A multi-ion source mass spectrometer

Abstract

The present invention belongs to multi-ion source mass spectrometry detection technology. The multi-ion source mass spectrometer of the present invention includes: a reagent inlet, a hollow cathode area, a reagent ion generation area, a reaction chamber, an electrode, a sample inlet, an EI sample inlet pipeline, a differential vacuum interface plate, a differential vacuum interface hole, and a high vacuum cavity; the reagent inlet, the hollow cathode area, the reagent ion generation area, the reaction chamber and the high vacuum cavity are connected in sequence; the sample inlet is arranged on the side of the reaction chamber close to the reagent ion generation area; there are multiple electrodes around the interior of the reaction chamber; the EI sample inlet pipeline is arranged between the electrode close to the side of the differential vacuum interface plate and the differential vacuum interface plate; the differential vacuum interface plate is at the connection between the reaction chamber and the high vacuum cavity, and a differential vacuum interface hole is arranged in the middle of the differential vacuum interface plate. The entire switching device of the present invention has no movable parts such as motors and magnets, and has a simple structure and high reliability.

Description

Technical Field

[0001] The invention belongs to multi-ion source mass spectrometry detection technology. Background Art

[0002] The ion source is a key component of the mass spectrometer to ionize samples. For gaseous samples, the most common ionization source is the EI electron bombardment ion source. It breaks up and ionizes sample molecules by emitting electrons with an energy of 70eV. The EI source has the characteristics of mature technology and a wide range of applications, especially the mature NIST spectral library can be used to search for components.

[0003] CI chemical ionization sources represented by PTR ion sources can obtain the molecular ion peaks of components. The characteristic of this principle is that it does not require GC separation and can obtain mass spectrometry analysis results very quickly. Because there is no separation process, some components with strong polarity can be analyzed.

[0004] The existing inventions are all aimed at studying ultraviolet photoionization sources, and cannot solve the problem of switching CI ion sources. Ultraviolet photoionization sources use light to softly ionize organic molecules, and their fixed ionization energy is about 11eV. The principles and methods are quite different, and the ionization components and CI ion sources have different focuses. Therefore, there is no mature solution for the composite (multi) ion source technology of CI ion sources. In addition, the relevant existing technologies still have the following deficiencies.

[0005] The composite ion source described in patents CN209843660U, CN102299038A, and CN213424922U uses both soft and hard ionization sources to ionize samples, which will result in a large number of non-standard spectral peaks, which is not conducive to automated processing. The main problem solved by these patents is to use EI and photoelectrons to ionize samples at the same time, thereby generating a more complex mass spectrum than EI electron bombardment, thereby obtaining more sample molecular information. This application is suitable for laboratories and scientific research occasions. It is not suitable for industrial applications such as online and cruise.

[0006] The composite ion source described in patent CN113539784A uses a motor to complete the switching optical path control, and has a complex structure. When the motor drives the reflector to switch, it is difficult to achieve high-frequency switching when the motor is used to realize the rotation of the reflector in the vacuum chamber.

[0007] CI ion source mass spectrometry has been fully applied in cruise and online monitoring as a rapid VOC detection technology. However, due to the lack of standard methods and standard spectral libraries, it is impossible to directly use mature databases such as the NIST spectral library, which to some extent limits the development and application of CI ion source mass spectrometry.

[0008] The difficulty in quickly switching between CI and EI ion sources is that the gases analyzed by the two ion sources and the working electric fields interfere with each other, resulting in the inability to quickly switch between the two.

[0009] The vacuum degree required for the EI ion source to work is higher than that of the CI source, and is not compatible with the conditions of the CI ion source, resulting in the two ion sources being combined in a way that the CI is in a rough vacuum upstream and the EI source is in a high vacuum downstream.

[0010] Because the CI ion source uses reagent ions to ionize the sample, the reagent ions and sample ions generated during operation are difficult to be quickly cleared when switching to the EI source, causing them to interfere with the products of the downstream EI ion source.

[0011] For invalid ions generated by CI source, electric field can be used to eliminate them. However, neutral gas molecules in CI ion source cannot be eliminated by electric field. When EI is working, the residual neutral molecules of CI will have an uncontrollable dilution effect on the sample, affecting the quantitative accuracy. In addition, these molecules will also carry some ions generated by CI when passing through the differential hole, which will significantly interfere with the analysis results of EI ion source.

