Electron Impact Ion Source Research Articles

Energy-Resolving Time-of-Flight Mass Spectrometry for Bulk Plasma Analysis.

This work presents a newly designed energy-resolving time-of-flight mass spectrometer (E-TOFMS) for analysing the energy and mass of ions in bulk plasma. The system comprises an electrostatic sector analyser (ESA) for energy-to-charge (E/Q) ratio resolution and an orthogonal reflectron TOFMS for mass-to-charge (m/Q) ratio analysis. The design choices are explained, providing insight into electron and ion path simulations. The instrument was characterised using various ion generation sources, including an electron impact ion source, high power impulse magnetron sputtering, and microwave plasma electron cyclotron resonance sources. To validate its functionality, the energy-resolving data was compared with data obtained under the same conditions using a Langmuir probe and a retarding field energy analyser (RFEA). The benefits of the proposed E-TOFMS were demonstrated by sputtering highly alloyed steel with multiple isotope-rich elements, such as Mo or W. This technique offers an E/Q ratio resolution of up to 0.15 V for a range up to 125 V and a m/Q ratio resolution of at least 700 Th for a range up to 250 Th, with a temporal resolution of 10 μs.

Propagation of nanosecond discharge in an air gap containing a water droplet: modelling and comparison with time-resolved images

The plasma-water interface is a complex medium characterized by interesting physical and chemical phenomena useful for many applications such as water processing or material synthesis. In this context, optimizing the transport of reactive species from plasma to water is crucial, and it may be achieved by increasing the surface-to-volume ratio of the processed object. Herein, we study the characteristics of a streamer produced by nanosecond discharge in air gap with a droplet of deionized water. The discharge is characterized experimentally by electrical measurements as well as by 1 ns-intergated ICCD images. To report plasma properties that are not accessible through experiment, such as the spatio-temporal evolution of electron density, electric field, and space charge density, a 2D fluid model is developed and adapted to the experimental geometry. Due to the fast propagation of the ionization front, the droplet is considered as a solid dielectric. The model solves Poisson’s equation as well as the drift-diffusion equation for electrons, positive ions, and negative ions. The utilized transport coefficients are tabulated as a function of the reduced electric field. Helmholtz equations are also included in the model to account for photoionization. The electron impact ionization source obtained from the model is compared to experimental 1 ns-integrated ICCD images, and a good agreement is observed. Finally, the model is used to investigate the influence of droplet dielectric permittivity and wetting angle (the angle between a liquid surface and a solid surface) on the properties of the discharge. Overall, the data reported herein demonstrate that the model can be used to investigate plasma properties under different conditions.

FEBIAD ionization development via a web-app for multidimensional characterization

The ISAC-FEBIAD is an electron impact ion source typically used to ionize radioactive molecules or isotopes of elements beyond the reach of either surface or laser ion sources. The FEBIAD’s key tuning parameters are the cathode temperature defining the number of electrons created; the anode voltage establishing the electron energy; and the magnetic field controlling the electron density inside the anode volume. However, these parameters are typically scanned in a small and limited range when optimizing the source. Recent investigations have shown the need to explore the entire range of operational values accessible by the power supplies, not only due to the intrinsic variations from source to source but also to operate the source at optimal settings. To address this, a scanning algorithm has been implemented as a web interface thanks to the High-Level-Application (HLA) infrastructure available at TRIUMF. The ion beam intensity during both offline and online commissioning of the web app are presented here as contour plots. The optimal settings found for stable 20Ne are confirmed as the optimal settings for radioactive 18Ne. The main takeaway, however, is that the optimal ion source parameters differ between singly-charged, doubly-charged, and molecular species. This development demonstrate and facilitate the need for element and charge state-specific parameter optimization. Additionally, the results highlight the possibility of parameter optimization to enhance the ratio of the species of interest to co-ionized contamination.

