Counter-current chromatography for high throughput analysis of natural products

Counter-current chromatography (CCC) is a unique support-free liquid-liquid partition chromatography winning wide applications in the separation of various components from natural or synthetic mixtures. It has been one of the prime methods for isolating compounds from Traditional Chinese Medicines (TCM) and other comprehensive natural products. Although early CCC models produced a long-standing false image that CCC is a time-consuming technique, rapid and high-performance CCC devices and methods for high-throughput analysis of natural mixtures have been advanced. For instances, multi-channel CCC, dual CCC, elution-extrusion CCC, and solvent simplification protocols can provide high-throughput CCC analysis and produce high purity of compounds or large natural product libraries for drug discovery. This review summarizes the recent advancements of CCC in the high-throughput analysis of natural product with an emphasis on the developments of instruments and methods.     

Separation of alkaloids from herbs using high-speed counter-current chromatography

Alkaloids represent a most widespread group of bioactive natural products. Because of their alkalinity and structural diversity, the fractionation and purification of the alkaloids from herbs can often present a number of practical difficulties using the conventional chromatographic techniques. High-speed counter-current chromatography (HSCCC) is a liquid-liquid partition chromatography with a support-free liquid stationary phase, and is gaining more and more popularity as a viable separation technique for bioactive compounds from natural resources. In the present review, focus is placed on the separation of alkaloids by both conventional HSCCC and pH-zone-refining counter-current chromatography (CCC) techniques from herbs. The review presents the separation of over 120 different alkaloid compounds from more than 30 plant species by the conventional HSCCC and pH-zone-refining CCC. Based on the data from the literature, the proper solvent systems for the separation of alkaloids by the conventional HSCCC and pH-zone-refining CCC are also summarized.     

2020年毛细管电泳技术年度回顾

该文为2020年毛细管电泳(capillary electrophoresis,CE)技术年度回顾.归纳总结了以"capillary electro-phoresis-mass spectrometry"或"capillary isoelectric focusing"或"micellar electrokinetic...     

Application of pH-Zone-Refining Countercurrent Chromatography in the Preparative Separation of Alkaloids from Traditional Chinese Medicine

pH-Zone-refining countercurrent chromatography (CCC) is a recently developed new preparative separation method based on conventional CCC. The method uses a retainer base (or acid) in the stationary phase to retain the analyses in the column and an eluent acid (or base) to elute the analyses according to their pKa values and hydrophobicities. It produces a succession of highly concentrated rectangular peaks with minimum overlap similar to those observed in displacement chromatography. pH-zone-refining CCC has important advantages over the conventional CCC including an over 10-fold increase (up to 10 gram or more) in sample loading capacity, high concentration of fractions, and concentration of minor impurities. pH-zone-refining CCC has been successfully applied to the preparative separation of a variety of compounds including both acidic and basic derivatives of amino acid, hydroxyxanthene dyes, peptides, alkaloids, indole auxins, structural, geometrial and optical isomers.     

Role of counter-current chromatography in the modernisation of Chinese herbal medicines

This review focuses on the growing popularity of using counter-current chromatography (CCC), with its liquid stationary phase, as one of the prime methods for isolating compounds from Chinese herbal medicines (CHMs). 198 publications are reviewed covering 108 different plant species from 56 plant families. These describe the isolation of 354 different molecules across a wide range of polarities, chemical classes and molecular weights (in the range 100–1000 Da). The suitability of CCC for the separation of active compounds from CHM, the phase systems used, how CCC has developed in China, compounds isolated, CCC instrumentation, performance, operational issues and innovations, all supported by detailed cross-referencing, are described. It is concluded that CCC is making an increasingly important contribution to the modernisation of Chinese herbal medicines.     

The most frequently cited adsorption research articles in the Science Citation Index (Expanded)

