Strong Iodine Tincture

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

Strong Iodine Tincture contains NLT 6.8 g and NMT 7.5 g of iodine (I) and NLT 4.7 g and NMT 5.5 g of potassium iodide (KI) in each 100 mL.

Prepare Strong Iodine Tincture as follows.

Dissolve Potassium Iodide in Purified Water. Add Iodine and agitate until the solution is effected. Add Alcohol to bring to final volume.

2 IDENTIFICATION

A. Analysis: Add 1 drop to a mixture of 1 mL of starch TS and 9 mL of water.

Acceptance criteria: A deep blue color is produced.

B. Identification Tests—General 〈191〉, Iodide

Analysis: Evaporate a few milliliters on a steam bath to dryness.

Acceptance criteria: The residue meets the requirements of the test for Iodide.

C. Potassium: The Sample obtained in Identification B imparts a violet color to a nonluminous flame. The presence of small quantities of sodium masks the color unless the yellow color produced by sodium is screened out by viewing through a blue fIlter that blocks the emission at 589 nm (sodium). It is transparent to the emission at 404 nm (potassium).[Note—Traditionally, cobalt glass has been used, but other suitable fIlters are commercially available.]

3 ASSAY

3.1 Iodine

Sample: 10 mL

Titrimetric system

Mode: Direct titration

Titrant: 0.1 N sodium thiosulfate VS

Endpoint detection: Visual

Analysis: Transfer the Sample into a glass-stoppered 500-mL flask and add 10 mL of water. Titrate with Titrant, adding 3 mL of starch TS as the endpoint is approached. Each milliliter of Titrant is equivalent to 12.69 mg of iodine (I).

Acceptance criteria: 6.8–7.5 g of iodine (I) in 100 mL

3.2 Potassium Iodide

Sample: 10 mL

Titrimetric system

Mode: Direct titration

Titrant: 0.05 M potassium iodate VS

Endpoint detection: Visual

Analysis: Transfer the Sample into a glass-stoppered 500-mL flask, add 30 mL of water and 50 mL of hydrochloric acid, cool to room temperature, and titrate with Titrant until the dark brown solution that is produced becomes pale brown. Add 1 mL of amaranth TS, and continue the titration slowly until the red color just changes to yellow. The difference between the volume of Titrant used and half the volume of 0.1 N sodium thiosulfate used in the Assay for Iodine, in milliliters, multiplied by 16.60, represents the number of milligrams of potassium iodide (KI) in the portion of Tincture taken.

Acceptance criteria: 4.7–5.5 g of potassium iodide (KI) in 100 mL

4 OTHER COMPONENTS

Alcohol Determination 〈611〉: 82.5%–88.5%

5 ADDITIONAL REQUIREMENTS

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