O desenvolvimento de metodologias eletroanalíticas altamente eficientes para a determinação de resíduos de pesticidas em amostras de alimentos usando a radiação de ultra-som (US) e o eletrodo de diamante dopado com boro (DDB) é reportado neste trabalho.Também são apresentadas tentativas para melhorar a degradação eletroquímica de pesticidas e de seus metabólitos no ambiente usando estas novas ferramentas (US e DDB) para minimizar o bloqueio da superfície eletródica que, usualmente, impede tais processos.A primeira parte do trabalho apresenta a determinação do metilparation (MP), do seu produto de degradação 4-nitrofenol (4-NF) e do carbaril em água pura e em amostras de alimentos, por voltametria de onda quadrada (SWV) na ausência e na presença do ultra-som usando o eletrodo de DDB. Os resultados obtidos em água pura foram comparados com os dados obtidos por cromatografia líquida de alta eficiência.As metodologias sonoeletroanalíticas para todos os analitos em água pura e nas matrizes de alimentos apresentaram maior sensibilidade e precisão e menores limites de detecção (LD) e de quantificação (LQ) em relação às medidas silenciosas. Para a redução do MP e do 4-NF e para a oxidação do carbaril em água pura, o LD diminuiu de 10,8 para 4,86 μg L-1, de 6,38 para 2,57 μg L-1 e de 2,96 para 2,08 μg L-1, respectivamente. Para a detecção do MP em extrato de batata e do 4-NF em suco de limão, o valor do LD diminuiu de 36,6 para 10,1 μg L-1 e de 13,8 para 8,32 μg L-1, respectivamente.Em todos os casos, foi observado que os valores de LD e LQ estão dentro da concentração máxima permitida para os compostos em amostras de alimentos (50 e 500 μg kg-1 para amostras de batata e de milho, respectivamente, de 1000 μg kg-1 para frutas cítricas e de 500 μg kg-1 para amostras de abacaxi). Satisfatórios valores de recuperação dos analitos nas amostras indicam a possibilidade da determinação direta do MP em extratos de batata e de milho (83 a 96 %) e do 4-NF em sucos de laranja e de limão (84 a 94 %) e também para a detecção do carbaril em suco de abacaxi após o procedimento de extração líquido-líquido (89 a 92 %). Inicialmente, não foram encontrados resíduos detectáveis dos compostos em todas essas amostras de alimentos.As vantagens observadas para os estudos na presença do ultra-som são devidas ao aumento do transporte de espécies até a superfície eletródica e também à limpeza da superfície, visto que a limpeza intermediária não é necessária, resultando em análises mais rápidas e reprodutíveis.Na segunda parte do trabalho, os efeitos benéficos do ultra-som, particularmente a limpeza da superfície eletródica, foram avaliados em associação às eletrólises potenciostáticas para a degradação do pentaclorofenol (PCF) a 0,9, 2,0 e 3,0 V vs. Ag/AgCl e do carbaril a 3,0 V vs. Ag/AgCl.Para o pentaclorofenol, as eletrólises a 0,9 V mostraram que o bloqueio da superfície eletródica foi mais rápido na sonoeletrólise em relação ao processo na ausência do ultra-som, devido à formação de um composto dimérico na superfície eletródica. Eletrólises a 2,0 V e a 3,0 V mostraram maiores níveis de decaimento das bandas do PCF para os estudos na presença do ultra-som em relação àqueles obtidos por medidas silenciosas, devido ao aumento do transporte de massa, minimização da inativação do eletrodo e geração simultânea de radicais hidroxila pelo ultra-som e pela superfície polarizada do DDB. Resultados similares àqueles obtidos para o pentaclorofenol no maior valor de potencial foram também observados para a degradação do carbaril a 3,0 V. / The development of highly efficient electroanalytical methodologies for the determination of pesticide residues in food samples using ultrasound radiation (US) and a boron-doped diamond (BDD) electrode is reported in this work.Also reported are attempts to improve the electrochemical degradation of pesticides and their metabolites in the environment by using those new tools (US and BDD) to minimize the blockage of the electrode surface that usually hinders such processes.The first part of the work presents the determination of methylparathion (MP), their degradation product 4-nitrophenol (4-NP) and carbaryl in pure water and food samples by square wave voltammetry (SWV) in the absence and presence of ultrasound using the BDD electrode. The results obtained in pure water were compared with the high performance liquid chromatography data.The sonoelectroanalytical methodologies for all analytes