CLASSIFICATION OF COUNTERCURRENT CHROMATOGRAPHY SOLVENT SYSTEMS ON THE BASIS OF THE CAPILLARY WAVELENGTH

Solvent systems used for countercurrent chromatography (CCC) have been classified in three groups, defined by Ito from experimental observations of their flow behaviors in a countercurrent chromatograph. To achieve good retention of one phase of a solvent system when the other one is pumped in the column, it is necessary to know to which of these groups it belongs. As the physics of the interface of biphasic liquid/liquid systems is governed by the capillary wavelength, one expects the latter to be a key parameter for partly describing the two-phase flow inside a CCC column. Parameters derived from the capillary wavelength, the characteristic settling velocities, can also be calculated from the physicochemical properties of the phases and their interfacial tension. Their values are utilized for classification purposes and applied to previously investigated solvent systems as well as six new systems used in CCC. The classification obtained is compared with that provided by the observed flow behavior. It is found that the classification based on the characteristic settling velocity of the lighter phase into the continuous heavier one provides a reasonably reliable prediction of the experimental flow behavior in CCC.