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Copyright of University Chemistry is the property of Peking University, College of Chemistry & Molecular Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of University Chemistry is the property of Peking University, College of Chemistry & Molecular Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of University Chemistry is the property of Peking University, College of Chemistry & Molecular Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of University Chemistry is the property of Peking University, College of Chemistry & Molecular Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Study of chemical properties of water radical cations is of great significance for elucidating related reactions process. In this paper, the reaction characteristics of (H2O)2+• prepared online with several benzene derivatives were investigated. The results showed that, when (H2O)2+• reacted with aromatic compounds without electron-withdrawing groups, such as benzene (C6H6, 78 u), anisole (C7H8O, 108 u) and 2,4-dimethylaniline (C8H11N, 121 u), the corresponding phenol product ((C6H5OH) +•, m/z 94), (C7H7O−OH)+•, m/z 124) and (C8H10NOH+H)+, m/z 138)) were observed, accompanied with the production of electron transfer (ET) products (C6H6) +•, (C7H8O) +•) or proton transfer (PT) product ((C8H11N+H)+). Isotope labeling experiments proved that OH in corresponding phenol products was originated from (H2O)2+•. Interestingly, when (H2O)2+• reacted with substituted benzenes bearing strong electron-withdrawing group, such as benzonitrile (C6H5CN, 103 u) and nitrobenzene (C6H5NO2, 123 u), the main products were the radical substituted adducts (C6H5CN+ H2O)+• (m/z 121) and (C6H5NO2+H2O)+• (m/z 141), respectively, without phenol products or substituted benzene radical cation were noticed. It was obvious that the reaction between (H2O)2+• and the substrate occurred through four competing processes: (a) electron transfer (ET) reaction, in which aromatic compounds release an electron to (H2O)2+• to from an aromatic radical cation; (b) proton transfer (PT) reaction in which aromatic compounds got a proton derived from the dissociation of (H2O)2+•; (c) dissociative electron transfer (DET) reaction, accompanied with the electron transfer process, C−H bond cleavage and C−OH bond formation; (d) radical substitution reaction in which a radical cation adduct consisting of aromatic molecule and H2O generates. It was speculated that the diverse reactivity of (H2O)2+• was owe to its two interchange structures ((H2O)H+−•OH and [H2O∴OH2]+•) generates. It was proposed that the electron withdrawing groups on the aromatic ring would benefit for the existence of two-center and three-electron structure of (H2O)2+• and induced the radical substitution reaction. In contrary, compounds without electron withdrawing groups or bearing electron donating groups on the aromatic ring would contribute to the presence of proton transfer structure of (H2O)2+• (containing H+ and •OH) and facilitate the C−OH bond formation. This study will help to elucidate the chemical reaction processes involving benzene or substituted benzenes and (H2O)2+•.

Quadrupole mass spectrometer is currently one of the most widely used small-scale mass spectrometry instruments. Studying the ions trajectory in a quadrupole field is very important for a deeper understanding of the behavior of ions in quadrupole field, which not only helps to propose new scientific and technological issues in mass spectrometry, but also has practical guidance for the development of instruments. The digital simulation of ions trajectory is an efficient mean for studying the motion of ions in quadrupole field. In this paper, a digital simulation model of quadrupole field, namely Sim-Quaq-COM-V1.0, was established based on COMSOL Multiphysics. The simulation results of the model are in good agreement with the theoretical calculation results, and it can be used as an accurate digital model to study the behavior of ions in quadrupole fields. On this basis, the motion behavior of ions in the hyperbolic quadrupole and the cylindrical quadrupole were compared, and the number of m/z 69 ions passing through the hyperbolic quadrupole field is about 4 times that of the cylindrical quadrupole field under the same conditions. The model has three advantages. Firstly, the self-designed general geometric model and grid were adopted as the built-in model, which can be used to simulate the cylindrical quadrupole field and hyperbolic quadrupole field of various geometric sizes. The modular design is simple and clear. Users only need to modify the geometric parameters and mesh parameters to generate the corresponding geometric model and high-precision mesh. Secondly, the parameters of the model could be configured uniformly in a text file, and the model parameters could be adjusted in batches by modifying the text file. Lastly, the function of multi-core and cluster in COMSOL were utilized to achieve large-scale parallel computing through multi-CPU server and quickly process a large number of ions at the same time. Compared with other models like the default COMSOL model for cylindrical quadrupole field, the simulation speed and accuracy of this model are improved. Through the simulation calculation model, the time of geometric design and modeling is saved, the global parameters can be quickly configured, and the difficulty of calculation is reduced. The model supports parallel computing technology. It is greatly improved in terms of calculation speed and calculation amount, thus can process a large number of ions at the same time, shorten the research cycle, and help the digital development of mass spectrometer design and research technology.

