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Proteomics is widely used in biological, pharmaceutical and pathological areas as a hot research topic in the post-genome era. The research areas of proteomics mainly cover qualitative analysis, such as protein expression profiles, protein post-translational modifications, protein-protein interactions, single cell proteomes, as well as proteome relative and absolute quantitative analysis. Mass spectrometry is an essential tool in proteome researches because of its sensitivity, accuracy and high throughput. In this paper, the identification and quantitative methods of proteomics based on mass spectrometry were reviewed, and the development direction of proteomics in the future was also prospected.
This study evaluated the protein identification capabilities of the Top14 high-abundance protein removal kit (Top14) and the DMB MagicOmics low-abundance enrichment kit (DMB) on serum samples from healthy individuals (HC) and hepatocellular carcinoma (HCC) patients. For HC samples, DMB treatment led to identifying 2.6 times proteins more than Top14 and 3.9 times more than untreated samples. For HCC samples, DMB achieved 3.7 times increase in protein identification over Top14 and 6.2 times increase over untreated samples. Although the Top14 kit was effective in removing high-abundance proteins, it was less proficient in detecting low-abundance proteins when compared to the DMB method. In terms of protein identification frequency, the DMB-treated samples had a significantly higher number of quantifiable proteins than both the Top14 and Blank groups. Over 50% of the proteins identified in the Top14 and Blank groups were also identified in the DMB group, ensuring a comprehensive proteome coverage as evidenced by KEGG analysis. The DMB method significantly outperformed the others in HCC serum samples, identifying 47 differentially expressed (DE) proteins, in contrast to 15 and 17 identified of the Top14 group and untreated samples, respectively, highlighting its superior ability to uncover critical biomarkers for disease analysis. KEGG pathway analysis showed that DE proteins identified by DMB were involved in 21 distinct pathways, significantly more than 5 and 1 pathways identified by Top14 group and untreated samples, demonstrating DMB’s advanced proteomic profiling capability. This study also underscored HSP90AB1, SPP1, ACTR3, SNCA, PECAM1, and SRC proteins increased in HCC serum samples based on DMB method, marking them as promising HCC biomarkers for disease screening.
Relying on its high sensitivity and strong anti-jamming capability, gas chromatography-tandem mass spectrometry(GC-MS/MS) was widely used in chemical, biological and environmental analysis. This paper overviewed recent progress on the application of GC-MS/MS since 2000. Most of the relevant works were in the area of pesticide residues, environmental pollutants (including PAHs, PCBs, PBDEs, PCDD/Fs) and steroid hormones. The discussion mainly contained two aspects. First, the advantages of GC-MS/MS in the analysis of different targets were compared to other instruments. Second, the methods of sample treatment were widely used and suitable for GC-MS/MS analysis. Furthermore, domestic application of GC-MS/MS was stated simply，and the future development of application in GC-MS/MS was reviewed.
In human body, the endocrine system, nervous system and immune system jointly shoulder the important responsibility of life support. Hormones are the material basis for coordination of endocrine system. Steroid hormones, also known as steride hormone, belong to a large category of hormones. The synthesis process of steroid hormones takes cholesterol as the precursor. Through the participation of various metabolic enzymes, steroid hormones are synthesized in the human adrenal cortex, mitochondria of placental cells, smooth Endoplasmic reticulum and gonads, producing 21C, 19C or 18C-backbones with different chemical structures. According to pharmacological effects, steroid hormones are mainly divided into progestogens, corticosteroids and sex hormones, which play an important role in regulating human growth, development, reproduction and maintaining the stability of human body environment. In clinical practice, the level of steroid hormones is used as diagnostic indicator for adrenal and psychiatric diseases. Therefore, accurate determination of steroid hormone content is very important. Steroid hormones in the human body can be detected using various methods, such as radioimmunoassay, chemiluminescence immunoassay, enzyme-linked immunosorbent assay, gas chromatography-tandem mass spectrometry (GC-MS/MS), and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Mass spectrometry has obvious advantages in terms of detection sensitivity and accuracy compared with immunoassay. GC-MS has been the main technique for steroid analysis due to its high specificity, wide analyte coverage, and sufficient sensitivity. However, the samples need to be derivatized, and the experimental processes are tedious. LC-MS/MS has the inherent advantages of high sensitivity and specificity, and has a high-throughput characteristic, thus it is an ideal tool for routine diagnosis. At present, common pretreatment techniques for serum samples include protein precipitation, liquid-liquid extraction, and solid phase extraction. Some new pretreatment methods have emerged in recent years, such as dispersed liquid-liquid extraction, ultrasonic-assisted extraction, and supramolecular extraction. Each pretreatment technique has its own advantages and disadvantages. For example, solid phase extraction (SPE) can achieve good recovery but requires more time and economic factors. In selection of pretreatment methods, the physical and chemical properties of analytes, the characteristics of matrices, the simplicity and durability of method establishment, and time, reliability, and cost required should be comprehensively considered. This article reviewed the application of LC-MS/MS in the determination of endogenous steroid hormones, especially in sample pretreatment, chromatographic and mass spectrometric conditions, so as to provide more accurate basis for clinical diagnosis and treatment based on steroid hormones.
