Pendular proteins in gases and new avenues for characterization of macromolecules by ion mobility spectrometry

Expanding Differential Ion Mobility Separations into the MegaDalton Range

Along with mass spectrometry (MS), ion mobility separations (IMS) are advancing to ever larger biomolecules. The emergence of electrospray ionization (ESI) and native MS enabled the IMS/MS analyses of proteins up to ∼100 kDa in the 1990s and whole protein complexes and viruses up to ∼10 MDa since the 2000s. Differential IMS (FAIMS) is substantially orthogonal to linear IMS based on absolute mobility K and offers exceptional resolution, unique selectivity, and steady filtering readily compatible with slower analytical methods such as electron capture or transfer dissociation (ECD/ETD). However, the associated MS stages had limited FAIMS to ions with m/z < 8000 and masses under ∼300 kDa. Here, we integrate high-definition FAIMS with the Q-Exactive Orbitrap UHMR mass spectrometer that can handle m/z up to 80,000 and MDa-size ions in the native ESI regime. In the initial evaluation, the oligomers of monoclonal antibody adalimumab (148 kDa) are size-selected up to at least the nonamers (1.34 MDa) with m/z values up to ∼17,000. This demonstrates the survival and efficient separation of noncovalent MDa assemblies in the FAIMS process, opening the door to novel analyses of the heaviest macromolecules.

Giving the Green Light to Photochemical Uncaging of Large Biomolecules in High Vacuum

The isolation of biomolecules in a high vacuum enables experiments on fragile species in the absence of a perturbing environment. Since many molecular properties are influenced by local electric fields, here we seek to gain control over the number of charges on a biopolymer by photochemical uncaging. We present the design, modeling, and synthesis of photoactive molecular tags, their labeling to peptides and proteins as well as their photochemical validation in solution and in the gas phase. The tailored tags can be selectively cleaved off at a well-defined time and without the need for any external charge-transferring agents. The energy of a single or two green photons can already trigger the process, and it is soft enough to ensure the integrity of the released biomolecular cargo. We exploit differences in the cleavage pathways in solution and in vacuum and observe a surprising robustness in upscaling the approach from a model system to genuine proteins. The interaction wavelength of 532 nm is compatible with various biomolecular entities, such as oligonucleotides or oligosaccharides.

Assessing the Dipole Moments and Directional Cross Sections of Proteins and Complexes by Differential Ion Mobility Spectrometry

Ion mobility spectrometry (IMS) has become a mainstream approach to fractionate complex mixtures, separate isomers, and assign the molecular geometries. All modalities were grouped into linear IMS (based on the absolute ion mobility, K) and field asymmetric waveform IMS (FAIMS) relying on the evolution of K at a high normalized electric field (E/N) that induces strong ion heating. In the recently demonstrated low-field differential (LOD) IMS, the field is too weak for significant heating but locks the macromolecular dipoles to produce novel separations controlled by the relevant directional collision cross sections (CCSs). Here, we show LODIMS for mass-selected species, exploring the dipole alignment across charge states for the monomers and dimers of an exemplary protein, the alcohol dehydrogenase. Distinct conformational families for aligned species are revealed with directional CCS estimated from the field-dependent trend lines. We set up a model to extract the fractions of pendular conformers as a function of field intensity and translate them into dipole moment distributions. These developments make a critical step toward establishing LODIMS as a new tool for top-down proteomics and integrative structural biology.

In a flash of light: X-ray free electron lasers meet native mass spectrometry

During the last years, X-ray free electron lasers (XFELs) have emerged as X-ray sources of unparalleled brightness, delivering extreme amounts of photons in femtosecond pulses. As such, they have opened up completely new possibilities in drug discovery and structural biology, including studying high resolution biomolecular structures and their functioning in a time resolved manner, and diffractive imaging of single particles without the need for their crystallization. In this perspective, we briefly review the operation of XFELs, their immediate uses for drug discovery and focus on the potentially revolutionary single particle diffractive imaging technique and the challenges which remain to be overcome to fully realize its potential to provide high resolution structures without the need for crystallization, freezing or the need to keep proteins stable at extreme concentrations for long periods of time. As the issues have been to a large extent sample delivery related, we outline a way for native mass spectrometry to overcome these and enable so far impossible research with a potentially huge impact on structural biology and drug discovery, such as studying structures of transient intermediate species in viral life cycles or during functioning of molecular machines.

