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Single cell analysis strives to probe molecular heterogeneity in morphologically similar cell populations through quantitative or qualitative measurements of genetic, proteomic, or metabolic products. Here, we applied mass analysis of single neurons to investigate cell-cell signaling peptides. The multiplicity of endogenous cell-cell signaling peptides is a common source of chemical diversity among cell populations. Certain peptides can undergo post-translational isomerization of select residues, which has important physiological consequences. The limited number of single cell analysis techniques that are sensitive to peptide stereochemistry make it challenging to study isomerization at the individual cell level. We performed capillary electrophoresis (CE) with mass spectrometry (MS) detection to characterize the peptide content of single cells. Using complementary trapped ion mobility spectrometry (TIMS) separations, we measured the stereochemical configurations of three neuropeptide gene products derived from the pleurin precursor in individual neurons (N = 3) isolated from the central nervous system of Aplysia californica. An analysis of the resultant mobility profiles indicated >98% of the detectable pleurin-derived peptides exist as the non-isomerized, all-L forms in individual neuron cell bodies. However, we observed 44% of the Plrn2 peptide from the pleurin precursor was present as the isomerized, D-residue-containing form in the nerve tissue. These findings demonstrate an unusual distribution of isomerized peptides in A. californica and establish CE–TIMS MS as a powerful analytical tool for investigating peptide stereochemistry at the single cell level.

Aqueous film-forming foams (AFFF) are mixtures formulated with numerous hydrocarbon- and fluoro-containing surfactants. AFFF use leads to environmental releases of unknown per- and polyfluoroalkyl substances (PFAS). AFFF composition is seldom disclosed, and their use elicits concerns from both regulatory agencies and the public because PFAS are persistent in the environment and potentially associated with adverse health effects. In this study, we demonstrate the use of coupled liquid chromatography, ion mobility spectrometry, and mass spectrometry (LC-IMS-MS) to rapidly characterize both known and unknown PFAS in AFFF. Ten AFFF formulations from seven brands were analyzed using LC-IMS-MS in both negative and positive ion modes. Untargeted analysis of the formulations was followed by feature identification of PFAS-like features utilizing database matching, mass defect and homologous series evaluation, and MS/MS fragmentation experiments. Across the tested AFFF formulations, we identified 33 homologous series; only ten of these homologous series have been previously reported. Among tested AFFF, the FireStopper (n = 85) contained the greatest number of PFAS-like features and Phos-Check contained zero. This work demonstrates that LC-IMS-MS-enabled untargeted analysis of complex formulations, followed by feature identification using data-processing algorithms, can be used for rapid exposure characterization of known and putative PFAS during fire suppression-related contamination events.

Glycoproteins play a central role in many biological processes including disease mechanisms. Nevertheless, because glycoproteins are heterogeneous entities, it remains unclear how glycosylation modulates the protein structure and function. Here, we assess the ability of tandem-trapped ion mobility spectrometry – mass spectrometry (tandem-TIMS/MS) to characterize the structure and sequence of the homo-tetrameric glycoprotein avidin. We show that (1) tandem-TIMS/MS retains native-like avidin tetramers with deeply buried solvent particles; (2) applying high activation voltages in the interface of tandem-TIMS results in collision-induced dissociation (CID) of avidin tetramers into compact monomers, dimers, and trimers with cross sections consistent with x-ray structures and reports from surface-induced dissociation (SID); (3) avidin oligomers are best described as heterogeneous ensembles with (essentially) random combinations of monomer glycoforms; (4) native top-down sequence analysis of the avidin tetramer is possible by CID in tandem-TIMS. Overall, our results demonstrate that tandem-TIMS/MS has the potential to correlate individual proteoforms to variations in protein structure.

Per- and polyfluoroalkyl substances (PFAS) are an ensemble of persistent organic pollutants of global interest because of their associations with adverse health outcomes. Currently, environmental PFAS pollution is prolific as a result of the widespread manufacturing of these compounds and their chemical persistence. In this work, we demonstrate the advantages of adding ion mobility spectrometry (IMS) separation to existing LC-MS workflows for PFAS analysis. Using a commercially available drift tube IMS-MS, we characterized PFAS species and isomeric content in both analytical standards and environmental water samples. Molecular trendlines based on intrinsic mass and structural relationships were also explored for individual PFAS subclasses (e.g. PFSA, PFCA, etc.). Results from rapid IMS-MS analyses provided a link between mass and collision cross sections (CCS) for specific PFAS families and are linked to compositional differences in molecular structure. In addition, CCS values provide additional confidence of annotating prioritized features in untargeted screening studies for potential environmental pollutants. Results from this study show that the IMS separation provides novel information to support traditional LC-MS PFAS analyses and will greatly benefit the evaluation of unknown pollutants in future environmental studies.

Detection and diagnosis of congenital disorders is the principal aim of newborn screening (NBS) programs worldwide. Mass spectrometry (MS) has become the preferred primary testing method for high-throughput NBS sampling because of its speed and selectivity. However, the ever-increasing list of NBS biomarkers included in expanding panels creates unique analytical challenges for multiplexed MS assays due to isobaric/isomeric overlap and chimeric fragmentation spectra. Since isobaric and isomeric systems limit the diagnostic power of current methods and require costly follow-up exams due to many false-positive results, here, we explore the utility of ion mobility spectrometry (IMS) to enhance the accuracy of MS assays for primary (tier 1) screening. Our results suggest that ∼400 IMS resolving power would be required to confidently assess most NBS biomarkers of interest in dried blood spots (DBSs) that currently require follow-up testing. While this level of selectivity is unobtainable with most commercially available platforms, the separations detailed here for a commercially available drift tube IMS (Agilent 6560 with high-resolution demultiplexing, HRdm) illustrate the unique capabilities of IMS to separate many diagnostic NBS biomarkers from interferences. Furthermore, to address the need for increased speed of NBS analyses, we utilized an automated solid-phase extraction (SPE) system for ∼10 s sampling of simulated NBS samples prior to IMS-MS. This proof-of-concept work demonstrates the unique capabilities of SPE-IMS-MS for high-throughput sample introduction and enhanced separation capacity conducive for increasing speed and accuracy for NBS.

