CN111199865B - Two-stage compression ion gate and control method - Google Patents

Two-stage compression ion gate and control method Download PDF

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CN111199865B
CN111199865B CN201811381284.8A CN201811381284A CN111199865B CN 111199865 B CN111199865 B CN 111199865B CN 201811381284 A CN201811381284 A CN 201811381284A CN 111199865 B CN111199865 B CN 111199865B
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ion
electric field
mesh
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CN111199865A (en
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李海洋
陈红
蒋丹丹
厉梅
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Dalian Institute of Chemical Physics of CAS
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • H01J49/02—Details
    • H01J49/06—Electron- or ion-optical arrangements
    • H01J49/067—Ion lenses, apertures, skimmers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
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Abstract

The invention relates to a two-stage compression ion gate and a control method. The ion gate consists of a first grid mesh, a second grid mesh and a third grid mesh which are arranged in parallel, coaxial and spaced with each other between an ion source and an ion receiving electrode Faraday disc in an ion migration tube. The area between the first grid and the ion source is a reaction area, and the area between the third grid and the Faraday disc is a migration area. The electric field between three grids in the ion gate is periodically controlled, so that two-stage compression of ions in the process of being injected into the migration region is realized. The ions are compressed once after passing through the third grid mesh and compressed once again after passing through the conductive ring behind the third grid mesh. The ion gate and the control method can perform two-stage compression on the injected ion cluster, and improve the resolution and the sensitivity at the same time.

