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 RSin methanol to contain 14mg per mL.

Test solution— Transfer 4.0mLof the Oral Solution into a separator,add 6mLof 1Nsodium hydroxide and 10mLof chloroform,shake for 2minutes,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 solventsufficient to develop the chromatogram,and allow to equilibrate.Apply separate 10-µLportions of the Test solutionand the Standard solutionto 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 15mLof perchloric acid with water to 100mL,and heat at 80for 2minutes:the principal spot obtained from the Test solutioncorresponds in RFvalue and color to that of the Standard solution.

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

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

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