A: Infrared Absorption 197K.

B: Prepare a solution of it in a mixture of chloroform and alcohol (3:1) containing 10 mg per mL. Prepare a solution of USP Desoximetasone RS in the same mixture, containing 10 mg per mL. Apply separately 20 µL of each solution to a thin-layer chromatographic plate coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram in a saturated chamber containing a mixture of chloroform and ethyl acetate (1:1). Allow the solvent front to move 10 cm beyond the application point. After drying, examine the plate under UV light at 254 nm. Spray the dried plate with a 1 in 5 solution of p-toluenesulfonic acid in alcohol. The major spot from the test solution corresponds in RF value (about 0.25) and appearance to that obtained from the Standard solution.

Test solution: 5 mg per mL, in chloroform.

Mobile phase— Prepare a suitable filtered and degassed solution of methanol, water, and glacial acetic acid (65:35:1), such that the retention time of desoximetasone is about 6 minutes.

Standard preparation— On the day of use, weigh accurately about 20 mg of USP Desoximetasone RS, and dissolve in methanol to obtain 50.0 mL. Dilute 10.0 mL of this solution with a mixture of methanol and acetonitrile (1:1) to 100.0 mL.

Assay preparation— Weigh accurately 40 mg of Desoximetasone, dissolve in 100.0 mL of methanol, and proceed as directed for Standard preparation, beginning with “Dilute 10.0 mL of this solution.”

Procedure— Using an injection loop, inject 10-µL portions of the Assay preparation and the Standard preparation into a high-pressure liquid chromatograph equipped with an UV detector capable of monitoring absorption at 254 nm. The instrument is equipped with a 4.6-mm × 15-cm stainless steel column that contains packing L7 and is operated at a flow rate of about 1 mL per minute. In a suitable chromatogram, five replicate injections of the Standard preparation show a relative standard deviation of not more than 2.0%, and the tailing factor is not more than 1.5. Calculate the quantity, in mg, of C22H29FO4 in the portion of Desoximetasone taken by the formula: in which C is the concentration, in mg per mL, of USP Desoximetasone RS in the Standard preparation, and HU and HS are the peak heights of desoximetasone obtained from the Assay preparation and the Standard preparation, respectively.