RATIONALE Tandem-ion mobility spectrometry/mass spectrometry methods have recently gained traction for the structural characterization of proteins and protein complexes. However, ion activation techniques currently coupled with tandem-ion mobility spectrometry/mass spectrometry methods are limited in their ability to characterize structures of proteins and protein complexes. METHODS Here, we describe the coupling of the separation capabilities of tandem-trapped ion mobility spectrometry/mass spectrometry (tTIMS/MS) with the dissociation capabilities of ultraviolet photodissociation (UVPD) for protein structure analysis. RESULTS We establish the feasibility of dissociating intact proteins by UV irradiation at 213 nm between the two TIMS devices in tTIMS/MS and at pressure conditions compatible with ion mobility spectrometry (2-3 mbar). We validate that the fragments produced by UVPD under these conditions result from a radical-based mechanism in accordance with prior literature on UVPD. The data suggest stabilization of fragment ions produced from UVPD by collisional cooling due to the elevated pressures used here ("UVnoD2"), which otherwise do not survive to detection. The data account for a sequence coverage for the protein ubiquitin comparable to recent reports, demonstrating the analytical utility of our instrument in mobility-separating fragment ions produced from UVPD. CONCLUSIONS The data demonstrate that UVPD carried out at elevated pressures of 2-3 mbar yields extensive fragment ions rich in information about the protein and that their exhaustive analysis requires IMS separation post-UVPD. Therefore, because UVPD and tTIMS/MS each have been shown to be valuable techniques on their own merit in proteomics, our contribution here underscores the potential of combining tTIMS/MS with UVPD for structural proteomics.

Per- and polyfluoroalkyl substances (PFAS) are persistent organic pollutants of concern because of their ubiquitous presence in surface and ground water; analytical methods that can be used for rapid comprehensive exposure assessment and fingerprinting of PFAS are needed. Following the fires at the Intercontinental Terminals Company (ITC) in Deer Park, TX in 2019, large quantities of PFAS-containing firefighting foams were deployed. The release of these substances into the Houston Ship Channel/Galveston Bay (HSC/GB) prompted concerns over the extent and level of PFAS contamination. A targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based study of temporal and spatial patterns of PFAS associated with this incident revealed presence of 7 species; their levels gradually decreased over a 6-month period. Because the targeted LC-MS/MS analysis was focused on about 30 PFAS molecules, it may have missed other PFAS compounds present in firefighting foams. Therefore, we utilized untargeted LC-ion mobility spectrometry-mass spectrometry (LC-IMS-MS)-based analytical approach for a more comprehensive characterization of PFAS in these water samples. We analyzed 31 samples from 9 sites in the HSC/GB that were collected over 5 months after the incident. Our data showed that additional 19 PFAS were detected in surface water of HSC/GB, most of them decreased gradually after the incident. PFAS features detected by LC-MS/MS correlated well in abundance with LC-IMS-MS data; however, LC-IMS-MS identified a number of additional PFAS, many known to be components of firefighting foams. These findings therefore illustrate that untargeted LC-IMS-MS improved our understanding of PFAS presence in complex environmental samples.

Ion mobility spectrometry coupled with mass spectrometry (IMS-MS) is a post-ionization separation technique that can be used for rapid multidimensional analyses of complex samples. IMS-MS offers untargeted analysis, including ion-specific conformational data derived as collisional cross section (CCS) values. Here, we combine nitrogen gas drift tube CCS ((DT)CCS(N2)) and Kendrick mass defect (KMD) analyses based on CH2 and H functional units to enable compositional analyses of petroleum substances. First, polycyclic aromatic compound standards were analyzed by IMS-MS to demonstrate how CCS assists the identification of isomeric species in homologous series. Next, we used case studies of a gasoline standard previously characterized for paraffin, isoparaffin, aromatic, naphthene, and olefinic (PIANO) compounds, and a crude oil sample to demonstrate the application of the KMD analyses and CCS filtering. Finally, we propose a workflow that enables confident molecular formula assignment to the IMS-MS-derived features in petroleum samples. Collectively, this work demonstrates how rapid untargeted IMS-MS analysis and the proposed data processing workflow can be used to provide confident compositional characterization of hydrocarbon-containing substances.

As monoclonal antibodies (mAbs) rapidly emerge as a dominant class of therapeutics, so does the need for suitable analytical technologies to monitor for changes in protein higher order structure (HOS) of these biomolecules. Reference materials (RM) serve a key analytical purpose of benchmarking the suitability and robustness of both established and emerging analytical procedures for both drug producers and regulators. Here, two simple enzymatic protocols for generating Fc-glycan variants from the NISTmAb RM are described and both global and localized changes in HOS between the RM and these Fc-glycan variants are characterized using hydrogen deuterium exchange-mass spectrometry (HDX-MS) and ion mobility spectrometry-mass spectrometry (IMS-MS) measurements. An alternative statistical approach is described where measurement thresholds that differentiate between measurement variability and significant structural changes were established on the basis of experimental data. Measurements revealed decreases in structural stability correlating with the degree of Fc-glycan structure loss, especially at the CH2/CH3 domain interface. These data promote the use of this RM and these Fc-glycan variants for establishing the sensitivity of and validating analytical methods for the detection of HOS measurements of mAbs.

Three-dimensional (3D) cancer cell cultures grown in the form of spheroids are effective models for the study of in vivo-like processes simulating cancer tumor pharmacological dynamics and morphology. In this study, we show the advantages of Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) combined with in situ Liquid Extraction Surface Analysis coupled to trapped Ion Mobility Spectrometry Mass Spectrometry (LESA-TIMS-TOF MS) for high spatial resolution mapping and quantitation of ABT-737, a chemotherapeutic drug, at the level of single human colon carcinoma cell spheroids (HCT 116 MCS). 2D-TOF-SIMS studies of consecutive sections (∼16 μm thick slices) showed that ABT-737 is homogenously distributed in the outer layers of the HCT 116 MCS. Complementary in situ LESA-TIMS-TOF MS/MS measurements confirmed the presence of the ABT-737 drug in the MCS slides by the observation of the molecular ion [M + H]+m/z and mobility, and the charateristic fragmentation pattern. LESA-TIMS-TOF MS allowed a quantitative assessment of the ABT-737 drug of the control MCS slice spiked with ABT-737 standard over the 0.4-4.1 ng range and MCS treated starting at 10 μM for 24 h. These experiments showcase an effective protocol for unambigous characterization and 3D mapping of chemotherapeutic drug distribution at the single MCS level.

