Simplified method for the estimation of inorganic phosphorus in body fluids.

A simplified procedure is described for the determination of inorganic phosphate in body fluids. The method employs two stable reagents and requires a minimum number of steps. Serum is deproteinized with trichioroacetic acid containing ferrous ion and thiourea. The supernatant is decanted and mixed with a small volume of molybdic acid. The phosphomolybdate formed is immediately reduced in situ by the ferrous ion to produce a blue color that is stable for several hours. The intensity of color is insensitive to changes in concentration of acid, molybdate, ferrous ion, and thiourea, and to losses in decanting the serum supernatant. Excellent conformity to Beer’s law is demonstrated over a wide range of phosphorus concentrations. Recoveries of phosphorus added to serum and urine are shown to be quantitative. A comparison is presented between this method and that of Fiske and SubbaRow (1).