The potentiometric measurements were carried out in double distilled water by using the Equip-tronics model EQ-602 potentiometer The pH measurements were made using an Elico LI model - 120 meter. The stock solutions (1.0 101 M) of metal ionswere prepared from their metal nitrate salts and test solutions of desired concentration were obtained by successive dilution of the stock solution with double distilled water. The pH adjustments were performed by using conc. nitric acid and hexamine solution. The detection limits of the potentiometric measurements were calculated by a similar way as per recommended by IUPAC [24]. All the voltammetric and potentiometric experiments were performed in triplicate at