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.
Along with the development of science and technology, chemical reactions exhibit an important role in various fileds including synthesis, chemical engineering, energy, environment, biology and medicine. The effective intermediates monitoring and mechanism exploration of chemical reactions can promote their development and contribute to the design of new chemical reactions. However, in the complex reaction matrix, a variety of intermediates with different molecular weights, life and dynamic changes will be generated at different reaction conditions, the effective capture and structure determinations of the short-lived and active reaction intermediates are hard to be achieved. In recent years, ambient mass spectrometry (AMS) has been widely used in the detection of chemical intermediates to explore reaction mechanisms, due to its advantages of high sensitivity, high selectivity, rapid analysis and in-situ monitoring. Herein, the research progress and development of AMS for the detection of reaction intermediates were reviewed, which involved the reactions in the fields of electrochemistry, photochemistry, plasma chemistry and microdroplet chemistry. For different types of reactions, the designs of different AMS detection technologies were introduced in details. Upon the different ionization strategies, different kinds of techniques have been reported, including desorption electrospray ionization mass spectrometry (DESI-MS), nano-electrospray ionization mass spectrometry (nESI-MS), extraction electrospray ionization mass spectrometry (EESI-MS), Venturi easy ambient sonic spray ionization mass spectrometry (VEASI-MS), spray-dependent plasma mass spectrometry (SDP-MS), accelerated plasma degradation coupled with electrospray ionization mass spectrometry (APD-MS), field-induced droplet ionization mass spectrometry (FIDI-MS) and so on. Subsequently, the progress and application of these mass spectrometry techniques in capturing intermediates of different kinds of reactions as well as the exploration of mechanisms were reviewed. Finally, the development of mass spectrometry for the detection of transient reaction intermediates in different chemical reactions, including electrochemical reactions, photochemical reactions, plasma reactions and microdroplet reactions were summarized and prospected. As reviewed, based on the characteristics of high throughput virtual screening and online monitoring, as well as the diversification of ion sources, AMS would be widely used in various fields including industrial production, environmental protection, energy and so on. In the future, the improved AMS techniques will be encouraged for examining more highly active intermediates with the increasing requirements for the examination of complicated reactions.
The blood, body fluid and other samples of patients collected by clinical laboratory can be detected to find disease markers through different methods, so as to provide clinicians with an important basis for disease prevention, diagnosis, curative effect and prognosis. LC-MS/MS is an analytical instrument with high sensitivity, high specificity, high resolution and high efficiency. In recent years, with the improvement of instrument sensitivity, LC-MS/MS showed great superiority, practicability and development potential in analytical and clinical practices, thus many diseases can be diagnosed accurately, quickly and sensitively in the early stage. For example, LC-MS/MS was used for neonatal screening, and it could screen more than 30 disease markers including various amino acids and carnitine simultaneously. Comparing with immunoassay, LC-MS/MS applied to endocrine hormones can simultaneously determine a variety of analytes and provide structural information of analytes. It has the advantages of high throughput and high specificity. Due to the expensive instruments and the cost of training, only a few clinical laboratories have the ability to develop and verify LC-MS/MS method. Based on the inherent limitations of the instrument, such as matrix effect and ion suppression effect, the efficiency of the method was decreased, resulting in challenges in the process of method development. In addition, the technical levels of different clinical laboratories are uneven, so it is necessary to establish corresponding reference measurement methods and reference ranges for clinical analysis. The standardization of quantitative results is significant for laboratory to build the traceability system. The research progress of the application of LC-MS/MS in clinical practices was introduced, and the advantages and disadvantages of the application of LC-MS/MS in neonatal screening, vitamin D detection, endocrine hormone detection, therapeutic drug concentration monitoring and protein quantitative analysis were discussed in the review. Finally the possible challenges and the recent advancement that clinical laboratories may confront in the application of LC-MS/MS were discussed.
