Use of shift gradient in the second dimension to improve the separation space in comprehensive two-dimensional liquid chromatography

High-efficiency effect-directed analysis (EDA) advancing toxicant identification in aquatic environments: Latest progress and application status

Facing the great threats to ecosystems and human health posed by the continuous release of chemicals into aquatic environments, effect-directed analysis (EDA) has emerged as a powerful tool for identifying causative toxicants. However, traditional EDA shows problems of low-coverage, labor-intensive and low-efficiency. Currently, a number of high-efficiency techniques have been integrated into EDA to improve toxicant identification. In this review, the latest progress and current limitations of high-efficiency EDA, comprising high-coverage effect evaluation, high-resolution fractionation, high-coverage chemical analysis, high-automation causative peak extraction and high-efficiency structure elucidation, are summarized. Specifically, high-resolution fractionation, high-automation data processing algorithms and in silico structure elucidation techniques have been well developed to enhance EDA. While high-coverage effect evaluation and chemical analysis should be further emphasized, especially omics tools and data-independent mass acquisition. For the application status in aquatic environments, high-efficiency EDA is widely applied in surface water and wastewater. Estrogenic, androgenic and aryl hydrocarbon receptor-mediated activities are the most concerning, with causative toxicants showing the typical structural features of steroids and benzenoids. A better understanding of the latest progress and application status of EDA would be beneficial to further advance in the field and greatly support aquatic environment monitoring.

A new chromatographic response function with automatically adapting weight factor for automated method development

A critical factor for automated method development in chromatography is the maximization or minimization of an objective function describing the quality (and speed) of the separation. In chromatography, this function is commonly referred to as a chromatographic response function (CRF). Many CRFs have previously been introduced, but many have unfavourable properties such as featuring multiple optima, insufficient discriminatory power, and a too strong dependence on the weight factors needed to balance resolution and time penalty components. To overcome these problems, the present study introduces a new type of CRF wherein the relative weight of the time penalty term is a self-adaptive function of the separation quality. The ability to unambiguously identify the optimal gradient settings of this newly proposed CRF is compared to that of some of the most frequently used CRFs in a study covering 100 randomly composed in silico samples. Doing so, the new CRF is found to flawlessly lead to the correct solution (=linear gradient parameters providing the highest resolution in the shortest potential time) in 100 % of the cases, while the most frequently used literature CRFs were off-target for about 50 to 60 % of the samples, even when considering the availability of spectral peak shape data. Some slight alterations to the proposed CRF are introduced and discussed as well.

High-Efficiency Effect-Directed Analysis Leveraging Five High Level Advancements: A Critical Review

Organic contaminants are ubiquitous in the environment, with mounting evidence unequivocally connecting them to aquatic toxicity, illness, and increased mortality, underscoring their substantial impacts on ecological security and environmental health. The intricate composition of sample mixtures and uncertain physicochemical features of potential toxic substances pose challenges to identify key toxicants in environmental samples. Effect-directed analysis (EDA), establishing a connection between key toxicants found in environmental samples and associated hazards, enables the identification of toxicants that can streamline research efforts and inform management action. Nevertheless, the advancement of EDA is constrained by the following factors: inadequate extraction and fractionation of environmental samples, limited bioassay endpoints and unknown linkage to higher order impacts, limited coverage of chemical analysis (i.e., high-resolution mass spectrometry, HRMS), and lacking effective linkage between bioassays and chemical analysis. This review proposes five key advancements to enhance the efficiency of EDA in addressing these challenges: (1) multiple adsorbents for comprehensive coverage of chemical extraction, (2) high-resolution microfractionation and multidimensional fractionation for refined fractionation, (3) robust in vivo/vitro bioassays and omics, (4) high-performance configurations for HRMS analysis, and (5) chemical-, data-, and knowledge-driven approaches for streamlined toxicant identification and validation. We envision that future EDA will integrate big data and artificial intelligence based on the development of quantitative omics, cutting-edge multidimensional microfractionation, and ultraperformance MS to identify environmental hazard factors, serving for broader environmental governance.

