Hydrophilic interaction chromatography

Deracemization of Benzoin and its Derivatives via Kinetic, Dynamic Kinetic, Aerobic Oxidative Kinetic, and Reagent-mediated resolution

The production of enantiomerically pure compounds remains a vital and valuable objective in modern organic chemistry due to their broad applications in fields such as biosensing, optics, electronics, photonics, catalysis, nanotechnology, and drug or DNA delivery. Optically pure α-hydroxy ketones, in particular, are key structural components in many drugs and natural products with significant biological activity. Among these, benzoin type α-hydroxy ketones, which possess two adjacent functional groups, a carbonyl and a hydroxy group, are especially important. These functional groups can be easily transformed into the significant organic compounds such as 1,2 amino alcohols and 1,2 diols etc, which are important intermediates for synthesis of high profile biological active natural products. Deracemization of racemic compounds remains one of the most effective strategies for producing optically pure compounds, despite recent advances in asymmetric synthesis. Due to the importance of chiral benzoins, numerous studies have focused on their asymmetric synthesis. At the same time, many research groups have developed various methods for resolving racemic benzoins, including kinetic resolution, dynamic kinetic resolution, metal-catalyzed aerobic oxidative kinetic resolution, and reagent-mediated resolution. In this context, we aim to provide a comprehensive review of the various resolution methods applied specifically to racemic benzoins. To the best of our knowledge, no comprehensive review on the resolution of racemic benzoins has been published to date.

Hydrophilic interaction chromatography coupled to high resolution mass spectrometry (HILIC-LC-HRMS): An approach to study natural peptides in Viperidae snake venom

Although proteins in snake venoms have been extensively studied and characterized, low-mass molecules remain relatively unexplored, mainly due to their low abundance, secondary role in envenomation, and some analytical technique limitations. However, these small molecules can provide new important data related to venom toxins' molecular structure, functions, and evolutionary relationships. This research aimed to characterize molecules below 10 kDa in the venoms of snakes from the Viperidae families (Bothrops, Agkistrodon, and Bitis) and compare two chromatographic approaches: reverse-phase chromatography (RP), a classic technique, and hydrophilic interaction liquid chromatography (HILIC), an alternative technique, both coupled with high-resolution mass spectrometry (HRMS). The results showed that the separation of the HILIC column provided a more efficient evenly distributed ion profile than RP, contributing to a 25.6% increase in the sequences identified. Homologous sequences for Bradykinin-potentiating peptides (BPPs) and fragments of major venom proteins, possibly cryptids, were found. In addition, BPP 13a, peptides rich in histidine and glycine (pHpG), and spacer sequences were identified in all snakes analyzed, especially with HILIC separation, suggesting that these sequences may be conserved within Viperidae. These findings indicate that the use of the HILIC column, compared to RP, is a promising approach for characterizing peptides in snake venom obtained by the ultrafiltration process. It contributes to the study of these still poorly understood molecules and is also a good option for studying other complex protein/peptide mixtures.

From Complexity to Clarity: Expanding Metabolome Coverage With Innovative Analytical Strategies

Metabolomics, a powerful discipline within systems biology, aims at comprehensive profiling of small molecules in biological samples. The challenges of biological sample complexity are addressed through innovative sample preparation methods, including solid-phase extraction and microextraction techniques, enhancing the detection and quantification of low-abundance metabolites. Advances in chromatographic separation, particularly liquid chromatography (LC) and gas chromatography (GC), coupled with high-resolution (HR) mass spectrometry (MS), have significantly improved the sensitivity, selectivity, and throughput of metabolomic studies. Cutting-edge techniques, such as ion-mobility mass spectrometry (IM-MS) and tandem MS (MS/MS), further expand the capacity for comprehensive metabolite profiling. These advanced analytical platforms each offer unique advantages for metabolomics, with continued technological improvements driving deeper insights into metabolic pathways and biomarker discovery. By providing a detailed overview of current trends and techniques, this review aims to offer valuable insights into the future of metabolomics in human health research and its translational potential in clinical settings. Toward the end, this review also highlights the biomedical applications of metabolomics, emphasizing its role in biomarker discovery, disease diagnostics, personalized medicine, and drug development.

Preparation of a titanium-functionalized polymeric material rich in hydrophilic groups for phosphoproteome and glycoproteome analyses in serum

The analysis of protein phosphorylation and glycosylation is critical for investigating disease development. In this work, 1,2-epoxy-5-hexene and N,N-methylenebisacrylamide were polymerized with vinyl phosphate to produce a polymer (denoted as PVME), which contained a variety of hydrophilic groups. The material's hydrophilicity was further enhanced by a ring-opening reaction with cysteine (the product was denoted as Cys-PVEM). Finally, titanium sulfate was combined with Cys-PVME to form titanium-rich polymers (Cys-PVME-Ti4+) for the enrichment of phosphopeptides and glycopeptides. Cys-PVME-Ti4+ has a good sensitivity (0.02 fmol) and selectivity (1 : 1000) with a loading capacity of 62 mg g-1, recyclability (9 cycles), and a good recovery rate (101.6 ± 0.60%) for phosphopeptides, and good sensitivity (0.01 fmol μL-1), selectivity (1 : 2000), a loading capacity of 62.5 mg g-1, recyclability (9 cycles), and a good recovery rate (98.7 ± 1.2%) for glycopeptides. In addition, after enrichment with this material, 27 phosphopeptides with 14 phosphoproteins and 223 glycopeptides associated with 88 glycoproteins were captured from the serum of colorectal cancer patients, while 27 phosphopeptides associated with 14 phosphoproteins and 210 glycopeptides associated with 111 glycoproteins were also captured from the serum of a normal control. Gene ontology (GO) analysis revealed that complement activation, extracellular region, extracellular space, blood coagulation, the IgG immunoglobulin complex, and heparin binding were different between normal control and colorectal cancer, implying that related pathways are likely involved in colorectal cancer pathogenesis.

Matrix effect evaluation using multi-component post-column infusion in untargeted hydrophilic interaction liquid chromatography-mass spectrometry plasma metabolomics

Metabolomics based on hydrophilic interaction liquid chromatography (HILIC) coupled with mass spectrometry (MS) is a powerful tool for polar metabolite identification and quantification to further contribute to biomarker discovery and disease mechanism elucidation. However, matrix effect (ME), which may lead to altered ionization efficiency due to co-eluting compounds, is a significant challenge during biological analysis. Therefore, ME evaluation plays a crucial role during method development. Two approaches to evaluate ME are using stable isotope labelled-internal standards (SIL-IS) and post-column infusion (PCI) of standards. In this study, we developed an untargeted HILIC-MS method by applying four PCI standards for ME evaluation. We found PCI is a compelling approach for ME assessment compared to SIL-IS method due to its advantage in untargeted analysis. Through the ME evaluation and chromatographic performance comparison of 18 SIL standards across three columns and three different mobile phase pH conditions, our findings revealed that the BEH-Z-HILIC column operated at pH 4 with 10 mM ammonium formate exhibited minimal ME and superior performance. The method showed exceptional linearity (R² > 0.98), reliable repeatability (RSD < 15 %), good inter-day precision (RSD < 30 %), and acceptable recovery (>75 %) for all SIL standards. Absolute matrix effect (AME) and relative matrix effect (RME) assessment in three plasma donors revealed a high consistency between PCI and SIL-IS approaches. Finally, this method coupled with the PCI approach was applied to 40 plasma samples. Fifty endogenous compounds were detected and their AME and RME were evaluated. Results showed that many compounds experienced severe ion suppression, though their ME variation between 40 samples is low. In conclusion, PCI method is a robust alternative for monitoring ME and evaluating ME of endogenous compounds during untargeted method optimization and biological analysis.

