Neste trabalho, são abordados os estudos eletroquímicos e químico-quânticos, bem como o desenvolvimento de metodologias analíticas para o antidepressivo tricíclico imipramina e para o neurotransmissor dopamina. Os experimentos foram realizados em solução tampão Britton Robinson (BR) 0,10 mol L-1 no pH de melhor resposta analítica para os referidos compostos. Com base nos parâmetros eletroquímicos extraídos das técnicas de voltametria cíclica e de onda quadrada, utilizando-se um eletrodo de grafite-poliuretana (GPU), foi possível diagnosticar o grau de reversibilidade das reações, a presença ou não de processos de adsorção e também o número de prótons e elétrons envolvidos nas reações eletroquímicas. Quanto aos cálculos químico-quânticos, a representação gráfica do HOMO (orbital molecular de mais alta energia ocupado) e os cálculos das cargas atômicas derivadas do potencial eletrostático forneceram uma estimativa do provável sítio de oxidação dos compostos. Os resultados indicaram que a reação de oxidação da imipramina é irreversível e dependente da adsorção do reagente na superfície do eletrodo, ocorrendo a formação subseqüente de um dímero em uma etapa química posterior à transferência de dois elétrons e um próton. O provável sítio de oxidação da molécula abrange a região do átomo de nitrogênio do anel, salientando que após a transferência de dois elétrons há uma deslocalização de cargas pelo anel aromático, fato este que sugere a formação do dímero na posição 2. Paralelamente, experimentos de eletrólise a potencial controlado foram realizados com o objetivo de gerar produtos de reação para serem analisados pela técnica de espectroscopia de massa com ionização por electrospray (ESI-MS). Tomando-se por base os resultados obtidos pelas técnicas voltamétricas, pelos cálculos químico-quânticos e pelos espectros de massa, foi sugerido o provável mecanismo de oxidação da imipramina nas condições estudadas. A metodologia analítica desenvolvida para a imipramina é rápida, sensível e exata para a análise de rotina em comprimidos de Tofranil®. A sensibilidade alcançada pela metodologia permitiu ainda a análise direta de concentrações plasmáticas terapêuticas do antidepressivo e de seu metabólito (desipramina) em amostra de soro humano sintético. No entanto, a seletividade da metodologia ficou comprometida pela proximidade dos potenciais de pico dos dímeros formados após a oxidação da imipramina (-41 mV) e da desipramina (23 mV). A aplicação de um método matemático de deconvolução (Origin 6.0) tornou possível a determinação simultânea da imipramina e da desipramina. A dopamina, por sua vez, é oxidada a dopamina orto quinona em um processo reversível com a adsorção de reagente e produto na superfície do eletrodo. O processo envolve a participação de dois elétrons e dois prótons. A metodologia analítica desenvolvida para a dopamina foi aplicada na análise de rotina em ampolas de Revivan® com boa exatidão e precisão. Além disso, a sensibilidade e a seletividade alcançada pela metodologia resultou na determinação de dopamina em fluído cerebrospinal sintético. A separação dos picos de oxidação da dopamina (Ep = 200 mV) e do ácido ascórbico (Ep = 40 mV) deve-se, provavelmente, às interações eletrostáticas favoráveis entre a superfície do eletrodo de GPU e o ânion ascorbato. De maneira geral, os resultados obtidos foram bastante satisfatórios para as determinações pretendidas, concluindo que o eletrodo de GPU é um material promissor para a análise de moléculas de interesse biológico. / In this work, the electrochemical and quantum-chemical studies are discussed, as well as the development of analytical methodologies for the imipramine tricyclic antidepressant and for the dopamine neurotransmitter. Experiments were performed in 0.10 mol L-1 Britton Robinson (BR) buffer solution at the best analytical response pH for the mentioned compounds. From the electrochemical parameters extracted of cyclic and square wave voltammetric techniques, using a graphite-polyurethane electrode (GPU), it was possible to diagnose the reactions reversible degree, the presence or not of adsorptions processes and also the number of protons and electrons involved in the electrochemical reactions. Concerning to the quantum-chemical calculations, the graphic representation of HOMO (Highest Occupied Molecular Orbital) and the calculation of the atomic charge derived from electrostatic potential provided an estimation of the