High-field asymmetric waveform ion migration tube with segmented cylinder structure

Abstract

The invention relates to a high-field asymmetric waveform ion migration tube with a sectional cylinder structure, which comprises a cylindrical insulating outer cylinder with openings at the left end and the right end and a cylindrical insulating inner column positioned in the insulating outer cylinder, an ionization source is arranged at a position close to the left port of the insulating outer cylinder, and an ion receiving electrode is arranged at a position close to the right port in the insulating outer cylinder; two or more pairs of sectional type separation electrode pairs (including a first electrode pair, a second electrode pair... an Nth electrode pair), an isolation ground electrode pair and an ion receiving electrode are arranged between the left port of the ionization source and the ion receiving electrode; different direct-current voltages and the same high-field asymmetric radio-frequency voltage are applied to the electrodes, located on the inner side of the insulating outer cylinder, in the first electrode pair, the second electrode pair... the Nth electrode pair, and the working air pressure range of the direct-current voltages applied to the electrodes correspondingly located on the outer surface of the insulating inner cylinder is 10 Pascals to 1 atmospheric pressure; the movement speed of ions in the X-axis direction can be reduced, and the resolution is improved. And the insulating outer cylinder, the insulating inner column and two electrodes in the sectional type separation electrode pair are coaxially arranged.

Description

Technical Field

[0001] The present invention is a segmented cylindrical high-field asymmetric waveform ion migration tube, which is characterized by a segmented structural design that utilizes a damping electric field opposite to the carrier gas movement direction to reduce the movement speed of ions in the X-axis direction and increase the residence time, thereby improving its resolution. Background Art

[0002] Ion mobility spectrometry is widely used in the detection of chemical agents, stimulants, anesthetics and explosives due to its advantages such as high sensitivity, fast analysis speed and portability. Different substances can be separated and analyzed by utilizing the different flight times of different ions in a uniform field under atmospheric pressure. Resolution and sensitivity are the two core indicators of ion mobility spectrometry. Most of the work is carried out around how to improve these two core indicators. The sensitivity of ion mobility spectrometry can be improved by developing efficient ionization sources, increasing ion injection volume and axial compression. During the flight of ions, due to the dual effects of concentration gradient and Coulomb repulsion, ions undergo diffusion losses in the axial direction and radial direction. Some work has been done on compression in the axial direction. For example, Du Yongzhai et al. invented a spatially focused ion gate assembly and a spatially focused ion migration tube (201110226912.7). The voltage applied to the ion gate or the metal ring in the migration zone is used to compress the ion cluster (beam), thereby improving the resolution and sensitivity of the ion migration tube. It achieves spatial compression in the axial direction, but does not achieve compression of radial ions. A pulsed field enrichment ion transfer tube invented by Chen Chuang et al. (CN201510397889.6). By applying a high-voltage pulse synchronized with the ion gate opening pulse to the pulse electrode set between the ion source and the ion gate, the movement speed of the ions is greatly increased during the period when the ion gate is open, so that more ions can pass through the ion gate; at the same time, the difference in electric field strength on both sides of the ion gate caused by the high-voltage pulse is used to spatially focus the ion clusters that have passed through the ion gate, thereby maintaining the original resolution of the ion transfer tube. However, the patent also does not avoid the divergence of radial ions.

[0003] If radial compression of ions can be achieved, the sensitivity of ion mobility spectrometry can be further improved. The present invention realizes radial ion compression by designing an electric field formed by compression electrodes of symmetrical structure, thereby improving ion detection efficiency and sensitivity. Ion mobility spectrometry has the advantages of high sensitivity, fast analysis speed, portability, etc., and is therefore widely used in detecting chemical agents, stimulants, anesthetics, and explosives. Among various types of ion mobility spectrometry, high-field asymmetric waveform ion mobility spectrometry technology has the advantages of high detection sensitivity, simple equipment, small size, easy to carry, low detection cost, etc., and is increasingly receiving attention.

