Isotope analysis system and isotope analysis method

Abstract

The invention relates to the technical field of nitrogen isotope analysis, and discloses an isotope analysis system and an isotope analysis method.The isotope analysis system comprises a gas sample input device, a field emission ion source, a magnetic mass analyzer and a Faraday cup acceptor, the ionization chamber is connected to the gas sample input device, and the field exit slit is used for emitting ion beams; the magnetic mass analyzer is connected to the field exit slit, and the magnetic mass analyzer is used for selecting ions in the ion beam to obtain ions to be measured; the Faraday cup receiver is connected to the magnetic mass analyzer, and the Faraday cup receiver is used for analyzing the ion beam intensity, the sample component information and / or the ion quantity of the to-be-detected ions. The field emission ion source is utilized to ionize the gas molecules of the gas sample to obtain the ion beam, so that the influence of impure background gas can be reduced, and the measurement precision and stability of the nitrogen cluster isotope are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of nitrogen isotope analysis, and particularly to an isotope analysis system and an isotope analysis method. Background Art

[0002] Nitrogen is one of the important elements in the earth's life system, and its isotope composition has wide application value in many fields such as earth science, climatology, environmental science, and agriculture, industry, and biology. Nitrogen has two main stable isotopes, namely nitrogen-14 (N 14 ), and nitrogen-15 (N 15 ). Different permutations and combinations of these two isotopes in nitrogen molecules can form nitrogen molecules with mass numbers of 28, 29, and 30. Among them, the nitrogen molecule with a mass number of 30, due to its composition of two rare isotopes (N 15 ), is also known as the nitrogen cluster isotope.

[0003] The ratio of nitrogen cluster isotopes, especially the ratio of nitrogen-15 to nitrogen-14, can reflect historical information of climate change and become an important tool for studying paleoclimate and nitrogen changes in the atmosphere. In paleoclimatology and climate models, this ratio is used as an indicator for studying changes in environmental factors such as temperature and precipitation. In addition, nitrogen has a very high content in the earth's atmosphere and actively participates in the global biogeochemical cycle, such as the nitrogen cycle. Therefore, measuring the isotope composition in nitrogen clusters helps to understand the flow and transformation processes of nitrogen in different sources (such as the atmosphere, soil, and ocean), and is of great significance for studying processes such as biological nitrogen fixation, nitrogen deposition, and nitrogen biological utilization.

[0004] However, traditional nitrogen isotope analysis methods, such as stable isotope mass spectrometers using the EI source (Electron Ionization Source, a commonly used ionization source) architecture, have many deficiencies. This method ionizes neutral nitrogen gas through a high-temperature filament, generates nitrogen ions and then conducts detection and analysis. However, this method is easily affected by impure background gas and generates impurities such as NO, which will seriously interfere with the measurement of N2 30+ (i.e., nitrogen ions with a mass number of 30). In addition, the stability and ionization efficiency of filament ionization are poor, which not only affects the stability of the measurement but also limits the detection limit, making it a great challenge for traditional methods to analyze nitrogen cluster isotopes.

[0005] In view of the above background, it is necessary to develop a new nitrogen isotope analysis method to solve the problems existing in the prior art. Summary of the Invention

[0006] The purpose of the present invention is to provide an isotope analysis system and an isotope analysis method to solve the problems existing in the above-mentioned prior art. A field emission ion source is used to ionize the gas molecules of a gas sample to obtain an ion beam, which can reduce the influence of impure background gas and improve the measurement accuracy and stability of nitrogen cluster isotopes.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] The present invention provides an isotope analysis system, comprising a gas sample input device, a field emission ion source, a magnetic mass analyzer and a Faraday cup receiver, wherein the field emission ion source comprises an ionization chamber and an exit slit, the ionization chamber is connected to the gas sample input device, and the exit slit is used to emit an ion beam; the magnetic mass analyzer is connected to the exit slit, and the magnetic mass analyzer is used to select ions in the ion beam to obtain ions to be measured; the Faraday cup receiver is connected to the magnetic mass analyzer, and the Faraday cup receiver is used to analyze the ion beam intensity, sample composition information and / or ion quantity of the ions to be measured.