probable oxidation sites of the compounds. The results indicated that the oxidation reaction of imipramine is reversible and dependent of the reagent adsorption at the electrode surface, occuring the formation of a dimer in a chemical step after the transference of two electrons and one proton. The probable oxidation site of the molecule includes the nitrogen atom region of the ring, emphasizing that after the transference of the two electrons there is a deslocalization of the charges though the aromatic ring, suggesting the formation of the dimeric specie at postion 2. At the same time, experiments of controlled potential electrolysis were carried out in order to generate reaction products to be analysed by electrospray ionization mass espectrosmmetry (ESI-MS). From the results obtained by voltammetric techniques, by quantum-chemical calculations and by mass spectroscopy, it was suggested a probable mechanism for the imipramine oxidation in the studied conditions. The analytical methodology developed for imipramine is fast, sensible and accurate for routine analysis in Tofranil® tablets. The reached sensibility also allowed the direct analysis of therapeutical plasmatic concentrations of the antidepressant and its methabolic (desipramine) in synthetic human serum sample. However, the selectivity of the methodology was compromised by the peak potentials proximity of the dimers formed after the oxidation of imipramine (-41 mV) and of desipramine (23 mV). The application of a deconvolution mathematical xviii method (Origin 6.0) permitted the simultaneous analysis of imipramine and desipramine. On the other hand, dopamine is oxidized to dopamine ortho-quinone in a reversible process with the adsorption of reagent and product at the electrode surface. The process involves the participation of two electrons and two protons. The analytical methodology developed for dopamine was applied in the routine analysis in Revivan® injections with good accuracy and precision. Besides that, the sensitivity and the selectivity reached by the methodology resulted in the determination of dopamine in synthetic cerebrospinal fluid. The separation of the oxidation peaks of dopamine (Ep = 200 mV) and of ascorbic acid (Ep = 40 mV) is probably due to the favorable electrostatic interactions between the GPU electrode surface and the ascorbate anion. In general way, the obtained results were very satisfatory for the desirable determinations, concluding that the GPU electrode is a promissing material for the analysis of biological interest molecules.

O presente trabalho apresenta um estudo eletroquímico da redução dos herbicidas 2,4-D e metribuzin bem como o desenvolvimento de metodologias analíticas para determinação destes compostos em amostras naturais. Os experimentos foram realizados sobre eletrodo compósito de grafite-poliuretana (GPU) utilizando a técnica de voltametria de onda quadrada (SWV). A técnica de Voltametria Cíclica (VC) foi utilizada para diagnosticar o grau de reversibilidade da reação de redução dos herbicidas assim como a natureza do transporte da material eletroativo para a superfície do eletrodo de GPU. Os eletrólitos suportes utilizados nos experimentos foram: tampão Britton-Robinson (BR) para o 2,4-D e água acidificada com H2SO4 0,1 mol L-1 para o metribuzin, ambos em pH 2. Os resultados indicaram que tanto o 2,4-D quanto para o metribuzin, apresentam um único pico de redução com características de processo irreversível controlado pela adsorção de reagente na superfície do eletrodo. Os parâmetros da técnica de SWV (freqüência, amplitude e incremento de varredura), bem como o tempo e potencial de acumulação foram otimizados para obtenção de maior sensibilidade analítica. Curvas analíticas dos dois herbicidas foram obtidas no intervalo de 1,5 a 12 µmol L-1 para os dois herbicidas. Os limites de detecção (LD) e de quantificação (LQ) obtidos para o 2,4-D, foram de 17,6 µg L-1 e 58,6 µg L-1, respectivamente. Para o metribuzin, o LD foi de 1,67 µg L-1 e o LQ 5,56 µg L-1. A precisão das metodologias desenvolvidas foi avaliada por meio da repetibilidade e a reprodutibilidade e a exatidão determinada pelo erro relativo. Os testes de recuperação realizados pelo método de adição de padrão forneceram valores de 104 % para o 2,4-D e 102 % para o metribuzin. As metodologias eletroanalíticas desenvolvidas para determinação do 2,4-D e do metribuzin, foram aplicadas em um estudo para avaliação do