Electron Ionization Research Articles

Feature-Based Molecular Network for New Psychoactive Substance Identification: The Case of Synthetic Cannabinoids in a Seized e-Liquid and Biological Samples.

The comprehensive detection of new psychoactive substances, including synthetic cannabinoids along with their associated metabolites in biological samples, remains an analytical challenge. To detect these chemicals, untargeted approaches using appropriate bioinformatic tools such as molecular networks are useful, albeit it necessitates as a prerequisite the identification of a node of interest within the cluster. To illustrate it, we reported in this study the identification of synthetic cannabinoids and some of their metabolites in seized e-liquid, urine, and hair collected from an 18-year-old poisoned patient hospitalized for neuropsychiatric disorders. A comprehensive analysis of the seized e-liquid was performed using gas chromatography coupled with electron ionization mass spectrometry, 1H NMR, and liquid chromatography coupled with high resolution tandem mass spectrometry combined with data processing based on molecular network strategy. It allowed researchers to detect in the e-liquid known synthetic cannabinoids including MDMB-4en-PINACA, EDMB-4en-PINACA, MMB-4en-PINACA, and MDMB-5F-PICA. Compounds corresponding to transesterification of MDMB-4en-PINACA with pentenol, glycerol, and propylene glycol were also identified. Regarding the urine sample of the patient, metabolites of MDMB-4en-PINACA were detected, including MDMB-4en-PINACA butanoic acid, dihydroxylated MDMB-4en-PINACA butanoic acid, and glucurono-conjugated MDMB-4en-PINACA butanoic acid. Hair analysis of the patient allowed the detection of MDMB-4en-PINACA and MDMB-5F-PICA in the two investigated hair segments. This untargeted analysis of seized materials and biological samples demonstrates the utility of the molecular network strategy in identifying closely related compounds and metabolites of synthetic cannabinoids. It also emphasizes the need for developing strategies to anchor molecular networks, especially for new psychoactive substances.

Quantum Chemistry-Based Prediction of Electron Ionization Mass Spectra for Environmental Chemicals.

There is a lack of experimental electron ionization high-resolution mass spectra available to assist compound identification. The in silico generation of mass spectra by quantum chemistry can aid annotation workflows, in particular to support the identification of compounds that lack experimental reference spectra, such as environmental chemicals. We present an open-source, semiautomated workflow for the in silico prediction of electron ionization high-resolution mass spectra at 70 eV based on the QCxMS software. The workflow was applied to predict the spectra of 367 environmental chemicals, and the accuracy was evaluated by comparison to experimental reference spectra acquired. The molecular flexibility, number of rotatable bonds, and number of electronegative atoms of a compound were negatively correlated with prediction accuracy. Few analytes are predicted to sufficient accuracy for the direct application of predicted spectra in spectral matching workflows (overall average score 428). The m/z values of the top 5 most abundant ions of predicted spectra rarely match ions in experimental spectra, evidencing the disconnect between simulated fragmentation pathways and empirical reaction mechanisms.

Analysis of Monte-Carlo collision method with argon and helium background gases at different RF-powers and pressures in ELTRAP device

The impact of confined excited electron with argon and helium background gases is systematically studied using Monte-Carlo particle-in-cell simulations for various low powers (1.0–8.0 V) and pressures (1.50 × 10−8 Torr and 3.75 × 10−9 Torr) in ELTRAP device. The results of these numerical studies showed that the heating effect of the excited confined electron plasma density of 5 × 1014 m−3 within the Brillouin limit (ne≤ε0B22me=31.086×1019m-3) resulted a higher temperature (eV) and increased collision time in argon as a background gas as compared to helium gas. The axial temperature (eV) has a higher value than the radial temperature (eV) and increases with the increase in RF-Powers and pressures. The maximum kinetic energy of excited confined electrons occurred in the range of 0.03–0.04 m radially due to the maximum self-electric field intensity in simulation time up to 20 µs. The electric field decreases when the collision frequency is increased. The secondary electron production and ionization are higher than expected at a background pressure of 1.50 × 10−8 Torr as compared to 3.75 × 10−9 Torr. The remaining secondary electrons were always ejected from the symmetry axis of the device. It was observed that the production of secondary electrons is proportional to the ionization rate.

