An in-situ electrochemical mass spectrometry ion source integrating a flow electrochemical cell and atmospheric pressure chemical ionization and an analysis method thereof

Abstract

The present invention provides an in-situ electrochemical mass spectrometry ion source and an analysis method thereof that integrates a flow electrochemical cell and atmospheric pressure chemical ionization, adopts a tubular flow electrolytic cell as the place where the electrochemical reaction occurs, and atmospheric pressure chemical ionization as the ionization mode, for in-situ mass spectrometry monitoring of the electrochemical reaction. Compared with the previous electrochemical-mass spectrometry method, the present invention separates the electrochemical process and the ionization process in space, can arbitrarily regulate the parameters of the electrochemical process and the ionization process, and realizes comprehensive monitoring of the electrochemical process under different conditions. The in-situ electrochemical mass spectrometry ion source provided by the present invention can also effectively avoid mutual interference between the electrochemical process and the mass spectrometry ionization process, and realizes precise control and measurement of the electrode potential. In addition, the atmospheric pressure chemical ionization used in the present invention has detection capabilities for relatively low polar substances, can expand the mechanism research related to electrochemical mass spectrometry in relatively low polar substances, and has broad promotion and application prospects.

Description

Technical Field

[0001] The present application relates to the technical field of analytical chemistry, and in particular to an in-situ electrochemical mass spectrometry ion source integrating a flow electrochemical cell and atmospheric pressure chemical ionization, and also to an analysis method of an in-situ electrochemical mass spectrometry ion source integrating a flow electrochemical cell and atmospheric pressure chemical ionization. Background Art

[0002] Electrochemistry has become an enabling technology for oxidation and reduction transformations in chemical synthesis, with widespread applications in research areas such as green chemistry and carbon neutrality. Controlling the current and potential during electrochemical reactions has a significant impact on reaction rates, yields, and the occurrence of different reaction pathways. Therefore, clarifying the electrochemical reaction mechanism is a crucial prerequisite for rationally controlling electrochemical reactions and improving their selectivity and yield.

[0003] The capture and analysis of electrochemical reaction intermediates is an important step in elucidating the mechanism of electrochemical reactions. Currently, researchers can analyze and identify intermediates in some key steps of electrochemical reactions through techniques such as in situ infrared spectroscopy, in situ electron paramagnetic resonance, and in situ X-ray photoelectron spectroscopy, providing strong evidence for the mechanism research of many electrochemical reaction processes. However, actual electrochemical catalysis and synthesis processes are often the result of multiple reaction pathways acting simultaneously, which requires the analytical method to not only provide reaction information of a specific intermediate, but also to continuously perform in situ, real-time, multi-component analysis of reactants, products, and intermediates of multiple reaction pathways.

[0004] Currently, electrochemical mass spectrometry (ECMS) can be categorized into traditional EMS and in-situ EMS. Traditional EMS consists of an electrochemical system (electrochemical cell) connected to an ionization system (mass spectrometry ion source) via a series of connecting pipes. Specific examples include differential electrochemical mass spectrometry (DEMS) (e.g., patents CN 110231377 B and CN 114002284 B) and online EMS (e.g., patent CN 115144355 A). These coupling methods suffer from poor in-situ performance due to the presence of these connecting pipes.

[0005] To improve the in-situ performance of electrochemical mass spectrometry, researchers, building on the principle of open ionization, integrated the electrochemical system with the ionization system to design and develop an in-situ electrochemical mass spectrometry ion source. This approach achieves near spatial and temporal alignment between the electrochemical system (electrochemical cell) and the ionization system (mass spectrometry ion source), further enhancing in-situ performance and enabling in-situ analysis and detection of electrochemical intermediates. The integration of the electrochemical reaction system and the ionization source has enabled microsecond-scale analysis of reaction intermediates, which, to a certain extent, meets the demand for in-situ monitoring of electrochemical reaction processes.

[0006] However, this simple integration strategy also brings new problems, such as interference between the electrochemical process and the mass spectrometry ionization process, and the inability to control and measure the electrode potential, which limits its further application in the study of electrochemical reaction mechanisms. In view of this, the present invention is proposed. Summary of the Invention

[0007] One of the objectives of the present invention is to provide an integrated flow electrochemical cell and atmospheric pressure chemical ionization in-situ electrochemical mass spectrometry ion source that can avoid mutual interference between the electrochemical process and the mass spectrometry ionization process and achieve precise control and measurement of the electrode potential.

