Fragmentation characteristics-based nontargeted screening method of exogenous chemical residues in animal-derived foods using reversed-phase and hydrophilic interaction liquid chromatography-high-resolution mass spectrometry

Fragmentation characteristics are crucial for nontargeted screening to discover and identify unknown exogenous chemical residues in animal-derived foods. In this study, first, fragmentation characteristics of 51 classes of exogenous chemical residues were summarized based on experimental mass spectra of standards in reversed-phase and hydrophilic interaction liquid chromatography-high-resolution mass spectrometry (MS) and mass spectra from the MassBank of North America (MoNA) library. According to the proportion of fragmentation characteristics to the total number of chemical residues in each class, four screening levels were defined to classify 51 classes of chemical residues. Then, a nontargeted screening method was developed based on the fragmentation characteristics. The evaluation results of 82 standards indicated that more than 90 % of the chemical residues with MS/MS spectra can be identified at concentrations of 100 and 500 μg/kg, and about 80 % can be identified at 10 μg/kg. Finally, the nontargeted screening method was applied to 16 meat samples and 21 egg samples as examples. As a result, eight chemical residues and transformation products (TPs) of 5 classes in the exemplary samples were found and identified, in which 3 TPs of azithromycin were identified by fragmentation characteristics-assisted structure interpretation. The results demonstrated the practicability of the nontargeted screening method for routine risk screening of food safety.

Preparation and evaluation of a piperidinium-sulfonate based zwitterionic monolith for HILIC separation

In this study, a novel piperidinium-sulfonate based zwitterionic hydrophilic monolith was prepared through thermally initiated co-polymerization of a piperidinium-sulfonate monomer 3-(4-((methacryloyloxy)methyl)-1-methylpiperidin-1-ium-1-yl)propane-1-sulfonate (MAMMPS), and a hydrophilic crosslinker N,N'-methylenebisacrylamide (MBA) using n-propanol and H2O as porogenic system. Satisfactory mechanical and chemical stabilities, good repeatability and high column efficiency (120,000 N/m) were obtained on the optimal monolith. The resulting poly(MAMMPS-co-MBA) monolith showed a typical HILIC retention behavior over an ACN content range between 5 and 95 %. Furthermore, this column exhibited good separation performance for various polar compounds. Compared to quaternary ammonium-sulfonate based zwitterionic hydrophilic monolith, i.e. poly(N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl)ammonium betaine-co-MBA), the poly(MAMMPS-co-MBA) monolith displayed stronger retention and better selectivity for the tested phenolic and amine compounds at different pH conditions. Finally, this column was applied for the separation of six sulfonamide antibiotics, and the analytical characteristics of the method were evaluated in terms of precision, repeatability, limits of detection (LOD) and quantitation (LOQ). Overall, this study not only developed a novel HILIC monolithic column, but also proved the potential of piperidinium-sulfonate based zwitterionic chemistry as stationary phase, which further increased the structure diversity of zwitterionic HILIC stationary phases.

IgG glycopeptide enrichment using hydrophilic interaction chromatography-based solid-phase extraction on an aminopropyl column

The sample preparation step is pivotal in glycoproteomic analysis. An effective approach in glycoprotein sample preparation involves enriching glycopeptides by solid-phase extraction (SPE) using polar stationary phases in hydrophilic interaction liquid chromatography (HILIC) mode. The aim of this work is to show how different experimental conditions influence the enrichment efficiency of glycopeptides from human immunoglobulin G (IgG) on an aminopropyl-modified SPE column. Different compositions of the elution solvent (acetonitrile, methanol, and isopropanol), along with varying concentrations of elution solvent acidifiers (formic and acetic acid), and different concentrations of acetonitrile for the conditioning and washing solvents (65%, 75%, and 85% acetonitrile) were tested to observe their effects on the glycopeptide enrichment process. Isopropanol proved less effective in enriching glycopeptides, while acetonitrile was the most efficient, with methanol in between. Higher formic acid concentrations in the elution solvent weakened the ionic interactions, particularly with sialylated glycopeptides. Substituting formic acid with acetic acid led to earlier elution of more glycopeptides. The acetonitrile concentration in conditioning and washing solutions played a key role; at 65% acetonitrile, glycopeptides were not retained on the SPE column and were detected in the flow-through fraction. Ultimately, it was proven that the enrichment method was applicable to human plasma samples, resulting in a significant decrease in the abundances of non-glycosylated peptides. To the best of our knowledge, this study represents the first systematic investigation into the impact of the mobile phase on glycopeptide enrichment using an aminopropyl-modified SPE column in HILIC mode. This study demonstrates the substantial impact of even minor variations in experimental conditions, which have not yet been considered in the literature, on SPE-HILIC glycopeptide enrichment. Consequently, meticulous optimization of these conditions is imperative to enhance the specificity and selectivity of glycoproteomic analysis, ensuring accurate and reliable quantification.

HILIC/MS quantitation of low-abundant phospholipids and sphingolipids in human plasma and serum: Dysregulation in pancreatic cancer

A new hydrophilic interaction liquid chromatography - mass spectrometry method is developed for low-abundant phospholipids and sphingolipids in human plasma and serum. The optimized method involves the Cogent Silica type C hydride column, the simple sample preparation by protein precipitation, and the removal of highly abundant lipid classes using the postcolumn valve directed to waste during two elution windows. The method allows a highly confident and sensitive identification of low-abundant lipid classes in human plasma (246 lipid species from 24 lipid subclasses) based on mass accuracy and retention dependencies in both polarity modes. The method is validated for quantitation using two internal standards (if available) for each lipid class and applied to human plasma and serum samples obtained from patients with pancreatic ductal adenocarcinoma (PDAC), healthy controls, and NIST SRM 1950. Multivariate data analysis followed by various statistical projection methods is used to determine the most dysregulated lipids. Significant downregulation is observed for lysophospholipids with fatty acyl composition 16:0, 18:0, 18:1, and 18:2. Distinct trends are observed for phosphatidylethanolamines (PE) in relation to the bonding type of fatty acyls, where most PE with acyl bonds are upregulated, while ether/plasmenyl PE are downregulated. For the sphingolipid category, sphingolipids with very long N-acyl chains are downregulated, while sphingolipids with shorter N-acyl chains were upregulated in PDAC. These changes are consistently observed for various classes of sphingolipids, ranging from ceramides to glycosphingolipids, indicating a possible metabolic disorder in ceramide biosynthesis caused by PDAC.

Multiply-mesoporous hydrophilic titanium dioxide nanohybrid for the highly-performed enrichment of N-glycopeptides from human serum

N-glycopeptide is considered as one of significant biomarkers which provide guidance for the diagnosis and drug design of diseases. However, the direct analysis of N-glycopeptides is nearly impracticable mainly owing to their extremely low abundance and grave signal suppression from other interfering substances in the bio-samples. In this research, a multiply-mesoporous hydrophilic TiO2 nanohybrid (mM-TiO2@Cys) was synthesized by immobilizing Cys on a TiO2 substrate with hierarchical mesopores to achieve the highly-performed enrichment of N-glycopeptides. With the advantages of superior hydrophilicity and multiply-mesoporous structure, the obtained material exhibited an excellent selectivity (IgG digests and BSA digests at the molar ratio of 1/500), a high sensitivity (1 fmol μL-1 for IgG digests) and a good size-exclusion ability (IgG digests, IgG and BSA at the molar ratio of 1/500/500) in the enrichment of N-glycopeptides from IgG digests. As a result, 281 N-glycopeptides corresponded with 109 glycoproteins were identified from 2 μL serum digests of the patients with nasopharyngeal carcinoma, and 181 N-glycopeptides corresponded with 78 glycoproteins were identified from 2 μL serum digests of the healthy volunteers, revealing the potential application value of mM-TiO2@Cys in glycoproteomics.

Analysis of glycosylated cardiolipins from thermophilic bacteria using GC-MS and LC-ESI-MS/MS methods

Unusual glucose-substituted cardiolipins (Glcx-CLs) in three genera of thermophilic bacteria, having more than one glycosidically linked glucose to the hydroxyl of the central glycerol of Glcx-CLs were identified for the first time in thermophilic bacteria of the genera Geobacillus, Meiothermus, and Thermus. The number of glucoses reached up to five units. The structure of glycosidically linked oligosaccharides was determined based on shotgun analysis MS (electrospray high-resolution tandem mass spectrometry), partially methylated alditol acetates were identified by GC-MS, both electron ionization (EI) and positive chemical ionization (PCI), hydrophilic interaction liquid chromatography (HILIC) separation and identification of CLs glycosides by high resolution MS-ESI, and digestion by specific glycosidases.