Protein content in food is an important indicator of the nutritional value of food, and it is also related to food safety and many other issues, therefore it is significant to accurately determine the protein content for the valuation of food nutrition and safety. The main elements in food include carbon, nitrogen, hydrogen and sulphur, of which nitrogen mainly comes from protein. The average nitrogen content in protein is 16%, so the conversion factor for “nitrogen-to-protein” is 6.25. Therefore, the protein content in food can be obtained by measuring the nitrogen content of food combined with “nitrogen-to-protein” conversion factor. The traditional methods of protein detection are Kjeldahl method, spectrophotometry, and Dumas combustion. The Kjeldahl method is time-consuming and consumes a large amount of reagents, which can cause environmental pollution. Spectrophotometry is susceptible to interference and the quantitative curve is not easy to draw. Dumas combustion is expensive in terms of consumables. In this paper, a platform of tube furnace-quadrupole mass spectrometer was set up to analyze the protein content in food. Food samples were heated at high temperatures in a tube furnace and combusted in an oxygen-rich environment. After the gas products were ionized, they were directly introduced into a quadrupole mass analyzer for detection, which eliminated the need for processes such as oxidation-reduction, adsorption-desorption by using the selection ion scan function of the mass spectrometer. Five kinds of food samples with different protein contents were selected as research object. Each food sample was weighed at 1 g. The food samples were fully combusted in tube furnace at high temperature (1 300 ℃). The gas products were infused through a drying and filtering tube to remove water and smoke, and then entered the EI ion source through a capillary for ionization. By electronic ionization, nitrogen element characteristic ions, N+, NO+, and NO2+ are generated. The peak intensity of the NO2+ ions were detected by the selection ion scan function of the quadrupole mass analyzer. A standard curve for nitrogen quantification is plotted to be y=115.64x+1 896.9 with the correlation coefficient (R2) of 0.99992 and the relative standard deviation (RSD) of 2.1%-6.1%. The nitrogen content can be calculated by using the peak intensity of NO2+ ions according to the standard curve. The experimental platform of tube furnace-mass spectrometer provides a green, rapid, accurate, and low-cost detection method for quantitative analysis of protein content in food.

A method of gas chromatography-mass spectrometry (GC-MS) was established to determine the migration of dibutyl sebacate, dioctyl sebacate, diisooctyl sebacate, decanedioic acid bis(2,2,6,6-tetramethyl-4-piperidinyl)ester in water-based, acidic and alcoholic food simulants, and olive oil and chemical alternative solvents. The 95% ethanol and isooctane chemical substitution solutions were directly analyzed by GC-MS. The olive oil samples were extracted with acetonitrile followed by QuEChERS purification, and then analyzed by GC-MS. Other simulants (water, 4% acetic acid, 10% ethanol, 20% ethanol, and 50% ethanol) were extracted with n-hexane and then determined by GC-MS. The results showed that the method is well performed under optimized conditions, with the correlation coefficient (r2) greater than 0.995. The limits of detection and the limits of quantitation of the four sebacic acid ester compounds in water, 4% acetic acid, 10% ethanol, 20% ethanol, 50% ethanol, 95% ethanol, isooctane, and olive oil simulants are 0.1-0.2 mg/kg, 0.3-0.5 mg/kg, respectively. Migration experiments on plastic samples were conducted, and spiking experiments at three concentration levels of 0.30, 2.0, 4.0 mg/kg in water, 4% acetic acid, 10% ethanol, 20% ethanol, 50% ethanol, 95% ethanol, and isooctane food simulants, and three concentration levels of 0.50, 2.0, 4.0 mg/kg in olive oil food simulants were carried out. The spiking recoveries range from 92.5% to 108%, and the relative standard deviations (RSDs) are 2.4%-8.8%. The method solves the problem that decanedioic acid bis(2,2,6,6-tetramethyl-4-piperidinyl)ester cannot be extracted into n-hexane in 4% acetic acid by adjusting pH value using ammonium hydroxide, the optimal pH range was determined by comparing the responses of four targets at different pH values. QuEChERS was firstly used for migration experiments of sebacic acid esters in food contact materials to solve the turbidity and partial oil precipitation of olive oil simulants in the concentration process after extraction. By optimizing the QuEChERS filling material, the interference of organic acids, fatty acids, sugar and other impurities on the targets were reduced, producing greater separation effect of the targets. The separation efficiency of four chromatographic columns with different polarity was compared, and the DB-17HT column was selected to detect the four sebacic acid esters simultaneously. Plastics such as polypropylene, polyethylene terephthalic acid terephthalate, polyvinyl chloride, composite membranes, paper cups, recycled PET and recycled PVC were collected and migration experiments were carried out, the migration of sebacic acid esters in these plastics materials was investigated. This method is highly sensitive, precise, and accurate, fully meeting the requirement for determining the migration of the sebacic acid esters in food contact materials and their products.

