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Per- and polyfluoroalkyl substances (PFAS) are used in food contact materials (FCMs), e.g. as production aids in the fabrication of PTFE based coatings for kitchenware or as additives in paper and board. Growing concerns about the environment and health related to PFAS have led to an increasing interest in monitoring PFAS levels in FCMs as well as their migration into food. In this study, method development for the analysis of PFAS by thermal desorption – gas chromatography – mass spectrometry (TD-GC-MS) was done. In addition to fluorotelomer alcohols (FTOHs), which are the only PFAS commonly analysed by GC-MS, it was proven that perfluorocarboxylic acids (PFCAs) and per- and polyfluoroether carboxylic acids (PFECAs) as well as their thermolysis products, perfluoroethers (PFEs) and perfluoroalkenes, can be analysed by GC-MS without prior derivatization. Screening for PFCAs and FTOHs was possible by electron impact ionization (EI) using group specific SIM fragments. Confirmation of identity has been done by EI scans as well as chemical ionization (CI) SIM measurements. LODs (limits of detection) of PFCAs, FTOHs and PFECAs in the TD-GC-MS instrument were in the low pg range. Thermal degradation of PFCAs and PFECAs during TD-GC-MS measurement was investigated. [ABSTRACT FROM AUTHOR]

The Earth's atmosphere is composed of an enormous variety of chemical species associated with trace gases and aerosol particles whose composition and chemistry have critical impacts on the Earth's climate, air quality, and human health. Mass spectrometry analysis as a powerful and popular analytical technique has been widely developed and applied in atmospheric chemistry for decades. Mass spectrometry allows for effective detection, identification, and quantification of a broad range of organic and inorganic chemical species with high sensitivity and resolution. In this review, we summarize recently developed mass spectrometry techniques, methods, and applications in atmospheric chemistry research in the past several years on molecular‐level. Specifically, new developments of ion‐molecule reactors, various soft ionization methods, and unique coupling with separation techniques are highlighted. The new mass spectrometry applications in laboratory studies and field measurements focused on improving the detection limits for traditional and emerging volatile organic compounds, characterizing multiphase highly oxygenated molecules, and monitoring particle bulk and surface compositions. [ABSTRACT FROM AUTHOR]

Chloroformates are prevalent in the atmosphere due to their utilization as fuel additives and industrial solvents. These species may undergo interactions with atmospheric water resulting in protonated chloroformates. This study delves into the gas‐phase dissociation of these protonated species. Tandem mass spectrometry was employed to scrutinize the unimolecular dissociation of protonated methyl (1), ethyl (2), neopentyl (3), and phenyl chloroformate (4). Notably, 1 and 4 exhibited HCl loss, yielding CH3OCO+ and C6H5OCO+, respectively, with 1 additionally generating neutral methanol and ClCO+. 4 additionally loses CO and CO2. In contrast, 2 and 3 each only exhibit a single fragmentation channel, with 2 losing C2H4 to generate protonated chloroformic acid and 3 generating protonated 2‐methylbutene by losing neutral chloroformic acid. Density functional theory at the B3LYP/6‐311+G(d,p) level of theory was employed to explore minimum energy reaction pathways for each ion, and CBS‐QB3 single‐point energy calculations were added to provide reliable energetics. The Rice–Ramsperger–Kassel–Marcus (RRKM) calculations of the rate constants for selected competing processes were carried out to link theory and experiment. One common unimolecular process observed was the 1,3‐H shift of the proton from the carbonyl oxygen to the ester oxygen before dissociation. [ABSTRACT FROM AUTHOR]

Gas chromatography-mass spectrometry (GC-MS) usually employs hard electron ionization, leading to extensive fragmentations that are suitable to identify compounds based on library matches. However, such spectra are less useful to structurally characterize unknown compounds that are absent from libraries, due to the lack of readily recognizable molecular ion species. We tested methane chemical ionization on 369 trimethylsilylated (TMS) derivatized metabolites using a quadrupole time-of-flight detector (QTOF). We developed an algorithm to automatically detect molecular ion species and tested SIRIUS software on how accurate the determination of molecular formulas was. The automatic workflow correctly recognized 289 (84%) of all 345 detected derivatized standards. Specifically, strong [M - CH3]+ fragments were observed in 290 of 345 derivatized chemicals, which enabled the automatic recognition of molecular adduct patterns. Using Sirius software, correct elemental formulas were retrieved in 87% of cases within the top three hits. When investigating the cases for which the automatic pattern analysis failed, we found that several metabolites showed a previously unknown [M + TMS]+ adduct formed by rearrangement. Methane chemical ionization with GC-QTOF mass spectrometry is a suitable avenue to identify molecular formulas for abundant unknown peaks.

The microsynthesis of 32 dialkyl derivatives of ethylphosphonic acid and the same number of monoalkyl derivatives was carried out to perform comparative studies using gas chromatography combined with mass spectrometry in chemical ionization mode which is one of the analytical techniques recommended by the Organisation for the Prohibition of Chemical Weapons (OPCW). The huge number of possible representatives makes it difficult to have complete spectral libraries of all substances in this class. Therefore, we decided to synthesize and instrumentally analyze only representatives of the selected series of homologues in this work. The analysis of the obtained results allowed us to find the rules for predicting mass spectra and the factors determining the retention parameters. Symmetrical diesters and monoesters of ethylphosphonic acid were selected for this study. During the conducted experiments using chemical ionization with methane as the reaction gas, protonated analyte molecules with high relative intensities were obtained; in many cases, these are base peaks in the spectrum. The obtained results allow grouping of the synthesized compounds depending on the introduced alkyl substituent. Retention data of the tested analytes were collected during the research by using electron ionization. The retention parameters of the tested compounds from each homologous series were also summarized and compared. Chemical Warfare Agents (CWA) analysis continues to be an important issue, especially in the context of the regular Proficiency Tests organized by the OPCW for identifying chemical compounds that are of interest to the Chemical Weapons Convention. Five compounds were synthesized whose spectra were not available in EI mass spectral libraries, and their retention indices were unknown. The identification of these substances was supported by the CI mass spectra and retention data, using previously developed relationships. Therefore, it is reasonable to conclude that the research method used is useful and effective. [ABSTRACT FROM AUTHOR]

Discrimination of aromatic positional isomers of methylbuphedrones and methoxybuphedrones was successfully achieved. Meta isomers were discriminated by chemical ionization‐tandem mass spectrometry (CI‐MS/MS) using acetonitrile as a reagent gas. Furthermore, all the aromatic positional isomers were discriminated by CI‐MS/MS using vinyltrimethylsilane as a reagent gas. [ABSTRACT FROM AUTHOR]

