Ion mobility-mass spectrometry separation of steroid structural isomers and epimers

Two-dimensional isotopic shifts for steroid isomer delineation with high-resolution cyclic ion mobility separations

Recently, the use of mass distribution-based isotopic shifts in high-resolution ion mobility spectrometry-mass spectrometry-based separations have enabled isomer delineation by measuring the relative arrival times of their heavy and light isotopologues. However, all previous efforts to induce such shifts have focused solely on the introduction of one type of isotopic substitution for a given molecule or isomer set. Herein, for the first time, we present a two-dimensional isotopic labeling strategy where two unique derivatizations are performed on various steroid isomer molecules to induce two distinct isotopic shifts and thus simultaneously measure them in a single ion mobility separations experiment. Derivatization strategies were chosen to target two specific functional groups in these steroids (i.e., hydroxyl and carbonyl), and heavy-labeled versions of the derivatizing reagents were used to induce isotopic shifts at each of these positions. We found that isotopic shifts were orthogonal to one another, diagnostic for certain steroid isomers, and that the simultaneous analysis of two different isotopic shifts was necessary for complete characterization of each steroid isomer set. We envision this multidimensional isotopic shift strategy as a new method for delineating amongst isomeric molecules, especially those with several different functional groups causing their isomerism.

Evaluating Ion Mobility Data Acquisition, Calibration, and Processing for Small Molecules: A Cross-Platform Assessment of Drift Tube and Traveling Wave Methodologies

As ion mobility spectrometry (IMS) separations continue to be added to analytical workflows due to their power in environmental and biological sample analyses, harmonization and capability understanding between existing and newly released instruments are desperately needed. Developments in IMS platforms often exhibit focus on increasing resolving power (Rp) to better separate molecules of similar structure. While the additional separation capacity is advantageous, ensuring these developments coincide with appropriate data extraction and analysis methods is imperative to ensure routine adoption. Herein, we assess the performance of the MOBILion MOBIE in relation to a commercially available drift tube IMS-MS, the Agilent 6560, and evaluate feature extraction and analysis pipelines. Both instruments were operated using matched conditions when possible, and performance metrics of scan speed, Rp, limits of detection (LOD), and propensity for isomer separation via LC-IMS-MS were evaluated. Similar scan speeds pertaining to IMS-MS frame generation were noted for both platforms, and collision cross section (CCS) values for the MOBIE were generally within ≤ 1% difference from previously reported drift tube values. Both platforms were also able to generate quantitative data (comparable limits of detection) in experiments with perfluoroalkyl substances (PFAS) mixtures in a cell-based model (both medium and cell lysates), as demonstrated in Skyline with adjusted mobility filtering parameters. Higher Rp was, however, noted on the MOBIE in comparison to the 6560 (200-300 vs 45-60 CCS/ΔCCS without data processing), allowing the detection of more PFAS isomers and indicating promise toward future applications in chemical exposomics studies and biomarker discovery when molecules exhibit similar structures.

Ion mobility spectrometry and ion mobility-mass spectrometry in clinical chemistry

Advancements in clinical chemistry have major implications in terms of public health, prompting many clinicians to seek out chemical information to aid in diagnoses and treatments. While mass spectrometry (MS) and hyphenated-MS techniques such as LC-MS or tandem MS/MS have long been the analytical methods of choice for many clinical applications, these methods routinely demonstrate difficulty in differentiating between isomeric forms in complex matrices. Consequently, ion mobility spectrometry (IM), which differentiates molecules on the basis of size, shape, and charge, has demonstrated unique advantages in the broad application of stand-alone IM and hyphenated IM instruments towards clinical challenges. Here, we highlight representative IM applications and approaches and describe contemporary commercial offerings of IM technology and how these can be, or are currently being, applied to the field of clinical chemistry.

Identifying and Quantifying Relative Concentrations of Epimers in Mixtures via Cyclic Ion Mobility Mass Spectrometry: Dexamethasone and Betamethasone as a Case Study

Epimers can show different biological activities and different pharmacological behaviors; therefore, their separation and analysis are crucial in the drug development process. Due to their similar chemical and physical properties, separation of epimers is challenging. This study demonstrates the application of cyclic ion mobility-mass spectrometry to separate, identify, and quantify dexamethasone and betamethasone in a binary mixture. Cyclic IMS separation of the isolated protonated dimer resulted in three peaks: dexamethasone homodimer, betamethasone homodimer, and their heterodimer. Besides providing improved separation over the protonated monomer, the presence of a heterodimer peak provides additional confirmation of an isomeric mixture. We identified the dexamethasone and betamethasone homodimer peaks by infusing pure solutions of each epimer and measuring each pure homodimer's arrival time. The measured peak areas indicated that the heterodimer is formed at twice the rate of each homodimer and that dexamethasone and betamethasone contribute equally to the heterodimer signal. Using this observation, we could accurately calculate the relative concentrations of each epimer by adding half of the heterodimer peak area to each homodimer peak area. These findings enable the identification and quantification of dexamethasone and betamethasone based on the arrival time distributions of their protonated dimers. This is the first demonstration of accurate relative quantification of epimers by separating charged dimers in the gas phase.

Direct Enantiomer Differentiation of Drugs and Drug-Like Compounds via Noncovalent Copper-Amino Acid Complexation and Ion Mobility-Mass Spectrometry

Drug enantiomers can possess vastly different pharmacological properties, yet they are identical in their chemical composition and structural connectivity. Thus, resolving enantiomers poses a great challenge in the field of separation science. Enantiomer separations necessitate interaction of the analyte with a chiral environment─in mass spectrometry-based analysis, a common approach is through a three-point interaction with a chiral selector commonly introduced during sample preparation. In select cases, the structural difference imparted through noncovalent complexation results in enantiomer-specific structural differences, facilitating measurement using a structurally selective analytical technique such as ion mobility-mass spectrometry (IM-MS). In this work, we investigate the direct IM-MS differentiation of chiral drug compounds using mononuclear copper complexes incorporating an amino acid chiral selector. A panel of 20 chiral drugs and drug-like compounds were investigated for separation, and four l-amino acids (l-histidine, l-tryptophan, l-proline, and l-tyrosine) were evaluated as chiral selectors (CS) to provide the chiral environment necessary for differentiation. Enantiomer differentiation was achieved for four chiral molecule pairs (R/S-thalidomide, R/S-baclofen, R/S-metoprolol, and d/l-panthenol) with two-peak resolution (Rp-p) values ranging from 0.7 (>10% valley) to 1.5 (baseline separation). Calibration curves relating IM peak areas to enantiomeric concentrations enabled enantiomeric excess quantitation of racemic thalidomide and metoprolol with residuals of 5.7 and 2.5%, respectively. Theoretical models suggest that CuII and l-histidine complexation around the analyte chiral center is important for gas-phase stereoselectivity. This study demonstrates the potential of combining enantioselective noncovalent copper complexation with structurally selective IM-MS for differentiating chiral drugs and drug-like compounds.

