The Thermodynamics of Chromatography - Other Thermodynamic Methods that are Used for Studying Chromatographic Systems > Optimum Operating Conditions for Chiral Separations in Liquid Chromatography > Page 69

The relationship between the corrected retention volume and the reciprocal of the volume fraction of one component of the mobile phase was established for mixtures of non-associating solvents by the pioneering work of Purnell and his group (16) They demonstarted that the corrected retention volume of a solute on a mixed phase in GC was proportional to the volume fraction of one component in the stationary phase mixture.

This was supported by the work of Scott (17), who showed that the retention of a solute in LC was inversely proportional to the volume fraction of one solvent in a mobile phase containing a binary mixture of dispersive solvents.

  

 

 

 

Figure 16 Graph of Corrected Retention Volume of (R) and (S) Solute against the Reciprocal of the Volume Fraction of Ethanol

This was interpreted by Scott and Kucera (18), as the volume fraction of a given solvent set the probability of a solvent molecule interacting with a solute molecule, in much the same way as the partial pressure of a gas determined the probability of a molecular collision with another molecule of gas. The simple relationship only applies if the components of the mobile phase do not strongly interact and form an associate (e.g. the relation ship would not hold for water/methanol mixtures).