Development of Comprehensive Online Two-Dimensional Liquid Chromatography/Mass Spectrometry Using Hydrophilic Interaction and Reversed-Phase Separations for Rapid and Deep Profiling of Therapeutic Antibodies

Solving the retention time repeatability problem of hydrophilic interaction liquid chromatography

Hydrophilic interaction (liquid) chromatography (HILIC) has become the first choice LC mode for the separation of hydrophilic analytes. Numerous studies reported the poor retention time repeatability of HILIC. The problem was often ascribed to slow equilibration and insufficient re-equilibration time to establish the sensitive semi-immobilized water layer at the interface of the polar stationary phase and the bulk mobile phase. In this study, we compare retention time repeatability in HILIC for borosilicate glass and PFA (co-polymer of tetrafluoroethylene and perfluoroalkoxyethylene) solvent bottles. During this study, we observed peak patterns shifting towards higher retention times (for metabolites and peptides) and lower retention times (oligonucleotide sample) with ongoing analysis time when standard borosilicate glass bottles were used as solvent reservoirs. It was hypothesized that release of ions (sodium, potassium, borate, etc.) from the borosilicate glass bottles leads to alterations (thickness and electrostatic screening effects) in the semi-immobilized water layer which is adsorbed to the polar stationary phase surface under acetonitrile-rich eluents in HILIC with concomitant shifts in retention. When PFA solvent bottles were employed instead of borosilicate glass, retention time repeatability was greatly improved and changed from average 8.4 % RSD for the tested metabolites with borosilicate glass bottles to 0.14 % RSD for the PFA solvent bottles (30 injections over 12 h). Similar improvements were observed for peptides and oligonucleotides. This simple solution to the retention time repeatability problem in HILIC might contribute to a better acceptance of HILIC, especially in fields like targeted and untargeted metabolomics, peptide and oligonucleotide analysis.

Multiscale metabolomics techniques: Insights into neuroscience research

The field of metabolomics examines the overall composition and dynamic patterns of metabolites in living organisms. The primary methods used in metabolomics include liquid chromatography (LC), nuclear magnetic resonance (NMR), and mass spectrometry (MS) analysis. These methods enable the identification and examination of metabolite types and contents within organisms, as well as modifications to metabolic pathways and their connection to the emergence of diseases. Research in metabolomics has extensive value in basic and applied sciences. The field of metabolomics is growing quickly, with the majority of studies concentrating on biomedicine, particularly early disease diagnosis, therapeutic management of human diseases, and mechanistic knowledge of biochemical processes. Multiscale metabolomics is an approach that integrates metabolomics techniques at various scales, including the holistic, tissue, cellular, and organelle scales, to enable more thorough and in-depth studies of metabolic processes in organisms. Multiscale metabolomics can be combined with methods from systems biology and bioinformatics. In recent years, multiscale metabolomics approaches have become increasingly important in neuroscience research due to the nervous system's high metabolic demands. Multiscale metabolomics can offer novel concepts and approaches for the diagnosis, treatment, and development of medication for neurological illnesses in addition to a more thorough understanding of brain metabolism and nervous system function. In this review, we summarize the use of multiscale metabolomics techniques in neuroscience, address the promise and constraints of these techniques, and provide an overview of the metabolome and its applications in neuroscience.

Formation of Micelles by Nonionic Detergent Molecules Leads to the Breakthrough Peak in Reversed-Phase Ultraperformance Liquid Chromatography (UPLC)

A peculiar phenomenon known as "breakthrough" occurs under reversed-phase ultraperformance liquid chromatography (UPLC) conditions and has been under scrutiny for decades. This effect takes place when a large volume of analyte solution, prepared in a solvent with an eluotropic strength significantly higher than that of the initial mobile phase solvent, is injected. According to the literature, under specific experimental conditions, a substantial portion of solutes is carried by the mobile phase and detected near the dead time of the chromatographic system. This phenomenon is typically observed when the injected volume of a particular analyte is sufficiently large. However, the underlying physicochemical principles governing this phenomenon have remained elusive. We present evidence demonstrating that breakthroughs can occur even when injecting a sample of a neat solvent devoid of any solute. By mass spectrometric analysis, we identified the breakthrough peak to represent the nonionic detergent Triton. When columns are equilibrated with water, Triton molecules, present as impurities in filtered water, accumulate on the nonpolar stationary phase. Upon the introduction of a solvent with a stronger elution strength, Triton molecules retained on the stationary phase are removed. As detergents, these Triton molecules aggregate into micelles featuring a hydrophobic inner core and a hydrophilic outer shell. These hydrophilic micelles are carried by the polar mobile phase and detected as the breakthrough peak at the dead time of the chromatographic system. When analytes are present, a portion of the injected solutes is captured by the micelles and transported with the breakthrough plug. This assertion was verified and confirmed by liquid chromatography-mass spectrometry (LC-MS) analysis of a methanolic solution of perfluorooctanoic acid (PFOA). The mass spectra corresponding to the breakthrough plug featured a peak for the PFOA anion (m/z 413) in addition to those for Triton.

Multidimensional LC-MS with 1D multi-method option and parallel middle-up and bottom-up MS acquisition for in-depth characterization of antibodies

Monoclonal antibodies (mAbs) are large and highly heterogeneous species typically characterized using a plethora of analytical methodologies. There is a trend within the biopharmaceutical industry to combine several of these methods in one analytical platform to simultaneously assess multiple structural attributes. Here, a protein analyzer for the fully automated middle-up and bottom-up liquid chromatography-mass spectrometry (LC-MS) analysis of charge, size and hydrophobic variants is described. The multidimensional set-up combines a multi-method option in the first dimension (1D) (choice between size exclusion - SEC, cation exchange - CEX or hydrophobic interaction chromatography - HIC) with second dimension (2D) on-column reversed-phase (RPLC) based desalting, denaturation and reduction prior to middle-up LC-MS analysis of collected 1D peaks and parallel on-column trypsin digestion of denatured and reduced peaks in the third dimension (3D) followed by bottom-up LC-MS analysis in the fourth dimension (4D). The versatile and comprehensive workflow is applied to the characterization of charge, hydrophobic and size heterogeneities associated with an engineered Fc fragment and is complemented with hydrogen-deuterium exchange (HDX) MS and FcRn affinity chromatography - native MS to explain observations in a structural/functional context.

Research of saccharides and related biocomplexes: A review with recent techniques and applications

Saccharides and biocompounds as saccharide (sugar) complexes have various roles and biological functions in living organisms due to modifications via nucleophilic substitution, polymerization, and complex formation reactions. Mostly, mono-, di-, oligo-, and polysaccharides are stabilized to inactive glycosides, which are formed in metabolic pathways. Natural saccharides are important in food and environmental monitoring. Glycosides with various functionalities are significant in clinical and medical research. Saccharides are often studied with the chromatographic methods of hydrophilic interaction liquid chromatography and anion exchange chromatograpy, but also with capillary electrophoresis and mass spectrometry with their on-line coupling systems. Sample preparation is important in the identification of saccharide compounds. The cases discussed here focus on bioscience, clinical, and food applications.