Algae cultivation in open raceway ponds is considered the most economical method for photosynthetically producing biomass for biofuels, chemical feedstocks, and other high-value products. One of the primary challenges for open ponds is diminished biomass yields due to attack by grazers, competitors, and infectious organisms. Higher-frequency observations are needed for detection of grazer infections, which can rapidly reduce biomass levels. In this study, real-time measurements were performed using chemical ionization mass spectrometry (CIMS) to monitor the impact of grazer infections on cyanobacterial cultures. Numerous volatile gases were produced during healthy growth periods from freshwater Synechococcus elongatus Pasteur Culture Collection (PCC) 7942, with 6-methyl-5-hepten-2-one serving as a unique metabolic indicator of exponential growth. Following the introduction of a Tetrahymena ciliate grazer, the concentrations of multiple volatile species were observed to change after a latent period as short as 18 h. Nitrogenous gases, including ammonia and pyrroline, were found to be reliable indicators of grazing. Detection of grazing by CIMS showed indicators of infections much sooner than traditional methods, microscopy, and continuous fluorescence, which did not detect changes until 37 to 76 h after CIMS detection. CIMS analysis of gases produced by PCC 7942 further shows a complex temporal array of biomass-dependent volatile gas production, which demonstrates the potential for using volatile gas analysis as a diagnostic for grazer infections. Overall, these results show promise for the use of continuous volatile metabolite monitoring for the detection of grazing in algal monocultures, potentially reducing current grazing-induced biomass losses, which could save hundreds of millions of dollars.

Single photon ionization (SPI) based on vacuum ultraviolet (VUV) lamps has been extensively investigated and applied due to its clean mass spectra as a soft ionization method. However, the photon energy of 10.6 eV and photon flux of 1011 photons s−1 of a commercial VUV lamp limits its range of ionizable analytes as well as its sensitivity. This work designs a chemical ionization focusing integrated (CIFI) ionization source time-of-flight mass spectrometry (TOFMS) based on a VUV lamp for the detection of volatile organic compounds (VOCs) and oxygenated volatile organic compounds (OVOCs). The photoelectrons obtained from the VUV lamp via the photoelectric effect ionized the oxygen and water in the air to obtain the reagent ions. The ion–molecule-reaction region (IMR) is constituted by a segmented quadrupole that radially focuses the ions using a radio-frequency electric field. This significantly enhances the yield and transport efficiency of the product ions leading to a great improvement in sensitivity. As a result, a 44-fold and 1154-fold increase in the signal response for benzene and pentanal were achieved, respectively. To verify the reliability of the ionization source, the linear correspondence and repeatability of benzene and pentanal were investigated. Satisfactory dynamic linearity was obtained in the mixing ratio range of 5–50 ppbv, and the relative standard deviation (RSD) of inter-day reached 3.91% and 6.26%, respectively. Finally, the CIFI−TOFMS was applied to the determination of OVOCs, and the LOD of 12 types of OVOCs reached the pptv level, indicating that the ionization source has the potential for accurate and sensitive online monitoring of atmospheric OVOCs. [ABSTRACT FROM AUTHOR]

Here, we present proof of principle studies to demonstrate how the product ions associated with the ion mobility peaks obtained from a High Kinetic Energy-Ion Mobility Spectrometer (HiKE-IMS) measurement of a volatile can be identified using a Proton Transfer Reaction/Selective Reagent Ion-Time-of-Flight-Mass Spectrometer (PTR/SRI-ToF-MS) when operating both instruments at the same reduced electric field value and similar humidities. This identification of product ions improves our understanding of the ion chemistry occurring in the ion source region of a HiKE-IMS. The combination of the two analytical techniques is needed, because in the HiKE-IMS three reagent ions (NO+, H3O+ and O2+•) are present at the same time in high concentrations in the reaction region of the instrument for reduced electric fields of 100 Td and above. This means that even with a mass spectrometer coupled to the HiKE-IMS, the assignment of the product ions to a given reagent ion to a high level of confidence can be challenging. In this paper, we demonstrate an alternative approach using PTR/SRI-ToF-MS that allows separate investigations of the reactions of the reagent ions NO+, H3O+ and O2+•. In this study, we apply this approach to four nitrile containing organic compounds, namely acetonitrile, 2-furonitrile, benzonitrile and acrylonitrile. Both the HiKE-IMS and the PTR/SRI-ToF-MS instruments were operated at a commonly used reduced electric field strength of 120 Td and with gas flows at the same humidities.

Here, we present proof of principle studies to demonstrate how the product ions associated with the ion mobility peaks obtained from a High Kinetic Energy-Ion Mobility Spectrometer (HiKE-IMS) measurement of a volatile can be identified using a Proton Transfer Reaction/Selective Reagent Ion-Time-of-Flight-Mass Spectrometer (PTR/SRI-ToF-MS) when operating both instruments at the same reduced electric field value and similar humidities. This identification of product ions improves our understanding of the ion chemistry occurring in the ion source region of a HiKE-IMS. The combination of the two analytical techniques is needed, because in the HiKE-IMS three reagent ions (NO+, H3O+ and O2+•) are present at the same time in high concentrations in the reaction region of the instrument for reduced electric fields of 100 Td and above. This means that even with a mass spectrometer coupled to the HiKE-IMS, the assignment of the product ions to a given reagent ion to a high level of confidence can be challenging. In this paper, we demonstrate an alternative approach using PTR/SRI-ToF-MS that allows separate investigations of the reactions of the reagent ions NO+, H3O+ and O2+•. In this study, we apply this approach to four nitrile containing organic compounds, namely acetonitrile, 2-furonitrile, benzonitrile and acrylonitrile. Both the HiKE-IMS and the PTR/SRI-ToF-MS instruments were operated at a commonly used reduced electric field strength of 120 Td and with gas flows at the same humidities. [ABSTRACT FROM AUTHOR]

