Medium: 0.01 N hydrochloric acid; 900 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

Standard preparation— Transfer about 27 mg of USP Pimozide RS, accurately weighed, to a 250-mL volumetric flask containing 1 mL of lactic acid. Heat on a steam bath to dissolve, add about 80 mL of hot water, and shake. Cool, dilute with water to volume, and mix. Dilute the solution quantitatively with 0.01 N hydrochloric 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 110 µg of pimozide (assuming complete dissolution), into a suitable container. Pipet an equal volume of the Standard preparation into a second container. To each container add 20 mL of 1 N sodium hydroxide and 20.0 mL of chloroform. Shake each mixture by mechanical means for 15 minutes, and centrifuge. Aspirate and discard the aqueous layers, and transfer the chloroform layers to separate clean beakers. Determine the amount of C28H29F2N3O dissolved 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 277 nm.

Tolerances— Not less than 80% (Q) of the labeled amount of C28H29F2N3O is dissolved in 30 minutes.

Procedure for content uniformity— Place 1 tablet in a 50-mL flask, add 5.0 mL of 0.1 N hydrochloric acid, and shake by mechanical means for 30 minutes. Add 20.0 mL of methanol, and shake by mechanical means for 20 minutes. Dilute, if necessary, quantitatively with methanol to obtain a solution having a concentration of about 40 µg of pimozide per mL, mix, and centrifuge. Concomitantly determine the absorbance of the supernatant and of a solution of USP Pimozide RS in the same medium having a known concentration of about 40 µg per mL in 1-cm cells at the wavelength of maximum absorbance at about 277 nm, with a suitable spectrophotometer, using a mixture of 0.1 N hydrochloric acid and methanol (1 in 10) as the blank. Calculate the quantity, in mg, of C28H29F2N3O in the Tablet taken by the formula: in which T is the labeled quantity, in mg, of pimozide in the Tablet, C is the concentration, in µg per mL, of USP Pimozide RS in the Standard solution, D is 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 AU and AS are the absorbances of the solution from the Tablet and the Standard solution, respectively.

(Official January 1, 2007)

Ammonium acetate solution— Dissolve 500 mg of ammonium acetate in 100 mL of 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 Suitability under Chromatography 621).

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 1 mg per mL.

Standard preparation— Transfer about 25 mg of USP Pimozide RS, accurately weighed, to a 50-mL volumetric flask, add 10 mL of 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 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 25 mg of pimozide, to a 50-mL volumetric flask. Add 10 mL of Internal standard solution and 20 mL of a mixture of methanol and tetrahydrofuran (1:1), and shake by mechanical means for 30 minutes. 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 621)—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 2 mL per 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 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 0.7 for pimozide and 1.0 for the internal standard. Calculate the quantity, in mg, of C28H29F2N3O in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Pimozide RS in the Standard preparation, and RU and RS are the ratios of the pimozide peak response to the internal standard peak response obtained from the Assay preparation and the Standard preparation, respectively.