Standard solution— Dilute 20.0 mL of USP Alcohol with methanol to volume in a 200-mL volumetric flask.

Internal standard solution— Dilute 20.0 mL of isopropyl alcohol with methanol to volume in a 100-mL volumetric flask.

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

Standard preparation— Pipet 6 mL of the Standard solution and 5 mL of the Internal standard solution into a 100-mL volumetric flask, dilute with methanol to volume, and mix.

Chromatographic system (see Chromatography 621)—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 40 mL per 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 (2 µL to 3 µL) of the Test preparation and the Standard preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the percentage (v/v) of C2H5OH in the Topical Solution taken by the formula: in which 95.45 is the percentage (v/v) of C2H5OH in USP Alcohol; and RU and RS are the peak response ratios obtained from the Test preparation and the Standard preparation, respectively: between 28.4% and 39.0% of C2H5OH is present.

Mobile phase— Use a mixture of acetonitrile and water (55:45). Make adjustments if necessary (see System Suitability under Chromatography 621).

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

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

Chromatographic system (see Chromatography 621)—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 mL per 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 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C26H32F2O7 in each mL of the Topical Solution taken by the formula: in which C is the concentration, in µg per mL, of USP Fluocinonide RS in the Standard preparation; V is the volume, in mL, of Topical Solution taken; and rU and rS are the peak responses due to fluocinonide obtained from the Assay preparation and the Standard preparation, respectively.