The simplest form of liquid-liquid extraction is the partitioning of a mixture of compounds between two immiscible liquid phases in a separatory funnel.
Countercurrent distribution, therefore, is a method of using a series of vessels (separatory funnels) to separate compounds by a sequence of liquid-liquid extraction operations.
First, a mixture is introduced to vessel 1 (V1) charged with both phases and the liquid-liquid extraction process is performed.
Early work in the development of liquid-liquid separation techniques was undertaken by Cornish et al. with a process called "systematic fractional distribution"[4] as well as Randall and Longtin,[5] however, the central figure is certainly Lyman C. Craig.
It was shown that a solvent system composed of benzene, n-hexane, methanol and water would separate mixtures of organic acids.
[8][9] Craig continued to pursue this method of separation by testing different compounds,[10] formulating biphasic solvent systems,[11] and most importantly developing a commercially viable instrument.