Standard solution— Dilute 20.0mLof USP Alcohol with methanol to volume in a 200-mLvolumetric flask.

Internal standard solution— Dilute 20.0mLof isopropyl alcohol with methanol to volume in a 100-mLvolumetric flask.

Test preparation— Using a “to contain”pipet,transfer 2mLof Topical Solution to a 100-mLvolumetric flask,rinsing the pipet 3times with methanol and collecting the rinsings in the volumetric flask.Add 5.0mLof Internal standard solution,dilute with methanol to volume,and mix.

Standard preparation— Pipet 6mLof the Standard solutionand 5mLof the Internal standard solutioninto a 100-mLvolumetric flask,dilute with methanol to volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The gas chromatograph is equipped with a flame-ionization detector and a 2-mm ×1.8-m glass column that is packed with 80-to 100-mesh packing S3.The carrier gas is nitrogen or helium,flowing at a rate of about 40mLper minute.The injection port and detector temperatures are maintained at about 225.The column temperature is maintained at about 130.Chromatograph the Standard preparation,record the chromatogram,and determine the peak response ratio as directed for Procedure.Adjust the carrier gas flow rate so that the resolution,R,of alcohol and isopropyl alcohol is not less than 1.5;the tailing factor of the alcohol peak is not more than 1.25;and the relative standard deviation for peak response ratios from replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (2µLto 3µL)of the Test preparationand the Standard preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the percentage (v/v)of C2H5OHin the Topical Solution taken by the formula: in which 95.45is the percentage (v/v)of C2H5OHin USP Alcohol;and RUand RSare the peak response ratios obtained from the Test preparationand the Standard preparation,respectively:between 28.4%and 39.0%of C2H5OHis present.

Mobile phase— Use a mixture of acetonitrile and water (55:45).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Fluocinonide RSin acetonitrile to obtain a solution containing about 500µg per mL.Transfer 2.0mLof this solution to a 25-mLvolumetric flask.Dilute with Mobile phaseto volume,and mix to obtain a solution having a known concentration of about 40µg of USP Fluocinonide RSper mL.

Assay preparation— Using a “to contain”pipet,transfer a volume of Topical Solution,equivalent to about 1mg of fluocinonide,to a 25-mLvolumetric flask,rinsing the pipet with about 5mLof Mobile phase,and adding the rinsings to the volumetric flask,dilute with Mobile phaseto volume,and mix.

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 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the tailing factor for the analyte peak is not more than 1.5;and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 20µL)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 C26H32F2O7in each mLof the Topical Solution taken by the formula: in which Cis the concentration,in µg per mL,of USP Fluocinonide RSin the Standard preparation;Vis the volume,in mL,of Topical Solution taken;and rUand rSare the peak responses due to fluocinonide obtained from the Assay preparationand the Standard preparation,respectively.