Paper spray ionization has been used as a fast sampling/ionization method for the direct mass spectrometric analysis of biological samples at ambient conditions. Here, we demonstrated that by utilizing paper spray ionization-mass spectrometry (PSI-MS) coupled with field asymmetric waveform ion mobility spectrometry (FAIMS), predictive metabolic and lipidomic profiles of routine breast core needle biopsies could be obtained effectively. By the combination of machine learning algorithms and pathological examination reports, we developed a classification model, which has an overall accuracy of 87.5% for an instantaneous differentiation between cancerous and noncancerous breast tissues utilizing metabolic and lipidomic profiles. Our results suggested that paper spray ionization-ion mobility spectrometry-mass spectrometry (PSI-IMS-MS) is a powerful approach for rapid breast cancer diagnosis based on altered metabolic and lipidomic profiles.

Ion Mobility Spectrometry (IMS) is a widely used technique for the post-ionization separation and structural characterization of biomolecules. Trapped IMS (TIMS) is a relatively recent advance in the field of linear IMS that has shown advantages for the study of biological problems when in tandem with mass spectrometry (TIMS-MS). TIMS's unique nature of holding ions using an electric field against a moving buffer gas allows for the tuning of the mobility separation by defining the scan rate as a function of the analytical challenge. TIMS can provide accurate CCS values (

Recently, we proposed a high-throughput screening workflow for the elucidation of agonistic or antagonistic growth hormone-releasing hormone (GHRH) potencies based on structural motif descriptors as a function of the starting solution. In the present work, we revisited the influence of solution and gas-phase GHRH molecular microenvironment using trapped ion mobility-mass spectrometry (TIMS-MS). The effect of the starting solvent composition (10 mM ammonium acetate (NH

The work presented below is related to our companion paper in this issue, entitled: Substance P in solution: trans-to-cis configurational changes of penultimate prolines initiate non-enzymatic peptide bond cleavages. Two-dimensional ion mobility spectrometry (IMS-IMS) and mass spectrometry techniques are used to investigate structural transitions for [M+3H](3+) ions of substance P (subP) upon collisional activation (CA) in the gas phase. In this approach, different conformations of ions having a specified mobility are selected after an initial IMS separation, collisionally activated to produce new conformers, and these product structures are separated again using a second IMS region. In this way it is possible to follow folding and unfolding transitions of different conformations. The analysis shows evidence for five conformations. Unlike other systems, every transition is irreversible. Studies as a function of activation voltage are used to discern pathways of structural changes prior to reaching the energy required for dissociation. Thresholds associated with the onsets of transitions are calibrated to obtain estimates of the energetic barriers between different structures and semi-quantitative potential-energy diagrams are presented. Overall, barriers associated with structural transitions of [subP+3H](3+) in the absence of solvent are on the order of ~40 kJ∙mol(−1), substantially lower than the ~90 kJ∙mol(−1) required for some similar structural transitions in solutions of ethanol. Comparisons of the transition energies in the gas-phase with thermochemistry for similar transitions in solution provide clues about why reverse transitions are prohibited.

Lasso peptides are a class of bioactive ribosomally synthesized and post-translationally modified peptides (RiPPs) characterized by a mechanically interlocked topology, where the C-terminal tail of the peptide is threaded and trapped within an N-terminal macrolactam ring. BI-32169 is a class III lasso peptide containing one disulfide bond that further stabilizes the lasso structure. In contrast to its branched-cyclic analog, BI-32169 has higher stability and is known to exert a potent inhibitory activity against the human glucagon receptor. In the present work, tandem mass spectrometry, using collision-induced dissociation (CID) and electron capture dissociation (ECD), and trapped ion mobility spectrometry-mass spectrometry (TIMS-MS) experiments were carried out to evidence specific structural signatures of the two topologies. CID experiments showed similar fragmentation patterns for the two topoisomers, where a part of the C-terminal tail remains covalently linked to the macrolactam ring by the disulfide bond, which cannot clearly constitute a signature of the lasso topology. ECD experiments of BI-32169 showed an increase of hydrogen migration events in the loop region when compared with those of its branched-cyclic topoisomer evidencing specific structural signatures for the lasso topology. The high mobility resolving power of TIMS resulted in the identification of multiple conformations for the protonated species but did not allow the clear differentiation of the two topologies in mixture. When in complex with cesium metal ions, a reduced number of conformations led to a clear identification of the two structures. Experiments reducing and alkylating the disulfide bond of BI-32169 showed that the lasso structure is preserved and heat stable and the associated conformational changes provide new insights about the role of the disulfide bond in the inhibitory activity against the human glucagon receptor. Graphical abstract ᅟ.

2-Hydroxyglutaric acid is a chiral metabolite whose enantiomers specifically accumulate in different diseases. An enantiomeric excess of the d-form in biological specimens reflects the existence of various pathogenic mutations in cancer patients, however, conventional methods using gas or liquid chromatography and capillary electrophoresis had not been used for large clinical studies because they require multiple analytical instruments and a long run time to separate the enantiomers. Here, we present a rapid separation method for dl-2-hydroxyglutaric acid using a chiral derivatizing reagent and field asymmetric waveform ion mobility spectrometry/mass spectrometry, which requires a single analytical instrument and

Persistent organic pollutants (POPs) are xenobiotic chemicals of global concern due to their long-range transport capabilities, persistence, ability to bioaccumulate, and potential to have negative effects on human health and the environment. Identifying POPs in both the environment and human body is therefore essential for assessing potential health risks, but their diverse range of chemical classes challenge analytical techniques. Currently, platforms coupling chromatography approaches with mass spectrometry (MS) are the most common analytical methods employed to evaluate both parent POPs and their respective metabolites and/or degradants in samples ranging from d rinking water to biofluids. Unfortunately, different types of analyses are commonly needed to assess both the parent and metabolite/degradant POPs from the various chemical classes. The multiple time-consuming analyses necessary thus present a number of technical and logistical challenges when rapid evaluations are needed and sample volumes are limited. To address these challenges, we characterized 64 compounds including parent per- and polyfluoroalkyl substances (PFAS), pesticides, polychlorinated biphenyls (PCBs), industrial chemicals, and pharmaceuticals and personal care products (PPCPs), in addition to their metabolites and/or degradants, using ion mobility spectrometry coupled with MS (IMS-MS) as a potential rapid screening technique. Different ionization sources including electrospray ionization (ESI) and atmospheric pressure photoionization (APPI) were employed to determine optimal ionization for each chemical. Collectively, this study advances the field of exposure assessment by structurally characterizing the 64 important environmental pollutants, assessing their best ionization sources, and evaluating their rapid screening potential with IMS-MS.

