Origin and Evolution of the Coil Planet Centrifuge: A Personal Reflection of My 40 Years of CCC Research and Development

Recent trends in multidimensional countercurrent chromatography

Countercurrent chromatography (CCC) is a potent separation approach known for its remarkable efficiency and capacity in preparation. It's applied as a substitute or combined with different chromatographic techniques, resulting in its rebranding as multidimensional CCC (MDCCC). Numerous essential mixtures from natural products contain hundreds or thousands of distinct components of importance. These mix types are too complicated to separate in any reasonable time using a single CCC dimension. However, if a multidimensional technique is utilized, where a complex mixture is separated by an initial dimension, smaller fractions of that separation are gathered. Each fraction is studied individually; complex mixes can be resolved relatively quickly. Thus, several MDCCC separation features have been studied to demonstrate their advantages, limitations, and prospective capacity to separate exceedingly complex mixtures. In this review, MDCCC aspects, including principles, multiple columns system, multilayer coil J-type, on-line monitoring system, and applications, have been thoroughly_explored.

Isolation of lanosterol and dihydrolanosterol from the unsaponifiable matter of lanolin by urea complexation and countercurrent chromatography in heart-cut recycling mode

4,4-Dimethyl-substituted sterols are bioactive minor sterols of most animal fats and plant oils, but higher shares are present in lanolin (wool grease). Here, the isolation of the 4,4-dimethyl-substituted sterols dihydrolanosterol and lanosterol from lanolin by countercurrent chromatography (CCC) is described. An initial examination of the hexane extract of saponified lanolin showed the presence of relatively high portions of fatty alcohols which were known to co-elute with the target analytes in CCC. Hence, fatty alcohols were precipitated by urea complexation. Unexpectedly, 4,4-dimethyl-substituted sterols were also found in the crystalline fraction, while cholesterol and other desmethylsterols were detected in the liquid phase. Urea complexation represented a useful preparative method for the separation of desmethylsterols and 4,4-dimethyl-substituted sterols from lanolin. Shake flask experiments of 4,4-dimethyl-substituted sterols and fatty alcohols with 14 biphasic solvent systems indicated suitable partition coefficients (K values) with n-hexane/ethanol/water (12:8:1, v/v/v) and n-hexane/benzotrifluoride/acetonitrile (20:7:13, v/v/v). After initial tests with conventional CCC, the application of CCC in heart-cut recycling mode provided 4,4-dimethyl-substituted sterols with purities of 99 % (dihydrolanosterol) and 95 % (lanosterol).

Online hyphenation of centrifugal partition chromatography with countercurrent chromatography (CPC-CCC) and its application to the separation of saturated alkylresorcinols

Centrifugal partition chromatography (CPC) and countercurrent chromatography (CCC) are two preparative techniques mainly used for the isolation and purification of natural products. While CPC benefits from a larger sample capacity, CCC typically provides better peak resolutions and hereby higher purities. In this study, we aimed to combine both advantages by the direct linking of CPC and CCC which was achieved by installation of switching valves and connection tube. The hyphenated CPC-CCC setup was tested with major alkylresorcinols which were obtained from a transesterified and hydrogenated rye extract. Injections of 1- and 5-g samples into the individual CCC system confirmed the limited sample capacity because of immediate flooding with the 5-g sample (total loss of stationary phase). In comparison, the CPC system was stable with 5- and 10-g samples but the peak resolution with 1-g sample was poorer than with the CCC system. Injections of 5- and 10-g samples into the CPC-CCC system were successful. However, a sample load of 10 g resulted in lower purities of the alkylresorcinols (80% or less) due to peak tailing. By contrast, injection of 5-g sample provided high amounts of ~ 1.2 g alkylresorcinols with purities of > 95%.

