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Abstract(s)
Os compostos fenólicos estão entre os químicos a que os humanos mais estão expostos. Atividades domésticas, industriais, naturais e a agricultura facilitam a entrada dos compostos fenólicos no ambiente aquático. Métodos como a cromatrografia gasosa com detectores de captura eletrônica, ionização de chama e espectroscopia de massa são utilizados para identificação e quantificação de alguns compostos fenólicos em amostras ambientais e biológicas. Embora essas técnicas apresentem alta precisão e exatidão, requerem aparatos onerosos, exigem técnicos especializados, consomem muito tempo de preparação da amostra, além de exigirem constante manutenção. Neste âmbito, as técnicas de voltametria cíclica e de onda quadrada são adequadas para desenvolver metodologias rápidas, por aplicação de elétrodos que permitam a quantificação destas substâncias, tendo como base reações de oxidação-redução. Por isso, o objetivo geral deste trabalho foi avaliar o desempenho de elétrodos compósitos de carbono (com base em resina epoxílica e grafite) construídos com ou sem aditivos (Al2O3 ou Ag), na análise de 4-clorofenol, fenol e 4-nitrofenol e comparar as suas capacidades analíticas com um elétrodo comercial de carbono vítreo.
Verificou-se por voltametria cíclica que todos os elétrodos compósitos e o de carbono vítreo funcionam corretamente, na análise de uma solução redox reversível, tendo-se obtido razão entre intensidades de pico catódica e anódica próximas da unidade para todos os elétrodos.
De forma geral, os elétrodos permitiram medir concentrações inferiores a 1x10-5 mol/L para o 4-clorofenol e 4-nitrofenol e de 2x10-4 mol/L para o fenol, confirmadas através de calibrações individuais, cujos modelos de calibração apresentaram coeficientes de correlação superiores a 0,99 para todos os elétrodos testados. Para alguns dos elétrodos foi possível a medição de concentrações de 4-clorofenol ou 4-nitrofenol com níveis inferiores ou iguais a 5x10-8 mol/L.
Nos ensaios efetuados com soluções de mistura dos três compostos fenólicos, verificou-se que os elétrodos testados permitiram a análise de concentração total dos compostos fenólicos e de 2 compostos fenólicos (4-clorofenol e fenol), obtendo-se relações lineares entre as concentrações previstas para o modelo e as experimentais com declives próximos da unidade (com valores de ordenada na origem não significativos) e coeficientes de determinação superiores a 0,991. Também se obtiveram modelos de previsão aceitáveis para a quantificação de cada composto fenólico isolado, predominando os dos compostos 4-clorofenol e 4-nitrofenol, mas não para todos elétrodos usados.
Considerando o objetivo de aplicar estes elétrodos na análise de águas naturais, verificou-se que a matriz de água de furo e rio não alterava de forma acentuada o sinal voltamétrico quando comparado com o voltamograma obtido para a solução branco, com exceção da água do mar. Os resultados obtidos mostraram que o elétrodo com melhor comportamento analítico para a análise voltamétrica das diferentes águas naturais é o elétrodo compósito C, considerando as sensibilidades em relação aos compostos fenólicos testados.