Rationale The protein kinase FGFR1 regulates cellular processes in human development. As over-activity of FGFR1 is implicated with cancer, effective inhibitors are in demand. Type I inhibitors, which bind to the active form of FGFR1, are less effective than type II inhibitors, which bind to the inactive form. Screening to distinguish between type I and type II inhibitors is required. Methods X-ray crystallography was used to indicate whether a range of potential inhibitors bind to the active or inactive FGFR1 kinase conformation. The binding affinity of each ligand to FGFR1 was measured using biochemical methods. Electrospray ionisation - ion mobility spectrometry - mass spectrometry (ESI-IMS-MS) in conjunction with collision-induced protein unfolding generated a conformational profile of each FGFR1-ligand complex. The results indicate that the protein's conformational profile depends on whether the inhibitor is type I or type II. Results X-ray crystallography confirmed which of the kinase inhibitors bind to the active or inactive form of FGFR1 kinase. Collision-induced unfolding combined with ESI-IMS-MS showed distinct differences in the FGFR1 folding landscape for type I and type II inhibitors. Biochemical studies indicated a similar range of FGFR1 affinities for both types of inhibitors, thus providing confidence that the conformational variations detected using ESI-IMS-MS can be interpretated unequivocally and that this is an effective screening method. Conclusions A robust ESI-IMS-MS method has been implemented to distinguish between the binding mode of type I and type II inhibitors by monitoring the conformational unfolding profile of FGFR1. This rapid method requires low sample concentrations and could be used as a high-throughput screening technique for the characterisation of novel kinase inhibitors.

α-Pinene ozonolysis is a key process that impacts the formation of new particles and secondary organic aerosol (SOA) in the atmosphere. The mechanistic understanding of this chemistry has been inconclusive despite extensive research, hindering accurate simulations of atmospheric processes. In this work, we examine the ozonolysis of two synthesized unsaturated carbonyl isomers (C11H18O) which separately produce the two Criegee intermediates (CIs) that would form simultaneously in α-pinene ozonolysis. Direct gas-phase measurements of peroxy radicals (RO2) from flowtube ozonolysis experiments by an iodide-adduct chemical ionization mass spectrometer suggest that the initial C10H15O4· RO2 from the CI with a terminal methyl ketone undergo autoxidation 20-fold faster than the CI with a terminal aldehyde and always outcompete the bimolecular reactions under typical laboratory and atmospheric conditions. These results provide experimental constraints on the detailed RO2 autoxidation mechanisms for understanding new particle formation in the atmosphere. Further, isomer-resolved characterization of the SOA formed from a continuous-flow stirred tank reactor using ion mobility spectrometry mass spectrometry suggests that the two structurally different CIs predominantly and unexpectedly form constituents with identical structures. These results open up possibilities of diverse isomerization pathways that the two CIs may undergo that form mutual products to a large extent toward their way forming the SOA. This work highlights new insights into α-pinene ozonolysis pathways and call for future studies to uncover the detailed mechanisms.

The complex chemical composition of crude oils presents many challenges for rapid chemical characterization in the case of a spill. A number of approaches are currently used to "fingerprint" petroleum-derived samples. Gas chromatography coupled with mass spectrometry (GC-MS) is the most common, albeit not very rapid, technique; however, with GC-MS alone, it is difficult to resolve the complex substances in crude oils. The present study examined the potential application of ion mobility spectrometry-mass spectrometry (IMS-MS) coupled with chem-informatic analyses as an alternative high-throughput method for the chemical characterization of crude oils. We analyzed 19 crude oil samples from on- and offshore locations in the Gulf of Mexico region in the United States using both GC-MS (biomarkers, gasoline range hydrocarbons, and n-alkanes) and IMS-MS (untargeted analysis). Hierarchical clustering, principal component analysis, and nearest neighbor-based classification were used to examine sample similarity and geographical groupings. We found that direct-injection IMS-MS performed either equally or better than GC-MS in the classification of the origins of crude oils. In addition, IMS-MS greatly increased the sample analysis throughput (minutes vs hours per sample). Finally, a tabletop science-to-practice exercise, utilizing both the GC-MS and IMS-MS data, was conducted with emergency response experts from regulatory agencies and the oil industry. This activity showed that the stakeholders found the IMS-MS data to be highly informative for rapid chemical fingerprinting of complex substances in general and specifically advantageous for accurate and confident source-grouping of crude oils. Collectively, the present study shows the utility of IMS-MS as a technique for rapid fingerprinting of complex samples and demonstrates its advantages over traditional GC-MS-based analyses when used for decision-making in emergency situations. Environ Toxicol Chem 2021;40:1034-1049. © 2020 SETAC.

Motivation Ion mobility spectrometry (IMS) separations are increasingly used in conjunction with mass spectrometry (MS) for separation and characterization of ionized molecular species. Information obtained from IMS measurements includes the ion’s collision cross section (CCS), which reflects its size and structure and constitutes a descriptor for distinguishing similar species in mixtures that cannot be separated using conventional approaches. Incorporating CCS into MS-based workflows can improve the specificity and confidence of molecular identification. At present, there is no automated, open-source pipeline for determining CCS of analyte ions in both targeted and untargeted fashion, and intensive user-assisted processing with vendor software and manual evaluation is often required. Results We present AutoCCS, an open-source software to rapidly determine CCS values from IMS-MS measurements. We conducted various IMS experiments in different formats to demonstrate the flexibility of AutoCCS for automated CCS calculation: (i) stepped-field methods for drift tube-based IMS (DTIMS), (ii) single-field methods for DTIMS (supporting two calibration methods: a standard and a new enhanced method) and (iii) linear calibration for Bruker timsTOF and non-linear calibration methods for traveling wave based-IMS in Waters Synapt and Structures for Lossless Ion Manipulations. We demonstrated that AutoCCS offers an accurate and reproducible determination of CCS for both standard and unknown analyte ions in various IMS-MS platforms, IMS-field methods, ionization modes and collision gases, without requiring manual processing. Availability and implementation https://github.com/PNNL-Comp-Mass-Spec/AutoCCS. Supplementary information Supplementary data are available at Bioinformatics online. Demo datasets are publicly available at MassIVE (Dataset ID: MSV000085979).