Impact of conditioning runs on hydrophilic interaction chromatography repeatability and its application as a second dimension in online comprehensive two-dimensional liquid chromatography

A common separation approach for polar compounds involves coupling reversed-phase liquid chromatography (RPLC) with hydrophilic interaction chromatography (HILIC) in two-dimensional chromatography. The higher proportion of acetonitrile used in the HILIC mobile phase, which enhances mass spectrometry detection, encourages its use in the second dimension. Previous studies demonstrated that the HILIC column can be partially equilibrated within very short timeframes without compromising retention time stability, rendering it suitable in online comprehensive two-dimensional liquid chromatography (LC×LC) setups. In addition, a specific number of conditioning cycles seems necessary to establish stable retention times. Here, the repeatability of HILIC when employed as second dimension in LC×LC was investigated, with a focus on determining the required number of conditioning cycles to achieve repeatable retention times. Various parameters influenced by the LC×LC online modulation system were studied, such as steep gradient slopes up to 8%, and very short equilibration times, less than or equal to dead time, as well as injection volume and solvent, which depend on the first dimension. Finally, the use of HILIC as a second dimension with tailored conditioning runs was applied to the analysis of hyaluronic acid hydrogel digests. The application of an RPLC×HILIC method using five conditioning runs yielded exceptional stability in second-dimension retention times.

Theoretical and practical guidelines for solvent dilution between the two dimensions in online comprehensive two-dimensional liquid chromatography

Online comprehensive two-dimensional liquid chromatography (online LC x LC) has become increasingly popular. Among the different chromatographic modes that can be combined, hydrophilic interaction chromatography (HILIC) and reversed-phase liquid chromatography (RPLC) are particularly interesting because they offer a high degree of orthogonality. However, this combination remains complex due to the incompatibility of the solvents in the two dimensions. To avoid this problem, it is possible to dilute the first dimension (1D) effluent with (zdilution -1) volumes of a weaker solvent added to one volume of 1D-effluent, where zdilution represents the extent to which the fraction volume has been multiplied. This can be done using either active solvent modulation technology or an additional pump, prior to the second dimension analysis. The objective of this study was to develop theoretical models to predict whether or not dilution can be effective, and, if so, what is the minimum zdilution value required. This approach is based on the calculation of the ratio (called xdilution) between the peak standard deviation due to the injection process and the peak standard deviation in the absence of extra-column dispersion. xdilution was calculated from theoretical relationships and plotted as a function of zdilution, to predict the value required to obtain good peak shapes for the compound of interest. The maximum xdilution value was found to be of the order of 1 for chromatographically acceptable peak shapes. The proposed theoretical approach was experimentally validated on a number of representative small molecules and peptides. Agreement between experimental results and theoretical models was very high, especially for small molecules. Finally, it is shown that this approach helps to predict the most appropriate set of conditions in HILIC x RPLC, depending on the compounds to be separated.

CE-MS/MS and CE-timsTOF to separate and characterize intramolecular disulfide bridges of monoclonal antibody subunits and their application for the assessment of subunit reduction protocols

Characterization at the subunit level enables detailed mass spectrometric characterization of posttranslational modifications (PTMs) of monoclonal antibodies (mAbs). The implemented reduction often leaves the intramolecular disulfide bridges intact. Here, we present a capillary electrophoretic (CE) method based on a neutral-coated capillary for the separation of immunoglobulin G-degrading enzyme of Streptococcus pyogenes (IdeS) digested and reduced mAb subunits followed by mass spectrometry (MS), MS/MS identification, and trapped ion mobility mass spectrometry (timsTOF). Our CE approach enables the separation of (i) different subunit moieties, (ii) various reduction states, and (iii) positional isomers of these partly reduced subunit moieties. The location of the remaining disulfide bridges can be determined by middle-down electron transfer higher energy collisional dissociation (EThcD) experiments. All these CE-separated variants show differences in ion mobility in the timsTOF measurements. Applying the presented CE-MS/MS method, reduction parameters such as the use of chaotropic salts were studied. For the investigated antibodies, urea improved the subunit reduction significantly, whereas guanidine hydrochloride (GuHCl) leads to multiple signals of the same subunit in the CE separation. The presented CE-MS method is a powerful tool for the disulfide-variant characterization of mAbs on the subunit level. It enables understanding disulfide bridge reduction processes in antibodies and potentially other proteins.

What should next-generation analytical platforms for biopharmaceutical production look like?

Biotherapeutic products, particularly complex products such as monoclonal antibodies (mAbs), have as many as 20-30 critical quality attributes (CQAs), thereby requiring a collection of orthogonal, high-resolution analytical tools for characterization and making characterization a resource-intensive task. As discussed in this Opinion, the need to reduce the cost of developing biotherapeutic products and the need to adopt Industry 4.0 and eventually Industry 5.0 paradigms are driving a reappraisal of existing analytical platforms. Next-generation platforms will have reduced offline testing, renewed focus on online testing and real-time monitoring, multiattribute monitoring, and extensive use of advanced data analytics and automation. They will be more complex, more sensitive, resource lean, and more responsive compared with existing platforms.

Application of two-dimensional reversed phase countercurrent chromatography × high-performance liquid chromatography to bioactivity-guided screening and isolation of α-glucosidase inhibitors from Rheum palmatum L

In the present work, comprehensive two-dimensional reversed-phase countercurrent chromatography × reversed-phase liquid chromatography combined (2D RPCCC × RPLC) with 2D microfraction bioactive evaluation was employed to screen and isolate α-glucosidase inhibitors from Rheum palmatum L. Countercurrent chromatography was employed to improve 2D analysis and preparative separation. A selected biphasic solvent system composed of petroleum ether/ethyl acetate/methanol/water with gradient elution mode was used for the first dimension RPCCC separation (1D RPCCC). Solid-phase extraction was applied to eliminate interfering polar compounds before the second dimension analysis (2D RPLC). 76 components were shown in 2D contour plot in UV 280 nm. 11 Candidates were separated by a scaled-up CCC and identified by 1H NMR and 13C NMR, including anthraquinones, flavonoids, stilbenes, phenols, and glucoside derivatives. In addition, it was found that two components, resveratrol-4'-O-(6″-galloyl)glucoside (36) and lyciumaside (43) were identified as natural α-glucosidase inhibitors in Rheum palmatum L. for the first time.

Automated online deconjugation of antibody-drug conjugate for small molecule drug profiling

Antibody-drug conjugates (ADCs) are designed by chemically linking highly potent cytotoxic small molecule drugs to monoclonal antibodies of unique specificity for targeted destruction of cancer cells. This innovative class of molecules incurs unique developmental challenges due to its structural complexity of having both small molecule and protein components. The stability of the small molecule payload on the ADC is a critical attribute as it directly relates to product efficacy and patient safety. This study describes the use of an end-to-end automated workflow for effective and robust characterization of the small molecule drug while it is conjugated to the antibody. In this approach, online deconjugation was accomplished by an autosampler user defined program and 1D size exclusion chromatography was utilized to provide separation between small molecule and protein species. The small molecule portion was then trapped and sent to the 2D for separation and quantification by reversed-phase liquid chromatography with identification of impurities and degradants by mass spectrometry. The feasibility of this system was demonstrated on an ADC with a disulfide-based linker. This fully automated approach avoids tedious sample preparation that may lead to sample loss and large assay variability. Under optimized conditions, the method was shown to have excellent specificity, sensitivity (LOD of 0.036 µg/mL and LOQ of 0.144 µg/mL), linearity (0.04-72.1 µg/mL), precision (system precision %RSD of 1.7 and method precision %RSD of 3.4), accuracy (97.4 % recovery), stability-indicating nature, and was successfully exploited to analyze the small molecule drug on a panel of stressed ADC samples. Overall, the workflow established here offers a powerful analytical tool for profiling the in-situ properties of small molecule drugs conjugated to antibodies and the obtained information could be of great significance for guiding process/formulation development and understanding pharmacokinetic/pharmacodynamic behavior of ADCs.

