The effect of buffer concentration and cation type in the mobile phase on retention of amino acids and dipeptides in hydrophilic interaction liquid chromatography

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

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.

Chromatographic behavior of new deazapurine ribonucleosides in hydrophilic interaction liquid chromatography

The chromatographic behavior of new biogenic purine nucleosides in hydrophilic interaction liquid chromatography was examined on three different stationary phases, namely bare silica, and amide- and cyclofructan-based stationary phases. The effects of buffer concentration, pH and acetonitrile-to-aqueous-part ratio in the mobile phase on retention and peak shape were assessed. The retention coefficients and peak symmetry values substantially differed with respect to analytes´ structures, stationary phase properties and mobile phase composition. The bare silica column was unsuitable for these compounds under the chromatographic conditions tested due to very broad and asymmetrical peaks. Furthermore, the cyclofructan-based stationary phase provided almost Gaussian peak shapes of all deazapurine nucleosides under most conditions tested. Therefore, the cyclofructan-based stationary phase is the most suitable choice for the chromatographic analysis of nucleosides.