In-situ electrochemical mass spectrum ion source integrating circulation electrochemical cell and atmospheric pressure chemical ionization and analysis method thereof

Abstract

The invention provides an in-situ electrochemical mass spectrum ion source integrating a circulation electrochemical cell and atmospheric pressure chemical ionization and an analysis method thereof, a tubular flowing electrolytic cell is used as a place where electrochemical reaction occurs, atmospheric pressure chemical ionization is used as an ionization mode, and the in-situ electrochemical mass spectrum ion source is used for in-situ mass spectrum monitoring of the electrochemical reaction. Compared with the conventional electrochemical-mass spectrometry method, the method has the advantages that the electrochemical process and the ionization process are spatially separated, the parameters of the electrochemical process and the ionization process can be regulated and controlled at will, and comprehensive monitoring of the electrochemical process under different conditions is realized. According to the in-situ electrochemical mass spectrum ion source provided by the invention, mutual interference between an electrochemical process and a mass spectrum ionization process can be effectively avoided, and accurate control and measurement of the electrode potential are realized. In addition, atmospheric pressure chemical ionization adopted by the invention has the capability of detecting low-polarity substances, can expand the mechanism research of electrochemical mass spectrometry related to the low-polarity substances, and has wide popularization 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 and is widely used in research fields such as green chemistry. The control of current and potential during electrochemical reactions has an important influence on the reaction rate, reaction yield, and the occurrence of different reaction pathways. Therefore, clarifying the electrochemical reaction mechanism is an important prerequisite for achieving rational regulation of electrochemical reactions and improving the selectivity and yield of reactions.

[0003] The capture and analysis of electrochemical reaction intermediates is an important step in explaining the mechanism of electrochemical reactions. At present, researchers can analyze and identify intermediates in some key steps of electrochemical reactions through in-situ infrared spectroscopy, in-situ electron paramagnetic resonance, in-situ X-ray photoelectron spectroscopy and other technologies, 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 analysis 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] At present, electrochemical mass spectrometry can be divided into traditional electrochemical mass spectrometry and in-situ electrochemical mass spectrometry. Traditional electrochemical mass spectrometry consists of an electrochemical system (electrochemical cell) and an ionization system (mass spectrometry ion source) connected by some connecting pipes. Specific examples include differential electrochemical mass spectrometry DEMS (such as patents with announcement numbers CN 110231377 B and CN 114002284 B) and online electrochemical mass spectrometry (such as patents with announcement number CN 115144355 A). This type of coupling method has poor in-situ performance due to the presence of connecting pipes.

[0005] In order to improve the in-situ performance of electrochemical mass spectrometry technology, based on the research idea of ​​open ionization, researchers integrated the electrochemical system with the ionization system, designed and developed an in-situ electrochemical mass spectrometry ion source, and made the electrochemical system (electrochemical cell) and the ionization system (mass spectrometry ion source) almost consistent in space and time, with higher in-situ performance, and achieved in-situ analysis and detection of electrochemical intermediates. The integration of the electrochemical reaction system and the ion source can already achieve microsecond-level reaction intermediate analysis, which to a certain extent has met the needs of in-situ monitoring of the electrochemical reaction process.

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

[0007] One of the purposes of the present invention is to provide an in-situ electrochemical mass spectrometry ion source that integrates a flow electrochemical cell and atmospheric pressure chemical ionization and 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] The second object of the present invention is to provide an analytical method for an integrated 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 purposes 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 component and a mass spectrometer; The tubular flow electrolytic cell comprises a tubular counter electrode, a filamentary working electrode, a flow injection interface, and a pneumatic atomization interface; the tubular counter electrode is sleeved on the outside of the filamentary working electrode and isolated by an insulating capillary; The flow injection interface comprises a first T-shaped three-way pipe fitting; the connecting end of the filamentary working electrode and the connecting end of the tubular counter electrode pass through 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; 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 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 comprises a conductor with a sharp end and a high voltage power supply; the sharp end of the conductor is in the same straight line as the filamentary working electrode and the ion source entrance 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.

[0010] The general idea of ​​the present invention is as follows: 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 circulating electrolytic cell / atmospheric pressure chemical ionization-mass spectrometry device to achieve potential scanning and in-situ mass spectrometry analysis of electrochemical reaction processes.