Alternative Extraction and Downstream Purification Processes for Anthocyanins

Anthocyanins are natural pigments displaying different attractive colors ranging from red, violet, to blue. These pigments present health benefits that increased their use in food, nutraceuticals, and the cosmetic industry. However, anthocyanins are mainly extracted through conventional methods that are time-consuming and involve the use of organic solvents. Moreover, the chemical diversity of the obtained complex extracts make the downstream purification step challenging. Therefore, the growing demand of these high-value pigments has stimulated the interest in designing new, safe, cost-effective, and tunable strategies for their extraction and purification. The current review focuses on the potential application of compressed fluid-based (such as subcritical and supercritical fluid extraction and pressurized liquid extraction) and deep eutectic solvents-based extraction methods for the recovery of anthocyanins. In addition, an updated review of the application of counter-current chromatography for anthocyanins purification is provided as a faster and cost-effective alternative to preparative-scale HPLC.

Liquid-Liquid Chromatography: Current Design Approaches and Future Pathways

Since its first appearance in the 1960s, solid support-free liquid-liquid chromatography has played an ever-growing role in the field of natural products research. The use of the two phases of a liquid biphasic system, the mobile and stationary phases, renders the technique highly versatile and adaptable to a wide spectrum of target molecules, from hydrophobic to highly polar small molecules to proteins. Generally considered a niche technique used only for small-scale preparative separations, liquid-liquid chromatography currently lags far behind conventional liquid-solid chromatography and liquid-liquid extraction in process modeling and industrial acceptance. This review aims to expose a broader audience to this high-potential separation technique by presenting the wide variety of available operating modes and solvent systems as well as structured, model-based design approaches. Topics currently offering opportunities for further investigation are also addressed.

Recent progress in separation prediction of counter-current chromatography

As a liquid-liquid partition chromatography, counter-current chromatography has advantages in large sample loading capacity without irreversible adsorption, which has been widely applied in separation and purification fields. The main factors, including partition coefficient, two-phase solvent systems, apparatus, and operating parameters greatly affect the separation process of counter-current chromatography. To promote the applications of counter-current chromatography, it is essential to develop theoretical research to master the principles of counter-current chromatographic separations so as to achieve predictions before laborious trials. In this article, recent progress about separation prediction methods are reviewed from a point of the steady and unsteady state of the mass transfer process of counter-current chromatography and its mass transfer characteristics, and then it is divided into three aspects: prediction of partition coefficient, modeling the thermodynamic process of counter-current chromatography, and modeling the dynamic process of counter-current chromatography.

Identification of two α-tocodienol isomers in palm oil after countercurrent chromatographic enrichment

Countercurrent chromatography (CCC) was used for the enrichment of α-tocodienol (α-T₂), a rare vitamin E-related minor compound previously tentatively detected in palm oil. Hitherto, only one isomer has been mentioned to occur at traces in palm oil. However, CCC fractionation followed by GC/MS measurements of all fractions resulted in the detection of two α-T₂ isomers in five different palm oil vitamin E dietary supplement capsules. Five repetitive CCC separations of ~ 1 g sample and additional purification steps by column chromatography provided ~ 2 mg of two equally abundant α-T₂ isomers with a purity of ~ 85%. The positions of the double bonds in the alkyl side chain could be assigned by means of two characteristic chemical shifts in the ¹H NMR spectrum. Accordingly, the structures of the α-T₂ isomers were 2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridec-3,11-dienyl)chroman-6-ol (double bonds in 3',11'-position) and 2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridec-7,11-dienyl)chroman-6-ol (double bonds in 7',11'-position). Natural occurrence of both isomers was proven by GC/MS screening of crude palm oil after saponification and CCC separation. Moreover, GC/MS analysis allowed the tentative assignment of γ-tocomonoenol (γ-T₁) and β-tocomonoenol (β-T₁) as trace compounds in palm oil.

