pH 6 Acetate buffer— Dissolve 250 g of sodium acetate in about 500 mL of water in a 1000-mL volumetric flask, add 5.0 mL of glacial acetic acid, dilute with water to volume, and mix.

Standard preparation— Transfer about 25 mg of USP Tetracaine Hydrochloride RS, accurately weighed, to a 100-mL volumetric flask, dissolve in isopropyl alcohol, add isopropyl alcohol to volume, and mix. Transfer 2.0 mL of this solution to another 100-mL volumetric flask, add 2.0 mL of pH 6 Acetate buffer, dilute with isopropyl alcohol to volume, and mix. The concentration of USP Tetracaine Hydrochloride RS in the Standard preparation is about 5 µg per mL.

Assay preparation— Transfer an accurately weighed portion of Cream, equivalent to about 4.5 mg of tetracaine, to a 50-mL beaker, add 25 mL of isopropyl alcohol, and warm on a steam bath to dissolve the specimen completely. Transfer the solution with the aid of isopropyl alcohol to a 100-mL volumetric flask, dilute with isopropyl alcohol to volume, and mix. Transfer 10.0 mL of this solution to another 100-mL volumetric flask, add 2.0 mL of pH 6 Acetate buffer, dilute with isopropyl alcohol to volume, and mix.

Procedure— Concomitantly determine the absorbances of the Assay preparation and the Standard preparation in 1-cm cells at the wavelength of maximum absorbance at about 310 nm, with a suitable spectrophotometer, using a 1 in 50 solution of pH 6 Acetate buffer in isopropyl alcohol as the blank. Calculate the quantity, in mg, of C15H24N2O2 in the portion of Cream taken by the formula: in which 264.36 and 300.82 are the molecular weights of tetracaine and tetracaine hydrochloride, respectively; C is the concentration, in µg per mL, of USP Tetracaine Hydrochloride RS in the Standard preparation; and AU and AS are the absorbances of the Assay preparation and the Standard preparation, respectively.