Enhancing the selectivity of polar hydrophilic analytes with a low concentration of barium ions in the mobile phase using geopolymers and silica supports

Abstract

Charged analytes such as organic sulfonic acids, sulfates, carboxylates, and phosphates are often analyzed by hydrophilic interaction liquid chromatography (HILIC). In many cases, these analytes do not show any selectivity and elute near the dead time using the conventional acetonitrile-ammonium acetate buffers. In this work, we introduce a powerful selectivity enhancing technique by using a trace amount of Ba2+ ion in the mobile phase as a general approach for HILIC with UV–Vis detection. Silica and a newly developed material called geopolymers are used as stationary phases. Geopolymers are X-ray amorphous aluminosilicate inorganic polymers with cation exchange properties. Barium exchanged geopolymers (Ba-NM-GP) are synthesized from metakaolin based geopolymer. Thorough characterization of Ba-NM-GP is reported using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Brunauer-Emmett-Teller (BET) surface area analyzer and laser diffraction particle size distribution analyzer for the determination of their shape, size, porosity, surface area and particle size distribution respectively. It is demonstrated that in the absence of Ba2+, baseline separations of sulfonates, carboxylates, and phosphates is not possible, whereas, in the presence of Ba2+ in the mobile phase, these analytes are easily separated. Barium perchlorate is suggested as an additive for it is UV transparent, and it has practically an unlimited solubility in acetonitrile.