Hydrophilic interaction liquid chromatography with mass spectrometry for the separation and identification of antisense oligonucleotides impurities and nusinersen metabolites

With the development of therapeutic oligonucleotides for antisense and gene therapies, the demand for analytical methods also increases. For the analysis of complex samples, for example plasma samples, where the use of mass detection is essential, hydrophilic interaction liquid chromatography is a suitable choice. The aim of the present work was to develop a method for separation and identification of the oligonucleotide impurities and metabolites by hydrophilic interaction liquid chromatography. First of all, the effects of different chromatographic conditions (e.g. pH of the aqueous part of the mobile phase, buffer concentration, column temperature) on the retention and separation of phosphorothioate oligonucleotides standards on the amide stationary phase were investigated. A set of model oligonucleotides containing a fully modified 21mer and its typical impurities (shortmers and oligonucleotides with different number of thiophosphate modifications) was used. The results showed that the concentration of the salt in the mobile phase as well as its pH, are the most influential parameters with regard to peak shape and separation. The knowledge gained was applied to the analysis of an unpurified 18mer oligonucleotides, analogues of the drug nusinersen used for the treatment of spinal muscular atrophy. The successful separation and identification of twenty-six and twenty-eight impurities was performed with the developed HILIC method. The method was applied to analysis of nusinersen metabolites of serum samples of patients treated with Spinraza.

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.

Characterization of synthetic guide ribonucleic acids through hydrophilic interaction chromatography coupled with mass spectrometry

In this study, we aimed to develop a hydrophilic interaction liquid chromatography (HILIC) method for the analysis of single guide ribonucleic acid (sgRNA), a critical reagent used in CRISPR genome editing. Our results showed that effective profiling of sgRNA can be achieved by suppressing the surface charge of the stationary phase in HILIC. We identified hydrogen bonding as the primary retention mechanism with potential weak partitioning in HILIC separation of large oligonucleotides like 100-mer sgRNA. Moreover, we demonstrated that direct coupling of HILIC with mass spectrometry (MS) allows the intact mass analysis of sgRNA and its impurities with minimal adduct present. Finally, we characterized the post peak shown in the low temperature HILIC and identified it as sgRNA aggregates. Our findings provide valuable insight into the characterization of sgRNA and highlight the potential of HILIC-MS as a powerful analytical tool for relatively large oligonucleotide analysis.

Implementing reversed-phase and hydrophilic interaction liquid chromatography into the characterization of DTPA-ramucirumab conjugate before radiolabeling

Radioimmunoconjugates represent a promising class of therapeutics and diagnostics. The characterization of intermediate chelator-antibody products, i.e., without the radionuclide, is frequently omitted, bringing significant uncertainty in the radioimmunoconjugate preparation. In the present study, we explored the utility of reversed-phase (RPLC) and hydrophilic interaction (HILIC) liquid chromatography with UV detection to characterize ramucirumab stochastically conjugated with p-SCN-Bn-CHX-A"-DTPA chelator (shortly DTPA). The conjugation was well reflected in RPLC chromatograms, while chromatograms from HILIC were significantly less informative. RPLC analyses at the intact level confirmed that the conjugation resulted in a heterogeneous mixture of modified ramucirumab. Moreover, the RPLC of DTPA-ramucirumab confirmed heterogeneous conjugation of all subunits. The peptide mapping did not reveal substantial changes after the conjugation, indicating that most parts of ramucirumab molecules remained unmodified and that the DTPA chelator was bound to various sites. Eventually, the RPLC method for analysis of intact ramucirumab was successfully applied to online monitoring of conjugation reaction in 1 h intervals for a total of 24 h synthesis, which readily reflected the structural changes of ramucirumab in the form of retention time shift by 0.21 min and increase in peak width by 0.22 min. The results were obtained in real-time, practically under 10 min per monitoring cycle. To the best of our knowledge, our study represents the first evaluation of RPLC and HILIC to assess the quality of intermediates during the on-site preparation of radioimmunoconjugates prior to radiolabeling.

Identification of a metabolite for the detection of the hydrophilic drug diisopropylamine for doping control

Diisopropylamine (DIPA), a hydrophilic chemical compound, is used as an intravenous antihypertensive agent. DIPA is prohibited for use in the horse racing industry due to its performance enhancing effects. A cyano (CN) hydrophilic interaction liquid chromatography (HILIC) column was used for the separation of DIPA from its metabolite. Ammonium formate was added to the mobile phase to increase the ionization of the basic substance. The metabolite was identified as an N-oxidized metabolite of DIPA, which eluted earlier than the parent drug and was less polar on the HILIC column. The main finding of the study was the identification of a metabolite with a mass shift of 15.9944. The in vitro experiment showed that the metabolite was produced as a result of N-oxidation processes, mainly mediated by flavin-containing monooxygenase (FMO). Methimazole was used to inhibit the FMO enzyme-mediated N-oxidation metabolism and metabolite production in a concentration-dependent manner. The metabolite was confirmed to be present in an actual horse urine sample that tested positive for DIPA. This study demonstrated that the metabolite could be screened using in vitro samples and their presence corresponded to a positive result in actual samples. This metabolite screening could therefore find application as a flexible way to test for new and modified banned substances in the racing industry.

Exploration and optimization of extraction, analysis and data normalization strategies for mass spectrometry-based DNA adductome mapping and modeling

Although interest in characterizing DNA damage by means of DNA adductomics has substantially grown, the field of DNA adductomics is still in its infancy, with room for optimization of methods for sample analysis, data processing and DNA adduct identification. In this context, the first objective of this study was to evaluate the use of hydrophilic interaction (HILIC) vs. reversed phase liquid chromatography (RPLC) coupled to high resolution mass spectrometry (HRMS) and thermal acidic vs. enzymatic hydrolysis of DNA followed by DNA adduct purification and enrichment using solid-phase extraction (SPE) or fraction collection for DNA adductome mapping. The second objective was to assess the use of total ion count (TIC) and median intensity (MedI) normalization compared to QC (quality control), iQC (internal QC) and quality control-based robust locally estimated scatterplot smoothing (LOESS) signal correction (QC-RLSC) normalization for processing of the acquired data. The results demonstrate that HILIC compared to RPLC allowed better modeling of the tentative DNA adductome, particularly in combination with thermal acidic hydrolysis and SPE (more valid models, with an average Q²(Y) and R²(Y) of 0.930 and 0.998, respectively). Regarding the need for data normalization and the management of (limited) system instability and signal drift, QC normalization outperformed TIC, MedI, iQC and LOESS normalization. As such, QC normalization can be put forward as the default data normalization strategy. In case of momentous signal drift and/or batch effects however, comparison to other normalization strategies (like e.g. LOESS) is recommended. In future work, further optimization of DNA adductomics may be achieved by merging of HILIC and RPLC datasets and/or application of 2D-LC, as well as the inclusion of Schiff base stabilization and/or fraction collection in the thermal acidic hydrolysis-SPE sample preparation workflow.

Evaluating orthogonality between ion-pair reversed phase, anion exchange, and hydrophilic interaction liquid chromatography for the separation of synthetic oligonucleotides

The orthogonality of separation between ion-pair reversed phase (IP-RP), anion exchange (AEX), and hydrophilic interaction liquid chromatography (HILIC) was evaluated for oligonucleotides. A polythymidine standard ladder was first used to evaluate the three methods and showed zero orthogonality, where retention and selectivity were based on oligonucleotide charge/size under all three conditions. Next, a model 23-mer synthetic oligonucleotide containing 4 phosphorothioate bonds with 2' fluoro and 2'-O-methyl ribose modifications typical of small interfering RNA was used for evaluating orthogonality. The resolution and orthogonality were evaluated between the three modes of chromatography in terms of selectivity differences for nine common impurities, including truncations (n-1, n-2), addition (n + 1), oxidation, and de-fluorination. We first evaluated different ion-pairing reagents that provided the best separation of the key impurities while suppressing diastereomer separation due to phosphorothioate linkages. Although different ion-pairing reagents affected resolution, very little orthogonality was observed. We then compared the retention times between IP-RP, HILIC, and AEX for each impurity of the model oligonucleotide and observed various selectivity changes. The results suggest that coupling HILIC with either AEX or IP-RP provide the highest degree of orthogonality due to the differences in retention for hydrophilic nucleobases and modifications under HILIC conditions. IP-RP provided the highest overall resolution for the impurity mixture, whereas more co-elution was observed with HILIC and AEX. The unique selectivity patterns offered by HILIC provides an interesting alternative to IP-RP or AEX, in addition to the potential for coupling with multidimensional separations. Future work should explore orthogonality for oligonucleotides with subtle sequence differences such as nucleobase modifications and base flip isomers, longer strands such as guide RNA and messenger RNA, and other biotherapeutic modalities such as peptides, antibodies, and antibody-drug-conjugates.