Residual host cell proteins (HCPs) can significantly impact the efficacy and safety of biologics, and are considered as critical quality attributes that require rigorous quality control. Currently, the enzyme-linked immunosorbent assay (ELISA) is the most common methodology for monitoring residual HCPs in biologics. However, the accuracy of ELISA is highly dependent on the specificity of the used antibodies, and it does not provide informations about the types and quantities of individual HCP, making it necessary to complement ELISA with other analytical methods. Mass spectrometry (MS) has emerged as key analytical and characterization technique for HCPs analysis. Without solely depending on antibody affinity recognition, MS enables the identification and quantification of individual HCP, which facilitates a deeper understanding of HCP profiles, clearance patterns, risk assessment, and problematic HCP monitoring. Moreover, the method of liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) offers faster development for new products. Despite its advantages, LC-MS/MS faces challenges in HCP analysis, such as the lack of standardized procedures and validation standards, signal suppression in the presence of high-abundance active pharmaceutical ingredient (API), and the high instrumentation cost and specialized expertise barriers in routine quality control settings. Researchers and industry experts are working towards establishing standardized procedures and validation guidelines for HCPs analysis using LC-MS/MS, which includes utilizing data dependent acquisition (DDA) for the construction of project-specific HCP libraries, data independent acquisition (DIA) for efficient HCP screening, and targeted strategy like multiple reaction monitoring (MRM) for absolute quantification of high-risk HCPs. Efforts are also underway to mitigate signal suppression effects and reduce instrumentation costs. To overcome high-abundance API interference in HCP detection, advanced techniques involving API-HCP separation, HCP enrichment, and non-denaturing enzymatic digestion have been developed, allowing for the monitoring of HCPs at exceptionally low levels (0.1 to 0.01 ppm). This paper provided an overview of MS-based HCPs analysis workflow utilized "proteomics" approach, covering essential considerations in instrument selection, sample preparation, LC separation, MS data acquisition, and data analysis and reporting, corresponding optimized practices were discussed. Nowadays ELISA is still a workhorse for residual HCP analysis, however, LC-MS/MS is a valuable tool for the analysis of residual HCPs in biologics. It offers a more comprehensive and detailed view of HCP profiles and their clearance patterns throughout the production process, enabling better risk assessment and monitoring of problematic HCPs. While challenges remain, ongoing research and development efforts are paving the way for the broader adoption of LC-MS/MS in the biopharmaceutical industry, ultimately ensuring the quality and safety of biologic products.