tempo de percolação dos mesmos em dois solos com características distintas. Os resultados indicaram que os dois herbicidas apresentam alta mobilidade nos solos estudados, pois 24 horas após a aplicação já foi possível detectar a presença dos mesmos na solução do solo extraída. Para o 2,4-D, 7 dias após o início do experimento, foram encontrados apenas resíduos de herbicida, enquanto que para o metribuzin obteve-se concentrações próximas a 1 mg L-1, mesmo depois de 14 dias. Após 100 dias do início do experimento observou-se um maior acúmulo de 2,4-D no solo arenoso, que pode ter ocorrido devido ao teor mais elevado de MO do solo argiloso, que proporciona uma quantidade maior de microorganismos no solo e que podem degradar o 2,4-D. Já para o metribuzin pode-se observar que este fica adsorvido nas primeiras profundidades do solo argiloso, possivelmente pelas maiores quantidades de MO e CTC. O eletrodo de GPU com a técnica de SWV apresentou bons resultados no que diz respeito à sensibilidade e ao tempo de análise, sendo uma excelente alternativa ao eletrodo de mercúrio, usualmente utilizado em medidas eletroanalíticas do 2,4-D e metribuzin. Os resultados obtidos com amostras de solo e formulação comercial dos herbicidas são bastante coerentes, considerando a dinâmica da dissipação espacial e temporal dos herbicidas no perfil do solo. / This research presents an electrochemical study of the herbicides 2,4-D and metribuzin reductions and the development of analytical methodologies for the determination of such substances in natural samples. The experiments were done with a graphite-polyurethane composite electrode (GPU) using the square wave voltammetry (SWV). The cyclic voltammetry (CV) was used to evaluate the reversibility degree of the herbicides reductions and thus the transport nature of the electroactive material to the surface of the GPU electrode. The supporting electrolytes used in the experiments were Britton-Robinson (BR) buffer for the 2,4-D and acidified water with H2SO4 0,1 mol L-1 for the metribuzin, both at pH 2. Results indicated that the 2,4-D and metribuzin show one reduction peak reduction with irreversible process characteristics, which are controlled by the adsorption of the reagent in the electrode surface. The SWV technique parameters (frequency, amplitude and scanning increment) and the time and potential of accumulation were optimized in order to obtain the highest analytic sensibility. Analytical curves were obtained from 0,33 mg L-1 to 2,62 mg L-1 for 2,4-D and 0,32 mg L-1 to 4,72 mg L-1 for metribuzin. The detection (LD) and quantification limits (LQ) obtained for 2,4-D were 17,6 µg L-1 and 58,6 µg L-1, respectively. For metribuzin, the LD was 1,67 µg L-1 and the LQ was 5,56 µg L-1. The precision of the developed methodologies was evaluated though its repeatability and reproductibility, besides the accuracy were determined by the relative error. Recovery experiments done by the standard addition method, provided values of 104 % for the 2,4-D and 102 % for the metribuzin. The electroanalytical methodologies developed for the determination of these herbicides were applied in two different soils with distinct characteristics, one sandy and other clayed soil. Results indicate that the herbicides present high mobility in the studied soils and 24 hours after its application it was possible to detect the presence of the herbicides in the soil solution extract. For the 2,4- D, seven days after the beginning of the experiment it was measured only residues, but for the metribuzin it is possible to measure concentrations around 1 mg L-1, even after fourteen days. After 100 days it was observed the highest accumulation of the 2,4-D in the sandy soil, that can be explained by the highest content of OM in the clay soil, which provides a higher content of 2,4-D degrading microorganisms. The herbicide metribuzin was adsorbed in the first layers of the clay soil, possibly due to the higher CTC and OM amounts in the soil profile. The GPU electrode with the SWV technique presented very good results when considered the sensibility and time analyses, being an excellent alternative for the mercury electrode usually used in the electroanalytical measurements of the 2,4-D and metribuzin. The obtained results with soil samples and commercial formulation of the herbicides are very consistent, considering the spatial and temporal dissipation dynamics of the herbicides in the soil.