Comprehensive analytical validation studies of a developed ion molecule reaction – mass spectrometer (IMR-MS) were undertaken for the real-time determination of volatile organic compounds (VOCs) in air. The instrument was developed with a focus on promoting chemical ionization (CI) in the reaction chamber by direct sample loading and enhancing maintenance efficiency and reliability of the results. Instrument stability was assessed through a system check and pre-performance check process, and consequently, the instrumental and analytical conditions including the plasma generation, pressure, temperature, and flow rate were successfully optimized. Relevant performance characteristics, such as mass resolution, mass detection range, accuracy, and precision were also investigated by VOC standards composed of benzene, toluene, perfluorotoluene, propylbenzene, and octane. To evaluate whether the performance of the technology is comparable to already accepted techniques, the quantitative results of the IMR-MS were compared with those of a commercial mass spectrometer. This evaluation was successful and suggests the applicability of the technology for spillage accidents of hazardous chemicals and identification of odor-causing substances as well as for real-time gas analysis. [ABSTRACT FROM AUTHOR]

A typical bottom-up proteomic workflow comprises sample digestion with trypsin, separation of the hydrolysate using reversed-phase HPLC, and detection of peptides via electrospray ionization (ESI) tandem mass spectrometry. Despite the advantages and wide usage of protein identification and quantification, the procedure has limitations. Some domains or parts of the proteins may remain inadequately described due to inefficient detection of certain peptides. This study presents an alternative approach based on sample acetylation and mass spectrometry with atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI). These ionizations allowed for improved detection of acetylated peptides obtained via chymotrypsin or glutamyl peptidase I (Glu-C) digestion. APCI and APPI spectra of acetylated peptides often provided sequence information already at the full scan level, while fragmentation spectra of protonated molecules and sodium adducts were easy to interpret. As demonstrated for bovine serum albumin, acetylation improved proteomic analysis. Compared to ESI, gas-phase ionizations APCI and APPI made it possible to detect more peptides and provide better sequence coverages in most cases. Importantly, APCI and APPI detected many peptides which passed unnoticed in the ESI source. Therefore, analytical methods based on chymotrypsin or Glu-C digestion, acetylation, and APPI or APCI provide data complementary to classical bottom-up proteomics. [ABSTRACT FROM AUTHOR]

N-nitrosamines are a class of carcinogenic chemical compound. Considering the large-scale application of agrochemicals globally, the elimination of N-nitrosamines from pesticides should be a priority for manufacturers and regulators. A set of methods was developed and validated for the determination of the toxicologically relevant N-nitrosamine impurity of ethalfluralin (ethyl-N-(2-methylallyl) N-nitroso amine—EMANA) in 33% w v−1 emulsifiable concentrate (EC) formulations. Solid Phase Extraction (SPE) was compared with the "dilute and shoot" approach. Gas chromatography (GC) was combined with Flame Ionization Detection (FID) and mass spectrometry (MS). For MS, two mass filtering modes (Selective Ion Monitoring—SIM, tandem mass spectrometry—MS/MS) and two ionization modes (Electron Ionization—EI, Positive chemical ionization—PCI) were applied. It was concluded that, in the case of samples with high nitrosamine concentration (>90 μg g−1), the "dilute and shoot" approach can be applied without compromising the quality of the results. SPE, however, is required to attain the LOQ (0.33 μg g−1) with good recovery (97.4–110.67%), linearity (R > 0.99) and precision (%RSD 0.68–1.74). The LOQ supersedes the limit set by EFSA (1 μg g−1) in the Technical Active Substance—TAS. The concentration range of the methods is 0.05–110 μg g−1. The methods were applied for the official surveillance program of the Greek agrochemicals market. [ABSTRACT FROM AUTHOR]

Polybrominated diphenyl ethers (PBDEs) are considered emerging organic contaminants that attract more attention in the environment. Herein, online coupling of solid-phase microextraction and ultrahigh-resolution mass spectrometry was developed for rapid screening of eight PBDEs in water samples. This procedure was completed in 22 min, about 6 times faster than the routine workflow such as solid-phase extraction coupled with gas chromatography-mass spectrometry. Thermal desorption and solvent-assisted atmospheric pressure chemical ionization were developed for the effective coupling of solid-phase microextraction (SPME) with ultrahigh-resolution mass spectrometry (UHRMS), which contributed to the signal enhancement and made the methodology feasible for environmental screening. The limits of detection and quantification were 0.01–0.50 ng/mL and 0.05–4.00 ng/mL, respectively. The recoveries were 57.2–75.2% for quality control samples at spiking levels of 0.8–10 ng/mL (4–50 ng/mL for BDE209), with relative standard deviation less than 19.0%. Twelve water samples from different river sites near industrial areas were screened using the developed method. The results showed that BDE-209 was the dominant PBDE (1.02–1.28 ng/mL in positive samples), but its amount was lower than the human health ambient water quality criteria. Consequently, the developed method provides a rapid and reliable way of evaluating contamination status and risks of PBDEs in aqueous environment. [ABSTRACT FROM AUTHOR]

Previously unknown methyl N-(3-substituted thiophen-2-yl)carbamimidothioates were synthesized in one preparative step from hetero-substituted allenes (methoxy-, 1-ethoxyethoxy-, and 1H-pyrrol-1-ylallenes) and aliphatic, cycloaliphatic, and aromatic isothiocyanates, and their behavior under electron impact (70 eV) and chemical ionization (reactant gas methane) was studied for the first time. Unstable molecular ion derived from the title compounds under electron impact decomposes mainly via C–N bond cleavage in the carbamimido-thioate fragment with charge localization on the imide nitrogen atom. A similar fragmentation pathway is observed in the chemical ionization mass spectra of these compounds. Characteristic but low-intense ion peaks in the electron impact mass spectra of methyl N-(3-methoxythiophen-2-yl)carbamimidothioates become predominating in their chemical ionization mass spectra. The base peak in the chemical ionization mass spectra of methyl N-[3-(1H-pyrrol-1-yl)thiophen-2-yl]carbamimidothioates is that of the [M – SMe]+ ion. The most abundant ion in the chemical ionization mass spectrum of methyl N-[3-(1-ethoxyethoxy)thiophen-2-yl]-carbamimidothioate was generated by successive elimination of ethoxyethene and methanethiol molecules from the [M + H]+ ion. [ABSTRACT FROM AUTHOR]

Presented in the article are the design and operation principles of ion sensors intended for detecting the propagating reaction fronts, the deflagration/detonation mode, apparent subsonic/supersonic propagation velocity of the reaction front, and duration of heat release by measuring the ion current in the reactive medium. The electrical circuits for ion sensors without and with intermediate amplifiers, with short response time and high sensitivity, as well as with the very wide dynamic range of operation in the reactive media with highly variable temperature and pressure, are provided and discussed. The main advantages of ion sensors are their very short response time of about 1 ms, versatility of design, and capability of detecting and monitoring reaction fronts of different intensities directly in combustion chambers. Several examples of ion sensor applications in sensing deflagration-to-detonation transition in pulsed detonation engines and developed detonations in rotating detonation engines operating on different fuel–air and fuel–oxygen mixtures are presented and discussed. [ABSTRACT FROM AUTHOR]