[0009] In one embodiment, the field emission ion source further includes a field emission electron gun, which includes an electron emission end and an attracting electrode, wherein the electron emission end and the attracting electrode are located on opposite sides of the ionization chamber, and the electron beam emitted by the electron emission end passes through the ionization chamber.

[0010] In one embodiment, the field emission ion source further comprises an accelerating electric field, and the accelerating electric field is used to accelerate ions in the ionization chamber to form an ion beam, and the ion beam is emitted from the exit slit.

[0011] In one embodiment, the field emission ion source further includes a focusing lens and a semi-high voltage plate, and the focusing lens and the semi-high voltage plate are sequentially arranged between the ionization chamber and the exit slit.

[0012] In one embodiment, the gas sample input device includes a water removal device, an oxygen removal device and an impurity removal device, wherein the water removal device includes a condenser and / or a molecular sieve, the oxygen removal device includes a reducing material, and the impurity removal device includes a chemical adsorbent.

[0013] In one embodiment, a vacuum system is also included, which includes a vacuum chamber and a vacuum pumping device connected to the vacuum chamber, the field emission ion source, the magnetic mass analyzer and the Faraday cup receiver are located in the vacuum chamber, and the vacuum pumping device is used to evacuate the vacuum chamber.

[0014] In one embodiment, it further includes an ion control system, which is connected to the field emission ion source, and is used to optimize and regulate the ion beam generated by the ion source by controlling the electrical parameters related to the ion source.

[0015] In one embodiment, it further includes a magnetic field control system, which is connected to the magnetic mass analyzer, and is used to select ions with different mass-to-charge ratios by controlling the magnetic induction intensity by controlling the current intensity of the electromagnet.

[0016] In one embodiment, it further includes a data processing system, which is connected to the Faraday cup receiver, and is used to amplify and filter the electrical signal obtained by the Faraday cup receiver, and finally obtain the analysis result of the nitrogen cluster isotope.

[0017] The present invention also provides an isotope analysis method, which applies the isotope analysis system described above, including the following content:

[0018] S1. Process the gas sample to remove impurities in the gas sample;

[0019] S2. Introduce the processed gas sample into the field emission ion source, and ionize the gas molecules of the gas sample in the field emission ion source to form and emit an ion beam outward;

[0020] S3. The emitted ion beam enters the magnetic mass analyzer, and under the action of the magnetic mass analyzer, select the ions that meet the requirements as the ions to be measured;

[0021] S4. Let the ions to be measured enter the Faraday cup receiver, and use the Faraday cup receiver to analyze the ion beam intensity, sample composition information and / or ion quantity of the ions to be measured.

[0022] The present invention has achieved the following technical effects compared with the prior art:

[0023] The present invention ionizes the gas molecules of the gas sample by using the field emission ion source to obtain an ion beam, which can reduce the influence of impure background gas, avoid the interference of impurities such as NO, improve the measurement accuracy and stability of nitrogen cluster isotopes, and meet the high-precision requirements for nitrogen isotope analysis in the fields of earth science, climatology, environmental science, and agriculture, industry and biology. Description of the Drawings

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 Schematic diagram of the composition of the isotope analysis system in the embodiment of the present invention;

[0026] Figure 2 Schematic diagram of the field emission ion source in the embodiment of the present invention;

[0027] Among them, 1. Electron emission end; 2. Attracting electrode; 3. Ionization chamber; 4. Focusing lens; 5. Semi-high voltage plate; 6. Exit slit; 7. Repelling electrode; 8. Grounding electrode; 10. Electron beam; 20. Ion beam. Specific embodiments

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0029] The purpose of the present invention is to provide an isotope analysis system and an isotope analysis method to solve the problems existing in the prior art. By using a field emission ion source to ionize gas molecules of a gas sample to obtain an ion beam, the influence of impure background gas can be reduced, and the measurement accuracy and stability of nitrogen cluster isotopes can be improved.

