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

Test preparation— Use the Assay preparation.

Procedure— Inject a volume (about 15µL)of the Test preparationinto the chromatograph,record the chromatogram,and measure the peak responses.Calculate the percentage of each impurity in the portion of Naftifine Hydrochloride taken by the formula: in which riis the peak response for each impurity,and rSis the sum of the responses of all of the peaks:not more than 0.1%of any individual impurity is found,and the sum of all impurities is not more than 1.0%.

Mobile phase— Prepare a filtered and degassed mixture of n-hexane,alcohol,dimethylformamide,and formic acid (200:60:40:2),cover tightly with a moisture-proof film,and allow to stand for 12hours at room temperature.Make adjustments,if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Naftifine Hydrochloride RSin Mobile phase,and dilute quantitatively,and stepwise,if necessary,with Mobile phaseto obtain a solution having a known concentration of about 0.2mg per mL.

Assay preparation— Transfer about 10mg of Naftifine Hydrochloride,accurately weighed,to a 50-mLvolumetric flask,dissolve in and dilute with Mobile phaseto volume.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 270-nm detector and a 4.6-mm ×25-cm column that contains 5-µm packing L3.The flow rate is about 2.0mLper minute.

Procedure— Separately inject equal volumes (about 15µL)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 Naftifine Hydrochloride 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.