Proposed Fragmentation Pathways Research Articles

A fragmentation study of disaccharide flavonoid C-glycosides using triple quadrupole mass spectrometry and its application for identification of flavonoid C-glycosides in Odontosoria chinensis.

Flavonoid C-glycosides have a wide range of pharmacological activities. However, there are few mass spectrometric research on C,O-disaccharide flavonoid C-glycosides and di-C,O-saccharide flavonoid C-glycosides. Their low-energy collision-induced dissociation (ESI-CID-MS/MS) fragmentation pattern and differences have not been reported, and the fragment ion library is incomplete. Therefore, it was essential to elucidate the fragmentation patterns of disaccharide flavonoid C-glycosides, which is described in this study. Four disaccharide flavonoid C-glycosides such as vitexin-4″-O-glucoside were analyzed by ultra-performance liquid chromatography-triple quadrupole tandem mass spectrometer (UPLC-MS/MS) using electrospray ionization (ESI) in both positive and negative ion modes. Each ion and its proposed fragmentation pathways of the four disaccharide flavonoid C-glycosides were analyzed comprehensively. Finally, ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS/MS) and the established fragmentation patterns have been used to identify disaccharide flavonoid C-glycosides in Odontosoria Chinensis. The fragmentation pathways of C,O-disaccharide flavonoid C-glycosides and di-C,O-saccharide flavonoid C-glycosides are similar. They both have the mass spectrometric characteristics of O-glycoside and C-glycoside. Product ions after mixed pathways of neutral fragments such as saccharide ring fragment, O-glycosides, H2O, and CH2O elimination appeared in both types of flavonoid C-glycosides, but their relative abundances are significantly different. According to the established fragmentation patterns, di-C,O-saccharide flavonoid glycosides were also found in Odontosoria chinensis. The fragment ions at m/z 431, 413, 341, 311, 293, and 282 in negative ion mode and m/z 293, 282, 577, 559, 541, 523, 529, and 499 in positive ion mode can serves as the main characteristics for identifying C,O-disaccharide flavonoid C-glycosides and di-C,O-saccharide flavonoid C-glycosides.

Systematic Characterisation of the Fragmentation of Flavonoids Using High-Resolution Accurate Mass Electrospray Tandem Mass Spectrometry.

Flavonoids are a class of polyphenolic secondary metabolites found in plants. Due to their ubiquity in our daily dietary intake and their major anti-oxidative, anti-inflammatory and anti-mutagenic activities, they have been a major focus of wide-ranging research for the past two decades. Mass spectrometry combined with liquid chromatography is one of the most popular techniques for the analysis of flavonoids. In this study, high-resolution accurate mass electrospray tandem mass spectrometry was used to study 30 flavonoids in both positive and negative ionisation modes. From the data obtained, common losses were summarised and compiled. Dominating neutral losses were tabulated. The radical loss of CH3· was observed in flavonoids containing methoxy groups and three key diagnostic product ions were identified. These were m/z 153 (indicative of two OH groups on ring A) m/z 167 (indicative of one OH and one methoxy group on ring A) and m/z 151 (a flavanol, with no ketone oxygen but two OH groups on ring A). These will be useful in structural elucidation of unknown flavonoids and flavonoid metabolites. Energy breakdown graphs were utilised to distinguish between three pairs of structural isomers, and to help rationalise proposed fragmentation pathways. Lastly, a competition of loss of CH3· and methane was reported for rhamnetin and isorhamnetin in the negative ion mode for the first time. Proposed fragmentation pathways were given to rationalise the differences in peak intensities for this competitive process.

Qualitative Analysis of Novel Flavonoid Adducts from Nerve Agent Tabun-Exposed Arabidopsis thaliana (L.) Based on Quadrupole-Time of Flight Mass Spectrometry.

