The Thermodynamics of Chromatography - Other Thermodynamic Methods that are Used for Studying Chromatographic Systems > Page 55
Other Thermodynamic Methods that are Used for Studying Chromatographic Systems
Thermodynamic argument can be readily employed to study a wide range of chromatographic systems. The application of thermodynamic analysis is particularly pertinent when temperature effects are being examined and when mixed phases are employed. The following two examples are typical of the thermodynamic approach to practical problems.
The Effect of the Composition of Non-Associating Binary Solvent Mixtures on Solute Selectivity.
Experimentally and (albeit qualitatively) it has been shown, that although the retention of a solute continually changes with solvent composition, there can be a specific temperature at which the separation ratio of a pair of closely eluting solutes (e.g., a pair of enantiomers) is independent of the solvent composition.This somewhat surprising result was not examined analytically to ascertain the conditions under which this situation could occur (13). However, it will be shown with the aid of thermodynamical argument that, from the relationship between retention, separation ratio, temperature and solvent composition, there are specific conditions that allow the separation ratio of a pair of solutes to be independent of solvent composition and there is a specific temperature at which this occurs.
Reiterating the expression for the distribution coefficient of a solute between two immiscible phases, one constituting a mixture of variable composition, that was developed by Katz et al.., (see book 7 of this series)