Nitromersol Topical Solution

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

Nitromersol Topical Solution yields NLT 180.0 mg and NMT 220.0 mg of nitromersol (C₇H₅HgNO₃) in each 100 mL.

Dissolve the Sodium Hydroxide and the Sodium Carbonate, Monohydrate in 50 mL of Purified Water. Add the Nitromersol, and stir until dissolved. Gradually add Purified Water to make 1000 mL.

[Note-Prepare dilutions of Nitromersol Topical Solution as needed, because they tend to precipitate upon standing.]

2 IDENTIFICATION

2.1 A.

Sample: 100 mL

Analysis: Add 3 mL of 3 N hydrochloric acid to the Sample.

Acceptance criteria: A yellowish precipitate is formed. Filter, and retain both the filtrate and the precipitate.

2.2 B.

Sample: The precipitate obtained from Identification test A

Analysis: Add the Sample to 20 mL of water and 2.5 mL of 1 N sodium hydroxide. Add 500 mg of sodium hydrosulfite, and heat to boiling.

Acceptance criteria: A heavy deposit of metallic mercury is formed.

3 ASSAY

3.1 Procedure

Sample: 50.0 mL of Topical Solution

Titrimetric system

• Mode: Direct titration
• Titrant: 0.1 N ammonium thiocyanate VS
• Endpoint detection: Visual

Analysis: Transfer the Sample to a 500-mL Kjeldahl flask, add a few glass beads, and evaporate to 5 mL. Add 15 mL of sulfuric acid, digest cautiously with occasional swirling over a flame until the solution becomes a clear, light yellowish brown. Cool, and add, dropwise, enough 30% Hydrogen peroxide to decolorize the solution. Digest for 2–3 min, adding more hydrogen peroxide, if necessary, to produce a colorless solution. Cool, dilute with water to 100 mL, and add potassium permanganate TS until a permanent pink color persists on heating. Then add hydrogen peroxide TS, dropwise, until the color is completely discharged. Cool, and add 5 mL of nitric acid that has been diluted with 10 mL of water. Add 5 mL of ferric ammonium sulfate TS, and titrate with Titrant. Each mL of Titrant is equivalent to 17.59 mg of nitromersol (C₇H₅HgNO₃).

Acceptance criteria: 180.0–220.0 mg of nitromersol (C₇H₅HgNO₃) in each 100 mL

4 SPECIFIC TESTS

4.1 Specific Gravity 〈841〉

1.005–1.010

4.2 Mercury Ions

Sample: The filtrate obtained from Identification test A

Analysis: To the Sample add an equal volume of hydrogen sulfide TS.

Acceptance criteria: No darkening in color is produced, although a small amount of a flocculent, light yellow precipitate may be formed.

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Package in tight, light-resistant containers.