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Title: Electroanalytical chemistry for biological and environmental applications
Author: Evans, Louise A.
ISNI:       0000 0001 3453 2150
Awarding Body: University of Hull
Current Institution: University of Hull
Date of Award: 2008
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Electroanalytical chemistry provides an elegant technique by which to explore, amongst others, various biological and environmental applications. To this end, four areas of electroanalytical chemistry are investigated in order to develop biologically- and environmentally-relevant sensors, together with exploring the electro-generation of a biologically important molecule and the diffusional factors that may affect this generation.The first study involves the dynamics of the bond cleavage involved in the electro-generation of nitric oxide from a range of N-nitrosoamines. Adsorption phenomena is found to be of pivotal significance in the release of nitric oxide from two of the compounds explored, namely cupferron and N-itrosodiphenylamine, whilst bis(nitroso)phenylenediamine released, as hoped, two moles of nitric oxide in a single step. The challenge is to isolate the product, and to determine which form of nitric oxide was generated, i.e. the cation, NO+ or nitric oxide, NO. Isolation remains a challenge, however analysis of the reaction mechanism does allow a prediction of the product, be it NO+ or NO. NO+ is a highly oxidising species and hence is difficult to isolate, therefore it is far more preferable to electro-generate NO, which cupferron was the only compound investigated that achieved this.The second study involved the investigation of axiosymmetric anisotropic diffusion to disc shaped microelectrodes, with theoretical expressions examined with experimental data in order to examine the factors. A ferrocene/PEG in acetonitrile system was examined in order to test this theory and to determine the effect of viscosity on the diffusion coefficients, and also if it was possible to investigate the anisotropy by effectively "blocking" either Dr or Dz. Excellent symmetry between theory and experiment was found, hence the focus turned to a ferricyanide in caesium pentadecafluorooctanoate/D2O system where once again the calculated value of root(Dr.Dz) affords a theoretical waveshape with reasonable agreement between theory and experiment. Potential step chronoamperometry then determined separate values for Dr and Dz, with the resulting values affording an anisotropic ratio of 1.7, suggesting radial diffusion dominance over planar diffusion.Third, the modification of electrodes is explored in order to develop biologically and environmentally relevant sensors. In a first strand, two liquid crystal ferrocene compounds are examined, immobilised on the surface of a glassy carbon electrode simply via solvent evaporation. Both compounds demonstrated typical ion transfer processes across the liquid | liquid interface, with both anion insertion and cation expulsion processes demonstrated. The differing voltammetry observed in the presence of different anions formed the basis of the anion sensor.In a second avenue in this modified electrode work a cation sensor is developed, working on the basis of a biofilm, i.e. developing a modification of the electrode surface to mimic the action of a biofilm in chelating with cations. With this in mind, a basal plane graphite electrode was modified with a diazonium salt and polyphenol, and through the introduction of alginic acid into the polyphenol layer a degree of selectivity between the Group 2 cations was demonstrated, although quantitative properties eluded the work.Last, an environmental sensor for cyanide was developed using an electrochemical probe, tetramethylphenylenediamine (TMPD). The reaction between the electro-generated TMPD.+ and cyanide is successfully followed colorimetrically, before product characterisation studies help to determine the reaction mechanism. Voltammetric studies form the basis of a sensor, with square wave voltammetry achieving a detection limit of 4.4 microM. The reaction between TMPD and cyanide allowed remediation studies to be undertaken, with river freshwater samples from North Yorkshire (54deg 15' 19.19" N, 1deg 46' 13.49" W) and the Rodalquilar mine, Spain, (36deg 50' 52.9" N, 2deg 02' 36.87" W) demonstrating the removal of cyanide by an impressive three orders of magnitude.
Supervisor: Wadhawan, Jay Sponsor: The University of Hull (Sponsor) ; EPSRC (Sponsor)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Chemistry