Sodium Sulfide

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

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

DOWNLOAD PDF HERE

Na₂S · 9H₂O 240.18

Sodium sulfide nonahydrate;

Disodium sulfide nonahydrate CAS RN®: 1313-84-4; UNII: C02T02993U.

1 DEFINITION

Sodium Sulfide contains NLT 98.0% and NMT 103.0% of sodium sulfide (Na₂S · 9H₂O).

2 IDENTIFICATION

A. Conduct this test in a fume hood.

Sample: 100 mg

Analysis: To the Sample add 10 mL of 3 N hydrochloric acid, and cover the top of the container with filter paper saturated with a 0.2 M lead acetate solution.

Acceptance criteria: A brownish or silvery-black color forms on the paper.

3 ASSAY

Procedure

Sample solution: Dissolve 275 mg of Sodium Sulfide in 30 mL of filtered and degassed water. Add 50.0 mL of 0.1 N iodine while mixing, add 2 mL of hydrochloric acid, and allow to stand for 15 min in a dark place.

Titrimetric system

Mode: Direct titration

Titrant: 0.1 N sodium thiosulfate VS

Endpoint detection: Visual

Analysis: Titrate the Sample solution with Titrant to a pale yellow color. Add 5 mL of starch TS, and titrate with Titrant to a clear endpoint.

Perform a blank determination, and make any necessary correction. Each mL of 0.1 N sodium thiosulfate is equivalent to 12.01 mg of sodium sulfide (Na₂S · 9H₂O).

Acceptance criteria: 98.0%–103.0%

4 IMPURITIES

Limit of Iron

Sample solution: 50 mg/mL in water

Acceptance criteria: The solution is clear and colorless.

Limit of Sulfite and Thiosulfate

Sample solution: Dissolve 3.0 g of Sodium Sulfide in 200.0 mL of filtered and degassed water. Add 100.0 mL of 0.2 N zinc sulfate, and allow to stand for 30 min. Filter, and add 1 mL of starch TS.

Titrimetric system

Mode: Direct titration

Titrant: 0.01 N iodine VS

Endpoint detection: Visual

Analysis: Titrate 100.0 mL of the filtrate from the Sample solution with Titrant.

Acceptance criteria: NMT 3.0 mL of Titrant is required.

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers, and store in a cool place.