A review on the application of high-field asymmetric waveform ion mobility spectrometry (FAIMS) in drug discovery

Theoretical and experimental study on the effect of scanning speed on FAIMS peaks

High-Field Asymmetric Ion Mobility Spectrometry (FAIMS) is a technique for ion separation and detection based on ion mobility variation under high electronic field. While compensation voltage scanning speed is a fundamental parameter in FAIMS, its impact on spectra remains unclear. In this work, a function referred to as F-EMG is introduced to describe the impact of compensation voltage scanning speed on FAIMS spectra, and the properties of the function are studied. Theoretical analysis emphasizes the impact of the scanning speed on peak height, position, and symmetry, as well as the capability of the F-EMG function to progressively approach Gaussian function at lower scanning speeds. Furthermore, the function indicates that spectra obtained in positive and negative scanning modes exhibits symmetry. An experimental validation, conducted with a custom FAIMS setup and analyzing hydrogen sulfide, ethylbenzene, toluene, styrene, benzene and ammonia, confirms the model's influence on peak features, fitting accuracy, and exhibits a closer alignment with the Gaussian function at lower scanning speeds. Additionally, the experimental data indicate that the spectra show symmetry in positive and negative scanning models. This work not only improves understanding of FAIMS spectral analysis but also introduces a robust method for enhancing data accuracy across varying scanning speeds.

Improved First-Principles Model of Differential Mobility Using Higher Order Two-Temperature Theory

Differential mobility spectrometry is a separation technique that may be applied to a variety of analytes ranging from small molecule drugs to peptides and proteins. Although rudimentary theoretical models of differential mobility exist, these models are often only applied to small molecules and atomic ions without considering the effects of dynamic microsolvation. Here, we advance our theoretical description of differential ion mobility in pure N₂ and microsolvating environments by incorporating higher order corrections to two-temperature theory (2TT) and a pseudoequilibrium approach to describe ion-neutral interactions. When comparing theoretical predictions to experimentally measured dispersion plots of over 300 different compounds, we find that higher order corrections to 2TT reduce errors by roughly a factor of 2 when compared to first order. Model predictions are accurate especially for pure N₂ environments (mean absolute error of 4 V at SV = 4000 V). For strongly clustering environments, accurate thermochemical corrections for ion-solvent clustering are likely required to reliably predict differential ion mobility behavior. Within our model, general trends associated with clustering strength, solvent vapor concentration, and background gas temperature are well reproduced, and fine structure visible in some dispersion plots is captured. These results provide insight into the dynamic ion-solvent clustering process that underpins the phenomenon of differential ion mobility.

Identification of amphetamine as a stimulant drug by pristine and doped C70 fullerenes: a DFT/TDDFT investigation

The density functional theory (DFT) was used to examine the electronic reactivity and sensitivity of a pristine, Si, and Al-doped fullerene C₇₀ with AM drug. AM drug has been shown to be physically absorbed by its N-head on the pristine C₇₀ with an adsorption energy of about - 1.09 kcal/mol and to have no impact on the electric conductivity of that cluster. The atom substitution of Si and Al for C atoms at C₇₀ significantly increases C₇₀ fullerene reactivity, with adsorption energy predictions of approximately - 31.09 and - 45.59 kcal/mol, respectively. The energy difference of LUMO and HOMO, i.e., Eg from C₇₀ fullerene, significantly affects AM drug. Significant LUMO destabilization in Al-C₇₀ by adsorption of the drug AM boosts the electrical conductivity of Al-C₇₀ while generating electric signals that are related to the environmental presence of AM drug. Hence, Al-doped C₇₀ is demonstrated to be an effective electronic AM drug sensor. In contrast to Si-C₇₀ fullerene, significant AM-drug adsorption effects on Fermi and Si-C₇₀ work functions make Si-C₇₀ an Ф-type candidate for AM drug sensor applications. The time-dependent theory of the functional density shows that the AM/Al-C₇₀ complex is steadily situated at a maximum peak of 784.15 nm.

