Hydrophilic interaction liquid chromatography: An efficient tool for assessing thorium interaction with phosphorylated biomimetic peptides

In the field of nuclear toxicology, the knowledge of the interaction of actinides (An) with biomolecules is of prime concern in order to elucidate their toxicity mechanism and to further develop selective decorporating agents. In this work, we demonstrated the great potential of hydrophilic interaction liquid chromatography (HILIC) to separate polar thorium (Th) biomimetic peptide complexes, as a key starting point to tackle these challenges. Th4+ was used as plutonium (Pu4+) analogue and pS16 and pS1368 as synthetic di- and tetra-phosphorylated peptides capable of mimicking the interaction sites of these An in osteopontin (OPN), a hyperphosphorylated protein. The objective was to determine the relative affinity of pS16 and pS1368 towards Th4+, and to evaluate the pS1368 selectivity when Th4+ was in competition complexation reaction with UO22+ at physiological pH. To meet these aims, HILIC was simultaneously coupled to electrospray ionization mass spectrometry (ESI-MS) and inductively coupled plasma mass spectrometry (ICP-MS), which allowed to identify online the molecular structure of the separated complexes and quantify them, in a single step. Dedicated HILIC conditions were firstly set up to separate the new dimeric Th2(peptide)2 complexes with good separation resolution (peptide = pS16 or pS1368). By adding pS16 and pS1368 in different proportions relatively to Th4+, we found that lower or equal proportions of pS16 with respect to pS1368 were not sufficient to displace pS1368 from Th2pS13682 and pS16 proportion higher than pS1368 led to the formation of a predominant ternary complex Th2(pS16)(pS1368), demonstrating preferential Th4+ binding to the tetra-phosphorylated peptide. Finally, online identification and quantification of the formed complexes when Th4+ and UO22+ were mixed in equimolar ratio relatively to pS1368 showed that in spite of pS1368 has been specifically designed to coordinate UO22+, pS1368 is also Th4+-selective and exhibits stronger affinity for this latter than for UO22+. Hence, the results gathered through this approach highlight the impact of Th4+ coordination chemistry on its interaction with pS1368 and more widely to its affinity for biomolecules.

A review of intact glycopeptide enrichment and glycan separation through hydrophilic interaction liquid chromatography stationary phase materials

Protein glycosylation, one of the most important biologically relevant post-translational modifications for biomarker discovery, faces analytical challenges due to heterogeneous glycosite, diverse glycans, and mass spectrometry limitations. Glycopeptide enrichment by removing abundant hydrophobic peptides helps overcome some of these obstacles. Hydrophilic interaction liquid chromatography (HILIC), known for its selectivity, glycan separations, intact glycopeptide enrichment, and compatibility with mass spectrometry, has seen recent advancements in stationary phases like Amide-80, glycoHILIC, amino acids or peptides for improved HILIC-based glycopeptide analysis. Utilization of these materials can improve glycopeptide enrichment through solid-phase extraction and separation via high-performance liquid chromatography. Additionally, using glycopeptides themselves to modify HILIC stationary phases holds promise for improving selectivity and sensitivity in glycosylation analysis. Additionally, HILIC has capability to assess the information about glycosites and structural information of glycans. This review summarizes recent breakthroughs in HILIC stationary materials, highlighting their impact on glycopeptide analysis. Ongoing research on advanced materials continues to refine HILIC's performance, solidifying its value as a tool for exploring protein glycosylation.

Chromatographic evaluation and application of nitrogenous heterocyclic ring-bonded stationary phase in hydrophilic interaction liquid chromatography

Hydrophilic interaction liquid chromatography (HILIC) based on polar stationary phases has vital research significance in the separation of polar compounds. Numerous HILIC stationary phases with different structures have been developed, which do not have universal properties and broad selectivity, making it a challenge to select the suitable column based on the properties of the samples. Consequently, it is particularly important to develop a bonded phase capable of separating a wide variety of samples, while having enhanced retention, improved selectivity, symmetric peak shape and good stability. Herein, a novel nitrogen-containing heterocyclic bonded phase with multiple functionalities, such as thioether, amino and hydroxyl groups (named AMTA) was employed as HILIC stationary phase. Detailed chromatographic evaluations were carried out, and the results showed that it was superior to other hydrophilic chromatographic columns in terms of selectivity, peak shapes and practical sample separation. Lastly, it has been verified that AMTA exhibited high orthogonality with the XBridge C18 column of reversed-phase liquid chromatography (RPLC) mode. In summary, we anticipate our assay to be instructive to other researchers in developing the HILIC stationary phase.

