Sodium Sulfide Topical Gel
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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)
1 DEFINITION
Sodium Sulfide Topical Gel contains NLT 90.0% and NMT 120.0% of the labeled amount of sodium sulfide (Na2S · 9H2O) in a suitable gel base.
2 IDENTIFICATION
A. Conduct this test in a fume hood.
Sample: 100 mg
Analysis: Add 10 mL of 3 N hydrochloric acid to the Sample, and cover the top of the container with filter paper saturated with 0.2 M lead acetate solution.
Acceptance criteria: A brownish or silvery-black color forms on the paper.
3 ASSAY
Procedure
Solution A: 67.0 g/L of edetate disodium and 36.0 g/L of ascorbic acid in 2.0 M sodium hydroxide solution
Sample solution: Transfer a portion of the Topical Gel, equivalent to 30 mg of sodium sulfide, to a 100-mL volumetric flask. Add 50 mL of Solution A, and shake by mechanical means until the Topical Gel is dispersed. Dilute with Solution A to volume.
Titrimetric system
Mode: Direct titration
Titrant: 0.01 M lead perchlorate VS
Endpoint detection: Potentiometric
Analysis: Transfer 30.0 mL of the Sample solution to a suitable beaker, and titrate with Titrant, determining the endpoint potentiometrically.
Perform a blank determination, and make any necessary correction. Each mL of 0.01 M lead perchlorate is equivalent to 2.4018 mg of sodium sulfide (Na2S · 9H2O).
Acceptance criteria: 90.0%–120.0%
4 SPECIFIC TESTS
pH 〈791〉: 11.5–13.5
5 ADDITIONAL REQUIREMENTS
Packaging and Storage: Preserve in tight containers at controlled room temperature or in a cool place.
