The selective permeation of Cu 2 + and UO 2 + 2 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 Cu 2 + , whereas the same has been used as masking agent for Fe 3 + , Cu 2 + , Ni 2 + and Zn 2 + during the selective permeation of UO 2 + 2 using Na 2 CO 3 or Tiron as a receiving solution. Selective permeation of Cu 2 + from a mixture of Fe 3 + and Cu 2 + after masking Fe 3 + with F - , SCN - and PO 3 - 4 was studied in detail. A lowering of permselectivity and the permeation of anions has been attributed to the simultaneous permeation of Fe 3 + through metal speciation.