A: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that of the Standard preparation, both relative to the internal standard, as obtained in the Assay.

B: Transfer a quantity of Ointment, equivalent to about 3 mg of mometasone furoate, to a 50-mL screw-capped centrifuge tube. Pipet 5.0 mL of methanol into the tube, and attach the cap. Heat in a steam bath until the ointment completely melts, and shake vigorously until the ointment resolidifies. Place in an ice-water bath for 10 minutes. Centrifuge, and filter a portion of the supernatant. Extract 1 mL of the filtrate with 1 mL of hexane; the lower phase obtained is the test solution. Apply 10 µL of the test solution and 10 µL of a Standard solution of USP Mometasone Furoate RS in methanol containing 0.6 mg per mL to a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram in methanol until the solvent front has moved 2 cm from the origin. Remove the plate from the developing chamber and air-dry. Develop the chromatogram in a second solvent system consisting of a mixture of chloroform and ethyl acetate (3:1), until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the spots to air-dry. Examine the plate under short-wavelength UV light: the RF value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.

Mobile phase , Diluting solution, Internal standard solution, Standard preparation, and Chromatographic system—Proceed as directed in the Assay under Mometasone Furoate.

Assay preparation— Transfer an accurately weighed portion of Ointment, equivalent to 1.0 mg of mometasone furoate, to a 50-mL screw-capped centrifuge tube. Pipet 10.0 mL of Internal standard solution and 10.0 mL of Diluting solution into the tube, and attach the cap. Heat in an 85 water bath until the ointment completely melts, and shake vigorously by hand until the ointment resolidifies. Repeat heating and shaking two more times. Place the tube in an ice-methanol bath for 10 minutes. Centrifuge to obtain a clear supernatant, and transfer 10.0 mL of the supernatant into a 25-mL volumetric flask. Dilute with Diluting solution to volume, and mix.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of mometasone furoate (C27H30Cl2O6) in the portion of Ointment taken by the formula: in which C is the concentration, in mg per mL, of USP Mometasone Furoate RS in the Standard preparation, and RU and RS are the ratios of the mometasone furoate peak to the internal standard peak obtained from the Assay preparation and the Standard preparation, respectively.