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 12cm in height,and top the column with a pledget of fine glass wool.

Procedure— Weigh and finely powder not less than 20Lozenges.Dissolve a portion of the powder,equivalent to about 500µg of cetylpyridinium chloride,in about 50mLof water,and immediately transfer this solution to the Chromatographic column.Discard the eluate,wash the column,successively,with 200mLof water,100mLof alcohol,100mLof water,and 100mLof 3Nhydrochloric acid,and discard the washings.Elute the column with 80mLof a solvent consisting of a mixture of 7volumes of alcohol and 3volumes of 1.2Nhydrochloric acid.Collect the eluate in a 100-mLvolumetric flask,dilute with the eluting solvent to volume,and mix:the UVabsorption spectrum of this solution,measured between 225and 300nm,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 5µg per mL,concomitantly measured.

0.004M 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 0.004M Sodium lauryl sulfate solution.]Dissolve 1.15g of sodium lauryl sulfate in 500mLof water,add 2mLof sulfuric acid,dilute with water to 1000mL,and mix.Determine the molarity of the solution as follows.Transfer to a glass-stoppered,100-mLcylinder 10.0mLof 0.004Mcetylpyridinium chloride (1.432mg of USP Cetylpyridinium Chloride RSper mLin water),add 5mLof 2Nsulfuric acid,20mLof chloroform,and 1mLof 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 400mLof water in a 500-mLvolumetric flask,dilute with water to volume,and mix.Transfer an accurately measured aliquot of this solution,equivalent to about 10mg of cetylpyridinium chloride,to a glass-stoppered,100-mLcylinder,and add 5mLof 2Nsulfuric acid,20mLof chloroform,and 1mLof methyl yellow TS.Insert the stopper,shake until the chloroform layer develops a bright yellow color,and titrate with 0.004M Sodium lauryl sulfate,shaking thoroughly after each addition,until the chloroform layer develops the first permanent orange-pink color.Each mLof 0.004M Sodium lauryl sulfateis equivalent to 1.432mg of C21H38ClN·H2O.