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- Cathodic voltammetric detection of diltiazem at a bismuth film electrode: application to human urine and pharmaceuticalsPublication . Catarino, Rita I. L.; Leal, M. Fernanda C.; Pimenta, Adriana M.; Souto, M. Renata S.; Lopes, Joana R. T.In this work it was developed a novel application of bismuth film electrodes (BiFEs) for the determination of the antihypertensive and coronary vasodilator diltiazem by square wave cathodic voltammetry. The bismuth film was deposited ex situ on a glassy carbon electrode for 90 s at -1.4 V vs. Ag/AgCl, from an acetate buffer (pH 4.5; 0.10 mol L-1) containing 5 or 30 mg L -1 Bi. Diltiazem analytical signal was obtained in phosphate buffer (pH 7.4; 0.25 mol L-1) where reduction takes place at -1.5 V vs. Ag/AgCl. The proposed methodology was applied to the quantification of diltiazem in pharmaceutical samples (dynamic linear range comprised between 90 and 900 μg L-1) and in human urine (dynamic linear range comprised between 45 and 270 μg L-1, and detection limit of 12 μg L -1).
- Ofloxacin determination in urine, serum and pharmaceuticals using an automatic flow potentiometric systemPublication . Pimenta, Adriana M.; Souto, M. Renata S.; Catarino, Rita I. L.; Leal, M. Fernanda C.; Lima, José L. F. CostaAn automatic system was developed to determine ofloxacin in biological fluids and pharmaceutical formulations. Drug detection was carried out by a potentiometric membrane sensor based on [bis(trifluoromethyl)phenyl]borate as molecular-recognition material. The tubular shaped detector system was solidly attached to the manifold, creating a high-throughput stable setup (50 samples per hour) appropriate for routine antibiotic assessment. Under the optimized flow conditions, the sensor displayed a mean detection limit of 1 × 10 -5 M, a linear response over the concentrations of 2 × 10 -5 to 5 × 10 -3 M (slope of 57.4 mV decade -1 ) and a wide working pH range (2.1-6.6). The procedure was successfully applied to ofloxacin analysis in pharmaceuticals (relative deviation lower than 6%) and biological fluids at levels usually found after drug administration of clinical doses (recoveries between 91 and 106%). No significant interference from common excipients found in commercial formulations and inorganic ions usually present in biological fluids was noticed.
- Sequential injection kinetic flow assay for monitoring glycerol in a sugar fermentation process by saccharomyces cerevisiaePublication . Hueso Domínguez, Karina B.; Tóth, Ildikó V.; Souto, M. Renata S.; Mendes, Filipa; García De María, Cándido; Vasconcelos, Isabel; Rangel, António O. S. S.A sequential injection system to monitor glycerol in a Saccharomyces cerevisiae fermentation process was developed. The method relies on the rate of formation of nicotinamide adenine dinucleotide in its reduced form (NADH, measured spectrophotometrically at 340 nm) from the reaction of glycerol with NAD+ cofactor, catalysed by the enzyme glycerol dehydrogenase present in solution. This procedure enables the determination of glycerol between 0.046 and 0.46 g/l, (corresponding to yeast fermentation samples with concentrations up to 50 g/l) with good repeatability (relative standard deviation for n = 10 lower than 2.2% for three different samples) at a sampling frequency of 25/h. The detection and quantification limits using a miniaturised spectrophotometer were 0.13 and 0.44 mM, respectively. Reagent consumption was of 0.45 μmol NAD+ and 1.8 μg enzyme per assay, and the waste production was 2.8 ml per determination. Results obtained for samples were in agreement with those obtained with a high-performance liquid chromatography method.