[0011] 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 also makes a number of improvements to the tubular electrolytic cell, including: the connection relationship and position relationship of the tubular counter electrode, the filamentary working electrode, the insulating capillary, the flow injection interface, and the pneumatic atomization interface, so as to improve the adaptability of the flow electrolytic cell to 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 sets independent control power supplies for the tubular flow electrolytic cell and the ionization component, respectively, and can arbitrarily regulate the parameters of the electrochemical process and the ionization process, thereby realizing comprehensive monitoring of the electrochemical process under different conditions.

[0012] 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.

[0013] Furthermore, the tubular counter electrode comprises one of a stainless steel capillary, a copper capillary, an iron capillary and a capillary with a conductive layer plated on the inner wall. The capillary with a conductive layer plated on the inner wall comprises a carbon fiber tube, a plastic tube, a glass tube, etc., in which a conductive coating of gold, silver or the like is prepared by chemical plating or the like.

[0014] In the present invention, the capillary is used as the counter electrode of the flow electrolytic cell, and while forming the electrolytic cell, it provides a small volume of liquid droplet precursors for the atomization and ionization process of the liquid. The matched pneumatic atomization interface helps the capillary mouth to atomize the small volume of liquid, and the matched flow injection interface ensures the smooth introduction of the liquid while fixing the electrode.

[0015] Furthermore, the filamentary working electrode includes platinum wire, copper wire, silver wire, gold wire, iron wire, carbon wire, etc., and also includes filamentary metal materials modified by physical sputtering, chemical bonding, etc., so as to be suitable for different electrochemical fields.

[0016] Furthermore, the electrode end of the filamentary working electrode exceeds the end of the adjacent insulating capillary by 0.5-3 mm. The present invention uses a metal wire as a working electrode, and the insulating capillary wraps most of the metal wire, leaving only the front end 0.5-3 mm exposed, ensuring that the solution after the electrochemical reaction on the surface of the metal wire can be immediately transferred to the mass spectrometer, ensuring the in-situ and timeliness of the test.

[0017] 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.

[0018] 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., so as to meet different ionization requirements.

[0019] Furthermore, the present invention controls the tubular counter electrode, the filamentary working electrode, the sharp end of the ionization component conductor and the mass spectrometer inlet to be in the same straight line and keep a short distance, so as to achieve spatial separation of the electrochemical process and the ionization process, and effectively avoid mutual interference between the electrochemical process and the mass spectrometry ionization process. Preferably, the distance between the sharp end of the conductor and the electrode end of the filamentary working electrode is 5-10mm, which can reduce the delay time between the electrochemical reaction and the mass spectrometry detection and enhance the in-situ nature of the detection method on the one hand; on the other hand, the appropriate distance can also prevent the high-voltage corona electrode from discharging to the mass spectrometer or electrochemical cell.

[0020] Furthermore, the insulating capillary is a glass capillary whose outer wall is coated with a polyimide coating.

[0021] Preferably, the outer diameter of the tubular counter electrode is 700 μm - 900 μm, and its inner diameter is less than the outer diameter of 200 μm and above and at least 500 μm. The present invention optimizes the diameter of the tubular counter electrode. On the one hand, a capillary with a relatively smaller inner diameter is used, and the droplet precursor at the tube mouth is smaller, and the droplet size after pneumatic atomization is smaller, which can produce a better ionization effect; on the other hand, the minimum value of the inner diameter of the tubular counter electrode is limited to ensure that there is enough space in the tube to place the filamentary working electrode with an insulating capillary.

[0022] Preferably, the outer diameter of the insulating capillary is smaller than the inner diameter of the tubular counter electrode by more than 100 μm, the inner diameter of the insulating capillary is smaller than the outer diameter of the insulating capillary by 150 μm and more and at least 50 μm greater than the diameter of the filamentary working electrode; the diameter of the filamentary working electrode is 100 μm and more. The present invention optimizes the diameter of the filamentary working electrode and the wall thickness of the insulating capillary, and uses a filamentary working electrode with a larger radius and a thinner insulating capillary isolation layer, so that the surface area of ​​the working electrode can be increased and the electrochemical reaction efficiency can be increased; by limiting the wall thickness of the insulating capillary (at least 150 μm), it can be ensured that the insulating capillary has sufficient mechanical strength, and better plays an isolating role between the filamentary working electrode and the tubular counter electrode to prevent the two from short-circuiting.