Structural Characterization of Human Histone H4.1 by Tandem Nonlinear and Linear Ion Mobility Spectrometry Complemented with Molecular Dynamics Simulations

Extracellular histone H4 is an attractive drug target owing to its roles in organ failure in sepsis and other diseases. To identify inhibitors using in silico methods, information on histone H4 structural dynamics and three-dimensional (3D) structural coordinates is required. Here, DNA-free histone H4 type 1 (H4.1) was characterized by utilizing tandem nonlinear and linear ion mobility spectrometry (FAIMS-TIMS) coupled to mass spectrometry (MS) complemented with molecular dynamics (MD) simulations. The gas-phase structures of H4.1 are dependent on the starting solution conditions, evidenced by differences in charge state distributions, mobility distributions, and collision-induced unfolding (CIU) pathways. The experimental results show that H4.1 adopts diverse conformational types from compact (C) to partially folded (P) and subsequently elongated (E) structures. Molecular dynamics simulations provided candidate structures for the histone H4.1 monomer in solution and for the gas-phase structures observed using FAIMS-IMS-TOF MS as a function of the charge state and mobility distribution. A combination of the FAIMS-TIMS experimental results with theoretical dipole calculations reveals the important role of charge distribution in the dipole alignment of H4.1 elongated structures at high electric fields. A comparison of the secondary and primary structures of DNA-free H2A.1 and H4.1 is made based on the experimental IMS-MS and MD findings.

Ion Mobility Spectrometry of Superheated Macromolecules at Electric Fields up to 500 Td

Since its inception in 1980s, differential or field asymmetric waveform ion mobility spectrometry (FAIMS) has been implemented at or near ambient gas pressure. We recently developed FAIMS at 15-30 Torr with mass spectrometry and utilized it to analyze amino acids, isomeric peptides, and protein conformers. The separations broadly mirrored those at atmospheric pressure, save for larger proteins that (as predicted) exhibited dipole alignment at ambient but not low pressure. Here we reduce the pressure down to 4.7 Torr, allowing normalized electric fields up to 543 Td-double the maximum in prior FAIMS or IMS studies of polyatomic ions. Despite the collisional heating to ∼1000 °C at the waveform peaks, the proteins of size from ubiquitin to albumin survived intact. The dissociation of macromolecules in FAIMS appears governed by the average ion temperature over the waveform cycle, unlike the isomerization controlled by the peak temperature. The global separation trends in this "superhot" regime extend those at moderately low pressures, with distinct conformers and no alignment as theorized. Although the scaling of the compensation voltage with the field fell below cubic at lower fields, the resolving power increased and the resolution of different proteins or charge states substantially improved.

Structural Heterogeneity of Human Histone H2A.1

Histones are highly basic chromatin proteins that tightly package and order eukaryotic DNA into nucleosomes. While the atomic structure of the nucleosomes has been determined, the three-dimensional structure of DNA-free histones remains unresolved. Here, we combine tandem nonlinear and linear ion mobility spectrometry (FAIMS-TIMS) coupled to mass spectrometry in parallel with molecular modeling to study the conformational space of a DNA-free histone H2A type 1 (H2A.1). Experimental results showed the dependence of the gas-phase structures on the starting solution conditions, characterized by charge state distributions, mobility distributions, and collision-induced-unfolding pathways. The measured H2A.1 gas-phase structures showed a high diversity of structural features ranging from compact (C) to partially folded (P) and then highly elongated (E) conformations. Molecular dynamics simulations provided candidate structures for the solution H2A.1 native conformation with folded N- and C-terminal tails, as well as gas-phase candidate structures associated with the mobility trends. Complementary collision cross section and dipole calculations showed that the charge distribution in the case of elongated gas-phase structures, where basic and acidic residues are mostly exposed (e.g., z > 15+), is sufficient to induce differences in the dipole alignment at high electric fields, in good agreement with the trends observed during the FAIMS-TIMS experiments.

