A: Infrared Absorption á197Kñ.

B: Ultraviolet Absorption á197Uñ—

Test solution: 10mg per mL,in chloroform.

Solution A— Prepare a filtered and degassed mixture of water and acetonitrile (13:7).

Solution B— Prepare a filtered and degassed mixture of acetonitrile and water (7:3).

Mobile phase— Use variable mixtures of Solution Aand Solution Bas directed for Chromatographic system.Make adjustments to either Solutionas necessary (see System Suitabilityunder Chromatography á621ñ).

System suitability solution— Dissolve suitable quantities of butylparaben and USP Amcinonide RSin Solution Bto obtain separate solutions containing 12.5µg per mLand 20µg per mL,respectively.

Standard preparation— Dissolve an accurately weighed quantity of USP Amcinonide RSin Solution B,and dilute quantitatively,and stepwise if necessary,with Solution Bto obtain a solution having a known concentration of about 0.02mg per mL.

Assay preparation— Transfer about 20mg of Amcinonide,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with Solution Bto volume,sonicate for 5minutes,and mix.Transfer 5mLof this solution to a 50-mLvolumetric flask,dilute with Solution Bto volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×25-cm column that contains packing L1,and is programmed to provide variable mixtures of Solution Aand Solution B.The flow rate is about 2mLper minute.Equilibrate the system with Solution A.From 2.5minutes to 10minutes after injection,linearly increase the amount of Solution Bto 100%.Chromatograph the System suitability solution,and record the peak responses as directed under Procedure:the relative retention times are about 0.78for butylparaben and 1.0for amcinonide,and the resolution,R,between butylparaben and amcinonide is not less than 8.0.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the tailing factor is not more than 1.5,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 preparation.Record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C28H35FO7in the portion of Amcinonide taken by the formula: in which Cis the concentration,in mg per mL,of USP Amcinonide RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.