[0004] High-field asymmetric waveform ion mobility spectrometry is a material analysis and detection technology that has been continuously developed based on traditional ion mobility spectrometry technology. It was first publicly reported in 1993 by Buryakov et al. It is based on the change in ion mobility in high field (E / N>40Td, 1Td=10-17Vcm2) and low field (E / N<2Td) to achieve the detection of different substances. The principle of asymmetric field ion mobility spectrometry is as follows: the carrier gas is used to make the material ions pass through the drift region perpendicular to the direction of the electric field. The drift region is applied with an asymmetric field with positive and negative switching of radio frequency. During the entire radio frequency cycle, the time average value of the voltage is zero. In this way, in the high and low field sections, the ions have a vertical displacement along the electric field at a mobility K. However, if the mobility under high field and low field is different, the ions will generally leave their original positions in the vertical direction within a cycle, resulting in a net displacement. After a certain period of accumulation, this displacement of the ions will cause them to hit the plate and be neutralized. In order to make such ions pass through the detection area smoothly, a DC electric field can be superimposed on the original electric field. When the DC electric field is appropriate, the net displacement of the ions in the vertical direction is zero, and they can pass through the detection channel smoothly and be detected. By scanning the above DC electric field, different ions can be detected.

[0005] High-field asymmetric waveform ion mobility spectrometry can achieve the separation of compounds with the same molecular weight but different structures, and can achieve the separation and analysis of isomers when combined with mass spectrometry. In addition, in the field of protein analysis, high-field asymmetric waveform ion mobility spectrometry can be used as a pre-separation stage for mass spectrometry to eliminate low-molecular-weight compounds from entering the mass spectrometry, greatly reduce background noise, improve signal-to-noise ratio, and increase sensitivity by 3 orders of magnitude. When traditional high-field asymmetric waveform ion mobility spectrometry is combined with mass spectrometry, it can only achieve ions entering the mass spectrometry at a certain point (Journal of the American Society for Mass Spectrometry 1999; 10: 492–501.), with low ion utilization and poor sensitivity. Later, in order to improve ion utilization, a dome structure was proposed (Analytical Chemistry 2005; 77: 6381–6388). In order to achieve the change of mobility under high and low fields, a very high field strength is often required; this means increasing the voltage and reducing the distance between the plates. In order to achieve miniaturization, the voltage that can be increased is limited. Therefore, the plate spacing of traditional high-field asymmetric waveform ion mobility spectrometers is often set to less than 1 mm. This means that the time in the separation zone needs to be reduced to avoid collision quenching between ions and the plates, thereby ensuring detection sensitivity. However, this results in lower resolution. Summary of the invention

[0006] The invention aims to solve the problem of low resolution of a high-field asymmetric waveform ion migration tube and improve the separation capability of the instrument.

[0007] To achieve this purpose, the technical solution adopted by the present invention is:

[0008] Based on the segmented cylindrical structure design, the damping electric field opposite to the direction of ion movement formed between different segments is utilized to reduce the residence time of ions in the high-field asymmetric waveform ion migration tube, achieve sufficient changes in ion mobility between high and low fields, realize effective separation of different ions, and thus improve resolution.

[0009] A segmented cylindrical structure high-field asymmetric waveform ion migration tube, comprising a cylindrical insulating outer cylinder with two openings on the left and right ends and a cylindrical insulating inner column located in the insulating outer cylinder, with the direction from left to right as the X-axis direction, the direction from top to bottom as the Y-axis direction, and the direction perpendicular to the X-axis and the Y-axis as the Z-axis direction;

[0010] An ion source is provided near the left port of the insulating outer cylinder, and an ion receiving electrode is provided near the right port inside the insulating outer cylinder, wherein the receiving electrode surface of the ion receiving electrode is parallel to the X-axis;

[0011] Two or more pairs of segmented separation electrode pairs (including the first, second ... Nth electrode pairs), isolated ground electrode pairs, and ion receiving electrodes are provided between the left port of the ionization source and the ion receiving electrode; two electrodes in the segmented separation electrode pairs are respectively fixed to the inner wall surface of the insulating outer cylinder and the outer wall surface of the insulating inner column, and they are arranged oppositely and are all cylindrical electrodes; the first, second ... Nth electrode pairs, isolated ground electrode pairs, and ion receiving electrodes are arranged in sequence along the X-axis direction;

[0012] Different DC voltages and the same high-field asymmetric RF voltage are applied to the electrodes located on the inner side of the insulating outer cylinder in the first, second ... Nth electrode pairs, and a DC voltage is applied to the corresponding electrodes located on the outer surface of the insulating inner column, where N is an integer greater than or equal to 2.