Anabolic steroids in livestock production: Background and implications for chemical food safety

The use of steroids in livestock animals is a source of concern for consumers because of the risks associated with the presence of their residues in foodstuffs of animal origin. Technological advances such as mass spectrometry have made it possible to play a fundamental role in controlling such practices, firstly for the discovery of marker metabolites but also for the monitoring of these compounds under the regulatory framework. Current control strategies rely on the monitoring of either the parent drug or its metabolites in various matrices of interest. As some of these steroids also have an endogenous status specific strategies have to be applied for control purposes. This review aims to provide a comprehensive and up-to-date knowledge of analytical strategies, whether targeted or non-targeted, and whether they focus on markers of exposure or effect in the specific context of chemical food safety regarding the use of anabolic steroids in livestock. The role of new approaches in data acquisition (e.g. ion mobility), processing and analysis, (e.g. molecular networking), is also discussed.

Detection and Imaging of Exposure-Related Metabolites and Xenobiotics in Hard Tissues by Laser Sampling and Mass Spectrometry

The utility of two novel laser-based methods, laser ablation electrospray ionization (LAESI) and laser desorption ionization (LDI) from silicon nanopost array (NAPA), is explored via local analysis and mass spectrometry imaging (MSI) of hard tissues (tooth and hair) for the detection and mapping of organic components. Complex mass spectra are recorded in local analysis mode from tooth dentin and scalp hair samples. Nicotine and its metabolites (cotinine, hydroxycotinine, norcotinine, and nicotine) are detected by LAESI-MS in the teeth of rats exposed to tobacco smoke. The intensities of the detected metabolite peaks are proportional to the degree of exposure. Incorporating ion mobility separation in the LAESI-MS analysis of scalp hair enables the detection of cotinine in smoker hair along with other common molecular species, including endogenous steroid hormones and some lipids. Single hair strands are imaged by MALDI-MSI and NAPA-LDI-MSI to explore longitudinal variations in the level of small molecules. Comparing spectra integrated from NAPA-LDI-MSI and MALDI-MSI images reveals that the two techniques provide complementary information. There were 105 and 82 sample-related peaks for MALDI and NAPA, respectively, with an overlap of only 16 peaks, indicating a high degree of complementarity. Enhanced molecular coverage and spatial resolution offered by LAESI-MS and NAPA-LDI-MSI can reveal the distributions of known and potential biomarkers in hard tissues, facilitating exposome research.

Calcium complexation by steroids involved in the steroidogenesis

Steroids that take part in the pathways of human steroidogenesis are involved in many biological mechanisms where they interact with calcium. In the present work, the binding selectivities and affinities for calcium of progestagens, mineralocorticoids, androstagens, and estrogens were studied by Electrospray Ionization-Mass Spectrometry (ESI-MS). The adduct profile of each steroid was characterized by high resolution and tandem mass spectrometry. The relative stability of the most important adducts was studied by threshold collision induced dissociation, E1/2. Doubly-charged steroid-calcium complexes [nM + Ca]2+ with n = 1-6 were predominant in the mass spectra. The adduct [5M + Ca]2+ was the base peak for most 3-keto-steroids, while ligands bearing hindered ketones or α-hydroxy-ketones also yielded [nM + Ca + mH2O]2+ with n = 3-4 and m = 0-1. Principal component analysis allowed us to spot the main differences and similarities in the binding behavior of these steroids. The isomers testosterone and dehydroepiandrosterone, androstanolone and epiandrosterone, and 17-α-hydroxyprogesterone and 11-deoxycorticosterone showed remarkable differences in their adduct profiles. Computational modeling of representative adducts was performed by density functional theory methods. The possible binding modes at low and high numbers of steroid ligands were determined by calcium Gas Phase Affinity, and through modeling of the complexes and comparison of their relative stabilities, in agreement with the experimental results.

Application of Ion Mobility Spectrometry and the Derived Collision Cross Section in the Analysis of Environmental Organic Micropollutants

Ion mobility spectrometry (IMS) is a rapid gas-phase separation technique, which can distinguish ions on the basis of their size, shape, and charge. The IMS-derived collision cross section (CCS) can serve as additional identification evidence for the screening of environmental organic micropollutants (OMPs). In this work, we summarize the published experimental CCS values of environmental OMPs, introduce the current CCS prediction tools, summarize the use of IMS and CCS in the analysis of environmental OMPs, and finally discussed the benefits of IMS and CCS in environmental analysis. An up-to-date CCS compendium for environmental contaminants was produced by combining CCS databases and data sets of particular types of environmental OMPs, including pesticides, drugs, mycotoxins, steroids, plastic additives, per- and polyfluoroalkyl substances (PFAS), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs), as well as their well-known transformation products. A total of 9407 experimental CCS values from 4170 OMPs were retrieved from 23 publications, which contain both drift tube CCS in nitrogen (DTCCSN2) and traveling wave CCS in nitrogen (TWCCSN2). A selection of publicly accessible and in-house CCS prediction tools were also investigated; the chemical space covered by the training set and the quality of CCS measurements seem to be vital factors affecting the CCS prediction accuracy. Then, the applications of IMS and the derived CCS in the screening of various OMPs were summarized, and the benefits of IMS and CCS, including increased peak capacity, the elimination of interfering ions, the separation of isomers, and the reduction of false positives and false negatives, were discussed in detail. With the improvement of the resolving power of IMS and enhancements of experimental CCS databases, the practicability of IMS in the analysis of environmental OMPs will continue to improve.

Improving LC-MS/MS measurements of steroids with differential mobility spectrometry

Introduction

Steroid measurements are important for diagnosis and monitoring of many conditions and treatment regiments; however, due to structural and chemical similarities amongst steroids, these analyses are challenging, even for highly specific techniques such as liquid chromatography-tandem mass spectrometry (LC-MS/MS). Differential mobility spectrometry (DMS) has the potential to improve these analyses by providing an orthogonal and complementary separation technique.

Methods

Initially, the potential for DMS to improve signal-to-noise ratio (S/N) and reduce interference was tested by comparing chromatograms acquired with and without DMS when performing measurements of six different steroids. Subsequently, a full clinical validation of cortisol and cortisone in urine was performed with the LC-DMS-MS/MS method.

Results and Discussion

DMS significantly reduced interferences observed in the chromatograms and boosted S/N by between 1.6 and 13.8 times. Additionally, DMS improved the agreement between quantifier/qualifier fragment ion results for cortisol and cortisone as indicated by the increase in R2 from approximately 0.81 to 0.98. All validation studies met acceptance criteria and we observed exceptional analytical performance in terms of precision, with % CVs less than 8%.

Conclusions

DMS improved the specificity of the steroid measurements by reducing interferences and improving S/N. The validation studies prove that these benefits did not come at the expense of other aspects of analytical performance. This study indicates that DMS has the potential to benefit not just clinical measurements of challenging analytes, but many clinical LC-MS/MS analyses.

