Ammonium sulfate [7783-20-2].
» Ammonium Sulfate contains not less than 99.0 percent and not more than 100.5 percent of (NH4)2SO4.
Packaging and storage Preserve in well-closed containers. No storage requirements specified.
Microbial enumeration tests 61 and Tests for specified microorganisms 62 The total aerobic microbial count does not exceed 1000 cfu per g, and the total combined molds and yeasts count does not exceed 10 cfu per g.
pH 791: between 5.0 and 6.0, in a solution (1 in 20).
Residue on ignition 281 Not more than 0.005%, determined on a 20-g sample.
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 (1015 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 [noteThe 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.
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USP32NF27 Page 1165Pharmacopeial Forum: Volume No. 30(3) Page 966