(197n) Molecular-Level Insights into Hydrophilic Interaction Liquid Chromatography Via Molecular Simulations

Monte Carlo simulations are carried out to provide molecular-level insights into the retention mechanism in hydrophilic interaction liquid chromatography (HILIC). The stationary phases investigated here include a 9-nm cristobalite silica slit pore and a 9-nm amorphous silica slit pore. The mobile phases are water/acetonitrile mixtures at three compositions (neat acetonitrile, 5 and 10% v/v water in acetonitrile). The analytes include C1-C6 linear alkanes and alcohols. The simulations are performed at two temperatures, 303 and 333 K, and a pressure of 10 MPa. The simulations indicate that the stationary phase is retentive to the hydroxyl group (separating a primary alcohol from the linear alkane with the same number of carbon atoms) since the linear alcohols can form hydrogen bonds with the surface silanols and water molecules adsorbed on the silica surface. The addition of water reduces the retention increment of the OH group because of the stronger solvophilic effect. However, the contribution from the stationary phase to the retention of the OH group does not increase significantly as the water composition increases. Analyses of simulation trajectories provide insights into the structure of the HILIC phases, the orientational distribution of the solvent and analyte molecules, and the propensities of the silanol-analyte, silanol-water, and water-analyte hydrogen bond formation.