Recent advances in differentiation of isomers by ion mobility mass spectrometry

Laser Photodissocation, Action Spectroscopy and Mass Spectrometry Unite to Detect and Separate Isomers

The separation and detection of isomers remains a challenge for many areas of mass spectrometry. This article highlights laser photodissociation and ion mobility strategies that have been deployed to tackle...

Profiling of Polyphenolic Compounds of Leontopodium alpinum Cass Callus Cultures Using UPLC/IM-HRMS and Screening of In Vitro Effects

Leontopodium alpinum Cass. (edelweiss) is recognized as a frequent constituent of anti-aging skin care products, providing increased antioxidant and anti-inflammatory defense. Considering the growing demand and the protected status of edelweiss in many countries, alternative methods of production have been developed, one of them being callus culturing. This study reports the phytochemical composition of a methanolic extract of L. alpinum callus cultures, characterized by liquid chromatography coupled to ion-mobility high resolution mass spectrometry (UPLC/IM-HRMS). The methanolic extract exhibited strong free radical scavenging activity (122.19 ± 7.28 mg AAE/g dw), while the quantitative evaluation revealed that four major constituents (phenylpropanoid derivatives) represent 57.13% (m/m) of the extract. Consequently, a screening of antiproliferative effects was performed on ten cancer cell lines, representative of prostate, colon, lung and breast cancer, showing inhibition of colony formation in all cases. These results provide a comprehensive phytochemical characterization of L. alpinum callus cultures using advanced IM-HRMS, while the in vitro explorations confirmed the potent antioxidant properties of edelweiss which are worth exploring further in cancer prevention.

Structural elucidation of C6H4+· using chemical reaction monitoring: Charge transfer versus bond forming reactions

Mass spectrometry is a powerful tool but when used on its own, without specific activation of ions, the ion mass is the single observable and the structural information is absent. One way of retrieving this information is by using ion-molecule reactions. We propose a general method to disentangle isomeric structures by combining mass spectrometry, tunable synchrotron light source, and quantum-chemistry calculations. We use reactive chemical monitoring technique, which consists in tracking reactivity changes as a function of photoionization energy i.e. the ionic structure. We illustrate the power of this technique with charge transfer reactions of C6H4+· isomers with allene and propyne and discuss its universal applicability. Furthermore, we emphasize the special reactivity characteristics of distonic ions, where strong charge transfer reactivity but very limited reactivity involving bond formation and following cleavages were observed and attributed to the unconventional ortho -benzyne distonic cation.

A Novel Approach to Characterize the Lipidome of Marine Archaeon Nitrosopumilus maritimus by Ion Mobility Mass Spectrometry

Archaea are differentiated from the other two domains of life by their biomolecular characteristics. One such characteristic is the unique structure and composition of their lipids. Characterization of the whole set of lipids in a biological system (the lipidome) remains technologically challenging. This is because the lipidome is innately complex, and not all lipid species are extractable, separable, or ionizable by a single analytical method. Furthermore, lipids are structurally and chemically diverse. Many lipids are isobaric or isomeric and often indistinguishable by the measurement of mass or even their fragmentation spectra. Here we developed a novel analytical protocol based on liquid chromatography ion mobility mass spectrometry to enhance the coverage of the lipidome and characterize the conformations of archaeal lipids by their collision cross-sections (CCSs). The measurements of ion mobility revealed the gas-phase ion chemistry of representative archaeal lipids and provided further insights into their attributions to the adaptability of archaea to environmental stresses. A comprehensive characterization of the lipidome of mesophilic marine thaumarchaeon, Nitrosopumilus maritimus (strain SCM1) revealed potentially an unreported phosphate- and sulfate-containing lipid candidate by negative ionization analysis. It was the first time that experimentally derived CCS values of archaeal lipids were reported. Discrimination of crenarchaeol and its proposed stereoisomer was, however, not achieved with the resolving power of the SYNAPT G2 ion mobility system, and a high-resolution ion mobility system may be required for future work. Structural and spectral libraries of archaeal lipids were constructed in non-vendor-specific formats and are being made available to the community to promote research of Archaea by lipidomics.

