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The chemical derivatization of multiple lipid classes was developed using benzoyl chloride as a nonhazardous derivatization agent at ambient conditions. The derivatization procedure was optimized with standards for 4 nonpolar and 8 polar lipid classes and measured by reversed-phase ultrahigh-performance liquid chromatography-tandem mass spectrometry. The derivatization and nonderivatization approaches were compared on the basis of the calibration curves of 22 internal standards from 12 lipid classes. The new method decreased the limit of detection 9-fold for monoacylglycerols (0.9-1.0 nmol/mL), 6.5-fold for sphingoid base (0.2 nmol/mL), and 3-fold for diacylglycerols (0.9 nmol/mL). The sensitivity expressed by the ratio of calibration slopes was increased 2- to 10-fold for almost all investigated lipid classes and even more than 100-fold for monoacylglycerols. Moreover, the benzoylation reaction produces a more stable derivative of cholesterol in comparison to the easily in-source fragmented nonderivatized form and enabled the detection of fatty acids in a positive ion mode, which does not require polarity switching as for the nonderivatized form. The intralaboratory comparison with an additional operator without previous derivatization experiences shows the simplicity, robustness, and reproducibility. The stability of the derivatives was determined by periodical measurements during a one month period and five freeze/thaw cycles. The fully optimized derivatization method was applied to human plasma, which allows the detection of 169 lipid species from 11 lipid classes using the high confidence level of identification in reversed-phase (RP)-ultra high performance liquid chromatography (UHPLC)/mass spectrometry (MS). Generally, we detected more lipid species for monoacylglycerols, diacylglycerols, and sphingoid bases in comparison with previously reported papers without the derivatization.

Direct infusion of lipid extracts into the ion source of a mass spectrometer is a well-established method for lipid analysis. In most cases, nanofluidic devices are used for sample introduction. However, flow injection analysis (FIA) based on sample infusion from a chromatographic pump can offer a simple alternative to shotgun-based approaches. Here, we describe important modification of a method based on FIA and tandem mass spectrometry (MS/MS). We focus on minimizing contamination of the FIA/MS both to render the lipidomic platform more robust and to increase its capacity and applicability for long-sequence measurements required in clinical applications. Robust validation of the developed method confirms its suitability for lipid quantitation in human plasma analysis. Measurements of standard human plasma reference material (NIST SRM 1950) and a set of plasma samples collected from kidney cancer patients and from healthy volunteers yielded highly similar results between FIA-MS/MS and ultra-high-performance supercritical fluid chromatography (UHPSFC)/MS, thereby demonstrating that all modifications have practically no effect on the statistical output. Newly modified FIA-MS/MS allows for the quantitation of 141 lipid species in plasma (11 major lipid classes) within 5.7 min. Finally, we tested the method in a clinical laboratory of the General University Hospital in Prague. In the clinical setting, the method capacity reached 257 samples/day. We also show similar performance of the classification models trained based on the results obtained in clinical settings and the analytical laboratory at the University of Pardubice. Together, these findings demonstrate the high potential of the modified FIA-MS/MS for application in clinical laboratories to measure plasma and serum lipid profiles.

Reversed-phase ultrahigh-performance liquid chromatography q mass spectrometry (RP-UHPLC/MS) method was developed with the aim to unambiguously identify a large number of lipid species from multiple lipid classes in human plasma. The optimized RP-UHPLC/MS method employed the C18 column with sub-2 μm particles with the total run time of 25 min. The chromatographic resolution was investigated with 42 standards from 18 lipid classes. The UHPLC system was coupled to high-resolution quadrupole – time-of-flight (QTOF) mass analyzer using electrospray ionization (ESI) measuring full scan and tandem mass spectra (MS/MS) in positive- and negative-ion modes with high mass accuracy. Our identification approach was based onm/zvalues measured with mass accuracy within 5 ppm tolerance in the full scan mode, characteristic fragment ions in MS/MS, and regularity in chromatographic retention dependences for individual lipid species, which provides the highest level of confidence for reported identifications of lipid species including regioisomeric and other isobaric forms. The graphs of dependences of retention times on the carbon number or on the number of double bond(s) in fatty acyl chains were constructed to support the identification of lipid species in homologous lipid series. Our list of identified lipid species is also compared with previous publications investigating human blood samples by various MS based approaches. In total, we have reported more than 500 lipid species representing 26 polar and nonpolar lipid classes detected in NIST Standard reference material 1950 human plasma.

