Packaging and storage— Preserve in tight,light-resistant containers.Store at a temperature not exceeding 30.

USP Reference standards á11ñ— USP Thioridazine RS.

Identification— [NOTE—Conduct this test without exposure to daylight,and with a minimum of exposure to artificial light.]Transfer 40mLof the combined chloroform extracts obtained for the Assayto a 50-mLbeaker,and reduce the volume to 1mLby evaporating the chloroform with the aid of a stream of nitrogen.Apply 25µLof this test solution and 25µLof a Standard solution of USP Thioridazine RSin chloroform containing 4mg per mLto a thin-layer chromatographic plate (see Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic silica gel mixture.Allow the spots to dry,and develop the chromatogram in a solvent system consisting of a mixture of toluene,acetone,solvent hexane,and diethylamine (15:15:15:1)until the solvent front has moved about 10cm from the origin.Remove the plate from the developing chamber,mark the solvent front,and locate the spots on the plate by viewing under short-wavelength and long-wavelength UVlight:the RFvalue of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.

Uniformity of dosage units á905ñ—

Deliverable volume á698ñ—

Specific gravity á841ñ: between 1.180and 1.310.

pHá791ñ: between 8.0and 10.0.

Assay— Transfer an accurately measured volume of Oral Suspension,freshly mixed but free from air bubbles,equivalent to about 100mg of thioridazine,to a 125-mLseparator,using a pipet calibrated to contain the required volume.Rinse the pipet with 10to 15mLof water,adding the rinsing to the separator.Render the mixture alkaline by adding several drops of ammonium hydroxide,and mix.Extract with six 30-mLportions of chloroform,and filter the extracts through anhydrous sodium sulfate,collecting the combined filtrates in a 200-mLvolumetric flask.Dilute quantitatively and stepwise with chloroform to obtain a solution having a concentration of about 100µg of thioridazine per mL.[NOTE—Reserve a 40-mLportion of this solution for the Identificationtest.]Transfer 5.0mLof this solution to a 100-mLvolumetric flask,dilute with chloroform to volume,and mix.Concomitantly determine the absorbances of this Assay solution and a Standard solution of USP Thioridazine RSin chloroform having a known concentration of about 5µg per mL,in 1-cm cells at the wavelength of maximum absorbance at about 266nm,with a suitable spectrophotometer,using chloroform as the blank.Calculate the quantity,in mg,of thioridazine (C21H26N2S2)in each mLof the Oral Suspension taken by the formula: in which Cis the concentration,in µg per mL,of USP Thioridazine RSin the Standard solution;Vis the volume,in mL,of Oral Suspension taken;and AUand ASare the absorbances of the Assay solution and the Standard solution,respectively.

Expert Committee:(PA3)Pharmaceutical Analysis 3

USP28–NF23Page 1916

Phone Number:1-301-816-8330