A combined nuclear magnetic resonance and computational study of monohydroxyflavones applied to product ion mass spectra

A method is presented for the estimation of 13C-chemical shifts for carbon atoms in protonated and deprotonated molecules; in principle, this method can be applied to ions in general. Experimental 13C-chemical shifts were found to vary linearly with computed atomic charges using the PM3 method. Pseudo-13C-chemical shifts for atoms in protonated and deprotonated molecules can be estimated from computed atomic charges for such atoms using the above linear relationship. The pseudo-13C-chemical shifts obtained were applied to the rationalization of product ion mass spectra of protonated and deprotonated molecules of flavone and 3-, 5-, 6-, 7-, 2'-, 3'-, and 4'-hydroxyflavones, where product ion formation is due to either cross-ring cleavage of the C-ring (retro-Diels-Alder reaction) or to cleavage of a C-ring bond followed by loss of either a small neutral molecule or a radical. The total product ion abundance ratio of C-ring cross cleavage to C-ring bond cleavage, gamma, varied by a factor of 660 for deprotonated monohydroxyflavones, i.e., from 0.014:1 to 9.27:1. The magnitude of gamma, which is dependent on the relative bond orders within the C-ring of the protonated and deprotonated molecules of monohydroxyflavones, can be rationalized on the basis of the magnitudes of the 13C- and 1H-chemical shifts as determined by nuclear magnetic resonance spectroscopy.     

Travelling‐wave ion mobility and negative ion fragmentation of high‐mannose N‐glycans

The isomeric structure of high‐mannose N‐glycans can significantly impact biological recognition events. Here, the utility of travelling‐wave ion mobility mass spectrometry for isomer separation of high‐mannose N‐glycans is investigated. Negative ion fragmentation using collision‐induced dissociation gave more informative spectra than positive ion spectra with mass‐different fragment ions characterizing many of the isomers. Isomer separation by ion mobility in both ionization modes was generally limited, with the arrival time distributions (ATD) often showing little sign of isomers. However, isomers could be partially resolved by plotting extracted fragment ATDs of the diagnostic fragment ions from the negative ion spectra, and the fragmentation spectra of the isomers could be extracted by using ions from limited areas of the ATD peak. In some cases, asymmetric ATDs were observed, but no isomers could be detected by fragmentation. In these cases, it was assumed that conformers or anomers were being separated. Collision cross sections of the isomers in positive and negative fragmentation mode were estimated from travelling‐wave ion mobility mass spectrometry data using dextran glycans as calibrant. More complete collision cross section data were achieved in negative ion mode by utilizing the diagnostic fragment ions. Examples of isomer separations are shown for N‐glycans released from the well‐characterized glycoproteins chicken ovalbumin, porcine thyroglobulin and gp120 from the human immunodeficiency virus. In addition to the cross‐sectional data, details of the negative ion collision‐induced dissociation spectra of all resolved isomers are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Ion mobility-mass spectrometry analysis of isomeric carbohydrate precursor ions

The rapid separation of isomeric precursor ions of oligosaccharides prior to their analysis by mass spectrometry to the nth power (MS ⁿ ) was demonstrated using an ambient pressure ion mobility spectrometer (IMS) interfaced with a quadrupole ion trap. Separations were not limited to specific types of isomers; representative isomers differing solely in the stereochemistry of sugars, in their anomeric configurations, and in their overall branching patterns and linkage positions could be resolved in the millisecond time frame. Physical separation of precursor ions permitted independent mass spectra of individual oligosaccharide isomers to be acquired to at least MS³, the number of stages of dissociation limited only practically by the abundance of specific product ions. IMS–MS ⁿ analysis was particularly valuable in the evaluation of isomeric oligosaccharides that yielded identical sets of product ions in tandem mass spectrometry experiments, revealing pairs of isomers that would otherwise not be known to be present in a mixture if evaluated solely by MS dissociation methods alone. A practical example of IMS–MSⁿ analysis of a set of isomers included within a single high-performance liquid chromatography fraction of oligosaccharides released from bovine submaxillary mucin is described.     

