A: Evaporate the remaining extract from the Assay on 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-mL portions of dimethylformamide, to a suitable glass-stoppered graduated cylinder, dilute with dimethylformamide to 15.0 mL, and mix: the optical rotation of the solution so obtained, in a 100-mm tube, after correcting for the blank, is between +0.06 and +0.11 (distinction from chlorpheniramine maleate).

B: Ultraviolet Absorption 197U: Assay preparation compared to Standard preparation from Assay.

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

Assay preparation— Transfer an accurately measured volume of Oral Solution, equivalent to about 40 mg of dexchlorpheniramine maleate, to a 250-mL separator, 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 1 N sodium hydroxide to a pH of 11, and cool. Extract with five 70-mL portions of solvent hexane, combine the hexane extracts in a 500-mL separator, and wash the hexane solution with two 10-mL portions of sodium hydroxide solution (1 in 250). Extract the combined alkaline washings with two 20-mL portions 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-mL volumetric flask, rinse the separator with portions of solvent hexane, pass the rinsings through the filter to add to volume, and mix. Transfer 50.0 mL of this solution to a separator (retain the remaining extract for Identification test A), and proceed as directed for Standard preparation, beginning with “Extract the hexane solution.”

Procedure— Concomitantly determine the absorbances of the Standard preparation and the Assay preparation in 1-cm cells at the wavelength of maximum absorbance at about 264 nm, using dilute hydrochloric acid (1 in 120) as the blank. Calculate the quantity, in mg, of dexchlorpheniramine maleate (C16H19ClN2·C4H4O4) in each mL of the Oral Solution taken by the formula: in which C is the concentration, in µg per mL, of USP Dexchlorpheniramine Maleate RS in the Standard preparation; V is the volume, in mL, of Oral Solution taken; and AU and AS are the absorbances of the Assay preparation and the Standard preparation, respectively.