Phenolic compounds are among the chemicals that most humans are exposed to. Domestic, industrial, natural and agricultural activities facilitate the entry of phenolic compounds into the aquatic environment. Methods such as gas chromatography with electron capture, flame ionization and mass spectroscopy detectors are used to identify and quantify some phenolic compounds in environmental and biological samples. Although these techniques are highly accurate, they require expensive apparatus, specialized technicians, consume a lot of sample preparation time, and require constant maintenance. In this context, the techniques of cyclic voltammetry and square wave voltammetry are adequate to develop fast methodologies, by the application of electrodes that allow the quantification of these substances, based on oxidation-reduction reactions. Hence, the objective of this work was to evaluate the performance of carbon composite electrodes (based on epoxy resin and graphite) constructed with or without additives (Al2O3 or Ag), in the analysis of 4-chlorophenol, phenol and 4-nitrophenol and compare their analytical capabilities with a commercial carbon glass electrode. It was verified, by cyclic voltammetry, that all the composite and vitreous carbon electrodes work correctly, in the analysis of a reversible redox solution, obtaining a ratio between cathodic and anode peak intensities close to the unit for all the electrodes. In general, the electrodes were able to measure concentrations lower than 1x10-5 mol/L for 4-chlorophenol and 4-nitrophenol and 2x10-4 mol/L for phenol, confirmed by individual calibrations, whose calibration models presented correlation coefficients higher than 0.99 for all electrodes tested. For some of the electrodes it was possible to measure 4-chlorophenol or 4-nitrophenol with concentrations levels lower than or equal to 5x10-8 mol/L. In the tests carried out with solutions of three phenolic compounds mixed, it was verified that the tested electrodes allowed the analysis of total concentration of the phenolic compounds and of 2 phenolic compounds (4-chlorophenol and phenol), obtaining linear relations between the predicted concentrations for the model and the experimental ones with slopes close to the unit (with non-significant intercepts values) and determination coefficients higher than 0.991. Also, acceptable prediction models were obtained for the quantification of each phenolic compound isolated, predominating those of the 4-chlorophenol or 4-nitrophenol compounds, but not for all electrodes used. Considering the objective of applying these electrodes in the analysis of natural waters, it was verified that the matrix of potable water and river water did not change markedly the voltammetric signal compared to the voltammogram obtained for the blanc solution, except for sea water. The results showed that the electrode with the best analytical behavior for the voltammetric analysis of the different natural waters is the carbon composite electrode, considering the sensitivities in relation to the phenolic compounds tested.
Phenolic compounds are among the chemicals that most humans are exposed to. Domestic, industrial, natural and agricultural activities facilitate the entry of phenolic compounds into the aquatic environment. Methods such as gas chromatography with electron capture, flame ionization and mass spectroscopy detectors are used to identify and quantify some phenolic compounds in environmental and biological samples. Although these techniques are highly accurate, they require expensive apparatus, specialized technicians, consume a lot of sample preparation time, and require constant maintenance. In this context, the techniques of cyclic voltammetry and square wave voltammetry are adequate to develop fast methodologies, by the application of electrodes that allow the quantification of these substances, based on oxidation-reduction reactions. Hence, the objective of this work was to evaluate the performance of carbon composite electrodes (based on epoxy resin and graphite) constructed with or without additives (Al2O3 or Ag), in the analysis of 4-chlorophenol, phenol and 4-nitrophenol and compare their analytical capabilities with a commercial carbon glass electrode. It was verified, by cyclic voltammetry, that all the composite and vitreous carbon electrodes work correctly, in the analysis of a reversible redox solution, obtaining a ratio between cathodic and anode peak intensities close to the unit for all the electrodes. In general, the electrodes were able to measure concentrations lower than 1x10-5 mol/L for 4-chlorophenol and 4-nitrophenol and 2x10-4 mol/L for phenol, confirmed by individual calibrations, whose calibration models presented correlation coefficients higher than 0.99 for all electrodes tested. For some of the electrodes it was possible to measure 4-chlorophenol or 4-nitrophenol with concentrations levels lower than or equal to 5x10-8 mol/L. In the tests carried out with solutions of three phenolic compounds mixed, it was verified that the tested electrodes allowed the analysis of total concentration of the phenolic compounds and of 2 phenolic compounds (4-chlorophenol and phenol), obtaining linear relations between the predicted concentrations for the model and the experimental ones with slopes close to the unit (with non-significant intercepts values) and determination coefficients higher than 0.991. Also, acceptable prediction models were obtained for the quantification of each phenolic compound isolated, predominating those of the 4-chlorophenol or 4-nitrophenol compounds, but not for all electrodes used. Considering the objective of applying these electrodes in the analysis of natural waters, it was verified that the matrix of potable water and river water did not change markedly the voltammetric signal compared to the voltammogram obtained for the blanc solution, except for sea water. The results showed that the electrode with the best analytical behavior for the voltammetric analysis of the different natural waters is the carbon composite electrode, considering the sensitivities in relation to the phenolic compounds tested.
Description
Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do Paraná
Keywords
Voltametria de onda quadrada Elétrodos de trabalho Análise de compostos fenólicos Águas naturais