Define Principle Colorimetric Method for the Estimation of Phosphorous?

The proteins in the blood are precipitated with the help of trichloroacetic acid. The protein free filtrate containing inorganic phosphorus is then treated with molybdic acid reagent and phosphomolybdic acid is formed. The phosphomolybdic acid is reduced to blue coloured molybdenum blue or hetropolymolybdenum blue (NH₄)₃{Po₄ (Mo0₃)₁₂}) by 1 amino 2 napthol4 sulfonic acid (ANSA). The intensity of the colour formed is directly proportional to the amount of inorganic phosphorus present. A mild reducing agent like ANSA is employed in order to avoid reduction of the excess of molybdate present.