Improved analysis of derivatized steroid hormone isomers using ion mobility-mass spectrometry (IM-MS)

Over the last decade, applications of ion mobility-mass spectrometry (IM-MS) have exploded due primarily to the widespread commercialization of robust instrumentation from several vendors. Unfortunately, the modest resolving power of many of these platforms (~40-60) has precluded routine separation of constitutional and stereochemical isomers. While instrumentation advances have pushed resolving power to >150 in some cases, chemical approaches offer an alternative for increasing resolution with existing IM-MS instrumentation. Herein we explore the utility of two reactions, derivatization by Girard's reagents and 1,1-carbonyldiimidazole (CDI), for improving IM separation of steroid hormone isomers. These reactions are fast (≤30 min), simple (requiring only basic lab equipment/expertise), and low-cost. Notably, these reactions are structurally selective in that they target carbonyl and hydroxyl groups, respectively, which are found in all naturally occurring steroids. Many steroid hormone isomers differ only in the number, location, and/or stereochemistry of these functional groups, allowing these reactions to "amplify" subtle structural differences and improve IM resolution. Our results show that resolution was significantly improved amongst CDI-derivatized isomer groups of hydroxyprogesterone (two-peak resolution of Rpp = 1.10 between 21-OHP and 11B-OHP), deoxycortisone (Rpp = 1.47 between 11-DHC and 21-DOC), and desoximetasone (Rpp = 1.98 between desoximetasone and fluocortolone). Moreover, characteristic collision cross section (DTCCSN2) measurements can be used to increase confidence in the identification of these compounds in complex biological mixtures. To demonstrate the feasibility of analyzing the derivatized steroids in complex biological matrixes, the reactions were performed following steroid extraction from urine and yielded similar results. Additionally, we applied a software-based approach (high-resolution demultiplexing) that further improved the resolving power (>150). Overall, our results suggest that targeted derivatization reactions coupled with IM-MS can significantly improve the resolution of challenging isomer groups, allowing for more accurate and efficient analysis of complex mixtures.

Mass Spectrometry Based on Chemical Derivatization Has Brought Novel Discoveries to Lipidomics: A Comprehensive Review

Lipids, as one of the most important organic compounds in organisms, are important components of cells and participate in energy storage and signal transduction of living organisms. As a rapidly rising field, lipidomics research involves the identification and quantification of multiple classes of lipid molecules, as well as the structure, function, dynamics, and interactions of lipids in living organisms. Due to its inherent high selectivity and high sensitivity, mass spectrometry (MS) is the "gold standard" analysis technique for small molecules in biological samples. The combination chemical derivatization with MS detection is a unique strategy that could improve MS ionization efficiency, facilitate structure identification and quantitative analysis. Herein, this review discusses derivatization-based MS strategies for lipidomic analysis over the past decade and focuses on all the reported lipid categories, including fatty acids and modified fatty acids, glycerolipids, glycerophospholipids, sterols and saccharolipids. The functional groups of lipids mainly involved in chemical derivatization include the C=C group, carboxyl group, hydroxyl group, amino group, carbonyl group. Furthermore, representative applications of these derivatization-based lipid profiling methods were summarized. Finally, challenges and countermeasures of lipid derivatization are mentioned and highlighted to guide future studies of derivatization-based MS strategy in lipidomics.

Tandem mass spectrometry approaches for recognition of isomeric compounds mixtures

The present review aims to collect the published literature pertaining the recognition of isobaric compounds (isomers or stereoisomers) using the features of tandem mass spectrometry (MS) experiments without any chromatographic separation or chemical modification (derivatization or isotopic enrichment) of the analytes. MS/MS methods possess high selectivity, wide dynamic range and high throughput capabilities. Generally, tandem MS has limited capability for distinguishing isomers that fragment similarly. However, some MS/MS methods have been developed and positively applied to isomers discrimination. Among the literature on this topic, the applications that fit on the review subject can be summarized as follow: (1) chiral discrimination by the kinetic method, (2) the use energy-resolved tandem mass spectra and the survival yield (SY) representation, (3) the kinetics evaluation of the ion-molecule interaction and (4) the postprocessing mathematical algorithm to resolve the isomers in MS/MS signal.

Development of a Rapid, Targeted LC-IM-MS Method for Anabolic Steroids

Anabolic steroids are of high biological interest due to their involvement in human development and disease progression. Additionally, they are banned in sport due to their performance-enhancing characteristics. Analytical challenges associated with their measurement stem from structural heterogeneity, poor ionization efficiency, and low natural abundance. Their importance in a variety of clinically relevant assays has prompted the consideration of integrating ion mobility spectrometry (IMS) into existing LC-MS assays, due primarily to its speed and structure-based separation capability. Herein we have optimized a rapid (2 min) targeted LC-IM-MS method for the detection and quantification of 40 anabolic steroids and their metabolites. First, a steroid-specific calibrant mixture was developed to cover the full range of retention time, mobility, and accurate mass. Importantly, this use of this calibrant mixture provided robust and reproducible measurements based on collision cross section (CCS) with interday reproducibility of <0.5%. Furthermore, the combined separation power of LC coupled to IM provided comprehensive differentiation of isomers/isobars within 6 different isobaric groups. Multiplexed IM acquisition also provided improved limits of detection, which were well below 1 ng/mL in almost all compounds measured. This method was also capable of steroid profiling, providing quantitative ratios (e.g., testosterone/epitestosterone, androsterone/etiocholanolone, etc.). Lastly, phase II steroid metabolites were probed in lieu of hydrolysis to demonstrate the ability to separate those analytes and provide information beyond total steroid concentration. This method has tremendous potential for rapid analysis of steroid profiles in human urine spanning a variety of applications from developmental disorders to doping in sport.

Characterization of Bile Acid Isomers and the Implementation of High-Resolution Demultiplexing with Ion Mobility-Mass Spectrometry

Bile acids (BAs) are a complex suite of clinically relevant metabolites that include many isomers. Liquid chromatography coupled to mass spectrometry (LC-MS) is an increasingly popular technique due to its high specificity and sensitivity; nonetheless, acquisition times are generally 10-20 min, and isomers are not always resolved. In this study, the application of ion mobility (IM) spectrometry coupled to MS was investigated to separate, characterize, and measure BAs. A subset of 16 BAs was studied, including three groups of isomers belonging to unconjugated, glycine-conjugated, and taurine-conjugated BA classes. A variety of strategies were explored to increase BA isomer separation such as changing the drift gas, measuring different ionic species (i.e., multimers and cationized species), and enhancing the instrumental resolving power. In general, Ar, N₂, and CO₂ provided the best peak shape, resolving power (R_p), and separation, especially CO₂; He and SF₆ were less preferable. Furthermore, measuring dimers versus monomers improved isomer separation due to enhanced gas-phase structural differences. A variety of cation adducts other than sodium were characterized. Mobility arrival times and isomer separation were affected by the choice of adduct, which was shown to be used to target certain BAs. Finally, a novel workflow that involves high-resolution demultiplexing in combination with dipivaloylmethane ion-neutral clusters was implemented to improve R_p dramatically. A maximum R_p increase was observed with lower IM field strengths to obtain longer drift times, increasing R_p from 52 to 187. A combination of these separation enhancement strategies demonstrates great potential for rapid BA analysis.

