Electrochemical and spectroelectrochemical techniques were employed to investigate the redox characteristics of dyes for dye sensitized solar cells (DSCs) adsorbed at the surface of fluorine-doped tin oxide (FTO) and FTO TiO2 electrodes. In this work are studied Ru-based dyes such as cis-bis(isothiocyanato)-bis(2,2’-bipyridyl- 4,4’dicarboxylato)-ruthenium(II) (N719) and (cis-RuLL'(SCN)2 with L=4,4'- dicarboxylic acid-2,2'-bipyridine and L'=4,4'-dinonyl-2,2'-bipyridine) known as Z907, and indoline organic dyes coded as D102, D131, D149, and D205. The adsorption, diffusion and stability of adsorbed dyes were studied using cyclic voltammetry in acetonitrile and 0.1 M NBu4PF6. The adsorption technique at FTO electrodes was optimized in order to be reproducible so that electrochemical studies as a function of dye coverage were carried out. Langmuirian binding constants were approximately estimated for all dyes adsorbed at FTO electrodes. Rate constants for the chemical degradation of the oxidized dye were also obtained. Is shown that degradation of the dyes mainly occurs at the surface of FTO and only insignificant degradation is evident once the dyes are adsorbed on TiO2. The degradation of dye adsorbed on FTO is shown to affect charge transport from the nonporous TiO2 via electron hopping. Spectroelectrochemical studies of indoline dyes adsorbed on FTO/TiO2 electrodes revealed a red shift of absorption peaks after oxidation and the presence of a strong charge transfer band in the near IR that suggest delocalization of holes in the dye layer. This is consistent with observation that the diffusion coefficient for hole conduction in the adsorbed dye layer is several orders of magnitude higher for the organic dyes compared to the Ru-based dyes. DSCs fabricated using indoline dyes showed good performance. Incident photon-tocurrent conversion efficiency (IPCE) spectra and I-V characteristics are presented.

This thesis has investigated several complex situations that may be encountered in electrochemical studies. Three main situations have been examined, they include the formation of polymer films on electrode surfaces during measurements, a novel nanocatalyst modified electrode surfaces, and organised carbon nanotube (CNT) structures on electrode surfaces. These have been utilised for different electrochemical applications owing to their dissimilar properties. Voltammetric techniques of cyclic voltammetry (CV), square wave voltammetry (SWV) and Fourier transformed large amplitude ac voltammetry (FTACV) have been utilised to examine these reactions. Chapter 3 reports the investigation of catechol oxidation and subsequent polymerisation through crosslinking with D-glucosamine or chitosan. Hydrogel can be formed on the electrode surface during the process, which changes the viscosity of the solution and thus affects the diffusion of chemical species. This process has been examined by several voltammetric techniques. A further examination of the chemical system has also been conducted using FTACV for the first time. Chapter 4 describes the preparation of carbon microsphere supported molybdenum disulfide. The material has been utilised as electrocatalysts for hydrogen evolution reaction (HER) in acidic media, and the performance tested by traditional linear sweep voltammetry (LSV) and advanced FTACV techniques. The FTACV technique has been used for the first time for HER processes. In addition, the synthesised particles have also been used for thermal catalytic decomposition of hydrogen sulfide, which shows a significant improvement in the conversion rate over conventional examples. Chapter 5 demonstrates the direct growth of vertically aligned CNT forests on a gold electrode. The electrochemical response of the fabricated electrode has also been examined with ferrocyanide as the redox species. Furthermore, the immobilisation of anthraquinone onto CNT forest has been attempted. The fabricated electrode was utilised as a pH sensor via CV and SWV, and both indicates a well correlated pH-potential relationship in the pH range of 2 to 12. The sensor has also been assessed by the FTACV technique.

