Mobile phase— Prepare 0.01 M of dibasic ammonium phosphate in water, and adjust with phosphoric acid to a pH of 3.0. Prepare a filtered and degassed mixture of this solution and acetonitrile (70:30). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Tetracaine Hydrochloride RS in water to obtain a solution having a known concentration of about 0.1 mg per mL.

Assay preparation— Transfer an accurately measured volume of Ophthalmic Solution, equivalent to about 10 mg of tetracaine hydrochloride, to a 100-mL volumetric flask, dilute with water to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 280-nm detector and a 4.6-mm × 25-cm column containing packing L10. The flow rate is about 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 500 theoretical plates; the tailing factor for the analyte peak 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 10 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 C15H24N2O2·HCl in each mL of the Ophthalmic Solution taken by the formula: in which C is the concentration, in mg per mL, of USP Tetracaine Hydrochloride RS in the Standard preparation; V is the volume, in mL, of Ophthalmic Solution taken; and rU and rS are the tetracaine peak responses obtained from the Assay preparation and the Standard preparation, respectively.