On the morphological and chemical stability of vitamin C crystals

Mass cooling crystallization of aqueous vitamin C solution was studied by applying different cooling rates, initial supersaturations and mixing intensity. The morphology of the products (size, habit and colour) well followed the changes of process parameters. Comparing a high purity (99.9%) standard with a yellow coloured heterodisperse product and a slowly grown single crystal, HPLC chromatography detected decreasing purity of the bigger single crystals, while X-ray and NMR analysis did not show any perceptible difference. It has been concluded that not the surface oxidation (chemical degredation), but rather the inclusions are the main sources of impurities within the crystals.