Ammonium Alum
AlNH4(SO4)2·12H2O 453.33

Sulfuric acid,aluminum ammonium salt (2:1:1),dodecahydrate.
Aluminum ammonium sulfate (1:1:2)dodecahydrate [7784-26-1].

Anhydrous 237.15 [7784-25-0].
»Ammonium Alum contains not less than 99.0percent and not more than 100.5percent of AlNH4(SO4)2,calculated on the dried basis.
Identification—
A: Add 1Nsodium hydroxide dropwise to a solution of it (1in 20):a precipitate is formed,and it dissolves in an excess of the reagent with the evolution of ammonia,recognizable by its odor and by its alkaline effect upon moistened red litmus paper exposed to the vapor.
B: Asolution (1in 20)responds to the tests for Aluminum á191ñand for Sulfate á191ñ.
Loss on drying á731ñ— Transfer 2.0g,in a tared porcelain crucible,to a muffle furnace at 200.Increase the temperature to 300,and dry at 300to constant weight.Cool in a desiccator,and weigh:it loses between 45.0%and 48.0%of its weight.
Limit of alkalies and alkaline earths— Completely precipitate the aluminum from a boiling solution of 1g of it in 100mLof water by the addition of sufficient 6Nammonium hydroxide to render the solution distinctly alkaline to methyl red TS,and filter.Evaporate the filtrate to dryness,and ignite:the weight of the residue does not exceed 5mg (0.5%).
Heavy metals,Method Iá231ñ— Dissolve 1g in water to make 20mL,and add 5mLof 0.1Nhydrochloric acid.Evaporate the solution in a porcelain evaporating dish to dryness.Treat the residue with 20mLof water,and add 50mg of hydroxylamine hydrochloride.Heat the solution on a steam bath for 10minutes,cool,dilute with water to 25mL,and proceed as directed,except to add 50mg of hydroxylamine hydrochloride to the Standard Preparation:the limit is 0.002%.
Iron— Add 5drops of potassium ferrocyanide TSto 20mLof a solution (1in 150):no blue color is produced immediately.
Assay—
Edetate disodium titrant— Dissolve 18.6g of edetate disodium in water to make 1000mL,and standardize the solution as follows.Weigh accurately about 2g of aluminum wire,transfer to a 1000-mLvolumetric flask,and add 50mLof a mixture of hydrochloric acid and water (1:1).Swirl the flask to ensure contact of the aluminum and the acid,and allow the reaction to proceed until all of the aluminum has dissolved.Dilute with water to volume,and mix.Pipet 10mLof this solution into a 250-mLbeaker,add,in the order named and with continuous stirring,25.0mLof Edetate disodium titrantand 20mLof acetic acid–ammonium acetate buffer TS,and boil gently for 5minutes.Cool,and add 50mLof alcohol,and 2mLof dithizone TS.Titrate with 0.05Mzinc sulfate VSto a bright rose-pink color.Perform a blank determination,substituting 10mLof water for the aluminum solution,and make any necessary correction.Calculate the molarity of the solution taken by the formula:
W/26.98V,
in which Wis the weight,in mg,of aluminum in the portion of solution taken;and Vis the volume,in mL,of Edetate disodium titrantconsumed.
Procedure— Transfer about 800mg of Ammonium Alum,accurately weighed,to a 400-mLbeaker,moisten with 1mLof glacial acetic acid,and add 50mLof water,50.0mLof Edetate disodium titrant,and 20mLof acetic acid-ammonium acetate buffer TS.Warm on a steam bath until solution is complete,and boil gently for 5minutes.Cool,add 50mLof alcohol and 2mLof dithizone TS,and titrate with 0.05Mzinc sulfate VSto a bright rose-pink color.Perform a blank determination,and make any necessary correction.Each mLof 0.05MEdetate disodium titrantis equivalent to 11.86mg of AlNH4(SO4)2.
Auxiliary Information— Staff Liaison:Lawrence Evans,III,Ph.D.,Scientist
Expert Committee:(PA6)Pharmaceutical Analysis 6
USP28–NF23Page 76
Phone Number:1-301-816-8389