Studies on the retention mechanism of solutes in hydrophilic interaction chromatography using stoichiometric displacement theory II. HILIC/RPLC dual-retention mechanism of solutes in hydrophilic interaction chromatography over the entire range of water concentration in mobile phase

This paper is a continuation of research into the retention behavior and mechanism of solutes in hydrophilic interaction chromatography (HILIC) using stoichiometric displacement theory (SDT). A HILIC/reversed-phase liquid chromatography (RPLC) dual-retention mechanism was studied in detail using a & beta;-CD HILIC column. The retention behaviors of three groups of solutes with varying polarities were studied over the entire range of water concentrations in the mobile phase on the & beta;-CD column, resulting in the formation of "U-shape" curves when lgk' was plotted against lg[H2O]. Additionally, the effect of hydrophobic distribution coefficient lgPO/W on the retention behaviors of solutes in HILIC and RPLC modes was also examined. A four-parameter equation derived from the SDT-R was found to accurately describe the "U-shaped" curves of solutes with RPLC/HILIC dual-retention mechanisms on & beta;-CD column. The theoretical lgk' values of solutes calculated using the equation were found to be in agreement with their experimental values, with correlation coefficients greater than 0.99. This indicates that the four-parameter equation derived from SDT-R can effectively describe the retention be-haviors of solutes over the entire range of water concentrations in the mobile phase in HILIC. As such, SDT can be used as a theoretical guide for the development of HILIC, including the exploration of new dual-function sta-tionary phases to enhance separation efficiency.