Comprehensive two-dimensional liquid chromatography with high resolution mass spectrometry to investigate the photoelectrochemical degradation of environmentally relevant pharmaceuticals and their degradation products in water

The widespread presence of organic micropollutants in the environment reflects the inability of traditional wastewater treatment plants to remove them. In this context, advanced oxidation processes (AOPs) have emerged as promising quaternary wastewater treatment technologies since they efficiently degrade recalcitrant components by generating highly reactive free radicals. Nonetheless, the chemical characterization of potentially harmful byproducts is essential to avoid the contamination of natural water bodies with hazardous substances. Given the complexity of wastewater matrices, the implementation of comprehensive analytical methodologies is required. In this work, the simultaneous photoelectrochemical degradation of seven environmentally relevant pharmaceuticals and one metabolite from the EU Watch List 2020/1161 was examined in ultrapure water and simulated wastewater, achieving excellent removal efficiencies (overall >95%) after 180 min treatment. The reactor unit was linked to an online LC sample manager, allowing for automated sampling every 15 min and near real-time process monitoring. Online comprehensive two-dimensional liquid chromatography (LC × LC) coupled with high resolution mass spectrometry (HRMS) was subsequently used to tentatively identify degradation products after photoelectrochemical degradation. Two reversed-phase liquid chromatography (RPLC) columns were used: an SB-C18 column operated with 5 mM ammonium formate at pH 5.8 (1A) and methanol (1B) as the mobile phases in the first dimension and an SB-Aq column using acidified water at pH 3.1 (2A) and acetonitrile (2B) as the mobile phases in the second dimension. This resulted in a five-fold increase in peak capacity compared to one-dimensional LC while maintaining the same total analysis time of 50 min. The LC x LC method allowed the tentative identification of 12 venlafaxine, 7 trimethoprim and 10 ciprofloxacin intermediates. Subsequent toxicity predictions suggested that some of these byproducts were potentially harmful. This study presents an effective hybrid technology for the simultaneous removal of pharmaceuticals from contaminated wastewater matrices and demonstrates how multidimensional liquid chromatography techniques can be applied to better understand the degradation mechanisms after the treatment of micropollutants with AOPs.

Two-dimensional separation of water-soluble polymers using size exclusion and reversed phase chromatography employing capillary-channeled polymer fiber columns

Polymeric materials are readily available, durable materials that have piqued the interest of many diverse fields, ranging from biomedical engineering to construction. The physiochemical properties of a polymer dictate the behavior and function, where large polydispersity among polymer properties can lead to problems; however, current polymer analysis methods often only report results for one particular property. Two-dimensional liquid chromatography (2DLC) applications have become increasingly popular due to the ability to implement two chromatographic modalities in one platform, meaning the ability to simultaneously address multiple physiochemical aspects of a polymer sample, such as functional group content and molar mass. The work presented employs size exclusion chromatography (SEC) and reversed-phase (RP) chromatography, through two coupling strategies: SEC x RP and RP x RP separations of the water-soluble polymers poly(methacrylic acid) (PMA) and polystyrene sulfonic acid (PSSA). Capillary-channeled polymer (C-CP) fiber (polyester and polypropylene) stationary phases were used for the RP separations. Particularly attractive is the fact that they are easily implemented as the second dimension in 2DLC workflows due to their low backpressure (<1000 psi at ∼70 mm sec-1) and fast separation times. In-line multi-angle light scattering (MALS) was also implemented for molecular weight determinations of the polymer samples, with the molecular weight of PMA ranging from 5 × 104 to 2 × 105 g mol-1, while PSSA ranges from 105 to 108 g mol-1. While the orthogonal pairing of SEC x RP addresses polymer sizing and chemistry, this approach is limited by long separation times (80 min), the need for high solute concentrations (PMA = 1.79 mg mL-1 and PSSA = 0.175 mg mL-1 to yield comparable absorbance responses) due to on-column dilution and subsequently limited resolution in the RP separation space. With RP x RP couplings, separation times were significantly reduced (40 min), with lower sample concentrations (0.595 mg mL-1 of PMA and 0.05 mg mL-1 of PSSA) required. The combined RP strategy provided better overall distinction in the chemical distribution of the polymers, yielding 7 distict species versus 3 for the SEC x RP coupling.

