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.

The main objective of this work was to develop simple and sensitive electrochemical sensors for the detection of bisphenol A. To investigate the electrochemical behavior of BPA on a bare glassy carbon electrode. To apply the developed biosensor for the determination BPA by differential pulse voltammetry, electrochemical impedance spectrometry, square wave voltammetry and steady-state amperometry. To characterize the synthesized PDMA-PSS by cyclic voltammetry (CV), UV-Vis spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM).

Magister Scientiae - MSc / The main objective of this work was to develop simple and sensitive electrochemical sensors for the detection of bisphenol A. To investigate the electrochemical behavior of BPA on a bare glassy carbon electrode. To apply the developed biosensor for the determination BPA by differential pulse voltammetry, electrochemical impedance spectrometry, square wave voltammetry and steady-state amperometry. To characterize the synthesized PDMA-PSS by cyclic voltammetry (CV), UV-Vis spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM). / South Africa

Magister Scientiae - MSc / This work reports the chemical synthesis, characterisation and electrochemical application of titanium dioxide (TiO2) and iron oxide (Fe2O3) nanoparticles in the determination of phthalates. The other part of this work involved electrochemical polymerization of aniline doped with titanium and iron oxide nanoparticles for the sensor platform in the electrolytic determination of phthalates. The TiO2 and Fe2O3 nanoparticles were prepared by sol gel and hydrothermal methods respectively. Particle sizes of 20 nm (TiO2) and 50 nm (Fe2O3) were estimated from transmission electron microscopy (TEM) The other technical methods used in this study for the characterization of the TiO2 and iron oxide Fe2O3 NPs were SEM, XRD and UV- visible spectroscopy. Cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy (EIS) were used to study the electrochemical properties of the nanoparticles. These electrochemical studies of the nanoparticles were performed with a Fe2O3 or TiO2/nafion/glassy carbon membrane electrode in 0.1 M phosphate buffer (pH 7.0) and 0.1 M lithium perchlorate (pH 6.8) under an aerobic condition. / South Africa

Magister Scientiae - MSc / In this study two medicinal plant species, namely Galenia africana and Elytropapus rhinocerotis, the former belonging to the family Aizoceae and the latter belonging to the family Asteraceae, have been investigated and different compounds isolated and characterized. Both species are important plants used in traditional medicine in Africa and particularly in South Africa. Flavanoids are secondary metabolites found in plants. They have a protective function against UV radiation and have a defence against invading illnesses due to their important antioxidant activity. Much of the food we eat and some beverages we drink contain flavonoids. The aim of this study was to investigate the electrochemistry of flavanoids isolated from these species. / South Africa

Magister Scientiae - MSc / In this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE). / South Africa

