Standard preparation— Transfer about 10mg of USP Mebendazole RS,accurately weighed,to a 100-mLvolumetric flask,and add 90mLof chloroform,7mLof isopropyl alcohol,and 2mLof 96percent formic acid.Agitate until the solid has dissolved,add isopropyl alcohol to volume,and mix.Transfer 5.0mLof this solution to a second 100-mLvolumetric flask,dilute with isopropyl alcohol to volume,and mix to obtain a solution having a known concentration of about 5µg per mL.

Assay preparation 1— Transfer an accurately measured quantity of Oral Suspension,equivalent to about 1000mg of mebendazole,to a 100-mLvolumetric flask,dilute with 96percent formic acid to volume,and mix.Transfer 10.0mLof this mixture to a second 100-mLvolumetric flask,add 40mLof 96percent formic acid,and heat in a water bath at a temperature of 50for 15minutes.Cool,add water to volume,mix,and pass through a medium-porosity,sintered-glass filter.Transfer 10.0mLof the filtrate to a 250-mLseparator,and add 50mLof water and 50mLof chloroform.Shake for about 2minutes,allow the phases to separate,and transfer the chloroform layer to a second 250-mLseparator.Wash the aqueous layer with two 10-mLportions of chloroform,add the chloroform washings to the second separator,and discard the aqueous layer.Wash the combined chloroform solutions with a mixture of 4mLof 1Nhydrochloric acid and 50mLof a 1in 10solution of 96percent formic acid in water,and transfer the chloroform layer to a 100-mLvolumetric flask.Extract the aqueous washing with two 10-mLportions of chloroform,add these chloroform extracts to the chloroform solution in the volumetric flask,add 2mLof 96percent formic acid and 7mLof isopropyl alcohol,dilute with chloroform to volume,and mix.Transfer 5.0mLof this solution to another 100-mLvolumetric flask,dilute with isopropyl alcohol to volume,and mix.

Assay preparation 2 (where the Oral Suspension is packaged in syringes calibrated to deliver stated increments of mebendazole)—Express an increment of Oral Suspension to a volumetric flask of an appropriate nominal volume so that when diluted with 96percent formic acid to volume a mixture containing about 10mg of mebendazole per mLis obtained.Transfer 10.0mLof this mixture to a 100-mLvolumetric flask,add 40mLof 96percent formic acid,and heat in a water bath at a temperature of 50for 15minutes.Proceed as directed for Assay preparation 1beginning with “Cool,add water to volume.”

Procedure— Mix 90mLof chloroform with 2mLof 96percent formic acid in a 100-mLvolumetric flask,add isopropyl alcohol to volume,and mix.Transfer 5.0mLof this solution to a second 100-mLvolumetric flask,dilute with isopropyl alcohol to volume,and mix to obtain a reagent blank.Concomitantly determine the absorbances of the relevant Assay preparationand the Standard preparationat the wavelength of maximum absorbance at about 247nm with a spectrophotometer,using the reagent blank to set the instrument.Calculate the quantity,in mg,of mebendazole (C16H13N3O3)in the portion of Oral Suspension taken to prepare Assay preparation 1by the formula: in which Cis the concentration,in µg per mL,of USP Mebendazole RSin the Standard preparation;and AUand ASare the absorbances of Assay preparation 1and the Standard preparation,respectively.Where appropriate,calculate the quantity,in mg,of mebendazole (C16H13N3O3)in the increment of Oral Suspension taken to prepare Assay preparation 2by the formula: in which Vis the volume,in mL,of the volumetric flask into which the increment of Oral Suspension was expressed;AUis the absorbance of Assay preparation 2;and the other terms are as defined above.