in pure water and food matrices showed greater sensitivity and precision and lower limits of detection (LOD) and quantification (LOQ) than the silent measurements. For the reduction of MP and 4-NP and oxidation of carbaryl in pure water, the LOD diminished from 10.8 to 4.86 μg L-1, from 6.38 to 2.57 μg L-1 and from 2.96 to 2.08 μg L-1, respectively. For the detection of MP in potato extract and of 4-NP in lemon juice, the LOD value diminished from 36.6 to 10.1 μg L-1 and from 13.8 to 8.32 μg L-1, respectively.In all cases, it was observed that the LOD and LOQ values are inside of the maximum allowed concentration for compounds in food samples (50 and 500 μg kg-1 for potato and corn samples, respectively, 1000 μg kg-1 for citrus fruit and 500 μg kg-1 for pineapple sample). Satisfactory recovery values for the analytes in the samples indicate the possibility of the direct determination of MP in potato and corn extracts (83 to 96 %) and 4-NP in orange and lemon juices (84 to 94 %) and also for the detection of carbaryl in a pineapple juice after a liquid-liquid extraction procedure (89 to 92 %). In all these food samples, no initial detectable residues of the compounds were found.The advantages observed for the insonated studies are due to the increase in the mass transport of species to the electrode surface and also to the cleaning of the surface, since the intermediary cleaning is not necessary thus resulting in a more rapid and reproducible analysis.In the second part of the work, the beneficial effects of the ultrasound, particularly the cleaning of electrode surface, were evaluated in association to potentiostatic electrolyses for the degradation of pentachlorophenol (PCP) at 0.9, 2.0 and 3.0 V vs. Ag/AgCl and for carbaryl at 3.0 V vs. Ag/AgCl.For pentachlorophenol the electrolyses at 0.9 V showed that the blockage of the electrode surface was faster in the sonoelectrolysis than in the absence of ultrasound due to the formation of a dimeric compound on the electrode surface. Electrolyses at 2.0 V and 3.0 V showed greater decay levels of the PCP bands for insonated studies than those obtained for the silent measurements, due the increase of mass transport, minimization of the electrode fouling and to the added generation of hydroxyl radicals by both ultrasound and the polarized BDD surface. Similar results to those for pentachlorophenol at the higher potential were also observed for the degradation of carbaril at 3.0 V.

The fabrication and characterization of boron-doped diamond microelectrodes for use in electrochemical detection coupled with capillary electrophoresis (CE-EC) is discussed. They exhibited low and stable background currents and sigmoidally shaped voltammetric curves for cysteine, cystine and Fe(CN)63-/4- . Evaluation of the CE-EC system and the electrode performance were accomplished using a 10 mM borate buffer, pH 8.8, run buffer, and a 70-cm-long fused-silica capillary (10-mm i.d.) with seven sulfur-containing amino acids (methionine, cysteine, cystine, homocysyeine, homocystine, glutathionine, glutathionine disulfide) as test analytes. Reproducible separation (elution time) and detection (peak current) of seven sulfur-containing amino acids were observed with response precisions of 5% or less.

The microstructure and electrochemical behavior of boron doped and undoped ultra thin diamond film electrodes have been studied in this work. The ultra thin diamond films are deposited on porous silicon (PSi) by microwave plasma chemical vapor deposition (MPCVD). In order to enlarge the surface area of diamond electrodes, the deposition of nano structured diamond thin films is performed only in a short time deposition under a negative bias, so that diamond nuclei grew from the tips of PSi nano structures and the thin film surface remained rough and nano fine structured. Diamond thin films were analyzed by Raman spectroscopy and SEM, and then fabricated to the electrode device. From SEM analysis, the morphology of diamond thin films on PSi reveals in the shape of nano rods diamond crystallites. The electro-chemical response was evaluated by performing cyclic voltammetry in the inorganic K4[Fe(CN)6] and a K2HPO4 buffer solution. Boron doped diamond thin film on porous silicon has demonstrated a high redoxidation current of cyclic voltammetry, which may be due to the rough surface providing more electrochemical surface area and more sp2 conducting bonds exposed on the surface.

