A: Infrared Absorption á197Kñ.

B: Prepare a solution of it in a mixture of chloroform and alcohol (3:1)containing 10mg per mL.Prepare a solution of USP Desoximetasone RSin the same mixture,containing 10mg per mL.Apply separately 20µLof each solution to a thin-layer chromatographic plate coated with a 0.25-mm layer of chromatographic silica gel mixture.Allow the spots to dry,and develop the chromatogram in a saturated chamber containing a mixture of chloroform and ethyl acetate (1:1).Allow the solvent front to move 10cm beyond the application point.After drying,examine the plate under UVlight at 254nm.Spray the dried plate with a 1in 5solution of p-toluenesulfonic acid in alcohol.The major spot from the test solution corresponds in RFvalue (about 0.25)and appearance to that obtained from the Standard solution.

Test solution: 5mg per mL,in chloroform.

Mobile phase— Prepare a suitable filtered and degassed solution of methanol,water,and glacial acetic acid (65:35:1),such that the retention time of desoximetasone is about 6minutes.

Standard preparation— On the day of use,weigh accurately about 20mg of USP Desoximetasone RS,and dissolve in methanol to obtain 50.0mL.Dilute 10.0mLof this solution with a mixture of methanol and acetonitrile (1:1)to 100.0mL.

Assay preparation— Weigh accurately 40mg of Desoximetasone,dissolve in 100.0mLof methanol,and proceed as directed for Standard preparation,beginning with “Dilute 10.0mLof this solution.”

Procedure— Using an injection loop,inject 10-µLportions of the Assay preparationand the Standard preparationinto a high-pressure liquid chromatograph equipped with an UVdetector capable of monitoring absorption at 254nm.The instrument is equipped with a 4.6-mm ×15-cm stainless steel column that contains packing L7and is operated at a flow rate of about 1mLper minute.In a suitable chromatogram,five replicate injections of the Standard preparationshow a relative standard deviation of not more than 2.0%,and the tailing factor is not more than 1.5.Calculate the quantity,in mg,of C22H29FO4in the portion of Desoximetasone taken by the formula: in which Cis the concentration,in mg per mL,of USP Desoximetasone RSin the Standard preparation,and HUand HSare the peak heights of desoximetasone obtained from the Assay preparationand the Standard preparation,respectively.