Mass spectrometry has become an invaluable tool for real-time reaction monitoring and capturing highly reactive intermediates, significantly contributing to the understanding of various chemical reactions mechanisms. Recent studies involving the capture of elusive carbocations from different reactions within water microdroplets have drawn considerable attention. Inspired by George Olah's pioneering works on carbocations and superacid chemistry, they attributed the stabilization of transient carbocations to the acidic environment spontaneously formed on the surface of microdroplets, as per microdroplets' intriguing feature. In this work, the electrospray ionization mass spectrometry (ESI-MS) was used to determine a variety of carbocation precursor molecules mentioned. It's important to note that commercial ESI sources are typically unaffected by microdroplet effects due to the short lifespan of the droplets, resulting from an extremely short flight distance and immediate evaporation facilitated by the drying gas. Surprisingly, even in the absence of the ultra-acidic environment considered necessary for the stabilization of carbocations, the carbocation signals are able to be detected under specific analytical conditions. By studying the mass spectra of the same analytes when changing the inlet capillary temperature and switching tube lens voltage, it was revealed that the precursor species might undergo in-source fragmentation due to the combined effects of the inlet capillary's high temperature and the high tube lens voltage. Tube lenses, designed to improve the ion transport efficiency, were located at the entrance from the first to the second pumping stage, where the remaining pressure could be around 133 Pa. The voltage was applied here right after the ions flow out of the inlet capillary. Therefore, the temperature and tube lens voltage might interact with each other, and together with the remaining pressure in this rough vacuum region, the ions could potentially collide with gaseous molecules, leading to the production of carbocation fragments. These fragments, which were in consistent with those generated from collision-induced disassociation (CID) of the precursor species, could possibly be misinterpreted as intermediates of some certain reactions, thereby misleading our understanding of the reaction mechanism. Through the detailed investigation of instrument parameters, and a closer look at the structure of the atmospheric pressure interface was achieved, this work highlights the importance of carefully considering various instrument parameters when mass spectrometry is used for reaction monitoring and intermediate capture studies, to ensure the accuracy of the results, and avoid such pitfalls.
Since it was introduced, the Orbitrap has been proved to be a powerful ion analyzer whose resolution is affected by the fringing field in the electrode structure. Orbitrap is an ultra-high precision instrument. The gap between two outer half electrodes and the design of ion perforation on one side of the outer electrode will produce fringing field effect, resulting in the distortion of the ideal electrostatic field. The distorted field formed in the internal space of Orbitrap will have a serious impact on the resolution. Thermo Fisher Scientific is the only company that has a patent on Orbitrap mass spectrometers and related technologies, however, it has not provided relevant materials to explain the problem in detail and specific solutions, and few researchers have conducted in-depth research. Therefore, it is necessary to study the influence of the distortion field caused by the ion perforation and the outer electrode gap on the resolution, and propose a solution to the fringing field effect. In this work, ion optical simulation software (SIMION) was used to establish ideal, distorted and corrected models, in order to measure the limiting resolution of the orbital trap by measuring the axial vibration period dispersion corresponding to different initial axial amplitudes and different orbital radius. By comparing the experimental and theoretical results of the ideal model, the reliability of the selection of simulation parameters and the calculation method of ion motion were verified. In the distortion model experiment, the ion axial motion period dispersion caused by the fringing field effect arising from the outer electrode gap and ion perforation and its influence on the resolution was investigated. In the correction model experiment, it was proved that the distortion field can be corrected by adjusting the voltage of the two compensating electrodes, so as to overcome the fringing field effect caused by the ion perforation and the outer electrode gap. In addition, it was also found that the axial flight period error caused by radial dispersion in the corrected model is smaller than that in the ideal model, and the difference between the two is small in the axial dispersion. The comprehensive result of the corrected model is better than that of the ideal model. Therefore, the error caused by scratches on the surface of the electrodes can be corrected by adjusting the voltage of the compensating electrodes. The final simulation results showed that the limiting mass resolution for m/z 100 ion can reach to 2 500 000.