Rapid determination of 15 N-nitrosamines in air-dried yak meat using one-step QuEChERS-gas chromatography-triple quadrupole mass spectrometry

A method based on gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) coupled with one-step QuEChERS technique was developed for the simultaneous determination of 15 N-nitrosamines in air-dried yak meat. The hydration volume, extraction solvent, extracting salt, and cleaning material were optimized according to the characteristics of the N-nitrosamines and sample matrix. The optimized conditions were as follows: 10 mL of purified water for sample hydration, acetonitrile as the extraction solvent for the sample after hydration, 4.0 g of anhydrous MgSO4 and 1.0 g of NaCl as extracting salts, 500 mg of MgSO4+25 mg of C18+50 mg of PSA as cleaning materials. Favorable recoveries of the 15 N-nitrosamines were obtained when the extraction solution was incompletely dried. Thus, the final extract was dried to below 0.5 mL under a mild nitrogen stream and then redissolved to 0.5 mL with acetonitrile. After filtration, 200 μL of the sample was transferred to an autosampler vial for GC-MS/MS analysis. The 15 N-nitrosamines were determined using GC-MS/MS on a DB-HeavyWAX column (30 m×0.25 mm×0.25 μm) with an electron impact ion source in multiple-reaction monitoring (MRM) mode, and quantified using an external standard method. Under the optimized experimental conditions, the results showed that the calibration curves exhibited good linearities for the 15 N-nitrosamines, with correlation coefficients (r2) greater than 0.9990. The limits of detection (LODs) and the limits of quantification (LOQs) ranged from 0.05 to 0.20 μg/kg and from 0.10 to 0.50 μg/kg, respectively. At spiked levels of 1LOQ, 2LOQ, and 10LOQ, the average recoveries were 79.4%-102.1%, 80.6%-109.5%, and 83.0%-110.6%, respectively, and the relative standard deviations were in the range of 0.8%-16.0%. The low matrix effects of the 15 N-nitrosamines indicated the high sensitivity of the proposed method. The method was applied to detect representative commercial air-dried yak meat samples obtained using different processing techniques. Seven N-nitrosamines, including N-nitrosodimethylamine, N-nitrosodiisobutylamine, N-nitrosodibutylamine, N-methyl-N-phenylnitrous amide, N-ethyl-N-nitrosoaniline, N-nitrosopyrrolidine, and N-nitrosodiphenylamine were detected in all samples. The average contents of the seven N-nitrosamines was 0.08-20.18 μg/kg. The detection rates and average contents of the N-nitrosamines in cooked air-dried yak meat samples were higher than those in traditional raw air-dried yak meat samples. Compared with the manual QuEChERS method, the one-step QuEChERS method developed integrated the extraction and clean-up procedures into one single run, and the detection efficiency was considerably improved. The developed method is simple, rapid, highly sensitive, and insusceptible to human errors. Thus, it is useful for the determination of N-nitrosamines in air-dried yak meat and can be extended to the qualitative and quantitative analysis of N-nitrosamines in other meat products. It also provides method support and a data reference for the general determination of N-nitrosamines, which is of great significance for food safety.

A 22-pole radiofrequency ion trap setup for laboratory astrophysical studies.

The formation of large interstellar molecules starting from small reactants constitutes the bottom-up approach in astrochemistry. An experimental setup wherein the ionic reactant is prepared and allowed to react with neutral reactants within a confined interaction space is most desirable for this approach. Here, we present our efforts in constructing a 22-pole radio-frequency ion trap experimental setup that could act as a reaction chamber for the neutral reactant and trapped ions. A compact piezo-based pulsed supersonic expansion discharge source was developed to achieve efficient production of anions, particularly metal-bearing ions. In addition, two other ion sources, namely, the electron impact ion source and the plasma supersonic discharge ion source, were developed to cater to the production of specific ions. The geometry of this experimental setup facilitates photo excitation of trapped ions. The trapping efficiency was studied by trapping SF5+ and SF6- for a few seconds. The control exhibited by various parameters on the efficiency of the trapping is discussed in detail. Potential studies that could be performed with this new experimental setup are also discussed.