[0023] 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 a peristaltic pump, a mechanical pump and an automatic sampling device.

[0024] Preferably, the size of the second T-shaped three-way pipe fitting of the pneumatic atomization interface is 1 / 8 (inch); the electrode end of the tubular counter electrode and the electrode end of the filamentary working electrode pass through the horizontal interface of the second T-shaped three-way pipe fitting and extend 1-2mm from the horizontal interface adjacent to the mass spectrometer. The horizontal interface adjacent to the mass spectrometer of the pneumatic atomization interface is connected to a sheath gas tube that is flush with the extension section of the tubular counter electrode, which is used to converge the high-pressure gas flow and improve the atomization effect. The high-pressure gas pipeline connected to the upper interface of the pneumatic atomization interface adopts a polyetheretherketone tube with an inner diameter of 1 / 8, and the high-pressure gas pipeline is connected to a high-pressure nitrogen cylinder.

[0025] 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.

[0026] 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.

[0027] 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; according to monitoring requirements, the working mode of the working electrode and the working mode of the ionization component are adapted to each other.

[0028] Furthermore, before monitoring the electrochemical reaction process, the tubular flow electrolytic cell is calibrated for potential, including 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, and 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.

[0029] The potential calibration method provided by the present invention can realize the conversion of the cell voltage of the tubular flow electrolytic cell into the electrode potential, and help researchers obtain the electrode potential information during the in-situ electrochemical reaction mass spectrometry monitoring process.

[0030] Preferably, the reference electrode is one of a silver / silver chloride electrode and a saturated calomel electrode.

[0031] Compared with the prior art, the present invention has the following beneficial effects: (1) The integrated flow electrochemical cell and atmospheric pressure chemical ionization in-situ electrochemical mass spectrometry ion source provided by the present invention separates the electrochemical process from the ionization process in space, can arbitrarily adjust the parameters of the electrochemical process and the ionization process, and realizes comprehensive monitoring of the electrochemical process under different conditions. The present invention can effectively avoid mutual interference between the electrochemical process and the mass spectrometry ionization process, and realize precise control and measurement of the electrode potential.

[0032] (2) The analytical method of the integrated flow electrochemical cell and atmospheric pressure chemical ionization in-situ electrochemical mass spectrometry ion source provided by the present invention adopts atmospheric pressure chemical ionization and has the ability to detect relatively low polar substances. It can expand the mechanism research related to electrochemical mass spectrometry in relatively low polar substances and has broad prospects for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of the structure of an in-situ electrochemical mass spectrometry ion source integrating a flow electrochemical cell and atmospheric pressure chemical ionization provided in an embodiment of the present invention; Figure 2 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 a potential-voltage calibration curve using Ag / AgCl as the reference electrode; Figure 3 The results of analysis of the 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; Figure 4 This is the voltage control experiment of Example 5; Figure 5This is a detection diagram of an electrochemically active intermediate with a lifetime of 1 μs in the in-situ verification of Example 6; Among them, 1- tubular counter electrode; 2- filamentary working electrode; 3- insulating 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

[0034] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0035] 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.

[0036] Please refer to Figure 1 An embodiment of the present invention provides 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 component and a mass spectrometer.

[0037] The tubular flow electrolytic cell includes a tubular counter electrode, a filamentary working electrode, a flow injection interface and a pneumatic atomization interface; the tubular counter electrode, the filamentary working electrode, a power supply and other optional electrical components (including voltage, current controllers and detectors, etc.) together constitute an electrolysis circuit. The ionization component includes a conductor with a sharp end and a high-voltage power supply. The ionization component realizes the atmospheric pressure chemical ionization process by corona discharge.

[0038] 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.

[0039] The tubular counter electrode is sleeved 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 in the tube by chemical plating or the like, 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 adopts a glass capillary with a polyimide coating on the outer wall.

[0040] 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.

[0041] The flow injection interface includes a first T-shaped three-way pipe fitting; the connecting end of the filamentary working electrode and the connecting end of the tubular counter electrode pass through 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.

