Elution-extrusion countercurrent chromatography: theory and concepts in metabolic analysis

One-step isolation of carnosic acid and carnosol from rosemary by centrifugal partition chromatography

Carnosic acid and carnosol are the main bioactive components responsible for the significant antioxidant activity of Rosmarinus officinalis. Nevertheless, they are known for their instability in solutions. Separation of both compounds from crude rosemary extract was successfully achieved by one-step centrifugal partition chromatography without any degradation. A two-phase solvent system, hexane/ethyl acetate/methanol/water (3:2:3:2 v/v) was run on a preparative scale applying the elution-extrusion technique in descending mode. A 900 mg quantity of the crude extract containing 39.7% carnosic acid and 12.3% carnosol was loaded onto a 500 mL column, rotating at 1800 rpm. Carnosic acid and carnosol were obtained at purities of 96.1 ± 1% and 94.4 ± 0.9%, with recoveries of 94.3 ± 4.4% and 94.8 ± 2.3%, respectively. The compounds were identified by mass spectrometry, tandem mass spectrometry, and comparison with authentic standards.

A combination strategy for extraction and isolation of multi-component natural products by systematic two-phase solvent extraction-(13)C nuclear magnetic resonance pattern recognition and following conical counter-current chromatography separation: Podophyllotoxins and flavonoids from Dysosma versipellis (Hance) as examples

Despite of substantial developments of extraction and separation techniques, isolation of natural products from natural resources is still a challenging task. In this work, an efficient strategy for extraction and isolation of multi-component natural products has been successfully developed by combination of systematic two-phase liquid-liquid extraction-(13)C NMR pattern recognition and following conical counter-current chromatography separation. A small-scale crude sample was first distributed into 9 systematic hexane-ethyl acetate-methanol-water (HEMWat) two-phase solvent systems for determination of the optimum extraction solvents and partition coefficients of the prominent components. Then, the optimized solvent systems were used in succession to enrich the hydrophilic and lipophilic components from the large-scale crude sample. At last, the enriched components samples were further purified by a new conical counter-current chromatography (CCC). Due to the use of (13)C NMR pattern recognition, the kinds and structures of major components in the solvent extracts could be predicted. Therefore, the method could collect simultaneously the partition coefficients and the structural information of components in the selected two-phase solvents. As an example, a cytotoxic extract of podophyllotoxins and flavonoids from Dysosma versipellis (Hance) was selected. After the systematic HEMWat system solvent extraction and (13)C NMR pattern recognition analyses, the crude extract of D. versipellis was first degreased by the upper phase of HEMWat system (9:1:9:1, v/v), and then distributed in the two phases of the system of HEMWat (2:8:2:8, v/v) to obtain the hydrophilic lower phase extract and lipophilic upper phase extract, respectively. These extracts were further separated by conical CCC with the HEMWat systems (1:9:1:9 and 4:6:4:6, v/v). As results, total 17 cytotoxic compounds were isolated and identified. In general, whole results suggested that the strategy was very efficient for the systematic extraction and isolation of biological active components from the complex biomaterials.

An improved design of spiral tube assembly for separation of proteins by high-speed counter-current chromatography

A new spiral tube assembly was designed to improve the column capacity and partition efficiency for protein separation. This spiral tube assembly has greater column capacity than the original tubing because of an increase in radial grooves from 4 to 12 to accommodate more spiral layers and 12 narrow spots instead of 4 in each circular loop to interrupt the laminar flow that causes sample band broadening. Standard PTFE tubing (1.6mm ID) and the modified flat-twisted tubing were used as the separation column. The performances of both assemblies were compared for separating three stable test proteins including cytochrome c, myoglobin, and lysozyme using a two phase aqueous-aqueous solvent system composed of polyethylene glycol 1000 (12.5% w/w) and dibasic potassium phosphate (12.5% w/w). All samples were run at 1, 2, 3, and 5mL/min at both 800rpm and 1000rpm. The separation of these three protein samples produced high stationary phase retentions at 1, 2, and 3mL/min, yet separated efficiently at 5mL/min in 40min. After comparing the separation efficiency in terms of the peak resolutions, theoretical plate numbers, and separation times, it was determined that the flat-twisted tubing was more effective in separating these protein samples. In order to validate the efficacy of this novel assembly, a mixture of five protein samples (cytochrome c, myoglobin, ovalbumin, lysozyme, and hemoglobin) were separated, under the optimal conditions established with these three protein samples, at 1mL/min with a revolution speed of 1000rpm. There were high stationary phase retentions of around 60%, with effective separations, demonstrating the efficiency of the flat-twisted spiral tube assembly. The separation time of 6h was a limitation but can potentially be shortened by improving the strength of the column that will permit an increase in revolution speed and flow rate. This novel spiral separation column will allow rapid and efficient separation of mixtures with high yield of the constituent components.