Triazine-structured covalent organic framework nanosheets with inherent hydrophilicity for the highly efficient and selective enrichment of glycosylated peptides

Protein glycosylation plays a crucial role in various biological processes and is related to various diseases. Highly specific enrichment of glycopeptides before mass spectrometry detection is crucial for comprehensive glycoproteomic analysis. However, it still remains a great challenge due to the absence of affinity materials with excellent enrichment efficiency. In this work, a triazine structure linked by a -NH- bond of two-dimensional (2-D) covalent organic framework (COF) nanosheets was synthesized as an affinity adsorbent for the selective capture of glycopeptides. In particular, by introducing hydrophilic monomers via a bottom-up approach, the 2-D COF (denoted as NENP-1) nanosheets were provided with abundant amino groups and inherent hydrophilicity. Owing to the specific surface area and excessive accessible sites for hydrophilicity, the resulting NENP-1 nanosheets exhibited an outstanding glycopeptide enrichment efficiency from standard samples with a superior detection sensitivity (1 × 10-10 M), good enrichment selectivity (1 : 800, HRP tryptic digest to BSA protein), excellent binding capacity (100 mg g-1), great reusability, and recovery (60.2%). Furthermore, using the NENP-1 nanosheet adsorbent, twenty-four endogenous glycopeptides in the serum of patients with gastric cancer were successfully identified by LC-MS/MS technology, which illustrates a promising prospective of hydrophilic COF nanosheets in glycoproteomics research.

Mass Spectrometry Strategies for O-Glycoproteomics

Glycoproteomics has accelerated in recent decades owing to numerous innovations in the analytical workflow. In particular, new mass spectrometry strategies have contributed to inroads in O-glycoproteomics, a field that lags behind N-glycoproteomics due to several unique challenges associated with the complexity of O-glycosylation. This review will focus on progress in sample preparation, enrichment strategies, and MS/MS techniques for the identification and characterization of O-glycoproteins.

Comprehensive analysis of the effective and intra-particle diffusion of weakly retained compounds in silica hydrophilic interaction liquid chromatography columns

A detailed analysis of intra-particle volumes and layer thicknesses and their effect on the diffusion of solutes in hydrophilic interaction liquid chromatography (HILIC) was made. Pycnometric measurements and the retention volume of deuterated mobile phase constituents (water and acetonitrile) were used to estimate the void volume inside the column, including not only the volume of the mobile phase but also part of the enriched water solvent acting as the stationary phase in HILIC. The mobile phase (hold-up) volume accessible to non-retained components was estimated using a homologous series approach. The joint analysis of the different approaches indicated the formation of enriched water layers on the hydrophobic silica mesopore walls with a thickness varying significantly with mobile phase composition. The maximal thickness of the enriched water layers, which corresponded to the minimum void volume accessible to unretained solutes, marked a transition in the retention behavior of the studied analytes. Discrepancies between deuterated solvent measurements and pycnometry were explained by the existence of an irreplaceable water layer adsorbed on the silica surface. Regarding the diffusion behavior in HILIC, peak parking experiments were used to interpret the influence of the acetonitrile content on the effective diffusion coefficient Deff. A systematic decrease in Deff and molecular diffusion Dm was observed with decreasing acetonitrile concentration, primarily attributed to variations in mobile phase viscosity. Notably, Deff/Dm remained nearly unaffected by variations in mobile phase composition. Finally, the effective medium theory was used to make a comprehensive analysis of Dpart/Dm to study the contribution to band broadening when the solute resides in the mesopores. The obtained data unveiled a curvature with a minimum corresponding to conditions of maximum water-layer thickness and retention. For the weakly retained compounds (k' < 0.5) the Dpart/Dm-values were found to be relatively high (order of 0.35-0.5), which directly reflects the high γsDs/Dm-values that were observed (order 0.35-7).

Maximal performance of intact N-glycopeptide enrichment using sequential HILIC and MAX columns

Low abundance and heterogeneity of N-glycosylation at the peptide level poses a great challenge to the structural and functional analysis of glycosylation in the field of glycobiology. Solving this conundrum requires a sufficient and specific method for intact N-glycopeptide enrichment. Using the C18 or HLB desalting column followed by the mixed-mode strong anion exchange (MAX) or hydrophilic interaction chromatography (HILIC) glycopeptide enrichment column are commonly applied approaches for sample preparation of intact N-glycopeptides from complex samples. Herein, we compared the effects of different combinations of two desalting columns and two enrichment columns using equal amounts of mouse brain tissues from the same source. The results revealed the C18 column was a bit superior to the HLB column, and the MAX and HILIC columns were complementary on intact N-glycopeptides enrichment. Additionally, the results also demonstrated that enriching glycopeptides using a HILIC column followed by a MAX column from the flow-through solution got a better enrichment performance than the reversed order. Based on these results, the sequential enrichment of glycopeptides using HILIC and then MAX columns could maximize the enrichment performance of intact N-glycopeptides, and therefore is an option for in-depth analysis of site-specific glycoproteome.

Common Post-translational Modifications (PTMs) of Proteins: Analysis by Up-to-Date Analytical Techniques with an Emphasis on Barley

Post-translational modifications (PTMs) of biomacromolecules can be useful for understanding the processes by which a relatively small number of individual genes in a particular genome can generate enormous biological complexity in different organisms. The proteomes of barley and the brewing process were investigated by different techniques. However, their diverse and complex PTMs remain understudied. As standard analytical approaches have limitations, innovative analytical approaches need to be developed and applied in PTM studies. To make further progress in this field, it is necessary to specify the sites of modification, as well as to characterize individual isoforms with increased selectivity and sensitivity. This review summarizes advances in the PTM analysis of barley proteins, particularly those involving mass spectrometric detection. Our focus is on monitoring phosphorylation, glycation, and glycosylation, which critically influence functional behavior in metabolism and regulation in organisms.

