Adsorptive behavior and electrochemical determination of the anti-fungal agent ketoconazole.

The adsorptive properties and electrochemical behavior of ketoconazole, an oral anti-fungal agent, are demonstrated at a glassy carbon electrode. The adsorption of the compound obeys the Frumkin isotherm with an interaction factor (alpha) of 0.985 and adsorptive coefficient (beta) of 1.98 x 10(6) L mol(-1). The Gibbs energy of adsorption (deltaG) is -3.59 x 10(4) J mol(-1) at 25 degrees C. A very sensitive electroanalytical method has been developed for determination of the drug with a detection limit of 4.0 x 10(-11) mol L(-1). Relationships between stripping current and concentration of ketoconazole were linear in the range 10(-6)-10(-10) mol L(-1) with different preconcentration periods. The method has been used to measure the ketoconazole content of tablets.

Semi-differential voltammetry with carbon fiber electrodes for in vivo determination of monoamine metabolites and ascorbic acid in rat corpus striatum.

Carbon fiber electrodes combined with semi-differential voltammetry were used to determine endogenous monoamine metabolites and ascorbic acid (AA). These electrodes treated by a new electrochemical procedure (30 microA for 30 s, then -2 V for 10 s) showed a significant improvement on the sensitivity and selectivity. In the rat corpus striatum, these electrodes allowed a distinct separation and continuous detection of AA, 3, 4-dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) simultaneously. The normal striatal levels of AA, DOPAC, and 5-HIAA were found to be 168.2 +/- 19.5, 21.4 +/- 3.9, and 3.3 +/- 0.5 mumol.L-1. Our method is credible for detecting the changes of monoamine metabolite contents induced by pharmacologic manipulations.

[Differential pulse voltammetric measurements of cholesterol based on its oxidation after adsorption at the mercury electrode].

Cholesterol can be adsorbed on the surface of the static mercury drop electrode, and then oxidized during anodic potential scan. The stripping peak potential in differential pulse voltammetry is at -0.08 V in 0.1 mol/L K2HPO4-KH2PO4 buffer solution. The stripping current is linear with the concentration of cholesterol in the range of 10(-7)-10(-6) mol/L. The detection limit found is 8 x 10(-8) mol/L after a 5 min pre-concentration period. The adsorption and oxidation mechanisms of cholesterol at the mercury electrode were then explored. The experimental conditions for measuring free cholesterol in human sera were examined.

Adsorptive preconcentration for voltammetric measurements of trace levels of chlorprothixene.

The psychotherapeutic drug chlorprothixene is shown to adsorb strongly onto a glassy carbon surface in an open circuit. By using this phenomenon to preconcentrate the drug at a glassy carbon electrode prior to differential-pulse voltammetric measurements, sensitivity at the ppb level is readily achieved. The adsorptive stripping response was evaluated with respect to electrolyte, solution pH, accumulation time, concentration dependence and other variables. A linear peak current-concentration relationship was observed up to 1 microgram ml-1 of chlorprothixene; the relative standard deviation (at the 0.6 microgram ml-1 level) is 3.2%. For a preconcentration time of 10 min, the detection limit was found to be 2 ng ml-1. The open circuit preconcentration/medium exchange/voltammetric scheme was used to eliminate interference from sample solutions. The application of the method to human urine samples is described.

[Adsorptive stripping voltammetry of chlorprothixene at glassy carbon electrode].

A new electrochemical stripping method for measuring the antipsychotic drug chlorprothixene was reported. The drug, which was adsorbed on the surface of glassy carbon electrode, showed a sharp oxidative stripping peak at about +0.7 V (vs. Ag-AgCl) in voltammetry. The response was linear over the 0.01-1 microgram/ml concentration range. The detection limit was 2 ng/ml, about 400 times higher than UV method. The electrode surface was polished with alumina between the measurements to activate the electrode and provide good reproducibility. The open circuit accumulation/medium exchange/stripping voltammetry scheme has been proposed to avoid interference. The method has been used for direct determination of chlorprothixene in tablets and urine samples.

[Stripping voltammetric determination of perphenazine and some antipsychotic drugs at carbon paste electrodes].

A sensitive electrochemical method for the determination of four drugs: perphenazine, fluphenazine chlorpromazine and trifluperazine is reported. These compounds exhibited accumulation at carbon paste electrodes in an open circuit. Differential pulse voltammetric determination gave linear calibration curves in the range of 0.02-1 microgram/ml. Detection limits found were 5-7 ng/ml. The drugs in tablets and body fluids were determined directly without separation. The preconcentration mechanism and determination conditions in a new kind of carbon paste piston electrode were investigated. Adsorption and extraction played important roles in accumulation process and the ratio of these two parts was measured by chronocoulometry.