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No description available.

This thesis presents the experimental work with the main aim of developing new electrochemical based methods for detecting thiol-containing molecules, specifically homocysteine, glutathione, and cysteine, with little to no sample treatment in an aqueous system. The first chapter introduces the principles and techniques of electrochemistry. The second chapter gives a brief introduction to the importance of thiol containing molecules in biological systems; thus, the need for its analytical determination and quantification. This thesis reports a suitable electrochemical methodology to selectively detect thiols using a combination of different ortho-quinone derived mediators and carbon electrode materials. The methodology exploits two ortho-quinone reaction pathways with a thiol molecule, electrocatalytic and 1,4-Michael addition reaction. Proof-of-concept was carried out in buffered systems then realized in synthetic and real biological sample; where ultimately, quantitative performance in 'real world' sample was shown to be analogous to a commercially available enzyme test. Finally, screen-printed electrodes are employed in the presented study to show the prospect for a point-of-care system. The compact design, such as having a three-electrode system printed onto a single strip, allows versatility and easy utilization. These electrochemical chips are ideal and advantageous for high throughput applications. Overall, the development of a quick, easy, and cheap methodology for thiol determination discussed in this thesis makes a significant contribution to the clinical and biomedical community as an alternative and simpler diagnostic pathway.

The work presented in this thesis aims at overcoming the limitations of current amperometric gas sensors. The applicability of room temperature ionic liquids to be employed as potential electrolyte in gas sensors has been examined. This thesis demonstrates that RTILs have great potential to replace conventional electrolytes due to their wide electrochemical windows, negligible vapour pressure, inherent conductivity and sensitivity. A model to simulate the current response at porous electrodes has also been proposed to provide a theoretical support for the future application of porous electrodes in gas sensors. The results of these researches are summarised as follows: Chapter 1 introduces the fundamentals of electrochemistry which are employed throughout this thesis. Chapter 2 presents a comprehensive review of the history and recent development of amperometric gas sensors with their specific applications and limitations presented. Room temperature ionic liquids, microelectrodes and porous electrodes are also introduced in this chapter to initially discuss their potential for gas sensors. Chapter 4 studies the interaction between carbon dioxide and an imidazolium cation based RTIL. The solubility and diffusion coefficient are determined by the analysis of chronoamperometry using the Shoup and Szabo equation. A mechanism of the interaction between CO2 and the RTIL is proposed and validated by theoretical modelling. Chapter 5 focuses on O2 uptake in a phosphonium cation based RTIL. A mechanism of O2 reduction in this RTIL is proposed, reflecting a two electron reduction pathway. Proof-of-concept for this RTIL to be developed into a CO2/O2 dual sensor is confirmed with by experiments with CO2/O2 gas mixtures. Oxygen uptake in a series of alkylammonium cation based RTILs has been carried out as described in Chapter 6. The diffusivity of O2 in RTILs does not follow the Stoke-Einstein equation but broadly decreases as the viscosity increases. Chapter 7 proposes a theoretical model for the electrochemical behaviour at porous electrodes. Studies with two types of porous electrodes are employed and validate the applicability for this model to simulate the current response at porous electrodes.

Low-resolution spectral absorptivities have been experimentally determined for water vapour, carbon dioxide and carbon monoxide in the near infra-red. The gases were contained in a "test" cell located within an electric furnace and surrounded by a pressure vessel containing inert nitrogen at the same pressure as the "test" gas. Thermal radiation from a Nernst filament enters and leaves the "test" cell and pressure vessel through infra-red transmitting windows, and the attenuated radiation is detected and analysed with respect to wavelength. The absorption bands studied were the 1.9 mum and 2.7 bands of water vapour, the 2.0 mum, 2.7 mum and 4.3 mum bands of carbon dioxide and the 2.35 mum band of carbon monoxide. Gas pressures were varied from 1 to 8 bar, temperatures from ambient (293K) to 900K and the mole fractions of the absorbing gas, in a mixture with nitrogen, ranged from 0.1 to 1.0. The radiation path length, as indicated by the length of the "test" cell, was 15.0 cm at ambient and 9-3 cm at all temperatures. Hence, absorber gas concentrations were 0.4 to 112 bar. cm.STP. Total absorptivity were calculated for all the absorption bands studied, and correlation equations developed to relate the band absorptivity with the gas partial pressure, total pressure, temperature and radiation path length. The accuracy and applicability of each of the correlations was determined as a result of comparisons with experimental data. The effects of mixtures of carbon dioxide and water vapour on spectral and band absorption have been commented on.

