In this work, polypyrrole films are electrosynthesized in aqueous media over graphite-epoxy resin composite; sulphate ions used to dope the polymer are obtained from different salts (Na2SO4, Li2SO4, (NH4)2SO4 and K2SO4). Potentiostatic techniques are used to induce the polymerization. Potentiometric response of Ppy-SO4-2 films was evaluated by calibration curves. Analyzing the slope sign, behavior of the different films can be classified in three responses: anionic, cationic and anionic-cationic. These behaviors were observed for all synthesized films, independently of the sulphate salt used. When analyzing the transients obtained for the different salts, similarities where found for those with the same potentiometric behavior, but significative differences where observed when comparing transients of different potentiometric response. It was determined that the cation size of the sulphate salt influences the Ppy-SO4-2 film response. Boundaries on the potentiostatic synthesis parameters are suggested to induce a specific potentiometric response.