Copper (Cu) is a crucial trace metal element in human body, which plays an important role in many life processes. Meanwhile, copper is strictly regulated in the human body and its homeostasis is closely related to the physiological state. The occurrences of many diseases are often accompanied by the copper imbalance. By monitoring the subtle variation in copper homeostasis, it can more accurately identify the factors that lead to abnormal changes in human physiology, especially the impact of environmental factors on the occurrence and development of diseases. In the past two decades, with the development of analytical instruments and improvement of analytical methods, non-traditional stable isotopic analysis has been widely applied in geochemistry and archaeology. Owing to its strong traceability, non-traditional stable isotopic analysis can also provide a new perspective to reveal the mechanisms of element homeostasis imbalance. Especially, stable copper isotopic analysis has a wide application prospect in environmental health research. Because of the virtues of wide application range and high analytical accuracy, multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has effectively promoted the process of copper isotopic analysis. In this paper, we reviewed the mechanisms of non-traditional stable isotope fractionation and analysis methods of Cu isotopes based on MC-ICP-MS, and the basic conception of mass dependent fractionation (MDF) and non-mass dependent fractionation (MIF) as well as the instrumental configuration of MC-ICP-MS. We also introduced the methods of copper isotopic analysis, and then summarized the main applications of copper isotopic analysis in environmental health research. We focused on two aspects, i.e., Cu isotopic analysis of population characteristics and research on disease indicators. In summarizing the relevant researches of Cu isotopic analysis of population characteristics, we reviewed the influence factors, such as age, gender, dietary habits, and other factors. Afterwards, the studies of copper isotopic analysis on some diseases, such as cancers, nervous diseases, disorders of copper transporters, and other diseases were summarized. Finally, we discussed the application prospects of copper isotopic analysis in environmental health research. Until now, the application of stable copper isotopic analysis in environmental health is still in the initial stage, and there still exist many difficulties and challenges. We primarily list four main difficulties and challenges in future studies, including high-throughput sample analysis, background population investigation, combination of other clinical indicators, and combination of multiple omics techniques.

Volatile organic compounds (VOCs) have been widely studied as potential biomarkers of cancer cells. Currently, in vitro cells are mostly cultured in two-dimensional (2D) adherent mode, which is different from in vivo tumor cells with three-dimensional structures. Tumor cell spheres cultured in three-dimensional mode have many similar characteristics to those of in vivo tumors, such as: 1) the structure of cell spheres is divided into proliferative, quiescent, and hypoxic zones; 2) the extracellular matrix deposited in the cell spheres not only increases the density of the spheres but also affects the tumor progression by intercellular interactions. In addition, VOCs detection is mainly accomplished by gas chromatography-mass spectrometry (GC-MS) combined with solid-phase microextraction (SPME), which permits both qualitative and quantitative analysis of VOCs. In this present work, lung cancer cells A549 and lung epithelial cells BEAS-2B were respectively taken as examples to construct three-dimensional (3D) culture models, and 2D models and culture media were used as controls. The VOCs released from cells were detected by SPME-GC-MS. Totally, 163 VOC chromatographic peaks were included in the statistical analyses using an untargeted strategy. Based on orthogonal partial least squares discriminant analysis (OPLS-DA) with the combined criteria of Mann-Whitney U test (p2), differential VOCs released by cells in 2D and 3D culture modes were screened out. There were four VOCs of acetic acid, 1-pyrroline, 4-methylheptane and 2,4-dimethyl-1-heptene released at differential levels from A549 cells cultured under 2D and 3D modes, and four VOCs of ethanol, 1-pyrroline, 4-methylheptane and 2,4-dimethyl-1-heptene released at various amounts from BEAS-2B cells cultured under 2D and 3D modes, respectively. In comparison to 2D models, 3D models released 2.11 to 12.81 times more of these VOCs. Afterwards, the possible biochemical sources of the differentially released VOCs and the possible mechanisms for the differences in the releases of VOCs in the 2D/3D models were discussed. These differentially released VOCs have been reported to be potential markers in lung cancer cells, liver cancer cells, and other biological samples in previous studies. In addition, compared to 2D models, 3D models can better simulate tumor growth in vivo as well as cellular microenvironments, including the creation of reactive oxygen species (ROS) and extracellular matrix deposition. These physiological microenvironments may promote the release of cellularly differential VOCs. In this paper, by constructing 3D cell models and analyzing differential changes in cellular VOCs, it was proved that 3D culture has a broad application prospect in the detection of cellular VOCs in vitro, and is expected to be a valuable research platform for cancer biomarker screening.