Single photon ionization (SPI) based on vacuum ultraviolet (VUV) lamps has been extensively investigated and applied due to its clean mass spectra as a soft ionization method. However, the photon energy of 10.6 eV and photon flux of 1011 photons s−1 of a commercial VUV lamp limits its range of ionizable analytes as well as its sensitivity. This work designs a chemical ionization focusing integrated (CIFI) ionization source time-of-flight mass spectrometry (TOFMS) based on a VUV lamp for the detection of volatile organic compounds (VOCs) and oxygenated volatile organic compounds (OVOCs). The photoelectrons obtained from the VUV lamp via the photoelectric effect ionized the oxygen and water in the air to obtain the reagent ions. The ion–molecule-reaction region (IMR) is constituted by a segmented quadrupole that radially focuses the ions using a radio-frequency electric field. This significantly enhances the yield and transport efficiency of the product ions leading to a great improvement in sensitivity. As a result, a 44-fold and 1154-fold increase in the signal response for benzene and pentanal were achieved, respectively. To verify the reliability of the ionization source, the linear correspondence and repeatability of benzene and pentanal were investigated. Satisfactory dynamic linearity was obtained in the mixing ratio range of 5–50 ppbv, and the relative standard deviation (RSD) of inter-day reached 3.91% and 6.26%, respectively. Finally, the CIFI−TOFMS was applied to the determination of OVOCs, and the LOD of 12 types of OVOCs reached the pptv level, indicating that the ionization source has the potential for accurate and sensitive online monitoring of atmospheric OVOCs.

The simultaneous determination method for prochloraz and its metabolite 2,4,6 -trichlorophenol in pepper was established by gas chromatography-negative chemical ionization mass spectrometry. The results showed that, high response for the detection of the targets in the chemical ionization mode was achieved, the purification effects of purification adsorbents PSA, C18 and GCB were compared, and C18 was finally selected as the pretreatment purification adsorbent. The limits of detection (LOD) was 0.05 mg/kg for prochloraz and 2,4,6-trichlorophenol. The recovery rate of prochloraz in pepper ranged from 85.0% to 92.3% and the relative standard deviation (RSD) was 0.3% to 2.3%. While the recovery rate and RSD of 2,4,6-trichlorophenol were 82.3%~96.4% and 0.8%~1.7%, respectively. The developed method was simple, fast and efficient, and could be used for simultaneous detection of prochloraz and 2,4,6-trichlorophenol pesticide residues. [ABSTRACT FROM AUTHOR]

Gas chromatography–mass spectrometry (GC-MS) usually employs hard electron ionization, leading to extensive fragmentations that are suitable to identify compounds based on library matches. However, such spectra are less useful to structurally characterize unknown compounds that are absent from libraries, due to the lack of readily recognizable molecular ion species. We tested methane chemical ionization on 369 trimethylsilylated (TMS) derivatized metabolites using a quadrupole time-of-flight detector (QTOF). We developed an algorithm to automatically detect molecular ion species and tested SIRIUS software on how accurate the determination of molecular formulas was. The automatic workflow correctly recognized 289 (84%) of all 345 detected derivatized standards. Specifically, strong [M − CH3]+ fragments were observed in 290 of 345 derivatized chemicals, which enabled the automatic recognition of molecular adduct patterns. Using Sirius software, correct elemental formulas were retrieved in 87% of cases within the top three hits. When investigating the cases for which the automatic pattern analysis failed, we found that several metabolites showed a previously unknown [M + TMS]+ adduct formed by rearrangement. Methane chemical ionization with GC-QTOF mass spectrometry is a suitable avenue to identify molecular formulas for abundant unknown peaks.

Introduction. Gestobutanoil is a synthetic pregnane steroid with gestagenic activity. Gestobutanoil has two pharmacologically active metabolites (AMOL and megestrol acetate). This implies the need for a detailed study of the kinetics of metabolites. It is rational to combine the study of the pharmacokinetics of gestobutanoil and its metabolites (AMOL and megestrol acetate). The simultaneous determination of several analytes in the rats’ serum can be carried out using chromatography-mass-spectrometry.Aim. Development of an analytical method for the simultaneous determination of gestobutanoil and two its metabolites in a biomatrix (rat serum).Materials and methods. The following methods were used to determine gestobutanoyl and two its metabolites in a biological matrix: GC-MS, HPLCESI-MS, HPLC-ESI-MS with derivatization, HPLC-APCI-MS.Results and discussion. When working with GC-MS, the chromatographic peaks of gestobutanoyl, AMOL, and megestrol acetate were strongly blurred and superimposed on each other, which is apparently due to the thermolability of the substances. The GC-MS method was abandoned in favor of HPLC. Analytes were separated by HPLC gradient elution on a C18 column. ESI ionization did not give typical protonated ions of gestobutanoyl and AMOL, and the intense signals of their cationized ions and fragment ions, which were observed in the spectra of AMOL and gestobutanoyl, could not ensure the reproducibility of the spectra, since the conditions of their formation are not suitable for routine analysis. Derivatization of analytes to form oximes and substituted hydrazones did not give the expected reaction products for HPLC-ESI-MS. APCI made it possible to remove intense cationized ions from the spectra of gestobutanoyl and AMOL and to increase the reliability of the method. The HPLCAPCI-MS technique was reproduced on model rat blood serum.Conclusion. An HPLC-MS method was developed for the simultaneous determination of gestobutanoyl, megestrol acetate, and AMOL. The technique was tested on a model rat blood serum containing all three analytes.

