DynamiGs of Two - Dimensional Diffusional Barrier Crossing

here; the transfer process can involve either partitioning or adsorption, the “solvent” being a surface in the latter case.) The principal solvation process in chromatographic separation is the creation of an acceptor cavity in (or on) the stationary‘phase and the destruction of the donor cavity in the mobile phase. Thus binding processes and chromatographic retention processes are quite different: the former requires only the change of cavity size in a single solvent; the latter requires creation of a cavity in one solvent and the destruction of a cavity in another solvent. The solvophobic theory is based on the premise that the only cavity which is relevant to retention is that in the mobile-phase solvent; it neglects the acceptor cavity in the stationary phase. Consequently, it predicts that retention should depend only on the surface tension of the mobile-phase solvent and not on the surface tension or other physical properties of the grafted stationary phase. In a partitioning theory such as the present one, cavities are described through the binary interaction constants, x; their differences account for the driving force for retention. The solvophobic theory therefore errs in important respects. For example: (i) it does not rationalize the general observationws that In k’should be a simple function of a relevant partition coefficient, and (ii) it specifies that retention should be independent of the nature of the grafted chain phase. There is much evidence that retention does depend on the grafted chain phase, some of which unambiguously cannot be interpreted in terms of effects of the phase ratio.35.58-61