Rationale Examining surface protein conformations, and especially achieving this with spatial resolution, is an important goal. The recently discovered ionization processes offer spatial-resolution measurements similar to matrix-assisted laser desorption/ionization (MALDI) and produce charge states similar to electrospray ionization (ESI) extending higher-mass protein applications directly from surfaces on high-performance mass spectrometers. Studying a well-interrogated protein by ion mobility spectrometry-mass spectrometry (IMS-MS) to access effects on structures using a solid vs. solvent matrix may provide insights. Methods Ubiquitin was studied by IMS-MS using new ionization processes with commercial and homebuilt ion sources and instruments (Waters SYNAPT G2(S)) and homebuilt 2 m drift-tube instrument; MS™ sources). Mass-to-charge and drift-time (td )-measurements are compared for ubiquitin ions obtained by inlet and vacuum ionization using laserspray ionization (LSI), matrix- (MAI) and solvent-assisted ionization (SAI), respectively, and compared with those from ESI under conditions that are most comparable. Results Using the same solution conditions with SYNAPT G2(S) instruments, td -distributions of various ubiquitin charge states from MAI, LSI, and SAI are similar to those from ESI using a variety of solvents, matrices, extraction voltages, a laser, and temperature only, showing subtle differences in more compact features within the elongated distribution of structures. However, on a homebuilt drift-tube instrument, within the elongated distribution of structures, both similar and different td -distributions are observed for ubiquitin ions obtained by MAI and ESI. MAI-generated ions are frequently narrower in their td -distributions. Conclusions Direct comparisons between ESI and the new ionization methods operational directly from surfaces suggest that the protein in its solution structure prior to exposure to the ionization event is either captured (frozen out) at the time of crystallization, or that the protein in the solid matrix is associated with sufficient solvent to maintain the solution structure, or, alternatively, that the observed structures are those related to what occurs in the gas phase with ESI- or MAI-generated ions and not with the solution structures.

The behavior of biomolecules as a function of the solution temperature is often crucial to assess their biological activity and function. While heat-induced changes of biomolecules are traditionally monitored using optical spectroscopy methods, their conformational changes and unfolding transitions remain challenging to interpret. In the present work, the structural transitions of bovine serum albumin (BSA) in native conditions (100 mM aqueous ammonium acetate) were investigated as a function of the starting solution temperature (T = ~23-70 °C) using a temperature-controlled nano-electrospray ionization source (nESI) coupled to a trapped ion mobility spectrometry – mass spectrometry (TIMS-MS) instrument. The charge state distribution of the monomeric BSA changed from a native-like, narrow charge state ([M + 12H](12+) - [M + 16H](16+) at ~23 °C) and narrow mobility distribution towards an unfolded-like, broad charge state (up to [M + 46H](46+) at ~70 °C) and broad mobility distribution. Inspection of the average charge state and collision cross section (CCS) distribution suggested a two-state unfolding transition with a melting temperature T(m) ~56 ± 1 °C; however, the inspection of the CCS profiles at the charge state level as a function of the solution temperature showcase at least six structural transitions (T1-T7). If the starting solution concentration is slightly increased (from 2 to 25 μM), this method can detect non-specific BSA dimers and trimers which dissociate early (T(d) ~34 ± 1 °C) and may disturb the melting curve of the BSA monomer. In a single experiment, this technology provides a detailed view of the solution, protein structural landscape (mobility vs solution temperature vs relative intensity for each charge state).

Poly(ethylene oxide), poly(propylene oxide), and their copolymer (poly(EO-co-PO)) were analyzed by electrospray ionization-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS). ESI produced multiply charged analytes of 2 to 5 Na+ additions, and they were separately observed in a 2D map of m/z value vs. drift time. The collision cross-section of the analyte polymers was almost linearly proportional to (molecular weight)0.644, except for the analytes with 2Na+ addition; a nonlinear relation called "folding" was significantly observed for the analytes with 2Na+ addition. An increase in electrostatic repulsion, because of the increase in Na+ addition, suppressed the folding of the polymer. Analyses of poly(EO-co-PO) with different EO compositions revealed that the copolymer with high EO composition tended to show folding. The separation of highly multiply charged poly(EO-co-PO)s with different EO contents by ESI-IMS-MS was successfully demonstrated.

Polyoxometalate clusters possess unique catalytic and electromagnetic properties. The structure and function of polyoxometalates is dictated by complex oligomerization processes, which in turn depend on the solution conditions. In this work, small gas-phase polyoxomolybdate nanoclusters HMonO3n+11-, n = 1--8, and MonO3n+12-, n = 2--8 were investigated after nanoelectrospray of an acidified solution of ammonium heptamolybdate heptahydrate by ion-mobility spectrometry--mass spectrometry (IMS--MS), infrared multiple photon dissociation (IRMPD) spectroscopy, and infrared action spectroscopy in helium nanodroplets. The spectra and collision cross-sections obtained were matched to predictions from density-functional theory (DFT) to unravel the structural progression of nanoclusters with increasing size. For doubly charged clusters, a transition between chain (n = 2--3), ring (n = 4--5), and compact (n ≥ 6) structures is observed in IM--MS and IR spectroscopy experiments, in agreement with low-energy structures from DFT calculations. For singly charged clusters, reduced Coulombic repulsion and hydrogen bonding interactions are found to strongly influence the most stable cluster structure. Notably, a noncovalent ring structure is observed for HMo3O101-, stabilized by a strong intramolecular hydrogen bond, and a compact structure is observed for HMo5O161-, in contrast to the ring structure favored for Mo5O162-.

Ion mobility spectrometry and circular dichroism spectroscopy are used to examine the populations of the small model peptide, polyproline-13 in water, methanol, ethanol, and 1-propanol over a range of solution temperatures (from 288 to 318 K). At low temperatures, the less-polar solvents (1-propanol and ethanol) favor the all-cis polyproline I helix (PPI); as the temperature is increased, the trans-configured polyproline II helix (PPII) is formed. In polar solvents (methanol and water), PPII is favored at all temperatures. From the experimental data, we determine the relative stabilities of the eight structures in methanol, ethanol, and 1-propanol, as well as four in water, all with respect to PPII. Although these conformers show relatively small differences in free energies, substantial variability is observed in the enthalpies and entropies across the structures and solvents. This requires that enthalpies and entropies be highly correlated: in 1-propanol, cis-configured PPI conformations are energetically favorable but entropically disfavored. In more polar solvents, PPI is enthalpically less favorable and entropy favors trans-configured forms. While either ΔH(0) or ΔS(0) can favor different structures, no conformation in any solvent is simultaneously energetically and entropically stabilized. These data present a rare opportunity to examine the origin of conformational stability.