The rapid increase in lipidomic data has triggered a community-based movement to develop guidelines and minimum requirements for generating, reporting and publishing lipidomic data. The creation of a dynamic checklist summarizing key details of lipidomic analyses using a common language has the potential to harmonize the field by improving both traceability and reproducibility.

Purpose: RCC, the most common type of kidney cancer, is associated with high mortality. A non-invasive diagnostic test remains unavailable due to the lack of RCC-specific biomarkers in body fluids. We have previously described a significantly altered profile of sulfatides in RCC tumor tissues, motivating us to investigate whether these alterations are reflected in collectible body fluids and whether they can enable RCC detection. Methods: We collected and further analyzed 143 plasma, 100 urine, and 154 tissue samples from 155 kidney cancer patients, together with 207 plasma and 70 urine samples from 214 healthy controls. Results: For the first time, we show elevated concentrations of lactosylsulfatides and decreased levels of sulfatides with hydroxylated fatty acyls in body fluids of RCC patients compared to controls. These alterations are emphasized in patients with the advanced tumor stage. Classification models are able to distinguish between controls and patients with RCC. In the case of all plasma samples, the AUC for the testing set was 0.903 (0.844–0.954), while for urine samples it was 0.867 (0.763–0.953). The models are able to efficiently detect patients with early- and late-stage RCC based on plasma samples as well. The test set sensitivities were 80.6% and 90%, and AUC values were 0.899 (0.832–0.952) and 0.981 (0.956–0.998), respectively. Conclusion: Similar trends in body fluids and tissues indicate that RCC influences lipid metabolism, and highlight the potential of the studied lipids for minimally-invasive cancer detection, including patients with early tumor stages, as demonstrated by the predictive ability of the applied classification models.

The applicability of ultrahigh-performance supercritical fluid chromatography coupled with mass spectrometry (UHPSFC/MS) for the qualitative analysis of metabolites with a wide polarity range (log P: -3.89-18.95) was evaluated using a representative set of 78 standards belonging to nucleosides, biogenic amines, carbohydrates, amino acids, and lipids. The effects of the gradient shape and the percentage of water (1, 2, and 5%) were investigated on the Viridis BEH column. The screening of eight stationary phases was performed for columns with different interaction sites, such as hydrogen bonding, hydrophobic, π-π, or anionic exchange type interactions. The highest number of compounds (67) of the set studied was detected on the Torus Diol column, which provided a resolution parameter of 39. The DEA column had the second best performance with 58 detected standards and the resolution parameter of 54. The overall performance of other parameters, such as selectivity, peak height, peak area, retention time stability, asymmetry factor, and mass accuracy, led to the selection of the Diol column for the final method. The comparison of additives showed that ammonium acetate gave a superior sensitivity over ammonium formate. Moreover, the influence of the ion source on the ionization efficiency was studied by employing atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI). The results proved the complementarity of both ionization techniques, but also the superior ionization capacity of the ESI source in the negative ion mode, for which 53% of the analytes were detected compared to only 7% for the APCI source. Finally, optimized analytical conditions were applied to the analysis of a pooled human plasma sample. 44 compounds from the preselected set were detected in human plasma using ESI-UHPSFC/MS in MS

Ultrahigh-performance supercritical fluid chromatography-mass spectrometry (UHPSFC/MS) has a great potential for the high-throughput lipidomic quantitation of biological samples; therefore, the full optimization and method validation of UHPSFC/MS is compared here with ultrahigh-performance liquid chromatography-mass spectrometry (UHPLC/MS) in hydrophilic interaction liquid chromatography (HILIC) mode as the second powerful technique for the lipid class separation. First, the performance of six common extraction protocols is investigated, where the Folch procedure yields the best results with regard to recovery rate, matrix effect, and precision. Then, the full optimization and analytical validation for eight lipid classes using UHPSFC/MS and HILIC-UHPLC/MS methods are performed for the same sample set and applied for the lipidomic characterization of pooled samples of human plasma, human serum, and NIST SRM 1950 human plasma. The choice of appropriate internal standards (IS) for individual lipid classes has a key importance for reliable quantitative workflows illustrated by the selectivity while validation and the calculation of the quantitation error using multiple internal standards per lipid class. Validation results confirm the applicability of both methods, but UHPSFC/MS provides some distinct advantages, such as the successful separation of both non-polar and polar lipid classes unlike to HILIC-UHPLC/MS, shorter total run times (8 vs. 10.5 min), and slightly higher robustness. Various types of correlations between methods (UHPSFC/MS and HILIC-UHPLC/MS), biological material (plasma and serum), IS (laboratory and commercially mixtures), and literature data on the standard reference material show the intra- and inter-laboratory comparison in the quantitation of lipid species from eight lipid classes, the concentration differences in serum and plasma as well as the applicability of non-commercially available internal standard mixtures for lipid quantitation.

