Spray reagent— Prepare as directed in the test for Chromatographic purityunder Clemastine Fumarate.

Standard preparation— Prepare a solution in a mixture of chloroform and methanol (1:1)having a concentration of about 2.5mg of USP Clemastine Fumarate RSper mL.

Test preparation— Place a portion of powdered Tablets,equivalent to about 2.5mg of clemastine fumarate,in a glass-stoppered flask.Add 10mLof a mixture of chloroform and methanol (1:1),and shake for 20minutes.Filter,wash the residue with two 5-mLportions of the mixture of chloroform and methanol (1:1),and evaporate the combined filtrate and washings to dryness under vacuum.Dissolve the residue so obtained in 1mLof the mixture of chloroform and methanol (1:1),and mix.

Procedure— Proceed as directed for Procedurein the test for Chromatographic purityunder Clemastine Fumarate,applying 5-µLportions of the Standard preparationand the Test preparationon the thin-layer chromatographic plate:the RFvalue of the principal spot obtained from the Test preparationcorresponds to that obtained from the Standard preparation.

pH4.0citrate buffer— Dissolve 20.0g of monohydrate citric acid in about 1000mLof water,add 22.0mLof sodium hydroxide solution (3in 10)and 8.8mLof hydrochloric acid,and dilute with water to 2000mL.Adjust,if necessary,with sodium hydroxide solution (1in 2)to a pHof 4.0.

Medium:pH4.0citrate buffer; 500mL.

Apparatus 2: 50rpm.

Time: 30minutes.

Procedure— Centrifuge 60mLof the solution under test for 20minutes at 4000rpm,and transfer 50.0mLof the supernatant to a 125-mLseparator.To a second 125-mLseparator transfer 50.0mLof a Standard preparation that is prepared by dissolving an accurately weighed quantity of USP Clemastine Fumarate RSin Dissolution Mediumand diluting quantitatively and stepwise with Dissolution Mediumto yield a solution having a known concentration comparable with that of the solution under test.To a third 125-mLseparator transfer 50.0mLof Dissolution Mediumto provide a blank.Treat each of the solutions in the three separators as follows.Add 10mLof methyl orange solution (2in 10,000),mix,add 20.0mLof chloroform,shake simultaneously by mechanical means for 10minutes,remove the chloroform layer,and centrifuge the chloroform layer for 10minutes at 4000rpm.Determine the amount of C21H26ClNO·C4H4O4dissolved from absorbances at the wavelength of maximum absorbance at about 420nm of the chloroform solutions obtained from the solution under test and the Standard preparation,using the chloroform solution obtained from the blank to set the instrument.

Tolerances— Not less than 75%(Q)of the labeled amount of C21H26ClNO·C4H4O4is dissolved in 30minutes.

Procedure for content uniformity—

Dye solution— Dissolve 100mg of bromocresol purple in 1000mLof 0.33Nacetic acid,and mix.

Acetous methanol— Dilute 100mLof methanol with sufficient 0.33Nacetic acid to prepare 1000mLof solution,and mix.

Standard preparation— Transfer about 27mg of USP Clemastine Fumarate RS,accurately weighed,to a 100-mLvolumetric flask,dissolve in 10mLof methanol,dilute with 0.33Nacetic acid to volume,and mix.Transfer 10.0mLof this solution to a 100-mLvolumetric flask,dilute with Acetous methanolto volume,and mix.

Test preparation— Mix 1finely powdered Tablet with an accurately measured volume of Acetous methanol,sufficient to obtain a solution having a concentration of about 27µg of clemastine fumarate per mL.Shake for 30minutes,and filter,discarding the first few mLof the filtrate.

Procedure— Transfer 15.0mLeach of the Standard preparation,the Test preparation,and Acetous methanolto provide the blank to individual 125-mLseparators.Add 25mLof Dye solutionand 50.0mLof chloroform to each,and shake by mechanical means for 15minutes.Allow the layers to separate,and filter the chloroform layers.Concomitantly determine the absorbances of the filtered solutions obtained from the Test preparationand the Standard preparationat the wavelength of maximum absorbance at about 406nm,using the blank to set the instrument.Calculate the quantity,in mg,of C21H26ClNO·C4H4O4in the Tablet taken by the formula: in which Tis the labeled quantity,in mg,of clemastine fumarate in the Tablet;Cis the concentration,in µg per mL,of USP Clemastine Fumarate RSin the Standard preparation;Dis the concentration,in µg per mL,of clemastine fumarate in the Test preparation,based on the labeled quantity per Tablet and the extent of dilution;and AUand ASare the absorbances of the solutions from the Test preparationand the Standard preparation,respectively.

pH7phosphate buffer— Transfer 9.47g of anhydrous dibasic sodium phosphate to a 1000-mLvolumetric flask,dilute with water to volume,and mix(flask A).Transfer 9.08g of monobasic potassium phosphate to a 1000-mLvolumetric flask,dilute with water to volume,and mix (flask B).Mix 612mLof Awith 388mLof B.

Dilute phosphate buffer— Prepare a mixture of 1volume of pH7phosphate bufferand 3volumes of water.

Mobile phase— Prepare a suitable and degassed solution of methanol and Dilute phosphate buffer(83:17).

Standard preparation— Dissolve an accurately weighed quantity of USP Clemastine Fumarate RSin a mixture of methanol and water (1:1)to obtain a solution having a known concentration of about 0.14mg per mL.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed quantity of the powder,equivalent to about 14mg of clemastine fumarate,to a 200-mLconical flask.Pipet 100mLof a mixture of methanol and water (1:1)into the flask,shake for 30minutes,centrifuge,and filter the supernatant.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm ×25-cm column that contains packing L7.The flow rate is about 4mLper minute.Chromatograph five replicate injections of the Standard preparation,and record the peak responses as directed under Procedure:the relative standard deviation is not more than 1.5%.

Procedure— Separately inject equal volumes (about 100µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C21H26ClNO·C4H4O4in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Clemastine Fumarate RSin the Standard preparation,and rUand rSare the peak responses of clemastine fumarate obtained from the Assay preparationand the Standard preparation,respectively.