ELECTROCHEMICAL STUDIES OF ETHAMIVAN AT GLASSY-CARBON AND PLATINUM-ELECTRODES AND ITS DETERMINATION IN URINE BY DIFFERENTIAL-PULSE VOLTAMMETRY

The electrochemical oxidation of ethamivan (N,N-diethyl-4-hydroxy-3-me thoxy-benzamide) was investigated using cyclic, linear scan and differ ential pulse voltammetry at glassy-carbon and platinum stationary elec trodes, and rotating disk voltammetry. The values of pK(a), 8.98 and 9 .03, were determinated by potentiometric and spectrophotometric method s. The compound showed an electrochemically reversible two electrons o xidation peak followed by an irreversible chemical reaction, and produ ced a new redox couple. The best defined peaks were obtained in 0.05 M sulphuric acid or 0.1 M hydrochloric acid at 0.87, 0.55 and 0.61 V (v s. Ag/AgCl/3 M KCl). The peak currents in cyclic voltammetry and the l imiting current at a rotating disk electrode are diffusion-controlled Using rotating disk voltammetry the mass-transport rate constant was 5 .26 x 10(-3) cm s(-1) for a rotation frequency of 20.34 Hz, the diffus ion coefficient was 6.5 x 10(-6) cm(2) s(-1), the charge-transfer cond itional rate constant was 1.2 x 10(-3) cm s(-1) and the charge transfe r coefficient (beta) was 0.91. By Linear scan voltammetry calibration plots were linear in the range 7.0 x 10(-5)-8.0 x 10(-4) M at the Pt e lectrode and in the range 4.0 x 10(-5)-1.0 x 10(-3) M at the GCE in 0. 05 M sulphuric acid at 50 mV s(-1). A method was also developed for th e electrochemical determination of ethamivan in human urine using diff erential pulse voltammetry with prior drug separation with C-18 cartri dges (Sep-Pak, Waters). The mean recovery was 92 +/- 6% (n = 8). The s tandard addition method was applied. The relative standard deviation w as lower than 9% (samples of 15 mu g ml(-1) ethamivan). The detection limit was 4 mu g per milliliter of urine.