(NH4)6Mo7O24·4H2O 1235.86

Molybdate (Mo7O246-),hexaammonium,tetrahydrate.
Hexaammonium molybdate tetrahydrate [12054-85-2].

Packaging and storage— Preserve in tight containers.

Identification— Dissolve 0.6g of it in 1.4mLof water and 1.45mLof ammonium hydroxide.Cool this mixture,and add slowly,with mixing,7.2mLof a well-cooled mixture of 3.2mLof nitric acid and 4mLof water.Allow to stand for 24to 48hours,and filter through a sintered-glass filter.To 5mLof the filtrate add 2mLof dibasic sodium phosphate TS:a yellow precipitate is formed,and it is soluble in an excess of 6Nammonium hydroxide.

Insoluble substances— Dissolve 20g in 200mLof water in a beaker,heat to boiling,cover,and heat on a steam bath for 1hour.Filter the hot solution through a tared filtering crucible,wash the insoluble residue with hot water,and dry at 105for 2hours:the weight of the residue so obtained does not exceed 1mg (0.005%).

Chloride á221ñ— A0.5-g portion shows no more chloride than 0.30mLof 0.001Nhydrochloric acid (0.002%).

Limit of nitrate— Dissolve 1g in 10mLof water containing 5mg of sodium chloride,and add 0.10mLof a 1in 1000solution of indigo carmine in 3.6Nsulfuric acid:the blue color is not completely discharged in 5minutes.

Sulfate á221ñ— A0.25-g portion shows no more sulfate than corresponds to 1.0mLof 0.001Nsulfuric acid (0.02%).

Arsenate,phosphate,and silicate— Dissolve 2.5g in 70mLof water in a container other than one of glass.Adjust with 1.2Nhydrochloric acid to a pHof between 3and 4,transfer to a glass container,add 2mLof bromine TS,and adjust with 1.2Nhydrochloric acid to a pHof 1.8±0.1.Heat almost to boiling,and cool to room temperature.Dilute with water to 90mL,add 10mLof hydrochloric acid,and transfer to a separator.Add 1mLof butyl alcohol and 30mLof 4-methyl-2-pentanone,shake vigorously,and allow the phases to separate.Discard the aqueous phase,and wash the ketone phase with three successive 10-mLportions of 1.2Nhydrochloric acid,discarding the washings.To the washed ketone phase add 10mLof 1.2Nhydrochloric acid to which has just been added 0.2mLof a freshly prepared 1in 50solution of stannous chloride in hydrochloric acid.Similarly treat a control solution prepared by dissolving 0.5g of specimen in 70mLof water and adding 2mLof sodium silicate solution (1in 20,000):any blue color in the test solution does not exceed that in the control solution.

Phosphate— Dissolve 20g in 100mLof 3Nammonium hydroxide,add 3.5mLof ferric nitrate solution (1in 10),and allow to stand for about 15minutes.Warm gently to coagulate the precipitate,and filter.Wash the filter several times with 1.5Nammonium hydroxide.Then wash the filter with 60mLof warm 4Nnitric acid to dissolve the residue on the filter,collecting the filtrate in a glass-stoppered,250-mLconical flask.Add 13mLof ammonium hydroxide,warm to 40,add 50mLof ammonium molybdate TS,shake for 5minutes,and allow to stand at 40for 2hours.Similarly treat 100mLof a Standard solution prepared by dissolving 143.3mg of dried monobasic potassium phosphate in water to make 1000mL,and then diluting 1.0mLof this solution with 3Nammonium hydroxide to 100mL:any yellow precipitate formed from the test solution does not exceed that obtained from the Standard solution (5ppm).

Magnesium and alkali salts— Dissolve 5.0g in 50mLof water,and filter.To the filtrate add 0.5g of sodium carbonate and 25mLof 2.5Nsodium hydroxide.Boil the solution gently for 5minutes,cool,and filter through an ignited and tared filter.Wash the filter with 1Nammonium hydroxide.Ignite the filter at 800±25for 30minutes:the weight of the residue so obtained does not exceed 1mg (0.02%).

Heavy metals— Dissolve 2.0g in about 20mLof water,add 10mLof 2.5Nsodium hydroxide and 2mLof ammonium hydroxide,and dilute with water to 40mL.To 10mLof this stock solution add 1.0mLof Standard Lead Solution,prepared as directed under Heavy Metals á231ñ,and dilute with water to 40mL(Control solution).Dilute the remaining 30-mLportion of the stock solution with water to 40mL(Test solution).To both solutions add 1.2mLof thioacetamide-glycerin base TSand 2mLof pH3.5Acetate Buffer,and allow to stand for 5minutes:any color in the Test solutiondoes not exceed that in the Control solution.The limit is 10µg per g.

Assay— Dissolve about 1g of Ammonium Molybdate,accurately weighed,in a mixture of 10mLof water and 1mLof ammonium hydroxide in a 250-mLvolumetric flask,dilute with water to volume,and mix.Filter the solution,and transfer 50.0mLof the filtrate to a 600-mLbeaker.Add 250mLof water,20g of ammonium chloride,15mLof hydrochloric acid,and 0.15mLof methyl orange TS,heat nearly to boiling,and add 18mLof lead acetate TS.To the hot solution add,slowly and with constant stirring,a saturated solution of ammonium acetate until the color turns yellow,and then add 15mLof lead acetate TS.Cover the beaker,and heat just below the boiling temperature until the precipitate has settled.Filter through a tared,porous porcelain crucible,wash with seven or eight successive portions of a mixture of water,saturated ammonium acetate solution,and nitric acid (890:100:10),and finally wash with three successive portions of hot water.Ignite to constant weight at 560to 625.Each mg of the lead molybdate so obtained is equivalent to 0.4809mg of (NH4)6Mo7O24·4H2O.

Expert Committee:(PA4)Pharmaceutical Analysis 4

USP28–NF23Page 139

Phone Number:1-301-816-8251