Chromatographic purity
Dissolve a suitable quantity of Dibucaine Hydrochloride, accurately weighed, in chloroform to obtain a
Test solution having a concentration of 40.0 mg per mL. Dissolve a suitable quantity of
USP Dibucaine Hydrochloride RS, accurately weighed, in chloroform to obtain a
Standard solution having a known concentration of about 40 mg per mL. Dilute portions of this solution quantitatively and stepwise with chloroform to obtain three
Comparison solutions having concentrations of 40, 120, and 200 µg per mL (0.1%, 0.3%, and 0.5%) of the
Standard solution, respectively. Apply separate 5-µL portions of the five solutions to the starting line of a suitable thin-layer chromatographic plate (see
Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Develop the chromatogram in a solvent system consisting of a mixture of toluene, acetone, methanol, and ammonium hydroxide (50:30:5:1) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the chamber, mark the solvent front, and air-dry. Spray the plate heavily with a 1 in 200 solution of potassium dichromate in dilute sulfuric acid (1 in 5). Place the plate in an oven at 140
for 10 minutes, and view under short-wavelength UV light: the principal spot obtained from the
Test solution corresponds in
RF value, color, and intensity to that obtained from the
Standard solution; the sum of the intensities of any secondary spots, if present in the chromatogram of the
Test solution, corresponds to not more than 1.0%, and the intensity of any secondary spot does not exceed 0.5% of that of the principal spot in the chromatogram of the
Standard solution on the basis of comparison with the spots obtained from the
Comparison solutions.
Assay
Mobile phase, Solvent mixture, Standard preparation, and Chromatographic system
Proceed as directed in the
Assay under
Dibucaine.
Assay preparation
Transfer about 100 mg of Dibucaine Hydrochloride, accurately weighed, to a 100-mL volumetric flask, add Solvent mixture to volume, and mix. Pass through a suitable filter having a 0.5-µm or finer porosity.
Procedure
Proceed as directed for
Procedure in the
Assay under
Dibucaine. Calculate the quantity, in mg, of C
20H
29N
3O
2·HCl in the portion of Dibucaine Hydrochloride taken by the formula:
100C(rU / rS)
in which
C is the concentration, in mg per mL, of
USP Dibucaine Hydrochloride RS in the
Standard preparation; and
rU and
rS are the responses of the dibucaine peaks obtained from the
Assay preparation and the
Standard preparation, respectively.