This manuscript is submittedby the international Lipidomics community underthe category 'Matters Arising' in Nature Communicationsin response to Vasilopoulou et al., Nature Comm, 11: ArtNo 331 (2020).&nbsp

Glycosphingolipids (GSL) represent a highly heterogeneous class of lipids with many cellular functions, implicated in a wide spectrum of human diseases. Their isolation, detection, and comprehensive structural analysis is a challenging task due to the structural diversity of GSL molecules. In this work, GSL subclasses are isolated from human plasma using an optimized monophasic ethanol–water solvent system capable to recover a broad range of GSL species. Obtained deproteinized plasma is subsequently purified and concentrated by C18-based solid-phase extraction (SPE). The hydrophilic interaction liquid chromatography coupled to electrospray ionization linear ion trap tandem mass spectrometry (HILIC-ESI-LIT-MS/MS) is used for GSL analysis in the human plasma extract. Our results provide an in-depth profiling and structural characterization of glycosph- ingolipid and some phospholipid subclasses identified in the human plasma based on their retention times and the interpretation of tandem mass spectra. The structural composition of particular lipid species is readily characterized based on the detailed interpretation of mass spectrometry (MS) and tandem mass spectrometry (MS/MS) spectra and further confirmed by specific fragmentation behavior following predictable patterns, which yields to the unambiguous identification of 154 GSL species within 7 lipid subclasses and 77 phospholipids representing the highest number of GSL species ever reported in the human plasma. The developed HILIC-ESI-MS/MS method can be used for further clinical and biological research of GSL in the human blood or other biological samples. Glykosfingolipidy (GSL) představují vysoce heterogenní třídu lipidů s mnoha buněčnými funkcemi, implikovanými do širokého spektra lidských onemocnění. Jejich izolace, detekce a komplexní strukturní analýza je náročným úkolem vzhledem ke strukturní rozmanitosti molekul GSL. V této práci jsou podtřídy GLS izolovány z lidské plazmy pomocí optimalizovaného monofázického systému rozpouštědla ethanol-voda schopného obnovit širokou škálu GSL. Získaná deproteinizovaná plazma se následně čistí a koncentruje extrakcí na pevné fázi na bázi C18 (SPE). Hydrofilní interakční kapalinová chromatografie spojená s tandemovou hmotnostní spektrometrií s elektrosprejovou ionizací a lineání iontovou pastí (HILIC-ESI-LIT-MS/MS) se používá pro analýzu GSL v lidském extraktu plazmy. Naše výsledky poskytují hloubkové profilování a strukturní charakterizaci glykosfingolipidu a některých fosfolipidových podtříd identifikovaných v lidské plazmě na základě jejich retenčních časů a interpretace tandemových hmotnostních spekter. Strukturní složení jednotlivých lipidů je snadno charakterizováno na základě podrobné interpretace hmotnostně spektrometrických (MS) a tandemových hmotnostně spektrometrických (MS/MS) spekter a dále potvrzeno specifickým fragmentačním chováním podle předvídatelných vzorců, což vede k jednoznačné identifikaci 77 fosfolipidů a 154 GSL v rámci 7 lipidových podtříd představujících nejvyšší počet GSL, který byl kdy v lidské plazmě hlášen. Vyvinutá metoda HILIC-ESI-MS/MS může být použita pro další klinický a biologický výzkum GSL v lidské krvi nebo jiných biologických vzorcích.