Enhancing Top-Down Proteomics of Brain Tissue with FAIMS

Proteomic investigations of Alzheimer's and Parkinson's disease have provided valuable insights into neurodegenerative disorders. Thus far, these investigations have largely been restricted to bottom-up approaches, hindering the degree to which one can characterize a protein's "intact" state. Top-down proteomics (TDP) overcomes this limitation; however, it is typically limited to observing only the most abundant proteoforms and of a relatively small size. Therefore, fractionation techniques are commonly used to reduce sample complexity. Here, we investigate gas-phase fractionation through high-field asymmetric waveform ion mobility spectrometry (FAIMS) within TDP. Utilizing a high complexity sample derived from Alzheimer's disease (AD) brain tissue, we describe how the addition of FAIMS to TDP can robustly improve the depth of proteome coverage. For example, implementation of FAIMS with external compensation voltage (CV) stepping at -50, -40, and -30 CV could more than double the mean number of non-redundant proteoforms, genes, and proteome sequence coverage compared to without FAIMS. We also found that FAIMS can influence the transmission of proteoforms and their charge envelopes based on their size. Importantly, FAIMS enabled the identification of intact amyloid beta (Aβ) proteoforms, including the aggregation-prone Aβ1-42 variant which is strongly linked to AD. Raw data and associated files have been deposited to the ProteomeXchange Consortium via the MassIVE data repository with data set identifier PXD023607.

High-Field Asymmetric Waveform Ion Mobility Spectrometry and Native Mass Spectrometry: Analysis of Intact Protein Assemblies and Protein Complexes

High-field asymmetric waveform ion mobility spectrometry (FAIMS) enables the separation of ions on the basis of their differential mobility in an asymmetric oscillating electric field. We, and others, have previously demonstrated the benefits of FAIMS for the analysis of peptides and denatured proteins. To date, FAIMS has not been integrated with native mass spectrometry of folded proteins and protein complexes, largely due to concerns over the heating effects associated with the high electric fields employed. Here, we demonstrate the newly introduced cylindrical FAIMS Pro device coupled with an Orbitrap Eclipse enables analysis of intact protein assemblies up to 147 kDa. No evidence for dissociation was detected suggesting that any field heating is insufficient to disrupt the noncovalent interactions governing these assemblies. Moreover, the FAIMS device was integrated into native liquid extraction surface analysis (LESA) MS of protein assemblies directly from thin tissue sections. Intact tetrameric hemoglobin (64 kDa) and trimeric reactive intermediate deiminase A (RidA, 43 kDa) were detected. Improvements in signal-to-noise of between 1.5× and 12× were observed for these protein assemblies on integration of FAIMS.

Native mass spectrometry provides sufficient ion flux for XFEL single-particle imaging

The SPB/SFX instrument at the European XFEL provides unique conditions for single-particle imaging (SPI) experiments due to its high brilliance, nano-focus and unique pulse structure. Promising initial results provided by the international LCLS (Linac Coherent Light Source) SPI initiative highlight the potential of SPI. Current available injection methods generally have high sample consumption and do not provide any options for pulsing, selection or orientation of particles, which poses a problem for data evaluation. Aerosol-injector-based sample delivery is the current method of choice for SPI experiments, although, to a lesser extent, electrospray and electrospinning are used. Single particles scatter only a limited number of photons providing a single orientation for data evaluation, hence large datasets are required from particles in multiple orientations in order to reconstruct a structure. Here, a feasibility study demonstrates that nano-electrospray ionization, usually employed in biomolecular mass spectrometry, provides enough ion flux for SPI experiments. A novel instrument setup at the SPB/SFX instrument is proposed, which has the benefit of extremely low background while delivering mass over charge and conformation-selected ions for SPI.