Countercurrent Separation of Natural Products: An Update

This work assesses the current instrumentation, method development, and applications in countercurrent chromatography (CCC) and centrifugal partition chromatography (CPC), collectively referred to as countercurrent separation (CCS). The article provides a critical review of the CCS literature from 2007 since our last review (J. Nat. Prod. 2008, 71, 1489-1508), with a special emphasis on the applications of CCS in natural products research. The current state of CCS is reviewed in regard to three continuing topics (instrumentation, solvent system development, theory) and three new topics (optimization of parameters, workflow, bioactivity applications). The goals of this review are to deliver the necessary background with references for an up-to-date perspective of CCS, to point out its potential for the natural product scientist, and thereby to induce new applications in natural product chemistry, metabolome, and drug discovery research involving organisms from terrestrial and marine sources.

Real-Time Volumetric Phase Monitoring: Advancing Chemical Analysis by Countercurrent Separation

Countercurrent separation (CCS) utilizes the differential partitioning behavior of analytes between two immiscible liquid phases. We introduce the first platform ("CherryOne") capable of real-time monitoring, metering, and control of the dynamic liquid-liquid CCS process. Automated phase monitoring and volumetrics are made possible with an array of sensors, including the new permittivity-based phase metering apparatus (PMA). Volumetric data for each liquid phase are converted into a dynamic real-time display of stationary phase retention (Sf) and eluent partition coefficients (K), which represent critical parameters of CCS reproducibility. When coupled with the elution-extrusion operational mode (EECCC), automated Sf and K determination empowers untargeted and targeted applications ranging from metabolomic analysis to preparative purifications.

A novel 9 × 9 map-based solvent selection strategy for targeted counter-current chromatography isolation of natural products

Counter-current chromatography (CCC) is an efficient liquid-liquid chromatography technique for separation and purification of complex mixtures like natural products extracts and synthetic chemicals. However, CCC is still a challenging process requiring some special technical knowledge especially in the selection of appropriated solvent systems. In this work, we introduced a new 9 × 9 map-based solvent selection strategy for CCC isolation of targets, which permit more than 60 hexane-ethyl acetate-methanol-water (HEMWat) solvent systems as the start candidates for the selection of solvent systems. Among these solvent systems, there are clear linear correlations between partition coefficient (K) and the system numbers. Thus, an appropriate CCC solvent system (i.e., sweet spot for K = 1) may be hit by measurement of k values of the target only in two random solvent systems. Besides this, surprisingly, we found that through two sweet spots, we could get a line ("Sweet line") where there are infinite sweet solvent systems being suitable for CCC separation. In these sweet solvent systems, the target has the same partition coefficient (K) but different solubilities. Thus, the better sweet solvent system with higher sample solubility can be obtained for high capacity CCC preparation. Furthermore, we found that there is a zone ("Sweet zone") where all solvent systems have their own sweet partition coefficients values for the target in range of 0.4 < K< 2.5 or extended range of 0.25 < K < 16. All results were validated by using 14 pure GUESSmix mimic natural products as standards and further confirmed by isolation of several targets including honokiol and magnolol from the extracts of Magnolia officinalis Rehd. Et Wils and tanshinone IIA from Salvia miltiorrhiza Bunge. In practice, it is much easier to get a suitable solvent system only by making a simple screening two to four HEMWat two-phase solvent systems to obtain the sweet line or sweet zone without special knowledge or comprehensive standards as references. This is an important advancement for solvent system selection and also will be very useful for isolation of current natural products including Traditional Chinese Medicines.