The 126 most frequently cited articles published in the adsorption field between 1900 and 2011 were identified and characterized using the Science Citation Index (Expanded). The data analyzed cover a range of publication years, journals, Web of Science categories, authors, institutions, countries/territories, life citation cycle curves, and characteristics of frequently cited articles. The 126 most-frequently-cited articles were each cited an average of 1014 times, ranging from 502 to 9922 citations per article from 1918 to 2006; 80% of these articles were published after 1970. Fifty-five journals were represented, led by the Journal of the American Chemical Society, and followed by Science and Nature. Three categories out of the 35 Web of Science categories constituted 60% of the citations. The three categories were: physical chemistry, multidisciplinary chemistry, and multidisciplinary sciences. Thirteen of the authors contributed three or more articles. Harvard University, the Massachusetts Institute of Technology, and the University of Washington led the list of 107 institutions, while the United States led the list of 17 countries/territories, comprising more than half of the articles. Collaboration among the top authors was a frequent occurrence, while inter-institutional collaboration and national collaboration was not obvious among the topmost articles. Moreover, the citation patterns as a function of time varied widely among the topmost articles. As evidenced by citation life cycles, the well known BET and Langmuir isotherms have received considerable attention during the study period, and will probably continue to be popular in the adsorption field. Some emerging hotspots are likely to receive particular attention in the near future; these include the new family of "M41S" materials, pseudo-second-order kinetic models, and the nudged elastic band method.     

Preparative separation of isomeric 2-(2-quinolinyl)-1H-indene-1,3(2H)-dione monosulfonic acids of the color additive D&C Yellow No. 10 (quinoline yellow) by pH-zone-refining counter-current chromatography

The main components of the color additive D&C Yellow No. 10 (Quinoline Yellow, Color Index No. 47005), 2-(2-quinolinyl)-1H-indene-1,3(2H)-dione-6'-sulfonic acid (6SA) and 2-(2-quinolinyl)-1H-indene-1,3(2H)-dione-8'-sulfonic acid (8SA), were isolated from the dye mixture by pH-zone-refining counter-current chromatography (CCC) in the ion-exchange mode. These positional isomers were separated from a portion of dye using sulfuric acid as the retainer acid and dodecylamine as the ligand (ion exchanger). The added ligand enhanced the partitioning of the hydrophilic components in the organic stationary phase of the two-phase solvent system that consisted of isoamyl alcohol-methyl tert.-butyl ether-acetonitrile-water (3:1:1:5). Thus, separation of 1.8 g of D&C Yellow No. 10 using the above method resulted in 0.6 g of 6SA and 0.18 g of 8SA of over 99% purity. The isolated compounds were characterized by mass spectrometry and proton nuclear magnetic resonance with correlated spectroscopy assignments. The study exemplifies a new field of applications for pH-zone-refining CCC, to the separation of positional isomers of strongly hydrophylic compounds containing sulfonic acid groups.     

pH-zone-refining counter-current chromatography: Origin,mechanism, procedure and applications

Since 1980, high-speed counter-current chromatography (HSCCC) has been used for separation and purification of natural and synthetic products in a standard elution mode. In 1991, a novel elution mode called pH-zone refining CCC was introduced from an incidental discovery that an organic acid in the sample solution formed the sharp peak of an acid analyte. The cause of this sharp peak formation was found to be bromoacetic acid present in the sample solution which formed a sharp trailing border to trap the acidic analyte. Further studies on the separation of DNP-amino acids with three spacer acids in the stationary phase revealed that increased sample size resulted in the formation of fused rectangular peaks, each preserving high purity and zone pH with sharp boundaries. The mechanism of this phenomenon was found to be the formation of a sharp trailing border of an acid (retainer) in the column which moves at a lower rate than that of the mobile phase. In order to facilitate the application of the method, a new method was devised using a set of retainer and eluter to form a sharp retainer rear border which moves through the column at a desired rate regardless of the composition of the two-phase solvent system. This was achieved by adding the retainer in the stationary phase and the eluter in the mobile phase at a given molar ratio. Using this new method the hydrodynamics of pH-zone-refining CCC was diagrammatically illustrated by three acidic samples. In this review paper, typical pH-zone-refining CCC separations were presented, including affinity separations with a ligand and a separation of a racemic mixture using a chiral selector in the stationary phase. Major characteristics of pH-zone-refining CCC over conventional HSCCC are as follows: the sample loading capacity is increased over 10 times; fractions are highly concentrated near saturation level; yield is improved by increasing the sample size; minute charged compounds are concentrated and detected at the peak boundaries; and elution peaks are monitored with a pH flow meter for compounds with no chromophore. Since 1994, over 70 research papers on pH-zone-refining CCC have been published with the trends increasing in the recent years.     