Integrated metabolomics and proteomics analysis of plasma lipid metabolism in Parkinson's disease

INTRODUCTION

Metabolomics and proteomics are two growing fields of science which may shed light on the molecular mechanisms that contribute to neurodegenerative diseases. Studies focusing on these aspects can reveal specific metabolites and proteins that can halt or reverse the progressive neurodegenerative process leading to dopaminergic cell death in the brain.

AREAS COVERED

In this article, an overview of the current status of metabolomic and proteomic profiling in the neurodegenerative disease such as Parkinson's disease (PD) is presented. We discuss the importance of state-of-the-art metabolomics and proteomics using advanced analytical methodologies and their potential for discovering new biomarkers in PD. We critically review the research to date, highlighting how metabolomics and proteomics can have an important impact on early disease diagnosis, future therapy development and the identification of new biomarkers. Finally, we will discuss interactions between lipids and α-synuclein (SNCA) and also consider the role of SNCA in lipid metabolism.

EXPERT OPINION

Metabolomic and proteomic studies contribute to understanding the biological basis of PD pathogenesis, identifying potential biomarkers and introducing new therapeutic strategies. The complexity and multifactorial nature of this disease requires a comprehensive approach, which can be achieved by integrating just these two omic studies.

Automated Online-Sampling Multidimensional Liquid Chromatography with Feedback-Control Capability as a Framework for Real-Time Monitoring of mAb Critical Quality Attributes in Multiple Bioreactors

Real-time monitoring of biopharmaceutical reactors is becoming increasingly important as the processes become more complex. During the continuous manufacturing of monoclonal antibodies (mAbs), the desired mAb product is continually created and collected over a 30 day process, where there can be changes in quality over that time. Liquid chromatography (LC) is the workhorse instrumentation capable of measuring mAb concentration as well as quality attributes such as aggregation, charge variants, oxidation, etc. However, traditional offline sampling is too infrequent to fully characterize bioprocesses, and the typical time from sample generation to data analysis and reporting can take weeks. To circumvent these limitations, an automated online sampling multidimensional workflow was developed to enable streamlined measurements of mAb concentration, aggregation, and charge variants. This analytical framework also facilitates automated data export for real-time analysis of up to six bioreactors, including feedback-controlling capability using readily available LC technology. This workflow increases the data points per bioreactor, improving the understanding of each experiment while also reducing the data turnaround time from weeks to hours. Examples of effective real-time analyses of mAb critical quality attributes are illustrated, showing substantial throughput improvements and accurate results while minimizing labor and manual intervention.

Quantitative analysis of therapeutic proteins in biological fluids: recent advancement in analytical techniques

Pharmaceutical application of therapeutic proteins has been continuously expanded for the treatment of various diseases. Efficient and reliable bioanalytical methods are essential to expedite the identification and successful clinical development of therapeutic proteins. In particular, selective quantitative assays in a high-throughput format are critical for the pharmacokinetic and pharmacodynamic evaluation of protein drugs and to meet the regulatory requirements for new drug approval. However, the inherent complexity of proteins and many interfering substances presented in biological matrices have a great impact on the specificity, sensitivity, accuracy, and robustness of analytical assays, thereby hindering the quantification of proteins. To overcome these issues, various protein assays and sample preparation methods are currently available in a medium- or high-throughput format. While there is no standard or universal approach suitable for all circumstances, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay often becomes a method of choice for the identification and quantitative analysis of therapeutic proteins in complex biological samples, owing to its high sensitivity, specificity, and throughput. Accordingly, its application as an essential analytical tool is continuously expanded in pharmaceutical R&D processes. Proper sample preparation is also important since clean samples can minimize the interference from co-existing substances and improve the specificity and sensitivity of LC-MS/MS assays. A combination of different methods can be utilized to improve bioanalytical performance and ensure more accurate quantification. This review provides an overview of various protein assays and sample preparation methods, with particular emphasis on quantitative protein analysis by LC-MS/MS.

Native SEC and Reversed-Phase LC-MS Reveal Impact of Fab Glycosylation of Anti-SARS-COV-2 Antibodies on Binding to the Receptor Binding Domain

The binding affinity of monoclonal antibodies (mAbs) for their intended therapeutic targets is often affected by chemical and post-translational modifications in the antigen binding (Fab) domains. A new two-dimensional analytical approach is described here utilizing native size exclusion chromatography (SEC) to separate populations of antibodies and bound antibody-antigen complexes for subsequent characterization of these modifications by reversed-phase (RP) liquid chromatography-mass spectrometry (LC-MS) at the intact antibody level. Previously, we utilized peptide mapping to measure modifications impacting binding. However, in this study, the large size of the modification (N-glycosylation) allowed assessing its impact from small amounts (∼20 ug) of intact antibody, without the need for peptide mapping. Here, we apply the native SEC-based competitive binding assay to quickly and qualitatively investigate the effects of Fab glycosylation of four antispike protein mAbs that were developed for use in the treatment of COVID-19 disease. Three of the mAbs were observed to have consensus N-glycosylation sites (N-X-T/S) in the Fab domains, a relatively rare occurrence in therapeutic mAbs. The goal of the study was to characterize the levels of Fab glycosylation present, as well as determine the impact of glycosylation on binding to the spike protein receptor binding domain (RBD) and the ability of the mAbs to inhibit RBD-ACE2 interaction at the intact antibody level, with minimal sample treatment and preparation. The three mAbs with Fab N-glycans were found to have glycosylation profiles ranging from full occupancy at each Fab (in one mAb) to partially glycosylated with mixed populations of two, one, or no glycan moieties. Competitive SEC analysis of mAb-RBD revealed that the glycosylated antibody populations outcompete their nonglycosylated counterparts for the available RBD molecules. This competitive SEC binding analysis was applied to investigate the three-body interaction of a glycosylated mAb blocking the interaction between endogenous binding partners RBD-ACE2, finding that both glycosylated and nonglycosylated mAb populations bound to RBD with high enough affinity to block RBD-ACE2 binding.

Why is there no biosimilar of Erbitux®?

Monoclonal antibody (mAb)-based therapies have been a major advance in oncology patient care, even though they represent a significant healthcare cost. Biosimilars, launched in Europe in 2004 are an economically attractive alternative to expensive originator biological drugs. They also increase the competitiveness of pharmaceutical development. This article focuses on the case of Erbitux® (cetuximab). This anti-EGFR (Epidermal Growth Factor Receptor) monoclonal antibody is indicated for metastatic colorectal cancer (2004) and squamous cell carcinoma of the head and neck (2006). However, despite the expiration of the patent in Europe in 2014 and estimated annual sales of 1.681 million US dollars in 2022, Erbitux® has not yet faced any approved biosimilar challenges in the United States or in Europe. Here, we outline the unique structural complexity of this antibody highlighted by advanced orthogonal analytical characterization strategies resulting in risks to demonstrate biosimilarity, which may explain the lack of Erbitux® biosimilars in the European and US markets to date. The development of Erbitux® biobetters are also discussed as alternative strategies to biosimilars. These biologics offer expected additional safety and potency benefits over the reference product but require a full pharmaceutical and clinical development as for New Molecular Entities.

