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

Medium: 0.01Nhydrochloric acid;1000mL.

Apparatus 2: 100rpm.

Time: 60minutes.

Procedure— Determine the amount of C21H26N2OS2dissolved by employing UVabsorption at the wavelength of maximum absorbance at about 261nm on filtered portions of the solution under test,suitably diluted with Medium,if necessary,in comparison with a Standard solution having a known concentration of USP Mesoridazine Besylate RSin the same Medium.[NOTE—Avolume of methanol not exceeding 1%of the final total volume may be used to prepare the Standard solution.]

Tolerances— Not less than 80%(Q)of the labeled amount of C21H26N2OS2is dissolved in 60minutes.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile,water,and triethylamine (850:150:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Mesoridazine Besylate RSin methanol,and dilute quantitatively,and stepwise if necessary,with methanol to obtain a solution having a known concentration of about 0.35mg per mL.

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 50mg of mesoridazine,to a 200-mLvolumetric flask.Add about 150mLof methanol,shake by mechanical means for about 15minutes,dilute with methanol to volume,and mix.Sonicate for 30minutes,and allow dispersed material to settle.Filter through a 0.25-µm disk,discarding the first 20mLof the filtrate.

System suitability preparation— Dissolve a suitable quantity of thioridazine hydrochloride in a portion of the Standard preparation,and mix to obtain a solution containing 0.025mg of thioridazine hydrochloride per mL.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 265-nm detector and a 4.6-mm ×25-cm column that contains packing L1.The flow rate is about 2.5mLper minute.Chromatograph the Standard preparationand the System suitability preparation,and record the peak areas as directed for Procedure:the resolution,R,between mesoridazine besylate and thioridazine hydrochloride is not less than 1.0;the column efficiency determined from the analyte peak is not less than 750theoretical plates;and the relative standard deviation for replicate injections of the Standard preparationis not more than 2.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the areas for the major peaks.Calculate the quantity,in mg,of mesoridazine (C21H26N2OS2)in the portion of Tablets taken by the formula: in which 386.59and 544.75are the molecular weights of mesoridazine and mesoridazine besylate,respectively;Cis the concentration,in mg per mL,of USP Mesoridazine Besylate RSin the Standard preparation;and rUand rSare the peak areas obtained from the Assay preparationand the Standard preparation,respectively.