Metal separation using conventional cation exchange resins, such as Amberlite IR-120, is usually unsatisfactory. In this work, effective exchange separation of two pairs of binary metals (Zn2+/Cu2+ and CO2+/Ni2+) from equimolar sulfate solutions was investigated using ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), and citrate as masking agents. Experiments were carried out at different aqueous pH values (1similar to6) and a fixed concentration ratio of masking agent to total metals of 0.5. It was found that the extent of enhancement strongly depended on the solution pH. A parameter that involves the overall formation constants of the masking ligands with two metals is proposed to correlate the exchange selectivities obtained between the two metal pairs and different masking agents. This correlation allows the selection of suitable type of masking agent for effective separation of a given pair of heavy metals.