O desenvolvimento de metodologias eletroanalíticas altamente eficientes para a determinação de resíduos de pesticidas em amostras de alimentos usando a radiação de ultra-som (US) e o eletrodo de diamante dopado com boro (DDB) é reportado neste trabalho.Também são apresentadas tentativas para melhorar a degradação eletroquímica de pesticidas e de seus metabólitos no ambiente usando estas novas ferramentas (US e DDB) para minimizar o bloqueio da superfície eletródica que, usualmente, impede tais processos.A primeira parte do trabalho apresenta a determinação do metilparation (MP), do seu produto de degradação 4-nitrofenol (4-NF) e do carbaril em água pura e em amostras de alimentos, por voltametria de onda quadrada (SWV) na ausência e na presença do ultra-som usando o eletrodo de DDB. Os resultados obtidos em água pura foram comparados com os dados obtidos por cromatografia líquida de alta eficiência.As metodologias sonoeletroanalíticas para todos os analitos em água pura e nas matrizes de alimentos apresentaram maior sensibilidade e precisão e menores limites de detecção (LD) e de quantificação (LQ) em relação às medidas silenciosas. Para a redução do MP e do 4-NF e para a oxidação do carbaril em água pura, o LD diminuiu de 10,8 para 4,86 μg L-1, de 6,38 para 2,57 μg L-1 e de 2,96 para 2,08 μg L-1, respectivamente. Para a detecção do MP em extrato de batata e do 4-NF em suco de limão, o valor do LD diminuiu de 36,6 para 10,1 μg L-1 e de 13,8 para 8,32 μg L-1, respectivamente.Em todos os casos, foi observado que os valores de LD e LQ estão dentro da concentração máxima permitida para os compostos em amostras de alimentos (50 e 500 μg kg-1 para amostras de batata e de milho, respectivamente, de 1000 μg kg-1 para frutas cítricas e de 500 μg kg-1 para amostras de abacaxi). Satisfatórios valores de recuperação dos analitos nas amostras indicam a possibilidade da determinação direta do MP em extratos de batata e de milho (83 a 96 %) e do 4-NF em sucos de laranja e de limão (84 a 94 %) e também para a detecção do carbaril em suco de abacaxi após o procedimento de extração líquido-líquido (89 a 92 %). Inicialmente, não foram encontrados resíduos detectáveis dos compostos em todas essas amostras de alimentos.As vantagens observadas para os estudos na presença do ultra-som são devidas ao aumento do transporte de espécies até a superfície eletródica e também à limpeza da superfície, visto que a limpeza intermediária não é necessária, resultando em análises mais rápidas e reprodutíveis.Na segunda parte do trabalho, os efeitos benéficos do ultra-som, particularmente a limpeza da superfície eletródica, foram avaliados em associação às eletrólises potenciostáticas para a degradação do pentaclorofenol (PCF) a 0,9, 2,0 e 3,0 V vs. Ag/AgCl e do carbaril a 3,0 V vs. Ag/AgCl.Para o pentaclorofenol, as eletrólises a 0,9 V mostraram que o bloqueio da superfície eletródica foi mais rápido na sonoeletrólise em relação ao processo na ausência do ultra-som, devido à formação de um composto dimérico na superfície eletródica. Eletrólises a 2,0 V e a 3,0 V mostraram maiores níveis de decaimento das bandas do PCF para os estudos na presença do ultra-som em relação àqueles obtidos por medidas silenciosas, devido ao aumento do transporte de massa, minimização da inativação do eletrodo e geração simultânea de radicais hidroxila pelo ultra-som e pela superfície polarizada do DDB. Resultados similares àqueles obtidos para o pentaclorofenol no maior valor de potencial