[0012] The CI source emits a radial ion beam from the differential aperture with a fast ion motion speed, while the EI source produces an approximately cylindrical ion beam with a slow ion motion speed. The shapes and ion motion states of the two are quite different, and it is difficult for the subsequent ion lens to be compatible with these two ion beams. Summary of the invention

[0013] In view of this, the present invention provides a multi-ion source mass spectrometer, comprising: a reagent inlet, a hollow cathode region, a reagent ion generating region, a reaction chamber, an electrode, a sample inlet, an EI sample inlet pipeline, a differential vacuum interface plate, a differential vacuum interface hole, and a high vacuum cavity; the reagent inlet, the hollow cathode region, the reagent ion generating region, the reaction chamber and the high vacuum cavity are connected in sequence; the sample inlet is arranged on a side of the reaction chamber close to the reagent ion generating region; a plurality of electrodes are arranged around the interior of the reaction chamber; the EI sample inlet pipeline is arranged between the electrode close to the side of the differential vacuum interface plate and the differential vacuum interface plate; the differential vacuum interface plate is provided with a differential vacuum interface hole in the middle of the differential vacuum interface plate at the place where the reaction chamber and the high vacuum cavity are connected.

[0014] In some specific embodiments of the present invention, the high vacuum chamber comprises: an EI ion source, a first lens and a second lens; the EI ion source, the first lens and the second lens are distributed in the high vacuum chamber from near to far from the differential vacuum interface plate; the outlet of the EI ion source faces the inlet of the first lens; the outlet of the first lens faces the inlet of the second lens.

[0015] In some specific embodiments of the present invention, the EI ion source includes: an EI source filament, an EI source receiving electrode A, an EI source receiving electrode B and an EI ion source chamber; the EI source filament and the EI source receiving electrode A are located on the same side of the EI ion source chamber; the EI source filament and the EI source receiving electrode A and the EI source receiving electrode B are located on both sides of the EI ion source chamber; the outlet of the EI ion source chamber is opposite to the entrance of the first lens.

[0016] In some specific embodiments of the present invention, a mechanical pump extraction port is further included, and the mechanical pump extraction port is arranged at the lower end of the reaction chamber.

[0017] The entire switching device of the present invention has no movable parts such as motors and magnets, and has a simple structure and high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural diagram of a multi-ion source mass spectrometer. 1 is the reagent inlet, 2 is the hollow cathode area, 3 is the reagent ion generation area, 4 is the reaction chamber, 5 is the sample inlet, 6 is the electrode, 7 is the EI sample inlet pipeline, 8 is the mechanical pump extraction port, 9 is the differential vacuum interface plate, 10 is the differential vacuum interface hole, 11 is the high vacuum chamber, 12 is the EI source filament, 13 is the EI source receiving electrode A, 14 is the EI ion source chamber, 15 is the first lens, 16 is the second lens, and 13 is the EI source receiving electrode B.

[0019] Figure 2 This is a diagram of the ion source simulation model.

[0020] Figure 3 This is a simulation diagram of the CI ion source working.

[0021] Figure 4 This is a simulation diagram of the EI ion source working. DETAILED DESCRIPTION

[0022] Example

[0023] CI ion source is a high-performance ion source suitable for organic analysis, with the advantages of high sensitivity, no need for GC separation, strong resistance to matrix interference, etc. It is now widely used in various organic detection occasions.

[0024] The EI electron impact ion source is a classic ionization source, usually configured inside a mass spectrometer with GC separation. There are many standard methods to support its application.

[0025] Due to the lack of standard support and the purpose of its own development, the CI ion source needs to be combined with the EI ion source to realize the functions of multi-ion source switching and collaborative analysis.

[0026] Ion source: Its function is to charge the molecules to be measured. In the ion source, the molecules lose electrons to generate charged molecular ions. Molecular ions may further break down to generate fragment ions with smaller mass.