Characterization of solute-solvent interactions in liquid chromatography systems: A fast method based on Abraham's linear solvation energy relationships

The Abraham's solvation parameter model, based on linear solvation energy relationships (LSER), allows the accurate characterization of the selectivity of chromatographic systems according to solute-solvent interactions (polarizability, dipolarity, hydrogen bonding, and cavity formation). However, this method, based on multilinear regression analysis, requires the measurement of the retention factors of a considerably high number of compounds, turning it into a time-consuming low throughput method. Simpler methods such as Tanaka's scheme are preferred. In the present work, the Abraham's model is revisited to develop a fast and reliable method, similar to the one proposed by Tanaka, for the characterization of columns employed in reversed-phase liquid chromatography and particularly in hydrophilic interaction liquid chromatography. For this purpose, pairs of compounds are carefully selected in order to have in common all molecular descriptors except for a specific one (for instance, similar molecular volume, dipolarity, polarizability, and hydrogen bonding basicity features, but different hydrogen bonding acidity). Thus, the selectivity factor of a single pair of test compounds can provide information regarding the extent of the dissimilar solute-solvent interactions and their influence on chromatographic retention. The proposed characterization method includes the determination of the column hold-up volume and Abraham's cavity term by means of the injection of four alkyl ketone homologues. Therefore, five chromatographic runs in a reversed-phase column (four pairs of test solutes and a mixture of four homologues) are enough to characterize the selectivity of a chromatographic system. Tanaka's method is also analyzed from the LSER point of view.

In-depth investigation of altered glycosylation in human haptoglobin associated cancer by mass spectrometry

Serum haptoglobin (Hp), a highly sialylated biomolecule with four N-glycosylation sites, is a positive acute-phase response glycoprotein that acts as an immunomodulator. Hp has gained considerable attention due to its potential as a signature molecule that exhibits aberrant glycosylation in inflammatory disorders and malignancies. Its glycosylation can be analyzed qualitatively and quantitatively by various methods using mass spectrometry. In this review, we have provided a brief overview of Hp structure and biological function and described mass spectrometry-based techniques for analyzing glycosylation ranging from macroheterogeneity to microheterogeneity of Hp in diseases and cancer. The sugars on haptoglobin can be a sweet bridge to link the potential of cancer-specific biomarkers to clinically relevant applications.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

Separation of nicotinamide metabolites using a PBr column packed with pentabromobenzyl group modified silica gel

Nicotinamide adenine dinucleotide, a coenzyme involved in the activation of sirtuins, contributes to various regulations in vivo. However, highly hydrophilic nicotinamide metabolites are difficult to separate by high-performance liquid chromatography (HPLC) using octadecyl (C₁₈) columns, which operate via hydrophobic interaction. PBr columns packed with silica gel modified with the pentabromobenzyl group having strong dispersion forces show good retention ability for various highly hydrophilic compounds. Additionally, the peak shape obtained with the PBr column did not collapse like that of the HILIC column, even when a large amount of water was injected. Separation of 11 highly hydrophilic nicotinamide metabolites using a PBr column under simple conditions resulted in baseline separation, but separation on a C₁₈ column was not complete. The peak shape for each compound was better than that in previous studies. Furthermore, the separation of nicotinamide metabolites in tomato using a PBr column enable a more sensitive detection than that using a C₁₈ column. SUBJECT CATEGORY: Chromatographic Technique.

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.

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A novel sensitive analytical method for the simultaneous analysis of vancomycin and teicoplanin in human urine via single high-performance liquid chromatography coupled with photodiode array and mass spectrometry in series

Analysis of vancomycin and teicoplanin in biological fluids is vital since they are used in the treatment of hospital infections. For the determination of both glycopeptides in urine, a sensitive and accurate analytical method using high‐performance liquid chromatography coupled with photodiode array and mass spectrometry was developed and validated. This research work is the first attempt to develop a chromatographic method for the determination of two glycopeptides with structural similarities. Moreover, the used non‐invasive sampling method is an advantage of this research effort, especially when the blood sampling is difficult. Urine was treated with acetonitrile and 5% trichloroacetic acid, followed by solid‐phase extraction. The chromatographic separation was established at a C18 column (4.6 × 150 mm, 5 μm), using a gradient method and an electrospray ionization source in a positive mode. The linearity of the method was R²≥ 0.9900. The precision was estimated with a maximum coefficient of variation below 15%, while the accuracy ranged from 64 to 121%. The limit of detection and quantification of both glycopeptides ranged from 0.076 up to 0.33 mg/L and 0.33 up to 2.1 mg/L, respectively, showing the same sensitivity as the triple quadrupole mass spectrometry, which is the most frequently used method.