Enzyme activity- and chemometrics-assisted comprehensive two-dimensional liquid chromatography coupled with ion mobility quadrupole time-of-flight mass spectrometry for the analysis of honeysuckle

A unique and effective comprehensive two-dimensional liquid chromatography system was established and applied for the analysis of bioactive components in honeysuckle. Under the optimal conditions, Eclipse Plus C₁₈ (2.1 × 100 mm, 3.5 μm, Agilent) and SB-C₁₈ (4.6 × 50 mm, 1.8 μm, Agilent) columns were chosen for the first dimension (¹D) and the second dimension (²D) separation. The optimal flow rates of ¹D and ²D were 0.12 mL/min and 2.0 mL/min, respectively. Additionally, the proportion of organic solution was optimized to enhance orthogonality and integrated shift, and full gradient elution mode was adopted to improve chromatographic resolution. Furthermore, a total of 57 compounds were identified by molecular weight, retention time and collision cross-section value obtained from ion mobility mass spectrometry. Based on the data obtained from the principal component analysis, partial least squares discriminant analysis, and hierarchical cluster analysis, the categories of honeysuckle in different regions were significantly different. Moreover, the half maximal inhibitory concentration values of most samples were between 0.37 and 1.55 mg/mL, and most samples were potent α-glucosidase inhibitors, which is better for the evaluation of the quality of drugs from two aspects of substance content and activity.

Three-dimensional characteristic chromatogram by online comprehensive two-dimensional liquid chromatography: Application to the identification and differentiation of ginseng from herbal medicines to various Chinese patent medicines

One bottleneck problem in the quality control of traditional Chinese medicine (TCM) is the accurate identification of easily confused herbal medicines from Chinese patent medicine (CPM). Ginseng products derived from the multiple parts (e.g., root/rhizome, leaf, and flower bud) of multiple Panax species (P. ginseng, P. quinquefolius, P. notoginseng, P. japonicus, and P. japonicus var. major) are globally popular; however, their authentication is very challenging. Using online comprehensive two-dimensional liquid chromatography (LC × LC), we propose the concept of a three-dimensional characteristic chromatogram (3D CC) by integrating enhanced LC × LC separation and a contour plot that visualizes the stereoscopic chromatographic peaks and examine its performance in authenticating various ginseng products. Targeted at the resolution of 17 ginsenoside markers, an online LC × LC/UV system with a 56 min analysis time was constructed: a CORTECS UPLC Shield RP 18 column running at 0.1 mL/min for the first-dimensional chromatography and a Poroshell SB-Aq column at 2.0 mL/min in shift gradient mode in the second dimension of separation. In particular, ginsenosides Rg1/Re and Rc/Ra1 were well resolved. According to the presence/absence of stereo peaks consistent with the main ginsenoside markers in the 3D CC and the depth of shade (depending on peak volume), it was feasible to use a single method to identify and distinguish among 12 different ginseng species as the drug materials and the use of ginseng simultaneously from 21 CPMs. Conclusively, a practical solution enabling the accurate identification of easily confused TCMs was provided, covering both the drug materials and the compound preparations.

Multi-2D LC × LC as a Novel and Powerful Implement for the Maximum Separation of Complex Samples

Achieving complete information about the chemical composition of complex samples requires the use of multianalytical platforms able to maximize the acquisition of high-quality data for unequivocal identification. However, this process requires long analysis times and several instruments. Food analysis is one of the analytical fields where the analysis of very complex samples has a huge impact. One of these complex samples is vermouth, a fortified wine based on the maceration of a large number of herbs, fruits, barks, seeds, and leaves. The application of conventional or even advanced analytical techniques like comprehensive two-dimensional (2D) liquid chromatography (LC × LC) does not provide enough separation power to resolve the complete profile of this sample. In this work, a novel 2DLC strategy called multi-²D LC × LC is developed. This new setup consists of the use of two different columns with different separation properties in the second dimension (²D) that can be selected during the LC × LC analysis accordingly to the chemical nature of the compounds eluted from the first dimension (¹D). The vermouth sample was analyzed using a ¹D-PFP and a combination of HILIC (from 0 to 30 min) and C18 (from 30 to the end) columns in the ²D. This setup increased both the peak capacity and the orthogonality of the analysis in comparison to the use of only one of the columns in the ²D. Multi-²D LC × LC is presented as an integrated 2DLC tool that maximizes the separation capacity for very complex samples.