Submitted by Jos? Henrique Henrique (jose.neves@ufvjm.edu.br) on 2018-06-26T00:47:56Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) eliziana_santana_gomes.pdf: 3970415 bytes, checksum: 2481c11516ababe53f6e97ce77e43efc (MD5) / Approved for entry into archive by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2018-07-18T12:49:10Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) eliziana_santana_gomes.pdf: 3970415 bytes, checksum: 2481c11516ababe53f6e97ce77e43efc (MD5) / Made available in DSpace on 2018-07-18T12:49:10Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) eliziana_santana_gomes.pdf: 3970415 bytes, checksum: 2481c11516ababe53f6e97ce77e43efc (MD5) Previous issue date: 2017 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / O estriol (C18H24O3, denominado E3) ? o principal esteroide estrog?nico produzido na gravidez. O uso do estriol ? comum para o tratamento da menopausa como alternativa ao 17?- estradiol, estrona ou a uma combina??o destes dois f?rmacos. O principal objetivo deste trabalho foi estudar o perfil voltam?trico do estriol utilizando a voltametria c?clica e desenvolver uma metodologia para a sua determina??o em comprimidos e urina utilizando a voltametria de pulso diferencial (DPV) e o eletrodo de carbono v?treo modificado com um filme de polimetionina e cobalto. Os resultados mostraram que em solu??o de tamp?o fosfato a 0,1 mol L-1 (pH 7,0) o E3 oxidou irreversivelmente no potencial de +0,58V, apresentando uma boa defini??o do pico. A curva anal?tica para o E3 foi linear no intervalo de concentra??o de 0,60 ?mol L-1 ? 4,76 ?mol L-1 (R2 = 0,996) e 5,66 ?mol L-1 ? 9,90 ?mol L-1 (R2 = 0,994), com limites de detec??o e de quantifica??o iguais a 3,40x10-8 mol L-1 e 1,13 x 10-7 mol L-1, respectivamente. A precis?o foi avaliada atrav?s de an?lises voltam?tricas do estriol realizadas em um mesmo dia e em dias diferentes e apresentaram desvios padr?es relativos (RSD) inferiores a 5,0%, mostrando que o m?todo desenvolvido ? preciso. Os estudos sobre interferentes mostraram que as subst?ncias presentes nas amostras de comprimido (lactose, estearato de magn?sio e amido) ou urina (?cido ?rico, ?cido asc?rbico e ?cido c?trico) n?o interferiram de maneira significativa na determina??o do E3. Al?m disso, o m?todo desenvolvido foi comparado estatisticamente com um m?todo citado na farmacop?ia atrav?s do teste-t e do teste-F. Os resultados mostraram que os valores de t e F calculados foram menores do que os valores de t e F cr?ticos, indicando que n?o houve diferen?a estat?stica significativa entre os m?todos. A exatid?o do m?todo foi avaliada tamb?m por estudos de adi??o e recupera??o. As recupera??es do E3 variaram de 97,7 ? 100,9% para a formula??o farmac?utica e 99,0 ? 100,9% para a urina, indicando que n?o houve efeitos de interfer?ncia de matriz significativos e que o m?todo apresenta boa exatid?o. Desta forma, a valida??o da metodologia desenvolvida demonstrou que o m?todo proposto pode ser aplicado com sucesso na determina??o do E3 em medicamentos e urina humana. / Disserta??o (Mestrado) ? Programa de P?s-gradua??o em Ci?ncias Farmac?uticas, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2017. / The estriol (C18H24O3, named as E3) is the main estrogenic steroid produced during pregnancy. The E3 is used to treatment of menopause as an alternative for 17?-estradiol, estrone or a combination of both. The main goal of this work was to study the voltammetric profile of E3 using cyclic voltammetry in order to develop a methodology for its determination in tablets and urine using differential pulse voltammetry (DPV) and the glass carbon electrode modified with a film of polymethionine and cobalt. The results showed that the E3 was oxidized at + 0.58V in a 0.1 molL-1 phosphate buffer solution (pH 7.0), giving a good peak definition. The analytical curve for E3 was linear in the concentration range of 0.60 ?molL-1 ? 4.76 ?molL-1 (R2 = 0.996) and 5.66 ?molL-1 ? 9.90 ?molL- 1 (R2 = 0.994 with lmits of detection and quantification of 3.40x10-8 molL-1 and 1.13x10-7 molL-1, respectively. The precision was evaluated by recording voltammograms of E3 on the same or different day. The relative standard deviations were lower than 5.0% for each test, indicating that the developed method has good precision. The interfering study showed that the tested substances do not interfered significantly in the determination of E3, as for both tablets (lactose, magnesium stearate and starch) or urine test (uric acid, ascorbic acid and citric acid). Furthermore, the developed method was compared to the suggested method from American Pharmacopoeia using the t-test and the F-test. The results showed that the calculated values of t and F were lower than their critical values, indicating no significant statistical difference between the methods. The accuracy of the method was also evaluated by studies of addition and recovery. The recovery of E3 ranged from 97.7 ? 100.9% for the pharmaceutical formulation and 99.0 ? 100.9% for the urine, indicating no significant effects of matrix interference and that the developed method presented accuracy. Thus, the validation of the developed methodology demonstrated that the proposed method can be applied successfully to the determination of E3 in drugs and human urine.

