ABSTRACT
Countercurrent distribution is particularly suited for separation of polar substances and has been extensively used for the purification of proteins. Many of the analytical applications of countercurrent distribution have been supplanted by advances in high pressure liquid chromatography, which is faster and requires an infinitely smaller sample. However, in instances where adsorption or sample denaturation occurs on columns, countercurrent distribution or countercurrent chromatography is advantageous. O. Post and L. C. Craig have also described a distribution train which allows a procedure called counter-double-current-distribution to be performed. In the US, countercurrent distribution is usually referred to as the Craig distribution after the man who, along with Post, developed the most successful device for the process. In countercurrent distribution, in contrast to chromatography, the partition coefficient is conventionally defined as Cupper/Clower. The Craig distribution apparatus, which transfers the upper phase can be operated in various ways.