Phytochemical Characterization of Rhus coriaria L. Extracts by Headspace Solid-Phase Micro Extraction Gas Chromatography, Comprehensive Two-Dimensional Liquid Chromatography, and Antioxidant Activity Evaluation

Rhus coriaria L. (Anacardiaceae), commonly known as sumac, has been used since ancient times for many different applications, and nowadays is used mostly as a spice obtained from its in the Mediterranean and the Middle ground fruits and employed for flavoring and garnishing food, predominantly Eastern regions. Traditionally, sumac has been also used in popular medicine for the treatment of many ailments including hemorrhoids, wound healing, diarrhea, ulcers, and eye inflammation. Sumac drupes are indeed rich in various classes of phytochemicals including organic acids, flavonoids, tannins, and others, which are responsible of their powerful antioxidant capacity, from which treatment of many common diseases such as cardiovascular disease, diabetes, and cancer could benefit. In this work we evaluated the influence of fruit ripeness, conservation, and processing. To this aim, a phytochemical characterization of six different samples of Rhus coriaria L. was carried out. Specifically, headspace solid-phase micro extraction gas chromatography coupled to mass spectrometry and comprehensive two-dimensional liquid chromatography coupled to photodiode array and mass spectrometry detection, were employed. A total of 263 volatile compounds, including terpene hydrocarbons, acids, and aldehydes, as well as 83 polyphenolic compounds, mainly gallic acid derivatives, were positively identified. All samples showed a significant antioxidant activity by means of oxygen radical absorbance capacity, in line with their polyphenolic content and composition. Such findings set a solid ground to support the utilization of this plant as an attractive target for novel nutraceutical approaches and for drug discovery.

Comprehensive two-dimensional temperature-responsive × reversed phase liquid chromatography for the analysis of wine phenolics

Phenolic compounds are an interesting class of natural products because of their proposed contribution to health benefits of foods and beverages and as a bio-source of organic (aromatic) building blocks. Phenolic extracts from natural products are often highly complex and contain compounds covering a broad range in molecular properties. While many 1D-LC and mass spectrometric approaches have been proposed for the analysis of phenolics, this complexity inevitably leads to challenging identification and purification. New insights into the composition of phenolic extracts can be obtained through online comprehensive two-dimensional liquid chromatography (LC × LC) coupled to photodiode array and mass spectrometric detection. However, several practical hurdles must be overcome to achieve high peak capacities and to obtain robust methods with this technique. In many LC × LC configurations, refocusing of analytes at the head of the ²D column is hindered by the high eluotropic strength of the solvent transferred from the ¹D to the ²D, leading to peak breakthrough or broadening. LC × LC combinations whereby a purely aqueous mobile phase is used in the ¹D and RPLC is used in the ²D are unaffected by these phenomena, leading to more robust methods. In this contribution, the combination of temperature-responsive liquid chromatography (TRLC) with RPLC is used for the first time for the analysis of phenolic extracts of natural origin to illustrate the potential of this alternative combination for natural product analyses. The possibilities of the combination are investigated through analysis of wine extracts by TRLC × RPLC-DAD and TRLC × RPLC-ESI-MS.

Reversed phase versus hydrophilic interaction liquid chromatography as first dimension of comprehensive two-dimensional liquid chromatography systems for the elucidation of the polyphenolic content of food and natural products

Comprehensive two-dimensional liquid chromatography is a well-established method for the unraveling of very complex real-world samples. With regard to food and natural products such a technique turned out to be a very promising approach due to its high resolving power and improved identification capability, especially in combination with mass spectrometry. In this context, polyphenols comprise a particular complex class of bioactive compounds, due to their nature and content in commonly consumed foodstuffs, making their analysis challenging. The present contribution shows an overview of the two commonly employed approaches used for polyphenol analysis, viz. RP-LC × RP-LC and HILIC × RP-LC. Furthermore, the latest implementations as well as limitations and future perspectives are critically reported.