[0008] A second object of the present invention is to provide an analytical method that integrates a flow electrochemical cell and an in-situ electrochemical mass spectrometry ion source for atmospheric pressure chemical ionization, which can avoid mutual interference between the electrochemical process and the mass spectrometry ionization process and achieve precise control and measurement of the electrode potential.

[0009] The technical solution adopted by the present invention to achieve one of the objectives is to provide an in-situ electrochemical mass spectrometry ion source integrating a flow electrochemical cell and atmospheric pressure chemical ionization, comprising: a tubular flow electrolytic cell, an ionization assembly and a mass spectrometer;

[0010] The tubular flow electrolysis cell includes a tubular counter electrode, a filamentary working electrode, a flow injection interface, and a pneumatic atomization interface; the tubular counter electrode is sheathed on the outside of the filamentary working electrode and isolated by an insulating capillary;

[0011] The flow injection interface includes a first T-shaped three-way pipe fitting; the connection end of the tubular counter electrode is located in a horizontal interface of the first T-shaped three-way pipe fitting; the connection end of the filamentary working electrode passes through two horizontal interfaces of the first T-shaped three-way pipe fitting, and the connection end of the filamentary working electrode extends out of the connection end of the tubular counter electrode; the lower interface of the first T-shaped three-way pipe fitting is connected to the flow injection pipeline;

[0012] The pneumatic atomization interface includes a second T-shaped three-way pipe fitting; the electrode end of the filamentary working electrode and the electrode end of the tubular counter electrode pass through two horizontal interfaces of the second T-shaped three-way pipe fitting and remain aligned; the electrode end of the filamentary working electrode protrudes from the end of the adjacent insulating capillary tube by 0.5-3 mm; the upper interface of the second T-shaped three-way pipe fitting is connected to the high-pressure gas pipeline;

[0013] The tubular counter electrode, the insulating capillary, the filamentary working electrode, the two horizontal interfaces of the first T-shaped three-way pipe fitting, and the two horizontal interfaces of the second T-shaped three-way pipe fitting are coaxially arranged;

[0014] The ionization assembly includes a conductor with a sharp end and a high-voltage power supply; the sharp end of the conductor is in a straight line with the filamentary working electrode and the ion source inlet of the mass spectrometer; the other end of the conductor is connected to the output end of the high-voltage power supply;

[0015] The tubular flow electrolytic cell and the ionization component are controlled by independent power supplies respectively.

[0016] The overall concept of the present invention is as follows:

[0017] Aiming at the requirements for precise control of electrode potential and scanning analysis during in-situ mass spectrometry monitoring of electrochemical reaction processes, the present invention proposes a strategy for constructing a flow-through electrolytic cell / atmospheric pressure chemical ionization-mass spectrometry device to achieve potential scanning and in-situ mass spectrometry analysis of the electrochemical reaction process.

[0018] In order to avoid mutual interference between the electrochemical process and the mass spectrometry ionization process and to achieve spatial separation of the electrochemical process and the ionization process, the present invention constructs an in-situ electrochemical mass spectrometry ion source that combines a tubular flow electrolytic cell with atmospheric pressure chemical ionization ionization. At the same time, the present invention has also made a number of improvements to the tubular electrolytic cell, including: the connection relationship and positional relationship of the tubular counter electrode, the filamentous working electrode, the insulating capillary, the flow injection interface and the pneumatic atomization interface, to improve the compatibility of the flow electrolytic cell with the atmospheric pressure chemical ionization ionization process. The present invention adopts an ionization component of atmospheric pressure chemical ionization, which has detection capabilities for relatively low polar substances and can expand the application of electrochemical mass spectrometry in the detection of relatively low polar substances. In addition, the present invention not only separates the electrochemical process and the ionization process in space, but also provides independent control power supplies for the tubular flow electrolytic cell and the ionization component, which can arbitrarily regulate the parameters of the electrochemical process and the ionization process, thereby achieving comprehensive monitoring of the electrochemical process under different conditions.

[0019] Furthermore, the electrolysis method of the tubular flow electrolytic cell includes one of a constant current method, a constant potential method, and a chronopotentiometry method.

[0020] Furthermore, the tubular counter electrode comprises one of a stainless steel capillary, a copper capillary, an iron capillary, and a capillary having an inner wall plated with a conductive layer. The capillary having an inner wall plated with a conductive layer comprises a carbon fiber tube, a plastic tube, a glass tube, etc., with a conductive coating of gold, silver, etc. prepared by chemical plating or the like.

