A new N-hydroxyethyliminodiacetic acid modified core–shell silica phase for chelation ion chromatography of alkaline earth, transition and rare earth elements

Bare core–shell silica (1.7 μm) has been modified with iminodiacetic acid functional groups via standard silane chemistry, forming a new N-hydroxyethyliminodiacetic acid (HEIDA) functionalised core–shell stationary phase. The column was applied in high-performance chelation ion chromatography and evaluated for the retention of alkaline earth, transition and heavy metal cations. The influence of nitric acid eluent concentration, addition of complexing agent dipicolinic acid, eluent pH and column temperature on the column performance was investigated. The efficiencies obtained for transition and heavy metal cations (and resultant separations) were comparable or better than those previously obtained for alternative fully porous silica based chelation stationary phases, and a similarly modified monolithic silica column, ranging from ∼15 to 56 μm HETP. Increasing the ionic strength of the eluent with the addition of KNO3 (0.75 M) and increasing the column temperature (70 °C) facilitated the isocratic separation of a mixture of 14 lanthanides and yttrium in under 12 min, with HETP averaging 18 μm (7 μm for Ce(III))