Ion Mobility Spectrometry: Fundamental Concepts, Instrumentation, Applications, and the Road Ahead

Ion mobility spectrometry (IMS) is a rapid separation technique that has experienced exponential growth as a field of study. Interfacing IMS with mass spectrometry (IMS-MS) provides additional analytical power as complementary separations from each technique enable multidimensional characterization of detected analytes. IMS separations occur on a millisecond timescale, and therefore can be readily nested into traditional GC and LC/MS workflows. However, the continual development of novel IMS methods has generated some level of confusion regarding the advantages and disadvantages of each. In this critical insight, we aim to clarify some common misconceptions for new users in the community pertaining to the fundamental concepts of the various IMS instrumental platforms (i.e., DTIMS, TWIMS, TIMS, FAIMS, and DMA), while addressing the strengths and shortcomings associated with each. Common IMS-MS applications are also discussed in this review, such as separating isomeric species, performing signal filtering for MS, and incorporating collision cross-section (CCS) values into both targeted and untargeted omics-based workflows as additional ion descriptors for chemical annotation. Although many challenges must be addressed by the IMS community before mobility information is collected in a routine fashion, the future is bright with possibilities.

Coupling Front-End Separations, Ion Mobility Spectrometry, and Mass Spectrometry For Enhanced Multidimensional Biological and Environmental Analyses

Ion mobility spectrometry (IMS) is a widely used analytical technique for rapid molecular separations in the gas phase. Though IMS alone is useful, its coupling with mass spectrometry (MS) and front-end separations is extremely beneficial for increasing measurement sensitivity, peak capacity of complex mixtures, and the scope of molecular information available from biological and environmental sample analyses. In fact, multiple disease screening and environmental evaluations have illustrated that the IMS-based multidimensional separations extract information that cannot be acquired with each technique individually. This review highlights three-dimensional separations using IMS-MS in conjunction with a range of front-end techniques, such as gas chromatography, supercritical fluid chromatography, liquid chromatography, solid-phase extractions, capillary electrophoresis, field asymmetric ion mobility spectrometry, and microfluidic devices. The origination, current state, various applications, and future capabilities of these multidimensional approaches are described in detail to provide insight into their uses and benefits.

High sensitivity field asymmetric ion mobility spectrometer

A high sensitivity field asymmetric ion mobility spectrometer (FAIMS) was designed, fabricated, and tested. The main components of the system are a 10.6 eV UV photoionization source, an ion filter driven by a high voltage/high frequency n-MOS inverter circuit, and a low noise ion detector. The ion filter electronics are capable to generate square waveforms with peak-to-peak voltages up to 1000 V at frequencies up to 1 MHz with adjustable duty cycles. The ion detector current amplifier has a gain up to 10¹² V/A with an effective equivalent input noise level down to about 1 fA/Hz^1/2 during operation with the ion filter at the maximum voltage and frequency. The FAIMS system was characterized by detecting different standard chemical compounds. Additionally, we investigated the use of a synchronous modulation/demodulation technique to improve the signal-to-noise ratio in FAIMS measurements. In particular, we implemented the modulation of the compensation voltage with the synchronous demodulation of the ion current. The analysis of the measurements at low concentration levels led to an extrapolated limit of detection for acetone of 10 ppt with an averaging time of 1 s.

Increased Ion Transmission for Differential Ion Mobility Combined with Mass Spectrometry by Implementation of a Flared Inlet Capillary

Differential ion mobility spectrometry (DIMS) is capable of separating components of complex mixtures prior to mass spectrometric analysis, thereby increasing signal-to-noise and signal-to-background ratios on millisecond timescales. However, adding a DIMS device to the front end of a mass spectrometer can reduce the signal intensity of subsequent mass spectrometric analysis. This is a result, in part, of ions lost due to inefficient transfer of ions from the DIMS device through the aperture leading into the mass spectrometer. This problem of transferring ions can be at least partially corrected by modifying the front end of the inlet capillary leading to the vacuum of the mass spectrometer. The inner diameter of the ion-sampling end of the inlet capillary was enlarged by drilling into the face. This results in a conical flare at the front end of the capillary, while the other end of the capillary remains unmodified. These flared capillaries allow for a greater number of ions from the DIMS device to be sampled relative to the unmodified standard capillary. Four flare dimensions were tested, differing by the angle between the wall of the flare and the outer wall of the inlet capillary. All flared capillaries showed greater signal intensity than the standard capillary with a DIMS device present without reducing the resolving power. It was also observed that the signal intensity increased as the flare angle decreased. The flared capillary with the smallest flare angle showed greater than a fivefold increase in signal intensity compared with the standard capillary. Graphical Abstract ᅟ.