[0021] In this invention, a capillary tube serves as the counter electrode of a flow electrolytic cell, simultaneously forming the cell and providing small-volume droplet precursors for the atomization and ionization processes of the liquid. A specially designed pneumatic atomization interface facilitates atomization of small-volume liquids at the capillary tube orifice, while a specially designed flow injection interface secures the electrode while ensuring smooth liquid introduction.

[0022] Furthermore, the filamentous working electrode includes platinum wire, copper wire, silver wire, gold wire, iron wire, carbon wire, etc., and also includes filamentous metal materials modified by physical sputtering, chemical bonding, etc., so as to be suitable for different electrochemical fields.

[0023] Furthermore, the electrode tip of the wire-shaped working electrode extends 0.5-3 mm beyond the end of the adjacent insulating capillary. The present invention uses a metal wire as the working electrode, with the insulating capillary enveloping most of the wire, leaving only the front 0.5-3 mm exposed. This ensures that the solution after the electrochemical reaction on the wire surface can be immediately transferred to the mass spectrometer, ensuring the in-situ and timely testing.

[0024] Furthermore, the insulating capillary extends 3-10 cm beyond the connection end of the tubular counter electrode; and the connection end of the filamentary working electrode extends 1-8 cm beyond the insulating capillary.

[0025] Furthermore, the conductor includes stainless steel needles, tungsten needles, etc., and also includes stainless steel needles, tungsten needles, etc. whose surfaces are modified by physical sputtering, chemical bonding, etc., to meet different ionization requirements.

[0026] Furthermore, the present invention aligns the tubular counter electrode, filamentary working electrode, sharp end of the ionization assembly conductor, and mass spectrometer inlet in a straight line and at a relatively short distance, spatially separating the electrochemical and ionization processes and effectively preventing interference between the electrochemical and mass spectrometry ionization processes. Preferably, the distance between the sharp end of the conductor and the electrode tip of the filamentary working electrode is 5-10 mm. This reduces the delay between the electrochemical reaction and mass spectrometry detection, enhancing the in-situ nature of the detection method. Furthermore, this appropriate distance prevents discharge of the high-voltage corona electrode into the mass spectrometer or electrochemical cell.

[0027] Furthermore, the insulating capillary is a glass capillary with an outer wall coated with a polyimide coating.

[0028] Preferably, the tubular counter electrode has an outer diameter of 700 μm to 900 μm, and an inner diameter that is less than an outer diameter of 200 μm or greater and at least 500 μm. The present invention optimizes the diameter of the tubular counter electrode. On the one hand, the use of a capillary with a relatively smaller inner diameter results in smaller droplet precursors at the tube orifice and smaller droplet size after pneumatic atomization, resulting in better ionization. On the other hand, a minimum inner diameter of the tubular counter electrode is defined to ensure sufficient space within the tube for the filamentous working electrode sheathed in the insulating capillary.

[0029] Preferably, the outer diameter of the insulating capillary is at least 100 μm smaller than the inner diameter of the tubular counter electrode, and the inner diameter of the insulating capillary is 150 μm or greater smaller than the outer diameter of the insulating capillary and at least 50 μm greater than the diameter of the filamentary working electrode; the diameter of the filamentary working electrode is 100 μm or greater. By optimizing the diameter of the filamentary working electrode and the wall thickness of the insulating capillary, the present invention uses a filamentary working electrode with a larger radius and a thinner insulating capillary isolation layer, thereby increasing the surface area of ​​the working electrode and the efficiency of the electrochemical reaction. By limiting the wall thickness of the insulating capillary (to at least 150 μm), the insulating capillary can be ensured to have sufficient mechanical strength, better isolating the filamentary working electrode from the tubular counter electrode and preventing short circuiting between the two.

[0030] Preferably, the size of the first T-shaped three-way pipe fitting of the flow injection interface is 1 / 16 (inch, international standard unit); the flow injection pipeline connected to the interface below it adopts a polyetheretherketone tube with an inner diameter of 1 / 16, and the flow injection pipeline is connected to the peristaltic pump, mechanical pump and automatic sampling equipment.

