Identification—
Treat 25mLof Syrup as directed in the
Assay,ending with “using a current of air only.”Dissolve the residue in 2.5mLof carbon disulfide,filter through paper if necessary,and determine the IRabsorption spectrum as directed under
Identification—Organic Nitrogenous Bases á181ñ,obtaining the spectrum of
USP Promethazine Hydrochloride RSas directed:the Syrup meets the requirements of the test.
Assay—
[NOTE—Use low-actinic glassware in this assay.
]Transfer an accurately measured volume of Syrup,equivalent to about 25mg of promethazine hydrochloride,to a 250-mLseparator.Add 10mLof ammonium hydroxide,and extract the promethazine base with six 40-mLportions of chloroform.Wash the combined chloroform extracts with 25mLof dilute hydrochloric acid (1in 9).Wash the acid solution with 25mLof chloroform,and add the washings to the main chloroform extract.Evaporate the chloroform extract on a steam bath,with the aid of a current of air,to a volume of 5to 10mL,and finally evaporate,using only a current of air,to dryness.Dissolve the residue,with slight warming,in dilute sulfuric acid (1in 100),and transfer to a 500-mLvolumetric flask with the aid of additional acid.Cool,add dilute sulfuric acid (1in 100)to volume,mix,and filter,rejecting the first half of the filtrate.Dissolve an accurately weighed quantity of
USP Promethazine Hydrochloride RSin dilute sulfuric acid (1in 100),and dilute quantitatively and stepwise with the dilute acid to obtain a Standard solution having a known concentration of about 50µg per mL.Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 298nm,with a suitable spectrophotometer,using dilute sulfuric acid (1in 100)as the blank.Calculate the quantity,in mg,of C
17H
20N
2S·HCl in each mLof the Syrup taken by the formula:
500(C/V)(AU/AS),
in which
Cis the concentration,in mg per mL,of
USP Promethazine Hydrochloride RSin the Standard solution;
Vis the volume,in mL,of Syrup taken;and
AUand
ASare the absorbances of the solution from the Syrup and the Standard solution,respectively.