Field corrected ion mobility spectrometer

Abstract

The present application provides a field correction ion mobility spectrometer, comprising an ionization source, an ionization region, a reaction region, a correction grid, an ion gate, a migration region and a signal detector. By inserting the correction grid into the ionization region and the reaction region of the ion mobility spectrometer migration tube and optimizing the position and the corresponding ion gate closing voltage, the non-uniform electric field existing in the ionization region and the reaction region can be effectively corrected, the spatial diffusion of ions in the ionization region and the reaction region is constrained, and the detection sensitivity and resolution of the ion mobility spectrometer are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of analytical instruments and detection - the field of ion mobility spectrometry, and particularly relates to a field-corrected ion mobility spectrometer, and more particularly to a field-corrected ion mobility spectrometer for improving detection sensitivity and resolution by correcting the non-uniform electric field in the ionization region and reaction region of the drift tube. BACKGROUND

[0002] Ion mobility spectrometry is a technology that uses the difference in the migration speed of ions in an electric field at atmospheric pressure to achieve rapid separation and detection of ions. It has high detection sensitivity and fast response speed. Taking a drift tube ion mobility spectrometer as an example, the ion mobility tube is formed by stacking electrode rings and insulating rings. Ions move in the tubular space formed by the two types of rings. Ion mobility spectrometry detection mainly includes three processes: ion generation, ion transmission, and ion detection. After the reaction ions and molecules generated by the ionization source undergo ion-molecule reactions in the reaction region, the product ion beam is converged in front of the ion gate. The ion gate is like an electronic switch. When the ion gate is closed, the ion beam converges in front of the gate. When the ion gate is opened, the ion beam enters the migration region in the form of a pulse. Ions with different masses or collision cross sections reach the detector at different times - migration times. The speed of ion movement v = KE, where K is the mobility of the ion and E is the electric field strength through the drift tube. From this formula, it can be seen that the core of ion mobility spectrometry detection is to accurately control the motion trajectory of ions through the electric field strength E, so that they can be accurately detected in the signal detection region. The sensitivity of the instrument is proportional to the number of ions that reach the detection region, and the resolution of the instrument is closely related to the radial and axial distribution of the ion beam in the migration motion.

[0003] The electric field in the drift tube is a uniform electric field in an ideal case, that is, the electric lines are parallel. However, when the ionization source voltage is higher than the voltage on the electrodes in the ionization and reaction regions, the electric field near the electrode edges in the ionization and reaction regions will be distorted, and the electric lines will be twisted, making it impossible to achieve complete parallelism of the electric lines. Ions in this non-uniform electric field region either diffuse towards the drift tube wall during motion, resulting in reduced resolution, or directly collide with the electrodes and are annihilated, reducing detection sensitivity. SUMMARY

[0004] The technical problem to be solved by the present application is to provide an ion mobility spectrometer for correcting non-uniform electric field in ionization area and reaction area of a migration tube to improve detection sensitivity and resolution, i.e. inserting a correction grid into the ionization area and the reaction area to correct the distorted electric field in the ionization area and the reaction area, to constrain the ions moving to the wall of the migration tube to the central direction of the migration tube, to suppress the radial diffusion of the ions in front of the ion gate, and to improve the number density of the ions in front of the ion gate.

[0005] The technical solution adopted by the present application to solve the above technical problem is an ion mobility spectrometer for correcting field, which improves detection sensitivity and resolution by correcting non-uniform electric field in ionization area and reaction area of a migration tube, and comprises an ionization source, ionization area, reaction area, correction grid, ion gate, migration area and signal detector.

[0006] Further, the voltage of the ionization source is higher than the voltage on the electrode in the downstream ionization area, resulting in non-uniform electric field between them.

[0007] Further, the voltage of the ionization source is further higher than the voltage on the electrode in the reaction area, resulting in non-uniform electric field between them.

[0008] Further, the correction grid is composed of a metal electrode, a metal grid and a nesting plate. The metal electrode matches the inner diameter of the migration ring of the ionization area and the reaction area, and is used to fix the metal grid. The assembly of the metal electrode and the metal grid is installed in the nesting plate made of insulating material, and the three constitute the correction grid. When the voltage of the ionization source is higher than the voltage of the ionization area and the reaction area, the non-uniform electric field existing near the ionization area and the reaction area will push the ions in this area to the wall of the migration tube, thereby affecting the motion trajectory and distribution of the ions, and reducing the detection performance of the ion mobility spectrometer. When the correction grid is inserted into the ionization area and the reaction area, the non-uniform electric field in the above areas can be corrected, and the ions moving to the wall of the migration tube are constrained to the central direction of the migration tube, thereby improving the number density of the ions in front of the ion gate. The distance between the correction grid and the ionization source is 0.2-4 cm.