[0027] EI ion source: The electron ionization source, also known as the EI source, is the most widely used ion source. It is mainly used for the ionization of volatile samples. The samples mostly enter the ion source in the form of gas, and the electrons emitted by the filament collide with the sample molecules to ionize the sample molecules. Generally, the voltage between the filament and the receiving electrode is 70 volts, and all standard mass spectra are made at 70 ev. Under the action of the 70 ev electron collision, the organic molecule may lose an electron to form a molecular ion, or the chemical bond may break to form a fragment ion.

[0028] CI ion source: refers to the process of ionizing one or more "reagents", such as CH 4 , NH 3 , H 2 O, O 2 Etc. These ionized molecules are then used to ionize the sample molecules. Since the ionization energy of this indirect ionization is low, a type of ionization technology based on molecular ion peaks can be obtained.

[0029] Differential orifice plate: In a vacuum system, it is used to establish the difference in vacuum degree between different vacuum chambers.

[0030] Reagent ion: Reagent ion is used to undergo ionization reaction with the analyte, that is, to ionize the analyte. For example, gas phase hydronium ion is a reagent ion.

[0031] Ionic reagent: The raw material used to produce reagent ions, such as deionized water, which is the reagent for producing gas-phase hydronium ions.

[0032] The present invention provides a multi-ion source mass spectrometer, which combines a CI ion source and an EI ion source and allows them to work alternately in different time periods, and synchronously analyzes the CI and EI ion sources of the same group of samples, thereby achieving the effect of multi-angle analysis and detection of samples.

[0033] The invention solves the problem of fast switching of CI ion source and EI electron bombardment source in seconds through electrostatic field structure design and sample introduction design.

[0034] The present invention connects the CI source and the EI source in series, sets the EI source on the high vacuum side of the vacuum differential hole, designs different sampling pipelines for the CI source and the EI source to solve the problem of neutral gas molecule interference, designs the differential hole plate as a switching control plate, and switches the CI source and the EI source through the voltage of the differential hole plate.

[0035] The present invention adopts two sets of electrostatic lenses to design ion beam focusing requirements compatible with CI and EI sources.

[0036] like Figure 1 As shown, the multi-ion source mass spectrometer described in the present invention includes: a reagent inlet, a hollow cathode area, a reagent ion generating area, a reaction chamber, a sample inlet, an electrode, an EI sample inlet pipeline, a mechanical pump extraction port, a differential vacuum interface plate, a differential vacuum interface hole, a high vacuum cavity, an EI source filament, an EI source receiving electrode A, an EI source receiving electrode B, an EI ion source chamber, a first lens and a second lens.

[0037] like Figure 1 As shown, the flow direction of reagent gas, sample and ions is from left to right, and the multiple ion mass spectrometer is distributed from left to right in the following order: hollow cathode area, reagent ion generation area, reaction chamber, differential vacuum interface plate, and high vacuum cavity.

[0038] The reagent inlet, hollow cathode region, reagent ion generation region, reaction chamber and high vacuum cavity are connected in sequence. The reagent gas enters the hollow cathode region from the reagent inlet, enters the reagent ion generation region after being ionized by glow discharge in the hollow cathode region, forms reagent ions that can be used to ionize organic molecules in the reagent ion generation region, and then enters the reaction chamber.

[0039] The reaction chamber is located downstream of the reagent ion generating area. There are multiple electrodes around the reaction chamber.

[0040] A sample inlet is provided on the side of the reaction chamber near the reagent ion generation area, and an EI sample inlet pipeline is installed between the electrode near the side of the differential vacuum interface board and the differential vacuum interface board. The differential vacuum interface board is at the connection between the reaction chamber and the high vacuum cavity. The outlet position of the reaction chamber is the differential vacuum interface board. There is a differential vacuum interface hole in the center of the differential vacuum interface board. One side of the reaction chamber of the differential vacuum interface board is low vacuum, and the other side (downstream side) is high vacuum. Downstream of the differential vacuum interface board is the high vacuum cavity.

[0041] The EI sample inlet pipeline is arranged near the differential vacuum interface plate, which can ensure that most of the EI sample flows to the vicinity of the differential vacuum interface hole after coming out of the EI sample inlet pipeline.