Determination of 15 preservative allergens in cosmetics by gas chromatography-tandem mass spectrometry

Most preservatives are irritating and can easily induce skin sensitivities. Therefore, both domestic and international regulations impose clear restrictions on the use of preservatives in cosmetics. Herein, gas chromatography-tandem mass spectrometry (GC-MS/MS) was employed to simultaneously analyze the levels of 15 preservative allergens in cosmetics. Further, a precise identification approach based on a two-column retention index and mass spectrometry matching degree was developed. Cosmetic samples were extracted via acetonitrile vortex ultrasound extraction and then dehydrated with anhydrous MgSO4. The preservative allergens were separated on two columns, namely, DB-5MS and DB-WAX. Targets were identified using electron impact ionization (EI) source and the multiple reaction monitoring (MRM) mode and characterized using a retention index calibrated by a series of n-alkane standards. Following two tests, the LODs for the 15 preservative allergens on the DB-5MS column were in the range of 0.02-0.2 mg/kg, while those for 12 preservative allergens on the DB-WAX column were in the range of 0.01-20 mg/kg. The preservative allergens on the DB-5MS and DB-WAX columns demonstrated strong correlations, with all correlation coefficients exceeding 0.99. The recoveries for the 15 preservative allergens were in the range of 70.1%-129.8% at low, medium, and high levels, and the relative standard deviations (RSDs) were all below 15% (n=6) when using water, lotion, facial mask, and cream as the representative matrix. Next, 80 batches of genuine samples were tested using the established method. Isopropyl 4-hydroxybenzoate, a prohibited preservative, was detected in two sample batches using the DB-5MS and DB-WAX columns. Additionally, 11 and 10 restricted preservative allergens were identified on the DB-5MS and DB-WAX columns, respectively. The test results indicate that the double-column system approach offers excellent accuracy, effectively preventing false-positive and false-negative results, and can detect the 15 preservative allergens in cosmetics. The use of the retention index for the qualitative detection of these preservative allergens offers valuable options for non-targeted screening and meeting regulatory criteria.

METHOD DEVELOPMENT AND VALIDATION OF DIMETHYL SULPHATE CONTENT IN ESOMEPRAZOLE MAGNESIUM DRUG SUBSTANCE BY GC-MS

Dimethyl sulfate is universally used as an alkylating, sulfating and sulfonating agent in organic synthesis; hence it is one of the probable impurities during the synthesis of the esomeprazole magnesium. As per ICH M7, it is genotoxic and mutagenic, so it needs to be controlled as per the acceptable intake of dimethyl sulfate and daily sample dosage. This method validation can be achieved by the hyphenated technique of gas chromatography with mass spectroscopy, which is used to develop the dimethyl sulfate impurity in esomeprazole magnesium drug substance containing salt. The method is achieved with a DB-1 column with electron impact ionization source in sim mode ion under electronic pneumatic pressure control and deliberate oven ramp programming temperature was used. A dissolved, extracted and auto-injection sample was implemented for sample introduction in a splitless mode. Dichloromethane and 2N NaOH was used as a diluent. The calibration curve showed good linearity over the 1.69 to 8.40 ppm (limit: 5.56 ppm) and its correlation coefficient was >0.999. A limit of detection 0.50 ppm and limit of quantitation 1.69 ppm was achieved when the samples were prepared at 50 mg/mL. While recovery proved to be 106.8 to 113.5%, hence it signified the matrix effect.