Khat is a kind of common drug plant. Many experiments have shown that the content of cathinone norpseudoephedrine and norephedrine in some varieties of Khat are similar. However, some studies showed that there are differences in the intensity of psychoactivity between these varieties. Therefore, it is speculated that other substances in Khat may affect the psychoactive strength of Khat. But currently there are some difficulties in non-targeted screening of unknown compounds without mass spectrometry database information and standard solutions. In this paper, the unknown cathinone alkaloids in Khat were discovered and resolved by HPLC-Q-TOF MS in-source fragmentation multistage mass spectrometry. The separation was carried out on a ZORBAX Eclipse Plus Phenyl-Hexyl column (3.0 mm×100 mm×1.8 μm) with a gradient elution using 0.1% formic acid in water (A)-acetonitrile (B) as the mobile phase. The mobile phase flow rate was 0.3 mL/min, and the column temperature was 30 ℃. The screening of unknown cathinone alkaloid components was realized by the in-source cleavage characteristics of cathinone alkaloids in single-stage mass spectrometry under full-scan mode using an ESI ion source, and then the molecular structures of the unknown cathinone alkaloid components were deduced from the multi-stage MS cleavage patterns of the unknown cathinone alkaloid components in the target ion acquisition mode. The results showed that this method can effectively realize the screening and resolution of the unknown alkaloid components in Khat. A total of three cathinone alkaloid components, including methcathinone, ethcathinone and 2-amino-1-phenyl-1-butanone, were identified in Khat. Methcathinone and ethcathinone were corroborated using standard substances, and 2-amino-1-phenyl-1-butanone needs to be further corroborated due to the lack of corresponding standard substances. The work provides a guideline for the further study of the psychoactive components in Khat, and a reference for the analysis of unknown compounds in other fields.

The study of catalytic reaction mechanism is a critical and extremely challenging project. Online monitoring of reactants, intermediates and products during catalytic reactions can provide key evidence for the in-depth study of complex catalytic reaction networks, reaction pathways and reaction kinetics. As an online mass spectrometry based on soft ionization technique, vacuum ultraviolet photoionization mass spectrometry (VUV-PIMS) has proven itself as a versatile and powerful analytical technique for online and real-time process monitoring, which has gradually become a highly concerned characterization technique for catalytic reaction processes due to its advantages of high molecular ion yield, simple spectrum interpretation and high sensitivity. Compared with other commonly used synchrotron radiation and laser-based VUV light sources, the low pressure discharge lamps filled with various rare gases are compact, easy to operate, and low cost, such as krypton discharge lamps. However, the relatively low photon intensity of these lamps limits their applications. The efforts have been taken to develop stronger VUV light sources or lamp-based efficient combined ion sources to solve this issue. In this paper, the development of VUV-PIMS technology, especially the research progress of photoionization ion sources based on the VUV lamp, were reviewed, such as high-pressure photoionization (HPPI) source, single photon ionization-photoelectron ionization (SPI-PEI) combined ion source, and single photon ionization-chemical ionization (SPI-CI) combined ion source. By combining capillary sampling technology or molecular beam sampling technology, the applications of VUV-PIMS for real-time and online monitoring of stable products and active intermediates in catalytic processes were introduced, such as ammonia synthesis, methane/ethane catalytic conversion, methanol to olefins. The applications in online monitoring of these catalytic reaction processes exhibited an excellent performance and wide potential applications of VUV-PIMS in process monitoring and reaction mechanism research. Finally, the future development trend of VUV-PIMS was prospected for the application requirements of accurate characterization of catalytic reaction process.

Metal nanoclusters (NCs) are stable aggregates at the molecular level, consisting of several to hundreds of metal atoms bound together by physical or chemical interaction. These nanoclusters exhibit unique physicochemical properties that have garnered significant attention in various fields, including biology, catalysis, sensing, and drug delivery. In the field of catalytic reactions, atomically precise metal nanoclusters have acted as an archetypical model for elucidating the structural evolution and structure-property relationship of nanomaterials. However, due to the factors such as the uncertainty of the growth mechanism, the complexity of the crystallization process, and the inherent poor stability, the cluster research faces some challenges in the precise synthesis, structural analysis as well as the comprehension of catalytic reaction mechanism which hinder the full exploration and understanding of these fascinating properties of clusters. Recent years, mass spectrometry (MS) has emerged as a crucial tool in biomolecular analysis and the detection of organic reaction intermediates due to its high sensitivity, high resolution, and fast response. In cluster chemistry, the researchers have also introduced this technique into the study of metal nanoclusters with precise atomic numbers, which have played an important role in the synthesis of clusters and the analysis of their structures as well as reaction mechanisms. The ion source, as the "heart" of the MS, can ionize the analyte and then be detected by MS. Currently, the main ionization methods used for cluster analysis are electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI). These two "soft" ionization techniques can obtain the quasi-molecular ion peaks of the clusters without destroying the structure of the clusters, thus determining the composition of the clusters. In addition, MS enables real-time characterization of the reaction process in solution, allowing for online monitoring of complex reaction components, providing an experimental basis for synthesis processes and catalytic reaction mechanisms of metal clusters. Notably, gas-phase ion-molecule reactions can provide catalytic primitive steps and reaction kinetics enabling in-depth analysis of microscopic reaction mechanisms at a strictly molecular level. For the structural characterization of clusters, tandem mass spectrometry (MS/MS) combined with quantum chemical calculation provides a powerful tool to study and understand the structural evolutions of clusters. By comparing and verifying the experimental and computational results, the correlation between the catalyst structure and its performance can be established, deepening our understanding of the catalytic reaction mechanism and process. This paper was focused on the latest development of soft ionization MS in monitoring intermediates of cluster synthesis, structure analysis, and catalytic reaction mechanism, and the emerging directions in this fascinating area of research were highlighted.