Synthesis and applications of ionic liquids for chromatographic analysis

Ionic liquids (ILs) have emerged as more desirable liquids than conventional solvents for chemistry, material science, engineering and environmental science. The scientific literature reveals an exponential increase in the number of research projects aimed at exploring the chromatographic features of ionic liquids. The review provides sound scientific data to examine the structural characteristics of ionic liquids that make them ideal for use in chromatography. This contribution is distinctive since it integrates the synthesis, benefits, drawbacks, and possible uses of ionic liquids in several chromatographic separation processes. Keeping the cation the same, the introduction of different anions is also possible, and this strategy leads to the synthesis of a series of different ionic liquids with varying properties. A detailed probe is given on the influence of ionic liquid structure and properties on their chromatographic behavior, both as stationary phase and mobile phase and/or mobile phase additives. Ionic liquid based immobilized stationary phases and their analyte retention mechanisms (hydrogen bonding, electrostatic forces of attraction, π-π stacking, ion exchange, and hydrophilic interactions, etc.) are critically discussed. Finally, a thorough analysis of the literature suggests that IL-based stationary phases may undergo multi-mode and more flexible retention mechanisms. Their dual polarity can facilitate interaction with both polar and non-polar compounds. Similarly, using IL as a mobile phase can offer more pragmatic and sustainable options for enantiomer separation.

Separation of nucleobases, nucleosides, nucleotides and oligonucleotides by hydrophilic interaction liquid chromatography (HILIC): A state-of-the-art review

The polar nature of nucleobases, nucleosides and nucleotides makes hydrophilic interaction chromatography (HILIC) a good choice of technology for separation. Both naturally occurring and modified nucleosides and nucleotides have been successfully separated in HILIC. A wide range of stationary phases with different retention and selectivity are suitable for the separation of nucleobases, nucleosides and nucleotides; and a sufficient knowledge base is also available to guide method development. Although oligonucleotides are significantly different from nucleotides in terms of polarity and charges, HILIC has been shown to be a viable alternative to ion-pairing reversed-phase liquid chromatography (IP-RPLC). Only a few polar stationary phases have been shown to provide satisfactory performance; however, the requirements for the mobile phase composition including organic solvent, mobile phase pH and salt concentration are sufficiently understood. This review provides a comprehensive evaluation of the chromatographic conditions with a historical perspective on adopting and developing HILIC for the separation of nucleobases, nucleosides, nucleotides and oligonucleotides. The areas for more research and potential directions for future development activities are identified and discussed.

Evaluating the potential of hydrophilic interaction liquid chromatography for collagen peptide mapping analysis

This study presents a systematic approach for developing an innovative hydrophilic interaction liquid chromatography (HILIC) method for collagen peptide mapping analysis. The predominant post-translational modification (PTM) of collagen, proline hydroxylation, introduces polar hydroxyl groups throughout the collagen sequence, making HILIC a promising alternative to classical reversed-phase liquid chromatography (RPLC) approaches. This study employs sixteen model peptides, selected from in silico predicted tryptic peptides with zero missed cleavages and representing diverse physicochemical properties and structural motifs of collagen. The peptides were used as standards to conduct detailed chromatographic evaluation. Various HILIC stationary phases and mobile phases were systematically examined to identify optimal separation conditions for collagen peptides, contributing to a better understanding of peptide behavior in HILIC. The study also explores the effects of sample diluent and injection mode, comparing classical injection with the Performance Optimizing Injection Sequence (POISe), to determine their impact on HILIC performance. Introducing a plug of weak solvent (acetonitrile) prior to sample injection, effectively mitigates the mismatch in eluent strength between the fully aqueous sample diluent (resulting from tryptic digestion) and the mobile phase, addressing issues of peak distortion. Different injection volumes (from 0.5 to 8 µL) and acetonitrile ratios (1:1, 1:2, 1:5 and 1:10) were tested to optimize sample injection and increase sensitivity of collagen tryptic peptides. Following method optimization, HILIC was coupled with mass spectrometry (MS) to evaluate its effectiveness in analyzing collagen-digested samples. This evaluation included the assessment of peptide sequence coverage and the method ability to identify hydroxylation patterns, thereby demonstrating its potential for detailed peptide analysis.

Preparation and evaluation of a pyridine sulfonate betaine-based zwitterionic stationary phase for hydrophilic interaction chromatography

A zwitterionic stationary phase comprising pyridinium cations and sulfonate anions was successfully developed through thiol-ene click chemistry. Using seven polar small molecules as probes, the zwitterionic stationary phase showed high separation selectivity and excellent column efficiency (35,200-54,800 plates/m) compared with two commercial columns. The influence of water proportion, salt concentration, and pH in the mobile phase, and column temperature, on the retention of six polar compounds was examined. The retention mechanism was explored by three hydrophilic retention models, Tanaka test and linear solvation energy relationship analysis. For the analysis of sample dairy products (milk powder, milk, and yogurt), the stationary phase was operated in hydrophilic interaction chromatography mode without the addition of buffer salts, facilitating rapid and efficient detection and quantification of melamine. The LOD and LOQ are 0.04 mg⋅g-1 and 0.13 mg⋅g-1, respectively, and the recovery rate is 90.3 - 102.8 %. The zwitterionic stationary phase has the advantages of simple preparation, good method reproducibility, good selectivity and high precision.

Peptide retention time prediction for hydrophilic interaction liquid chromatography at acidic pH in formic-acid based eluents

Peptide separation selectivity was evaluated for hydrophilic interaction liquid chromatography (HILIC) ZIC-HILIC, ZIC-cHILIC, and XBridge Amide sorbents using formic acid as eluent additive (pH 2.7). Sequence-specific retention prediction algorithms were trained using retention datasets of ∼30,000 peptides for each column. Our retention models were able to attain ∼0.98 R2-value and yielded retention coefficients that can be probed to understand peptide-stationary phase interaction. Overall, the hydrophilicity for these columns decreased when the mobile phase changed pH from 4.5 to 2.7, when using 0.1 % formic acid in the mobile phase. The acidic residues became protonated, and the resultant hydrophilic interaction is dampened at the lower pH, leaving only the basic residues as the primary hydrophilic interactors. Hence, peptides of increasing charge have higher retention. In this comparison between the three columns, ZIC-HILIC has the highest chromatographic resolution between groups of peptides of different charge. From the position-dependent retention coefficients for ZIC-HILIC at pH 2.7, we found that the amino acids at the terminal positions of the peptide modulate the basicity of the N-terminal amino group or the C-terminal Arg/Lys for tryptic peptides. With respect to the separation orthogonality between HILIC and acidic pH RPLC for two dimensional separations, the orthogonality values were lower at pH 2.7 than operating HILIC at pH 4.5 for the first dimension. We also demonstrate that ZIC-HILIC was able to distinguish citrullinated and deamidated peptides based on predicted retention values.

