A: The retention times of the two major peaks in the chromatogram of the Assay preparation Ccorrespond to those in the chromatogram of the Resolution solution,as obtained in the Assay.

B: It meets the requirements of the flame test for Sodium á191ñ.

C: Mix 10mg with 10mLof ethanol,and heat to boiling on a water bath,shaking frequently.Filter immediately,and evaporate to dryness.Dissolve the residue in 7mLof water,add 3mLof diluted hydrochloric acid,and evaporate the solution to half its volume.Allow to cool,and filter.To the filtrate,add 1mLof barium chloride solution (6in 100):a white crystalline precipitate is formed.

Dichloroacetic acid solution— Dilute 67mLof dichloroacetic acid to 300mLwith water,and neutralize to blue litmus paper using ammonia TS.Cool,add 33mLof dichloroacetic acid,and dilute with water to 600mL.

Sodium chloride— Dissolve about 5g of Sodium Cetostearyl Sulfate,accurately weighed,in 50mLof water,and add diluted nitric acid dropwise until the solution is neutral to blue litmus paper.Add 1mLof potassium chromate TS,and titrate with 0.1Nsilver nitrate VS,determining the endpoint potentiometrically.Calculate the percentage of sodium chloride (NaCl)in the Sodium Cetostearyl Sulfate taken by the formula: in which 5.844is the equivalence factor for sodium chloride;Vis the volume,in mL,of silver nitrate solution;Nis the normality of silver nitrate;and Wis the weight,in g,of the Sodium Cetostearyl Sulfate taken.

Sodium sulfate— Dissolve 0.5g of Sodium Cetostearyl Sulfate,accurately weighed,in 20mLof water,warming gently if necessary,and add 1mLof a solution containing 0.5g per Lof dithizone in acetone.If the solution is red,add 1Nnitric acid dropwise until a bluish-green color is obtained.Add 2.0mLof Dichloroacetic acid solutionand 80mLof acetone,and titrate with 0.01Mlead nitrate VSuntil a persistent orange-red color is obtained.Calculate the percentage of sodium sulfate (Na2SO4)in the Sodium Cetostearyl Sulfate taken by the formula: in which 14.20is the equivalence factor for sodium sulfate;Vis the volume,in mL,of lead nitrate solution;Mis the molarity of lead nitrate;and Wis the weight,in g,of the Sodium Cetostearyl Sulfate taken.The sum of the percentages of sodium chloride and sodium sulfate is not more than 8.0%.

100(Aa+Ba)×Wah/(Sa(corr)×Wa),

Resolution solution— Dissolve accurately weighed quantities of USP Cetyl Alcohol RSand USP Stearyl Alcohol RSin alcohol to obtain a solution having a known concentration of about 5mg of each per mL.

Internal standard solution— Prepare a solution of 1-heptadecanol in alcohol having a concentration of about 4mg per mL.

Assay preparation A— Dissolve 300mg of Sodium Cetostearyl Sulfate in 50mLof alcohol,and add 2mLof the Internal standard solutionand 48mLof water.Extract the solution with four 25-mLportions of pentane,adding 10-15mLof saturated sodium chloride solution,if necessary,to facilitate the separation of the layers.Combine the organic layers,and reserve the hydro-alcoholic layers for the preparation of Assay preparations Cand D.Wash the organic layer with two 30-mLportions of water,dry over anhydrous sodium sulfate,and filter.

Assay preparation B— Dissolve 300mg of Sodium Cetostearyl Sulfate in 50mLof alcohol,and add 50mLof water.Extract the solution with four 25-mLportions of pentane,adding 10to 15mLof saturated sodium chloride solution,if necessary,to facilitate the separation of the layers.Combine the organic layers,wash with two 30-mLportions of water,dry over anhydrous sodium sulfate,and filter.

Assay preparation C— Transfer 25mLof the hydro-alcoholic solution obtained in the preparation of the Assay preparation Ato a 200-mLflask that can be fitted with a reflux condenser.Add 20mLof hydrochloric acid and 10mLof the Internal standard solution,and boil under reflux for 2hours.Allow to cool.Extract with four 20-mLportions of pentane.Wash the combined organic layer with two 20-mLportions of water,dry over anhydrous sodium sulfate,and filter.

Assay preparation D— Transfer 25mLof the hydro-alcoholic solution obtained in the preparation of the Assay preparation Ato a 200-mLflask that can be fitted with a reflux condenser.Add 20mLof hydrochloric acid and 10mLof alcohol,and boil under reflux for 2hours.Allow to cool.Extract with four 20-mLportions of pentane.Wash the combined organic layer with two 20-mLportions of water,dry over anhydrous sodium sulfate,and filter.

Chromatographic system (see Chromatography á621ñ)— The gas chromatograph is equipped with a flame-ionization detector,a 0.25-mm ×25-m fused silica capillary column that contains phase G2,and a split injection system with a split ratio of about 1:100.The carrier gas is nitrogen,flowing at a rate of 1mLper minute.The column temperature is maintained at 150at the time of injection,then programmed to increase at the rate of 5per minute to 250,and maintained at 250for the duration of the analysis.The injection port and the detector temperatures are maintained at about 250.Chromatograph the Resolution solution,and record the peak responses as directed for Procedure:the resolution,R,between cetyl alcohol and stearyl alcohol is not less than 4.0;and the relative standard deviation for replicate injections is not more than 1.5%.

Correction for interference— Inject about 1µLof each of the Assay preparations Aand Binto the chromatograph,record the chromatograms,and measure the areas for the major peaks.If the chromatogram of the Assay preparation Bshows a peak at the same retention time as the internal standard peak in the chromatogram of the Assay preparation A,calculate the ratio,r: in which Scbis the area of the cetyl alcohol peak;and Siis the area of the peak with the same retention time as the internal standard,respectively,in the chromatogram of the Assay preparation B.If ris less than 300,calculate the corrected area,Sa(corr),of the peak corresponding to the internal standard in the chromatogram of the Assay preparation A: in which Shaand Scaare the areas of the internal standard peak and the cetyl alcohol peak,respectively,in the chromatogram of the Assay preparation A.

Procedure— Inject equal volumes of the Resolution solutionand Assay preparations Cand Dinto the chromatograph,record the chromatograms,and measure the areas for the major peaks.The substances are eluted in the following order:cetyl alcohol,1-heptadecanol (internal standard),and stearyl alcohol.Identify the cetyl alcohol and stearyl alcohol peaks in the chromatograms of the Assay preparationsby comparison with the Resolution solution.Calculate the percentage of sodium cetyl sulfate in the portion of Sodium Cetostearyl Sulfate taken by the formula: in which Acis the area of the cetyl alcohol peak in the chromatogram of the Assay preparation C;Wchis the weight of the internal standard,in mg,added in the preparation of the Assay preparation C;and Wcis the weight,in mg,of Sodium Cetostearyl Sulfate taken to prepare the Assay preparation C,calculated on the anhydrous basis.