Double-flight-time two-dimensional rapid separation chemical ionization mass spectrometer and isomer separation and detection method thereof

Abstract

The invention discloses a double-flight-time two-dimensional rapid separation chemical ionization mass spectrometer and an isomeride separation and detection method thereof, and belongs to the technical field of analysis and detection.The chemical ionization mass spectrometer comprises an ionization source, a reaction tube, a migration tube, a transition cavity and a mass spectrum cavity which are connected through coaxial small holes from left to right; a funnel electrode is arranged in the reaction tube; an ion gate, a guide electrode, a sectional type quadrupole rod guide electrode and a Faraday plate which are coaxially distributed from left to right are arranged in the migration tube; a small hole is formed in the center of the Faraday plate; the reaction tube is connected with a sample introduction pipeline; the transition cavity guide electrode is positioned in the transition cavity; the flight time mass spectrum detector is positioned in the mass spectrum cavity; the transition cavity guide electrode and an ion inlet of the time-of-flight mass spectrometry detector are coaxially distributed; the sectional type quadrupole rod guide electrode is composed of a plurality of sections of quadrupole rods which are distributed coaxially. According to the invention, rapid separation and high-sensitivity detection of the isomeride can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of analysis and detection, and in particular relates to a chemical ionization mass spectrometer with dual time-of-flight two-dimensional rapid separation and an isomer separation and detection method thereof. Background Art

[0002] Chemical ionization mass spectrometry is a mass spectrometry technique based on the principle of ion-molecule reaction. The most representative one is proton transfer reaction mass spectrometry, in which the reaction ion is usually H3O + If the proton affinity of the volatile organic compound M is greater than that of H2O, it can be combined with H3O + Proton transfer reaction occurs (H3O + +M—>MH + +H2O), the analyte M is ionized into the protonated ion peak MH + , MH + Ultimately, it can be detected by mass spectrometry to obtain molecular weight and concentration information. Chemical ionization mass spectrometry has the advantages of high sensitivity, fast response, and soft ionization. In recent years, it has been increasingly valued in the field of volatile organic compound monitoring and analysis.

[0003] Although chemical ionization mass spectrometry (CIMS) has been widely used in the detection of volatile organic compounds (VOCs), it has long been plagued by a technical bottleneck: its inability to distinguish substances with identical molecular weights. This is because mass spectrometry only provides information on the mass-to-charge ratio of the substance being tested and cannot identify substances with identical molecular weights, such as isomers. To address this issue, existing technologies have incorporated gas chromatography (GC) into CIMS, enabling the identification of substances with identical molecular weights. However, the introduction of GC increases single analysis times from several minutes to tens of minutes, making it impossible to achieve rapid separation and detection on the order of seconds. This limits the application of CIMS in scenarios where the types and concentrations of isomers are rapidly changing. Existing technologies have incorporated migration tubes into CIMS, enabling rapid separation and detection of isomers. However, ions within traditional migration tubes are affected by ion-molecule collisions and disperse, making them difficult to detect through the small aperture at the end of the migration tube. This reduces the sensitivity of the entire mass spectrometry system. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A dual-time-of-flight two-dimensional rapid separation chemical ionization mass spectrometer comprises: an ionization source, a reaction tube, a migration tube, a transition cavity and a mass spectrometer cavity connected from left to right via coaxial pinholes;

[0006] The reaction tube includes a funnel electrode, which is composed of a series of coaxial circular electrodes or four-petal electrodes with gradually decreasing inner diameters from left to right;

[0007] The migration tube includes an ion gate, a guide electrode, a segmented quadrupole guide electrode and a Faraday plate, which are coaxially distributed from left to right; a small hole is opened in the center of the Faraday plate;

[0008] The reaction tube is connected to the sampling pipeline; the transition cavity guide electrode is located in the transition cavity; the time-of-flight mass spectrometer detector is located inside the mass spectrometer cavity; the transition cavity guide electrode and the ion inlet of the time-of-flight mass spectrometer detector are coaxially distributed; the vacuum pump is connected to the left end of the migration tube through the vacuum pump valve, and is located between the reaction tube and the ion gate; the carrier gas source is connected to the right end of the migration tube through the carrier gas source valve, and is located at the front end of the Faraday plate; the Faraday plate is connected to the oscilloscope; the segmented quadrupole guide electrode is composed of multiple segments of coaxially distributed quadrupoles.

