Measured Mass Spectra Research Articles

Масс-спектрометрия молекулы ксилита

AbstractThe technique and results of a mass spectrometric study on the yield of positive ions formed upon ionization of xylitol molecules by electron impact are discussed. The mass spectra of xylitol are studied in the range of mass numbers of 10–160 Da and in the range of bombarding electrons energies of 5–80 eV. Based on the analysis of the measured mass spectra, a scheme of xylitol fragmentation is proposed, which contains the most probable channels of formation of ion-fragments upon electron impact, when the energy of the incident electrons significantly exceeds the ionization potential of the molecule. The appearance energies of ionized fragments of xylitol are determined for the first time from the energy dependences of the effective cross-section formation of the ions upon electron impact. The dynamics of ionized fragment formation is studied in the temperature range of the initial substance evaporation of 340–410 K. The behavior of the temperature dependence indicates that the formation processes of water and oxonium cations compete with each other.

Mass spectrometric research glutamine molecule

Background : Amino acids are molecules of vital organic compounds, which simultaneously contain amino (-NH 2 ) and carboxyl (-СООН) groups. Currently, a large number of amino acids are found in interstellar clouds, meteorites. This contributes to the propagation of the hypothesis of the extraterrestrial origin of life on Earth. In general, the penetration of physical methods of research into the study of complex organic molecules is predicted and promises many discoveries in the path of knowledge of the mystery of living matter. Methods : One of the important methods of studying the structure of matter and physical processes that occur in it is mass spectrometry and spectral analysis. The experiment was performed on a monopole mass spectrometer (MX) type MX-7304A, which belongs to the class of dynamical mass spectrometers with ionization by electron impact The monopole mass analyzer, in contrast to the quadrupole, divides the ions not only orthogonally, but also in the direction of the input of particles into the analyzer. Thus, a bundle of ions at the outlet of the ion source should be parallel, monokinetic and directed along the axis of the analyzer. A bundle of investigated glutamine molecules was obtained using an effusion source whose temperature could vary widely. This made it possible to investigate the temperature dependence of the formation of various fragments of the investigated molecule. Measurements of mass spectra were carried out in such a way as to ensure accuracy of 3-5%. Temperature dependences of the formation of positive ions of fragments were measured using a special precision feedback device, which allowed maintaining the temperature of the molecules in the gas phase with an accuracy of ±0,05K. Results : Mass spectrometric studies of glutamine have been carried out by the method of bundles, which are transformed in the range of bombarding electrons energy 6-70 eV and at temperatures of 340-460 K. The dominant mass spectrum is the peak that corresponds to the ion-fragment with m / z = 84 a.o.m., which corresponds to the fragment C 3 H 2 NO 2 + . The smallest energy is the C-C, N-C, C-O bonds, which leads to the fragmentation of the glutamine molecule by electron impact and the appearance of a carboxylic, amino group in the mass spectrum of the ion-fragments. Conclusions: The high efficiency of the occurrence of ionic fragments of glutamate molecules and the strong temperature dependence of their formation in interaction with electrons indicate a very complex mechanism of electronic fragmentation of the glutamine molecule, which in turn significantly influences the composition of fluorophores.

Analysis of the one-neutron transfer to O16,Si28 , and Ni64 induced by the (O18,O17) reaction at 84 MeV

Background: Recently, a systematic exploration of two-neutron transfer induced by the ($^{18}$O, $^{16}$O) reaction on different targets has been performed. The high resolution data have been collected at the MAGNEX magnetic spectrometer of the INFN-LNS laboratory in Catania and analyzed with the coupled reaction channel (CRC) approach. The simultaneous and sequential transfers of the two neutrons have been considered under the same theoretical framework without the need of adjustable factors in the calculations. Purpose: A detailed analysis of the one-neutron transfer cross sections is important to study the sequential two-neutron transfer. Here, we examine the ($^{18}$O, $^{17}$O) reaction on $^{16}$O, $^{28}$Si and $^{64}$Ni targets. These even-even nuclei allow for investigation of one-neutron transfer in distinct nuclear shell spaces. Method: The MAGNEX spectrometer was used to measure mass spectra of ejectiles and extract differential cross sections of one-neutron transfer to low-lying states. We adopted the same CRC formalism used in the sequential two-neutron transfer, including relevant channels and using spectroscopic amplitudes obtained from shell model calculations. We also compare with one-step distorted wave Born approximation (DWBA). Results: For the $^{18}$O + $^{16}$O and the $^{18}$O + $^{28}$O systems we used two interactions in the shell model. The experimental angular distributions are reasonably well reproduced by the CRC calculations. In the $^{18}$O + $^{64}$Ni system, we considered only one interaction and the theoretical curve describes the shape and order of magnitude observed in the experimental data. Conclusions: Comparisons between experimental, DWBA and CRC angle-integrated cross sections suggest that excitations before or after the transfer of neutron is relevant in the $^{18}$O + $^{16}$O and $^{18}$O + $^{64}$Ni systems.

