ИСТИНА

Selectivity of stationary phases for hydrophilic interaction liquid chromatography (HILIC) is crucial for choosing a column for separating target polar compounds. It is important to know the effect of each functional group on the chromatographic properties of the material. Establishing the trends in selectivity changes with variations of adsorbent structure at different stages of preparation is useful for regulating the interactions of the stationary phase with analytes and creating novel materials with improved performance. This work compares a set of home-made silica-based stationary phases for HILIC with various types of coatings, including monomeric amide ligands, linear polymers such as poly(ethylene glycol) (PEG) and polyethyleneimine, glycopeptide antibiotic macromolecules, and zwitterions. Functional groups were attached to the substrate either directly or using 1,4- butanedioldiglycidyl ether as a linker. Synthesized adsorbents were characterized and compared using the Tanaka test for hydrophilic stationary phases. Their chromatographic performance was evaluated using model mixtures of neutral, zwitterionic, and negatively and positively charged polar analytes. Discussion of the modification pathways leading to better selectivity and efficiency toward each class of analytes is presented. The role of the linker used for attaching different structure units is also demonstrated in the work. Evaluating electrostatic interactions impact on HILIC retention for polar charged analytes provided a possibility for choosing the column with reasonable retention and high separation selectivity for both positively and negatively charged compounds. The prepared columns were compared to commercially available ones in terms of their hydrophilic retention and partitioning properties. Introducing highly hydrophilic amide groups or polar polymers provided the highest hydrophilic partitioning properties, while polymer-coated phases demonstrated improved hydrophilic retention among the home-made and commercially available columns. PEG-coated phases demonstrated the highest retention factors for sugars and amino acids but required their longer separation. Creating amide functionality resulted in the highest efficiency for all the tested classes of compounds (up to 50 000 N/m) and the best separation of either sugars or water-soluble vitamins. The obtained results provided better understanding of the factors affecting stationary phase selectivity and allowed to reveal the columns with improved performance for certain class of analytes. It was also shown that changing conditions and including analytes providing specific interactions with particular surfaces allowed to complement column characterization and simplify the prediction of retention and selectivity parameters.