Thimerosal Tincture

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

1 DEFINITION

Thimerosal Tincture contains, in each 100 mL, NLT 90 mg and NMT 110 mg of thimerosal.

[Note—Thimerosal Tincture is sensitive to some metals.]

2 IDENTIFICATION

A.

Sample: 25 mL of Tincture

Analysis: Heat the Sample on a steam bath until the odors of alcohol and acetone are no longer perceptible. Cool and pass hydrogen sulfide through the solution.

Acceptance criteria: No black discoloration or black precipitate is formed.

B.

Sample: 50 mL of Tincture

Analysis: Evaporate the Sample on a steam bath to a volume of approximately 20 mL, cool, and add 3 or 4 drops of bromine. Add 5 mL of 3 N hydrochloric acid, filter, and pass hydrogen sulfide through the filtrate.

Acceptance criteria: A black precipitate is formed.

3 ASSAY

Procedure

The Standard solutions and Sample solution may be diluted with water, if necessary, to yield solutions of suitable concentration, adaptable to the linear or working range of the instrument.

Solution A: Dissolve 50 g of stannous chloride in 100 mL of hydrochloric acid on a steam bath, cool, dilute with water to 500 mL, and mix. Use within 3 months.

Standard stock solution A: 1.8 μg/mL of USP Thimerosal RS

Standard stock solution B: 2.0 μg/mL of USP Thimerosal RS

Standard stock solution C: 2.2 μg/mL of USP Thimerosal RS

Standard solution A: Pipet 20 mL of Standard stock solution A into a 100-mL volumetric flask. Add 5 mL of sulfuric acid, cool, add 3 mL of nitric acid, and mix. Add potassium permanganate crystals, while mixing, until the purple color persists for NLT 15 min. Add 200 mg of potassium persulfate, mix, and heat on a steam bath for 2 h. Cool, and dilute with water to volume.

Standard solution B: Pipet 20 mL of Standard stock solution B into a 100-mL volumetric flask. Add 5 mL of sulfuric acid, cool, add 3 mL of nitric acid, and mix. Add potassium permanganate crystals, while mixing, until the purple color persists for NLT 15 min. Add 200 mg of potassium persulfate, mix, and heat on a steam bath for 2 h. Cool, and dilute with water to volume.

Standard solution C: Pipet 20 mL of Standard stock solution C into a 100-mL volumetric flask. Add 5 mL of sulfuric acid, cool, add 3 mL of nitric acid, and mix. Add potassium permanganate crystals, while mixing, until the purple color persists for NLT 15 min. Add 200 mg of potassium persulfate, mix, and heat on a steam bath for 2 h. Cool, and dilute with water to volume.

Sample stock solution: Pipet 2 mL of Tincture into a 1000-mL volumetric flask, and dilute with water to volume.

Sample solution: Pipet 20 mL of Sample stock solution into a 100-mL volumetric flask. Add 5 mL of sulfuric acid, cool, add 3 mL of nitric acid, and mix. Add potassium permanganate crystals, while mixing, until the purple color persists for NLT 15 min. Add 200 mg of potassium persulfate, mix, and heat on a steam bath for 2 h. Cool, and dilute with water to volume.

Instrumental conditions

Mode: Flameless atomic absorption spectroscopy

Lamp: Mercury hollow-cathode

Blank solution: Pipet 20 mL of water into a 100-mL volumetric flask. Add 5 mL of sulfuric acid, cool, add 3 mL of nitric acid, and mix. Add potassium permanganate crystals, while mixing, until the purple color persists for NLT 15 min. Add 200 mg of potassium persulfate, mix, and heat on a steam bath for 2 h. Cool, and dilute with water to volume.

Analysis

Samples: Standard solutions A, B, and C, Sample solution, and Blank solution

Proceed with each of the Samples as follows. Separately pipet 3 mL into the scrubbing chamber of a suitable system designed for determination of mercury. Dilute with water to 150 mL, and add hydroxylamine hydrochloride solution (1 in 10) to reduce the excess permanganate. Add 5 mL of Solution A, and immediately attach the scrubbing chamber to the system. Concomitantly determine the absorbance of the vapor from each solution at an integration time of 15 s. Use the absorbance of the Blank solution to correct the absorbances of Standard solutions A, B, and C, and the Sample solution. Plot the corrected absorbances of the standards versus the respective concentrations of the Standard stock solutions, in μg/mL, and from the curve so obtained, determine the concentration, C, in μg/mL, of the Sample solution.

Calculate the quantity, in mg, of thimerosal in each 100 mL of Tincture taken:

Result = C × D × V × F

C = measured concentration of the Sample solution (μg/mL)

D = dilution of the Sample stock solution, 500

V = volume of Tincture, 100 mL

F = unit conversion, 1 mg/1000 μg

Acceptance criteria: 90–110 mg

4 SPECIFIC TESTS

Alcohol Determination, Method II〈611〉: 45.0%–55.0% of C H OH

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight, light-resistant containers, and avoid exposure to excessive heat.

USP Reference Standards 〈11〉

USP Thimerosal RS