Introducing Enantioselective Ultrahigh-Pressure Liquid Chromatography (eUHPLC): Theoretical Inspections and Ultrafast Separations on a New Sub-2-μm Whelk-O1 Stationary Phase

A new chiral stationary phase for UHPLC applications was prepared by covalent attachment of the Whelk-O 1 selector to spherical high surface area 1.7 μm porous silica particles. Columns of varying dimensions (50, 75, 100, 150 mm length and 3.0 or 4.6 mm internal diameter) were packed and charac-terized in terms of permeability, efficiency, retention and enantioselectivity using either organic and water-rich mobile phases. A conventional HPLC Whelk-O 1 column based on 5.0 μm porous silica par-ticles and packed in a 250 x 4.6 mm column was used as reference. Van Deemter curves, generated with low molecular weight solutes on a 100 x 4.6 mm column packed with the 1.7 μm particles, showed Hmin (μm) and νopt (mm/s) values of 4.10 and 5.22 under normal phase and 3.74 and 4.34 under re-versed phase elution conditions. The flat C term of the van Deemter curves observed with the 1.7 μm particles allowed the use of higher than optimal flow rates without significant efficiency loss. Kinetic plots constructed from van Deemter data confirmed the ability of the column packed with the 1.7 μm particles to afford sub-minute separations with good efficiency and its superior performances in the high speed regime compared to the column packed with 5.0 μm particles. Resolutions in the time scale of seconds were obtained using a 50 mm long column in the normal phase or polar organic mode. The intrinsic kinetic performances of 1.7 μm silica particles are retained in the Whelk-O 1 chiral stationary phase, clearly demonstrating the potentials of enantioselective UHPLC in terms of high speed, throughput and resolution.