Adduct ion formation as a tool for the molecular structure assessment of ten isomers in traveling wave and trapped ion mobility spectrometry

Separation of triacylglycerol (TAG) isomers by cyclic ion mobility mass spectrometry

Triacylglycerols (TAGs), a major lipid class in foods and the human body, consist of three fatty acids esterified to a glycerol backbone. They can occur in various isomeric forms, including sn-positional, cis/trans configurational, acyl chain length, double bond positional, and mixed type isomers. Separating isomeric mixtures is of great interest as different isomers can have distinct influence on mechanisms, such as digestibility, oxidative stability, or lipid metabolism. However, TAG isomer separation remains challenging with established analytical methodologies such as liquid-chromatography coupled to mass spectrometry (LC-MS). In this study, we developed a method with cyclic ion mobility mass spectrometry (cIMS-MS) for the separation and identification of all types of TAG isomers. First, the influence of different adducts (Li+, NH4+, Na+, and K+) on the separation was studied. Overall, it was concluded that the sodium adduct is the best choice to efficiently separate all types of TAG isomers. In addition, trends were found in the influence of specific structural features on the drift time order. An order of relative influence (from high to low) was established; (1) degree of unsaturation of the fatty acid(s) on an exterior position (if the total degree of unsaturation(s) is equal in both TAGs), (2) acyl chain length on the exterior positions, (3) cis/trans configuration, and (4) double bond (DB)-position. Finally, various cIMS-MS strategies were developed for the separation of mixtures containing four, five, and six isomers. To conclude, the developed methods can be used for separation of complex mixtures of TAG isomers and have great potential to be expanded to isomers of similar types of lipids such as di- and monoacylglycerols. This study also shows the potential of cIMS-MS to be used for the application on real TAG samples.

Investigating the Potential of Drift Tube Ion Mobility for the Analysis of Oxidized Lipids

Epilipids, a subset of the lipidome that comprises oxidized, nitrated, and halogenated lipid species, show important biochemical activity in the regulation of redox lipid metabolism by influencing cell fate decisions, including death, health, and aging. Due to the large chemical diversity, reversed-phase liquid chromatography-high-resolution mass spectrometry (RPLC-HRMS) methods have only a limited ability to separate numerous isobaric and isomeric epilipids. Ion mobility spectrometry (IMS) is a gas-phase separation technique that can be combined with LC-HRMS to improve the overall peak capacity of the analytical platform. Here, we illustrate the advantages and discuss the current limitations of implementing IMS in LC-HRMS workflows for the analysis of oxylipins and oxidized complex lipids. Using isomeric mixtures of oxylipins, we demonstrated that while deprotonated ions of eicosanoids were poorly resolved by IMS, sodium acetate and metal adducts (e.g., Li, Na, Ag, Ba, K) of structural isomers often showed ΔCCS% above 1.4% and base peak separation with high-resolution demultiplexing (HRDm). The knowledge of the IM migration order was also used as a proof of concept to help in the annotation of oxidized complex lipids using HRDm and all-ion fragmentation spectra. Additionally, we used a mixture of deuterium-labeled lipids for a routine system suitability test with the purpose of improving harmonization and interoperability of IMS data sets in (epi)lipidomics.

Technological advances for analyzing the content of organ-on-a-chip by mass spectrometry

Three-dimensional (3D) cell cultures, including organ-on-a-chip (OOC) devices, offer the possibility to mimic human physiology conditions better than 2D models. The organ-on-a-chip devices have a wide range of applications, including mechanical studies, functional validation, and toxicology investigations. Despite many advances in this field, the major challenge with the use of organ-on-a-chips relies on the lack of online analysis methods preventing the real-time observation of cultured cells. Mass spectrometry is a promising analytical technique for real-time analysis of cell excretes from organ-on-a-chip models. This is due to its high sensitivity, selectivity, and ability to tentatively identify a large variety of unknown compounds, ranging from metabolites, lipids, and peptides to proteins. However, the hyphenation of organ-on-a-chip with MS is largely hampered by the nature of the media used, and the presence of nonvolatile buffers. This in turn stalls the straightforward and online connection of organ-on-a-chip outlet to MS. To overcome this challenge, multiple advances have been made to pre-treat samples right after organ-on-a-chip and just before MS. In this review, we summarised these technological advances and exhaustively evaluated their benefits and shortcomings for successful hyphenation of organ-on-a-chip with MS.