Flavonoids are a kind of secondary metabolite which widely exist in plants. They contain a lot of active hydroxyls, which can react with toxic chemicals to produce potential exposure biomarkers. In this article, the model plant Arabidopsis thaliana (L.) was exposed to the nerve agent O-Ethyl N,N-dimethyl phosphoramidocyanidate (Tabun). By comparing with the plant not exposed to Tabun, some characteristic ions were identified by quadrupole-time of flight mass spectrometry in the acetonitrile extract of the exposed leaves. These characteristic ions were selected as parent ions to produce product ion mass spectra (PIMS). Some interesting fragmentation pathways were revealed, including neutral loss of glucoside, rhamnose and ethylene. O-Ethyl N,N-dimethyl phosphoryl modified flavonoids were deduced from assignment of the PIMS. The element components and the accurate mass of the product ions from each parent ion matched well with those of the proposed fragmentation pathways. Through comparison with the PIMS of structurally closely related chemical of Isobutyl methylphosphonyl modified flavonoids, the structures and the fragmentation pathways of the O-Ethyl N,N-dimethyl phosphoryl modified flavonoids were finally confirmed. Successfully finding and identifying these three specific exposure biomarkers in plants provided a new strategy for the retrospective analysis of organophosphorus exposure and forensic analysis.

Development of a sensitive and selective bioanalytical method of chebulinic acid by liquid chromatography‐electrospray tandem mass spectrometry and its pharmacokinetic application

AbstractChebulinic acid (CA), a polyphenolic compound extracted from the fruits of Terminalia chebula, has been recently reported as a novel neuraminidase inhibitor against the influenza A virus and also for various biological activities that require pharmacokinetic estimation. We report a proposed fragmentation pathway for the formation and selection of sodium and ammonium adducts using molecular thermodynamics. The chebulinic acid ammonium adduct was reproducible and stable compared to the earlier reported sodium adduct to quantify chebulinic acid by liquid chromatography‐tandem mass spectrometry. Chebulinic acid was extracted from plasma by protein precipitation followed by single‐step liquid‐liquid extraction by removing interfering metal adducts such as sodium. chebulinic acid resolution was achieved from the C18 column with mobile phase acetonitrile: methanol mixture and ammonium acetate buffer at a flow rate of 0.5 ml/min. The linear calibration curve (r2 ≥ 0.995) range was 3.52–1800 ng/ml. Finally, we report the oral pharmacokinetic profile of chebulinic acid in male Swiss albino mice plasma using the developed method.

Application of lithium cationization tandem mass spectrometry for structural analysis of lignin model oligomers with β-β' and β-O-4' linkages.

Structural elucidation of lignin degradation products is a requirement for successfully developing lignin valorization technology. Most of mass spectrometry-based techniques have utilized negative ion mode mass spectrometry for structural elucidation of lignin-derived compounds. Unfortunately, simple deprotonation can lead to in-source fragmentation and may not be suitable for condensed lignin structures without acidic moieties. Herein, we present a lithium cationization methodology for mass spectrometry sequencing of advanced lignin oligomers having β-β' and β-O-4' bonding motifs. To do so, two advanced lignin oligomers were first synthesized through a step-by-step synthetic route, and then subjected to two different ESI mass spectrometry techniques in positive ion mode using lithium cations for ionization. An orbitrap mass spectrometer was used to obtain exact mass information, and higher-energy collisional dissociation (HCD) was used to sequence the lignin model oligomers. Based on the sequence-specific fragment ions, sequence rules were proposed. Multi-stage (MSn) collision-induced dissociation (CID) using an ion trap mass spectrometer provided data to investigate the origin of each fragment ion and to further confirm proposed fragmentation pathways. In addition to β-O-4' bond cleavage, the presented lithium cationization approach led to cleavage of β-β' bonds on the model oligomers in both ion trap and orbitrap mass spectrometry experiments. Additionally, MSn experiments were used to investigate possible lithium cationization sites on the model oligomers. Lithium cationization in positive ion mode mass spectrometry proved to be a robust tool for characterization and sequencing of advanced lignin oligomers with different bonding motifs.

Determination of Cyazofamid and Its Metabolite in Oily Agricultural Products with HPLC-MS/MS.

A high-performance liquid chromatography-tandem mass spectrometry method was developed for the determination of cyazofamid and its major metabolite 4-Chloro-5-(4-tolyl)-1H-imidazole-2-carbonitrile (CCIM) in oily samples. Samples were extracted with acetonitrile, which contained 1% acetic acid and cleaned-up with C18 and Florisil absorbents. Recoveries ranged from 75.91% to 109.85% with coefficients of variation from 5.14% to 10.69%. The limits of detection (LODs) and the limits of quantification (LOQs) were >0.0020mgkg-1 and ≤0.0040 mg·kg-1, respectively, which were smaller than maximum residue levels established by Australia for oily samples. The proposed fragmentation pathway of cyazofamid and CCIM were discussed.