Pancreatic cancer has the worst prognosis among all cancers1. Cancer screening programs based on the analysis of body fluids can improve the survival time of patients, who are often diagnosed too late at an incurable stage2. Several studies have reported the dysregulation of lipid metabolism in tumor cells and tissues3, suggesting that the changes of blood lipidome may accompany tumor growth and progression. Analytical methods based on mass spectrometry (MS) using either direct infusion or chromatographic separation4 are convenient for high-throughput lipidomic profiling. Here we show that the comprehensive quantitation of a wide range of serum lipids reveals statistically significant differences between pancreatic cancer patients and healthy controls visualized by multivariate data analysis. Initial results for 364 human serum samples in the discovery phase were subsequently verified in the qualification phase on 554 samples measured by three independent laboratories, and finally on 830 samples from four blood collection sites in the verification phase. Concentrations suggestive of dysregulation of some very long chain sphingomyelins (SM 42:1, SM 41:1, SM 39:1, and SM 40:1), ceramides (Cer 41:1, and Cer 42:1), and (lyso)phosphatidylcholines (LPC 18:2) were recorded. Some lipid species indicated a potential as biomarkers of survival. The sensitivity and specificity to diagnose pancreatic cancer is over 90%, which outperforms CA 19-9, especially in early stage, and is comparable to established imaging diagnostic methods. The accuracy of lipidomic approach is not influenced by the cancer stage, analytical method, or blood collection site.

Effects of blood collection tubes, the time period, the sample origin, and the method used on the lipidomic profile are investigated by ultrahigh-performance supercritical fluid chromatography - mass spectrometry (UHPSFC/MS) and hydrophilic interaction liquid chromatography ultrahigh-performance liquid chromatography - mass spectrometry (HILIC-UHPLC/MS). Heparin plasma samples have been obtained from 99 healthy volunteers at three time points separated by six-month intervals together with one collection for EDTA plasma and serum. Furthermore, lipid concentrations in heparin plasma collected at two different sites are compared. 171 lipid species from eight lipid classes are quantified with UHPSFC/MS, and 122 lipid species from four lipid classes with HILIC-UHPLC/MS. The accuracy of both methods is monitored by the quantitation error using two internal standards (IS) per individual lipid classes. No significant differences in lipid profiles are observed for different time points and types of collection tubes (heparin plasma, EDTA plasma, and serum). Most pronounced lipid concentration differences are observed for the comparison of NIST SRM 1950 human plasma and mean lipid concentrations of the investigated cohort. Furthermore, differences in lipid concentrations are observed between employed methods (UHPSFC/MS vs. HILIC-UHPLC/MS), which can be compensated by the normalization using NIST SRM 1950 human plasma used as the quality control sample.

Tumor heterogeneity is one of the hallmarks of glioblastoma multiforme (GBM). Morphology within a given GBM tumor can be extremely variable where some regions of the tumor have a soft, gel-like structure while other areas are dense and fibrous. Abnormal mechanical stress and tissue stiffening caused by cancer proliferation are believed to affect vascularity by compressing structurally weak blood vessels and restricting the supply of nutrients and oxygen to the tissue. These effects contribute to a hypoxic microenvironment that promotes disease progression and chemoresistance. The genetic and molecular mechanisms that govern tissue stiffness within GBM tumors, however, are largely unknown. Magnetic Resonance Elastography (MRE) is an emerging technique for quantifying tissue stiffness non-invasively. We have evaluated 10 GBM patients by MRE imaging obtained prior to surgical resection. During surgery, 2–7 stereotactically navigated biopsies were collected from locations within the tumor with varying degrees of measured stiffness. Biopsies were processed to extract RNA, proteins, polar metabolites and lipids. Biomolecules were analyzed on relevant -omics platforms (RNA sequencing, MS-proteomics and lipidomics, NMR of polar metabolites). Differential expression and gene set enrichment analysis of patient paired biopsies indicate an overall increase in macrophage infiltration and extracellular matrix re-organization associated with increased tumor stiffness. Among the most highly upregulated genes in stiff tumor tissue were lymphatic endothelial hyaluronic acid receptor 1 (LYVE-1) and macrophage receptor with collagenous structure (MARCO), both of which have been associated with immune cell infiltration and tissue stiffness. Our preliminary findings offer novel insights into tumor morphology in GBM that can be inferred from imaging prior to surgery. This can be used to identify tumor regions with high risk of progression and infiltration, thereby informing and guiding surgical strategy and may ultimately lead to novel treatment strategies.