An integrated two-step filtering strategy of collision cross-section interval predicting and mass defect filtering for targeted identification of analogues in herbal medicines using liquid chromatography-ion mobility-mass spectrometry

Rapid identification of chemical analogues in herbal medicines using liquid chromatography-mass spectrometry was an efficient tool for discoveries of potentially active ingredients. Multi-dimensional combination of various separation technologies could significantly enhance the capacities for detection of trace components and discrimination of multiple isomers. In this study, an integrated two-step filtering strategy on liquid chromatography-ion mobility tandem with quadrupole-time-of-flight mass spectrometry (LC-IM-QTOF MS) was developed for identification of analogues in complex matrixes. The extracted raw data were preliminarily filtered by a collision-cross section (CCS) interval generated from power regression with confidence level at 99% for prediction of analogues. Then, the remained ions were further screened using a mass defect filtering (MDF) window based on m/z and decimal m/z of potential skeletons and substituents. By applying this strategy, 86, 102, 73, and 57 isoquinoline alkaloids were identified in herbal materials of Coptis chinensis Franch (CC), C. deltoidea C.Y.Cheng et Hsiao (CD), C. teeta Wall (CT), and Corydalis yanhusuo W.T.Wang (CY). The integrated two-step filtering presented higher efficiencies on exclusion of the background interference and reducing the false-positive rates than previously reported approaches. This study facilitated the application of LC-IM-MS on small molecular analysis and promoted the discoveries of bioactive components of herbal medicines for further pharmacological researches and quality control.

Distinction of chiral penicillamine using metal-ion coupled cyclodextrin complex as chiral selector by trapped ion mobility-mass spectrometry and a structure investigation of the complexes

Penicillamine (Pen) is a common chiral drug that is obtained from penicillin. Between the two enantiomers of Pen, only D-Pen can be used to treat cystinuria and rheumatoid arthritis while L-Pen is toxic. Therefore, it requires great efforts for the research of the rigorous analysis and distinction of the two enantiomers. The non-covalent combination of chiral molecules and chiral selectors (CSs) has been proved as a unique strategy for chiral distinction by ion mobility spectrometry in coupling with -mss spectrometry (IM-MS). Here, we developed a simple method to distinguish D, L-Pen by using special CSs for IM-MS separation. The CSs utilized here include cyclodextrins (CD) and linear chain oligosaccharides plus metal ions. We found that non-covalent complexes [Pen+β-CD + Li]⁺ could be easily formed by electrospray ionization of the mixture of the solution, and the chirality of Pen could be effectively recognized by measuring their mobilities due to the different collision cross collision sections of [D-Pen+β-CD + Li]⁺ and [L-Pen+β-CD + Li]⁺. A detailed analysis of [Pen+β-CD + Li]⁺ was then conducted by the optical rotation measurements and NMR experiments to reveal their structural differences. Furthermore, DFT calculation showed the differences of molecular conformation between the complexes. The results provide a new powerful method for fast analysis and recognition of chirality of Pen compounds by IM-MS.

Investigating the Structure of α/β Carbohydrate Linkage Isomers as a Function of Group I Metal Adduction and Degree of Polymerization as Revealed by Cyclic Ion Mobility Separations

In high-resolution ion mobility spectrometry-mass spectrometry (IMS-MS)-based separations individual, pure, oligosaccharide species often produce multiple IMS peaks presumably from their α/β anomers, cation attachment site conformations, and/or other energetically favorable structures. Herein, the use of high-resolution traveling wave-based cyclic IMS-MS to systematically investigate the origin of these multiple peaks by analyzing α1,4- and β1,4-linked d-glucose homopolymers as a function of their group I metal adducts is presented. Across varying degrees of polymerization, and for certain metal adducts, at least two major IMS peaks with relative areas that matched the ∼40:60 ratio for the α/β anomers of a reducing-end d-glucose as previously calculated by NMR were observed. To further validate that these were indeed the α/β anomers, rather than other substructures, the reduced versions of several maltooligosaccharides were analyzed and all produced a single IMS peak. This result enabled the discovery of a mobility fingerprint trend: the β anomer was always higher mobility than the α anomer for the cellooligosaccharides, while the α anomer was always higher mobility than the β anomer for the maltooligosaccharides. For maltohexaose, a spurious, high mobility, fourth peak was present. This was hypothesized to potentially be from a highly compacted conformation. To investigate this, α-cyclodextrin, a cyclic oligosaccharide, produced similar arrival times as the high mobility maltohexaose peak. It is anticipated that these findings will aid in the data deconvolution of IMS-MS-based glycomics workflows and enable the improved characterization of biologically relevant carbohydrates.

