Medium: water;900mL.

Apparatus 2: 50rpm.

Time: 45minutes.

Procedure— Determine the amount of C17H21NO·C7H7ClN4O2dissolved by employing UVabsorption at the wavelength of maximum absorbance at about 276nm on filtered portions of the solution under test,suitably diluted with Dissolution Medium,if necessary,in comparison with a Standard solution having a known concentration of USP Dimenhydrinate RSin the same Medium.

Tolerances— Not less than 75%(Q)of the labeled amount of C17H21NO·C7H7ClN4O2is dissolved in 45minutes.

Ammonium bicarbonate solution,Diluent,Solution A,Solution B,Mobile phase,Internal standard solution,and Chromatographic system— Prepare as directed in the Assay.

Standard solution— Prepare as directed forStandard preparation in theAssay.

Test solution— Prepare as directed forAssay preparation in theAssay.

Procedure— Separately inject equal volumes (about 10µL)of theStandard solution and theTest solution into the chromatograph,record the chromatograms,and measure the areas for the major peaks.Calculate the quantity,in mg,of 8-chlorotheophylline (C7H7ClN4O2)per Tablet taken by the formula: in which 214.61and 469.96are the molecular weights of 8-chlorotheophylline and dimenhydrinate,respectively;Wis the weight,in mg,of USP Dimenhydrinate RSin theStandard solution;and RUand RSare peak area ratios of 8-chlorotheophylline to the internal standard obtained from the Test solutionand the Standard solution,respectively.An amount of 8-chlorotheophylline that is between 43.4%and 47.9%of the amount of dimenhydrinate is found.

Ammonium bicarbonate solution— Dissolve 4g of ammonium bicarbonate in 250mLof water.

Diluent— Dissolve 4g of ammonium bicarbonate in 200mLof water.Add 50mLof methanol,and mix.

Solution A— Dissolve 0.8g of ammonium bicarbonate in 800mLof water.Add 200mLof methanol,filter,and degas.

Solution B— Dissolve 0.8g of ammonium bicarbonate in 150mLof water.Add 850mLof methanol,filter,and degas.

Mobile phase— Use variable mixtures ofSolution AandSolution Bas directed forChromatographic system.Make adjustments if necessary (seeSystem Suitability under Chromatography á621ñ).

Internal standard solution— Prepare a solution in methanol containing 2.0mg of 2-hydroxybenzyl alcohol per mL.

Standard preparation— Accurately weigh about 50mg of USP Dimenhydrinate RS,add about 5mLof Ammonium bicarbonate solutionand 20.0mLof Internal standard solution,and mix.To 1mLof this solution add about 9mLof Diluent,and mix.

Assay preparation— Transfer 5Tablets into a 250-mLvolumetric flask,add 25mLof Ammonium bicarbonate solution,and shake gently to disperse,sonicating if necessary.Add 100.0mLof Internal standard solution,shake vigorously for 30minutes,and centrifuge.To 1mLof the clear supernatant add about 9mLof Diluent,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 229-nm detector and a 4.6-mm ×25-cm column that contains packing L7.The flow rate is about 1.5mLper minute.The chromatograph is programmed as follows. Chromatograph the Standard preparation,and record the peak areas as directed for Procedure:the relative retention times are about 0.3for 8-chlorotheophylline,0.5for the internal standard,and 1.0for diphenhydramine;the resolution,R,between 8-chlorotheophylline and the internal standard is not less than 4.5;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the areas for the major peaks.Calculate the quantity,in mg,of dimenhydrinate (C17H21NO·C7H7ClN4O2)per Tablet taken by the formula: in which Wis the weight,in mg,of USP Dimenhydrinate RSin the Standard preparation;and RUand RSare the peak area ratios of diphenhydramine to the internal standard obtained from the Assay preparationand the Standard preparation,respectively.