Comprehensive Coverage of Glycolysis and Pentose Phosphate Metabolic Pathways by Isomer-Selective Accurate Targeted Hydrophilic Interaction Liquid Chromatography-Tandem Mass Spectrometry Assay

The accurate liquid chromatography-tandem mass spectrometry analysis of phosphorylated isomers from glycolysis and pentose phosphate pathways is a challenging analytical problem in metabolomics due to extraction problems from the biological matrix, adherence to stainless steel surfaces leading to tailing in LC, and incomplete separation of hexose and pentose phosphate isomers. In this study, we present a targeted HILIC-ESI-MS/MS method based on a BEH amide fully porous 1.7 μm particle column with an inert surface coating of column hardware and multiple reaction monitoring (MRM) acquisition fully covering the glycolysis and pentose phosphate pathway metabolites. To minimize contact of the phosphorylated analytes with stainless steel surfaces, a μ-ESI-MS probe with a hybrid electrode made of PEEKsil was employed. Optimized HILIC gradient elution conditions with 100 mM ammonium formate (pH 11) provided the separation of hexose monophosphate and pentose phosphate isomers. To ensure good retention time repeatability in HILIC, perfluoroalkoxy alkane bottles were used for the mobile phase (with sd over 60 runs between 0.01 and 0.02 min). For the quantitative assay, the U-13C-labeled cell extract was spiked prior to extraction by metal oxide-based affinity chromatography (MOAC) with TiO2 beads. The concentrations of the 24 targets were quantified in HeLa and human embryonic kidney (HEK293) cells. Erastin-induced ferroptosis in HEK293 cells was accompanied by enhanced levels of fructose-1,6-bis-phosphate, 2- and 3-phosphoglycerate, and 2,3-bis-phosphoglycerate.

Optimization of Plant Oxalate Quantification and Generation of Low-Oxalate Maize (Zea mays L.) through O7 Overexpression

Oxalate, the simplest dicarboxylic acid, is a prevalent antinutrient that chelates with various metals and can lead to the formation of kidney stones in humans. The accurate detection of the oxalate concentration in food and the cultivation of low-oxalate crops are important for enhancing public health. In this study, we established a high-throughput and highly sensitive technique for oxalate detection using ultra-high-performance liquid chromatographic-triple quadrupole tandem mass spectrometry (UPLC-QqQ-MS/MS). Additionally, we overexpressed the gene O7, which encodes oxalyl-CoA synthetase in the maize oxalate degradation pathway, resulting in O7-OE lines. By employing the UPLC-QqQ-MS/MS method to measure oxalate levels in these transgenic lines, we observed that the oxalate content in the kernels of O7-OE lines was reduced by approximately 43%, with a concurrent increase in some micronutrients such as zinc. Importantly, the transgenic maize showed normal seed storage compound accumulation or other agronomic characteristics. In summary, we developed a high-throughput detection method that advances oxalate measurement. Furthermore, by generating new maize germplasm with diminished oxalate, our work offers potential health advantages to consumers.

Understanding retention and intra-particle diffusivity of alkylsulfobetaine-bonded Ethylene Bridged Particles with different mesopore sizes for hydrophilic interaction liquid chromatography applications

The role of the average pore diameter (APD) of 1.7μm AtlantisTM Premier BEHTM Particles derivatized with a zwitterionic group (propylsulfobetaine) on the efficiency of their 2.1 × 50 mm hydrophilic interaction liquid chromatography (HILIC) packed columns is investigated experimentally. Van Deemter plots for toluene (neutral, hydrophobic), cytosine (neutral, polar), tosylate (negatively charged), bretylium and atenolol (positively charged) were measured on three HILIC columns packed with BEH Z-HILIC Particles having APDs of 95 Å, 130 Å, and 300 Å. The intraparticle diffusivities of the analytes across these three BEH Z-HILIC Particles were measured by the peak parking method. The experimental data reveal that the slope of the C-branch of the van Deemter plots can be reduced by factors of about 15 for toluene, 2.5 for cytosine, 6 for atenolol, 5 for tosylate, and 14 for bretylium with increasing the APD from 95 Å to 300 Å. This observation is explained by: (1) the reduced amount of the highly viscous water diffuse layer and subsequent increase of the amount of acetonitrile-rich eluent in the mesopores, (2) the localized electrostatic adsorption of the retained analytes onto the zwitterion-bonded BEH Particles, and (3) depletion/excess of the analytes into the water diffuse layer. A general model of intraparticle diffusivity was then proposed to account for the impact of the APD of Z-HILIC Particles on the solid-to-liquid mass transfer resistance of small molecules. The model highlights the relevance of the thickness of the water diffuse layer, the access of the bulk eluent into the mesopore, the localized electrostatic adsorption, and the partitioning constant of the retained analyte between the bulk eluent and the water diffuse layer.

Dysregulated Purinergic Signalling in Fragile X Syndrome Cortical Astrocytes

The symptoms of fragile X syndrome (FXS), caused by a single gene mutation to Fmr1, have been increasingly linked to disordered astrocyte signalling within the cerebral cortex. We have recently demonstrated that the purinergic signalling pathway, which utilizes nucleoside triphosphates and their metabolites to facilitate bidirectional glial and glial-neuronal interactions, is upregulated in cortical astrocytes derived from the Fmr1 knockout (KO) mouse model of FXS. Heightened Fmr1 KO P2Y purinergic receptor levels were correlated with prolonged intracellular calcium release, elevated synaptogenic protein secretion, and hyperactivity of developing circuits. However, due to the relative lack of sensitive and reproducible quantification methods available for measuring purines and pyrimidines, determining the abundance of these factors in Fmr1 KO astrocytes was limited. We therefore developed a hydrophilic interaction liquid chromatography protocol coupled with mass spectrometry to compare the abundance of intracellular and extracellular purinergic molecules between wildtype and Fmr1 KO mouse astrocytes. Significant differences in the concentrations of UDP, ATP, AMP, and adenosine intracellular stores were found within Fmr1 KO astrocytes relative to WT. The extracellular level of adenosine was also significantly elevated in Fmr1 KO astrocyte-conditioned media in comparison to media collected from WT astrocytes. Glycosylation of the astrocyte membrane-bound CD39 ectonucleotidase, which facilitates ligand breakdown following synaptic release, was also elevated in Fmr1 KO astrocyte cultures. Together, these differences demonstrated further dysregulation of the purinergic signalling system within Fmr1 KO cortical astrocytes, potentially leading to significant alterations in FXS purinergic receptor activation and cellular pathology.

Insights into the selectivity of polar stationary phases based on quantitative retention mechanism assessment in hydrophilic interaction chromatography

Hydrophilic interaction chromatography (HILIC) offers different selectivity than reversed-phase liquid chromatography (RPLC). However, our knowledge of the driving force for selectivity is limited and there is a need for a better understanding of the selectivity in HILIC. Quantitative assessment of retention mechanisms makes it possible to investigate selectivity based on understanding the underlying retention mechanisms. In this study, selected model compounds from the Ikegami selectivity tests were evaluated on different polar stationary phases. The study results revealed significant insights into the selectivity in HILIC. First, hydroxy and methylene selectivity is driven by hydrophilic partitioning; but surface adsorption for 2-deoxyuridine or 5-methyluridine reduces the selectivity factor. Furthermore, the retention of 2-deoxyuridine or 5-methyluridine by surface adsorption in combination with the phase ratio explain the difference in hydroxy or methylene selectivity observed among different stationary phases. Investigations on xanthine positional isomers (1-methylxanthine/3-methylxanthine, theophylline/theobromine) indicate that isomeric selectivity is controlled by surface adsorption; however, hydrophilic partitioning may contribute to resolution by enhancing overall retention. In addition, two pairs of nucleoside isomers (adenosine/vidarabine, 2'-deoxy and 3'-deoxyguanosine) provide an example that isomeric selectivity can also be controlled by hydrophilic partitioning if their partitioning coefficients are significantly different in HILIC. Although more data is needed, the current study provides a mechanistic based understanding of the selectivity in HILIC and potentially a new way to design selectivity tests.