Identification of four novel flavonoid adducts in Arabidopsis thaliana (L.) exposed to isobutyl S-2-diethylaminoethyl methylphosphonothiolate as potential plant exposure biomarkers.

As vegetation is part of our lives, plants are good candidates as indicators of toxic chemicals. Numerous components in plants may react with toxic chemicals to produce exposure biomarkers. Plant biomarkers formed by the modification of endogenous plant components by chemical warfare agents have not been reported. In this article, the model plant Arabidopsis thaliana (L.) was exposed to the nerve agent isobutyl S-2-diethylaminoethyl methylphosphonothiolate (iBuVX). Some characteristic ions were identified by liquid chromatography-high resolution mass spectrometry and their product ion mass spectra were recorded and interpreted. Some interesting fragmentation pathways were revealed including neutral loss of glucoside, rhamnose and isobutylene. Isobutyl methylphosphonyl modified flavonoids were deduced from assignment of product ions. The element components and the accurate mass of the product ions matched well with those of the proposed fragmentation pathways. The binding site of the nerve agent on flavonoids was proved to be the hydroxyl group on the benzene ring of the flavonoids by density functional theory computation and by the synthesis of the reference chemical, which was confirmed by 1H-31P HMBC NMR. The phosphonyl-modified flavonoids were evaluated for specificity in different plants. Four new flavonoid adducts as potential biomarkers were identified in the leaves of the iBuVX-exposed plant, which provided a novel strategy for the retrospective analysis of organophosphorus exposure for chemical weapon verification and forensic analysis.

Gas-phase fragmentation of protonated 3-phenoxy imidazo[1,2-a] pyridines using tandem mass spectrometry and computational chemistry.

Imidazo[1,2-a] pyridine is one of the pharmaceutically important scaffolds and has been widely studied due to its extensive biological activities. In this work, electrospray ionization tandem mass spectrometry (ESI-MS/MS) in positive mode was used to study the gas-phase fragmentation behavior of a series of 3-phenoxy imidazo[1,2-a] pyridines. Proposed fragmentation pathways were supported by ESI-MS/MS data and computational thermochemistry. Homolytic cleavage of the 3-phenoxy C-O bond was the characteristic fragmentation of 3-phenoxy imidazo [1,2-a] pyridines. The eliminations of the one substituted phenoxy radical and CO produced other diagnostic ions for 3-phenoxy imidazo [1,2-a] pyridines, which were useful to identify the 3-phenoxy group and imidazo [1,2-a] pyridine scaffold. The results contribute to the further understanding of the gas-phase fragmentation of 3-phenoxy imidazo [1,2-a] pyridines and the identification of other analogs using tandem mass spectrometry techniques.

Evidence of the presence of minor tautomeric forms in selected nitroanilines.

RationaleNitroanilines can exist in several tautomeric forms: nitro‐amino, nitro‐imino, and aci‐imino. The importance of evaluating minor tautomeric species comes from the fact that even less abundant tautomers have been proved to play important roles in reaction mechanisms.MethodsElectron ionization mass spectra of the pesticide Pendimethalin and four related nitroanilines were recorded at 70 eV to find information about the presence of minor tautomeric forms in the gas phase. The existence of the possible tautomers was evaluated by studying specific fragmentation pathways, which were confirmed by tandem mass spectrometry (MS/MS) experiments. Further supporting information was obtained by studying the structures of some intermediate compounds by theoretical calculations at the B3LYP 6‐311++G(d,p) level.ResultsThe mass spectrum of Pendimethalin suggests the coexistence of the nitro‐amine tautomer (the most stable form) with four possible less stable tautomers in equilibrium. The fragmentation routes were used to explain analogous peaks in two related compounds. However, the spectra of two other related compounds that cannot follow the proposed route of fragmentation for nitro‐imine tautomers do not show the analogous peak. Theoretical calculations were used to correlate the precursor cation with the proposed fragmentation pathway.ConclusionsBy the study of mass spectra and proposed fragmentation pathways it can be concluded that, although the nitro‐amine is the most abundant species within the system, minor tautomers (nitro‐imine and aci‐imine) coexist in the gas phase.

Electron ionization induced fragmentation of fluorinated derivatives of bisphenols.

