Assay—
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 C
15H
24N
2O
2 in the portion of Cream taken by the formula:
(264.36/300.82)(C)(AU / AS),
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.
197U
:
Assay preparation compared to the Standard preparation from the Assay.