A: Infrared Absorption 197M.

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

Test solution: 10 mg 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 Suitability under Chromatography 621).

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

Standard solution— 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 1.0 mg per mL.

Test solution— Transfer about 100 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 210-nm detector and a 4.6-mm × 30-cm column that contains 4-µm packing L1. The flow rate is about 1.5 mL per 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 10,000 theoretical plates; and the tailing factor is not more than 1.3.

Procedure— Inject a volume (about 15 µL) of the Test solution into 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 ri is the peak response for each impurity, and rs is 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.

(Official January 1, 2007)

Mobile phase— Prepare a filtered and degassed mixture of water and tetrahydrofuran (4:1). Make adjustments if necessary (see System Suitability under Chromatography 621).

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

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 200 µg per mL.

Assay preparation— Transfer about 20 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 215-nm detector and a 3.0-mm × 3.0-cm column that contains 3-µm packing L7. The flow rate is about 3 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 1800 theoretical 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 10 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 C23H36N2O2 in the portion of Finasteride 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.