O biodiesel vem se consolidando como combustível alternativo devido às suas vantagens e importância econômica. Conforme seu percentual no diesel comercial cresce, o monitoramento da qualidade se torna cada vez mais importante para uma comercialização segura. No entanto, a estabilidade oxidativa do biodiesel é inferior à do diesel fóssil, assim antioxidantes sintéticos, tais como BHA, BHT, PG e TBHQ, são adicionados para prevenir a degradação do mesmo, evitando danos ao sistema de combustão automotivo. Os métodos para avaliar a estabilidade oxidativa e a quantidade de antioxidantes são em geral demorados, requerem preparação amostral ou equipamentos de alto custo. Com o objetivo de contornar tais problemas, neste trabalho foi aplicada uma metodologia para análise direta de antioxidantes em amostras de biodiesel por meio de voltametria de pulso diferencial. Conjuntamente, foi estudada a viabilidade da associação dessa metodologia com técnicas quimiométricas para a determinação simultânea desses antioxidantes em misturas de antioxidantes em biodiesel. Para permitir uma análise direta, sem extração e pré-concentração dos analitos, o biodiesel foi diluído em meio etanólico. Medidas de voltametria de pulso diferencial para cada antioxidante individualmente mostraram relação linear entre as concentrações dos antioxidantes e a corrente de oxidação. Os limites de detecção individuais obtidos foram de 20,5 mg L-1 para BHA, 32,4 mg L-1 para BHT, 35,5 mg L-1 para PG e 26,5 mg L-1 para TBHQ. A modelagem quimiométrica foi aplicada por meio das ferramentas Mínimos Quadrados Clássico (CLS), Mínimos Quadrados Parciais (PLS), Redes Neuronais Artificiais (ANN), Componentes Principais-Redes Neuronais Artificiais (PC-ANN) e Árvore de Decisão-Redes Neuronais Artificiais (DT-ANN). O modelo construído por PLS se mostrou melhor quando comparado à modelagem por CLS. O modelo construído por ANN’s sem seleção de dados de entrada apresentou erros semelhantes ao PLS. Quando a redução da quantidade de dados de entrada foi aplicada em conjunto com ANN’s através de Análise por Componentes Principais (PCA) e DT, a aplicação de PCA levou a aumento de 10,2% no erro de predição, enquanto que na seleção por DT os erros de predição foram reduzidos em 8,5%. A determinação simultânea dos quatro compostos pelo modelo DT-ANN apresentou precisão satisfatória, com recuperação de 98% para BHA, 97% para BHT, 103% para PG e 100% para TBHQ, o que indica que a técnica analítica e a modelagem quimiométrica são viáveis e promissoras para aplicação no controle de qualidade do biodiesel, bem como em análises de monitoramento nas plantas industriais. / Biodiesel is becoming established as an alternative fuel because its advantages and economic importance. As the levels of biodiesel in commercial diesel grows, quality monitoring becomes increasingly important for safe marketing. However, the oxidative stability of biodiesel is smaller than that of fossil diesel and synthetic antioxidants such as BHA, BHT, PG and TBHQ are added to it in order to prevent its degradation, avoiding damage to the automotive combustion system. Methods for evaluating oxidative stability and the amount of antioxidants are usually time-consuming, require sample preparation or expensive equipment. In order to overcome such problems, in this work a methodology was applied for direct analysis of antioxidants in biodiesel samples by means of differential pulse voltammetry. The viability of associating this methodology with chemometric techniques was studied for the simultaneous determination of these antioxidants in biodiesel. To allow a direct analysis, without extraction and preconcentration of analytes, biodiesel was diluted in ethanolic medium. Differential pulse voltammetric measurements for each antioxidant individually showed a linear relationship between antioxidant concentrations and oxidation current. The individual detection limits were 20,5 mg L-1 for BHA, 32,4 mg L-1 for BHT, 35,5 mg L-1 for PG and 26,5 mg L-1 for TBHQ. The chemometric modeling was applied using the Classical Least Squares (CLS), Partial Least Squares (PLS), Artificial Neural Networks (ANN), Principal Component-Artificial Neural Networks (PC-ANN) and Decision Tree-Artificial Neural Networks (DT-ANN) techniques. The model constructed by PLS was better than that obtained with CLS. The model constructed by ANN’s without input selection presented similar deviations in comparison to PLS. When amount of input data reduction was applied together with ANNs through Principal Component Analysis (PCA) and DT, the PCA application led to a 10.2% increase in prediction error, whereas in the selection by DT prediction errors were reduced by 8,5%. The simultaneous determination of the four compounds by the DT-ANN model presented satisfactory accuracy with 98% recovery for BHA, 97% for BHT, 103% for PG and 100% for TBHQ, indicating that the analytical technique and the chemometric modeling are feasible and promising for application in biodiesel quality control, as well as in monitoring analyzes in the industrial plants.

