A: The relative retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay for fluorometholone acetate.

B: Allow the Ophthalmic Suspension to settle, and decant 1 mL of the supernatant into a test tube. Add 0.1 g of sodium sulfate, mix, and centrifuge: the clear supernatant so obtained meets the requirements for Identification test A under Tobramycin.

(Official January 1, 2007)

Mobile phase , 2,4-Dinitrofluorobenzene reagent, Tris(hydroxymethyl)aminomethane reagent, Standard preparation, Resolution solution, and Chromatographic system—Proceed as directed in the Assay under Tobramycin.

Assay preparation— Transfer an accurately weighed portion of Ophthalmic Suspension, equivalent to about 4.5 mg of tobramycin, to a 50-mL volumetric flask, dilute with water to volume, and mix.

Derivatization procedure— Proceed as directed in the Assay under Tobramycin, except to use 10.0 mL of Assay preparation instead of 4.0 mL.

Procedure— Proceed as directed in the Assay under Tobramycin. Calculate the quantity of tobramycin (C18H37N5O9), in mg, in the portion of Ophthalmic Suspension taken by the formula: in which the terms are as defined therein.

Mobile phase— Prepare a suitable mixture of acetonitrile and water (50:50). Pass through a filter having a 1-µm or finer porosity, and degas. Make adjustments if necessary (see System Suitability under Chromatography 621). Reduce the proportion of acetonitrile to increase the retention time of fluorometholone acetate.

Resolution solution— Prepare a solution in acetonitrile containing 0.04 mg each of USP Fluorometholone RS and USP Fluorometholone Acetate RS per mL.

Standard preparation— Prepare a solution of USP Fluorometholone Acetate RS in acetonitrile having a known concentration of about 0.04 mg 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 fluorometholone acetate, to a 25-mL volumetric flask, dilute with acetonitrile to volume, and mix. Transfer 4.0 mL of this solution to a 10-mL volumetric flask, dilute with acetonitrile to volume, and mix. Transfer a portion of this solution to a test tube, and centrifuge for about 15 minutes. Use the clear supernatant.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 25-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the Resolution solution, and record the peak areas as directed for Procedure: the relative retention times are about 0.7 for fluorometholone and 1.0 for fluorometholone acetate; and the resolution, R, between fluorometholone and fluorometholone acetate is not less than 2.0. Chromatograph the Standard preparation, and record the areas as directed for Procedure: the capacity factor, k¢, determined from fluorometholone acetate peak is between 1.0 and 5.0; the column efficiency is not less than 1000 theoretical plates; the tailing factor is not more than 1.35; 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 peak areas. Calculate the quantity, in mg, of fluorometholone acetate (C24H31FO5) in each mL of Ophthalmic Suspension taken by the formula: in which C is the concentration, in mg per mL, of USP Fluorometholone Acetate RS in the Standard preparation; V is the volume, in mL, of Ophthalmic Suspension taken; and rU and rS are the fluorometholone acetate peak areas obtained from the Assay preparation and the Standard preparation, respectively.