Countercurrent Chromatography(CCC) or Partition Chromatography is a category of liquid-liquid chromatography techniques. Chromatography in general is used to separate components of a mixture based on their differing affinities for mobile and stationary phases of a 'column'. The components can then be analyzed separatly by various sorts of detectors which may or may not be integrated into an apparatus. In liquid-liquid chromatography, both the mobile and stationary phases are liquid. In contrast, standard column chromatography uses a solid stationary phase and a liquid mobile phase, while gas chromatography uses a liquid stationary phase on a solid support and a gaseous mobile phase. By eliminating solid supports, permanent adsorption of the analyte onto the column is avoided, and a near 100% recovery of the analyte can be acheived. The instrument is also easily switched between various modes of operation by simply changing solvents. With liquid-liquid chromatography, researchers are not limited by the composition of the columns comercially available for their instrument. Nearly any pair of immiscible solutions can be used in liquid-liquid chromatography, and most instruments can be operated in standard or reverse-phase modes. Solvent costs are also generally cheaper than for HPLC. Another advantage is that experiments conducted in the lab can easily be scaled to industrial volumes. When GC or HPLC is done with large volumes, resolution is lost due to issues with surfact-to-volume ratios and flow dynamics; this is avoided when both phases are liquid. Chromatography is a family of analytical chemistry techniques for the separation of mixtures. ...

CCC can be thought of as occuring in three stages, mixing, settling, and separation (although they often occur continuously). Mixing of the phases is necesary so that the interface between them has a large area, and the analyte can move between the phases according to it's partition coefficient. A partition coeficient is a ratio of the amount of analyte found in each of the solvents at equilibrium, and is related to the analyte's affinity for one over the other. The mobile phase then settles at one end of the column so that it may be separated without removing any of the stationary phase from the column.

Direct Countercurrent Chromatography (DCCC)

This is also called Droplet CCC and is the oldest form of CCC, and uses only gravity to move the mobile phase through the stationary phase. In descending mode, droplets of the mobile phase and sample are allowed to fall through a column of the stationary phase using only gravity. If a less dense mobile phase is used it will rise through the stationary phase, this is called ascending mode. The eluent from one column is transferred to another; the more columns that are used, the more theoretical plates can be achieved. The disadvantage of DCCC is that flow rates are low, and poor mixing is acheived, which makes this technique both time-consuming and inefficient.

Centrifugal Partition Chromatography (CPC)

CPC uses centrifugal force to speed separation and acheive greater flow rates than DCCC (which relies on gravity). The 'columns' are cut into a rotor, oriented out from the middle, and connected by channels. The rotor is filled with the stationary phase, and the mobile phase is pumped through it as the rotor spins. A disadvantage is that this type of instrument requires a rotory seal that frequently needs to be replaced. CPC can also be operated in either descending or ascending mode, where the direction is relative to the force generated by the rotor rather than gravity.

High-Speed Countercurrent Chromatography

This technique also uses centrifugal force to improve flow rates as well as to enhance mixing. Rather than a rotor, a coil is moved in "planetary motion" on several axes. The advantage is that very high resolution can be acheived, and no rotory seal is needed.

Modes of Operation

• Single Mode: a one direction separation, either normal phase or reverse phase based on polarity (not the same as ascending and descending, which is based on density)
• Dual-Mode: The solvent is switched part way through the run to acheive better separation for compounds with a high affinity for the stationary phase.
• Gradient Mode: The concentration of one or more components in the mobile phase is varied throughout the run to acheive optimal resolution across a wider range of polarities.
• Elution Extrusion Mode: The mobile phase is extruded after a certain point by replacing the mobile phase with the same solution as the stationary phase, similar to dual-mode. This also allows for good resolution of compounds with high mobile-phase affinities. It requires only one column voume of solvent and leaves the column full of fresh staionary phase.
• pH Zone Refining: Acidic and basic solvents are used to elute analytes based on their pKa