Design and construction of electron impact ion source controller for Mass spectrometer system

قدرت تفکیک دستگاه طیف‌نگار جرمی به صورت مستقیم به شدت یون خروجی و انرژی آن بستگی دارد. مقدار یون تولید شده به جریان و انرژی باریکه الکترونی وابسته است. از جمله وظایف مدار کنترل چشمه برخورد الکترونی تنظیم جریان و انرژی باریکه الکترونی برای رسیدن به قدرت تفکیک بهینه می‌باشد. در ساخت مدار کنترل چشمه برخورد الکترونی پارامترهایی نظیر تثبیت جریان باریکه الکترونی و انرژی آن، تنظیم دقیق پتانسل الکتریکی لنز و الکترودهای چشمه یونی بسیار حایز اهمیت می‌باشد. در این مقاله مدار کنترل چشمه یونی با قابلیت تنظیم و تثبیت دقیق جریان انتشار الکترون، انرژی باریکه و پتانسیل الکتریکی نقاط طراحی و ساخته شد. این مدار کنترلر بر روی دستگاه طیف نگار جرمی 44Varian MAT نصب و مورد آزمایش قرار گرفت. مدار کنترل ساخته شده قادر به تثبیت جریان و انرژی الکترون بهتر از %1 می‌باشد.

Ionization wave propagation of a surface dielectric barrier discharge with a flexible-structure plasma sheet

Plasma sources based on flexible substrates are receiving attention due to their unique adaptability to irregular surfaces and large range of plasma coverage, which endows them with irreplaceable advantages in the fields of material processing and biomedical treatment. Numerous studies have been carried out focusing on the application effects of these flexible plasma sources, while their surface discharge characteristics and mechanisms still lack revelation. In this work, a flexible plasma sheet with a surface dielectric barrier discharge structure is realized via a printed circuit board, and its multiple surface ionization wave (SIW) propagation on curved gas–solid interfaces is studied via experiments and 2D fluid simulation models. Qualitative agreement is achieved between the experiments and simulations. It is found that a positive and a negative discharge are generated at the rising and falling edges of the excitation pulse, respectively. In the positive discharge, SIWs originate at the grounded mesh edge and then propagate to the center in a petal-like pattern, which is shaped by the space electric field. Controlled by electron collision reactions, the development of the excited states of N2 and O2 molecules is similar to that of electrons. In the negative discharge, electrons dissipate and no SIW is generated. The evolution of heavy particles shows differences in this period, which is attributed to the disparate rate coefficients of their consumption reactions. Further study shows that when the plasma sheet changes from convex to concave, the electron density and electron temperature above its surface increase, but the petal patterns of the SIW propagation have no variation. The electron density, electron temperature, and electron impact ionization source will rise as a result of the increasing pulse amplitude or the decreasing duration of the pulse rising edge.

Structural confirmation of synthetic cannabinoids in seized electronic cigarette oil: A combined mass spectrometric and computational study.

Synthetic cannabinoids are some of the most used and abused new psychoactive substances, because they can produce a stronger intense pleasure than natural cannabis. Most of the new synthetic cannabinoids are structurally similar to existing synthetic cannabinoids and can be obtained by modifying partial structures of the latter without changing their effects. Therefore, the derivatization rules and common fragmentation patterns of synthetic cannabinoids could be used for rapid screening and structural identification of them. The derivatization rules of synthetic cannabinoids are summarized, and the common fragmentation pattern of synthetic cannabinoids including three typical cleavage pathways was explored and extended in this work based on combined mass spectrometry (MS) and density functional theory studies. Five synthetic cannabinoids in electronic cigarette oil from a drug case were separated and characterized using gas chromatography with MS and liquid chromatography coupled to high-resolution quadrupole Orbitrap MS. The structures of five synthetic cannabinoids in seized electronic cigarette oil were deduced from electron impact ion source (EI) MS and high-resolution electrospray ionization (ESI) MSn data, along with the derivatization rules and common fragmentation pattern of synthetic cannabinoids. The proposed structures of these synthetic cannabinoids were further verified via reference substances. Computational study showed that selective cleavage of these compounds was mainly controlled by spin population in EI-MS, but a tunneling effect arose from proton transfer in ESI-MSn detection, which has been rarely reported in previous works. Our results showed that EI-MS was suitable for identifying synthetic cannabinoids with aromatic ketone structure, which could also be extended to adamantane linked group. Nevertheless, synthetic cannabinoids with carbamoyl linked group were better characterized by high-resolution ESI-MSn compared to EI-MS. This study demonstrated a method with promising potential for rapid and reliable screening of synthetic cannabinoids in mixtures with enhanced detection throughput and operation simplicity.