Parallel gradients in comprehensive multidimensional liquid chromatography enhance utilization of the separation space and the degree of orthogonality when the separation mechanisms are correlated

Comprehensive two-dimensional liquid chromatography (LC×LC) offers increased peak capacity, resolution and selectivity compared to one-dimensional liquid chromatography. It is commonly accepted that the technique produces the best results when the separation mechanisms in the two dimensions are completely orthogonal, which necessitates the use of gradient elution for each second-dimension fraction. Recently, the use of similar separation mechanisms in both dimensions has been gaining popularity, but full or shifted gradients are still used for each second dimension fraction. Herein, we argue that when the separation mechanisms are correlated in the two dimensions, the best results can be obtained with the use of parallel gradients in the second dimension, which makes the technique nearly as user-friendly as comprehensive two-dimensional gas chromatography. This has been illustrated through the separation of a mixture of 39 pharmaceutical compounds using reversed phase in both dimensions. Different selectivity in the second dimension was obtained through the use of different stationary phase chemistries and/or mobile phase organic modifiers. The best coverage of the separation space was obtained when parallel gradients were applied in both dimensions, and the same was true for practical peak capacity.

Evaluation of LC-MS and LC×LC-MS in analysis of zebrafish embryo samples for comprehensive lipid profiling

In this study, both conventional one-dimensional liquid chromatography (1DLC) and comprehensive two-dimensional liquid chromatography (2DLC) coupled to a high-resolution time-of-flight mass spectrometer (HR-TOF MS) were used for full-scale lipid characterization of lipid extracts from zebrafish embryos. We investigated the influence on annotated lipids and different separation mechanisms (HILIC, C18, and PFP), and their different orders arranged in the first and the second dimensions. As a result, the number of lipid species annotated by conventional one-dimensional LC-MS was between 212 and 448. In contrast, the number of individual lipids species annotated by C18×HILIC, HILIC×C18, and HILIC×PFP were 1784, 1059, and 1123, respectively. Therefore, it was evident that the performance of comprehensive 2DLC, especially the C18×HILIC method, considerably exceeded 1DLC. Interestingly, a comparison of the HILIC×C18 and C18×HILIC approaches showed, under the optimized conditions, similar orthogonality, but the effective separation power of the C18×HILIC was much higher. A comparison of the HILIC×C18 and the HILIC×PFP methods demonstrated that the HILIC×PFP separation had superior orthogonality with a small increase on its effective peak capacity, indicating that the HILIC×PFP combination maybe a promising platform for untargeted lipidomics in complex samples. Finally, from the comprehensive lipid profiling respective, the C18×HILIC was selected for further studies.

Determination of the Metabolite Content of Brassica juncea Cultivars Using Comprehensive Two-Dimensional Liquid Chromatography Coupled with a Photodiode Array and Mass Spectrometry Detection

Plant-based foods are characterized by significant amounts of bioactive molecules with desirable health benefits beyond basic nutrition. The Brassicaceae (Cruciferae) family consists of 350 genera; among them, Brassica is the most important one, which includes some crops and species of great worldwide economic importance. In this work, the metabolite content of three different cultivars of Brassica juncea, namely ISCI Top, “Broad-leaf,” and ISCI 99, was determined using comprehensive two-dimensional liquid chromatography coupled with a photodiode array and mass spectrometry detection. The analyses were carried out under reversed-phase conditions in both dimensions, using a combination of a 250-mm microbore cyano column and a 50-mm RP-Amide column in the first and second dimension (²D), respectively. A multi (three-step) segmented-in-fraction gradient for the ²D separation was advantageously investigated here for the first time, leading to the identification of 37 metabolites. In terms of resolving power, orthogonality values ranged from 62% to 69%, whereas the corrected peak capacity values were the highest for B. juncea ISCI Top (639), followed by B. juncea “Broad-leaf” (502). Regarding quantification, B. juncea cv. “Broad-leaf” presented the highest flavonoid content (1962.61 mg/kg) followed by B. juncea cv. ISCI Top (1002.03 mg/kg) and B. juncea cv. ISCI 99 (211.37 mg/kg).