[0031] Preferably, the second T-shaped three-way fitting of the pneumatic atomization interface is 1 / 8 inch in size; the electrode ends of the tubular counter electrode and the filament working electrode pass through the horizontal interface of the second T-shaped three-way fitting and extend 1-2 mm beyond the horizontal interface adjacent to the mass spectrometer. The horizontal interface adjacent to the mass spectrometer is connected to a sheath gas tube aligned with the extended section of the tubular counter electrode to converge the high-pressure gas flow and improve the atomization effect. The high-pressure gas line connected to the upper interface of the pneumatic atomization interface uses polyetheretherketone tubing with an inner diameter of 1 / 8 inch and is connected to a high-pressure nitrogen cylinder.

[0032] Furthermore, each connection of the tubular flow electrolytic cell is sealed with a polyetheretherketone finger-tight joint, and if necessary, a polyetheretherketone sleeve of suitable size is used to assist in sealing.

[0033] The technical solution adopted by the present invention to achieve the second purpose is: to provide an analysis method of the in-situ electrochemical mass spectrometry ion source according to one of the purposes of the present invention.

[0034] Furthermore, the working mode of the working electrode is selected from one of an oxidation mode or a reduction mode; the working mode of the ionization component is selected from one of a positive ion mode or a negative ion mode; and according to monitoring requirements, the working mode of the working electrode and the working mode of the ionization component are adapted to each other.

[0035] Furthermore, before monitoring the electrochemical reaction process, the tubular flow electrolytic cell is subjected to potential calibration, comprising the following steps: immersing the electrode end of the tubular counter electrode and the electrode end of the filament working electrode of the tubular flow electrolytic cell in an electrolyte, introducing a reference electrode into the electrolyte, and when a DC voltage is applied to the filament working electrode and the tubular counter electrode of the tubular flow electrolytic cell, measuring the potential difference between the working electrode and the reference electrode to obtain a voltage-potential correlation curve.

[0036] The potential calibration method provided by the present invention can realize the conversion of the cell voltage of a tubular flow electrolytic cell into the electrode potential, helping researchers to obtain electrode potential information during in-situ electrochemical reaction mass spectrometry monitoring.

[0037] Preferably, the reference electrode is a silver / silver chloride electrode or a saturated calomel electrode.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The present invention integrates a flow-through electrochemical cell with an in-situ electrochemical mass spectrometry ion source for atmospheric pressure chemical ionization, spatially separating the electrochemical process from the ionization process. This allows for arbitrary control of the parameters of both processes, enabling comprehensive monitoring of the electrochemical process under varying conditions. The present invention effectively avoids mutual interference between the electrochemical process and the mass spectrometry ionization process, enabling precise control and measurement of the electrode potential.

[0040] (2) The analytical method provided by the present invention integrates a flow electrochemical cell and an in-situ electrochemical mass spectrometry ion source for atmospheric pressure chemical ionization. It uses atmospheric pressure chemical ionization and has the ability to detect relatively low polar substances. It can expand the research on the mechanism of electrochemical mass spectrometry related to relatively low polar substances and has broad prospects for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A schematic structural diagram of an in-situ electrochemical mass spectrometry ion source integrating a flow-through electrochemical cell and atmospheric pressure chemical ionization provided by an embodiment of the present invention;

[0042] Figure 2 Figure 1 shows the potential calibration process of the in-situ electrochemical mass spectrometry ion source. In the figure, a) is a schematic diagram of the potential calibration device; b) is the potential-voltage calibration curve using Ag / AgCl as the reference electrode.

[0043] Figure 3 Analytical results of electrochemical reaction intermediates or products in Examples 1-4; in the figure, a) is the electrochemical oxidation of propanol; b) is the electrochemical oxidation of xanthene; c) is the electrochemical reduction coupling of 2-cyclohexene-enone; d) is the electrochemical reduction coupling of ethyl cinnamate;

[0044] Figure 4 This is the voltage control experiment of Example 5;

[0045] Figure 5 This is a detection diagram of an electrochemically active intermediate with a lifetime of 1 μs in the in-situ verification of Example 6;

[0046] Among them, 1- tubular counter electrode; 2- filament working electrode; 3- insulated capillary; 4- flow injection interface; 5- flow injection pipeline; 6- pneumatic atomization interface; 7- sheath gas tube; 8- high-pressure gas pipeline; 9- reference electrode; 10- conductor; 11- high-voltage power supply. DETAILED DESCRIPTION

[0047] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0048] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0049] Please refer to Figure 1 An embodiment of the present invention provides an in-situ electrochemical mass spectrometry ion source that integrates a flow electrochemical cell and atmospheric pressure chemical ionization, including: a tubular flow electrolytic cell, an ionization component and a mass spectrometer.