Electrochemical interfaces are the core of various important fields, such as energy conversion and storage, biochemistry, sensors, and corrosion. The investigations of the structure-performance relationship of electrochemical solid-liquid interfaces have become a hot topic yet extremely challenging due to the fact that the interfaces are ultrathin, highly dynamic and extremely complex. Mass spectrometric techniques coupled with electrochemistry are powerful and have been widely applied in investigations of mechanisms of electrochemical reactions. However, traditional mass spectrometry (MS) is difficult to characterize the electrode-electrolyte interfaces in an in situ manner due to inherent limitations existing in their ionization processes. In recent years, the state-of-the-art in situ liquid time-of-flight secondary ion MS (ToF-SIMS) based on high-vacuum compatible microfluidic devices has been developed to tackle with this challenge. This review mainly reviewed the principle, characteristics and rapid development of in situ liquid ToF-SIMS in real-time and in situ investigations of electrochemical solid-liquid interfaces during the past decade. In situ liquid ToF-SIMS possesses shallow information depth (nm), high temporal resolution (μs) and high detection sensitivity (10-6-10-9). Besides, it ionizes the electrochemical interfaces in a truly in situ manner and provides direct molecular evidences of chemical evolution of both electrode/electrocatalyst surfaces and reactants/intermediates/products in electrolytes at the interfaces simultaneously. Being attributed to its uniqueness, in situ liquid ToF-SIMS has become a powerful and versatile molecular "eye" in in situ and real-time tracking dynamic electrochemical solid-liquid interfaces, such as capturing electrochemical reaction intermediates, identification of electrocatalytic active sites, probing fine structures of electrochemical double layers, and unraveling the formation chemistry of solid-electrolyte interphases in batteries. Further innovations of microfluidic electrochemical devices and ToF-SIMS instruments are desired to promote the enhanced performance and wider applications of in situ liquid ToF-SIMS in the electrochemical field, and in situ liquid ToF-SIMS will make significant contributions to the understanding of the structure-performance relationship of interfaces in complex electrochemical assays and guide the engineering of better electrochemical interfaces in important fields, such as electrocatalysis and batteries.
Cells are the most basic structural and functional unit of living organisms. In recent years, people have paid more attention to cell heterogeneity. In order to characterize the heterogeneity of cells and prevent the life information in an individual cell from being overwhelmed by the average level of the population gained from traditional cell biology research, many new analytical techniques have been developed for single-cell analysis. However, single-cell analysis is extremely challenging due to the minimal cell volume, low content and wide variety of analytes in single cells, some of analytes change rapidly in cells and others may interfere with each other during analysis. Mass spectrometry has gradually become an ideal tool for single-cell analysis due to its high sensitivity, high resolution and high selectivity. In this review, several techniques of single-cell analysis based on mass spectrometry in the recent five years were systematically summarized and discussed including electrospray ionization mass spectrometry (ESI-MS), laser desorption ionization mass spectrometry (LDI-MS), secondary ion mass spectrometry (SIMS) and inductively coupled plasma mass spectrometry (ICP-MS). Finally, this review also looked into future developments of these mass spectrometry-based techniques. With the development of cell biology, the requirement for single-cell analysis technology is increasing as well. In the meanwhile, single-cell analysis, which focuses on studying the mechanisms of cellular and molecular behavior, has aroused more and more attention from various branches of life sciences in recent years. Although higher spatial resolution and detection sensitivity have become the development trends for single-cell mass spectrometry, none of these mass spectrometry-based techniques can be recognized flawless, which means they all have certain flaws to some extent. Consequently, single-cell analysis technology based on mass spectrometry is developing towards methodological diversification. On the one hand, it is of great importance to choose one suitable mass spectrometry-based technique according to the research purpose and actual conditions. On the other hand, it should be also emphasized that different methods can complement each other and jointly provide a more comprehensive analysis environment for single-cell mass spectrometry, thereby improving and innovating existing single-cell analysis techniques based on mass spectrometry. This review will provide insights into better understanding on and development of single-cell analysis by mass spectrometry.