DFT studies on N-(1-(2-bromobenzoyl)-4-cyano-1H-pyrazol-5-yl)

In this work, molecular descriptors of N-(1-(2-bromobenzoyl)-4-cyano-1H-pyrazol-5-yl) halogenated benzamides (1a-h) have been computed using a quantum chemical technique through DFT. Prior work involved the synthesis of compounds (1a-h) and the assessment of their anticancer activity on breast, colon, and liver tumors: MCF-7, HCT-116, and HepG-2 cell lines respectively. Since 1a, 1b, and 1d showed the most potential anticancer impact, their ability to inhibit EGFRWT was investigated. Based on the biological data, 1b inhibited EGFRWT the most. According to the docking evaluation, an H-bond with the threonine residue was one of the main non-covalent contacts between 1b and the EGFRWT active site residues. PES, MESP, HOMOs, LUMOs, energy band gap, global reactivity indices [electron affinity (A), ionization energies (I), electrophilicity index (ω), nucleophilicity index (ε), chemical potential (μ), electronegativity (χ), hardness (η), and softness (S)], condensed Fukui functions, NBO, and NCIs are the molecular descriptors of 1a-h that were computed using DFT technique. According to the theoretical investigation results, compounds (1a-h) might have anticancer effects; these findings are consistent with the biological findings from our previous research. Compound 1b had the lowest binding energy, according to an assessment of the binding energies between the threonine and the three most active compounds (1a, 1b, and 1d). This is consistent with the outcomes of the docking study and the biological examination of the influence of 1a, 1b, and 1d on EGFRWT.

Fe3O4@PS-DVB microspheres modified with urea functional groups for rapid and green extraction of fluorinated aromatic carboxylic acids from tap and formation water

The present study describes the trace analysis of 23 fluorinated aromatic carboxylic acids based on the dispersive magnetic solid phase extraction (m-SPE) technique coupled with the gas chromatography coupled with mass spectrometry (GC–MS) electron ionization (EI) technique. A commercial hydrophilic-lipophilic balanced (HLB) material polystyrene divinyl benzene having urea functional groups was modified with magnetite nanoparticles and employed as a sorbent for dispersive m-SPE of fluorobenzoic acids (FBAs) from the tap and formation water samples. The extraction occurred due to π- π interaction between the aromatic ring of synthesized sorbent and the aromatic ring of FBAs, the hydrogen bond formation between the urea functional group of the sorbent and carbonyl oxygen, fluorine of the FBAs. As a result, the method was precise, rapid, reproducible, and calibrated with the coefficient of variation (R2) greater than 0.98 for all 23 compounds. The instrument detection limit (IDL) and method detection limit (MDL) were found in the range of 2.60 – 8.25 ng/mL and 0.08 – 0.28 ng/mL respectively. Extraction efficiencies were found in the range of 83.80–100 % for tap water samples and 78.41–98.92 % for formation water samples, respectively, with an enrichment factor of 33.33–66.66 and a maximum RSD of 7.07 %. The recyclability and magnetic properties of the synthesized material were also investigated, resulting in the material being reused for six cycles without impacting its performance; hence, the method offers rapid determination and high throughput analysis of FBAs. In addition, simulation studies were performed using the adsorption location tool of Material Studio, confirming the interaction sites of sorbent with FBAs. AGREE evaluated the analytical greenness of the method, and the score was found to be 0.51.

