Test solution: 20 mg, undried, per mL, in chloroform.

Mobile phase and Chromatographic system— Prepare as directed in the Assay.

Test solution— Dissolve an accurately weighed quantity of Diflorasone Diacetate in water-saturated chloroform to obtain a solution having a concentration of about 6 mg per mL.

Procedure— Inject a volume (about 10 µL) of the Test solution into the chromatograph, record the chromatogram for a period equal to 5 times the retention time of the major peak, and measure the areas of all the peaks. Calculate the percentage of each impurity in the portion of Diflorasone Diacetate taken by the formula: in which ri is the peak area for each impurity; and rs is the sum of the areas of all the peaks: not more than 1.0% of any individual impurity is found; and not more than 2.0% of total impurities is found.

Mobile phase— Prepare a solution containing a mixture of water-saturated n-butyl chloride, water-saturated methylene chloride, glacial acetic acid, and tetrahydrofuran (350:125:15:10). Make adjustments if necessary (see System Suitability under Chromatography 621).

Internal standard solution— Using water-saturated chloroform, prepare a solution of isoflupredone acetate containing about 0.04 mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Diflorasone Diacetate RS in Internal standard solution to obtain a solution having a known concentration of about 33 µg per mL.

Assay preparation— Transfer about 15 mg of Diflorasone Diacetate, accurately weighed, to a 500-mL volumetric flask. Add Internal standard solution to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 10-cm column that contains 3-µm packing L3. The flow rate is about 2.5 mL per minute. Chromatograph the Standard preparation, and record the peak areas as directed for Procedure: the resolution, R, between the analyte and internal standard peaks is not less than 12; and the relative standard deviation for not less than four replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the areas for the major peaks. The relative retention times are about 1.0 for diflorasone diacetate and 2.4 for the internal standard. Calculate the quantity, in mg, of C26H32F2O7 in the portion of Diflorasone Diacetate taken by the formula: in which C is the concentration, in µg per mL, of USP Diflorasone Diacetate RS in the Standard preparation; and RU and RS are the ratios of the peak areas for diflorasone diacetate and the internal standard areas obtained from the Assay preparation and the Standard preparation, respectively.