M962_02
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2.3.03 AOAC Official Method 962.02 Phosphorus (Total) in Fertilizers Gravimetric Quinolinium Molybdophosphate Method First Action 1962 Final Action 1965 A. Reagents (Store solutions in polyethylene bottles.) (a) Citric-molybdic acid reagent.—Dissolve 54 g 100% molybdic anhydride (MoO 3 ) and 12 g NaOH with stirring in 400 mL hot H 2 O, and cool. Dissolve 60 g citric acid in mixture of 140 mL HCl and 200 mL H 2 O, and cool. Gradually add molybdic solution to citric acid solution with stirring. Cool, filter, and dilute to 1 L. (Solution may be green or blue; color deepens on exposure to light.) If necessary, add 0.5% KBrO 3 solution dropwise until green color pales. Store in dark. (b) Quinoline solution.—Dissolve 50 mL synthetic quinoline, with stirring, in mixture of 60 mL HCl and 300 mL H 2 O. Cool, dilute to 1 L, and filter. (c) Quimociac reagent.—Dissolve 70 g sodium molybdate ⋅ 2H 2 O in 150 mL H 2 O. Dissolve 60 g citric acid in mixture of 85 mL HNO 3 and 150 mL H 2 O, and cool. Gradually add molybdate solution to citric acid-HNO 3 mixture with stirring. Dissolve 5 mL synthetic quinoline in mixture of 35 mL HNO 3 and 100 mL H 2 O. Gradually add this solution to molybdate-citric acid-HNO 3 solution, mix, and let stand 24 h. Filter, add 280 mL acetone, dilute to 1 L with H 2 O, and mix. B. Preparation of Solution Treat 1 g sample as in 957.02B (see 2.3.01), diluting to 200 mL. C. Determination Pipet, into 500 mL Erlenmeyer, aliquot containing ≤25 mg P 2 O 5 and dilute to ca 100 mL with H 2 O. Continue by one of the following methods: (a) Add 30 mL citric-molybdic acid reagent and boil gently 3 min. (Solution must be precipitate-free at this time.) Remove from heat and swirl carefully. Immediately add 10 mL quinoline solution from buret with continuous swirling. (Add first 3–4 mL dropwise and remainder in steady stream.) Or: (b) Add 50 mL quimociac reagent, cover with watch glass, place on hot plate in well-ventilated hood, and boil 1 min. After treatment by (a) or (b), cool to room temperature, swirl carefully 3–4 times during cooling, filter into Gooch with glass fiber filter paper previously dried at 250° and weighed, and wash with five 25 mL portions of H 2 O. Dry crucible and contents 30 min at 250°, cool in desiccator to room temperature, and weigh as (C 9 H 7 N) 3 H 3 [PO 4 ⋅12MoO 3 ]. Subtract weight reagent blank. Multi- ply by 0.03207 to obtain weight P 2 O 5 (or by 0.01400 for P). Report as % P 2 O 5 (or % P). References: Z. Anal. Chem. 189, 243(1962). JAOAC 45, 40, 999(1962); 46, 579(1963); 47, 420(1964). CAS-7723-14-0 (phosphorus) CAS-1314-56-3 (phosphorus pentoxide) Copyright 1998 AOAC INTERNATIONAL
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M962
Transcript of M962_02
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2.3.03AOAC Official Method 962.02
Phosphorus (Total) in FertilizersGravimetric Quinolinium Molybdophosphate Method
First Action 1962Final Action 1965
A. Reagents(Store solutions in polyethylene bottles.)
(a) Citric-molybdic acid reagent.Dissolve 54 g 100%molybdic anhydride (MoO3) and 12 g NaOH with stirring in 400 mLhot H2O, and cool. Dissolve 60 g citric acid in mixture of 140 mLHCl and 200 mL H2O, and cool. Gradually add molybdic solutionto citric acid solution with stirring. Cool, filter, and dilute to 1 L.(Solution may be green or blue; color deepens on exposure to light.)If necessary, add 0.5% KBrO3 solution dropwise until green colorpales. Store in dark.
(b) Quinoline solution.Dissolve 50 mL synthetic quinoline,with stirring, in mixture of 60 mL HCl and 300 mL H2O. Cool, diluteto 1 L, and filter.
(c) Quimociac reagent.Dissolve 70 g sodium molybdate 2H2O in 150 mL H2O. Dissolve 60 g citric acid in mixture of 85 mLHNO3 and 150 mL H2O, and cool. Gradually add molybdate solutionto citric acid-HNO3 mixture with stirring. Dissolve 5 mL syntheticquinoline in mixture of 35 mL HNO3 and 100 mL H2O. Graduallyadd this solution to molybdate-citric acid-HNO3 solution, mix, andlet stand 24 h. Filter, add 280 mL acetone, dilute to 1 L with H2O,and mix.B. Preparation of Solution
Treat 1 g sample as in 957.02B (see 2.3.01), diluting to 200 mL.C. Determination
Pipet, into 500 mL Erlenmeyer, aliquot containing 25 mg P2O5and dilute to ca 100 mL with H2O. Continue by one of the followingmethods:
(a) Add 30 mL citric-molybdic acid reagent and boil gently 3min. (Solution must be precipitate-free at this time.) Remove fromheat and swirl carefully. Immediately add 10 mL quinoline solutionfrom buret with continuous swirling. (Add first 34 mL dropwiseand remainder in steady stream.) Or:
(b) Add 50 mL quimociac reagent, cover with watch glass, placeon hot plate in well-ventilated hood, and boil 1 min.
After treatment by (a) or (b), cool to room temperature, swirlcarefully 34 times during cooling, filter into Gooch with glass fiberfilter paper previously dried at 250 and weighed, and wash withfive 25 mL portions of H2O. Dry crucible and contents 30 min at250, cool in desiccator to room temperature, and weigh as(C9H7N)3H3[PO4 12MoO3]. Subtract weight reagent blank. Multi-ply by 0.03207 to obtain weight P2O5 (or by 0.01400 for P). Reportas % P2O5 (or % P).References: Z. Anal. Chem. 189, 243(1962). JAOAC 45, 40,
999(1962); 46, 579(1963); 47, 420(1964).CAS-7723-14-0 (phosphorus)CAS-1314-56-3 (phosphorus pentoxide)
Copyright 1998 AOAC INTERNATIONAL
