Identification—
Weigh an amount of Cream, equivalent to about 2.5 mg of fluocinonide, into a glass-stoppered, 100-mL centrifuge tube containing 5 mL of water and 10 mL of methanol. Add 20 mL of cyclohexane, shake vigorously, centrifuge, and discard the upper phase. Add 20 mL of water and 5 mL of chloroform, shake vigorously, centrifuge until the lower phase is clear, and discard the upper phase. The clear chloroform extract is the
Test solution. Separately apply 10 µL of the
Test solution and 10 µL of a Standard solution having a concentration of 0.5 mg per mL of
USP Fluocinonide RS in chloroform to equidistant points about 2 cm from one end of a thin-layer chromatographic plate (see
Chromatography 
621
), coated with a 0.25-mm layer of chromatographic silica gel. Allow the applications to dry, and develop the chromatogram in a suitable chromatographic chamber using a mixture of chloroform and acetone (4:1). Air-dry, and view under short-wavelength UV light: the principal spot from the
Test solution corresponds to that obtained from the Standard solution.
Assay—
Mobile phase—
Prepare a filtered and degassed mixture of acetonitrile and water (1:1). 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 having a known concentration of about 200 µg per mL. Transfer 10.0 mL of this solution and 10.0 mL of water to a 100-mL volumetric flask. Dilute with acetonitrile to volume, and mix. The final concentration of
USP Fluocinonide RS is 20 µg per mL.
Assay preparation—
Transfer an accurately weighed quantity of Cream, containing about 2 mg of fluocinonide, to a 100-mL volumetric flask. Add about 60 mL of acetonitrile, and dissolve the cream by heating on a steam bath. Add 10.0 mL of water, and allow to cool. Dilute with acetonitrile to volume, and mix. Filter the mixture through a fine-sintered glass funnel, using vacuum, and use the filtrate.
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 2 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the column efficiency is not less than 4500 theoretical plates and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure—
Chromatograph equal volumes (about 20 µL) of the
Assay preparation and the
Standard preparation, record the chromatograms, and measure the peak responses due to fluocinonide. Calculate the quantity, in mg, of fluocinonide (C
26H
32F
2O
7) in the portion of Cream taken by the formula:
0.1C(rU / rS),
in which
C is the concentration, in µg per mL, of
USP Fluocinonide RS in the
Standard preparation; and
rU and
rS are the peak responses due to fluocinonide obtained from the
Assay preparation and the
Standard preparation, respectively.