Integrating the potential of ion mobility spectrometry-mass spectrometry in the separation and structural characterisation of lipid isomers

It is increasingly evident that a more detailed molecular structure analysis of isomeric lipids is critical to better understand their roles in biological processes. The occurrence of isomeric interference complicates conventional tandem mass spectrometry (MS/MS)-based determination, necessitating the development of more specialised methodologies to separate lipid isomers. The present review examines and discusses recent lipidomic studies based on ion mobility spectrometry combined with mass spectrometry (IMS-MS). Selected examples of the separation and elucidation of structural and stereoisomers of lipids are described based on their ion mobility behaviour. These include fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, and sterol lipids. Recent approaches for specific applications to improve isomeric lipid structural information using direct infusion, coupling imaging, or liquid chromatographic separation workflows prior to IMS-MS are also discussed, including: 1) strategies to improve ion mobility shifts; 2) advanced tandem MS methods based on activation of lipid ions with electrons or photons, or gas-phase ion-molecule reactions; and 3) the use of chemical derivatisation techniques for lipid characterisation.

Improved Ion Mobility Separation and Structural Characterization of Steroids using Derivatization Methods

Steroids are an important class of biomolecules studied for their role in metabolism, development, nutrition, and disease. Although highly sensitive GC- and LC-MS/MS-based methods have been developed for targeted quantitation of known steroid metabolites, emerging techniques including ion mobility (IM) have shown promise in improved analysis and capacity to better identify unknowns in complex biological samples. Herein, we couple LC-IM-MS/MS with structurally selective reactions targeting hydroxyl and carbonyl functional groups to improve IM resolution and structural elucidation. We demonstrate that 1,1-carbonyldiimidazole derivatization of hydroxyl stereoisomer pairs such as testosterone/epitestosterone and androsterone/epiandrosterone results in increased IM resolution with ΔCCS > 15%. Additionally, performing this in parallel with derivatization of the carbonyl group by Girard's Reagent P resulted in unique products based on relative differences in number of each functional group and C17 alkylation. These changes could be easily deciphered using the combination of retention time, collision cross section, accurate mass, and MS/MS fragmentation pattern. Derivatization by Girard's Reagent P, which contains a fixed charge quaternary amine, also increased the ionization efficiency and could be explored for its potential benefit to sensitivity. Overall, the combination of these simple and easy derivatization reactions with LC-IM-MS/MS analysis provides a method for improved analysis of known target analytes while also yielding critical structural information that can be used for identification of potential unknowns.

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

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

Enhancing the Performance of Analytical Methods to Combat Doping in Sport

Ion mobility–mass spectrometry (IM–MS) has become a cornerstone bioanalytical technique over the last two decades. Major advances have included new technology and software that enabled higher resolving power measurements; however, chemistry-based approaches, such as derivatization reactions, have also shown tremendous promise. This article demonstrates our work using IM–MS to detect anabolic steroids and describes how this technology could one day find its way into the anti-doping world.

Enantiomer Differentiation of Amino Acid Stereoisomers by Structural Mass Spectrometry Using Noncovalent Trinuclear Copper Complexes

Previous work has demonstrated that copper complexation strategies can be used with tandem MS (MS/MS) and, more recently, ion mobility-mass spectrometry (IM-MS) to differentiate chiral isomers based upon enantiomeric-specific binding. In this study, we investigate the separation of chiral amino acids (AAs) forming trinuclear complexes that can be directly resolved by IM-MS analyses. Twenty standard AAs of both d- and l-chirality were investigated. Specific AAs including d/l-histidine, d/l-proline, d/l-glutamine, d/l-tyrosine, and d/l-tryptophan were evaluated as "chiral selectors" that, when combined with copper, were found to promote selective complexation with specific AA enantiomers. Significant enantiomer differentiation was observed in the IM spectra for hydrophobic AAs acids with peak-to-peak resolutions ranging from 0.63 to 1.15. Among the chiral selectors investigated, histidine provided the best enantioselectivity, followed by tryptophan, suggesting the aromatic structure plays an important role in forming chiral-specific ion complexes. Unlike MS/MS methods where chiral selectors with l-stereochemistry enhance the differentiation, the chirality of the selector was found to have no significant effect on observed IM separation with both d- and l-selectors providing similar resolutions but with inverted IM arrival time ordering. To investigate the structural differences between resolvable chiral complexes, a combination of MS/MS, collision cross-section (CCS) measurements, and molecular mechanics techniques was used. Candidate trinuclear structures of the stoichiometry [(Cu²⁺)₃(d/lIle)₃(lHis)₂ - 5H]⁺ were constructed with guidance from empirical MS/MS results. Of the 48 theoretical structures generated, one enantiomeric cluster pair yielded close correlation (<1%) with experimental CCS measurements, suggesting the most enantioselective ion complexes observed in this work are bridged by three coppers.

Cyclic Peptide Protomer Detection in the Gas Phase: Impact on CCS Measurement and Fragmentation Patterns

With the recent improvements in ion mobility resolution, it is now possible to separate small protomeric tautomers, called protomers. In larger molecules above 1000 Da such as peptides, a few studies suggest that protomers do exist as well and may contribute to their gas-phase conformational heterogeneity. In this work, we observed a CCS distribution that can be explained by the presence of protomers of surfactin, a small lipopeptide with no basic site. Following preliminary density functional theoretical calculations, several protonation sites in the gas phase were energetically favorable in positive ionization mode. Experimentally, at least three near-resolved IM peaks were observed in positive ionization mode, while only one was detected in negative ionization mode. These results were in good agreement with the DFT predictions. CID breakdown curve analysis after IM separation showed different inflection points (CE₅₀) suggesting that different intramolecular interactions were implied in the stabilization of the structures of surfactin. The fragment ratio observed after collision-induced fragmentation was also different, suggesting different ring-opening localizations. All these observations support the presence of protomers on the cyclic peptide moieties of the surfactin. These data strongly suggest that protomeric tautomerism can still be observed on molecules above 1000 Da if the IM resolving power is sufficient. It also supports that the proton localization involves a change in the 3D structure that can affect the experimental CCS and the fragmentation channels of such peptides.

Separation of Isomeric Metabolites and Gangliosides with High Performance (Drift Tube) Ion Mobility–Mass Spectrometry

The study of metabolites and gangliosides is increasingly important in drug discovery (1) and immunology (2). Accurate analysis of biologically relevant isomers is important because their structure affects their molecular properties. Typically, the isomers are separated using chromatography prior to mass spectrometry (MS) analysis. However, specialized chromatographic methods that distinguish isomers frequently require a complex setup and long runs. Techniques that allow accurate results to be acquired quickly and efficiently would be beneficial.

“Targeted Glucocorticoid Analysis using Ion Mobility-Mass Spectrometry (IM-MS)”

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Liquid chromatography-ion mobility-mass spectrometry (LC-IM-MS) for glucocorticoids.

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Determination of collision cross sections (CCS) for isomers.

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Different cation adducts shifted mobility and improved IM separation.

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Changing drift gas (He, Ar, CO₂) shifted mobility and improved resolution.

Introduction

Ion mobility-mass spectrometry (IM-MS) is an emerging technique in the -omics fields that has broad potential applicability to the clinical lab. As a rapid, gas-phase structure-based separation technique, IM-MS offers promise in isomer separations and can be easily combined with existing LC-MS methods (i.e., LC-IM-MS). Several experimental conditions, including analyte cation adducts and drift composition further provide a means to tune separations for global and/or targeted applications.

Objectives

The primary objective of this study was to demonstrate the utility of IM-MS under a range of experimental conditions for detection of glucocorticoids, and specifically for the separation of several isomeric pairs.