One-shot synthesis of sequence-controlled polymers with versatile succimide motifs for post-modifications

Herein, we have successfully prepared sequence-controlled polymers with versatile succimide motifs by one-shot reversible addition-fragmentation chain-transfer (RAFT) polymerization of styrene and furan-protected maleimide. Succimide motifs at desired positions along the polymer chain were highly reactive for post-modifications in both nucleophilic substitution and Mitsunobu condensation reactions. 1H NMR, FT-IR, MALDI-TOF mass spectrum and SEC measurements were used to demonstrate the efficiencies of the nucleophilic substitution reaction and Mitsunobu condensation reaction. Then, we used methoxy terminated polyethylene glycols (mPEG, Mn = 400 Da) as side chains to prepare sequence-controlled amphiphilic brush polymers by performing Mitsunobu condensation reaction. There was no doubt that the reactions were extremely efficient. Therefore, we could design varied side chains to prepare sequence-controlled brush polymers, which would advance the structure-property relationship and potential applications of sequence-controlled polymers in research.

Diagnostics of argon cluster ion beam for materials treatment

The important parameters for materials surface processing by a gas cluster ions are the mass composition, total energy and energy per atom in the cluster, which depends on the ion beam charge state. The purpose of this work is an experimental characterization of argon cluster ion beam, based on an original time-of-flight technique. The mean sizes of the cluster ions obtained from the measured mass spectra are compared with the mean sizes of the primary neutral clusters. By analyzing the mass spectra at different electron ionization current, the average charge state of cluster ion beam is evaluated.

Monolithic thin-layer chromatography plates with covalently bonded matrix for hyphenation with matrix-assisted laser desorption/ionization.

Monolithic layers prepared by the copolymerization of ethylene dimethacrylate and glycidyl methacrylate and deposited onto the surface of glass and silicon plates were investigated as thin-layer chromatography separation media in hyphenated thin-layer chromatography with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis. Varying composition of the polymerization mixture and polymerization conditions layers of different porosities and MALDI-MS compatibility were synthesized. Compatibility with MALDI-MS was tested using polyethylene glycol and it was demonstrated that layers prepared without glycidyl methacrylate are not compatible with MALDI-MS and do not allow obtaining any mass spectra. Best results were achieved with layers containing 19 to 29% glycidyl methacrylate. These layers allow the measurement of mass spectra without additional depositing matrix compounds supplying mass spectra almost "clean" in low molar mass range.

Experimental and theoretical spectroscopic studies in relation to molecular structure investigation of para chloro, para fluoro and para nitro maleanilinic acids

In the present work novel para chloro, para fluoro and para nitro maleanilic acid derivatives were prepared and investigated using FT-IR, thermal analyses (TA) measurements (TGA/DTG and DTA) in comparison with mass spectral (MS) fragmentation at 70 eV. The crystallographic structures of studied compounds were investigated by X-ray diffraction (XRD). The vibrational frequencies and the corresponding normal modes were evaluated at the optimized geometry. Vibrational modes were analyzed using GAUSSVIEW software. Experimental FT-IR and Raman spectra of the three newly prepared derivatives, namely, (E) – oxo -4- ((4- nitro phenyl) amino)-4- oxobut-2-enoic acid (p-NMA), (E) -4- ((4- chloro phenyl)amino)-4- oxobut -2- enoic acid (p-ClMA), (E) -4- ((4- fluoro phenyl) amino)- 4- oxobut -2- enoic acid (p-FMA) were compared with the theoretically calculated one. FT-IR and the observed vibrational frequencies were assigned; thermal analysis and mass spectrum measurements of the maleanilic acid derivatives were recorded and discussed. The computational calculations were carried out by DFT - B3LYP method with 6-311++G(d,p) basis sets and the corresponding results were tabulated. The alternations of structures of p-FMA, p-ClMA and p-NMA due to the subsequent substitutions were investigated. This correlation between experimental and theoretical calculations provided a good confirmation of the proposed structures of the newly prepared compounds. The derivatives were found to be highly effective against Hepatocellular carcinoma cells > Breast carcinoma cells > colon carcinoma cells. It was recognized, that cancer cells over expression promotes tumorigenic functions; can be suppressed by p-NMA > p-FMA > p-ClMA inhibitors.

