A RAPID AND HIGHLY SELECTIVE METHOD FOR THE ESTIMATION OF PYROPHOSPHATES, TRIPHOSPHATES AND ORTHOPHOSPHATES

A rapid, highly selective and simple method has been developed for the quantitative determination of pyro-, tri- and orthophosphates. The me thod is based on the formation of a solid complex of bis(ethylenediami ne)cobalt(III) species with pyrophosphate at pH 4.2-4.3, with triphosp hate at pH 2.0-2.1 and with orthophosphate at pH 8.2-8.6. The proposed method for pyro- and triphosphates differs from the available method, which is based on the formation of an adduct with tris(ethylenediamin e)cobalt(III) species. The complexes have the composition [Co(en)(2)HP 2O7]4H(2)O and [Co(en)(2)H2P3O10]2H(2)O, respectively. The precipitati on is instantaneous and quantitative under the recommended optimum con ditions giving 99.5% gravimetric yield in both cases. There is no inte rferences from orthophosphate, trimetaphosphate and pyrophosphate spec ies in the triphosphate estimation up to 5% of each component. The eff icacy of the method has been established by determining pyrophosphate and triphosphate contents in various matrices. In the case of orthopho sphate, the proposed method differs from the available methods such as ammonium phosphomolybdate, vanadophosphomolybdate and quinoline phosp homolybdate, which are based on the formation of a precipitate, follow ed by either titrimetry or gravimetry. The precipitation is instantane ous and the method is simple. Under the recommended pH and other react ion conditions, gravimetric yields of 99.6-100% are obtainable. The me thod is applicable to orthophosphoric acid and a variety of phosphate salts.