A: The retention time of the major peak for levamisole in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of the Standard preparation,as obtained in the Assay.

B: The RFvalue of the principal spot obtained from Test solution Bin the Chromatographic puritytest corresponds to that from Standard solution A.

Medium: 0.01Nhydrochloric acid;900mL.

Apparatus 2: 50rpm.

Time: 45minutes.

Procedure— Determine the amount of levamisole (C11H12N2S)dissolved by employing UVabsorption at the wavelength of maximum absorbance at about 214nm 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 Levamisole Hydrochloride RSin the same Medium.

Tolerances— Not less than 80%(Q)of the labeled amount of C11H12N2Sis dissolved in 45minutes.

Test solution A— Transfer an amount of powdered Tablets,equivalent to 100mg of levamisole,to a glass test tube.Add 5.0mLof methanol,shake for 2minutes,and filter.

Test solution B— Dilute 1.0mLof Test solution Ato 10mLwith methanol,and mix.

Standard solution A— Prepare a solution of USP Levamisole Hydrochloride RSin methanol having a concentration of 2.4mg per mL(equivalent to 2.0mg of levamisole per mL).

Standard solution B— Dilute 1.0mLof Standard solution Ato 20mLwith methanol,and mix.

Procedure— Apply separate 10-µLportions of Test solutions Aand Band Standard solutions Aand Bto the starting line of a suitable thin-layer chromatographic plate (see Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic silica gel mixture.Allow the spots to dry,and develop the chromatogram in a solvent system consisting of a mixture of toluene,acetone,and ammonium hydroxide (60:40:1)until the solvent front has moved about three-fourths of the length of the plate.Remove the plate from the developing chamber,and dry the plate at 105for 15minutes.Locate the spots on the plate by examination under short-wavelength UVlight:any spot obtained from Test solution A,other than that of levamisole,does not exceed,in size or intensity,the principal spot obtained from Standard solution B,corresponding to not more than 0.5%of any individual impurity.Expose the plate to iodine vapor in a closed chamber for 15minutes,and locate the spots on the plate:any spot obtained from Test solution A,other than that of levamisole,does not exceed,in size or intensity,the principal spot obtained from Standard solution B,corresponding to not more than 0.5%of any individual impurity.

Solution A— Prepare a 0.75%solution of monobasic ammonium phosphate in water,and adjust with diisopropylamine to a pHof 7.

Solution B— Use acetonitrile.

Mobile phase— Use variable mixtures of Solution Aand Solution Bas directed for Chromatographic system.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Diluent: a mixture of methanol and water (1:1).

Standard preparation— Transfer about 20mg of USP Levamisole Hydrochloride RS,accurately weighed,to a 100-mLvolumetric flask,add 10mLof water,and swirl to dissolve.Dilute with methanol to volume,and mix to obtain a solution having a known concentration of about 0.2mg of USP Levamisole Hydrochloride RSper mL.

Resolution solution— Dissolve 20mg of Levamisole Hydrochloride in 5mLof 0.1Nsodium hydroxide,and heat at 100in a closed vial for 5hours.Allow to cool,and dilute 1mLof the solution to 25mLwith methanol.

Assay preparation— Transfer an accurately counted number of Tablets,equivalent to about 150mg of levamisole (C11H12N2S),to a 100-mLvolumetric flask.Add 25mLof water,and shake by mechanical means for 30minutes.Dilute with water to volume,and mix.Transfer 10.0mLof this solution to a second 100-mLvolumetric flask,dilute with methanol to volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 215-nm detector and a 4.6-mm ×10-cm column that contains 3-µm packing L1.The flow rate is about 2mLper minute.The chromatograph is programmed as follows. Chromatograph the Resolution solution,and record the peak responses as directed for Procedure:the relative retention times are 1.0for levamisole and about 1.3for the major degradation product;and the resolution,R,between levamisole and the major degradation product is not less than 6.0.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the capacity factor,k¢,is not less than 3.0;the tailing factor is not more than 1.8;and the relative standard deviation for replicate injections is 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 levamisole (C11H12N2S)in the Tablets taken by the formula: in which 204.29and 240.75are the molecular weights of levamisole and levamisole hydrochloride,respectively;Cis the concentration,in mg per mL,of USP Levamisole Hydrochloride RSin the Standard preparation;and rUand rSare the levamisole peak responses obtained from the Assay preparationand the Standard preparation,respectively.