A: Tablets meet the requirements under Identification—Organic Nitrogenous Bases 181.

B: Shake a quantity of finely powdered Tablets, equivalent to about 150 mg of dexchlorpheniramine maleate, with 100 mL of 1 N acetic acid for 10 minutes, filter through a sintered-glass funnel into a suitable vessel, adjust the filtrate with sodium hydroxide solution (1 in 10) to a pH of 11, and extract the solution with six 100-mL portions of solvent hexane, filtering each hexane extract using suitable means to effect separation of the hexane layer from the aqueous layer. Concentrate the combined extracts on a steam bath to a small volume, transfer 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, mix, and centrifuge if necessary: the optical rotation of the solution so obtained, in a 100-mm tube, after correcting for the blank, is between +0.24 and +0.35 (distinction from chlorpheniramine maleate).

Medium: water; 500 mL.

Apparatus 2: 50 rpm.

Time: 45 minutes.

Internal standard solution— Prepare a solution of Dexbrompheniramine Maleate in water having a final concentration of about 90 µg per mL.

Standard solution— Dissolve an accurately weighed quantity of USP Dexchlorpheniramine Maleate RS in water, and dilute quantitatively and stepwise with water to obtain a stock solution having a known concentration of about 12.5 µg per mL. Pipet 5 mL of this stock solution into a 50-mL centrifuge tube, add 10.0 mL of water and 1.0 mL of Internal standard solution, and mix. Adjust with sodium hydroxide solution (1 in 2) to a pH of 11 ± 0.1, and add 3.0 mL of chromatographic solvent hexane. Insert the stopper in the tube, shake by mechanical means for 3 minutes, centrifuge, and use the clear supernatant hexane layer.

Test solution— Pipet 15 mL of a portion of the solution under test into a 50-mL centrifuge tube, add 1.0 mL of Internal standard solution, and mix. Proceed as directed for Standard solution, beginning with “Adjust with sodium hydroxide solution (1 in 2).”

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and a 2-mm × 1.8-m column that contains a packing consisting of 1.2 percent phase G16 and 0.5 percent potassium hydroxide on support S1AB. The carrier gas is helium maintained at a flow rate of about 60 mL per minute. The column, injector, and detector temperatures are maintained at 205, 250, and 250, respectively. Chromatograph replicate injections of the Standard solution, and record the peak response as directed for Procedure: the relative retention times are about 0.7 for dexchlorpheniramine and 1.0 for dexbrompheniramine; the resolution, R, between dexchlorpheniramine and dexbrompheniramine is not less than 1.9; and the relative standard deviation is not more than 2.0%.

Procedure— Separately inject equal volumes (about 2 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the amount of C16H19ClN2·C4H4O4 dissolved by comparison of the peak response ratios.

Tolerances— Not less than 75% (Q) of the labeled amount of C16H19ClN2·C4H4O4 is dissolved in 45 minutes.

Standard preparation— Prepare as directed in the Assay under Dexchlorpheniramine Maleate Oral Solution. The concentration of USP Dexchlorpheniramine Maleate RS in the Standard preparation is about 40 µg per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 8 mg of dexchlorpheniramine maleate, to a 250-mL separator, mix with 50 mL of water for 10 minutes, adjust with sodium hydroxide solution (1 in 10) to a pH of 11, and cool to room temperature. Extract the mixture with two 75-mL portions of solvent hexane, and combine the extracts in a second separator. Extract the solvent hexane solution with three 50-mL portions of dilute hydrochloric acid (1 in 120), combining the acid extracts in a 200-mL volumetric flask. Add dilute hydrochloric acid (1 in 120) to volume, and mix.

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