[0050] The tubular flow electrolysis cell includes a tubular counter electrode, a filamentary working electrode, a flow injection interface, and a pneumatic atomization interface. These components, along with a power supply and other optional electrical components (including voltage and current controllers and detectors), form the electrolysis circuit. The ionization assembly, comprising a conductor with a sharp end and a high-voltage power supply, achieves atmospheric pressure chemical ionization through corona discharge.

[0051] The sharp end of the conductor of the ionization component is in the same straight line as the filamentary working electrode and the ion source entrance of the mass spectrometer. The filamentary working electrode and the tip of the conductor of the ionization component are kept at a distance of 5-10 mm to achieve the purpose of in-situ analysis. The other end of the conductor is connected to the output end of the high-voltage power supply.

[0052] The tubular counter electrode is sheathed on the outside of the filamentary working electrode and isolated by an insulating capillary; the tubular counter electrode includes a stainless steel capillary, a copper capillary, an iron capillary, and also includes a carbon fiber tube, a plastic tube, a glass tube, etc. with a conductive coating of gold, silver, etc. prepared by chemical plating or the like inside the tube, so as to be applicable to different electrochemical fields. The filamentary working electrode includes one of platinum wire, copper wire, silver wire, gold wire, iron wire, and carbon wire, and also includes a filamentary metal material modified by physical coating, chemical bonding, electrochemical polymerization, etc., so as to be applicable to different electrochemical fields. The insulating capillary is a glass capillary with an outer wall coated with a polyimide coating.

[0053] The conductor of the ionization component includes one of a stainless steel needle and a tungsten needle, and also includes a stainless steel needle or a tungsten needle modified by physical coating, chemical bonding, electrochemical polymerization, etc., to meet different ionization requirements.

[0054] The flow injection interface includes a first T-shaped three-way pipe fitting; the connecting end of the tubular counter electrode stays in a horizontal interface of the first T-shaped three-way pipe fitting; the connecting end of the filamentary working electrode passes through the two horizontal interfaces of the first T-shaped three-way pipe fitting, and the connecting end of the filamentary working electrode extends out of the connecting end of the tubular counter electrode; the lower interface of the first T-shaped three-way pipe fitting is connected to the flow injection pipeline.

[0055] The pneumatic atomization interface includes a second T-shaped three-way pipe fitting; the electrode end of the filamentary working electrode and the electrode end of the tubular counter electrode pass through the two horizontal interfaces of the second T-shaped three-way pipe fitting and remain aligned; the electrode end of the filamentary working electrode extends beyond the end of the adjacent insulating capillary by 0.5-3 mm; the upper interface of the second T-shaped three-way pipe fitting is connected to the high-pressure gas pipeline.

[0056] The tubular counter electrode, the insulating capillary, the filamentary working electrode, the two horizontal interfaces of the first T-shaped three-way pipe fitting, and the two horizontal interfaces of the second T-shaped three-way pipe fitting are coaxially arranged;

[0057] The tubular flow electrolytic cell and ionization assembly are controlled by independent power supplies, facilitating independent control of the tubular flow electrolytic cell and the ionization assembly. The output and ground terminals of the low-voltage DC power supply can be arbitrarily connected to the connection terminals of the tubular counter electrode and the tubular counter electrode in the tubular flow electrolytic cell. The polarity of the high-voltage power supply in the ionization assembly can also be arbitrarily controlled. This allows for arbitrary control of the positive / negative mode of oxidation / reduction reactions and ionization at the working electrode.

[0058] The analysis method of the integrated flow electrochemical cell and the in-situ electrochemical mass spectrometry ion source of atmospheric pressure chemical ionization provided by the present application will now be described with respect to a common application scenario.

[0059] Please refer again Figure 1 A low-voltage DC power supply serves as the electrolysis power source. The output and input terminals are connected to the tubular counter electrode and filament-shaped working electrode, respectively. Positive / reverse polarity allows for adjustment of the oxidation / reduction reaction at the working electrode. A high-voltage DC power supply serves as the ionization power source, connected to the non-tip end of the conductive stainless steel needle. Positive / negative high-voltage DC power can be selected to adjust the positive / negative mode of the ionization process. The electrolysis and ionization processes do not interfere with each other, allowing for arbitrary adjustment of parameters for both processes.

[0060] It is worth noting that to prevent short circuit, the wire-shaped working electrode needs to be pre-inserted into the insulating capillary.