[0013] The direction of carrier gas flow is along the X-axis direction, and the electric field force in the axial direction on ions in the segmented high-field asymmetric waveform ion migration tube is opposite to the direction of carrier gas flow and is smaller than the carrying force generated by the carrier gas; the residence time of ions in the segmented high-field asymmetric waveform ion migration tube can be controlled by changing DC1, DC2...DCN, U1, U2...UN applied to the first, second...Nth electrode pairs; the voltage difference between DC1 and U1 is the same as the voltage difference between DC2 and U2 and the voltage difference between DCN and UN, and the amplitudes of U1, U2...UN increase (or decrease) monotonically.

[0014] There are at least two pairs of segmented separation electrode pairs (preferably 3 pairs, that is, N=3, the first, second ... Nth electrode pairs are the first, second, and third electrode pairs, and the spacing between each pair of electrodes is 0.01 to 2 mm; the spacing between the segmented separation electrode pairs is 0.1 to 5 mm.

[0015] The isolated ground electrode pair is connected to the earth;

[0016] Apply a 1-10V DC voltage to the ion receiving electrode.

[0017] Its operating pressure range is 10 Pascals to 1 atmosphere;

[0018] It can reduce the movement speed of ions in the X-axis direction and improve the resolution;

[0019] The insulating outer cylinder, the insulating inner column and two electrodes in the segmented separation electrode pair are coaxially arranged. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The invention relates to a segmented cylindrical structure high-field asymmetric waveform ion migration tube, comprising an ionization source (1), an insulating outer cylinder (2), a cylindrical insulating inner cylinder (3), first, second, third, fourth and fifth separation electrode pairs (4, 4', 5, 5', 6, 6', 7, 7', 8, 8'), an isolated ground electrode pair (9, 9') and an ion receiving electrode (10, 10').

[0021] Figure 2 Detection spectrum of DMMP. DETAILED DESCRIPTION

[0022] A segmented cylindrical structure high-field asymmetric waveform ion transfer tube, comprising a cylindrical insulating outer cylinder 2 with two openings at the left and right ends and a cylindrical insulating inner column 3 located in the insulating outer cylinder 2, with the direction from left to right as the X-axis direction, the direction from top to bottom as the Y-axis direction, and the direction perpendicular to the X-axis and the Y-axis as the Z-axis direction;

[0023] An ion source 1 is provided near the left end of the insulating outer tube 2, and ion receiving electrodes 10, 10' are provided near the right end of the insulating outer tube 2, and the receiving electrode surfaces of the ion receiving electrodes 10, 10' (ion receiving electrode pair) are parallel to the X axis;

[0024] Between the left port of the ionization source 1 and the ion receiving electrodes 10, 10', 5 pairs of segmented separation electrode pairs are provided: including the first, second, third, fourth, and fifth segmented separation electrode pairs 4, 4', 5, 5', 6, 6', 7, 7', 8, 8'; between the fifth segmented separation electrode and the ion receiving electrodes 10, 10', an isolated ground electrode pair 9, 9' is provided; the isolated ground electrode pair, the ion receiving electrode, and two electrodes in the segmented separation electrode pair are respectively fixed to the inner wall surface of the insulating outer cylinder 2 and the outer wall surface of the insulating inner column 3, they are arranged oppositely and are all cylindrical electrodes; the first, second, third, fourth, and fifth electrode pairs 4, 4', 5, 5', 6, 6', 7, 7', 8, 8', the isolated ground electrode pair 9, 9', and the ion receiving electrodes 10, 10 are sequentially spaced along the X-axis direction;

[0025] Different DC voltages (DC1, DC2, DC3, DC4, DC5) and the same high-field asymmetric radio frequency voltage are applied to the electrodes 4, 5, 6, 7, 8 located on the inner side of the insulating outer cylinder 2 in the first, second, third, fourth, and fifth electrode pairs 4, 4', 5, 5', 6, 6', 7, 7', 8, 8', and corresponding DC voltages U1, U2, U3, U4, U5 are applied to the electrodes 4', 5'...6' located on the outer surface of the insulating inner column (3).

