Separation of enantiomers of chiral weak acids with polysaccharide-based chiral columns and aqueous-organic mobile phases in high-performance liquid chromatography: Typical reversed-phase behavior?

• HILIC-like behavior of polysaccharide-based chiral stationary phases under aqueous-organic mobile phase conditions was observed.
• Redistribution of polar- and hydrophobic forces involved in chiral recognition based on the content of water in the mobile phase may lead to a reversal of enantiomer elution order in HPLC.
• Very different effect of water and n-hexane additives on the retention and enantioselectivity on polysaccharide-based chiral stationary phases was observed.

When polysaccharide-based chiral columns are used in combination with aqueous-organic mobile phases for the separation of enantiomers in high-performance liquid chromatography the separation mode is commonly called “reversed-phase” in analogy to achiral separations. In several earlier and recent studies on neutral and basic chiral analytes it was shown by our and other groups that due to multiple type of interactions involved in selector-selectand binding and enantioselective recognition with polysaccharide derivatives, the above mentioned separation system may not always behave like a reversed-phase system. In the present study additional examples of non-reversed-phase behavior are described for the first time for weak acidic chiral analytes. In addition, the reversal of enantiomer elution order was observed again for the first time for several analytes based on water-content in the mobile phase.