Medium: water;900mL.

Apparatus 2: 50rpm.

Time: 45minutes.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and water (29:21).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Diluting solution— Prepare a solution of acetonitrile and water (7:3).

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 approximately equivalent to the sample under test.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm ×5-cm column that contains packing L1.The column temperature is maintained at 45.The flow rate is about 2mLper minute.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the capacity factor,k¢,is not less than 2.0;the column efficiency is not less than 1000theoretical plates;the tailing factor is not more than 2.0;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 200µL)of the solution under test and the Standard solutioninto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity of C23H36N2O2dissolved.

Tolerances— Not less than 75%(Q)of the labeled amount of C23H36N2O2is dissolved in 45minutes.

Mobile phase— Prepare a filtered and degassed mixture of 2.5mMphosphoric acid and acetonitrile (1:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Diluting solution— Prepare a solution of acetonitrile and water (7:3).

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 100µg per mL.

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an amount of powder equivalent to about 10mg 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 240-nm detector and a 4.6-mm ×10.0-cm column that contains packing L1.The column temperature is maintained at 45.The flow rate is about 1.5mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the capacity factor,k¢,is not less than 2.0;the column efficiency is not less than 1000theoretical plates;the tailing factor is not more than 2.0;and the relative standard deviation for replicate injections is not more than 2.0%.

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 finasteride (C23H36N2O2)in the portion of Tablets 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.