Methods

LC-IM-MS was used to characterize 16 glucocorticoids including three isomer pairs: cortisone/prednisolone, betamethasone/dexamethasone, and flunisolide/triamcinolone acetonide. Collision cross section (CCS) values were measured for all common adducts (e.g., protonated and sodiated) using both step-field and single-field methods. Alternative alkali, alkaline earth, and transition metals were introduced, such that their adducts could also be measured. Finally, four different drift gases (helium, nitrogen, argon, and carbon dioxide) were compared for their relative separation capability.

Results

LC-IM-MS offered a robust, multidimensional separation technique that allowed for the 16 glucocorticoids to be analyzed and separated in three-dimensions (retention time, CCS, and m/z). Despite the relatively modest resolution of isomer pairs under standard conditions (i.e., nitrogen drift gas, sodiated ions, etc.), improvements were observed for alkaline earth and transition metals (notable barium adducts) and in carbon dioxide drift gas.

Conclusion

In summary, LC-IM-MS offers potential as a clinical method due to its ease of coupling with traditional LC-MS methods and its promise for tuning separations to better resolve targeted and/or global isomers in complex biological samples.

A tandem liquid chromatography and tandem mass spectrometry (LC/LC-MS/MS) technique to separate and quantify steroid isomers 11β-methyl-19-nortestosterone and testosterone

Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) has become a mainstay analytical technique in pharmaceutical research and development and clinical diagnosis due to several advantages including excellent selectivity, specificity, and high sensitivity. LC-MS/MS has become the method of choice for steroids analysis due to its fast analytical time and improved specificity yet has a challenge in the separation and measurement of isomers with the same product ions. Here we describe a high-sensitivity LC/LC-MS/MS method that combines chiral chromatography and reverse-phase chromatography (LC/LC) along with MS/MS to rapidly separate and quantify steroid isomers of 11ß-methyl-19-nortestosterone (11ß-MNT) and endogenous testosterone in serum.

Toward Routine Analysis of Anabolic Androgenic Steroids in Urine Using Ion Mobility-Mass Spectrometry

Anabolic androgenic steroids (AAS) make up one of the most prevalent classes of performance-enhancing drugs banned by the World Anti-Doping Agency (WADA) due to the competitive advantage they can afford athletes. Mass spectrometry-based methods coupled with chromatographic separations have become the gold standard for AAS analysis because of the superior sensitivity and selectivity provided. However, emerging analytical techniques including ion mobility spectrometry (IMS) have been demonstrated in recent applications as a means to further characterize and identify potential unknowns while simultaneously delivering improved sensitivity by filtering noise. Herein we outline the next crucial steps in bringing IMS to the routine drug testing workflow by combining it with established chromatographic and mass spectrometry methods (i.e., LC-IM-MS) for the detection of AAS in human urine. In addition to robust measurement of collision cross sections which can be used for identification purposes, functional group microtrends provide a structural basis on which to elucidate the structure of future novel anabolic agents. Lastly, the developed workflow is tested by analysis of testosterone in a realistic matrix (human urine) and demonstrates a limit of detection of 524 pg/mL, which surpasses the WADA Minimum Required Performance Levels for anabolic steroids. This work is expected to pave the way toward routine incorporation of IMS into analytical drug testing workflows to augment both qualitative and quantitative measure of performance enhancing drugs in the future.

Lipid analysis by ion mobility spectrometry combined with mass spectrometry: A brief update with a perspective on applications in the clinical laboratory

Ion mobility spectrometry (IMS) is an analytical technique where ions are separated in the gas phase based on their mobility through a buffer gas in the presence of an electric field. An ion passing through an IMS device has a characteristic collisional cross section (CCS) value that depends on the buffer gas used. IMS can be coupled with mass spectrometry (MS), which characterizes an ion based on a mass-to-charge ratio (m/z), to increase analytical specificity and provide further physicochemical information. In particular, IMS-MS is of ever-increasing interest for the analysis of lipids, which can be problematic to accurately identify and quantify in bodily fluids by liquid chromatography (LC) with MS alone due to the presence of isomers, isobars, and structurally similar analogs. IMS provides an additional layer of separation when combined with front-end LC approaches, thereby, enhancing peak capacity and analytical specificity. CCS (and also ion mobility drift time) can be plotted against m/z ion intensity and/or LC retention time in order to generate in-depth molecular profiles of a sample. Utilization of IMS-MS for routine clinical laboratory testing remains relatively unexplored, but areas do exist for potential implementation. A brief update is provided here on lipid analysis using IMS-MS with a perspective on some applications in the clinical laboratory.

Trapped Ion Mobility Incorporated in LC-HRMS Workflows as an Integral Analytical Platform of High Sensitivity: Targeted and Untargeted 4D-Metabolomics in Extra Virgin Olive Oil

Trapped ion mobility spectrometry (TIMS) is a promising technique for the separation of isomers based on their mobility. In the present work, TIMS coupled to liquid chromatography (LC) and high-resolution mass spectrometry (HRMS) was applied as a comprehensive analytical platform to address authenticity challenges, focusing on extra virgin olive oil (EVOO). Isomers detected in EVOO's phenolic fraction, classified into secoiridoids group, were successfully separated. Thanks to parallel accumulation serial fragmentation (PASEF) acquisition mode, high-quality spectra were obtained, facilitating identification. Moreover, a four-dimensional (4D) untargeted metabolomics approach was implemented to evaluate EVOO's global profile in cases of both variety and geographical origin discrimination. Potential authenticity markers, attributed to isomers, were successfully identified through the proposed workflow that incorporates ion mobility information along with LC-HRMS analytical evidence (i.e., mass accuracy, retention time, isotopic pattern, MS/MS fragmentation). Our study establishes LC-TIMS-HRMS in food authenticity and highlights mobility-enhanced metabolomics in four dimensions.

Analysis of positional isomers of 2-3-4-alkoxyphenylcarbamic acid derivatives by a combination of TLC and IMS

In this study, we have demonstrated a separation of positional isomers of some derivatives of alkoxyphenylcarbamic acid. These compounds belong to drugs with local anesthetics activity. The low volatility compounds were analysed by a Thin Layer Chromatography (TLC) and Ion Mobility Spectrometry (IMS) using diode laser desorption for sample introduction to IMS. This combined approach allowed the identification of compounds. Also, we have carried out IMS studies of all compounds and determined their ion mobilities The ion mobilities were increasing with the geometry change from position ortho to para of alkoxy chain, which is in agreement with their different collision cross section (CCS).