[0061] The following is a demonstration of the potential calibration process of the flow electrolytic cell and the analysis results of several specific electrochemical reaction intermediates or products in conjunction with specific embodiments. It mainly introduces the method for capturing and analyzing electrochemically active intermediates in electrochemical reactions related to low-polarity compounds using a flow electrolytic cell mass spectrometer. When the electrochemical reaction is an oxidation / reduction reaction, the output end of the low-voltage DC power supply is connected to the working electrode / counter electrode respectively. When the mass spectrometry detection mode is positive / negative mode, the high-voltage power supply in the ionization component is correspondingly selected as a positive / negative DC high-voltage power supply. Since the electrochemical process and the ionization process do not interfere with each other, the flow electrolytic cell can achieve full coverage monitoring of the electrochemical oxidation / reduction process in the positive / negative monitoring mode.

[0062] In Examples 1-6 of the present invention, the tubular working electrode employed a stainless steel tube with an outer diameter of 850 μm and an inner diameter of 600 μm; the filamentary working electrode employed a platinum wire with a diameter of 150 μm; and the insulating capillary had an inner diameter of 200 μm and an outer diameter of 350 μm. The electrode tip of the filamentary working electrode protruded 2 mm beyond the end of the adjacent insulating capillary, and the insulating capillary protruded 5 cm beyond the connecting end of the tubular counter electrode; the connecting end of the filamentary working electrode also protruded 5 cm beyond the insulating capillary.

[0063] The conductor of the ionization assembly is a stainless steel needle, and the distance between the sharp end of the stainless steel needle and the electrode end of the wire-shaped working electrode is 5 mm.

[0064] The first T-shaped fitting of the flow injection interface is 1 / 16 in diameter; the flow injection line connected to the lower interface uses 1 / 16 in inner diameter polyetheretherketone (PEEK) tubing, which connects to the peristaltic pump, mechanical pump, and automatic sample injection equipment. The second T-shaped fitting of the pneumatic nebulizer interface is 1 / 8 in diameter; the electrode ends of the tubular counter electrode and the filament working electrode pass through the horizontal interface of the second T-shaped fitting and extend 2 mm beyond the horizontal interface adjacent to the mass spectrometer. The pneumatic nebulizer interface is connected to a sheath gas line that is flush with the extension of the tubular counter electrode. The high-pressure gas line connected to the upper interface of the pneumatic nebulizer interface uses 1 / 8 in inner diameter PEEK tubing and is connected to a high-pressure nitrogen cylinder. All connections of the tubular flow electrolysis cell are sealed with PEEK finger-tight fittings or supplemented with PEEK sleeves of appropriate size.

[0065] Example 1

[0066] This embodiment provides a Figure 1 The analytical method shown is an integrated flow-through electrochemical cell with an atmospheric pressure chemical ionization in situ electrochemical mass spectrometry ion source (EC-APCI-MS):

[0067] First, perform potential calibration on the flow electrolysis cell. Figure 2 As shown in a, the tubular counter electrode 1 of the flow electrolysis cell, the "working end" of the working electrode platinum wire 2 and the Ag / AgCl reference electrode are immersed in the electrolyte. The electrolyte is composed of 10 mM LiCF3SO3 dissolved in acetonitrile / water (9:1). The flow injection interface of the flow electrolysis cell is connected to a microinjection pump, and a solution with the same composition as the electrolyte is injected into the stainless steel tube at a flow rate of 10 μL / min. The output and input ends of the low-voltage DC power supply are connected to the platinum wire and the stainless steel tube respectively. When the voltage of the low-voltage DC power supply is adjusted from 0-20V, the potential difference between the platinum wire and the Ag / AgCl reference electrode is measured by a multimeter, and finally the following is obtained. Figure 2 b The voltage-potential correlation curve is shown.

[0068] In the positive ion mode, the electrochemical oxidation reaction of propanol ([M+H] + , m / z 61.0648) was used to monitor the electrocatalytic oxidation reaction ( Figure 3 a) In the mass spectra in the positive ion mode before and after electrolysis, it can be clearly observed that the reaction substrate decreases with electrochemical oxidation, and the product propionaldehyde ([M+H] + , m / z 59.0491) and the product propionic acid ([MH] - , m / z 73.0259).

[0069] Example 2

[0070] First, the flow electrolytic cell was calibrated in the same manner as in Example 1.

