A: Infrared Absorption á197Kñ.

B: The appearance of the principal spot in the chromatogram of the Test solutioncorresponds to that in the chromatogram of Standard solution 1,as obtained in the test for Related compounds.

Diluent— Prepare a mixture of ethyl acetate and glacial acetic acid (4:1).

Standard solution 1— Dissolve a quantity of USP Oxfendazole RSin Diluentto obtain a solution having a concentration of 0.1mg per mL.

Standard solution 2— Dissolve a quantity of USP Fenbendazole RSin Diluentto obtain a solution having a concentration of 0.05mg per mL.

Standard solution 3— Prepare a mixture of Standard solution 1and Standard solution 2(1:2).

Test solution— Dissolve 25mg of Oxfendazole in Diluent,dilute with Diluentto 5mL,and mix.

Procedure— Separately apply 20µLportions of Standard solution 1,Standard solution 2,Standard solution 3,and the Test solutionto a thin-layer chromatographic plate (see Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic silica gel mixture.Develop the chromatograms in a solvent system consisting of a mixture of ethyl acetate and glacial acetic acid (95:5)until the solvent front has moved about three-fourths of the length of the plate.Remove the plate from the chromatographic chamber,and allow to air-dry.Examine the plate under short-wavelength UVlight:the chromatogram obtained from Standard solution 3shows two clearly separated principal spots.In the chromatogram obtained from the Test solution,no spot corresponding to fenbendazole is more intense than the spot in the chromatogram obtained from Standard solution 2(1%),and no spot other than the principal spot and no spot corresponding to fenbendazole is more intense than the spot in the chromatogram obtained from Standard solution 1(2%).