[0009] A method for isomer separation and detection of a chemical ionization mass spectrometer with dual time-of-flight two-dimensional rapid separation, used in the chemical ionization mass spectrometer with dual time-of-flight two-dimensional rapid separation, comprising:

[0010] Step 1: The isomeric organic compound to be measured enters the reaction tube through the sample inlet pipe, undergoes ion-molecule reaction with the reactive ions generated by the ionization source to generate product ions, and the product ions are focused and guided by the funnel electrode and efficiently enter the migration tube;

[0011] Step 2: Open the ion gate and energize the segmented quadrupole guide electrode. Under the action of the guide electrode, the product ions enter the segmented quadrupole guide electrode for focused transmission. Most of the product ions pass through the central hole of the Faraday plate and enter the transition chamber. A small number of ions hit the Faraday plate to form a current signal. The migration time of different ions is measured by an oscilloscope connected to the Faraday plate;

[0012] In step 3, the product ions in the transition cavity are efficiently injected into the mass spectrometry cavity under the action of the transition cavity guide electrode; the time-of-flight mass spectrometry detector obtains two spectra by scanning. The first is a traditional mass spectrum with different mass-to-charge ratios and their signal intensities. The mass-to-charge ratio corresponds to the flight time of the product ions in the time-of-flight mass spectrometry detector, which is a one-dimensional time-of-flight; the second is a migration spectrum with different migration times and mass spectrometry signal intensities at the same mass-to-charge ratio. The migration time corresponds to the flight time of the product ions in the migration tube, which is a two-dimensional time-of-flight.

[0013] The present invention has the following beneficial effects:

[0014] (1) By introducing a migration tube after the chemical ionization mass spectrometry reaction tube and improving the migration tube structure of the traditional circular electrode to a segmented quadrupole guide electrode, the ion transmission efficiency is improved while achieving isomer separation, and the resolution is improved by reducing radial ion fluctuations, thereby achieving rapid separation and highly sensitive detection of isomers by chemical ionization mass spectrometry.

[0015] (2) The novel migration tube structure is combined with chemical ionization mass spectrometry to achieve rapid separation and highly sensitive detection of isomers. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of a dual-time-of-flight two-dimensional rapid separation chemical ionization mass spectrometer of the present invention; wherein: 1-ionization source, 2-reaction tube, 3-drift tube, 4-transition chamber, 5-mass spectrometer chamber, 6-funnel electrode, 7-ion gate, 8-guide electrode, 9-segmented quadrupole guide electrode, 10-Faraday plate, 11-oscilloscope, 12-transition chamber guide electrode, 13-time-of-flight mass spectrometer detector, 14-carrier gas source, 15-vacuum pump, 16-carrier gas source valve, 17-vacuum pump valve, 18-injection line;

[0017] Figure 2 Schematic diagram of the power-on of the segmented quadrupole guide electrode;

[0018] Figure 3 Schematic diagram of the spectrum of a dual-time-of-flight two-dimensional rapid separation chemical ionization mass spectrometer; (a) is a traditional mass spectrum with different mass-to-charge ratios and their signal intensities, and (b) is a migration spectrum with different migration times and their signal intensities at the same mass-to-charge ratio. DETAILED DESCRIPTION