Investigation into Small Molecule Isomeric Glucuronide Metabolite Differentiation Using In Silico and Experimental Collision Cross-Section Values

Identifying isomeric metabolites remains a challenging and time-consuming process with both sensitivity and unambiguous structural assignment typically only achieved through the combined use of LC-MS and NMR. Ion mobility mass spectrometry (IMMS) has the potential to produce timely and accurate data using a single technique to identify drug metabolites, including isomers, without the requirement for in-depth interpretation (cf. MS/MS data) using an automated computational pipeline by comparison of experimental collision cross-section (CCS) values with predicted CCS values. An ion mobility enabled Q-Tof mass spectrometer was used to determine the CCS values of 28 (14 isomeric pairs of) small molecule glucuronide metabolites, which were then compared to two different in silico models; a quantum mechanics (QM) and a machine learning (ML) approach to test these approaches. The difference between CCS values within isomer pairs was also assessed to evaluate if the difference was large enough for unambiguous structural identification through in silico prediction. A good correlation was found between both the QM- and ML-based models and experimentally determined CCS values. The predicted CCS values were found to be similar between ML and QM in silico methods, with the QM model more accurately describing the difference in CCS values between isomer pairs. Of the 14 isomeric pairs, only one (naringenin glucuronides) gave a sufficient difference in CCS values for the QM model to distinguish between the isomers with some level of confidence, with the ML model unable to confidently distinguish the studied isomer pairs. An evaluation of analyte structures was also undertaken to explore any trends or anomalies within the data set.

Ion mobility-based sterolomics reveals spatially and temporally distinctive sterol lipids in the mouse brain

Aberrant sterol lipid metabolism is associated with physiological dysfunctions in the aging brain and aging-dependent disorders such as neurodegenerative diseases. There is an unmet demand to comprehensively profile sterol lipids spatially and temporally in different brain regions during aging. Here, we develop an ion mobility-mass spectrometry based four-dimensional sterolomics technology leveraged by a machine learning-empowered high-coverage library (>2000 sterol lipids) for accurate identification. We apply this four-dimensional technology to profile the spatially resolved landscapes of sterol lipids in ten functional regions of the mouse brain, and quantitatively uncover ~200 sterol lipids uniquely distributed in specific regions with concentrations spanning up to 8 orders of magnitude. Further spatial analysis pinpoints age-associated differences in region-specific sterol lipid metabolism, revealing changes in the numbers of altered sterol lipids, concentration variations, and age-dependent coregulation networks. These findings will contribute to our understanding of abnormal sterol lipid metabolism and its role in brain diseases.

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

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Ion Mobility-High-Resolution Mass Spectrometry (IM-HRMS) for the Analysis of Contaminants of Emerging Concern (CECs): Database Compilation and Application to Urine Samples

Ion mobility mass spectrometry (IM-MS)-derived collision cross section (CCS) values can serve as a valuable additional identification parameter within the analysis of compounds of emerging concern (CEC) in human matrices. This study introduces the first comprehensive database of ^DTCCS_N2 values of 148 CECs and their metabolites including bisphenols, alternative plasticizers (AP), organophosphate flame retardants (OP), perfluoroalkyl chemicals (PFAS), and others. A total of 311 ions were included in the database, whereby the ^DTCCS_N2 values for 113 compounds are reported for the first time. For 105 compounds, more than one ion is reported. Moreover, the ^DTCCS_N2 values of several isomeric CECs and their metabolites are reported to allow a distinction between isomers. Comprehensive quality assurance guidelines were implemented in the workflow of acquiring ^DTCCS_N2 values to ensure reproducible experimental conditions. The reliability and reproducibility of the complied database were investigated by analyzing pooled human urine spiked with 30 AP and OP metabolites at two concentration levels. For all investigated metabolites, the ^DTCCS_N2 values measured in urine showed a percent error of <1% in comparison to database values. ^DTCCS_N2 values of OP metabolites showed an average percent error of 0.12% (50 ng/mL in urine) and 0.15% (20 ng/mL in urine). For AP metabolites, these values were 0.10 and 0.09%, respectively. These results show that the provided database can be of great value for enhanced identification of CECs in environmental and human matrices, which can advance future suspect screening studies on CECs.

Analytical Methods for the Determination of Neuroactive Steroids

Neuroactive steroids are a family of all steroid-based compounds, of both natural and synthetic origin, which can affect the nervous system functions. Their biosynthesis occurs directly in the nervous system (so-called neurosteroids) or in peripheral endocrine tissues (hormonal steroids). Steroid hormone levels may fluctuate due to physiological changes during life and various pathological conditions affecting individuals. A deeper understanding of neuroactive steroids' production, in addition to reliable monitoring of their levels in various biological matrices, may be useful in the prevention, diagnosis, monitoring, and treatment of some neurodegenerative and psychiatric diseases. The aim of this review is to highlight the most relevant methods currently available for analysis of neuroactive steroids, with an emphasis on immunoanalytical methods and gas, or liquid chromatography combined with mass spectrometry.

The Charge-State and Structural Stability of Peptides Conferred by Microsolvating Environments in Differential Mobility Spectrometry

The presence of solvent vapor in a differential mobility spectrometry (DMS) cell creates a microsolvating environment that can mitigate complications associated with field-induced heating. In the case of peptides, the microsolvation of protonation sites results in a stabilization of charge density through localized solvent clustering, sheltering the ion from collisional activation. Seeding the DMS carrier gas (N₂) with a solvent vapor prevented nearly all field-induced fragmentation of the protonated peptides GGG, AAA, and the Lys-rich Polybia-MP1 (IDWKKLLDAAKQIL-NH₂). Modeling the microsolvation propensity of protonated n-propylamine [PrNH₃]⁺, a mimic of the Lys side chain and N-terminus, with common gas-phase modifiers (H₂O, MeOH, EtOH, iPrOH, acetone, and MeCN) confirms that all solvent molecules form stable clusters at the site of protonation. Moreover, modeling populations of microsolvated clusters indicates that species containing protonated amine moieties exist as microsolvated species with one to six solvent ligands at all effective ion temperatures (T_eff) accessible during a DMS experiment (ca. 375-600 K). Calculated T_eff of protonated GGG, AAA, and Polybia-MPI using a modified two-temperature theory approach were up to 86 K cooler in DMS environments seeded with solvent vapor compared to pure N₂ environments. Stabilizing effects were largely driven by an increase in the ion's apparent collision cross section and by evaporative cooling processes induced by the dynamic evaporation/condensation cycles incurred in the presence of an oscillating electric separation field. When the microsolvating partner was a protic solvent, abstraction of a proton from [MP1 + 3H]³⁺ to yield [MP1 + 2H]²⁺ was observed. This result was attributed to the proclivity of protic solvents to form hydrogen-bond networks with enhanced gas-phase basicity. Collectively, microsolvation provides analytes with a solvent "air bag," whereby charge reduction and microsolvation-induced stabilization were shown to shelter peptides from the fragmentation induced by field heating and may play a role in preserving native-like ion configurations.

An emerging powerful technique for distinguishing isomers: Trapped ion mobility spectrometry time-of-flight mass spectrometry for rapid characterization of estrogen isomers

RATIONALE

Isomer metabolites are involved in metabolic pathways, and their characterization is essential but remains challenging even using high-performance analytical platforms. The addition of ion mobility prior to mass analysis can help to separate isomers. Here, the ability of a recently developed trapped ion mobility spectrometry system to separate metabolite isomers was examined.

METHODS

Three pairs of estrogen isomers were studied as a model of isomeric metabolites under both negative and positive electrospray ionization (ESI) modes using a commercial trapped ion mobility spectrometry-TOF mass spectrometer. The standard metabolites were also spiked into human urine to evaluate the efficiency of trapped ion mobility spectrometry to separate isomers in complex mixtures.

