Counter-current motion in counter-current chromatography☆
Introduction
After CCC2012 meeting, I have received an e-mail from Prof. Berthod stating “The technique denomination: countercurrent chromatography (CCC) is confusing by itself and needs some explanations. In normal CCC use, there is no countercurrent circulation of any fluid. The stationary phase is liquid but motionless, most often maintained steady by centrifugal fields. The liquid mobile phase is flown through the liquid stationary phase as in any other chromatographic techniques. The technique naming was coined in the early 1970s by its inventor, Yoichiro Ito, as a reference to the Craig's countercurrent distribution method [1]. Unfortunately, the countercurrent term is a misnomer. The term chromatography is correct but it frightens process chemists who do not like the cost and complexity supposedly attached to any preparative chromatographic techniques. Consequently, it is proposed to call the purification methods using liquid–liquid exchanges between a mobile and a stationary phase: liquid–Liquid Separations (LLS)”. Since I named countercurrent chromatography, I am compelled to address my comments on this issue. In order to justify the new name for CCC suggested by the above letter, I first, consulted through Google search which will furnish the common usage of terms in various fields including science. The results are shown in Table 1.
In this table Google search items are each evaluated by the number of matches, the number of CCC listed in the first 10 matches and its major contents. The first search on liquid–liquid separation, that was suggested as a new term in the above letter, yielded over 10 million matches, but it does not contain CCC in the first 10 hits. Besides, this name is already given to a totally different technique for separating two liquid phases from emulsified liquid, and the method is extensively used in oil industries and dairy factories. Over one hundred of instruments have been developed for this purpose. Second, the centrifugal separation, that was suggested as an alternative new name for CCC, gave 15 million matches including no CCC in the first 10 matches. It contained various other centrifugal techniques. Next, liquid–liquid chromatography or liquid partition chromatography showed 15 – 1 million matches but without CCC in the first 10 matches. It contained mostly liquid chromatography with solid support. This clearly indicates that “liquid–liquid chromatography uses always solid support” is the common understanding. When the term “without solid support” was added to these terms, the name CCC starts to appear in the first 10 matches. And the search on countercurrent chromatography contained CCC in all of the first 10 matches. From the results of these Google searches, it is certain that changing the CCC name to liquid–liquid separations or centrifugal separations would produce tremendous confusion in the scientific community.
As mentioned in the above letter, the term “countercurrent chromatography” was coined in our Science publication in 1970 [2]. At that time there were two major preparative separation techniques, namely, countercurrent distribution method (CCD) [1] and liquid chromatography. Then, we developed a new hybrid method which could share their merits with these two methods while eliminating their problems: CCC is more efficient than CCD while it provides higher yields by avoiding irreversible adsorption of samples onto the solid support used in liquid chromatography. Since neither CCD nor liquid chromatography has a capability of countercurrent, this F1 hybrid is not expected to have countercurrent motion of two phases. However, it is surprising to find that CCC literally exhibits countercurrent motion of the two phases in the separation column in both hydrodynamic and hydrostatic equilibrium systems.
Section snippets
Seal-free flow-through centrifuge systems
Fig. 1 shows a series of rotary-seal-free centrifuge systems developed for performing CCC [3]. In all these centrifuge systems a bundle of flow tubes from the cylindrical column holder supported at the upper end of the centrifuge axis is free from twisting so that the solvent can be continuously eluted through the rotating column without the conventional rotary seal device which may become a potential source of complications such as leakage and contamination. These systems are divided into
Counter-current motion of two phases enclosed in a coiled tube under two typical hydrodynamic CCC systems
Fig. 2 shows the motion of the two immiscible phases enclosed in the coiled tube subjected to the above two different planetary motions. In this figure an end-closed coiled tube at the top is filled with two immiscible solvent phases half-and-half and subjected to these two different types of planetary motion. On the left diagram, the coiled tube is filled with the black phase on the head side and the white phase on the tail side (or vice versa), and subjected to the type-I planetary motion.
