DETERMINATION OF EPHEDRINE IN HUMAN URINE USING A GLASSY-CARBON ELECTRODE

The electrochemical behaviour of ephedrine at a glassy carbon electrode was studied using linear-sweep and differential-pulse voltammetry at a stationary electrode and a rotating disc electrode. The studies were performed using 0.04 M Britton-Robinson buffer (pH 10.0), which allowed the evaluation of the diffusion constant, the charge-transfer coefficient and the conditional charge-transfer rate constant. A method was also devised for the electrochemical determination of ephedrine in human urine samples using differential-pulse voltammetry with prior drug separation. If this separation method is applied, either calibration graphs or standard additions can be used to determine ephedrine at concentrations between 7 and 20 mug ml-1, with relative errors lower than 6.0% and relative standard deviations lower than 5.8%. The presence of norephedrine at levels 20% lower than those of ephedrine has no influence on ephedrine determination.