Basic Fuchsin

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

Basic Fuchsin is a mixture of rosaniline and pararosaniline hydrochlorides. It contains the equivalent of NLT 88.0% of rosaniline hydrochloride (C₂₀H₁₉N₃·HCl), calculated on the dried basis.

2 IDENTIFICATION

A.

Sample solution: 1 mg/mL

Analysis: To 5 mL of the Sample solution, add a few drops of hydrochloric acid.

Acceptance criteria: A yellow color is produced (distinction from acid fuchsin).

B.

Sample solution: 2 mg/mL

Analysis: To 5 mL of the Sample solution, add a few drops of tannic acid TS.

Acceptance criteria: A red precipitate is formed.

C.

Sample solution: 2 mg/mL

Analysis: To 10 mL of the Sample solution, add 10 mL of ammonia TS and 500 mg of zinc dust, and agitate the mixture. The solution becomes decolorized. Place a few drops of the decolorized solution on filter paper, and nearby on the same paper, place a few drops of 3 N hydrochloric acid.

Acceptance criteria: A red color develops at the zone of contact.

3 ASSAY

Procedure

Solution A: 300 mg/mL of sodium tartrate in water

Solution B: 200 mg/mL of titanium trichloride in water

Solution C: Prepare 500 mL of a mixture of water, Solution B, and hydrochloric acid (400:40:40) to which about 10 mg of safranin O has been added.

Sample: 100 mg

Titrimetric system

Mode: Direct titration

Titrant: 0.05 N titanium trichloride VS

Endpoint detection: Visual

Analysis: Dissolve the Sample in 175 mL of water in a 500-mL closed system titration vessel fitted with a gas inlet tube, a gas outlet tube, an upright reflux condenser, and a buret. Add about 25 mL of Solution A and a polytef-coated magnetic stirring bar, and heat to boiling. Flush this titration vessel for 15 min with nitrogen that has been passed through two successive gas washing bottles, each containing 500 mL of Solution C. Continue the heating and nitrogen flow, and while stirring, titrate with titrant to a yellow endpoint.

Calculate the percentage of rosaniline hydrochloride (C₂₀H₁₉N₃·HCl) in the portion of Basic Fuchsin taken:

Result = [(V × N × F)/W] × 100

V = Titrant volume consumed by the Sample (mL)

N = Titrant normality (mEq/mL)

F = equivalency factor, 67.58 mg/mEq

W = Sample weight (mg)

Acceptance criteria: NLT 88.0% on the dried basis

4 IMPURITIES

Alcohol-Insoluble Substances

Sample: 1 g

Analysis: Boil the Sample with 50 mL of alcohol under a reflux condenser for 15 min, and filter through a tared filtering crucible. Wash the residue on the filter with hot alcohol until the washings cease to be colored violet, and dry the crucible at 105° for 1 h.

Acceptance criteria: The amount of insoluble residue is NMT 1.0%.

Residue on Ignition 〈281〉

Sample: 1 g

Analysis: Ignite the Sample with 0.5 mL of sulfuric acid.

Acceptance criteria: NMT 0.3%.

Loss on Drying 〈731〉

Analysis: Dry at 105° to constant weight.

Acceptance criteria: NMT 5.0%

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.