Recommendations for reporting ion mobility Mass Spectrometry measurements

Here we present a guide to ion mobility mass spectrometry experiments, which covers both linear and nonlinear methods: what is measured, how the measurements are done, and how to report the results, including the uncertainties of mobility and collision cross section values. The guide aims to clarify some possibly confusing concepts, and the reporting recommendations should help researchers, authors and reviewers to contribute comprehensive reports, so that the ion mobility data can be reused more confidently. Starting from the concept of the definition of the measurand, we emphasize that (i) mobility values (K0 ) depend intrinsically on ion structure, the nature of the bath gas, temperature, and E/N; (ii) ion mobility does not measure molecular surfaces directly, but collision cross section (CCS) values are derived from mobility values using a physical model; (iii) methods relying on calibration are empirical (and thus may provide method-dependent results) only if the gas nature, temperature or E/N cannot match those of the primary method. Our analysis highlights the urgency of a community effort toward establishing primary standards and reference materials for ion mobility, and provides recommendations to do so. © 2019 The Authors. Mass Spectrometry Reviews Published by Wiley Periodicals, Inc.

Understanding proton capture and cation-induced dimerization of [Ag29(BDT)12]3−clusters by ion mobility mass spectrometry

We present a unique reaction of [Ag₂₉(BDT)₁₂]³⁻cluster with protons and dimerization of the cluster induced by alkali metal ions.

Differential Mobility Spectrometry-Hydrogen Deuterium Exchange (DMS-HDX) as a Probe of Protein Conformation in Solution

Differential mobility spectrometry (DMS) is an ion mobility technique that has been adopted chiefly as a pre-filter for small- to medium-sized analytes (<1 000 Da). With the exception of a handful of studies that employ an analogue of DMS-field asymmetric waveform ion mobility spectroscopy (FAIMS)-the application of DMS to intact biomacromolecules remains largely unexplored. In this work, we employ DMS combined with gas-phase hydrogen deuterium exchange (DMS-HDX) to probe the gas-phase conformations generated from proteins that were initially folded, partially-folded, and unfolded in solution. Our findings indicate that proteins with distinct structural features in solution exhibit unique deuterium uptake profiles as function of their optimal transmission through the DMS. Ultimately we propose that DMS-HDX can, if properly implemented, provide rapid measurements of liquid-phase protein structural stability that could be of use in biopharmaceuticals development. Graphical Abstract ᅟ.

Dependences of Q-branch integrated intensity of linear-molecule pendular spectra on electric-field strength and rotational temperature and its potential applications

We calculate the pendular-state spectra of cold linear molecules, and investigated the dependences of “Q-branch” integrated intensity of pendular spectra on both electric-field strength and molecular rotation-temperature. A new multi-peak structure in the “Q-branch” spectrum is appearing when the Stark interaction strength ω = μE/B equal to or larger than the critical value. Our study shows that the above results can be used not only to measure the electric-field vector and its spatial distribution in some electrostatic devices, such as the Stark decelerator, Stark velocity filter and electrostatic trap and so on, but also to survey the orientation degree of cold linear molecules in a strong electrostatic field.

To What Extent is FAIMS Beneficial in the Analysis of Proteins?

High field asymmetric waveform ion mobility spectrometry (FAIMS), also known as differential ion mobility spectrometry, is emerging as a tool for biomolecular analysis. In this article, the benefits and limitations of FAIMS for protein analysis are discussed. The principles and mechanisms of FAIMS separation of ions are described, and the differences between FAIMS and conventional ion mobility spectrometry are detailed. Protein analysis is considered from both the top-down (intact proteins) and the bottom-up (proteolytic peptides) perspective. The roles of FAIMS in the analysis of complex mixtures of multiple intact proteins and in the analysis of multiple conformers of a single protein are assessed. Similarly, the application of FAIMS in proteomics and targeted analysis of peptides are considered.

