Aluminum Sulfate
Al2(SO4)3·xH2O(anhydrous) 342.15

Sulfuric acid,aluminum salt (3:2),hydrate.
Aluminum sulfate (2:3)hydrate [17927-65-0].

Anhydrous 342.16 [10043-01-3].
»Aluminum Sulfate contains not less than 54.0percent and not more than 59.0percent of Al2(SO4)3.It contains a varying amount of water of crystallization.
Packaging and storage— Preserve in well-closed containers.
Identification— Asolution (1in 10)responds to the tests for Aluminumand for Sulfate á191ñ.
pHá791ñ: not less than 2.9,in a solution (1in 20).
Water,Method Iá921ñ: not less than 41.0%and not more than 46.0%.
Heavy metals á231ñ— Dissolve 1.0g in 2mLof 1Nacetic acid,and dilute with water to 25mL.The limit is 20µg per g.
Limit of alkalies and alkaline earths— To a boiling solution of 1.0g in 150mLof water add a few drops of methyl red TSand then add 6Nammonium hydroxide just until the color of the solution changes to a distinct yellow.Add hot water to restore the volume to 150mL,and filter while hot.Evaporate 75mLof the filtrate to dryness,and ignite to constant weight:not more than 2mg of residue remains (0.4%).
Limit of ammonium salts— Heat 1g with 10mLof 1Nsodium hydroxide on a steam bath for 1minute:the odor of ammonia is not perceptible.
Iron— To 20mLof a solution (1in 150)add 0.3mLof potassium ferrocyanide TS:no blue color is produced immediately.
Organic volatile impurities,Method IVá467ñ: meets the requirements.
Assay—
Edetate disodium titrant— Prepare and standardize as directed in the Assayunder Ammonium Alum.
Procedure— Transfer about 7.5g of Aluminum Sulfate,accurately weighed,to a 250-mLvolumetric flask,and dissolve in water.Dilute with water to volume,mix,and pipet 10mLof the solution into a 250-mLbeaker.Proceed as directed in the Assay for aluminum oxideunder Aluminum Acetate Topical Solution,beginning with “add,in the order named.”Each mLof 0.05MEdetate disodium titrantis equivalent to 8.554mg of Al2(SO4)3.
Auxiliary Information— Staff Liaison:Behnam Davani,Ph.D.,MBA,Senior Scientist
Expert Committee:(PA7)Pharmaceutical Analysis 7
USP28–NF23Page 97
Phone Number:1-301-816-8394