title: A multiple chemical equilibria approach to modeling and interpreting the separation of amino acid enantiomers by chiral ligand-exchange chromatography.
abstract: A model of chiral ligand-exchange chromatography (CLEC) is presented that combines the non-ideal equilibrium-dispersion equation for solute transport with equations describing all chemical equilibria within the column. The model connects elution band profiles to the time and space resolved formation of diastereomeric complexes in both the mobile and stationary phases, thereby providing insights into the overall separation mechanism. The stoichiometries and formation constants for all equilibrium complexes formed in the mobile phase are taken from standard thermodynamic databases and independent potentiometric titration experiments. Formation constants for complexes formed with the stationary phase ligand are determined from potentiometric titration data for a water-soluble analogue of the ligand. Together this set of pure thermodynamic parameters can be used to calculate the equilibrium composition of the system at any operating condition. The model includes a temperature-dependent pure-component parameter, determined by regression to a single elution band for the pure component, that corrects for subtle effects associated with immobilizing the ligand (i.e., the chiral selector) onto the stationary phase. Model performance is assessed through comparison with chromatograms for two hydrophobic amino acid racemates loaded on the Nucleosil Chiral-1 CLEC column. The model is also applied to a restricted optimization of column operating conditions to assess its predictive power. In both cases, model predictions compare well with experiment while also providing a molecular understanding of the separation process and its dependence on column operating conditions.
authors.affiliation: Michael Smith Laboratories and The Department of Chemical and Biological Engineering, 2185 East Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada.
authors.forename: Nooshafarin
authors.initials: N
authors.lastname: Sanaie
authors.forename: Charles A
authors.initials: CA
authors.lastname: Haynes
mesh_terms: D000596:Amino Acids / Q000032:analysis / Q000737:chemistry; D002845:Chromatography / Q000379:methods*; D008024:Ligands; D008962:Models, Theoretical; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: D000596:Amino Acids; D008024:Ligands