Integrated metabolomic analysis and molecular docking: Unveiling the potential of Nephrolepis exaltata (L.) Schott phytocompounds for mosquito control via glutathione-S-transferase targeting

Plants contain a wide range of potential phytochemicals that are target-specific, and less toxic to human health. The present study aims to investigate the metabolomic profile of Nephrolepis exaltata (L.) Schott and its potential for mosquito control by targeting Glutathione-S-Transferase, focusing on the larvicidal activity against Culex pipiens. Crude extracts (CEs) were prepared using ethanol, ethyl acetate and n-hexane. CEs have been used for assessment of mosquitocidal bioassay. The metabolomic analyses for CEs were characterized for each CE by gas chromatography-mass spectrometry (GC-MS). The most efficient CE with the highest larval mortality and the least LC50 was the hexane CE. Then, alkaline phosphatase (ALP) activity, and glutathione-S-transferase (GST) activity were assessed in larvae treated with the hexane CE. The results demonstrated a decline in protein content, induction of ALP activity, and reduction in GST activity. Finally, molecular docking and dynamic simulation techniques were employed to evaluate the interaction between the hexane phytochemicals and the GST protein. D-(+)-Glucuronic acid, 3TMS derivative and Sebacic acid, 2TMS derivative showed best binding affinities to GST protein pointing to their interference with the enzyme detoxification functions, potentially leading to reduced ability to metabolize insecticides.

Quartz Crystal Microbalance as a Holistic Detector for Quantifying Complex Organic Matrices during Liquid Chromatography: 2. Compound-Specific Isotope Analysis

In carbon-compound-specific isotope analysis (carbon CSIA) of environmental micropollutants, purification of samples is often required to guarantee accurate measurements of a target compound. A companion paper has brought forward an innovative approach to couple a quartz crystal microbalance (QCM) with high-performance liquid chromatography (HPLC) for the online quantification of matrices during a gradient HPLC purification. This work investigates the benefit for isotope analysis of polar micropollutants typically present in environmental samples. Here, we studied the impact of the natural organic matter (NOM) on the isotopic integrity of model analytes and the suitability of the NOM-to-analyte ratio as a proxy for the sample purity. We further investigated limitations and enhancement of HPLC purification using QCM on C18 and C8 phases for single and multiple targets. Strong isotopic shifts of up to 3.3% toward the isotopic signature of NOM were observed for samples with an NOM-to-analyte ratio ≥10. Thanks to QCM, optimization of matrix removal of up to 99.8% of NOM was possible for late-eluting compounds. The efficiency of HPLC purification deteriorated when aiming for simultaneous purification of two or three compounds, leading to up to 2.5% less NOM removal. Our results suggest that one optimized HPLC purification can be achieved through systematic screening of 3 to 5 different gradients, thereby leading to a shift of the boundaries of accurate carbon CSIA by up to 2 orders of magnitude toward lower micropollutant concentrations.

The potential of polyaniline-coated stationary phase in hydrophilic interaction liquid chromatography-based solid-phase extraction for glycopeptide enrichment

Glycopeptide enrichment is a crucial step in glycoproteomic analysis, often achieved through solid-phase extraction (SPE) on polar stationary phases in hydrophilic interaction liquid chromatography (HILIC). This study explores the potential of polyaniline (PANI)-coated silica gel for enriching human immunoglobulin G (IgG). Experimental conditions were varied to assess their impact on glycopeptide enrichment efficiency, comparing PANI-cotton wool SPE with conventional cotton wool as SPE sorbents. Two formic acid concentrations (0.1% and 1%) in elution solvent were tested, revealing that higher concentrations led to earlier elution of studied glycopeptides, especially for sialylated glycopeptides. Substituting formic acid with acetic acid increased the interaction of neutral glycopeptides with the PANI-modified sorbent, while sialylated glycopeptides showed no significant change in enrichment efficiency. Acetonitrile concentration in the elution solvent (5%, 10%, and 20%) affected the enrichment efficiency with most glycopeptides eluting at the lowest acetonitrile concentration. The acetonitrile concentration in conditioning and washing solutions (65%, 75%, and 85%) played a crucial role; at 65% acetonitrile, glycopeptides were least retained on the stationary phase, and neutral glycopeptides were even detected in the flow-through fraction. This study shows the potential of in-house-prepared PANI-modified sorbents for SPE-HILIC glycopeptide enrichment, highlighting the crucial role of tuning experimental conditions in sample preparation to enhance enrichment efficiency and selectivity.

Comprehensive analysis of phospholipid in milk and their biological roles as nutrients and biomarkers

Phospholipids (PL) have garnered significant attention due to their physiological activities. Milk and other dairy products are important dietary sources for humans and have been extensively used to analyze the presence of PL by various analytical techniques. In this paper, the analysis techniques of PL were reviewed with the eight trigrams of phospholipidomics and a comprehensive fingerprint of 1295 PLs covering 8 subclasses in milk and other dairy products, especially. Technology is the primary productive force. Based on phospholipidomics technology, we further review the relationship between the composition of PL and factors that may be involved in processing and experimental operation, and emphasized the significance of the biological role played by PL in dietary supplements and biomarkers (production, processing and clinical research), and providing the future research directions.

Retention behavior of carbohydrates on metal loaded chelating stationary phase under conditions of hydrophilic interaction liquid chromatography

The chromatographic retention of carbohydrates on chelating stationary phase loaded with different metal ions was studied under conditions of hydrophilic interaction chromatography (HILIC). The chelating stationary phases represented silica microparticles with immobilized 2-hydroxyethyliminodiacetic acid (HEIDA) groups in loose form and saturated with Ca2+, Pb2+, and La3+form. The role of loaded metal ion, the acetonitrile and methanol content in the mobile phase, buffer pH and column temperature on the retention of l-(+)-arabinose, d-(+)-maltose, l-(+)-rhamnose, d-(+)-lactose, d-(+)-xylose, glucose, fructose, sucrose, mannose, maltotriose and d-(+) raffinose was studied. The investigation was mainly focused on possible contribution of the complexation in the stationary phase on retention of carbohydrates as well as on effect of the presence metal ion in HEIDA-silica on resulting HILIC behavior of. It is shown that adsorbents with immobilized metal complexes have a good potential for the separation of organic ligands under HILIC mode.

Development of targeted hydrophilic interaction liquid chromatography-tandem mass spectrometry method for acyl-Coenzyme A covering short- to long-chain species in a single analytical run

Acyl-CoAs play a significant role in numerous physiological and metabolic processes making it important to assess their concentration levels for evaluating metabolic health. Considering the important role of acyl-CoAs, it is crucial to develop an analytical method that can analyze these compounds. Due to the structural variations of acyl-CoAs, multiple analytical methods are often required for comprehensive analysis of these compounds, which increases complexity and the analysis time. In this study, we have developed a method using a zwitterionic HILIC column that enables the coverage of free CoA and short- to long-chain acyl-CoA species in one analytical run. Initially, we developed the method using an LC-QTOF instrument for the identification of acyl-CoA species and optimizing their chromatography. Later, a targeted HILIC-MS/MS method was created in scheduled multiple reaction monitoring mode using a QTRAP MS detector. The performance of the method was evaluated based on various parameters such as linearity, precision, recovery and matrix effect. This method was applied to identify the difference in acyl-CoA profiles in HepG2 cells cultured in different conditions. Our findings revealed an increase in levels of acetyl-CoA, medium- and long-chain acyl-CoA while a decrease in the profiles of free CoA in the starved state, indicating a clear alteration in the fatty acid oxidation process.