Evaluation of Inter-Apparatus Separation Method Transferability in Countercurrent Chromatography and Centrifugal Partition Chromatography

In the countercurrent chromatography and centrifugal partition chromatography, separation method transfer and scale-up is often described as an easy and straightforward procedure. Separation methods are usually developed on lab scale columns and subsequently transferred using linear scale-up factors to semi-preparative or preparative columns of the same column design. However, the separation methods described in the literature have been developed on various columns of different design and size. This is accompanied by differences in the separation behavior of the columns and therefore makes separation method transfer difficult. In the current study, the separation performances of different columns were evaluated and compared. Linear correlations of stationary phase retention and column efficiency as a function of flow rate were found to be applicable for the calculation of separation resolution in the typical operating range of each column. In this context, a two-point short-cut approach for a fast column characterization is recommended. This allows a quick prediction of the separation method transferability between columns, which saves experimental time and effort. In the current study, the transferability between five different columns from lab scale countercurrent chromatography (CCC) (18 mL) to semi-preparative centrifugal partition chromatography (CPCs) (250 mL) with different cell numbers and design is investigated.

Metallic and semiconducting carbon nanotubes separation using an aqueous two-phase separation technique: a review

It is known that carbon nanotubes show desirable physical and chemical properties with a wide array of potential applications. Nonetheless, their potential has been hampered by the difficulties in acquiring high purity, chiral-specific tubes. Considerable advancement has been made in terms of the purification of carbon nanotubes, for instance chemical oxidation, physical separation, and myriad combinations of physical and chemical methods. The aqueous two-phase separation technique has recently been demonstrated to be able to sort carbon nanotubes based on their chirality. The technique requires low cost polymers and salt, and is able to sort the tubes based on their diameter as well as metallicity. In this review, we aim to provide a review that could stimulate innovative thought on the progress of a carbon nanotubes sorting method using the aqueous two-phase separation method, and present possible future work and an outlook that could enhance the methodology.

Purification of active myrosinase from plants by aqueous two-phase counter-current chromatography

INTRODUCTION

Myrosinase (thioglucoside glucohydrolase; E.C. 3.2.1.147), is a plant enzyme of increasing interest and importance to the biomedical community. Myrosinase catalyses the formation of isothiocyanates such as sulforaphane (from broccoli) and 4-(α-l-rhamnopyranosyloxy)benzyl isothiocyanate (from moringa), which are potent inducers of the cytoprotective phase-2 response in humans, by hydrolysis of their abundant glucosinolate (β-thioglucoside N-hydroxysulphate) precursors.

OBJECTIVE

To develop an aqueous two-phase counter-current chromatography (CCC) system for the rapid, three-step purification of catalytically active myrosinase.

METHODS

A high-concentration potassium phosphate and polyethylene glycol biphasic aqueous two-phase system (ATPS) is used with a newly developed CCC configuration that utilises spiral-wound, flat-twisted tubing (with an ovoid cross-section).

RESULTS

Making the initial crude plant extract directly in the ATPS and injecting only the lower phase permitted highly selective partitioning of the myrosinase complex before a short chromatography on a spiral disk CCC. Optimum phase retention and separation of myrosinase from other plant proteins afforded a 60-fold purification.

CONCLUSION

Catalytically active myrosinase is purified from 3-day broccoli sprouts, 7-day daikon sprouts, mustard seeds and the leaves of field-grown moringa trees, in a CCC system that is predictably scalable.

Isolation of specific small-diameter single-wall carbon nanotube species via aqueous two-phase extraction

Aqueous two-phase extraction is demonstrated to enable isolation of single semiconducting and metallic single-wall carbon nanotube species from a synthetic mixture. The separation is rapid and robust, with remarkable tunability via modification of the surfactant environment set for the separation.