RESULTS

The estradiol glucuronide isomers (E₂ β-3G and E₂ β-17G) could be distinguished as deprotonated species, while the estradiol epimers (E₂ β and E₂ α) and the methoxyestradiol isomers (2-MeO-E₂ β and 4-MeO-E₂ β) were separated as lithiated adducts in positive ionization mode. When performing analyses in the urine matrix, no alteration in the ion mobility resolving power was observed and the measured collision cross section (CCS) values varied by less than 1.0%.

CONCLUSIONS

The trapped ion mobility spectrometry-TOF mass spectrometer enabled the separation of the metabolite isomers with very small differences in CCS values (ΔCCS% = 2%). It is shown to be an effective tool for the rapid characterization of isomers in complex matrices.

Improved Identification of Isomeric Steroids Using the Paternò-Büchi Reaction with Ion Mobility-Mass Spectrometry

The Paternò-Büchi (PB) reaction is a common organic reaction in which a carbonyl radical formed by exposure to UV radiation reacts with an alkene to form an oxetane ring. Recent analytical applications of this reaction have included the determination of C═C bond position in lipid fatty acyl tails using tandem mass spectrometry. Our group has recently investigated methods for structurally modifying steroid isomers to improve their identification and resolution using ion mobility spectrometry. Herein, we report the first application of the Paternò-Büchi reaction to form steroid oxetanes using a simple, low-cost, and high efficiency method with a low pressure mercury lamp. This methodology is performed on several endogenous steroid isomers, resulting in unique ion mobility spectra that provide a unique fingerprint for each. These fingerprint spectra can add confidence in identification of those compounds, especially in complex biological matrixes. Testosterone and epitestosterone, an epimer pair commonly interrogated in a number of applications such as for their use as performance enhancing drugs, displayed one and three unique ion mobility peaks, respectively. These spectra and their measured collision cross sections (CCS) allow for unambiguous differentiation of these and several other steroid isomer groups analyzed in this work. Finally, multiple anabolic androgenic steroids prohibited by the World Anti-Doping Agency were tested with this method and resulted in unique CCS for their PB reaction products. This approach can offer improved confidence in their identification as well as for many other banned substances.

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

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

Direct Drug Analysis in Polymeric Implants Using Desorption Electrospray Ionization - Mass Spectrometry Imaging (DESI-MSI)

PURPOSE

Desorption electrospray ionization mass spectrometry imaging (DESI-MSI) coupled with gas-phase ion mobility spectrometry was used to characterize the drug distribution in polymeric implants before and after exposure to accelerated in vitro release (IVR) media. DESI-MSI provides definitive chemical identification and localization of formulation components, including 2D chemical mapping of individual components with essentially no sample preparation.

METHODS

Polymeric implants containing 40% (w/w) entecavir and poly(D,L-lactide) (PLA) were prepared and then exposed to either acidified PBS (pH 2.5) or MeOH:H₂O (50:50, v/v) medias during a 7-day IVR test using continuous flow-through (CFT) cell dissolution. The amount of drug released from the polymer matrix during the 7-day IVR test was monitored by online-ultraviolet spectroscopy (UV) and HPLC-UV. After that period, intact implants and radial sections of implants were analyzed by DESI-MSI with ion mobility spectrometry. The active ingredient along with impurities and contaminants were used to generate chemical maps before and after exposure to the release medias.

RESULTS

Bi-phasic release profiles were observed for implants during IVR release using both medias. During the second phase of release, implants exposed to PBS, pH 2.5, released the entecavir faster than the implants exposed to MeOH:H₂O (50:50, v/v). Radial images of the polymer interior show that entecavir is localized along the central core of the implant after exposure to MeOH:H₂O (50:50, v/v) and that the drug is more uniformly distributed throughout the implant after exposure to acidified PBS (pH 2.5).

CONCLUSIONS

DESI-MSI coupled with ion mobility analysis produced chemical images of the drug distribution on the exterior and interior of cylindrical polymeric implants before and after exposure to various release medias. These results demonstrated the utility of this technique for rapid characterization of drug and impurity/degradant distribution within polymeric implants with direct implications for formulation development as well as analytical method development activities for various solid parenteral and oral dosage forms. These results are especially meaningful since samples were analyzed with essentially no preparative procedures.

Advancements in the gold standard: Measuring steroid sex hormones by mass spectrometry

Sex hormones, such as testosterone and estrogens, play an essential role in regulating physiological and reproductive development throughout the lifetime of the individual. Although variation in levels of these hormones are observed throughout the distinct stages in life, significant deviations from reference ranges can result in detrimental effects to the individual. Alterations, by either an increase or decrease, in hormone levels are associated with physiological changes, decreased reproductive capabilities, and increased risk for diseases. Hormone therapies (HTs) and assisted reproductive technologies (ARTs) are commonly used to address these factors. In addition to these treatments, gender-affirming therapies, an iteration of HTs, are also a prominent treatment for transgender individuals. Considering that the effectiveness of these treatments relies on achieving therapeutic hormone levels, monitoring of hormones has served as a way of assessing therapeutic efficay. The need for reliable methods to achieve this task has led to great advancements in methods for evaluating hormone concentrations in biological matrices. Although immunoassays are the more widely used method, mass spectrometry (MS)-based methods have proven to be more sensitive, specific, and reliable. Advances in MS technology and its applications for therapeutic hormone monitoring have been significant, hence integration of these methods in the clinical setting is desired. Here, we provide a general overview of HT and ART, and the immunoassay and MS-based methods currently utilized for monitoring sex hormones. Additionally, we highlight recent advances in MS-based methods and discuss future applications and considerations for MS-based hormone assays.

Separation of Structurally Similar Anabolic Steroids as Cation Adducts in FAIMS-MS

Novel synthetic anabolic androgenic steroids have been developed not only to dodge current antidoping tests at the professional sports level, but also for consumption by noncompetitive bodybuilders. These novel anabolic steroids are commonly referred to as "designer steroids" and pose a significant risk to users because of the lack of testing for toxicity and safety in animals or humans. Manufacturers of designer steroids dodge regulation by distributing them as nutritional or dietary supplements. Improving the throughput and accuracy of screening tests would help regulators to stay on top of illicit anabolic steroids. High-field asymmetric-waveform ion mobility spectrometry (FAIMS) utilizes an alternating asymmetric electric field to separate ions by their different mobilities at high- and low-fields as they travel through the separation space. When coupled to mass spectrometry (MS), FAIMS enhances the separation of analytes from other interfering compounds with little to no increase in analysis time. Here we investigate the effects of adding various cation species to sample solutions for the separation of structurally similar or isomeric anabolic androgenic steroids. FAIMS-MS spectra for these cation-modified samples show an increased number of compensation field (CF) peaks, some of which are confirmed to be unique for one steroid isomer over another. The CF peaks observed upon addition of cation species correspond to both monomer steroid-cation adduct ions and larger multimer ion complexes. Notably, the number of CF peaks and their CF shifts do not appear to have a straightforward relationship with cation size or electronegativity. Future directions aim at investigating the structures for these analyte-cation adduct ions for building a predictive model for their FAIMS separations.