Molecular Mapping of Neutral Lipids Using Silicon Nanopost Arrays and TIMS Imaging Mass Spectrometry

We demonstrate the utility of combining silicon nanopost arrays (NAPA) and trapped ion mobility imaging mass spectrometry (TIMS IMS) for high spatial resolution and specificity mapping of neutral lipid classes in tissue. Ionization of neutral lipid species such as triglycerides (TGs), cholestryl esters (CEs), and hexosylceramides (HexCers) from biological tissues has remained a challenge for imaging applications. NAPA, a matrix-free laser desorption ionization substrate, provides enhanced ionization efficiency for the above-mentioned neutral lipid species, providing complementary lipid coverage to matrix-assisted laser desorption ionization (MALDI). The combination of NAPA and TIMS IMS enables imaging of neutral lipid species at 20 μm spatial resolution while also increasing molecular coverage greater than 2-fold using gas-phase ion mobility separations. This is a significant improvement with respect to sensitivity, specificity, and spatial resolution compared to previously reported imaging studies using NAPA alone. Improved specificity for neutral lipid analysis using TIMS IMS was shown using rat kidney tissue to separate TGs, CEs, HexCers, and phospholipids into distinct ion mobility trendlines. Further, this technology allowed for the separation of isomeric species, including mobility resolved isomers of Cer(d42:2) (m/z 686.585) with distinct spatial localizations measured in rat kidney tissue section.

Trapped ion mobility spectrometry time-of-flight mass spectrometry for high throughput and high resolution characterization of human milk oligosaccharide isomers

The microbiome and immune system of infants are shaped by various bioactive components of human breastmilk, notably human milk oligosaccharides (HMOs). HMOs represent the third component of breastmilk and exhibit extremely high structural diversity with many isomers. Here, we propose a high throughput and high resolution approach to characterize main oligosaccharides present in breastmilk with high identification level thanks to ion mobility spectrometry. Four pairs of standard HMO isomers, that are (LNT/LNnT), (LNFP I/LNFP V), (3'-SL/6'-SL) and (2'-FL/3-FL), were first investigated under both positive and negative ionization mode using direct introduction-trapped ion mobility spectrometry-time-of-flight mass spectrometry (TIMS-TOF). By examining all the ionic species formed (i.e. protonated and deprotonated ions as well as adduct species), every isomer pair could be distinguished through the separation of at least one species, even with a small difference in collision cross section values (as small as 1.5%) thanks to the flexible resolution capacity of the TIMS instrument. Although multiple mobility peaks resulting from different glycan anomeric conformers, open-ring and/or different ionic isomer structures (i.e. various charge site locations), could be observed for some HMO species. The reduction at the reducing-end of HMOs did not significantly facilitate the isomer distinction. Finally, the unambiguous identification of the studied HMOs in a breastmilk sample showed the potential of the approach combining ion mobility separation and MS/MS experiments for high throughput distinction of HMO isomers in complex breastmilk samples without laborious sample preparation.

Tracking the deprotonation site of dehydroandrographolide with electrospray ionization mass spectrometry by deuteration

RATIONALE

Dehydroandrographolide (DA) is a diterpene compound of biological interest that contains one α,β-unsaturated lactone group and two hydroxy groups. In the ESI (electrospray ionization) negative ion mode mass spectral analysis of 15-dideuterodehydroandrographolide (15-D₂ -DA), the deuterium nucleus at the γ position of the α,β-unsaturated lactone was more easily dedeuterated than deprotonation of the protons from the hydroxy groups. Exploring the rationality of deuteration as a tool for deprotonation position tracking is significant for gas-phase acidity.