Fluorinated derivatization agents allow for the identification and quantification of emerging pollutants with high sensitivity, yet details of their potential applications using electron ionization are lacking. The fluorine atom itself does not effectively participate in electron ionization. Furthermore, limited information exists regarding the effect of fluorine during electron ionization-induced fragmentation. To fill this gap, this report presents the fragmentation pathways of the fluorinated derivatives of ten bisphenol analogues as exemplary emerging pollutants. The bisphenols were derivatized by the acetylation reagent trifluoroacetic anhydride and a new silylation reagent, namely dimethyl(3,3,3-trifluoropropyl)silyldiethylamine (DIMETRIS; previously applied for the analysis of selected pharmaceuticals in environmental samples), and analyzed using GC/MS (electron ionization, 70 eV). Deuterated bisphenol A was added to the group of analytes to confirm the proposed fragmentation pathways. The specific chemical structure of bisphenols gives the possibility of several resonance hybrids of C-centered radicals. This, in turn, results in several fragmentation pathways, unique for each resonance hybrid. Sequential losses of radicals and neutral fragments were observed in both types of derivative, with final stable carbenium ions. McLafferty-type rearrangements were observed between the native structure of the analytes and the introduced substituents. The gamma-shift of F onto Si in the Si(CH2 )2 CF3 substituent is proposed to explain the loss of the fragment with a mass of 78 u. Both types of derivatization reagent used were found to be applicable, although the use of DIMETRIS was limited for high-mass bisphenols. The introduction of fluorine by derivatization brings benefits for the qualitative and quantitative analysis of bisphenol-type compounds using GC/MS because of the presence of characteristic ions in the mass spectra.

Systematic analysis and identification of the absorption and metabolic components of Zengye decoction in type 2 diabetic rats by HPLC-ESI-Q-TOF\u2013MS/MS

BackgroundZengye decoction (ZYD) has been widely used in the treatment of type 2 diabetes mellitus (T2DM). Exploring the fate of various components of ZYD in vivo is of considerable significance for pharmacological research and molecular mechanism elaboration. However, the systematic analysis on the metabolic behavior of chemical components of ZYD in T2DM rats has not been reported.MethodsTo screen and characterize the complex chemical compositions of ZYD, and metabolism fate in plasma, urine, bile, and feces of T2DM rats, the model of T2DM rats was prepared. A rapid procedure using high-performance liquid chromatography coupled with electrospray ionization quadrupole time of flight tandem mass spectrometry (HPLC-ESI-Q-TOF–MS/MS) was established. Data were acquired and analyzed by Agilent MassHunter Workstation Qualitative Analysis software version B.07.00 and PCDL manager B.07.00.ResultsA total of 80 compounds were identified or tentatively characterized in ZYD, 31 more than previously detected. Besides, 36 prototype components and 49 metabolites of ZYD were found and characterized in T2DM rats, and the proposed fragmentation pathways and possible metabolic behaviors of the main types of compounds were described.ConclusionsThis study developed the understanding of the composition of ZYD as well as the cleavage rules and metabolic pathways of the prototype compounds. Besides, this study provided abundant data for further research and for study of the metabolism of traditional Chinese medicine prescriptions.

The influence of chemical modifications on the fragmentation behavior of fentanyl and fentanyl-related compounds in electrospray ionization tandem mass spectrometry.

Fentanyl is a synthetic opioid that has been approved by the FDA as a general anesthetic because of its rapid onset and high potency. However, since 2013 an opioid epidemic involving fentanyl or fentanyl-related compounds (FRCs) has swept the United States and caused numerous deaths in every state. The identification of novel FRCs is complicated by the rapid turnover of modifications to the core fentanyl structure. In this study, a series of 16 FRCs were analyzed using electrospray ionization tandem mass spectrometry (ESI-MS/MS) to gain a deeper understanding of the conserved and unique fragmentation behaviors associated with substitution to the core fentanyl structure. This work provides an approach, based on the product ions from ESI-MS/MS, to identify the modification site(s) on the core fentanyl structure for FRCs. Five common locations of substitution to the core fentanyl structure were used to assess the effect of substitution on the fragmentation behavior of FRCs. The proposed fragmentation pathways are supported through the combination of isotopic labeling, multi-stage mass spectrometry (MSn ), and accurate mass measurements with high-resolution mass spectrometry (HRMS). The identification of primary product ions specific to regions of substitution provides an additional tool for the identification of the location of substitution to the core fentanyl structure, which ultimately will assist toxicologists and seized drug analysts in the identification of emerging FRCs.

