(Official January 1, 2007)

Standard preparation— Dissolve a suitable quantity of USP Pramoxine Hydrochloride RS, accurately weighed, in 0.5 N sulfuric acid, and dilute quantitatively with the same solvent to obtain a solution having a known concentration of about 150 µg per mL.

Assay preparation— [NOTE—If emulsions form, 2 to 5 mL of alcohol may be added to separate the phases.] Transfer an accurately weighed quantity of Jelly, equivalent to about 15 mg of pramoxine hydrochloride, to a small beaker, and dissolve the Jelly in 0.1 N sulfuric acid, using four 5-mL portions, warming each portion on a steam bath, and transferring to a 125-mL separator. Shake the separator vigorously after each transfer to complete dissolution of the Jelly. To the cooled solution in the separator add 20 mL of ether, shake carefully, and proceed as directed for Assay Preparation under Salts of Organic Nitrogenous Bases 501, beginning with “filter the acid phase into a second 125-mL separator,” except to combine the final 0.5 N sulfuric acid extracts in a 100-mL volumetric flask, dilute with the acid to volume, and mix.

Procedure— Proceed as directed under Salts of Organic Nitrogenous Bases 501, diluting 20.0 mL each of the Standard preparation and the Assay preparation with 0.5 N sulfuric acid to 50.0 mL, and determining the absorbances at the wavelength of maximum absorbance at about 286 nm. Calculate the quantity, in mg, of C17H27NO3·HCl in the portion of Jelly taken by the formula: in which C is the concentration, in µg per mL, of USP Pramoxine Hydrochloride RS in the Standard preparation.