Description

Two-stage compression ion gate and control method
Technical Field
The invention relates to a mobility spectrum ion gate device and a control method.
Background
The ion mobility spectrometry is widely applied to detection of chemical toxicants, explosives, drugs and the like due to the advantages of high analysis speed, high sensitivity, small volume, simple operation and the like.[1]In addition, ion mobility spectrometry can separate isomers, and is often used in combination with mass spectrometry to detect biological samples.[2]In recent years, the application of ion mobility spectrometry has been advanced to the field of medical diagnosis, such as the detection of small molecule metabolites in exhaled breath, anesthetics in blood, and the like.[3,4]For the detection of complex samples, higher resolution and sensitivity are required. The ion gate is one of the key parts in the migration tube, and the function of the ion gate is to periodically inject a mass of ions into the migration region for separation and detection. Therefore, the performance of the ion gate largely determines the resolving power and sensitivity of the mobility spectrum.
The most commonly used ion gate in ion mobility tubes is the Bradbury-Nielsen gate (BN gate),[1]the ion gate is composed of two groups of parallel, insulated, sequentially and alternately arranged metal wires in the same plane. When the door is opened, the potentials on the two sets of wires are the same. When the door is closed, a voltage is superposed on one group of filaments or opposite voltages are superposed on the two groups of filaments, so that an electric field perpendicular to the migration electric field is formed between the two adjacent filaments to prevent the ions from passing through. However, when the ion gate is actually closed, the closing voltage is applied to the ion gateThe front and rear regions generate non-uniform electric fields and form a clear region, a dilute region and a compact region behind the ion gate.[5]The presence of these regions, on the one hand, causes the implanted ions to be jagged, and the smaller the gate opening time, the more non-uniform the implanted ions, resulting in a peak tailing phenomenon.
Another relatively common ion gate in an ion mobility tube is a field-switched ion gate.[1]The ion gate is constructed as a metal grid. When the door is opened, the potential of the ion source is increased by hundreds or even thousands of volts, and the ions in the ionization region are all injected into the migration region. Such an ion gate does not cause an inhomogeneous electric field in the vicinity of the ion gate. But the application range is narrow, and the device is not suitable for an ionization source with a longer ionization range, such as a vacuum ultraviolet lamp, or an ionization source which needs to maintain a certain potential to work, such as an electrospray ionization source or a corona discharge ionization source.[6]
In the process of injecting ion clusters by an ion gate, if an attempt is made to move the ion clusters from a high electric field to a low electric field, the ion clusters are compressed, the ion thickness is narrowed, and the density is increased. The faraday disk receives a higher and narrower signal peak, and resolution and sensitivity are simultaneously improved.
[1]EICEMAN G A,KARPAS Z,HILL JR H H.ion mobility spectrometry[M].3rd ed.:CRC Press,2013；
[2]JIANG W,ROBINSON R A S.Ion Mobility-Mass Spectrometry[M].John Wiley&Sons,Ltd,2013；
[3]JIANG D,LI E,ZHOU Q,et al.Online Monitoring of Intraoperative Exhaled Propofol by Acetone-Assisted Negative Photoionization Ion Mobility Spectrometry Coupled with Time-Resolved Purge Introduction[J].Analytical Chemistry,2018,90(8):5280-9；
[4]WANG X,ZHOU Q,JIANG D,et al.Ion mobility spectrometry as a simple and rapid method to measure the plasma propofol concentrations for intravenous anaesthesia monitoring[J].Scientific Reports,2016,6；
[5]DU Y,WANG W,LI H.Resolution enhancement of ion mobility spectrometry by improving the three-zone properties of the Bradbury-Nielsen gate[J].Anal Chem,2012,84(3):1725-31；
[6]CHEN C,TABRIZCHI M,WANG W,et al.Field Switching Combined with Bradbury-Nielsen Gate for Ion Mobility Spectrometry[J].Anal Chem,2015,87(15):7925-30。
Disclosure of Invention
The invention aims to provide a two-stage compression ion gate and a control method, which are used for performing two-time space compression on ions injected when the ion gate is opened, so that the resolution and the sensitivity of a mobility spectrum are improved simultaneously.
In order to achieve the above purpose, the invention adopts the technical scheme that:
three circular grids are sequentially coaxially, parallelly, at intervals and in an insulating way between an ion source and a Faraday disc in the cylindrical ion migration tube to form an ion gate, and the three circular grids are sequentially defined as a grid I, a grid II and a grid III; the area between the first grid and the ion source is a reaction area, and the area between the third grid and the Faraday disc is a migration area.
The ion source, the first grid mesh, the second grid mesh, the third grid mesh and the Faraday disc are sequentially arranged at intervals, the first grid mesh, the second grid mesh and the third grid mesh are sequentially separated by two annular insulating sheets, and each insulating sheet is parallel to and coaxially arranged with the adjacent metal grid mesh and is tightly matched with the adjacent metal grid mesh.
The three grids forming the ion gate are wire grids or porous metal grids with flat surfaces.
The passing of ions can be accurately controlled by periodically controlling the electric field among three grids in the ion gate;
each cycle has three successive states:
in the first state, the ion gate opens the door, the ion source, the first grid, the second grid, the third grid and the Faraday plate are sequentially reduced in potential; after the first state is maintained for a period of time, the potential on the grid II is increased to be higher than the potential on the grid I, a second state is started, and the ion gate is closed in the second state; after the second state is maintained for a period of time, reducing the potential on the second grid mesh to enable the second grid mesh to return to the same potential as the first state, simultaneously increasing the potential of the third grid mesh to enable the third grid mesh to be higher than the potential on the second grid mesh, starting a third state, and closing the ion gate in the third state; after the third state is maintained for a period of time, the whole process is periodic;
and after one cycle is finished, switching to the first state again, and carrying out the next cycle.
The second state start time should be before the ions passing through grid two during the first state sustain reach grid three.
Ions passing through the second grid mesh in the first state maintaining process can pass through the third grid mesh in the second state maintaining time period or partially, and then the third state can be started.
The first and second stages may be maintained for a period of time of several to several hundred microseconds, typically 1-999 microseconds; the period of time for which the third stage is maintained may be a few to one hundred milliseconds, typically 1-100 milliseconds.
In the second state, the direction of the electric field between the first grid mesh and the second grid mesh is opposite to the direction of the migration electric field, so that ions are prevented from passing through the second grid mesh, the direction of the electric field between the second grid mesh and the third grid mesh is the same as the direction of the migration electric field, and the electric field strength is improved, so that the ions are compressed once due to the reduction of the electric field strength after passing through the third grid mesh;
