Medium: water; 900 mL.

Apparatus 2: 50 rpm.

for products labeled as 5-mg tablets—

for products labeled as 1-mg tablets—

Mobile phase— Prepare a filtered and degassed mixture of 2.5 mM phosphoric acid and acetonitrile (1:1). Make adjustments if necessary (see System Suitability under Chromatography 621).

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

Standard preparation— Dissolve an accurately weighed quantity of USP Finasteride RS in Diluting solution, and dilute quantitatively, and stepwise if necessary, with Diluting solution to obtain a solution having a known concentration of about 100 µg per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an amount of powder equivalent to about 10 mg of finasteride, accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with Diluting solution to volume, and mix.

Chromatographic system (see Chromatography 621)— 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 1.5 mL per 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 1000 theoretical 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 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 finasteride (C23H36N2O2) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Finasteride RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.