1 Method Summary
In the 0.65~1.63mol/l nitric acid medium, the phosphorus-molybdenum heteropoly acid produced by phosphorus and ammonium molybdate could be extracted by butyl acetate, deoxidize phosphorus-molybdenum heteropoly acid with stannous chloride and back extract to the water phase, and then measure its absorbance at the wave length of 680nm.
The extraction solution contains 2.5μg of zirconium, 20μg of arsenic, 25μg of niobium and tantalum, 50μg of titanium, 500μg of cerium, 1.5mg of wolfram, 2mg of copper, 3mg of cobalt, 5mg of chromium and 5mg aluminum as well as 50mg of nickel but they don't interfere the determination.
If the above-mentioned limits are exceeded, arsenic shall be removed with hydrochloric acid or hydrobromic acid; vanadium shall be deoxidized with ferrous iron; zirconium shall be screened with hydrofluoric acid; chromium shall be volatilized and removed after being oxidized into a higher valence; wolfram performs precipitation separation of phosphorus taking bergllium as carrier in EDTA ammoniacal solution; niobium, titanium, zirconium and tantalum shall be extracted and removed with cupferron or methenyl choloride.
2 Reagents