[0071] During the electrochemical oxidation of xanthenes ( Figure 3 b), before electrolysis, the reaction substrate xanthene ([M+H] + , m / z 183.0804) mass spectrometry signal, the mass spectrometry signal of the reaction substrate decreased after electrolysis, and the oxidation product ([M+H] + , m / z The signal of 181.0648) appears in the mass spectrum.

[0072] Example 3

[0073] First, the flow electrolytic cell was calibrated in the same manner as in Example 1.

[0074] For the electrochemical reduction reaction, the device was used to reduce 2-cyclohexen-1-one ([M+H] + , m / z 97.0642) was monitored for electrocatalytic reduction reaction ( Figure 3 c) In the mass spectra in the positive ion mode before and after electrolysis, it can be clearly observed that the reaction substrate decreases with electrochemical reduction, and the coupling product ([M+H] + , m / z 195.1384) appears in the mass spectrum after electrolysis.

[0075] Example 4

[0076] First, the flow electrolytic cell was calibrated in the same manner as in Example 1.

[0077] For ethyl cinnamate ([M+H] + , m / z 177.0910) electrochemical reduction reaction ( Figure 3 d), in the mass spectra in the positive ion mode before and after electrolysis, it can be clearly observed that the reaction substrate decreases with electrochemical reduction, and the coupling product ([M+H] + , m / z 355.1904) appears in the mass spectrum after electrolysis.

[0078] Example 5

[0079] In the integrated flow electrochemical cell and atmospheric pressure chemical ionization in-situ electrochemical mass spectrometry ion source (EC-APCI-MS) provided in Example 1, the independence of the electrochemical system allows for flexible control of the voltage applied to the electrochemical cell, facilitating monitoring of electrochemical reactions at various voltages. Voltage control experiments were conducted on the flow electrochemical cell as follows:

[0080] Dopamine ([M+H] + =154.0863) is oxidized to dopaquinone ([M+H] + =152.0706) as an example, a 9:1 acetonitrile:water (volume ratio) solution containing 1 mM dopamine, 10 mM lithium trifluoromethanesulfonate, and 1% formic acid was used as the reaction solution. The flow rate was set at 10 μL / min, and the sheath gas pressure was 0.4 MPa. Voltage control was performed using a continuous sweep method at a rate of 50 mV / s over a range of 0 to 3 V.

[0081] like Figure 4 As shown, the entire experiment lasted 1 minute. At 0.55 minutes, the voltage reached 1.65V, and the mass spectrometry signal of dopaquinone, the oxidation product of dopamine, began to appear and continued to rise. This process demonstrates the device's ability to control electrochemical system parameters during electrochemical reaction monitoring. During in-situ monitoring of electrochemical reactions, the electrochemical system parameters (voltage, current) can be controlled to reach specific values ​​or states at a specific moment, as required.

[0082] Example 6

[0083] To evaluate the in-situ performance of the EC-APCI-MS platform provided in Example 1, specific electrochemically active reactants were placed in the EC-APCI-MS platform for electrochemical reaction and mass spectrometry detection. The lifetime of the detected electrochemically active intermediates was used to evaluate the in-situ performance of the platform. The in-situ performance evaluation process for the platform was as follows:

[0084] According to the report (Timothy A. Brown et al., Angew. Chem. Int. Ed. Engl., 2015,54, 11183-11185), it is known that when the reaction system N, N When the concentration of -dimethylaniline reached 4.7 mM, the electrochemical oxidation of N, N -Dimethylaniline cationic radical (DMA• + , m / z 121.0886) has a lifetime of approximately 1 μs. Based on this, 4.7 mM N, N-dimethylaniline and 1 mM LiCF3SO3 dissolved in acetonitrile were used as the reaction solution, the flow rate was set to 10 μL / min, the sheath gas pressure was 0.4 MPa, the electrolysis voltage was set to 5 V, and the voltage was turned on and off multiple times to verify DMA• + The correlation between the generation and electrolysis.

[0085] like Figure 5 As shown in a, when the electrolysis is not turned on, no DMA is found. + signal, and when electrolysis is turned on, the mass spectrometer can detect obvious DMA• + In addition, if Figure 5 As shown in b, by turning the voltage on and off, DMA• + The mass spectrometric signal of the ions exhibits periodic rises and falls, indicating that their generation is dependent on electrolysis. Therefore, the EC-APCI-MS platform can detect electrochemically active intermediates with a lifetime of 1 μs.