As reduções eletroquímicas dos complexos de ferro(II) FeL32+, com ligantes diimínicos alifáticos, L=CH3-N=C(R)-C-(R\')=N-CH3, onde R,R\' = H,H; H,CH3; CH3,CH3; e ligantes diimínicos mistos, L = C5H4N-C(R\')=N-(R\"), onde R\',R\"= H,CH3; CH3,CH3 foram estudadas através de polarografia e voltametria cíclica em acetonitrila em perclorato de tetraetilamônio 0,2M a 25,0ºC. Utilizam-se eletrodo plano de platina.ou eletrodo gotejante de mercúrio como eletrodos de trabalho para a voltametria cíclica e polarografia, respectivamente. Os eletrodos auxiliar e de referência são fio de platina e Ag/AgCl , respectivamente. Os polarogramas obtidos para esses complexos no intervalo de potenciais de 0,0 a -2,4 V vs Ag/AgCl mostram duas a quatro ondas de redução. As duas primeiras etapas são controladas por difusão e os processos de eletrodo podem ser descritos como monoeletrônicos e reversíveis, com a estabilização dos baixos estados de oxidação Fe(I) e F:(0) em acetonitrila. Para o derivado R,R\' = H,CH3, observam-se três ondas reversíveis e monoeletrônicas indicando a estabilização do complexo com ferro no estado de oxidação formal (-I).Comportamento semelhante foi encontrado para complexos de ferro(II) com 2,2\'-dipiridina e 1,10 fenantrolina (. Electrochim. Acta. 13. 335 (1968) ). A estabilização dos baixos estados de oxidação deve-se ao caráter aceptor de elétrons dosoligantes diimínicos, como indicado pelo espectro de transferência de carga e,depende da presença do grupo cromofórico. Verifica-se ainda que quanto maior o valor de 10 Dq, maior a retrodoação e, maior a estabilização dos baixos estados de oxidação. Os voltamogramas cíclicos apresentam dois a três picos de redução no intervalo de potenciais de 0,0 a - 2,2V vs Ag/AgCl. A primeira etapa de redução é bem caracterizada como processo monoe1etrônico e reversível Na redução dos derivados alifáticos R,R\' = H,H; CH3.CH3; há um grande aumento da corrente de pico e os potenciais são deslocados cerca de 0,18V para regiões mais negativas. Isso é interpretado em termos de adsorção do reagente na superfície do eletrodo de platina. É interessante notar que apenas os complexos. que apresentam substituintes simétricos adsorvem na superfície do eletrodo. / The electrochemical reduction of the iron(II) complexes, FeL32+ with aliphatic diimine ligands, CH3-N=C(R)-C(R\')=N-CH3, where R,R\'= H,H; H,CH3; CH3,CH3, and mixed diimine ligands. L = C5H4N-C(R\')=N(R\"), where R\',R\" = H, CH3; CH3,CH3, was studied by means of polarography, and cyclic voltammetry in acetonitrile containing 0,2M tetraethylammonium perchlorate at 25,0ºC. A platinum disk or a dropping mercury electrode were used as working e1ectrodes for the cyclic voltammetric and polarographic experiments, respectively. A platinum wire and Ag/AgCl were employed as auxiliar and reference electrodes, respectively. The polarograms obtained for these complexes in the 0.0 to -2,4 V vs Ag/AgCl potential range exhibit two to four reduction waves. The first two reduction waves were shown to correspond to reversible one electron reductions yielding stable complexes of iron in the formal oxidation states (I) and (O). For the derivative R\',R\" = H,CH3, three reversible one electron waves were found, indicating the stability of the complex with iron in the formal oxidation state (-I). A similar be havior has been found for the 2,2\'-dipyridine and 1,10-phenan -throline complexes of iron(II) (Electrochim. Acta,.13, 335(1968)). The stabilization of the low valence states is due to the strong acceptor properties of the diimine ligands. This acceptor character is reflected in the appearence of a characteristic intense inverse charge transfer band in the visible region. in the presence of the diimine chromophore. Increased stabilization of the low oxidation states is correlated with an increase in the magnitude of the ligand-field strength (10 Dq), i.e., increased back-donation. Two or three reduction peaks were observed in the cyclic voltammograms in the region of 0.0 to -2.2 V vs Ag/AgCl. The first reduction of the aliphatic derivatives R,R =\' H,H ; CH3, CH3, there is a large increase in peak currents and a shift of 0.18 V to more negative potentials. This is interpretable in terms of the platinum electrode, It is interesting to note that only the complexes which have symmetrical ligands exhibit adsorption at the electrode surface.