Correlation of Electron Configuration, Electronegativity, and Ionization Energy of Strontium on the Modification of Eutectic Si in High-Pressure Die Cast A380 Al–Si Alloys

Correlation of Electron Configuration, Electronegativity, and Ionization Energy of Strontium on the Modification of Eutectic Si in High-Pressure Die Cast A380 Al–Si Alloys

Experimental study of electron bombardment ion electric propulsion based on a CO2/Xe mixed working medium

An experimental study was carried out on the use of a mixture of CO2 and Xe as the propellant for an electron bombardment ion thruster. The working performance parameters of the ion thruster under different flow mixing conditions were investigated using measurements and diagnostics such as power supply electrical parameter measurements, thrust measurements, and plasma diagnostics. In-depth studies of the particle species and the main electron collision reactions in the discharge chamber were carried out. The results showed that the CO2 in the discharge chamber led to a significant increase in the mean anode voltage and voltage oscillation amplitude, and the direct participation of CO2 in the discharge reaction could effectively improve the beam current and thrust of the ion thruster. When 5 sccm of CO2 was injected into the discharge chamber, the maximum measured thrust was increased by approximately 31.8 % compared to the state without CO2 injection. The addition of Xe led to a significant decrease in the discharge voltage and hence an increase in the electron number density, which significantly promoted CO2 dissociation and ionization. The insights obtained from this work can provide ideas for subsequent research related to an ion thruster using a mixed propellant.

Dielectric barrier discharge ionization procures characteristic adducts of polyfluoroalkyl substances (PFAS) amenable by gas chromatography-mass spectrometry

Fluorotelomer alcohols (FTOHs) and acrylates (FTACs) have been reported as precursors of perfluoroalkyl acids and are known to contaminate biotic and abiotic compartments. Here, a detailed study was carried out for assessing the capability of dielectric barrier discharge ionization (DBDI) to be used as soft ionization technique, as alternative to the more energetic electron ionization (EI), for the quantitative determination of four FTOHs and two FTACs in environmental, biological or food samples by gas chromatography-mass spectrometry. While gas chromatography-EI-mass spectrometry (GC-EI-MS) shows significant fragmentation of the compounds, the ionization obtained by gas chromatography-DBDI-high resolution mass spectrometry (GC-DBDI-HRMS) affords dominant molecular adducts on the spectra. In the positive ion mode, the ion [M + H3O]+ and, of lower intensity, [M + H]+ are observed in the spectra of FTOHs, while the ion [M + H]+ is the most abundant in the spectra of FTACs and accompanied by a lower signal attributed to the ion [M + NO]+. In the negative ion mode, the FTOHs give rise to carbon dioxide and oxygen adducts observed with ions [M − H + CO2]- and [M + O2]-. Structure assignments were confirmed with stable isotope-labelled FTOH analogs and 13CO2. Gas chromatographic separation of the six compounds reveals room for development of methods applicable to soils, plants, water, food and biological materials.

High-Resolution Electron Ionization Mass Spectrometry of Stannane: Deconvolution of Superimposed Fragmentation Patterns.

In a pulsed laser plasma driven extreme ultraviolet (EUV) light, tin droplets undergo evaporation, eventually depositing on different surfaces. The removal of surface bound tin is commonly achieved with a hydrogen plasma, resulting in the formation of stannane (SnH4). The mechanisms leading to the formation and decomposition of stannane remain incompletely understood. To analyze these mechanisms mass spectrometrically, a reference is crucial, necessitating a high-resolution and thoroughly characterized mass spectrum of stannane. In this paper, a high-resolution 70 eV electron ionization (EI) mass spectrum of stannane is presented. The mass spectrum comprises all ten natural isotopes of the stannane fragments generated through EI. Utilizing the custom analysis program RASP, the relative distribution of fragments is calculated from the isotopically superimposed mass signals, offering crucial insights into the occurring processes. Furthermore, the dependence of fragment formation on ion source pressure and temperature was determined.