N-nitrosamines are a class of carcinogenic chemical compound. Considering the large-scale application of agrochemicals globally, the elimination of N-nitrosamines from pesticides should be a priority for manufacturers and regulators. A set of methods was developed and validated for the determination of the toxicologically relevant N-nitrosamine impurity of ethalfluralin (ethyl-N-(2-methylallyl) N-nitroso amine—EMANA) in 33% w v−1 emulsifiable concentrate (EC) formulations. Solid Phase Extraction (SPE) was compared with the “dilute and shoot” approach. Gas chromatography (GC) was combined with Flame Ionization Detection (FID) and mass spectrometry (MS). For MS, two mass filtering modes (Selective Ion Monitoring—SIM, tandem mass spectrometry—MS/MS) and two ionization modes (Electron Ionization—EI, Positive chemical ionization—PCI) were applied. It was concluded that, in the case of samples with high nitrosamine concentration (>90 μg g−1), the “dilute and shoot” approach can be applied without compromising the quality of the results. SPE, however, is required to attain the LOQ (0.33 μg g−1) with good recovery (97.4–110.67%), linearity (R > 0.99) and precision (%RSD 0.68–1.74). The LOQ supersedes the limit set by EFSA (1 μg g−1) in the Technical Active Substance—TAS. The concentration range of the methods is 0.05–110 μg g−1. The methods were applied for the official surveillance program of the Greek agrochemicals market.

A typical bottom-up proteomic workflow comprises sample digestion with trypsin, separation of the hydrolysate using reversed-phase HPLC, and detection of peptides via electrospray ionization (ESI) tandem mass spectrometry. Despite the advantages and wide usage of protein identification and quantification, the procedure has limitations. Some domains or parts of the proteins may remain inadequately described due to inefficient detection of certain peptides. This study presents an alternative approach based on sample acetylation and mass spectrometry with atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI). These ionizations allowed for improved detection of acetylated peptides obtained via chymotrypsin or glutamyl peptidase I (Glu-C) digestion. APCI and APPI spectra of acetylated peptides often provided sequence information already at the full scan level, while fragmentation spectra of protonated molecules and sodium adducts were easy to interpret. As demonstrated for bovine serum albumin, acetylation improved proteomic analysis. Compared to ESI, gas-phase ionizations APCI and APPI made it possible to detect more peptides and provide better sequence coverages in most cases. Importantly, APCI and APPI detected many peptides which passed unnoticed in the ESI source. Therefore, analytical methods based on chymotrypsin or Glu-C digestion, acetylation, and APPI or APCI provide data complementary to classical bottom-up proteomics.

New particle formation (NPF) is the primary source of nanoparticles and contributes a large number of concentrations of cloud condensation nuclei. In recent years, field campaigns and laboratory experiments have been conducted to promote cognition of the mechanism for NPF and its following growth processes. The chemical composition measurement of nanoparticles could help deepen understanding of the initial step of particulate matter formation. In this work, we developed a nanoparticle chemical ionization mass spectrometer to measure nanoparticles' chemical compositions during their initial growth stage. Meanwhile, a non-radioactive ion source was designed for aerosol charging and chemical ionization. Time of flight mass spectrometer coupled with integrated aerosol size selection and collection module would guarantee the picogram level detection limit and high-resolution ability to measure the matrix of ambient samples. The performance of this equipment was overall evaluated, including the transmission efficiency and collection efficiency of custom-built nano differential mobility analyzer, chemical ionization efficiency, and mass resolution of the mass spectrometer. The high sensitivity measurement of ammonium sulfate and methylammonium sulfate aerosols with diameters ranging from 10 to 25 nm could guarantee the application of this instrument in the ambient measurement. [Display omitted] [ABSTRACT FROM AUTHOR]

The current research is constructed for considering the chemical ionization and dissociation of perindopril in the positive mode of corona discharge ion mobility spectrometry. Four product ion peaks are observed in the ion mobility spectrum of perindopril erbumine at the cell temperature of 473 K. These peaks are assigned through the obtained intensity variation analysis in the ion mobility spectra over the elapsed time accompanied by the calculations backed by the validated density functional theory (DFT). In this regard, the most stable ionic species associated with each peak and the corresponding reliable generation pathways are found by the well‐confirmed meta hybrid density functional method, M06‐2X. The peaks are assigned to the protonated perindopril and its dissociation products, including counter ion and the related fragment ions. However, the structures of the neutral perindopril in the gas phase are thoroughly assessed to find a more stable one. The predicted chemical ionization products by the theory are in excellent agreement with our presented experiment here. Theoretical evaluations demonstrated that the production of a fragment by dissociation process occurs when perindopril gets a proton from the ionization region. Also, without protons, there is no dissociation process. Therefore, our mechanism investigated here is the proton transfer one. All possible sites of perindopril are considered theoretically for protonation along with their possible reactions. In addition to the computed PES, the assigned ions for obtained spectra are confirmed by the computed equilibrium constants and rate constants. Our theoretical results show that the peak of the main fragment is for M‐CH3CH2OH produced by a reaction pathway involving no barrier. This study opens new perspectives in interpreting large molecules spectra for future studies. [ABSTRACT FROM AUTHOR]

The fragmentation of 5-[(cyanomethyl)sulfanyl]- and 5-[(1,3-dioxolan-2-ylmethyl)sulfanyl]-1H-pyrrol-2-amines under electron impact (70 eV) and chemical ionization with methane as reactant gas has been studied for the first time. Electron impact ionization of 5-[(cyanomethyl)sulfanyl]-substituted pyrroles generates low-stability molecular ions {M+·, Irel 4–22%; cf. Irel 16–69% for 5-[(1,3-dioxolan-2-ylmethyl)sulfanyl] analogs} whose primary fragmentation involves cleavage of the C–S bond with expulsion of NCCH2 radical. Other fragmentation pathways of the molecular ions include formation of [M – CHR4]+· ions (R4 = CN) and substituent decomposition products. The mass spectra of 5-[(1,3-dioxolan-2-ylmethyl)sulfanyl]pyrroles characteristically show [M – SCH2R4]+ ion peak. The most intense ion peaks in the chemical ionization mass spectra of 5-[(cyanomethyl)sulfanyl] derivatives are those of M+· (Irel 18–69%) and [M + H]+ (Irel 34–100%). Both 5-[(cyanomethyl)sulfanyl]- and 5-[(1,3-dioxolan-2-ylmethyl)sulfanyl]pyrroles decompose mainly through cleavage of the CH2–S and C5–S bonds with the formation of stable [M – CH2R4]+ (Irel 92–100%), [M + H – CH2R4]+· (Irel 22–75%), and [M + H – SCH2R4]+· ions (Irel 6–25%). [ABSTRACT FROM AUTHOR]

Presented in the article are the design and operation principles of ion sensors intended for detecting the propagating reaction fronts, the deflagration/detonation mode, apparent subsonic/supersonic propagation velocity of the reaction front, and duration of heat release by measuring the ion current in the reactive medium. The electrical circuits for ion sensors without and with intermediate amplifiers, with short response time and high sensitivity, as well as with the very wide dynamic range of operation in the reactive media with highly variable temperature and pressure, are provided and discussed. The main advantages of ion sensors are their very short response time of about 1 ms, versatility of design, and capability of detecting and monitoring reaction fronts of different intensities directly in combustion chambers. Several examples of ion sensor applications in sensing deflagration-to-detonation transition in pulsed detonation engines and developed detonations in rotating detonation engines operating on different fuel–air and fuel–oxygen mixtures are presented and discussed.