Automated ion exchange chromatography screening combined with in silico multifactorial simulation for efficient method development and purification of biopharmaceutical targets

Bioprocess development of increasingly challenging therapeutics and vaccines requires a commensurate level of analytical innovation to deliver critical assays across functional areas. Chromatography hyphenated to numerous choices of detection has undeniably been the preferred analytical tool in the pharmaceutical industry for decades to analyze and isolate targets (e.g., APIs, intermediates, and byproducts) from multicomponent mixtures. Among many techniques, ion exchange chromatography (IEX) is widely used for the analysis and purification of biopharmaceuticals due to its unique selectivity that delivers distinctive chromatographic profiles compared to other separation modes (e.g., RPLC, HILIC, and SFC) without denaturing protein targets upon isolation process. However, IEX method development is still considered one of the most challenging and laborious approaches due to the many variables involved such as elution mechanism (via salt, pH, or salt-mediated-pH gradients), stationary phase's properties (positively or negatively charged; strong or weak ion exchanger), buffer type and ionic strength as well as pH choices. Herein, we introduce a new framework consisting of a multicolumn IEX screening in conjunction with computer-assisted simulation for efficient method development and purification of biopharmaceuticals. The screening component integrates a total of 12 different columns and 24 mobile phases that are sequentially operated in a straightforward automated fashion for both cation and anion exchange modes (CEX and AEX, respectively). Optimal and robust operating conditions are achieved via computer-assisted simulation using readily available software (ACD Laboratories/LC Simulator), showcasing differences between experimental and simulated retention times of less than 0.5%. In addition, automated fraction collection is also incorporated into this framework, illustrating the practicality and ease of use in the context of separation, analysis, and purification of nucleotides, peptides, and proteins. Finally, we provide examples of the use of this IEX screening as a framework to identify efficient first dimension (¹D) conditions that are combined with MS-friendly RPLC conditions in the second dimension (²D) for two-dimensional liquid chromatography experiments enabling purity analysis and identification of pharmaceutical targets.

Characterization of a highly stable zwitterionic hydrophilic interaction chromatography stationary phase based on hybrid organic/inorganic particles

We have characterized a sulfobetaine stationary phase based on 1.7 μm ethylene-bridged hybrid organic/inorganic particles, which is intended for use in hydrophilic interaction chromatography. The efficiency of columns packed with this material were determined as a function of flow rate, demonstrating a minimum reduced plate height of 2.4. The batch-to-batch reproducibility was assessed using the separation of a mixture of acids, bases and neutrals. We compared the retention and selectivity of the hybrid sulfobetaine stationary phase to that of several benchmark materials. The hybrid sulfobetaine material gave strong retention for polar neutrals and high selectivity for methyl groups, hydroxy groups and configurational isomers. Large differences in cation and anion retention were observed among the columns. We characterized the acid and base stability of the hybrid sulfobetaine stationary phase, using accelerated tests at pH 1.3 and 11.0, both at 70°C. The results support a recommended pH range of 2 to 10. We also investigated the performance of columns packed with this material for metal-sensitive analytes, comparing conventional stainless steel column hardware to hardware that incorporates hybrid surface technology to mitigate interactions with metal surfaces. Compared to the conventional columns, the hybrid surface technology columns showed greatly improved peak shape. This article is protected by copyright. All rights reserved.

Recent Advances in Drug-Antibody Ratio Determination of Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) are biopharmaceuticals produced by chemically linking small molecules (payloads) to antibodies that possess specific affinity for the target cell. The ADCs currently on the commercially market are the result of a stochastic conjugation of highly-potent payloads to multiple sites on the monoclonal antibody, resulting in a heterogeneous drug-antibody ratio (DAR) and drug distribution. The heterogeneity inherent to ADCs not produced site-specifically may not only be detrimental to the quality of the drug but also is less-desirable from the perspective of regulatory science. An ideal method or unified approach used to measure the DAR for ADCs, a critical aspect of their analysis and characterization, has not yet been established in the ADC field and remains an often-challenging issue for bioanalytical chemists. In this review we describe, compare, and evaluate the characteristics of various DAR determination methods for ADCs featuring recently reported technologies. The future landscape of bioconjugate DAR analysis is also discussed.

Enabling development, manufacturing, and regulatory approval of biotherapeutics through advances in mass spectrometry

Rapid technological advances have significantly improved the capability, versatility, and robustness of mass spectrometers which has led to them playing a central role in the development, characterization, and regulatory filings of biopharmaceuticals. Their application spans the entire continuum of drug development, starting with discovery research through product development, characterization, and marketing authorization and continues well into product life cycle management. The scope of application extends beyond traditional protein characterization and includes elements like clone selection, cell culture physiology and bioprocess optimization, investigation support, and process analytical technology. More recently, advances in the MS-based multi-attribute method are enabling the introduction of MS in a cGMP environment for routine release and stability testing. While most applications of MS to date have been for monoclonal antibodies, the successes and learnings should translate to the characterization of next-gen biotherapeutics where modalities like multispecifics could be more prevalent. In this review, we describe the most significant advances in MS and correlate them to the broad spectrum of applications to biotherapeutic development. We anticipate rapid technological improvements to continue that will further accelerate widespread deployment of MS, thereby elevating our overall understanding of product quality and enabling attribute-focused product development.