Identification and quantification of IEPOX in ambient aerosols, using electron and chemical ionization sources GC/MS as their trimethylsilyl ethers, and using H-NMR

Isoprene is the most abundant non-methane hydrocarbon (NMHC) emitted by vegetation, and the precursor that makes the greatest contribution to secondary organic aerosols (SOA) in the troposphere. Atmospheric oxidation of isoprene produces a series of reactive intermediates, isoprene epoxydiols (IEPOX). The reactive uptake of IEPOX is the significant formation pathway of atmospheric SOA. In this work, four isomers of IEPOX were synthesized, derivatized by silylation reagents, and measured by gas chromatography/mass spectrometry (GC/MS). The electron-impact (EI) and methane chemical ionization (CI) sources mass spectra of trimethylsilyl ester (TMS) derivatives of IEPOX isomers were obtained and the fragmentation behaviors of the derivatives were examined. Moreover, the hydrogen nuclear magnetic resonance (H-NMR) spectra of IEPOX isomers were also obtained and the peak intensities in the H-NMR spectra were analyzed. Based on the standard spectra, IEPOX isomers were identified in ambient PM2.5 aerosols in the Gongga Mountain (China). The peak sequence of TMS derivatives of IEPOX isomers in GC/MS chromatogram was δ4-IEPOX, δ1-IEPOX, cis-β-IEPOX and trans-β-IEPOX. The isomers with the highest concentrations were δ1-IEPOX (threo- and erythro-). The mass ratios of IEPOX to 2-methyltetrols were 0.02–6.0 and the concentrations of IEPOX were 0.8–41.6 ng/m3 in the PM2.5 aerosols. The current study verified the core roles of IEPOX as active intermediates in photo oxidation of isoprene in ambient atmosphere.

Characteristics and health risk assessment of volatile N-nitrosamines in the plasma of adults in Guangdong Province, China

N-nitrosamines are strong carcinogens that are widely present in the environment. This study developed a method, and analyzed the concentrations of volatile N-nitrosamines (VNAs) in the plasma of adults in Guangdong Province, China. Finally, the health risks to adults in Guangdong Province, China, with dietary exposure to VNAs were assessed. Gas chromatography/mass spectrometry (GC/MS) in electron impact (EI) ionization source mode was used to quantitatively analyze VNAs, and to perform accurate mass determination. The lower limit of detection (LOD) of nine nitrosamines are ranged from 0.01 to 2.14 ng/mL. The recovery rate ranged from 83 % to 116 %, and the relative standard deviation (RSD) was < 10 %. The method developed is simple, rapid, and provides good reproducibility and high sensitivity. N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), N-nitrosodinbutylamine (NDBA), N-nitrosopiperidine (NPIP), N-nitrosopyrrolidine (NPYR), N-nitrosomorpholine (NMOR) and N-nitrosodiphenylamine (NDPhA) were detected in 92 adult plasma samples. NDMA and NMEA were detected in 56.5 % and 44.6 % of the samples, followed by NPIP (34.8 %). NDMA had the highest median concentration (43.7 ng/mL) in the total samples. There were gender-related differences found in the concentrations of NDBA and NDPhA. The exposure risk assessment results showed that the two highest daily dietary intakes of VNAs were N-nitrosodi-n-propylamine (NDPA) and NDMA, and aquatic products and pickled vegetables contributed the most total nitrosamine intake. The lifetime cancer risk of adults ranged from 2.88 × 10−10 to 7.46 × 10−5, and the risk associated with NDMA, NDPA, N-nitrosodiethylamine (NDEA), NMEA and NPIP are important and should attract more attention. This study aimed to explore the exposure levels of VNAs in the plasma of adults in Guangdong Province, China, and to assess the health risks of dietary intake of VNAs, which provides a basis of the effect of VNAs exposure on human health.