Electron ionization (EI) and chemical ionization (CI) mass spectra of methylphosphonic acid phosphates and phosphonates (surrogates of respective chemical war agents) and silyl derivatives and its O-alkyl esters (markers of hydrolysis products of chemical war agents) were investigated and respective limits of detection were determined by GC/MS (EI) and GC/MS (CI) in a single ion monitoring mode. Atmospheric pressure photo- and photochemical ionization (APPI/APPCI) mass spectra of the same compounds were investigated by GC/MS (APPI/APPCI) and conditions providing the registration of mass spectra consisting of only one peak, corresponding to the M+ or [M + H]+ ion, were chosen and the limits of detection in the single ion monitoring mode were determined. In addition, the limits of detection for all of the studied compounds by GC with a flameless thermionic detector (FTID) were determined. The limits of detection for phosphates and phosphonates by GC/MS (EI) (MS/MS), GC/MS (CI), GC/MS (APPI), and GC/MS (APPCI) and in the single ion monitoring mode were 0.2–1.0 pg, 1.0–6.0 pg, 10–30 pg, and 0.1–0.3 pg, respectively. For methylphosphonic acid silyl derivatives and its O-alkyl esters, the respective limits of detection were 0.2–4.0 pg, 1.0–5.0 pg, 10–25 pg, and 1.0–3.0 pg. The limits of detection for all the studied compounds by GC with FTID were 0.3–0.4 pg. This means that the rapid screening of the samples to be investigated should be based on the last named method and GC/MS must be used only for the selected samples. [ABSTRACT FROM AUTHOR]

In a typical bottom-up proteomics workflow, proteins are enzymatically cleaved, and the resulting peptides are analyzed by HPLC with electrospray ionization (ESI) tandem mass spectrometry. This approach is practical and widely applied. It has, however, limitations mostly related to less efficient or even inefficient ionization of some peptides in ESI sources. Gas-phase ionization methods like atmospheric-pressure chemical ionization (APCI) or atmospheric-pressure photoionization (APPI) offer alternative ways of detecting various analytes. This work is a systematic study of the ionization efficiencies of peptides in ESI, APCI, and APPI and the applicability of the mentioned ionizations in proteomics. A set of peptide standards and bovine serum albumin digests were examined using a high-resolution mass spectrometer coupled to an ultra HPLC system. Since the ionization efficiency in APCI and APPI depends strongly on experimental conditions, the ion source settings and mobile phase compositions were optimized for each ionization technique. As expected, tryptic peptides were best detected using ESI. The numbers of chymotrypsin peptides successfully detected by ESI, APPI, and APCI were comparable. In the case of Glu-C digest, APPI detected the highest number of peptides. The results suggest that gas-phase ionization techniques, particularly APPI, are an interesting alternative for detecting peptides and delivering complementary data in proteomics.

Absract: —The theoretical and experimental results of the use of electric probes to obtain information on the effective chemiionization rate in high-temperature chemically reacting nonequilibrium gas mixtures of complex composition downstream of reflected shock waves in shock tubes are discussed. The data of measurements of time-dependent electrical currents towards electrically conducting and insulated probes in various gas mixtures are given. The theoretical model that describes the probe operation in high-temperature nonequilibrium chemically reacting gas mixtures at the atmospheric pressure is constructed to interpret such measurements. [ABSTRACT FROM AUTHOR]

The number of priority and emerging contaminants nowadays exceeds several thousands. As a consequence, it is a daunting task to monitor thousands of compounds using classical gas chromatography–mass spectrometry (GC–MS). Preliminary non-targeted screening is thus usually performed to identify the most relevant contaminants. Here we analyzed complex environmental samples of snow, rain water and cloud water from the Arctic, France, Chile, and Russia by two-dimensional gas chromatography (GC × GC) with ionization methods including electron ionization (EI), positive chemical ionization (PCI), and electron capture negative ionization (ECNI) modes, combined with high-resolution mass spectrometry. This approach combines the separation capacity of GC × GC, detailed EI mass spectral libraries, the softness of PCI, and the selectivity of ECNI. Switching between ionization modes without any hardware change allowed to increase the information capacity and reliability of analysis. The structural elucidation becomes easier and more reliable due to the detection of molecular ions in PCI and ECNI modes with corresponding extensive fragmentation in EI, while the ECNI mode improves about 100 times the detection limits for environmentally relevant halogenated and nitro compounds. Overall, a notable enhancement of the analytical capabilities for both targeted and non-targeted purposes is achieved. [ABSTRACT FROM AUTHOR]

Miniature VUV lamp is suitable for ionization source for portable mass spectrometer due to its small size and low power-consumption. However, the sensitivity based on VUV lamp is limited by low brightness and poor ion utilization in irradiation area. A radio-frequency enhancement single photoionization/chemical ionization (RF-SPI/CI) source based on VUV lamp was developed, which could increase detection sensitivity by improving ion transmission and chemical ionization methods. The sensitivity of radio-frequency enhancement ion source was 26 folds as high as that of single photoionization. The limit of detection (LOD) of benzene, toluene and p-xylene were 52, 53, 71 ng/m3, respectively. The RF-SPI/CI source has the advantages of small size and high sensitivity, which is suitable for portable mass spectrometer. [ABSTRACT FROM AUTHOR]