Isolation and chemical identification of lipid derivatives from avocado (Persea americana) pulp with antiplatelet and antithrombotic activities

Bioassay-guided isolation of acetogenins from avocado pulp within vitroantiplatelet aggregation andin vivoantithrombotic effects in CD1 mice.

Qualitative and quantitative evaluation of solvent systems for countercurrent separation

Rational solvent system selection for countercurrent chromatography and centrifugal partition chromatography technology (collectively known as countercurrent separation) studies continues to be a scientific challenge as the fundamental questions of comparing polarity range and selectivity within a solvent system family and between putative orthogonal solvent systems remain unanswered. The current emphasis on metabolomic investigations and analysis of complex mixtures necessitates the use of successive orthogonal countercurrent separation (CS) steps as part of complex fractionation protocols. Addressing the broad range of metabolite polarities demands development of new CS solvent systems with appropriate composition, polarity (π), selectivity (σ), and suitability. In this study, a mixture of twenty commercially available natural products, called the GUESSmix, was utilized to evaluate both solvent system polarity and selectively characteristics. Comparisons of GUESSmix analyte partition coefficient (K) values give rise to a measure of solvent system polarity range called the GUESSmix polarity index (GUPI). Solvatochromic dye and electrical permittivity measurements were also evaluated in quantitatively assessing solvent system polarity. The relative selectivity of solvent systems were evaluated with the GUESSmix by calculating the pairwise resolution (αip), the number of analytes found in the sweet spot (Nsw), and the pairwise resolution of those sweet spot analytes (αsw). The combination of these parameters allowed for both intra- and inter-family comparison of solvent system selectivity. Finally, 2-dimensional reciprocal shifted symmetry plots (ReSS(2)) were created to visually compare both the polarities and selectivities of solvent system pairs. This study helps to pave the way to the development of new solvent systems that are amenable to successive orthogonal CS protocols employed in metabolomic studies.

Recent progress on countercurrent chromatography modeling

As countercurrent chromatography is becoming an established method in chromatography for many kinds of products, it is becoming increasingly important to model the process and to be able to predict the peaks for a given process. The CCC industries are looking for rapid methods to analyze the processes of countercurrent chromatography and select suitable solvent system. In this paper, recent progress is reviewed in the development and demonstration of several types of models of countercurrent chromatography. Literature lists a number of countercurrent chromatography (CCC) models that can predict the retention time and to a certain extent the peak width of a solute eluting from a CCC column, such as cell model, CCD model, CSTRs model, probabilistic model, temperature dependence plate model, physical models, etc.

Orthogonal Analysis Underscores the Relevance of Primary and Secondary Metabolites in Licorice

Licorice botanicals are produced from the roots of Glycyrrhiza species (Fabaceae), encompassing metabolites of both plant and rhizobial origin. The composition in both primary and secondary metabolites (1°/2°Ms) reflects the physiologic state of the plant at harvest. Interestingly, the relative abundance of 1°Ms vs 2°Ms in licorice extracts remains undetermined. A centrifugal partition chromatography (CPC) method was developed to purify liquiritin derivatives that represent major bioactive 2°Ms and to concentrate the polar 1°Ms from the crude extract of Glycyrrhiza uralensis. One objective was to determine the purity of the generated reference materials by orthogonal UHPLC-UV/LC-MS and qHNMR analyses. The other objectives were to evaluate the presence of 1°Ms in purified 2°Ms and define their mass balance in a crude botanical extract. Whereas most impurities could be assigned to well-known 1°Ms, p-hydroxybenzylmalonic acid, a new natural tyrosine analogue, was also identified. Additionally, in the most polar fraction, sucrose and proline represented 93% (w/w) of all qHNMR-quantified 1°Ms. Compared to the 2°Ms, accounting for 11.9% by UHPLC-UV, 1°Ms quantified by qHNMR defined an additional 74.8% of G. uralensis extract. The combined orthogonal methods enable the mass balance characterization of licorice extracts and highlight the relevance of 1°Ms, and accompanying metabolites, for botanical quality control.

