The Mechanism of Chromatographic Retention - Mixed Phases > Page 21

These workers measured the retention of a series of solutes on different binary mixtures of stationary phases. They employed GC as opposed to LC because retention was solely controlled by the interactions in the stationary phase and was not confused by significant interactions in the mobile phase. They arrived at the surprising conclusion that, for a wide range of binary mixtures, the corrected retention volume of a solute was linearly related to the volume fraction of either one of the two phases.

This relationship was quite unexpected as, at that time, the assumption was in vogue that the retention volume would be some form of the exponent of the stationary phase composition. Purnel's conclusions can be put in the following form,

V'r(A) = KAaVS +KB(1-a)VS

 

where V'r(AB) is the retention volume of the solute on a mixture of stationary phases (A) and (B),
(KA) is the distribution coefficient of the solute with respect to the pure stationary phase (A),
(KB) is the distribution coefficient of the solute with respect to the pure stationary phase (B),
(VS) is the total volume of stationary phase in the column
and(a) is the volume fraction of phase (A) in the stationary phase mixture