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

B: Place a volume of Injection, equivalent to about 30 mg of dibucaine hydrochloride, in a suitable evaporating dish, and concentrate on a steam bath to a volume of about 10 mL. Transfer the solution to a separator, render distinctly alkaline with 1 N sodium hydroxide, and extract with four 20-mL portions of ether. Wash the combined ether extracts with 5 mL of water, discarding the washing. Evaporate the ether extracts with the aid of a current of air to dryness, and dry the residue over phosphorus pentoxide for 3 hours: the dibucaine so obtained melts between 62 and 65.

Mobile phase and Chromatographic system— Proceed as directed in the Assay under Dibucaine.

Standard preparation— Transfer about 50 mg of USP Dibucaine Hydrochloride RS, accurately weighed, to a 100-mL volumetric flask, add an accurately measured volume of water, equivalent to the volume of Injection taken to prepare the Assay preparation, dilute with methanol to volume, and mix. Where the Assay preparation is prepared in a 50-mL volumetric flask, transfer about 25 mg of USP Dibucaine Hydrochloride RS, accurately weighed, to a 100-mL volumetric flask, add an accurately measured volume of water, equivalent to twice the volume of Injection taken to prepare the Assay preparation, dilute with methanol to volume, and mix. Pass through a suitable filter having a 0.5-µm or finer porosity.

Assay preparation— Transfer an accurately measured volume of Injection, equivalent to about 50 mg of dibucaine, to a 100-mL volumetric flask. Dilute with methanol to volume, and mix. Where the Injection is labeled to contain 1 mg or less of dibucaine hydrochloride per mL, transfer an accurately measured volume of Injection, equivalent to about 13 mg of dibucaine hydrochloride, to a 50-mL volumetric flask, dilute with methanol to volume, and mix. Pass through a suitable filter having a 0.5-µm or finer porosity.

Procedure— Separately inject equal volumes (about 10 µL, or 20 µL where the concentration of dibucaine hydrochloride is about 0.25 mg per mL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the area responses for the major peaks. Calculate the quantity, in mg, of dibucaine hydrochloride (C20H29N3O2·HCl) in each mL of the Injection taken by the formula: in which C is the concentration, in mg per mL, of USP Dibucaine Hydrochloride RS in the Standard preparation; v is the volume, in mL, of the Assay preparation; V is the volume, in mL, of Injection taken; and rU and rS are the area responses of the dibucaine peaks obtained from the Assay preparation and the Standard preparation, respectively.