A: Infrared Absorption 197K.

B: Prepare a test solution in chloroform containing 10 mg per mL. Separately apply 5 µL of this solution and 5 µL of a Standard solution of USP Rimexolone RS in chloroform containing 10 mg per mL to a thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of a mixture of chloroform and methanol (19:1) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate. Observe the plate under short-wavelength UV light: the RF value of the principal spot obtained from the test solution corresponds to that of the principal spot obtained from the Standard solution.

Test solution: 20 mg per mL, in chloroform.

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

Test solution— Proceed as directed for Assay preparation in the Assay.

Procedure— Inject a volume (about 20 µL) of the Test solution into the chromatograph, record the chromatogram, and measure the peak responses. Calculate the percentage of each impurity in the portion of Rimexolone taken by the formula: in which ri is the peak response for each impurity, and rs is the sum of the responses of all of the peaks: not more than 1.0% of any individual impurity is found, and the sum of all impurities is not more than 2.0%.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and water (6:4). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Rimexolone RS in methanol, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.2 mg per mL.

Assay preparation— Transfer about 25 mg of Rimexolone, accurately weighed, to a 25-mL volumetric flask, dissolve in and dilute with methanol to volume. Transfer 5.0 mL of this solution to a 25 mL-volumetric flask, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 242-nm detector and a 4.6-mm × 25-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 capacity factor, k¢, is not less than 1.5, the column efficiency is not less than 3000 theoretical plates, the tailing factor is not more than 2.0, and the relative standard deviation for replicate injections is not more than 2.0%.

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 C24H34O3 in the portion of Rimexolone taken by the formula: in which C is the concentration, in mg per mL, of USP Rimexolone RS in the Standard preparation, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.