Retention mechanism study of imidazole derivatives on a beta-cyclodextrin-bonded stationary phase. Thermal analysis contributions.
The high-performance liquid chromatography retention mechanism of a series of six imidazole derivatives was investigated over a wide range of mobile-phase compositions, pH, and column temperatures using a beta-cyclodextrin (beta-CD)-bonded chiral stationary phase. Thermodynamic constants for the transfer of a solute from the mobile to the beta-CD stationary phase were determined. Different van't Hoff plot shapes were observed with mobile-phase pH values, indicating a change in the retention mechanism. Enthalpy-entropy compensation revealed that the solute retention mechanism was independent of the compound molecular structure, the same at pH 7 and 7.5, but changed at pH 6.5, 8, and 8.5. Differential scanning calorimetry and thermogravimetric analysis were used to show different thermal features for the beta-CD stationary phase at pH 6.5, 8, and 8.5 and at pH 7 and 7.5. A new theory was presented to explain the beta-CD cavity structure balance between an ordered and disordered state. Variations of column temperature and mobile-phase pH tend to cause this phase transition between these two states, explaining the thermodynamic constant variations with pH and temperature.
Laboratoire de Chimie Physique et Minérale, Faculté de Médecine et de Pharmacie, Besançon, France.
N
N
Morin
Y C
YC
Guillaume
E
E
Peyrin
J C
JC
Rouland
D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003505:Cyclodextrins / Q000737:chemistry*; D004055:Differential Thermal Analysis; D007093:Imidazoles / Q000737:chemistry*; D008433:Mathematics; D012995:Solubility; D047392:beta-Cyclodextrins
D003505:Cyclodextrins; D007093:Imidazoles; D047392:beta-Cyclodextrins; C029899:imidazole; C031215:betadex