Mass Spectrometry-based Proteomics and Glycoproteomics in COVID-19 Biomarkers Identification: A Mini-review

The first corona-pandemic, coronavirus disease 2019 (COVID-19) caused a huge health crisis and incalculable damage worldwide. Knowledge of how to cure the disease is urgently needed. Emerging immune escaping mutants of the virus suggested that it may be potentially persistent in human society as a regular health threat as the flu virus. Therefore, it is imperative to identify appropriate biomarkers to indicate pathological and physiological states, and more importantly, clinic outcomes. Proteins are the performers of life functions, and their abundance and modification status can directly reflect the immune status. Protein glycosylation serves a great impact in modulating protein function. The use of both unmodified and glycosylated proteins as biomarkers has also been proved feasible in the studies of SARS, Zika virus, influenza, etc. In recent years, mass spectrometry-based glycoproteomics, as well as proteomics approaches, advanced significantly due to the evolution of mass spectrometry. We focus on the current development of the mass spectrometry-based strategy for COVID-19 biomarkers' investigation. Potential application of glycoproteomics approaches and challenges in biomarkers identification are also discussed.

Current approaches for the purification of antibody-drug conjugates

In the past two decades, antibody-drug conjugates have gained increasing attention because they expand the therapeutic index when compared with that of traditional chemotherapies. Antibody-drug conjugates are highly complex structures consisting of antibodies covalently conjugated with small-molecule cytotoxic drugs. The complex structure of antibody-drug conjugates makes chemistry, manufacturing, and control difficult. In contrast to antibody production, distinct purification methods following conjugation of antibodies with drug-linkers are required for the manufacturing. For process development of antibody drug conjugates, the drug-to-antibody ratio, free drug-linkers, and aggregates are critical quality attributes that must be strictly controlled and removed by appropriate purification techniques. In this review, features of various purification methods used to purify antibody drug conjugates are described and evaluated. The future landscape of the antibody-conjugates field is also discussed briefly.

Evaluation of multiple hydrophilic interaction chromatography columns and surrogate matrix for arginine quantification in saliva by high-resolution mass spectrometry

Arginine, a pivotal ingredient in many biochemical synthetic pathways, can be used as a biomarker for many oral care clinical applications. It is still a challenge to develop a sensitive and reliable chromatographic method to quantify arginine as a biomarker in saliva, with or without arginine product pretreatment. The current method solved two critical issues for arginine quantitation in human saliva. The first issue was how to optimize arginine peak shape. A hydrophilic interaction chromatography method based on the column selection, pH and pK_a relationship, mobile phase ionic strength, organic solvent consideration, and temperature effects was developed. An optimized chromatographic condition for arginine quantitation in the saliva matrix was obtained. The second issue was how to build confidence in the use of a simple surrogate matrix methodology to replace the more complex traditional standard addition methodology. The surrogate matrix methodology we developed is applicable to the measurement of arginine as a potential non-invasive biomarker in human saliva. The method detection and quantification limit reached 2 and 6 ng/mL. The tailing factor was within the 0.9-1.1 range even though arginine had three pK_a values at 2.18, 9.09, and 13.2.

Separation of labeled isomeric oligosaccharides by hydrophilic interaction liquid chromatography - the role of organic solvent in manipulating separation selectivity of the amide stationary phase

The advantages of using mixtures of organic solvents for the separation of labeled oligosaccharides on the amide stationary phase under hydrophilic interaction liquid chromatography conditions are presented. The effect of the type of buffer as well as solvent or their mixtures on retention of uracil, saccharide labeling reagents (2-aminobenzoic acid, 2-aminobenzamide, ethyl 4-aminobenzoate, procainamide), and corresponding labeled saccharides were evaluated. The successful isocratic separation of labeled isomeric trisaccharides (maltotriose, panose, and isomaltotriose) was achieved in the mobile phase consisting of a 90% (v/v) mixture of organic solvents (methanol/acetonitrile 60:40) and 10% (v/v) 30 mM ammonium formate, pH 3.3. Changing the volume ratio between methanol/acetonitrile from 60:40 to 50:50 (v/v) allowed to obtain the separation of di-, tri-, and tetrasaccharides labeled by ethyl 4-aminobenzoate in less than 10.5 min.

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.

Analytical characterization of DNA and RNA oligonucleotides by hydrophilic interaction liquid chromatography-tandem mass spectrometry

Liquid chromatography-mass spectrometry has been widely implemented as a powerful tool for providing in-depth characterization of nucleic acid therapeutic modalities, such as anti-sense oligonucleotides and small interfering RNAs (siRNAs). In this study, we developed a generic hydrophilic interaction liquid chromatography (HILIC) hyphenated with tandem mass spectrometry method in the absence of ion-pairing reagents and demonstrated its capability as an attractive and robust alternative for oligonucleotide and siRNA analysis. HILIC separation of mixtures of unmodified and fully phosphorothioate-modified DNA oligonucleotides and their synthetic 3' exonuclease-digested metabolites were also assessed. High-resolution mass spectrometric (HRMS) analysis was used to determine the deconvoluted masses of oligonucleotide and siRNA standards and their impurities. To enable unbiased sequence characterization with tandem mass spectrometry (MS/MS), we also optimized higher-energy C-trap dissociation (HCD) on improving the sequence coverage of DNA and RNA oligonucleotides. Lastly, we evaluated on-column sensitivity for a phosphorothioate oligonucleotide by performing targeted analysis with either targeted selected ion monitoring (tSIM) or parallel reaction monitoring (PRM). Higher on-column sensitivity of 13 ng, equivalent to 2.0 pmol, of a phosphorothioate oligonucleotide was achieved by tSIM analysis as compared to PRM analysis.

