Evaluation of Retention Mechanisms of Polar Compounds on Polar Stationary Phases Based on Type C Silica

Polar compounds can be separated on polar stationary phases attached on the surface of silica hydride (Type C silica). Although aqueous normal phase (ANP) chromatography has been used to denote this mode of separation, there have been no detailed studies on the retention mechanisms. We have applied the quantitative assessment methodology to investigate the retention mechanisms of polar compounds on the silica-hydride-based polar phases using a widely used hybrid silica-based amide phase for comparison. The study results indicate that the silica-hydride-based polar phases are not fundamentally different from the hybrid silica-based phase in terms of the adsorbed water layer and the retention mechanisms for polar compounds. Similar forces governing the retention in HILIC (i.e., partitioning, adsorption, and electrostatic interactions) are sufficient to describe the retention mechanisms of polar compounds on the silica-hydride-based polar phases. However, some small differences in selectivity are observed between the silica-hydride-based and hybrid silica-based phases.