Differential ion mobility separations in up to 100% helium using microchips

The performance of differential IMS (FAIMS) analyzers is much enhanced by gases comprising He, especially He/N2 mixtures. However, electrical breakdown has limited the He fraction to ~50%-75%, depending on the field strength. By the Paschen law, the threshold field for breakdown increases at shorter distances. This allows FAIMS using chips with microscopic channels to utilize much stronger field intensities (E) than "full-size" analyzers with wider gaps. Here we show that those chips can employ higher He fractions up to 100%. Use of He-rich gases improves the resolution and resolution/sensitivity balance substantially, although less than for full-size analyzers. The optimum He fraction is ~80%, in line with first-principles theory. Hence, one can now measure the dependences of ion mobility on E in pure He, where ion-molecule cross section calculations are much more tractable than in other gases that form deeper and more complex interaction potentials. This capability may facilitate quantitative modeling of high-field ion mobility behavior and, thus, FAIMS separation properties, which would enable a priori extraction of structural information about the ions.

A comparison of the electromechanical properties of structurally diverse proteins by molecular dynamics simulation

Proteins are subjected to electric fields both within the cell and during routine biochemical analysis. We have used atomistic molecular dynamics simulations to study conformational changes within three structurally diverse proteins subjected to high electric fields. At electric fields in excess of .5 V/nm, major structural changes were observed in all three proteins due to charge redistribution within the biomolecule. However, the electromechanical resilience was found to be highly dependent on the protein secondary structure, with α-helices showing a particularly high susceptibility to deformation by the applied electric field.

Baseline resolution of isomers by traveling wave ion mobility mass spectrometry: investigating the effects of polarizable drift gases and ionic charge distribution

We have studied the behavior of isomers and analogues by traveling wave ion mobility mass spectrometry (TWIM-MS) using drift-gases with varying masses and polarizabilities. Despite the reduced length of the cell (18 cm), a pair of constitutional isomers, N-butylaniline and para-butylaniline, with theoretical collision cross-section values in helium (ΩHe ) differing by as little as 1.2 Å(2) (1.5%) but possessing contrasting charge distribution, showed baseline peak-to-peak resolution (Rp-p ) for their protonated molecules, using carbon dioxide (CO2), nitrous oxide (N2O) and ethene (C2H4 ) as the TWIM drift-gas. Near baseline Rp-p was also obtained in CO2 for a group of protonated haloanilines (para-chloroaniline, para-bromoaniline and para-iodoaniline) which display contrasting masses and theoretical ΩHe , which differ by as much as 15.7 Å(2) (19.5%) but similar charge distributions. The deprotonated isomeric pair of trans-oleic acid and cis-oleic acid possessing nearly identical theoretical ΩHe and ΩN2 as well as similar charge distributions, remained unresolved. Interestingly, an inversion of drift-times were observed for the 1,3-dialkylimidazolium ions when comparing He, N2 and N2O. Using density functional theory as a means of examining the ions electronic structure, and He and N2-based trajectory method algorithm, we discuss the effect of the long-range charge induced dipole attractive and short-range Van der Waals forces involved in the TWIM separation in drift-gases of differing polarizabilities. We therefore propose that examining the electronic structure of the ions under investigation may potentially indicate whether the use of more polarizable drift-gases could improve separation and the overall success of TWIM-MS analysis.

High-definition differential ion mobility spectrometry with resolving power up to 500

As the resolution of analytical methods improves, further progress tends to be increasingly limited by instrumental parameter instabilities that were previously inconsequential. This is now the case with differential ion mobility spectrometry (FAIMS), where fluctuations of the voltages and gas pressure have become critical. A new high-definition generator for FAIMS compensation voltage reported here provides a stable and accurate output than can be scanned with negligible steps. This reduces the spectral drift and peak width, thus improving the resolving power (R) and resolution. The gain for multiply-charged peptides that have narrowest peaks is up to ~40%, and R ~400-500 is achievable using He/N(2) or H(2)/N(2) gas mixtures.