SummaryBackground The amino sulphonic acid taurine reduces oxidative endoplasmatic reticulum stress and inhibits hepatic stellate cell activation, which might lead to reduction of portal pressure in cirrhosis. Aim To assess the haemodynamic effects of taurine supplementation in patients with cirrhosis and varices. Methods Patients with hepatic venous pressure gradient (HVPG) ≥12 mm Hg were included in this prospective proof of concept study. Concomitant nonselective beta-blockers therapy was not allowed. Patients received either 4 weeks of oral taurine (6 g/day), or placebo, prior to evaluation of HVPG response. Results Thirty patients were screened and 22 included in the efficacy analysis (12 taurine/10 placebo; 64% male, mean age: 52 ± 11 years, Child A: 9%, B:64%, C:27%, ascites:68%). In the taurine group, mean HVPG dropped from 20 mm Hg (±4) at baseline to 18 mm Hg (±4) on day 28 (mean relative change: −12%, P = .0093). In the placebo group, mean HVPG increased from 20 mm Hg (±5) at baseline to 21 mm Hg (±5) on day 28 (mean relative change:+2%, P = .4945). Taurine had no significant effects on systemic haemodynamics. Seven of 12 patients (58%) on taurine achieved a HVPG response >10%, compared to none in the placebo group (P = .0053). In a multivariate linear model, HVPG reduction was significantly larger in the taurine group compared to placebo group (P = .0091 and P = .0109 for absolute and relative change respectively). Treatment-related adverse events included gastrointestinal discomfort and fatigue, and were usually mild and comparable between treatment groups. Conclusion Taurine is safe and may reduce portal pressure in cirrhotic patients. More studies on the underlying mechanisms of action and long-term effects of taurine supplementation are warranted.

Major differences in the chromatographic performance of a zwitterion ion-exchange type (ZWIX) chiral stationary phase (CSP) in supercritical fluid chromatography (SFC) and high-performance liquid chromatography (HPLC) have been observed. To explain these differences, transition from HPLC to SFC conditions has been performed. The amount of a protic organic modifier in supercritical carbon dioxide (scCO2) was stepwise increased and the effect of this change studied using acidic, basic and ampholytic analytes. At the same time, the effect of various basic additives to the mobile phase and transient acidic buffer species, formed by the reaction of scCO2 with the organic modifier and additives, was assessed. Evidence is provided that a transient acid together with the intrinsic counter-ions present in the ZWIX selector structure drive the elution of analytes even when no buffer is employed. We show that the tested analytes can be enantioseparated under both SFC and HPLC conditions; the best conditions for the resolution of ampholytes are in the so-called enhanced-fluidity mobile phase region. As a consequence, subcritical fluid and enhanced-fluidity mobile phase regions seem to be chromatographic modes with a high potential for operating ZWIX CSPs.

For acceptance of supercritical fluid chromatography (SFC) as a routine analysis method, the hyphenation to mass spectrometry (MS), which is typically achieved either by a splitting device or by the employment of an additional make up flow, has to be improved. Direct coupling of SFC to MS (/MS) would simplify the handling of this method. Consequently, this work focused on the direct coupling of SFC to mass spectrometry and the influence of the employed ion source on signal intensities of polar and ionic compounds in biological samples. A method for separating metabolites of the tryptophan pathway as well as other amino acids is shown. Results demonstrate that SFC is capable of separating analytes of polar and ionic nature. Modifications of the SFC system by cryostat cooling lead to higher temperature stability in the booster pump and therefore to a better reproducibility of retention times and a low dispersion nozzle inside the active back pressure regulator (ABPR) significantly improves peak shape and sensitivity when using the MS. The comparison of the ionization efficiencies using electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) in positive and negative ion mode shows analyte depending sensitivities. However, results indicate that APCI is better suitable for the ionization of amino acids with polar side chains, whereas ESI proved superior for the ionization of amino acids featuring hydrophobic residues. Analyte signals were suppressed with ESI when using a complex matrix such as human serum, but rather enhanced when using APCI.

Ultrahigh-performance supercritical fluid chromatography - mass spectrometry (UHPSFC/MS), ultrahigh-performance liquid chromatography - mass spectrometry (UHPLC/MS), and matrix-assisted laser desorption/ionization (MALDI) - MS techniques were used for the lipidomic characterization of exosomes isolated from human plasma. The high-throughput methods UHPSFC/MS and UHPLC/MS using a silica-based column containing sub-2 μm particles enabled the lipid class separation and the quantitation based on exogenous class internal standards in

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.