Simple and efficient preparation of high-purity trehalulose from the waste syrup of isomaltulose production using solid-phase extraction followed by hydrophilic interaction chromatography

A simple and efficient method was developed for the preparation of high-purity trehalulose from the waste syrup of isomaltulose production. The waste syrup was pre-treated with C18 solid-phase extraction, where 98% decolorization and 97% reducing sugar recovery were obtained, followed by hydrophilic interaction liquid chromatography separation on a cysteine-bonded zwitterionic column. Under optimized conditions, trehalulose was separated from isomaltulose isomer and prepared on a semi-preparative scale with >99% purity. The structure of the prepared trehalulose was subsequently confirmed by nuclear magnetic resonance, and three tautomers of trehalulose (α-D-glucosylpyranosyl-1,1-β-D-fructopyranose, α-D-glucosylpyranosyl-1,1-β-D-fructofuranose, and α-D-glucosylpyranosyl-1,1-α-D-fructofuranose) were detected and completely characterized by ¹³ C NMR spectroscopy for the first time in this study. The tautomerization of α-D and β-D type transition was observed by hydrophilic interaction liquid chromatography on an AdvanceBio Glycan Mapping column, with smaller particle size (2.7 μm). Furthermore, the prepared trehalulose was applied as a standard for trehalulose quantification during the sucrose conversion by Klebsiella sp. LX3. The combination of solid-phase extraction and hydrophilic interaction liquid chromatography offers a new avenue for the preparation of sugar isomers from complex natural or fermentation products.

Isolation of three polyoxins by reversed-phase liquid chromatography with pure aqueous mobile phase

Developing methods for the isolation of highly polar compounds from complex samples is of great significance. In this study, three polyoxins were successfully isolated from a complex sample (PN1-1^# ) by preparative high-performance liquid chromatography. Separation was carried out on five polar reversed-phase stationary phases, using pure aqueous as mobile phase, where the C18HC column can provide the best performance for PN1-1^# . Next, the effects of the mobile phase composition were studied. It was found that adding NaClO₄ can enhance the retention and resolution, and adding NaH₂ PO₄ was beneficial to maintain good peak shapes when the sample loading increased. Therefore, the optimized mobile phase consisting of 20 mmol NaH₂ PO₄ and 20 mmol NaClO₄ (adding H₃ PO₄ to adjust pH 2) was used to separate PN1-1^# . This method of using 100% aqueous phase can effectively improve both the retention and the solubility of polar samples. Eventually, through further purification, three compounds, namely, polyoxins B, D, and G, were obtained. This paper provided an effective and eco-friendly strategy for the preparative-scale separation of polar samples.

Fluorescence Assisted Capillary Electrophoresis of Glycans Enabled by the Negatively Charged Auxochromes in 1-Aminopyrenes

A compact and negatively charged acceptor group, N-(cyanamino)sulfonyl, is introduced for dye design and its influence on the absorption and emission spectra of the "push-pull" chromophores is demonstrated with 1,3,6-tris[(cyanamino)sulfonyl]-8-aminopyrene. The new sulfonamides, including O-phosphorylated (3-hydroxyazetidine)-N-sulfonyl, are negatively charged electron acceptors and auxochromes. 1-Aminopyrenes decorated with the new sulfonamides have three or six negative charges (pH ≥8), low m/z ratios, high mobilities in an electric field, and yellow to orange emission. We labeled maltodextrin oligomers by reductive amination, separated the products by electrophoresis, and demonstrated their high brightness in a commercial DNA analyzer and the distribution of the emission signal among the detection channels.

Multi-dimensional LC-MS: the next generation characterization of antibody-based therapeutics by unified online bottom-up, middle-up and intact approaches

This review presents an overview of current analytical trends in antibody characterization by multidimensional LC-MS approaches.

Functionalization using polymer or silane? A practical test method to characterize hydrophilic interaction chromatography phases in terms of their functionalization method

Herein, commercially available columns employed in hydrophilic interaction chromatography (HILIC) were characterized by determining their ability to selectively distinguish the minute structural differences between small molecules such as nucleosides and xanthines in complex sample matrices. Principal component analysis (PCA) was applied to the data obtained from structurally similar analytes, and the results showed that HILIC columns could generally be classified into two groups: (i) silane-modified columns that were prepared from either native silica particles or silica particles modified with low-molecular-weight silanes and (ii) polymer-modified columns obtained from silica particles functionalized with organic polymers. These two groups could be further subdivided based on the functionalities attached to the respective stationary phases. These results were confirmed via cluster analysis by preparing a dendrogram using the morphology-based selectivity parameters associated with the respective columns. We were able to determine the selectivity of columns for the OH groups, i.e., α(OH) and the prevailing pH conditions (cation- and anion-exchanging natures) on the surface of the respective stationary phases; α(theobromine/theophylline) was employed to obtain a similar two-dimensional plot. This test scheme, in which five compounds were analyze for each column, was helpful for understanding the impact of factors such as the hydrophilicity, degree of hydration, acidity/basicity, or the weak ion-exchange nature of the respective stationary phases on the separation characteristics of new HILIC stationary phases. The selectivity of columns for the CH₂ group was also examined. The cation-exchange nature of the HILIC columns significantly influenced native silica columns and some polymer-modified columns. Herein, 45 commercially available HILIC columns were classified according to this method, and the results proved useful for understanding distinct separation characteristics of each HILIC column, enabling improved column selection.