Enhancing biological analyses with three dimensional field asymmetric ion mobility, low field drift tube ion mobility and mass spectrometry (μFAIMS/IMS-MS) separations

Multidimensional high throughput separations are ideal for analyzing distinct ion characteristics simultaneously in one analysis. We report on the first evaluation of a platform coupling a high speed field asymmetric ion mobility spectrometry microchip (μFAIMS) with drift tube ion mobility and mass spectrometry (IMS-MS). The μFAIMS/IMS-MS platform was used to analyze biological samples and simultaneously acquire multidimensional FAIMS compensation fields, IMS drift times, and accurate ion masses for the detected features. These separations thereby increased the overall measurement separation power, resulting in greater information content and more complete characterization of the complex samples. The separation conditions were optimized for sensitivity and resolving power by the selection of gas compositions and pressures in the FAIMS and IMS separation stages. The resulting performance provided three dimensional separations, benefitting both broad complex mixture studies and targeted analyses by improving isomeric separations and allowing detection of species obscured by interfering peaks.

Improved Differential Ion Mobility Separations Using Linked Scans of Carrier Gas Composition and Compensation Field

Differential ion mobility spectrometry (DIMS) separates ions based on differences in their mobilities in low and high electric fields. When coupled to mass spectrometric analyses, DIMS has the ability to improve signal-to-background by eliminating isobaric and isomeric compounds for analytes in complex mixtures. DIMS separation power, often measured by resolution and peak capacity, can be improved through increasing the fraction of helium in the nitrogen carrier gas. However, because the mobility of ions is higher in helium, a greater number of ions collide with the DIMS electrodes or housing, yielding losses in signal intensity. To take advantage of the benefits of helium addition on DIMS separations and reduce ion losses, linked scans were developed. In a linked scan the helium content of the carrier gas is reduced as the compensation field is increased. Linked scans were compared with conventional compensation field scans with constant helium content for the protein ubiquitin and a tryptic digest of bovine serum albumin (BSA). Linked scans yield better separation of ubiquitin charge states and enhanced peak capacities for the analysis of BSA compared with compensation field scans with constant helium carrier gas percentages. Linked scans also offer improved signal intensity retention in comparison to compensation field scans with constant helium percentages in the carrier gas.

Precise determination of nonlinear function of ion mobility for explosives and drugs at high electric fields for microchip FAIMS

High-field asymmetric waveform ion mobility spectrometry (FAIMS) separates ions by utilizing the characteristics of nonlinear ion mobility at high and low electric fields. Accurate ion discrimination depends on the precise solution of nonlinear relationships and is essential for accurate identification of ion species for applications. So far, all the nonlinear relationships of ion mobility obtained are based at low electric fields (E/N <65 Td). Microchip FAIMS (μ-FAIMS) with small dimensions has high electric field up to E/N = 250 Td, making the approximation methods and conclusions for nonlinear relationships inappropriate for these systems. In this paper, we deduced nonlinear functions based on the first principle and a general model. Furthermore we considered the hydrodynamics of gas flow through microchannels. We then calculated the specific alpha coefficients for cocaine, morphine, HMX, TNT and RDX, respectively, based on their FAIMS spectra measured by μ-FAIMS system at ultra-high fields up to 250 Td. The results show that there is no difference in nonlinear alpha functions obtained by the approximation and new method at low field (<120 Td), but the error induced by using approximation method increases monotonically with the increase in field, and could be as much as 30% at a field of 250 Td.

