Mobile phase and Chromatographic system—Proceed as directed in the Assayunder Betamethasone Valerate.

Internal standard solution— Transfer about 20mg of beclomethasone dipropionate to a 50-mLvolumetric flask,add a 1in 1000solution of glacial acetic acid in alcohol to volume,and mix.

Standard preparation— Transfer about 30mg of USP Betamethasone Valerate RS,accurately weighed,to a 50-mLvolumetric flask,add a 1in 1000solution of glacial acetic acid in alcohol 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 an accurately weighed portion of Ointment,equivalent to about 2.5mg of betamethasone,to a 50-mLcentrifuge tube.Add 10.0mLof the Internal standard solutionand 5.0mLof a 1in 1000solution of glacial acetic acid in alcohol.Insert the stopper into the tube,and place in a water bath held at 70until the specimen melts.Remove from the bath,and shake vigorously until the specimen resolidifies.Repeat the heating and shaking two more times.Place the tube in an ice-methanol bath for 20minutes,then centrifuge to separate the phases.Decant the clear supernatant into a suitable stoppered flask,and allow to warm to room temperature.

Procedure— Proceed as directed for Procedurein the Assayunder Betamethasone Valerate.Calculate the quantity,in mg,of C22H29FO5in the portion of Ointment taken by the formula: in which 392.46and 476.59are the molecular weights of betamethasone and betamethasone valerate,respectively;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.