Improvement of Chiral Discrimination of Acidic Enantiomers on Teicoplanin Stationary Phase by the Use of Chaotropic Effect

Abstract

This work reveals new advantages of using inorganic salts with chaotropic anions (perchlorate, hexafluorophosphate) as mobile phase additives in enantioseparation of acidic compounds (mandelic acid, tropic acid, phenyllactic acid, 2-(p-methoxyphenoxy)-propionic acid) on teicoplanin-based stationary phase in reversed phase mode. It was observed that the retention factors (k) and the separation factors (α) of acidic analytes increased in the presence of salts in the mobile phase. The standard changes in enthalpy (ΔH⁰), entropy (ΔS⁰), and the free energy (at 20°C) (ΔG⁰) of the binding interactions between enantiomers and the chiral selector in the stationary phase were calculated from the experimental relationships of ln k vs 1/T in the presence of chaotropic salts in eluent systems. The Van't Hoff plots reveal that the interaction mechanism in the presence of chaotropic additives is enthalpy driven. Enthalpy-entropy compensation (EEC) studies revealed mechanistic similarity in retention of the investigated compounds.

Keywords:

• Chao-tropic effect
• Enantiomer separation
• Teicoplanin chiral stationary phase
• Thermodynamic analysis