Adsolubilization of drugs onto natural clinoptilolite modified by adsorption of cationic surfactants

The combined adsorption onto purified natural clinoptilolite (NZ) of the cationic surfactant benzalkonium chloride (BC) and the model drugs metronidazole and sulfamethoxazole has been studied in order to design systems for the storage and release of drugs. The equilibrium adsorption of benzyldimethylalkylammonium chloride surfactants with hydrocarbon chain lengths corresponding to 12, 14 and 16 carbon atoms (BC12, BC14 and BC16) onto NZ from aqueous solutions was compared to that of BC. The effect of exchangeable cations on the NZ structure and that of acid–base pre-treatment of NZ on the adsorption capacity of BC was evaluated. It was shown that the nature of the exchangeable cations had little influence on the adsorption of BC onto NZ, and that acid–base treatments of NZ led to a decrease in the amount of surfactant adsorbed. The results indicated that the adsorption of the less polar drug, sulfamethoxazole, was enhanced by the presence of BC12 at the solid–liquid interface, whereas the uptake of metronidazole was independent of the surfactant adsorption.