METHODS

The mass spectra of DA and 15-D₂ -DA in positive and negative ion mode were acquired by liquid chromatography/ion trap time-of-flight mass spectrometry (LC/IT-TOF) systems. The deprotonation and dedeuteration energies at specific sites were calculated by the B3LYP and M06-2X density functional theory (DFT) methods with the program Gaussian 16.

RESULTS

The [M + H]⁺ ion of 15-D₂ -DA was 2 amu larger than that of DA due to the substitution of two hydrogens with two deuteriums; however, the anion base peak of 15-D₂ -DA was only 1 amu larger than that of the [M - H]^- ion of DA. Dedeuteration at the C15 site was proposed according to the mass spectral data. The deprotonation (dedeuteration) energies calculated by the B3LYP/6-311++G(3df,3pd)//B3LYP/6-31 + G(d) and M06-2X-D3/ma-TZVP methods showed that the C-H and C-D bonds at the C15 site have lower deprotonation (dedeuteration) energies than the energies of the hydroxy groups of DA, making their deprotonation (dedeuteration) more thermodynamically favourable.

CONCLUSIONS

Deuteration of DA provided direct evidence of the deprotonation site of DA in the ESI source of the mass spectrometer, and the DFT method well predicted the gas-phase deprotonation site of DA.

Suspect Screening of Fentanyl Analogs Using Matrix-Assisted Ionization and a Miniature Mass Spectrometer with a Custom Expandable Mass Spectral Library

The reliable identification of fentanyl and its analogs is of great significance for public security. However, with the growing prevalence of fentanyl compounds, current analytical strategies cannot fully meet the need for fast and high-throughput detection. In this study, a simple, rapid, and on-site analytical protocol was developed based on a miniature mass spectrometer. A dramatically simplified workflow was implemented using matrix-assisted ionization, bypassing complex sample pretreatment and chromatographic separation. The tandem mass spectrometry (MS/MS) capability afforded by the miniature ion trap mass spectrometer facilitated the investigation of fragmentation patterns for 49 fentanyl analogs during collision-induced dissociation, revealing valuable information on marker fragment ions and characteristic neutral loss. Calculations on Laplacian bond order values further verified the mass spectrometric behavior. A computation-assisted expandable mass spectral library was constructed in-house for fentanyl compounds. Smart suspect screening was carried out based on the full-scan MS and MS/MS data. The present study demonstrates an appealing potential for forensic applications, enabling streamlined screening for the presence of illicit fentanyl compounds at the point of seizures of suspect samples.

Proteoform Differentiation using Tandem Trapped Ion Mobility, Electron Capture Dissociation, and ToF Mass Spectrometry

Comprehensive characterization of post-translationally modified histone proteoforms is challenging due to their high isobaric and isomeric content. Trapped ion mobility spectrometry (TIMS), implemented on a quadrupole/time-of-flight (Q-ToF) mass spectrometer, has shown great promise in discriminating isomeric complete histone tails. The absence of electron activated dissociation (ExD) in the current platform prevents the comprehensive characterization of unknown histone proteoforms. In the present work, we report for the first time the use of an electromagnetostatic (EMS) cell devised for nonergodic dissociation based on electron capture dissociation (ECD), implemented within a nESI-TIMS-Q-ToF mass spectrometer for the characterization of acetylated (AcK18 and AcK27) and trimethylated (TriMetK4, TriMetK9 and TriMetK27) complete histone tails. The integration of the EMS cell in a TIMS-q-TOF MS permitted fast mobility-selected top-down ECD fragmentation with near 10% efficiency overall. The potential of this coupling was illustrated using isobaric (AcK18/TriMetK4) and isomeric (AcK18/AcK27 and TriMetK4/TriMetK9) binary H3 histone tail mixtures, and the H3.1 TriMetK27 histone tail structural diversity (e.g., three IMS bands at z = 7+). The binary isobaric and isomeric mixtures can be separated in the mobility domain with R_IMS > 100 and the nonergodic ECD fragmentation permitted the PTM localization (sequence coverage of ∼86%). Differences in the ECD patterns per mobility band of the z = 7+ H3 TriMetK27 molecular ions suggested that the charge location is responsible for the structural differences observed in the mobility domain. This coupling further enhances the structural toolbox with fast, high resolution mobility separations in tandem with nonergodic fragmentation for effective proteoform differentiation.