[0042] 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 upper interface of the second T-shaped three-way pipe fitting is connected to the high-pressure gas pipeline.

[0043] 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 tubular flow electrolytic cell and the ionization component are controlled by independent power supplies, respectively, so as to independently control the tubular flow electrolytic cell and the ionization component. Among them, the output end and the ground end of the low-voltage DC power supply can correspond to the connection end of the tubular counter electrode in the tubular flow electrolytic cell and the connection end of the tubular counter electrode, and the polarity of the high-voltage power supply of the ionization component can be arbitrarily adjusted. In this way, the positive / negative mode of oxidation / reduction reaction and ionization of the working electrode can be arbitrarily adjusted.

[0044] 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 is now described with respect to a common application scenario.

[0045] Please refer again Figure 1, a low-voltage DC power supply is used as an electrolysis power supply, and the output and input ends are connected to the connection ends of the tubular counter electrode and the filamentary working electrode respectively. The oxidation / reduction reaction at the working electrode can be adjusted by positive / reverse connection. A high-voltage DC power supply is used as an ionization power supply and is connected to the non-tip end of the conductive stainless steel needle. Positive / negative high-voltage DC power supplies can be selected to adjust the positive / negative mode of the ionization process. The electrolysis process and the ionization process do not interfere with each other, and the parameters of the two processes can be adjusted arbitrarily.

[0046] It is worth noting that in order to prevent short circuit, the wire-shaped working electrode needs to be pre-inserted into the insulating capillary.

[0047] 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, mainly introducing the method for capturing and analyzing electrochemically active intermediates in electrochemical reactions related to low-polarity compounds through a flow electrolytic cell mass spectrometer. When the electrochemical reaction is an oxidation / reduction reaction, the output ends of the low-voltage DC power supply are respectively connected to the working electrode / counter electrode. When the mass spectrometry detection mode is a 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.

[0048] In Examples 1-6 of the present invention, the tubular working electrode uses a stainless steel tube with an outer diameter of 850 μm and an inner diameter of 600 μm; the filamentary working electrode uses a platinum wire with a diameter of 150 μm; the inner diameter of the insulating capillary is 200 μm and the outer diameter is 350 μm. The electrode end of the filamentary working electrode extends 2 mm beyond the end of the adjacent insulating capillary, the insulating capillary extends 5 cm beyond the connecting end of the tubular counter electrode; the connecting end of the filamentary working electrode extends 5 cm beyond the insulating capillary.

[0049] The conductor of the ionization component 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.

[0050] The size of the first T-shaped three-way pipe fitting of the flow injection interface is 1 / 16; the flow injection pipeline connected to the lower interface 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. The size of the second T-shaped three-way pipe fitting of the pneumatic atomization interface is 1 / 8; the electrode end of the tubular counter electrode and the electrode end of the filamentary working electrode pass through the horizontal interface of the second T-shaped three-way pipe fitting and extend 2mm from the horizontal interface adjacent to the mass spectrometer. The pneumatic atomization interface and the horizontal interface adjacent to the mass spectrometer are connected to a sheath gas tube that is flush with the extension section of the tubular counter electrode. The high-pressure gas pipeline connected to the upper interface of the pneumatic atomization interface adopts a polyetheretherketone tube with an inner diameter of 1 / 8, and the high-pressure gas pipeline is connected to a high-pressure nitrogen cylinder. Each connection of the tubular flow electrolytic cell is sealed with a polyetheretherketone hand-tight joint or a polyetheretherketone sleeve of suitable size is used for auxiliary sealing.

[0051] Example 1 This embodiment provides a Figure 1 The analytical method of integrating flow-through electrochemical cell with atmospheric pressure chemical ionization in situ electrochemical mass spectrometry ion source (EC-APCI-MS) is shown: First, perform a potential calibration on the flow cell. Figure 2 As shown in a, the counter electrode tube 1 of the flow electrolytic cell, the "working end" of the working electrode platinum wire 2 and the Ag / AgCl reference electrode are immersed in the electrolyte, and the electrolyte is composed of 10 mM LiCF3SO3 dissolved in acetonitrile / water (9:1). The flow injection interface of the flow electrolytic cell is connected to a micro-injection 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 shown in FIG.