A Pragmatic Guide to Enrichment Strategies for Mass Spectrometry-Based Glycoproteomics

Glycosylation is a prevalent, yet heterogeneous modification with a broad range of implications in molecular biology. This heterogeneity precludes enrichment strategies that can be universally beneficial for all glycan classes. Thus, choice of enrichment strategy has profound implications on experimental outcomes. Here we review common enrichment strategies used in modern mass spectrometry-based glycoproteomic experiments, including lectins and other affinity chromatographies, hydrophilic interaction chromatography and its derivatives, porous graphitic carbon, reversible and irreversible chemical coupling strategies, and chemical biology tools that often leverage bioorthogonal handles. Interest in glycoproteomics continues to surge as mass spectrometry instrumentation and software improve, so this review aims to help equip researchers with the necessary information to choose appropriate enrichment strategies that best complement these efforts.

An exploratory approach for an oriented development of an untargeted hydrophilic interaction liquid chromatography-mass spectrometry platform for polar metabolites in biological matrices

The analysis of polar metabolites based on liquid chromatography-mass spectrometry (LC-MS) methods should take into consideration the complexity of interactions in LC columns to be able to cover a broad range of metabolites of key biological pathways. Therefore, in this study, different chromatographic columns were tested for polar metabolites including reversed-phase and hydrophilic interaction liquid chromatography (HILIC) columns. Based on a column screening, two new generations of zwitterionic HILIC columns were selected for further evaluation. A tree-based method optimization was applied to investigate the chromatographic factors affecting the retention mechanisms of polar metabolites with zwitterionic stationary phases. The results were evaluated based on a scoring system which was applied for more than 80 polar metabolites with a high coverage of key human metabolic pathways. The final optimized methods showed high complementarity to analyze a wide range of metabolic classes including amino acids, small peptides, sugars, amino sugars, phosphorylated sugars, organic acids, nucleobases, nucleosides, nucleotides and acylcarnitines. Optimized methods were applied to analyze different biological matrices, including human urine, plasma and liver cell extracts using an untargeted approach. The number of high-quality features (< 30% median relative standard deviation) ranged from 3,755 for urine to 5,402 for the intracellular metabolome of liver cells, showing the potential of the methods for untargeted purposes.

Glycine additive facilitates site-specific glycosylation profiling of biopharmaceuticals by ion-pairing hydrophilic interaction chromatography mass spectrometry

Many biotherapeutics such as monoclonal antibodies (mAb) and Fc-domain fusion proteins contain heterogeneous glycan contents at one or multiple glycosylation site(s). Site-specific glycan profile characterization is critical for monitoring the quality of these molecules during different stages of drug development. Hydrophilic interaction chromatography (HILIC) as an orthogonal separation method to reversed-phase liquid chromatography (RPLC) can achieve better glycopeptide identification due to the effective separation between individual glycoforms as well as the separation of glycopeptides from high-abundance non-glycosylated peptides, which can be further improved by modifying the mobile phases with ion-pairing agents (IP-HILIC). However, an online IP-HILIC coupled to mass spectrometry (MS) detection may suffer from the suppression of mass spectrometry signal during electrospray ionization due to the trifluoroacetic acid (TFA), commonly used as an ion-pairing agent. Here, we reported an optimized experimental condition for IP-HILIC-MS where glycine is added in the TFA-containing mobile phases to enhance the MS detection sensitivity for glycopeptides up to ~ 50-fold by eliminating the ion-suppression effect of an ion-pairing agent while still retaining excellent separation capacity. We demonstrated that with enhanced detection sensitivity, IP-HILIC-MS can confidently identify an increased number of site-specific N-linked glycans for IgG1, and IgG4 mAbs as well as an Fc-domain fusion protein (containing five N-glycosylation sites) through MS/MS-based search in the data-dependent acquisition mode, meanwhile, achieve comparable quantitative results compared with the traditional methods. We also demonstrated that IP-HILIC-MS can be used to identify low-level O-glycosylation and non-consensus N-glycosylation on mAbs without any enrichment prior to LC-MS analysis. Graphical abstract.