[0030] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0031] Such as Figure 1 And Figure 2As shown in the figure, the present invention provides an isotope analysis system, including a gas sample input device, a field emission ion source, a magnetic mass analyzer, and a Faraday cup receiver. The field emission ion source includes an ionization chamber 3 and an exit slit 6. The exit slit 6 corresponds to the ion exit of the ionization chamber 3. The ionization chamber 3 is connected to the gas sample input device. Through the gas sample input device, the gas sample to be analyzed is introduced into the ionization chamber 3. The gas sample generates ions and forms an ion beam 20 after being ionized by an electron beam 10 in the ionization chamber 3. The generated ion beam 20 is emitted from the ionization chamber 3 through the exit slit 6. The ionization chamber 3 floats on a high electric potential as a whole, and the exit slit 6 is grounded with a zero electric potential. On the one hand, it can accelerate the ionized ions, and on the other hand, it enables the ionized ions to form an ion beam 20. The magnetic mass analyzer is connected to the exit slit 6. The ion beam 20 emitted from the exit slit 6 enters the magnetic mass analyzer. Under the action of the magnetic mass analyzer, the trajectories of different ions in the ion beam 20 are different. Ions with a specific mass-to-charge ratio (m / z) are emitted along a specific trajectory, so as to select the ions in the ion beam 20 by using the magnetic mass analyzer and obtain the ions to be measured. The Faraday cup receiver is connected to the magnetic mass analyzer. After the ions to be measured enter the Faraday cup receiver from the magnetic mass analyzer, under the action of the Faraday cup receiver, parameters such as the intensity of the ion beam 20 of the ions to be measured, the sample composition information, and / or the number of ions are analyzed, and finally an accurate quantitative analysis result is obtained.

[0032] The present invention ionizes the gas molecules of the gas sample by using a field emission ion source to obtain an ion beam 20, which can reduce the influence of impure background gas, avoid the interference of impurities such as NO, improve the measurement accuracy and stability of nitrogen cluster isotopes, and meet the high-precision requirements for nitrogen isotope analysis in the fields of earth science, climatology, environmental science, and agriculture, industry, and biology.

[0033] In one embodiment, the field emission ion source further includes a field emission electron gun, which is the core of the field emission ion source. The field emission electron gun includes an electron emission end 1 and an attracting electrode 2. The electron emission end 1 and the attracting electrode 2 are located on opposite sides of the ionization chamber 3, and the electron beam 10 emitted by the electron emission end 1 penetrates the ionization chamber 3. The function of the field emission electron gun is to ionize gas molecules by colliding the emitted high-energy electron beam 10 with gas molecules. The principle is that under the action of a strong electric field, electrons on the solid surface overcome the surface potential energy and "escape" from the material surface to form the electron beam 10. When the externally applied electric field strength is large enough (usually an electric field strength of several hundred volts per micrometer), the electron energy on the material surface can overcome its surface barrier and enter the vacuum state to form the electron beam 10. The field emission electron source usually uses a metal or carbon material in the shape of a tip, and utilizes the strong electric field concentration effect at the tip to improve the electron emission efficiency. Once the electrons are emitted from the metal surface, they will be accelerated and hit the gas molecules or the sample surface, ionizing them to generate ions. At this time, the interaction between the electrons and the gas molecules will cause the ionization or excitation of the gas molecules, forming charged ions. The electron emission end 1 is usually made of high-purity metal (such as tungsten) or nanomaterials (such as carbon nanotubes). The electric field strength at the tip part is extremely high, which can effectively promote the field emission of electrons. The shape of the tip (such as a conical shape) helps to concentrate the electric field and enhance the field emission effect.

