Due to its excellent selectivity control, one of the most successful chromatographic techniques for the determination of metal cations in high ionic strength samples is that of high performance chelation ion chromatography (HPCIC). Iminodiacetic acid derivatives are widely used for the preparation of chelating adsorbents. The limiting factor in the development of HPCIC is column efficiency. Fully porous silica particles are usually used for the preparation of chelating phases in HPCIC. However, novel advanced silica supports, such as monolithic or core-shell silica can significantly improve separation efficiency and reduce analysis time. To date, very few publications on preparation and characterisation of chelating monolithic porous phases for the application in HPCIC have been reported, and no data in the literature on the use for this purpose of core-shell silica particles.
Here, a commercially available porous silica monolithic column (Onyx Monolithic Si, 100 x 4.6 mm I.D.) was in-situ modified with 2-hydroxyethyliminodiacetic acid (HEIDA) functional groups. Additionally, a column (50 x 4.6 mm I.D.), packed with 1.8 µm core-shell silica particles modified with HEIDA was prepared. Both columns were characterised and compared for their chromatographic selectivity towards alkaline earth, transition and rare-earth metal cations. The, complete investigation into the influence of eluent concentration, ionic strength, the addition of complexing agent (dipicolinic acid), eluent pH and column temperature was performed.
An isocratic separation of a mixture of 14 lanthanides and yttrium was achieved in just 8.5 mins using HEIDA core-shell column, with peak efficiencies of up to 200,000 N/m, while it was shown that monolithic HEIDA column cannot be used for this application due to specific effects originated from the silica backbone. However, the latter has been successfully applied to the fast direct analysis of seawater and various shellfish samples.