On-line comprehensive two-dimensional normal-phase liquid chromatography×reversed-phase liquid chromatography for preparative isolation of toad venom

A comprehensive study on solvent effect and establishment of n-hexane solvent system based normal-phase liquid chromatography × reversed-phase liquid chromatography for isolation of natural products

Reversed-phase liquid chromatography (RPLC) represents an effective separation method, and is widely employed as the second dimension in most 2D-LC systems. Nevertheless, the solvent effect of the eluent from the first dimension on RPLC presents a challenge to the online coupling of RPLC with other separation modes, particularly normal phase liquid chromatography (NPLC). To address this issue, a comprehensive understanding of the solvent effect is essential. Following a comprehensive investigation into the influence of diverse solvents on RPLC separations, it was observed that alkane solvents, such as n-hexane, exhibited a pronounced tendency to be retained during RPLC separations. Such solvents do not affect the analysis of samples with weaker retention abilities than themselves, even when a large injection volume is used. The solvent effect was thus reduced by employing n-hexane-based solvent dilution. Leveraging the markedly enhanced solvent tolerance and extensive injection volume in RPLC, a versatile integration of the NPLC and RPLC was devised, necessitating merely a purge pump and a 10 port 2 position valve in conjunction with two sample loops. The novel 2D-LC system was then deployed for the analysis of propolis, a naturally occurring complex sample, and demonstrated remarkable separation efficiency.

An online preparative high-performance liquid chromatography system with enrichment and purification modes for the efficient and systematic separation of Panax notoginseng saponins

In this study, an online preparative high-performance liquid chromatography (prep-HPLC) system based on the combination of the enrichment and purification modes for the efficient and systematic separation of Panax notoginseng saponins (PNS) was achieved. Five separation columns were used for the first and second separation of target components, eighteen trap columns were used to capture the effluents from the first separation or loading the trapped sample effluents, and a two-position eight-port valve was used to switch between the first and second separations. The conditions for the first and second separation of PNS were simulated and optimized with the online prep-HPLC system. Then, the PNS were separated using optimized chromatographic conditions. Notably, 14 monomer compounds with >90% purity (11 compounds with purity >97%) were simultaneously isolated from PNS using the above self-developed device, and their chemical structures were identified. Moreover, the separation time was less than 33.0 h. After 6 repeated enrichment and purification, the weight of each compound obtained was more than 5.0 mg, with compound 2 weighing over 900 mg. In brief, the self-developed prep-HPLC system, which integrated enrichment and purification, is suitable for the efficient and systematic separation of PNS and has broad application prospects, especially for the separation of complex chemical components in natural products.

Diluting modulation-based two dimensional-liquid chromatography coupled with mass spectrometry for simultaneously determining multiclass prohibited substances in cosmetics

Developing efficient and comprehensive screening methods for prohibited substances in cosmetics is critical for ensuring the quality and safety of cosmetics used in everyday life. This study proposed a heart-cutting two-dimensional liquid chromatography-mass spectrometry (2D-LC-MS) method based on online diluting modulation for detecting multiclass prohibited substances in cosmetics. The 2D-LC-MS method combines HILIC and RPLC techniques. Compounds near the dead time that the first dimensional HILIC could not separate were transferred to the second dimensional RPLC by valve switch, achieving good separation with a wide range of polarities. Moreover, the online diluting modulation solved the problem of mobile phase incompatibility, realizing an excellent column-head focusing effect and reducing the loss of sensitivity. Besides, the first dimensional analysis did not restrict the flow rate of the second dimensional analysis owing to the diluting modulation. We demonstrated the 2D-LC-MS system by determining 126 prohibited substances in cosmetic products, including hormones, local anesthetics, anti-infectives, adrenergic agents, antihistamines, pesticides, and other chemicals. All correlation coefficients of the compounds were above 0.9950. The LODs and the LOQs ranged from 0.000259 ng/mL to 16.6 ng/mL and 0.000864 ng/mL to 55.3 ng/mL, respectively. The RSDs% for intra-day and inter-day precision were within 6% and 14%, respectively. Compared with conventional one-dimensional liquid chromatography methods, the established method expanded the analytical coverage of cosmetics-prohibited substances with reduced matrix effects for most compounds and improved sensitivity for polar analytes. The results indicated that the 2D-LC-MS method was a powerful tool for screening multiclass prohibited substances in cosmetics.

Less Configuration and More Dimensionality: Preparative Heart-Cut Multidimensional Liquid Chromatography Based on Trapping Arrays

The resolving power of multiple dimensional liquid chromatography (mD-LC) is multiplicative as it adds dimensions. However, the issue in creating a preparative mD-LC system is that the higher the dimensionality, the more complicated the system configuration. Thus, we presented a new configuration of preparative mD-LC using one set of LC modules and trapping array-based multiple heart-cut interfaces. A preparative two-dimensional liquid chromatography (2D-LC) separation of herbal medicine formulation produced 40 compounds with a purity of >90%. During the separation process, the interface stores the fractions and allocates positions for the fractions from a different dimension; LC draws the fraction from the interface, makes ⁿD separation, and sends isolated fractions to the interface. By repeating this process, we achieved variable dimensionality of LC separations. We also presented a preparative 3D-LC separation of herbal medicines to validate the principle of "less configuration and more dimensionality". Thus, we can explore the higher dimensional preparative separations. The developed preparative mD-LC displayed exceptional power in the isolation of various compounds and has great potential in the application of natural products.

