Monographs: Pharmaceutical substances: Potassium iodide (Kalii iodidum)

Molecular formula. KI

Relative molecular mass. 166.0

Chemical name. Potassium iodide; CAS Reg. No. 7681-11-0.

Description. Colourless crystals or a white, granular powder; odourless.

Solubility. Soluble in 0.7 part of water, in 17 parts of ethanol (~750 g/l) TS, in 2 parts of glycerol R, and in 75 parts of acetone R.

Category. Antifungal, expectorant.

Storage. Potassium iodide should be kept in a well-closed container, protected from light.

Requirements

Definition. Potassium iodide contains not less than 99.0% and not more than 101.0% of KI, calculated with reference to the dried substance.

Identity tests

A. To a 0.05 g/mL solution add 2 mL of sodium hydroxide (~80 g/l) TS; it yields the reaction described under 2.1 General identification tests as characteristic of potassium.

B. A 0.05 g/mL solution yields reaction B, described under 2.1 General identification tests as characteristic of iodides.

Heavy metals. Use 1.0 g for the preparation of the test solution as described under 2.2.3 Limit test for heavy metals, Procedure 1; determine the heavy metals content according to Method A; not more than 10 μg/g.

Barium. Dissolve 0.5 g in 10 mL of carbon-dioxide-free and ammonia-free water R and add 1 mL of sulfuric acid (~100 g/l) TS; no turbidity is produced within 1 minute.

Iodates. Dissolve 0.5 gin 10 mL of carbon-dioxide-free water R, and add 2 drops of sulfuric acid (~100 g/l) TS, followed by 1 drop of starch TS; there is no immediate production of a blue colour.

Nitrates, nitrites and ammonia. To a solution of 1.0 g in 5 mL of water contained in a test-tube of about 40 mL capacity, add 5 mL of sodium hydroxide (~80 g/l) TS and about 0.2 g of aluminium R wire. Insert a small plug of purified cotton wool in the upper part of the test-tube, and place a piece of moistened red litmus paper R over the mouth of the tube. Heat the test-tube with its contents in a water-bath for 15 minutes; no blue coloration of the paper is discernible.

Sulfates. Dissolve 2.5 g in 20 mL of water and proceed as described under 2.2.2 Limit test for sulfates; the sulfate content is not more than 0.2 mg/g.

Thiosulfates. Dissolve 1.0 g in 10 mL of carbon-dioxide-free water R and add 0.1 mL of starch TS; not more than 0.05 mL of iodine (0.01 mol/l) VS is required to produce a blue colour.

Clarity and colour of solution. A solution of 1.0 g in 10 mL of water is clear and colourless.

Loss on drying. Dry to constant weight at 105°C; it loses not more than 10 mg/g.

Alkalinity. Dissolve 1.0 g in 10 mL of carbon-dioxide-free water R, add 0.1 mL of sulfuric acid (0.05 mol/l) VS, and 1 drop of phenolphthalein/ethanol TS; no colour is produced.

Assay. Dissolve about 0.3 g, accurately weighed, in 10 mL of water. Add 10 mL of a mixture of 50 mL of starch TS and 1 drop of iodine/ethanol TS. Titrate with silver nitrate (0.1 mol/l) VS until a pale yellow colour is produced. Each mL of silver nitrate (0.1 mol/l) VS is equivalent to 16.60 mg of KI.

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