Recent Advances and Perspectives in Relation to the Metabolomics-Based Study of Diabetic Retinopathy

Diabetic retinopathy (DR), a prevalent microvascular complication of diabetes, is a major cause of acquired blindness in adults. Currently, a clinical diagnosis of DR primarily relies on fundus fluorescein angiography, with a limited availability of effective biomarkers. Metabolomics, a discipline dedicated to scrutinizing the response of various metabolites within living organisms, has shown noteworthy advancements in uncovering metabolic disorders and identifying key metabolites associated with DR in recent years. Consequently, this review aims to present the latest advancements in metabolomics techniques and comprehensively discuss the principal metabolic outcomes derived from analyzing blood, vitreous humor, aqueous humor, urine, and fecal samples.

Reversed HILIC Gradient: A Powerful Strategy for On-Line Comprehensive 2D-LC

The aim of the present work is to evaluate the possibilities and limitations of reversed hydrophilic interaction chromatography (revHILIC) mode in liquid chromatography (LC). This chromatographic mode consists of combining a highly polar stationary phase (bare silica) with a gradient varying from very low (1-5%) to high (40%) acetonitrile content (reversed gradient compared to HILIC). The retention behavior of revHILIC was first compared with that of reversed-phase LC (RPLC) and HILIC using representative mixtures of peptides and pharmaceutical compounds. It appears that the achievable selectivity can be ranked in the order RPLC > revHILIC > HILIC with the two different samples. Next, two-dimensional liquid chromatography (2D-LC) conditions were evaluated by combining RPLC, revHILIC, or HILIC with RPLC in an on-line comprehensive (LC × LC) mode. evHILIC × RPLC not only showed impressive performance in terms of peak capacity and sensitivity, but also provided complementary selectivity compared to RPLC × RPLC and HILIC × RPLC. Indeed, both the elution order and the retention time range differ significantly between the three techniques. In conclusion, there is no doubt that revHILIC should be considered as a viable option for 2D-LC analysis of small molecules and also peptides.

Technological development of multidimensional liquid chromatography-mass spectrometry in proteome research

Liquid chromatography-mass spectrometry (LC-MS) is the method of choice for high-throughput proteomic research. Limited by the peak capacity, the separation performance of conventional single-dimensional LC hampers the development of proteomics. Combining different separation modes orthogonally, multidimensional liquid chromatography (MDLC) with high peak capacity was developed to address this challenge. MDLC has evolved rapidly since its establishment, and the progress of proteomics has been greatly facilitated by the advent of novel MDLC-MS-based methods. In this paper, we will review the advances of MDLC-MS-based methodologies and technologies in proteomics studies, from different perspectives including novel application scenarios and proteomic targets, automation, miniaturization, and the improvement of the classic methods in recent years. In addition, attempts regarding new MDLC-MS models are also mentioned together with the outlook of MDLC-MS-based proteomics methods.

Optimizing transfer and dilution processes when using active solvent modulation in on-line two-dimensional liquid chromatography

Two-dimensional liquid chromatography (2D-LC) is becoming increasingly popular for the analysis of complex samples, which is partly due to the recent introduction of commercial 2D-LC systems. To deal with the mobile phase incompatibility between highly orthogonal retention mechanisms, such as hydrophilic interaction liquid chromatography (HILIC) and reversed-phase LC (RPLC), several strategies have been introduced over the years. One of these strategies is active solvent modulation (ASM), a valve-based approach allowing the on-line dilution of the effluent eluting from the first dimension before transfer to the second dimension. This strategy has gained a lot of attention and holds great potential, however, no clear guidelines are currently in place for its use. Therefore, this study aims to investigate how the ASM process can be optimized when using highly incompatible LC combinations, such as HILIC and RPLC, in a simplified selective comprehensive 2D-LC set-up (sHILIC x RPLC) to suggest guidelines for future users. Using a representative sample, the dilution factor (DF), the duration of the ASM phase, the filling percentage of the sample loops, and their unloading configuration are investigated and optimized. It is observed that a DF of 10 with an optimal ASM phase duration, a sample loop filling of maximum 25%, and an unloading configuration in backflush mode, result in the best peak shapes, intensities, and recoveries for early eluting compounds, while keeping the total analysis time minimal. Based on these results, some general recommendations are made that could also be applied in other 2D-LC modes, such as comprehensive 2D-LC (LC x LC), heart-cutting 2D-LC (LC-LC), and other chromatographic combinations with mobile phase incompatibility issues.

A detailed evaluation of the advantages and limitations of online RP-LC×HILIC compared to HILIC×RP-LC for phenolic analysis

The combination of hydrophilic interaction chromatography (HILIC) and reversed-phase liquid chromatography (RP-LC) has proved effective in the LC × LC analysis of polyphenols due to the high degree of orthogonality associated with these separation modes for various classes of phenolic compounds. However, despite the growing number of such applications, HILIC is almost exclusively used as the first dimension (¹D) separation mode, and RP-LC in the second dimension (²D). This is somewhat surprising in light of the potential advantages of swapping these separation modes. In this contribution, we present a detailed evaluation of the potential of online RP-LC × HILIC-MS for the analysis of phenolic compounds, comparing the performance of this system to the more established HILIC × RP-LC-MS configuration. Method development was performed using a predictive optimisation program, and fixed solvent modulation was employed to combat the solvent incompatibility between HILIC and RP-LC mobile phases. Red wine, rooibos tea, Protea and chestnut phenolic extracts containing a large diversity of phenolic compound classes were analysed by both HILIC × RP-LC- and RP-LC × HILIC-MS in order to compare the separation performance. Overall, the kinetic performance of HILIC × RP-LC was found to be clearly superior, with higher peak capacities and better resolution obtained for the majority of samples compared to RP-LC × HILIC analyses using similar column dimensions. Dilution of the ¹D solvent combined with large volume injections proved insufficient to focus especially phenolic acids in the ²D HILIC separation, which resulted in severe ²D peak distortion for these compounds, and negatively impacted on method performance. On the other hand, a noteworthy improvement in the sensitivity of RP-LC × HILIC-MS analyses was observed due to higher ESI-MS response for the ²D HILIC mobile phase and greater sample loading capacity of the ¹D RP-LC column, brought on by the high solubility of phenolic samples in aqueous solutions. As a result, a significantly higher number of compounds were detected in the RP-LC × HILIC-MS separations. These findings point to the potential advantage of RP-LC × HILIC as a complementary configuration to HILIC × RP-LC for phenolic analysis.