Separation of nine compounds from Salvia plebeia R.Br. using two-step high-speed counter-current chromatography with different elution modes

Nine compounds were successfully separated from Salvia plebeia R.Br. using two-step high-speed counter-current chromatography with three elution modes. Elution-extrusion counter-current chromatography was applied in the first step, while classical counter-current chromatography and recycling counter-current chromatography were used in the second step. Three solvent systems, n-hexane/ethyl acetate/ethanol/water (4:6.5:3:7, v/v), methyl tert-butyl ether/ethyl acetate/n-butanol/methanol/water (6:4:1:2:8, v/v) and n-hexane/ethyl acetate/methanol/water (5:5.5:5:5, v/v) were screened and optimized for the two-step separation. The separation yielded nine compounds, including caffeic acid (1), 6-hydroxyluteuolin-7-glucoside (2), 5,7,3',4'-tetrahydroxy-6-methoxyflavanone-7-glucoside (3), nepitrin (4), rosmarinic acid (5), homoplantaginin (6), nepetin (7), hispidulin (8), and 5,6,7,4'-tertrahydroxyflavone (9). To the best of our knowledge, 5,7,3',4'-tetrahydroxy-6-methoxyflavanone-7-glucoside and 5,6,7,4'-tertrahydroxyflavone have been separated from Salvia plebeia R.Br. for the first time. The purities and structures of these compounds were identified by high-performance liquid chromatography, electrospray ionization mass spectrometry, (1)H and (13)C NMR spectroscopy. This study demonstrates that high-speed counter-current chromatography is a useful and flexible tool for the separation of components from a complex sample.

Airborne antituberculosis activity of Eucalyptus citriodora essential oil

The rapid emergence of multi- and extensively drug-resistant tuberculosis (MDR/XDR-TB) has created a pressing public health problem, which mostly affects regions with HIV/AIDS prevalence and represents a new constraint in the already challenging disease management of tuberculosis (TB). The present work responds to the need to reduce the number of contagious MDR/XRD-TB patients, protect their immediate environment, and interrupt the rapid spread by laying the groundwork for an inhalation therapy based on anti-TB-active constituents of the essential oil (EO) of Eucalyptus citriodora. In order to address the metabolomic complexity of EO constituents and active principles in botanicals, this study applied biochemometrics, a 3-D analytical approach that involves high-resolution CCC fractionation, GC-MS analysis, bioactivity measurements, and chemometric analysis. Thus, 32 airborne anti-TB-active compounds were identified in E. citriodora EO: the monoterpenes citronellol (1), linalool (3), isopulegol (5), and α-terpineol (7) and the sesquiterpenoids spathulenol (11), β-eudesmol (23), and τ-cadinol (25). The impact of the interaction of multiple components in EOs was studied using various artificial mixtures (AMxs) of the active monoterpenes 1, 2, and 5 and the inactive eucalyptol (33). Both neat 1 and the AMx containing 1, 2, and 33 showed airborne TB inhibition of >90%, while the major E. citriodora EO component, 2, was only weakly active, at 18% inhibition.

Two-dimensional countercurrent chromatography × high performance liquid chromatography for preparative isolation of toad venom

In this work, a new on-line two-dimensional chromatography coupling of flow programming counter-current chromatography and high-performance liquid chromatography (2D CCC×HPLC) was developed for preparative separation of complicated natural products. The CCC column was used as the first dimensional isolation and a preparative ODS column operated in reversed-phase (RP) mode as the second dimension. The CCC was operated at a controlled flow rate to ensure that each fraction eluted within one hour, corresponding to the isolation time of the 2nd dimensional preparative HPLC. The eluent from the 1st dimensional CCC was diluted using a makeup pump and trapped onto holding column, before been eluted and transferred to the 2nd dimensional HPLC. The performance of the holding column was evaluated, in terms of column size, dilution ratio and diameter-height ratio, as well as system pressure, for the solution to the issue of online trapping of low pressure eluent from a CCC column. Satisfactory trapping efficiency and tolerable CCC pressure can be achieved using a commercially available 15mm×30mm i.d. ODS pre-column. The present integrated system was successfully applied in a one-step preparative separation of 12 compounds, from the crude methanol extract of venom of Bufo bufo gargarizans. Compounds 1-12 were isolated in overall yield of 1.0%, 0.8%, 2.0%, 1.3%, 2.0%, 1.5%, 1.9%, 3.6%, 6.1%, 4.8%, 3.5% and 4.1%, with HPLC purity of 99.9%, 99.7%, 90.6%, 99.9%, 77.0%, 99.9%, 90.4%, 99.9%, 52.0%, 99.9%, 99.3%, and 85.0%, respectively. All the results demonstrate that the flow programming CCC×HPLC method is an efficient and convenient way for the separation of compounds from toad venom and it can also be applied to isolate other complex multi-component natural products.