Empirical calibration for helium abundance determinations in active galactic nuclei

ABSTRACT For the first time, a calibration between the He i$\lambda 5876$/H $\beta$ emission line ratio and the helium abundance y = 12 + log(He/H) for Narrow line regions of Seyfert 2 Active Galactic Nuclei is proposed. In this context, observational data (taken from the SDSS-DR15 and from the literature) and direct abundance estimates (via the $T_{\rm e}$-method) for a sample of 65 local ($z \: \lt \: 0.2$) Seyfert 2 nuclei are considered. The resulting calibration estimates the y abundance with an average uncertainty of 0.02 dex. Applying our calibration to spectroscopic data containing only strong emission lines, it yields a helium abundance distribution similar to that obtained via the $T_{\rm e}$-method. Some cautions must be considered to apply our calibration for Seyfert 2 nuclei with high values of electron temperature (${\gtrsim} 20\, 000$ K) or ionization parameter ($\log U \ \gt\ {-}2.0$).

Experimental and Theoretical Study on Electron Ionization and Fragmentation of Propylene Oxide─the First Chiral Molecule Detected in the Interstellar Medium.

Propylene oxide, CH3CHOCH2, is the first chiral molecule detected in space and the third C3 oxide detected toward the Sagittarius B2 (Sgr B2 (N)) molecular cloud, the others being propanal, CH3CH2CHO, and acetone, (CH3)2CO. With homochirality being ubiquitous in the building blocks of living matter, the formation and decay paths of propylene oxide in space are of specific interest. Motivated by the significant role of photo- and secondary electrons in astrochemistry, we have studied electron ionization and fragmentation of propylene oxide. Ion appearance energies are determined and compared to threshold values for the respective processes calculated at the G4MP2 level of theory, and potential reaction pathways are computed at the DFT level of theory. Electron ionization is found to destabilize propylene oxide, leading to barrierless opening of the C1-C2 bond of the epoxy ring, hydrogen transfer, and fragmentation over the methyl vinyl ether or rupture of the C2-O bond of the epoxy ring and fragmentation of the allyl alcohol cation as an intermediate, rather than direct bond ruptures.

Gas chromatography/mass spectrometry analysis of reaction products of Chemical Weapons Convention-related 2-(N,N-dialkylamino)ethylchlorides with 2-(N,N-dialkylamino)ethanols.

The Chemical Weapons Convention (CWC) mandates rigorous screening of chemical weapons and their potential degradation/reaction products, which is essential to identify such products in suspected samples. The reaction between 2-(N,N-dialkylamino)ethylchlorides and 2-(N,N-dialkylamino)ethanols (precursors/degradation products of VX agents) produces a new class of reaction products that are not explored. The reaction products, bis(2-N,N-dialkylaminoethyl)ethers (1-10), were synthesized using established synthetic procedures, and gas chromatography/mass spectrometry (GC/MS) (electron ionization [EI] and chemical ionization [CI]) methods were developed for their identification. The GC/MS experiments were performed on an Agilent GC/MSD system using an HP-5MS capillary column. Methane gas was used as the CI reagent gas for GC/CIMS experiments. GC/retention index (RI) values of 1-10 were calculated using the retention times of the hydrocarbon mixture and the analytes. The GC/EI spectra of 1-10 exhibited [M-H]+ ions and distinctive fragments that provided valuable structural information. The selective fragmentation of the alkyl groups on nitrogen facilitated the discrimination of possible isomeric compounds. Interpretation of EI fragments in the high mass region is important for unambiguous identification of 1-10, because the major ions significantly match other CWC-related compounds containing the 2-(N,N-dialkylaminoethyl) group. GC/CI (methane) spectra included M+., [M + H]+, [M-H]+, reagent-specific adduct ions, and a few structure-indicative fragments. The spiking experiments in soil and water samples revealed that the target analytes were stable, easily extractable, and detectable using GC/MS. The reaction products, 1-10, could be successfully synthesized and characterized using GC/MS (EI and CI). The GC/MS and GC/RI data provide important insights into the unambiguous identification of the target molecules in challenging CWC verification and are helpful in participation in the Organization for the Prohibition of Chemical Weapons proficiency tests.

