Internal standard solution— Transfer 10.0mLof n-propyl alcohol to a 200-mLvolumetric flask,dilute with water to volume,and mix.

Standard solution— Prepare a mixture containing an accurately weighed quantity of alcohol in water having a known concentration of about 10.0mg of alcohol per mL.Transfer 3.0mLof Internal standard solutionto a 10-mLvolumetric flask,dilute with the alcohol solution,and mix.

Test solution— Transfer about 250mg of Gel,accurately weighed,to a suitable container.Add 14.0mLof water and 6.0mLof Internal standard solution,and shake for 15minutes.

Chromatographic system (see Chromatography á621ñ)—The gas chromatograph is equipped with a flame-ionization detector and a 3.2-mm ×1.5-m column packed with 80-to 100-mesh support S3.The column temperature is maintained at 170,and the injection port and detector are maintained at 200.Nitrogen is used as the carrier gas,flowing at a rate of 45mLper minute.Chromatograph the Standard solution,and record the peak responses as directed under Procedure:the resolution,R,between alcohol and the internal standard is not less than 2.0,the capacity factor,k¢,is between 2.0and 3.5for alcohol and between 6.0and 8.0for the internal standard,the tailing factor is not more than 2.5,and the relative standard deviation for replicate injections is not more than 2.5%.

Procedure— Inject equal volumes (about 1µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C2H5OHin the portion of Gel taken by the formula: in which Cis the concentration,in mg per mL,of C2H5OHin the Standard solution,and RUand RSare the ratios of the peak responses for alcohol to those of the internal standard obtained from the Test solutionand the Standard solution,respectively:the content of C2H5OHis between 40%and 45%.

Mobile phase ,Standard preparation,and Chromatographic system—Proceed as directed in the Assayunder Naftifine Hydrochloride.

Assay preparation— Transfer about 1000mg of Gel,accurately weighed,to a 100-mLvolumetric flask,dissolve in 60mLof methanol,mix vigorously for 2minutes,and dilute with methanol to volume.Heat at 45for 5minutes,and cool to room temperature.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C21H21N·HCl in the portion of Gel taken by the formula: in which Cis the concentration,in mg per mL,of USP Naftifine Hydrochloride RSin the Standard preparation,and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.