[0019] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0020] like Figure 1As shown, a dual time-of-flight two-dimensional rapid separation chemical ionization mass spectrometer of the present invention comprises an ionization source 1, a reaction tube 2, a migration tube 3, a transition chamber 4 and a mass spectrometry chamber 5; the ionization source 1, the reaction tube 2, the migration tube 3, the transition chamber 4 and the mass spectrometry chamber 5 are connected from left to right through coaxial small holes; the reaction tube 2 comprises a funnel electrode 6, which is composed of a series of coaxial circular electrodes or four-petal electrodes with gradually decreasing inner diameters from left to right; the migration tube 3 comprises an ion gate 7, a guide electrode 8, a segmented quadrupole guide electrode 9 and a Faraday plate 10; the ion gate 7, the guide electrode 8, the segmented quadrupole guide electrode 9 and the Faraday plate 10 The pole guide electrode 9 and the Faraday plate 10 are coaxially distributed from left to right; the reaction tube 2 is connected to the sampling line 18; the transition cavity guide electrode 12 is located in the transition cavity 4; the time-of-flight mass spectrometer detector 13 is located inside the mass spectrometer cavity 5; the ion inlet of the transition cavity guide electrode 12 and the time-of-flight mass spectrometer detector 13 are coaxially distributed; the vacuum pump 15 is connected to the left end of the migration tube 3 through the vacuum pump valve 17, specifically located between the reaction tube 2 and the ion gate 7; the carrier gas source 14 is connected to the right end of the migration tube 3 through the carrier gas source valve 16, specifically located at the front end of the Faraday plate 10; the Faraday plate 10 is connected to the oscilloscope 11.

[0021] The isomer separation and detection method of the dual-time-of-flight two-dimensional rapid separation chemical ionization mass spectrometer of the present invention comprises:

[0022] Step 1: The isomer organic compound to be measured enters the reaction tube 2 through the sampling line 18, undergoes ion-molecule reaction with the reaction ions generated by the ionization source 1 to generate product ions. The product ions are focused and guided by the funnel electrode 6 and efficiently enter the migration tube 3;

[0023] Step 2: Open the ion gate 7 and energize the segmented quadrupole guide electrode 9. Under the action of the guide electrode 8, the product ions enter the segmented quadrupole guide electrode 9 for focused transmission. Most of the product ions pass through the central aperture of the Faraday plate 10 and enter the transition chamber 4. A small portion of the ions hit the Faraday plate 10 to form a current signal. The migration time of different ions is measured by the oscilloscope 11 connected to the Faraday plate 10;

[0024] In step 3, the product ions in the transition chamber 4 are efficiently injected into the mass spectrometry chamber 5 under the action of the transition chamber guide electrode 12. The time-of-flight mass spectrometer detector 13 obtains two spectra through scanning. The first is a traditional mass spectrum with different mass-to-charge ratios and signal intensities. The mass-to-charge ratio corresponds to the flight time of the product ions in the time-of-flight mass spectrometer detector 13, which is a one-dimensional time-of-flight. The second is a migration spectrum with different migration times and mass spectrometry signal intensities at the same mass-to-charge ratio. The migration time corresponds to the flight time of the product ions in the migration tube 3, which is a two-dimensional time-of-flight. Different migration times can be used to distinguish isomers, and the mass spectrometry signal intensity can be used for quantitative analysis, thereby achieving dual-time-of-flight two-dimensional rapid separation and qualitative and quantitative detection of isomeric organic compounds.

[0025] In order to obtain a better ionization effect, the ionization source 1 is a glow discharge ionization source, a plasma ionization source or a photochemical ionization source.

[0026] To obtain the most sensitive detection effect, the reaction tube 2 includes a funnel electrode 6, which is a circular electrode radio frequency funnel or a four-petal electrode radio frequency funnel; the air pressure range in the reaction tube 2 is 0.5mbar~50mbar, and the effective electric field range in the reaction tube 2 is 5V / cm~50V / cm.

[0027] According to different vacuum configurations, the air pressure in the migration tube 3 is set to a range of 0.2 mbar to 10 mbar, which is specifically adjusted by the vacuum pump 15 and the vacuum pump valve 17 .

