Calcium 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)
CaSO4 136.14
CaSO4. 2H2O 172.17
Sulfuric acid, calcium salt (1:1);
Calcium sulfate (1:1) CAS RN: 7778-18-9.
Dihydrate CAS RN®: 10101-41-4.
1 DEFINITION
Calcium Sulfate is anhydrous or contains two molecules of water of hydration. It contains NLT 98.0% and NMT 101.0% of CaSO4, calculated on the dried basis.
2 IDENTIFICATION
2.1 A. IDENTIFICATION TESTS GENERAL, Calcium (191),
Sample solution: Dissolve 200 mg by warming in a mixture of 4 mL of 3 N hydrochloric acid and 16 ml of water.
Acceptance criteria: Meets the requirements
2.2 B. IDENTIFICATION TESTS GENERAL, Sulfate(191).
Sample solution: Dissolve 200 mg by warming in a mixture of 4 mL of 3 N hydrochloric acid and 16 mL of water.
Acceptance criteria: Meets the requirements
3 ASSAY
3.1 PROCEDURE
3.1.1 Sample
Dissolve 300 mg of Calcium Sulfate in 100 mL of water and 4 mL of 3 N hydrochloric acid. Boil, if necessary, to dissolve, and cool before titrating.
3.1.2 Titrimetric system
(See Titrimetry (541).)
Mode: Direct titration
Titrant: 0.05 M edetate disodium VS
Endpoint detection: Visual
3.1.3 Analysis
While stirring, preferably with a magnetic stirrer, add to the Sample solution, in the order named, 0.5 mL of triethanolamine, 300 mg of hydroxy naphthol blue, and, from a 50-ml buret, 30 mL of 0.05 M edetate disodium VS. Add sodium hydroxide solution (45 in 100) until the initial red color changes to clear blue, continue to add dropwise until the color changes to violet, and add an additional 0.5 mL. The pH is 12.3-12.5. Continue the titration dropwise with 0.05 M edetate disodium VS to the appearance of a clear-blue endpoint that persists for
NLT 60 s.
Calculate the percentage of Calcium Sulfate (CaSO4) in the Sample taken:
Result = [(V x M x F)/W] x 100
V = volume of Titrant consumed by the Sample (mL)
M = actual molarity of the Titrant (mM/mL)
F = equivalency factor, 136.14 mg/mM
W = weight of the Sample (mg)
3.1.4 Acceptance criteria
98.0%-101.0% on the dried basis
4 IMPURITIES
Change to read:
4.1 IRON (241), Procedures, Procedure 1 (CN 1-JUN-2023)
Sample solution: Dissolve 100 mg in 8 mL of 3 N hydrochloric acid, and dilute with water to 47 mL.
Acceptance criteria: NMT 100 ppm
5 SPECIFIC TESTS
5.1 LOSS ON DRYING (731)
Samples: Neat
Analysis: Dry a sample at a temperature NLT 250° to constant weight.
Acceptance criteria: NMT 1.5% for the anhydrous form and 19.0%-23.0% for the dihydrate
6 ADDITIONAL REQUIREMENTS
PACKAGING AND STORAGE: Preserve in well-closed containers.
LABELING: Label it to indicate whether it is anhydrous or the dihydrate.
