A:Infrared Absorption á197Mñ.

B:Thin-Layer Chromatographic Identification Test á201ñ—

Test solution: 10mg per mL,in dioxane.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile,water,and glacial acetic acid (550:450:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Test solution— Transfer about 4mg of Betamethasone Valerate,accurately weighed,to a suitable flask.Add 10mLof Mobile phase,and shake until dissolved.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×15-cm column that contains packing L1.The flow rate is about 1mLper minute.Chromatograph the Test solution,and record the peak responses as directed for Procedure:the resolution,R,between betamethasone valerate and any impurity is not less than 1.5;and the column efficiency is not less than 9000theoretical plates.

Procedure— Inject a volume (about 10µL)of the Test solutioninto the chromatograph,record the chromatogram,and measure all of the peak responses.Calculate the percentage of each impurity in the portion of Betamethasone Valerate taken by the formula: in which riis the peak response for each impurity;and rsis the sum of all the peak responses:not more than 1.0%of any individual impurity is found;and not more than 2.0%of total impurities is found.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and water (3:2).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Transfer about 40mg of beclomethasone dipropionate to a 100-mLvolumetric flask,add a solution of glacial acetic acid in methanol (1in 1000)to volume,and mix.

Standard preparation— Transfer about 30mg of USP Betamethasone Valerate RS,accurately weighed,to a 50-mLvolumetric flask,add a solution of glacial acetic acid in methanol (1in 1000)to volume,and mix.Transfer 5.0mLof this solution to a suitable stoppered vial,add 10.0mLof Internal standard solution,and mix to obtain a solution having a known concentration of about 0.2mg of USP Betamethasone Valerate RSper mL.

Assay preparation— Transfer about 60mg of Betamethasone Valerate,accurately weighed,to a 100-mLvolumetric flask,add a solution of glacial acetic acid in methanol (1in 1000)to volume,and mix.Transfer 5.0mLof this solution to a suitable stoppered vial,add 10.0mLof Internal standard solution,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 relative retention times are about 1.7for beclomethasone dipropionate and 1.0for betamethasone valerate;the resolution,R,between betamethasone valerate and beclomethasone dipropionate is not less than 4.5;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.Calculate the quantity,in mg,of C27H37FO6in the portion of Betamethasone Valerate taken by the formula: in which Cis the concentration,in mg per mL,of USP Betamethasone Valerate RSin the Standard preparation;and RUand RSare the peak response ratios obtained from the Assay preparationand the Standard preparation,respectively.