Iodometric microdetermination of phosphorus in organic compounds

Abstract

Two methods are described for the iodometric microdetermination of phosphorus in organic compounds. These methods depend on combustion by the oxygen flask, absorption of the combustion products in H 2O and conversion to orthophospheric acid with bromine water. The phosphoric acid produced is then determined iodometrically after removal of excess bromine through boiling. In the first method orthophosphoric acid behaves as a monobasic acid on reaction with KI and KIO 3 solutions. In the second method, orthophosphoric acid functions as a tribasic acid through reaction with zinc and ammonium ions and subsequent addition of excess solid KI and KIO 3. The liberated iodine is titrated, as usual, with thiosulfate solution using starch as indicator. The two methods, in general, and the second method in particular, are simple, rapid, and accurate.