Test solution: 10 mg per mL, in chloroform.

Mobile phase, Assay preparation, and Chromatographic system— Prepare as directed in the Assay.

Procedure— Inject about 20 µL of the Assay preparation into the chromatograph, record the chromatograms, and measure the area responses for the peaks. The relative retention times are about 0.87 for -ethynodiol diacetate, and 1.0 for ethynodiol diacetate. Calculate the area percentages of the individual impurities by the formula: in which ri is the area of each individual peak appearing in the chromatogram between the solvent front and the ethynodiol diacetate peak, and rt is the sum of the areas of all peaks appearing after the solvent front. Not more than 1.5% of -ethynodiol diacetate is found; not more than 0.5% of any other individual impurity is found; and the sum of all impurities is not more than 2.0%.

Mobile phase— Prepare a filtered and degassed mixture of water and acetonitrile (59:41). Adjust as necessary (see System Suitability under Chromatography 621).

Standard preparation— Transfer about 25 mg of USP Ethynodiol Diacetate RS, accurately weighed, to a 10-mL volumetric flask, add 5.0 mL of acetonitrile, and sonicate until dissolved. Dilute with water to volume, and mix. Dilute 5.0 mL of this solution with a mixture of water and acetonitrile (59:41) to 50.0 mL, and mix to obtain a solution having a known concentration of about 0.25 mg per mL.

Assay preparation— Transfer about 25 mg of Ethynodiol Diacetate, accurately weighed, to a 10-mL volumetric flask, add 5.0 mL of acetonitrile, and sonicate until dissolved. Dilute with water to volume, and mix. Dilute 5.0 mL of this solution with a mixture of water and acetonitrile (59:41) to 50.0 mL, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 200-nm detector and a 4.6-mm × 15-cm column that contains packing L11. The flow rate is about 2.0 mL per minute. The column is maintained at 40. Chromatograph the Standard preparation, record the chromatogram, and measure the peak response as directed under Procedure: the retention time for ethynodiol diacetate is not less than 18 minutes, the tailing factor for ethynodiol diacetate is not less than 0.75 and not more than 2.0, and the relative standard deviation for replicate injections is not more than 0.7%.

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 C24H32O4 in the portion of Ethynodiol Diacetate taken by the formula: in which C is the concentration, in mg per mL, of USP Ethynodiol Diacetate RS in the Standard preparation, and rU and rS are the peak responses of the major peaks obtained from the Assay preparation and the Standard preparation, respectively.