Determination of inorganic phosphate with molybdate and Triton X-100 without reduction.

A new colorimetric procedure is described for inorganic phosphate determination using the color reaction between inorganic phosphate and acidified ammonium molybdate in the presence of Triton X-100. The method is simple and specific, and produces results comparable with those of the widely used method of Fiske-Subbarow [C. H. Fiske and Y. Subbarow (1925) J. Biol. Chem. 66, 375]. The linearity of the standard curve is observed up to an absorbance of 0.410, compared to 0.370 in the Fiske-Subbarow method. Trichloroacetic acid and tungstic acid are found to interfere in the assay. However, the method is not disturbed by nonionic detergents and can therefore be used for the determination of inorganic phosphate contaminated with nonionic detergents.