To date there is a rather large arsenal of chiral stationary phases (CSPs) and related columns for analytical and preparative enantiomer separations by liquid chromatography available. These CSPs are based on a diversified spectrum of chiral selectors (SOs) of which the polysaccharide derived ones are dominating.

From a mechanistic but also practical point of view we concentrated our efforts towards the development of enantioselective ion exchange type selector systems encompassing chiral anion (WAX), chiral cation (SCX) and chiral zwitterionic (ZWIX) ion exchangers.

For these systems electrostatic interactions via ion pairing between the chargeable sites of the chiral selector (SO) and the chiral selectands (SAs) are the driving forces to generate retention as it is common in ion exchange chromatography. In concert with spatially arranged chiral motifs of the SO and SA units additional binding sites for intermolecular SO-SA interactions of hydrogen bonding, aryl-aryl, and/or hydrophobic character will come into play for tuning the stereoselective molecular recognition concepts.

Chiral ion exchangers take advantage of intrinsic feature as of: (i) they work without restrictions in polar organic, hydro-organic and SFC mobile phase mode, (ii) retention is tuneable via pH and buffer concentration of mobile phase, and (iii) the loadability of SA can be very high according to stoichiometric binding and displacement model.

Of particular interest are the ZWIX type selectors as they take advantage of a simultaneously occurring double ion pairing concept with zwitterionic SAs. This enables the retention and resolution of diverse free alpha, beta and gamma amino acids, peptides, peptomimetics, etc. Respective molecular recognition mechanisms will be discussed and supported by practical examples.