Mass spectral studies of silyl derivatives of partially hydrolyzed products of nitrogen mustards: Important markers of nitrogen mustard exposure.

Nitrogen mustards (NMs) are vesicant class of chemical warfare agents. From the viewpoint of the Chemical Weapons Convention partially hydrolyzed products of nitrogen mustards (pHpNMs) are considered as important markers of nitrogen mustard exposure. The detection of pHpNMs from biological or environmental samples is highly useful for obtaining forensic evidence of exposure to NMs. Gas chromatography interfaced with tandem mass spectrometry (GC/MS/MS) is a widely used tool for the identification and sensitive detection of metabolites of NMs in complex matrices. The pHpNMs were derivatized using silylating agents as they are highly polar and non-amenable to GC. The mass spectral studies of these silyl derivatives of pHpNMs were performed using GC/MS/MS in both electron ionization (EI) and chemical ionization (CI) mode. Various approaches have been proposed to assess the fragmentation pathways of the trimethylsilyl (TMS) and tert-butyldimethylsilyl (TBDMS) derivatives of pHpNMs. All the proposed fragmentation pathways were based on the product and/or precursor ion scanning of corresponding ions in both EI and CI mode. In the case of EI, most of the fragmentation pathways involved either α-cleavage or inductive cleavage. This is the first report on the MS study of the silyl derivatives of pHpNMs. The study of the two different derivatives of pHpNMs using both EI- and CI-MS provides a reliable, unambiguous identification of pHpNMs in complex environmental and biomedical matrices (such as plasma and urine) during any verification activities.

Comprehensive mass spectrum analysis of two flavone-6,8-C-di-glycosides and its application by high resolution electrospray ionization tandem mass spectroscopy in both negative and positive ion modes

The tandem mass spectrum of apigenin-6,8-C-di-glucoside( 1) and apigenin-6-C-glucose-8-C-rhamnoside( 2) were obtained by high resolution electrospray ionization mass spectrometry( HR-ESI-MS/MS) in both positive and negative ion modes. The elemental composition of each ion was determined according to its accurate mass-to-charge,hence,the fragmentation pathways of each compound were proposed in both negative and positive ion modes. Comprehensive analysis of each ion and its proposed fragmentation pathways of the two compounds was initially conducted in both negative and positive ion mode HR-ESI-MS/MS to explore the diagnostic ions for flavone-6,8-C-di-glycosides and the characteristic ions for each compound and their cleavage rules. The results showed that a family of fragmentation ions with m/z 353,325,311,297 in ESI(-)-MS and m/z 355,325,307,295 in ESI( +)-MS could be the diagnostic ions of flavone-6,8-C-di-glycoside,and characteristic neutral loss could be assigned to glycosyl substitution,for example,neutral losses of C_4H_8O_4( 120),C_3H_6O_3( 90),C_2H_4O_2( 60) for glucoside substitution while neutral losses of C_4H_8O_3(104),C_3H_6O_2( 74),C_2H_4O( 44) for rhamnoside substitution. Furthermore,only one H_2O loss from mother ion( [M-H]-) was observed for 1 & 2 in ESI(-)-MS while five to six H2 O loss from mother ion( [M+H]+) was observed for 1 & 2 in ESI( +)-MS to produce a family of ions by subsequent loss of H_2O,which could be applied for glucosyl difference. The flavone-6,8-C-di-glycosides in both ESI( +)-MS and ESI(-)-MS showed the cleavage similarity at sugar substitutions. However,there were much more differences by the fragmentation pathways and neutral losses between ESI( +)-MS and ESI(-)-MS as following,hyperconjugation ions by subsequent loss of H_2O from precursor ions of flavone-6,8-C-di-glycosides in ESI( +)-MS were not observed in ESI(-)-MS; the subsequent neutral loss of CH_2O in ESI( +)-MS were rarely observed in ESI(-)-MS; the loss of CO only happen at C-ring of flavone ESI( +)-MS other than glycosyl position in ESI(-)-MS; the C4-chain neutral loss of flavone-6,8-C-di-glycosides happened at 8-C-glycosyl position other than at 6-C-glycosyl position. The above cleavage rules and diagnostic ions of ESI( +)-MS were successfully applied for the structure identification of 4 flavone-6 C,8 C-diglycosides from the stem extract of Dendrobium officinale as vicenin Ⅱ,vicenin Ⅰ,isoschaftoside,schaftoside as well as one flavone-O-glysoside named rutin,which were supported by ESI(-)-MS data as well.

