Understanding the transition from high-selective to high-efficient chiral separations by changing the organic modifier with zwitterionic-teicoplanin chiral stationary phase

The retention behavior of small molecules and N-protectedaminoacids on a zwitterionic teicoplanin chiral stationary phase (CSP),prepared on superficially porous particles (SPPs) of 2.0 mu mparticle diameter, has shown that efficiency and enantioselectivity,and so enantioresolution, dramatically change depending on the employedorganic modifier. In particular, it was found that while methanolpermits the boost of enantioselectivity and resolution of the aminoacids, at the cost of efficiency, acetonitrile allows for the abilityto reach extraordinary efficiency even at high flow rates (with reducedplate height <2 and up to 300,000 plates/m at the optimum flowrate). To understand these features, an approach based on the investigationof mass transfer through the CSP, the estimation of the binding constantsof amino acids on the CSP, and the assessment of compositional propertiesof the interfacial region between bulk mobile phase and solid surfacehas been adopted.