A: Infrared Absorption á197Mñ.

B: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of the Standard preparation,as obtained in the Assay.

Test solution: 10mg per mL,in methanol.

Mobile phase— Prepare a filtered and degassed mixture of water,tetrahydrofuran,and acetonitrile (8:1:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Diluting solution— Prepare a solution of water and acetonitrile (1:1).

Standard solution— Dissolve an accurately weighed quantity of USP Finasteride RSin Diluting solution,and dilute quantitatively,and stepwise if necessary,with Diluting solutionto obtain a solution having a known concentration of about 1.0mg per mL.

Test solution— Transfer about 100mg of Finasteride,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with Diluting solutionto volume,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm ×30-cm column that contains 4-µm packing L1.The flow rate is about 1.5mLper minute.The column temperature is maintained at 60.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the column efficiency is not less than 10,000theoretical plates;and the tailing factor is not more than 1.3.

Procedure— Inject a volume (about 15µL)of the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses.Calculate the percentage of each impurity in the portion of Finasteride taken by the formula: in which riis the peak response for each impurity,and rsis the sum of the responses of all peaks:not more than 0.5%of any individual impurity is found;and not more than 1.0%of total impurities is found.

Mobile phase— Prepare a filtered and degassed mixture of water and tetrahydrofuran (4:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Diluting solution— Prepare a solution of water and acetonitrile (1:1).

Standard preparation— Dissolve an accurately weighed quantity of USP Finasteride RSin Diluting solution,and dilute quantitatively,and stepwise if necessary,with Diluting solutionto obtain a solution having a known concentration of about 200µg per mL.

Assay preparation— Transfer about 20mg of Finasteride,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with Diluting solutionto volume,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 215-nm detector and a 3.0-mm ×3.0-cm column that contains 3-µm packing L7.The flow rate is about 3mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the column efficiency is not less than 1800theoretical plates;the tailing factor is not more than 1.3;and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 10µL)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 C23H36N2O2in the portion of Finasteride taken by the formula: in which Cis the concentration,in mg per mL,of USP Finasteride RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.