Abstract: H+ was freed from H2PO-4 by adding La(NO3)3 solution as precipitation releasing agent.The concentration of the freed H+ was directly titrated by the standard NaOH solution.The content of phosphorus of Ca3(PO4)2 or CaHPO4 was calculated by the consumption of the standard NaOH solution.All the operations of titration and pH adjustment were completed by the Automatic Potentiometric Titrator.These operations in this method were simple and rapid with good precision .The complex processes in the standard method such as precipitation and filtration and scrubbing,were omitted in this method,but the results of the method were the same as those of the standard method.This method may be used to tast water soluble phosphate at pH=4.2.

Key words: Ca3(PO4)2 CaHPO4 La(NO3)3 pH=4.2 The Automatic Potentiometric Titrator