[0052] In positive ion mode, the electrochemical oxidation reaction of propanol ([M+H] + , m / z 61.0648) 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).

[0053] Example 2 First, the flow electrolytic cell was calibrated in the same manner as in Example 1; During the electrochemical oxidation of xanthenes ( Figure 3 b), before electrolysis, the reaction substrate xanthene ([M+H] + , m / z 183.0804), the mass spectrometric signal of the reaction substrate decreased after electrolysis, and the mass spectrometric signal of the oxidation product ([M+H] + , m / z 181.0648)) signal appears in the mass spectrum.

[0054] Example 3 First, the flow electrolytic cell was calibrated in the same manner as in Example 1; For the electrochemical reduction reaction, the device was used to treat 2-cyclohexen-1-one ([M+H] + , m / z 97.0642) to monitor the 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.

[0055] Example 4 First, the flow electrolytic cell was calibrated in the same manner as in Example 1; 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.

[0056] Example 5 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 flexible control of the voltage applied to the electrolytic cell, facilitating monitoring of electrochemical reactions at various voltages. The voltage control experiment of the flow electrolytic cell is as follows: Dopamine ([M+H] + =154.0863) is oxidized to dopaquinone ([M+H] +=152.0706) as an example, acetonitrile: water (volume ratio 9:1) solution containing 1 mM dopamine, 10 mM lithium trifluoromethanesulfonate and 1% formic acid was used as the reaction solution, the flow rate was set to 10 μL / min, and the sheath gas pressure was 0.4 MPa. The voltage was controlled by continuous scanning, with a scanning speed of 50 mV / s and a scanning range of 0 - 3V.

[0057] like Figure 4 As shown in the figure, the whole experiment lasted for 1 min. When the time was 0.55 min, the voltage reached 1.65 V, and the mass spectrometry signal of dopaquinone, the oxidation product of dopamine, began to appear and continued to rise. This process proves the ability of the device to control the parameters of the electrochemical system during the electrochemical reaction monitoring process. During the in-situ monitoring of the electrochemical reaction, the electrochemical system parameters (voltage, current) can be made to reach a specific size or state at a certain moment according to the needs.

[0058] Example 6 In order 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, and the in-situ performance of the platform was evaluated based on the lifetime of the detected electrochemically active intermediates. The in-situ performance evaluation process of the platform is as follows: According to reports (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 about 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 production and electrolysis.

[0059] like Figure 5 As shown in a, when the electrolysis was not turned on, no DMA was found. + signal, and when electrolysis was turned on, the mass spectrometer could detect obvious DMA. + In addition, Figure 5 As shown in b, by turning the voltage on and off, DMA•+ The mass spectrometric signal of α shows periodic rise and fall, indicating that its generation depends on electrolysis. Therefore, the EC-APCI-MS platform can detect electrochemically active intermediates with a lifetime of 1 μs.

[0060] The above examples fully demonstrate that the EC-APCI-MS platform provided by the present invention can monitor the electrochemical reaction process, and can capture and structurally identify active intermediates and products in the reaction process.

[0061] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. An in-situ electrochemical mass spectrometry ion source integrating a flow 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 comprises a tubular counter electrode, a filamentary working electrode, a flow injection interface, and a pneumatic atomization interface; The tubular counter electrode is sleeved on the outside of the filamentary working electrode and isolated by an insulating capillary; The flow injection interface comprises a first T-shaped three-way pipe fitting; the connecting end of the filamentary working electrode and the connecting end of the tubular counter electrode pass through 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; 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 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 comprises a conductor with a sharp end and a high voltage power supply; the sharp end of the conductor is in the same straight line as the filamentary working electrode and the ion source entrance 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 electrode end of the wire-shaped working electrode exceeds the end of the adjacent insulating capillary by 0.5-3 mm.

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

7. 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.

8. 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.

9. An analysis method of an in-situ electrochemical mass spectrometry ion source according to any one of claims 1 to 8, 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.

10. The analysis method according to claim 9, characterized in that Before monitoring the electrochemical reaction process, the tubular flow electrolytic cell is calibrated with a potential, comprising the following steps: The electrode end of the tubular counter electrode and the electrode end 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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