ELUTION BEHAVIOR OF ANIONS AND CATIONS ON A MIXED-BED STATIONARY-PHASE OF ANION AND CATION-EXCHANGE RESINS

The retention mechanism of anions and cations on a mixed-bed column pa cked with a mixture of strong anion and cation exchange resins has bee n studied. Organic acids and inorganic anions have showed the same elu tion behaviour on the mixed-bed column as on a single anion exchange c olumn. In contrast, different elution behaviours for cations have been observed between the mixed-bed column and a single cation exchange co lumn. On the mixed-bed column, cations would be eluted by a mixed rete ntion mechanism. The primary retention mechanism is ion exchange with eluent cation (H+) for al cations. The ion exchange mechanism on the s ites occupied by anion exchange groups makes a greater contribution fo r monovalent cations. A partition mechanism between the stationary pha se and mobile phase contributes to the separation of Mg2+ and Ca2+ by forming neutral compounds.