On an aerodynamic mechanism to enhance ion transmission and sensitivity of FAIMS for nano-electrospray ionization-mass spectrometry

Simulations show that significant ion losses occur within the commercial electrospray ionization-field asymmetric waveform ion mobility spectrometer (ESI-FAIMS) interface owing to an angular desolvation gas flow and because of the impact of the FAIMS carrier gas onto the inner rf (radio frequency) electrode. The angular desolvation gas flow diverts ions away from the entrance plate orifice while the carrier gas annihilates ions onto the inner rf electrode. A novel ESI-FAIMS interface is described that optimizes FAIMS gas flows resulting in large improvements in transmission. Simulations with the bromochloroacetate anion showed an improvement of ~9-fold to give ~70% overall transmission). Comparable transmission improvements were attained experimentally for six peptides (2+) in the range of m/z 404.2 to 653.4 at a chromatographic flow rate of 300 nL/min. Selected ion chromatograms (SIC) from nano-LC-FAIMS-MS analyses showed 71% (HLVDEPQNLIK, m/z 653.4, 2+) to 95% (LVNELTEFAK, m/z 582.3, 2+) of ion signal compared with ion signal in the SIC from LC-MS analysis. IGSEVYHNLK (580.3, 2+) showed 24% more ion signal compared with LC-MS and is explained by enhanced desolvation in FAIMS. A 3-10 times lower limits of quantitation (LOQ) (<15% RSD) was achieved for chemical noise limited peaks with FAIMS. Peaks limited by ion statistics showed subtle improvement in RSD and yielded comparable LOQ to that attained with nano-LC-MS (without FAIMS). These improvements were obtained using a reduced FAIMS separation gap (from 2.5 to 1.5 mm) that results in a shorter residence time (13.2 ms ± 3.9 ms) and enables the use of a helium free transport gas (100% nitrogen).

Data-independent microbial metabolomics with ambient ionization mass spectrometry

Atmospheric ionization methods are ideally suited for prolonged MS/MS analysis. Data-independent MS/MS is a complementary technique for analysis of biological samples as compared to data-dependent analysis. Here, we pair data-independent MS/MS with the ambient ionization method nanospray desorption electrospray ionization (nanoDESI) for untargeted analysis of bacterial metabolites. Proof-of-principle data and analysis are illustrated by sampling Bacillus subtilis and Pseudomonas aeruginosa directly from Petri dishes. We found that this technique enables facile comparisons between strains via MS and MS/MS plots which can be translated to chemically informative molecular maps through MS/MS networking. The development of novel techniques to characterize microbial metabolites allows rapid and efficient analysis of metabolic exchange factors. This is motivated by our desire to develop novel techniques to explore the role of interspecies interactions in the environment, health, and disease. This is a contribution to honor Professor Catherine C. Fenselau in receiving the prestigious ASMS Award for a Distinguished Contribution in Mass Spectrometry for her pioneering work on microbial mass spectrometry.

High-field asymmetric waveform ion mobility spectrometry for mass spectrometry-based proteomics

High-field asymmetric waveform ion mobility spectrometry (FAIMS) is an atmospheric pressure ion mobility technique that separates gas-phase ions by their behavior in strong and weak electric fields. FAIMS is easily interfaced with electrospray ionization and has been implemented as an additional separation mode between liquid chromatography (LC) and mass spectrometry (MS) in proteomic studies. FAIMS separation is orthogonal to both LC and MS and is used as a means of on-line fractionation to improve the detection of peptides in complex samples. FAIMS improves dynamic range and concomitantly the detection limits of ions by filtering out chemical noise. FAIMS can also be used to remove interfering ion species and to select peptide charge states optimal for identification by tandem MS. Here, the authors review recent developments in LC-FAIMS-MS and its application to MS-based proteomics.

