Standard dilutions—
Dissolve an accurately weighed quantity of
USP Stanozolol RS in a mixture of chloroform and methanol (9:1) to obtain a solution having a known concentration of about 20 mg per mL. Dilute this solution with the same medium to obtain
Standard dilutions having known concentrations of about 50, 100, 200, and 400 µg per mL, respectively.
Procedure—
Score a 20- × 20-cm thin-layer chromatographic plate coated with a 0.25-mm layer of chromatographic silica gel mixture (binder-free) into channels 10 mm wide. Apply 10-µL portions, in two 5-µL increments, of a test solution prepared by dissolving Stanozolol in a mixture of chloroform and methanol (9:1) to obtain a solution containing about 20 mg per mL, and of each of the four
Standard dilutions in the center of the channels at points about 2.5 cm from one edge of the plate. Develop the plate in a suitable chamber, lined with filter paper and previously equilibrated with 200 mL of a mixture of chloroform and methanol (188:12), for 15 minutes, taking care to ensure that the filter paper has been wetted completely with the solvent mixture. Allow the plate to develop until the solvent front has moved about 15 cm above the line of application. Remove the plate, and allow the solvent to evaporate completely. Spray it with 20% sulfuric acid, and heat in an oven at 100
for 15 minutes. Examine the plate under long-wavelength UV light: the channel for the test solution exhibits its principal spot at the same
RF value as the spots for the
Standard dilutions. Estimate the concentration of any spots in the channel for the test solution, other than the principal spot, by comparison with the spots from the
Standard dilutions. The spots from the 50-, 100-, 200-, and 400-µg-per-mL dilutions correspond to 0.25%, 0.5%, 1.0%, and 2.0% of chromatographic impurities, respectively, and the sum of the chromatographic impurities in the test solution is not greater than 2.0%.
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