Activity-guided identification of acetogenins as novel lipophilic antioxidants present in avocado pulp (Persea americana)

Avocado fruit is a rich source of health-related lipophilic phytochemicals such as monounsaturated fatty acids, tocopherols, carotenes, acetogenins and sterols. However, limited information is available on the contribution of specific phytochemicals to the overall antioxidant capacity (AOC) of the fruit. Centrifugal partition chromatography was used as fractionation tool, guided by an in vitro chemical assay of oxygen radical absorbance capacity (ORAC). Subsequent experiments focused on isolation and characterization of the chemical nature of the main contributors to lipophilic AOC of avocado pulp. ORAC values obtained for acetogenins were contrasted with results from an isolated kidney mitochondria membrane lipid peroxidation bioassay. The present study established that lipophilic AOC of the pulp was significantly higher than its hydrophilic AOC. Our results confirmed the presence of acetogenins in the fractions with highest lipophilic AOC, and for the first time linked them as contributors to lipophilic-ORAC values. Further HPLC-PDA/MS-TOF analysis led to structural elucidation of two novel acetogenins, not previously reported as present in avocado pulp, along with five already known related-compounds. Antioxidant properties observed for avocado pulp acetogenins by the ORAC assay suggested that, in the presence of an emulsifying agent, acetogenins could serve as novel lipophilic antioxidants in a food matrix. Results from isolated mitochondria lipid peroxidation bioassay, indicated that L-ORAC values which may have relevance for food matrix applications, should not be interpreted to have a direct relevance in health-related claims, compounds need to be evaluated considering the complexity of biological systems.

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.

Isolation and structure elucidation of avocado seed (Persea americana) lipid derivatives that inhibit Clostridium sporogenes endospore germination

Avocado fruit extracts are known to exhibit antimicrobial properties. However, the effects on bacterial endospores and the identity of antimicrobial compounds have not been fully elucidated. In this study, avocado seed extracts were tested against Clostridium sporogenes vegetative cells and active endospores. Bioassay-guided purification of a crude extract based on inhibitory properties linked antimicrobial action to six lipid derivatives from the family of acetogenin compounds. Two new structures and four compounds known to exist in nature were identified as responsible for the activity. Structurally, most potent molecules shared features of an acetyl moiety and a trans-enone group. All extracts produced inhibition zones on vegetative cells and active endospores. Minimum inhibitory concentrations (MIC) of isolated molecules ranged from 7.8 to 15.6 μg/mL, and bactericidal effects were observed for an enriched fraction at 19.5 μg/mL. Identified molecules showed potential as natural alternatives to additives and antibiotics used by the food and pharmaceutical industries to inhibit Gram-positive spore-forming bacteria.

Novel linear and step-gradient counter-current chromatography for bio-guided isolation and purification of cytotoxic podophyllotoxins from Dysosma versipellis (Hance)

Dysosma versipellis (Hance) is a famous traditional Chinese medicine for the treatment of snakebite, weakness, condyloma accuminata, lymphadenopathy, and tumors for thousands of years. In this work, four podophyllotoxin-like lignans including 4'-demethylpodophyllotoxin (1), α-peltatin (2), podophyllotoxin (3), β-peltatin (4) as major cytotoxic principles of D. versipellis were successfully isolated and purified by several novel linear and step gradient counter-current chromatography methods using the systems of hexane/ethyl acetate/methanol/water (4:6:3:7 and 4:6:4:6, v/v/v/v). Compared with isocratic elution, linear and step-gradient elution can provide better resolution and save more time for the separation of photophyllotoxin and its congeners. Their cytotoxicities were further evaluated and their structures were validated by high-resolution electrospray TOF MS and nuclear magnetic resonance spectra. All components showed potent anticancer activity against human hepatoma cells HepG2.

