with different acetic acid–sodium acetate buffer solution and sodium hydroxide for much higher pH. The result was shown in Fig. 2a. It can be seen that the extraction efficiency of the complex was increased as the pH of the aqueous solution was increased from 3.5 to 4.8. The maximum absorbance remained constant in the pH range of 4.8–6.0 which belongs to the buffer range of acetic acid–acetate. At pH lower than 3.5, the complex of Fe(II)-5-Br-PADAP cannot form readily although Fe3+ is reduced by ascorbic acid. A pH greater than 6 will result in the decrease in absorbance due to the hydrolysis of Fe3+ or Fe2+. Therefore, pH 5.5 was found to be best for the extraction of Fe(II)-5-Br-PADAP complex.