Infrared spectroscopy of isomers of C3H4+ in superfluid helium droplets.

Superfluid helium nanodroplets are unique nanomatrices for the isolation and study of transient molecular species, such as radicals, carbenes, and ions. In this work, isomers of C3H4+ were produced upon electron ionization of propyne and allene molecules and interrogated via infrared spectroscopy inside He nanodroplet matrices. It was found that the spectrum of C3H4+ has at least three distinct groups of bands. The relative intensities of the bands depend on the precursor employed and its pickup pressure, which indicates the presence of at least three different isomers. Two isomers were identified as allene and propyne radical cations. The third isomer, which has several new bands in the range of 3100-3200cm-1, may be the elusive vinylmethylene H2C=CH-CH+ radical cation. The observed bands for the allene and propyne cations are in good agreement with the results of density functional theory calculations. However, there is only moderate agreement between the new bands and the theoretically calculated vinylmethylene spectrum, which indicates more work is necessary to unambiguously assign it.

Theoretical Study of Electron Capture, Excitation, and Ionization Processes in H+−H(2l) Collisions

The processes of single-electron charge exchange, excitation, and ionization during proton impact on H(2l) are investigated. We employ two different theoretical methods that are suitable for different collision energy regions: the full quantum-mechanical molecular orbital close-coupling method for energies from 0.001 to 1 keV u−1 and the two-center atomic orbital close-coupling (TC-AOCC) method for energies between 0.3 and 100 keV u−1. For charge exchange and excitation processes, the total and nl-resolved cross sections to the final reaction channels of H (nl, n = 1–4) have been obtained over a broad energy region. Moreover, the ionization cross sections in the TC-AOCC calculation are also reported for both H(2s) and H(2p) initial target states. The present results are all compared with those from other sources when available. It is found that the magnitude and energy behavior of nl-resolved excitation cross sections for H+–H(2p) collisions are significantly distinct from those of the H(2s) initial state in the entire energy range considered, particularly in the low-energy region. The energy behaviors of the nl-resolved charge exchange cross sections from the H(2p) initial state are similar to those from the H(2s) initial state, but their magnitudes are larger. The present accurate cross-section data are anticipated to provide insight into the research of astrophysics and controlled fusion plasmas.

A neutrino floor for the Migdal effect

Neutrino-nucleus scatterings in the detector could induce electron ionization signatures due to the Migdal effect. We derive prospects for a future detection of the Migdal effect via coherent elastic solar neutrino-nucleus scatterings in liquid xenon detectors, and discuss the irreducible background that it constitutes for the Migdal effect caused by light dark matter-nucleus scatterings. Furthermore, we explore the ionization signal induced by some neutrino electromagnetic and non-standard interactions on nuclei. In certain scenarios, we find a distinct peak on the ionization spectrum of xenon around 0.1 keV, in clear contrast to the Standard Model expectation.

Characterization and risk assessment of polycyclic aromatic hydrocarbons from the emission of different power generator

Epileptic power supply in Sub-Saharan countries of Africa has warranted the use of power generators as an alternative source of power supply. Exhaust emission from these generators is associated with Polycyclic Aromatic Hydrocarbon (PAHs). Hence, this study focused on the determination of levels of PAHs in the emission of different brands of power generators used in Nigeria. Exhaust emissions of different power generators were sampled using a filter-sorbent sampling system with polyurethane foam (PUF) as an adsorbent material. Analysis of PAHs was carried out using a Gas Chromatograph coupled to a mass selective detector (GC- MS) operated on Electron Ionization (EI) mode. The results showed the ∑ PAHs range 14.91–26.0 μgm−3. Bap was the most abundant of all the compounds with a concentration of 2.6 μgm−3 with a range of 2.08–3.07 μgm−3. The Incremental Life Cancer Risk (ILCR) values of all the generator's emission sampled are higher than 10− 4 for both children and adult which indicate a high potential cancer risk from inhalation of emission from these generators while Hazard Quotient (HQ) values from all the power generating set in this study are all above 1 which indicated high associated non-carcinogenic. The study revealed the levels of PAHs associated with the emission of power generators in Nigeria.

