bulk, and is also pH dependent. Further, thicknesses of interfacial layers were found to be pH dependent and vary from ~6 (pH 1) to ~9 nm (pH 9). Gouy-Chapman-Stern double layer was found to be inadequate to satisfactorily describe observed trends. In addition, surface enhanced infrared absorbance phenomenon was also observed that aided increased quality of resulting IR spectra.The analysis of residual water-methanol layers formed by forced dewetting at octadecylsilane-modified silica surface as a function of gas phase atmosphere shows that the structure of the interfacial layer is highly dependent on the composition of gas phase. The observed changes indicate that condensation of methanol from gas phase into residual layer and/or evaporation of water from residual layer into gas phase may occur in used experimental setup used in this dissertation. For that reason, more precise quantification of relative amounts of water and methanol in residual layers was precluded. Yet, regardless of investigational conditions, two different hydrogen bonding environments for methanol were distinctively observed.

The aim of this work was to investigate and apply new DLLME systems coupled with LA-ICP-MS and ultra-performance liquid chromatography (UPLC) techniques for the preconcentration and determination of Cr(VI), Co(II), Cu(II) ir Ni(II) ions. / Šioje daktaro disertacijoje apibendrintų mokslinių tyrimų tikslas – ištirti ir pritaikyti naujus Cr(VI), Co(II), Cu(II) ir Ni(II) koncentravimo ir nustatymo metodus apjungiant dispersinę skystafazę mikroekstrakciją (DSME) su lazerinio išgarinimo induktyviai sužadintos plazmos masių spektrometrijos (LA-ICP-MS) bei ultraefektyviosios skysčių chromatografijos (UESCh) metodais.

A process was developed for the production of hexafluoropropylene oxide via the gas-phase oxidation of hexafluoropropylene with molecular oxygen. The non-catalytic oxidation reaction was investigated in an isothermal, laminar flow reactor at a total pressure of 4.5 bar and over the temperature range of 453 to 503 K. Feed mixtures comprising 20 to 67% HFP in oxygen were used at total flow-rates between 150 and 550 cm3 min-1. The reactor was fabricated from 1/8 inch nominal sized, copper refrigeration tubing and was 114.3 m long. The reactor was used in the form of a helical coil. Gas-chromatographic analysis was used for reactant and stable product quantification. The reaction gave hexafluoropropylene oxide, trifluoroacetyl fluoride and carbonyl fluoride as major products. Minor products included tetrafluoroethylene and hexafluorocyclopropane. The oxidation reaction also produced high molecular weight oligomers that were retained on the inner surface of the reactor tube. The operating conditions for the non-catalytic oxidation were optimized independently for HFPO selectivity and yield using quadratic response surface methodology. A maximum HFPO selectivity of 55.81% was identified at 478.2 K, a HFP/O2 molar feed ratio of 1.34 mol mol-1 and a space time of 113 seconds. An optimum HFPO yield of 40.10% was identified at 483.2 K, a HFP/O2 molar feed ratio of 1.16 mol mol-1 and a space time of 121 seconds. Using the weighted-sum-of-squared-objective-functions (WSSOF) multi-response optimization technique, a combined optimum HFPO selectivity and yield of 56% and 40%, respectively, was obtained at 480 K, with a HFP/O2 molar feed ratio of 1.21 and a space time of 118 seconds. This represented the best trade-off between these two performance criteria. A kinetic reaction scheme involving 8 species and 7 reactions was developed, based on the results of the experimental study, and was used to model the non-catalytic oxidation of HFP. The initial steps in this scheme encompassed the addition of oxygen to the double bond of the fluoro-olefin and transformation of the resultant dioxetane intermediate to form HFPO and the haloacetyl fluorides. Subsequent steps included the thermal decomposition of HFPO to yield CF3COF, C2F4 and c-C3F6, as well as elimination of C2F4, and to a lesser extent CF3COF, through oxidation. Rate parameters for the oxidation reactions were determined through a least-squares minimization procedure. The investigation was extended by considering the catalyzed synthesis of HFPO. Four different catalysts were studied viz., 1wt% Au/A12O3, 1wt% Au/ZnO, 10wt% CuO/SiO2 as well as 10wt% CuO/SiO2 doped with caesium. The gold-based catalysts were found to be completely inactive for the oxidation reaction. The caesium promoted, copper-based catalyst appeared to be the most stable and active, with no observable decomposition to copper fluoride. At 453 K, a HFP/O2 molar feed ratio of 0.86 and a weight-hourly-space-velocity of 0.337 h-1, a HFPO selectivity of 85.88% was obtained. This was significantly greater than what was achieved in the non-catalytic system. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2012.

Bibliography: leaves 151-166. / xi, 166 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis describes the development of two novel and complementary analytical approaches for assaying cyanoalanine non-protein amino acids. These assays are used to determine the distribution of these compounds both within and between plants and to identify accessions of common vetch which contain low levels of the cyanoalanine non-protein amino acids in germplasm collections. These analytical tools are used to correlate toxicity observed in animal feeding experiments with the cyanoalanine content. This thesis covers also the first report of the use of diffuse reflectance using dispersive infrared spectrometry for the "in situ" quantification of specific organic components from plant tissue as well as the first use of micellar electrokinetic chromatography for the quantitative analysis of 9-fluorenylmethyl chloroformate (FMOC) derivatised and non-derivatised components of extracts from plant material. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1997

Thesis (Ph. D.)--University of Adelaide, Dept. of Plant Science, 1997. / Includes bibliographical references (leaves 151-166).

Thesis (M.Sc. (Pharmacy)) - Rhodes University, 2008

Mémoire (M.Ress.Renouv.)--Université du Québec à Chicoutimi, 1997. / Document électronique également accessible en format PDF. CaQCU

Thesis (MSc.(Pharmacology)--Faculty of Health Sciences)-University of Pretoria, 2007.

Thesis (M.S.)--University of Delaware, 2006. / Includes bibliographical references.