Besides the strongly basic quaternary amines as well-known in the literature, the presence of pyridine groups at the interface of Selemion AMV membrane was evidenced by X-ray Photoelectron Spectroscopy and Infrared techniques for the first time. Quantity of the weak base functionalities was determined via the exceptional sorption properties of sulfuric acid in the membrane. This work also offered a simple way for quantitative analysis of both the sorbed acid content and the weak amine amount together. Increase in ion exchange capacity of the membrane in acidic solution due to the protonation reaction of these weakly basic groups altered the conformation and hydrophilicity of the functionalized polyelectrolyte phase which, in turn, affected the content of sorbed non-exchange acid as well as the volume fraction of the interstitial solution within the membrane. On the basis of the obtained results in this work and those recently published by the other research groups, our suggestion is the dominant role of the gel phase toward the overall membrane properties. Full membrane characterization also led to evaluate the chronopotentiometric curves of the AMV in H2SO4 and HCl solutions which show a typical behavior of homogeneous ion exchange membranes. Only sulfate anions are responsible for the electric transport inside the membrane in contact with 0.1 M sulfuric acid notwithstanding the fact that the bulk solution is mainly occupied by bisulfate counter-ions (about 90%) and the membrane contains both quaternary amines and pyridinium cations as fixed ionic groups. (C) 2013 Elsevier Ltd. All rights reserved.