Hydrophilic retention mechanism of imidazoline and serotonin receptor ligands in thin-layer and high-performance liquid chromatography systems

Abstract

We investigated and compared hydrophilic retention mechanism (HILIC) of ten compounds (imidazoline and serotonin receptor ligands) in the thin-layer chromatographic (TLC) system and the high-performance liquid chromatographic (HPLC) system. The TLC and HPLC stationary phases were the chemically bonded amino (NH2) phases. In the TLC mode, the binary mobile phases were composed of acetonitrile (as the main component) and water or methanol (as the modifier). In the HPLC mode, the binary mobile phase was composed of acetonitrile (as the main component) and methanol (as the modifier). For each compound, we determined this region for which linear relationship between the retention and volume fraction of the mobile phase modifier was observed, and the retention behaviour was described by the linear solvent strength (LSS) model. With the obtained regression constant values (log k0, RM0) in mind, we selected molecular parameters influencing retention mechanism in the considered chromatographic systems. Lipophilicity plays an important role in the TLC mode with the acetonitrile‒methanol mobile phase, while geometrical characteristics of the test compounds (ring complexity, number of multiple bonds) play a predominant role in the TLC mode with the acetonitrile‒water mobile phase. It was also established that the hydrophilic mechanisms are different for the non-aqueous TLC vs. aqueous TLC systems and for the TLC vs. HPLC systems. As a result, different elution orders and separation performances can be expected for the imidazoline and serotonin receptor ligands, depending on the chromatographic system employed.