The effect of volume of extraction solvent on the absorbance was also studied in the range of 50–200 lL. According to Fig. 2b,the absorbance of the complex was increased with increasing the volume of CCl4 from 50 to 100 lL. Then the absorbance of the complex decreases gradually when the volume of CCl4 was higher than 120 lL. Hence, 100 lL CCl4 was selected as optimum volume.