The content of ethanol in wine can affect its quality. Some edible alcohol contains small amounts of methanol, and its accumulation can cause serious health problems. Therefore, it is very important to test the contents of methanol and ethanol in alcohol products. In this paper, a rapid method for the determination of methanol and ethanol by ambient corona discharge ionization mass spectrometry was developed. The method is based on the interaction of water radical cation with methanol and ethanol, respectively. In the positive ion mode, the water dimer radical cation (H2O)2+· (m/z 36) with ambient corona discharge ionization source was prepared by using ambient corona discharge ionization source, and it was introduced into the mass spectrometer with methanol or ethanol through a dual-channel low-energy corona discharge ionization device. The two reacted with each other to form the corresponding water radical cationic complex [CH3OH+H2O]+· (m/z 50) and [CH3CH2OH+H2O]+· (m/z 64), which realized the direct and rapid qualitative and quantitative analysis of methyl alcohol and ethanol in different kinds of alcoholic beverages. The result showed that the limits of detection and the limits of quantification of methanol and ethanol were 0.011 and 0.004 mg/L, 0.038 and 0.014 mg/L, respectively. The correlation coefficients of the target ionic strength curves obtained by the interaction of different concentrations of standard methanol and ethanol with water free radical cation could reach to 0.990 4 and 0.991 1, respectively. By using this method, no methanol was detected in common alcoholic drinks, and the ethanol content in liquor was higher than beer. In the actual work, the method has good practicability through the experimental exploration and verification of different wines. This method does not require sample pretreatment, has the advantages of simple operation and fast analysis, and is especially suitable for the detection of aqueous system. This study has important guiding significance for the quantitative detection and analysis of methanol and ethanol in complex system, provides technical support for the detection of alcoholic beverages and food, and also provides an effective strategy for the quantitative detection of the content of small and medium molecular alcohols in actual samples.

Microdroplets have many unique features such as small size and high electric field, therefore they can be accelerated to initiate chemical reactions and even promote some reactions that cannot be carried out in liquid phase. N, N-Dimethylaniline (DMA) is commonly used in medicine as a raw material for the synthesis of pharmaceutical intermediates. At present, the study involving in the detection of DMA is mainly focused on quantitative detection, and there is few reports on oxidation reaction and gas phase dissociation reaction of DMA. In this paper, the oxidation behavior and dissociation reaction of DMA and related compounds were studied by microdroplet spray mass spectrometry and tandem mass spectrometry. It was found that the ultra-high electric field spontaneously generated by microdroplets at the air-water interface can enable the oxidation reaction of DMA and related compounds to form abundant radical cation DMA+·. By changing the reaction distance, carrier gas pressure, injection velocity, sample concentration and substituent groups, the influence of experimental conditions and substituent modes on the generation of DMA+· was explored. The result showed that the presence of electron donor groups is benefit for the stability of radical cations. After the dissociation of DMA+·, the main product ions were generated by elimination of hydrogen radical and a successive elimination of HC≡N via methyl migration reaction. In addition, when the electron-donating CH3 group was connected with DMA, the intensity of related radical cation increased obviously, indicating that the electron-donating groups promoted the migration reaction. In conclusion, the stable transient intermediate DMA+· that is difficult to prepare by other means, was obtained by microdroplet reaction in this study. This method is helpful to deepen the understanding of the chemical promoted oxidation reaction characteristics of water droplets and enriches the rearrangement reaction types of aniline compounds in gas phase dissociation. It is expected that the prepared active species such as high reactivity radical cations will be applied to chemical industry or pharmaceutical fields in the future.