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The work described in this thesis deals with the use of (^29)Si and (^27)Al NMR to obtain information about the chemical structure of aqueous silicate and aluminosilicate solutions. This has extended the knowledge gained in previous studies. A wide range of alkaline and tetraalkylammonium hydroxide silicate and aluminosilicate solutions (mostly also containing sodium) has been examined. Such solutions are shown to contain a large range of anions. The first highly-resolved (^27)Al NMR spectra of alkaline aluminosilicate solutions are presented and discussed. The linewidths and number of resolved lines are shown to depend critically on several factors, especially the pH and Si:Al ratio, as well as the concentration of various components. At least thirteen separate peaks or bands are observed at the optimum conditions of pH~10.35 and Si:Al = 1. Tentative assignments of some bands are presented, based on (^27)Al and (^29)Si shift omparability, (^27)Al linewidths and (^27)Al spin-lattice relaxation measurements. Relative intensities of the various (^27)Al signals are given for the pH ~10.35 solution. A correlation of (^27)A1 and (^29)Si chemical shifts has been established. Dilution effects and dynamic equilibria are considered for the aluminosilicate solutions. Trends in the spectra with changing concentrations of the various components have been identified. Under certain conditions, additional peaks are observed. Two of these are tentatively assigned to aluminium nuclei in "three-membered" rings. Moreover, a few very sharp hues (i.e. with very low electric field gradients), currently of unknown origin, are observed in several spectra. At certain concentrations chemical exchange can be shown to take place. The effects of tetraalkylammonium (TAA) and alkali metal cations on the equilibrium distribution of aluminosilicate oligomers in aqueous alkaline aluminosilicate solutions have been investigated using evolution with time of Al-27 NMR spectra. The results indicate that there are no observable differences in the initial distribution of aluminosilicate species (i.e. immediately following solution mixing) involving a mixture of TAA and Na cations and those involving alkali metal cations alone. However, in the latter case, this distribution, in contrast to those for TAA/Na solutions, is not stable, the species quickly re-equilibrating, giving broad signals of q(^3) and perhaps q(^4) type. The effect of Al and Si concentration on the formation of gel in?aluminosilicate solutions is also investigated with ^^Al NMR spectra. It is shown that the gel time strongly depends on the Al concentration and the temperature. A graph of Al and Si concentrations with gel time has been established.Silicon-29 NMR spectra have been obtained for more than 20 aqueous alkaline silicate solutions containing methanol. A signal assigned to CH(_3)OSi(OH)(_3) or one of its deprotonated congeners is studied in detail for the first time for the solution conditions involved. Its appearance has been monitored as a function of the solution composition. The equilibrium constant for its formation is of the order of 0.65. The effects of alcohol, silicate and TAAOH concentration and of the nature of the alkylammonium base on this reaction have been investigated.

<p> Many recent efforts in the field of microfluidics have been focused on reducing the size and the complexity of devices and on simplifying the methods of analysis performed with them. Gradient elution moving boundary electrophoresis (GEMBE) is a recently described counterflow electrophoresis method that was developed to simplify the analysis of ions in complex matrices. In this thesis, the improvement of the limit of detection of GEMBE and reduction of the GEMBE channel length is investigated. </p><p> Integration of simple and robust device components required for the successful adaptation of many analytical methods to multiplexed and field-portable devices often has negative effects on detection sensitivity, such as in the optical detection components in a capillary electrophoresis (CE) system. One of the simplest methods to improve sensitivity in the CE field is known as sample stacking. This method involves preparing the sample in a buffer with a different concentration (and conductivity) than that of the run buffer, such that when an electric field is applied the analyte concentration is increased at the boundary between the two different buffer concentrations. A method in which the sample is prepared in a buffer at a lower concentration than the run buffer has been implemented. This method achieves a significantly greater signal enhancement than expected for sample stacking. The concentration enhancement ability of this method is demonstrated utilizing GEMBE with channel current detection. </p><p> Current GEMBE device construction methods impose limitations on the minimum length of the separation channel. One technique well suited for minimizing the size of the GEMBE separation channel is multiphoton absorption polymerization (MAP). Because MAP is a non-linear optical fabrication method, polymerization is limited to a small region near the focal point of a laser beam. As a result, three-dimensional structures with small feature sizes can be easily created. The 3D capabilities of MAP have been exploited to create channels with circular cross sections and &sim;300 &mgr;m lengths for GEMBE. The integration of device components fabricated with MAP and molded with PMDS allows visualization of the GEMBE separations, and provides insights into the effect of channel length on GEMBE step width.</p>

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The aim of this study was to exploit the sensitivity of the chemiluminescent ruthenium tris(2,2'-bipyridme) redox system for analytical purposes by producing electrochemically regenerable electrodes modified with a polymer derivative of this complex. Ruthenium tris(4-meth)i-4' -vinyl-2,2' -bipyridine) bis(hexafluorophosphate) was synthesised and subsequently polymerised onto an electrode surface using the technique of cyclic voltammetry. A potential was applied to the resulting Chemically Modified Electrode (CME) and upon reaction of the ruthenium centres with an analyte in solution, chemiluminescence was observed. Measurement of the emission intensity was used for the determination of the analyte concentration The ruthenium centres were subsequently regenerated by the reversal of the applied potential Very littie environmentally unfriendly and expensive waste results from this process. This is in direct contrast with current methods which traditionally use the ruthenium tris(2,2'-bipyndine) complex either in solution or immobilised within a membrane for analyses of this type. Attention was focused upon detection of the oxalate ion and the ruthenium tris(2,2'-bipyridine)/oxalate redox system reported in the literature was used as a model to investigate the capabilities of the CME's produced. A scan rate of 10 V/s between the potential limits of + 0.5 to + 1.5 V at pH 6.5 was established as the optimum conditions. A linear working range for oxalate was observed from 1.9 x 10'^ M to the limit of detection, 1.1 x 10'^ M. The lifetime of a CME was investigated and although the chemiluminescent signal diminished with time, the electrode was still functioning after 24 weeks, a total of over 200 regenerations. A series of amines and valine were also successfully detected using CME's. In addition, a similar sensor was fabricated from the electropolymerization of a novel ruthenium complex, ruthenium tris(4-methyl-4'-(£-prop-2-enyl>2,2'-bipyridine) bis(hexafluorophosphate). This was also shown to be capable of chemiluminescence emission and was successfully regenerated Two electrochemically regenerable CME's were therefore produced and this research is a valuable advance in the field of chenuluminescent detectors.

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No description available.