Combining multidimensional chromatography-mass spectrometry and feature-based molecular networking methods for the systematic characterization of compounds in the supercritical fluid extract of Tripterygium wilfordii Hook F

Tripterygium wilfordii Hook F from the family Celastraceae is a traditional Chinese medicine (TCM) whose principal chemical constituents are terpenoids, including sesquiterpene alkaloids and diterpenoids, which have unique and diverse structures and remarkable biological activities. In order to advance pharmacological research and guide the preparation of monomer compounds derived from T. wilfordii, a systematic approach to efficiently discover new compounds or their derivatives is needed. Herein, compound separation and identification were performed by offline reversed-phase × supercritical fluid chromatography coupled mass spectrometry (RP × SFC-Q-TOF-MS/MS) and Global Natural Product Social (GNPS) molecular networking. The 2D chromatography system exhibited a high degree of orthogonality and significant peak capacity, and SFC has an advantage during the separation of sesquiterpene alkaloid isomers. Feature-based molecular networking offers the great advantage of quickly detecting and clustering unknown compounds, which greatly assists in intuitively judging the type of compound, and this networking technique has the potential to dramatically accelerate the identification and characterization of compounds from natural sources. A total of 324 compounds were identified and quantitated, including 284 alkaloids, 22 diterpenoids and 18 triterpenoids, which means that there are numerous potential new compounds with novel structures to be further explored. Overall, feature-based molecular networking provides an effective method for discovering and characterizing novel compounds and guides the separation and preparation of targeted natural products.

The Future of Method Development for Two-Dimensional Liquid Chromatography – Work Smarter, Not Just Harder?

The potential for wider use of two-dimensional liquid chromatography (2D-LC) is becoming more evident as the complexity of samples that must be handled continues to increase in application areas ranging from biopharmaceuticals to biosourced consumer products. Although the sophistication and ease of use have improved in recent years for commercial 2D-LC instruments, many analysts are still intimidated by the method development process for 2D methods because of the larger number of variables involved compared to conventional liquid chromatography. In this article, I share my perspective on the trends in this area, and the developments we are likely to see in the field in the near future.

Liquid chromatography and capillary electrophoresis in glycomic and glycoproteomic analysis

Glycosylation is one of the most significant and abundant post-translational modifications in cells. Glycomic and glycoproteomic analyses involve the characterization of oligosaccharides (glycans) conjugated to proteins. Glycomic and glycoproteomic analysis is highly challenging because of the large diversity of structures, low abundance, site-specific heterogeneity, and poor ionization efficiency of glycans and glycopeptides in mass spectrometry (MS). MS is a key tool for characterization of glycans and glycopeptides. However, MS alone does not always provide full structural and quantitative information for many reasons, and thus MS is combined with some separation technique. This review focuses on the role of separation techniques used in glycomic and glycoproteomic analyses, liquid chromatography and capillary electrophoresis. The most important separation conditions and results are presented and discussed.

Graphical abstract

Development of a sub-hour on-line comprehensive cation exchange chromatography x RPLC method hyphenated to HRMS for the characterization of lysine-linked antibody-drug conjugates

This study details the development of on-line two-dimensional liquid chromatography (2D-LC) methods combining cation-exchange chromatography (CEX) and reversed-phase liquid chromatography (RPLC) for the separation of the charge variants of a lysine-linked antibody-drug conjugate (ADC). This combination gives an excellent example of the potential benefits of 2D-LC approaches for the analysis of such complex protein formats. CEX is considered the reference technique for the separation of protein charge variants but its retention mechanism usually requires the use of a high concentration of non-volatile salts, which impedes its compatibility with MS detection. In this context, the use of an on-line 2D-LC-MS approach not only allows on-line desalting and indirect coupling of CEX with mass spectrometry (MS) detection but it also provides increased and complementary information within a single analysis. The first part of this study was devoted to the choice of stationary phases and the optimization of chromatographic conditions in both dimensions. Based on the results obtained in 1D-CEX with ultraviolet detection (UV) and 1D-RPLC with UV and high-resolution mass spectrometry (HRMS) detections, an on-line comprehensive two-dimensional liquid chromatography method combining CEX and RPLC was developed. The last part of this study was devoted to the identification of the separated species using HRMS detection and in the comparison of three ADC samples exposed to different durations of thermal stress.

A systematic investigation of the effect of sample solvent on peak shape in nano- and microflow hydrophilic interaction liquid chromatography columns

A frequently encountered problem in the practical application of nano- and microflow hydrophilic interaction chromatography (HILIC) columns is the distortion of peak shapes arising from a mismatch between the sample solvent and the mobile phase. An unmatched or improperly matched sample solvent can distort the peak shape of analytes and influence their retention times, thereby affecting the quality of the resulting chromatogram. In this work, the effect of sample solvent composition (mixtures of acetonitrile, water, methanol and isopropanol in different ratios) and injection volume (20-100 nL) was systematically investigated using a selection of neutral and charged compounds on a series of zwitterionic and charged small I.D. (0.1-0.3 mm) HILIC columns. For retained compounds, pure ACN was demonstrated to be the best sample solvent to obtain narrow peaks, while for compounds that eluted very close to the solvent peak, the peak shape was distorted when the sample solvent consisted of pure ACN. A highly aqueous sample solvent, which interferes with the partitioning of polar analytes into the stationary phase, was demonstrated to be detrimental for the peak shape of retained neutral compounds, while for unretained compounds that do not or hardly interact with the stationary phase, a high amount of water in the sample solvent was not problematic. For charged compounds, water in the sample solvent favored the electrostatic attraction with the stationary phase. Therefore, the retention time of charged analytes was shown to increase with increasing water content in the sample solvent. Even when a large amount of water was present in the sample solvent, the peak shapes of these compounds were still acceptable. For highly polar compounds with a limited solubility in aqueous sample solvents, it was found that a mixture of ACN and MeOH or IPA is a good alternative.

Strategies to circumvent the solvent strength mismatch problem in online comprehensive two-dimensional liquid chromatography

On-line comprehensive two-dimensional liquid chromatography is a powerful technique for the separation of highly complex samples. Due to the addition of the second dimension of separation, impressive peak capacities can be obtained within a reasonable analysis time compared to one-dimensional liquid chromatography. In online comprehensive two-dimensional liquid chromatography, the separation power is maximized by selecting two separation dimensions as orthogonal as possible, which most often requires the combination of different mobile phases and stationary phases. The online transfer of a given solvent from the first dimension to the second dimension may cause severe injection effects in the second dimension, mostly due to solvent strength mismatch. Those injection effects may include peak broadening, peak distortion, peak splitting or breakthrough phenomenon. They are often found to reduce significantly the peak capacity and the peak intensity. To overcome such effects, arising specifically in online comprehensive two-dimensional liquid chromatography, different methods have been developed over the years. In this review, we focused on the most recently reported ones. A critical discussion, supported by a theoretical approach, gives an overview of their advantages and drawbacks.

Enrichment and separation of high-polar compounds from Saussurea obvallata using solid-phase extraction combining with offline two-dimensional liquid chromatography

The high-polar compounds from natural products are often used as medicines due to their good bioactivities. However, owing to the complexity and diversity of their structure, the separation of high-polar compounds is still a challenging work. For this, an efficient method for enrichment and separation of the high-polar compounds from Saussurea obvallata was developed. First, the target compounds were enriched from the total extract using a solid-phase extraction method. An offline two-dimensional liquid chromatography method was used for the separation of pure compounds from the enriched sample. After optimization of chromatographic conditions, high separation selectivity of target compounds was obtained on a polar-modified C18 column and a HILIC XAmide column. Hence, a two-dimensional reversed-phase × hydrophilic interaction liquid chromatography system was constructed and enlarged from the analytical level to the preparative level. In the first dimension, four fractions were obtained on the XCharge C18 column with a recovery rate of 71.2%. In the second-dimension preparation on the XAmide column, eight high-polar compounds with more than 96% purity were isolated. All compounds were isolated from Saussurea obvallata for the first time. The results demonstrated that this developed strategy is effective for preparative-scale isolation of high-polar compounds from natural products.

