After acid digestion, the sample solution is neutralized with sodium hydroxide to form sodium dihydrogen phosphate. An excess of lanthanum nitrate is added and the released nitric acid is then titrated with sodium hydroxide solution.
NaH2PO4 + La(NO3)3 → LaPO4 + 2 HNO3 + NaNO3
This determination method is suitable for higher phosphate concentrations.