An ultrafast and highly efficient enrichment method for both N-Glycopeptides and N-Glycans by bacterial cellulose

A powerful and fast glycopeptide/glycan enrichment method is critical for the efficiency and throughput of mass spectrometry (MS)-based glycoproteomic and glycomic analyses, especially for large-scale sample analysis. Here, we report an ultrafast and effective method for both intact N-glycopeptide and N-glycan enrichment and apply it to human serum samples. In this method, a natural hydrophilic material, bacterial cellulose (BC), was adopted and fully optimized for enrichment. This method offers the following advantages: (i) The enrichment material has natural hydrophilicity and is low-cost, biocompatible, biodegradable and easily accessible; (ii) the whole enrichment procedure is remarkably simple and fast. It takes only 10 min for intact glycopeptides/glycans to be easily purified from mixtures; (iii) the specificity of this method is over 94% for both glycan and glycopeptide enrichment; and (iv) the outstanding specificity of this technique enables high isolation efficiency for the enrichment of both intact glycopeptides and glycans. A total of 36 N-glycans and 31 N-glycopeptides were identified from human immunoglobulin G (IgG). The glycan and glycopeptide absorption capacity of BC was as high as 333 μg/mg and 250 μg/mg (IgG/BC) respectively. The selectivity for glycan and glycopeptide enrichment reached 1:100 (IgG/bovine serum albumin (BSA), molar ratio) and 1:200 (maltoheptaose (DP7)/BSA, molar ratio), respectively. Furthermore, a total of 159 N-glycans and 523 N-glycopeptides were identified in human serum by using this method. Overall, the BC-based enrichment method we present here provides an ultrafast and highly efficient method for the enrichment of both N-glycopeptides and N-glycans in complex samples and shows great potential in large-scale glycoproteomic and glycomic analyses.

New multimodal stationary phases prepared by Ugi multicomponent approach

Eight different stationary phases based on two aminopropyl silicas of different brands suitable for multimodal chromatography applications have been prepared by a four-component Ugi reaction. The intention was to synthesize stationary phases significantly differing in their properties hereby demonstrating flexibility of the Ugi synthetic protocol. Diverse functional groups including a nonpolar long aliphatic chain, phenyl moiety, cholic acid scaffold, phenylboronic and monosaccharide units, charged betaine, and arginine moieties were immobilized on a silica surface. The novel sorbents were extensively characterized by elemental analysis, Raman spectroscopy, and chromatography. Considering the anchored chemical structures covalently bonded to the silica surface, reversed-phase, hydrophilic, and ion-exchange separation modes were expected. The chromatographic evaluation was performed directed to map the potential of the individual columns specifically in the mentioned chromatographic modes. The Ugi synthetic protocol has proven to be a simple, feasible, and versatile tool for the synthesis of sorbents of variable properties. The newly prepared stationary phases differed considerably in hydrophobicity and ion-exchange ability. A significant influence of the supporting aminopropyl silica on the final chromatographic behavior was observed. Finally, one practical example confirming applicability of the newly prepared sorbents was demonstrated in separation of cytarabine.

Therapeutic Fc-fusion proteins: Current analytical strategies

Fc-Fusion proteins represent a successful class of biopharmaceutical products, with already 13 drugs approved in the European Union and United States as well as three biosimilar versions of etanercept. Fc-Fusion products combine tailored pharmacological properties of biological ligands, together with multiple functions of the fragment crystallizable domain of immunoglobulins. There is a great diversity in terms of possible biological ligands, including the extracellular domains of natural receptors, functionally active peptides, recombinant enzymes, and genetically engineered binding constructs acting as cytokine traps. Due to their highly diverse structures, the analytical characterization of Fc-Fusion proteins is far more complex than that of monoclonal antibodies and requires the use and development of additional product-specific methods over conventional generic/platform methods. This can be explained, for example, by the presence of numerous sialic acids, leading to high diversity in terms of isoelectric points and complex glycosylation profiles including multiple N- and O-linked glycosylation sites. In this review, we highlight the wide range of analytical strategies used to fully characterize Fc-fusion proteins. We also present case studies on the structural assessment of all commercially available Fc-fusion proteins, based on the features and critical quality attributes of their ligand-binding domains.

Evaluating Relative Retention of Polar Stationary Phases in Hydrophilic Interaction Chromatography

A large number of polar stationary phases with diverse chemistry have been developed for various applications in hydrophilic interaction chromatography (HILIC). However, column manufacturers employ different testing procedures to evaluate retention of the polar stationary phases. This renders the retention data impossible for comparison and makes it difficult for the users to select the right stationary phase based on retention. We have evaluated 25 polar stationary phases using cytosine and uracil as the model compounds in various mobile phase conditions. These stationary phases show a wide range of retention characteristics for the model compounds. The ranking of the stationary phases does not change drastically with the acetonitrile level in the mobile phase.

Evaluating the Adsorbed Water Layer on Polar Stationary Phases for Hydrophilic Interaction Chromatography (HILIC)

The water-rich liquid layer immobilized on the surface of the polar stationary phases is critical to the retention of polar compounds in hydrophilic interaction chromatography (HILIC). Although the presence of the adsorbed water layer has been investigated and confirmed by multiple techniques, there is a lack of quantitative measures that can be easily determined and linked to chromatographic parameters. This study proposes a simple measure termed volume ratio (the ratio of the adsorbed water layer volume and the mobile phase volume) that can be easily determined using toluene elution volume. The volume ratio values measured using the proposed method indicate that the volume of the adsorbed water layer varies in a wide range in the stationary phases commonly used in HILIC separation. It was observed that the volume ratio increases with the acetonitrile content and ammonium acetate concentration in the mobile phase. In addition, increasing the column temperature had the effect of reducing the volume ratio and diminishing the adsorbed water layer.