in the third state, the direction of the electric field between the first grid mesh and the second grid mesh is the same as the direction of the migration electric field, the direction of the electric field between the second grid mesh and the third grid mesh is opposite to the direction of the migration electric field, ions are prevented from passing through, and meanwhile, the electric field intensity between the third grid mesh and the following conductive ring is improved, so that the ions are compressed again due to the reduction of the electric field intensity after passing through the conductive ring.
The invention has the advantages that:
and performing two-stage compression on the injected ions when the ion door is opened.
While improving resolution and sensitivity.
The structure is simple.
Drawings
Fig. 1 is a schematic view of an ion transfer tube structure. Wherein 1 is an ion migration tube cavity, 2 is an ion source, 3 is a Faraday plate, 4 is a reaction zone, 5 is a migration zone, 6 is a first grid, 7 is a second grid, 8 is a third grid, 9 is a first conducting ring, 10 is a second conducting ring, 11 is a floating gas inlet, 12 is a carrier gas inlet, and 13 is a tail gas outlet.
Fig. 2 is a schematic diagram of the pulse application mode on the second grid and the third grid.
Fig. 3 is a schematic diagram of the potential and ion movement at various stages in a cycle.
Fig. 4 is a schematic diagram of electric field and ion motion at various stages in a cycle.
Fig. 5 is a comparison of spectra obtained using the ion gate and control scheme of the present invention with spectra obtained using a BN gate.
Detailed Description
Fig. 1 is a schematic view of an ion mobility tube structure according to the present invention, fig. 2 is a schematic view of a pulse application method, fig. 3 is a schematic view of potentials at various stages of a cycle, and fig. 4 is a schematic view of electric fields at various stages of a cycle.
The ion migration tube 1 is a hollow cylindrical cavity, one end of the cavity is provided with an ion source 2 of a sample ion generating device, and the other end of the cavity is provided with a Faraday disc 3 of an ion receiving device. Three grids which form the ion gate are sequentially coaxially, alternately and parallelly arranged between the ion source and the Faraday disc and are sequentially defined as a grid I6, a grid II 7 and a grid III 8. The first grid mesh, the second grid mesh and the third grid mesh are sequentially separated by two annular insulating sheets, and each insulating ring is parallel to and coaxially arranged with the adjacent metal grid mesh and is tightly matched with the adjacent metal grid mesh. The area between the first grid and the ion source is a reaction area 4, and the area between the third grid and the Faraday disc is a migration area 5.
The passage of ions is precisely controlled by periodically controlling the electric field between three grids in the ion gate. Each cycle has three states: in the first state (0-t)1) The ion source, the first grid, the second grid, the third grid and the Faraday plate are sequentially reduced in electric potential, the directions of electric fields between two adjacent grids are the same as those of electric fields of the reaction region and the migration region, and ions can enter the migration region from the reaction region through the three grids; the first state is maintained for a period of time t1Then, the voltage on the grid II is increased to be higher than that on the grid I, the potential at other positions is unchanged, and the second state is started (t)1～t2) The electric field is characterized in that the direction of the electric field between the first grid mesh and the second grid mesh is opposite to the direction of the electric field of the reaction region and the migration region, so that ions are prevented from passing through the electric field, and the direction of the electric field between the second grid mesh and the third grid mesh is the same as the direction of the electric field of the migration region and the reaction region; after the second state is maintained for a period of time, when the ions passing through the second grid mesh in the opening stage of the first state are ensured to completely or partially pass through the third grid mesh but do not reach the conductive ring behind the third grid mesh, the potential of the second grid mesh is reduced to the same potential as that in the first state, meanwhile, the potential on the third grid mesh is increased to be higher than that on the second grid mesh, and the third state is opened (t)2T) and the electric field is characterized in that the direction of the electric field between the first grid and the second grid is the same as that of the electric field in the reaction region and the migration region, and the direction of the electric field between the second grid and the third grid is opposite to that of the electric field in the migration region and the reaction region. The third state is maintained until one period is finished (T ═ T), the first state is switched again, and the next period is started.
In the second state, the electric field between the second grid and the third grid is higher than the electric field behind the third grid due to the increase of the potential on the second grid. When ions move from a high electric field between the second grid mesh and the third grid mesh to a low electric field behind the third grid mesh, the ions are compressed for the first time, the thickness is reduced, and the density is increased.
In the third state, because the electric potential on the grid mesh three is increased, the electric field between the grid mesh three and the conducting ring two is higher than the electric field behind the conducting ring two, and when ions move from the high electric field between the grid mesh three and the conducting ring two to the low electric field behind the conducting ring two, the ions are compressed for the second time, the thickness is further reduced, and the density is further increased.
Example 1
As shown in fig. 363In the Ni ionization source-positive ion mode ion mobility spectrometry, the two-stage compression ion gate and the control method are adopted to compare with the spectrogram of acetone detection by adopting a conventional BN gate. Wherein the square hole stainless steel metal grid with the thickness of 50 mu m of the grid mesh used in the embodiment has the aperture size of 1 mm. In two kindsIn the ion gate, the distance between two adjacent grids is 4 mm. When the ion gate is used, the ion gate is opened in the first state, the potentials on the grid I, the grid II and the grid III are 5100V, 5050V and 5000V respectively, and the opening time is 50 microseconds; in the second state, the potentials on the grid I, the grid II and the grid III are 5100V, 5450V and 5000V respectively, and the maintaining time is 100 mu s. In the third state, the potentials on the grid I, the grid II and the grid III are 5100V, 5050V and 5500V respectively, and the maintaining time is 9.75 ms. When the BN door is used, the potentials on two groups of wires of the BN door are 5000V when the door is opened, and the door opening time is 50 microseconds. When the door is closed, the potential on one group of wires is increased to 5100V, the potential on the other group of wires is unchanged, and the door closing time is 9.92 ms. Other experimental conditions were the same using both ion gates. As can be seen from FIG. 3, the ion gate and the control method of the invention and the BN gate are used, the former is far higher than the latter in peak height of the acetone, and the half-peak width ratio is obviously lower than the latter. It is shown that sensitivity and resolution can be simultaneously improved using this ion gate control method.

