A capillary zone electrophoretic assay has been developed and validated for analysis of magnesium, calcium, sodium, and potassium in blood plasma samples. Optimum results were obtained with 20 mmol L(-1) imidazole (pH 2.8) and 0.5 mmol L(-1) oxalic acid containing 5% methanol, capillary temperature 25 degrees C, applied voltage 30 kV, hydrodynamic injection time 3 s, and a poly(vinyl alcohol)-coated capillary (i.d. 50 microm, total length 64.5 cm and effective length 56 cm). Indirect detection was performed at 214 nm. Cadmium was used as internal standard. The migration times of magnesium, calcium, sodium, and potassium were 4.25, 3.79, 3.96, and 2.79 min, respectively. The method was applied to the determination of magnesium, calcium, sodium, and potassium in blood plasma samples. The results were compared with those from atomic absorption spectrophotometry and no statistically significant difference was found (P > 0.05).
The electrochemical reduction of lansoprazole was investigated by cyclic voltammetry and direct current and differential pulse polarography. The reduction potential was -1.32 V vs. Ag/AgCl with a dropping mercury electrode in a supporting electrolyte consisting of phosphate buffer (pH 9.0)-tetramethylammonium iodide (4 + 1). The reversibility of the electrode reaction and the type of limiting current were studied. The temperature coefficient and the diffusion constant were determined. A mechanism for the electrode reaction was proposed. A new simple and sensitive differential pulse polarographic method was also developed for the quantification of lansoprazole. A linear calibration graph was obtained in the range 0.04-11.35 micrograms ml-1. The limit of detection was 0.03 microgram ml-1 and the intra- and inter-day precisions were 0.84-2.32 and 0.72-3.09%, respectively. The developed method was applied to six different commercial pharmaceutical capsule preparations containing enteric-coated granules. The relative standard deviations ranged from 1.36 to 2.85%. Recovery studies for the accuracy of the method were performed by adding a synthetic mixture to known amounts of lansoprazole and the mean recovery was 100.45%. The data obtained from commercial preparations were compared with those from a published spectrophotometric method. No difference was found statistically.
The electrochemical reduction of fenofibrate at a hanging mercury drop electrode (HMDE) was investigated by cyclic voltammetry, square-wave voltammetry, and chronoamperometry. Different buffer solutions were used over a wide pH range (3.0-10.0). The best definition of the analytical signals was found in borate buffer (pH 9.0)-tetrabutylammonium iodide mixture containing 12.5% (v/v) methanol at -1.2 V (versus Ag/AgCl). According to cyclic voltammetric studies, the reduction was irreversible and diffusion controlled. The diffusion coefficient was 2.38x10(-6) cm2 s(-1) as determined by chronoamperometry. Under optimized conditions of square-wave voltammetry, a linear relationship was obtained between 0.146-4.96 microg mL(-1) of fenofibrate with a limit of detection of 0.025 microg mL(-1). Validation parameters such as sensitivity, accuracy, precision, and recovery were evaluated. The proposed method was applied to the determination of fenofibrate in pharmaceutical formulations. The results were compared with those obtained by a published high-performance liquid chromatography method. No difference was found statistically.
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