The effect of H+ ion concentration on the ion-exchange selectivity of Nafion 117 cation-exchange membrane toward Zn2+ Pb2+; Cu2+, Al3+, and Fe3+ have been studied. A selective transport of any particular metal ion was not possible by controlling the pH alone. However, selective permeation of Zn2+ across the membrane could be accomplished by selectively masking the metal ion as the cationic 1,10-phenanthroline complex while the permeation of other interfering ions could be suppressed by masking them as their anionic EDTA complex. About 20% of Zn2+ selectively permeated from the mixture in 6 hours and the quantity increased to 67% after 60 hours of permeation.