Electrochemical studies of ethamivan at glassy-carbon and platinum electrodes and its determination in urine by differential pulse voltammetry

Abstract

The electrochemical oxidation of ethamivan ( N, N-diethyl-4-hydroxy-3-methoxy-benzamide) was investigated using cyclic, linear scan and differential pulse voltammetry at glassy-carbon and platinum stationary electrodes, and rotating disk voltammetry. The values of p K a , 8.98 and 9.03, were determinated by potentiometric and spectrophotometric methods. The compound showed an electrochemically reversible two electrons oxidation peak followed by an irreversible chemical reaction, and produced 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 (vs. Ag/AgCl/3 M KCl). The peak currents in cyclic voltammetry and the limiting current at a rotating disk electrode are diffusion-controlled. Using rotating disk voltammetry the mass-transport rate constant was 5.26 × 10 −3cms −1 for a rotation frequency of 20.34 Hz, the diffusion coefficient was 6.5 × 10 −6 cm 2 s −1, the charge-transfer conditional rate constant was 1.2 × 10 −3cm s −1 and the charge transfer coefficient (β) was 0.91. By linear scan voltammetry calibration plots were linear in the range 7.0 × 10 −5−8.0 × 10 −4M at the Pt electrode and in the range 4.0 × 10 −5 − 1.0 × 10 −3M at the GCE in 0.05 M sulphuric acid at 50 mV s −1. A method was also developed for the electrochemical determination of ethamivan in human urine using differential pulse voltammetry with prior drug separation with C 18 cartridges (Sep-Pak, Waters). The mean recovery was 92 ± 6% ( n = 8). The standard addition method was applied. The relative standard deviation was lower than 9% (samples of 15 μg ml −1 ethamivan). The detection limit was 4 μg per milliliter of urine.