A:
Prepare a test solution by dissolving a quantity of it in methanol to obtain a concentration of about 1mg of novobiocin per mL.Similarly prepare a Standard solution,using
USP Novobiocin RS.Separately apply 1-µLportions of the test solution and the Standard solution to a suitable thin-layer chromatographic plate (see
Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic silica gel mixture,and allow the spots to dry.Place the plate in a chromatographic chamber equilibrated with a solvent system consisting of a mixture of chloroform,methanol,and ammonium hydroxide (75:25:1),and develop the chromatogram.When the solvent front has moved about three-fourths of the length of the plate,remove the plate from the chamber,and allow to dry.Locate the spots on the plate by examination under short-wavelength UVlight:the
RFvalue of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.