Solution: 1 in 20.

Medium: chloroform.

Test solution: 10 mg per mL, in dioxane.

Test preparation— Prepare a solution of Norethynodrel in chloroform containing 10 mg per mL.

Standard solution— Prepare a solution of USP Norethindrone RS in chloroform to contain 1 mg per mL. Dilute 2 mL of the solution with chloroform to 10 mL.

Procedure— Apply 10-µL volumes of the Test preparation and the Standard solution (see Chromatography 621) to a thin-layer chromatographic plate coated with a 0.25-mm layer of chromatographic silica gel mixture, and allow not more than 5 minutes between spotting the plate and starting development of the chromatogram. Place the plate in a suitable chromatographic chamber previously equilibrated with a mixture of cyclohexane, ethyl acetate, and methanol (60:40:2), and allow the solvent front to move 15 cm. Spray the plate with dilute sulfuric acid (1 in 2), heat the plate at 105 for 5 minutes, and view under long-wavelength UV light. Locate any norethindrone impurity in the Test preparation by comparison with the RF value from the Standard solution. If present, the norethindrone spot from the Test preparation is not larger or more intense than the spot from the Standard solution (2.0%).

Test solution: chloroform.

Standard solution: chloroform.

Eluant: ether.

Visualization: 5, followed by viewing under long-wavelength UV light.

Standard preparation— Dissolve a suitable quantity of USP Norethynodrel RS, accurately weighed, in methanol, and dilute quantitatively with methanol to obtain a solution having a known concentration of about 1 mg per mL.

Assay preparation— Dissolve about 100 mg of Norethynodrel, accurately weighed, in methanol to make 100.0 mL, and mix.

Procedure— Transfer 10.0 mL each of the Standard preparation and the Assay preparation to separate 100-mL volumetric flasks. To each flask add 40 mL of methanol, then add 5 mL of a mixture of 3 volumes of hydrochloric acid and 2 volumes of water, mix quickly, and allow to stand at a temperature of about 25 for 1 hour, accurately timed. Prior to the end of the 1-hour period, prepare blanks as follows. Add 1.0 mL each of the Standard preparation and the Assay preparation to separate 100-mL volumetric flasks, each containing a mixture of 50 mL of methanol and 2 mL of water, dilute each with methanol to volume, and mix. At the end of the 1-hour reaction period, dilute each of the acid-containing solutions with methanol to volume, and mix. Transfer 10.0 mL of each into separate 100-mL volumetric flasks, add 2 mL of water to each, dilute with methanol to volume, and mix. Concomitantly determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 240 nm, with a suitable spectrophotometer, relative to the corresponding blanks. Calculate the quantity, in mg, of C20H26O2 in the portion of Norethynodrel taken by the formula: in which C is the concentration, in mg per mL, of USP Norethynodrel RS in the Standard preparation, and AU and AS are the absorbances of the solutions from the Assay preparation and the Standard preparation, respectively.