Microdetermination of phosphorus in organic compounds by ion chromatography

A modified ion chromatographic (IC) microdetermination of phosphorus in organic compounds was developed. The recoveries of phosphorus (measured as PO43-) by the conventional flask combustion method were rather low and dispersed, 47 similar to 98% (4 compounds), when dilute aqueous hydrogen peroxide was used as an absorbing solution for collecting the combustion products, probably due to the production of phosphorus-containing anions other than phosphate. The IC method was applied to separate the polyphosphate components collected in the combustion solution, demonstrating the presence of orthophosphate (PO43-), pyrophophosphate (P2O74-) and tripolyphosphate (P3O105-). Boiling of the combustion sample solution in the presence of dilute sulfuric acid on a hot plate (200 degrees C) for 20 min was shown to convert all the phosphorus-containing anion species to orthophosphate. The simultaneous microdetermination of chlorine, bromine, sulfur and phosphorus in organic compounds was achieved by incorporating this post-combustion hydrolysis step into the conventional procedure. The analytical values thus obtained were in good agreement, within +/-0.3%, with the theoretical values for four compounds tested.