Internal standard solution— Dissolve fluoxymesterone in acetonitrile to obtain a solution containing about 100 µg per mL.

Mobile solvent— Prepare a solution containing butyl chloride, water-saturated butyl chloride, tetrahydrofuran, methanol, and glacial acetic acid (95:95:14:7:6).

Standard preparation— Dissolve a suitable quantity of USP Fluorometholone RS, accurately weighed, in Internal standard solution to obtain a solution having a known concentration of about 50 µg per mL.

Assay preparation— Transfer an accurately weighed quantity of Cream, equivalent to about 1 mg of fluorometholone, into a suitable container, add 20.0 mL of Internal standard solution, and mix.

Procedure— Treat 20.0 mL each of the Standard preparation and the Assay preparation in the following manner. To each add 10.0 mL of hexane, and shake for about 15 minutes, then allow the layers to separate, and centrifuge, if necessary. Using a suitable microsyringe or sampling valve, inject equal volumes of lower (acetonitrile) layers obtained from the Standard preparation and the Assay preparation into a suitable high-pressure liquid chromatograph (see Chromatography 621) of the general type equipped with a detector for monitoring UV light absorption at about 254 nm, equipped with a suitable recorder, capable of providing column pressure up to about 1000 psi. The instrument contains a 4-mm × 30-cm stainless steel column that contains packing L3. In a suitable chromatogram, the resolution factor, R (see Chromatography 621), is not less than 2.4 between peaks for fluorometholone and the internal standard, and the lowest and highest peak area ratios (RS) of three replicate injections of the Standard preparation agree within 2.0%. Calculate the quantity, in mg, of fluorometholone (C22H29FO4) in the portion of Cream taken by the formula: in which C is the concentration, in mg per mL, of USP Fluorometholone RS in the Standard preparation; and RU and RS are the peak area ratios of the fluorometholone peak and the internal standard peak obtained from the Assay preparation and the Standard preparation, respectively.