Improved sample introduction approach in hydrophilic interaction liquid chromatography to avoid breakthrough of proteins

When therapeutic proteins are analysed under hydrophilic interaction liquid chromatography (HILIC) conditions, there is an inherent mismatch between the sample diluent (proteins must be solubilised in aqueous media) and the mobile phase, which is mostly composed of aprotic solvent (acetonitrile). This difference in eluent strength between sample diluent and mobile phase is responsible for severe analyte breakthrough and peak distortion. As demonstrated with therapeutic proteins of different sizes (insulin of 6 kDa, anakinra of 17 kDa and rituximab subunits of 25 and 50 kDa), only very small volumes of 0.1-0.2 µL can be injected without breakthrough effects, when performing rapid analysis on short HILIC columns of 20-50 mm, leading to poor sensitivity. In order to avoid the undesired effect of the strong sample diluent, a special injection program should be preferred. This consists in the addition and automatic injection of a defined volume of weak solvent (acetonitrile) along with the sample to increase retention factors during sample loading. Various injection programs were tested, including the addition of a pre-injection or post-injection or both (bracketed injection) of acetonitrile plugs. Several weak to strong injection solvent ratios of 1:1, 1:2, 1:4 and 1:10 were tested. Our work proves that the addition of a pre-plug solvent with a weak vs. strong injection solvent ratio of 1:10 is a valuable strategy to inject relatively large volumes of proteins in HILIC, regardless of column dimensions, thus maximising sensitivity. No peak deformation or breakthrough was observed under these conditions. However, it is important to note that peak broadening (40 % larger peaks) was observed when the injection program increased the injection solvent ratio from 1:1 to 1:10. Finally, this strategy was applied to a wide range of therapeutic mAb products with different physico-chemical properties. In all cases, relatively large volumes can be successfully injected onto small volume HILIC columns using a purely aqueous sample diluent, as long as an appropriate (weak) solvent pre-injection is applied.

Hydrophilic Partitioning or Surface Adsorption? A Quantitative Assessment of Retention Mechanisms for Hydrophilic Interaction Chromatography (HILIC)

Retention mechanisms in HILIC have been investigated and reported in literature. However, the current understanding of retention mechanisms is qualitative and lacks quantitative details. Previously, mechanism elucidation was based on indirect evidence, and unambiguous assignment of retention mechanisms has not been reported based on direct data. This study aims to quantitatively determine the contributions of two major retention mechanisms in HILIC, hydrophilic partitioning and surface adsorption to the overall retention of neutral compounds. Using the methodologies we developed previously, the phase ratio for adsorbed water layer and distribution coefficients were measured and used to calculate the retention factors contributed by hydrophilic partitioning. The methodology allows the determination of the contribution of surface adsorption simultaneously. The evaluation of five test compounds demonstrates that the retention may be controlled by hydrophilic partitioning, surface adsorption or both depending on compound characteristics. Quantitative assessment of retention mechanisms also makes it possible to better understand the effect of acetonitrile on retention in HILIC.

Application of chromatography in purification and structural analysis of natural polysaccharides: A review

Polysaccharides are widely distributed in natural sources from monocytic microorganisms to higher animals, and are found in a variety of biological activities in recent decades. Natural polysaccharides have the characteristics of large molecular weight, diverse composition, and complex structure, so their purification and structural analysis are difficult issues in research. Chromatography as a powerful separation technique, plays an irreplaceable role in the separation and structural analysis of natural polysaccharides, especially in the purification of polysaccharides, the separation of hydrolysates, and the analysis of monosaccharide composition. The separation mechanisms and application of different chromatographic methods in the studies of polysaccharides were summarized in this review. Moreover, the advantages and drawbacks of various chromatography methods were discussed as well.

A novel hydrophilic polymer-coated magnetic nanomaterial based on the HILIC strategy for fast separation of glycopeptides and glycosylated exosomes

Novel hydrophilic poly(N, N-methylenebisacrylamide/1,2-epoxy-5-hexene) coated magnetic nanospheres functionalized with 2-aminopurine (denoted as Fe3O4@poly(MBA/EH)@2AP) for enriching glycopeptides and glycosylated exosomes were successfully obtained using a simple and green method on the basis of the HILIC (hydrophilic interaction liquid chromatography) enrichment strategy. The high density of polar groups endows the material with amazing hydrophilicity, enabling the nanomaterial to successfully capture glycopeptides and glycosylated exosomes within 1 min. Meanwhile, the materials demonstrated great sensitivity (0.01 fmol/μL), good loading capability (125 μg/mg), high selectivity (BSA:HRP = 1000:1), and repeatability (more than 10 times). Besides, the material was applied in the analysis of bio-samples, a total of 290 glycosylated peptides and 184 glycosylation sites mapping to 185 glycoproteins were identified in the serum of uremic patients. Besides, 42 glycopeptides were enriched from the saliva of healthy people. At the same time, it was verified by TEM and western blot that the complete glycosylated exosomes were successfully captured from the serum of the uremic patients. All experiments have demonstrated that Fe3O4@poly(MBA/EH)@2AP has a promising future in practical applications.

A Predictive Model to Correlate Amino Acids and Aromatic Compounds in Calabrian Honeys

To better understand the biochemistry of the organoleptic properties of honey influencing its commercial value, a predictive model for correlating amino acid profiles to aromatic compounds was built. Because the amino acid composition of different varieties of honey plays a key role as a precursor of specific aroma bouquets, it is necessary to relate the amino acid typesetting to aromatic molecules. A selection of unifloral honeys produced in Calabria, South Italy, were used, and a new methodology based on the use of HILIC-UHPLC-ESI-MS/MS and HS-SPME-GC-MS combined with multivariate processing has been developed. This study, carried out for the first time on honey, shows its excellent potential as a modern analytical tool for a rapid multicomponent analysis of food-quality indicators. Data obtained showed strong positive linear correlations between aldehydes and isoleucine, valine, leucine, and phenylalanine. Furans are correlated with isoleucine, leucine, and phenylalanine; hydrocarbons with serine, glutamic acid, and aspartic acid; and ketones with serine, alanine, glutamine, histidine, asparagine, and lysine. Alcohols were more associated with tyrosine than esters with arginine. Proline, tryptophan, and threonine showed poor correlations with all the classes of aroma compounds.

Isomeric separation of native N-glycans using nano zwitterionic- hydrophilic interaction liquid chromatography column

Changes in the expression of glycan isomers have been implicated in the development and progression of several diseases. However, the analysis of structurally diverse isomeric N-glycans by LC-MS/MS is still a major analytical challenge, particularly due to their large number of possible isomeric conformations. Common approaches derivatized the N-glycans to increase their hydrophobicity and to gain better detection in the MS system. Unfortunately, glycan derivatization is time-consuming and, in many cases, adds complexity because of the multiple reaction and cleaning steps, incomplete chemical labeling, possible degradation, and unwanted side reactions. Thus, analysis of native glycans, especially for samples with low abundance by LC-MS/MS, is desirable. Normal phase chromatography, which employs HILIC stationary phase, has been commonly employed for the identification and separation of labeled glycans. In this study, we focused on achieving efficient isomeric separation of native N-glycans using a nano ZIC-HILIC column commonly employed to separate labeled glycans and glycopeptides. Underivatized sialylated and oligomannose N-glycans derived from bovine fetuin and Ribonuclease B were initially utilized to optimize chromatographic conditions, including column temperature, pH of mobile phases, and gradient elution time. The optimized condition was then applied for the isomeric separation of native N-glycans derived from alpha-1 acid glycoprotein, as well as from biological samples. Finally, we confirmed the stability and reproducibility of the ZIC-HILIC column by performing run-to-run comparisons of the full width at half height (FWHM) and retention time on different N-glycans. The variability in FWHM was less than 0.5 min, while that of retention time was less than 1.0 min with %RSD less than 1.0%.