The application of on-line two-dimensional liquid chromatography (2DLC) in the chemical analysis of herbal medicines

Herbal medicines are complicated chemical systems containing hundreds of small molecules of various polarities, structural types, and contents. Thus far, the chromatographic separation of herbal extracts is still a big challenge. Two-dimensional liquid chromatography (2DLC) has become an attractive separation tool in the past few years. Particularly, a lot of attention has been paid to on-line 2DLC. In this review, we aim to give an overview on applications of on-line 2DLC in the chemical analysis of herbal medicines since 2010. Firstly, classification and general configurations of on-line 2DLC were briefly introduced. Then, we summarized main applications in herbal medicines of heart-cutting 2DLC (LC-LC), comprehensive 2DLC (LC × LC), and their combinations, with emphasis on LC × LC. Mass spectrometry is the most popular detector coupled with 2DLC, which allows sensitive and accurate structural characterization of herbal compounds. Finally, future developments in on-line 2DLC techniques were also discussed.

Untargeted profiling of Glycyrrhiza glabra extract with comprehensive two-dimensional liquid chromatography-mass spectrometry using multi-segmented shift gradients in the second dimension: Expanding the metabolic coverage

Metabolic profiling of Glycyrrhiza glabra using comprehensive two-dimensional liquid chromatography (LC × LC) coupled with photodiode array (PDA) and mass spectrometry (MS) detection is described. The separation was conducted under reversed-phase conditions, using a combination of first dimension (1 D) 150 mm microbore cyano column utilising 2.7 μm diameter (dp ) particles, and second dimension (2 D) 50 mm superficially porous octadecylsilica column with 2.7 μm dp particles. A multi-segmented shift gradient (MSG) for the 2 D separation was developed, and the orthogonality achieved was compared with other modes of gradients, such as full in-fraction, and shift gradient systems. Results demonstrated a significant expansion of metabolic coverage using MSG in 2 D, providing the highest measure of orthogonality compared to other gradient modes. Compound identifications were performed by employing complementary data from PDA and MS detection, with reference to structural group-type distribution in 2D space. A total of ca. 120 compounds were detected, and among them 37 were tentatively identified, distributed over the chemical families of glycosylated flavanones, triterpene saponins, and others. In comparison with one-dimensional LC, the total number of compounds detected was ca. 2-fold greater when LC × LC was employed. To the best of our knowledge, this is the first demonstration of the MSG mode in LC × LC, representing a powerful strategy to expand the metabolic coverage for analysis of plant-derived extracts, containing a multitude of different phytochemical classes.

Contaminant screening of wastewater with HPLC-IM-qTOF-MS and LC+LC-IM-qTOF-MS using a CCS database

Non-target analysis has become an important tool in the field of water analysis since a broad variety of pollutants from different sources are released to the water cycle. For identification of compounds in such complex samples, liquid chromatography coupled to high resolution mass spectrometry are often used. The introduction of ion mobility spectrometry provides an additional separation dimension and allows determining collision cross sections (CCS) of the analytes as a further physicochemical constant supporting the identification. A CCS database with more than 500 standard substances including drug-like compounds and pesticides was used for CCS data base search in this work. A non-target analysis of a wastewater sample was initially performed with high performance liquid chromatography (HPLC) coupled to an ion mobility-quadrupole-time of flight mass spectrometer (IM-qTOF-MS). A database search including exact mass (±5 ppm) and CCS (±1 %) delivered 22 different compounds. Furthermore, the same sample was analyzed with a two-dimensional LC method, called LC+LC, developed in our group for the coupling to IM-qTOF-MS. This four dimensional separation platform revealed 53 different compounds, identified over exact mass and CCS, in the examined wastewater sample. It is demonstrated that the CCS database can also help to distinguish between isobaric structures exemplified for cyclophosphamide and ifosfamide. Graphical Abstract Scheme of sample analysis and database screening.

Recent advances in 2D-LC for bioanalysis

This article summarizes the most important developments in the use of 2D-LC for bioanalysis in the last 5 years. While several interesting and powerful applications have been developed recently, this work has been supported by continued, significant development of theoretical concepts, instrument development and practical aspects of method development. Some of the most exciting applications have been focused on the use of 2D-LC and characterize proteins both as biotherapeutic drug substances, and in formulations. These materials are inherently complex, difficult to resolve chromatographically and present problems that are essentially unknown (e.g., aggregation) in the small molecule world, thus 2D-LC can be leveraged very effectively to address these challenges.

