NEW STATISTICAL APPROACH TO A GAS-CHROMATOGRAPHY RETENTION MODEL - APPLICATION TO DICHLOROPHENOL ISOMERS

The retention mechanism of a series of six positional isomers of dichl orophenol in gas chromatography was investigated using pure alpha-, be ta-, and gamma-cyclodextrin (CD) stationary phases. For each CD, the v alues of enthalpy (Delta H) and entropy (Delta S) of transfer of an is omer from the gas to the CD stationary phase were determined. These da ta demonstrated the leading role of enthalpy according to entropy. Ent halpy-entropy compensation revealed that the retention mechanism was i ndependent of both the chloro group position on the phenol ring and th e size and shape of the CD cavity. A model based on the number of CD i nclusion complexes with an isomer was also presented. This model expla ins current experimental data including the reverse elution order obse rved for certain pairs of isomers.