Identification—
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 not more than +0.01
(
distinction from dexchlorpheniramine maleate).
Assay—
Transfer 10 mL of Oral Solution, accurately measured, to a separator. Transfer about 40 mg of
USP Chlorpheniramine Maleate RS, accurately weighed, to a 100-mL volumetric flask, dilute with water to volume, mix, and pipet 10 mL of this Standard solution into a separator similar to that containing the Oral Solution. Treat each solution as follows. Add 10 mL of sodium hydroxide solution (1 in 10), and extract with two 50-mL portions of solvent hexane. Combine the extracts in a second separator, wash with 10 mL of sodium hydroxide solution (1 in 250), and discard the washing. Extract the hexane solution with two 40-mL portions of dilute hydrochloric acid (1 in 100), collect the extracts in a 100-mL volumetric flask, add the same dilute acid to volume, and mix. Wash 50-mL portions of each solution, and of dilute hydrochloric acid (1 in 100), respectively, with three 30-mL portions of chloroform and then with 50 mL of solvent hexane, and discard the washings. Filter the acid phases through paper, discarding the first few mL of each filtrate, and determine the absorbances of the solutions obtained from the Oral Solution and the Standard solution in 1-cm cells at the wavelength of maximum absorbance at about 264 nm, with a suitable spectrophotometer, using the extracted acid as the blank. Calculate the quantity, in µg, of chlorpheniramine maleate (C
16H
19ClN
2·C
4H
4O
4) in each mL of the Oral Solution taken by the formula:
C(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Chlorpheniramine Maleate RS in the Standard solution; and
AU and
AS are the absorbances of the solutions from the Oral Solution and the Standard solution, respectively.
Chlorpheniramine Maleate Syrup
Ultraviolet Absorption 
197U
—