O comportamento eletroquímico da cafeína (CAF) e moléculas análogas, tais como teobromina (TB), teofilina (TF) e xantina (XA), foi estudado utilizando eletrodo de carbono vítreo. Técnicas como voltametria cíclica (VC), voltametria de pulso diferencial (VPD) e onda quadrada (VOQ) e cronoamperometria foram utilizadas para elucidação do mecanismo de oxidação da CAF. Os voltamogramas cíclicos mostraram que todos os compostos estudados apresentaram um único pico irreversível de oxidação na seguinte sequência: Epa(CAF) 1,50V > Epa(TB) 1,34V > Epa(TF) 1,0 V > Epa(XA) 0,74V. Os coeficientes angulares das curvas Ep vs pH foram de 20 mV pH-1, 35 mV pH-1, 58mVpH-1 e 59mVpH-1, respectivamente. A oxidação da TF e XA ocorre envolvendo o mesmo número de elétrons (n) e prótons (H+), enquanto para a cafeína e teobromina, o número de prótons não é igual ao número de elétrons. Este último, foi calculado utilizando os valores de largura de pico à meia altura de corrente dos voltamogramas de pulso diferencial e, exceto a XA, todos os demais derivados foram oxidados em um processo envolvendo 1 elétron. Para a cafeína, o valor de n, coincidiu com aquele calculado pela equação de Randles-Ševcik para sistemas irreversíveis, usando o coeficiente de difusão, D0 = 1,46 x10-5 cm2s-1 e coeficiente de transferência de carga, α, de 0,63. No intervalo de 10 ≤ v ≤ 75mVs-1, os coeficientes angulares dos gráficos (Epa log v) para CAF, TB, TF e XA, foram de 26, 34, 21 mV e 22 mV (década de v)-1, que é o indicativo de um processo de oxidação envolvendo a formação de cátion radical. O número de elétrons determinado por cronoamperometria para a CAF e TB foi n=1 e, comopara TF e XA foram n= 2 e 3,0. Voltamogramas cíclicos e de onda quadrada obtidos em meio de DMSO usando terafluoroborato de tetrabutilamônio mostraram no segundo ciclo, o aparecimento de um par redox quase reversível com E1/2 de + 0,50 V (versus Ag/AgCl), processo atribuído à oxidação do dímero. Para avaliar efeitos de adsorção eletroquímica da CAF na superfície do eletrodo, experimentos de espectroscopia de impedância eletroquímica (EIE) e de potencial de circuito aberto (PCO) foram utilizadas para caracterizar a superfície de eletrodos de carbono vítreo polido (p-ECV), carbono vítreo previamente tratado em solução tampão BR, pH 4,0 (BR-ECV) e carbono vítreo previamente tratado em solução de CAF (CAF-ECV). Os valores de Rct para CAF-ECV foram maiores do que os valores obtidos para o p-ECV, usando solução de K3[Fe(CN)]6 como sonda eletroquímica. / The electrochemical behavior of Caffeine (CAF) and similar molecules such as theobromine (TB), theophylline (TF) and xanthine (XA) was studied using glassy carbon electrode. Techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), square wave voltammetry (VOQ) and chronoamperometry were used to elucidate the CAF oxidation mechanism. Cyclic voltammetry showed that all studied compounds had a single irreversible oxidation peak in the following sequence: Epa (CAF) 1.50V> Epa (TB) 1.34V> Epa (TF) 1.0 V> Epa (XA) 0 .74V. The angular coefficients of Ep versus pH curves were 20, 35, 58 and 59mV/pH, respectively. Oxidation of TF and X occurs involving the same number of electrons (n) and protons (H+), while for caffeine and theobromine, the number of protons is not equal to the number of electrons. The last one was calculated using the peak width values at half-maximum current obtained from the differential pulse voltammograms and, all other derivatives, except for XA, were oxidized in a process involving one electron. For caffeine, the value of n, coincided with that calculated by the Randles-Sevcik equation for irreversible systems, using the diffusion coefficient D0 = 1.46 x10-5 cm2s-1 and the charge transfer coefficient, α, of 0.63. In the range of 10 ≤ v ≤ 75mVs-1, the slopes of the graphs (Epa - log v) to CAF, TB, TF and XA were 26, 34, 21 and 22 mV(v decade)-1, which is indicative