Centrifugal partition chromatography

Centrifugal partition chromatography (CPC) is a special chromatographic technique where both stationary and mobile phase are liquid, and the stationary phase is immobilized by a strong centrifugal force. CPC consists of a series-connected network of extraction cells, which operates as elemental extractors, and the efficiency is guaranteed by the cascade.^[1]

Operation

The extracion cells consists of hollow bodies with inlets and oulets of liquid connection. The cells are first filled with the liquid chosen to be the stationary phase. Under rotation, the pumping of the mobile phase is started, which enters the cells from the inlet. When entering the flow of mobiles phase forms small droplets according to the Stokes' law, which is called atomization. These droplets fall through the stationary phase, creating a high interfacial area, which is called the extraction. At the end of the cells, these droplets unite due to the surface tension, which is called settling.

When a sample mixture is injected as a plug into the flow of mobile phase the compounds of the mixtures elute according to their partition coefficients: ${\displaystyle V_{elution}=V_{dead-volume}+K_{upper/lower}*V_{stationary-phase}}$

As CPC requies only a biphasic mixture of solvents, by varying the constitution of the solvent system it is possible to tune the partition coefficients of different compounds so, that separation is guaranteed by the high selectivity.

Comparison with countercurrent chromatography

Countercurrent chromatography (CCC) and centrifugal partition chromatography are two different instrumental realization of the same liquid–liquid chomatographic theory. CCC usually uses a planetary gear motion without rotary seals, while CPC uses circular rotation with rotary seals for liquid connection. CCC has interchagning mixing and settling zones in the coil tube, so atomization, extraction and settling are time and zone separated. Inside CPC all three steps happen continuously in one time, inside the cells.

Adventages of CPC:

• Higher flow rate for same volume size Laboratory scale example: 250 mL CPC has optimal flow rate of 5–15 mL/min, 250 mL CCC has optimal flow rate of 1–3 mL/min. Process scale example: 25 L CCC has optimal flow rate of 100–300 ml/min, 25 L CPC has optimal flow rate of 1000–3000 ml/min.
• Higher productivity (due to higher flow rate and faster separation time)
• Scalable up to tonnes per month^[2]
• Better stationary phase retention for most phases

Disadventages of CPC:

• Higher pressure than CCC (typical operation pressures of 40160 bar vs 5–25 bar)
• Rotary seal wear over time

Laboratory scale

CPC has been extensively used for isolation and purification of natural products for 40 years.^[3] Due to the ability to get very high selectivity, and the ability to tolerate samples containing particulated matter, it is possible to work with direct extracts of biomass, opposed to traditional liquid chromatography, where impurities degrade the solid stationary phase so that separation become impossible.

There are numerous laboratory scale CPC manufacturers around the world, like Armen Instrument (Gilson), RotaChrom, Kromaton (Rousselet Robatel), and AECS-QUIKPREP. These instruments operate at flow rates of 1–500 mL/min. with stationary phase retentions of 40–80% and column volumes of 25 mL to 25 L.

Production scale

As CPC does not uses any solid stationary phase it guarantees a cost-effective separation for the highest industiral levels. Opposed to CCC it is possible to get very high flow rates (for example 10 liters / min) with active stationary phase ratio of >80%, which guarantees good separation and high productivity. As in CPC material is dissolved, and loaded the column in mass / volume units, loading capability can be much higher than standard solid-liquid chromatographic techniques, where material is loaded to the active surface area of the stationary phase, which takes up less than 10% of the column.

Industrial instrument differ from laboraotry scale instruments by the applicable flow rate with staisfactory stationary phase retention (70-90%). Industrial instruments have flow rates of multiple liter / minutes, while able to purify materials from 10 kg to tonnes per month.

References

1. P, Foucault, Alain (1995). Centrifugal Partition Chromatography. New York: Marcel Dekker, Inc. ISBN 0-8247-9257-2.
2. Laszlo, Lorantfy. "Development of Industrial Scale CPC". RotaChrom. RotaChrom Technologiai Kft. Retrieved 2016-03-21.
3. Guido, F. Pauli (2008). "Countercurrent Separation of Natural Products". Journal of Natural Products. doi:10.1021/np800144q.

• Centrifugal partition Chromatography - Chromatographic Science Series - Volume 68, Editor: Alain P. Foucault, Marcel Dekker Inc