Post-synthesis of covalent organic frameworks as a hydrophilic platform for specific detection of egg ovalbumin under physiological pH

Ovalbumin (OVA) is an important protein source in our daily life. Unfortunately, the food safety problem has become more and more serious, such as protein allergy and contaminated protein. Therefore, it is necessary to detect vital proteins efficiently and rapidly. Mass spectrometry (MS) is a powerful tool for the detection of proteins. Herein, dual amino acids functionalized covalent organic frameworks containing disulfide covalent bonds (COF@SS@GC, where G is glutathione and C is cysteine) were facilely prepared for OVA enrichment through hydrophilic interaction liquid chromatography (HILIC) under physiological pH. The results showed that COF@SS@GC had displayed sensitive detection (0.1 fmol), good selectivity (OVA: BSA = 1:100), adsorption capacity (311 mg/g), stability, reproducibility, linearity, LOQ level (42 μg/mL) and recovery ratio (64.83 %) for OVA. COF@SS@GC also demonstrated satisfactory purification ability in the enrichment of egg white, indicating that COF@SS@GC had great potential in the enrichment of protein from complex samples.

Augmented region of interest for untargeted metabolomics mass spectrometry (AriumMS) of multi-platform-based CE-MS and LC-MS data

In mass spectrometry (MS)-based metabolomics, there is a great need to combine different analytical separation techniques to cover metabolites of different polarities and apply appropriate multi-platform data processing. Here, we introduce AriumMS (augmented region of interest for untargeted metabolomics mass spectrometry) as a reliable toolbox for multi-platform metabolomics. AriumMS offers augmented data analysis of several separation techniques utilizing a region-of-interest algorithm. To demonstrate the capabilities of AriumMS, five datasets were combined. This includes three newly developed capillary electrophoresis (CE)-Orbitrap MS methods using the recently introduced nanoCEasy CE-MS interface and two hydrophilic interaction liquid chromatography (HILIC)-Orbitrap MS methods. AriumMS provides a novel mid-level data fusion approach for multi-platform data analysis to simplify and speed up multi-platform data processing and evaluation. The key feature of AriumMS lies in the optimized data processing strategy, including parallel processing of datasets and flexible parameterization for processing of individual separation methods with different peak characteristics. As a case study, Saccharomyces cerevisiae (yeast) was treated with a growth inhibitor, and AriumMS successfully differentiated the metabolome based on the augmented multi-platform CE-MS and HILIC-MS investigation. As a result, AriumMS is proposed as a powerful tool to improve the accuracy and selectivity of metabolome analysis through the integration of several HILIC-MS/CE-MS techniques.

Evaluation of hydrophilic interaction chromatography versus reversed-phase chromatography for fast aqueous species distribution analysis of Nickel(II)-Histidine complex species

Nickel (Ni) is a trace heavy metal of importance in biological and environmental systems, with well documented allergy and carcinogenic effects in humans. With Ni(II) as the dominant oxidation state, the elucidation of the coordination mechanisms and labile complex species responsible for its transportation, toxicity, allergy, and bioavailability is key to understanding its biological effects and location in living systems. Histidine (His) is an essential amino acid that contributes to protein structure and activity and in the coordination of Cu(II) and Ni(II) ions. The aqueous low molecular weight Ni(II)-Histidine complex consists primarily of two stepwise complex species Ni(II)(His)₁ and Ni(II)(His)₂ in the pH range of 4 to 12. Four chromatographic columns, including the superficially porous Poro-shell EC-C₁₈, Halo RP-amide and Poro-shell bare silica-HILIC columns, alongside a Zic-cHILIC fully porous column, were evaluated for the fast separation of the individual Ni(II)-Histidine species. Of these the Zic-cHILIC exhibited high efficiency and selectivity to distinguish between the two stepwise species Ni(II)His₁ and Ni(II)His₂ as well as free Histidine, with a fast separation within 120 s at a flow rate of 1 ml/min. This HILIC method utilizing the Zic-cHILIC column was initially optimized for the simultaneous analysis of Ni(II)-His-species using UV detection with a mobile phase consisting of 70% ACN and sodium acetate buffer at _w^wpH 6. Furthermore, the aqueous metal complex species distribution analysis for the low molecular weight Ni(II)-histidine system was chromatographically determined at various metal-ligand ratios and as a function of pH. The identities of Ni(II)His₁ and Ni(II)-His₂ species were confirmed using HILIC electrospray ionization- mass spectrometry (HILIC-ESI-MS) at negative mode.

Hydrophilic interaction liquid chromatography-electrospray ionization mass spectrometry combined with fabric phase sorptive extraction for therapeutic drug monitoring of pioglitazone, repaglinide, and nateglinide in human plasma

Polypharmacy in type 2 diabetes is an issue of major concern as the prescription of multiple medi-cations for the management of diabetes-associated comorbidities can lead to drug-to-drug interactions, which can pose serious risks to patients' health. Within this context, the development of bioanalytical methods for monitoring the therapeutic levels of antidiabetic drugs is notably useful to ensure patients' safety. In the present work, a liquid chromatography-mass spectrometry method for the quantitation of pioglitazone, repaglinide, and nateglinide in human plasma is described. Sample preparation was performed by fabric phase sorptive extraction (FPSE), and hydrophilic interaction liquid chromatography (HILIC) was implemented for the chromatographic separation of the analytes, using a ZIC®-cHILIC analytical column (150 × 2.1 mm, 3 µm) under isocratic elution. The mobile phase consisted of 10 mM ammonium formate aqueous solution (pH = 6.5)/ acetonitrile, 10/90 v/v, and was pumped at a flow rate of 0.2 mL min^-1. Design of Experiments was used during the development of the sample preparation method to gain deeper insight into the effect of various experimental parameters on extraction efficiency, their potential interactions and to optimize the recovery rates of the analytes. The linearity of the assay was assessed over the ranges of 25 to 2000, 6.25 to 500, and 125 to 10000 ng mL^-1 for pioglitazone, repaglinide, and nateglinide, respectively. The presented method was fully validated and can be used for the therapeutic monitoring of the targeted analytes in human plasma samples.

Liquid chromatography-mass spectrometry metabolite library for metabolomics: Evaluating column suitability using a scoring approach

Untargeted metabolomic studies require an extensive set of analyte (metabolic) information to be obtained from each analyzed sample. Thus, highly selective, and efficient analytical methodologies together with reversed-phase (RP) or hydrophilic interaction liquid chromatography (HILIC) are usually applied in these approaches. Here, we present a performance comparison of five different chromatographic columns (C18, C8, RP Amide, zicHILIC, OH5 HILIC phases) to evaluate their sufficiency of analysis for a large analyte library, consisting of 817 authentic standards. By taking into account experimental chromatographic parameters (i.e. retention time, peak tailing and asymmetry, FWHM, signal-to-noise ratio and peak area and intensity), the proposed column scoring approach provides a simple criterion that may assist analysis in the select of a stationary phase for those metabolites of interest. RPLC methods offered better results regarding metabolic library coverage, while the zicHILIC stationary phase delivered a bigger number of properly eluted compounds. This study demonstrates the importance of choosing the most suitable configuration for the analysis of different metabolic classes.

