IMPEDANCE STUDY OF THE ELECTROCHEMICAL REDUCTION OF ADRENOCHROME ON GLASSY-CARBON

The electrochemical reduction of adrenochrome on a glassy carbon elect rode was investigated by ac impedance in a constant ionic strength McI lvaine buffer solution. When the frequency was lower than 60 kHz, -Z ' ' against Z' showed straight lines whose inclined angles with the real axis were within the range 71-76 degrees in the diagrams of the compl ex impedance plane obtained at different de potentials. In the corresp onding admittance diagrams, distorted semicircles appeared. The electr ode reaction involves adsorption of electroactive species and the effe ct of concentration polarization cannot be neglected. Based upon the a dmittance model of the equivalent circuit, the optimal estimated value s of some model parameters were obtained by using a Gauss-Newton algor ithm and non-linear curve fitting. The characteristics of the electrod e process are also discussed. (C) 1998 Elsevier Science S.A. All right s reserved.