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