STDS study for the identification of released compounds from commercial ion-exchange resins

Physical and chemical stability of polymeric sorbents, including ion-exchange resins, is among the main concerns of both manufacturers and users. Different countries are gradually introducing regulations for the use of ion exchangers in water conditioning, food and beverage processing, separation of pharmaceutical products, and also for the use of reference materials as drugs and medical devices. Since all the applications mentioned may directly influence human health, the treated products must be free of any trace toxic compound potentially released by the polymeric matrix of the sorbent. The System for Thermal Diagnostic Studies (STDS) has recently been introduced commercially as a new versatile and powerful technique for the identification of the products evolved after thermal stress of solid phases. In this paper are presented the results of an STDS investigation to simulate the release of organic compounds from commercial weak and strong electrolyte anion and cation resins, differing for the type of polymeric matrix (polystyrene and polyacrylic based), porosity (gel and macroporous type), and functional groups, including sulfonic and carboxylate functionalities for the cation resins, and secondary, tertiary amine and quaternary ammonium functionalities for the anion resins. STDS determinations were carried out at 130, 200, 250 and 300 degrees C by using a constant reaction time (10 min) and an inert (He) gas atmosphere. The thermally released compounds were cryofocused at -60 degrees C and separated by temperature-programmed gas chromatography. The qualitative identification of the released compounds was made by searching the MS library NBS 54K. Thermogravimetric determinations were also carried out on a set of cation resins to complement STDS data.