A polyethyleneimine-functionalized polymer substrate polar stationary phase

A polyethyleneimine (PEI)-functionalized polymer substrate polar stationary phase was prepared for hydrophilic interaction chromatography (HILIC) by grafting PEI onto poly(styrene-divinylbenzene) (PS-DVB) microspheres. The phase shows a U-shape retention profile and it exhibits typical hydrophilic characteristic when the organic solvent fraction in the mobile phase is > 60%. Hydrogen bonding, anion exchange, and hydrophobic interaction are involved in the retention mechanism. Good separation and unique selectivity for acidic, basic and neutral polar analytes were achieved. It showed extremely low column bleed (comparable to that of blank) under gradient elution mode (even to 50% fraction of water) and wide pH tollerance range (at least 1-13).

Determination of oxalic acid in herbal medicines by semi-micro hydrophilic interaction liquid chromatography coupled with electrochemical detection

In this study, the determination of oxalic acid in herbal medicines was performed by using a hydrophilic interaction liquid chromatography coupled with electrochemical detection (HILIC-ECD) method. A semi-micro column packed with amide-silica particles and an acetonitrile-30 mM phosphate buffer (pH 6.8) mixture (65:35, v/v) were used as the stationary and mobile phases, respectively, in the HILIC-ECD. A potential of + 1.1 V vs. Ag/AgCl was applied to a glassy carbon working electrode. The ratio of the peak height of oxalic acid to that of the internal standard (synephrine) was proportional to the concentration of 0.45 μg L^-1 to 1.8 mg L^-1 with a correlation coefficient of 0.999. The detection limit (signal-to-noise ratio, S/N = 3) of oxalic acid was 0.17 μg L^-1. By the HILIC-ECD, the oxalic acid content in crude drugs and Kampo medicine extract granules (Zingiberis Rhizoma Processum, Pinelliae Tuber, Sho-seiryu-to, Hange-shashin-to, etc.) were determined with less than 2.9% relative standard deviation (RSD, n = 6), and their recoveries were more than 88.7% with less than 3.3% RSD (n = 6). In conclusion, we demonstrated that the HILIC-ECD performed measurements that were quite selective, accurate, and precise for the determination of oxalic acid in herbal medicines.

Analyzing Activities of Lytic Polysaccharide Monooxygenases by Liquid Chromatography and Mass Spectrometry

Lytic polysaccharide monooxygenases perform oxidative cleavage of glycosidic bonds in various polysaccharides. The majority of LMPOs studied so far possess activity on either cellulose or chitin and analysis of these activities is therefore the main focus of this review. Notably, however, the number of LPMOs that are active on other polysaccharides is increasing. The products generated by LPMOs from cellulose are either oxidized in the downstream end (at C1) or upstream end (at C4), or at both ends. These modifications only result in small structural changes, which makes both chromatographic separation and product identification by mass spectrometry challenging. The changes in physicochemical properties that are associated with oxidation need to be considered when choosing analytical approaches. C1 oxidation leads to a sugar that is no longer reducing but instead has an acidic functionality, whereas C4 oxidation leads to products that are inherently labile at high and low pH and that exist in a keto-gemdiol equilibrium that is strongly shifted towards the gemdiol in aqueous solutions. Partial degradation of C4-oxidized products leads to the formation of native products, which could explain why some authors claim to have observed glycoside hydrolase activity for LPMOs. Notably, apparent glycoside hydrolase activity may also be due to small amounts of contaminating glycoside hydrolases since these normally have much higher catalytic rates than LPMOs. The low catalytic turnover rates of LPMOs necessitate the use of sensitive product detection methods, which limits the analytical possibilities considerably. Modern liquid chromatography and mass spectrometry have become essential tools for evaluating LPMO activity and this chapter provides an overview of available methods together with a few novel tools. The methods described constitute a suite of techniques for analyzing oxidized carbohydrate products, which can be applied to LPMOs as well as other carbohydrate-active redox enzymes.

Mass Spectrometry-Based Untargeted Metabolomics and Lipidomics Platforms to Analyze Cell Culture Extracts

Metabolites represent the most downstream level of the cellular organization. Hence, an in vitro untargeted metabolomics approach is extremely valuable to deepen the understanding of how endogenous metabolites in cells are altered under a given biological condition. This chapter describes a robust liquid chromatography-high-resolution mass spectrometry-based metabolomics and lipidomics platform applied to cell culture extracts. The analytical workflow includes an optimized sample preparation procedure to cover a wide range of metabolites using liquid-liquid extraction and validated instrumental operation procedures with the implementation of comprehensive quality assurance and quality control measures to ensure high reproducibility. The lipidomics platform is based on reversed-phase liquid chromatography for the separation of slightly polar to apolar metabolites and covers a broad range of lipid classes, while the metabolomics platform makes use of two hydrophilic interaction liquid chromatography methods for the separation of polar metabolites, such as organic acids, amino acids, and sugars. The chapter focuses on the analysis of cultured HepaRG cells that are derived from a human hepatocellular carcinoma; however, the sample preparation and analytical platforms can easily be adapted for other types of cells.

Direct analysis of biodegradable chelating agents based on liquid chromatography/electrospray ionization mass spectrometry using a metal-free hydrophilic interaction liquid chromatographic column

Recently, biodegradable aminopolycarboxylic acid chelating agents have attracted attention as an alternative to environmentally persistent chelating agents such as ethylenediamine-N,N,N',N'-tetraacetic acid. However, the detection of chelating agents requires complexation with metals or derivatization by esterification reagents, and their direct detection using the currently available analytical methods still represents a challenge. Herein, we describe a direct analytical method for the biodegradable chelating agents ethylenediamine-N,N'-disuccinic acid, 3-hydroxy-2,2'-iminodisuccinic acid, methylglycine-N,N'-diacetic acid, and N,N-bis(carboxymethyl)-L-glutamic acid, via ultra-performance liquid chromatography/electrospray ionization quadrupole/time-of-flight mass spectrometry. Satisfactory retention and separation with a good peak shape were successfully achieved using a metal-free hydrophilic interaction liquid chromatographic column. The calibration curves showed good linearity in the range of 1.0-50 μM with correlation coefficients greater than 0.9988. The detection limits ranged from 0.04 to 0.12 μM. Furthermore, the developed method could be applied to the quantitative analysis of the four chelating agents in biodegradation and photodegradation experiments at the laboratory level. The proposed method, which offers the advantages of quickness, sensitivity, and requiring no complicated pretreatment steps, is expected to contribute significantly to the practical analysis of chelating agents in environmental water samples.

Dendritic organic molecular gel coating with molecular shape selectivity and its application in selective separation by liquid chromatography

Dendritic organic molecular gels are a promising class of three-dimensional network compounds. Here, we have synthesized a new type of dendritic organic molecular gel stationary phase (SiO₂-G3) by using benzyl alcohol as raw material and dimethyl 5-hydroxyisophthalate as growth unit to synthesize a third-generation organic molecular gel G3, which grafted onto the silica surface by cyanogen chloride (CC). The developed stationary phase not only exhibits high molecular shape selectivity but also has a RPLC/HILIC/IEC mixed-mode characteristic for HPLC due to the ordered structure, the multiple strong π-π stacking interactions and the introduction of a hydrophilic triazine fraction during the grafting process. Compared with a commercial C₁₈ column, the developed column exhibited flexible selectivity, enhanced separation performance and excellent separation of monosubstituted benzene, polycyclic aromatic hydrocarbons (PAHs), positional isomers, nucleosides and nucleobases, benzoic acid and aniline compounds. In addition, the new column provided baseline separation of polycyclic aromatic hydrocarbon contaminants in Yellow River water, verifying its potential for application in the analysis of real samples.

A hyperbranched polyglycerol-functionalized polymer polar stationary phase

A polymer polar stationary phase functionalized with hyperbranched polyglycerol for hydrophilic interaction chromatography (HILIC) is described. It is prepared via surface-initiated ring-opening polymerization of hyperbranched polyglycerol onto hydrolzed poly(glycidyl methacrylate-divinylbenzene) microspheres. The capacity of the functional groups can be maniputed by repeating hyperbranch layers. The phase showed typical HILIC character with good separation performance towards tested polar analytes. It also exhibited wider pH tolerance range (e.g. at least 2 to 12) and as well negligible bleed level under gradient elution mode (even to 50% fraction of water).