Synthesis of a novel N-alkoxyamine containing compound and its application as an effective flame retardant for polypropylene film by quenching free radical

A novel N-alkoxyamine containing compound 2,4,6-tri-(1-cyclohexyloxy-4-imino-2,2,6,6-tetramethylpiperidine)-1,3,5-triazine defined as T-TEMPOC was synthesized. Its chemical structure was well characterized and confirmed. The synthesized T-TEMPOC was incorporated into polypropylene (PP) to preparing flame retardant PP film (NOR-PP film). The NOR-PP film with the thickness of 0.2 mm successfully passed UL-94 VTM-0 rating during vertical burning test and its limiting oxygen index value reached 27.3% when 2.0 wt% T-TEMPOC was incorporated, and the heat release rate and total heat release were decreased obviously. The incorporation of T-TEMPOC inhibited the initial thermal degradation of PP on heating and then enhanced the thermal stability of PP film. The NOR-PP film maintained excellent mechanical performance with the introduction of T-TEMPOC. T-TEMPOC could decompose and generate nitroxyl radical, which confirmed by pyrolysis gas chromatography mass spectra measurement. The nitroxyl radical could quench the active free radicals to block the radical chain reaction during combustion, thus suppressed and even extinguished the flame. Moreover, nitroxyl radical was regenerated under the existing of the peroxide. The cyclic process of nitroxyl radical quenching active free radicals and self-regeneration were constructed, which was critical for improving the flame retardant efficiency for PP film. The results might have a promising prospect for flame retardant polymer film.

Molecular hydrogen formation on interstellar PAHs through Eley-Rideal abstraction reactions

We present experimental data on H2 formation processes on gas-phase polycyclic aromatic hydrocarbon (PAH) cations. This process was studied by exposing coronene radical cations, confined in a radio-frequency ion trap, to gas-phase H atoms. Sequential attachment of up to 23 hydrogen atoms has been observed. Exposure to atomic D instead of H allows one to distinguish attachment from competing abstraction reactions, as the latter now leave a unique fingerprint in the measured mass spectra. Modelling of the experimental results using realistic cross-sections and barriers for attachment and abstraction yield a 1:2 ratio of abstraction to attachment cross-sections. The strong contribution of abstraction indicates that H2 formation on interstellar PAH cations is an order of magnitude more relevant than previously thought.

Tests of the Electromagnetic Calorimeter for HADES Experiment at GSI

Measurements of mass spectra of dilepton pairs in the HADES experiment in the energy domain of SIS18 and SIS100 (FAIR, Darmstadt, Germany) are very important for studing the excitation function of the virtual photon radiation from dense nuclear matter. A detail study of this phenomenon in the intermediate mass region (0.14 < M < 0.6 GeV/c2) demands precise measurements of inclusive cross sections of

Identification of specific sources of airborne particles emitted from within a complex industrial (steelworks) site

A case study is provided of the development and application of methods to identify and quantify specific sources of emissions from within a large complex industrial site. Methods include directional analysis of concentrations, chemical source tracers and correlations with gaseous emissions. Extensive measurements of PM10, PM2.5, trace gases, particulate elements and single particle mass spectra were made at sites around the Port Talbot steelworks in 2012. By using wind direction data in conjunction with real-time or hourly-average pollutant concentration measurements, it has been possible to locate areas within the steelworks associated with enhanced pollutant emissions. Directional analysis highlights the Slag Handling area of the works as the most substantial source of elevated PM10 concentrations during the measurement period. Chemical analyses of air sampled from relevant wind directions is consistent with the anticipated composition of slags, as are single particle mass spectra. Elevated concentrations of PM10 are related to inverse distance from the Slag Handling area, and concentrations increase with increased wind speed, consistent with a wind-driven resuspension source. There also appears to be a lesser source associated with Sinter Plant emissions affecting PM10 concentrations at the Fire Station monitoring site. The results are compared with a ME2 study using some of the same data, and shown to give a clearer view of the location and characteristics of emission sources, including fugitive dusts.

