Systematic experiments were performed on an electrolytic cell using different ionic species and covering a large range of concentration values. Experimental data indicate that cell impedance is well described by a series combination of discrete circuit elements different from that originally proposed by Randles. A first-principle model describing diffusion and migration of the ionic species excited by an applied electric field was able to describe our data. This model relates the spectral decomposition of the measured impedance to spatially distributed sample properties, and opens the possibility of getting information concerning sample structure using this experimental technique. (C) 2010 Elsevier Ltd. All rights reserved.