Identification—
Place a quantity of finely powdered Tablets, equivalent to about 10 mg of ethynodiol diacetate, in a stoppered 15-mL centrifuge tube. Add 10 mL of acetonitrile, insert the stopper in the tube, and mix by shaking and inversion for about 2 minutes. Centrifuge at about 1200 rpm for 10 minutes, and decant the supernatant through filter paper into a suitable container. Evaporate a 5-mL aliquot of the filtrate on a steam bath with the aid of a stream of nitrogen, and dissolve the residue in 1 mL of chloroform. Apply 20 µL each of the solution under test, a Standard solution of
USP Ethynodiol Diacetate RS in chloroform containing 5 mg per mL, and a Standard solution of
USP Ethinyl Estradiol RS in chloroform containing 0.25 mg per mL at points about 3 cm from one end of a thin-layer chromatographic plate (see
Chromatography 
621
) coated with a 0.25-mm layer of chromatographic silica gel mixture. Place the plate in a developing chamber containing a mixture of 3 volumes of ethyl acetate and 7 volumes of cyclohexane to a depth of 2 cm, the developing chamber previously having been equilibrated with the solvent mixture as described under
Thin-Layer Chromatography under
Chromatography 621. Remove the plate when the solvent moves to about 15 cm above the initial spots, allow it to dry in air at room temperature, spray it with a 1 in 10 solution of phosphomolybdic acid in alcohol, and heat it at 80
for 10 minutes: the spots from the solution under test and the Standard solutions appear dark on a light-green background. The ethynodiol diacetate and ethinyl estradiol spots from the solution under test have the same relative positions on the plate as the spots from the Standard solutions. The
RF values of ethynodiol diacetate and of ethinyl estradiol in this system are about 0.8 and about 0.4, respectively.
Assay—
Mobile phase—
Prepare a filtered and degassed mixture of methanol, acetonitrile, and water (15:35:50). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard preparation—
Dissolve, with the aid of sonication if necessary, accurately weighed quantities of
USP Ethynodiol Diacetate RS and
USP Ethinyl Estradiol RS in
Mobile phase, and dilute quantitatively, and stepwise if necessary, with
Mobile phase to obtain a solution having known concentrations, in mg per mL, of the Reference Standards, corresponding to about one-twenty-fifth of the labeled amounts of ethynodiol diacetate and ethinyl estradiol in the Tablets.
Assay preparation—
Place 10 Tablets in a 250-mL volumetric flask. Add a portion of Mobile phase, and sonicate until the Tablets are completely disintegrated. Cool to room temperature, dilute with Mobile phase to volume, mix, and filter.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm × 25-cm column that contains packing L10. The flow rate is about 2 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed under
Procedure: the tailing factor is not more than 1.5, and the column efficiency is not less than 3000 theoretical plates, both based on the ethynodiol diacetate peak, and the relative standard deviation for replicate injections is not more than 2.0% for each peak due to ethynodiol diacetate and ethinyl estradiol.
Procedure—
Separately inject equal volumes (about 50 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 ethynodiol diacetate (C
24H
32O
4) and ethinyl estradiol (C
20H
24O
2) in each Tablet taken by the formula:
25C(rU / rS),
in which
C is the concentration, in mg per mL, of the appropriate Reference Standard in the
Standard preparation, and
rU and
rS are the peak responses, at the corresponding retention times, obtained from the
Assay preparation and the
Standard preparation, respectively.