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.

Comparing two models of gradient elution in counter-current chromatography

Gradient change of mobile phase composition is commonly used in liquid chromatography to shorten analysis duration. Gradient elution is possible in counter-current chromatography if it is demonstrated that the mobile phase composition changes are not associated with liquid stationary phase composition changes. Also, the solute distribution ratios in initial (1) and final (2) eluting systems must be known. If the solute distribution ratios during the changing mobile phase composition are modeled, the full gradient separation can be modeled using classical equations of liquid chromatography. Another approach allowed modeling empirically the gradient step. It considered the decreasing volume of mobile phase 1 and the increasing volume of mobile phase 2 used at each gradient time to derive a very simple equation. The two equations were compared computing the retention volumes of five test solutes. A remarkable agreement was observed considering the very different mathematical expressions of the two models. The step-gradient method was also modeled and its results compared to those of the linear gradient method.

Modeling gradient elution in countercurrent chromatography: efficient separation of tanshinones from Salvia miltiorrhiza Bunge

Countercurrent chromatography (CCC) is a support-free liquid-liquid chromatography using centrifugal fields to hold the liquid stationary phase. CCC has been widely applied in the separation of various natural and synthetic components using a variety of biphasic liquid systems. The related hexane or heptane/ethyl acetate/methanol or ethanol/water biphasic liquid systems demonstrated their significance in CCC. Gradient is difficult in CCC since any composition change in one phase induces a composition change of the other phase to maintain phase equilibrium. This work provides a new insight into linear gradient elution in CCC that is feasible with some biphasic liquid systems such as selected compositions of the hexane/ethyl acetate/ethanol/water systems. The equations modeling solute motion inside the CCC column are proposed. Particular compositions of the liquid system, namely the hexane/ethyl acetate/ethanol/water 8:2:E:W compositions with E + W = 10, were studied from W = 1 to 9. They showed moderate changes in the upper organic phase compositions. The model is tested with the separation of tanshinones from the rhizome of Salvia miltiorrhiza Bunge. Different linear solvent gradient profiles were experimentally performed between 8:2:5:5 and 8:2:3:7 compositions and the results were evaluated using the proposed model. Five tanshinones including dihydrotanshinone I, cryptotanshinone, tanshinone I, 1,2-dihydrotanshinquinone, and tanshinone IIA have been successfully separated (>95% purities) using a gradient profile optimized by the developed model. The gradient model can be used only with biphasic liquid systems in which one phase shows minimum composition changes when the other phase composition changes notably. This case is not the general case for biphasic liquid systems but can be applied with specific compositions of the quaternary hexane or heptane/ethyl acetate/methanol or ethanol/water most useful CCC liquid systems.

Separation of nucleobases and their derivatives with organic-high ionic strength aqueous phase systems by spiral high-speed counter-current chromatography

A set of nucleic acid constituents were separated with ultra polar two-phase solvent systems by a spiral multilayer coil mounted on the rotary frame of a type-J coil planet centrifuge. These two-phase systems were composed of 1-butanol/ethanol/50% saturated aqueous ammonium sulfate at various volume ratios. Nucleobases including adenine, cytosine, uracil, and thymine; nucleosides including adenosine, guanosine, cytidine, and uridine; and nucleotides including, AMP, GMP, CMP, UMP, and TMP are partitioned in each group with suitable solvent ratios. Adenine derivatives such as adenosine, AMP, ADP, and ATP were well resolved in the most polar solvent system composed of ethanol/50% saturated aqueous ammonium sulfate at a volume ratio of 1:2. It was found that cytosine and cytidine peaks showed some irregular two peaks probably due to their keto and enol isomers, while the separation of AMP forms two peaks especially when TMP was added in the sample solution, the mechanism of which is now under investigation in our laboratory.

Separation of natural products by countercurrent chromatography

Countercurrent Chromatography (CCC) provides the natural product chemist with a high-resolution separatory method, which is uniquely applicable to sensitive (unstable) compounds and which allows virtually quantitative recovery of the load sample. Different instruments use different means of retaining a stationary liquid phase. The solvent system (SS) can be chosen to optimize the separatory power and the number of systems available is limitless. Several examples are provided to illustrate the power of the method and to guide the chemist in choice of an appropriate SS.