In Silico Multifactorial Modeling for Streamlined Development and Optimization of Two-Dimensional Liquid Chromatography

Continued adoption of two-dimensional liquid chromatography (2D-LC) in industrial laboratories will depend on the development of approaches to make method development for 2D-LC more systematic, less tedious, and less reliant on user expertise. In this paper, we build on previous efforts in these directions by describing the use of multifactorial modeling software that can help streamline and simplify the method development process for 2D-LC. Specifically, we have focused on building retention models for second dimension (²D) separations involving variables including gradient time, temperature, organic modifier blending, and buffer concentration using LC simulator (ACD/Labs) software. Multifactorial retention modeling outcomes are illustrated as resolution map planes or cubes that enable straightforward location of ²D conditions that maximize resolution while minimizing analysis time. We also illustrate the practicality of this approach by identifying conditions that yield baseline separation of all compounds co-eluting from a first dimension (¹D) separation using a single combination of ²D stationary phase and elution conditions. The multifactorial retention models were found to be very accurate for both the ¹D and ²D separations, with differences between experimental and simulated retention times of less than 0.5%. Pharmaceutical applications of this approach for multiple heartcutting 2D-LC were demonstrated using IEC-IEC or achiral RPLC-chiral RPLC for 2D separations of multicomponent mixtures. The framework outlined here should help make 2D-LC method development more systematic and streamline development and optimization for a variety of 2D-LC applications in both industry and academia.

Current Challenges and Recent Developments in Mass Spectrometry-Based Metabolomics

High-resolution mass spectrometry (MS) has advanced the study of metabolism in living systems by allowing many metabolites to be measured in a single experiment. Although improvements in mass detector sensitivity have facilitated the detection of greater numbers of analytes, compound identification strategies, feature reduction software, and data sharing have not kept up with the influx of MS data. Here, we discuss the ongoing challenges with MS-based metabolomics, including de novo metabolite identification from mass spectra, differentiation of metabolites from environmental contamination, chromatographic separation of isomers, and incomplete MS databases. Because of their popularity and sensitive detection of small molecules, this review focuses on the challenges of liquid chromatography-mass spectrometry-based methods. We then highlight important instrumentational, experimental, and computational tools that have been created to address these challenges and how they have enabled the advancement of metabolomics research.

A comprehensive study on the phenomenon of total breakthrough in liquid chromatography

Differences in elution strength between the sample solvent and the mobile phase usually give rise to undesirable effects on the chromatographic separation, which may range from slight broadening to severe peak deformation or even splitting. In the most extreme case, the retention factor of the analyte at the head of the column is so small at the time of injection that part of the analyte goes through the column with very little interaction with the stationary phase and hence elutes very close to the column dead time. This phenomenon is known as breakthrough. Usually, during breakthrough, the retained peak displays a wide array of deformations and it is not rare that multiple retained peaks appear for a given injected analyte. However, under certain conditions, it has been demonstrated that these deleterious effects could fully disappear, leaving only one breakthrough peak and one symmetrical peak on the chromatogram. This so-called "total breakthrough" phenomenon was recently highlighted in the specific context of the 2D-LC separation of peptides but has yet to be explained. In the present paper, we describe the results of a comprehensive study aiming to better understand and define the conditions of emergence of both breakthrough and total breakthrough phenomena in liquid chromatography. The effects of a broad range of parameters, including the nature of the solute, the retention mechanism, the injection and elution conditions, the column temperature, and the injected sample concentration on the occurrence of both phenomena were investigated. While breakthrough was found to occur for all studied compounds, it appears that the presence of positive charges on the molecule is a prerequisite for observing a total breakthrough phenomenon. Among all the parameters investigated in this work, only the injection conditions and the analyte retention were found to be impactful on the onset of both phenomena. This finding allowed us to suggest one necessary and sufficient condition, relying on the injection of critical volumes to observe each respective phenomenon. These critical volumes only depend on the column dead volume and the retention factor of the analyte in the injection solvent.

Comparison of the steric selectivity on hydrophilic interaction chromatography columns modified with poly(acrylamide) possessing different morphology

Poly(acrylamide) (PAAm)-modified hydrophilic interaction chromatography (HILIC) columns were prepared via surface-initiated atom transfer radical polymerization (SI-ATRP) and free radical polymerization (FRP) to generate brush-like and mushroom-like polymer chains on silica particles, respectively. The maltose homologues (MHs) and cyclodextrins (CDs) were chosen as analytes to evaluate steric selectivity by the different polymer morphologies in the ATRP-PAAm and the FRP-PAAm columns. The ATRP-PAAm exhibited superior retention than the FRP-PAAm and three commercial HILIC columns. The house-made PAAm columns provided significant hydrophilicity that enabled to analysis the oligosaccharides even in 60:40 mixture of acetonitrile-aqueous buffer. In the case of three ATRP-PAAm columns characterized by different polymer lengths and the density on the silica particles, those are different thickness of the water-enriched layer, and phase ratio φ, based on hydrophilicity of them columns. The logarithm of the retention factor (ln k) displayed a non-linear dependence on the inverse of the temperature (1/T, T = 278-333 K). Notably, a similar correlation was observed to exist between the logarithm of the phase ratio (ln φ), and 1/T. A van't Hoff plot was used to determine the thermodynamic parameters of the partition process for each MH. The values of the Gibbs free energy (ΔG°) for the analytes partition on the ATRP-PAAm columns were smaller than their counterparts measured for the FRP-PAAm columns; by contrast, the opposite trend was observed for the ΔG° values measured for CDs. The standard entropy ΔS° for MHs and CDs were comparable for the two types PAAm columns, while, the standard enthalpy, ΔH° displays significant difference between the ATRP and the FRP PAAm columns. These findings indicate that the differences between PAAm morphology and polymer densities on the stationary phase surface affect analyte differentiation on the basis of molecular steric factors. The higher selectivity for MHs and CDs displayed by ATRP-PAAm columns with respect to their FRP-PAAm and commercial amide columns will be useful for the fine separation of oligosaccharides.

