Chromatographic column— Pack a pledget of fine glass wool in the base of a 10-mm × 200-mm chromatographic tube. Add styrene-divinylbenzene cation-exchange resin (strong acid form), to form a uniform column 12 cm in height, and top the column with a pledget of fine glass wool.

Procedure— Weigh and finely powder not fewer than 20 Lozenges. Dissolve a portion of the powder, equivalent to about 500 µg of cetylpyridinium chloride, in about 50 mL of water, and immediately transfer this solution to the Chromatographic column. Discard the eluate, wash the column, successively, with 200 mL of water, 100 mL of alcohol, 100 mL of water, and 100 mL of 3 N hydrochloric acid, and discard the washings. Elute the column with 80 mL of a solvent consisting of a mixture of 7 volumes of alcohol and 3 volumes of 1.2 N hydrochloric acid. Collect the eluate in a 100-mL volumetric flask, dilute with the eluting solvent to volume, and mix: the UV absorption spectrum of this solution, measured between 225 and 300 nm, exhibits maxima and minima at the same wavelengths as that of a solution of USP Cetylpyridinium Chloride RS, in the same medium at a concentration of 5 µg per mL, concomitantly measured.

(Official January 1, 2007)

0.004 M Sodium lauryl sulfate— [NOTE—Sulfuric acid is included in this solution to inhibit precipitate formation. If a precipitate forms under storage, discard the solution, and prepare and standardize a fresh 0.004 M Sodium lauryl sulfate solution.] Dissolve 1.15 g of sodium lauryl sulfate in 500 mL of water, add 2 mL of sulfuric acid, dilute with water to 1000 mL, and mix. Determine the molarity of the solution as follows. Transfer to a glass-stoppered, 100-mL cylinder 10.0 mL of 0.004 M cetylpyridinium chloride (1.432 mg of USP Cetylpyridinium Chloride RS per mL in water), add 5 mL of 2 N sulfuric acid, 20 mL of chloroform, and 1 mL of methyl yellow TS, and titrate with the sodium lauryl sulfate solution, with frequent vigorous shaking, until the chloroform layer acquires the first permanent orange-pink color. Calculate the molarity, and restandardize before each use.

Procedure— Dissolve an accurately determined number (about 100) of Cetylpyridinium Chloride Lozenges in about 400 mL of water in a 500-mL volumetric flask, dilute with water to volume, and mix. Transfer an accurately measured aliquot of this solution, equivalent to about 10 mg of cetylpyridinium chloride, to a glass-stoppered, 100-mL cylinder, and add 5 mL of 2 N sulfuric acid, 20 mL of chloroform, and 1 mL of methyl yellow TS. Insert the stopper, shake until the chloroform layer develops a bright yellow color, and titrate with 0.004 M Sodium lauryl sulfate, shaking thoroughly after each addition, until the chloroform layer develops the first permanent orange-pink color. Each mL of 0.004 M Sodium lauryl sulfate is equivalent to 1.432 mg of C21H38ClN·H2O.