A Quick Determination of SO_4~(2-) and Holophsphate Content in Ordinary Superphosphate Phosphate Fertilizer

In this paper a method,potentiometric titration,has been found to quickly determine SO_4~(2-) and polyphosphates content in ordinary superhosphate phosphate fertilizer.Dissolving the measured sample with concentrated nitric acid,the interference positive ion is eliminated through the positive ion-exchange resin by adding hexamine-nitric acid to control the reagent acidity (pH=5.4).The potentiometric titration is implemented with lead nitrate standard solution.The used lead nitrate for end point of titration is determined with the second order differentiation and labeled as V1.Then again in the same way the interference ion is eliminated through the ion-exchange resin and the used lead nitrate for end point of titration is determined and labeled as V2.The result of V1 subtracting V2 is the lead nitrate volume of used SO_4~(2-).The RSD of the method SO_4~(2-) is 0.62～0.85 and the recovery is 102.8%～103.2%.The RSD of the method polyphosphates content is 0.68～0.72 and the recovery is 99.82%～100.1%.