Single-step total fractionation of single-wall carbon nanotubes by countercurrent chromatography

Development of simple processes to fractionate synthetic mixtures of single-wall carbon nanotubes (SWCNTs) into individual species is crucial to many applications. Existing methods for single-chirality SWCNT purification are cumbersome, often requiring multiple steps and different conditions for different species. Here, we report a method to achieve total fractionation of a synthetic SWCNT mixture by countercurrent chromatography, resulting in purification of many single-chirality SWCNT species in a single run. This method is based on a tunable partition of sodium deoxycholate dispersed SWCNTs in a polyethylene glycol/dextran aqueous two-phase system. By running the mobile phase with 0.02% of sodium deoxycholate and a gradient of sodium dodecyl sulfate from 0.1% to 0.7% (w/w), we observe clear diameter-dependent elution, with ∼ 90% total recovery. Among all the fractions collected, a number of them are enriched in single-chirality (9,4), (7,5), (7,6), (8,3), (6,5) species, while most of the remaining ones contain no more than 2-3 major species. We also observe strong (n,m)-dependent elution peak width due to the enantiomer-resolved partition. These results demonstrate countercurrent chromatography (CCC) as an effective way to obtain high purity (n, m) species, and suggest the potential of CCC as an analytical tool for chirality distribution mapping of synthetic SWCNT mixtures.

Steady-state and non-steady state operation of counter-current chromatography devices

Different variants of separation processes based on steady-state (continuous sample loading) and non-steady state (batch) operating modes of CCC columns have been analyzed and compared. The analysis is carried out on the basis of the modified equilibrium cell model, which takes into account both mechanisms of band broadening - interphase mass transfer and axial mixing. A full theoretical treatment of the intermittent counter-current chromatography with short sample loading time is performed. Analytical expressions are presented allowing the simulation of the intermittent counter-current chromatography separations for various experimental conditions. Chromatographic and extraction separations have been compared and advantages and disadvantages of the two methods have been evaluated. Further technical development of the CCC machines to implement counter-current extraction separations is considered.

State-of-the-art separation of ginsenosides from Korean white and red ginseng by countercurrent chromatography

Ginseng (Panax ginseng C. A. Meyer) has been one of the most popular herbs used for nutritional and medicinal purposes by the people of eastern Asia for thousands of years. Ginsenosides, the mostly widely studied chemical components of ginseng, are quite different depending on the processing method used. A number of studies demonstrate the countercurrent chromatography (CCC) separation of ginsenosides from several sources; however, there is no single report demonstrating a one-step separation of all of these ginsenosides from different sources. In the present study, we have successfully developed an efficient CCC separation methodology in which the flow-rate gradient technique was coupled with a new solvent gradient dilution strategy for the isolation of ginsenosides from Korean white (peeled off dried P. ginseng) and red ginseng (steam-treated P. ginseng). The crude samples were initially prepared by extraction with butanol and were further purified with CCC using solvent gradients composed of methylene chloride-methanol-isopropanol-water (different ratios, v/v). Gas chromatography coupled with flame ionization detector was used to analyze the components of the two-phase solvent mixture. Each phase solvent mixture was prepared without presaturation, which saves time and reduces the solvent consumption. Finally, 13 ginsenosides have been purified from red ginseng with the new technique, including Rg1, Re, Rf, Rg2, Rb1, Rb2, Rc, Rd, Rg3, Rk1, Rg5, Rg6, and F4. Meanwhile, eight ginsenosides have been purified from white ginseng, including Rg1, Re, Rf, Rh1, Rb1, Rb2, Rc, and Rd by using a single-solvent system. Thus, the present technique could be used for the purification of ginsenosides from all types' ginseng sources. To our knowledge, this is the first report involving the separation of ginsenoside Rg2 and Rg6 and the one-step separation of thirteen ginsenosides from red ginseng by CCC.