Current lipidomics workflows are centered around acquisition of large data sets followed by lengthy data processing. A dual nESI-DIMS-MS platform was developed to perform real-time relative quantification between samples, providing data required for biomarker discovery and validation more quickly than traditional ESI-MS approaches. Nanosprayer activity and DIMS compensation field settings were controlled by a LabVIEW program synced to the accumulation portion of the ion trap scan function, allowing for full integration of the platform with a commercial mass spectrometer. By comparing samples with short electrospray pulses rather than constant electrospray, the DIMS and MS performance is normalized within an experiment, as signals are compared between individual mass spectra (ms time scale) rather than individual experiments (min-hr time scale). The platform was validated with lipid standards and extracts from nitrogen-deprived microalgae. Dual nESI-DIMS requires minimal system modification and is compatible with all traditional ion activation techniques and mass analyzers, making it a versatile improvement to shotgun lipidomics workflows.

Lasso peptides are a fascinating class of bioactive ribosomal natural products characterized by a mechanically interlocked topology. In contrast to their branched-cyclic forms, lasso peptides have higher stability and have become a scaffold for drug development. However, the identification and separation of lasso peptides from their unthreaded topoisomers (branched-cyclic peptides) is analytically challenging since the higher stability is based solely on differences in their tertiary structures. In the present work, a fast and effective workflow is proposed for the separation and identification of lasso from branched cyclic peptides based on differences in their mobility space under native nanoelectrospray ionization-trapped ion mobility spectrometry-mass spectrometry (nESI-TIMS-MS). The high mobility resolving power ( R) of TIMS resulted in the separation of lasso and branched-cyclic topoisomers ( R up to 250, 150 needed on average). The advantages of alkali metalation reagents (e.g., Na, K, and Cs salts) as a way to increase the analytical power of TIMS is demonstrated for topoisomers with similar mobilities as protonated species, efficiently turning the metal ion adduction into additional separation dimensions.

A two-dimensional GC (2D-GC) method was developed and coupled to an ion mobility-high resolution mass spectrometer, which enables the separation of complex samples in four dimensions (2D-GC, ion mobilility spectrometry and mass spectrometry). This approach works as a continuous multiheart-cutting GC-system (GC+GC), using a long modulation time of 20s, which allows the complete transfer of most of the first dimension peaks to the second dimension column without fractionation, in comparison to comprehensive two-dimensional gas chromatography (GCxGC). Hence, each compound delivers only one peak in the second dimension, which simplifies the data handling even when ion mobility spectrometry as a third and mass spectrometry as a fourth dimension are introduced. The analysis of a plant extract from Calendula officinales shows the separation power of this four dimensional separation method. The introduction of ion mobility spectrometry provides an additional separation dimension and allows to determine collision cross sections (CCS) of the analytes as a further physicochemical constant supporting the identification. A CCS database with more than 800 standard substances including drug-like compounds and pesticides was used for CCS data base search in this work.

Ion mobility spectrometry – mass spectrometry (IMS-MS) provides information about the structures of gas-phase ions in the form of a collision cross section (CCS) with a neutral buffer gas. Indicating relative ion size, a CCS value alone is of limited utility. Although such information can be used to propose different conformer types, finer details of structure are not captured. The increased accessibility of IMS-MS measurements with commercial instrumentation in recent years has ballooned its usage in combination with separate measurements to provide enhanced data from which greater structural inferences can be drawn. This short review presents recent outstanding developments in scientific research that employs complementary measurements that when combined with IMS-MS data are used to characterize the structures of a wide range of compounds.

Ion mobility spectrometry-mass spectrometry offers the potential to characterize structures of transient protein assemblies and protein isoforms by means of their orientationally-averaged momentum transfer cross-sections. A commonly observed phenomenon is the compaction of a protein in the ion mobility measurement, that is, the cross section measured for the protein by ion mobility spectrometry is smaller than the cross section expected for its native structure. Consequently, this compaction means that at least some structural changes of the protein must have occurred during the ion mobility measurement. A major challenge is then to identify which aspects of the solution structure are retained in the ion mobility measurement and which ones are not. Here, we apply our recently developed Structure Relaxation Approximation (SRA) method in conjunction with trapped ion mobility spectrometry-mass spectrometry (TIMS-MS) to probe compaction of the human protein chemokine (C-C motif) ligand 5 (also CCL5). Ion mobility spectra are recorded for various charge states and solution conditions of CCL5 under both “soft” and collisionally-activated conditions. Our data show that the SRA reproduces the overall trends in the experimental spectra: (1) the compaction of the CCL5 structure as seen in the experiments; (2) the general increase in the cross section for the various charge states; and (3) the increase in cross section after collisional-activation. The SRA attributes the compaction of the CCL5 structure mainly to the folding of the unstructured N-terminus onto the central Greek key motif of CCL5. By contrast, the SRA indicates that native residue-residue contacts present in the NMR structure are largely retained. Additionally, our analysis indicates that accurate treatment of proton transfer processes during the structural relaxation process would significantly improve the structural interpretation of ion mobility data by the SRA.

On-line analysis of coffee roasting was performed using ion mobility spectrometry–mass spectrometry (IMS–MS) with corona discharge ionization. This is the first time that formation of volatile organic compounds (VOCs) during coffee roasting was monitored not only in positive but also in negative ion mode, and not only with mass spectrometry, but also with ion mobility spectrometry. The temporal evolution of more than 150 VOCs was monitored during the roasting of Brazilian Coffea arabica. Mass-selective ion mobility spectrometry allowed a separation of isobaric and isomeric compounds. In positive ion mode, isomers of alkyl pyrazines were found to exhibit distinct time-intensity profiles during roasting, providing a unique insight into the complex chemistry of this important class of aroma active compounds. Negative ion mode gave access to species poorly detectable by other on-line methods, such as acids. In this study, the release of fatty acids during coffee roasting was investigated in detail. These increase early on in the roasting process followed by a decrease at the same time as other VOCs start to be formed.

Successful pregnancy is dependent upon discrete biological events, which include embryo implantation, decidualization, and placentation. Problems associated with each of these events can cause infertility or conditions such as preeclampsia. A greater understanding of the molecular changes associated with these complex processes is necessary to aid in identifying treatments for each condition. Previous nuclear magnetic resonance spectroscopy and mass spectrometry studies have been used to identify metabolites and lipids associated with pregnancy-related complications. However, due to limitations associated with conventional implementations of both techniques, novel technology developments are needed to more fully understand the initiation and development of pregnancy related problems at the molecular level. In this perspective, we describe current analytical techniques for metabolomic and lipidomic characterization of pregnancy complications and discuss the potential for new technologies such as ion mobility spectrometry-mass spectrometry and mass spectrometry imaging to contribute to a better understanding of the molecular changes that affect the placenta and pregnancy outcomes.

