A: Filter a portion of Ophthalmic Suspension, freshly mixed but free from air bubbles, equivalent to about 60 mg of prednisolone acetate, discarding the filtrate. Wash the filter with about 10 mL of water, and dry at 105 for 3 hours: the IR absorption spectrum of a potassium bromide dispersion of the dried residue on the filter so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of USP Prednisolone Acetate RS.

B: The chromatogram of the Assay preparation obtained as directed in the Assay for prednisolone acetate exhibits a major peak for prednisolone acetate, the retention time of which corresponds to that exhibited in the chromatogram of the Standard preparation obtained as directed in the Assay for prednisolone acetate.

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

Internal standard solution— Prepare a solution of betamethasone in tetrahydrofuran containing 10 mg per mL. Dilute this solution with water-saturated chloroform, and mix to obtain a solution having a concentration of about 1 mg per mL.

Standard preparation— Dissolve about 5 mg of USP Prednisolone Acetate RS, accurately weighed, in 10.0 mL of Internal standard solution. Use sonication, if necessary, dilute with water-saturated chloroform to 200.0 mL, and mix to obtain a solution having a known concentration of about 25 µg per mL.

Assay preparation— Transfer an accurately measured volume of Ophthalmic Suspension, freshly mixed and free from air bubbles, equivalent to about 2.5 mg of prednisolone acetate, to a suitable container, add 5.0 mL of Internal standard solution and about 100 mL of water-saturated chloroform, and shake by mechanical means for about 15 minutes. Allow to separate for about 15 minutes, and use the clear chloroform layer as the Assay preparation.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 30-cm column that contains packing L3. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between the analyte and internal standard peaks is not less than 3.0, and the relative standard deviation for 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 responses for the major peaks. The relative retention times are about 1.6 for betamethasone and 1.0 for prednisolone acetate. Calculate the quantity, in mg, of prednisolone acetate (C23H30O6) in each mL of the Ophthalmic Suspension taken by the formula: in which C is the concentration, in µg per mL, of USP Prednisolone Acetate RS in the Standard preparation, V is the volume, in mL, of Ophthalmic Suspension taken, and RU and RS are the peak response ratios of prednisolone acetate to betamethasone obtained from the Assay preparation and the Standard preparation, respectively.