[0028] To obtain better resolution, the carrier gas source 14 may contain nitrogen, argon, or helium, etc., and its flow rate is controlled by the carrier gas source valve 16 .

[0029] In order to achieve control of the initial product ions in the drift tube 3 , the ion gate 7 is a Tyndall-Powell type ion gate or a Bradbury-Neilson type ion gate.

[0030] In order to obtain better product ion transmission efficiency and resolution, the segmented quadrupole guide electrode 9 is composed of multiple segments of coaxially distributed quadrupole rods, preferably 5 to 15 segments.

[0031] In order to ensure the working pressure of the migration tube 3 and the high passing efficiency of the product ions, a small hole is opened in the center of the Faraday plate 10, and the diameter of the hole is 0.2mm~5mm.

[0032] In order to achieve optimal ion guidance in the transition chamber 4 and improve the detection sensitivity of the instrument, the transition chamber guide electrode 12 is set to be an electrostatic lens, a radio frequency funnel or a quadrupole guide.

[0033] Figure 2A schematic diagram of the power-on of the segmented quadrupole guide electrode 9 is provided. In the four cylindrical metal rods of the same group, the two opposite metal rods apply the same radio frequency voltage through a capacitor, and the two adjacent metal rods apply radio frequency voltages with the same amplitude and opposite polarity through a capacitor. This voltage application method forms a quadrupole focusing field inside the quadrupole, compressing the product ions toward the central axis, which can improve the sensitivity by improving the product ion transmission efficiency and improve the resolution by reducing the radial fluctuation of the product ions. In addition, the quadrupoles of different segments use resistors with the same resistance value to evenly divide the voltage, providing an electrostatic field for the axial movement of the product ions. The segmented quadrupole guide electrode 9 of the present invention is used in conjunction with a chemical ionization mass spectrometer as a migration tube 3. While achieving rapid separation of isomers, it improves the transmission efficiency of the product ions in the migration tube 3, and can achieve rapid and highly sensitive detection of isomers by chemical ionization mass spectrometry.

[0034] Figure 3 A schematic diagram of the spectrum of a dual time-of-flight two-dimensional rapid separation chemical ionization mass spectrometer is given; wherein, Figure 3 (a) is the traditional mass spectrum of different mass-to-charge ratios and their signal intensities. Figure 3 (b) is a migration spectrum with different migration times and signal intensities at the same mass-to-charge ratio. The time-of-flight mass spectrometer 13 obtains two spectra through scanning: the first is a traditional mass spectrum with different mass-to-charge ratios and signal intensities, and the second is a migration spectrum with different migration times and signal intensities at the same mass-to-charge ratio. When the first, second, and third substances are not isomers, qualitative and quantitative detection can be achieved solely through the mass spectrum. When the first, second, and third substances are isomers of organic matter, the m / z values ​​of the three substances in the mass spectrum are the same and cannot be distinguished. However, the migration times in the migration spectrum can be used to distinguish them, thereby achieving qualitative and quantitative detection of the isomers.

[0035] The above descriptions are merely embodiments of the present invention and are not intended to limit the scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied to other related system fields, are also included in the scope of protection of the present invention.

[0036] The contents not described in detail in the specification of the present invention belong to the prior art known to those skilled in the art.

Claims

1. A chemical ionization mass spectrometer with dual time-of-flight two-dimensional rapid separation, characterized in that: include: From left to right, the ionization source, reaction tube, migration tube, transition chamber and mass spectrometer chamber are connected through the coaxial small hole respectively; The reaction tube includes a funnel electrode, which is composed of a series of coaxial circular electrodes or four-petal electrodes with gradually decreasing inner diameters from left to right; The migration tube includes an ion gate, a guide electrode, a segmented quadrupole guide electrode and a Faraday plate, which are coaxially distributed from left to right; a small hole is opened in the center of the Faraday plate; The reaction tube is connected to the sampling pipeline; the transition cavity guide electrode is located in the transition cavity; the time-of-flight mass spectrometer detector is located inside the mass spectrometer cavity; the transition cavity guide electrode and the ion inlet of the time-of-flight mass spectrometer detector are coaxially distributed; the vacuum pump is connected to the left end of the migration tube through the vacuum pump valve, and is located between the reaction tube and the ion gate; the carrier gas source is connected to the right end of the migration tube through the carrier gas source valve, and is located at the front end of the Faraday plate; the Faraday plate is connected to the oscilloscope; the segmented quadrupole guide electrode is composed of multiple segments of coaxially distributed quadrupoles.