of an oxidation process involving the formation of radicalar cation. The number of electrons determined by chronoamperometry for CAF and TB oxidation was n = 1, but for TF and XA were n = 2 and 3.0, respectively. Cyclic and square wave voltammograms obtained in DMSO containing terafluoroborato tetrabutylammonium shown, in the second cycle, a quasi-reversible redox couple almost E1/2 + 0.50 V (vs. Ag / AgCl), attributed to the oxidation of a caffeine dimer. To evaluate the electrochemical adsorption effect of CAF on the electrode surface, electrochemical impedance spectroscopy experiments (IEE) and open circuit potential (OCP) were used to characterize the surface of polished glassy carbon electrodes (p-ECV), glassy carbon previously treated in BR buffer, pH 4.0, (BR-ECV), and glassy carbon previously treated in CAF solution, pH 4,0, (CAF-ECV). The Rct and OCP values for CAF-ECV were larger than the values obtained for p-ECV solution using K3[Fe(CN)6] as the electrochemical probe.

The majority of power generated worldwide is from combustion of fossil fuels. The sustainability and environmental impacts of this non renewable process are severe. Alternative fuels and power generation systems are needed, however, to cope with increasing energy demands. Ammonia shows promise for use in power generation, however it is costly to produce and very few methods of using it as a fuel are developed. To address the need for alternative methods of ammonia synthesis, this research designed and tested a bioelectrochemical device that generates NH3 through electrode induced enzyme catalysis. The ammonia generating device consists of an electrode modified with a polymer that contains whole cell Anabaena variabilis, a photosynthetic cyanobacterium. A. variabilis contains nitrogenase and nitrate/nitrite reductase, catalysts for the production of ammonia. In this system, the electrode supplies driving force and generates a reductive microenvironment near cells to facilitate enzymatic production of NH3 at ambient temperatures and pressures. Farm animal wastes contain significant amounts of NO2- and NO3-, which can leech into groundwater sources and contaminate them. The system described here recycles NO2- and NO3- to NH4sup+ by the nitrate/nitrite reductase enzyme. Unlike nitrogen fixation by the nitrogenase enzyme whose substrate is atmospheric N2, the substrates for nitrate/nitrite reductase are NO2- and NO3-. The ammonia produced by this system shows great potential as a crop fertilizer. While the substrates and enzymatic basis for ammonia production by nitrogenase and nitrate/nitrite reductase are very different, there is utility in the comparison of commercially produced ammonia by the Haber Bosch synthesis and by the bioelectrocatalytic device described here. In one day, the Haber Bosch process produces 1800 tons of NH3 at an energetic cost of $500/ton. Per ton of ammonia, the Haber Bosch process consumes 28 GJ of energy. The bioelectrocatalytic device produces 1 ton of NH3 for $10/ton, consuming only 0.04 GJ energy, which can be obtained by sunlight via installation of a photovoltaic device. Thus, the system presented here demonstrates ammonia production with significant impact to the economy. NH3 production by the bioelectrocatalytic is dependent upon A. var. cell density and electrode polarization. The faradaic current response from cyclic voltammetry is linearly related to cell density and ammonia production. Without electrode polarization, immobilized A. var. do not produce ammonia above the basal level of 2.8 ± 0.4 ΜM. Ten minutes after cycled potential is applied across the electrode, average ammonia output increases to 22 ± 8 ΜM depending on the mediator and substrate chemicals present. Ammonia is produced by this system at 25 °℃ and 1 atm. The electrochemical basis for enhanced NH3 by immobilized cyanobacteria is complex with multiple levels of feedback.

