The term, Partition Coefficient (Kd), has been used for many decades in chemistry as a measure of how a compound distributes between two immiscible solvent phases. The octanol-water partition coefficient of a given compound, long used as a measure of lipophilicity, is defined as the concentration of the compound in upper phase divided by concentration in the lower phase when the analyte is distributed between octanol and water.
All the while, the term "distribution constant" has been used in the engineering sciences to describe essentially the same phenomenon. More precisely, the Distribution Constant is defined as the ratio of an analyte in a specific form (a given ionic or complexed form) in one phase to the other phase. A synonym for Distribution Constant is "Partition Ratio".
The "distribution ratio" is defined as the ratio of the total analytical concentration of a given analyte in each phase of a two-phase system, regardless of ionization, complexation, or chemical reaction.
Except for ionizable, complexable, and/or highly reactive analytes, all of these terms are synonomous for all practical purposes in the context of CCC. There is some controversy currently being resolved as to what is the most preferred term.
For high-resolution CCC-based separations in a practical amount of time, solvent systems have traditionally been selected such that the compound of interest has a Kd value between 0.5 and 2.0. Modern instrument technology (HPCCC, FCPC) and operation methods (e.g. [EECCC]), greatly extend the range of practical Kd values for CCC-based separations.
A much more comprehensive treatment of using CCC to determine partition coefficients is warranted. Pertinent literature includes:
Eltayar, N.; Tsai, R. S.; Vallat, P.; Altomare, C.; Testa, B. Measurement of Partition-Coefficients by Various Centrifugal Partition Chromatographic Techniques - a Comparative-Evaluation. Journal of Chromatography 1991, 556, 181-194.
Vallat, P.; Eltayar, N.; Testa, B.; Slacanin, I.; Marston, A.; Hostettmann, K. Centrifugal Countercurrent Chromatography, a Promising Means of Measuring Partition-Coefficients. Journal of Chromatography 1990, 504, 411-419.
Shibusawa, Y.; Shoji, A.; Yanagida, A.; Shindo, H. Determination of log P-o/w for catechins and their isomers, oligomers, and other organic compounds by stationary phase controlled high speed countercurrent chromatography. Journal of Liquid Chromatography & Related Technologies 2005, 28, 2819-2834.
Berthod, A.; Carda-Broch, S. Determination of liquid-liquid partition coefficients by separation methods. Journal of Chromatography A 2004, 1037, 3-14.