Reconsidering mass spectrometric fragmentation in electron ionization mass spectrometry - new insights from recent instrumentation and isotopic labelling exemplified by ketoprofen and related compounds.

In various fields of chemical analyses, structurally unknown analytes are considered. Proper structure confirmation may be challenged by the low amounts of analytes that are available, e.g. in early stage drug development, in metabolism studies, in toxicology or in environmental analyses. In these cases, mass spectrometric techniques are often used to build up structure proposals for these unknowns. Fragmentation reactions in mass spectrometry are known to follow definite pathways that may help to assign structural elements by fragment ion recognition. This work illustrates an investigation of fragmentation reactions for gas chromatography/electron ionization mass spectrometric characterization of benzophenone derivatives using the analgesic drug ketoprofen and seven of its related compounds as model compounds. Deuteration and 18 O-labelling experiments along with high-resolution accurate mass and tandem mass spectrometry (MS/MS) were used to further elucidate fragmentation pathways and to substantiate rationales for structure assignments. Low-energy ionization was investigated to increase confidence in the identity of the molecular ion. The high-resolution mass analyses yielded unexpected differences that led to reconsideration of the proposals. Site-specific isotopic labelling helped to directly trace back fragment ions to their respective structural elements. The proposed fragmentation pathways were substantiated by MS/MS experiments. The described method may offer a perspective to increase the level of confidence in unknown analyses, where reference material is not (yet) available.

Analysis of mononucleotides by tandem mass spectrometry: investigation of fragmentation pathways for phosphate- and ribose-modified nucleotide analogues

Synthetic nucleotide and nucleic acid analogues are useful research tools and modern therapeutics. Hence, methods for the rapid and unambiguous identification of mononucleotides derived from organic syntheses or biological materials are of broad interest. Here, we analysed over 150 mononucleotides (mostly nucleoside 5′-mono-, 5′-di-, and 5′-triphosphates) and their structurally related nucleobase-, phosphate-, and ribose-modified analogues by electrospray tandem mass spectrometry (ESI/MS/MS), identifying characteristic fragmentation ions that may be helpful in structure determination. While positive-ion mode yielded fragments derived mainly from nucleobases, negative-ion mode provided insight into the structures of phosphoryl and phosphoribosyl moieties, enabling the determination of structural features such as the number of phosphate groups and the presence of ribose or phosphate substitutions. Based on these data, we proposed fragmentation pathways that were confirmed by experiments with [18O]-isotopologues. We demonstrated the utility of ESI(−)/MS/MS in the analysis of structurally related compounds by analysing isomeric and isobaric nucleotides and applying ESI(−)/MS/MS to rapid identification of nucleotide synthesis products. We formulated general rules regarding nucleotide structure–fragmentation pattern relationships and indicating characteristic fragmentation ions for the interpretation of ESI(−)/MS/MS spectra of nucleotides and their analogues. The ESI(−)/MS/MS spectra of all nucleotides are available in an on-line database, msTide, at www.msTide-db.com.

Inspection of the Fragmentation Pathway for Thiamethoxam

Thiamethoxam is one of the main suspect in honeybee colony collapse disorder (CCD). Due to this reason, thiamethoxam including imidacloprid and clothianidin has been banned for two years in some Europe countries. The CCD phenomenon has also been reported in Korea. Regarding this issue and needs, a new project has started to develop the method for the quatitation of thiamethoxam using isotope dilution mass spectrometry (IDMS). In the process of optimization for the IDMS method with thiamethoxam and thiamethoxam-d3, we observed that the fragment peaks did not correspond to the fragmentation pathway as published elsewhere. Here, we proposed a candidate fragmentation pathway. To validate the proposed fragmentation pathway, another isotope analogue, thiamethoxam-d4, was introduced and the MS/MS spectra of both isotope analogues were compared. In addition, the MS/MS/MS spectra of thiamethoxam were inspected for more evidence of the candidate pathway. Those spectra indicated that the proposed fragmentation pathway could be used to assign the fragment peaks of thiamethoxam.

Analysis of the lithiated leucosceptroids from Leucosceptrum canum to facilitate their identification and differentiation by electrospray ionization tandem mass spectrometry.

