Enthalpy as a Thermodynamic Property in Retention Studies

The chromatographic retention parameters used in correlation studies are normally assumed to be proportional to the free energy change. 

Adsorption is accompanied by a loss of surface free energy. Free energy change is related to enthalpy, AH, and entropy, AS, changes by the Gibbs equation  

The retention factor is related to the thermodynamic equilibrium constant K for solute binding by k = (IK, where f is the phase ratio of the column. The free-energy change for the chromatographic process is expressed by 

A van t Hoff plot of In k against l/T yields a straight line if the stationary phase is not deformed. The relation Ink and —AH/RT is used to study the temperature-dependent selectivity of the stationary phase.33-35 

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