Ammonium Sulfate
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
(NH4)2SO4 132.14
Ammonium sulfate CAS RN: 7783-20-2.
1 DEFINITION
Ammonium Sulfate contains NLT 99.0% and NMT 100.5% of ammonium sulfate [(NH4)2SO4].
2 IDENTIFICATION
A. IDENTIFICATION TESTS GENERAL (191), Chemical Identification Tests, Ammonium: A solution (1 in 20) meets the requirements.
B. IDENTIFICATION TESTS GENERAL (191), Chemical Identification Tests. Sulfate: A solution (1 in 20) meets the requirements.
3 ASSAY
3.1 PROCEDURE
3.1.1 Sample
2.5 g of Ammonium Sulfate
3.1.2 Titrimetric system
(See Titrimetry (541).)
Mode: Residual titration
Titrant: 1 N sodium hydroxide VS
Back titrant: 1 N sulfuric acid VS
Endpoint detection: Colorimetric
Blank: 50.0 mL of 1 N sodium hydroxide VS, accurately measured
3.1.3 Analysis
Add the Sample to a 500-ml. conical flask and dissolve in 50 mL of water. Add 50.0 mL of Titrant, place a filter funnel loosely in the neck of the flask, and boil until ammonia is expelled (about 10-15 min), as determined with litmus paper. Cool, add 0.15 mL of thymol blue TS, and titrate the excess sodium hydroxide with the Back titrant. Perform a blank determination.
Calculate the percentage of ammonium sulfate [(NH4)2SO4] in the portion of the Sample taken:
Result = [(VB - VS) x NA x F x 100] / W
VB = volume of the Back titrant consumed by the Blank (mL)
VS = volume of the Back titrant consumed by the Sample (mL)
NA = actual normality of the Back titrant (mEq/mL) A
F = equivalency factor, 66.07 mg/mEq
W = weight of the Sample (mg)
3.1.4 Acceptance criteria
99.0%-100.5%
4 IMPURITIES
4.1 RESIDUE ON IGNITION (281)
Sample: 20 g
Analysis: Volatilize the Sample completely by slowly applying gentle heat. Cool the crucible, and moisten the residue with 0.5 mL of sulfuric acid. Ignite the crucible until white fumes of sulfur trioxide cease to evolve. Then, ignite at 800 ± 25° for 15 min.
Acceptance criteria: NMT 0.005%
4.2 LIMIT OF INSOLUBLE MATTER
Sample: 20 g
Analysis: Transfer the Sample to a covered beaker, and dissolve in 200 mL of water. Heat to boiling, and warm on a steam bath for 1 h. Filter the hot solution through a tared sintered-glass crucible of medium pore size (10-15 µm). Wash the beaker and the filter with hot water, dry the crucible at 105", cool in a desiccator, and weigh.
Acceptance criteria: NMT 1 mg of insoluble matter is found (0.005%).
4.3 LIMIT OF PHOSPHATE
Standard phosphate solution, Phosphate reagent A, and Phosphate reagent B: Prepare as directed for Reagents, 6. General Tests for Reagents, 6.11 Phosphate in Reagents.
Sample: 4.0 g
Control: 0.2 mL of Standard phosphate solution
Analysis
[NOTE-The tests for the Sample and the Control are made preferably in matched color-comparison tubes.]
Dissolve the Sample in 25 mL of 0.5 N sulfuric acid, add 1 mL each of Phosphate reagent A and Phosphate reagent B, and allow to stand at room temperature for 2 h. Proceed with the Control using the same quantities of the same reagents as in the test for the Sample.
Acceptance criteria: Any blue color obtained from the Sample should not exceed that produced from the Control (NMT 5 ppm).
4.4 CHLORIDE AND SULFATE (221), Chloride
Standard chloride solution: Transfer 165 mg of sodium chloride to a 100-mL volumetric flask. Dissolve in and dilute with water to volume.
Transfer 10.0 mL to a 1000-mL volumetric flask, and dilute with water to volume to obtain a solution having a concentration of 10 µg/mL of chloride.
Acceptance criteria: A 2-g portion shows no more chloride than corresponds to 1.0 mL of the Standard chloride solution (NMT 5 ppm).
4.5 LIMIT OF NITRATE
Standard nitrate solution and Brucine sulfate solution: Prepare as directed for Reagents, 6. General Tests for Reagents. 6.9 Nitrate in Reagents.
Sample 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 the Standard nitrate solution add 1.0 g of Ammonium Sulfate, then add Brucine sulfate solution to make 50 mL.
Blank: 50 mL of Brucine sulfate solution
Analysis: Heat the Sample solution, Control solution, and Blank in a boiling water bath for 15 min with periodic gentle swirling, then cool rapidly in an ice bath to room temperature. Adjust a suitable spectrophotometer with the Blank to zero absorbance at 410 nm. Determine the absorbance of the Sample solution, note the result, and adjust the instrument with the Sample solution to zero absorbance. Determine the absorbance of the Control solution.
Acceptance criteria: The absorbance reading for the Sample solution does not exceed that for the Control solution (NMT 10 ppm).
Change to read:
4.6 IRON (241), Procedures, Procedure 1 (CN 1-JUN-2023)
Sample solution: Dissolve 2.0 g in 40 mL of water, and add 2 mL of hydrochloric acid.
Acceptance criteria: NMT 5 ppm
5 SPECIFIC TESTS
5.1 MICROBIAL ENUMERATION TESTS (61), and TESTS FOR SPECIFIED MICROORGANISMS (62)
The total aerobic microbial count does not exceed 1000 cfu/g, and the total combined molds and yeasts count does not exceed 10 cfu/g.
5.2 PH (791)
5.0-6.0 in a solution (1 in 20)
6 ADDITIONAL REQUIREMENTS
PACKAGING AND STORAGE: Preserve in well-closed containers. No storage requirements are specified.
