Made available in DSpace on 2015-05-14T13:21:30Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3679854 bytes, checksum: 205bff7f378aac18a609a434ae6abfdd (MD5) Previous issue date: 2013-09-17 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Methomyl is a carbamate insecticide widely used to control pests in crops. It is a potential contaminant in groundwater (half-life of 50 weeks) showing harmful effects to fish, aquatic invertebrates, and mammals, reported several cases of human poisoning, affecting the central nervous system. In general, involves the analytical chromatographic methods, fluorometric, spectrophotometric fluorescence X-rays, and the use of cyclic voltammetry and amperometric biosensors with gold electrode, demonstrating the use of electrochemical methods for determination of methomyl. This study made use of an electrode of boron-doped diamond due to its intrinsic properties: wide potential window and low adsorption of organic molecules. Thus, we studied the electrochemical behavior of methomyl using CV, SWV and DPV, being proposed methodologies for the determination of methomyl by SWV and DPV. Through the study of pH, determined by means of VPD were observed five oxidation processes (Ep1  + 1,2 V, Ep2  + 1,6 V, Ep3  + 1,8 V, Ep4 ≈ +1,5 V and Ep5  + 0,8 vs. EAg/AgCl) on DDB cathodically polarized, being more sensitive P2. A methodology was developed using VOQ, being the best analysis conditions: pH 3.0 (BR buffer 0.1 mol L-1), f = 35 s 1, Es = 4 mV, Ep = 40 mV, td = 10 s and  = 1500 rpm, obtaining a linear range of 6,6 × 10 5 a 4,2 × 10 4 mol L-1, However, this method did not provide the acceptable recovery at the concentration studied level for methomyl, according to AOAC-I. The VPD technique was used as an alternative for the determination of methomyl. The best conditions for the analysis of VPD that provided the most sensitive voltammetric response were: pH 2.0 (BR buffer 0.1 mol L-1), IT = 0,2 s, Es = 4 mV, Ep = 50 mV, td =10 s and rpm. The material excellent response preconcentrate allowed the development of an analytical with a linearity range from 5.0 × 10-6 to 4.1 × 10-4 mol L-1 with limits of detection and quantification 1.2 × 10-6 and 4.1 × 10-6 mol L-1, respectively. The sensor showed good repeatability (RSD = 1.1%) and reproducibility (RSD = 1.7%), being feasible with recoveries around 87% for commercial formulations. / Metomil é um inseticida carbamato amplamente empregado no controle de pragas em culturas agrícolas. É um contaminante em potencial das águas subterrâneas (meia-vida de 50 semanas) apresentando efeitos nocivos aos peixes, invertebrados aquáticos e mamíferos, sendo relatados vários casos de envenenamento humano, prejudicando o sistema nervoso central. Em geral, sua determinação analítica envolve métodos cromatográficos, fluorimétricos, espectrofotométricos de fluorescência de raios X, além do uso de biossensores amperométricos e voltametria cíclica com eletrodo de ouro, demonstrando o uso de metodologias eletroquímicas para determinação de metomil. Neste estudo se fez uso de um eletrodo de diamante dopado com boro devido às suas propriedades intrínsecas: ampla janela de potencial e baixa adsorção de moléculas orgânicas. Assim, foi estudado o comportamento eletroquímico do metomil usando VC, VOQ e VPD, sendo propostas metodologias para a determinação de metomil por VOQ e VPD. Através do estudo de pH, realizado pela técnica VPD, foram observados cinco processos de oxidação (Ep1  + 1,2 V, Ep2  + 1,6 V, Ep3  + 1,8 V, Ep4 ≈ +1,5 V e Ep5  + 0,8 vs. EAg/AgCl) em DDB catodicamente polarizado, sendo P2 mais sensível. Uma metodologia empregando VOQ foi desenvolvida, sendo as melhores condições de análise: pH 3,0 (tampão BR 0,1 mol L 1), f = 35 s 1, Es = 4 mV, Ep = 40 mV, td = 10 s e  = 1.500 rpm, obtendo uma faixa linear de 6,6 × 10 5 a 4,2 × 10 4 mol L-1, contudo esse método não apresentou recuperação aceitável para o nível de concentração de metomil estudado, conforme AOAC-I. A técnica de VPD foi utilizada como uma alternativa para a determinação de metomil. As melhores condições de análise da VPD que proporcionaram a resposta voltamétrica mais sensível foram: pH 2,0 (tampão BR 0,1 mol L 1), IT = 0,2 s, Es = 4 mV, Ep = 50 mV, td =10 s e rpm. A excelente resposta do material pré-concentrado permitiu o desenvolvimento de uma metodologia analítica com uma faixa de linearidade de 5,0 × 10-6 até 4,1 × 10-4 mol L 1 com limites de detecção e quantificação de 1,2 × 10 6 e 4,1 × 10 6 mol L 1, respectivamente. O sensor apresentou repetibilidade (DPR = 1,1%) e reprodutibilidade (DPR = 1,7%), mostrando-se viável com recuperações em torno de 87% para formulações comerciais.

The aim of this thesis is the study of electrochemical oxidation of para-substituted phenol derivates using cyclic voltammetry (CV) and ,,direct current" voltammetry (DCV) on boron-doped diamond electrode (BDD) and comparison with some analogous meta-substituted compounds. Among the studied substances were p-cresol, 4-methoxyphenol, 4-hydroxybenzoic acid, 3-(4-hydroxyphenyl)propionic acid, 4-nitrophenol, 4-chlorophenol and 3-(trifluoromethyl)phenol. The oxidation of the analytes was performed in an acidic (pH 2,0) and basic (pH 11,0) Britton-Robinson buffer on mechanically polished, oxidated and hydrogenated surfaces. Another subject of the thesis is to analyze the influence of different substituents, characterized by the Hammett constant, on the oxidation potential of selected phenols. They are oxidized at more positive redox potentials in acidic media, than in basic media, where they are dissociated. The oxidation on the polished and hydrogenated surfaces were similar, whereas were shifted to higher values on the oxidated surface. Further, the signal intensity decreased on the oxidated one, and the oxidation of phenols was not recognizable in basic media. The passivation of the electrode was less significant in pH 2,0 buffer. The best result of Hammett correlation was achieved on a polished and...

The aim of this diploma thesis was to develop an electrochemical method for three phytosterols, namely stigmasterol β-sitosterol and ergosterol using voltammetry techniques on glassy carbon electrode and boron doped diamond electrode. The work builds on previous results, where it was shown that the electrochemical oxidation of phytosterols requires perchloric acid in acetonitrile. When this acid is used, a dehydration reaction occurs. Calibration dependences were measured here for all phytosterols in an environment with a water content of 0.43%. The stability of the signal with increasing distilled water content was further investigated. Then the calibration dependences in the increased water content were measured again. If we want to use HPLC-type separation techniques, we must first find out how the phytosterols will behave in this environment, and therefore the signal stability on the buffer content was investigated. The buffers used were phosphate and acetate buffer. Subsequently, the concentration dependence was measured in an environment with a higher content of phosphate buffer. Furthermore, the possibility of detecting two phytosterols at once was investigated. Key words: dehydration, glassy carbon electrode, boron doped diamond electrode, oxidation, phytosterols, voltammetry