Leucosceptroids, isolated from Leucosceptrum canum (L.canum), are sesterterpenoids with novel molecular scaffolds which possess potent antifeedant activities. Their molecular scaffolds comprise a 5,6,5-framework with a great diversity due to different hydroxylation and substituent positions. The biological activities of leucosceptroids are affected by the subtle structural differences. The structural characterization and differentiation of the leucosceptroid isomers are of great importance. Firstly, different kinds of cation adducts of leucosceptroids were examined by adding alkali metal ions to the solution, and the lithiated adducts of leucosceptroid were found to be readily formed and yielded characteristic fragment ions under collision-induced dissociation (CID). Then, a systematic mass spectrometric investigation of the [M+Li](+) ions was carried out to clarify their characteristic fragment pathways by electrospray ionization quadrupole time-of-flight-type tandem mass spectrometry (ESI-QTOF-MS/MS). The proposed fragmentation pathways were confirmed through ion trap ESI-MS(n) (n≥3) spectra. Finally, the proposed MS/MS method was applied to investigate the extracts of L.canum. A specific fragmentation pathway of the lithiated adduct, which leads to the production of diagnostic ions of leucosceptroids, was observed. This fragmentation is initiated by cleavage of the C-ring and leads to formation of two types of ions by further dissociation. Both pathways could yield characteristic fragment ions, which could be used to define the substituents at the skeletal structure and at the C-ring. The representative characteristic fragmentations of [M+Li](+) ions and the proposed fragmentation pathways were successfully adopted to investigate the L.canum extracts, and a total of eleven leucosceptroids were identified or tentatively characterized. The characteristic fragmentation pathways of [M+Li](+) species of leucosceptroid isomers were proposed. Three types of leucosceptroid isomers were successfully differentiated. Eleven leucosceptroids were characterized from L.canum extracts. The fragmentation knowledge will facilitate the analysis of leucosceptroids and other sesterterpenoids in future research. Copyright © 2016 John Wiley & Sons, Ltd.

Investigation on fragmentation pathways of bisphenols by using electrospray ionization Orbitrap mass spectrometry.

Bisphenols, such as bisphenol A (BPA) and bisphenol S (BPS), are widely used in industrial products, although they have been demonstrated to be environmental contaminants with toxicity. However, few studies on the mass spectrometric fragmentation pathway of these compounds have been reported using high-resolution mass spectrometry (HRMS). The MS/MS fragmentations of nine bisphenols, together with several corresponding isotope-labeled compounds, were studied by Orbitrap MS using electrospray ionization (ESI) in negative ion mode and higher energy collisional-dissociation (HCD). The [M-H](-) ions of the compounds formed by ESI were selected as the precursor ions for MS/MS. The accurate m/z values for product ions were acquired to deduce the elemental compositions and fragmentation pathways. The elemental compositions of the ions were calculated from the accurate mass data. Common MS/MS product ions and characteristic neutral losses were summarized. Six bisphenols formed the common product ion at m/z 93 (C6 H5 O). The [M-H](-) ions of five bisphenols were found to lose a phenol group (C6 H5 OH). Four bisphenols formed the [M-H-CH4 ](-) ion. The proposed fragmentation pathways of representative compounds of BPA and BPS were verified from the analysis of isotope-labeled compounds. The MS/MS fragmentation pathways of nine bisphenols were, for the first time, systematically investigated with HRMS. The obtained data could be valuable for the identification of a variety of bisphenols in environmental and biological samples.

Characterization of cylindrospermopsin decomposition products formed under irradiation conditions

Cylindrospermopsin (CYN) is a cytotoxic alkaloid produced by several species of cyanobacteria. Research on its decomposition process and the products formed under abiotic factors is still limited. In this study, we examined the impact of UV-B or photosynthetically active radiation (PAR, 400–700nm) on CYN stability, with particular emphasis on the structural characterization of decomposition products. CYN was stable under UV-B irradiation under acidic conditions, and its slow decomposition was observed in a neutral environment. Meaningful CYN decomposition under UV-B irradiation occurred under alkaline conditions. Within 24h, the initial toxin concentration at pH10 decreased to 2%, whereas at pH12, the toxin degraded totally. Six CYN decomposition products were formed during UV-B irradiation under alkaline conditions. We elucidated their chemical structures and proposed fragmentation pathways. PAR, as well as irradiation in the presence of a photosensitizer such as phycocyanin, did not influence CYN stability in a wide range of pH values over a 24h period. The obtained results contribute to a better understanding of CYN stability under abiotic factors.