Strategies of solvent system selection for the isolation of flavonoids by countercurrent chromatography

Flavonoids form a large class of important naturally occurring bioactive compounds. Their isolation and purification from natural sources can sometimes be very difficult and time‐consuming when traditional phytochemical techniques are used. Countercurrent chromatography (CCC), a support‐free liquid–liquid partition chromatography technique, is very useful for the isolation of polar compounds and its use is increasing in the natural products field. In this paper, we propose strategies of solvent system selection for the isolation of flavonoids by CCC, based on data from the literature, plus incorporation of own practical experiences. The selected references report the isolation of over 300 different flavonoid compounds from more than 100 plant species, using 40 different solvent systems, showing the versatility of this technique. The solvent system hexane‐ethylacetate‐methanol‐water is proposed as a starting point for the separation of samples containing free flavonoids, as it was cited in more than 60% of the papers. A “fine tuning” step is proposed at each level of this solvent family. Other modifications include exchanging the alcohol in the system as well as introducing a fifth solvent. The solvent system ethyl‐acetate‐butanol‐water is proposed as the starting point for glycosylated flavonoids. Other solvent systems are also discussed. The use of gradients is proposed for samples containing both free and glycosylated flavonoids, as the polarity window is larger in these cases. High‐speed countercurrent chromatography was used in 89% of the reviewed data.     

Research in the Spotlight

ELECTROPHORESIS and the Journal of Separation Science (JSS) are two complementary separation science journals published by Wiley‐VCH. For the reader to realize the full benefits from both journals, a compilation of key research articles from JSS is reported here in this spotlight section. Similarly, JSS has created a spotlight section that compiles key research and review articles from ELECTROPHORESIS. Initially, this corner will be published bimonthly and may become a monthly publication later on.     

Advances in the determination of inorganic anions by ion chromatography

The time period covered for this review includes articles published from 1997 to 1999, with the addition of a few classic references. The purpose of the review is to include the most relevant works from each topic area of the determination of inorganic anions by ion chromatography, including new sample pretreatments, new separation methods, new detection systems and the latest applications in the field of environmental, water, foods, etc. samples. Experimental conditions such as stationary phase, eluent, detection mode, as well as matrix are summarized in a table.     

A comparative study of upright counter-current chromatography and high-performance liquid chromatograpohy for preparative isolation and purification ofphenolic compounds from Magnoliae officinalis

A comparative study of preparative isolation and purification of the phenolic compounds magnolol and honokiol from the Chinese medicinal plant Magnoliae officinalis by upright counter-current chromatography (CCC) and semi-preparative HPLC is presented. The comparison reveals that with a two-phase solvent system composed of light petroleum (bp 60-90 degrees C)-ethyl acetate-tetrachloromethane-methanol-water (1:1:8:6:1, v/v), 1250 mg of honokiol and 520 mg of magnolol, with a purity of 98.7 and 99.5%, respectively, were obtained from 2.0 g of a crude sample of Magnoliae officinalis in a single CCC separation. In contrast, semi-preparative HPLC allowed isolation and purification of these two phenolic compounds with significantly lower productivity and higher solvent consumption. Structures of the purified compounds were identified by 1H and 13C NMR.     

Application of Conducting Polymers in Chemical Analysis

This paper presents recent achievements in the field of analytical application of conducting polymers, most of which were published in the last five years. Based on 171 references mainly to original papers in international scientific journals, the applications of conducting polymers in the design of electrochemical and optical sensors, enzymatic biosensors and immunosensors are reviewed together with applications in analytical preconcentration procedures and high-performance separation techniques.     

Hermann Staudinger Award 2006

Macromolecular News: This section contains news of the macromolecular community all over the world. Articles about, for example, people, projects, and market trends are welcome. Suggestions should be sent to the editorial office of the Macromolecular journals, preferably by E-mail to macromol@wiley-vch.de. The editorial office decides which articles will be published.     

Research in the Spotlight

ELECTROPHORESIS and the Journal of Separation Science (JSS) are two complementary separation science journals published by Wiley‐VCH. For the reader to realize the full benefits from both journals, a compilation of key research articles from JSS is reported here in this spotlight section. Similarly, JSS has created a spotlight section that compiles key research and review articles from ELECTROPHORESIS. Initially, this corner will be published bimonthly and may become a monthly publication later on. The abstracts listed below have been reduced in length to accommodate as many important papers as possible within the allotted space.     

Research in the Spotlight

ELECTROPHORESIS and the Journal of Separation Science (JSS) are two complementary separation science journals published by Wiley‐VCH. For the reader to realize the full benefits from both journals, a compilation of key research articles from JSS is reported here in this spotlight section. Similarly, JSS has created a spotlight section that compiles key research and review articles from ELECTROPHORESIS. Initially, this corner will be published bimonthly and may become a monthly publication later on. The abstracts listed below have been reduced in length to accommodate as many important papers as possible within the allotted space.     

