Capillary zone electrophoretic separation and determination of imidazolic antifungal drugs.

Capillary zone electrophoresis (CZE) was adapted to the simultaneous determination of a mixture of three imidazolic antifungal drugs. Separation was achieved by using a fused-silica capillary column with an acetic acid-Tris buffer at pH 5.18 and UV detection at 196 nm. Several electrophoretic parameters were investigated: pH and buffer concentration, applied voltage, temperature and injection conditions. The optimized CZE method was applied to the individual determination of ketoconazole, clotrimazole and econazole in pharmaceutical forms, after a previous single extraction step in methanol, with recoveries of 98.00, 99.96 and 99.58% respectively. The antifungal drugs can be determined at a concentration level lower than 1.0 x 10(-7) M.

Cathodic stripping voltammetric determination of doxazosin in urine and pharmaceutical tablets using carbon paste electrodes.

Several voltammetric techniques were used to explore the reductive behaviour of the antihypertensive agent doxazosin on a bare carbon paste (CPE) and a Tenax-modified carbon paste electrode (TMCPE). The results indicate that the process is irreversible and fundamentally controlled by adsorption, which allows doxazosin to be accumulated at the electrode surface. The cathodic adsorptive stripping (AdS) response was evaluated with respect to pH, accumulation variables and instrumental parameters, using differential-pulse (DPV) and square-wave voltammetry (SWV) as redissolution techniques. In both cases, a voltammetric peak close to 0 V in Britton-Robinson buffer (pH 6.6) was obtained after a preconcentration step at 0.55 V for 3 min (2000 rpm) and a subsequent cathodic scan. When the TMCPE was used, the limits of detection were 4.35 x 10(-11) and 5.18 x 10(-11) M for AdS-DPV and AdS-SWV, respectively. The deposition time (3 min) was improved relative to that obtained by means of CPE (6 min). Under the optimum operational conditions, the doxazosin reduction peak showed a linear response in the range from 6 x 10(-11) to 1 x 10(-9) M by using AdS-DPV, with an RSD of 3.39% for 3 x 10(-8) M doxazosin solution (n = 10). A method was developed for the determination of doxazosin in human urine and formulations.

Study of the electro-adsorptive behaviour of the herbicide nitralin by means of voltammetric techniques.

The electroanalytical behaviour of the herbicide Nitralin has been studied by means of different voltammetric techniques. Nitralin is adsorbed on the mercury electrode and gives 2 reduction waves at -0.6 and -0.7 V versus Ag AgCl reference electrode, for pH values > 10. The electrochemical process is irreversible and strongly influenced by pH solution. A systematic study of the several instrumental and accumulation variables affecting the stripping response was carried out using square wave (SWV; Osteryoung's method) and differential pulse voltammetry (DPV) as redissolution techniques. The limits of detection were 4.4 x 10(-1) mol 1(-1) (AdS-SWV) and 3.5 x 10(-11) mol 1(-1) (AdS-DPV), with variation coefficients of 4.17 and 3.90% respectively, at a concentration level of 8 x 10(-9) mol 1(-1) (n = 10). A method, based on AdS-DPV, for the determination of Nitralin in ground-water is proposed. A detection limit of 8.7 x 10(-11) mol 1(-1) (AdS-DPV) was reached in real samples.

Use of derivatization reactions with adsorptive stripping voltammetry for determining fotemustine in biological samples.

A method is described for determining the new fotemustine antineoplastic in human serum. The method is based on the derivatization of the original molecule by means of diazotization and coupling reactions. The derivatization product is determined by means of adsorptive stripping voltammetry. The calibration graphs were linear over the range 6 x 10(-9)-8 x 10(-7) and 6 x 10(-10)-8 x 10(-8) M, according to whether the coupling reagent was 1-naphthylamine or 1-naphthol, respectively. At the same time, the detection limits are 4.1 x 10(-9) and 1.4 x 10(-10) M, respectively. The method was applied to determine this antineoplastic in human serum, after a liquid-liquid extraction process, from which recovery factors of 95.6% has been obtained.