Rapid analysis of lubricants by atmospheric solid analysis probe–ion mobility mass spectrometry

Formulated lubricants are complex mixtures composed of base oil(s) and additives with various functions (detergents, corrosion inhibiter, antioxidant, viscosity modifiers, etc.). Because of the aliphatic nature of base oil and the chemical diversity of additives, the characterization of lubricant is currently a long and complex process. The comprehensive analysis of lubricant samples involves several techniques such as nuclear magnetic resonance, mass spectrometry, chromatography and infrared spectroscopy. The coupling of atmospheric solid analysis probe (ASAP) with ion mobility‐mass spectrometry (IM‐MS) has been shown to be an efficient tool for the characterization of complex mixture containing vaporizable polar to non‐polar compounds. This approach affords the coupling of a direct ionization technique that does not require sample preparation, with a bi‐dimensional separation method with high peak capacity. In this work, we show that ASAP‐IM‐MS is a suitable method for rapid and direct characterization of lubricant samples. Indeed, base oil and additives yielded, by ASAP, ions series which could be separated by IM‐MS. Molecular additives such as Zn‐dithiocarbamate, phosphite, thiophosphate and Alkyl diphenylamine were ionized as molecular ions [M]^+? or protonated molecules [M + H]⁺, depending of their polarity. In some cases, fragment ions were observed, confirming the additive identification. In addition, high molecular weight polymeric additives such as poly(alkyl methacrylate) (PAM) were pyrolized in the ASAP source leading to characteristic fragment ions. ASAP‐IM‐MS is shown to be a powerful tool for studying complex mixtures, allowing the first comprehensive analysis of lubricants in just a few minutes. Copyright © 2014 John Wiley & Sons, Ltd.     

Ion mobility-mass spectrometry

This review article compares and contrasts various types of ion mobility-mass spectrometers available today and describes their advantages for application to a wide range of analytes. Ion mobility spectrometry (IMS), when coupled with mass spectrometry, offers value-added data not possible from mass spectra alone. Separation of isomers, isobars, and conformers; reduction of chemical noise; and measurement of ion size are possible with the addition of ion mobility cells to mass spectrometers. In addition, structurally similar ions and ions of the same charge state can be separated into families of ions which appear along a unique mass-mobility correlation line. This review describes the four methods of ion mobility separation currently used with mass spectrometry. They are (1) drift-time ion mobility spectrometry (DTIMS), (2) aspiration ion mobility spectrometry (AIMS), (3) differential-mobility spectrometry (DMS) which is also called field-asymmetric waveform ion mobility spectrometry (FAIMS) and (4) traveling-wave ion mobility spectrometry (TWIMS). DTIMS provides the highest IMS resolving power and is the only IMS method which can directly measure collision cross-sections. AIMS is a low resolution mobility separation method but can monitor ions in a continuous manner. DMS and FAIMS offer continuous-ion monitoring capability as well as orthogonal ion mobility separation in which high-separation selectivity can be achieved. TWIMS is a novel method of IMS with a low resolving power but has good sensitivity and is well intergrated into a commercial mass spectrometer. One hundred and sixty references on ion mobility-mass spectrometry (IMMS) are provided.     

Differentiation of isomeric dinitrotoluenes and aminodinitrotoluenes using electrospray high resolution mass spectrometry

Explosive detection and identification play an important role in the environmental and forensic sciences. However, accurate identification of isomeric compounds remains a challenging task for current analytical methods. The combination of electrospray multistage mass spectrometry (ESI‐MSⁿ) and high resolution mass spectrometry (HRMS) is a powerful tool for the structure characterization of isomeric compounds. We show herein that resonant ion activation performed in a linear quadrupole ion trap allows the differentiation of dinitrotoluene isomers as well as aminodinitrotoluene isomers. The explosive‐related compounds: 2,4‐dinitrotoluene (2,4‐DNT), 2,6‐dinitrotoluene (2,6‐DNT), 2‐amino‐4,6‐dinitrotoluene (2A‐4,6‐DNT) and 4‐amino‐2,6‐dinitrotoluene (4A‐2,6‐DNT) were analyzed by ESI‐MS in the negative ion mode; they produced mainly deprotonated molecules [M ? H]^?. Subsequent low resolution MSⁿ experiments provided support for fragment ion assignments and determination of consecutive dissociation pathways. Resonant activation of deprotonated dinitrotoluene isomers gave different fragment ions according to the position of the nitro and amino groups on the toluene backbone. Fragment ion identification was bolstered by accurate mass measurements performed using Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR/MS). Notably, unexpected results were found from accurate mass measurements performed at high resolution for 2,6‐DNT where a 30‐Da loss was observed that corresponds to CH₂O departure instead of the expected isobaric NO^? loss. Moreover, 2,4‐DNT showed a diagnostic fragment ion at m/z 116, allowing the unambiguous distinction between 2,4‐ and 2,6‐DNT isomers. Here, CH₂O loss is hindered by the presence of an amino group in both 2A‐4,6‐DNT and 4A‐2,6‐DNT isomers, but nevertheless, these isomers showed significant differences in their fragmentation sequences, thus allowing their differentiation. DFT calculations were also performed to support experimental observations. Copyright © 2014 John Wiley & Sons, Ltd.     

