ИСТИНА

Using polymers is promising for creating new hydrophilic stationary phases. The formation of a polymeric functional layer can effectively shield the substrate and reduce its influence on the retention of analytes. In this work it is proposed to use the flexible multicomponent Ugi reaction for creating a polymeric functional layer on the substrate surface by “one-pot” synthesis. Novel adsorbents were obtained by covalent modification of 3-aminopropyl silica substrate with acetaldehyde, 2-morpholinoethyl isocyanide, and different polymeric acids such as polylactic, polyacrylic, and poly(acrylic acid-co-maleic acid). To characterize and compare the synthesized adsorbents, the Tanaka test for hydrophilic stationary phases and model mixtures of polar compounds were used. The influence of the polymer structure on the stationary phase performance was evaluated, namely, the effect of the polymer layer attachment to the silica surface, the number of carboxyl groups in its structure, molecular weight of the polymer, and substrate-to-polymer mass ratio. Increasing the number of carboxyl groups in the functional layer resulted in increased hydrophilicity and improved separation selectivity for nitrogenous bases and nucleosides and other polar compounds followed by a decrease of anion exchange selectivity. Using polylactic acid in the Ugi reaction led to a decreased hydrophilicity and anion-exchange selectivity of the adsorbent as compared to polyacrylic acid. Different substrate-to-polymer ratios used for the synthesis allowed to manipulate both hydrophilicity and anion-exchange selectivity. An increase in the molecular weight of the polymeric acid determined an improvement in the separation efficiency for all classes of model analytes. Incorporating different polymeric acids into the functional layer of the adsorbents via the Ugi reaction also resulted in reasonable retention and separation of hydrophobic alkylbenzenes in reversed-phase HPLC mode. Thus, the factors influencing chromatographic properties of novel HILIC adsorbents were established, which could help to govern their selectivity and efficiency and initiate mixed-mode behavior of the stationary phase.