Internal standard solution— Transfer 10.0 mL of n-propyl alcohol to a 200-mL volumetric 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 10.0 mg of alcohol per mL. Transfer 3.0 mL of Internal standard solution to a 10-mL volumetric flask, dilute with the alcohol solution, and mix.

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

Chromatographic system (see Chromatography 621)—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 45 mL per 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 2.0 and 3.5 for alcohol and between 6.0 and 8.0 for 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 1 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C2H5OH in the portion of Gel taken by the formula: in which C is the concentration, in mg per mL, of C2H5OH in the Standard solution, and RU and RS are the ratios of the peak responses for alcohol to those of the internal standard obtained from the Test solution and the Standard solution, respectively: the content of C2H5OH is between 40% and 45%.

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

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

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into 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 C is the concentration, in mg per mL, of USP Naftifine Hydrochloride RS in the Standard preparation, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.