[The use of enthalpy-entropy compensation in the study of retention mechanism of aromatic positional isomers].
In this paper, the thermodynamic parameters of the separation process of six groups of aromatic positional isomers on nine crown ether polysiloxane, OV-1701 and Carbowax-20M capillary chromatographic columns have been investigated systematically. The Gibbs free energies for every compound at harmonic mean temperature, calculated were given. The enthalpy-entropy compensation effect of these chromatographic process was examined by using of Krug's ANOVA method. In the light of the axiom of extrathermodynamic relationship, the retention mechanisms of these aromatic compounds on each crown ether stationary phase have been expounded. We come to conclusion that, as a whole, the separation of various aromatic isomers on crown ether stationary phase is governed by multiple retention mechanisms, but the separation of some groups of aromatic isomer on the same crown ether phase can be led to single interaction mechanism since the phenomena of enthalpy-entropy compensation is observed. It may be that a kind of interaction parameter, which varies with the configuration of solutes, plays the main role in retention process of these isomers.
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Chemistry Department of Wuhan University, Wuhan, 430072.
Wu
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