After selection of the optimum volume of 1-decanol, the volume of THF was examined by varying from 100 to 450 mL. The quantitative results were obtained between 350 and 450 mL (Fig. 3). 400 mL of THF was selected as optimum value. The results shown in Figs. 2 and 3 indicate that higher extraction efficiency for Cu(II)–DMDC can be achieved when the 1-decanol/THF volume ratio was set at 0.313.