The inhibitor activity of some azo compound derivatives using density functional theory and molecular dynamics simulations

Corrosion poses a significant challenge for metals and alloys, carrying considerable economic and safety consequences. Various manufacturing processes, including surface preparation techniques, further exacerbate it. While corrosion inhibitors are employed to safeguard these materials from corrosion, they can also induce oxidative damage. This study aims to determine the corrosion inhibition efficiency of the specified materials. Density Functional Theory (DFT) and molecular dynamics simulations (MDS) were used to investigate the electronic characteristics of diverse compounds. The study included key parameters including highest occupied molecular orbital energy (EHOMO), lowest unoccupied molecular orbital energy (ELUMO), energy gap (Eg) between ELUMO and EHOMO, dipole moment, global hardness, softness (σ), ionization energy (I), electron affinity (A), electronegativity (χ), back-donation energy Eb-d, global electrophilicity (ω), electron transfer, global nucleophilicity (ε), and total energy (sum of electronic and zero-point energies). The calculations were executed utilizing the DFT method, employing a 6-311G++(d,p) basis set at the B3LYP level. Our research aimed to rank materials based on their effectiveness in inhibiting corrosion by considering EHOMO, ELUMO, and Eg. The order of effectiveness was found to be as follows: S4 > S3 > S1 > Mad1 > Mad3 > Mad4 > P-azo > Bad4. Additionally, our Investigation delved into alterations in electron affinity (A) and ionization potential (I) within different solvent phases, highlighting their importance in determining the chemical reactivity and stability of the studied compounds. The reactive sites were selected using Fukui indices, and the molecular electrostatic potential (MESP) surface was characterized—a Monte Carlo simulation to further understand these chemicals' adsorption behavior on Fe (110) surfaces. Our findings revealed that these compounds exhibit corrosion inhibition potential due to their high EHOMO, A, σ, ΔN, ΔE-back-donation, and low Eg, ELUMO, I, and η. Moreover, our MESP surface analysis demonstrated their ability to donate electrons to the metal's d-orbitals and receive electrons through back-donation. The compounds investigated in this study exhibit the potential to be employed as corrosion inhibitors in various industrial sectors. As a result, through the use and determination of quantum computational chemistry parameters, the level of corrosion resistance was as follows S3 > S1 > Bad4 > Mad4 > Mad3 > S4 > Mad1 > P-azo.

Essential oils from fennel plants as valuable chemical products: gas chromatography–mass spectrometry, FTIR, quantum mechanical investigation, and antifungal activity

