The present work aims to obtain more insights into the effects of the electrochemical polymerization of a 4-hydroxybenzaldehyde + formaldehyde (resol) mixture on the electrochemical properties of modified glassy carbon electrodes, Different redox couples, having a permanent positive charge (Fe-phenathroline), a permanent negative charge (K3Fe(SNC)(6)) and either a positive or negative charge, depending on solution pH (L-Dopa), have been analyzed. Cyclic voltammetry and impedance spectroscopy experiments were performed at different deposited polymer charge and pH values for the proposed redox systems and the comparison with polished electrodes is also analyzed. Electrophoretic mobilities were investigated and acid-base titrations were also carried out in order to prove that the surface is negatively charged. Electrochemical measurements showed an important electrostatic effect between the electrode surface and the couples analyzed. This effect plays an important role on the electrode response when used for analytical purposes.