A: Mix a portion of Oral Suspension,equivalent to about 0.5g of thiabendazole,with about 20mLof water,and filter.Wash the residue with 20mLof water,discard the washing,dissolve the residue in 30mLof 0.1Nhydrochloric acid,and filter.Collect the filtrate in a separator,render it alkaline with 1Nsodium hydroxide,and extract with 10mLof carbon disulfide.Pass the carbon disulfide layer through a dry filter,collecting the filtrate in an evaporating dish.Evaporate the solvent with the aid of gentle heat and a stream of nitrogen.[Caution—Do not overheat the residue. ]The residue so obtained responds to Identificationtest Aunder Thiabendazole.

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

FOR ORAL SUSPENSION PACKAGED IN SINGLE-UNIT CONTAINERS: meets the requirements.

FOR ORAL SUSPENSION PACKAGED IN MULTIPLE-UNIT CONTAINERS: meets the requirements.

pH3.1Phosphate buffer— Dissolve 13.8g of monobasic sodium phosphate in water to obtain 2000mLof solution.Adjust this solution with phosphoric acid to a pHof 3.1±0.05.

Mobile phase— Prepare a filtered and degassed mixture of pH3.1Phosphate bufferand methanol (65:35).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Thiabendazole RSin 0.1Nhydrochloric acid,and dilute quantitatively,and stepwise if necessary,with 0.1Nhydrochloric acid to obtain a solution containing about 2mg per mL.Transfer 5.0mLof this solution to a 50-mLvolumetric flask,dilute with water to volume,and mix to obtain a Standard preparationhaving a known concentration of about 0.2mg of USP Thiabendazole RSper mL.

Assay preparation— Transfer an accurately measured volume of Oral Suspension,equivalent to about 0.5g of thiabendazole,to a 250-mLvolumetric flask;dilute with 0.1Nhydrochloric acid to volume;and mix.Transfer 5.0mLof this solution to a 50-mLvolumetric flask,dilute with water to volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4-mm ×30-cm column that contains packing L1.The flow rate is about 2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the column efficiency determined from the analyte peak is not less than 960theoretical plates,the tailing factor for the analyte peak is not more than 2.0,and the relative standard deviation for replicate injections is not more than 2%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in g,of thiabendazole (C10H7N3S)in each mLof the Oral Suspension taken by the formula: in which Cis the concentration,in mg per mL,of USP Thiabendazole RSin the Standard preparation;Vis the volume,in mL,of Oral Suspension taken;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.