The Thermodynamics of Chromatography - The Thermodynamic Analysis of the Dispersive Interactions that Can Take Place between Different Solutes and High Molecular Weigh > Page 23

Different portions of the standard free energy of distribution can be allotted to different parts of a molecule and, thus, their contribution  to solute retention can be disclosed. In addition, from the relative values of the standard enthalpy and standard entropy of each portion or group, the manner in which the different groups interact with the stationary phase may also be revealed.

Another interesting relationship arises from the above treatment and that is the standard entropy term tends to increase with the standard enthalpy term. This relationship between entropy and enthalpy has been reported many times in the literature. An example of a graph relating (DHo) to (DSo), produced by Martire and his group (K), is shown in figure 11.

From a theoretical point of view, this relationship between standard enthalpy and standard entropy is to be expected. Any increase in enthalpy indicates that more energy is used up in the association of the solute molecule with the molecules of the stationary phase.



Figure 11. Graph of Standard Free Entropy against Standard Free Enthalpy for an Ether, Thioether and Amine