Silica-based metal chelate affinity sorbents I. Preparation and characterization of iminodiacetic acid affinity sorbents prepared via different immobilization techniques

Abstract

Iminodiacetic Acid (IDA) was immobilised on silica supports using either activated chromatographic supports or silanes carrying IDA in ω-position to silicium. Through reaction of IDA with glycidoxypropyltrimethoxysilane (GLYMO) before immobilization, a new and simple method is introduced which provides a metal chelate affinity sorbent of both high capacity for Cu(II) (28 μmol/ml) and almost identical chromatographic characteristics to soft gel metal chelate affinity sorbents. By immobilization of IDA through n-alkyl spacers exclusive of an epoxy group a different chemical neighborhood to the chelator is obtained. These metal chelate sorbents demonstrated higher capacities for Cu(II) (39 μmol/ml). The selectivity for lysine was higher, for histidine lower, compared to epoxy-immobilized IDA chelates. It is concluded that the β-hydroxyl group, evolved during reaction with epoxy groups, is integrated with the metal chelate, thus forming a N-(hydroxyethyl)iminodiacetic acid (HEIDA). The most distinct chromatographic behaviour was observed with CDI-immobilised IDA chelates, which displayed higher selectivity for acidic amino acids than common IDA chelates.