Atmospheric pressure chemical ionization studies of non-polar isomeric hydrocarbons using ion mobility spectrometry and mass spectrometry with different ionization techniques

The ionization pathways were determined for sets of isomeric non-polar hydrocarbons (structural isomers, cis/trans isomers) using ion mobility spectrometry and mass spectrometry with different techniques of atmospheric pressure chemical ionization to assess the influence of structural features on ion formation. Depending on the structural features, different ions were observed using mass spectrometry. Unsaturated hydrocarbons formed mostly [M - 1]+ and [(M - 1)2H]+ ions while mainly [M - 3]+ and [(M - 3)H2O]+ ions were found for saturated cis/trans isomers using photoionization and 63Ni ionization. These ionization methods and corona discharge ionization were used for ion mobility measurements of these compounds. Different ions were detected for compounds with different structural features. 63Ni ionization and photoionization provide comparable ions for every set of isomers. The product ions formed can be clearly attributed to the structures identified. However, differences in relative abundance of product ions were found. Although corona discharge ionization permits the most sensitive detection of non-polar hydrocarbons, the spectra detected are complex and differ from those obtained with 63Ni ionization and photoionization.     

Time-of-flight ion mobility spectrometry and differential mobility spectrometry: A comparative study of their efficiency in the analysis of halogenated compounds

The ion mobilities of halogenated aromatics which are of interest in environmental chemistry and process monitoring were characterized with field-deployable ion mobility spectrometers and differential mobility spectrometers. The dependence of mobility of gas-phase ions formed by atmospheric-pressure photoionization (APPI) on the electric field was determined for a number of structural isomers. The structure of the product ions formed was identified by investigations using the coupling of ion mobility spectrometry with mass spectrometry (APPI-IMS-MS) and APPI-MS. In contrast to conventional time-of-flight ion mobility spectrometry (IMS) with constant linear voltage gradients in drift tubes, differential mobility spectrometry (DMS) employs the field dependence of ion mobility. Depending on the position of substituents, differences in field dependence were established for the isomeric compounds in contrast to conventional IMS in which comparable reduced mobility values were detected for the isomers investigated. These findings permit the differentiation between most of the investigated isomeric aromatics with a different constitution using DMS.     

A fragmentation study of isoflavones in negative electrospray ionization by MSn ion trap mass spectrometry and triple quadrupole mass spectrometry

This study has elucidated the fragmentation pathway for deprotonated isoflavones in electrospray ionization using MS(n) ion trap mass spectrometry and triple quadrupole mass spectrometry. Genistein-d(4) and daidzein-d(3) were used as references for the clarification of fragment structures. To confirm the relationship between precursor and product ions, some fragments were traced from MS(2) to MS(5). The previous literature for the structurally related flavones and flavanones located the loss of ketene (C(2)H(2)O) to ring C, whereas the present fragmentation study for isoflavones has shown that the loss of ketene occurs at ring A. In the further fragmentation of the [M-H-CH(3)](-*) radical anion of methoxylated isoflavones, loss of a hydrogen atom was commonly found. [M-H-CH(3)-CO-B-ring](-) is a characteristic fragment ion of glycitein and can be used to differentiate glycitein from its isomers. Neutral losses of CO and CO(2) were prominent in the fragmentation of deprotonated anions in ion trap mass spectrometry, whereas recyclization cleavage accounted for a very small proportion. In comparison with triple quadrupole mass spectrometry, ion trap MS(n) mass spectrometry has the advantage of better elucidation of the relationship between precursor and product ions.     