Differential ion mobility spectrometry (DMS) has emerged to be particularly well suited for the rapid and selective identification of gas phase ions at atmospheric pressure. DMS can overcome some limitations associated with mass spectrometry (MS) and conventional ion mobility spectrometry such as the use of vacuum systems. Miniaturization of DMS to the size of a palm portable device using state-of-art microelectromechanical systems significantly lowers power consumption, decreases analysis times (sub milliseconds) and reduces sample consumption. Microscale DMS can be used as a standalone ion detector or coupled to MS and gas and liquid chromatography platforms to enable the detection of a wide range of chemical species. Here, recent significant progress in the development and application of microscale DMS is comprehensively reviewed. The advantages, limitations, and future challenges for microscale DMS instrumentation for analytical, environmental, and bioanalytical chemistry applications are addressed.

Atmospheric pressure drift tube ion mobility spectrometry (AP-DTIMS) was coupled with Fourier transform Orbitrap mass spectrometry. The performance capabilities of this versatile new arrangement were demonstrated for different DTIMS ion gating operation modes and Orbitrap mass spectrometer parameters with regard to sensitivity and resolving power. Showcasing the optimized AP-DTIMS-Orbitrap MS system, isobaric peptide and sugar isomers were successfully resolved and the identities of separated species validated by high-energy collision dissociation experiments.

Globular proteins, such as cytochrome c (cyt c), display an organized native conformation, maintained by a hydrogen bond interaction network. In the present work, the structural interrogation of kinetically trapped intermediates of cyt c was performed by correlating the ion-neutral collision cross section (CCS) and charge state with the starting solution conditions and time after desolvation using collision induced activation (CIA), time resolved hydrogen/deuterium back exchange (HDX) and trapped ion mobility spectrometry - mass spectrometry (TIMS-MS). The high ion mobility resolving power of the TIMS analyzer allowed the identification of new ion mobility bands, yielding a total of 63 mobility bands over the +6 to +21 charge states and 20 mobility bands over the −5 to −10 charge states. Mobility selected HDX rates showed that for the same charge state, conformers with larger CCS present faster HDX rates in both positive and negative ion mode, suggesting that the charge sites and neighboring exchange sites on the accessible surface area define the exchange rate regardless of the charge state. Complementary molecular dynamic simulations permitted the generation of candidate structures and a mechanistic model of the folding transitions from native (N) to molten globule (MG) to kinetic intermediates (U) pathways. Our results suggest that cyt c major structural unfolding is associated with the distancing of the N- and C- terminal helices and subsequent solvent exposure of the hydrophobic, heme-containing cavity.

The present work focused on the high-throughput screening and quantitation of guanidino compounds (GCs) and ureido compounds (UCs) in human thyroid tissues. The strategy employed benzylic rearrangement stable isotope labeling (BRSIL) for the sample preparation and then detection using liquid chromatography-drift tube ion mobility spectrometry-quadrupole time of flight mass spectrometry (LC-DTIMS-QTOF MS). A short reversed-phase LC realized an on-line desalting and a measurement cycle of 5.0 min. DTIMS separation enhanced the better specificity and selectivity for the benzil labeled GCs and UCs. The elevated mass resolution of QTOF MS enabled measure of the characteristic ions at accurate mass in MS and tandem MS spectra. Collision cross section (CCS) from DTIMS and accurate mass from QTOF MS were used as two qualifiers for the profiling and identification of GCs and UCs. In addition, an integral abundance arising from 3-D ion features (retention time, drift time, m/z) was applied to quantify the GCs and UCs in human thyroid tissues. The quantitative validation indicated good linearity (coefficient values ≥ 0.9981), good precision (1.0%–12.3% for intra-day and 0.9%–7.8% for inter-day) and good accuracy (91%–109%). The results demonstrated that the developed BRSIL coupled with LC-DTIMS-QTOF MS can be a powerful analysis platform to investigate GCs and UCs in human thyroid tissues.

Due to the recently uncovered health benefits and anti-HIV activities of dicaffeoylquinic acids (diCQAs), understanding their structures and functions is of great interest for drug discovery efforts. DiCQAs are analytically challenging to identify and quantify since they commonly exist as a diverse mixture of positional and geometric (cis/trans) isomers. In this work, we utilized ion mobility spectrometry coupled with mass spectrometry to separate the various isomers before and after UV irradiation. The experimental collision cross sections were then compared with theoretical structures to differentiate and identify the diCQA isomers. Our analyses found that naturally the diCQAs existed predominantly as trans/trans isomers, but after 3 h of UV irradiation, cis/cis, cis/trans, trans/cis, and trans/trans isomers were all present in the mixture. This is the first report of successful differentiation of cis/trans diCQA isomers individually, which shows the great promise of IMS coupled with theoretical calculations for determining the structure and activity relationships of different isomers in drug discovery studies.

Full scan field asymmetric waveform ion mobility spectrometry (FAIMS) combined with liquid chromatography and mass spectrometry (LC-FAIMS-MS) is shown to enhance peak capacity for omics applications. A miniaturized FAIMS device capable of rapid compensation field scanning has been incorporated into an ultrahigh performance liquid chromatography (UHPLC) and time-of-flight mass spectrometry analysis, allowing the acquisition of full scan FAIMS and MS nested data sets within the time scale of a UHPLC peak. Proof of principle for the potential of scanning LC-FAIMS-MS in omics applications is demonstrated for the nontargeted profiling of human urine using a HILIC column. The high level of orthogonality between FAIMS and MS provides additional unique compound identifiers with detection of features based on retention time, FAIMS dispersion field and compensation field (DF and CF), and mass-to-charge (m/z). Extracted FAIMS full scan data can be matched to standards to aid the identification of unknown analytes. The peak capacity for features detected in human urine using LC-FAIMS-MS was increased approximately threefold compared to LC-MS alone due to a combination of the reduction of chemical noise and separation of coeluting isobaric species across the entire analytical space. The use of FAIMS-selected in source collision induced dissociation (FISCID) yields fragmentation of ions, which reduces sample complexity associated with overlapping fragmentation patterns and provides structural information on the selected precursor ions.