Intrinsic disorder in proteins: a challenge for (un)structural biology met by ion mobility–mass spectrometry

The link between structure and function of a given protein is a principal tenet of biology. The established approach to understand the function of a protein is to ‘solve’ its structure and subsequently investigate interactions between the protein and its binding partners. However, structure determination via crystallography or NMR is challenging for proteins where localized regions or even their entire structure fail to fold into a three-dimensional form. These so called IDPs (intrinsically disordered proteins) or intrinsically disordered regions constitute up to 40% of all expressed proteins, and a much higher percentage in proteins involved in the proliferation of cancer. For these proteins, there is a need to develop new methods for structural characterization which exploit their biophysical properties. IM (ion mobility)–MS is uniquely able to examine both absolute conformation(s), populations of conformation and also conformational change, and is therefore highly applicable to the study of IDPs. The present article details the technique of IM–MS and illustrates its use in assessing the relative disorder of the wild-type p53 DNA-core-binding domain of cellular tumour antigen p53. The IM data were acquired on a Waters Synapt HDMS instrument following nESI (nanoelectrospray ionization) from ‘native’ and low-pH solution conditions.

Protein analyses using differential ion mobility microchips with mass spectrometry

Differential ion mobility spectrometry (FAIMS) integrated with mass spectrometry (MS) is a powerful new tool for biological and environmental analyses. Large proteins occupy regions of FAIMS spectra distinct from peptides, lipids, or other medium-size biomolecules, likely because strong electric fields align huge dipoles common to macroions. Here we confirm this phenomenon in separations of proteins at extreme fields using FAIMS chips coupled to MS and demonstrate their use to detect even minor amounts of large proteins in complex matrixes of smaller proteins and peptides.

Separation and classification of lipids using differential ion mobility spectrometry

Correlations between the dimensions of a 2-D separation create trend lines that depend on structural or chemical characteristics of the compound class and thus facilitate classification of unknowns. This broadly applies to conventional ion mobility spectrometry (IMS)/mass spectrometry (MS), where the major biomolecular classes (e.g., lipids, peptides, nucleotides) occupy different trend line domains. However, strong correlation between the IMS and MS separations for ions of same charge has impeded finer distinctions. Differential IMS (or FAIMS) is generally less correlated to MS and thus could separate those domains better. We report the first observation of chemical class separation by trend lines using FAIMS, here for lipids. For lipids, FAIMS is indeed more independent of MS than conventional IMS, and subclasses (such as phospho-, glycero-, or sphingolipids) form distinct, often non-overlapping domains. Even finer categories with different functional groups or degrees of unsaturation are often separated. As expected, resolution improves in He-rich gases: at 70% He, glycerolipid isomers with different fatty acid positions can be resolved. These results open the door for application of FAIMS to lipids, particularly in shotgun lipidomics and targeted analyses of bioactive lipids.

Separation of peptide isomers with variant modified sites by high-resolution differential ion mobility spectrometry

Many proteins and proteolytic peptides incorporate the same post-translational modification (PTM) at different sites, creating multiple localization variants with different functions or activities that may coexist in cells. Current analytical methods based on liquid chromatography (LC) followed by tandem mass spectrometry (MS/MS) are challenged by such isomers that often coelute in LC and/or produce nonunique fragment ions. The application of ion mobility spectrometry (IMS) was explored, but success has been limited by insufficient resolution. We show that high-resolution differential ion mobility spectrometry (FAIMS) employing helium-rich gases can readily separate phosphopeptides with variant modification sites. Use of He/N(2) mixtures containing up to 74% He has allowed separating to >95% three monophosphorylated peptides of identical sequence. Similar separation was achieved at 50% He, using an elevated electric field. Bisphosphorylated isomers that differ in only one modification site were separated to the same extent. We anticipate FAIMS capabilities for such separations to extend to other PTMs.

