Spectrophotometric determination of aminophenol isomers by Prussian blue formation

A spectroscopic method was developed to estimate the isomers of aminophenols (ortho, meta- and para-aminophenol) by oxidation reactions of these compounds using ferric chloride to produce ferrous ions which subsequently  react with potassium ferric cyanide and forming prussian blue complex. These products had maximum absorption at the wavelengths of 690, 688 and 704 nm for each of them, respectively. The molar absorbances were 1.19×10⁴, 2.51×10⁴, and 1.54×10⁴ L/mol.cm for concentrations, that followed Beer’s law in the range of 0.5-10, 0.125-8.75, and 0.125-15 μg/ml, for the above compounds, respectively. The accuracy of the method ranged between 98.60% and 102.71%, while the precision was less than 1.2% for all studied compounds, and that the average of stability constant for the formed complexes is 2.60 x 10¹³, 1.42 x 10¹⁰, and 6.02 x 10¹² L²/mol² for each of the products of ortho, meta, and para-aminophenol, respectively, which indicates good stability of these products.