Abstract
Until less than 10 years ago, chiral separations were carried out with columns packed with 5 or 3 μm fully porous particles (FPPs). Times to resolve enantiomeric mixtures were easily larger than 30 min, or so. Pushed especially by stringent requirements from medicinal and pharmaceutical industries, during the last years the field of chiral separations by liquid chromatography has undergone what can be defined a “true revolution”. With the purpose of developing ever faster and efficient method of separations, indeed, very efficient particle formats, such as superficially porous particles (SPPs) or sub-2 μm FPPs, have been functionalized with chiral selectors and employed in ultrafast applications. Thanks to the use of short column (1–2 cm long), packed with these extremely efficient chiral stationary phases (CSPs), operated at very high flow rates (5–8 mL/min), resolution of racemates could be accomplished in very short time, in many cases less than 1 s in normal-, reversed-phase and HILIC conditions. These CSPs have been found to be particularly promising also to carry out high-throughput separations under supercritical fluid chromatography (SFC) conditions. The most important results that have been recently achieved in terms of ultrafast, high-throughput enantioseparations both in liquid and supercritical fluid chromatography with particular attention to the very important field of bioactive chiral compounds will be reviewed in this manuscript. Attention will be focused not only on the latest introduced CSPs and their applications, but also on instrumental modifications which are required in some cases in order to fully exploit the intrinsic potential of new generation chiral columns.
Highlights
Separation of chiral compounds has always been one of the most challenging applications of liquid chromatography (LC)
For over thirty years, research activities in the field of LC enantioseparations have been essentially focused on the development of novel chiral stationary phases (CSPs), able to resolve the largest number of enantiomeric pairs
They compared CSPs based on different chiral selectors operated in different chromatographic modes, including RP, hydrophilic interaction chromatography (HILIC), polar organic mode (POM) [2,14,15,16,17,18]
Summary
Separation of chiral compounds has always been one of the most challenging applications of liquid chromatography (LC). The most comprehensive work aimed at investigating kinetic performance of columns packed with both sub-2 μm FPPs and second-generation SPPs is that by Armstrong’s group They compared CSPs based on different chiral selectors (i.e., polysaccharides, cyclofructans, macrocyclic glycopeptides) operated in different chromatographic modes, including RP, hydrophilic interaction chromatography (HILIC), polar organic mode (POM) [2,14,15,16,17,18]. This suggests that slurry packing polar SPPs (such as chiral ones) could be more difficult than for hydrophobic ones for which, on the other hand, it has been largely demonstrated a smaller contribution of eddy diffusion if compared to FP counterparts Another important point is that in chiral chromatography an additional source of band broadening must be considered, that is adsorption-desorption kinetics. Particular attention will be focused on instrumental modifications required on chromatographic equipments in order to fully exploit the intrinsic potential of new generation chiral columns
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