NOTE—Throughout the following procedures,protect test or assay specimens,the Reference Standard,and solutions containing them,by conducting the procedures without delay,under subdued light,or using low-actinic glassware.

Palladium chloride solution— Add 5mLof hydrochloric acid to a beaker containing 500mg of palladium chloride.Warm on a steam bath to obtain a complete solution.Slowly add 200mLof hot water.(If necessary,continue warming and add additional hydrochloric acid to maintain complete solution.)Transfer the solution to a 500-mLvolumetric flask,and dilute with water to volume.To 50mLof this solution add 250mLof 2Msodium acetate,and adjust with hydrochloric acid to a pHof 4.0.Transfer the solution to a 500-mLvolumetric flask,dilute with water to volume,and mix.

Standard preparation— Using an accurately weighed quantity of USP Promethazine Hydrochloride RS,prepare a solution in 0.05Nhydrochloric acid containing about 0.1mg in each mL.Protect the solution from light.

Assay preparation— Weigh 10Suppositories and calculate the average.Carefully melt them,avoiding the use of excessive heat,and mix.Add 30mLof hexanes to an accurately weighed portion,equivalent to about 50mg of promethazine hydrochloride.Warm gently to dissolve,and transfer to a low-actinic separator.Rinse the transfer container with several small portions of the hexanes and 0.05Nhydrochloric acid,and add the rinsings to the separator.Extract with five 20-mLportions of 0.05Nhydrochloric acid shaking gently to avoid emulsions.Drain through glass wool prewashed with 0.05Nhydrochloric acid.Collect in a 500-mLlow-actinic volumetric flask.Rinse the glass wool with additional 0.05Nhydrochloric acid,dilute the combined filtrate with 0.05Nhydrochloric acid to volume,and mix.

Procedure— Pipet 2.0mLof the Standard preparation,Assay preparation,and 0.05Nhydrochloric acid into separate test tubes.Add 3.0mLof Palladium chloride solutionto each,and mix.Concomitantly determine the absorbances of the Standard preparationand the Assay preparationin 1-cm cells at the wavelength of maximum absorbance at about 450nm,with a suitable spectrophotometer,using the hydrochloric acid-palladium chloride solution as the reagent blank in the reference cell.Calculate the quantity,in mg,of C17H20N2S·HCl in the portion of Suppositories taken by the formula: in which Cis the concentration,in mg per mL,of USP Promethazine Hydrochloride RSin the Standard preparation,and AUand ASare the absorbances of the solutions from the Assay preparationand the Standard preparation,respectively.