A: Evaporate the remaining extract from the Assayon a steam bath to a small volume,then transfer it to a smaller,more suitable vessel,and evaporate just to the point where hexane vapors are no longer perceptible.Transfer the oily residue,with the aid of four 3-mLportions of dimethylformamide,to a suitable glass-stoppered graduated cylinder,dilute with dimethylformamide to 15.0mL,and mix:the optical rotation of the solution so obtained,in a 100-mm tube,after correcting for the blank,is between +0.06and +0.11(distinction from chlorpheniramine maleate).

B:Ultraviolet Absorption á197Uñ: Assay preparationcompared to Standard preparationfrom Assay.

Standard preparation— Transfer about 40mg of USP Dexchlorpheniramine Maleate RS,accurately weighed,to a 100-mLvolumetric flask,add water to volume,and mix.Transfer 10.0mLof this solution to a separator,adjust with 1Nsodium hydroxide to a pHof 11,and cool.Extract with two 50-mLportions of solvent hexane,shaking each portion for 2minutes before separating the phases,and combining the hexane extracts in a second separator.Extract the hexane solution with two 40-mLportions of dilute hydrochloric acid (1in 120),combine the acid extracts in a 100-mLvolumetric flask,add dilute hydrochloric acid (1in 120)to volume,and mix.Filter the solution into a glass-stoppered conical flask,discarding the first few mLof the filtrate.The concentration of USP Dexchlorpheniramine Maleate RSin the Standard preparationis about 40µg per mL.

Assay preparation— Transfer an accurately measured volume of Syrup,equivalent to about 40mg of dexchlorpheniramine maleate,to a 250-mLseparator,using a pipet calibrated “to contain”the required volume.Rinse the pipet with small portions of water,add the rinsings to the separator,adjust with 1Nsodium hydroxide to a pHof 11,and cool.Extract with five 70-mLportions of solvent hexane,combine the hexane extracts in a 500-mLseparator,and wash the hexane solution with two 10-mLportions of sodium hydroxide solution (1in 250).Extract the combined alkaline washings with two 20-mLportions of solvent hexane,and add these extracts to the bulk of the alkali-washed hexane solution.Filter the hexane solution through a pledget of cotton that previously has been saturated with solvent hexane into a 500-mLvolumetric flask,rinse the separator with portions of solvent hexane,pass the rinsings through the filter to add to volume,and mix.Transfer 50.0mLof this solution to a separator (retain the remaining extract for Identificationtest A),and proceed as directed for Standard preparation,beginning with “Extract the hexane solution.”

Procedure— Concomitantly determine the absorbances of the Standard preparationand the Assay preparationin 1-cm cells at the wavelength of maximum absorbance at about 264nm,using dilute hydrochloric acid (1in 120)as the blank.Calculate the quantity,in mg,of C16H19ClN2·C4H4O4in each mLof the Syrup taken by the formula: in which Cis the concentration,in µg per mL,of USP Dexchlorpheniramine Maleate RSin the Standard preparation;Vis the volume,in mL,of Syrup taken;and AUand ASare the absorbances of the Assay preparationand the Standard preparation,respectively.