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

The electrochemical oxidation of mefexamide N-[2-(diethylamino)ethyl]-2-(4- methoxyphenoxy)acetamide was investigated using cyclic, linear scan and rot ating disk voltammetry at glassy-carbon electrodes. The value of pK(a) (9.0 1) was determined by the potentiometric method. In cyclic voltammetry, in n eutral 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 rea ction, 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 sulf ate. The Ox1 and Ox2 peak currents were diffusion-controlled, showing an ad sorption effect for low mefexamide concentrations (1.0 x 10(-4) M) and cali bration plots at 20 mV s(-1), being linear in the range 5.0 x 10(-5)-5.0 x 10(-4) M. The limiting currents in a rotating disk electrode were mass tran sport controlled for rotation speeds lower than 3000 rpm. The anodic charge transfer coefficient, the mass-transport rate constant, the diffusion coef ficient and the charge-transfer conditional constant were determined. Also, a method for the electrochemical determination of mefexamide in human urin e was developed using differential pulse voltammetry, in 0.010 M Britton-Ro binson buffer (pH 6.0), being extracted with dichloromethane. The standard addition method was applied. The detection limit was 0.8 mu g of mefexamide per milliliter of urine. The statistical validation reveals that the metho d is free from significant systematic errors. (C) 2000 Elsevier Science S.A . All rights reserved.