Philosophiae Doctor - PhD / Nitric oxide (NO) plays a key role as biological messenger in the biological system, however detection and quantification thereof has always posed significant problems. NOx is a principal constituent of air pollutants. There are seven oxides of nitrogen of which N2O, NO and NO2 are most important. NO is a free radical and reacts extremely fast with oxygen, peroxides and superoxides. It’s these reactions which are responsible for NO’s fleeting existence. The specific detection and quantification of NO still remains challenging. Most techniques rely on the measurements of secondary nitrite and nitrate species. Electrochemical techniques using ultra micro-electrode systems presented the possibility of direct detection of NO, offering a range of favourable characteristics; good selectivity towards NO, good sensitivity, fast response, long-term stability and ease of handling. Electrochemical detection of NO relies on the modification of electrode surfaces and exploiting the redox properties of NO. NO can either be oxidized or reduced electrochemically depending on the nature of the solution. Under cathodic current NO is reduced to nitrosyl, a highly unstable derivative of NO. These nitrosyls are subject to a serious of chemical reactions to eventually form nitrous oxide. Due to the interferences presented by the electrochemical reduction of NO, the electro oxidation of NO is therefore the methodology of choice for NO detection. The electrochemical oxidation of NO occurs at positive potentials around 800 mV vs. Ag/AgCl. However this potential range is not only favourable to NO oxidation but can lead to the oxidation of several other biological species. These interfering species are biologically present at concentrations higher than NO therefore selectivity is of the highest order when designing these electrode systems. Some nitric oxide sensors are limited in their sensitivity, stability and reproducibility. Direct electron transfer between redox proteins and conductive membrane layers has been scrutinized for years in an attempt to reproduce the mechanistic charge transfer processes for sensor application. However, literature reports have presented many arguments on the complexities associated with depositing these enzymes on electrode surfaces for the purpose of reproducing direct electron transfer at metalloprotein centres. The study sets out to design a material which could mimic the electrochemistry of denatured cytochrome-c. To achieve this it was imperative to design a polymer which could reproduce the electrochemistry of the ligands coordinated to the metal centre of the metalloprotein. A novel Schiff base was synthesized by cross-linking naphthalene to pyrrole to produce the monomer, N,N-bis((1H-pyrrol-2-yl)methylene)naphthalene-2,3-diamine). The monomer was electrodeposited on a screen print carbon electrode (SPCE) vs. Ag/AgCl and served as a supporting layer for denatured cytochrome-c. Cytochrome-c is classified as a metalloprotein. These metalloproteins possess metal centres which when denatured unfolds and allows access to the metal centre. Cytochrome-c was subjected to thermal denaturation which opened up the iron centre. The denatured metalloprotein was cross-linked to the ligand to reconstruct the heme centre environment. This was believed to facilitate the electrochemical activity of the system and allow for electrochemical analysis of these metalloproteins for sensor application. The redox behaviour of the sensors were modelled in phosphate buffer solution (PBS) with cyclic voltammetry. Electrochemical analysis reported the sensors to possess reversible electrochemistry with diffusion control characteristics. The sensor recorded a redox system in the negative potentials range. Following the establishment of the electrochemical profile of the sensor an attempt was made to produce a synthetic analogue of denatured cytochrome-c. Iron (II) was chelated to the monomer N,N-bis((1H-pyrrol-2-yl)methylene)naphthalene-2,3-diamine) to form an iron ligand complex. The complex was subjected to a series of characterization techniques which confirmed coordination to the metal centre. The iron ligand complex was electrodeposited on a SPCE over the potential window of -1 V and 1 V to model the electrochemical behaviour of the sensor. The material was found to be electroactive. Subsequent electrochemical analysis revealed the system to have electrochemical properties, analogous to that of the denatured cytochrome-c system. The sensor was applied in NO and NO2 studies and displayed an affinity towards NO. Based on extrapolated values it was postulated that the lower limit range for NO detection was in the range of 30 to 40 nM. The potentials recorded were lower than the reported oxidation potentials for nitric oxide. The sensor displayed stability and selectivity towards nitric oxide within a complex matrix. The complex matrix employed in this study was synthetic urine that was synthesised in the lab. The sensor displayed the capacity for linear range of NO detection with very low error margins. / 2021-09-01