Fast choice of separation conditions for analyses by capillary zone electrophoresis using an information system Xemic

An information system Xemic applicable in analytical chemistry is described and its use in capillary electrophoresis for searching suitable separation conditions is demonstrated. This system is capable to provide suitable separation conditions even for analytes for which no electrophoretic experiments have been published so far. The system works with a database of components of anionic character the analyses of which have been performed, published in reviewed scientific journals, and included into a database created by an expert. Moreover, the system learned to search also in abstracts or complete scientific articles to find articles dealing with the determination of a substance in a given sample matrix. When no experiments have been published so far for a defined substance in a specific matrix, Xemic shows the separation conditions for determination of the substance regardless of the matrix. When no response can be found for the analyte of interest at all, the system Xemic works like an expert in the field and searches chemically similar substances and offers a series of substances the physicochemical properties of which are close to the followed analyte with respect to the behavior in the electric field, and shows working conditions for their analysis. Thus, the analyst puts only the order in the form of a given analyte in a given matrix and obtains a recommendation of a separation system that should enable to perform a successful separation. The system is not rigid and enables the operator to change the importance of individual attributes used in similarity search so as to obtain a broader or narrower group of similar components. With a certain probability the analyte of interest can be successfully analyzed under separation conditions that suited for the analysis of the most similar substances in the given matrix.     

Dual-mode high-speed counter-current chromatography: retention, resolution and examples

Counter-current chromatography (CCC) is a very versatile technique offering high resolution power in recovering very pure compounds from complex matrices. Dual-mode CCC where the phase role is reversed during the separation is investigated here; it ensures elution of all the injected species from the column while, unlike backflush, the separation is still progressing after phase reversal; equations giving retention and retention factor are derived from the basic equations of chromatography. Compared to normal-mode CCC, it is shown that enhanced resolution in dual-mode CCC can be obtained in conditions derived from a theoretical model. The experimental section provides the validation of the retention prediction while resolution is also proven to be enhanced in dual-mode CCC. However, equations given in the theoretical section cannot fully explain the results obtained for resolution because they do not deal with kinetics. Dual-mode CCC has also been applied to separation of polyoxypropylene glycol polymers; separation can be achieved with a small number of experiments because all the injected compounds are eluted by reversing the phases. Dual-mode CCC also gave improved yields in the purification of antibiotics compared with previous results using normal-mode CCC.     

60th Birthday of Prof. Dr. Dr. h.c. Heino Finkelmann

This section contains news of the macromolecular community all over the world. Articles about, for example, people, projects, and market trends are welcome. Suggestions should be sent to the editorial office of the Macromolecular journals, preferably by E‐mail to macromol@wiley‐vch.de. The editorial office decides which articles will be published.     

Preparative counter-current chromatography isolation of liensinine and its analogues from embryo of the seed of Nelumbo nucifera GAERTN. using upright coil planet centrifuge with four multilayer coils connected in series

Preparative counter-current chromatography (CCC) isolation of liensinine and its analogues, isoliensinine and neferine from embryo of the seed of Nelumbo nucifera GAERTN. has been successfully performed for the first time using upright coil planet centrifuge with four multilayer coils connected in series with 1600 mL capacity. Two kinds of two-phase solvent systems were applied to preparative CCC isolation. The first was the system composed of light petroleum (b.p. 60-90 degrees C)-ethyl acetate-tetrachloromethane-chloroform-methanol-water (1:1:4:4:6:2, v/v) which was very suitable for fast and small-scale CCC isolation. The second was the system composed of ethyl acetate-tetrachloromethane-methanol-water (1:6:4:1, v/v), which was the optimum for large-scale CCC isolation. Using the first system, 1102 mg of the crude alkaloid was purified in one-step separation of 150 min, yielding 350 mg neferine, 100 mg isoliensinine and 95 mg liensinine with over 95% purity. While using the second solvent system, 5850 mg of the crude alkaloid was purified in one-step separation of 9 h, yielding 2545 mg neferine, 698 mg isoliensinine and 650 mg liensinine with over 97% purity. Structures of the compounds were identified by electrospray ionization multiple mass spectrometry, one- and two-dimensional NMR.