Modelling of elution-extrusion counter-current chromatography using perfect replacement approach

Basing on the perfect replacement approach the equilibrium cell model is developed to describe the separation process in elution-extrusion counter-current chromatography (EECCC). As is known, EECCC consists of three steps: classical elution, sweeping elution, and extrusion. The perfect replacement approach means that during sweeping elution step, the mobile phase contained in the column moves and interacts with the "old" stationary phase in the same mode as during the classical elution step; the "new" and "old" stationary phases do not mix; and after the contacting with the mobile phase the concentration of solutes in the "old" stationary phase remains constant and this stationary phase volume is pushed ahead to the exit of the column. Equations are presented allowing the simulation of the chromatogram of solutes eluted from the column with the mobile phase during the elution period and the chromatogram of solutes pushed out of the column with the stationary phase during the extrusion period of EECCC. These equations can help to choose the optimal conditions for conducting elution-extrusion counter-current chromatography.

Controlled-cycle pulsed liquid-liquid chromatography. A modified version of Craig's counter-current distribution

A new liquid-liquid chromatography technique developed from a combination of controlled-cycle operation and a pulsed-mixing technique is suggested and validated. The controlled-cycle pulsed liquid-liquid chromatography (CPLC) system operates without involving a centrifuge and consists, of a series of multistage units, and a method for imparting pulsation motion to the liquids inside the units (the pulsation cycle). This chromatography technique can be considered as an improved continuous form of Craig's counter-current distribution method, or, alternatively, as a form of droplet chromatography with the cycling mode of operation. The theoretical model has been designed to account for the effects of the basic parameters influencing the CPLC operation. The theoretical model's suitability was proved by direct comparison between the experimental and model responses. The CPLC devices containing 1, 2, 4 and 5 multistage columns (each column was divided into 26 stages) have been designed, fabricated and tested; experiments were conducted to test the chromatographic behavior of organic (monocarboxylic) and mineral acids. The mass transfer rate in the stages depends on the nature of both--phase and sample systems: the highest values were achieved in experiments with acetic acid by using the octane/water biphasic system, where an equilibrium concentration distribution between stationary and mobile phases in the stages was attained. The results obtained demonstrated the potential of the new technique for preparative and industrial scale separations.

Integrated countercurrent extraction of natural products: a combination of liquid and solid supports

An integrated online column-switching countercurrent chromatography (CCC) with a solid-phase trapping/preconcentration interface is presented. The interface is systematically evaluated in terms of sorbent type, column size, and kinetic factor from the view of the unique CCC process. Results indicate that satisfactory trapping efficiency can be achieved using a 25 mm x 10 mm i.d. column packed with Oasis HLB materials. In addition to the analyte focusing effect, large volume injection is avoided, thereby allowing the use of totally different biphasic liquid systems to enhance the system orthogonality. The present integrated system simply combines the liquid and solid supports and is successfully applied in a one-step preparative separation of four antioxidative compounds from the ethyl acetate extract of traditional Chinese herbal medicine Rubia cordifolia L. (Rubiaceae), exhibiting great advantages in peak resolution, peak capacity, and instrument integration compared with conventional CCC separations.

Isolation and purification of macrocyclic components from Penicillium fermentation broth by high-speed counter-current chromatography

In this paper, high-speed counter-current chromatography (HSCCC), assisted with ESI-MS, was first successfully applied to the preparative separation of three macrolide antibiotics, brefeldin A (12.6 mg, 99.0%), 7'-O-formylbrefeldin A (6.5 mg, 95.0%) and 7'-O-acetylbrefeldin A (5.0 mg, 92.3%) from the crude extract of the microbe Penicillium SHZK-15. Considering the chemical nature and partition coefficient (K) values of the three target compounds, a two-step HSCCC isolation protocol was developed in order to obtain products with high purity. In the two-step method, the crude ethyl acetate extract was first fractionated and resulted in two peak fractions by HSCCC using solvent system n-hexane/ethyl acetate/methanol/water (HEMWat) (3:7:5:5 v/v/v/v), then purified using solvent systems HEMWat (3:5:3:5 v/v/v/v) and HEMWat (7:3:5:5 v/v/v/v) for each fraction. The purities and structures of the isolated compounds were determined by HPLC, X-ray crystallography, ESI-MS and NMR. The results demonstrated that HSCCC is a fast and efficient technique for systematic isolation of bioactive compounds from the microbes.

