Seemingly identical chromatographic conditions result in drastically different enantioseparations on amylose tris(3,5-dimethylphenylcarbamate) (ADMPC) columns in mixtures of 2-propanol and methanol. Selectivities of structurally diverse enantiomer pairs depend on the direction from which the composition of the eluent is approached. An alteration in the structure of the chiral stationary phase (CSP) is the only realistic reason behind the dissimilar selectivities in the same eluent. History-dependent retention and recognition mechanisms are indicated by van't Hoff plots and even by a reversal of the enantiomer elution order. The most notable observation is the easy access to markedly different states of the CSP in the same solvent mixture by a short pretreatment with 2-propanol in one case and with methanol in the other, while the transition between the two states is hindered enough to ensure long-term stability for both. Repeatability strongly depends on the composition of the eluent and it is key to utilization and also to rationalization of the phenomenon. From a theoretical point of view, this so-called hysteretic behavior poses another challenge to consider when modeling chiral interactions.
Keywords: Chiral HPLC; Conformational transition; Enantiomer elution order; Hysteresis; Polysaccharides; Solvation.
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