High-resolution ion mobility spectrometry-mass spectrometry for isomeric separation of prostanoids after Girard's reagent T derivatization

RATIONALE

Isomeric separation of prostanoids is often a challenge and requires chromatography and time-consuming sample preparation. Multiple prostanoid isomers have distinct in vivo functions crucial for understanding the inflammation process, including prostaglandins E₂ (PGE₂ ) and D₂ (PGD₂ ). High-resolution ion mobility spectrometry (IMS) based on linear ion transport in low-to-moderate electric fields and nonlinear ion transport in strong electric fields emerges as a broad approach for rapid separations prior to mass spectrometry.

METHODS

Derivatization with Girard's reagent T (GT) was used to overcome inefficient ionization of prostanoids in negative ionization mode due to poor deprotonation of the carboxylic acid group. Three high-resolution IMS techniques, namely linear cyclic IMS, linear trapped IMS, and nonlinear high-field asymmetric waveform IMS, were compared for the isomeric separation and endogenous detection of prostanoids present in intestinal tissue.

RESULTS

Direct infusion of GT-derivatized prostanoids proved to increase the ionization efficiency in positive ionization mode by a factor of >10, which enabled detection of these molecules in endogenous concentration levels. The high-resolution IMS comparison revealed its potential for rapid isomeric analysis of biologically relevant prostanoids. Strengths and weaknesses of both linear and nonlinear IMS are discussed. Endogenous prostanoid detection in intestinal tissue extracts demonstrated the applicability of our approach in biomedical research.

CONCLUSIONS

The applied derivatization strategy offers high sensitivity and improved stereoisomeric separation for screening of complex biological systems. The high-resolution IMS comparison indicated that the best sensitivity and resolution are achieved by linear and nonlinear IMS, respectively.

Separation of flavonoid isomers by cyclic ion mobility mass spectrometry

Analytical techniques, such as liquid chromatography coupled to mass spectrometry (LC-MS) or nuclear magnetic resonance (NMR), are widely used for characterization of complex mixtures of (isomeric) proteins, carbohydrates, lipids, and phytochemicals in food. Food can contain isomers that are challenging to separate, but can possess different reactivity and bioactivity. Catechins are the main phenolic compounds in tea; they can be present as various stereoisomers, which differ in their chemical properties. Currently, there is a lack of fast and direct methods to monitor interconversion and individual reactivity of these epimers (e.g. epicatechin (EC) and catechin (C)). In this study, cyclic ion mobility mass spectrometry (cIMS-MS) was explored as a potential tool for the separation of catechin epimers. Formation of sodium and lithium adducts enhanced IMS separation of catechin epimers, compared to deprotonation and protonation. Baseline separation of the sodium adducts of catechin epimers was achieved. Moreover, we developed a fast method for the identification and semi-quantification of cIMS-MS separated catechin epimers. With this method, it is possible to semi-quantify the ratio between EC and C (1:5 to 5:1, within 50-1200 ng mL^-1) in food samples, such as tea. Finally, the newly developed approach for cIMS-MS separation of flavonoids was demonstrated to be successful in separation of two sets of positional isomers (i.e. morin, tricetin, and quercetin; and kaempferol, fisetin, luteolin, and scutellarein). To conclude, we showed that both epimers and positional isomers of flavonoids can be separated using cIMS-MS, and established the potential of this method for challenging flavonoid separations.

Ion mobility mass spectrometry in the omics era: Challenges and opportunities for metabolomics and lipidomics

Researchers worldwide are taking advantage of novel, commercially available, technologies, such as ion mobility mass spectrometry (IM-MS), for metabolomics and lipidomics applications in a variety of fields including life, biomedical, and food sciences. IM-MS provides three main technical advantages over traditional LC-MS workflows. Firstly, in addition to mass, IM-MS allows collision cross-section values to be measured for metabolites and lipids, a physicochemical identifier related to the chemical shape of an analyte that increases the confidence of identification. Second, IM-MS increases peak capacity and the signal-to-noise, improving fingerprinting as well as quantification, and better defining the spatial localization of metabolites and lipids in biological and food samples. Third, IM-MS can be coupled with various fragmentation modes, adding new tools to improve structural characterization and molecular annotation. Here, we review the state-of-the-art in IM-MS technologies and approaches utilized to support metabolomics and lipidomics applications and we assess the challenges and opportunities in this growing field.