[0034] The field emission electron gun usually includes a heated cathode, an anode for accelerating electrons, and a magnetic field for controlling the direction and intensity of the electron beam 10. Among them, the cathode can be used as the electron emission end 1, and the anode can be used as the attracting electrode 2. The electrons generated by the emission of the electron emission end 1 will generate an electron beam 10 that traverses the ionization chamber 3 under the action of the ionization chamber 3 and the attracting electrode 2. When the electron beam 10 collides with the neutral gas molecules in the ionization chamber 3, elastic or inelastic collisions occur between the electrons and the gas molecules, resulting in the ionization of the gas molecules. The ionization chamber 3 controls the focusing of the electron beam 10 through a tiny metal aperture.

[0035] In one embodiment, the field emission ion source further includes an accelerating electric field, which is used to accelerate the ions in the ionization chamber 3 to form an ion beam 20, and the ion beam 20 is emitted from the exit slit 6 and then directed to an analyzer or other processing systems. The formation of the accelerating electric field can include a repelling electrode 7 and a grounding electrode 8. The repelling electrode 7 is located in the ionization chamber 3 and has a high electric potential, and the grounding electrode 8 is connected to the exit slit 6 and has a zero electric potential.

[0036] In one embodiment, the field emission ion source further includes a focusing lens 4 and a half - high - voltage plate 5. The focusing lens 4 and the half - high - voltage plate 5 are sequentially arranged between the ionization chamber 3 and the exit slit 6. The half - high - voltage plate 5, which is a high - voltage plate with a voltage added between high voltage and ground approximately half of the maximum voltage (usually adjustable), and its English name is half plate, is used to form a relatively stable and gradually changing high - voltage electric field in a set area to deflect or focus the ion beam 20 to the desired direction. Therefore, the arrangement of the focusing lens 4 and the half - high - voltage plate 5 can better focus the ion beam 20 and help guide the ions from the ionization region to the magnetic mass analyzer.

[0037] In one embodiment, the function of the gas sample input device is to ensure that the gas collection and transmission system does not introduce any additional contaminants or affect the isotope composition of the sample. Gas is collected through gas cylinders or sample bags. Usually, special containers are required to prevent gas mixing and decomposition. Using metal or glass gas cylinders can reduce chemical reactions between the sample and the container. Gas samples often contain impurities such as water vapor, oxygen, carbon dioxide, sulfur dioxide, etc. These impurities not only interfere with isotope measurements but may also affect the operation of the analysis equipment. Therefore, the gas purification step is crucial. The gas sample input device includes a water removal device, an oxygen removal device, and an impurity removal device. The water removal device includes a condenser and / or molecular sieve, and a condenser or molecular sieve (such as molecular sieve) is used to remove moisture. The oxygen removal device includes a reducing material, such as a zinc - containing reducing agent, which removes oxygen through a reduction reaction. The impurity removal device includes a chemical adsorbent. For example, desiccants such as calcium hydride (CaH2) or lithium aluminum hydride (LiAlH4) are used to remove water again, and chemical adsorbents are used to remove sulfur dioxide, etc.

[0038] In one embodiment, a vacuum system is further included. The vacuum system includes a vacuum chamber and a vacuum pumping device connected to the vacuum chamber. The field emission ion source, the magnetic mass analyzer, and the Faraday cup receiver are located in the vacuum chamber, and the vacuum pumping device is used to pump the vacuum chamber. The vacuum pumping device can use a molecular pump and a dry pump to achieve a higher vacuum degree through double - stage vacuum. All electrical interfaces are completed through electrode flanges.

[0039] In one embodiment, an ion control system is further included. The ion control system is connected to the field emission ion source, and the ion control system is used to optimize and regulate the ion beam 20 generated by the ion source by controlling the electrical parameters related to the ion source. The electrical parameters mentioned here include electrical parameters such as voltage and current.