Distinguishment of Glycan Isomers by Trapped Ion Mobility Spectrometry

The in-depth study of glycan has drawn large research interests since it is one of the main biopolymers on the earth with a variety of biological functions. However, the distinguishment of glycans is still difficult due to the similarity of the monosaccharide building block, the anomer, and the linkage of glycosidic bonds. In this study, four novel and representative copper-bound diastereoisomeric complex ions were simultaneously detected in a single measurement by trapped ion mobility mass spectrometry, including mononuclear copper-bound dimeric ions [(Cu²⁺)(A)(l-Ser)-H]⁺ and [(Cu²⁺)(A)(l-His)-H]⁺, the mononuclear copper-bound trimeric ion [(Cu²⁺)(A)(l-Ser)(l-His)-H]⁺, and the binuclear copper-bound tetrameric ion [(Cu²⁺)₂(A)(l-Ser)₂(l-His)-3H]⁺ (where A denotes an oligosaccharide, and l-Ser and l-His denote l-serine and l-histidine, respectively). By combining the collision cross sections of complex ions, 23 oligosaccharide isomers were successfully distinguished including two pairs of sialylated glycan linkage isomers. In addition, due to the unique dissociation pathways of the trimeric ion, both the relative and absolute quantification of the individual isomer in the mixture could be determined using a mass spectrometry-based kinetic method. Finally, the method established above was successfully applied to the identification and quantification of glycan isomers in dairy beverages and juice. The method in the present study was sensitive to the fine difference of glycan isomers and might have wide applicability in glycoscience.

Perspective on Emerging Mass Spectrometry Technologies for Comprehensive Lipid Structural Elucidation

Lipids and metabolites are of interest in many clinical and research settings because it is the metabolome that is increasingly recognized as a more dynamic and sensitive molecular measure of phenotype. The enormous diversity of lipid structures and the importance of biological structure-function relationships in a wide variety of applications makes accurate identification a challenging yet crucial area of research in the lipid community. Indeed, subtle differences in the chemical structures of lipids can have important implications in cellular metabolism and many disease pathologies. The speed, sensitivity, and molecular specificity afforded by modern mass spectrometry has led to its widespread adoption in the field of lipidomics on many different instrument platforms and experimental workflows. However, unambiguous and complete structural identification of lipids by mass spectrometry remains challenging. Increasingly sophisticated tandem mass spectrometry (MS/MS) approaches are now being developed and seamlessly integrated into lipidomics workflows to meet this challenge. These approaches generally either (i) alter the type of ion that is interrogated or (ii) alter the dissociation method in order to improve the structural information obtained from the MS/MS experiment. In this Perspective, we highlight recent advances in both ion type alteration and ion dissociation methods for lipid identification by mass spectrometry. This discussion is aimed to engage investigators involved in fundamental ion chemistry and technology developments as well as practitioners of lipidomics and its many applications. The rapid rate of technology development in recent years has accelerated and strengthened the ties between these two research communities. We identify the common characteristics and practical figures of merit of these emerging approaches and discuss ways these may catalyze future directions of lipid structural elucidation research.

Food safety and quality assessment: comprehensive review and recent trends in the applications of ion mobility spectrometry (IMS)

Ion mobility spectrometry (IMS) is an analytical separation and diagnostic technique that is simple and sensitive and a rapid response and low-priced technique for detecting trace levels of chemical compounds in different matrices. Chemical agents and environmental contaminants are successfully detected by IMS and have been recently considered to employ in food safety. In addition, IMS uses stand-alone or coupled analytical diagnostic tools with chromatographic and spectroscopic methods. Scientific publications show that IMS has been applied 21% in the pharmaceutical industry, 9% in environmental studies and 13% in quality control and food safety. Nevertheless, applications of IMS in food safety and quality analysis have not been adequately explored. This review presents the IMS-related analysis and focuses on the application of IMS in food safety and quality. This review presents the important topics including detection of traces of chemicals, rate of food spoilage and freshness, food adulteration and authenticity as well as natural toxins, pesticides, herbicides, fungicides, veterinary, and growth promoter drug residues. Further, persistent organic pollutants (POPs), acrylamide, polycyclic aromatic hydrocarbon (PAH), biogenic amines, nitrosamine, furfural, phenolic compounds, heavy metals, food packaging materials, melamine, and food additives were also examined for the first time. Therefore, it is logical to predict that the application of the IMS technique in food safety, food quality, and contaminant analysis will be impressively increased in the future. HighlightsCurrent status of IMS for residues and contaminant detection in food safety.To assess all the detected contaminants in food safety, for the first time.Identified IMS-related parameters and chemical compounds in food safety control.

