A:Infrared Absorption á197Mñ.

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

Test solution: 30mg per mL,in dioxane.

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

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

Standard preparations A,B,C,D,E,and F— Dilute accurately measured volumes of Standard stock solutionquantitatively with Methanol-dichloromethane solutiondesignated below (as parts by volume of Standard stock solutionin 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— (4in 5);200µg per mL(2.0%).

B— (3in 5);150µg per mL(1.5%).

C— (2in 5);100µg per mL(1.0%).

D— (3in 10);75µg per mL(0.75%).

E— (2in 10);50µg per mL(0.50%).

F— (1in 10);25µg per mL(0.25%).

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

Procedure— Apply separately 25µLof the Test preparationand 25µLof each Standard preparationto a suitable thin-layer chromatographic plate (see Chromatography á621ñ),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 UVlight,and compare the intensities of any secondary spots observed in the chromatogram of the Test preparationwith those of the principal spots in the chromatograms of the Standard preparations:the sum of the intensities of secondary spots obtained from the Test preparationcorresponds to not more than 3.0%of related compounds.

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

Mobile phase— Prepare a filtered and degassed mixture of methanol and 0.05M Monobasic potassium phosphate(2:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

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

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

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

Chromatographic system(see Chromatography á621ñ)— 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 1.2mLper 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 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.The relative retention times are about 0.7for alclometasone dipropionate and 1.0for betamethasone dipropionate.Calculate the quantity,in mg,of C28H37ClO7in the portion of Alclometasone Dipropionate taken by the formula: in which Cis the concentration,in mg per mL,of USP Alclometasone Dipropionate RSin the Standard preparation;and RUand RSare the peak height ratios obtained from the Assay preparationand the Standard preparation,respectively.