Two-dimensional chromatography in screening of bioactive components from natural products

INTRODUCTION

Screening and analysis of bioactive components from natural products is a fundamental part of new drug development and innovation. Two-dimensional (2D) chromatography has been demonstrated to be an effective method for screening and preparation of specific bioactive components from complex natural products.

OBJECTIVE

To collect details of application of 2D chromatography in screening of natural product bioactive components and to outline the research progress of different separation mechanisms and strategies.

METHODOLOGY

Three screening strategies based on 2D chromatography are reviewed, including traditional separation-based screening, bioactivity-guided screening and affinity chromatography-based screening. Meanwhile, in order to cover these aspects, selections of different separation mechanisms and modes are also presented.

RESULTS

Compared with traditional one-dimensional (1D) chromatography, 2D chromatography has unique advantages in terms of peak capacity and resolution, and it is more effective for screening and identifying bioactive components of complex natural products.

CONCLUSION

Screening of natural bioactive components using 2D chromatography helps separation and analysis of complex samples with greater targeting and relevance, which is very important for development of innovative drug leads.

Heat-Assisted Dual Neutral Spray Ionization for High-Performance Online Desalting in Mass Spectrometric Analysis

In mass spectrometry (MS), nonvolatile salts contaminate the transmission system and cause ion suppression, hampering MS analysis. When MS is combined with liquid chromatography (LC) that uses a salty mobile phase, the problems become more intractable due to long analysis time. Here, a novel heat-assisted dual neutral spray ionization (HADSI) method was developed, which projected sample solution spray and solvent spray onto a heated plate to achieve online desalting and high ionization. The experimental parameters of HADSI were optimized, which indicated that the plate temperature was crucial for ionization and desalination. Eight drug compounds dissolved in various commonly used buffers were directly analyzed using HADSI-MS, even though the concentration of PBS buffer reached 500 mmol/L. The established method showed considerable sensitivity in the positive ion mode with the limits of detection at the level of nmol/L, and good linearity (R² > 0.99) was achieved for all the analyzed compounds. The repeatability and intra- and interday precisions of the method were evaluated, demonstrating the feasibility and reliability of the analysis of salty samples by HADSI-MS. Further, the method was demonstrated to tolerate the long-time analysis of high-salt LC eluates and the device was easy to maintain. Finally, a crude roxithromycin product was separated by LC and then analyzed by HADSI-MS, and seven unknown impurities and nine known impurities were successfully detected. Our results indicated that HADSI-MS may have potential applications in academic and industrial fields.

A novel online preparative high-performance liquid chromatography system with the multiple trap columns-valve switch technique for the rapid and efficient isolation of main flavonoids from Epimedium koreanum Nakai

In this work, a new online preparative high-performance liquid chromatography was developed for the fast and efficient separation of complex chemical mixtures from natural products. This system integrates two chromatographic systems into an online automatic separation system using the technique of multiple trap columns with valve switching. The sample was first separated into 18 subfractions in the online preparative high-performance liquid chromatography, and the sample eluents were then diluted and captured online on 18 trap columns by the multiple trap columns technique, respectively. Each subfraction retained on the trap column was transferred online to the separation column for the second separation. Finally, the target compounds were purified by appropriate separation conditions and multiple heart-cutting strategies. Importantly, the system was successfully used to separate 18 high-purity flavonoids from the crude extract of Epimedium koreanum Nakai online in one step. The entire separation time was approximately 20 h, and the structures were characterized by the high-performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry and nuclear magnetic resonance. This online preparative high-performance liquid chromatography system represents an efficient and rapid separation system that has the potential for a wide array of applications in the separation of complex chemical components from natural products.

Distribution of major toxins in Rhinella marina parotoid macroglands using Desorption-Electrospray-Ionization mass spectrometry imaging (DESI-MSI)

Amphibian cutaneous glands secrete toxins used in different vital functions including passive defense. Through Desorption Electrospray Ionization-Imaging we analyzed the distribution of the major toxins of the toad Rhinella marina parotoid macroglands. Alkaloids and steroids showed characteristic distribution and intensity within the glands and were also present at lower levels on the skin surface. A comprehensive overview of toxins distribution in toads’ skin might help to understand their full biological role within the amphibians.

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Amphibians possess granular glands associated to chemical defense.

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Actual tissue distribution of toads' toxins remains unknown.

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We have pinpointed some toad toxins in the parotoid macroglands.

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Alkaloids are distributed throughout the gland; whereas steroids are peripheral.

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Toxins are stored within the macrogland, presenting large concentration variation.