Solar photo-Fenton treatment of the anti-cancer drug anastrozole in different aqueous matrices at near-neutral pH: Transformation products identification, pathways proposal, and in silico (Q)SAR risk assessment

Anastrozole (ANZ) is a breast cancer drug that was introduced onto the pharmaceutical market in the 1990s and is still one of the most widely consumed cytotoxic compounds. Due to the persistence of the drug, its continued presence after passing through wastewater treatment plants can lead to harm to aquatic environments. The present study investigates use of the solar photo-Fenton (SPF) process applied for ANZ degradation, considering the fate of ANZ and its transformation products (TPs). The SPF process was performed using different concentrations of ferrous iron (Fe²⁺) and H₂O₂ in solutions produced with deionized water (DW) and hospital wastewater (HWW), at pH close to neutrality. When solar irradiation in the SPF process was carried out the best ANZ removal rates were found under the following conditions: (i) for the DW matrix, [ANZ]₀ = 50 μg L^-1, [Fe²⁺] = 5 mg L^-1, and [H₂O₂]₀ = 25 mg L^-1, achieving 95% primary ANZ elimination; (ii) for the HWW matrix, [ANZ]₀ = 50 μg L^-1, [Fe²⁺] = 10 mg L^-1(multiple additions), and [H₂O₂]₀ = 25 mg L^-1, achieving 51% primary ANZ elimination. LC-QTOF MS analysis allowed to identify tentatively five transformation products (TPs) formed during the ANZ degradation process in DW, and two TPs when HWW was used. The main proposed degradation pathways were demethylation and hydroxylation. Different in silico models free available (quantitative) structure-activity relationship ((Q)SAR) software were used to predict the ecotoxicities and environmental fates of ANZ and the TPs. The in silico (Q)SAR predictions indicated that ANZ and the TPs were non-biodegradable compounds. In silico (Q)SAR predictions for mutagenicity and carcinogenicity end-points identified some TPs that require further study. Attention is drawn to the formation of several TPs for which statistical and rule-based positive alerts for mutagenic activities were found, requiring further confirmatory in vitro validation tests.

Effective Chiral Discrimination of Amino Acids through Oligosaccharide Incorporation by Trapped Ion Mobility Spectrometry

Chiral analysis is critical to many research fields due to different biological functions of enantiomers in living systems. Although the use of ion mobility spectrometry (IMS) has become an alternative technology in the area of chiral measurements, there is still a lack of a general chiral selector for IMS-based chiral recognition, especially for small chiral molecules. Here, a new method using oligosaccharides as the chiral selector has been developed to discriminate chiral amino acids (AAs) by trapped ion mobility spectrometry-mass spectrometry (TIMS-MS). We analyzed 21 chiral amino acids, including small molecules (e.g., alanine and cysteine). Our data showed that the use of nonreducing tetrasaccharides was effective for the separation of chiral AAs, which differentiated 21 chiral AAs without using metal ions. By further incorporating a copper ion, the separation resolution could be improved to 1.64 on average, which accounts for an additional 52% improvement on top of the already achieved separation in metal-free analysis. These results indicate that the use of tetrasaccharides is an effective strategy for the separation of AA enantiomers by TIMS. The method developed in this study may open up a new strategy for effective IMS-based chiral analysis.