During inflammation, proteins and lipids act in a concerted fashion, calling for combined analyses. Fibroblasts are powerful mediators of chronic inflammation. However, little is known about eicosanoid formation by human fibroblasts. The aim of this study was to analyze the formation of the most relevant inflammation mediators including proteins and lipids in human fibroblasts upon inflammatory stimulation and subsequent treatment with dexamethasone, a powerful antiphlogistic drug. Label-free quantification was applied for proteome profiling, while an in-house established data-dependent analysis method based on high-resolution mass spectrometry was applied for eicosadomics. Furthermore, a set of 188 metabolites was determined by targeted analysis. The secretion of 40 proteins including cytokines, proteases, and other inflammation agonists as well as 14 proinflammatory and nine anti-inflammatory eicosanoids was found significantly induced, while several acylcarnithins and sphingomyelins were found significantly downregulated upon inflammatory stimulation. Treatment with dexamethasone downregulated most cytokines and proteases, abrogated the formation of pro- but also anti-inflammatory eicosanoids, and restored normal levels of acylcarnithins but not of sphingomyelins. In addition, the chemokines CXCL1, CXCL5, CXCL6, and complement C3, known to contribute to chronic inflammation, were not counter-regulated by dexamethasone. Similar findings were obtained with human mesenchymal stem cells, and results were confirmed by targeted analysis with multiple reaction monitoring. Comparative proteome profiling regarding other cells demonstrated cell-type-specific synthesis of, among others, eicosanoid-forming enzymes as well as relevant transcription factors, allowing us to better understand cell-type-specific regulation of inflammation mediators and shedding new light on the role of fibroblasts in chronic inflammation.

A set of new mixed-mode ion-exchange stationary phases is presented. The backbone of organic selectors is formed by a linear hydrocarbon chain, which is divided into two parts of various lengths by a heteroatom (oxygen or nitrogen). In all studied cases, there is a sulfonic acid moiety as the terminal group. Therefore, selectors bearing oxygen gave rise to strong cation ion-exchange stationary phases, while selectors with an embedded nitrogen atom (inducing a weak anion exchange capacity) were used to create zwitterion ion-exchange stationary phases. The new mixed-mode stationary phases were chromatographically evaluated in high performance liquid chromatography (HPLC) and supercritical fluid chromatography (SFC) using isocratic elution conditions to disclose their chromatographic potential. In HPLC mode, aqueous-rich reversed phase chromatography, acetonitrile-rich hydrophilic interaction liquid chromatography and methanolic ion-exchange chromatography mobile phases were employed. In these chromatographic modes, retention factors and selectivity values for a test set of basic and zwitterionic analytes were determined. The results were compared and principal component analysis for each chromatographic mode was performed. For all chromatographic modes, the component 1 in the principal component analysis reflected the elution order. The application of different mobile phases on a particular column resulted not only in variation in retention, but also in modified selectivity, and different elution order of the analytes. The orthogonality of the elution order depending on the employed mobile phase conditions was especially reflected for structurally closely related analytes, such as melatonin and N-acetyl-serotonin, tryptamine and serotonin or noradrenalin and octopamine. However, ion-exchange interactions remain the main driving force for retention. From all investigated stationary phases, the SCX 2 (C5-linker and C4-spacer) seems to be the best choice for the separation of basic analytes using different mobile phase conditions.

This review summarizes available mass spectrometry (MS) based approaches for the quantitative analysis of lipids in biological samples in the cancer research, which is termed here as oncolipidomics. The methodological part shows possible configurations of stand-alone MS or MS coupled to liquid-phase separation techniques. For the characterization of various lipids with the special emphasis on methods convenient for robust high-throughput lipidomic quantitation of biological samples, such as body fluids, tissues, and cell lines. The critical assessment of lipid species dysregulated in various cancer types is provided with the goal to summarize and generalize the typical up and down regulated lipids associated with the progress of tumor growth and evaluate possible future use of lipidomic analysis in the early cancer diagnosis.