Separation and purification of isorhamnetin 3-sulphate from Flaveria bidentis (L.) Kuntze by counter-current chromatography comparing two kinds of solvent systems

The first preparative separation of a flavonoid sulphate isorhamnetin 3-sulphate from Flaveria bidentis (L.) Kuntze by counter-current chromatography (CCC) was presented. Two kinds of solvent systems were used. A conventional organic/aqueous solvent system n-butanol-ethyl acetate-water (4:1:5, v/v) was used, yielding isorhamnetin 3-sulphate 2.0 mg with a purity of 93.4% from 83 mg of pre-enriched crude extract obtained from 553 mg ethanol extract by macroporous resin. A one-component organic/salt-containing system composed of n-butanol-0.25% sodium chloride aqueous solution (1:1, v/v) was also used, and the LC column packed with macroporous resin has been employed for desalination of the target compound purified from CCC. As a result, 2.1 mg of isorhamnetin 3-sulphate with a purity of over 97% has been isolated from 402 mg of crude extract without pre-enrichment. Compared with the conventional organic/aqueous system, the one-component organic/salt-containing aqueous system was more suitable for the separation of isorhamnetin 3-sulphate, and purer target compound was obtained from the crude extract without pre-enrichment using the new solvent system. The chemical structure was confirmed by ESI-MS and (1)H, (13)C NMR. In summary, our results indicated that CCC using one-component organic/salt-containing aqueous solution is very promising and powerful for high-throughput purification of isorhamnetin 3-sulphate from Flaveria bidentis (L.) Kuntze.

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.

Counter-current chromatographic method for preparative scale isolation of picrosides from traditional Chinese medicine Picrorhiza scrophulariiflora

Apocynin, androsin, together with picroside I, II and III from crude extracts of Picrorhiza scrophulariiflora were isolated by means of high-speed counter-current chromatography (CCC) combining elution-extrusion (EE) and cycling-elution (CE) approach. The EECCC took full advantages of the liquid nature of the stationary phase for a complete sample recovery and extended the solute hydrophobicity window, while CECCC showed its unique advantage in achieving effective separation of special compounds through preventing stationary phase loss. In the present work, the biphasic liquid system composed of n-hexane/ethyl acetate/methanol/water (1:2:1:2, v/v/v/v) was used for separation of apocynin and androsin, ethyl acetate/n-butanol/water/formic acid (4:1:5:0.005, v/v/v/v) for picroside I, II and III. However, due to the extremely similar K values (K1 /K2 ≈1.2), picroside I and III were always eluted together by several biphasic solvent systems. In this case, the CECCC exhibited great superiority and baseline separated in the sixth cycle using ethyl acetate/water (1:1, v/v) as biphasic liquid system. Each fraction was analyzed by UPLC-UV and ESI-MS analysis, and identified by comparing with the data of reference substances. Compared with classical elution, the combination of EE and CE approach exhibits strong separation efficiency and great potential to be a high-throughput separation technique in the case of complex samples.

Numerical model for the investigation of countercurrent chromatography

A numerical model is developed to describe the separation process of countercurrent chromatography (CCC) in this work. The theory of countercurrent extraction table (TCCET) is first proposed to calculate concentration distributions of chemical components in the CCC, which is essential for a numerical model to describe the dynamic equilibrium of mass transfer. According to the theory of countercurrent extraction, the concentration in chromatography obeys binomial distribution, while the outflow from the n-th stage is a negative binomial distribution. As a result of the central limit theorem, they will obey normal distribution for sufficiently large n. Row-stage ratio (R(RS)) is then defined to determine the K value or retention time because it has a linear relationship to K value and retention time. The stage for a certain K value can be subsequently obtained with a very simple form, n(k)=1/(2piq(k)X(2)(k, max)), which can be calculated from the peak height obtained from experiments. Finally, the actual stage for a separation chromatogram can be acquired with using this simple expression. The agreement between theoretic and experimental results is quite satisfactory in the normal-phase and reversed-phase elution mode.