Enantiomeric analysis of drugs in water samples by using liquid-liquid microextraction and nano-liquid chromatography

The nano-LC technique is increasingly used for both fast studies on enantiomeric analysis and test beds of novel stationary phases due to the small volumes involved and the short conditioning and analysis times. In this study, the enantioseparation of 10 drugs from different families was carried out by nano-LC, utilizing silica with immobilized amylose tris(3-chloro-5-methylphenylcarbamate) column. The effect on chiral separation caused by the addition of different salts to the mobile phase was evaluated. To simultaneously separate as many enantiomers as possible, the effect of buffer concentration in the mobile phase was studied, and, to increase the sensitivity, a liquid-liquid microextraction based on the use of isoamyl acetate as sustainable extraction solvent was applied to pre-concentrate four chiral drugs from tap and environmental waters, achieving satisfactory recoveries (>70%).

Multidimensional Separations in Top-Down Proteomics

Top-down proteomics (TDP) identifies, quantifies, and characterizes proteins at the intact proteoform level in complex biological samples to understand proteoform function and cellular mechanisms. However, analyzing complex biological samples using TDP is still challenging due to high sample complexity and wide dynamic range. High-resolution separation methods are often applied prior to mass spectrometry (MS) analysis to decrease sample complexity and increase proteomics throughput. These separation methods, however, may not be efficient enough to characterize low abundance intact proteins in complex samples. As such, multidimensional separation techniques (combination of two or more separation methods with high orthogonality) have been developed and applied that demonstrate improved separation resolution and more comprehensive identification in TDP. A suite of multidimensional separation methods that couple various types of liquid chromatography (LC), capillary electrophoresis (CE), and/or gel electrophoresis-based separation approaches have been developed and applied in TDP to analyze complex biological samples. Here, we reviewed multidimensional separation strategies employed for TDP, summarized current applications, and discussed the gaps that may be addressed in the future.

Studies on the retention mechanism of solutes in hydrophilic interaction chromatography using stoichiometric displacement theory II. HILIC/RPLC dual-retention mechanism of solutes in hydrophilic interaction chromatography over the entire range of water concentration in mobile phase

This paper is a continuation of research into the retention behavior and mechanism of solutes in hydrophilic interaction chromatography (HILIC) using stoichiometric displacement theory (SDT). A HILIC/reversed-phase liquid chromatography (RPLC) dual-retention mechanism was studied in detail using a β-CD HILIC column. The retention behaviors of three groups of solutes with varying polarities were studied over the entire range of water concentrations in the mobile phase on the β-CD column, resulting in the formation of "U-shape" curves when lgk' was plotted against lg[H₂O]. Additionally, the effect of hydrophobic distribution coefficient lgP_O/W on the retention behaviors of solutes in HILIC and RPLC modes was also examined. A four-parameter equation derived from the SDT-R was found to accurately describe the "U-shaped" curves of solutes with RPLC/HILIC dual-retention mechanisms on β-CD column. The theoretical lgk' values of solutes calculated using the equation were found to be in agreement with their experimental values, with correlation coefficients greater than 0.99. This indicates that the four-parameter equation derived from SDT-R can effectively describe the retention behaviors of solutes over the entire range of water concentrations in the mobile phase in HILIC. As such, SDT can be used as a theoretical guide for the development of HILIC, including the exploration of new dual-function stationary phases to enhance separation efficiency.

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.

Silica microparticles modified with ionic liquid bonded chitosan as hydrophilic moieties for preparation of high-performance liquid chromatographic stationary phases

Two novel stationary phases, 1-(4-bromobutyl)-3-methylimidazolium bromide bonded chitosan modified silica and 1-(4-bromobutyl)-3-methylimidazolium bromide bonded chitosan derivatized calix[4]arene modified silica stationary phase, were synthesized using 1-(4-bromobutyl)-3-methylimidazolium bromide bonding chitosan as a polarity regulator solving the limitation of the strong hydrophobicity of calixarene in the application of hydrophilic field. The resulting materials were characterized by solid-state nuclear magnetic resonance, Fourier-transform infrared spectra, scanning electron microscopy, elemental analysis, and thermogravimetric analysis. Based on the hydrophilicity endowed by 1-(4-bromobutyl)-3-methylimidazolium bromide bonded chitosan, the retention mode of ILC-Sil and ILCC4-Sil could be effectively switched from the hydrophilic mode to a hydrophilic/hydrophobic mixed mode and could simultaneously provide various interactions with solutes, including hydrophilic, π-π, ion-exchange, inclusion, hydrophobic, and electrostatic interactions. On the basis of these interactions, successful separation and higher shape selectivity were achieved among compounds that vary in polarity under both reverse-phase and hydrophilic interactive liquid chromatography conditions. Moreover, the ILCC4-Sil was successfully applied to the determination of morphine in actual samples using solid-phase extraction and mass spectrometry. The LOD and LOQ were 15 pg/mL and 54 pg/mL, respectively. This work presents an exceptionally flexible adjustment strategy for the retention and selectivity of a silica stationary phase by tuning the modification group.

Retention and mass transfer properties of the series of unbonded, amide-bonded, and alkylsulfobetaine-bonded ethylene bridged hybrid hydrophilic interaction liquid chromatography columns

This work investigates the link between the retentivity and the stationary phase to mobile phase mass transfer resistance of hydrophilic interaction liquid chromatography (HILIC) columns packed with the same base ethylene-bridged hybrid particles (BEH). The retention volumes, the plate heights, and the volume of the adsorbed water layer were measured for the ACQUITY^TM UPLC^TM BEH^TM 130 Å HILIC Column (unbonded BEH), ACQUITY UPLC BEH 130 Å Amide Column (amide group attached), and Atlantis^TM Premier BEH 95 Å Z-HILIC (zwitterionic group attached) Column. The method of Guo (toluene retention volumes in pure acetonitrile and in the HILIC eluent) was validated from the UNIFAC group-contribution method and applied to measure accurately the water layer volumes in these columns. A strong correlation was found between the retention volumes of most neutral polar analytes and the volume of the water layer adsorbed in the HILIC column. The fraction of the pore volume occupied by the water layer increases significantly from the BEH HILIC Column to the BEH Amide Column, and to the BEH Z-HILIC Column. This is explained by the water solvation of the attached ligands in the pore volume of the BEH Particles and to the smaller average mesopore size of the BEH Z-HILIC Particles. A second and strong correlation is also observed between the water content in the HILIC particle and the stationary phase to mobile phase mass transfer resistance of the HILIC columns at high mobile phase linear velocities. The measured intra-particle diffusivity normalized to the bulk diffusion coefficient decreased from 0.33 (BEH HILIC Column) to 0.10 (BEH Amide Column) and to only 0.03 (BEH Z-HILIC Column) for comparable retention of cytosine. These results are fully consistent with the higher viscosity of the internal eluent (higher water content) and higher internal obstruction for diffusion (smaller mesopores and internal porosity) in the BEH Z-HILIC Particles. Still, in gradient elution mode, the peak capacity was found to be 18% higher for the BEH Z-HILIC Column than that on the BEH Amide Column because the retention factors at elution were smaller when maintaining the same analysis time and starting eluent composition.

