A: Dilute a volume of Injection, equivalent to about 50 mg of bupivacaine hydrochloride, with 0.01 N hydrochloric acid to 25 mL, and proceed as directed under Identification—Organic Nitrogenous Bases 181, beginning with “Transfer the liquid to a separator.” The Injection meets the requirements of the test.

B: The retention time of the bupivacaine peak in the chromatogram of the Assay preparation corresponds to that of the bupivacaine peak in the chromatogram of the Standard preparation, as obtained in the Assay.

(Official January 1, 2007)

pH 6.8 Phosphate buffer— Dissolve 1.94 g of monobasic potassium phosphate and 2.48 g of dibasic potassium phosphate in 1000 mL of water. Adjust, if necessary, with 1 N potassium hydroxide or 1 M phosphoric acid to a pH of 6.8.

Mobile phase— Prepare a fresh solution of acetonitrile and pH 6.8 Phosphate buffer (65:35). Adjust, if necessary, with 1 M phosphoric acid to a pH of 7.7 ± 0.2. Filter the solution through a membrane filter of 1-µm or finer porosity, and degas.

Internal standard solution— Prepare a solution of dibutyl phthalate in methanol containing about 1.3 mg per mL.

Standard preparation— Dissolve about 50 mg of USP Bupivacaine Hydrochloride RS, accurately weighed, in 10.0 mL of water, using sonication if necessary, in a 100-mL volumetric flask. Add 10 mL of Internal standard solution, dilute with methanol to volume, and mix.

Assay preparation— Transfer an accurately measured volume of Injection, equivalent to about 50 mg of bupivacaine hydrochloride, to a 100-mL volumetric flask, add 10.0 mL of Internal standard solution, dilute with methanol to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 263-nm detector and a 4-mm × 30-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph three replicate injections of the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation of the ratios of the bupivacaine hydrochloride peak to the dibutyl phthalate peak is not more than 1.0%, and the resolution R, factor, between bupivacaine hydrochloride and dibutyl phthalate is not less than 2.0.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 1.2 for dibutyl phthalate and 1.0 for bupivacaine hydrochloride. Calculate the quantity, in mg, of C18H28N2O·HCl in the volume of Injection taken by the formula: in which W is the weight, in mg, of USP Bupivacaine Hydrochloride RS, calculated on the anhydrous basis, in the Standard preparation, and RU and RS are the ratios of the peak responses of bupivacaine hydrochloride to those of the internal standard obtained from the Assay preparation and the Standard preparation, respectively.