Determining the stoichiometry and binding constants of inclusion complexes formed between aromatic compounds and beta-cyclodextrin by solid-phase microextraction coupled to high-performance liquid chromatography.

The complexation of native beta-cyclodextrin (CD) and seven aromatic compounds, namely, phenetole, toluene, m-xylene, naphthalene, biphenyl, fluorene and phenanthrene, has been studied for first time utilizing a solid-phase microextraction (SPME)-high-performance liquid chromatography (HPLC) method. The stoichiometries of the analyte:beta-CD complexes were found to be either 1:1 or 1:2. The formation of 1:2 complexes was confirmed for naphthalene, biphenyl, fluorene, and phenanthrene only when utilizing relatively high concentrations of beta-CD (up to 6.6 mM). The 1:2 stoichiometries were confirmed using the classical modified Benesi-Hildebrand (BH) method. The calculated binding constants for 1:1 stoichiometries (K(1)) using the SPME method varied from 115.3M(-1) for toluene to 3510 M(-1) for phenanthrene, whereas the corresponding values to the 1:2 stoichiometries (K(3)) varied from 7.30 x 10(5) M(-2) for biphenyl to 9.03 x 10(6)M(-2) for naphthalene.