Test solution: 10mg per mL,in chloroform.

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

Procedure— Inject about 20µLof the Assay preparationinto the chromatograph,record the chromatograms,and measure the area responses for the peaks.The relative retention times are about 0.87for a-ethynodiol diacetate,and 1.0for ethynodiol diacetate.Calculate the area percentages of the individual impurities by the formula: in which riis the area of each individual peak appearing in the chromatogram between the solvent front and the ethynodiol diacetate peak,and rtis the sum of the areas of all peaks appearing after the solvent front.Not more than 1.5%of a-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 Suitabilityunder Chromatography á621ñ).

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

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

Chromatographic system (see Chromatography á621ñ)—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 2.0mLper 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 18minutes,the tailing factor for ethynodiol diacetate is not less than 0.75and 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 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 C24H32O4in the portion of Ethynodiol Diacetate taken by the formula: in which Cis the concentration,in mg per mL,of USP Ethynodiol Diacetate RSin the Standard preparation,and rUand rSare the peak responses of the major peaks obtained from the Assay preparationand the Standard preparation,respectively.