SPE–MS analysis of absorption, distribution, metabolism and excretion assays: a tool to increase throughput and steamline workflow

In an effort to create faster and more efficient bioanalytical methods for drug development, many investigators have evaluated a variety of SPE–MS systems. Over the past 15 years online systems have evolved from run times of >1.5 min/sample to <10 s/sample. High-throughput SPE–MS methods for in vitro absorption, distribution, metabolism and excretion screening assays have been described by several laboratories and shown to produce results comparable to conventional LC–MS/MS systems. While quantitative analysis of small molecules in biological matrixes holds many challenges, for several applications SPE–MS methods have achieved comparable results to LC–MS/MS with the benefit of 10–30-times the throughput. Based on its distinct advantages of throughput and streamlined workflow efficiencies, SPE–MS is a useful tool for the analysis of many in vitro absorption, distribution, metabolism and excretion assays and in vivo bioanalytical studies. Further development of SPE–MS methods and analysis workflows has the potential to expand the capabilities of this technology for other challenging bioanalytical applications.

10 years of MS instrumental developments--impact on LC-MS/MS in clinical chemistry

The combination of liquid chromatography and mass spectrometry (LC-MS) is a powerful and indispensable analytical tool that is widely applied in many areas of chemistry, medicine, pharmaceutics and biochemistry. In this review recent MS instrumental developments are presented as part of a special issue covering various aspects of liquid chromatography tandem mass spectrometry (LC-MS/MS) in clinical chemistry. Improvements, new inventions as well as new combinations in ion source technology are described focusing on dual or multimode sources and atmospheric pressure photoionization (APPI). Increasing demands regarding sensitivity, accuracy, resolution and both quantitation and identification guarantee on-going improvements in mass analyzer technology. This paper discusses new hybrid MS instruments that can perform novel scan modes as well as high-resolution mass spectrometers (HRMS) that finally seem to be able to overcome, or at least significantly reduce, their weaknesses in quantitative applications. Ion mobility-mass spectrometry (IMMS) itself is not an invention of the last 10 years, but a lot of progress was made within the last decade that reveals the potential benefits of this combination. This is clearly reflected by the increased number of commercially available instruments and the various designs of IMMS are covered in detail in this review. Selected applications for all these instrumental developments are given focusing on the perspective of clinical chemistry.

Separation of peptides from detergents using ion mobility spectrometry

Mass spectrometry (MS) has dramatically evolved in the last two decades and has been the driving force of the spectacular expansion of proteomics during this period. However, the very poor compatibility of MS with detergents is still a technical obstacle in some studies, in particular on membrane proteins. Indeed, the high hydrophobicity of membrane proteins necessitates the use of detergents for their extraction and solubilization. Here, we address the analytical potential of high-field asymmetric waveform ion mobility spectrometry (FAIMS) for separating peptides from detergents. The study was focused on peptides from the human integral membrane protein CD9. A tryptic peptide was mixed with the non-ionic detergents Triton X-100 or beta-D-dodecyl maltoside (DDM) as well as with the ionic detergents sodium dodecyl sulfate (SDS) or sodium deoxycholate (SDC). Although electrospray ionization (ESI) alone led to a total suppression of the peptide ion signal on mass spectra with only detection of the detergents, use of FAIMS allowed separation and clear identification of the peptide with any of the detergents studied. The detection and identification of the target compound in the presence of an excess of detergents are then feasible. FAIMS should prove especially useful in the structural and proteomic analysis of membrane proteins.

Photo-SRM: laser-induced dissociation improves detection selectivity of Selected Reaction Monitoring mode

Selected Reaction Monitoring (SRM) carried out on triple-quadrupole mass spectrometers coupled to liquid chromatography has been a reference method to develop quantitative analysis of small molecules in biological or environmental matrices for years and is currently emerging as a promising tool in clinical proteomic. However, sensitive assays in complex matrices are often hampered by the presence of co-eluted compounds that share redundant transitions with the target species. On-the-fly better selection of the precursor ion by high-field asymmetric waveform ion mobility spectrometry (FAIMS) or increased quadrupole resolution is one way to escape from interferences. In the present work we document the potential interest of substituting classical gas-collision activation mode by laser-induced dissociation in the visible wavelength range to improve the specificity of the fragmentation step. Optimization of the laser beam pathway across the different quadrupoles to ensure high photo-dissociation yield in Q2 without detectable fragmentation in Q1 was assessed with sucrose tagged with a push-pull chromophore. Next, the proof of concept that photo-SRM ensures more specific detection than does conventional collision-induced dissociation (CID)-based SRM was carried out with oxytocin peptide. Oxytocin was derivatized by the thiol-reactive QSY® 7 C(5)-maleimide quencher on cysteine residues to shift its absorption property into the visible range. Photo-SRM chromatograms of tagged oxytocin spiked in whole human plasma digest showed better detection specificity and sensitivity than CID, that resulted in extended calibration curve linearity. We anticipate that photo-SRM might significantly improve the limit of quantification of classical SRM-based assays targeting cysteine-containing peptides.

