No abstract

Um método eletroanalítico original e rápido para a determinação de naproxeno em formulações farmacêuticas usando análise por injeção em batelada (BIA) com detecção amperométrica pulsada é descrito. Eletrodo de carbono vítreo foi usado como eletrodo de trabalho e solução tampão fosfato 0,05 mol L -1 como eletrólito suporte. O método amperométrico envolveu a aplicação contínua de dois pulsos de potencial ao eletrodo de trabalho com intuito de detectar naproxeno pela sua oxidação eletroquímica (+1,5 V por 200 ms) e de limpar a superfície do eletrodo de produtos de adsorção (+1,0 V por 100 ms), evitando contaminação do eletrodo. O método proposto possui várias vantagens para análises de rotina, incluindo: baixo desvio padrão relativo (3,0%, n = 10), elevada frequência analítica (90 h -1 ), exatidão satisfatória (baseado em determinações comparativas por espectrofluorimetria) e baixo limite de detecção (0,3 µmol L -1 ).A novel and fast electroanalytical method for naproxen determination in pharmaceutical formulations using batch injection analysis (BIA) with pulsed amperometric detection is described. Bare glassy carbon electrode was used as working electrode and 0.05 mol L -1 phosphate buffer solution as supporting electrolyte. The amperometric method involved the continuous application of two sequential potential pulses to the working electrode in order to detect naproxen by its electrochemical oxidation (+1.5 V for 200 ms) and to clean the electrode surface from adsorption products (+1.0 V for 100 ms), avoiding electrode contamination. The proposed method has several advantages for routine analysis, including: a low relative standard deviation between injections (3.0%, n = 10), high analytical frequency (90 h -1 ), satisfactory accuracy (based on comparative determinations by spectrofluorimetry) and low limit of detection (0.3 µmol L -1 ).Keywords: batch injection analysis, multiple-pulse amperometry, non-steroidal antiinflammatory drug IntroductionNaproxen, 2-(6-methoxynaphthalen-2-yl) propanoic acid, is a non-steroidal anti-inflammatory drug (NSAID) derived from propionic acid and has been widely used as an over-the-counter analgesic, anti-inflammatory and antipyretic agent. It is also commonly used for the reduction of stiffness caused by conditions including kidney stones, rheumatoid arthritis and other inflammatory rheumatic diseases. 1,2 NSAIDs have been associated with the increasing number of potentially cardiovascular events. However, a recent study classified naproxen as the least harmful NSAID in cardiovascular terms. 3 Different analytical methods have been proposed for the determination of naproxen in pharmaceutical formulations including spectrophotometry (UV region), 4,5 spectrofluorimetry, 6-8 capillary isotachophoresis 9 and high-performance liquid-chromatography (HPLC) coupled with spectrophotometric, 10 amperometric 11 and mass spectrometric detectors. 1 Nevertheless, these analytical methods require expensive equipment and reagents, are time-consuming and often necessitate laborious pre-and pos...

h i g h l i g h t s " Galvanised and carbon steels have proven to be compatible with biodiesel. " Biodiesel properties were not affected for a storage time of 56 days. " Zinc release in non-stabilised biodiesel did not stimulate biodiesel deterioration. " TBHQ was rapidly consumed in the first days of the corrosion immersion test. " TBHQ acted as a corrosion inhibitor and enhanced storage stability of biodiesel. a b s t r a c tThe storage stability and corrosive character of soybean biodiesel stabilised with tert-butylhydroquinone (TBHQ) was investigated through static immersion corrosion tests. Coupons of carbon steel and galvanised steel were immersed in soybean biodiesel with and without TBHQ for 12 weeks. Measurements of total acid number, peroxide value, oxidation stability (Rancimat induction period), metal release, and TBHQ consumption at different stages of corrosion were performed. After 12 weeks of the static immersion test with both steels, the non-stabilised biodiesels presented induction times below the EN 14214 limit (6 h); these results were in agreement with increase in the peroxide values. Zinc release was only detected in the non-stabilised biodiesel exposed to galvanised steel, whilst iron was not detected in any biodiesel samples exposed to carbon steel. The absence of zinc in the TBHQ-doped biodiesel exposed to galvanised steel indicates that TBHQ may have acted as a corrosion inhibitor. Additionally, TBHQ was rapidly consumed in the first 3 days of experiments, providing evidence of its activity. For a storage period of up to 56 days, both galvanised and carbon steels were shown to be compatible with biodiesel even in the absence of an antioxidant. The presence of zinc (>2 lg g À1 after 28 days of immersion) due to corrosion did not promote biodiesel deterioration.

No abstract

The electrochemical oxidation of ibuprofen at a boron‐doped diamond electrode (BDDE) and its voltammetric determination is reported for the first time. A well‐defined oxidation peak was observed at around 1.6 V in 0.1 mol L−1 H2SO4 solution with 10 % (v/v) ethanol at the BDDE surface activated by either cathodic or anodic pretreatments. A differential‐pulse voltammetric method for the determination of ibuprofen in pharmaceutical formulations was optimized with a detection limit of 5 µmol L−1 and compared with the British Pharmacopeia method.