Comparative study on camphor enantiomers behavior under the conditions of gas–liquid chromatography and reversed-phase high-performance liquid chromatography systems modified with α- and β-cyclodextrins

The dependence of retention and selectivity parameters of camphor enantiomers on the concentration of α- and β-cyclodextrins were studied under conditions of GLC (matrix solvent: Glycerol, 95°C) and RP-HPLC (matrix solvent: Aqueous methanolic, 20°C). It has been found that β-cyclodextrin forms complex of 1:1 stoichiometry and does not recognize enantiomers of camphor. In contrast α-CD forming complexes of 1:2 stoichiometry appeared to be very efficient chiral selector of (+) and (−)-camphor. Relatively considerable differences have been observed between stability constants determined by GLC and RP-HPLC, what may be explained by the various natures of the matrix solvents and the various temperatures of the measurements. On the contrary, the enantioseparation factor α observed at higher concentrations of α-cyclodextrin stabilizes on the very similar value α+/−GLC≅α−/+HPLC≅1.6. Simple theoretical considerations focusing on the differences in the mechanisms of the studied processes have been performed. According to them the enantiomer forming the more stable complex with the cyclodextrin should be eluted from the RP-HPLC column first and GLC column last. This fact has been confirmed experimentally.