pH 7.5 buffer— Dissolve 6.8 g of monobasic potassium phosphate in 1000 mL of water, add 5 mL of triethylamine, and adjust with 5 N potassium hydroxide to a pH of 7.5. Filter through a filter having a porosity of 0.5 µm or finer, and degas.

Mobile phase— Prepare a mixture of pH 7.5 buffer and acetonitrile (60:40). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Transfer about 25 mg of USP Proparacaine Hydrochloride RS, accurately weighed, to a 25-mL volumetric flask, dissolve in and dilute with water to volume, and mix. Transfer 5.0 mL of this stock solution to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix. [note—Use this solution within 6 hours.]

Assay preparation— Transfer an accurately measured volume of Ophthalmic Solution, equivalent to about 10 mg of proparacaine hydrochloride, to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix. [note—Use this solution within 6 hours.]

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 270-nm detector and a 4.6-mm × 15-cm column that contains 5-µm spherical packing L10. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor is not more than 1.5, the column efficiency is not less than 3000 theoretical plates, 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 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 C16H26N2O3·HCl in each mL of the Ophthalmic Solution taken by the formula: in which C is the concentration, in mg per mL, of USP Proparacaine Hydrochloride RS in the Standard preparation, V is the volume, in mL, of Ophthalmic Solution taken, and rU and rS are the proparacaine peak responses obtained from the Assay preparation and the Standard preparation, respectively.