This study describes the use of uncured polydimethylsiloxane (PDMS) as a binder agent to prepare carbon paste electrodes (CPEs). A comparative study between the properties of CPEs prepared with PDMS and mineral oil Nujol®, the most common binder agent for CPEs, was carried out. Cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry showed that PDMS-CPEs presented higher electrical conductivity, active electrochemical area, and wider useful potential window compared with Nujol®-CPEs. Moreover, PDMS-CPEs were more stable in aqueous mixtures containing 50% (v/v) of ethanol or methanol than Nujol®-CPEs. PDMS-CPEs have also provided higher sensitivity and lower limit of detection to propranolol than Nujol®-CPE. Therefore, this study demonstrated that PDMS is a promising alternative binder agent able to produce CPEs with superior chemical/electrochemical stability and improved analytical performance.

Cellulose derivatives still receive special attention in today biomedical applications due to their biocompatibility, ability to form resistant membranes and compatibility with various bioactive agents. In this work, cellulose acetate (CA) was used to prepare membranes with different morphologies aiming to evaluate the release profile of the drug ibuprofen (IBF). The IBF incorporation was performed by the addition of 10% of the drug in an 8% (w/w) CA/acetone solution. The morphology of the membranes was modified by the addition of water, used as porogenic agent. Drug release assays showed the effect of morphology on the cumulative drug release curves. The symmetric membrane exhibited retention of significant amounts of the drug and a slow release process that lasted for more than 50 hours. The asymmetric porous membranes presented different behavior with greater amount of drug released in less time of release. The kinetic parameters calculated from the Higuchi and Korsmeyer/Peppas models indicated release profiles controlled by diffusion/solution process in the polymer matrix. The results revealed that the interactions established between IBF, CA and the matrix morphology are significant factors for the kinetic control of the drug release process and enable to choose different applications of the membranes loaded with IBF.

This work presents a voltammetric method for Zn2+ determination in antiseptic dusting powder and multivitamin commercial samples, combining an alkaline extraction using NaOH aqueous solution with a carbon paste electrode chemically modified with Bi anchored on Amberlite® IR120 ion exchange resin (CPEAmb/Bi). The best conditions for electrode preparation were: 10% (m/m) of Amberlite® IR 120; 30 s Bi3+ accumulation time (open circuit) in 0.5 mmol L-1 Bi3+ solution prepared in 0.1 mol L-1 acetate buffer (pH = 5.5). The analytical curve for Zn2+ using the CPEAmb/Bi presented linear range from 0.05 to 8.2 µmol L-1 and the limit of detection was 10 nmol L-1. The voltammetric method was simple, fast, efficient and low-cost for the Zn2+ determination in antiseptic dusting powder and multivitamin samples.

This paper describes a comparative study between the procedures of deconvolution and the second-order derivative of square wave voltammograms to achieve separation of the voltammetric peaks of levofloxacin (LEVO) and norfloxacin (NOR), for their simultaneous quantification in urine samples. The obtained results indicate that the use of second-derivative voltammograms coupled with carbon screen-printed electrodes is the most efficient approach for completely separating the voltammetric peaks of LEVO and NOR. In addition, this approach has produced detection limits lower than 1.0 µmol L-1 and a wide linear range for both drugs. The proposed method was successfully used to simultaneously determine LEVO and NOR in spiked human and bovine urine samples with recovery percentages close to 100% for all analyzed samples.

This work describes a simple and inexpensive flow injection analysis system in which gravity force provides fluid propulsion while needles for insulin administration or metallic wires act as electrodes for amperometric detection. The proposed system was able to demonstrate the influence of several operational parameters on the transient signals. Moreover, this system was successfully used to evaluate both the stoichiometry of Cu2+-EDTA complex and the effect of pH on the kinetics of the reaction between ferricyanide and ascorbic acid. Therefore, the proposed system can be regarded as an efficient and accessible didactic tool for the teaching of FIA principles.

Um eletrodo de pasta de carbono preparado com parafina sólida como aglutinante e quimicamente modificado com sílica funcionalizada com grupos 2-aminotiazol foi empregado na quantificação simultânea de Pb2+ e Cu2+ em amostras de água por meio de voltametria de redissolução anódica. O presente método emprega um tempo curto de pré-concentração (180 s), o qual permitiu a quantificação simultânea e confiável de Pb2+ e Cu2+ de maneira bastante rápida. Foram obtidos limites de detecção de 7,3 e 90 nmol L-1 para Pb2+ e Cu2+, respectivamente. Estes valores estão abaixo das concentrações máximas permitidas destes metais em água potável segundo a legislação brasileira, indicando que o método proposto é aplicável para o monitoramento de Pb2+ e Cu2+ em amostras de água. Estudos de recuperação foram realizados em quatro amostras de água enriquecidas, sendo obtidas porcentagens de recuperação próximas a 100% para todas as amostras analisadas, demonstrando a boa acuracidade do método proposto

A solid paraffin-based carbon paste electrode modified with 2-aminothiazole functionalized silica-gel was used for simultaneous quantification of Pb2+ and Cu2+ in water samples by anodic stripping voltammetry. The present method uses short preconcentration time (180 s), which allowed reliable and simultaneous quantification of Pb2+ and Cu2+ in a very fast way. Detection limits of 7.3 and 90 nmol L-1 were obtained for Pb2+ and Cu2+, respectively. These values are below their maximum concentrations allowed in drinking water by Brazilian legislation, indicating that the proposed method is useful to monitoring Pb2+ and Cu2+ in water samples. Recovery studies were performed in four spiked water samples and the results shown recovery percentages close to 100% for all analyzed samples, demonstrating the good accuracy of the proposed method