Made available in DSpace on 2016-08-19T12:56:46Z (GMT). No. of bitstreams: 1 Dissertacao Helmara.pdf: 1239564 bytes, checksum: f5a4e670235603269ce13bb3db2a2938 (MD5) Previous issue date: 2013-06-06 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Due to the implementation of more restricted environmental regulation laws, the control of pollution agent such as sulfur compounds has provides the development of new analytic methodologies for its quantification on different matrices, including biodiesel fuel. Thus, this work aims to compare three different sensors - film bismuth and mercury film on the surface of a glassy carbon electrode and solid silver amalgam (dental) - for the determination of sulfur in biodiesel, by means of stripping voltammetric cathodic square wave mode (VRC/SW) as supporting electrolyte with a solution of sodium acetate (1,4 mol.Lˉ¹) and acetic acid (0.33 mol.Lˉ¹) in metanol/2-propanol. In general, the mercury film electrode (MFE) has presented the best electrochemical behavior to the definition of peak reduction, being then selected as standard electrode to the measurements. The sulfur quantization on biodiesel samples was performed by adding 70 μL of soybean biodiesel and tallow fatty with TMAH, adding later, aliquots of standard sulfur. The method showed good linearity (0.998), suggesting an average sulfur concentration of 6,870x10ˉ7 (± 6,857x10ˉ⁸) mol.Lˉ¹, within a confidence interval of 95%, to a limit of detection 3,294x10ˉ¹º mol.Lˉ¹ and quantification limit of 1,098x10ˉ9 mol.Lˉ¹. Besides, for the untreated sample, the experimental has provided a LD of 6,54 x 10ˉ9 mol.Lˉ¹. Finally the proposed method has been compared with the results of a collaborative study (ANP 01/2012) of the same sample using the Teste-t de Student, verifying that the proposed method and official methods (EN ISO 20846, EN ISO 20884) are statistically equivalent to a confidence level of 95%, thereby demonstrating the feasibility of the method. / O controle da poluição ambiental tem exigido, cada vez mais, a determinação de enxofre em uma variedade de matrizes. Diferentes métodos analíticos têm sido desenvolvidos para determinação deste analito em biodiesel, empregando várias técnicas, que vão desde a análise cromatográfica aos métodos espectroanalíticos. No presente trabalho são apresentados os resultados da avaliação de diferentes sensores eletroquímicos para determinação de enxofre em Biodiesel, utilizando a técnica voltamétrica de redissolução catódica no modo onda quadrada (VRC/SW) tendo como eletrólito suporte uma solução de acetato de sódio (1,4 mol.Lˉ¹) e ácido acético (0,33 mol.Lˉ¹), em metanol/2-propanol. Foram avaliados três sensores (filme de bismuto e filme de mercúrio na superfície de carbono vítreo, e eletrodo sólido de amálgama de prata dentária) na determinação de enxofre, sendo observado que o eletrodo de filme de mercúrio (EFM) apresentou os melhores resultados relacionados ao comportamento eletroquímico na definição do pico de redução. Portanto, o EFM foi o sensor escolhido para aplicação na amostra de biodiesel. A determinação do analito em Biodiesel foi realizada adicionando-se 70 μL de Biodiesel de Soja e Sebo (01/2012, interlaboratorial) tratado com TMAH, adicionando, posteriormente, alíquotas de padrão de enxofre. O método apresentou uma boa linearidade (0,998), determinando-se assim uma concentração média de enxofre de 3,687 x 10ˉ7± 6,857 x 10ˉ⁸ mol.Lˉ¹, a um intervalo de confiança de 95%, para um limite de detecção de 3,294 x 10-10 mol.Lˉ¹ e limite de quantificação de 1,098 x 10ˉ9 mol.Lˉ¹, o que demonstra uma boa sensibilidade da técnica. Além disso, avaliou-se o estudo sem tratamento da amostra, na qual obteve-se LD de 6,54 x 10ˉ9 mol.L-1. O presente método foi comparado com os resultados de um estudo interlaboratorial (ANP 01/2012) da mesma amostra, utilizando o Teste-t de Student, verificando que o método proposto e os métodos oficiais (EN ISO 20846; EN ISO 20884) são estatisticamente equivalentes a um nível de confiança de 95%, demonstrando assim a viabilidade do método.