Study of the Mechanism of Enantioseparation. IX. Effect of Temperature on Retention of Chiral Compounds on a Methylated Teicoplanin Chiral Stationary Phase

Abstract

The isocratic retention of enantiomers of chiral analytes (1‐methyl‐2‐piperidinoethylesters of 2‐, 3‐, and 4‐alkoxyphenylcarbamic acid, potential local anaesthetic drugs) was studied on a methylated teicoplanin CSP, at different temperatures (in the range of 0–50°C with 10°C increments) in the polar organic mode (the mobile phase composition consisted of methanol with 17.5 mmol/L acetic acid and 4.8 mmol/L diethylamine). The natural logarithms of the retention factors (ln k _i ) of the investigated chiral compounds depended linearly on the inverse of temperature (1/T). van't Hoff plots afforded thermodynamic parameters, such as the apparent change in enthalpy (ΔH _i ), the apparent change in entropy (ΔS _i ), and the apparent change in Gibbs free energy (ΔG _i ) for the transfer of analyte between the mobile phase and the stationary phase. The thermodynamic parameters were calculated in order to promote an understanding of the thermodynamic driving forces for retention in this chromatographic system. Enthalpy–entropy compensation plots showed that all of the compounds in this study separate via the same enthalpy driven chiral recognition mechanism.

Keywords:

• Chiral separation
• HPLC
• Methylated teicoplanin CSP
• Thermodynamic study
• Enthalpy–entropy compensation
• Chiral compounds
• Alkoxysubstituted esters of phenylcarbamic acid

Acknowledgments

Authors acknowledge the support of the Grant Agency of Slovak Republic (VEGA 1/1186/04 and 1/9127/02) and the Agency for International Science and Technology Cooperation in Slovakia (Grant No. 035/2001, USA‐SK). Support of this work by the National Institutes of Health, NIH RO1 GM53825‐08 is gratefully acknowledged.