Enantioseparation of chiral amines with HPLC has developed into a widely used analytical and preparative tool. Chiral basic molecules, which act as cationic species upon protonation, are suited for an enantioselective cation exchange process. Novel strong cation exchangers (SCX) based on different 3,5-disubstituted benzoic acids functionalized with trans-(R,R)- and trans-(S,S)-2-aminocyclohexanesulfonic acid as the chiral selector (SO) and ion exchange unit were synthesized. Employing 1,3-dipolar cycloaddition (azide-yne click chemistry), the SOs were immobilized onto azidopropyl-modified silica gel. This immobilization strategy enables controlled loading of the SO, and especially, high SO density on the silica surface compared to the thiol-ene click immobilization. The performance of the novel SCX chiral stationary phases was evaluated under polar organic mode conditions with different ratios of methanol and acetonitrile, thereby changing the polarity of the bulk mobile phase. The type of co- and counterion additives employed in the mobile phase was varied as well. The influence of the formed 1,2,3-triazol spacer as well as different substitution patterns in the benzene unit on the chiral recognition properties of the SOs is discussed.

A new strong cation exchange type chiral stationary phase (SCX CSP) based on a syringic acid amide derivative of trans-(R, R)-2-aminocyclohexanesulfonic acid was applied to subcritical fluid chromatography (SFC) for separation of various chiral basic drugs and their analogues. Mobile phase systems consisting of aliphatic alcohols as polar modifiers and a broad range of amines with different substitution patterns and lipophilicity were employed to evaluate the impact on the SFC retention and selectivity characteristics. The observed results point to the existence of carbonic and carbamic acid salts formed as a consequence of reactions occurring between carbon dioxide, the alcoholic modifiers and the amine species present in the sub/supercritical fluid medium, respectively. Evidence is provided that these species are essential for affecting ion exchange between the strongly acidic chiral selector units and the basic analytes, following the well-established stoichiometric displacement mechanisms. Specific trends were observed when different types of amines were used as basic additives. While ammonia gave rise to the formation of the most strongly eluting carbonic and carbamic salt species, simple tertiary amines consistently provided superior levels of enantioselectivity. Furthermore, trends in the chiral SFC separation characteristics were investigated by the systematic variation of the modifier content and temperature. Different effects of additives are interpreted in terms of changes in the relative concentration of the transient ionic species contributing to analyte elution, with ammonia-derived carbamic salts being depleted at elevated temperatures by decomposition. Additionally, in an effort to optimize SFC enantiomer separation conditions for selected analytes, the impact of the type of the organic modifier, temperature, flow rate and active back pressure were also investigated.

The aim of this study was developing a supercritical fluid chromatography tandem mass spectrometry (SFC-MS/MS) method and an ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method, for the analysis of N-acetyl-serotonin (NAS) and melatonin (Mel) in human serum, and to compare the performance of these methods. Deuterated isotopologues of the neurotransmitters were synthesized and evaluated for suitability as internal standards in sample preparation. Liquid-liquid extraction was selected as sample preparation procedure. With chloroform, the best extraction solvent tested, an extraction yield of 48 ± 2% for N-acetyl-serotonin and 101 ± 10% for melatonin was achieved. SFC separation was accomplished within 3 min on a BEH stationary phase, employing isocratic elution with 90% carbon dioxide and 0.1% formic acid as well as 0.05% ammonium formate in methanol. For the 4 min UHPLC gradient separation with 0.1% formic acid in water and methanol, respectively, a Kinetex XB-C18 was used as stationary phase. Both chromatographic techniques were optimized regarding mobile phase composition, additives to the mobile phase and column temperature. Multiple reaction monitoring (MRM) analysis was used for quantification of the metabolites. Both methods were validated regarding retention time stability, LOD, LOQ, repeatability and reproducibility of quantification, process efficiency, extraction recovery and matrix effects. LOD and LOQ were 0.017 and 0.05 pg μL(-1) for NAS and 0.006 and 0.018 pg μL(-1) for Mel in SFC-MS/MS compared to 0.028 and 0.1 pg μL(-1) for NAS and 0.006 and 0.017 pg μL(-1) for Mel in UHPLC-MS/MS.

