Desoximetasone Gel
»Desoximetasone Gel contains not less than 90.0percent and not more than 110.0percent of the labeled amount of C22H29FO4.
Packaging and storage— Preserve in collapsible tubes,at controlled room temperature.
Identification— Transfer an amount of Gel,equivalent to 100µg of desoximetasone,to a 15-mLcentrifuge tube.Add 3mLof acetonitrile,sonicate for approximately 1minute,centrifuge,and transfer the clear supernatant to another 15-mLcentrifuge tube.Evaporate the solution under nitrogen at a temperature between 35and 45to dryness.Dissolve the residue in 100µLof methanol,using a sonicator.Streak separately the entire test solution and 100µLof a Standard solution of USP Desoximetasone RSin methanol containing 1mg per mLon a thin-layer chromatographic plate (see Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic silica gel mixture and an area of preadsorbent material on which specimens are applied.Allow the streaks to dry,and develop the chromatogram in a saturated chamber containing a mixture of acetone and chloroform (1:1).Allow the solvent front to move not less than 10cm beyond the origin.After drying,examine the plate under UVlight at 254nm:the RFvalue of the principal spot obtained in the chromatogram of the test solution corresponds to that of the Standard solution.
Minimum fill á755ñ: meets the requirements.
Alcohol content— Transfer about 2.5g of Gel,accurately weighed,to a 50-mLvolumetric flask.Dissolve in methanol,dilute with methanol to volume,and mix.Determine the alcohol content of the specimen thus prepared by the Method II—Gas-Liquid Chromatographic Method(see Alcohol Determination á611ñ),using isopropyl alcohol as the internal standard and using methanol in place of water as the solvent:between 18.0%and 24.0%(w/w)of C2H5OHis found.
Assay—
Mobile phase— Prepare a suitable filtered and degassed solution of methanol,water,and glacial acetic acid (65:35:1).Adjust the ratio,if necessary,so that the retention time of desoximetasone is about 8minutes.
Standard preparation— Using an accurately weighed quantity of USP Desoximetasone RS,prepare a solution in methanol containing 0.5mg per mL.Dilute an accurately measured volume of this solution with methanolic calcium chloride dihydrate solution (1.5in 100)to obtain a Standard preparationhaving a known concentration of about 0.025mg per mL.
Assay preparation— Transfer an accurately weighed quantity of Gel,equivalent to about 1.25mg of desoximetasone,to a 50-mLvolumetric flask,add approximately 40mLof methanolic calcium chloride dihydrate solution (1.5in 100),and sonicate to disperse the gel.Dilute with the same solution to volume,mix,and centrifuge.Use the clear supernatant.
Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm ×30-cm column that contains packing L1.The flow rate is about 1.5mLper minute.Chromatograph five replicate injections of the Standard preparation,and record the peak responses as directed for Procedure:the relative standard deviation is not more than 2.0%.
Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph by means of a sampling valve,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C22H29FO4in the portion of Gel 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 of desoximetasone 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 584
Phone Number:1-301-816-8139