Separation ability and stoichiometry of cyclodextrin complexes

Gas–liquid chromatography has been applied to search relations between selectivity towards isomers and stoichiometry of cyclodextrin complexes. The model tested compounds were: dimethylnaphthalenes and α- and β-pinenes as constitutional isomers; cis/trans decalins, anetholes and isosafroles as diastereomers and as enantiomers (+/−)-α-pinenes and (+/−)-camphenes. Experimental retention data are used to confirm a simple theoretical model that allows distinguishing formation of G·CD complexes (1:1) and G·CD2 complexes (1:2). Based on the experimental data, stability constants K were evaluated. It has been found that remarkable selectivity factor α may appear both within the range of 1:1 stoichiometry (β-CD complexes of decalins and of α- and β-pinenes) and 1:2 stoichiometry (α-CD complexes with (+/−)-α-pinenes and (+/−)-camphenes). Occasionally selectivity arises from a different composition, when one isomer forms a 1:1 stoichiometry complex while another forms a 1:2 complex (dimethylnaphthalenes, cis/trans-anetholes and cis/trans-isosafroles).