The well-known reaction of aluminium trichloride with phosphorus trichloride and an alkyl chloride to give a complex of the type (RPCl[3+])(AlCl[4-]) has been investigated with the chlorides AlCl[3], BCl[3], SiCl[4], GeCl[4], SnCl[4], TiCl[4], ZrCl[4], NbCl[5], TaCl[4], MoCl[5], WCl[6] and ReCl[5]. The alkylating agent used was t-butyl chloride. The chlorides BCl[3], GeCl[4], SnCl[4], TiCl[4], NbCl[5], TaCl[5] and WCl[6] have also been used with methyl-dichlorophosphine and t-butyl chloride. No reaction occurred with SiCl[4] and GeCl[4]. Vacuum line and glove box preparative techniques have been used. The compounds prepared are ionic complexes containing either the t-butyltrichlorophosphonium or t-butylmethyldichlorophosphonium cations. With the use of infrared and Raman spectroscopy, the anions BCl[4-], AlCl[4], SnCl[5-], Ti[2]Cl[9-], Zr[2]Cl[9-], NbCl[6-], TaCl[6-], Mo[2]Cl[9-], WCl[6-] and Re[4]Cl[15] have been identified. The latter species was found to be the mixed system, (ReCl[6][2-])(Re[3]Cl[9]). The results for molybdenum, tungsten and rhenium are supplemented with magnetic data and solid-state, ultraviolet and visible, diffuse reflectance spectra. The mass spectrum of the ReCl15 complex is reported. The general reaction schemes Bu[t]Cl + PCl[3] + nMClx ? (Bu[t]PCl[3+])(MnCl[2n+1]) and Bu[t]Cl + MePCl[2] + nMCl[x] ? (Bu[t]MePCl[2+]) (MnCl 2n+1) are proposed. With MoCl5, WCl6 and ReCl5, the reactions are accompanied by simultaneous reduction of the metal ion. The reaction BCl3 + NePCl2 + Bu t Cl did not give the expected complex (Bu[t]MePCl[2+])(BCl[4-]) but the adduct MePCl[2].BCl[3] was obtained which is in equilibrium with an ionic complex (MePCl[+]) (BCl[4-]). The same product was obtained in absence of t-butyl chloride. The reaction TiCl[4] + PBr[3] + Bu[t]Cl was found to give the complex (Bu[t]PBr[3+]) (Ti[2]Cl[9-]). A tentative reaction mechanism is suggested. The reaction TiCl[4] + PCl[3] + Bu[t]Cl in the presence of benzene has been found to give the complex (Bu[t]PCl[3+])(Ti[2]Cl[9-]) and a hydrocarbon of formula C[18]H[30]. Several possible structures are suggested on the basis of infrared and mass spectral data.

This thesis deals with the analytical utility of high performance liquid chromatography (HPLC) for the determination of metals as metal complexes, using thin-layer chromatography as a pilot technique. The requirements for the successful application of the method are discussed. The Co(II), Cu(II), Mg(II), Ni(II) and Zn(II) complexes of acetyl-acetone, benzoylacetone and dibenzoylmethane, and the Fe(III) and A1(III) complexes of dibenzoylmethane were found to be chromatographically unstable in a variety of thin-layer chromatographic and HPLC systems. The complexes of Cu(II) and Fe(III) with dibenzoylmethane were, however, stable during HPLC in the exclusion mode and a separation was obtained. The complexes of Co(III) and Cr(III) with the three ligands were stable in several thin-layer chromatographic and HPLC systems and separations of the acetyl acetone and dibenzoylmethane complexes were obtained by HPLC using a microparticulate silica substrate. The possibility of extraction of Co(III) and Cr(III) from aqueous solution as the dibenzoylmethane complexes was demonstrated. Several complexes of thiodibenzoylmethane were also found to be chromatographically unstable during thin-layer chromatography and HPLC on silica. The Ni(II) and Co(III) complexes were stable, however, and could be separated by HPLC on a microparticulate silica substrate. A surface effect in the presence of water was indicated as a possible cause of decomposition of the Cu(II) complex. The solvent extraction properties of the Ni(II) and Co(III) complexes were investigated and extraction was found to be rapid and quantitative. Interference from excess ligand in the determination of Ni(II) and Co(III) could be avoided by back-extraction with sodium hydroxide solution. The development of an HPLC method for the determination of traces of Ni and Co is described and the effect of many diverse ions investigated. Fe(III), Cr(III) and Sn(II)/(IV) were the most significant interfering ions but the other ions investigated were tolerated in 100 - 1000-fold excess. The extreme sensitivity of the detector enabled 3 x 10-11 g of Ni and Co to be detected as the complexes and Ni and Co concentrations of approximately 6 ng/ml in aqueous solution were determined in routine analysis. The application of the method to a variety of specimens selected to demonstrate the versatility of the technique is described.