Zinc Sulfate Tablets

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

Zinc Sulfate Tablets contain NLT 95.0% and NMT 105.0% of the labeled amount of zinc sulfate monohydrate (ZnSO₄ · H₂O). It may contain one or more suitable flavors and sweeteners.

2 IDENTIFICATION

2.1 A. Sulfate

Sample solution: Dissolve a portion of powdered Tablets, nominally equivalent to 5 g of zinc sulfate, in 100 mL of water, filter in a Buchner funnel under vacuum, and use the filtrate.

Hydrochloric acid solution: Dilute 20 g of hydrochloric acid with water to 100 mL.

Barium chloride solution: 61 mg/mL of barium chloride

Analysis: To 5 mL of the Sample solution add 1 mL of Hydrochloric acid solution and 1 mL of Barium chloride solution.

Acceptance criteria: A white precipitate is formed.

2.2 B. Zinc

Sample solution: Proceed as directed in Identification test A.

Sodium hydroxide solution: 420 mg/mL of sodium hydroxide

Ammonium chloride solution: 107 mg/mL of ammonium chloride

Glycerin solution: A mixture of glycerin and water (85:15)

Sodium sulfide solution: Dissolve 12 g of sodium sulfide with heating in a 45-mL mixture of Glycerin solution and water (29:10). Allow to cool, and dilute with the same mixture of solvents to 100 mL. The solution should be colorless.

Analysis: To 5 mL of the Sample solution add 0.2 mL of Sodium hydroxide solution.

Acceptance criteria: A white precipitate is formed. When an additional 2 mL of Sodium hydroxide solution is added, the precipitate dissolves.

When 10 mL of Ammonium chloride solution is added, the solution remains clear. When 0.1 mL of Sodium sulfide solution is added, a white precipitate is formed.

3 ASSAY

Procedure

Sample: Portion of the powder, equivalent to 90 mg of zinc (about 247 mg of zinc sulfate monohydrate), from NLT 20 finely powdered Tablets

Blank: Proceed as directed in the Analysis, but without the Sample.

Titrimetric system

(See Titrimetry 〈541〉.)

Mode: Direct titration

Titrant: 0.1 M edetate disodium VS

Endpoint detection: Visual

Analysis: Transfer the Sample to a suitable flask or beaker. Dissolve in 15 mL of dilute acetic acid, and sonicate for 15 min. Add 200 mL of water and 50 mg of xylenol orange triturate, and mix. [Note - For preparation of xylenol orange triturate, triturate 1 part of xylenol orange with 99 parts of potassium nitrate. Xylenol orange triturate, 1% is also commercially available.¹ Neutralize the solution with 2 g of methenamine until the solution is a violet-pink color. Titrate with Titrant until the solution is yellow. [Note - Add the titrant slowly near the endpoint with expedited stirring.] Perform a Blank determination.

Calculate the percentage of the labeled amount of zinc sulfate monohydrate (ZnSO₄ · H₂O) in the Sample taken:

Result = {[(V_S − V_B) × M × F]/W} × 100

V_S = Titrant volume consumed by the Sample (mL)

V_B = Titrant volume consumed by the Blank (mL)

M = actual molarity of the Titrant (mM/mL)

F = equivalency factor, 179.46 mg/mM

W = nominal amount of zinc sulfate monohydrate in the Sample (mg)

Acceptance criteria: 95.0%–105.0%

4 PERFORMANCE TESTS

 Disintegration 〈701〉

Time: 60 s

Acceptance criteria: Meet the requirements

Uniformity of Dosage Units 〈905〉: Meet the requirements

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers, and store at controlled room temperature.

Labeling: Label the Tablets in terms of zinc sulfate monohydrate (ZnSO₄ · H₂O) and in terms of elemental zinc.

¹ Ricca Chemical Company, part number 9395-100.