A comparative study on the potentiostatic polymerization of polyaniline (PANI) in inorganic (sulfuric and perchloric) acid and mixed poly(2-acryalamido-2-methyl-1-propane-sulfonic) (PAMPSA)/inorganic acid solutions is carried out through combined electrochemical and microgravimetric techniques. It is established that polymerization in the presence of small amounts of PAMPSA in the mixed solutions results in immobilization of the polyanions in the PANI layers. The redox behavior of the PAMPSA-doped PANI layers, studied in acidic, neutral and slightly alkaline solutions shows that the electroactivity is preserved up to pH 9. PAMPSA seems to operate as a buffer, providing the necessary protons for the PANI layer in the range pH 7 to pH 9. Detailed microgravimetric measurements in buffer solutions with various cationic (Na+ and Cs+) and anionic (Cl− and ClO4−) species are used to elucidate the ionic transport occurring in the course of the PANI redox transition in neutral solutions. It is found that cations (different than protons) are involved in the early stage of oxidation whereas the participation of anionic species seems to be limited. Small mass fluxes and minor changes in the viscoelastic properties are observed during the redox transition in neutral and slightly alkaline solutions.Highlights► Incorporation of polyanions in PANI during electrosynthesis in inorganic acids. ► Preserved electroactivity of PANI up to pH 9. ► Small mass fluxes at PANI redox transition in neutral and slightly alkaline solutions.