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: 75rpm.

Time: 60minutes.

Procedure— Determine the amount of C21H26N2S2·HCl dissolved by employing UVabsorption at the wavelength of maximum absorbance at about 262nm on filtered portions of the solution under test,suitably diluted with Dissolution Medium,if necessary,in comparison with a Standard solution having a known concentration of USP Thioridazine Hydrochloride RSin the same Medium.

Tolerances— Not less than 75%(Q)of the labeled amount of C21H26N2S2·HCl is 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 Thioridazine Hydrochloride RSin methanol with the aid of sonication,and dilute quantitatively and stepwise,if necessary,with methanol to obtain a solution having a known concentration of about 125µg per mL.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 100mg of thioridazine hydrochloride,to a 100-mLvolumetric flask.Add about 80mLof methanol,and shake by mechanical means for 30minutes.Dilute with methanol to volume,and sonicate for 45minutes with intermittent shaking.Allow the undissolved solids to settle,and filter,discarding the first 20mLof the filtrate.Transfer 25.0mLof the clear filtrate to a 200-mLvolumetric flask,dilute with methanol to volume,and mix.Filter through a 0.45-µm disk before injecting into the chromatograph.

System suitability preparation— Dissolve 100mg of mesoridazine besylate in 100mLof methanol.Mix 1.0mLof this solution with 9.0mLof the Standard preparation.

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 responses as directed for Procedure:the resolution,R,between the mesoridazine and thioridazine peaks is not less than 1.0,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 responses for the major peaks.Calculate the quantity,in mg,of C21H26N2S2·HCl in the portion of Tablets taken by the formula: in which Cis the concentration,in µg per mL,of USP Thioridazine Hydrochloride RSin the Standard preparation,and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.