Assay—
Standard preparation—
Dissolve about 20 mg of
USP Tetracaine Hydrochloride RS, accurately weighed, in water to make 100.0 mL, and mix. Pipet 5 mL of this solution into a 100-mL volumetric flask, add 5 mL of dilute hydrochloric acid (1 in 200) and 10 mL of
Buffer No. 6, 10 percent, pH 6.0 (see
Phosphate Buffers 
81
), dilute with water to volume, and mix.
Assay preparation—
Transfer an accurately measured volume of Injection, equivalent to about 10 mg of tetracaine hydrochloride, to a separator, dilute with water to about 50 mL, and render alkaline by the addition of 5 mL of
sodium carbonate TS. Extract immediately with two 50-mL portions of ether, collecting the extracts in a separator. Wash the ether extracts with 20 mL of water, discarding the wash solution, and extract the ether solution with two 20-mL portions and one 5-mL portion of dilute hydrochloric acid (1 in 200), collecting the extracts in a 50-mL volumetric flask. Dilute with water to volume, and mix. Transfer a 5.0-mL aliquot to a 100-mL volumetric flask, add 10 mL of
Buffer No. 6, 10 percent, pH 6.0 (see
Phosphate Buffers and Other Solutions under
Antibiotics—Microbial Assays 81), dilute with water to volume, and mix.
Procedure—
Concomitantly determine the absorbances of the
Assay preparation and the
Standard preparation at the wavelength of maximum absorbance at about 310 nm, with a suitable spectrophotometer, using water as the blank. Calculate the quantity, in mg, of tetracaine hydrochloride (C
15H
24N
2O
2·HCl) in the volume of Injection taken by the formula:
C(AU / AS),
in which
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.
Assay for dextrose—
Determine the angular rotation of the Injection in a suitable polarimeter tube (see
Optical Rotation 781). Calculate the percentage (g per 100 mL) of dextrose (C
6H
12O
6) in the portion of Injection taken by the formula:
(100/52.9)AR,
in which 100 is the percentage; 52.9 is the midpoint of the specific rotation range for anhydrous dextrose, in degrees;
A is 100 mm divided by the length of the polarimeter tube, in mm; and
R is the observed rotation, in degrees.