foram também observados para a degradação do carbaril a 3,0 V. / The development of highly efficient electroanalytical methodologies for the determination of pesticide residues in food samples using ultrasound radiation (US) and a boron-doped diamond (BDD) electrode is reported in this work.Also reported are attempts to improve the electrochemical degradation of pesticides and their metabolites in the environment by using those new tools (US and BDD) to minimize the blockage of the electrode surface that usually hinders such processes.The first part of the work presents the determination of methylparathion (MP), their degradation product 4-nitrophenol (4-NP) and carbaryl in pure water and food samples by square wave voltammetry (SWV) in the absence and presence of ultrasound using the BDD electrode. The results obtained in pure water were compared with the high performance liquid chromatography data.The sonoelectroanalytical methodologies for all analytes in pure water and food matrices showed greater sensitivity and precision and lower limits of detection (LOD) and quantification (LOQ) than the silent measurements. For the reduction of MP and 4-NP and oxidation of carbaryl in pure water, the LOD diminished from 10.8 to 4.86 μg L-1, from 6.38 to 2.57 μg L-1 and from 2.96 to 2.08 μg L-1, respectively. For the detection of MP in potato extract and of 4-NP in lemon juice, the LOD value diminished from 36.6 to 10.1 μg L-1 and from 13.8 to 8.32 μg L-1, respectively.In all cases, it was observed that the LOD and LOQ values are inside of the maximum allowed concentration for compounds in food samples (50 and 500 μg kg-1 for potato and corn samples, respectively, 1000 μg kg-1 for citrus fruit and 500 μg kg-1 for pineapple sample). Satisfactory recovery values for the analytes in the samples indicate the possibility of the direct determination of MP in potato and corn extracts (83 to 96 %) and 4-NP in orange and lemon juices (84 to 94 %) and also for the detection of carbaryl in a pineapple juice after a liquid-liquid extraction procedure (89 to 92 %). In all these food samples, no initial detectable residues of the compounds were found.The advantages observed for the insonated studies are due to the increase in the mass transport of species to the electrode surface and also to the cleaning of the surface, since the intermediary cleaning is not necessary thus resulting in a more rapid and reproducible analysis.In the second part of the work, the beneficial effects of the ultrasound, particularly the cleaning of electrode surface, were evaluated in association to potentiostatic electrolyses for the degradation of pentachlorophenol (PCP) at 0.9, 2.0 and 3.0 V vs. Ag/AgCl and for carbaryl at 3.0 V vs. Ag/AgCl.For pentachlorophenol the electrolyses at 0.9 V showed that the blockage of the electrode surface was faster in the sonoelectrolysis than in the absence of ultrasound due to the formation of a dimeric compound on the electrode surface. Electrolyses at 2.0 V and 3.0 V showed greater decay levels of the PCP bands for insonated studies than those obtained for the silent measurements, due the increase of mass transport, minimization of the electrode fouling and to the added generation of hydroxyl radicals by both ultrasound and the polarized BDD surface. Similar results to those for pentachlorophenol at the higher potential were also observed for the degradation of carbaril at 3.0 V.

No description available.

No description available.

