The effect of concentration of 5-Br-PADAP on the absorbance was evaluated in the range of 0.1 105
results are given in Fig. 2d. The absorbance of the complex increases with increasing 5-Br-PADAP concentration up to 0.5 105 mol concentrations. The excessive chromogenic agent could be co-extracted into the organic phase. Therefore, 2.5 105 mol 5-Br-PADAP was selected as the optimal concentration in present study.