Test solution— Transfer about 1.5g of Ointment to a glass-stoppered,50-mLcentrifuge tube.Add 15mLof methanol–hydrochloric acid solution prepared by mixing 1volume of dilute hydrochloric acid (1in 120)with 4volumes of methanol.Shake to obtain a homogeneous mixture.Add 30mLof solvent hexane,mix for 10minutes,and centrifuge.Using a suitable syringe,transfer the lower aqueous phase to a second centrifuge tube,add about 20mLof water,and mix.Extract this aqueous mixture with chloroform by shaking,centrifuging,and removing the lower,chloroform phase with a syringe.Evaporate the chloroform on a steam bath with the aid of a stream of nitrogen to dryness,cool,and dissolve the residue in chloroform to obtain a solution containing about 150µg of betamethasone dipropionate per mL.

Standard solution: USP Betamethasone Dipropionate RSin chloroform containing 150µg per mL.

Application volume: 40µL.

Developing solvent system: a mixture of chloroform and acetone (7:1).

Procedure— Proceed as directed in the chapter.

Mobile phase— Prepare as directed in the Assayunder Betamethasone Dipropionate.

Internal standard solutionand Standard preparation— Prepare as directed in the Assayunder Betamethasone Dipropionate Cream,except to use alcohol containing acetic acid (1in 1000)as the solvent.

Assay preparation— Transfer an accurately weighed quantity of Ointment,equivalent to about 2mg of betamethasone dipropionate,to a capped 50-mLcentrifuge tube.Add 5.0mLof Internal standard solutionand 10.0mLof alcohol containing acetic acid (1in 1000).Heat in a water bath at 70,shaking intermittently until the assay specimen melts.Remove from the bath,and shake vigorously until the ointment has solidified.Repeat the heating and shaking operation.Proceed as directed for Assay preparationin the Assayunder Betamethasone Dipropionate Cream,beginning with “Freeze in an ice-methanol bath.”

Procedure— Proceed as directed for Procedurein the Assayunder Betamethasone Dipropionate Cream.