Electron impact (70 eV) and chemical ionization (methane as reactant gas) mass spectra of 1-alkyl- and 1-[2-(vinyloxy)ethyl]-5-(prop-2-yn-1-ylsulfanyl)-1H-pyrrol-2-amines have been studied for the first time. The title compounds under electron impact form stable molecular ions which decompose mainly along pathways typical of the molecular ions derived from the corresponding intramolecular cyclization products, 7-alkyl- and 7-[2-(vinyloxy)ethyl]-2,7-dihydrothiopyrano[2,3-b]pyrrol-6-amines. In addition, fragment ions that could be formed only via decomposition of unrearranged molecular ion were detected. The main fragmentation pathway of their molecular ions involves cleavage of the N1-CAlk bond with the formation of stable [M − R3]+ ions (Irel 85–100%) {except for N,N-diethyl- and N,N-dipropyl-1-[2-(vinyloxy)emyl]-5-(prop-2-yn-1-ylsulfanyl)-1H-pyrrol-2-amines}. The results of quantum chemical calculations at the B3LYP/6-311+G(d,p) level of theory are consistent with the experimental data. In the chemical ionization mass spectra of 5-(prop-2-yn-1-ylsulfanyl)-1H-pyrrol-2-amines, the major peaks were those corresponding to M+· (Irel 65–100%) and [M + H]+ (Irel 75–100%). The title compounds have been found to undergo partial (5–10%) thermally induced isomerization to 5-(prop-1-yn-1-ylsulfanyl)-1H-pyrrol-2-amines under the chemical ionization conditions. [ABSTRACT FROM AUTHOR]

We report a post-plasma chemical ionization approach to evaluate solution cathode glow discharge (SCGD) for S and P elemental analysis. Here, the SCGD serves as a reactor to produce chemical vapors for S and P from organic compounds containing these elements, while a corona discharge operated in negative mode is used to ionize the products. The approach creates long-lived ions in atmospheric pressure, enabling direct investigation of chemical vapor products via mass spectrometric and ion mobility separations. The investigations indicate that SCGD converts S and P to H 2 SO 4 and H 3 PO 4 , respectively. These species are then ionized as HSO 4 HNO 3 − and H 3 PO 4 NO 3 HNO 3 − via reactions with NO 3 HNO 3 − produced by corona discharge. The response factors for P among several small molecules varies within 10% of the average response from the compounds, suggesting a reasonable species-independent characteristic. The response factors for S show larger variations among compounds, indicating a higher dependence of chemical vapor generation efficiency on analytes' chemical structures. Detection limits of 15 and 29 ng/mL are achieved for P and S detection, respectively. These figures are limited by background equivalent concentrations and low ion flux in the utilized ion mobility-time of flight mass spectrometer, indicating potential for significant improvements. In particular, the specificity of clustering for S and P-containing ions produced in this approach suggest facile analysis of S and P using quadrupole-based mass spectrometers for improved analytical performance. [Display omitted] • A new plasma-based MS technique is developed for S and P detection. • Solution cathode glow discharge converts S and P in compounds to H 2 SO 4 and H 3 PO 4. • Negative mode chemical ionization produces long-lived H 3 PO 4 NO 3 HNO 3 − and HSO 4 HNO 3 −. • Ion mobility and ion clustering are used to remove isobaric interferences. • P response is species-independent but larger variations in S response are observed. [ABSTRACT FROM AUTHOR]

Measurements of Cl2 in coastal urban air were made in Irvine, California from Aug.-Nov., 2005, using negative ion atmospheric pressure chemical ionization with tandem mass spectrometry. Cl2 ranged from

The feasibility of using ionization sensor for the investigation and diagnosis of the fuel combustion process in piston power plants with spark ignition is substantiated. It is shown that in order to expand the functions and increase the reliability of operation and signal processing accuracy of the ionization sensor it is necessary to know the impact of the flame fluctuating velocity on the latter. Based on the analysis of published data and in-house research a mechanism of the effect of fluctuation velocity on the electrical conductivity of hydrocarbon flame is proposed, estimated by the value of ion current. A formula for calculating the ion current is proposed, which includes the fluctuation velocity, the flame temperature and the concentration of carbon particles in the fuel. For methane-air flame, it was revealed that for U' 8 m/s an increase of ion current is observed, which is due to increased flame temperature and concentration of carbonaceous fuel particles in the zone of chemical reactions of the flame. When U' 8 m/s the ion current decreases due to the growth of heat consumption for heating the incoming fuel in the flame front, directly proportional to the fluctuation velocity. The results can be used to predict and monitor characteristics of turbulence in the combustion chambers of power plants with the aid of the ionization sensor.

In this study, we present reactions of NH4+ with a series of analytes (A): acetone (C3H6O), methyl vinyl ketone (C4H6O), methyl ethyl ketone (C4H8O), and eight monoterpene isomers (C10H16) using a Selective Reagent Ionization Time-of-Flight Mass Spectrometer (SRI-ToF-MS). We studied the ion-molecule reactions at collision energies of 55 and 80 meV. The ketones, having a substantially lower proton affinity than NH3, produce only cluster ions NH4+(A) in detectable amounts at 55 meV. At 80 meV, no cluster ions were detected meaning that these adduct ions are formed by strongly temperature dependent association reactions. Bond energies of cluster ions and proton affinities for most monoterpenes are not known and were estimated by high level quantum chemical calculations. The calculations reveal monoterpene proton affinities, which range from slightly smaller to substantially higher than the proton affinity of NH3. Proton affinities and cluster bond energies allow to group the monoterpenes as a function of the enthalpy for the dissociation reaction NH4+A→AH++NH3. We find that this enthalpy can be used to predict the NH4+(A) cluster ion yield. The present study explains product ion formation involving NH4+ ion chemistry. This is of importance for chemical ionization mass spectrometry (CIMS) utilizing NH4+ as well as NH4+(H2O) as reagent ions to quantitatively detect atmospherically important organic compounds in real-time.

The fatty acid compositions, including isomer compositions, of seven seed oils containing conjugated fatty acids (CFA) were determined. Seed oils were extracted using a modified Folch extraction, converted to fatty acid methyl esters, and analyzed by gas chromatography (GC) with mass spectrometry and flame ionization detection. The MS detector was operated in positive-ion chemical ionization mode using methane reagent gas. GC was performed using two columns providing different retention characteristics: a poly(ethylene glycol) column and a more polar biscyanopropyl column. The complimentary information provided by the two columns was crucial to peak identification in several cases. The major CFA species in the samples are well known but all contained lesser amounts of additional CFA that have not been widely reported. All samples contained multiple species of conjugated linolenic acid, and two samples also contained small amounts of conjugated linoleic acid. The seed oils of Jacaranda mimosifolia and Calendula officinalis were found to contain 8c,10t,12t-18:3, the natural occurrence of which has only been recently reported in some other samples. The seed oil of Impatiens balsamina has been reported to contain four conjugated 18:4 species, and we present evidence for a fifth conjugated 18:4 isomer.