UPLC-ESI-MRM/MS for Absolute Quantification and MS/MS Structural Elucidation of Six Specialized Pyranonaphthoquinone Metabolites From Ventilago harmandiana

Pyranonaphthoquinones (PNQs) are important structural scaffolds found in numerous natural products. Research interest in these specialized metabolites lies in their natural occurrence and therapeutic activities. Nonetheless, research progress has thus far been hindered by the lack of analytical standards and analytical methods for both qualitative and quantitative analysis. We report here that various parts of Ventilago harmandiana are rich sources of PNQs. We developed an ultraperformance liquid chromatography-electrospray ionization multiple reaction monitoring/mass spectrometry method to quantitatively determine six PNQs from leaves, root, bark, wood, and heartwood. The addition of standards in combination with a stable isotope of salicylic acid-D₆ was used to overcome the matrix effect with average recovery of 82% ± 1% (n = 15). The highest concentration of the total PNQs was found in the root (11,902 μg/g dry weight), whereas the lowest concentration was found in the leaves (28 μg/g dry weight). Except for the root, PNQ-332 was found to be the major compound in all parts of V. harmandiana, accounting for ∼48% of the total PNQs quantified in this study. However, PNQ-318A was the most abundant PNQ in the root sample, accounting for 27% of the total PNQs. Finally, we provide novel MS/MS spectra of the PNQs at different collision induction energies: 10, 20, and 40 eV (POS and NEG). For structural elucidation purposes, we propose complete MS/MS fragmentation pathways of PNQs using MS/MS spectra at collision energies of 20 and 40 eV. The MS/MS spectra along with our discussion on structural elucidation of these PNQs should be very useful to the natural products community to further exploring PNQs in V. harmandiana and various other sources.

Direct and simultaneous recognition of the positional isomers of aminobenzenesulfonic acid by TIMS-TOF-MS

Positional isomer recognition is a challenging scientific issue. Fast and accurate detection of isomers is required for understanding their chemical properties. Here, we describe a method for simultaneous recognition of three positional isomers of 2-aminobenzenesulfonic acid (2-ABSA), 3-ABSA, and 4-ABSA using trapped ion mobility spectroscopy-time-of-flight mass spectrometry (TIMS-TOF-MS). The three ABSA positional isomers were recognized by measuring the different ion mobility of the ternary complexes of [β-cyclodextrin (CD)+ABSA + Li]⁺ or [λ-CD + ABSA + Na]⁺, because their different collision cross-sections or different spatial conformations. The collision-induced dissociation mechanism of the different complexes of [β-CD + ABSA + Li]⁺ and [λ-CD + ABSA + Na]⁺ using tandem mass spectrometry exhibited the same dissociation process with slightly different dissociation energies, which the smaller cross-section requires higher collision energy that means the smaller complex with tighter and more stable conformation than a larger complex for the ABSA complexes. In addition, relative quantification of the ABSA isomers was studied by measuring any two of the three ABSA isomer complexes at different molar ratio of 10:1 to 1:10 in the μM range, good linearity (R² > 0.99) with precision between 2.14% and 2.58%, and accuracy ≥ 97.1% were obtained. The method for fast determination and recognition of ABSA positional isomers by combination with CD and alkali metal ions possesses the advantages of being simple, direct, rapid, sensitive, cost-effective, and needs no chemical derivatives or chromatographic separation before analysis. Therefore, the proposed method would be a powerful tool for the analysis of ABSA isomers or even other positional isomers.

Recent applications of ion mobility spectrometry in natural product research

Ion mobility spectrometry (IMS) is a rapid separation technique capable of extracting complementary structural information to chromatography and mass spectrometry (MS). IMS, especially in combination with MS, has experienced inordinate growth in recent years as an analytical technique, and elicited intense interest in many research fields. In natural product analysis, IMS shows promise as an additional tool to enhance the performance of analytical methods used to identify promising drug candidates. Potential benefits of the incorporation of IMS into analytical workflows currently used in natural product analysis include the discrimination of structurally similar secondary metabolites, improving the quality of mass spectral data, and the use of mobility-derived collision cross-section (CCS) values as an additional identification criterion in targeted and untargeted analyses. This review aims to provide an overview of the application of IMS to natural product analysis over the last six years. Instrumental aspects and the fundamental background of IMS will be briefly covered, and recent applications of the technique for natural product analysis will be discussed to demonstrate the utility of the technique in this field.