A:
Prepare a test solution by dissolving a quantity of it in methanol to obtain a concentration of about 1 mg of novobiocin per mL. Similarly prepare a Standard solution, using
USP Novobiocin RS. Separately apply 1-µL portions of the test solution and the Standard solution to a suitable thin-layer chromatographic plate (see
Chromatography 621) 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 UV light: the
RF value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.