[0042] The sample to be tested enters the reaction chamber from the side of the sample inlet, and the sample airflow and the reagent ion flow intersect at a certain angle (angle 10-170°).

[0043] The high vacuum chamber includes an EI ion source, a first lens and a second lens, and the EI ion source, the first lens and the second lens are distributed in the high vacuum chamber from near to far from the differential vacuum interface plate. Among them, the EI ion source includes an EI source filament, an EI source receiving electrode A, an EI source receiving electrode B and an EI ion source chamber. The entrance side of the EI ion source chamber is fitted with the high vacuum side of the differential vacuum interface plate, or the high vacuum side of the differential vacuum interface plate is used as the entrance of the EI ion source chamber. The EI source filament is located outside the EI ion source chamber, facing the electron beam through hole of the EI ion source chamber. The EI source receiving electrode A and the EI source filament are respectively located on both sides of the EI ion source chamber, and both are facing the electron beam through hole of the EI ion source chamber. The EI source receiving electrode B and the EI source filament are located on one side of the EI ion source chamber.

[0044] The entrance of the first lens faces the exit of the EI ion source chamber.

[0045] The entrance of the second lens is opposite to the exit of the first lens.

[0046] The working pressure of CI source is about 1-10mbar, and the working pressure of EI source is usually less than 10 -4 mbar. Considering the design of the vacuum system, the CI source is placed in the rough vacuum area and the EI source is placed in the high vacuum area. The EI source is placed behind the differential orifice plate at the exit of the CI ionization chamber, that is, in the high vacuum area. The electron beam of the EI source can cover the sample gas flowing out of the differential orifice plate and realize electron bombardment ionization of these gases.

[0047] In EI source mode, the voltage of the differential aperture plate is high, forming a repeller to push the ions generated by the EI source toward the lens. In CI source mode, the voltage of the differential aperture plate is low, and the aperture plate plays the role of providing the CI source exit potential.

[0048] The samples of the multi-ion source instrument are introduced in two ways. When using the CI source, the sample flows in from the injection pipeline at the front end of the reaction chamber. When using the EI source, the sample is introduced through the non-metallic pipeline located between the last plate and the penultimate plate (the non-metallic pipeline has almost no effect on the electric field). A local high-pressure area is formed on the high-pressure side of the differential hole, and the original gas molecules in the CI source are squeezed to a position far away from the differential hole and pumped away with a mechanical pump. In this way, the interference of neutral gas molecules in the CI source on EI analysis is solved.

[0049] A method for analyzing gas using a multi-ion source mass spectrometer comprises the following steps:

[0050] 1. Set the working time of CI source and EI respectively, and set the working pressure of CI source reaction chamber according to the best working condition obtained by tuning. The working pressure is set to 1.2 mbar.

[0051] 2. Close the EI source sample inlet pipeline through the EI source sample control valve, close the EI source receiving electrode A, and open the bypass EI source receiving electrode B to achieve the effect of guiding and deflecting the bombarding electron beam.

[0052] 3. The sample flow rate is controlled by the CI source sample control valve so that the pressure of the CI source reaction chamber reaches a set state value; the pressure is 1.2 mbar.

[0053] Open the CI source reagent valve, set the reaction chamber inlet voltage to 90V, the reaction chamber outlet voltage to 10V, reduce the differential vacuum interface plate voltage to 0V, so that the ions remaining in the reaction chamber flow toward the differential vacuum interface orifice plate and finally leave the reaction chamber through the differential vacuum interface orifice.

[0054] Set the voltage of the first lens and the second lens to the CI source working mode; the voltage of the first lens plate is 1V, -55V, 1V from left to right, and the voltage of the second lens plate is 0V, 0V from left to right, to achieve focused transmission of ions.

[0055] 4. After waiting for the CI source working time to complete, use the CI source reagent valve to close the CI source reagent ion generation area, use the CI source sample control valve to close the CI source sample reagent inlet, set the reaction chamber inlet voltage to 10V and the reaction chamber outlet voltage to 20V, increase the differential vacuum interface board voltage to 10V, and let the ions generated by the EI source flow into the mass spectrometer with the differential vacuum interface board as the repeller.