Comparison of existing strategies for keeping symmetrical peaks in on-line Hydrophilic Interaction Liquid Chromatography x Reversed-Phase Liquid Chromatography despite solvent strength mismatch

In two-dimensional liquid chromatography, the combination of hydrophilic interaction liquid chromatography (HILIC) and reversed-phase liquid chromatography (RPLC) is very attractive due to the complementarity of their separation mechanisms. On-line comprehensive HILIC x RPLC is well-known to give rise to a large retention space coverage when dealing with ionisable compounds. However, method development in on-line HILIC x RPLC is challenging due to the reversed solvent strength between both dimensions, which can greatly affect the peak shapes in the second RPLC dimension, and thus the separation quality and the method sensitivity. In the present contribution, we compared four strategies designed to avoid this problem: (1) flow splitting, which consists in reducing the injection volume in the second dimension (²D), (2) on-line dilution with a make-up flow and (3) on-line dilution with Active Solvent Modulation (ASM), which both consist in reducing the solvent strength of the injected fractions, and (4) Total Breakthrough Strategy, which we recently proposed. Unlike the three preceding strategies, this latter one consists in injecting large volumes of strong solvent in ²D. The performance of each strategy was evaluated for sub-hour separations of a tryptic digest in on-line HILIC x RPLC. In this work, we considered the critical case for which the same column internal diameters (i.e. 2.1 mm here) are used in both dimensions. Peak capacity, peak shapes and peak intensities were considered for this evaluation. The highest peak capacity could be achieved with Total Breakthrough Strategy while the lowest one with on-line dilution using ASM. Peak intensities were usually higher with on-line dilution approaches (make-up flow and ASM). However, despite the presence of breakthrough, peak intensities were approximately 7-fold higher with Total Breakthrough Strategy than with flow splitting.

Constant pressure mode of operation in the second dimension of two-dimensional liquid chromatography: A proof of concept

The use of two-dimensional liquid chromatography (2D-LC) continues to grow as the advantages over 1D-LC become increasingly clear in specific application areas, and the number of experienced 2D-LC users increases. As with any technique, however, there is always room for innovation that could improve the performance of 2D-LC. In recent years the technical aspects and potential benefits of a volume-based mode of operation were studied in detail for 1D-LC. The salient features of this approach that are immediately interesting for use in 2D-LC are two-fold. First, the ability to maintain a nominally constant pressure in the second dimension by dynamically adjusting the flow rate to compensate for changes in the viscosity of the fluid in the ²D flow path provides a means to more fully utilize the pressure capability of the pumping system, and accelerates separations in the second dimension (²D). Second, constant pressure operation minimizes physical stress on the system components and the ²D column. In this paper we discuss the aspects of volume-based operation of LC that are particularly relevant to 2D-LC systems. The proof-of-concept experiments illustrate the viability of the constant pressure mode of operation for the second dimension of 2D-LC. In the described separations the throughput improvement is on the order of 10%; this gain will be strongly application-dependent, and may be as large as several tens percent in some cases. Future work will involve a detailed investigation of the impact of the constant pressure mode on robustness of ²D separations.

Implications of dispersion in connecting capillaries for separation systems involving post-column flow splitting

It is common practice in liquid chromatography to split the flow of the effluent exiting the analytical column into two or more parts, either to enable parallel detection (e.g., coupling the separation to two destructive detectors such as light scattering and mass spectrometry (MS)), or to accommodate flow rate limitations of a detector (e.g., electrospray ionization mass spectrometry). In these instances the user must make choices about split ratio and dimensions of connecting tubing that is used between the split point and the detector, however these details are frequently not mentioned in the literature, and rarely justified. In our own work we often split the effluent following the second dimension (²D) column in two-dimensional liquid chromatography systems coupled to MS detection, and we have frequently observed post ²D column peak broadening that is larger than we would expect to result from dispersion in the MS ionization source itself. For the present paper we describe a series of experiments aimed at understanding the impact of the split ratio and post-split connecting tubing dimensions on dispersion of peaks exiting an analytical column. We start with the simple idea - based on the principle of conservation of mass - that analyte peaks entering the split point are split into two parts such that the analyte mass (and thus peak volume) entering and exiting the split point is conserved, and directly related to the ratio of flow rates entering and exiting the split point. Measurements of peak width and variance after the split point show that this simple view of the splitting process - along with estimates of additional dispersion in the post-split tubing - is sufficient to predict peak variances at the detector with accuracy that is sufficient to guide experimental work (median error of about 10% over a wide range of conditions). We feel it is most impactful to recognize that flow splitting impacts apparent post-column dispersion not because anything unexpected happens in the splitting process, but because the split dramatically reduces the volume of the analyte peak, which then is more susceptible to dispersion in connecting tubing that would not cause significant dispersion under conditions where splitting is not implemented. These results will provide practitioners with a solid basis on which rational decisions about split ratios and dimensions of post-split tubing can be made.

Fast Afucosylation Profiling of Glycoengineered Antibody Subunits by Middle-Up Mass Spectrometry

Middle-up LC-MS antibody characterization workflows using reduction or IdeS digestion for a focused assessment of N-glycan profiling of three representative glycoengineered monoclonal antibodies (mAbs), namely, obinutuzumab (GlycomAb technology, Glycart/Roche), benralizumab (Potelligent Technology, BioWa, Kyowa Kirin) and mAb B (kifunensine) and compared to mAb A, produced in a common CHO cell line. In addition, EndoS or EndoS2 enzyme are used for quantitative determination of Fc-glycan core afucosylation and high mannose for these antibodies, as requested by health authorities for Fc-competent therapeutics mAbs critical quality attributes (CQAs).

Mapping the Separation Landscape in Two-Dimensional Liquid Chromatography: Blueprints for Efficient Analysis and Purification of Pharmaceuticals Enabled by Computer-Assisted Modeling

Recent developments in two-dimensional liquid chromatography (2D-LC) now make separation and analysis of very complex mixtures achievable. Despite being such a powerful chromatographic tool, current 2D-LC technology requires a series of arduous method development activities poorly suited for a fast-paced industrial environment. Recent introductions of new technologies including active solvent modulation and a support for multicolumn 2D-LC are helping to overcome this stigma. However, many chromatography practitioners believe that the lack of a systematic way to effectively optimize 2D-LC separations is a missing link in securing the viability of 2D-LC as a mainstay for industrial applications. In this work, a computer-assisted modeling approach that dramatically simplifies both offline and online 2D-LC method developments is introduced. Our methodology is based on mapping the separation landscape of pharmaceutically relevant mixtures across both first (¹D) and second (²D) dimensions using LC Simulator (ACD/Labs) software. Retention models for ¹D and ²D conditions were built using a minimal number of multifactorial modeling experiments (2 × 2 or 3 × 3 parameters: gradient slope, column temperature, and different column and mobile phase combinations). The approach was first applied to online 2D-LC analysis involving achiral and chiral separations of complex mixtures of enantiomeric species. In these experiments, the retention models proved to be quite accurate for both the ¹D and ²D separations, with retention time differences between experiments and simulations of less than 3.5%. This software-based concept was also demonstrated for offline 2D-LC purification of drug substances.