Simultaneous Quantification of Opioids in Blood and Urine by Gas Chromatography-Mass Spectrometer with Modified Dispersive Solid-Phase Extraction Technique.

Common methodologies such as liquid-liquid extraction and solid-phase extraction are applied for the extraction of opioids from biological specimens i.e., blood and urine. Techniques including LC-MS/LC-MSMS, GC-MS, etc. are used for qualitative or quantitative determination of opioids. The goal of the present work is to design a green, economic, rugged, and simple extraction technique for famous opioids in human blood and urine and their simultaneous quantification by GC-MS equipped with an inert plus electron impact (EI) ionization source at SIM mode to produce reproducible and efficient results. Morphine, codeine, 6-acetylmorphine, nalbuphine, tramadol and dextromethorphan were selected as target opioids. Anhydrous Epsom salt was applied for dSPE of opioids from blood and urine into acetonitrile extraction solvent with the addition of sodium phosphate buffer (pH 6) and n-hexane was added to remove non-polar interfering species from samples. BSTFA was used as a derivatizing agent for GC-MS. Following method validation, the LOD/LLOQ and ULOQ were determined for morphine, codeine, nal-buphine, tramadol, and dextromethorphan at 10 ng/mL and 1500 ng/mL, respectively, while the LOD/LLOQ and ULOQ were determined for 6-acetylmorphine at 5 ng/mL and 150 ng/mL, respectively. This method was applied to real blood and urine samples of opioid abusers and the results were found to be reproducible with true quantification.

Development of an electron impact ion source with high ionization efficiency for future planetary missions

Ion sources using electron impact ionization (EI) methods have been widely accepted in mass spectrometry for planetary exploration missions because of their simplicity. Previous space-borne mass spectrometers were primarily designed with the EI method using rhenium tungsten alloy filaments, enabling up to 200 uA emission in typical cases. The emission level is desired to be enhanced because the sensitivity of mass spectrometers is a critical requirement for the future in situ mass spectrometry related to the measurement of trace components in planetary samples. In this study, we developed a new high-emission EI ion source using a Y2O3-coated iridium filament, which has a lower work function than rhenium tungsten alloy. The size of the ion source was 30 mm * 26 mm * 70 mm, and its weight was 70 g. We confirmed that when consuming 3.0 W power, the ion source emits more than 2 mA electrons, which is 10 times greater than the previous models electron emission level. Ionization efficiency of the EI ion source is proportional to the amount of electron emission, which implies our new model increased the ionization efficiency 10 times. We conducted performance tests on the prototype with the 3.0 W heating condition, confirming a high ionization efficiency (10^4 nA/Pa). In addition, we conducted endurance tests of the ion source and demonstrated the persistence of the ionization efficiency for 30 min * 100 cycles.

Fentanyl pharmacokinetics in blood of cancer patients by Gas Chromatography – Mass Spectrometry

In order to find a correlation between Fentanyl action on pain and inter-individual variability in different cancer patients, the pharmacokinetic characterization of the drug becomes essential. Therefore, a gas chromatographic–mass spectrometric (GC–MS) in SIM mode analytical procedure has been developed and validated for the determination of Fentanyl in human blood. The sample preparation consisted of a liquid-liquid extraction (LLE) from whole blood. The analysis were carried out with Agilent 7820 A series gas chromatograph equipped with a 5977E series mass selective single quadrupole detector (MSD) with an electron impact (EI) source (70 eV), under a temperature gradient elution. The limit of detection (LoD) and the limit of quantification (LoQ) values were found to be 5.60E-02 ± 3.50E-02 ng mL−1 and 1.86E-01 ± 1.18E-01 ng mL−1 respectively. The developed method was found selective and sensitive and therefore suitable for a fast determination of Fentanyl in human blood and for its pharmacokinetic characterization. Blood samples from 31 cancer patients treated with transdermal Fentanyl (doses in the range of 12–100 µg h−1) were collected at fixed intervals during an overall exposure time of 72 h. The analysis of data and the pharmacokinetic parameters revealed dissimilar pharmacokinetic profiles in the patients examined. Patients were therefore grouped in three categories representing the different trends observed: high, medium and slow responders. These preliminary data provided significant outcomes for a correlation to clinical response.