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-07-20T14:04:12Z No. of bitstreams: 1 lucasviniciusdefaria.pdf: 2100582 bytes, checksum: 25d968a4baa8a369f530d1dff0826872 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-08-09T12:56:13Z (GMT) No. of bitstreams: 1 lucasviniciusdefaria.pdf: 2100582 bytes, checksum: 25d968a4baa8a369f530d1dff0826872 (MD5) / Made available in DSpace on 2017-08-09T12:56:13Z (GMT). No. of bitstreams: 1 lucasviniciusdefaria.pdf: 2100582 bytes, checksum: 25d968a4baa8a369f530d1dff0826872 (MD5) Previous issue date: 2017-02-23 / Produtos cosméticos como sombra para os olhos, pó compacto e batom são utilizados demasiadamente pela sociedade feminina em busca de uma melhor aparência. Entretanto é importante destacar que nem todos produtos estão isentos de impurezas como metais, os quais podem ser tóxicos ao ser humano. O objetivo deste trabalho foi otimizar um procedimento adequado para o tratamento de amostra de cosméticos faciais (batom, pó compacto e sombra) empregando planejamento de experimentos (Box Behnken e fatorial 32 com triplicata no ponto central) com digestões em chapa de aquecimento e forno micro-ondas utilizando misturas de ácido nítrico e clorídrico concentrados, para a determinação eletroquímica de cobre, chumbo e zinco. Para análise destes metais trabalhou-se com um conjunto de três eletrodos: eletrodo de carbono vítreo modificado com mercúrio (trabalho), Ag/AgCl (referência) e platina (auxiliar). A modificação do eletrodo de carbono vítreo com mercúrio foi feita in situ, isto é, simultaneamente com a deposição dos analitos, sendo necessário o tempo de 300 s para deposição. Parâmetros envolvidos com a etapa de redissolução da voltametria de onda quadrada como frequência, amplitude e incremento de potencial foram otimizados de modo univariado, sendo as condições otimizadas respectivamente (60 Hz, 45 mV e 7 mV). As análises de cobre e chumbo foram feitas simultaneamente utilizando como eletrólito suporte ácido clorídrico 0,1 mol L-1, enquanto que o zinco foi analisado separadamente empregando o tampão acetato 0,1 mol L-1 (pH=4,6) como eletrólito suporte. O forno micro-ondas foi o método escolhido para digestão de todas as amostras de cosméticos faciais, onde as recuperações variaram de 83108%, 67-76% e 75-103% respectivamente para cobre, chumbo e zinco. Os limites de detecção do método para cobre, chumbo e zinco variaram de 0,05-0,36 µg g-1, e os limites de quantificação de 0,36-1,16 µg g-1. Foram analisadas 9 amostras, sendo que as concentrações de Cu, Pb e Zn variaram respectivamente em 14-26,68 µg g-1; 1,31-9,74 µg g-1 e 7,1-42064 µg g1. Para validação dos resultados obtidos eletroquimicamente, empregou-se a F AAS (Cu e Zn) e GF AAS (Pb). A partir de testes estatísticos verificou-se que não houve evidências de diferenças significativas entre o método desenvolvido eletroquimicamente e F AAS, GF AAS com 95% de confiança. Os níveis de concentrações encontrados para os metais ficaram abaixo do nível estabelecido pela sociedade europeia, não oferecendo risco a saúde humana, no que tange aos metais analisados. / Cosmetic products such as eye shadow, compact powder and lipstick are used too much by the feminine society in search of a better appearance. However, it is important to note that not all products are free from impurities such as metals, which can be toxic to humans. The objective of this work was to optimize a suitable procedure for the treatment of facial cosmetic samples (lipstick, compact powder and eye shadow), employing experiment planning (Box Behnken and factorial 32 with triplicate at the central point), With digestion in heating plate and microwave oven using