Quantification and in silico analysis of taste dipeptides generated during dry-cured ham processing

Small peptides such as dipeptides contribute to a great extent to the characteristic taste of dry-cured hams. In this study, hydrophilic interaction liquid chromatography (HILIC) combined to tandem mass spectrometry was used to separate, identify, and quantify seven dipeptides in dry-cured hams sampled at different processing times (6, 12, 18, and 24 months). Results showed an increased concentration of dipeptides DA, DG, EE, ES, and EV with the length of processing, obtaining values up to 23 μg/g of dry-cured ham, which suggests an intense action of muscle enzymes dipeptidyl peptidases during the process. The dipeptide VG significantly decreased from 7 to 4 μg/g of dry-cured ham as the processing increased from 6 to 24 months, whereas the dipeptide PA showed low values between 380 and 550 ng/g of dry-cured ham at all the sampling times. Additionally, in silico analyses reported the sensory characteristics of the studied dipeptides, mostly giving bitter and umami taste, and predicted their allergenicity, toxicity, and physicochemical properties. These results could be useful for further studies related to the pleasant taste of dry-cured hams.

Performance of free-flow field-step electrophoresis as cleanup step for the non-target analysis of environmental water samples

For the analysis of low concentrations of micropollutants in environmental water samples, efficient sample enrichment and cleanup are necessary to reduce matrix effects and to reach low detection limits. For analytes of low and medium polarity, solid-phase extraction is used, but robust methods for the preconcentration of highly polar or ionizable analytes are scarce. In this work, field-step electrophoresis (FSE) was developed as an environmental sample cleanup technique for ionizable micropollutants and ionic transformation products. The FSE electrolyte system preconcentrated 15 acidic model analytes (pK_a from −2.2 to 9.1) present in aqueous samples in two fractions by factors of 5–10. Simultaneously, highly mobile matrix compounds were removed including inorganic ions such as sulfate and chloride. The fractions were either directly injected for downstream analysis by reversed-phase liquid chromatography (RPLC) or further processed by evaporative preconcentration with subsequent reconstitution in an organic solvent suitable for separation methods like hydrophilic interaction chromatography. The FSE/RPLC-MS method exhibited high quantitative precision with RSDs of 3–6%. The method was successfully applied to a spiked river water sample and its performance compared with common solid-phase extraction and evaporative concentration, demonstrating a high analyte coverage. FSE combined with non-target screening by RPLC-MS revealed a strong reduction in matrix load especially at low retention times. Seventeen compounds were identified in the FSE fractions sampled at the field step boundary by retention time, accurate mass, and mass fragments. Suspect screening by FSE/RPLC-MS was facilitated by FSE’s selectivity for anionic compounds.

Hydrophilic interaction LC-MS/MS method to avoid endogenous interference in the analysis of 4-hydroxy isoleucine from dietary supplementation of fenugreek

4-Hydroxy isoleucine is one of the potent hypoglycaemic active constituents of fenugreek seeds. A method capable of reducing biological interferences is required for bio-availability studies. An isocratic separation of 4-hydroxy isoleucine from endogenous interferences was achieved in ZIC-cHILIC column using 0.1% formic acid in water and acetonitrile (20:80, % v/v) pumped at 0.5 mL/min. Quantification was performed in multiple reaction monitoring mode using the transitions of m/z 148.1→102.1 and m/z 276.1→142.2 for 4-hydroxy isoleucine and homatropine (as internal standard), respectively. After full method validation, 4-Hydroxy isoleucine levels in human plasma and commercial fenugreek formulations were determined. This method showed good linearity in the range of 50-2000 ng/mL. Intra-day and inter-day accuracy were in the range of 90.64-109.0% and precision was <4.82 % CV. The mean (SD) plasma concentration of 4-hydroxy isoleucine in healthy individuals at 2 hrs post oral administration of fenugreek tablet was found to be 1590 (260) ng/mL. Half of marketed formulations were found to contain < 0.05 % of 4-Hydroxy isoleucine content. We developed a rapid hydrophilic interaction LC-MS/MS method for analysis of 4-hydroxy isoleucine in human plasma. This method can be applied directly to conduct the clinical pharmacokinetics studies of 4-hydroxy isoleucine in human population. This article is protected by copyright. All rights reserved.

Multiclass cyanotoxin analysis in reservoir waters: Tandem solid-phase extraction followed by zwitterionic hydrophilic interaction liquid chromatography-mass spectrometry

The presence of cyanobacteria and cyanotoxins in all water bodies, including ocean water and fresh water sources, represents a risk for human health as eutrophication and climate change are enhancing their level of proliferation. For risk assessment and studies on occurrence, the development of reliable and sensitive analytical approaches able to cover a wide range of cyanotoxins is essential. This work describes the development of an HILIC-MS/MS multiclass method for the simultaneous analysis of eight cyanotoxins in reservoir water samples belonging to three different classes according to their chemical structure: cyclic peptides (microcystin-LR, microcystin-RR and nodularin), alkaloids (cylindrospermopsin, anatoxin-a) and three non-protein amino acids isomers such as β-methylamino-L-alanine, 2,4-diaminobutyric acid and N-(2-aminoethyl)glycine). A SeQuant ZIC-HILIC column was employed to achieve the chromatographic separation in less than 12 min. Previously, a novel sample treatment based on a tandem solid-phase extraction (SPE) system using mixed cation exchange (MCX) and Strata-X cartridges was investigated with the aim of extracting and preconcentrating this chemically diverse group of cyanotoxins. The Strata-X cartridge, which was configured first in the line of sample flow, retained the low polar compounds and the MCX cartridge, which was at the bottom of the dual system, retained mainly the non-protein amino acids. The optimization procedure highlighted the importance of sample ion content for the recoveries of some analytes such as the isomers β-N-methylamino-L-alanine and 2-4-diaminobutyric acid. Method validation was carried out in terms of linearity, limit of detection (LOD) and quantification (LOQ), recoveries, matrix effect and precision in terms of repeatability and intermediate precision. This work represents the first analytical method for the simultaneous analysis of these multiclass cyanotoxins in reservoir water samples, achieving LOQs in the very low range of 7·10^-3 - 0.1 μg L^-1. Despite high recoveries obtained at the LOQ concentration levels (101.0-70.9%), relative standard deviations lower than 17.5% were achieved.

Grafting copolymer brushes on polyhedral oligomeric silsesquioxanes silsesquioxane-decorated silica stationary phase for hydrophilic interaction liquid chromatography

A strategy is proposed to develop a stationary phase for hydrophilic interaction liquid chromatography (HILIC) using the synergistic effect of polyhedral oligomeric silsesquioxane (POSS) and copolymer brushes. Octahedral octa-aminopropylsisesquioxane (8NH₂-POSS) was first bound to silica gel, followed by bromination to form a cubic initiator. Then, using acrylamide (AM) and dihydroxypropyl methacrylate (DPMA) as mixed monomers, surface initiated-atom transfer radical polymerization was conducted to prepare a stationary phase comprising cubic copolymer brushes with amide and diol groups. The characterization of the stationary phase confirmed the successful synthesis of Sil-NH₂-POSS/Poly(AM-co-DPMA). The chromatographic properties were investigated using nucleosides, organic acids and β-agonists to find that our designed column has superior hydrophilic property, better separation performance compared with classical HILIC columns consisting of diol- or amino-modified silica. The systematic investigation of the retention mechanism and separation selectivity using various types of polar compounds revealed that Sil-NH₂-POSS/Poly(AM-co-DPMA) follows a mixed-mode retention composed of HILIC and electrostatic interactions. Besides, it exhibits good column efficiency and stability. The role of 8NH₂-POSS in the separation was evaluated by comparing the performance of Sil-NH₂-POSS/Poly(AM-co-DPMA) and poly(AM-co-DPMA)-modified silica without 8NH₂-POSS. In conclusion, our designed based on POSS and hydrophilic copolymer brushes can contribute to the development of HILIC separation materials with enhanced performance.