[0040] In one embodiment, a magnetic field control system is further included. The magnetic field control system is connected to the magnetic mass analyzer, and the magnetic field control system is used to control the magnetic induction intensity by controlling the current intensity of the electromagnet to select ions with different charge - to - mass ratios.

[0041] The accelerated ions enter a region of strong magnetic field, and under the action of the strong magnetic field, the ions are deflected. According to the principle of Lorentz force:

[0042] F = q(v × B)

[0043] where F is the Lorentz force, q is the charge of the ion, v is the velocity of the ion, and B is the magnetic induction intensity.

[0044] When the ions move in the magnetic field, they will be subjected to a force perpendicular to the directions of the velocity and the magnetic field, which causes the ions to move along a circular arc trajectory. The deflection radius of the ions is related to their mass-to-charge ratio (m / z), and the specific relationship is:

[0045] r = mv / qB;

[0046] where r is the deflection radius of the ions, m is the mass of the ions, v is the velocity of the ions, q is the charge of the ions, and B is the magnetic induction intensity.

[0047] Therefore, ions of different masses will be deflected along different trajectories, thereby achieving mass separation. Under the action of the magnetic field, the ions move along circular arc trajectories of different radii. By adjusting the intensity of the magnetic field, different trajectories can be selected and ions of a specific mass can be made to reach the detector (for example, a Faraday cup receiver). Only ions with a specific mass-to-charge ratio (m / z) will reach the detector along a specific trajectory. By precisely controlling the magnetic induction intensity, ions within a certain mass range can be precisely selected.

[0048] In one embodiment, a data processing system is further included. The data processing system is connected to the Faraday cup receiver and is used to perform amplification and filtering processing on the electrical signals obtained by the Faraday cup receiver, and finally obtain the analysis results of the nitrogen cluster isotopes.

[0049] The charged ions enter the Faraday cup receiver from the magnetic mass analyzer. The Faraday cup receiver is a groove or cup-shaped device made of a conductive material, which can completely capture the incoming ions and prevent the ions from escaping. The captured ions accumulate charges on the cup wall, generating a tiny current. The magnitude of this current is proportional to the number of incoming ions. The current signal of the ions is transmitted to an amplifier and a current detection system through a circuit connected to the Faraday cup receiver. Through a highly sensitive current amplifier, these weak current signals are amplified for subsequent analysis and recording. The amplified signal is transmitted to the data processing system, and the intensity of the ion beam 20 or the sample composition information is obtained through data analysis. The Faraday cup receiver can accurately measure the number of ions, thereby providing accurate quantitative analysis results.

[0050] Refer again to Figure 1 and Figure 2, the present invention also provides an isotope analysis method, which applies the isotope analysis system described above, including the following steps:

[0051] S1. Process the gas sample. Use the gas sample input device to remove impurities in the gas sample. The impurities mentioned here include water, carbon dioxide, oxygen, sulfur dioxide, etc. The gas sample input device includes a water removal device, an oxygen removal device, and an impurity removal device. Remove water through the water removal device, remove oxygen through the oxygen removal device, and remove the remaining other impurities through the impurity removal device.

[0052] S2. Introduce the processed gas sample into the field emission ion source. The field emission ion gun emits a high-energy electron beam 10. The electron beam 10 collides with gas molecules to ionize the gas molecules and obtain ions. The ions obtained by ionization are formed and emitted as an ion beam 20 in the field emission ion source.

[0053] S3. The emitted ion beam 20 enters the magnetic mass analyzer. The magnetic mass analyzer can select the required ions according to the mass-to-charge ratio (m / z) of different ions. That is, under the action of the magnetic mass analyzer, ions that meet the requirements can be selected as the ions to be measured. In the present invention, nitrogen ions N2 + can be selected according to their mass-to-charge ratio (m / z), and after moving along a specific trajectory, they enter the Faraday cup receiver from the outlet of the magnetic mass analyzer.