concentrated nitric and hydrochloric acid mixtures, for the electrochemical determination of copper, lead and zinc. For analysis of these metals we worked with a set of three electrodes: mercury modified glass carbon electrode (work), Ag / AgCl (reference) and platinum (auxiliary).The modification of the glassy carbon electrode with mercury was done in situ, that is, simultaneously with the deposition of the analytes, being necessary the time of 300 s for deposition. Parameters involved with the step of redissolution of the square wave voltammetry frequency, amplitude and potential increase were optimized univariate. being the conditions optimized respectively (60 Hz, 45 mV and 7 mV). Copper and lead analyzes were performed simultaneously using 0.1 M hydrochloric acid as the electrolyte, While the zinc was analyzed separately using the 0.1 M acetate buffer (pH = 4.6) as the electrolyte. The microwave oven was the method chosen for digestion of all samples of facial cosmetics, where recoveries varied from 83-108%, 67-76% and 75-103% respectively for copper, lead and zinc. Limits of detection of the method for copper, lead and zinc varied from 0,05-0,36 μg g -1, and the limits of quantification of 0,36-1,16 μg g -1. Nine samples were analyzed, with concentrations of Cu, Pb and Zn varying respectively in 14-26.68 μg g-1; 1.319.74 μg g-1 and 7.1-42064 μg g -1. For the validation of the results obtained electrochemically, an F AAS (Cu and Zn) and GF AAS (Pb) were used. From statistical tests it was verified that there was no evidence of significant differences between the electrochemically developed method and F AAS, GF AAS with 95% confidence. The concentration levels found for metals are below the level established by the European company and do not pose a risk to human health as regards the metals analyzed.

Philosophiae Doctor - PhD / The need for clean, non-toxic drinking water supplies, free of pollutants and metal contamination is vital in impoverished areas and the developing world alike. With this in mind, the development of accurate, inexpensive, portable and simple devices for remote sensing applications is therefore pivotal for early detection and the prevention of illnesses. Over the last two decades, adsorptive stripping voltammetry (AdSV) has emerged as a superior detection method over common analytical techniques due to its low-cost instrumentation, unskilled labour and ability to detect a wide range of analytes. / 2020-08-31

Magister Scientiae - MSc (Dept. of Chemistry) / This study reports the synthesis of graphene by oxidizing graphite to graphite oxide using H2SO4 and KMnO4 and reducing graphene oxide to graphene by using NaBH4. Graphene was then characterized using FT-IR, TEM, AFM, XRD, Raman spectroscopy and solid state NMR. Nafion-Graphene in combination with a mercury film electrode, bismuth film electrode and antimony film electrode was used as a sensing platform for trace metal analysis in 0.1 M acetate buffer (pH 4.6) at 120 s deposition time, using square-wave anodic stripping voltammetry (SWASV). Detection limits were calculated using 3σblank/slope. For practical applications recovery studies was done by spiking test samples with known concentrations of metal ions and comparing the results to inductively coupled plasma mass spectrometry (ICPMS). This was then followed by real sample analyses. / South Africa

