Centrifugal partition chromatography
(CPC) is a new and unique method of liquid-liquid chromatography. CPC
enables the separation of components with nearly identical partition
ratios, and is performed without the aid of a solid support. The method is
used for chromatographic reaction in addition to chromatographic
separation.
Centrifugal partition chromatography
is a type of countercurrent chromatography, which is an automated
liquid-liquid extraction process permitting hundreds of automatic
successive extractions. CPC is also a type of partition chromatography, a
technique involving a liquid stationary phase and a liquid mobile phase.
The solute equilibrates between the stationary and mobile liquids.
Finally, CPC utilizes a centrifugal force. Centrifugal means "fleeing from
the center" (Young) and describes an outward force resulting from a
spinning motion. Centrifugal partition chromatography is a chromatographic
method that combines ideas from each of the terms which comprise its name.
CPC is unique because no solid
support is used for the stationary phase. Instead, the liquid stationary
phase is retained in the column by a combination of centrifugal force, the
special tortuous column geometry and the density difference between the
two liquid phases. The CPC apparatus consists of coil columns "undergoing
one particular mode of planetary motion generated by a synchronous coil
planet centrifuge". The column contains one or more
cartridges in which channels are engraved, attached to a rotor. The less
dense stationary phase remains in the column because of the centrifugal
force created by the spinning rotor. Consequently, the mobile phase is
able to pass through the stationary phase.
When a mixture of components is
introduced into the mobile phase of the CPC column, it distributes
according to the individual components' distribution coefficients while
passing through the column. The centrifugal force field applied to the
coiled columns promotes the retention of the stationary phase against a
continuous flow of mobile phase. The mobile phase flow enables the two
phases interact sufficiently for partition to occur. Chromatographic
separation results, and separation is sufficiently complete as hundreds to
thousands of theoretical plates can be achieved.
The degree of separation in
centrifugal partition chromatography depends primarily on the partition
coefficient of the solute between the two phases. Other important
parameters in the separation process include mass transfer coefficients,
flow rate, rotational frequency, and the identity of the two phases. A
variety of the two-phase systems are possible using the CPC column. Both
organic and aqueous systems are feasible. In fact, using CPC
chromatography, aqueous two-phase systems can be used for separation. The
total total volume of the system should not exceed approximately one
liter.
Clearly, CPC provides successful
chromatographic separation. This chromatographic technique is also used
for chromatographic reaction. The technique causes the equilibrium of a
reversible reaction to shift. Reaction takes place in the stationary
phase, while products are separated into the mobile phase. Since
chromatographic separation of the products occurs simultaneously with
production, the reverse reaction is impeded. Therefore, reactions beyond
thermodynamic equilibrium are achieved.
The applications of centrifugal
partition chromatography are profuse and diverse. One special feature of
the new technique is that partition can be achieved between two distinct
aqueous phases. This aqueous two-phase system, ATPS, is created when one
or more polymers and a salt are added to water. When the concentrations of
polymer and salt become high enough, two-phases result which are both more
than fifty percent water by weight. Such a two-phase aqueous system is
important because it lends itself to biological applications. Organic
systems are typically not mild enough for biochemical compounds.
Additionally, the separation of amino acids is not possible in organic
systems due to low solubility.
CPC is used for many types of
separations. Racemic mixtures can be separated into chirally pure
compounds. Natural products and amino acids are commonly separated on
centrifugal partition columns. CPC is also utilized for enzymatic
reaction. CPC reactions are advantageous because the reactions proceed
beyond thermodynamic equilibrium. Additionally, reaction kinetics can be
measured in addition to partitioning and mass transfer.
Since CPC is a new technique, much
work remains to be done. Optimization of the columns, study of non-linear
systems, and development of new applications are some aspects of the
method currently being explored.
References
Aarnink, M. "Integrated reaction and separation in
centrifugal partitioning chromatography," http://www.kluyver.stm.tudelft.nl/R_Proj/bst/P_buel.htm,
Delft University of Technology.
Den Hollander, J. L. "Centrifugal partition chromatographic reaction for
the production of chiral amino acids," Journal of chromatography B., 711
(1998) 223-235.
Pharma-Tech Research Corporation. "Information on Countercurrent
Chromatography ("CCC")," http://www.pharma-tech.com/cccinfo.htm#introduction.
Skoog, West, Holler. Fundamentals of Analytical Chemistry, 7th Ed.
Van Der Wielen, L. A. M. "Scale-up of centrifugal partition
chromatography," http://www.kluyver.stm.tudelft.nl/R_Proj/bst/P_buel.htm,
Delft University of Technology.
Young, Hugh D. University Physics, 8th Ed., Volume 1, 129.