2. The dual-time-of-flight two-dimensional rapid separation chemical ionization mass spectrometer according to claim 1, characterized in that: The ionization source is a glow discharge ionization source, a plasma ionization source or a photochemical ionization source.

3. The dual time-of-flight two-dimensional rapid separation chemical ionization mass spectrometer according to claim 1, characterized in that: The funnel electrode is a circular electrode radio frequency funnel or a four-petal electrode radio frequency funnel.

4. The dual time-of-flight two-dimensional rapid separation chemical ionization mass spectrometer according to claim 1, characterized in that: The carrier gas source contains nitrogen, argon or helium.

5. The dual-time-of-flight two-dimensional rapid separation chemical ionization mass spectrometer according to claim 1, characterized in that: The ion gate is a Tyndall-Powell type ion gate or a Bradbury-Nelson type ion gate.

6. The dual time-of-flight two-dimensional rapid separation chemical ionization mass spectrometer according to claim 1, characterized in that: The number of quadrupole rods constituting the segmented quadrupole guide electrode is 5 to 15.

7. The dual time-of-flight two-dimensional rapid separation chemical ionization mass spectrometer according to claim 1, characterized in that: The transition cavity guide electrode is configured as an electrostatic lens, a radio frequency funnel or a quadrupole guide.

8. A method for isomer separation and detection in a dual-time-of-flight two-dimensional rapid separation chemical ionization mass spectrometer, used in the dual-time-of-flight two-dimensional rapid separation chemical ionization mass spectrometer according to any one of claims 1 to 7, characterized in that: include: Step 1: The isomeric organic compound to be measured enters the reaction tube through the sample inlet pipe, undergoes ion-molecule reaction with the reactive ions generated by the ionization source to generate product ions, and the product ions are focused and guided by the funnel electrode and efficiently enter the migration tube; Step 2: Open the ion gate and energize the segmented quadrupole guide electrode. Under the action of the guide electrode, the product ions enter the segmented quadrupole guide electrode for focused transmission. Most of the product ions pass through the central hole of the Faraday plate and enter the transition chamber. A small number of ions hit the Faraday plate to form a current signal. The migration time of different ions is measured by an oscilloscope connected to the Faraday plate; In step 3, the product ions in the transition cavity are efficiently injected into the mass spectrometry cavity under the action of the transition cavity guide electrode; the time-of-flight mass spectrometry detector obtains two spectra by scanning. The first is a traditional mass spectrum with different mass-to-charge ratios and their signal intensities. The mass-to-charge ratio corresponds to the flight time of the product ions in the time-of-flight mass spectrometry detector, which is a one-dimensional time-of-flight; the second is a migration spectrum with different migration times and mass spectrometry signal intensities at the same mass-to-charge ratio. The migration time corresponds to the flight time of the product ions in the migration tube, which is a two-dimensional time-of-flight.

9. The isomer separation and detection method according to claim 8, characterized in that: In step 2, when the segmented quadrupole guide electrode is powered, the two opposing metal rods in the same group of four cylindrical metal rods are applied with the same radio frequency voltage through capacitors, and the two adjacent metal rods are applied with radio frequency voltages of the same amplitude and opposite polarity through capacitors.

10. The isomer separation and detection method according to claim 8, characterized in that: In step 2, in the segmented quadrupole guide electrode, quadrupoles of different segments use resistors with the same resistance value to evenly divide the voltage, providing an electrostatic field for the axial motion of product ions.

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