The price of crude glycerol has significantly decreased worldwide because of its oversupply. Many chemical and biological processes have been proposed to transform glycerol into numerous value-added products, such as glycolic acid, 1,3-propanediol (1,3-PDO), 1,2-propanediol (1,2-PDO), glyceric acid, and lactic acid. However, these processes suffer from several drawbacks, including high production cost. Therefore, in this study, a simple and robust electrochemical synthesiswas developed to convert glycerol into various value-added compounds. This study reports for the first time the use of Amberlyst-15 as a reaction mediumand redox catalyst for electrochemical conversion of glycerol. In the first part, the electrochemical performance of Amberlyst-15 over platinum (Pt)electrode was compared with that of conventional acidic (H2SO4) and alkaline (NaOH) media. Other parameters such as reaction temperature [room temperature (27°C) to 80 °C] and applied current (1.0 A to 3.0 A) were also examined. Under the optimized experimental condition, this novel electrocatalytic method successfully converted glycerol into glycolic acid after 8 h of electrolysis, with a yield of 45% and selectivity of 65%, as well as to glyceric acid after 3 h of electrolysis, with a yield of 27% and selectivity of 38%. In the second part of this study, two types of cathode electrodes, namely, activated carbon composite(ACC) and carbon black diamond (CBD) electrodes, were used in electrochemical conversion of glycerol. To the best of our knowledge, electrochemical studies of glycerol conversion using these electrodes have not been reported yet. Glycerol was also successfully reduced to lactic acid, 1,2-PDO, and 1,3-PDO, in addition to oxidation compounds (e.g. glycolic acid). Three operating parameters, namely, catalyst amount (6.4% to 12.8% w/v), reaction temperature [room temperature (27 °C) to 80 °C], and applied current (1.0 A to 3.0 A), were tested. In the presence of 9.6% w/v Amberlyst-15 at 2.0 A and 80 °C, the selectivity of glycolic acid can reach 72% and 68% (with yield of 66% and 58%) for ACC and CBD electrodes, respectively. Lactic acid was obtained as the second largest compound, withselectivity of 16% and yield of 15% for the ACC electrode and 27% selectivity and 21% yield for the CBD electrode. Finally, electro-oxidation and electroreduction of glycerol were performed in a two-compartment cell separated by a cation exchange membrane (Nafion 117). This study only focused on the electroreduction region. Three cathode electrodes (Pt, ACC, and CBD) were evaluated under the following conditions: 2.0 A, 80 °C, and 9.6% w/v Amberlyst-15. ACC demonstrated excellent performance in the electroreduction study and successfully reduced glycerol to 1,2-PDO, with a high selectivity of 85%. The selectivity of 1,2-PDO on Pt and CBD was 61% and 68%, respectively. Acetol and diethylene glycol were also obtained. The reaction mechanisms underlying the formation of these products are then proposed.

>Magister Scientiae - MSc / The main aim of this study is to investigate theelectrochemical determination of two beneficial (selenium and zinc) and two toxic (chromium and vanadium) metals in the potable water within the City of Cape Town's distribution area. The Water Laboratory of the City's Scientific Services Branch analyses for these metals in their elemental state, using the Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). This is a standard method used for the detection of trace metals. The most sensitive voltammetric method for determining these metals is by adsorptive stripping voltammetry, using a thin mercury film electrode with a glassy carbon support. This voltammetric method is used for quantitative determination of specific ionic species. Because of mercury's toxicity it is not really favoured for trace metals anymore. Many other possibilities are under investigation, e.g. bismuth-film, modified glassy carbon and antimony electrodes. The boron-doped diamond (BDD) electrode has distinct advantages when used to determine metal concentrations. Advantages of BDD electrodes include lower detection limit, speciation and wider potential window. In this study cyclic voltammetry (CV) was used to determine the copper, cadmium and lead concentrations in potable water by means of square wave voltammetry (SWV) and a bare glassy carbon electrode (GCE). Furthermore, a boron-doped diamond electrode (BDDE) was used to investigate the possibilities of determining selenium, chromium and vanadium by SWV. Real samples (potable water samples) were analysed electrochemically to qualify and quantify these metals and determine whether they comply with the SANS 241:2006 drinking water guidelines.The copper, cadmium, lead and selenium peaks appear very close to the theoretical values, which indicate that these metals can be detected by SWV method, but further analysis with more samples is advised. Even though responses were observed for vanadium and chromium, it was not reliable and requires further investigation. Further studies into the analyses of zinc are also advised.

