Study on the chromogenic reaction of malachite green with phosphorus-vanadium-molybdenum heteropoly acid

In H_2SO_4 containing polyvinyl alcohol, phosphate reacted with vanadate and molybdate to form P-V-Mo heteropoly acid. The heteropoly acid reacted with malachite green to form MV-P-V-Mo tetrabasic associated complex, leading to a color change of the solution. The wavelength of maximum absorption of the complex was at 590 nm, the molar absorption coefficient was 1.7×10~5 L·mol~(-1)·cm~(-1). The absorbance was directly proportional to the concentration of P(V) in the range 0～(0.12 μg/mL). Conditions of the chromogenic reaction, effects of some coexistent ion, and the formation of the complex were studied. The method was applied to the determination of P(V) in synthetic samples with satisfactory results.