Synthesis and evaluation of fosfomycin group end-capped packing materials for hydrophilic interaction liquid chromatography

Hydrophilic interaction liquid chromatography (HILIC) plays an important role in the analysis of compounds having high polarity. In this study, fosfomycin (F) was chosen as a new end-capping reagent, owing to the facile hydrolysis reaction of its epoxy group. Zirconia coated silica (ZrO₂/SiO₂) materials having good chemical and physical stability were prepared. D-glucose-6-phosphate (G) and D-fructose1,6-bisphosphate (FDP) were modified onto the inner and outer surfaces of the ZrO₂/SiO₂ microbeads. The new end-capping reagent (F) was then bonded onto the surface of the modified material through Lewis acid-base interactions. The properties (morphology, Zr content, pore size, pore volume, and carbon content) of the stationary phases (SPs) were characterized. Finally, the resulting end-capped SPs were employed to separate alkaloids and benzoic acids. Multiple interactions, including HILIC, electrostatic repulsion, ion exchange and hydrogen bonding, contributed to the retention of the analytes on the SPs. On the F-FDP-ZrO₂/SiO₂ column, a theoretical plate number of 31,700 plates/m and an asymmetry factor of 1.63 were achieved for berberine, exhibiting good chromatographic performance. Furthermore, the FDP-ZrO₂/SiO₂ column showed good acid-base stability and good potential for the analysis of benzoic acid in Sprite and ginsenoside separations. Thus, the results indicated the significant potential of using F as an end-capping reagent.

Synthesis of octadecylamine-derived carbon dots and application in reversed phase/hydrophilic interaction liquid chromatography

In order to make up for the deficiencies of traditional C18 column for separating strong polar compounds, combined with the good hydrophilicity of carbon dots (CDs), novel octadecylamine-derived CDs denoted as C18-CDs are designed, synthesized and applied in RPLC/HILIC mixed-mode chromatography with good separation performance towards both hydrophobic and hydrophilic compounds. C18-CDs are synthesized by simple one-step solvothermal method using octadecylamine and citric acid as carbon sources, and C18-CDs with proper polarity are collected through column chromatography purification. This C18-CDs decorated silica column showed good separation performance for polycyclic aromatic hydrocarbons and alkylbenzenes under RPLC mode. Hydrophilic compounds including sulfonamides, nucleosides and nucleobases also achieved good resolution in HILIC mode. Hydrophobic and π-π stacking interactions play major retaining roles in RPLC, whereas hydrophilic partitioning and hydrogen bond interactions turn to the main retention interactions under HILIC mode. This C18-CDs/SiO₂ column was applied for the fast detection of chloramphenicol in milk without complex sample pretreatment process. Quantitative relationship between the peak area and the concentration of chloramphenicol was established with linear equation of A = 1677c + 173. Satisfactory spiked recoveries in the range of 94.1-109.0% were obtained. This work not only proposes a simple method for improving the polarity of C18 column through forming octadecane into CDs, but also provides novel CDs with certain hydrophobicity/hydrophily suitable for mixed-mode chromatography.

Comparison of water adsorption in common stationary phases and eluents

Pycnometric and homologous series retention methods are used to determine the volume and mean composition of the water-rich layers partially adsorbed on the surface of several hydrophilic interaction liquid chromatography (HILIC) column fillings with acetonitrile-water and methanol-water as eluents. The findings obtained in this work confirm earlier studies using direct methods for measuring the stationary phase water content performed by Jandera's and Irgum's research groups. Water is preferentially adsorbed on the surface of the HILIC bonded phase in hydroorganic eluents containing more than 40% acetonitrile or 70% methanol, and a gradient of several water-rich transition layers between the polar bonded phase and the poorly polar bulk mobile phase is formed. These layers of reduced mobility act as HILIC stationary phases, retaining polar solutes. The volume of these layers and concentration of adsorbed water is much larger for acetonitrile-water than for methanol-water mobile phases. In hydroorganic eluents with less than 20-30% acetonitrile or 40% methanol the amount of preferentially adsorbed water is very small, and the observed retention behavior is close to the one in reversed-phase liquid chromatography (RPLC). In eluents with intermediate acetonitrile-water or methanol-water compositions a mixed HILIC-RPLC behavior is presented. Comparison of several HILIC columns shows that the highest water enrichment in the HILIC retention region for acetonitrile-water mobile phases is observed for zwitterionic and aminopropyl bonded phases, followed in minor grade for diol and polyvinyl alcohol functionalizations. Pentafluorophenyl bonded phase, usually considered a HILIC column, does not show significant water adsorption, nor HILIC retention.

Discrimination of sulfated isomers of chondroitin sulfate disaccharides by HILIC-MS

Chondroitin sulfate (CS) glycosaminoglycans are biologically active sulfated polysaccharides that pose an analytical challenge for their structural analysis and functional evaluation. In this study, we developed a hydrophilic interaction liquid chromatography separation method and its on-line coupling to mass spectrometry (MS) allowing efficient differentiation and sensitive detection of mono-, di-, and trisulfated CS disaccharides and their positional isomers, without requiring prior derivatization. The composition of the mobile phase in terms of pH and concentration showed great influence on the chromatographic separation and was varied to allow the distinction of each CS without signal overlap for a total analysis time of 25 min. This methodology was applied to determine the disaccharide composition of biological reaction media resulting from various enzymatic transformations of CS, such as enzymatic desulfation of CS disaccharides by a CS 4-O-endosulfatase, and depolymerization of the CS endocan by chondroitinase lyase ABC.

Quantification of advanced glycation end products and amino acid cross-links in foods by high-resolution mass spectrometry: Applicability of acid hydrolysis

An analytical method was developed and validated for simultaneous identification and quantification of advanced glycation end products (AGEs), amino acid cross-links, lysine and arginine in foodstuffs based on acid hydrolysis, hydrophilic interaction chromatography and high-resolution mass spectrometry. The method proved to be sensitive, reproducible and accurate for furosine, N-Ɛ-(carboxymethyl)lysine, N-Ɛ-(carboxyethyl)lysine, methylglyoxal and glyoxal-derived hydroimidazolones (MG-H and GO-H isomers, respectively), glyoxal lysine dimer, lysinoalanine, lanthionine, lysine and arginine. LOD and LOQ values in water were found to be 0.9-15.5 ng/mL and 2.8-47 ng/mL, respectively, and increased to 1.4-60 ng/mL and 4.4-182 ng/mL in liquid infant formula. Recovery values ranged from 76 to 118% in four different food matrices. Microwave-assisted hydrolysis for 11 min had similar efficiency as conventional hydrolysis, which requires overnight incubation. Acid stability of each compound was determined during microwave and conventional hydrolysis, and showed that the MG-H1 isomer is partially converted to the MG-H3 isomer during acid hydrolysis.

Separation of multiphosphorylated cyclopeptides and their positional isomers by hydrophilic interaction liquid chromatography (HILIC) coupled to electrospray ionization mass spectrometry (ESI-MS)

Peptides are efficient models used in different fields such as toxicology to study the interactions of several contaminants at the molecular scale, requiring the development of bio-analytical strategies. In this context, Hydrophilic interaction liquid chromatography (HILIC) coupled to electrospray ionization mass spectrometry (ESI-MS) was used to separate synthetic multiphosphorylated cyclopeptides and their positional isomers at physiological pH. We assessed (i) the selectivity of eleven HILIC columns, from different manufacturers and packed with diverse polar sorbents, and (ii) the effect of mobile phase composition on the separation selectivity. The best selectivity and baseline resolution were achieved with the columns grafted by neutral sorbents amide and diol. Furthermore, we investigated the HILIC retention mechanism of these peptides by examining the effect of the number of phosphorylated residues in the peptide scaffold on their retention. The peptide behavior followed the classical hydrophilic partitioning mechanism exclusively on amide and diol columns. This trend was not fully respected on bare and hybrid silica due to the attractive/repulsive interactions of the deprotonated surface silanol groups with the Arginine or Glutamate residues in the peptide scaffold according to the peptide sequence. The position of the phosphorylated amino acid in the peptide backbone also showed to have an impact on the retention, making possible the separation of positional isomers of these multiphosphorylated cyclic peptides using HILIC.