New cysteine-S-conjugate precursors of volatile sulfur compounds in bell peppers (Capsicum annuum L. cultivar)

The objective of this study was to verify whether the volatile organic sulfur compounds recently discovered in bell pepper (Capsicum annuum, L. cultivars), such as the mercapto-ketones: 4-sulfanyl-2-heptanone and 2-sulfanyl-4-heptanone, the mercapto-alcohols: 4-sulfanyl-2-heptanol and 2-sulfanyl-4-heptanol, and heptane-2,4-dithiol, originate from their corresponding cysteine-S-conjugates. Analysis of aqueous extracts of red and green bell pepper by ultraperformance liquid chromatography-mass spectrometry with electrospray ionization in the positive mode (UPLC-MS ESI(+)) displayed masses corresponding to the expected cysteine-S-conjugates. To confirm this observation, four cysteine-S-conjugates were prepared as authentic samples: S-(3-hydroxy-1-methylhexyl)-L-cysteine, S-(3-hydroxy-1-propylbutyl)-L-cysteine, S-(3-oxo-1-propylbutyl)-L-cysteine, and (2R,2'R)-3,3'-(4-hydroxyheptane-2,6-diyl)bis(sulfanediyl) bis(2-aminopropanoic acid). By comparison with the fragmentation patterns and retention times of synthetic mixtures of cysteine-S-conjugate diastereoisomers, the natural occurrence of cysteine conjugates was confirmed in bell peppers. In addition, the cysteine-S-conjugates from red and green bell pepper extracts were concentrated by ion exchange chromatography and the fractions incubated with a β-lyase (apotryptophanase). The liberated thiols were concentrated by affinity chromatography, and their occurrence, detected by gas chromatography-mass spectrometry, confirmed our predictions. Moreover, 3-sulfanyl-1-hexanol was also detected and the occurrence of S-(1(2-hydroxyethyl)butyl)-L-cysteine confirmed. A quantitative estimation based on external calibration curves, established by UPLC-MS ESI(+) in selected reaction monitoring mode, showed that cysteine-S-conjugates were present at concentrations in the range of 1 to 100 μg/kg (±20%).

Two-dimensional chromatography of complex polymers, 8. Separation of fatty alcohol ethoxylates simultaneously by end group and chain length

A comprehensive two-dimensional liquid chromatography system was developed to precisely describe the molecular heterogeneity of fatty alcohol ethoxylates. The end-group functionality was analyzed by gradient HPLC while ethylene oxide oligomer distributions were characterized by liquid adsorption chromatography. A baseline separation of all functionality fractions irrespective of the ethylene oxide oligomer chain length was achieved on nonpolar X-Terra(®) C(18) with a methanol-water gradient, whereas an isocratic flow of isopropanol-water on a polar Chromolith(®) Si column gave a separation according to the oligomer chain length without interference of the end-group distribution. The combination of these two methods to conduct online two-dimensional liquid chromatography experiments resulted in a comprehensive two-dimensional picture on the molecular heterogeneity of the sample.

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.

Screening of antioxidant phenolic compounds in Chinese rhubarb combining fast counter-current chromatography fractionation and liquid chromatography/mass spectrometry analysis

In this paper, an effective method combing fast elution-extrusion counter-current chromatography (CCC) and LC/MS for rapid screening of antioxidative phenolic compounds in Chinese Rhubarb is presented. An integrated three-coil CCC column (40 mL each coil) was used to accomplish the optimization of biphasic liquid system. In a single run (approximately 40 min), the solvent system composed of n-hexane/ethyl acetate/methanol/water (1:1:1:1, v/v) was selected as optimum CCC liquid system for fast fractionation of the crude ethanol extract. With a 140 mL-capacity CCC instrument, 100 mg Chinese Rhubarb extract was separated under the optimized conditions, producing six fractions in only 100 min. The quantities of each fraction were approximately 15 mg. In addition, each fraction was subjected to antioxidant activity assay and characterized by LC/MS analysis. Fifty compounds, including phenolic acids, phenolic glucosides and hydroxyanthraquinones, were detected by LC/MS/MS analysis. As a result, gallic acid together with Fr I showed excellent antioxidant activity, which was well consistent with previous studies and exhibited great potential for natural drug discovery program of the present method.