The method is based on the interaction of silicic acid with ammonium molybdate to form a yellow silicomolybdic heteropoly acid, which is reduced by ascorbic acid to a blue silicomolybdic complex
The method is based on the formation of phosphomolybdic heteropoly acid with its subsequent reduction by ascorbic acid in the presence of potassium antimonyl tartrate to a complex compound colored d blue, and photometry of the colored solution at a wavelength of 880 nm.