Internal gravity waves play a fundamental role in the dynamics of stably stratified regions of the atmosphere and ocean. In addition to the radiation of momentum and energy remote from generation sites, internal waves drive vertical transport of heat and mass through the ocean by wave breaking and the mixing subsequently produced. Identifying regions where internal gravity waves contribute to ocean mixing and quantifying this mixing are therefore important for accurate climate and weather predictions. Field studies report significantly enhanced measurements of turbulence near 'rough' ocean topography compared with those recorded in the ocean interior or near more gradually varying topography (e.g. Toole et al. 1997, J. Geophys. Res. 102). Such observations suggest that interaction of waves with rough topography may act to skew wave energy spectra to high wavenumbers and hence promote wave breaking and fluid mixing. This thesis examines the high wavenumber scatter and spatial partitioning of wave energy at 'rough' topography containing features that are of similar scales to those characterising incident waves. The research presented here includes laboratory experiments using synthetic schlieren and PIV to visualise two-dimensional wavefields produced by small amplitude oscillations of cylinders within linear salt-water stratifications. Interactions of wavefields with planar slopes and smoothly varying sinusoidal topography are compared with those with square-wave, sawtooth and pseudo knife-edge profiles, which have discontinuous slopes. Far-field structures of scattered wavefields are compared with linear analytical models. Scatter to high wavenumbers is found to be controlled predominantly by the relative slopes and characterising length scales of the incident wavefield and topography, as well as the shape and aspect ratio of the topographic profile. Wave energy becomes highly focused and the spectra skewed to higher wavenumbers by 'critical' regions, where the topographic slope is comparable with the slope of the incident wave energy vector, and at sharp corners, where topographic slope is not defined. Contrary to linear geometric ray tracing predictions (Longuet-Higgins 1969, J. Fluid Mech. 37), a significant back-scattered field can be achieved in near-critical conditions as well as a forward scattered wavefield in supercritical conditions, where the slope of the boundary is steeper than that of the incident wave. Results suggest that interaction with rough benthic topography could efficiently convert wave energy to higher wavenumbers and promote fluid mixing in such ocean regions.

Des méthodes électrochimiques à potentiel et à courant imposé appliquées à l'étude des réactions avec dépôt métallique sur un métal de même nature ou sur un substrat étranger sont examinées. Des précisions inédites concernant la voltamétrie à escalier de potentiel et la voltamétrie à signaux carrés de potentiel pour les réactions rapides et lentes avec et sans nucléation tridimensionnelle sont apportées. Les conclusions théoriques sont validées par l'étude du couple Ag(I)/Ag sur les électrodes d'or et d'argent dans HNO3 1 M, KNO3 1 M et dans le liquide ionique [EMIM][NTf2] anhydre ou humide. Le dépôt d'argent s'effectue sans aucune surtension de nucléation tridimensionnelle seulement dans HNO3 et dans [EMIM][NTf2] anhydre. La réaction électrochimique est rapide dans les solutions aqueuses et dans [EMIM][NTf2] humide tandis qu'elle est lente dans [EMIM][NTf2] anhydre. Les paramètres cinétiques sont déterminés par simulation numérique. / Electrochemical methods with potential or current imposing for the study of reactions with metal deposition on the same metal and on foreign substrate are reviewed. New information is provided on staircase voltammetry and square wave voltammetry for fast and slow electrode reactions with and without three-dimensional nucleation. Theory is validated through the study of Ag(I)/Ag couple on gold and silver electrodes in 1 M HNO3, 1 M KNO3 and in dry or wet [EMIM][NTf2] ionic liquid. Silver deposition takes place without any three-dimensional nucleation overvoltage only in HNO3 and in dry [EMIM][NTf2]. The electrochemical reaction is fast in aqueous solutions and in wet [EMIM][NTf2] while it is slow in dry [EMIM][NTf2]. Kinetic parameters are determined by numerical simulation.