AbstractIn the present study, the biomass produced by fennel plants (Foeniculum vulgare Mill.) was converted to yield bioactive chemicals, and the hydrodistillation method was used to extract the essential oils (EOs) from both the leaves and the umbels. The antifungal activity of the EOs was tested using bioassay against the development of Fusarium oxysporum MW854649 and Alternaria solani MT279570. Molecular spectroscopic detection techniques were used to evaluate the EO products using gas chromatography–mass spectrometer (GC–MS) and Fourier transform infrared spectroscopy (FTIR). GC–MS equipped with single quadruple analyzers have been used to measure the electron ionization (EI) mass spectra of the primary constituents of fennel EOs at 70 eV. The main chemical compounds in the EO from leaves were anethole, estragole, D-limonene, trans-β-ocimene, and fenchone, with percentages of 37.94, 35.56, 17.46, 1.53, and 1.49%, respectively. The abundant compounds in the EO from umbels were estragole, anethole, D-limonene, fenchone, and γ-terpinene, with percentages of 51.18, 25.08, 12.22, 6.57, and 2.86%, respectively. EI mass spectral fragmentation of the major compounds D-limonene, estragole, anethole, and fenchone has been investigated. Umbels and leaf EOs at 5000 mg/L displayed the strongest suppression of fungal growth against A. solani, with values of 87.78% and 79.63%, respectively, compared to the positive control (94.44%). The EOs from umbels and leaves at 5000 mg/L showed the highest inhibition of fungal growth against F. oxysprium as compared to the positive control (94.44%), with values of 77.77% and 72.96%, respectively. All of the important ions—including a few distinctive fragment ions—have comprehensive fragmentation pathways defined. Based on EI, the main routes of fragmentation for the primary compounds have been identified. The existence of alkenes, aliphatic alcohols, ethers, carboxylic acids, ester compounds, alkanes, hydrogen-bonded alcohols, and phenols was demonstrated by the FTIR analysis of fennel EOs. On the other hand, the reactive behavior of the studied molecules has been investigated using two quantum mechanics method: the modified neglect of diatomic overlap (MNDO), a semi-empirical method, and the density functional theory (DFT)/B3LYP hybrid density functional method with the 6-311G (d, p) basis set in the ground state for gas phase. The optimum geometries have been obtained through the execution of computations and electrostatic potential. The obtained analytical and calculated results were then used to understand the activity of the studied EOs in further medical applications.

Electron ionization mass spectrometry feature peak relationships combined with deep classification model to assist similarity algorithm for fast and accurate identification of compounds.

Gas chromatography-mass spectrometry (GC-MS) combines chromatography and MS, providing full play to the advantages of high separation efficiency of GC, strong qualitative ability of MS, and high sensitivity of detector. In GC-MS data processing, determining the experimental compounds is one of the most important analytical steps, which is usually realized by one-to-one similarity calculations between the experimental mass spectrum and the standard mass spectrum library. Although the accuracy of the algorithm has been improved in recent years, it is still difficult to distinguish structurally similar mass spectra, especially isomers. At the same time, the library capacity is very large and increasing every year, and the algorithm needs to perform large numbers of calculations with irrelevant compounds in the library to recognize unknown compounds, which leads to a significant reduction in efficiency. This work proposed to exclude a large number of irrelevant mass spectra by presearching, perform preliminary similarity calculations using similarity algorithms, and finally improve the accuracy of similarity calculations using deep classification models. The replica library of NIST17 is used as the query data, and the master library is used as the reference database. Compared with the traditional recognition algorithm, the preprocessing algorithm has reduced the time by 4.2h, and by adding the deep learning models 1 and 2 as the final determination, the recognition accuracy has been improved by 1.9% and 6.5%, respectively, based on the original algorithm. This method improves the recognition efficiency compared to conventional algorithms and at the same time has better recognition accuracy for structurally similar mass spectra and isomers.

Characteristic structures of liquid crystal monomers in EI-MS analysis and the potential application in suspect screening

Liquid crystal monomers (LCMs) are of emerging concern due to their ubiquitous presence in indoor and outdoor environments and their potential negative impacts on human health and ecosystems. Suspect screening approaches have been developed to monitor thousands of LCMs that could enter the environment, but an updated suspect list of LCMs is difficult to maintain given the rapid development of material innovations. To facilitate suspect screening for LCMs, in-silico mass fragmentation model and quantitative structure-activity relationship (QSPR) models were applied to predict electron ionization (EI) mass spectra of LCMs. The in-silico model showed limited predictive power for EI mass spectra, while the QSPR models trained with 437 published mass spectra of LCMs achieved an acceptable absolute error of 12 percentage points in predicting the relative intensity of the molecular ion, but failed to predict the mass-to-charge ratio of the base peak. A total of 41 characteristic structures were identified from an updated suspect list of 1606 LCMs. Multi-phenyl groups form the rigid cores of 85% of LCMs and produce 154 characteristic peaks in EI mass spectra. Monitoring the characteristic structures and fragments of LCMs may help identify new LCMs with the same rigid cores as those in the suspect list.