Published: Journal of Chromatographic Science,
ISSN 0021-9665 Volume
38, Number 1, January 2000, pp. 38-45
Elution Characteristics of Natural Cyclodextrins on Porous
Graphitic Carbon
Igor Clarot, Dominique Clédat, Laoussine Boulkanz,
Emmanuel Assidjo, Thierry Chianéa, and Philippe J.P. Cardot
Laboratoire de Chimie
Analytique et de Bromatologie, Université de Limoges, Faculté
de Pharmacie, 2 rue du Docteur Marcland, 87025 Limoges Cedex, France
The retention
behavior of natural a-, b-,
and g-cyclodextrins on a porous graphitic carbon (PGC)
stationary phase is investigated. Unusual retention properties for reversed-phase
chromatographic conditions are observed with acetonitrile–methanol and water–methanol
mixtures as mobile phases. It is assumed that the retention process is governed
not only by the standard solvophobic effect but also by specific interactions
described as “CD-PGC” effect. The retention factor versus the volumetric
methanol fraction in the mobile phase show second-order curves expressing this
double mechanism hypothesis. van’t Hoff plots demonstrate the contribution
of these two retention processes. The retention factor of each natural cyclodextrin
is shown to depend on the mobile phase property to act as a proton acceptor, according
to the solvent selectivity classification described by Snyder. The “CD-PGC”
effect is interpreted as an equilibrium between different interactions: cyclodextrin–PGC
stationary phase, London dispersion forces, and cyclodextrin–mobile phase
hydrogen bonding. The balance of these interactions may monitor the orientation
of the cyclodextrin molecule facing the carbon surface, which is therefore suspected
to be the major parameter of this retention mechanism.
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