Rare earth and actinide metals, critical to security, medicine, and the economy, have been processed through methods such as solvent extraction and electrorefining. To minimize radiological waste and improve yield, a 'chloride volatility' process--also known as the chlorination and volatilization process (CVP)--has been proposed and demonstrated for processing rare earths. The process takes advantage of the low vapor pressure of rare earth chlorides (<700 >°C), CaCl2 was added to LaCl3 to lower the melting temperature. LaCl3 electrochemical behavior has not previously been studied in CaCl2. Cyclic voltammetry (CV) and square wave voltammetry (SWV) were applied to LaCl3 salts in CaCl2-LiCl and CaCl2 to study the metal ion behavior. Various electrode materials were compared at low CV scan rates (s-1) to determine compatibility with chlorine gas evolution. Experiments of eutectic LaCl3-CaCl2 were performed and analyzed to determine the efficacy of chlorine gas generation via electrolysis for the CVP. Through galvanostatic electrolysis, oxidation of chloride ions and subsequent chlorination of rare earth was demonstrated, with cerium chosen as the representative rare earth metal. Through a quadrupole mass spectrometer plumbed in line with the electrolytic cell, the quality of the generated gas was analyzed.

Electrochemical biosensors are renowned for their ability to detect a wide range of analytes in biological fluids for clinical diagnosis. The implementation of biomarkers in electrochemical biosensors for clinical diagnosis is essential for the specific and accurate diagnosis of the disease with high sensitivity and selectivity. Therefore, this thesis evaluates the challenges pertaining to the stability, reproducibility, and obtaining a low limit of detection for the internal/external biomarkers associated with two distinct electrochemical biosensors. The first study tackles the challenge of detecting low analyte concentrations in a label-free biosensor. It introduces an innovative label-free electrochemical biosensing method for the detection of glycosylated hemoglobin (HbA1c) and C-reactive protein (CRP) to predict Coronary Heart Disease (CHD) progression using tailored redox probes, proposing a dual biomarker biosensing platform for future research. Calibration curves reveal an LOD of 5 mg/mL in PBS (8) FeCN (II) and 6 mg/mL in SB for a linear range of 0 – 30 mg/mL of HbA1c. Similarly, an LOD of 0.007 mg/mL and 0.008 mg/mL in PBS (7.4) PcA-NO2 and SB, respectively, is reported for a linear range of 0 – 0.05 mg/mL of CRP. The second study focuses on stabilizing a biomolecule-free sensor for the ultra-low detection of Δ9-tetrahydrocannabinol (THC) in roadside testing. Pre-depositing THC, an external biomarker for drug-impaired driving, onto the biosensor's working electrode enhances its interaction with analytes. However, THC's oxidative nature compromises sensor stability during manufacturing. Consequently, optimal electrode storage conditions were explored, indicating frozen storage as ideal for up to six months, effectively preventing THC oxidation at -18°C, while degradation occurs at 4°C. Modified electrodes stored under optimal conditions exhibit improved calibration curves when exposed to various THC samples. / Thesis / Master of Applied Science (MASc) / An electrochemical biosensor is a sensing device with the ability to detect biological species via the transduction of a specific biological event into electrochemical signals. These sensors are extremely useful for the detection of analytes in biological fluids for clinical diagnostics, to determine the presence or absence of diseases. This manuscript addresses the challenges associated with the stability, reproducibility, and the low limits of detection associated with screen-printed carbon electrodes used in electrochemical biosensing. Subsequently, due to the strong correlation between glycated hemoglobin (HbA1c) and C-reactive protein (CRP) to connote the risk of contracting coronary heart disease (CHD), the manuscript presents a novel label-free electrochemical biosensing method for the detection of HbA1c and CRP with low detection limits. Secondly, the manuscript identifies ambient storage conditions for the long-term stability of a biomolecule-free sensing device for the roadside detection of ultra-low concentrations of Δ9-tetrahydrocannabinol (THC).