In this paper an equivalent circuit model is employed in the characterization of the impedance measurements of saline solutions at physiological glucose concentrations. The impedance data are obtained using a three electrodes cell configuration since it allows measuring the potential accurately in the working electrode independently from the counter electrode. As excitation signal an odd random phase multisine is employed which allows identifying the best linear approximation, the noise level and the non-linear distortions present in the system. The results show a significant change in the impedance as a function of the glucose at the interphase electrode-electrolyte as well as in the bulk solution. This is an important step towards the development of glucose measurement systems based in electrochemical impedance spectroscopy (EIS).