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Abstract A simple and precise colorimetric method of determining orthophosphate in aqueous solutions containing labile organic and inorganic P compounds is described. It involves a rapid formation of molybdenum blue color by the reaction of orthophosphate with molybdate ions in the presence of ascorbic acid‐trichloroacetic acid and citrate‐arsenite reagents and complexation of the excess molybdate ions to prevent further formation of blue color from the phosphate derived from hydrolysis of the acid‐labile P compounds. The color is stable up to 24 hours. The method is sensitive and accurate, and it permits determination of microgram quantities of orthophosphate in samples containing large amounts of acid‐labile P compounds. Tests with a wide range of condensed phosphate and organic phosphate compounds showed that none of the P compounds studied interfered with this method. Results by this method are compared with those obtained by the method of Murphy and Riley.
Dick et al. (1977) studied this question.