Characterization of a 2.6 μm Kinetex porous shell hydrophilic interaction liquid chromatography column in supercritical fluid chromatography with a comparison to 3 μm totally porous silica

The first systematic study of the performance of a porous shell, hydrophylic interaction liquid chromatography (HILIC) column in supercritical fluid chromatography (SFC) is presented. Observed efficiency on 2.6-mu m porous shell particles exceeded all reports using UHPLC on 100-mm long columns packed with <2-mu m totally porous particles. A Kinetex 4.6 x 150 mm, 2.6 mu m HILIC column significantly outperformed a 3 mu m Luna totally porous silica of the same length and diameter. A 17 component, low molecular weight test mix, consisting of a range of small drug-like molecules was separated isocratically on each column, with similar selectivity, but the porous shell column required 1/2 the time (approximate to 2 min vs. 4 min), with almost 50% higher efficiency. Even little retained compounds (k < 0.5) exhibited more than 30,000 plates under some conditions. Reduced plate heights were higher than previously reported on porous shell particles in both HILIC and rHPLC, with the lowest value of 1.62. Significant fronting was sometimes observed. The cause of the fronting was not determined. The least symmetrical peaks showed the highest apparent efficiency. Pressure drop at optimum velocity (2.5 ml/min) and low modifier concentrations was <60 bar, and only exceeded 250 bar at near double optimum flow and 65% modifier. Peak widths were mostly just over 0.01 min (20 Hz) wide. There was a loss of efficiency when the injection volume was increased. The chromatograph was shown to have extremely low extra-column dispersion, on the order of 5-10 mu L-2, which is also the lowest reported in an SFC, in spite of using standard components. This is likely due to turbulent flow in the tubing and fittings. (C) 2011 Elsevier B.V. All rights reserved.