Scale-up in centrifugal partition chromatography: The “free-space between peaks” method

Scale-up of Aflatoxin Purification by Centrifugal Partition Chromatography

Aflatoxins (AFs) are a group of secondary metabolites that cause several diseases in both animals and humans. Since the discovery of this group of toxins, several effects were revealed, such as hepatic changes, carcinoma, failure, and cancer of the liver. In the European Union, there are concentration limits for this group of mycotoxins in food and feed products; thus, these substances are required in their pure forms to prepare reference standards or certified reference materials. In our present work, a liquid–liquid chromatographic method utilizing a toluene/acetic acid/water ternary system was improved. In order to enhance the purification and gain a higher amount of pure AFs in one separation run, a scale-up of the previous separation was carried out. In several scale-up steps—including the determination of the maximum concentration and volume to load on a 250 mL rotor via a loop and via a pump as well, and the quadruplication of the entire separation procedure to a 1000 mL rotor—an efficient scale-up was achieved. Utilizing a 250 mL rotor in an 8-hour workday, altogether approximately 2.2 g of total AFs could be purified with 8.2 liters of solvent, while on a 1000 mL column, approximately 7.8 g AFs could be prepared, utilizing around 31 liters of solvents.

Anthocyanins in Different Food Matrices: Recent Updates on Extraction, Purification and Analysis Techniques

Anthocyanins (ANCs), a kind of natural pigments, are widely present in food substrates. Evidence has shown that ANCs can promote health in terms of anti-oxidation, anti-tumor, and anti-inflammation. However, the oxidative stability of ANCs limits accurate quantitation and analysis. Therefore, faster, more accurate, and highly sensitive extraction and determination methods are necessary for understanding the role of ANCs in medicine and food. This review presents an updated overview of pretreatment and detection techniques for ANCs in various food substrates since 2015. Liquid-liquid extraction and various green solvent extraction methods, such as accelerated solvents extraction, deep eutectic solvents extraction, ionic liquids extraction, and supercritical fluid extraction, are commonly used pretreatment methods for extraction and purification of ANCs. Liquid chromatography coupled with different detectors (tandem mass spectrometry and UV detectors) and spectrophotometry methods are some of the determination methods for ANC. This study has updated, compared, and discussed different pretreatment and analysis methods. Moreover, the advanced methods and development prospects in this field are comprehensively summarized, which can provide references for further utilization of ANCs.

Preparation of 5-hydroxymethylfurfural from Schisandra chinensis (Turcz.) Baill by high-speed counter-current chromatography: Comparison of conventional and consecutive separation

Schisandra chinensis is a kind of plant with high medicinal value, which contains many medicinal ingredients, including 5-hydroxymethylfurfural. In the present study, an efficient method based on high-speed counter-current chromatography was established for the preparation of 5-hydroxymethylfurfural from Schisandra chinensis. Petroleum ether-ethyl acetate-methanol-water (2:5:2:5, v/v) was selected as the solvent system for high-speed counter-current chromatography. In order to improve the yield of single separation, the sample size was continuously optimized and improved. The result showed that 1250 mg was the most suitable sample size, and 41 mg of the target compound with 97% purity was obtained by a single run. To further improve the yield, consecutive high-speed counter-current chromatography was introduced and compared with the results of high-speed counter-current chromatography single run. The results showed that although the purity was reduced to 92%, 430 mg of the target compound was obtained from 12.5 g of ethanol extract within 670 min after 10 consecutive injections. It indicated that consecutive separation not only increased the yield of the target compound, but also saved the separation time and greatly improved the separation efficiency of high-speed counter-current chromatography.

Intermittent sample loading technique as a tool for obtaining high- concentration elution bands in recycling liquid-liquid chromatography: Theoretical study of periodic and semi-continuous separation processes

To improve the efficiency of countercurrent chromatography (CCC) separations, we have previously proposed a new sample loading method called intermittent sample loading (ISL), in which continuous sample feed alternates with short periods of "clean" mobile phase feed to the CCC device. In semi-continuous separation processes, during sample feed periods, the sample is loaded in separate batches, each consisting of a series of intermittent sample loads. It was shown that the application of the intermittent sample loading method in the conventional isocratic CCC separations significantly increased process productivity and the concentration of compounds in the separated fractions. In this study, to further improve the CCC separations with intermittent sample loading, we discuss the application of the ISL method in the processes of close-loop recycling counter-current chromatography (CLR CCC). The advantage of the ISL CLR CCC over the ISL CCC is higher resolution and lower solvent consumption. Equations are presented that allow the simulation of periodic and semi-continuous ISL CLR CCC separations and the selection of optimal operational conditions for these separation processes. It is shown that the use of ISL technique in CLR CCC separations makes it possible to produce fractions of compounds with a much higher concentration than when using the conventional single sample loading method.

