Electrochemical study of mefexamide at glassy-carbon electrodes and its determination in urine by differential pulse voltammetry

Abstract

The electrochemical oxidation of mefexamide N-[2-(diethylamino)ethyl]-2-(4-methoxyphenoxy)acetamide was investigated using cyclic, linear scan and rotating disk voltammetry at glassy-carbon electrodes. The value of pKa (9.01) was determined by the potentiometric method. In cyclic voltammetry, in neutral media, the compound shows two electrochemical irreversible oxidation peaks (both 2e−), Ox1 and Ox2. A new redox couple Red3/Ox3, formed as a result of the oxidation Ox1 peak, followed for an irreversible chemical reaction, appears on the reverse negative sweep. In acidic media, only the Ox1 peak was observed. The most defined peaks were obtained in 0.040 M Britton–Robinson buffer (pH 6.0) and 0.010 M sulfuric acid with 0.10 M sodium sulfate. The Ox1 and Ox2 peak currents were diffusion-controlled, showing an adsorption effect for low mefexamide concentrations (1.0×10−4 M) and calibration plots at 20 mV s−1, being linear in the range 5.0×10−5–5.0×10−4 M. The limiting currents in a rotating disk electrode were mass transport controlled for rotation speeds lower than 3000 rpm. The anodic charge transfer coefficient, the mass-transport rate constant, the diffusion coefficient and the charge-transfer conditional constant were determined. Also, a method for the electrochemical determination of mefexamide in human urine was developed using differential pulse voltammetry, in 0.040 M Britton–Robinson buffer (pH 6.0), being extracted with dichloromethane. The standard addition method was applied. The detection limit was 0.8 μg of mefexamide per milliliter of urine. The statistical validation reveals that the method is free from significant systematic errors.