Homoisoflavonoids profiling of Ophiopogon japonicus by off-line coupling high-speed countercurrent chromatography with high-performance liquid chromatography-diode array detector-quadrupole time-of-flight tandem mass spectrometry

Roots of Ophiopogon japonicus have been used as a functional food ingredient and traditional Chinese medicine for a long time in China. Homoisoflavonoids are one of the major kinds of bioactive compounds in O. japonicus; however, literature data about its homoisoflavonoids profile are scarce because of the complex ingredients with low abundance. Here, homoisoflavonoid fraction was prepared by petroleum ether extraction. Then, a high-speed countercurrent chromatography off-line coupling with high-performance liquid chromatography-diode array detector-quadrupole time-of-flight tandem mass spectrometry was developed for systematic identification of homoisoflavonoids. After that, 39 homoisoflavonoids, including 29 homoisoflavanone and 10 homoisoflavone, were unambiguously or tentatively identified, while 12 of them were reported in O. japonicus for the first time. Finally, eight available homoisoflavonoids were sensitively, precisely, and accurately determined by standard calibration curves, with limit of detection and limit of quantification in the range of 0.05-0.30 μg/mL and 0.12-0.66 μg/mL, relative standard deviation less than 7.3% for intra- and interday variations, and recovery at 94.5-105.2%. Collectively, our developed method is efficient, reliable, and valuable to profile chemical components of complex natural products.

Comparison between centrifugal partition chromatography and preparative liquid chromatography as first dimensions in off-line two-dimensional separation: Application to the isolation of multi-targeted compounds from Edelweiss plant

Preparative two-dimensional chromatography is gaining interest in the elucidation of complex samples as it allows the recovery of a large number of molecules without the risks inherent to tedious multi-step sample preparation. While the second dimension is often selected to be liquid chromatography, it may be of interest to compare the specificities of two different techniques, namely liquid chromatography and centrifugal partition chromatography, to be used as first dimension. A fair comparison between off-line CPCxLC and prepLCxLC in selective comprehensive mode for preparative purposes is carried out in this study, illustrated by the isolation of five compounds from high-value Edelweiss plant. The method development of each configuration is achieved on laboratory scale instruments. The quality of separation is compared using 2D-contour plots. The prepLCxLC exhibits a large separation space that leads to an overall large peak capacity, which is of great interest for complex samples. But its limited loading capacity involves a large number of 2 D runs increasing the running costs for preparative purposes. On the other hand, CPCxLC provides a low peak capacity due to the poor efficiency provided by CPC. However, this liquid-liquid technique can be finely tuned to generate a high selectivity, decreasing the number of runs necessary to produce a limited number of target solutes.

An Efficient Strategy Based on Liquid-Liquid Extraction with Three-Phase Solvent System and High Speed Counter-Current Chromatography for Rapid Enrichment and Separation of Epimers of Minor Bufadienolide from Toad Meat

This study presents an efficient strategy based on liquid-liquid extraction with three-phase solvent system and high speed counter-current chromatography for rapid enrichment and separation of epimers of minor bufadienolide from toad meat. The reflux extraction conditions were optimized by response surface methodology first, and a novel three-phase solvent system composed of n-hexane/methyl acetate/acetonitrile/water (3:6:5:5, v/v) was developed for liquid-liquid extraction of the crude extract. This integrative extraction process could enrich minor bufadienolide from complex matrix efficiently and minimize the loss of minor targets induced by repeated extraction with different kinds of organic solvents occurring in the classical liquid two-phase extraction. As a result, four epimers of minor bufadienolide were greatly enriched in the middle phase and total content of these epimers of minor bufadienolide was increased from 3.25% to 46.23%. Then, the enriched four epimers were separated by HSCCC with a two-phase solvent system composed of chloroform/methanol/water (4:2:2, v/v) successfully. Furthermore, we tested Na⁺,K⁺-ATPase (NKA) inhibitory effect of the four epimers. 3β-Isomers of bufadienolide showed stronger (>8-fold) inhibitory activity than 3α-isomers. The characterization of minor bufadienolide in toad meat and their significant difference of inhibitory effect on NKA would promote the further quantitative analysis and safety evaluation of toad meat as a food source.

Comprehensive two-dimensional normal-phase liquid chromatography × reversed-phase liquid chromatography for analysis of toad skin

An analytical two-dimensional normal-phase liquid chromatography × reversed-phase liquid chromatography (2D NPLC × RPLC) system was constructed with a newly developed thermal evaporation assisted adsorption (TEAA) interface. This novel TEAA interface with heating temperature above solvent boiling point allowed fast removal of organic NPLC solvent and successfully solved the solvent incompatibility problem between NPLC and RPLC. The system achieved rapid on-line solvent exchange between the two dimensions within a short modulation time of 190 s and was applied in the analysis of an extract from the skin of Bufo bufo gargarizans. This is the first time to realize the on-line comprehensive analysis of a moderate polar natural product by coupling NPLC with reversed phase ultra-high performance liquid chromatography (UHPLC). To be highlighted, with the TEAA interface, the 2D NPLC × RPLC system provided excellent resolution and orthogonality (75.2%), when compared with that of 2D RPLC × RPLC.