A: Infrared Absorption 197M.

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

Test solution: 30 mg per mL, in dioxane.

Methanol-dichloromethane solution— Dilute 250 mL of methanol with dichloromethane to 500 mL, and mix.

Standard stock solution— Transfer 25 ± 1 mg of USP Alclometasone Dipropionate RS to a 100-mL volumetric flask, add Methanol-dichloromethane solution to volume, and mix to obtain a solution having a known concentration of 250 ± 10 µg per mL.

Standard preparations A, B, C, D, E, and F— Dilute accurately measured volumes of Standard stock solution quantitatively with Methanol-dichloromethane solution designated below (as parts by volume of Standard stock solution in total parts by volume of the finished Standard preparation) to obtain Standard preparations, designated below by letter, having the following concentrations and percentage assignments:

A— (4 in 5); 200 µg per mL (2.0%).

B— (3 in 5); 150 µg per mL (1.5%).

C— (2 in 5); 100 µg per mL (1.0%).

D— (3 in 10); 75 µg per mL (0.75%).

E— (2 in 10); 50 µg per mL (0.50%).

F— (1 in 10); 25 µg per mL (0.25%).

Test preparation— Transfer 50 ± 2 mg of Alclometasone Dipropionate to a 5-mL volumetric flask, add Methanol-dichloromethane solution to volume, and mix.

Procedure— Apply separately 25 µL of the Test preparation and 25 µL of each Standard preparation to a suitable thin-layer chromatographic plate (see Chromatography 621), coated with a 0.25-mm layer of chromatographic silica gel mixture. Position the plate in a saturated, unlined chromatographic chamber, and develop the chromatograms in a solvent system consisting of a mixture of chloroform and acetone (7:1) 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 solvent to evaporate. Observe the plate under short-wavelength UV light, and compare the intensities of any secondary spots observed in the chromatogram of the Test preparation with those of the principal spots in the chromatograms of the Standard preparations: the sum of the intensities of secondary spots obtained from the Test preparation corresponds to not more than 3.0% of related compounds.

0.05 M Monobasic potassium phosphate— Transfer 3.40 g of monobasic potassium phosphate to a 500-mL volumetric flask, add water to volume, and mix.

Mobile phase— Prepare a filtered and degassed mixture of methanol and 0.05 M Monobasic potassium phosphate (2:1). Make adjustments if necessary (see System Suitability under Chromatography 621).

Internal standard solution— Transfer about 50 mg of betamethasone dipropionate to a 25-mL volumetric flask, add methanol to volume, and mix.

Standard preparation— Transfer about 30 mg of USP Alclometasone Dipropionate RS, accurately weighed, to a 25-mL volumetric flask, add methanol to volume, and mix. Transfer 4.0 mL of this solution to a second 25-mL volumetric flask, add 4.0 mL of Internal standard solution, dilute with methanol to volume, and mix to obtain a Standard preparation having a known concentration of about 0.2 mg of USP Alclometasone Dipropionate RS per mL.

Assay preparation— Transfer about 30 mg of Alclometasone Dipropionate, accurately weighed, to a 25-mL volumetric flask, add methanol to volume, and mix. Transfer 4.0 mL of this solution to a second 25-mL volumetric flask, add 4.0 mL of Internal standard solution, dilute with methanol to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 30-cm column that contains packing L1. The flow rate is about 1.2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between the analyte and internal standard peaks is not less than 3.0; and the relative standard deviation for replicate injections is not more than 2%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 0.7 for alclometasone dipropionate and 1.0 for betamethasone dipropionate. Calculate the quantity, in mg, of C28H37ClO7 in the portion of Alclometasone Dipropionate taken by the formula: in which C is the concentration, in mg per mL, of USP Alclometasone Dipropionate RS in the Standard preparation; and RU and RS are the peak height ratios obtained from the Assay preparation and the Standard preparation, respectively.