A: Infrared Absorption á197Mñ.

B: The principal spot obtained in the chromatogram of Test solution Bprepared as directed in the test for Chromatographic puritycorresponds in size and RFvalue to that of the principal spot obtained from Standard solution B.

C: Transfer about 10mg to a test tube,add 1mLof sodium carbonate TS,mix,boil for 30seconds,and cool (Test solution A).Transfer about 10mg to a second test tube,add 1mLof sodium carbonate TS,and mix (Test solution B).[NOTE—The Methylparaben partly dissolves in Test solution B.]Prepare a solution of 4-aminoantipyrine in pH9.0alkaline borate buffer containing 1mg per mL.Simultaneously add 5mLof the 4-aminoantipyrine solution and 0.5mLof potassium ferricyanide TSto Test solution Aand Test solution B,and mix:Test solution Bbecomes yellow to orange-brown and Test solution Abecomes orange to red,with the color of Test solution Abeing clearly more intense than any similar color that may be obtained with Test solution B.

Test solutions— Prepare a solution of Methylparaben in acetone containing 10mg per mL(Test solution A).Transfer 1.0mLof this solution to a 10-mLvolumetric flask,dilute with acetone to volume,and mix (Test solution B).

Standard solutions— Transfer 0.5mLof Test solution Ato a 100-mLvolumetric flask,dilute with acetone to volume,and mix (Standard solution A).Dissolve an accurately weighed quantity of USP Methylparaben RSin acetone,and mix to obtain a solution having a known concentration of about 1mg per mL(Standard solution B).Transfer about 10mg of USP Ethylparaben RS,accurately weighed,to a 10-mLvolumetric flask,dissolve in 1mLof Test solution A,dilute with acetone to volume,and mix (Standard solution C).

Procedure— Separately apply 2µLof each Test solutionand 2µLof each Standard solutionto a thin-layer chromatographic plate (see Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic octadecylsilanized silica gel mixture.Develop the chromatogram in a solvent system consisting of a mixture of methanol,water,and glacial acetic acid (70:30:1)until the solvent front has moved about three-fourths of the length of the plate.Remove the plate from the chamber,mark the solvent front,and allow the solvent to evaporate.Examine the plate under short-wavelength UVlight,and compare the intensities of any secondary spots observed in the chromatogram of Test solution Awith that of the principal spot in the chromatogram of Standard solution A:the intensity of any individual secondary spot in the chromatogram of Test solution Ais not greater than that of the principal spot obtained in the chromatogram of Standard solution A(0.5%).The test is not valid unless the chromatogram obtained with Standard solution Cshows two clearly separated principal spots.