Neste trabalho, a redução eletroquímica do amebicida Teclozan (TEC) foi estudada sobre um eletrodo de carbono vítreo em meio de acetonitrila. Eletrólises com potencial controlado foram realizadas visando, tanto a determinação do número de elétrons envolvidos na redução do fármaco, quanto a identificação dos produtos eletrogerados, os quais foram isolados por extração líquido-líquido e caracterizados por ¹H RMN. Foi verificado que o TEC apresenta dois picos voltamétricos, cada um associado à quebra redutiva de duas ligações C-Cl. Em presença de um doador de prótons, foi observado que o primeiro pico voltamétrico em -1,8 V corresponde principalmente à redução dos grupamentos -CHCl2 a -CH2Cl; enquanto o segundo pico em -2,2 V é responsável pela redução dos grupos -CH2Cl a CH3, fornecendo como único produto o derivado totalmente desalogenado do TEC, com rendimentos entre 82 e 97%. Este trabalho descreve também o desenvolvimento de um método eletroanalítico baseado na detecção amperométrica do TEC em condições hidrodinâmicas, o qual forneceu um limite de detecção de 8,9 × 10-6 mol L-1.

The electrochemical reduction of amoebicide Teclozan (TEC) was studied on a glassy carbon electrode in acetonitrile. Controlled-potential electrolyses were performed for coulometric and preparative purposes. The electrogenerated products were isolated by liquid-liquid extraction and characterized by ¹H NMR. It was observed that TEC presents two voltammetric peaks, each one associated with the cleavage of two C-Cl bonds. In presence of a proton donor it was observed that the first peak at -1.8 V promotes mainly the reduction of the groups CHCl2 to CH2Cl and the second one at -2.2 V promotes the reduction of the groups CH2Cl to CH3 giving as the sole product the completely dechlorinated TEC derivative with yields between 82 and 97%. In addition, a comparative study between the analytical performance of voltammetric techniques and amperometric detection of TEC in hydrodynamic conditions was performed. The amperometric detection was more sensitive than all evaluated voltammetric techniques, providing a detection limit of 8.9 × 10-6 mol L-1.

A redução eletroquímica do Furoato de Diloxanida (FD) em acetonitrila sobre um eletrodo de carbono vítreo foi estudada neste trabalho. Foi observado que o FD é reduzido após uma transferência reversível de um elétron seguida por uma reação química irreversível, diagnosticada, como uma ruptura de uma ligação C-Cl. A redução do FD foi estudada por voltametria de varredura linear (LSV), pulso diferencial (DPV) e onda quadrada (SWV). Curvas analíticas foram obtidas usando todas as técnicas voltamétricas estudadas. Para a técnica de LSV obteve-se um intervalo linear (LR) de 5,0 x 10-4 a 1,0 x 10-2 mol L-1, com limite de detecção (DL) de 1,5 x 10-4 mol L-1 e sensibilidade (S) de 2,1 x 10(4) µA mol-1 L . Os parâmetros analíticos obtidos com a técnica de DPV foram: LR = 5,0 x 10-4 a 2,2 x 10-3 mol L-1, DL = 7,8 x 10-5 mol L-1, S = 3,7 x 10(4) µA mol-1 L. Para a técnica de SWV foram obtidos os seguintes parâmetros analíticos LR = 7,5 x 10-6 a 1,2 x 10-3 mol L-1, DL = 5,5 x 10-6 mol L-1 e S = 2,8 x 10(5) µA mol-1 L. Assim, a técnica de SWV foi a mais sensível, podendo ser empregada para a quantificação de FD em baixos níveis de concentração. Métodos estatísticos foram utilizados para avaliar o procedimento analítico, recuperações próximas a 100% e desvios padrão relativos inferiores a 5,0% (N=5) foram obtidos. Através do teste-t verificou-se que não há evidências de erros sistemáticos em nenhuma das técnicas estudadas.

The electrochemical reduction of diloxanide furoate (DF) in acetonitrile on glassy carbon electrode was studied in this work. It was observed that DF is reduced after a reversible one-electron transfer followed by an irreversible chemical reaction, diagnosed as C-Cl bond cleavage. Its reduction was followed by linear (LSV), differential pulse (DPV) and square wave voltammetry (SWV). Analytical curves were obtained for DF determination using all the investigated voltammetric techniques. For LSV was obtained a linear range (LR) from 5.0 x 10-4 to 1.0 x 10-2 mol L-1, with detection limit (DL) of 1.5 x 10-4 mol L-1 and sensitivity (S) of 2.1 x 10(4) µA mol-1 L. The analytical parameters obtained by DPV were: LR = 5.0 x 10-4 to 2.2 x 10-3 mol L-1, DL = 7.8 x 10-5 mol L-1, S = 3.7 x 10(4) µA mol-1 L. For SWV were obtained a LR = 7.5 x 10-6 to 1.2 x 10-3 mol L-1, DL = 5.5 x 10-6 mol L-1 and S = 2.8 x 10(5) µA mol-1 L. Thus, the SWV was the most sensible technique, which can be used for DF determination at low concentration levels. Statistics methods were used to evaluate the analytical procedure, where recovery around to 100% was obtained for all voltammetric techniques. Relative standard deviations were lower than 5.0% (N=5). The obtained t values evaluating all the three voltammetric methods were less than the tabulated ones, indicating that there are no evidences of systematic error.