A: Tablets meet the requirements underIdentification—Organic Nitrogenous Bases á181ñ.

B: Shake a quantity of finely powdered Tablets,equivalent to about 150mg of dexchlorpheniramine maleate,with 100mLof 1Nacetic acid for 10minutes,filter through a sintered-glass funnel into a suitable vessel,adjust the filtrate with sodium hydroxide solution (1in 10)to a pHof 11,and extract the solution with six 100-mLportions 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-mLportions of dimethylformamide,to a suitable glass-stoppered graduated cylinder,dilute with dimethylformamide to 15.0mL,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 +0.24and +0.35(distinction from chlorpheniramine maleate).

Medium: water;500mL.

Apparatus 2: 50rpm.

Time: 45minutes.

Procedure— Determine the amount of C16H19ClN2·C4H4O4dissolved,using the following procedure.

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

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

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

Chromatographic system(see Chromatography á621ñ)— The gas chromatograph is equipped with a flame-ionization detector and a 2-mm ×1.8-m column that contains a packing consisting of 1.2percent phase G16and 0.5percent potassium hydroxide on support S1AB.The carrier gas is helium maintained at a flow rate of about 60mLper minute.The column,injector,and detector temperatures are maintained at 205,250,and 250,respectively.Chromatograph replicate injections of theStandard solution,and record the peak response as directed forProcedure:the relative retention times are about 0.7for dexchlorpheniramine and 1.0for 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 2µL)of theStandard solutionand theTest solutioninto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the amount of C16H19ClN2·C4H4O4dissolved by comparison of the peak response ratios.

Tolerances— Not less than 75%(Q)of the labeled amount of C16H19ClN2·C4H4O4is dissolved in 45minutes.

Standard preparation— Prepare as directed in theAssay underDexchlorpheniramine Maleate Syrup(Oral Solution,Official June 1,2005).The concentration of USP Dexchlorpheniramine Maleate RSin theStandard preparation is about 40µg per mL.

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

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