Identification—
The UVabsorption spectrum of the solution employed for measurement of absorbance in the
Assayexhibits maxima and minima at the same wavelengths as that of the solution of
USP Dibucaine Hydrochloride RSprepared as directed in the
Assay.
Assay—
Mobile phase and Chromatographic system—
Proceed as directed in the
Assayunder
Dibucaine.
Standard preparation—
Transfer about 55mg of
USP Dibucaine Hydrochloride RS,accurately weighed,to a 50-mLvolumetric flask,add 24.0mLof 0.1Nhydrochloric acid,and swirl to dissolve.Dilute with a mixture of methanol and 1.0Nhydrochloric acid (13:12)to volume,and mix.Transfer 10.0mLof this solution to a 50-mLvolumetric flask,dilute with methanol to volume,and mix.Filter through a suitable filter of 0.5-µm or finer porosity.
Assay preparation—
Weigh accurately a portion of Ointment,equivalent to about 50mg of dibucaine,transfer to a separator containing 50mLof ether,and mix to dissolve.Extract successively with 50-mL,40-mL,and 30-mLportions of 0.1Nhydrochloric acid,combining the extracts in a 250-mLvolumetric flask.Dilute with methanol to volume,and mix.Filter through a suitable filter of 0.5-µm or finer porosity.
Procedure—
Separately inject equal volumes (about 10µL)of the
Standard preparationand the
Assay preparationinto the chromatograph,record the chromatograms,and measure the area responses for the major peaks.Calculate the quantity,in mg,of dibucaine (C
20H
29N
3O
2)in the portion of Ointment taken by the formula:
(343.46/379.93)(250C)(rU/rS),
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 area responses of the dibucaine peaks obtained from the
Assay preparationand the
Standard preparation,respectively.