Procedure
Weigh and finely powder not less than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 75 µg of norgestrel, to a 30-mL separator containing 5 mL of water. Extract with three 5-mL portions of chloroform, shaking for about 1 minute each time, and collecting the chloroform extracts through glass wool, previously moistened with chloroform, into a glass-stoppered test tube. Add 1 mL of dilute hydrochloric acid (1 in 12) to the remaining aqueous phase and extract with a fourth 5-mL portion of chloroform, collecting this chloroform extract as before and combining it with the previous three. To another glass-stoppered test tube transfer 20.0 mL of a solution of
USP Norgestrel RS, in chloroform, having a known concentration of about 3.75 µg per mL. Evaporate the contents of both tubes in a water bath with the aid of a current of air to dryness. Add 5.0 mL of
Isoniazid reagent to each tube, insert the stopper in each tube, and swirl occasionally for 1 hour. Concomitantly determine the absorbances of both solutions in 1-cm cells, at the wavelength of maximum absorbance at about 380 nm, using a suitable spectrophotometer, and using
Isoniazid reagent as the blank. Calculate the quantity, in µg, of C
21H
28O
2 in the portion of Tablets taken by the formula:
20C(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Norgestrel RS in the Standard solution, and
AU and
AS are the absorbances of the solutions from the Tablets and the Standard solution, respectively.