In this report, we explored the benefits of cyclic ion mobility (cIM) mass spectrometry in the analysis of isomeric post-transcriptional modifications of RNA. Standard methyl-cytidine samples were initially utilized to test the ability to correctly distinguish different structures sharing the same elemental composition, and thus molecular mass. Analyzed individually, the analytes displayed characteristic arrival times (t(D)) determined by the different positions of the modifying methyl groups onto the common cytidine scaffold. Analyzed in mixture, the widths of the respective signals resulted in significant overlap that initially prevented their resolution on the t(D) scale. The separation of the four isomers was achieved by increasing the number of passes through the cIM device, which enabled to fully differentiate the characteristic ion mobility behaviors associated with very subtle structural variations. The placement of the cIM device between the mass-selective quadrupole and the time-of-flight analyzer allowed us to perform gas-phase activation of each of these ion populations, which had been first isolated according to a common mass-to-charge ratio, and then separated on the basis of different ion mobility behaviors. The observed fragmentation patterns confirmed the structures of the various isomers, thus substantiating the benefits of complementing unique t(D) information with specific fragmentation data to reach more stringent analyte identification. These capabilities were further tested by analyzing natural mono-nucleotide mixtures obtained by exonuclease digestion of total RNA extracts. In particular, the combination of cIM separation and post-mobility dissociation allowed us to establish the composition of methyl-cytidine and methyl-adenine components present in the entire transcriptome of HeLa cells. For this reason, we expect that this technique will benefit not only epitranscriptomics studies requiring the determination of identity and expression levels of RNA modifications, but also metabolomics investigations involving the analysis of natural extracts that may possibly contain subsets of isomeric/isobaric species.

International audience

The non-covalent interactions between small drug molecules and disease-related proteins (ligand-target interactions) mediate various pharmacological processes in the treatment of different diseases. The development of the analytical methods to assess those interactions, including binding sites, binding energies, stoichiometry and association-dissociation constants, could assist in clarifying the mechanisms of action, precise treatment of targeted diseases as well as the targeted drug discovery. For the last decades, mass spectrometry (MS) has been recognized as a powerful tool to study the non-covalent interactions of the ligand-target complexes with the characteristics of high sensitivity, high-resolution, and high-throughput. Soft ionization mass spectrometry, especially the electrospray mass spectrometry (ESI-MS) and matrix assisted laser desorption ionization mass spectrometry (MALDI-MS), could achieve the complete transformation of the target analytes into the gas phase, and subsequent detection of the small drug molecules and disease-related protein complexes, and has exerted great advantages for studying the drug ligands-protein targets interactions, even in case of identifying active components as drug ligands from crude extracts of medicinal plants. Despite of other analytical techniques for this purpose, such as the NMR and X-ray crystallography, this review highlights the principles, research hotspots and recent applications of the soft ionization mass spectrometry and its hyphenated techniques, including hydrogen-deuterium exchange mass spectrometry (HDX-MS), chemical cross-linking mass spectrometry (CX-MS), and ion mobility spectrometry mass spectrometry (IMS-MS), in the study of the non-covalent interactions between small drug molecules and disease-related proteins.

International audience; Collision cross section (CCS) values are descriptors of the 3D structure of ions which can be determined by ion mobility spectrometry (IMS). Currently, most lipidomic studies involving CCS value determination concern eukaryote samples (e.g. human, bovine) and to a lower extent prokaryote samples (e.g. bacteria). Here, we report CCS values obtained from traveling wave ion mobility spectrometry (TWCCSN2) measurements from the bacterial membrane of Pseudomonas aeruginosa—a bacterium ranked as priority 1 for the R&D of new antibiotics by the World Health Organization. In order to cover the lack of reference compounds which could cover the m/z and CCS ranges of the membrane lipids of P. aeruginosa, three calibrants (polyalanine, dextran and phospholipids) were used for the TWCCSN2 calibration. A shift from the published lipid CCS values was systematically observed (ΔCCS% up to 9%); thus, we proposed a CCS correction strategy. This correction strategy allowed a reduction in the shift (ΔCCS%) between our measurements and published values to less than 2%. This correction was then applied to determine the CCS values of Pseudomonas aeruginosa lipids which have not been published yet. As a result, 32 TWCCSN2 values for [M+H]+ ions and 24 TWCCSN2 values for [M−H]− ions were obtained for four classes of phospholipids (phosphatidylethanolamines (PE), phosphatidylcholines (PC), phosphatidylglycerols (PG) and diphosphatidylglycerols—known as cardiolipins (CL)).

Lipids are a major class of molecules that play key roles in different biological processes. Understanding their biological roles and mechanisms remains analytically challenging due to their high isomeric content (e.g., varying acyl chain positions and/or double bond locations/geometries) in eukaryotic cells. In the present work, a combination of liquid chromatography (LC) followed by high resolution trapped ion mobility spectrometry-mass spectrometry (TIMS-MS) was used to investigate common isomeric glycerophosphocholine (PC) and diacylglycerol (DG) lipid species from human plasma. The LC dimension was effective for the separation of isomeric lipid species presenting distinct double bond locations or geometries but was not able to differentiate lipid isomers with distinct acyl chain positions. High resolution TIMS-MS resulted in the identification of lipid isomers that differ in the double bond locations/geometries as well as in the position of the acyl chain with resolving power ( R) up to ∼410 ( R ∼ 320 needed on average). Extremely small structural differences exhibiting collision cross sections (CCS) of less than 1% (down to 0.2%) are sufficient for the discrimination of the isomeric lipid species using TIMS-MS. The same level of performance was maintained in the complex biological mixture for the biologically relevant PC 16:0/18:1 lipid isomers. These results suggest several advantages of using complementary LC-TIMS-MS separations for regular lipidomic analysis, with the main emphasis in the elucidation of isomer-specific lipid biological activities.

The structural characterization of metal porphyrins has been traditionally challenging as a result of their large structural and compositional diversity. In the present paper, we show the advantages of gas-phase, postionization separations for the fast identification and structural characterization of metal octaethylporphyrins (Me–OEP) from complex mixtures using trapped ion mobility spectrometry (TIMS) coupled to ultrahigh-resolution mass spectrometry (FT-ICR MS). TIMS–FT-ICR MS allows for the separation of Me–OEP (Me = Mn, Ni, Zn, V═O, and Ti═O) within a crude oil sample based on accurate mass and mobility signatures (with a mobility resolving power of RIMS ∼ 150–250). Accurate collision cross sections are reported for Me–OEP in nitrogen as bath gas (CCSN2). Inspection of the Me–OEP mobility spectra showed a single mobility component distribution for Me–OEP (Me = Mn, Ni, and Zn) and a multi-component distribution for the two metal carbonyls, vanadyl (V═O) and titanyl (Ti═O) Me–OEP. Candidate structures ...