Counter-current motion of the two phases in the type-J hydrodynamic CCC system
The above bilateral hydrodynamic equilibrium of the two phases is efficiently utilized for performing high-speed CCC as shown in Fig. 4 where all coiled columns were each drawn as a straight tube for simplicity. The column at the top shows the bilateral hydrodynamic equilibrium described above. This equilibrium condition indicates that the white phase, if introduced at the tail end, would move toward the head, and similarly the black phase introduced at the head end would move toward the tail.
Counter-current motion of two phases in the hydrostatic system
Fig. 6 shows a portion of the single column of droplet CCC, a typical hydrostatic CCC system [7]. The upper phase introduced into the straight vertical column previously filled with the lower stationary phase forms a series of droplets at regular intervals. In this droplet CCC, the rising droplets of the upper phase steadily produce countercurrent movement of the lower phase downward through the column as indicated by curved arrows in the figure.
Conclusion
As presented above, the stationary phase of CCC is not stationary in the column, but locally repeats active countercurrent motion against the mobile phase in both hydrodynamic and hydrostatic CCC systems. I believe that CCC is the only chromatographic system which exhibits countercurrent movement of two phases in the column among all the existing chromatographic systems. I think that this justifies the term countercurrent chromatography.
References (7)
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Countercurrent chromatography: liquid–liquid partition chromatography without solid support
Science
(1970) High-speed countercurrent chromatography
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Cited by (10)
Preparative separation of specific triterpenoids from Inonotus obliquus based on negative-pressure cavitation extraction and high-speed counter-current chromatography
2021, Journal of the Taiwan Institute of Chemical EngineersCitation Excerpt :Hence, a more effective technology is needed to separate triterpenoids from Inonotus obliquus. High-speed counter-current chromatography (HSCCC), a typical liquid-liquid partition chromatography method, was developed by Yoichiro Ito at the National Institutes of Health (Bethesda, MD, USA) [16]. HSCCC has been widely and reasonably used for separation and purification of bioactive compounds from plants according to distribution of different compounds between two insoluble solution without a solid support [17,18].
Magnetic nanoparticles and high-speed countercurrent chromatography coupled in-line and using the same solvent system for separation of quercetin-3-O-rutinoside, luteoloside and astragalin from a Mikania micrantha extract
2017, Journal of Chromatography ACitation Excerpt :New separation techniques of flavonoids continue to be of great interest since these compounds have significant effectiveness in coronary heart disease, senile dementia and cerebral ischemia and are widely used in herbal medicines and health foods. Though methods of macroporous resin [3], aqueous two-phase extraction [4], solid-phase extraction (SPE) [5], magnetic solid phase extraction (MSPE) [6,7], preparative high performance liquid chromatography (HPLC) [8] and high-speed countercurrent chromatography (HSCCC) [9,10] were widely used to separate flavonoids, most of these methods were non-coupled fashion. Even though some references reported that the two methods mentioned above were combined during flavonoid separation, two solvent systems were used [3,11].
The 8th International Conference on Counter-current Chromatography held at Brunel University, London, UK, July 23–25, 2014
2015, Journal of Chromatography ACitation Excerpt :There had been talk at the conference about changing the name of counter-current chromatography as users argued that it was not really counter-current as there was a stationary phase. Yoichiro Ito [28], the founder of the technology, had submitted a paper defending the term counter-current chromatography as the combination of counter-current distribution and liquid chromatography, which can under certain circumstances be set up with counter-current flow. Alain Berthod replied [29] by giving a summary of what was concluded at CCC2014: “the counter-current or counter-current terms and the CCC acronym are accepted to represent all chromatographic techniques working with two liquid phases without any solid support.
Comments on "Counter-current motion in counter-current chromatography" by Yoichiro Ito
2014, Journal of Chromatography ARecent trends in multidimensional countercurrent chromatography
2024, Journal of Separation Science
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Presented at the 8th International Conference on Countercurrent Chromatography – CCC 2014, 23–25 July 2014, Uxbridge, United Kingdom.