Machine Learning-Based Retention Time Prediction of Trimethylsilyl Derivatives of Metabolites.

In gas chromatography–mass spectrometry-based untargeted metabolomics, metabolites are identified by comparing mass spectra and chromatographic retention time with reference databases or standard materials. In that sense, machine learning has been used to predict the retention time of metabolites lacking reference data. However, the retention time prediction of trimethylsilyl derivatives of metabolites, typically analyzed in untargeted metabolomics using gas chromatography, has been poorly explored. Here, we provide a rationalized framework for machine learning-based retention time prediction of trimethylsilyl derivatives of metabolites in gas chromatography. We compared different machine learning paradigms, in addition to exploring the influence of the computational molecular structure representation to train the prediction models: fingerprint class and fingerprint calculation software. Our study challenged predicted retention time when using chemical ionization and electron impact ionization sources in simulated and real cases, demonstrating a good correct identity ranking capability by machine learning, despite observing a limited false identity filtering power in cases where a spectrum or a monoisotopic mass match to multiple candidates. Specifically, machine learning prediction yielded median absolute and relative retention index (relative retention time) errors of 37.1 retention index units and 2%, respectively. In addition, fingerprint class and fingerprint calculation software, as well as the molecular structural similarity between the training and test or real case sets, showed to be critical modulators of the prediction performance. Finally, we leveraged the structural similarity between the training and test or real case set to determine the probability that the prediction error is below a specific threshold. Overall, our study demonstrates that predicted retention time can provide insights into the true structure of unknown metabolites by ranking from the most to the least plausible molecular identity, and sets the guidelines to assess the confidence in metabolite identification using predicted retention time data.

A cold electron-impact ion source driven by a photo-cathode – New opportunities for the delivery of radioactive molecular beams?

The thick-target ISOL (Isotope mass Separation OnLine) method provides beams of more than 1000 radionuclides of 74 elements. The method is well established for elements with sufficiently high volatility at ca. 2000 °C. To extract non-volatile elements the formation of a volatile molecule is required. While successful in some cases (e.g. carbon or boron), most of these elements are not yet available as ISOL beam. A variety of volatile carrier molecules has been proposed for all elements produced in the target material, but their probability of survival during the extraction and ionization process is often limited by the high temperatures required for isotope diffusion in the thick targets and for ion source operation. While cold target concepts have already been proposed, the normal mode of operation of the typically used Versatile Arc Discharge Ion Source (VADIS) with a hot cathode is not well suited. Here, we report about first measurements with an electron-impact ion source operated at ambient temperature using electrons that were liberated via the photo-electric effect from a copper cathode.

Characteristic studies on positive and negative streamers of double-sided pulsed surface dielectric barrier discharge

The mechanisms of streamer generation and propagation in double-sided pulsed surface dielectric barrier discharge (SDBD) on both sides have been analyzed and investigated by experiment and numerical simulation. The fully exposed asymmetric SDBD has two discharge processes located on the high voltage electrode (HVE) side and the ground electrode (GE) side. Discharge images of the HVE side and GE side are taken by a digital camera under continuous pulse and ICCD (Intensified Charge Coupled Device) is utilized to diagnose the generation and propagation of streamers in single pulse discharge. In order to understand the physical mechanisms of streamer evolution more deeply, we establish a 2D simulation model and analyze it from the aspects of electron density, ion density, reduced electric field and electron impact ionization source term. The results show that the primary and secondary discharges on the HVE side and the GE side of the double-sided SDBD are composed of positive streamer and negative streamer, respectively. On the HVE side, the accumulation of positive charges on the dielectric surface causes the direction of the electric field to reverse, which is the principal factor for the polarity reversal of the streamer. On the GE side, both the negative charges accumulated on the dielectric surface and the falling voltage are the key factors for the streamer polarity switch.