Seasonal variability in chemical composition and source apportionment of sub-micron aerosol over a high altitude site in Western Ghats, India

This manuscript reports the seasonal variation of chemically speciated sub-micron aerosol particles (diameter < 1 μm). An Aerosol Chemical Speciation Monitor (ACSM) was used to measure the mass concentration of non-refractory particulate matter (NR-PM1) at a high-altitude site in the Western Ghats, India from March 2016 to February 2017. The mass concentration of NR-PM1 averaged at 7.5 ± 6.5 μgm–3, with major contributions from organics (59%) and sulfates (23%). Positive matrix factorization (PMF) was applied on the measured mass spectra of organic aerosol (OA) to derive the sources distinctive of each season (Summer, Monsoon, Post-Monsoon and Winter). The four OA factors (two primary OA and two oxygenated OA) resolved during summer, post-monsoon and winter season. However, only one oxygenated factor resolved during monsoon and contributed only 20% to the total OA. The factors associated with primary emissions dominated during the monsoon, whereas factors related to secondary formation dominated in other three seasons. During summer, an isoprene derived SOA – IEPOX-OA (isoprene-epoxydiol OA) contributed ∼17% to the total OA. Cluster and concentration weighted trajectory (CWT) analyses were performed to identify the possible source regions of NR-PM1 mass concentration observed at the receptor site. The analysis identifies Central India as the potential source region of transported aerosol during post-monsoon and winter season. Our study suggests that contributions from both local sources and regional transport are important in governing mass concentration of PM1 over Mahabaleshwar.

Hydrogen rearrangements in the fragmentation of anthracene by low-energy electron impact

We have measured mass spectra for positive ions produced by low-energy electron impact on anthracene using a reflectron time-of-flight mass spectrometer. The electron impact energy has been varied from 0 to 100 eV in steps of 0.5 eV. Ion yield curves of most of the fragment ions have been determined by fitting groups of adjacent peaks in the mass spectra with sequences of normalized Gaussians. Appearance energies for all these ions have been determined, and we report the first direct measurement of the triple ionization energy of anthracene at 45.5 +/- 0.5 eV. The groups of fragments containing 8-13 carbon atoms provide evidence for hydrogen rearrangements during the fragmentation, involving retention or loss of one or two additional hydrogen atoms. Groups of fragments with 6 and 7 carbon atoms clearly show the presence of doubly-charged fragments. The smaller fragments with 1-4 carbon atoms all show broadened peaks, and these fragments may be partly or mostly due to energetic charge-separation fragmentations of doubly-charged anthracene.

A Model of Titan-like Chemistry to Connect Experiments and Cassini Observations

Abstract A numerical model is presented for interpreting the chemical pathways that lead to the experimental mass spectra acquired in the Titan Haze Simulation (THS) laboratory experiments and for comparing the electron density and temperature of the THS plasma to observations made at Titan by the Cassini spacecraft. The THS plasma is a pulsed glow-discharge experiment designed to simulate the reaction of N2/CH4-dominated gas in Titan's upper atmosphere. The transient, one-dimensional model of THS chemistry tracks the evolution of more than 120 species in the direction of the plasma flow. As the minor species C2H2 and C2H4 are added to the N2/CH4-based mixture, the model correctly predicts the emergence of reaction products with up to five carbon atoms in relative abundances that agree well with measured mass spectra. Chemical growth in Titan's upper atmosphere transpires through ion–neutral and neutral–neutral chemistry, and the main reactions involving a series of known atmospheric species are retrieved from the calculation. The model indicates that the electron density and chemistry are steady during more than 99% of the 300 μs long discharge pulse. The model also suggests that the THS ionization fraction and electron temperature are comparable to those measured in Titan's upper atmosphere. These findings reaffirm that the THS plasma is a controlled analog environment for studying the first and intermediate steps of chemistry in Titan's upper atmosphere.