Ion mobility spectrometry-tandem mass spectrometry strategies for the on-line monitoring of a continuous microflow reaction

Continuous flow chemistry is an efficient, sustainable and green approach for chemical synthesis that surpasses some of the limitations of the traditional batch chemistry. Along with the multiple advantages of a flow reactor, it could be directly connected to the analytical techniques for on-line monitoring of a chemical reaction and ensure the quality by design. Here, we aim to use ion mobility, mass and tandem mass spectrometry (IMS-MS and MS/MS) for the on-line analysis of a pharmaceutically relevant chemical reaction. We carried out a model hetero-Diels Alder reaction in a microflow reactor directly connected to the IMS-MS and MS/MS using either electrospray or atmospheric pressure photo ionization methods. We were able to monitor the reaction mechanism of the Diels Alder reaction and structurally characterize the reaction product and synthesis side-products. The chosen approach enabled identification of two isomers of the main reaction product. A new strategy to annotate the ion mobility spectrum in the absence of standard molecules was introduced and tested for its validity. This was achieved by determining the survival yield of each isomer upon ion mobility separation and density functional theory calculations. This approach was verified by comparing the theoretically driven collision cross section values to the experimental data. In this paper, we demonstrated the potential of combined IMS-MS and MS/MS on-line analysis platform to investigate, monitor and characterize structural isomers in the millisecond time scale.

Enantio-separation of pregabalin by ternary complexation using trapped ion mobility spectrometry

Rationale The rapid identification of small-molecule chiral drugs is challenging due to subtle structural differences. Different enantiomers of chiral drugs may produce inverse biological effects through their different pharmacokinetics. Therefore, it is highly desirable to distinguish the chirality of drug molecules.

METHODS

The chirality of pregabalin was distinguished by studying the ion mobility spectra of the ternary non-covalent complexes formed with cyclodextrins (CDs), pregabalin, and alkali-earth cations using trapped ion mobility spectrometry (TIMS). The ternary non-covalent complex ions were determined by electrospray ionization of mixed solutions. The analyzed sample was simply mixed, without derivatization or sample pretreatment. The relative contents of pregabalin enantiomers were derived using a calibration curve method.

RESULTS

The ion mobility spectra of several ternary non-covalent complexes formed with α-, β-, and γ-CD, pregabalin, and alkali-earth cations were obtained. We compared their ability to distinguish the chirality of pregabalin. The best peak-to-peak resolution (R_p-p ) was estimated to be 2.20 for [2β-CD + pregabalin + Sr]²⁺ , which can be ascribed as baseline separation. The derived relative contents for S-pregabalin were in agreement with the actual contents.

CONCLUSIONS

A novel and convenient method for discriminating the chirality of the pregabalin molecule by TIMS was developed and optimized. The chirality of pregabalin was recognized by studying the ion mobility spectra of the ternary non-covalent complexes, such as [2β-CD + pregabalin + Sr]²⁺ . This TIMS method could also be used to quantify the relative contents of pregabalin enantiomers.

The use of UHPLC, IMS, and HRMS in multiresidue analytical methods: A critical review

Residue chemists who analyse pesticides in vegetables or veterinary drugs in animal-based food are currently facing a situation where there is a requirement to detect more and more compounds at lower and lower concentrations. Conventional tandem quadrupole instruments provide sufficient sensitivity, but speed and selectivity appear as future limitations. This will become an even larger issue when there is a need to not only detect active compounds but also their degradation products and metabolites. This will likely lead to a situation in which the conventional targeted approach must be expanded or augmented by a certain non-targeted strategy. High-resolution mass spectrometry provides such capabilities, but it frequently requires an additional degree of selectivity for the unequivocal confirmation of analytes present at trace levels in highly complex and variable food matrices. The hyphenation of ultrahigh performance liquid chromatography with ion mobility and high-resolution mass spectrometry provides analytical chemists with a new tool for performing such a demanding multiresidue analysis. The objective of this paper is to investigate the benefits of the added ion mobility dimension as well as to critically discuss the current limitations of this commercially available technology.