Selective molecular characterization of olefins in hydrocarbon mixtures by Ag+ complexation ESI high-resolution mass spectrometry

Molecular characterization of olefins in the complex hydrocarbon mixture is of vital importance for the various hydrocarbon upgrading processes. According to the strong interaction of Ag+ with unsaturated hydrocarbon, Ag+ complexation was adopted in this study as a tool to achieve selective olefin ionization in electrospray ionization (ESI). High-resolution mass spectrometry (HR MS) was used to characterize ionized olefin molecular composition. Various model compounds, including paraffins, naphthenes, olefins, and aromatics, were used to verify the ionization selectivity. The observed olefin carbon number distribution from Ag+ complexation ESI HR MS was in agreement with those from gas chromatography-mass spectrometry equipped with the electron impact ion source (GC-EI-MS). The proposed method can be conveniently used for direct molecular characterization of olefins in mixtures without time-consuming olefin pre-separation or chemical derivatization. Olefins in coker diesel, coal tar liquid, and Fischer-Tropsch wax were successfully analyzed by the proposed method.

Simultaneous determination of monochloropropanediol esters and glycidyl esters in vegetable oils by acidic transesterification-gas chromatography-mass spectrometry

建立了一种气相色谱-质谱同时测定植物油中3-氯丙二醇酯、2-氯丙二醇酯和缩水甘油酯的方法。称取0.25 g样品,依次加入内标工作液、四氢呋喃和酸性溴化钠溶液,50 ℃水浴反应15 min,加入6 g/L碳酸氢钠溶液终止反应,使用正己烷提取,上层液经氮气吹干后用四氢呋喃溶解。随后加入1.8%(v/v)硫酸-甲醇溶液于40 ℃恒温水浴中反应16 h,加入饱和碳酸氢钠溶液终止反应。样液再经过净化、衍生、提取、氮吹后,以1 mL正己烷定容,过膜,进样测定。采用毛细管气相色谱柱DB-5MS(30 m×0.25 mm×1 μm)分离,程序升温,电子轰击电离(EI)源检测,在选择离子扫描模式下,以保留时间和特征离子信息进行定性分析,内标法定量。结果表明,3-氯丙二醇酯、2-氯丙二醇酯和缩水甘油酯在0.01~0.80 mg/L范围内线性关系良好,相关系数(r2)均在0.999以上,方法的检出限(S/N=3)和定量限(S/N=10)分别为25、25、20 μg/kg和75、75、60 μg/kg。选取4种不同基质类型的样品,在低、中、高3个不同添加水平下的平均回收率为89.0%~98.7%,相对标准偏差(RSD)在2.05%~7.81%之间。采用该方法测定了市售112份植物油样本,其中有84份样本检出3-氯丙二醇酯、2-氯丙二醇酯和缩水甘油酯。与已建立的国家标准方法(GB 5009.191-2016)和行业标准方法(SN/T 5220-2019)相比,该方法所采用的酸性酯交换法可避免副反应(碱性条件下3-氯丙二醇、2-氯丙二醇及3-溴丙二醇向游离态缩水甘油转化)的发生,同时该方法也弥补了国家标准和行业标准无法对3-氯丙二醇酯、2-氯丙二醇酯和缩水甘油酯同时进行测定的缺失。该方法实验操作更高效,结果更准确、重复性更好,对我国植物油中3-氯丙二醇酯、2-氯丙二醇酯和缩水甘油酯污染水平的控制、检测标准的制定和生产工艺的优化具有一定的理论和现实意义。