Comparison of human IgG glycopeptides separation using mixed-mode hydrophilic interaction/ion-exchange liquid chromatography and reversed-phase mode

Glycoproteomics is a challenging branch of proteomics because of the micro- and macro-heterogeneity of protein glycosylation. Hydrophilic interaction liquid chromatography (HILIC) is an advantageous alternative to reversed-phase chromatography for intact glycopeptide separation prior to their identification by mass spectrometry. Nowadays, several HILIC columns differing in used chemistries are commercially available. However, there is a lack of comparative studies assessing their performance, and thus providing guidance for the selection of an adequate stationary phase for different glycoproteomics applications. Here, we compare three HILIC columns recently developed by Advanced Chromatography Technologies (ACE)- with unfunctionalized (HILIC-A), polyhydroxy functionalized (HILIC-N), and aminopropyl functionalized (HILIC-B) silica- with a C18 reversed-phase column in the separation of human immunoglobulin G glycopeptides. HILIC-A and HILIC-B exhibit mixed-mode separation combining hydrophilic and ion-exchange interactions for analyte retention. Expectably, reversed-phase mode successfully separated clusters of immunoglobulin G1 and immunoglobulin G2 glycopeptides, which differ in amino acid sequence, but was not able to adequately separate different glycoforms of the same peptide. All ACE HILIC columns showed higher separation power for different glycoforms, and we show that each column separates a different group of glycopeptides more effectively than the others. Moreover, HILIC-A and HILIC-N columns separated the isobaric A2G1F1 glycopeptides of immunoglobulin G, and thus showed the potential for the elucidation of the structure of isomeric glycoforms. Furthermore, the possible retention mechanism for the HILIC columns is discussed on the basis of the determined chromatographic parameters.

Preparation and evaluation of a polymer-based sulfobetaine zwitterionic stationary phase

We describe a polymer-based sulfobetaine zwitterionic stationary phase for hydrophilic interaction liquid chromatography (HILIC). It was prepared by grafting acrylamide-type sulfobetaine monomer instead of common methacrylate-type sulfobetaine onto hydrolysed poly (glycidyl methacrylate-divinylbenzene) (GMA-DVB) microspheres via pendant double bonds of DVB. The phase has been characterized by elemental analysis, scanning electron micrograph and N₂ adsorption-desorption experiment. It shows wider pH tolerance range (from 2 to 12) and excellent separation ability towards common strong polar analytes such as nucleosides and nucleic bases, water-soluble vitamins, amino acids, inorganic anions and cations. Notably, it exhibits negligible baseline noise level (~0.15 pA) under typical HILIC mobile phase. Excellent selectivity in separation of α- and β-anomers of reducing sugars and lactose/lactulose has also been observed.

Amphipathic carbon quantum dots-functionalized silica stationary phase for reversed phase/hydrophilic interaction chromatography

Carbon quantum dots (CQDs) are considered as good chromatographic separation materials. However, due to the hydrophily of the synthesized CQDs, their applications in HPLC are limited to HILIC for separating strong polar compounds only. In this work, a novel amphipathic CQDs with both hydrophobicity and hydrophily is developed as mixed-mode stationary phase for RPLC/HILIC. To give CQDs certain hydrophobicity, 1,8-diaminooctane is chosen as one of the carbon sources for introducing alkyl chain into CQDs. The amphipathic CQDs modified silica (CQDs/SiO₂) stationary phase has typical characteristic of RPLC/HILIC. Both hydrophobic and hydrophilic compounds including alkylbenzenes, polycyclic aromatic hydrocarbons, nucleosides and bases, amino acids, β-adrenoceptor blockers and agonists, sulfonamides, antibiotics and alkaloids obtain satisfactory separation on this CQDs/SiO₂ column. 14 nucleosides and bases commonly existing in living organisms achieve good separation on this amphipathic CQDs/SiO₂ column within 25 min and the resolutions reach 1.33-13.83 with an average column efficiency of 18,800. The retention mechanism of this novel CQDs/SiO₂ column is investigated by linear solvation energy relationship model. It is found that hydrophobic interaction, π-π stacking, hydrogen-bonding and electrostatic interactions are main retention interactions under RPLC mode. This work provides a new approach for synthesis of amphipathic CQDs. Also, it indicates that amphipathic CQDs with versatile functional properties have great prospect in separation science.

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.

Intra-laboratory comparison of four analytical platforms for lipidomic quantitation using hydrophilic interaction liquid chromatography or supercritical fluid chromatography coupled to quadrupole - time-of-flight mass spectrometry

The lipidomic research is currently devoting considerable effort to the harmonization that should enable the generation of comparable and accurate quantitative lipidomic data across different laboratories and regardless of the mass spectrometry-based platform used. In the present study, we systematically investigate the effects of the experimental setup on quantitative lipidomics data obtained by two lipid class separation approaches, hydrophilic interaction liquid chromatography (HILIC) and ultrahigh-performance supercritical fluid chromatography (UHPSFC), coupled to two different quadrupole - time of flight (QTOF) mass spectrometers from the same vendor. This approach is applied for measurements of 268 human plasma samples of healthy volunteers and renal cell carcinoma patients resulting in four data sets. We investigate and visualize differences among these data sets by multivariate data analysis methods, such as principal component analysis (PCA), orthogonal partial least square discriminant analysis (OPLS-DA), box plots, and logarithmic correlations of molar concentrations of individual lipid species. The results indicate that even measurements in the same laboratory for the same samples using different analytical platforms may yield slight variations in the molar concentrations determined. The normalization to a reference sample with defined lipid concentrations can further diminish these small differences, resulting in highly homogenous molar concentrations of individual lipid species. This strategy indicates a potential approach towards the reporting of comparable quantitative results independent from the quantitative approach and mass spectrometer used, which is important for a wider acceptance of lipidomics data in various biomarker inter-laboratory studies and ring trials.

Development of comprehensive two-dimensional low-flow liquid-chromatography setup coupled to high-resolution mass spectrometry for shotgun proteomics

Bottom-up proteomics provides often small amounts of highly complex samples that cannot be analysed by direct mass spectrometry (MS). To gain a better insight in the sample composition, liquid chromatography (LC) and (comprehensive) two-dimensional liquid chromatography (2D-LC or LC × LC) can be coupled to the MS. Low-flow separations are attractive for HRMS analysis, but they tend to be lengthy. In this work, a low-flow, online, actively modulated LC × LC system, based on hydrophilic-interaction liquid chromatography (HILIC) in the first dimension and reversed-phase liquid chromatography (RPLC) in the second dimension, was developed to separate complex mixtures of peptides. Miniaturization permitted the analysis of small sample amounts (1-5 μg) and direct coupling with micro-ESI MS (1 μL min^-1). All components were focused and automatically transferred from HILIC to RPLC using stationary-phase-assisted active modulation (C18 traps) to deal with solvent-incompatibility or dilution issues. Optimization of the setup was performed for the HILIC columns and the RPLC columns to provide a more efficient separation and higher identification rates than obtained using one-dimensional (1D) LC. A 60% increase in peak capacity was obtained with the 2D setup compared to a 1D-RPLC separation and a 17-34% increase in the number of proteins identified was achieved for the samples analysed (2D-yeast-8280 peptides and 2D-kidney tissue-8843 peptides), without increasing the analysis time (2 h).

Performance evaluation of silica microspheres functionalized by different amine-ligands for hydrophilic interaction chromatography

In this work, for the first time five amine-ligands including mono-amine, di-amine, tri-amine, secondary and tertiary amine, were functionalized on mesoporous micro-silicas and developed as stationary phases for hydrophilic interaction liquid chromatography (HILIC). The investigations about the retention mechanisms, effects of different chromatographic conditions and stability were systematically conducted. Three kinds of polar and hydrophilic compounds (saccharides, sulfonamides, nucleosides and nucleobases) were selected as probe molecules to evaluate their separation performances. Among the five stationary phases, only aminopropyl-bonded silica has already gained wide developments and applications. Whereas, there are no related researches about the other four to be utilized as separation media. By a series of chromatographic evaluations, the results revealed the other four mesoporous micro-silica materials functionalized with di-amine, tri-amine, secondary and tertiary amine, had great potential to be explored as novel stationary phases of HILIC. Particularly, the two stationary phases functionalized with di-amine and tri-amine exhibited outstanding separation and retention abilities. This work offered some insights on the understanding of retention in HILIC mode and provided us possibility to explore other amine-based HILIC stationary phases.