[0026] The direction of the carrier gas flow is along the X-axis direction, and the electric field force in the axial direction on the ions in the segmented high-field asymmetric waveform ion migration tube is opposite to the direction of the carrier gas flow and is smaller than the carrying force generated by the carrier gas; by changing the DC1, DC2, DC3, DC4, DC5, U1, U2, U3, U4, U5 applied to the first, second, third, fourth, and fifth electrode pairs 4, 4', 5, 5', 6, 6', 7, 7', 8, 8', the residence time of the ions in the segmented high-field asymmetric waveform ion migration tube can be adjusted; the voltage difference between DC1 and U1, the voltage difference between DC2 and U2, the voltage difference between DC3 and U3, the voltage difference between DC4 and U4, and the voltage difference between DC5 and U5 are the same, and the amplitudes of U1, U2, U3, U4, and U5 increase (or decrease) monotonically.

[0027] The distance between the first, second, third, fourth and fifth electrode pairs 4, 4', 5, 5', 6, 6', 7, 7', 8, 8', the isolated ground electrode pair 9, 9' and the adjacent ion receiving electrodes 10, 10 is 0.5 mm.

[0028] The distance between each pair of electrodes is 0.5 mm; the isolated ground electrode pair 9, 9' is connected to the ground;

[0029] A 1V DC voltage is applied to the ion receiving electrodes 10 and 10'.

[0030] Its working pressure range is 1 atmosphere;

[0031] It can reduce the movement speed of ions in the X-axis direction and improve the resolution.

[0032] The insulating outer cylinder 2, the insulating inner column 3, the segmented separation electrode pair, the isolated ground electrode pair, and two electrodes of the ion receiving electrode are coaxially arranged.

[0033] Example:

[0034] An ionization source (1), an insulating outer cylinder (2), a cylindrical insulating inner cylinder (3), a separation electrode pair (4, 4', 5, 5', 6, 6', 7, 7', 8, 8'), an isolated ground electrode pair (9, 9'), and an ion receiving electrode (10, 10').

[0035] DMMP enters the separation zone formed by the separation electrode pairs (4, 4', 5, 5', 6, 6', 7, 7', 8, 8') through the vacuum ultraviolet ionization source 1. The mobility changes under the action of high and low fields in each separation electrode pair. Since the DC voltages applied to different separation electrode pairs are different, the damping force in the axial direction is formed to reduce the flight speed of the ions on the axis, thereby increasing the residence time in the separation zone and improving the separation effect. Finally, the ions pass through the area between the isolation electrode pairs (9, 9') and enter the detection zone formed by the ion receiving electrodes (10, 10'). The typical spectrum of dimethyl methylphosphonate in the cylindrical structure high-field asymmetric waveform ion mobility spectrum with three-segment electrode pairs under different segmented voltage differences is shown in the figure below. Figure 2 As shown. Experimental conditions: RF is 1.2MHz square wave asymmetric high voltage, high field is 1500V, low field is 500V, high field time to low field time ratio is 0.3 microseconds: 0.9 microseconds, the voltage difference between DC and U is 4V. The plate spacing is 0.5mm, and the spacing between the segmented electrode pairs is 0.5mm. U1-U2, U2-U3, U3-U4, U4-U5 have the same δU. Figure 2 From top to bottom, the results of δU are given as 0.1V, 0.12V, 0.13V, 0.14V, and 0.15V respectively.