Theoretical study on the structure and stability of neutral and cationic butanone clusters

The molecular clusters have attracted increasing attention in recent years due to their applications in areas of laser, synchrotron radiation, molecular beam and time-of-flight mass spectrometry. The cluster structures can be speculated by the mass spectrum measurement and predicted by the quantum chemical methods. It is very important for understanding the solvation kinetics and nucleation to explore the formation and growth of clusters. Meanwhile, it is also beneficial to understanding the atomic or intermolecular interactions in the clusters. The molecular clusters have been studied in our previous work. The acetone clusters (CH3COCH3)n (n 12) were observed by 355 nm pumping laser. The structures of (CH3COCH3)n with n=2-7 were calculated by density functional theory, and some structures of clusters with low energy were given. Subsequently, several butanone cluster fragment ions and protonated butanone (CH3COC2H5, which is formed by taking a methyl change into ethyl from acetone CH3COCH3) clusters were observed by measuring the mass spectra under the irradiations of 355 nm and 118 nm laser lights, respectively. It is important to determine the stable cluster structures and explain the dynamics of the clusters by theoretical calculation. The stable geometric structures of neutral and cationic butanone clusters are optimized at B3LYP/6-31G* and B3LYP/6-311+G** levels based on the density functional theory. The structural characteristics and stabilities of butanone clusters with various sizes are also analyzed. The average binding energy, first-order difference energy, HOMO-LUMO gap and ionized energy are further discussed systematically in the present work. The results show that the structures of (CH3COC2H5)n and (CH3COC2H5)n+ have similar characteristics, single-ring structure is the most stable for them when n=3-7, and the structures also occur in some hydrogen bonded clusters, such as (H2O)n (n=3-6), (NH3)n (n=3-6), (CH3OH)n (n=3-6), and (HCHO)n (n=3-8). Moreover, the stability of double ring structure rises with cluster size increasing. The (CH3COC2H5)3 has the best stability in neutral clusters (CH3COC2H5)n with n=2-7, and it corresponds to the strongest peak in experiment. In addition, the (CH3COC2H5)4+ is the most stable in the cationic clusters with corresponding sizes. Furthermore, the vertical ionization energy of butanone molecule is 9.535 eV via theoretical calculation, which is in agreement with the experimental data. At the same time, the structures of (CH3COC2H5)2+ and (CH3COC2H5)2 are proved to be different by the ionization energy. The results provide a theoretical basis for the formation mechanism of butanone cluster fragment ions in experiment, and it is beneficial to the further study of growing the ketone clusters.

Colorimetric and fluorescent probes for real-time naked eye sensing of copper ion in solution and on paper substrate.

In this paper, BT ((E)-2-(4-(4-(bis(pyridin-2-ylmethyl)amino)styryl)-3-cyano-5,5-dimethylfuran-2(5H)-ylidene)malononitrile) with strong donor–π-acceptor structure was synthesized, which showed both colorimetric and fluorescent sensing ability toward Cu2+ with high selectivity and sensitivity. Job plot and mass spectra measurement revealed a 1 : 1 coordination mode between Cu2+ and probe BT in ethanol/HEPES (1 : 4 v/v) buffer (pH 7.2) solution, and the binding constant was calculated to be 3.6 × 104 M–1. The colour of BT solution (10 µM) immediately turned from purple red to yellow and the red fluorescence was quenched obviously when a certain amount of Cu2+ was added, which enabled a dual-channel detection of Cu2+. A paper strip pre-stained with BT solution was further fabricated and it also showed excellent sensing ability toward Cu2+ with a detection limit as low as 10−6 M with the naked eye, which represents better portability and operation simplicity that is favourable for on-site analysis of Cu2+ in water.

An imaging photoelectron-photoion coincidence investigation of homochiral 2R,3R-butanediol clusters.