LC-QqQ-MS/MS methodology for determination of purine and pyrimidine derivatives in unifloral honeys and application of chemometrics for their classification

The new liquid chromatographic-triple quadrupole tandem mass spectrometry (LC-QqQ-MS/MS) method for determination of purine and pyrimidine derivatives in honey produced by Apis mellifera was developed. 13 compounds were determined in total of 130 unifloral honey samples of 13 varieties: uracil, thymine, thymidine, xanthine, guanine, adenine, uridine, pseudouridine, xanthosine, inosine, hypoxanthine, guanosine and cytidine. The levels of some of these compounds varied between the specific honey types. The most abundant were uridine (up to 44.66 mg/kg), xanthine (up to 20.48 mg/kg) and xanthosine (up to 19.22 mg/kg). The data were evaluated by principal component analysis (PCA) and k-nearest neighbors (k-NN) classification (selected 9 and 8 honey types, respectively) to examine differences between the honey varieties allowing their discrimination based on purine and pyrimidine derivatives amounts. The data allowed to distinguish between 8 honey types (balanced accuracy 82%) and for most of the varieties obtained classification rates ranged from 96 to 100%.

Synthesis and chromatographic evaluation of pyrazinedicarboxylic anhydride bonded stationary phase

A silica based hydrophilic stationary phase bonding with 2,3-pyrazinedicarboxylic anhydride and amino groups was synthesized via amino-acid anhydride ring opening reaction. The bonded groups could not only provide hydrophilic interaction, but also electrostatic, π-π and hydrogen bonding interactions, etc. The results of characterization with elemental analysis and solid-state ¹³C cross-polarization magic-angle-spinning NMR indicated the successful preparation of amino and carboxyl bonded stationary phase named ZAC. The ζ-potential of ZAC stationary phase showed the negatively charge was dominate at pH larger than 3.5. Chromatographic evaluation revealed that ZAC stationary phase behaved well under HILIC mode. It showed different selectivity and retention compared to some typical commercial columns, and it was validated by the separation of chitooligosaccharides, flavonoid glycosides, organic acids and alkaloid samples. Based on the different selectivity between ZAC stationary phase and C18 columns, ZAC stationary phase also showed different selectivity with C18. And it was verified by the separation of Lonicerae Japonicae Flos and Menispermi Rhizoma extracts.

The theory and practice of ultrafast liquid chromatography: A tutorial

Modern high-throughput experimentation and challenging analytical problems of academic/industrial research have put the responsibility on separation scientists to develop new fast separation approaches. With the availability of high-pressure pumps, small particles with hydrolytically stable surface chemistries, reduced extra-column band broadening, and low volume detectors with fast signal processing, it is now feasible to do sub-minute to sub-second chromatography. Herein, the fundamental theoretical principles of ultrafast chromatography, along with practical solutions, are reviewed. Approaches for rapid separations in packed beds, narrow open tubular columns, and monoliths are demonstrated, along with the challenges that were faced. The instrumentation requirements (pumps, injection systems, detectors, column packing process) for using short columns ranging from 0.5 to 5 cm are examined, followed by real applications. One of the main problems in ultrafast chromatography is partial or complete peak overlap. As per Gidding's statistical overlap theory, peak overlap cannot be avoided for a completely random sample for a column with a given peak capacity. Signal processing techniques based on Fourier transform deconvolution of band broadening, power laws, derivatives, and iterative curve fitting are explained to help improve the chromatographic resolution. An example of ten peaks separated in under a second is shown and discussed. Other ultrafast separations in supercritical fluid chromatography or capillary electrophoresis are briefly mentioned to provide a complete understanding of this emerging field.

Facile preparation of bifunctional adsorbents for efficiently enriching N-glycopeptides and phosphopeptides

In bottom-up strategy, specific enrichment of glycopeptides and phosphopeptides from complicated biological samples is a prerequisite for efficient identifying glycosylation and phosphorylation by mass spectrometry. Although there were a plethora of materials used as either hydrophilic interaction liquid chromatography (HILIC) or immobilized metal affinity chromatography (IMAC) adsorbents, even several bifunctional materials for simultaneous enrichment of glycopeptides and phosphopeptides, most of them are not easily commercialized as many other well-performing adsorbents due to the complicated preparation process. In our case, a one-step modification strategy was developed to prepare bifunctional adsorbents for HILIC and IMAC, employing O-phospho-l-serine as the modifier and poly(GMA-co-EDMA) microspheres, a kind of macroporous adsorption resin (MAR) with epoxy groups, as the matrix. The MARs were directly modified with O-phospho-l-serine under facile condition for HILIC strategy and further chelated with Ti⁴⁺ for IMAC strategy. A total of 522 unique N-glycopeptides and 442 unique N-glycosylation sites mapped to 275 N-glycoproteins was identified from HeLa cell proteins, showing excellent enrichment efficiency in HILIC. Additionally, 3141 unique phosphopeptides were unambiguously identified from 200 μg of digest of HeLa cell proteins, demonstrating great enrichment efficiency in IMAC. Moreover, these materials have been successfully applied in the analysis of multiple biological samples including human serum and milk, demonstrating their feasibility for real sample applications and potential business value.

Development of a direct LC-ESI-MS method for the measurement of human serum carnosinase activity

Carnosine (β-alanyl-L-histidine) is a natural peptide that have been described as a potential pharmacological agent owing to some positive outcomes from several pharmacological tests in animal models of human diseases. However, carnosine has limited activity in humans since the peptide upon absorption is rapidly hydrolyzed in the serum by the enzyme carnosinase (i.e. CN1; E.C. 3.4.13.20). Over the years the main approaches aimed at limiting carnosine hydrolysis have been focused on obtaining CN1-stable derivatives with an increased bioavailability and unmodified or enhanced activity. Only recently the hypothesis of co-administration of carnosine and selective inhibitors of CN1 have been proposed. Such an approach requires reliable methods for screening the effect on carnosine hydrolysis rate operated by CN1 in a throughput scale allowing to test from few compounds up to whole compound libraries. The only assay with such features available in literature relies on ortho-phtalaldehyde (OPA) derivatization of the hydrolysis product (i.e. histidine), followed by a fluorimetric read. Herein, we propose an alternative method based on a direct measurement of the residual substrate by liquid chromatography-mass spectrometry (LC-MS). The assay demonstrated to be reliable since gave results comparable to literature data concerning the hydrolysis rate of carnosine as determined into human serum. Moreover, the method was quite flexible and easily adaptable to a substrate change, as demonstrated by the measurement of the hydrolysis rate of all the natural analogs of carnosine. In this context the data collected for anserine suggest that our method looked more reliable and substrate change can undergo an underestimation of hydrolytic activity in OPA -based assays.

Development of a new LC-MS method for accurate and sensitive determination of 33 pyrrolizidine and 21 tropane alkaloids in plant-based food matrices

Setting of maximum limits for a number of plant alkaloids is under discussion in the EU. The novel method developed and optimized in this study enables simultaneous determination of 21 tropane alkaloids (TAs) and 33 pyrrolizidine (PAs) together with their N-oxides (PANOs). For analysis of aqueous-methanolic extract, reversed phase ultra-high-performance liquid chromatography and tandem mass spectrometry (RP-U-HPLC-MS/MS) was employed. The method was validated for frequently contaminated matrices (i) sorghum, (ii) oregano, and (iii) mixed herbal tea. The recoveries at two spiking levels were in the range of 82-115%, 80-106%, and 78-117%, respectively, and repeatabilities were less than 19% for all analyte/matrix combinations. As regards the achieved limits of quantification (LOQ), their values were in the range of 0.5-10 μg kg^-1. The crucial problem encountered during method development, co-elution of multiple groups of isomeric alkaloids, was overcome by subsequent sample separation in the second chromatographic system, hydrophilic interaction liquid chromatography (HILIC), providing different separation selectivity. Lycopsamine, echinatine, and indicine (co-elution group 1) and N-oxides of indicine and intermedine (co-elution group 2), which could not be resolved on the commonly used RP column, were possible to separate fully by using the HILIC system.

Glycan-specific precipitation of glycopeptides in high organic content sample solvents used in HILIC

The composition of a sample solvent has a crucial impact on separations in hydrophilic interaction liquid chromatography (HILIC). In this short communication, we studied the effect of an organic modifier in the sample solvent on the solubility of different tryptic glycopeptides of hemopexin and haptoglobin proteins. The results showed that the solubility of glycopeptides in solvents with a high acetonitrile content depends on the type of attached N-glycan. We observed lower solubility in larger glycans attached to the same peptide backbone, and we demonstrated that glycopeptides containing sialic acids precipitate more readily than those without sialic acid. Therefore, the sample solvent composition in HILIC must be carefully optimized for accurate quantitative data collection and for adequate separation.