Claims

1. A segmented cylindrical high-field asymmetric waveform ion transfer tube, characterized in that: It comprises a cylindrical insulating outer cylinder (2) with openings at both ends, and a cylindrical insulating inner cylinder (3) located inside the insulating outer cylinder (2), with the direction from left to right being the X-axis direction, the direction from top to bottom being the Y-axis direction, and the direction perpendicular to the X-axis and the Y-axis being the Z-axis direction; An ion source (1) is provided near the left end of the insulating outer cylinder (2), and ion receiving electrodes (10, 10') are provided inside the insulating outer cylinder (2) near the right end, wherein the receiving electrode surfaces of the ion receiving electrodes (10, 10') are parallel to the X-axis; Two or more pairs of segmented separation electrode pairs (including first, second ... Nth segmented separation electrode pairs (4, 4', 5, 5', N, N')), isolated ground electrode pairs (9, 9'), and ion receiving electrodes (10, 10', i.e., detection electrode pairs) are provided between the left port of the ionization source (1) and the ion receiving electrode (10, 10'); two electrodes in the segmented separation electrode pairs are respectively fixed to the inner wall surface of the insulating outer cylinder (2) and the outer wall surface of the insulating inner column (3), and they are arranged opposite to each other and are both cylindrical electrodes; The first, second ... Nth electrode pairs (4, 4', 5, 5', N, N'), the isolated ground electrode pair (9, 9'), and the ion receiving electrodes (10, 10') are sequentially arranged at intervals along the X-axis direction; Different DC voltages (DC1, DC2 ... DCN) and the same high-field asymmetric radio frequency voltage are applied to the electrodes (4, 5 ... N) located inside the insulating outer cylinder (2) in the first, second ... Nth electrode pairs (4, 4', 5, 5' ... N, N'), and DC voltages (U1, U2 ... UN) are applied to the corresponding electrodes (4', 5' ... N') located on the outer surface of the insulating inner column (3), N being an integer greater than or equal to 2 (i.e., the segmented separation electrode pairs are the first electrode pair, the second electrode pair, ...).

2. The segmented cylindrical high-field asymmetric waveform ion transfer tube according to claim 1, characterized in that: The carrier gas flow direction is along the X-axis direction, and the electric field force in the axial direction on the ions in the segmented high-field asymmetric waveform ion migration tube is opposite to the carrier gas flow direction and is smaller than the carrier force generated by the carrier gas; the residence time of the ions in the segmented high-field asymmetric waveform ion migration tube can be adjusted by changing DC1, DC2...DCN, U1, U2...UN applied to the first, second...Nth electrode pairs (4, 4', 5, 5'...N, N'); the voltage difference between DC1 and U1 is the same as the voltage difference between DC2 and U2 and the voltage difference between DCN and UN, and the amplitudes of U1, U2...UN increase (or decrease) monotonically.

3. The segmented cylindrical high-field asymmetric waveform ion transfer tube according to claim 1 or 2, characterized in that: There are at least two pairs of segmented separation electrode pairs (preferably 3 pairs, i.e. N=3, the first, second ... Nth electrode pairs (4, 4', 5, 5' ... 6, 6') are the first, second, third electrode pairs (4, 4', 5, 5', 6, 6')), and the spacing between each pair of electrodes is 0.01 to 2 mm; the spacing between the segmented separation electrode pairs is 0.1 to 5 mm.

4. The segmented cylindrical high-field asymmetric waveform ion transfer tube according to claim 1, characterized in that: The isolated ground electrode pair (9, 9') is connected to the ground; A DC voltage of 1-10 V is applied to the ion receiving electrodes (10, 10').

5. The segmented cylindrical high-field asymmetric waveform ion transfer tube according to claim 1, characterized in that: Its operating pressure range is from 10 Pascals to 1 atmosphere.

6. The segmented cylindrical high-field asymmetric waveform ion transfer tube according to claim 1, characterized in that: It can reduce the movement speed of ions in the X-axis direction and improve the resolution.

7. The segmented cylindrical high-field asymmetric waveform ion transfer tube according to claim 1, characterized in that: The insulating outer cylinder (2), the insulating inner column (3), the segmented separation electrode pair, the isolated ground electrode pair, and two electrodes of the ion receiving electrode are coaxially arranged.

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