Separately apply 10-µL portions of the solutions to a suitable thin-layer chromatographic plate (see
Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of a mixture of chloroform, methanol, and ammonium hydroxide (80:20:1) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate. Expose the plate to iodine vapors for 2 hours, and locate the spots on the plate by examination under short-wavelength UV light. Compare the intensities of any secondary spots observed in the chromatogram of the test solution, excluding the origin spot due to the maleate anion, with those of the principal spots in the chromatograms of the Standard solutions: no secondary spot is more intense than the principal spot obtained from Standard solution A (0.4%), and the sum of the intensities of all secondary spots, excluding any having intensities less than the principal spot obtained from Standard solution C, does not exceed 1.0%.