Dans cette thèse, nous présentons la détection électrochimique des herbicides, c'est-à-dire le paraquat et l'isoproturon dans des échantillons aqueux. Leur utilisation intensive est une source de contamination de l'environnement et leur toxicité constitue une menace pour la santé. La détection électrochimique est une technique prometteuse et avantageuse par rapport aux méthodes de détection conventionnelles en raison de ses propriétés telles que l'analyse rapide, la facilité d'utilisation, la rentabilité et la sensibilité élevée résultant de la modification de l'électrode de travail. Ici, nous avons modifié les électrodes modifiées avec des films minces de silice mésoporeuse pour agir comme capteurs d'herbicide. Ces électrodes ont été modifiées par un processus d'auto-assemblage assisté par électrochimie, un processus bien établi pour la modification des électrodes par notre groupe. Dans la première partie, l'adhérence du film de silice mésoporeux aux électrodes de carbone a été améliorée à l'aide d'une amine primaire qui a agi comme colle moléculaire pour une meilleure fixation de ces films à la surface des électrodes. Dans la partie suivante, ces électrodes modifiées ont été utilisées pour la détection électrochimique des herbicides susmentionnés. Les électrodes modifiées ont montré une sensibilité accrue et une limite de détection basse par rapport aux électrodes non modifiées. L'effet des différents paramètres de la solution ainsi que l'épaisseur du film et la géométrie de l'électrode ont également été étudiés et ont un impact critique sur la sensibilité du système / In this thesis, we present the electrochemical detection of herbicides i.e. paraquat and isoproturon in aqueous samples. These herbicides are used worldwide extensively for weed control in different crops. Their intensive use is a source of environmental contamination and their toxicity is a threat to Human health. Electrochemical sensing is a promising and advantageous technique as compared to conventional detection methods due to its properties such as rapid analysis, ease of operation, cost effectiveness and high sensitivity as a result of working electrode modification. Here, we modified electrodes modified with mesoporous silica thin films to act as herbicide sensors. These electrodes were modified by electrochemically assisted self-assembly process, a well-established process for electrode modification by our group. In the first part adhesion of mesoporous silica film at carbon electrodes was improved with the help of a primary amine which acted as molecular glue for better attachment of these films at electrodes surface. In the next part these modified electrodes were used for electrochemical detection of above stated herbicides. Modified electrodes showed enhanced sensitivity and low limit of detection as compared to unmodified ones. Effect of different solution parameters as well as film thickness and electrode geometry was also studied and found to have critical impact on sensitivity of the system

Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work describes the voltammetric determination of Hg, Ag, Zn, Cd, Pb and Tl using solid electrodes as working electrodes in samples of dialysate concentrates (DCs). These contain a very high ionic strengt (~ 4.1 mol L-1), which makes the direct analysis of other analytical techniques such as ETAAS. Voltammetric methods were suitable for the determination of analytes in samples of DCs without the need for dilution, masking agents or pre-concentration steps. The experimental conditions were optimized in order to increase the selectivity and sensitivity of the current signals of each analyte. Were developed two individual methods, which enable the analysis of metals in a study with adequate sensitivity required by law. Were used a glassy carbon electrode as working electrode and as electrode support for the changes. In this electrode and Ag was determined sequentially with the film formation of bismuth, Zn, Cd, Pb. With the addition of DTPA (diethylene triamine pentaacetic acid) was analyzed Tl. Searching a second modification, the second method has the application of cysteine on the film of bismuth, showed that with adequate sensitivity for the determination of mercury. The methods were used for the analysis of commercial samples of CPHD, comparing the voltammograms of each analyte with a non-saline medium. The limit of quantification values ranging from 0.23 to 5.32 μg L-1, and the values obtained from tests for recoveries ranging from 93.6 to 106.3%. / Neste trabalho é descrita a determinação voltamétrica de Hg, Ag, Zn, Cd, Pb e Tl utilizando eletrodos sólidos como eletrodos de trabalho em amostras de concentrado polieletrolítico de hemodiálise (CPHD). Estas possuem uma elevada força iônica (~ 4,1 mol L-1), o que impossibilita a análise direta em outras técnicas analíticas, como ETAAS. Métodos voltamétricos mostraram-se adequados para a determinação dos analitos em amostras de CPHD, sem ser necessário diluição, agentes mascarantes ou etapas de pré-concentração. As condições experimentais foram otimizadas com o objetivo de aumentar a seletividade e sensibilidade dos sinais de corrente de cada analito. Foram desenvolvidos dois métodos independentes, que permitem a análise dos metais em estudo com adequada sensibilidade, conforme é exigido pela legislação. Foi utilizado o eletrodo de carbono vítreo como eletrodo de trabalho e também como suporte para as modificações. Nesse eletrodo foi possível determinar Ag e, sequencialmente, com a formação do filme de bismuto, Zn, Cd, Pb. Com a adição de DTPA (Ácido Dietilenotriaminopentacético), determinou-se Tl. Buscando a determinação de mercúrio com adequada sensibilidade, uma segunda modificação foi realizada, e o segundo método apresenta a aplicação de cisteína sobre o filme de bismuto. Os métodos foram utilizados nas amostras de CPHD comerciais, comparando o comportamento individual dos analitos, com um meio não-salino. Os valores de limite de quantificação variam de 0,23 a 5,32 μg L-1, e os valores obtidos nos ensaios de recuperações variam entre 93,6 a 106,3%.

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.