SEPARATION WITH A LIQUID STATIONARY-PHASE - THE COUNTERCURRENT CHROMATOGRAPHY TECHNIQUE

Countercurrent chromatography (CCC) does not necessarily involve two liquid phases flowing in opposite directions. CCC is a liquid chromatography technique with a liquid stationary phase and an immiscible liquid mobile phase. It is not a liquid-liquid extraction technique, but a chromatographic technique. It is shown that high performance liquid chromatography (HPLC) and CCC do not operate in the same range of capacity factors and partition coefficients. The efficiency is low in CCC compared to HPLC. However, this drawback is compensated by the phase ratio V-S/V-M (stationary phase volume over mobile phase volume) which can be higher than 1 in CCC and is lower than 0.05 in LC. The resolution factor, Rs, can be higher than 1.5 in CCC for solutes with partition coefficients around 1. The solutes access the volume of the liquid stationary phase which explains the high possible loadability of CCC compared to HPLC. The two types of modern high speed CCC apparatuses, hydrostatic and hydrodynamic, are discussed. The commercially available instruments are briefly described.