Quantification of countercurrent distribution: From molecular partition to animal behavior

Countercurrent distribution is a very effective method for separating a variety of substances including molecules, cells, and animals on the basis of partition between two solvent or behavioral phases. Distribution of a substance in this multi-cycle procedure can be described in terms of its partition coefficient (K) or the fraction of the substance that moves to the mobile phase in each cycle (p). It is currently difficult to calculate the value of p or K directly from an experimental distribution. Such direct calculation will simplify comparison of various experimental populations for the properties which determine their distribution, such as the surface properties of cells or behavioral preferences of animals. This report describes, and provides a theoretical basis for, an extremely simple method to calculate p or K directly from an experimental countercurrent distribution.