Desoximetasone Ointment
»Desoximetasone Ointment contains not less than 90.0percent and not more than 110.0percent of the labeled amount of desoximetasone (C22H29FO4).
Packaging and storage— Preserve in collapsible tubes,at controlled room temperature.
Identification— Transfer an accurately weighed quantity of Ointment,equivalent to about 5mg of desoximetasone,to a 50-mLcentrifuge tube.Add 20mLof hexane,heat gently to 60,and shake until the Ointment is completely dispersed.Add 8mLof acetonitrile,insert the stopper in the tube,and shake vigorously for 5minutes.Cool to room temperature,and centrifuge until the lower layer is clear.Transfer the lower layer to a 10-mLvolumetric flask,dilute with acetonitrile to volume,and mix.Prepare a solution of USP Desoximetasone RSin acetonitrile containing 0.5mg per mL.Separately apply 5µLof each solution to a thin-layer chromatographic plate (see Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic silica gel mixture.Allow the spots to dry,and develop the plate in a saturated chamber containing a mixture of ethyl acetate and chloroform (4:1)until the solvent front has moved about three-fourths of the length of the plate.Remove the plate,and allow to air-dry.Examine under short-wavelength UVlight.Spray the dried plate with a 1in 5solution of p-toluenesulfonic acid in alcohol.Heat the plate at 100for 5minutes,and examine under long-wavelength UVlight:the RFvalue and appearance (brownish yellow fluorescent spot)of the principal spot from the test solution,correspond to those of the principal spot from the Standard solution.
Minimum fill á755ñ: meets the requirements.
Assay—
Mobile phase— Prepare a filtered and degassed mixture of methanol,water,and glacial acetic acid (65:35:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).
Standard preparation— Dissolve an accurately weighed quantity of USP Desoximetasone RSin methanol to obtain a solution having a known concentration of about 0.4mg per mL.Quantitatively dilute 1volume of this solution with 9volumes of a 1:1mixture of methanol and spectrophotometric acetonitrile that is saturated with n-heptane,and mix.
Assay preparation— Transfer an accurately weighed amount of Ointment,equivalent to about 2mg of desoximetasone,to a 50-mLcentrifuge tube.Add 20mLof n-heptane that has been previously saturated with spectrophotometric acetonitrile,and heat gently with occasional shaking until the Ointment is completely dispersed.Allow to cool slightly,and extract with a 10-mLportion of spectrophotometric acetonitrile.Shake vigorously,centrifuge,remove the bottom layer of acetonitrile with a syringe and needle,and transfer to a 50-mLvolumetric flask.Using the same needle and syringe,extract the desoximetasone with successive 10-mLand 8-mLportions of acetonitrile,combining all acetonitrile layers in the 50-mLflask.Dilute with methanol nearly to volume,mix,and allow the solution to reach room temperature.Dilute with methanol to volume,and mix.
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 L7.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the tailing factor for the analyte peak is not more than 2.0,the resolution,R,between the analyte and solvent peaks is not less than 5.0,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.Calculate the quantity,in mg,of C22H29FO4in the portion of Ointment taken by the formula:
50C(rU/rS),
in which Cis the concentration,in mg per mL,of USP Desoximetasone RSin the Standard preparation,and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.
Auxiliary Information— Staff Liaison:Clydewyn M.Anthony,Ph.D.,Scientist
Expert Committee:(PA1)Pharmaceutical Analysis 1
USP28–NF23Page 585
Phone Number:1-301-816-8139