Test solution: 10mg per mLin dioxane.

Mobile phase ,System suitability solution,and Chromatographic system—Proceed as directed in the Assay.

Test solution— Dissolve an accurately weighed quantity of Clobetasol Propionate in Mobile phaseto obtain a solution containing about 0.1mg per mL.

Procedure— Inject a volume (about 10µL)of the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses.Calculate the percentage of each impurity in the portion of Clobetasol Propionate taken by the formula: in which riis the peak response for each impurity,and rsis the sum of the responses of all of the peaks:not more than 1.0%of any individual impurity is found,and the sum of all impurities is not more than 2.5%.

Solvent— Use dimethyl sulfoxide.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile,0.05Mmonobasic sodium phosphate (adjusted with 85%phosphoric acid to a pHof 2.5),and methanol (95:85:20).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Dissolve an accurately weighed quantity of beclomethasone dipropionate in methanol to obtain a solution having a known concentration of about 0.2mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Clobetasol Propionate RSin methanol and Internal standard solutionto obtain a final solution containing about 0.04mg of USP Clobetasol Propionate RSper mLand 0.08mg of beclomethasone dipropionate per mL.

System suitability solution— Dissolve suitable quantities of USP Clobetasol Propionate Related Compound A RSand USP Clobetasol Propionate RSin Mobile phaseto obtain a solution containing about 0.001and 0.1mg per mL,respectively.

Assay preparation— Transfer about 4mg of Clobetasol Propionate,accurately weighed,to a 100-mLvolumetric flask.Add 40.0mLof Internal standard solution,dilute with methanol to volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 240-nm detector and a 4.6-mm ×15-cm column that contains packing L1.The flow rate is about 1.0mLper minute.Chromatograph the System suitability solution,and record the peak responses as directed for Procedure:the relative retention times are about 1.1for clobetasol propionate related compound A,and 1.0for clobetasol propionate;the resolution,R,between clobetasol propionate and clobetasol propionate related compound Ais not less than 1.5;the column efficiency determined from the clobetasol propionate peak is not less than 5000theoretical plates;the tailing factor for the clobetasol propionate peak is not more than 2.0;and the relative standard deviation for replicate injections is not more than 2.0%.

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 1.0for clobetasol propionate and 1.6for beclomethasone dipropionate.Calculate the quantity,in mg,of C25H32ClFO5in the portion of Clobetasol Propionate taken by the formula: in which Cis the concentration,in mg per mL,of USP Clobetasol Propionate RSin the Standard preparation;and RUand RSare the ratios of the clobetasol propionate peak to the internal standard peak obtained from the Assay preparationand the Standard preparation,respectively.