Ammonium Sulfate

Limit of insoluble matter— Transfer 20 g to a covered beaker, and dissolve in 200 mL of water. Heat to boiling, and warm on a steam bath for 1 hour. Filter the hot solution through a tared sintered-glass crucible of medium porosity (10–15 µm). Wash the beaker and the filter with hot water, dry the crucible at 105

, cool in a desiccator, and weigh: not more than 1 mg of insoluble matter is found (0.005%).

Limit of phosphate—

Standard Phosphate Solution, Phosphate Reagent A, and Phosphate Reagent B— Prepare as directed for Phosphate in Reagents in General Tests for Reagents under Reagents, Indicators, and Solutions.

Procedure— [note—The tests with the specimen and the control are made preferably in matched color-comparison tubes.] Dissolve 4.0 g of Ammonium Sulfate in 25 mL of 0.5 N sulfuric acid, add 1 mL each of Phosphate Reagents A and B, mix, and allow to stand at room temperature for 2 hours. Any blue color should not exceed that produced in a control made with 0.2 mL of the Standard Phosphate Solution and the same quantities of the same reagents as in the test with the specimen: not more than 5 µg of phosphate per g is found.

Limit of chloride—

Standard chloride solution— Transfer 165 mg of sodium chloride to a 100-mL volumetric flask, and dissolve in and dilute with water to volume. Transfer 10.0 mL of this solution to a 1000-mL volumetric flask, and dilute with water to volume to obtain a solution having a concentration of 10 µg of chloride per mL.

Procedure— Proceed as directed in the test for Chloride

221

. A 2-g portion shows no more chloride than corresponds to 1.0 mL of Standard chloride solution: not more than 5 µg of chloride per g is found.

Limit of nitrate—

Standard Nitrate Solution and Brucine Sulfate Solution— Prepare as directed for Nitrate in Reagents in General Tests for Reagents under Reagents, Indicators, and Solutions.

Test solution— Dissolve 1.0 g in 3 mL of water by heating in a boiling water bath, and add Brucine Sulfate Solution to make 50 mL.

Control solution— To 1.0 mL of Standard Nitrate Solution, add 1.0 g of ammonium sulfate, then add Brucine Sulfate Solution to make 50 mL.

Blank solution— Use 50 mL of Brucine Sulfate Solution.

Procedure— Heat the Test solution, Control solution, and Blank solution in a boiling water bath for 15 minutes with periodic gentle swirling, then cool rapidly in an ice bath to room temperature. Adjust a suitable spectrophotometer to zero absorbance at 410 nm with the Blank solution. Determine the absorbance of the Test solution, note the result, and adjust the instrument to zero absorbance with the Test solution. Determine the absorbance of the Control solution. The absorbance reading for the Test solution does not exceed that for the Control solution: not more than 0.001% is found.

Limit of iron

241

— Dissolve 2.0 g in 40 mL of water, add 2 mL of hydrochloric acid, and mix: not more than 5 µg of iron per g is found.

Assay— Transfer about 2.5 g of Ammonium Sulfate, accurately weighed, into a 500-mL conical flask, and dissolve in 50 mL of water. Add 50.0 mL of 1 N sodium hydroxide VS, place a filter funnel loosely in the neck of the flask, and boil until ammonia is expelled (about 10 to 15 minutes) as determined with litmus paper. Cool, add 0.15 mL of thymol blue TS, and titrate the excess sodium hydroxide with 1 N sulfuric acid VS. Perform a blank determination (see Residual Titrations under Titrimetry

541

). Each mL of 1 N sodium hydroxide is equivalent to 66.07 mg of (NH4)2SO4.

Auxiliary Information— Please check for your question in the FAQs before contacting USP.

Topic/Question	Contact	Expert Committee
Monograph	Robert H. Lafaver, B.A. Scientist 1-301-816-8335	(EM105) Excipient Monographs 1
61	Radhakrishna S Tirumalai, Ph.D. Senior Scientist 1-301-816-8339	(MSA05) Microbiology and Sterility Assurance
62	Radhakrishna S Tirumalai, Ph.D. Senior Scientist 1-301-816-8339	(MSA05) Microbiology and Sterility Assurance

USP32–NF27 Page 1165

Pharmacopeial Forum: Volume No. 30(3) Page 966