Identification and subsequent removal of an interference by FAIMS in the bioanalysis of dianicline in animal plasma

Background: The determination of pharmacokinetic parameters requires accurate and reliable bioanalytical methods. Even using highly selective MS/MS, interferences can occur. This paper describes the source of some of these interferences with an example discussed involving the problem of a ketamine interference in a plasma assay. Results: The introduction of field asymmetric waveform ion mobility spectrometry (FAIMS) removed the interference, enhanced signal-to-background and met GLP acceptance criteria. Relative to the non-FAIMS method, assay calibration characteristics were improved. The FAIMS source gave optimal performance following the introduction of a split in order to reduce the inlet flow to approximately 0.4 ml/min. Conclusion: The introduction of ion-mobility separation into a bioanalytical LC–MS/MS method can remove unexpected isobaric interferences without the need to redevelop the chromatography.

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.

On-tissue protein identification and imaging by MALDI-ion mobility mass spectrometry

MALDI imaging mass spectrometry (MALDI-IMS) has become a powerful tool for the detection and localization of drugs, proteins, and lipids on-tissue. Nevertheless, this approach can only perform identification of low mass molecules as lipids, pharmaceuticals, and peptides. In this article, a combination of approaches for the detection and imaging of proteins and their identification directly on-tissue is described after tryptic digestion. Enzymatic digestion protocols for different kinds of tissues--formalin fixed paraffin embedded (FFPE) and frozen tissues--are combined with MALDI-ion mobility mass spectrometry (IM-MS). This combination enables localization and identification of proteins via their related digested peptides. In a number of cases, ion mobility separates isobaric ions that cannot be identified by conventional MALDI time-of-flight (TOF) mass spectrometry. The amount of detected peaks per measurement increases (versus conventional MALDI-TOF), which enables mass and time selected ion images and the identification of separated ions. These experiments demonstrate the feasibility of direct proteins identification by ion-mobility-TOF IMS from tissue. The tissue digestion combined with MALDI-IM-TOF-IMS approach allows a proteomics "bottom-up" strategy with different kinds of tissue samples, especially FFPE tissues conserved for a long time in hospital sample banks. The combination of IM with IMS marks the development of IMS approaches as real proteomic tools, which brings new perspectives to biological studies.

Improving FAIMS sensitivity using a planar geometry with slit interfaces

Differential mobility spectrometry or field asymmetric waveform ion mobility spectrometry (FAIMS) is gaining broad acceptance for analyses of gas-phase ions, especially in conjunction with largely orthogonal separation methods such as mass spectrometry (MS) and/or conventional (drift tube) ion mobility spectrometry. In FAIMS, ions are filtered while passing through a gap between two electrodes that may have planar or curved (in particular, cylindrical) geometry. Despite substantial inherent advantages of the planar configuration and its near-universal adoption in current stand-alone FAIMS devices, commercial FAIMS/MS systems have employed curved FAIMS geometries that can be more effectively interfaced to MS. Here we report a new planar (p-) FAIMS design with slit-shaped entrance and exit apertures that substantially increase ion transmission in and out of the analyzer. The entrance slit interface effectively couples p-FAIMS to multi-emitter electrospray ionization (ESI) sources, improving greatly the ion current introduced to the device and allowing liquid flow rates up to approximately 50 microL/min. The exit slit interface increases the transmission of ribbon-shaped ion beams output by the p-FAIMS to downstream stages such as a MS. Overall, the ion signal in ESI/FAIMS/MS analyses increases by over an order of magnitude without affecting FAIMS resolution.

