Application of Cinchona alkaloid-based zwitterionic chiral stationary phases in supercritical fluid chromatography for the enantioseparation of Nα-protected proteinogenic amino acids.
Stereoselective supercritical fluid chromatographic separations of the enantiomers of a large set of Nα-Fmoc proteinogenic amino acids were carried out on the recently developed Cinchona alkaloid-based zwitterionic chiral stationary phases Chiralpak ZWIX(+)™ and ZWIX(-)™ with protic solvents as co-solvents. The effects of the mobile phase composition, the natures and concentrations of the acid or base additives, the co- and counter-ions and temperature on the separations were investigated. The retention time in most cases slightly increased, while the separation factor decreased with increasing temperature. The changes in standard enthalpy, Δ(ΔH°), entropy, Δ(ΔS°), and free energy, Δ(ΔG°), were calculated from the linear van't Hoff plots derived from the lnα vs 1/T curves in the studied temperature range (20-60°C). The values of the thermodynamic parameters depended on the natures of the selectors and the structures of the analytes. On both ZWIX(+)™ and ZWIX(-)™ columns, enthalpically-driven separations were observed. The elution sequence was determined in all cases and was observed to be opposite on ZWIX(+)™ and ZWIX(-)™ which acted for the presented applications as chiral anion exchanger.
Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, H-6720 Szeged, Hungary; Institute of Pharmaceutical Chemistry, University of Szeged, Eötvös u. 6, H-6720 Szeged, Hungary.
Gyula
G
Lajkó
Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, H-6720 Szeged, Hungary.
István
I
Ilisz
Institute of Medical Chemistry, University of Szeged, Dóm tér 8, H-6720 Szeged, Hungary.
Gábor
G
Tóth
Institute of Pharmaceutical Chemistry, University of Szeged, Eötvös u. 6, H-6720 Szeged, Hungary.
Ferenc
F
Fülöp
Department of Analytical Chemistry, University of Vienna, Währingerstrasse 38, 1090 Vienna, Austria.
Wolfgang
W
Lindner
Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, H-6720 Szeged, Hungary. Electronic address: apeter@chem.u-szeged.hu.
Antal
A
Péter
D000596:Amino Acids / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D025924:Chromatography, Supercritical Fluid; D002930:Cinchona Alkaloids / Q000737:chemistry*; D005449:Fluorenes / Q000737:chemistry*; D013237:Stereoisomerism; D013696:Temperature; D013816:Thermodynamics
D000596:Amino Acids; D002930:Cinchona Alkaloids; D005449:Fluorenes; C016456:N(alpha)-fluorenylmethyloxycarbonylamino acids
Enantiomer separation; N(α)-Fmoc-protected proteinogenic amino acids; Supercritical fluid chromatography; Temperature effect; Zwitterionic chiral stationary phases