Current role of LC-MS(/MS) in doping control

Liquid chromatography–(tandem) mass spectrometry [(LC-MS(/MS)] has become an integral part of modern sports drug testing as it offers unique capabilities complementing immunological and gas chromatography–(tandem) mass spectrometry [(GC-MS(/MS)]-based detection methods for prohibited compounds. The improved options of fast and sensitive targeted analysis as well as untargeted screening procedures utilizing high resolution/high accuracy mass spectrometry have considerably expanded the tools available to anti-doping laboratories for initial testing and confirmation methods. One approach is to focus on pre-selected target analytes that are measured with utmost specificity and sensitivity using diagnostic precursor–product ion pairs in low resolution tandem mass spectrometers. The other scenario is to measure and plot extracted ion chromatograms of protonated or deprotonated molecules as well as product ions as recorded in the full scan mode with high resolution/high accuracy mass spectrometry. Examples of recent applications of sports drug testing procedures published between 2007 and 2010 are presented and discussed, outlining the particular advantages of the selected approaches as well as their limitations in a short- and long-term perspective.     

Separation and identification of the Z and E isomers of 2-(3-pentenyl)pyridine by capillary electrophoresis and nuclear magnetic resonance spectroscopy

A mixture of the Z and E isomers of 2-(3-pentenyl)pyridine has been separated with baseline resolution by capillary electrophoresis. Using molecular modelling it was proposed that the smaller more rapidly migrating peak would be the Z isomer. This agreed with a 38:62 (Z/E) composition by nuclear magnetic resonance spectroscopy. The sample was also investigated by gas chromatography coupled to mass spectrometry.     

Identification of RNA sequence isomer by isotope labeling and LC–MS/MS

Recently, we developed a method for modified ribonucleic acid (RNA) analysis based on the comparative analysis of RNA digests (CARD). Within this CARD approach, sequence or modification differences between two samples are identified through differential isotopic labeling of two samples. Components present in both samples will each be labeled, yielding doublets in the CARD mass spectrum. Components unique to only one sample should be detected as singlets. A limitation of the prior singlet identification strategy occurs when the two samples contain components of unique sequence but identical base composition. At the first stage of mass spectrometry, these sequence isomers cannot be differentiated and would appear as doublets rather than singlets. However, underlying sequence differences should be detectable by collision‐induced dissociation tandem mass spectrometry (CID MS/MS), as y‐type product ions will retain the original enzymatically incorporated isotope label. Here, we determine appropriate instrumental conditions that enable CID MS/MS of isotopically labeled ribonuclease T1 (RNase T1) digestion products such that the original isotope label is maintained in the product ion mass spectrum. Next, we demonstrate how y‐type product ions can be used to differentiate singlets and doublets from isomer sequences. We were then able to extend the utility of this approach by using CID MS/MS for the confirmation of an expected RNase T1 digestion product within the CARD analysis of an Escherichia coli mutant strain even in the presence of interfering and overlapping digestion products from other transfer RNAs. Copyright © 2014 John Wiley & Sons, Ltd.     

Mass spectral characterization of phloroglucinol derivatives hyperforin and adhyperforin

Active phloroglucinol constituents of Hypericum perforatum (St. John's wort) extracts, hyperforin and adhyperforin, have been studied following ion activation using tandem mass spectrometry (MS/MS) and complemented by accurate mass measurements. These two compounds were readily analyzed as protonated and deprotonated molecules with electrospray ionization. MS/MS and MS3 data from a quadrupole-linear ion trap tandem mass spectrometer were employed to elucidate fragmentation pathways. Fourier transform ion cyclotron resonance measurements afforded excellent mass accuracies for the confirmation of elemental formulae of product ions formed via infrared multiphoton dissociation and sustained off-resonance irradiation collision-induced dissociation. Fragmentation schemes have been devised for the dissociation of hyperforin and adhyperforin in negative and positive ion modes. This information is expected to be especially valuable for the characterization of related compounds, such as degradation products, metabolites and novel synthetic analogs of hyperforin.     

