Zinc Oxide Compounded Paste

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

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Zinc oxide Compounded Paste contains NLT 24.0% and NMT 26.0% of zinc oxide (ZnO). Prepare Zinc Oxide Compounded (USP 1-May-2019) Paste as follows.

Mix the ingredients.

2 IDENTIFICATION

A. The residue obtained in the Assay is yellow when hot and white when cool.

3 ASSAY

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Procedure

Sample solution: Transfer 600 mg of Paste to a porcelain crucible. Heat gently until melted, and continue heating, gradually raising the temperature until the mass is thoroughly charred. Ignite the mass until the residue is uniformly yellow, and cool. Dissolve the residue in 10 mL of 2 N sulfuric acid, warming if necessary to dissolve.

Titrimetric system

(See Titrimetry 〈541〉.) (USP 1-May-2019)

Mode: Direct titration

Titrant: 0.05 M edetate disodium VS

Endpoint detection: Visual

Analysis: Transfer the Sample solution to a beaker, and rinse the crucible with small portions of water until the combined solution and rinsings measure 50 mL. Add 15 mL of ammonia–ammonium chloride buffer TS and 1 mL of eriochrome black TS, and titrate with Titrant until the solution is blue in color. Each milliliter of Titrant is equivalent to 4.069 mg of zinc oxide (ZnO).

Acceptance criteria: 24.0%–26.0%

4 PERFORMANCE TESTS

Minimum Fill 〈755〉: Meets the requirements

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Package in well-closed containers, and avoid prolonged exposure to temperatures exceeding 30°.