The role of solvents in the imbibition of ascorbic acid by zeolites

Ascorbic acid is commonly used as an antioxidant agent in form of a powder. This allows the immediate availability of the molecule but cannot avoid the rapid inactivation of the excess. Sodium zeolites have frequently been proposed as agents for the controlled release of absorbed molecules. In order to prepare controlled release antioxidant agents, we treated sodium X and Y zeolites with ascorbic acid dissolved in organic solvents in order to establish how much acid they were able to retain and understand the retention and release mechanism. We found that the acid: (i) undergoes a dissociation and H+/Na+ exchange with zeolite; (ii) is retained as sodium salt while the zeolite is protonated; (iii) is released as a function of the sodium salt solubility into the solvent used. Thus, the imbibition was function of the nature of the solvent and, in aqueousorganic solvent mixtures, it was a direct function of the water concentration in the range 0–1% and an inverse function in the range 1–11%. It follows from above that, when sodium zeolite is used as a support for ascorbic acid, water percent in the range 0–11% may control the release as the ascorbate salt into aqueous–organic solvent mixtures.