A: It meets the requirements for neomycin under Thin-Layer Chromatographic Identification Test 201BNP.

B: The Assay preparation, prepared as directed in the Assay for dexamethasone phosphate, meets the requirements for the Identification test under Dexamethasone Sodium Phosphate Cream.

(Official January 1, 2007)

0.002 M Phosphate buffer— Dissolve 0.57 g of dibasic sodium phosphate in water to obtain 2000 mL of solution.

0.10 M Phosphate buffer— Dissolve 13.80 g of monobasic sodium phosphate in water to obtain 1000 mL of solution.

Mobile phase— Prepare a suitable filtered mixture of 0.10 M phosphate buffer and acetonitrile (690:310). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Dexamethasone Phosphate RS in 0.002 M Phosphate buffer to obtain a solution having a known concentration of about 125 µg per mL. Transfer 20.0 mL of this solution to a 100-mL volumetric flask, dilute with 0.002 M Phosphate buffer to volume, mix, and pass through a suitable filter of 1 µm or finer porosity. This solution contains about 25 µg per mL.

Assay preparation— Transfer an accurately measured volume of Ophthalmic Solution, equivalent to about 2.5 mg of dexamethasone phosphate, to a 100-mL volumetric flask, slowly dilute with 0.002 M Phosphate buffer to volume, mix, and pass through a suitable filter of 1 µm or finer porosity.

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 L1. The flow rate is about 1.3 mL per minute. Chromatograph the Standard preparation, and measure the peak responses as directed under Procedure: the column efficiency is not less than 2000 theoretical plates, the capacity factor, k¢, for the dexamethasone phosphate peak is not less than 1.05, and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— [NOTE—Use peak areas where peak responses are indicated.] Separately inject equal volumes (about 50 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the quantity, in mg, of dexamethasone phosphate (C22H30FO8P), in each mL of the Ophthalmic Solution taken by the formula: in which C is the concentration, in µg per mL, of USP Dexamethasone Phosphate RS in the Standard preparation; V is the volume, in mL, of Ophthalmic Solution taken; and rU and rS are the dexamethasone phosphate peak responses obtained from the Assay preparation and the Standard preparation, respectively.