Support-free pulsed liquid-liquid chromatography

A simple technique of support-free liquid-liquid chromatography is suggested that operates without incorporation of a centrifuge. The pulsed chromatography apparatus consists of a stationary coiled tube and a pulsation device to produce reciprocating motion of liquid phases within each individual coil segment. This reciprocating motion generates a centrifugal force field varying in intensity and direction that leads to an improved mixing of the two liquid phases and retains the stationary phase in the coiled tubing. The intensity of the back and forth motion of liquid phases within each coil unit can be varied by varying the frequency and/or the amplitude of the pulsations generated by the pulsation device. As the magnitude of the stationary phase retention is of paramount importance for success of the technique, the retention of the stationary phase in the pulsed coil column was experimentally studied. A few experiments were conducted to test the chromatographic behavior of valeric (n-pentanoic) and caproic (n-hexanoic) acids. The results obtained demonstrate the potential of the new separation method for preparative purposes.

Advantages of a small-volume counter-current chromatography column

Counter-current chromatography (CCC) works with a support-free liquid stationary phase. This allows for preparative separations and purifications. However, there are serious technical constraints because of the need to keep a liquid stationary phase in a column. Centrifugal fields are used. A new commercial hydrodynamic 18mL column made with a narrow-bore 0.8mm Teflon tubing was evaluated by comparing it with older hydrodynamic CCC columns and a similar 19mL column but made with 1.6mm Teflon tubing. A small-volume CCC column allows for reliable and fast solute partition coefficient determination. When resolution is required, both high efficiency and liquid stationary phase retention are needed. Unfortunately, these two requirements bear technical contradictions. A column coiled with a narrow tubing bore will provide a high chromatographic efficiency while a column containing wider tubing bore will achieve higher stationary phase retention. In all cases, increasing the magnitude of the centrifugal field also increases the stationary phase retention. The solution is to build centrifuges able to produce high fields that will provide acceptable liquid phase retention with narrow-bore tubes. The new 18mL 0.8mm tubing bore column is able to rotate as fast as 2100rpm generating a 240xg field. The two older CCC columns cannot compete with the new one. However, the small 19mL column with 1.6mm bore tubing can be useful when fast results are desired without top resolution.

Countercurrent separation of natural products

An assessment of the technology and method development in countercurrent chromatography (CCC) and centrifugal partition chromatography (CPC), collectively referred to as countercurrent separation (CS), is provided. More than six decades of CS theory and applications are critically reviewed and developed into a practical guide to CS for natural products research. The necessary theoretical foundation is given for better use of CS in the separation of biological molecules of any size, small to large, and from any matrix, simple to complex. The three operational fundamentals of CS--instrumentation, biphasic solvent systems, and theory--are covered in a prismatic fashion. The goal of this review is to provide the necessary background and references for an up-to-date perspective of CS and to point out its potential for the natural products scientist for applications in natural products chemistry, metabolome, and proteome research involving organisms from terrestrial and marine sources.

Spiral coils for counter-current chromatography using aqueous polymer two-phase systems

Retention properties of polyethylene glycol-phosphate aqueous two-phase systems in a spiral coil (5 mm I.D.) on Type-J synchronous counter-current chromatographic devices have been compared for the elution mode where the lower phase is the mobile phase and flows from the inside head terminal. This was achieved with the aid of digital imaging under stroboscopic illumination, an image analysis and measurement of the displaced volume of the stationary phase. For the spiral coil, high and stable stationary phase retention at mobile phase flow rates up to 64 ml/min has been obtained. Wave-like disturbance of the interface near the proximal point was observed and analyses have been made for possible use in protein separation.