[0056] 5. Open the EI sample inlet pipeline through the EI source sample control valve, and control the EI source sample flow rate to be 5% to 100% higher than the CI source sample flow rate. Close the bypass EI source receiving electrode B, open the EI source receiving electrode A, and let the bombarding electron beam pass through the EI source chamber normally.

[0057] Set the voltage of the first lens and the second lens to the EI source working mode. The voltage of the first lens plate is 1V, -40V, and 0V from left to right, and the voltage of the second lens plate is 1.5V and -140V from left to right to achieve focused transmission of ions.

[0058] 6. After waiting for the EI source working time to complete,

[0059] The EI source sample inlet pipeline is closed through the EI source sample control valve, the EI source receiving electrode A is closed, and the bypass EI source receiving electrode B is opened to achieve the effect of guiding and deflecting the bombarding electron beam.

[0060] Ion source standby status:

[0061] When the EI source is working, the CI source continues to ionize the sample in the reaction chamber, but due to the control of the electric field, the generated ions will not enter the next stage, but will be trapped before the penultimate plate. New ions are continuously generated but cannot enter the next stage, and the old ions will touch other plates or walls and be annihilated, or be pumped away by a mechanical pump. In order to balance the sample volume of the EI source, when the EI source is turned on and the sample is introduced, the original CI source injection volume is reduced accordingly, and the total amount of gas entering the reaction chamber per unit time is kept unchanged to ensure that the reaction chamber pressure does not fluctuate.

[0062] When the CI source is working, close the valve of the EI source sample pipeline and stop the introduction of the EI sample. Since the EI source needs a long time of preheating to output electrons normally. Therefore, the filament of the EI source does not go out when the CI mode is working. By closing the normal receiving electrode A and opening the bypass receiving electrode B, the effect of guiding and deflecting the electron flow is achieved. After deflection, the electrons no longer pass through the gas flow out of the differential hole, so that the gas out of the differential hole will not be re-ionized by the EI source. Finally, the electric field distribution and the differential orifice voltage in the CI source are changed, so that the ions remaining in the reaction chamber flow toward the mechanical pump extraction port, and the instrument enters the normal CI source working mode.

[0063] The sample used by the EI source is introduced directly into the front end of the differential vacuum interface hole using non-metallic (such as PEEK or glass capillaries).

[0064] A local pressure environment with a pressure of 110%-1000% of the pressure of the reaction chamber is formed locally at the front end of the differential vacuum interface hole to achieve the effect of repelling neutral gas molecules in the CI ion source.

[0065] A mechanical pump extraction port is also provided at the lower end of the reaction chamber, which can realize the extraction of a large number of gas molecules.

[0066] The sample used in the CI source is introduced at the sample inlet and injected into the reaction chamber at a certain angle to the flow direction of the ion reagent.

[0067] The flow rate of the sample used in the EI ion source is adjusted according to the setting of the pressure of the CI ion source reaction chamber to ensure that the EI sample gas generates sufficient pressure to repel the gas in the CI ion source.

[0068] When the EI ion source is working, the sample gas flow rate injected through the EI sample inlet pipeline is consistent with the reduced flow rate of the CI sample inlet, thereby maintaining the pressure in the reaction chamber unchanged.

[0069] The EI ion source filament is on the high vacuum side of the differential vacuum interface plate.

[0070] The EI ion source has two receiving electrodes, and only one of the two electrodes works at the same time. The EI source receiving electrode A and the EI source filament are located on both sides of the sample differential hole. When the EI source receiving electrode A is working, the electrons generated by the EI source filament pass through the airflow ejected from the differential vacuum interface hole to achieve ionization. The EI source receiving electrode B and the EI source filament are located on the same side of the differential hole. When the EI source receiving electrode B is working, the electrons generated by the EI source filament will not contact the airflow ejected from the differential hole and will not produce ionization on it.

[0071] When the EI ion source is working, the voltage of the differential vacuum interface board increases, which on the one hand blocks the ions generated in the CI source, and on the other hand forms a repulsion voltage to push the ions generated by the EI source toward the ion lens.

[0072] When the EI ion source is working, the reagent gas and sample gas flow paths of the CI ion source are not closed, but the sample gas flow rate is reduced to ensure that the total amount of gas entering the reaction chamber remains unchanged.

