ABSTRACT
The successful development of modern laboratory-scale countercurrent extraction began in the 1930s, although mixer-settler units, as well as countercurrent extraction units, were used in industrial processes prior to that time. E. G. Sheibel described countercurrent extraction columns with mixing and settling zones in 1948. The machines developed by Ito and collaborators are the most efficient countercurrent chromatographs yet developed for small-scale separation of samples ranging from a few micrograms to a few hundred milligrams. One variant of discontinuous countercurrent distribution designed by O. Post and L. C. Craig is termed counter-double-current distribution to indicate that both phases move in opposite directions. In centrifugal countercurrent chromatography (CCC), analogous to the Craig distribution, one phase remains stationary while the second is passed through the segments of stationary phase. The columns in most centrifugal CCC apparatus consist of helical coils of plastic or glass tubing.
