Solution: Dilute a portion of the Injectable Suspension with methanol to obtain a solution having a concentration of about 20 µg per mL.

(Official January 1, 2007)

Mobile solvent— Prepare a mixture of isooctane, tetrahydrofuran, and alcohol (89:10:8).

Standard preparation— Dissolve an accurately weighed quantity of USP Prednisolone Tebutate RS in a mixture of tetrahydrofuran and isooctane (1:1) to obtain a solution having a known concentration of about 1 mg per mL.

Assay preparation— Transfer to a separator an accurately measured volume, freshly mixed, of Injectable Suspension, equivalent to about 100 mg of prednisolone tebutate, and dilute with about 10 mL of water. Extract with three 25-mL portions of methylene chloride, filtering each portion through methylene chloride-washed cotton into a 100-mL volumetric flask. Add methylene chloride to volume, and mix. Pipet 10 mL of this solution into a 50-mL centrifuge tube, evaporate the methylene chloride on a steam bath just to dryness, cool, and dissolve the residue in 10.0 mL of tetrahydrofuran and isooctane (1:1). Filter through a 1-µm membrane filter.

Procedure— Introduce equal volumes, about 10 µL, of the Assay preparation and the Standard preparation into a high-pressure liquid chromatograph (see Chromatography 621), operated at room temperature, by means of a suitable microsyringe or sampling valve, adjusting the sample size and other operating parameters such that the peak obtained with the Standard preparation is about 0.6 full-scale. Typically, the apparatus is fitted with a 3.9-mm × 30-cm column containing packing L3 and is equipped with an UV detector capable of monitoring absorption at 254 nm and a suitable recorder. In a suitable chromatogram, the coefficient of variation for five replicate injections of a single specimen is not more than 3.0%. Measure the height of the peaks, at identical retention times, obtained with the Assay preparation and the Standard preparation. Calculate the quantity, in mg, of C27H38O6, in the volume of Injectable Suspension taken by the formula: in which C is the concentration, in mg per mL, of USP Prednisolone Tebutate RS in the Standard preparation, and rU and rS are the peak heights obtained from the Assay preparation and the Standard preparation, respectively.