Phosphate test

A range of qualitative and quantitative tests have been developed to detect phosphate ions (PO3−4) in solution.

A quantitative method to determine the amount of phosphate present in samples, such as boiler feedwater, is as follows.

A measured amount of boiler water is poured into a mixing tube and ammonium heptamolybdate reagent is added.

A small amount of the sample is acidified with concentrated nitric acid, to which a little ammonium molybdate is added.

The presence of phosphate ions is indicated by the formation of a bright yellow precipitate layer of ammonium phosphomolybdate.