Microwave plasma torch (MPT) has the advantages of low power consumption, convenient operation, simple structure, etc. It can be used with mass spectrometer for rapid analysis of elements. Inductively coupled plasma mass spectrometer (ICP-MS) has many advantages, such as high sensitivity and wide range of analyzed elements, but its high gas consumption and power consumption of ion source make the detection and analysis cost high. In order to effectively reduce the cost of mass spectrometry for the detection and analysis of alkali metal elements, this study reported a self-made low power-consuming microwave plasma torch time-of-flight mass spectrometer (MPT-TOF MS), including a three-cone system consisting of an ion source, a sampling cone, an interception cone, a super-interceptor cone, an ion transport lens set, a time-of-flight mass analyzer, a sample injection device, and a data acquisition system. The effects of five experimental factors, namely, maintenance gas flow rate, carrier gas flow rate, super-interception cone voltage, MPT torch flame position and microwave power, on the detection of alkali metal elements were investigated. The performance of the instrument was systematically investigated, covering the linear range, mass resolution, and isotopic accuracy of measurement. The results showed that the MPT-TOF MS has the advantages of low gas consumption (800 mL/min for argon maintenance gas, 400 mL/min for argon carrier gas, and 2 000 mL/min for nitrogen drying gas), low power consumption of the ion source (100 W), and long-time stable operation when working, and the linear range of the measurement of this device covers five orders of magnitude with high mass resolution. The detection limits of lithium, sodium, potassium, rubidium and cesium are 0.49, 3.05, 1.31, 0.74, 0.34 μg/L, respectively, which are better than the results of ICP-MS. The instrument was used for the rapid detection of lithium, sodium, potassium, rubidium and cesium alkali metal elements in the salt lake. Our study showed that the MPT-TOF-MS instrument can be used as an alternative to the elemental detection of ICP-MS, and can be further developed into an on-line analytical method.
Methotrexate (MTX) is a therapeutic drug that is widely used in clinic for treatment of a variety of cancers. However, MTX has limited selectivity and serious cytotoxicity, at the same time, there are problems such as narrow therapeutic window and large individual variability in metabolism and excretion of MTX. Therefore, blood concentration monitoring is required for MTX administration in clinical practice. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) has the advantages of strong specificity, good separation characteristics, high sensitivity and fast detection speed, which has become the internationally recognized “gold standard” for blood concentration monitoring of drugs. In this study, an isotope dilution mass spectrometry method was developed for accurate measurement of MTX in serum by the house-made QLIT-6610MD quadrupole-linear ion trap liquid chromatography-mass spectrometer. Unlike the traditional triple quadrupole QqQ tandem mass spectrometer, the quadrupole-linear ion trap (Q-LIT) mass spectrometer adopts the quadrupole-linear ion trap direct axial coupling design, i.e., a single linear ion trap is used to replace the QqQ tandem mass spectrometer’s back-end fragmentation cell and the quadrupole, and no other components are installed between the quadrupole and linear ion trap, which greatly streamlines the quality and efficiency of the mass spectrometer while ensuring the original performance of the instrument. With this unique configuration, the QLIT-6610MD instrument uses a simultaneous fragmentation and accumulation technique, which remarkedly reduces matrix-induced interferences and effectively reduces space charge effects. Serum samples were pretreated with methanol to precipitate proteins and the supernatants were measured by QLIT-6610MD spectrometer. The linear correlation coefficient (
Metabolomics is the study of comprehensive identification and quantification of endogenous small-molecular metabolites in the biological system. The biological samples are highly complex due to a large number of metabolites, tremendous physical/chemical diversity, and a wide concentration range. Global metabolome analysis is a great challenge for analytical techniques. Mass spectrometry is one of the key analytical methods in metabolomics investigations. With the rapid development of high-resolution mass spectrometry (HRMS), it has become an indispensable approach owing to high sensitivity, high resolution, good mass accuracy, and wide dynamic ranges. A variety of novel metabolomics methods based on HRMS have been proposed. In this review, new advances of analytical methods, metabolome identification based on HRMS in metabolomics in the last five years were presented, including micro/nano-ultrahigh performance liquid chromatography-HRMS, multi-dimensional liquid chromatography-HRMS, direct injection-HRMS, mass spectrometry imaging, and strategies for metabolite annotations. Future perspectives for HRMS-based metabolomics were highlighted.