In this study the possibilities of utilization of boron-doped diamond (BDD) electrodes for electrochemical reduction of organic compounds and their determination in aqueous media were investigated. For this purpose BDD electrodes have several advantages (relative wide potential window in cathodic region, low sensitivity towards oxygen evolution) but are not frequently used. For the study were selected biologically active organic compounds with typical reducible groups. Vanillin (natural essential oil, synthetic aroma; reducible aromatic aldehyde) is not reducible at BDD electrode. Azidothymidine (antiviral drug; reducible azido group) shows voltammetric signal in Britton -Robinson buffer at pH 6.0 - 8.0, but its analytical utilization is difficult due to the close positioning to the decomposition of the supporting electrolyte. The height and potential of the reduction signal of 5-nitroquinoline (environmental pollutant; reducible nitro group on the aromatic nucleus and at higher potentials reducible heterocycle) is significantly influenced by the boron concentration in BDD film. Reduction of quinoline skeleton is visible in the range of pH6.0 - 11.0 in BR buffer. For differential pulse and DC voltammetry (reduction of nitro group) in BR buffer pH 5.0 limits of detection 0.2 µmol.l-1 and 2.7...

nÃo hà / Este trabalho descreve o desenvolvimento de uma proposta de procedimento eletroanalÃtico para a determinaÃÃo do antidepressivo tricÃclico imipramina (IMP) em formulaÃÃes farmacÃuticas comerciais, utilizando eletrodo de diamante dopado com boro (EDDB) e voltametria de onda quadrada (VOQ). Os estudos da oxidaÃÃo eletroquÃmica da IMP foram realizados em soluÃÃo de tampÃo Britton-Robbinson (BR) 0,04 mol L-1. Os resultados utilizando VOQ mostraram dois picos de oxidaÃÃo bem definidos, com pico 1 em 0,04 V e pico 2 em 0,82 V versus Ag/AgCl/Cl- 3 mol L-1. Para o desenvolvimento dos estudos foi utilizado o pico 1 por ter se apresentado mais sensÃvel e seletivo. O efeito dos parÃmetros experimentais e voltamÃtricos foram avaliados e as melhores condiÃÃes foram obtidas em pH 7,4, frequÃncia de aplicaÃÃo de pulsos de potencial de 100 s-1, incremento de potencial de 2 mV e amplitude de 50 mV. Sob estas condiÃÃes, foram construÃdas curvas analÃticas com resposta linear na faixa de concentraÃÃo de 1,73 x 10-7 mol L-1 a 2,53 x 10-6 mol L-1 (r = 0,9984), com um limite de detecÃÃo e de quantificaÃÃo de 4,35 x 10-8 mol L-1 e 1,45 x 10-7 mol L-1, respectivamente. O mÃtodo proposto foi aplicado com sucesso na determinaÃÃo de IMP em formulaÃÃes farmacÃuticas comerciais e validado por comparaÃÃo com mÃtodo padrÃo de determinaÃÃo de imipramina. Os resultados obtidos estiveram de acordo, em um nÃvel de confianÃa de 95%, com aqueles obtidos usando o mÃtodo oficial da FarmacopÃia BritÃnica. / This research describes the development of an electroanalytical procedure proposal for the determination of tricyclic antidepressant imipramine (IMP) in commercial pharmaceutical formulations, using Boron-Doped Diamond Electrode (BDDE) and Square-Wave Voltammetry (SWV). The electrochemical oxidation of imipramine was studied in 0.04 mol L-1 Britton-Robbinson buffer solution (BR). The results using VOQ showed two well-defined oxidation peaks with potentials of 0.04 V and 0.82 V versus Ag/AgCl/Cl- 3 mol L-1 for peaks 1 and 2, respectively. For the studiesâ development was used the peak 1 because it demonstrated to be more sensitive and selective. The effect of the experimental and voltammetric parameters were evaluated and the best performance was obtained in pH 7.4, pulses application frequency of potential of 100 s-1, potential increment of 2 mV and amplitude of 50 mV. Under these conditions, the analytical curves were obtained in the linear range of concentration from 1.73 x 10-7 mol L-1 to 2.53 x 10-6 mol L-1 (r = 0,9984), with detection and quantitation limits 4.35 x 10-8 mol L-1 e 1.45 x 10-7 mol L-1, respectively. The proposed method was applied with success in the determination of IMP in commercial pharmaceutical formulations and validated by comparison with standard method for determination of imipramine. The obtained results were in close agreement, at a 95% confidence level, with those obtained using an official method of the British Pharmacopoeia.