In order to determine the concentration 2-HIYPMI required for quantitative recoveries of all investigated metal ions, the proposed method was applied. Firstly, some works were carried out without ligands at optimum pH 6 and it was observed that the Cr3+, Cu2+, Zn2+ and Ni2+ ions were not quantitatively recovered in the absence of ligands. Therefore, the studies were performed with the various amounts of 2-HIYPMI and results are presented in Fig. 2. It can be seen that the recoveries of the metal ions increased with increasing concentration of 2-HIYPMI added and reached a constant value