Metabolome analysis via comprehensive two-dimensional liquid chromatography: identification of modified nucleosides from RNA metabolism

Modified nucleosides derived from the RNA metabolism constitute an important chemical class, which are discussed as potential biomarkers in the detection of mammalian breast cancer. Not only the variability of modifications, but also the complexity of biological matrices such as urinary samples poses challenges in the analysis of modified nucleosides. In the present work, a comprehensive two-dimensional liquid chromatography mass spectrometry (2D-LC-MS) approach for the analysis of modified nucleosides in biological samples was established. For prepurification of urinary samples and cell culture supernatants, we performed a cis-diol specific affinity chromatography using boronate-derivatized polyacrylamide gel. In order to establish a 2D-LC method, we tested numerous column combinations and chromatographic conditions. In order to determine the target compounds, we coupled the 2D-LC setup to a triple quadrupole mass spectrometer performing full scans, neutral loss scans, and multiple reaction monitoring (MRM). The combination of a Zorbax Eclipse Plus C18 column with a Zorbax Bonus-RP column was found to deliver a high degree of orthogonality and adequate separation. By application of 2D-LC-MS approaches, we were able to detect 28 target compounds from RNA metabolism and crosslinked pathways in urinary samples and 26 target compounds in cell culture supernatants, respectively. This is the first demonstration of the applicability and benefit of 2D-LC-MS for the targeted metabolome analysis of modified nucleosides and compounds from crosslinked pathways in different biological matrices.

Comprehensive two-dimensional liquid chromatography coupled to high resolution time of flight mass spectrometry for chemical characterization of sewage treatment plant effluents

For the first time a comprehensive two-dimensional liquid chromatography (LC×LC) system coupled with a high resolution time-of-flight mass spectrometer (HR-ToF MS) was developed and applied for analysis of emerging toxicants in wastewater effluent. The system was optimized and validated using environmental standard compound mixtures of e.g. carbamate pesticides and polycyclic aromatic hydrocarbons (PAHs), to characterize the chromatographic system, to test the stability of the retention times and orthogonality. Various stationary phases in the second dimension were compared for the LC×LC analysis of silicon rubber passive sampler extracts of a wastewater effluent. A combination of C18 and Pentafluorophenyl (PFP) was found to be most effective. Finally, the hyphenation of LC×LC with HR-ToF MS was optimized, including splitter settings, transfer of data files between the different software packages and background subtraction using instrument software tools, after which tentative identification of 20 environmental contaminants was achieved, including pesticides, pharmaceuticals and food additives. As examples, three pesticides (isoproturon, terbutryn and diazinon) were confirmed by two-dimensional retention alignment.

Comprehensive two-dimensional liquid chromatography tandem diode array detector (DAD) and accurate mass QTOF-MS for the analysis of flavonoids and iridoid glycosides in Hedyotis diffusa

The analysis of chemical constituents in Chinese herbal medicines (CHMs) is a challenge because of numerous compounds with various polarities and functional groups. Liquid chromatography coupled with quadrupole time-of-flight (QTOF) mass spectrometry (LC/MS) is of particular interest in the analysis of herbal components. One of the main attributes of QTOF that makes it an attractive analytical technique is its accurate mass measurement for both precursor and product ions. For the separation of CHMs, comprehensive two-dimensional chromatography (LCxLC) provides much higher resolving power than traditional one-dimensional separation. Therefore, a LCxLC-QTOF-MS system was developed and applied to the analysis of flavonoids and iridoid glycosides in aqueous extracts of Hedyotis diffusa (Rubiaceae). Shift gradient was applied in the two-dimensional separation in the LCxLC system to increase the orthogonality and effective peak distribution area of the analysis. Tentative identification of compounds was done by accurate mass interpretation and validation by UV spectrum. A clear classification of flavonol glycosides (FGs), acylated FGs, and iridoid glycosides (IGs) was shown in different regions of the LCxLC contour plot. In total, five FGs, four acylated FGs, and three IGs were tentatively identified. In addition, several novel flavonoids were found, which demonstrates that LCxLC-QTOF-MS detection also has great potential in herbal medicine analysis.