[0086] The above examples fully demonstrate that the EC-APCI-MS platform provided by the present invention can monitor the electrochemical reaction process and capture and structurally identify active intermediates and products in the reaction process.

[0087] The above are only preferred embodiments of the present invention and do not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the present invention specification should be included in the protection scope of the present invention.

Claims

1. An in-situ electrochemical mass spectrometry ion source integrating a flow-through electrochemical cell and atmospheric pressure chemical ionization, characterized in that: include: tubular flow electrolysis cells, ionization components, and mass spectrometers; The tubular flow electrolytic cell includes a tubular counter electrode, a filamentous working electrode, a flow injection interface, and a pneumatic atomization interface; The tubular counter electrode is sheathed on the outside of the filamentary working electrode and isolated by an insulating capillary; The flow injection interface includes a first T-shaped three-way pipe fitting; the connection end of the tubular counter electrode is located in a horizontal interface of the first T-shaped three-way pipe fitting; the connection end of the filamentary working electrode passes through two horizontal interfaces of the first T-shaped three-way pipe fitting, and the connection end of the filamentary working electrode extends out of the connection end of the tubular counter electrode; the lower interface of the first T-shaped three-way pipe fitting is connected to the flow injection pipeline; The pneumatic atomization interface includes a second T-shaped three-way pipe fitting; the electrode end of the filamentary working electrode and the electrode end of the tubular counter electrode pass through two horizontal interfaces of the second T-shaped three-way pipe fitting and remain aligned; the electrode end of the filamentary working electrode protrudes from the end of the adjacent insulating capillary tube by 0.5-3 mm; the upper interface of the second T-shaped three-way pipe fitting is connected to the high-pressure gas pipeline; The tubular counter electrode, the insulating capillary, the filamentary working electrode, the two horizontal interfaces of the first T-shaped three-way pipe fitting, and the two horizontal interfaces of the second T-shaped three-way pipe fitting are coaxially arranged; The ionization assembly includes a conductor with a sharp end and a high-voltage power supply; the sharp end of the conductor is in a straight line with the filamentary working electrode and the ion source inlet of the mass spectrometer; the other end of the conductor is connected to the output end of the high-voltage power supply; The tubular flow electrolytic cell and the ionization component are controlled by independent power supplies respectively.

2. The in-situ electrochemical mass spectrometry ion source according to claim 1, characterized in that: The electrolysis method of the tubular flow electrolytic cell includes one of a constant current method, a constant potential method, and a chronopotentiometry method.

3. The in-situ electrochemical mass spectrometry ion source according to claim 1, characterized in that: The tubular counter electrode comprises one of a stainless steel capillary, a copper capillary, an iron capillary and a capillary with an inner wall plated with a conductive layer.

4. The in-situ electrochemical mass spectrometry ion source according to claim 1, characterized in that: The wire-shaped working electrode includes one of platinum wire, copper wire, silver wire, gold wire, iron wire and carbon wire.

5. The in-situ electrochemical mass spectrometry ion source according to claim 1, characterized in that: The insulating capillary extends 3-10 cm beyond the connection end of the tubular counter electrode; the connection end of the filamentary working electrode extends 1-8 cm beyond the insulating capillary.

6. The in-situ electrochemical mass spectrometry ion source according to claim 1, characterized in that: The conductor includes one of a stainless steel needle and a tungsten needle.

7. The in-situ electrochemical mass spectrometry ion source according to claim 1, characterized in that: The distance between the sharp end of the conductor and the electrode end of the wire-shaped working electrode is 5-10 mm.

8. An analysis method using an in-situ electrochemical mass spectrometry ion source according to any one of claims 1 to 7, characterized in that: The working mode of the working electrode is selected from one of an oxidation mode and a reduction mode; the working mode of the ionization component is selected from one of a positive ion mode and a negative ion mode; according to the monitoring requirements, the working mode of the working electrode and the working mode of the ionization component are adapted to each other.

9. The analysis method according to claim 8, characterized in that Before monitoring the electrochemical reaction process, the tubular flow electrolytic cell is subjected to potential calibration, comprising the following steps: The electrode ends of the tubular counter electrode and the electrode ends of the filament working electrode of the tubular flow electrolytic cell are immersed in an electrolyte, and a reference electrode is introduced into the electrolyte. When a DC voltage is applied to the filament working electrode and the tubular counter electrode of the tubular flow electrolytic cell, the potential difference between the working electrode and the reference electrode is measured to obtain a voltage-potential correlation curve.

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