[0073] Both CI and EI ion sources use direct injection.

[0074] The present invention designs a multi-ion source mass spectrometer, organically combining CI ion source and EI ion source. Rapid switching of the two ion sources is achieved through electric field switching and sample control. The entire switching device of the present invention has no moving parts such as motors and magnets, has a simple structure, and has high reliability.

Claims

1. A multi-ion source mass spectrometer, characterized in that: include: Reagent inlet, hollow cathode region, reagent ion generation region, reaction chamber, electrode, sample inlet, EI sample inlet pipeline, differential vacuum interface plate, differential vacuum interface hole, high vacuum chamber and mechanical pump extraction port; The reagent inlet, the hollow cathode region, the reagent ion generation region, the reaction chamber and the high vacuum cavity are connected in sequence; The sample inlet is arranged on one side of the reaction chamber close to the reagent ion generating area; There are multiple electrodes around the interior of the reaction chamber; The EI sample inlet pipeline is arranged between the electrode close to one side of the differential vacuum interface plate and the differential vacuum interface plate; The differential vacuum interface plate is located at the connection point between the reaction chamber and the high vacuum cavity, and a differential vacuum interface hole is provided in the middle of the differential vacuum interface plate; The high vacuum chamber comprises: an EI ion source, a first lens and a second lens; The EI ion source, the first lens and the second lens are distributed in the high vacuum chamber from near to far from the differential vacuum interface plate; The outlet of the EI ion source faces the inlet of the first lens; The outlet of the first lens faces the inlet of the second lens; The EI ion source comprises: an EI source filament, an EI source receiving electrode A, an EI source receiving electrode B and an EI ion source chamber; The EI source filament and the EI source receiving electrode A are located on the same side of the EI ion source chamber; The EI source filament and the EI source receiving electrode A and the EI source receiving electrode B are located on both sides of the EI ion source chamber; The outlet of the EI ion source chamber is directly opposite to the inlet of the first lens; The mechanical pump extraction port is arranged at the lower end of the reaction chamber.

2. The method for analyzing gas using a multi-ion source mass spectrometer according to claim 1, characterized in that: The steps include: Close the EI source sample inlet pipeline, close the EI source receiving electrode A, and open the EI source receiving electrode B; Control the sample flow rate so that the pressure in the CI source reaction chamber reaches the set state; Set the reaction chamber inlet voltage to 90V, the reaction chamber outlet voltage to 10V, and reduce the differential vacuum interface board voltage to 0V; Set the voltage of the first lens and the second lens to CI source working mode; After the CI source working time is completed, the CI source reagent ion generating area is turned off, the reagent inlet of the CI source sample is turned off, the reaction chamber inlet voltage is set to 10V and the reaction chamber outlet voltage is set to 20V, and the differential vacuum interface board voltage is increased to 10V; Open the EI sample inlet pipeline and control the EI source sample flow rate to be 5% to 100% higher than the CI source sample flow rate; Close the bypass EI source receiving electrode B and open the EI source receiving electrode A; Set the voltage of the first lens and the second lens to the EI source working mode; After the EI source working time is completed, the EI source sample inlet pipeline is closed, the EI source receiving electrode A is closed, and the bypass EI source receiving electrode B is opened.

3. The method for analyzing gas using a multi-ion source mass spectrometer according to claim 2, characterized in that: The pressure of the CI source reaction chamber is 1.2 mbar.

4. The method for analyzing gas using a multi-ion source mass spectrometer according to claim 2, characterized in that: The first lens plate voltage is the voltage in the CI source working mode, which is 1V, -55V, and 1V from left to right.

5. The method for analyzing gas using a multi-ion source mass spectrometer according to claim 2, characterized in that: The voltage of the second lens plate is 0V, 0V from left to right in the CI source working mode.

6. The method for analyzing gas using a multi-ion source mass spectrometer according to claim 2, characterized in that: The voltage of the first lens plate is the voltage of the EI source working mode, which is 1V, -40V, and 0V from left to right.

7. The method for analyzing gas using a multi-ion source mass spectrometer according to claim 2, characterized in that: The voltage of the second lens plate is 1.5V and -140V from left to right in the EI source working mode.

Images