Effect of temperature on retention of alkali and alkaline-earth metal ions on some aminocarboxylic acid functionalised silica based ion exchangers

The temperature effect on retention of alkali and alkaline earth cations on three different carboxylic acid cation exchangers was investigated. The silica-bonded 2,6-diaminohexanoic (lysine), 2-aminoglutaric (glutamic acid) and iminodiacetic acids were used as cation exchangers and compared with hare silica. Perchloric acid was used as the eluent in all experiments. The dependence of retention (log k') from reciprocal temperature (1/T) is linear for all cations in the case of silica-bound lysine and glutamic acid. An abnormal parabolic dependence of log k' vs 1/T was observed for iminodiacetic acid functionalized silica. The possible impact of complexation between functional groups of cation exchangers and retained cations and the effect of two carboxylic groups in a single ion-exchange site on retention are discussed. The calculated values of heats of adsorption are in the range 4-9 kJ/mol. (C) 1998 Published by Elsevier Science B.V. All rights reserved.