The selective permeation of Cu2+ and UO22+ in the presence of common cations through a Nafion 117 ionomer membrane have been studied. EDTA served as a receiving agent for an effective permeation of Cu2+, whereas the same has been used as masking agent for Fe3+, Cu2+, Ni2+ and Zn2+ during the selective permeation of UO22+ using Na2CO3 or Tiron as a receiving solution. Selective permeation of Cu2+ from a mixture of Fe3+ and Cu2+ after masking Fe3+ with F-, SCN- and PO43- was studied in detail. A lowering of permselectivity and the permeation of anions has been attributed to the simultaneous permeation of Fe3+ through metal speciation.