Measurement of Adsorption Characteristics of Enantiomers on Chiral Columns: Comparison of the Frontal and Elution Chromatographic Techniques

Abstract

This study measured the adsorption characteristics of 1,1′-bi-2-naphthol on Pirkle-type (3,5-dinitrobenzoyl phenylglycine covalently bonded to silica gel) chiral columns. The single-component isotherm of each isomer was measured by the elution on a plateau (EP) and the frontal analysis (FA) methods. The results showed that the R-isomer is more retained than the S-isomer, and the separation factor between them is about 1.1. The adsorption behavior of each isomer conforms to the Langmuir model in the concentration range studied. The isosteric heat of adsorption was constant regardless of the amount adsorbed for both the R-isomer and the S-isomer. These results suggest that Pirkle covalent D-phenylglycine has an energetically homogeneous surface. In contrast, the isotherm data obtained by the FA and EP methods are in good agreement with errors within about 5% for both components. The FA method was selected as the more rapid, precise, and accurate method for isotherm measurement. However, the EP method was used to measure the other adsorption characteristics, e.g., the axial dispersion coefficient and the diffusion coefficient of each solute, besides the equilibrium isotherm.

Keywords:

• Enatiomers
• Chiral columns
• Measurement of adsorption characteristics
• Frontal chromatography
• Elution chromatography

ACKNOWLEDGMENT

The authors thank the National Science Council of the Republic of China for the financial support received under Grant NSC 86–2214-E-224–001.