Continuous short time Fourier transformation transforms of the sinusoidal perturbation signal and current have been found for the first order electrode reaction. The electrode impedance has been determined in the joint time-frequency domain. Measurements of the Cd(II) reduction reaction have been performed on a hanging mercury electrode (HDME) as a function of potential. The possibility of instantaneous impedance spectra generation has been presented. The dependence of the charge transfer resistance, Warburg coefficient and double layer capacitance on potential has been described. (C) 2003 Elsevier Science B.V. All rights reserved.