Validated quantitation method for a peptide in rat serum using liquid chromatography/high-field asymmetric waveform ion mobility spectrometry

The analysis of peptides presents serious challenges for bioanalytical scientists including low total ion current and non-selective fragmentation during tandem mass spectrometry (MS/MS). During method validation of a peptide in rat serum matrix some interferences could not be easily removed and thus prevented accurate and precise measurement. These problems associated with peptide quantitation were resolved by using FAIMS (high-Field Asymmetric waveform Ion Mobility Spectrometry). This selectivity-enhancing technique filters out matrix interferences, and the resulting pseudo-selected reaction monitoring (pseudo-SRM) chromatograms were nearly free from interferences. Control blank matrix samples contained an acceptable level of interference (only 7% signal as compared to the lower level of quantitation). Chromatographic peaks were easily, accurately and precisely integrated resulting in a validated liquid chromatography (LC)/FAIMS-MS/MS method for the analysis of a peptide drug in rat serum according to United States Food and Drug Administration (US FDA) bioanalytical guidelines. These results confirm that new selectivity-enhancing technologies aid the pharmaceutical industry in reliably producing acceptable pharmacokinetic data.

Advances in bioanalytical LC–MS using the Orbitrap™ mass analyzer

The continuing desire to analyze complex biological samples with the minimum number of steps places high demands on increasing speed, dynamic signal range, quantitative capability and the facility with which the mass spectrometers can interface with chromatographic separation methods. Reliable identification of metabolites in complex mixtures requires robust mass spectrometers with high resolving power, mass accuracy, sensitivity and dynamic range, while tandem MS is an invaluable tool for further structural characterization. This review begins with a discussion of the key properties of the Orbitrap™ mass analyzer: mass accuracy, resolution, fidelity of isotope pattern abundancies and dynamic range. The main objective is to provide an overview of Orbitrap applications in the field of bioanalysis. Specific areas of drug metabolism, doping control and food contaminants are discussed in detail illustrating the performance and versatility of the Orbitrap mass analyzer.

Sample preparation and separation techniques for bioanalysis of morphine and related substances

In present time the use or misuse of morphine and its derivatives are monitored by assaying the presence of the drug and its metabolites in biofluids. In the present review, focus is placed on the sample preparation and on the separation techniques used in the current best practices of bioanalysis of morphine and its major metabolites. However, as methods for testing the misuse of heroin, a morphine derivative, often involve bioanalytical methods that cover a number of other illicit drug substances, such methods are also included in the review. Furthermore, the review also includes bioanalysis in a broader perspective as analysis of plant materials, cell cultures and environmental samples. The review is not intended to cover all publications that include bioanalysis of morphine but is more to be considered a view into the current best practices of bioanalysis of morphine, its metabolites and other related substances.

Trace level impurity method development with high-field asymmetric waveform ion mobility spectrometry: systematic study of factors affecting the performance

For the determination of trace level impurities, analytical chemists are confronted with complex mixtures and difficult separations. New technologies such as high-field asymmetric waveform ion mobility spectrometry (FAIMS) have been developed to make their work easier; however, efficient method development and troubleshooting can be quite challenging if little prior knowledge of the factors or their settings is available. We present the results of an investigation performed in order to obtain a better understanding of the FAIMS technology. The influence of eight factors (polarity of dispersion voltage, outer bias voltage, total gas flow rate, composition of the carrier gas (e.g. %He), outer electrode temperature, ratio between the temperatures of the inner and outer electrodes, flow rate and composition of the make-up mobile phase) was assessed. Five types of responses were monitored: value of the compensation voltage (CV), intensity, width and asymmetry of the compensation voltage peak, and resolution between two peaks. Three types of studies were performed using different test mixtures and various ionisation modes to assess whether the same conclusions could be drawn across these conditions for a number of different types of compounds. To extract the maximum information from as few experiments as possible, a Design of Experiment (DoE) approach was used. The results presented in this work provide detailed information on the factors affecting FAIMS separations and therefore should enable the user to troubleshoot more effectively and to develop efficient methods.