Ozone-Induced Cleavage of Endocyclic C═C Double Bonds within Steroid Epimers Produces Unique Gas-Phase Conformations

Herein we demonstrate the first application of ozone-induced cleavage of endocyclic C═C double bonds for improved steroid isomer separation using ion mobility-mass spectrometry. Steroids represent a challenging biomolecular class for ion mobility (IM) separations due to their structural rigidity and subtle stereochemical differences. In this work, we compare the effects of ozonolysis on the relative mobilities of a model stereoisomer pair, testosterone and epitestosterone. A solution-phase ozonolysis approach is used due to its simplicity, relatively low cost, and potential for rapid, online analysis. Despite the presence of solvent-based addition products, we observe that these steroids undergo an ozone-based cleavage resulting in unique, stable gas-phase conformations. The resulting resolution between testosterone and epitestosterone, with collision cross section values of 176.6 and 193.3 Ų, respectively, demonstrates a significant improvement in comparison with previous IM-based approaches. The significantly smaller conformation observed for epitestosterone is stabilized by a three-point interaction between the oxygen-containing functional groups and a sodium ion; this same conformation cannot be sterically achieved by testosterone. Identification of this specific structural difference is strengthened by experimental results showing the disappearance of this conformation following in-source water loss, which eliminates the potential for that three-point interaction. Computational modeling of the lowest energy gas-phase structures for these ozone products corroborates the experimental results. In conclusion, this approach provides tremendous potential as a rapid IM separation method for steroid isomers and other endocyclic C═C double bond containing molecules.

Applications of Mass Spectrometry for Clinical Diagnostics: The Influence of Turnaround Time

This critical review discusses how the need for reduced clinical turnaround times has influenced chemical instrumentation. We focus on the development of modern mass spectrometry (MS) and its application in clinical diagnosis. With increased functionality that takes advantage of novel front-end modifications and computational capabilities, MS can now be used for non-traditional clinical analyses, including applications in clinical microbiology for bacteria differentiation and in surgical operation rooms. We summarize here recent developments in the field that have enabled such capabilities, which include miniaturization for point-of-care testing, direct complex mixture analysis via ambient ionization, chemical imaging and profiling, and systems integration.

Fundamentals of Ion Mobility-Mass Spectrometry for the Analysis of Biomolecules

Ion mobility-mass spectrometry (IM-MS) combines complementary size- and mass-selective separations into a single analytical platform. This chapter provides context for both the instrumental arrangements and key application areas that are commonly encountered in bioanalytical settings. New advances in these high-throughput strategies are described with description of complementary informatics tools to effectively utilize these data-intensive measurements. Rapid separations such as these are especially important in systems, synthetic, and chemical biology in which many small molecules are transient and correspond to various biological classes for integrated omics measurements. This chapter highlights the fundamentals of IM-MS and its applications toward biomolecular separations and discusses methods currently being used in the fields of proteomics, lipidomics, and metabolomics.

Steroid analysis by ion mobility spectrometry

Steroids are an important biomolecule class for analysis due to their promise as biomarkers for various diseases and their abuse as performance enhancers in sports. Current analytical methods, including chromatography and nuclear magnetic resonance spectroscopy, fall short of being able to confidently analyze steroids, partly due to the large number of steroid isomers. Ion mobility spectrometry (IMS), a gas-phase ion separator, has shown potential for steroid analysis both in conjunction with liquid chromatography (LC) and as a stand-alone technique. This review will examine the current literature on IMS analysis of steroids. Analysis by LC-IMS will include examination of steroids and steroid glucuronides in human urine and serum samples for enhanced signal-to-noise ratios and higher confidence of identification. The stand-alone IMS analysis will examine the use of derivatization of steroids and formation of multimers to enhance resolution for steroid isomers analysis, where both methods have been shown to greatly increase the separation of steroid isomer species. However, these methods have not been applied to biological mixtures to assess their applicability to medical and forensic applications, which should be a future direction of this field.

Imaging Isomers on a Biological Surface: A Review

Mass spectrometry imaging is an imaging technology that allows the localization and identification of molecules on (biological) sample surfaces. Obtaining the localization of a compound in tissue is of great value in biological research. Yet, the identification of compounds remains a challenge. Mass spectrometry alone, even with high-mass resolution, cannot always distinguish between the subtle structural differences of isomeric compounds. This review discusses recent advances in mass spectrometry imaging of lipids, steroid hormones, amino acids and proteins that allow imaging with isomeric resolution. These improvements in detailed identification can give new insights into the local biological activity of isomers.

Liquid chromatography-ion mobility spectrometry-mass spectrometry analysis of multiple classes of steroid hormone isomers in a mixture

Methods for the analysis of steroids have long been of interest due to the multiple uses for such methods in medical applications, sports monitoring, and environmental science. The analysis of steroids involves inherent analytical hurdles due to their low biological concentrations, poor ionization efficiencies, and frequent occurrence of isomerism. One analytical technique that has been recently applied to steroid analysis is ion mobility spectrometry (IMS). While previous work has focused on the use of metal adduction and multimer formation to enhance separation through IMS analysis coupled to mass spectrometry (MS), this work furthers this approach by coupling IMS-MS with liquid chromatography (LC). Three different LC methods with varying tradeoffs between chromatographic resolution and run time were developed, with one of these achieving a resolution above 1.5 for all steroid isomers. These results also indicate that the coupling of LC to IMS-MS can increase the overall resolution of steroid isomers relative to what can be achieved by either LC or IMS alone. Furthermore, the use of LC and IMS in concert can allow for a more rapid analysis of steroid isomers than can be achieved by LC-MS alone. Finally, the IMS dimension provided for measurements of ion-neutral collision cross sections (CCSs), which were found to be in good agreement with previously reported measurements. Thus, this approach provides three complementary quantitative parameters (retention time, CCS, and mass-to-charge ratio) that can contribute the identification of analytes. Overall, the work presented here demonstrates the potential of coupling LC, IMS, and MS for the analysis of isomeric steroid hormones.

Ion Mobility Spectrometry and Tandem Mass Spectrometry Analysis of Estradiol Glucuronide Isomers

Estradiol is an estrogenic steroid that can undergo glucuronidation at two different sites, which results in two estradiol glucuronide regioisomers. These isomers can be produced by different enzymes and can have different biological activities before being eliminated from the body. Although there have been previous methods that can distinguish the two isomers, these methods often have long acquisition times or high cost per analysis. In this study, traveling wave ion mobility spectrometry (TWIMS) coupled with mass spectrometry (MS) was employed to separate estradiol glucuronides using alkali metal adduction in positive ion mode, where the sodiated dimer adduct provided adequate separation both in single-component standards and in two-component mixtures. Additionally, in negative ion mode, tandem mass spectrometry (MS/MS) was used to quantitatively determine the relative composition of the two isomers. This was possible due to differences in the energetic requirements for loss of the glucuronic acid, which was characterized by energy-resolved collision-induced dissociation (CID). This work demonstrated that the intensity of the glucuronic acid neutral loss product as compared with the intensity of the intact precursor ion can be used to determine the percentage of each isomer present in a mixture. Overall, TWIMS successfully separated estradiol glucuronide isomers in positive ion mode and MS/MS via CID enables relative quantitation of each isomer in negative ion mode.