Thioridazine Oral Suspension
Thioridazine Oral Suspension contains NLT 90.0% and NMT 110.0% of the labeled amount of thioridazine (C21H26N2S2).
[Note—Throughout the following procedures, protect the samples, the Reference Standard, and the solutions containing them by conducting the procedures without delay, under subdued light, or by using low-actinic glassware. ]
•  A. Thin-Layer Chromatograpic Identification Test
Standard solution:  4 mg/mL of USP Thioridazine RS in chloroform
Sample solution:  Transfer 40 mL of the combined chloroform extracts obtained for the Assay to a 50-mL beaker, and reduce the volume to 1 mL by evaporating the chloroform with the aid of a stream of nitrogen.
Chromatographic system 
Mode:  TLC
Adsorbent:  0.25-mm layer of chromatographic silica gel mixture
Application volume:  25 µL
Developing solvent system:  Toluene, acetone, solvent hexane, and diethylamine (15:15:15:1)
Samples:  Standard solution and Sample solution
Apply the Sample solution and Standard solution to a thin-layer chromatographic plate. Allow the spots to dry, and develop the chromatogram in the Developing solvent system until the solvent front has moved about 10 cm 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 UV light.
Acceptance criteria:  The RF value of the principal spot from the Sample solution corresponds to that from the Standard solution.
•  Procedure
Standard solution:  5 µg/mL of USP Thioridazine RS in chloroform
Sample stock solution:  Transfer a measured volume of Oral Suspension, freshly mixed but free from air bubbles, equivalent to 100 mg of thioridazine, to a 125-mL separator. Render the mixture alkaline by adding several drops of ammonium hydroxide, and mix. Extract with six 30-mL portions of chloroform, and filter the extracts through anhydrous sodium sulfate, collecting the combined filtrates in a 200-mL volumetric flask. Dilute a portion of the extract with chloroform to obtain a solution with a nominal concentration of 100 µg/mL of thioridazine. [Note—Reserve a 40-mL portion of this solution for the Identification test. ]
Sample solution:  Nominally 5 µg/mL thioridazine in chloroform, from Sample stock solution
Instrumental conditions 
Mode:  UV-Vis
Analytical wavelength:  266 nm
Cell:  1 cm
Blank:  Chloroform
Samples:  Standard solution, Sample solution, and Blank
Calculate the percentage of thioridazine (C21H26N2S2) in each mL of Oral Suspension taken:
Result = (AU/AS) × (CS/CU) × 100
AU== absorbance of the Sample solution
AS== absorbance of the Standard solution
CS== concentration of USP Thioridazine RS in the Standard solution (µg/mL)
CU== nominal concentration of thioridazine in the Sample solution (µg/mL)
Acceptance criteria:  90.0%–110.0%
•  Uniformity of Dosage Units 905: Meets the requirements for Oral Suspension packaged in single-unit containers
•  Deliverable Volume 698: Meets the requirements for Oral Suspension packaged in multiple-unit containers
•  Specific Gravity 841: 1.180–1.310
•  pH 791: 8.0–10.0
•  Packaging and Storage: Preserve in tight, light-resistant containers. Store at a temperature not exceeding 30.
•  USP Reference Standards 11
USP Thioridazine RS Click to View Structure
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Hariram Ramanathan, M.S.
Associate Scientific Liaison
(SM42010) Monographs - Small Molecules 4
Reference Standards RS Technical Services
USP35–NF30 Page 4847
Pharmacopeial Forum: Volume No. 29(6) Page 1992