Selective Separation of Vanillic Acid from Other Lignin-Derived Monomers Using Centrifugal Partition Chromatography: The Effect of pH

In this work, centrifugal partition chromatography (CPC) assisted by a polyethylene glycol (PEG)/sodium polyacrylate (NaPA) aqueous biphasic system (ABS) was applied in the separation of five lignin-derived monomers (vanillin, vanillic acid, syringaldehyde, acetovanillone, and p-hydroxybenzaldehyde). The influence of the system pH (unbuffered, pH 5, and pH 12) and added electrolytes (inorganic salts or ionic liquids (ILs)) on the compound partition was initially evaluated. The obtained data revealed that ILs induced more adequate partition coefficients (K < 5) than inorganic salts (K > 5) to enable separation performance in CPC, while alkaline conditions (pH 12) demonstrated a positive impact on the partition of vanillic acid. CPC runs, with buffered ABS at pH 12, enabled a selective separation of vanillic acid from other lignin monomers. Under these conditions, a distinct interaction between the top (PEG-rich) and bottom (NaPA-rich) phases of the ABS with the double deprotonated form of vanillic acid is expected when compared to the remaining lignin monomers (single deprotonated). This is an impactful result that shows the pH to be a crucial factor in the separation of lignin monomer compounds by CPC, while only unbuffered systems have been previously studied in the literature. Finally, the recovery of vanillic acid up to 96% purity and further recycling of ABS phase-forming components were approached as a proof of concept through the combination of ultrafiltration and solid-phase extraction steps.

A strategy to process hundred-gram level complex sample using liquid-liquid-refining extraction and consecutive counter-current chromatography: Toona sinensis case study

Large-scale preparation of target compounds from complex samples is facing great challenges. In the present study, an efficient strategy for large-scale preparation of target compound was proposed and successfully applied in the separation of active components from Toona sinensis. The pretreatment technology of liquid-liquid refining extraction (LLRE) combined with consecutive high-speed counter-current chromatography (HSCCC) was used to process hundred grams of extractions. Firstly, two phase solvent systems composed of n-hexane-ethyl acetate-methanol-water (5:5:5:5, v/v) and (2:5:2:5, v/v) were used to remove low polar and high polar impurities from 100 g crude extracts of T. sinensis, respectively, and 9.25 g of crude sample was obtained. And then, n-hexane-ethyl acetate-methanol-water (2.5:5:2.5:5, v/v) was used as the solvent system for HSCCC separation. The isocratic elution mode with max loading and consecutive injections mode were investigated to obtain more target compound. As a result, ethyl gallate with purity of 97% was successfully separated by 5 times consecutive counter-current chromatography. The separation was repeated once. Finally, ethyl gallate (3.73 g) was isolated from 9.25 g of crude sample (100 g crude extracts). The results demonstrated that the yield increased from 0.26 g/h/L of untreated crude extract to 0.93 g/h/L of LLRE pre-treated sample for single injection, and further increased to 1.62 g/h/L for 5 consecutive injections mode with the present method.

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.

Operating mode and parameter selection in liquid-liquid chromatography

The presence of a liquid stationary phase in liquid-liquid chromatography (LLC) allows for high versatility of operation as well as adaptability to different sample types and separation tasks. LLC, also known as countercurrent chromatography (CCC) or centrifugal partition chromatography (CPC), offers the user a variety of operating modes, many of which have no direct equivalent in conventional preparative liquid-solid chromatography. These operating modes have the potential to greatly improve LLC separation performance compared to the standard "classical" isocratic batch injection mode, and they often require minimal to no addition of equipment to the standard set-up. However, reports of the use of alternative LLC operating modes make up only a fraction of the literature. This is likely due, at least in part, to the lack of clear guidelines and methods for operating mode and parameter selection, leaving alternative process options to be avoided and underutilized. This review seeks to remedy this by providing a thorough overview of the available LLC operating modes, identifying the key characteristics, advantages and disadvantages, and areas of application of each. Additionally, the equations and short-cut models aiding in operating mode and parameter selection are presented and critiqued, and their notation is unified for clarity. By rendering LLC and its alternative operating modes more accessible to current and prospective users, it is hoped to help expand the application of this technology and support the achievement of its full potential.

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.

Purification of two valepotriates from Centranthus ruber by centrifugal partition chromatography: From analytical to preparative scale

Considering chemical complexity of plant crude extracts, purification of natural products is a rate limiting process to identify new compounds as well as to obtain standard references for quantitative or qualitative purposes. In the present work, a centrifugal partition chromatography (CPC) method was developed to isolate and produce high quality reference standards of valtrate and 7-homovaltrate from Centranthus ruber L. roots. These two compounds are controversial aglycon iridioids regulated by the legislation on plant-based dietary supplements. A new biphasic solvent system suitable for CPC separation of valepotriates was developed. It was composed of methanol/hexane/water (5/5/0.8, v/v/v). It yielded a partition coefficient near 1 and a theoretical selectivity of 1.3 between both targeted compounds. Optimization of CPC experimental parameters at the analytical scale (50 mL- and 100 mL-column capacity) enabled compounds' separation with a flow rate of 8 mL/min at 2500 rpm. Then a scale up from a 100 mL-column capacity to a 1000 mL-column capacity has been studied using the "free-space between peaks" concept. It allowed an injected quantity 16 times higher in comparison to the maximal loading capacity of the 100 mL-column. Both valtrate and 7-homovaltrate were recovered in one single step with a purity over 97%. Further MS and NMR characterization allowed to confirm unambiguously the compounds' structures. The highly efficient CPC separation developed in this work provides valepotriates in amounts suitable for further study and strong bases for future industrial development.

