A novel cationic polymeric coating is here reported, consisting of a N-methylpolyvinylpyridinium, quaternary ion. This coating, combined with an isoelectric, aspartic acid as BGE, offers excellent separations of low- to high-M, proteins, of low- to high-pI values, coupled to very high run-to-run repeatability. The importance of a hydrophilic coating is also illustrated, whereas the N-methylpolyvinylpyridinium quaternary ion does not seem to adsorb even a large size protein as human albumin, separations are already distorted in the N-ethyl derivative and totally ruined in the N-octyl derivative, due to its high hydrophobicity.