Medium: 0.01Nhydrochloric acid;900mL.

Apparatus 2: 50rpm.

Time: 30minutes.

Standard preparation— Transfer about 27mg of USP Pimozide RS,accurately weighed,to a 250-mLvolumetric flask containing 1mLof lactic acid.Heat on a steam bath to dissolve,add about 80mLof hot water,and shake.Cool,dilute with water to volume,and mix.Dilute the solution quantitatively with 0.01Nhydrochloric acid to obtain a solution having a known concentration approximately the same as that of the solution under test (assuming complete dissolution).

Procedure— Transfer a portion of the solution under test to a suitable container,and centrifuge until clear.Pipet a volume of the supernatant,estimated to contain about 110µg of pimozide (assuming complete dissolution),into a suitable container.Pipet an equal volume of the Standard preparationinto a second container.To each container add 20mLof 1Nsodium hydroxide and 20.0mLof chloroform.Shake each mixture by mechanical means for 15minutes,and centrifuge.Aspirate and discard the aqueous layers,and transfer the chloroform layers to separate clean beakers.Determine the amount of C28H29F2N3Odissolved from absorbances of the chloroform layers obtained from the solution under test and the Standard preparation,in 5-cm cells at the wavelength of maximum absorbance at about 277nm.

Tolerances— Not less than 80%(Q)of the labeled amount of C28H29F2N3Ois dissolved in 30minutes.

Procedure for content uniformity— Place 1tablet in a 50-mLflask,add 5.0mLof 0.1Nhydrochloric acid,and shake by mechanical means for 30minutes.Add 20.0mLof methanol,and shake by mechanical means for 20minutes.Dilute,if necessary,quantitatively with methanol to obtain a solution having a concentration of about 40µg of pimozide per mL,mix,and centrifuge.Concomitantly determine the absorbance of the supernatant and of a solution of USP Pimozide RSin the same medium having a known concentration of about 40µg per mLin 1-cm cells at the wavelength of maximum absorbance at about 277nm,with a suitable spectrophotometer,using a mixture of 0.1Nhydrochloric acid and methanol (1in 10)as the blank.Calculate the quantity,in mg,of C28H29F2N3Oin the Tablet taken by the formula: in which Tis the labeled quantity,in mg,of pimozide in the Tablet,Cis the concentration,in µg per mL,of USP Pimozide RSin the Standard solution,Dis the concentration,in µg per mL,of pimozide in the solution from the Tablet based upon the labeled quantity per Tablet and the extent of dilution,and AUand ASare the absorbances of the solution from the Tablet and the Standard solution,respectively.

Ammonium acetate solution— Dissolve 500mg of ammonium acetate in 100mLof water,and mix.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and Ammonium acetate solution(65:35),making adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Dissolve 3,4-dimethylbenzophenone in a mixture of methanol and tetrahydrofuran (1:1)to obtain a solution having a concentration of about 1mg per mL.

Standard preparation— Transfer about 25mg of USP Pimozide RS,accurately weighed,to a 50-mLvolumetric flask,add 10mLof Internal standard solution,dilute with a mixture of methanol and tetrahydrofuran (1:1)to volume,and mix.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 25mg of pimozide,to a 50-mLvolumetric flask.Add 10mLof Internal standard solutionand 20mLof a mixture of methanol and tetrahydrofuran (1:1),and shake by mechanical means for 30minutes.Dilute with a mixture of methanol and tetrahydrofuran (1:1)to volume,and centrifuge.Use the clear supernatant as the Assay preparation.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 280-nm detector and a 4.6-mm ×25-cm column that contains 5-µm packing L1.The flow rate is about 2mLper minute.Chromatograph replicate injections of the Standard preparation,and record the peak responses as directed for Procedure:the relative standard deviation is not more than 2.0%,and the resolution,R,between the analyte and the internal standard peaks is not less than 1.3.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.The relative retention times are about 0.7for pimozide and 1.0for the internal standard.Calculate the quantity,in mg,of C28H29F2N3Oin the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Pimozide RSin the Standard preparation,and RUand RSare the ratios of the pimozide peak response to the internal standard peak response obtained from the Assay preparationand the Standard preparation,respectively.