Structure Elucidation of the Diagnostic Product Ion at <Emphasis Type="Italic">m/z</Emphasis> 97 Derived from Androst-4-en-3-One-Based Steroids by ESI-CID and IRMPD Spectroscopy

Structure elucidation of steroids by mass spectrometry has been of great importance to various analytical arenas and numerous studies were conducted to provide evidence for the composition and origin of (tandem) mass spectrometry-derived product ions used to characterize and identify steroidal substances. The common product ion at m/z 97 generated from androst-4-ene-3-one analogs has been subject of various studies, including stable isotope-labeling and (high resolution/high accuracy) tandem mass spectrometry, but its gas-phase structure has never been confirmed. Using high resolution/high accuracy mass spectrometry and low resolution tandem mass spectrometry, density functional theory (DFT) calculation, and infrared multiple photon dissociation (IRMPD) spectroscopy employing a free electron laser, the structure of m/z 97 derived from testosterone was assigned to protonated 3-methyl-2-cyclopenten-1-one. This ion was identified in a set of six cyclic C₆H₉O⁺ isomers as computed at the B3LYP/6-311++G(2d,2p) level of theory (protonated 3-methyl-2-cyclopenten-1-one, 2-methyl-2-cyclopenten-1-one and 2-cyclohexen-1-one). Product ions of m/z 97 obtained from MS² and MS³ experiments of protonated 3-methyl-2-cyclopenten-1-one, 2-methyl-2-cyclopenten-1-one, 2-cyclohexen-1-one, and testosterone corroborated the suggested gas-phase ion structure, which was eventually substantiated by IRMPD spectroscopy yielding a spectrum that convincingly matched the predicted counterpart. Finally, the dissociation pathway of the protonated molecule of testosterone to m/z 97 was revisited and an alternative pathway was suggested that considers the exclusion of C-10 along with the inclusion of C-5, which was experimentally demonstrated with stable isotope labeling.     

A new method for the identification and the structural characterisation of carotenoid esters in freshwater microorganisms by liquid chromatography/electrospray ionisation tandem mass spectrometry

Liquid chromatography/electrospray ionisation mass spectrometry (LC/ESI-MS) has been employed to identify carotenoid esters present in raw organic extracts of pigmented freshwater microalgae and to gain structural information on these compounds. In particular, acyl carotenoid derivatives of Haematococcus pluvialis and Euglena sanguinea have been characterised by tandem mass spectrometry (MS/MS) in a quadrupole ion trap. ESI-MS/MS allows recognition of the presence of carotenoid esters in complicated mixtures without any initial chromatographic work-up and without the need to use UV-Vis photo-diode array (PDA) detectors. Product ion scans of the [M + Na]+ ion lead to known neutral losses of the C7H8 and C8H10 residues from the conjugated polyene moiety of the carotenoid unit, that permit the unambiguous identification of the carotenoid itself. These structurally relevant ions are not observed in positive or negative ion APCI (atmospheric pressure chemical ionisation) mass spectra. Moreover, the several product ions observed in positive and/or negative ion ESI-MS/MS not only are a diagnostic signature of the main structural features of the acyl chains such as length, position and unsaturation, but also display the nominal mass of the parent xanthophyll. Our methodology has been validated (i) by using esters of astaxanthin obtained from off-line purification of the H. pluvialis extracts and structurally elucidated through proton nuclear magnetic resonance (1H-NMR) spectroscopy and (ii) by product analysis of esters by alkaline hydrolysis. The characterisation of the unknown carotenoid esters of E. sanguinea is a demonstration of the capabilities of this methodology.     

基于多重氢键组装的双杯冠合成及对铯离子的络合

合成了一种基于多重氧键组装形成的新型双杯冠化合物,利用核磁共振氢谱(1H NMR)和碳谱(13C NMR)以及高分辨质谱(ESI-HRMS)对组装前体分子结构进行了表征.通过一维和二维核磁共振氢谱(2D NOESY)研究了该双杯冠的的自组装结构,并采用核磁共振和紫外-可见光谱的方法测定了其对铯离子的络合.实验表明,通过氢键组装形成的双杯冠化合物,由于阻止了单杯冠分子内组装而限制了冠醚环构象改变,其萃取率由单杯冠的82％提高到96％.     