We report an experimental investigation of homochiral cluster formation in seeded molecular beam expansions of (2R,3R)-butanediol. Synchrotron radiation vacuum ultraviolet photoionization measurements have been performed using a double imaging electron-ion spectrometer in various configurations and modes of operation. These include measurements of the cluster ion mass spectra, wavelength scanned ion yields, and threshold electron spectra. Protonated cluster ions ranging up to n = 7 have been observed and size-selected photoelectron spectra and photoelectron circular dichroism (PECD) have been recorded by velocity map imaging, recorded in coincidence with ions, at a number of fixed photon energies. Translation temperatures of the cluster ions have been further examined by ion imaging measurements. As well as the sequence of protonated clusters with integral numbers of butanediol monomer units, a second series with half-integral monomer masses is observed and deduced to result from a facile cleavage of a butanediol monomer moiety within the nascent cluster. This second sequence of half-integral masses displays quite distinct behaviours. PECD measurements are used to show that the half-integral mass cluster ions do not share a common parentage with whole integer masses. Using an analogy developed with simple theoretical calculations of butanediol dimer structures, it is inferred that the dissociative branching into integral and half-integral ion mass sequences is controlled by the presence of different butanediol monomer conformations within the hydrogen bonded clusters.

Investigation on pyrolysis of intumescent flame-retardant polypropylene (PP) composites based on synchrotron vacuum ultraviolet photoionization combined with molecular-beam mass spectrometry

The pyrolysis of intumescent flame-retardant polypropylene (PP) composites was studied by synchrotron vacuum ultraviolet photoionization combined with molecular-beam mass spectrometry (SVUV-PIMS). Pyrolytic products of intumescent flame-retardant PP composite formed at certain temperature have been identified by the measurement of photoionization mass spectra at different photon energies. By using SVUV-PIMS, some isomers were identified. Meanwhile, the effect of high-efficient flame-retardant synergist–nanoporous nickel phosphate on pyrolytic products of intumescent flame-retardant PP composite was also studied. By analyzing the pyrolysis of the intumescent flame-retardant PP composites with or without the flame-retardant synergist, the synergistic flame-retardant mechanism was discussed as the condensed-phase flame-retardant mechanism not gas flame-retardant mechanism as expected. The studies in this work are much helpful for further understanding the flame-retardant mechanism of intumescent flame-retardant PP composites.

Protein and peptide cross sections and mass spectra in an electrostatic ion beam trap

Among the advantages of an electrostatic ion beam trap (EIBT), which is based on purely electrostatic fields, are mass-unlimited trapping and ease of operation. We have developed a new system that couples an electrospray ion source to an EIBT. Between the source and EIBT there is a Paul trap in which the ions are accumulated before being extracted and accelerated. After the ion bunch has entered the EIBT, the ions are trapped by rapidly raising the voltages on the entrance mirror. The oscillations of the bunch are detected by amplifying the charge induced on a pickup ring in the center of the trap, the ion mass being directly proportional to the square of the oscillation period. The trapping of biomolecules in the RF-bunching mode of the EIBT is used for measurement of mass spectra and collision cross sections. Coalescence of bunches of ions of nearby mass in the self-bunching mode is also demonstrated.

A &amp;ldquo;turn on&amp;rdquo; fluorescent probe based on Tb(III) complex for the detection of organophosphorus pesticides

The abuse of organophosphate pesticides and chemical-warfare agents has made severe effects on human and animal health. Consequently, it is vital to develop sensitive and selective strategies for the detection of organophosphates. In this work, the Tb(III) complex— TbL 3+ , consisting of a 1,4,7-triazacyclononane derivative as ligand was synthesized. As TbL 3+ contains no aromatic groups (function as an antenna), its intrinsic luminescence is thus minimized. The coordination of cyanophos to TbL 3+ could largely sensitize its luminescence ( I / I 0=55) because the energy of the triplet state of benzene is slightly higher in energy than the 5D4 of Tb(III). The detection limit for cyanophos was determined as 59 nmol/L. High resolution mass spectrum measurements, luminescence titration experiment and luminescence lifetime measurements reveal that TbL 3+ is bound with two cyanophos molecules and one methanol molecule. However, other organophosphates such as profenofos, chlopyrifos, dimethoate, diazinon, phoxim, fenthion, methyl parathion and dichlorvos almost did not induce any changes on luminescence intensity under the same conditions. By this work, we prepared a new luminescence probe for cyanophos with good selectivity and sensitivity.