SELECTIVITY OF CHEMICALLY BONDED ZWITTERION-EXCHANGE STATIONARY PHASES IN ION CHROMATOGRAPHY

A number of zwitterion-exchange stationary phases were prepared by immobilization of amino acids of different structure (Asp, Glu, Val, Tyr, Pro, Hypro, Arg and Lys) on a silica surface. The occurrence of oppositely charged groups in a single ion-exchange site provided cation-, anion- and zwitterion-exchange properties. The chromatographic behaviour of these stationary phases was evaluated by the retention of a series of test organic compounds of different ionogenic nature. The role of the type and structure of the ion-exchange site was considered. The structure of the bonded molecules and the pH of the eluent were shown to be key parameters influencing the ion-exchange properties of amino acid-bended silicas. The cation-exchange selectivity of phases containing primary or secondary amino groups was investigated for alkali and alkaline earth metal ions. The application of amino acid-bonded silicas to the ion chromatographic separation of anions and cations is described.