Further Evaluation of the Base Stability of Hydrophilic Interaction Chromatography Columns Packed with Silica or Ethylene-Bridged Hybrid Particles

One of the fundamental attributes of a liquid chromatography column is its stability when exposed to acidic and basic mobile phases. However, there have been relatively few reports to date on the stability of hydrophilic interaction chromatography (HILIC) columns. Here, we report the results of stability evaluations carried out for HILIC columns packed with ethylene-bridged hybrid or silica particles using accelerated conditions, employing a 100% aqueous pH 11.3 ammonium bicarbonate mobile phase at 70 °C. Under these conditions, the primary mode of column failure was a loss of efficiency due to the formation of voids resulting from the hydrolysis of the particles. We investigated the dependence of stability on the surface area of both unbonded and sulfobetaine-bonded ethylene-bridged hybrid stationary phases. The results show a clear trend of stability increasing as the surface area decreases. Several commercially available HILIC columns that are recommended for use with high-pH mobile phases were also evaluated. The results show times to 50% loss of the initial efficiency ranging from 0.3 to 9.9 h. Columns containing unbonded, sulfobetaine-bonded or diol-bonded ethylene-bridged hybrid stationary phases had longer lifetimes than amino-bonded silica or sulfobetaine-bonded, hybrid-coated, superficially porous silica columns.

MS-based glycomics and glycoproteomics methods enabling isomeric characterization

Glycosylation is one of the most significant and abundant posttranslational modifications in mammalian cells. It mediates a wide range of biofunctions, including cell adhesion, cell communication, immune cell trafficking, and protein stability. Also, aberrant glycosylation has been associated with various diseases such as diabetes, Alzheimer's disease, inflammation, immune deficiencies, congenital disorders, and cancers. The alterations in the distributions of glycan and glycopeptide isomers are involved in the development and progression of several human diseases. However, the microheterogeneity of glycosylation brings a great challenge to glycomic and glycoproteomic analysis, including the characterization of isomers. Over several decades, different methods and approaches have been developed to facilitate the characterization of glycan and glycopeptide isomers. Mass spectrometry (MS) has been a powerful tool utilized for glycomic and glycoproteomic isomeric analysis due to its high sensitivity and rich structural information using different fragmentation techniques. However, a comprehensive characterization of glycan and glycopeptide isomers remains a challenge when utilizing MS alone. Therefore, various separation methods, including liquid chromatography, capillary electrophoresis, and ion mobility, were developed to resolve glycan and glycopeptide isomers before MS. These separation techniques were coupled to MS for a better identification and quantitation of glycan and glycopeptide isomers. Additionally, bioinformatic tools are essential for the automated processing of glycan and glycopeptide isomeric data to facilitate isomeric studies in biological cohorts. Here in this review, we discuss commonly employed MS-based techniques, separation hyphenated MS methods, and software, facilitating the separation, identification, and quantitation of glycan and glycopeptide isomers.

(Glycan Binding) Activity‐Based Protein Profiling in Cells Enabled by Mass Spectrometry‐Based Proteomics

The presence of glycan modifications at the cell surface and other locales positions them as key regulators of cell recognition and function. However, due to the complexity of glycosylation, the annotation of which proteins bear glycan modifications, which glycan patterns are present, and which proteins are capable of binding glycans is incomplete. Inspired by activity-based protein profiling to enrich for proteins in cells based on select characteristics, these endeavors have been greatly advanced by the development of appropriate glycan-binding and glycan-based probes. Here, we provide context for these three problems and describe how the capability of molecules to interact with glycans has enabled the assignment of proteins with specific glycan modifications or of proteins that bind glycans. Furthermore, we discuss how the integration of these probes with high resolution mass spectrometry-based technologies has greatly advanced glycoscience.

Isomer selectivity of one- and two-dimensional approaches of mixed-mode and hydrophilic interaction liquid chromatography coupled to tandem mass spectrometry for sugar phosphates of glycolysis and pentose phosphate pathways

In this study, the chromatographic behavior of mixed-mode and hydrophilic interaction liquid chromatography (HILIC) with the mixed-mode HILIC/strong anion-exchange (SAX) column HILICpak VT-50 2D and the two HILIC columns Atlantis Premier BEH Z-HILIC and Acquity Premier BEH Amide was assessed with regard to their separation capability of the metabolites from the glycolysis and pentose phosphate pathways. Chromatographic conditions were evaluated with the aim of achieving separation of the isomeric glycolytic phosphorylated carbohydrate metabolites free from isomeric interferences and thus allowing for selective targeted analysis by liquid chromatography with tandem mass spectrometry (MS/MS) using multiple reaction monitoring acquisition. The effects of pH values (8.0/9.0/10.0) of the ammonium bicarbonate buffer and gradient time were investigated during HILIC-MS/MS analysis, with the optimal conditions found at pH = 10.0. Separation of the pentose phosphate isomers (ribose 5- and 1-phosphate, xylulose 5-phosphate and ribulose 5-phosphate) was achieved on the mixed-mode HILIC/SAX (HILICpak VT-50 2D) column and HILIC BEH Amide column. Column performance was evaluated based on the direct comparison of chromatographic parameters, i.e. peak width at 50% and peak tailing factors of the individual metabolites. Parity plots were generated allowing a direct comparison between the normalized retention times and assessment of orthogonality of all 3 stationary phases evaluated. Separation of 7 biologically relevant hexose monophosphates metabolites turned out to be challenging by HILIC-MS/MS, with the BEH Amide providing the best individual results for such a separation. However, fructose 6-phosphate and glucose 1-phosphate co-eluted. Therefore, an on-line heart-cutting HILIC-Mixed Mode 2D-LC-QToF experiment was conducted, allowing the separation of this critical isomer pair. In this setup, the BEH Amide column in the ¹D separated the majority of target metabolites, while a heart-cut of the peak from totally coeluted fructose 6-phosphate and glucose 1-phosphate was separated in the ²D with HILICpak VT50-2D column, thus allowing undisturbed determination of the glycolytic phosphorylated carbohydrate metabolites due to their chromatographic separation from hexose monophosphate metabolites. The assay specificity towards 7 common hexose monophosphates was characterized (glucose 1- and 6-phosphate, galactose 1- and 6-phosphate, fructose 6-phosphate, mannose 1- and 6-phosphate). The selectivity of some rare hexose monophosphates (allose 6-phosphate, tagatose 6-phosphate, sorbose 1-phosphate) was also tested.

A Compendium of the Principal Stationary Phases Used in Hydrophilic Interaction Chromatography: Where Have We Arrived?

Hydrophilic interaction liquid chromatography (HILIC) today is a well-known and largely applied technique to analyse polar compounds such as pharmaceuticals, metabolites, proteins, peptides, amino acids, oligonucleotides, and carbohydrates. Due to the large number of stationary phases employed for HILIC applications, this review aims to help the reader in choosing a proper stationary phase, which often represents the critical point for the success of a separation. A great offer is present for achiral applications in contrast to the chiral phases developed for HILIC enantioseparations. In the last case, up-to-date solutions are presented.