Behaviour of tetraalkylammonium ions in high-field asymmetric waveform ion mobility spectrometry

High-field asymmetric waveform ion mobility spectrometry (FAIMS) is an ion-filtering technique recently adapted for use with liquid chromatography/mass spectrometry (LC/MS) to remove interferences during analysis of complex matrices. This is the first systematic study of a series of singly charged tetraalkylammonium ions by FAIMS-MS. The compensation voltage (CV) is the DC offset of the waveform which permits the ion to emerge from FAIMS and it was determined for each member of the series under various conditions. The electrospray ionization conditions explored included spray voltage, vaporizer temperature, and sheath and auxiliary gas pressure. The FAIMS conditions explored included carrier gas flow rate, electrode temperature and composition of the carrier gas. Optimum desolvation was achieved using sufficient carrier gas (flow rate > or = 2 L/min) to ensure stable response. Low-mass ions (m/z 100-200) are more susceptible to changes in electrode temperature and gas composition than high mass ions (m/z 200-700). As a result of this study, ions are reliably analyzed using standard FAIMS conditions (dispersion voltage -5000 V, carrier gas flow rate 3 L/min, 50% helium/50%nitrogen, inner electrode temperature 70 degrees C and outer electrode temperature 90 degrees C). Variation of FAIMS conditions may be of great use for the separation of very low mass tetraalkylammonium (TAA) ions from other TAA ions. The FAIMS conditions do not appear to have a major effect on higher mass ions.

Application of FAIMS to anabolic androgenic steroids in sport drug testing

Mass spectrometric identification of anabolic androgenic steroids challenges standard doping-control methods. To reveal a doping offence the presence of prohibited anabolic androgenic steroids at trace levels in the picogram-per-millilitre range must be confirmed as reliable. Human urine samples containing epitrenbolone, metandienone metabolite (17beta -hydroxymethyl-17alpha-methyl-18-norandrost-1,4,13-trien-3-one), stanozolol, 16beta-hydroxystanozolol and 4beta-hydroxystanozolol were analysed using LC-FAIMS-MS/MS. These substances are prohibited in sport according to World Anti-Doping Agency (WADA) regulations. Glucuronides were hydrolysed and prepared by liquid-liquid extraction. Excellent recovery and precision were obtained for all compounds. Linear calibration results for epitrenbolone and metandienone metabolite were obtained and concentration information could be determined in the ranges of reliable response between 750-1200 and 100-600 pg/mL, respectively. Limits of detection were estimated at 25 pg/mL (stanozolol), 50 pg/mL (metandienone metabolite, 16beta-hydroxystanozolol), 100 pg/mL (4beta-hydroxystanozolol) and 500 pg/mL (epitrenbolone). The assay was applied to doping-control samples. For all analytes, LC-FAIMS-MS/MS resulted in excellent interference removal, which effectively extends the post-dose detection time.

Ultrafast differential ion mobility spectrometry at extreme electric fields in multichannel microchips

The maximum electric field intensity (E) in field asymmetric waveform ion mobility spectrometry (FAIMS) analyses was doubled to E > 60 kV/cm. In earlier devices with >0.5 mm gaps, such strong fields cause electrical breakdown for nearly all gases at ambient pressure. As the Paschen curves are sublinear, thinner gaps permit higher E: here, we established 61 kV/cm in N(2) using microchips with 35 microm gaps. As FAIMS efficiency is exceptionally sensitive to E, such values can in theory accelerate analyses at equal resolution by over an order of magnitude. Here we demonstrate FAIMS filtering in approximately 20 micros or approximately 1% of the previously needed time, with a resolving power of about half that for "macroscopic" units but sufficing for many applications. Microscopic gaps enable concurrent ion processing in multiple (here, 47) channels, which greatly relaxes the charge capacity constraints of planar FAIMS designs. These chips were integrated with a beta-radiation ion source and charge detector. The separation performance is in line with first-principles modeling that accounts for high-field and anisotropic ion diffusion. By extending FAIMS operation into the previously inaccessible field range, the present instrument advances the capabilities for research into ion transport and expands options for separation of hard-to-resolve species.