Potassium Iodide

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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KI 166.00

Potassium iodide CAS RN^®: 7681-11-0; UNII: 1C4QK22F9J.

1 DEFINITION

Potassium lodide contains NLT 99.0% and NMT 101.5% of KI, calculated on the dried basis.

2 IDENTIFICATION

A. IDENTIFICATION TESTS-GENERAL, Potassium (191): Meets the requirements

B. IDENTIFICATION TESTS-GENERAL, lodide(191): Meets the requirements

3 ASSAY

PROCEDURE

Sample solution: Dissolve 500 mg of Potassium lodide in 10 mL of water.

Analysis: Add 35 mL of hydrochloric acid to the Sample solution, and titrate with 0.05 M potassium iodate VS until the dark brown solution that is produced becomes pale brown. Add 2-3 drops of amaranth TS, and continue the titration slowly until the red color just changes to yellow. Each mL of 0.05 M potassium iodate is equivalent to 16.60 mg of KI.

Acceptance criteria: 99.0%-101.5% on the dried basis

4 IMPURITIES

4.1 IODATE

lodate solution: Dilute 1 mL of potassium iodate solution (1 in 2500) with water to 100 mL.

Standard solution: Dissolve 100 mg of Potassium lodide in ammonia- and carbon dioxide-free water, and add 1 mL of lodate solution to obtain 10 mL of solution. Transfer to a color-comparison tube, add 1 mL of starch TS and 0.25 mL of 1.0 N sulfuric acid, and mix.

Sample solution: Dissolve 1.1 g in sufficient ammonia- and carbon dioxide-free water to obtain 10 mL of solution. Transfer to a color-comparison tube, add 1 mL of starch TS and 0.25 mL of 1.0 N sulfuric acid, and mix.

Acceptance criteria: Any color produced in the Sample solution does not exceed that produced in the Standard solution (NMT 4 µg/g).

4.2 LIMIT OF NITRATE, NITRITE, AND AMΜΟΝΙΑ

Sample solution: Dissolve 1 g in 5 mL of water.

Analysis: To the Sample solution contained in a test tube of 40-mL capacity add 5 mL of 1 N sodium hydroxide and 200 mg of aluminum wire. Insert a pledget of purified cotton in the upper portion of the test tube, and place a piece of moistened red litmus paper over the mouth of the tube. Heat the test tube and its contents in a steam bath for 15 min.

Acceptance criteria: No blue coloration of the paper is discernible.

4.3 THIOSULFATE AND BARIUM

Sample solution: Dissolve 0.5 g in 10 mL of ammonia- and carbon dioxide-free water.

Analysis: Add 2 drops of 2 N sulfuric acid.

Acceptance criteria: No turbidity develops within 1 min.

5 SPECIFIC TESTS

5.1 ALKALINITY

Sample solution: Dissolve 1.0 g of Potassium lodide in 10 mL of water.

Analysis: Add 0.1 mL of 0.1 N sulfuric acid and 1 drop of phenolphthalein TS to the Sample solution.

Acceptance criteria: No color is produced.

5.2 LOSS ON DRYING (731)

Dry a sample at 105° for 4 h: it loses NMT 1.0% of its weight.

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in well-closed containers.