A: The IRabsorption spectrum of a mineral oil dispersion of it,previously dried,exhibits maxima only at the same wavelengths as that of a similar dispersion of the residue prepared by dissolving 30mg of USP Dibucaine Hydrochloride RSin 5mLof 0.5Nsodium hydroxide,extracting the resulting solution with 5mLof ether,evaporating the ether,and drying the residue over phosphorus pentoxide.

B: Ultraviolet Absorption á197Uñ—

Mobile phase— Dissolve 1.20g of sodium lauryl sulfate,0.20g of sodium acetate,and 2.0mLof triethylamine in 300mLof water.Adjust with glacial acetic acid to a pHof 5.6,add 700mLof methanol,mix,and filter through a suitable filter having a porosity of 0.5µm or finer.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Solvent mixture— Prepare a mixture of methanol and water (70:30).

Standard preparation— Dissolve an accurately weighed quantity of USP Dibucaine Hydrochloride RSin Solvent mixtureto obtain a solution having a known concentration of about 1mg per mL.Filter through a suitable filter having a porosity of 0.5µm or finer.

Assay preparation— Transfer about 90mg of Dibucaine,accurately weighed,to a 100-mLvolumetric flask,add Solvent mixtureto volume,and mix.Filter through a suitable filter having a porosity of 0.5µm or finer.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm ×30-cm column that contains packing L1.The flow rate is about 1.5mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the column efficiency,determined from the analyte peak,is not less than 1500theoretical plates,the tailing factor for the analyte peak is not more than 3.0,and the relative standard deviation for replicate injections is not more than 2%.

Procedure— [NOTE—Use peak areas where peak responses are indicated.]Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C20H29N3O2in the portion of Dibucaine taken by the formula: in which 343.46and 379.93are the molecular weights of dibucaine and dibucaine hydrochloride,respectively,Cis the concentration,in mg per mL,of USP Dibucaine Hydrochloride RSin the Standard preparation,and rUand rSare the responses of the dibucaine peaks obtained from the Assay preparationand the Standard preparation,respectively.