Packaging and storage—
Preserve in tight containers, and avoid freezing.
Identification—
A:
Place about 1 g in a flask equipped with a stopper and glass tubing, the tip of which is immersed in
calcium hydroxide TS in a test tube. Add 5 mL of 3 N hydrochloric acid to the flask, and immediately insert the stopper: gas evolves in the flask and a precipitate is formed in the test tube.
B:
The solution remaining in the flask responds to the tests for
Aluminum 
191
.
Microbial limits 61—
Its total aerobic microbial count does not exceed 100 cfu per mL, and it meets the requirements of the test for the absence of
Escherichia coli.
Acid-neutralizing capacity 301—
Not less than 65.0% of the expected mEq value, calculated from the results of the
Assay, is obtained. Each mg of Al(OH)
3 has an expected acid-neutralizing capacity value of 0.0385 mEq.
pH 791:
between 5.5 and 8.0, determined potentiometrically.
Chloride—
Transfer an accurately measured quantity of the Gel, equivalent to 0.6 g of Al(OH)
3, to a porcelain dish. Add 0.1 mL of
potassium chromate TS and 25 mL of water. Stir, and add 0.10 N silver nitrate until a faint, persistent pink color is obtained: not more than 8.0 mL of 0.10 N silver nitrate is required [4.7%, based on the Al(OH)
3 content].
Sulfate 221—
Add 5.0 mL of 3 N hydrochloric acid to an accurately measured quantity of the Gel, equivalent to 0.3 g of Al(OH)
3, and heat to dissolve the specimen under test. Cool, dilute with water to 250 mL, and filter if necessary: a 20-mL portion of the filtrate shows no more sulfate than corresponds to 0.20 mL of 0.020 N sulfuric acid [0.8%, based on the Al(OH)
3 content].
Arsenic, Method I 211—
Prepare a
Standard Preparation as directed in the test for
Arsenic 211, except to prepare it to contain 5 µg of arsenic instead of 3 µg. Prepare the
Test Preparation as follows. Dissolve an accurately measured quantity of the Gel, equivalent to 0.5 g of Al(OH)
3, in 20 mL of 7 N sulfuric acid. The limit is 0.001%, based on the Al(OH)
3 content.
Heavy metals 231—
Dissolve an accurately measured quantity of the Gel, equivalent to 0.24 g of Al(OH)
3, 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 0.0083%, based on the Al(OH)
3 content.
Assay—
Edetate disodium titrant—
Prepare and standardize as directed in the
Assay under
Ammonium Alum.
Procedure—
Transfer an accurately measured quantity of Gel, equivalent to about 1.5 g of Al(OH)
3, to a beaker, add 15 mL of hydrochloric acid, and heat gently until solution is complete. 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 until the color changes from green-violet to rose-pink. Perform a blank determination, substituting 20 mL of water for the sample, and make any necessary correction. Each mL of 0.05 M
Edetate disodium titrant consumed is equivalent to 3.900 mg of Al(OH)
3.