Prediction of polarity-dependent environmental behaviors of humic substances (HS) using a HS hydrophobicity index based on hydrophilic interaction chromatography

A variety of analytical methods have been applied to describe the properties of aquatic humic substances (HS). However, there are only a few methods available to probe HS hydrophobicity because of the heterogeneous character of HS. In this study, hydrophilic interaction chromatography (HILIC) equipped with a UV detector was employed to describe the heterogeneous distribution of HS with respect to its hydrophobicity and to suggest a representative HS hydrophobicity index. To this end, various mobile phases were explored to achieve the optimal separation capability of HILIC. The highest resolution was obtained with a mobile phase comprising acetonitrile and water at a ratio of 70:30 (v:v). A calibration curve was successfully constructed using eight different HS precursor compounds, which allowed for the successful conversion of the retention time (RT) into the octanol-water partition coefficient (K_ow) (log K_ow = -2.83 × (RT) + 17.44, R² = 0.950). Several possible HS hydrophobicity indices were derived from the HILIC chromatogram. Among those, the weight-average log K_OW value exhibited the strongest negative correlation with the well-known polarity index, (O + N)/C ratios, of seven reference HS samples. This new HILIC-based index (i.e., average log K_OW) also presented a good relationship with the HS binding coefficients with pyrene as well as the extent of HS adsorption onto kaolinite at a given solution chemistry (i.e., at a high ionic strength and a neutral pH), both of which are known to be largely governed by the hydrophobic nature of HS. This study demonstrated that the average K_OW value based on HILIC is an intuitive and robust HS hydrophobicity index to fully represent the heterogeneous distribution of hydrophobicity within a bulk HS and could be applied to predict many environmental behaviors related to HS hydrophobicity or HS polarity.

Contribution of ionic interactions to stationary phase selectivity in hydrophilic interaction chromatography

We compared the separation selectivities of 19 different hydrophilic interaction chromatography columns. The stationary phases included underivatized silica and hybrid particles, cyano-bonded silica, materials with neutral ligands such as amide, diol, pentahydroxy, and urea, zwitterionic sorbents, and mixed-mode materials with amine functionalities. A set of 77 small molecules was used to evaluate the columns. We visualized the retention behavior of the different columns using retention time correlation plots. The analytes were classified as cations, anions, or neutral based on their estimated charge under the separation conditions. This involved adjusting the dissociation constants of the analytes for the acetonitrile content of the mobile phase and experimentally determining the pH of the mobile phase containing 70% acetonitrile. The retention correlation plots show that the selectivity differences strongly depended on ionic interactions. Comparisons of the neutral stationary phases (e.g., diol vs. amide) showed more similar selectivity than did comparisons of neutral columns versus columns with cation or anion exchange activity (bare silica or amine columns, respectively). The zwitterionic columns did not behave as perfectly neutral. The correlation plots indicated that they exhibited either cation or anion exchange activity, although to a lesser degree than the silica and amine-containing stationary phases.

Recognition in the Domain of Molecular Chirality: From Noncovalent Interactions to Separation of Enantiomers

It is not a coincidence that both chirality and noncovalent interactions are ubiquitous in nature and synthetic molecular systems. Noncovalent interactivity between chiral molecules underlies enantioselective recognition as a fundamental phenomenon regulating life and human activities. Thus, noncovalent interactions represent the narrative thread of a fascinating story which goes across several disciplines of medical, chemical, physical, biological, and other natural sciences. This review has been conceived with the awareness that a modern attitude toward molecular chirality and its consequences needs to be founded on multidisciplinary approaches to disclose the molecular basis of essential enantioselective phenomena in the domain of chemical, physical, and life sciences. With the primary aim of discussing this topic in an integrated way, a comprehensive pool of rational and systematic multidisciplinary information is provided, which concerns the fundamentals of chirality, a description of noncovalent interactions, and their implications in enantioselective processes occurring in different contexts. A specific focus is devoted to enantioselection in chromatography and electromigration techniques because of their unique feature as "multistep" processes. A second motivation for writing this review is to make a clear statement about the state of the art, the tools we have at our disposal, and what is still missing to fully understand the mechanisms underlying enantioselective recognition.

Retention mechanisms of imidazoline and piperazine-related compounds in non-aqueous hydrophilic interaction and supercritical fluid chromatography based on chemometric design and analysis

The experimental design methodology based on central composite design of experiments was applied to compare the retention mechanisms in supercritical fluid chromatography (SFC) and non-aqueous hydrophilic interaction liquid chromatography (NA-HILIC). The selected set consists of 26 compounds that belong to imidazoline and serotonin receptor ligands. The different chemometric tools (multiple linear regression, principal component analysis, parallel factor analysis) were used to examine the retention, as well as to identify the most significant retention mechanisms. The retention mechanism was investigated on two different stationary phases (diol, and mixed-mode diol). In NA-HILIC, the mobile phase contains acetonitrile as a main component, and methanolic solution of ammonium formate (+ 0.1% of formic acid) as a modifier. The same mobile phase modifier was used in SFC, with a difference in the main component of the mobile phase which was CO₂. The retention behaviour differs significantly between HILIC and SFC conditions. The retention pattern in HILIC mode was more partition-like, while in SFC the solute-sorbent interactions allowed retention. The retention mechanism between mixed-mode diol and the diol phases varies depending on the applied chromatographic mode, e.g., in HILIC the type of stationary phase significantly affects the elution order, while in SFC this was not the case. The HILIC retention behaviour was influenced by the number of tertiary amines-aliphatic, and N atom-centred fragments in tested compounds. On the other hand, the number of pyrrole and pyridine rings in the structure of the compound showed correlation with their SFC retention, simultaneously increasing the molecular weight and rapid elution of larger compounds. It was found that temperature surprisingly plays a major role in SFC mode. The increase in temperature reduces the relative contribution of enthalpy factors to total retention, so the separation in SFC was more entropy-controlled. For further pharmaceutical research and optimization, the SFC would be considered more beneficial compared to HILIC since it gives good selectivity in separation of chosen impurities.

A story of peptides, lipophilicity and chromatography - back and forth in time

Peptides, as part of the beyond the rule of 5 (bRo5) chemical space, represent a unique class of pharmaceutical compounds. Because of their exceptional position in the chemical space between traditional small molecules (molecular weight (MW) < 500 Da) and large therapeutic proteins (MW > 5000 Da), peptides became promising candidates for targeting challenging binding sites, including even targets traditionally considered as undruggable - e.g. intracellular protein-protein interactions. However, basic knowledge about physicochemical properties that are important for a drug to be membrane permeable is missing but would enhance the drug discovery process of bRo5 molecules. Consequently, there is a demand for quick and simple lipophilicity determination methods for peptides. In comparison to the traditional lipophilicity determination methods via shake flask and in silico prediction, chromatography-based methods could have multiple benefits such as the requirement of low analyte amount, insensitivity to impurities and high throughput. Herein we elucidate the role of peptide lipophilicity and different lipophilicity values. Further, we summarize peptide analysis via common chromatographic techniques, in specific reversed phase liquid chromatography, hydrophilic interaction liquid chromatography and supercritical fluid chromatography and their role in drug discovery and development process.

Evaluation of the Base Stability of Hydrophilic Interaction Chromatography Columns Packed with Silica or Ethylene-Bridged Hybrid Particles

Stability as a function of mobile phase pH is an important consideration when selecting a chromatographic column. While the pH stability of reversed-phase columns is widely studied, there are relatively few reports of the stability of hydrophilic interaction chromatography (HILIC) columns. We evaluated the stability of silica and ethylene-bridged hybrid HILIC columns when used with mobile phases containing basic buffers. The predominant mode of column degradation observed in our studies was a decrease in efficiency due to voiding, resulting from the hydrolysis of the silica particles. Associated with this were increases in tailing factors. Retention factor changes were also noted but were smaller than the efficiency losses. The dependence of the rate of efficiency decrease on the key variables of temperature, mobile phase pH and water content were studied for an unbonded silica column. The effect of the acetonitrile concentration on the pH of the mixed aqueous/acetonitrile mobile phases was also investigated. Using conditions found to cause a 50% decrease in efficiency after approximately five hours of exposure to the basic solution, we evaluated eight different commercially available HILIC columns containing silica or ethylene-bridged hybrid particles. The results show large differences between the stability of the silica and ethylene-bridged hybrid particle stationary phases, with the latter exhibiting greater stability.