[0054] S4. Introduce the ions to be measured into the Faraday cup receiver, and use the Faraday cup receiver to analyze the intensity of the ion beam 20, the sample composition information, and / or the number of ions of the ions to be measured.

[0055] In the present invention, specific examples are used to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. An isotope analysis system, characterized in that, Comprising: A gas sample input device; A field emission ion source, the field emission ion source comprising an ionization chamber and an exit slit, the ionization chamber being connected to the gas sample input device, the exit slit being used for emitting an ion beam; A magnetic mass analyzer, the magnetic mass analyzer being connected to the exit slit, the magnetic mass analyzer being used for selecting ions in the ion beam to obtain ions to be measured; And a Faraday cup receiver, the Faraday cup receiver being connected to the magnetic mass analyzer, the Faraday cup receiver being used for analyzing the ion beam intensity, sample composition information and / or ion quantity of the ions to be measured.

2. The isotope analysis system according to claim 1, characterized in that: The field emission ion source further comprises a field emission electron gun, the field emission electron gun comprising an electron emission end and an attracting electrode, the electron emission end and the attracting electrode being located on opposite sides of the ionization chamber, and the electron beam emitted by the electron emission end passing through the ionization chamber.

3. The isotope analysis system according to claim 2, characterized in that: The field emission ion source further comprises an accelerating electric field, the accelerating electric field being used for accelerating the ions in the ionization chamber to form an ion beam, which is emitted by the exit slit.

4. The isotope analysis system according to claim 2, characterized in that: The field emission ion source further comprises a focusing lens and a semi-high voltage plate, the focusing lens and the semi-high voltage plate being sequentially arranged between the ionization chamber and the exit slit.

5. The isotope analysis system according to claim 1, characterized in that: The gas sample input device comprises a water removal device, an oxygen removal device and an impurity removal device, the water removal device comprising a condenser and / or a molecular sieve, the oxygen removal device comprising a reducing material, and the impurity removal device comprising a chemical adsorbent.

6. The isotope analysis system according to claim 1, wherein: It further comprises a vacuum system, the vacuum system comprising a vacuum chamber and a vacuum pumping device connected to the vacuum chamber, the field emission ion source, the magnetic mass analyzer and the Faraday cup receiver being located in the vacuum chamber, and the vacuum pumping device being used for pumping vacuum on the vacuum chamber.

7. The isotope analysis system according to claim 1, wherein: It further comprises an ion control system, the ion control system being connected to the field emission ion source, the ion control system being used for optimizing and regulating the ion beam generated by the ion source by controlling the electrical parameters related to the ion source.

8. The isotope analysis system according to claim 1, characterized in that: It further comprises a magnetic field control system, the magnetic field control system being connected to the magnetic mass analyzer, the magnetic field control system being used for controlling the magnetic induction intensity by controlling the current intensity of the electromagnet to select ions with different charge-to-mass ratios.

9. The isotope analysis system according to claim 1, wherein: It further comprises a data processing system, the data processing system being connected to the Faraday cup receiver, the data processing system being used for amplifying and filtering the electrical signals obtained by the Faraday cup receiver, and finally obtaining the analysis result of the nitrogen cluster isotope.

10. An isotope analysis method, characterized in that, Applying the isotope analysis system according to any one of claims 1-9, comprising the following steps: S1. Processing the gas sample to remove impurities in the gas sample; S2. Feeding the processed gas sample into the field emission ion source, ionizing the gas molecules of the gas sample in the field emission ion source to form and emit an ion beam outward; S3. The emitted ion beam enters the magnetic mass analyzer, and under the action of the magnetic mass analyzer, selecting ions that meet the requirements as ions to be measured; S4. Introduce the ion to be measured into the Faraday cup receiver, and use the Faraday cup receiver to analyze the ion beam intensity, sample composition information, and / or the number of ions of the ion to be measured.

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