Dried Aluminum Hydroxide Gel
Al(OH)3 78.00

Aluminum hydroxide [21645-51-2].
» Dried Aluminum Hydroxide Gel is an amorphous form of aluminum hydroxide in which there is a partial substitution of carbonate for hydroxide. It contains the equivalent of not less than 76.5 percent of Al(OH)3, and it may contain varying quantities of basic aluminum carbonate and bicarbonate.
Packaging and storage— Preserve in tight containers.
Labeling— Where the quantity of dried aluminum hydroxide gel equivalent is stated in the labeling of any preparation, this shall be understood to be on the basis that each mg of dried gel is equivalent to 0.765 mg of Al(OH)3.
USP Reference standards 11
USP Dried Aluminum Hydroxide Gel RS
B: Dissolve 500 mg in 10 mL of 3 N hydrochloric acid, with gentle warming: the solution responds to the tests for Aluminum 191.
Acid-neutralizing capacity 301: not less than 25.0 mEq per g, 400 mg being tested as directed for Powders under Test Preparation.
pH 791: not higher than 10.0, in an aqueous dispersion (1 in 25).
Chloride 221 Dissolve 1.0 g in 30 mL of 2 N nitric acid, heat to boiling, add water to make 100 mL, and filter: a 5.0-mL portion of the filtrate, diluted with an equal volume of water, shows no more chloride than corresponds to 0.60 mL of 0.020 N hydrochloric acid (0.85%).
Sulfate 221 Dissolve 330 mg in 15 mL of 3 N hydrochloric acid, heat to boiling, add water to make 250 mL, and filter: a 25-mL portion of the filtrate shows no more sulfate than corresponds to 0.20 mL of 0.020 N sulfuric acid (0.6%).
Arsenic, Method I 211 Dissolve 1.5 g in 80 mL of 7 N sulfuric acid, and dilute with water to 220 mL: 55 mL of the resulting solution meets the requirements of the test, the addition of 20 mL of 7 N sulfuric acid specified under Procedure being omitted. The limit is 8 ppm.
Heavy metals 231 Dissolve 330 mg in 10 mL of 3 N hydrochloric acid with the aid of heat, filter if necessary, and dilute with water to 25 mL: the limit is 0.006%.
Edetate disodium titrant— Prepare and standardize as directed in the Assay under Ammonium Alum.
Procedure— Weigh accurately about 2 g of Gel, and dissolve in 15 mL of hydrochloric acid, with the aid of heat. Cool, transfer to a 500-mL volumetric flask, dilute with water to volume, and mix. Pipet 20 mL of this solution into a 250-mL beaker, and add, in the order named and with continuous stirring, 25.0 mL of Edetate disodium titrant and 20 mL of acetic acid–ammonium acetate buffer TS, then heat the solution near the boiling point for 5 minutes. Cool, and add 50 mL of alcohol and 2 mL of dithizone TS. Titrate the solution with 0.05 M zinc sulfate VS to a bright rose-pink color. Perform a blank determination, substituting 20 mL of water for the sample solution, and make any necessary correction. Each mL of 0.05 M Edetate disodium titrant is equivalent to 3.900 mg of Al(OH)3.
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