A new technique that has applications for the detection of nonvolatile organics on Ocean Worlds has been developed. Here, liquid mixtures of fatty acids (FAs) and/or amino acids (AAs) are introduced directly into a miniature quadrupole ion trap mass spectrometer (QITMS) developed at Jet Propulsion Laboratory and analyzed. Two ionization methods, electron impact and chemical ionization (EI and CI, respectively), are compared and contrasted. Further, multiple CI reagents are tested to explore their potential to "soften" ionization of FAs and AAs. Both EI and CI yield mass spectra that bear signatures of FAs or AAs; however, soft CI yields significantly cleaner mass spectra that are easier to interpret. The combination of soft CI with tandem mass spectrometry (MS/MS) has also been demonstrated for AAs, generating "fingerprint" mass spectra of fragments from protonated parent ions. To mimic potential Ocean World conditions, water is used as the primary collision gas in MS/MS experiments. This technique has the potential for the in situ analysis of molecules in the cryogenic plumes of Ocean Worlds (e.g., Enceladus) and comets with the ultimate goal of detecting potential biosignatures. [ABSTRACT FROM AUTHOR]

Short chain volatile iodinated organic compounds (VIOCs) are of great importance in many fields that include atmospheric chemistry, agriculture, and environmental chemistry related to nuclear power plant safety. Proton-transfer-reaction mass spectrometry (PTR-MS) allows for fast, sensitive, and online quantification of VIOCs if the chemical ionization (CI) reaction rate coefficients are known. In this work, the theoretical CI rate coefficients for the reactions of hydronium ions (H3O+) and oxygen ions (O+2) with selected atmospherically important short chain VIOCs are determined. The neutral CH3I, CH2I2, C2H5I, iso-C3H7I, n-C3H7I, n-C4H9I, 2-C4H9I, n-C5H11I, 2-C5H11I, and 3-C5H11I have been chosen because these compounds are of atmospheric and environmental importance in the field of safety of nuclear plant reactors. Theoretical ion-molecule collision rate coefficientswere determined using the Su andChesnavich theory based on parametrized trajectory calculations. The proton affinity, ionization energy, dipole moment, and polarizability values of the neutralmolecules were determined from density functional theory and coupled-cluster calculations. The newly calculated rate constants facilitate the use of the CI mass spectrometry in the atmospheric quantification of selected VIOCs. [ABSTRACT FROM AUTHOR]

Electron impact (70 eV) and chemical ionization (methane as reactant gas) mass spectra of alkyl 5-amino-3-methyl-4-(1H-pyrrol-1-yl)thiophene-2-carboxylates have been studied for the first time. All compounds, except for tert-butyl thiophene-2-carboxylate, under electron impact give rise to stable molecular ions which decompose along two paths, depending on the site of positive charge localization (at the ester fragment or amino nitrogen atom). The main fragmentation pathway of the molecular ions is elimination of alkoxy radical from the ester group. Chemical ionization of alkyl 5-amino-3-methyl-4-(1H-pyrrol-1-yl)-thiophene-2-carboxylates involves protonation and electrophilic addition with the base peak corresponding to the [M + H]+ ion. [ABSTRACT FROM AUTHOR]

Abstract Electron capture detectors (ECDs) and detectors used in ion mobility spectrometry (IMS) have been successfully used for the detection of numerous compounds including hazardous substances. The general principles of their operations are similar and based on sample component ionization and measurement of the signal using the differences in the mobility of electric charge carriers. Differences in sensitivity result from various parameters of these instruments. Value of electric field intensity in ionic reactors have an influence on ionization process. The main goal of the performed tests was to compare the analytical properties of ECD and two types of IMS detectors: a drift tube spectrometer (DT IMS) and a differential mobility spectrometer (DMS). In the work performed, the efficiency of ionization and the response of detectors to selected analytes were compared. ECD, DT IMS and DMS were equipped with 63-Ni radioactive sources. Analytes have been ionized via electron capture process or dissociative electron transfer. Results obtained for oxygen and chloro-substituted organic compounds (carbon tetrachloride, benzyl chloride, chloroform, 2-chloroethyl ethyl sulfide) were used to calculate the relative signal and to compare the ionization efficiency for three detectors. The phenomena observed experimentally were related to energy dependencies and electron capture cross-sections of analytes. The efficiency of ionization in DT IMS was also compared for electron capture when nitrogen was used as the carrier gas, and when the ionization process was based on the collisions of the analyte molecules with the O 2 - with the use of air. Graphical abstract fx1 Highlights • Electron capture is effective method of ionization in ion mobility spectrometry. • Different types of detectors are compared. • Limits of detection of below 1 ppb level are achieved. • Electron energy is the factor determining ionization efficiency. • In some cases dissociative charge transfer is the effective way for ionization. [ABSTRACT FROM AUTHOR]

Comprehensive two‐dimensional gas chromatography (GC × GC) coupled to time‐of‐flight mass spectrometry is a powerful separation tool for complex petroleum product analysis. However, the most commonly used electron ionization (EI) technique often makes the identification of the majority of hydrocarbons impossible due to the exhaustive fragmentation and lack of molecular ion preservation, prompting the need of soft‐ionization energies. In this study, three different soft‐ionization techniques including photo ionization (PI), chemical ionization (CI), and field ionization (FI) were compared against EI to elucidate their relative capabilities to reveal different base oil hydrocarbon classes. Compared with EI (70 eV), PI (10.8 eV) retained significant molecular ion (M+·) information for a large number of isomeric species including branched‐alkanes and saturated monocyclic hydrocarbons along with unique fragmentation patterns. However, for bicyclic/polycyclic naphthenic and aromatic compounds, EI played upper hand by retaining molecular as well as fragment ions to identify the species, whereas PI exhibited mainly molecular ion signals. On the other hand, CI revealed selectivity towards different base oil groups, particularly for steranes, sulfur‐containing thiophenes, and esters, yielding protonated molecular ions (M + H)+ for unsaturated and hydride abstracted ions (M‐H+) for saturated hydrocarbons. FI, as expected, generated intact molecular ions (M+·) irrespective to the base oil chemical classes. It allowed elemental composition by TOFMS with a mass resolving power up to 8000 (FWHM) and a mass accuracy of 1 mDa, leading to the calculation of heteroatomic content, double bond equivalency, and carbon number of the compounds. The qualitative and quantitative results presented herein offer a unique perspective into the detailed comparison of different ionization techniques corresponding to several hydrocarbon classes. [ABSTRACT FROM AUTHOR]