Reversal of elution order during the chiral separation in high performance liquid chromatography

The elution order of the enantiomers is one of the most important topics in the field of chiral separations. The reversal of enantiomeric elution order, although rare, could be observed during the investigations of chiral discrimination in high performance liquid chromatography (HPLC). Scrutinizing these phenomena must be helpful in determining the optical purities because it is favorable to elute the minor enantiomeric impurity before the major component. In this mini-review, several examples of such unusual behavior will be described from the point of mechanistic rationale.