无溶剂条件下α-羟基磷酸酯的合成

在无溶剂条件下,以碳酸钾做催化剂,芳香醛与亚磷酸酯在室温下通过研磨,合成了一系列磷酸酯类化合物.该反应条件温和,操作简单,时间短,对环境友好,是一种绿色的合成方法.产物结构经IR,MS,1HNMR等方法表征.     

Mass spectrometric methods for the analysis of chlorinated and nitrated isoflavonoids: a novel class of biological metabolites

Electrospray ionization combined with tandem mass spectrometry was applied to a study of some representative chlorinated and nitrated isoflavones-potential metabolites of isoflavones in inflammatory cells. Upon collision-induced dissociation of deprotonated [M - H](-) ions of these compounds, a number of structurally characteristic product ions were produced. The product ion analysis of 3'- and 8-chlorodaidzein in the tandom mass spectra led to ready differentiation of these isomers. 3-Nitro derivatives of both genistein and daidzein have product ions due to the losses of HNO(2) and two OH groups. Chlorinated derivatives of isoflavones were detected in cell-based experiments and their structures were proposed by comparing the tandem mass spectra of their product ions with those of standards. This work provides a suitable analytical basis to aid the characterization of chlorinated and nitrated metabolites in studies in vivo and in vitro.     

Investigation of ion/molecule reactions as a quantification method for phosphorylated positional isomers. an FT-ICR approach

A rapid and accurate method of quantifying positional isomeric mixtures of phosphorylated hexose and N-acetylhexosamine monosacchrides by using gas-phase ion/molecule reactions coupled with FT-ICR mass spectrometry is described. Trimethyl borate, the reagent gas, reacts readily with the singly charged negative ions of phosphorylated monosaccharides to form two stable product ions corresponding to the loss of one or two neutral molecules of methanol from the original adduct. Product distribution in the ion/molecule reaction spectra differs significantly for isomers phosphorylated in either the 1- or the 6-position. As a result, the percents of total ion current of these product ions for a mixture of the two isomers vary with its composition. In order to determine the percentage of each isomer in an unknown mixture, a multicomponent quantification method is utilized in which the percents of total ion current of the two product ions for each pure monosaccharide phosphate and the mixture are used in a two-equation, two-unknown system. The applicability of this method is demonstrated by successfully quantifying mock mixtures of four different isomeric pairs: Glucose-1-phosphate and glucose-6-phosphate; mannose-1-phosphate and mannose-6-phosphate; galactose-1-phosphate and galactose-6-phosphate; N-acetylglucosamine-1-phosphate and N-acetylglucosamine-6-phosphate. The effects of mixture concentrations and ion/molecule reaction conditions on the quantification are also discussed. Our results demonstrate that this assay is a fast, sensitive, and robust method to quantify isomeric mixtures of phosphorylated monosaccharides.     

Evaluating the multiple benefits offered by ion mobility-mass spectrometry in oil and petroleum analysis

Ion mobility-mass spectrometry is starting to be considered as a useful tool in the deconvolution of complex oil and petroleum samples. While ultrahigh resolution mass spectrometry is the incumbent technology in this field, ion mobility offers complementary information related to species size and shape, and also the ability to resolve structural isomers. In this work, a sample of the resins portion of the Saturates, Aromatics, Resins, and Asphaltenes (SARA) fractions of crude oil was analysed using an orthogonal acceleration quadrupole time-of-flight mass spectrometer (oa-QToF MS) that incorporates a travelling wave ion mobility spectrometry (TWIMS) region. The ion mobility data were compared with previously acquired ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) data and various nitrogen containing families were identified. Ion mobility data were processed in the typical way for the oil and petroleum industry; and the use of high resolution exact mass coupled with mobility data to provide enhanced species resolution was examined. Double bond equivalence (DBE) and carbon number groups were identified using patterns in the ion mobility data, which demonstrated the utility of ion mobility for discovering species relationships within the crude oil sample. The ability to calibrate the ion mobility cell and generate sizes for the detected ions was also recognised as potentially having particular value for the implementation of conversion or hydrotreatment processes in the oil industry.