Charge variant analysis of protein-based biopharmaceuticals using two-dimensional liquid chromatography hyphenated to mass spectrometry

The profile of charge variants represents an important critical quality attribute of protein-based biopharmaceuticals, in particular of monoclonal antibodies, and must therefore becontrolled. In this work, 2D-LC methods for charge variant analysis were developed using a strong cation-exchange chromatography (SCX) as first dimension (¹D) separation. Non-porous SCX (3 µm) particle columns and different mobile phases were evaluated using a test mixture of some standard proteins of different size and pI (comprising myoglobin, bovine serum albumin, cytochrome c, lysozyme and β-lactoglobulin) and two monoclonal IgG1 antibodies (NIST mAb and Secukinumab). The most promising ¹D eluent for SCX was a salt-mediated pH-gradient system using a ternary mobile phase system with 2-(N-morpholino)ethanesulfonic acid, 1,3-diamino-2-propanol and sodium chloride. For the second dimension (²D), a desalting reversed-phase liquid chromatography (RP-LC) was chosen to enable the hyphenation of the charge variant separation with mass spectrometric (MS) detection. While for intact mAbs the ²D just served for desalting without additional selectivity, the ²D contributed some orthogonal selectivity for the mAb fragment separation. Various core-shell and monolithic columns were tested and variables such as gradient time and flow rate systematically optimized. Unexpectedly, a C4 400 Å column (3.4 µm diameter with 0.2 µm porous shell) provided higher peak capacities compared to the same 1000 Å column (2.7 µm diameter with 0.5 µm porous shell). A thinner shell appeared to be more advantageous than wider pores under high flow regime. An ultra-fast RP-LC method with a run time of one minute was developed using trifluoroacetic acid which was later replaced by formic acid as additive for better MS compatibility. The successful hyphenation of the two orthogonal separation modes, SCX and RP-LC, could be demonstrated in the multiple heart-cutting and the full comprehensive mode. MS analysis using a high-resolution quadrupole time-of-flight instrument enabled to identify different glycoforms and some major charge variants of the antibody at the intact protein level as well as on the subunit level (Fc/2, Lc, Fd') in a middle-up approach by 2D-LC-ESI-MS analysis.

Monitoring of immunoglobulin N- and O-glycosylation in health and disease

Protein N- and O-glycosylation are well known co- and post-translational modifications of immunoglobulins. Antibody glycosylation on the Fab and Fc portion is known to influence antigen binding and effector functions, respectively. To study associations between antibody glycosylation profiles and (patho) physiological states as well as antibody functionality, advanced technologies and methods are required. In-depth structural characterization of antibody glycosylation usually relies on the separation and tandem mass spectrometric (MS) analysis of released glycans. Protein- and site-specific information, on the other hand, may be obtained by the MS analysis of glycopeptides. With the development of high-resolution mass spectrometers, antibody glycosylation analysis at the intact or middle-up level has gained more interest, providing an integrated view of different post-translational modifications (including glycosylation). Alongside the in-depth methods, there is also great interest in robust, high-throughput techniques for routine glycosylation profiling in biopharma and clinical laboratories. With an emphasis on IgG Fc glycosylation, several highly robust separation-based techniques are employed for this purpose. In this review, we describe recent advances in MS methods, separation techniques and orthogonal approaches for the characterization of immunoglobulin glycosylation in different settings. We put emphasis on the current status and expected developments of antibody glycosylation analysis in biomedical, biopharmaceutical and clinical research.

Development of an Online 2D Ultrahigh-Pressure Nano-LC System for High-pH and Low-pH Reversed Phase Separation in Top-Down Proteomics

The development of novel high-resolution separation techniques is crucial for advancing the complex sample analysis necessary for high-throughput top-down proteomics. Recently, our group developed an offline 2D high-pH RPLC/low-pH RPLC separation method and demonstrated good orthogonality between these two RPLC formats. Specifically, ultrahigh-pressure long capillary column RPLC separation has been applied as the second dimensional low-pH RPLC separation for the improvement of separation resolution. To further improve the throughput and sensitivity of the offline approach, we developed an online 2D ultrahigh-pressure nano-LC system for high-pH and low-pH RPLC separations in top-down proteomics. An online microtrap column with a dilution setup was used to collect eluted proteins from the first dimension high-pH separation and inject the fractions for ultrahigh-pressure long capillary column low-pH RPLC separation in the second dimension. This automatic platform enables the characterization of 1000+ intact proteoforms from 5 μg of intact E. coli cell lysate in 10 online-collected fractions. Here, we have demonstrated that our online 2D pH RP/RPLC system coupled with top-down proteomics holds the potential for deep proteome characterization of mass-limited samples because it allows the identification of hundreds of intact proteoforms from complex biological samples at low microgram sample amounts.

Recent advances on protein separation and purification methods

Protein, as the material basis of vita, is the crucial undertaker of life activities, which constitutes the framework and main substance of human tissues and organs, and takes part in various forms of life activities in organisms. Separating proteins from biomaterials and studying their structures and functions are of great significance for understanding the law of life activities and clarifying the essence of life phenomena. Therefore, scientists have proposed the new concept of proteomics, in which protein separation technology plays a momentous role. It has been diffusely used in the food industry, agricultural biological research, drug development, disease mechanism, plant stress mechanism, and marine environment research. In this paper, combined with the recent research situation, the progress of protein separation technology was reviewed from the aspects of extraction, precipitation, membrane separation, chromatography, electrophoresis, molecular imprinting, microfluidic chip and so on.

Metabolomics: A Tool for Cultivar Phenotyping and Investigation of Grain Crops

The quality of plants is often enhanced for diverse purposes such as improved resistance to environmental pressures, better taste, and higher yields. Considering the world’s dependence on plants (nutrition, medicine, or biofuel), developing new cultivars with superior characteristics is of great importance. As part of the ‘omics’ approaches, metabolomics has been employed to investigate the large number of metabolites present in plant systems under well-defined environmental conditions. Recent advances in the metabolomics field have greatly expanded our understanding of plant metabolism, largely driven by potential application to agricultural systems. The current review presents the workflow for plant metabolome analyses, current knowledge, and future directions of such research as determinants of cultivar phenotypes. Furthermore, the value of metabolome analyses in contemporary crop science is illustrated. Here, metabolomics has provided valuable information in research on grain crops and identified significant biomarkers under different conditions and/or stressors. Moreover, the value of metabolomics has been redefined from simple biomarker identification to a tool for discovering active drivers involved in biological processes. We illustrate and conclude that the rapid advances in metabolomics are driving an explosion of information that will advance modern breeding approaches for grain crops and address problems associated with crop productivity and sustainable agriculture.

Comparison of Online Comprehensive HILIC × RP and RP × RP with Trapping Modulation Coupled to Mass Spectrometry for Microalgae Peptidomics

In this work, two online comprehensive two-dimensional liquid chromatography platforms, namely Hydrophilic interaction liquid chromatography × Reversed phase (HILIC × RP) and Reversed phase × Reversed Phase (RP × RP) coupled to mass spectrometry, were compared for the analysis of complex peptide samples. In the first dimension, a HILIC Amide and C18 Bioshell peptide (150 × 2.1 mm, 1.7 and 2.0 μm) columns were selected, while, in the second dimension, a short C18 (50 × 3.0 mm, 2.7 μm) Bioshell peptide column was used. Two C18 trapping columns (10 × 3.0 mm, 1.9 μm), characterized by high retention and surface area, were employed as modulation interface in both HILIC × RP and RP × RP methods. The LC × LC platforms were coupled to UV and tandem mass spectrometry detection and tested for the separation and identification of two gastro-intestinal digests of commercial microalgae formulations (Spirulina Platensis and Klamath). Their performances were evaluated in terms of peak capacity, maximum number and properties of identified phycocyanin peptides. Our results showed that the HILIC × RP approach provided the highest peak capacity values (nc HILIC × RP: 932 vs. nc RP × RP: 701) with an analysis time of 60 min, while the RP × RP approach was able to identify a slight higher number of phycocyanin derived peptides (HILIC × RP: 88 vs. RP × RP: 103). These results point out the flexibility and potential of HILIC × RP and RP × RP based on trapping modulation for peptide mapping approaches.

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.