Metal ion solution (1-2 mL) containing (0- 50 ug) was transferred to a volumetric flask. (10 ml) and was added reagent solution (1 mL; 0.2% w/v in methanol) and appropriate buffer solution (2 mL). The volume was adjusted to mark with methanol. The absorption spectrum was recorded in visible region within 700-350 nm against reagent blank in the same solvent system.