Spectrophotometric determination of diclofenac in pharmaceutical preparations assisted by microwave oven

Neste trabalho é proposto um método eficaz e de baixo custo para a determinação de diclofenaco de sódio (ou potássio) na forma pura e em preparações farmacêuticas. O método é baseado na reação de diclofenaco com tetracloro-p-benzoquinona (p-cloranil) em meio de metanol. Esta reação foi acelerada pela irradiação da mistura reagente com energia microondas (1100W) por 27 segundos, produzindo um complexo de transferência de carga com um máximo de absorção em 535 nm. As condições ótimas da reação, tais como: concentração de reagentes, tempo de aquecimento e a estabilidade do produto da reação foram determinadas. A lei de Beer é obedecida num intervalo de concentração de 1,25x10-4 a 2,00x10-3 mol l-1 com um coeficiente de correlação de 0,9993 e absortividade molar de 0,49x10³ l mol-1 cm-1. O limite de detecção (LOD) do método foi de 1,35x10-5 mol l-1 e o limite de quantificação (LOQ) foi 4,49x10-5 mol l-1. Não foram observadas interferências de substâncias comumente encontradas junto com diclofenaco em preparações farmacêuticas, tais como: glicose, lactose, talco, amido, estearato de magnésio, sulfito de sódio, dióxido de titânio, polietilenoglicol, polivinilpirrolidona, manitol e álcool benzílico. Os resultados analíticos obtidos a partir da aplicação do método proposto estão em muito boa concordância com aqueles obtidos pelo método padrão da Farmacopéia Americana. As recuperações obtidas para o diclofenaco a partir de um estudo com várias preparações farmacêuticas estiveram dentro de 95,9% a 103,3%, com desvio padrão variando de 0,2% a 1,8%.In this work, an effective and low-cost method for the determination of sodium or potassium diclofenac is proposed in its pure form and in their pharmaceutical preparations. The method is based on the reaction between diclofenac and tetrachloro-p-benzoquinone (p-chloranil), in methanol medium. This reaction was accelerated by irradiating of reactional mixture with microwave energy (1100 W) during 27 seconds, producing a charge transfer complex with a maximum absorption at 535 nm. The optimal reaction conditions values such as reagent concentration, heating time and stability of the reaction product were determined. Beer's law is obeyed in a concentration range from of 1.25x10-4 to 2.00x10-3 mol l-1 with a correlation coefficient of 0.9993 and molar absorptivity of 0.49 x10³ l mol-1 cm-1. The limit of detection (LOD) was 1.35x10-5 mol l-1 and the limit of quantification (LOQ) was 4.49x10-5 mol l-1. In the presence of the common excipients, such as glucose, lactose, talc, starch, magnesium stearate, sodium sulphite, titanium dioxide, polyethyleneglycol, polyvinylpirrolidone, mannitol and benzilic alcohol no interferences were observed. The analytical results obtained by applying the proposed method compare very favorably with those given by the United States Pharmacopeia standard procedure. Recoveries of diclofenac from various pharmaceutical preparations were within 95.9% to 103.3%, with standard deviations ranging from 0.2% to 1.8%.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

The effect of alloying in Pt-Sn/C electrocatalysts in the performance of a direct ethanol fuel cell

Work on Pt-Sn-C catalysts for ethanol oxidation showed that a thermal treatment at moderate temperatures leads to a significant increase in activity. The best activity was observed for Pt3Sn1 thermally treated at 200 degrees C and ascribed to a Pt3Sn1 phase plus a cleaning effect. However, electronic effects may be very important and these were not evaluated in the Pt3Sn1 phase. Therefore, in this work we investigated the effect of the degree of alloy on the electronic structure of Pt3Sn1 electrocatalysts by performing electrochemical in situ X-ray absorption (XAS) experiments in the Pt L-III XANES region. Overall, the results show that although the occupancy of the Pt 5d band depends on the degree of alloy other factors, such as the presence of tin oxides/hydroxides in the materials, have to be considered to understand the performance of the DEFC