Continuous Synthesis and Purification by Coupling a Multistep Flow Reaction with Centrifugal Partition Chromatography

Continuous-flow multistep synthesis is combined with quasi-continuous final-product purification to produce pure products from crude reaction mixtures. In the nucleophilic aromatic substitution of 2,4-difluoronitrobenzene with morpholine followed by a heterogeneous catalytic hydrogenation, the desired monosubstituted product can be continuously separated from the co- and by-products in a purity of over 99 % by coupling a flow reactor sequence to a multiple dual-mode (MDM) centrifugal partition chromatography (CPC) device. This purification technique has many advantages over HPLC, such as higher resolution and no need for column replacement or silica recycling, and it does not suffer from irreversible adsorption.

Trapping multiple dual mode centrifugal partition chromatography for the separation of intermediately-eluting components: Throughput maximization strategy

Trapping multiple dual mode centrifugal partition chromatography (trapping MDM CPC) is an alternative to isocratic pulse injections for the separation of intermediately-eluting components from complex mixtures using liquid-liquid chromatography. In this work, a throughput maximization strategy is developed and validated to investigate the full potential of trapping MDM CPC as a preparative technique. In the proposed approach, shake flask and stationary phase retention experiments are used to determine the maximum feed concentration and flow rate, respectively. A model-based parameter selection process combining a mathematical short-cut method and simulations based on the equilibrium cell model is used to obtain the column loading and step durations resulting in maximized process throughput. The proposed throughput maximization strategy is experimentally validated for the separation of a ternary model mixture of parabens. A preliminary comparison of trapping MDM CPC separation performance to that of stacked pulse injections is also made.

Centrifugal partition chromatography in a biorefinery context: Optimisation and scale-up of monosaccharide fractionation from hydrolysed sugar beet pulp

The isolation of component sugars from biomass represents an important step in the bioprocessing of sustainable feedstocks such as sugar beet pulp. Centrifugal partition chromatography (CPC) is used here, as an alternative to multiple resin chromatography steps, to fractionate component monosaccharides from crude hydrolysed sugar beet pulp pectin. CPC separation of samples, prepared in the stationary phase, was carried out using an ethanol: ammonium sulphate (300gL^-1) phase system (0.8:1.8v:v) in ascending mode. This enabled removal of crude feedstream impurities and separation of monosaccharides into three fractions (l-rhamnose, l-arabinose and d-galactose, and d-galacturonic acid) in a single step. Throughput was improved three-fold by increasing sample injection volume, from 4 to 16% of column volume, with similar separation performance maintained in all cases. Extrusion of the final galacturonic acid fraction increased the eluted solute concentration, reduced the total separation time by 24% and removed the need for further column regeneration. Reproducibility of the separation after extrusion was validated by using multiple stacked injections. Scale-up was performed linearly from a semi-preparative 250mL column to a preparative 950mL column with a scale-up ratio of 3.8 applied to mobile phase flow rate and sample injection volume. Throughputs of 9.4gL^-1h^-1 of total dissolved solids were achieved at the preparative scale with a throughput of 1.9gL^-1h^-1 of component monosaccharides. These results demonstrate the potential of CPC for both impurity removal and target fractionation within biorefinery separations.

Effect of operating parameters on a centrifugal partition chromatography separation

Centrifugal partition chromatography (CPC) is the branch of countercurrent chromatography (CCC) that works with single axis hydrostatic columns with rotary seals. The hydrodynamic of the liquid stationary phase-liquid mobile phase equilibrium in the CPC chambers has been studied theoretically and with specially designed CPC columns. In this work, we selected a simple analytical separation (no loading study) of three test solutes, coccine red, coumarin and carvone, with a commonly used heptane/ethyl acetate/methanol/water 1:1:1:1v/v biphasic liquid system and two different rotors: a commercially available 30-mL CPC instrument and a 80-mL prototype rotor designed for productivity. We fully studied this separation in many possible practical operating conditions of the two rotors, aiming at a generic column characterization. The rotor rotation was varied between 1000 and 2800rpm, the aqueous mobile phase flow rate was varied between 1 and 22mL/min with the 30-mL rotor and 10 and 55mL/min with the 80-mL rotor, the upper limits being mechanical constraints and some liquid stationary phase remaining in the rotor. The variations of Sf, the volume ratio of stationary phase in the rotor, were studied versus mobile phase flow rate and rotor rotation speed. A maximum mobile phase linear velocity was found to depend on the centrifugal field for the 30-mL rotor. This maximum velocity was not observed with the 80-mL rotor. Studying the changes in coumarin and carvone peak efficiencies, it is established that the number of cells required to make one theoretical plate, i.e. one chromatographic exchange, is minimized at maximal rotation speed and, to a lesser extent, at high mobile phase flow rate (or linear velocity). Considering the throughput, there is evidence of an optimal flow rate depending on the rotor rotation that is not necessarily the highest possible.