It is of great significance to analyze the heavy metal speciation and identify the organic compounds in soil. By now, the most of existed methods can not be used for simultaneously analyzing metal-containing compounds and organic components, which require tedious sample preparation and offline separation processes before detection, increasing analytical errors and lengthening analysis time. Herein, based on our previous research, a novel electrochemical mass spectrometry (EC-MS) device was fabricated for online sequential qualitative detection of metal species and organics in soil without sample pretreatment. Firstly, the components were divided into four species, including water soluble, lipid soluble, insoluble and oxidable speciation, and then dissociated by extraction, reaction and electrolysis online. Ultrapure water and CH3OH were employed as eluents to extract water-soluble and lipid soluble species, respectively. EDTA-2Na (CH3OH:H2O=1:1,
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.
Mass resolution of Foureir transform mass spectrometer (FTMS) highly depends on the acquisition time of image charge/current signal. In order to achieve higher resolution with a shorter transient time, apart from increasing the field strength of the analyzer, the high order harmonics in the image charge signal may also be exploited. The image charge or current signal obtained from the planar electrostatic ion trap has a non-sinusoidal waveform which contains many high-order harmonic components. However, presence of high harmonics increases the complexity of spectral analysis, such as identification of a peak for its correct harmonic order, and avoiding quantitation error due to the peak overlapping from different harmonic groups. A new quantitative algorithm consists of a scoring-based peak classification and the least square fitting (SC-LSF), which has been developed to convert image charge or current signal to mass spectrum. The scoring process will go through all the peaks identified above the noise background, for assumptions that the peak belongs to a certain harmonic order. The score will go up when a relevant lower harmonic peak is confirmed. The harmonic order which achieves the highest score, is assigned to the peak so its fundamental frequency can be determined. Through the SC tests, the candidates of all fundamental frequencies are found for all possible
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
Electrochemical reaction is a continuous dynamic process, accompanied by electron transfer and generation of short-lived intermediates. The mechanism investigation of electrochemical interfaces is pivotal for the progression of energy storage, electro-organic synthesis, electrocatalysis, and electroanalysis. The valuable insights for optimizing performance, improving efficiency, and developing novel methodologies can be attained by elucidating the complicated pathways involved in the electrochemical processes. Thus, how to monitor transient intermediates formed at the solid-liquid interface becomes the critical point in unraveling these intricate processes. To this end, a series of in-situ analytical methods such as in-situ electron paramagnetic resonance spectroscopy (in-situ EPR), in-situ Raman spectroscopy, in-situ infrared spectroscopy (in-situ IR) and in-situ electrochemical mass spectrometry (in-situ EC-MS) have been exploited to probe the chemical transformations at the electrode/electrolyte interface. Among them, due to the superior specificity for interpreting molecular information, EC-MS has progressively gained extensive attention as a powerful and reliable tool for capturing intermediates and revealing the mechanisms in electrochemical reactions. In this review, the research progresses in the recent advancements in the detection of transient reaction intermediates through electrochemical mass spectrometry were presented. The discussion centered on elucidating the principle and configuration of the devices employed in EC-MS, with a specific focus on electrospray ionization mass spectrometry (ESI-MS), atmospheric pressure ionization mass spectrometry (AIMS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). In addition, the review delved into the wide-ranging applications of EC-MS in monitoring electrochemical processes in electro-organic synthesis, electrocatalysis, lithium-ion batteries, electrochemiluminescence, and bioelectrochemical reactions. Despite the remarkable progress has made, the challenges in the field of EC-MS are prospected. There is still an urgent need for further improvement of the experimental apparatus to enhance the sampling efficiency and time resolution to capture short-lived and low-concentration reaction intermediates. In the future, we anticipate that EC-MS will be combined with other in situ analytical techniques, such as in situ infrared or Raman spectroscopy, enabling multi-dimensional characterization and monitoring of electrochemical reaction intermediates.
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