Chromatographic Modes of Column Separation

The basic principle of chromatographic separations can be described in terms of thermodynamics by means of the distribution coefficient K  

AG is the change in free energy between the species in the stationary phase and the mobile phase. 

In GPC separations, the enthalpic contribution to the free energy term vanishes when we assume no energetic interaction between the analyte and sorbent  

AS is the entropy loss when a molecule enters a pore of the stationary phase. 

In the case of no steric exclusion of the molecule from parts of the stationary phase, the retention can be described by the enthalpic term alone  

---