Tuneable peak deformations in chiral liquid chromatography

Modern chiral stationary phases are often combined with eluents comprising a mixture of organic solvents and polar additives. The latter may cause extreme deformations of the eluted enantiomer bands in both, analytical and preparative separations. In this work, we give a theoretical background for these deformations. As an experimental verification, we separate the enantiomers of different beta-blockers on a teicoplanin stationary phase (Chirobiotic T) in the presence of triethylamine/acetic acid. We show that it is possible to tune the peak shapes of the two enantiomers by varying the organic solvent composition. An advantageous situation occurs when the first eluted peak is transformed to an anti-Langmuirian shape while keeping the second enantiomer in a normal Langmuirian shape. In this situation, the two peaks tail in opposite directions with their sharp sides pointing closely to each other. It is then possible to obtain baseline resolution at higher load than when both enantiomer peaks tail in the same direction. Adsorption isotherm parameters were determined using the inverse method; no other method could be used due to the system complexity. Computer simulations, based on these parameters, agreed very well with the observed deformations, thus confirming our hypothesis of their origin.