Chromatographic Selectivity of Rare Earth Elements on Iminodiacetate-Type Chelating Resins Having Spacer Arms of Different Lengths: Importance of Steric Flexibility of Functional Group in a Polymer Chelating Resin

Abstract

Three types of chelating resins containing iminodiacetic acid homologues (IDA resins) with spacer arms of different lengths were prepared and examined as the column stationary phase for ion chromatography. The chromatographic retention behavior of rare earth elements (REEs) on the IDA resins was evaluated with respect to a capacity factor (k') to elucidate the selectivity profile of the resins. The k' values for a series of REEs on the IDA resins were compared with the chelate formation constants (K(ML)) of the corresponding free ligands of analogous structure. Selectivity of the chelating resins having longer spacer arms between the ligand group and the polymer matrix showed a better correlation with the corresponding monomeric ligands in solution. This trend has been attributed to the increase in steric flexibility of the ligand group by the presence of the spacer arm.