Test solution: 20 mg per mL, in chloroform.

Mobile phase— Prepare a solution of acetonitrile and water (55:45), mix, and degas. The acetonitrile concentration may be varied slightly to meet system suitability test requirements and to provide a suitable elution time.

Solvent mixture— Mix 60 volumes of water and 40 volumes of acetonitrile.

Internal standard solution— Transfer about 80 mg of propylparaben to a 100-mL volumetric flask, dissolve in acetonitrile, add acetonitrile to volume, and mix.

Standard preparation— Using an accurately weighed quantity of USP Megestrol Acetate RS, prepare a solution in acetonitrile containing about 1 mg per mL. Transfer 4.0 mL of this solution and 5.0 mL of Internal standard solution to a 50-mL volumetric flask, dilute with Solvent mixture to volume, and mix. The Standard preparation has a known concentration of about 80 µg of megestrol acetate per mL.

Assay preparation— Transfer about 100 mg of Megestrol Acetate, accurately weighed, to a 100-mL volumetric flask. Dissolve in acetonitrile, add acetonitrile to volume, and mix. Transfer 4.0 mL of this solution and 5.0 mL of Internal standard solution to a 50-mL volumetric flask, dilute with Solvent mixture to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with an UV detector that monitors absorption at 280 nm and 3.9-mm × 30-cm column containing packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are about 0.4 for propylparaben and 1.0 for megestrol acetate; the resolution factor, R (see Chromatography 621), between the peaks for propylparaben and megestrol acetate is not less than 8.0; and the relative standard deviation of the peak response ratio, RS, for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 25 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the peak responses of the major peaks. Calculate the quantity, in mg, of C24H32O4 in the portion of Megestrol Acetate taken by the formula: in which C is the concentration, in µg per mL, of USP Megestrol Acetate RS in the Standard preparation; and RU and RS are the ratios of the peak responses of megestrol acetate and propylparaben obtained from the Assay preparation and the Standard preparation, respectively.