note—Throughout the following procedures, protect test or assay specimens, the USP Reference Standard, and solutions containing them, by conducting the procedures without delay, under subdued light, or using low-actinic glassware.

Standard solution— Prepare a solution of USP Mesoridazine Besylate RS in methanol to contain 14 mg per mL.

Test solution— Transfer 4.0 mL of the Oral Solution into a separator, add 6 mL of 1 N sodium hydroxide and 10 mL of chloroform, shake for 2 minutes, and filter the chloroform layer through anhydrous sodium sulfate into a small, glass-stoppered conical flask.

Developing solvent— To a separator add benzene, alcohol, and ammonium hydroxide (10:2:1), shake, and allow the layers to separate. Use the upper layer.

Procedure— Into a suitable chromatographic chamber arranged for thin-layer chromatography, place a volume of Developing solvent sufficient to develop the chromatogram, and allow to equilibrate. Apply separate 10-µL portions of the Test solution and the Standard solution to a suitable thin-layer chromatographic plate coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate in a fume hood. Spray the plate with a solution prepared by diluting 15 mL of perchloric acid with water to 100 mL, and heat at 80 for 2 minutes: the principal spot obtained from the Test solution corresponds in RF value and color to that of the Standard solution.

for oral solution packaged in single-unit containers: meets the requirements.

for oral solution packaged in multiple-unit containers: meets the requirements.

Standard preparation— Transfer about 14 mg of USP Mesoridazine Besylate RS, accurately weighed, to a 125-mL separator containing 30 mL of water. Render the solution alkaline with 10 mL of 1 N sodium hydroxide, and extract with three 30-mL portions of chloroform. Filter the extracts through anhydrous sodium sulfate into a 100-mL volumetric flask. Rinse the filter with small portions of chloroform, collecting the rinsings in the volumetric flask, dilute with chloroform to volume, and mix. Dilute 10.0 mL of this solution with chloroform to 100.0 mL, and mix.

Assay preparation— Pipet a volume of Oral Solution, equivalent to about 100 mg of mesoridazine, into a separator containing 30 mL of water. Proceed as directed under Standard preparation, beginning with “Render the solution alkaline.” Pipet 10.0 mL of this solution into a third 100-mL volumetric flask, dilute with chloroform to volume, and mix.

Procedure— Concomitantly determine the absorbances of the Standard preparation and the Assay preparation in 1-cm cells at the wavelength of maximum absorbance at about 267 nm, with a suitable spectrophotometer, using chloroform as the blank. Calculate the quantity, in mg, of mesoridazine (C21H26N2OS2) in each mL of the Oral Solution taken by the formula: in which 386.59 and 544.75 are the molecular weights of mesoridazine and mesoridazine besylate, respectively; C is the concentration, in µg per mL, of USP Mesoridazine Besylate RS in the Standard preparation; V is the volume, in mL, of Oral Solution taken; and AU and AS are the absorbances of the Assay preparation and the Standard preparation, respectively.