Claims (6)

1. A method of controlling a two-stage compression ion gate, comprising:
three circular grids are sequentially coaxially, parallelly, at intervals and in an insulating way between an ion source and a Faraday disc in the cylindrical ion migration tube to form an ion gate, and the three circular grids are sequentially defined as a grid I, a grid II and a grid III; the area between the first grid and the ion source is a reaction area, and the area between the third grid and the Faraday disc is a migration area; the control method controls the electric field between three grids in the ion gate periodically to accurately control the passing of ions;
each cycle has three successive states:
in the first state, the ion gate opens the door, the ion source, the first grid, the second grid, the third grid and the Faraday plate are sequentially reduced in potential; after the first state is maintained for a period of time, the potential on the grid II is increased to be higher than the potential on the grid I, a second state is started, and the ion gate is closed in the second state; after the second state is maintained for a period of time, reducing the potential on the second grid mesh to enable the second grid mesh to return to the same potential as the first state, simultaneously increasing the potential of the third grid mesh to enable the third grid mesh to be higher than the potential on the second grid mesh, starting a third state, and closing the ion gate in the third state; after the third state is maintained for a period of time, the whole process is periodic;
after one cycle is finished, switching to the first state again, and carrying out the next cycle;
in the second state, because the electric potential on the second grid is increased, the electric field between the second grid and the third grid is higher than the electric field behind the third grid, and the ions are compressed for the first time when moving from the high electric field between the second grid and the third grid to the low electric field behind the third grid;
in the third state, the electric field between the third grid and the second conducting ring is higher than the electric field behind the second conducting ring due to the fact that the electric potential on the third grid is increased, and the ions are compressed for the second time when moving from the high electric field between the third grid and the second conducting ring to the low electric field behind the second conducting ring.
2. The control method according to claim 1, characterized in that:
the ion source, the first grid mesh, the second grid mesh, the third grid mesh and the Faraday disc are sequentially arranged at intervals, the first grid mesh, the second grid mesh and the third grid mesh are sequentially separated by two annular insulating sheets, and each insulating sheet is parallel to and coaxially arranged with the adjacent metal grid mesh and is tightly matched with the adjacent metal grid mesh.
3. The control method according to claim 1 or 2, characterized in that:
the three grids forming the ion gate are wire grids or porous metal grids with flat surfaces.
4. The control method according to claim 1, characterized in that:
the second state start time should be before the ions passing through grid two during the first state sustain reach grid three.
5. The control method according to claim 1, characterized in that:
ions passing through the second grid mesh in the first state maintaining process can pass through the third grid mesh in the second state maintaining time period or partially, and then the third state can be started.
6. The control method according to claim 1, characterized in that:
the first stage and the second stage are maintained for 1-999 microseconds;
the third stage is maintained for a period of 1-100 milliseconds.
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CN111755315B (en) * 2020-07-07 2023-02-24 湘潭大学 Device and method for improving sensitivity and resolution of ion mobility spectrometry
CN113345791B (en) * 2021-07-01 2023-07-25 中国科学院大连化学物理研究所 Multi-switching pulse voltage waveform for ion mobility spectrometry
CN113539781B (en) * 2021-07-01 2023-07-25 中国科学院大连化学物理研究所 Pulse voltage waveform applied to BN ion gate

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CN106340436A (en) * 2015-07-08 2017-01-18 中国科学院大连化学物理研究所 Field-switching ion gate and field-switching ion gate ion migration tube

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