The concepts of electroneutrality coupling and electron-hopping, which are useful for the incorporation of functional components and transportation of electrons, were applied in this project. Discrete layered structures were fabricated by sequential electropolymerization to modulate the performances of formate biosensors. Different types of layers, with or without enzyme, were successfully grown on the electrode surface. The presence of the enzyme (formate dehydrogenase), co-factor (B-nicotinamide adenine dinucleotide) and an electron mediator in the polypyrrole film was verified by scanning electron microscopy, chronopotentiometry, cyclic voltammetry and amperometric measurements. Monolayer, bilayer and trilayer formate biosensors were successfully fabricated for different analytical purposes. The utilisation of the biosensing membrane for the reliable batch and FIA determination of formate based on a amperometric mode of detection are explored. Electron mediators such as ferrocyanide, Prussian Blue, ferrocene and ferrocene carboxylic acid were incorporated into the polypyrrole film to lower the required applied potential for amperometric sensing and to maintain the conductivity and stability of the polypyrrole backbone. The application of artificial neural networks (ANN) to overcome the problem of reusability and reproducibilty in a nonlinear and complicated dynamic system is also considered. The resulting system was trained with a new neural network based software package, Turbo Neuron, for prediction of the concentration of formate, based on the entire collected data, which contain the history of the detection experiments. The proposed integrated ANN conducting polymer biosensor enables the determination of formate concentration, both online and in real time / Doctor of Philosophy (PhD)

A large part of the work presented in this thesis describes the development and use of a novel electrochemical detector designed to allow the electrochemical characterisation of compounds in flowing solution by means of cyclic voltammetry. The detector was microprocessor controlled, which provides digital generation of the potential waveform and collection of data for subsequent analysis. Microdisk working electrodes are employed to permit both thermodynamic and kinetically controlled processes to be studied under steady-state conditions in flowing solutions without the distortion or hysteresis normally encountered with larger sized electrodes. The effect of electrode size, potential scan rate, and solution flow rate are studied extensively with the oxidation of ferrocene used as an example of a thermodynamically controlled process and a series of catecholamines as examples of a kinetically controlled process. The performance of the detector was best demonstrated when used as a HPLC post-column detector. The 3-dimensional chromatovoltammograms obtained allow on-line characterisation of each fraction as it elutes from the column. The rest of the work presented in this thesis involves the study of the oxidative degradation pathway of dithranol. The oxidative pathway was shown to involve a complex free radical mechanism, dependent on the presence of both oxygen and, in particular light. The pathway is further complicated by the fact that dithranol may exist in either a keto or enol form, the enol being most susceptible to oxidation. A likely mechanism is proposed from studies performed with cyclic voltammetry and controlled potential electrolysis, then defined by subsequent kinetic studies.

In this thesis, cyclic biamperometry (CB) as a new method in electrochemistry, has been introduced and investigated. The hallmark of this method is the absence of a reference electrode which potentially allows simplification and miniaturization of the measurement apparatus. Similarities and differences of this method and cyclic voltammetry (CV) have been studied and it was shown that under conditions of using standard electrodes, CB has a better sensitivity and a lower detection limit than CV. A new equivalent circuit model for the cell has been proposed and parameters affecting the sensitivity of CB, such as keeping the concentration of one redox species in excess and having a larger W2 electrode, have been described. The redox cycling effect in biamperometric systems has been investigated and it is shown that improvements of at least two orders of magnitude in sensitivity can be achieved by using interdigitated electrodes (IDEs). In addition, an example for applications of this method, including biamperometric dead-stop titration of 1-naphthol with ferricyanide, has been presented and possible fields in which CB can be incorporated (e.g. monitoring the activity of alkaline phosphatase) have been illustrated. Finally, a few suggestions for future studies and further improvements have been outlined.