Color Development Based on the Ion Association of Molybdophosphate with Cationic Dye Chloro-Malachite Green

Color development based on the ion association of molybdophosphate with a cationic dye, a chloro derivative of Malachite Green (Cl-MG), was investigated in an aqueous acidic solution. Cl-MG is very stable as its quinoid form in an acidic medium, and can easily react with molybdophosphate to form a green ion associate, which shows maximum absorption at 685nm. The experimental conditions for optimum color development have been examined. This color development reaction could be applied to the determination of trace amounts of orthophosphate. The molar absorptivity was 1.3×105dm3 mol-1cm-1 at 685nm.