文摘
The retentive principle of hydrophilic interaction liquid chromatography (HILIC) with a water (W)鈥揳cetonitrile (ACN) mobile phase (MP) and a hydrophilic stationary phase is the formation of a W-rich layer with a rigid and diffuse part in the immediate and extended surface region, respectively. Through molecular dynamics simulations of the adsorption of W鈥揳cetone (Ace), W鈥搈ethanol (MeOH), and MeOH鈥揂CN mixtures to a hydrophilic silica surface, we evaluate their MP potential for aqueous and nonaqueous HILIC. We analyze solvent and hydrogen-bond density profiles, solvent鈥搒urface coordination, as well as local solvent orientation, mobility, and composition. Our data show that W鈥揂ce mixtures closely mimic the behavior of W鈥揂CN mixtures, whereas W鈥揗eOH mixtures fail as HILIC MP because the similar affinity of the silica surface for W and MeOH prevents preferential adsorption of W. MeOH鈥揂CN mixtures form a rigid MeOH layer that reverses the surface polarity and prohibits formation of a diffuse MeOH layer in the extended surface region. Generally, a rigid layer at a hydrophilic surface is formed by binary mixtures whose solvents have sufficiently different hydrogen-bonding abilities, and a diffuse layer is formed when the rigid layer maintains hydrophilic properties.