In this study we attempted to describe in a comparative manner the enantioselectivity performance of six different polysaccharide- and two strong cation exchanger-type chiral stationary phases (CSPs) for the resolution of free and N-protected β-carboline derivatives. On commercially available cellulose- or amylose-based CSPs, the enantioseparations were carried out in normal-phase mode by variation of the nature and the concentration of the alcohol modifier in n-hexane as mobile phase. With the application of strong cation exchanger-type CSPs, the enantioseparations were optimized by the variation of methanol-acetonitrile bulk solvent compositions in the presence of various amounts of acid and base additives acting as counter-ions. Detailed thermodynamic investigations revealed that in all cases the enantioseparations observed were enthalpically driven, i.e. the retention and selectivity decreased with increasing temperature. Elution sequences were determined routinely; no general rule was found on polysaccharide-based CSPs, while on the two enantiomeric strong cation exchanger-type CSPs the predicted reversal of the elution sequence could be confirmed on switching from one enantiomeric CSP to the other form.

The synthesis, ab initio calculations, and a comparative nuclear magnetic resonance study of a novel chiral mefloquine-based selector (SO) are presented. On a series of variously N-acyl protected leucine selectands (SAs), a feasibility study of mefloquine carbamate as a basic chiral solvating agent, and potential fluorophilic high-performance liquid chromatography selector has been undertaken and evaluated. An analogy is drawn between the new SO and tert-butylcarbamoyl quinidine as a reference.

We present the enantioseparation of new designer drugs from the cathinone family on structurally different chiral ion-exchange type stationary phases. A novel strong cation-exchange type chiral stationary phase was synthesized and its performance compared with previously reported ion-exchange type chiral stationary phases. The influence of structural elements of the chiral selectors on their chromatographic performance was studied and the possibilities of tuning chromatographic parameters by varying the polarity of the employed mobile phases were determined. Evidence is provided that a change in mobile phase composition strongly influences the solvation shell of the polarized and polarizable units of the selectors and analytes, as well as ionizable mobile phase additives. Furthermore, the structural features of the selectors (e.g. the size of aromatic units and their substitution pattern) are shown to play a key role in the effective formation of diastereomeric complexes with analytes. Thus, we have achieved the enantioseparation of all test analytes with a mass spectrometry-compatible mobile phase with a chiral strong cation-exchange type stationary phase.

Enantioseparation of chiral amines with HPLC has developed into a widely used analytical and preparative tool. Chiral basic molecules, which act as cationic species upon protonation, are suited for an enantioselective cation exchange process. Novel strong cation exchangers (SCX) based on different 3,5-disubstituted benzoic acids functionalized with trans-(R,R)- and trans-(S,S)-2-aminocyclohexanesulfonic acid as the chiral selector (SO) and ion exchange unit were synthesized. Employing 1,3-dipolar cycloaddition (azide-yne click chemistry), the SOs were immobilized onto azidopropyl-modified silica gel. This immobilization strategy enables controlled loading of the SO, and especially, high SO density on the silica surface compared to the thiol-ene click immobilization. The performance of the novel SCX chiral stationary phases was evaluated under polar organic mode conditions with different ratios of methanol and acetonitrile, thereby changing the polarity of the bulk mobile phase. The type of co- and counterion additives employed in the mobile phase was varied as well. The influence of the formed 1,2,3-triazol spacer as well as different substitution patterns in the benzene unit on the chiral recognition properties of the SOs is discussed.

The performance of a strong cation exchange-type (SCX) chiral stationary phase (CSP) was evaluated with subcritical fluid chromatography (subFC) and high performance liquid chromatography (HPLC). The chromatographic conditions in subFC were optimized by changing the amount of polar organic modifier, concentration of a basic additive in the modifier, system pressure and temperature. In this way the concentration of in situ formed transient ionic species could be varied. The gradual change of the concentration of the transient buffer, i.e. gradient elution conditions in subFC, was found beneficial for separation of a mixture of racemic compounds. The strength and amount of the in situ formed buffer was estimated on the basis of comparative experiments in subSFC and HPLC.

The synthesis, ab initio calculations, and a comparative nuclear magnetic resonance study of a novel chiral mefloquine-based selector (SO) are presented. On a series of variously N-acyl protected leucine selectands (SAs), a feasibility study of mefloquine carbamate as a basic chiral solvating agent, and potential fluorophilic high-performance liquid chromatography selector has been undertaken and evaluated. An analogy is drawn between the new SO and tert-butylcarbamoyl quinidine as a reference.