The redox behavior of p-toluene sulfonate-doped polypyrrole films was investigated in aqueous solutions containing various salts. It was found that the presence of bulky cations such as tetraethylammonium and pyridinium in the electrolytic solution hinders the redox processes of the films electropolymerized in magnetic fields above 0.2 T. This behavior was applied to a modified electrode with a wider potential window.