[0009] Further, by changing the fixed position of the nesting plate in the drift tube, the relative position of the metal mesh to the ionization source in the ionization region and the reaction region is changed. First, the initial relative position of the metal mesh and the ionization source is measured, and then the target position is determined. According to the experimental requirements, the distance that needs to be moved is determined. The distance that needs to be moved from the initial position to the target position is calculated. This can be achieved by measuring the distance between the current metal mesh position and the ideal position. The nesting plate usually has adjustable supports or screws for precise positioning. After adjusting the nesting plate, the position of the metal mesh relative to the ionization source is re-measured to ensure that it reaches the target position. Precise measuring tools such as vernier calipers or micrometer screws or laser range finders can be used to confirm the accuracy of the position adjustment. If the initial adjustment fails to reach the target position, the nesting plate needs to be adjusted multiple times and the measurement needs to be repeated until the metal mesh position meets the requirements.

[0010] Further, the ion gate can be a Tyndall-Powell (TP) type or a Bradbury-Nielsen (BN) type ion gate. When the correct grid is inserted into the ionization region and the reaction region at the right position, more ions are concentrated near the ion gate in the center of the drift tube under the action of the correct grid correction electric field during the ion gate closing period. When the ion gate is opened, the number of ions entering the drift region of the drift tube increases, and the sensitivity of the ion mobility spectrometer is enhanced. Furthermore, based on the above reasons, most of the ions entering the drift region converge near the center of the drift tube, with small spatial diffusion, so that the ion time distribution to the signal detector is more concentrated, i.e. the signal resolution of the ion mobility spectrum is improved. The ion gate closing voltage value can be adjusted according to the position of the correct grid; wherein the voltage value of the TP type ion gate is 100 V to 600 V, and the voltage value of the BN type ion gate is 80 V to 500 V.

[0011] The advantages of the present application compared with the prior art are:

[0012] (1) The present application uses the correct grid to correct the non-uniform electric field in the ionization region and the reaction region, so that more ions are confined in front of the ion gate, and the number density of ions in front of the ion gate is increased when the ion gate is closed. When the ion gate is opened, a larger number of ions enter the drift region and reach the signal detection region to be detected, thereby improving the sensitivity of the ion mobility spectrometer.

[0013] (2) In the present application, when the ion gate is closed, the ions are confined near the center of the drift tube, and the spatial distribution of the ions is more concentrated. When the ion gate is opened, the spatial diffusion of the ions is relatively small during the process of entering the drift region, so that the ion time distribution to the signal detector is more concentrated, i.e. the signal resolution of the ion mobility spectrum is improved. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1It is a field correction ion mobility spectrometer schematic diagram provided by the embodiment of the present application.

[0015] The meaning of the reference signs in the figure is that 1 is an ionization source; 2 is an ionization region; 3 is a reaction region; 4 is a correction grid; 5 is an ion gate; 6 is a migration region; 7 is a signal detector; 8 is a metal electrode; 9 is a metal grid; and 10 is a nested plate.

[0016] Fig. 2 (a) is an ionization region and reaction region electric field simulation of a conventional ion mobility spectrometer provided by the embodiment of the present application; and Fig. 2 (b) is the motion trajectory of ions in the non-uniform electric field formed in the ionization region and the reaction region.

[0017] Fig. 3 (a) is an ionization region and reaction region electric field simulation of a field correction ion mobility spectrometer provided by the embodiment of the present application; and Fig. 3 (b) is the motion trajectory of ions in the correction electric field formed in the ionization region and the reaction region.

[0018] Figure 4 In the figure, (a) is a spectrum of a conventional ion mobility spectrometer provided by the embodiment of the present application; and (b) is a spectrum of a field correction ion mobility spectrometer provided by the embodiment of the present application. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort fall within the protection scope of the present application.

[0020] As shown in the figure: Figure 1

[0021] The field correction ion mobility spectrometer designed in the present application is different from the conventional ion mobility spectrometer in that when the voltage of the ionization source 1 is higher than the voltage on the electrodes in the ionization region 2 and the reaction region 3, the correction grid 4 is inserted into the ionization region 2 and the reaction region 3 of the migration tube to correct the non-uniform electric field in the ionization region 2 and the reaction region 3 of the migration tube, thereby improving the detection sensitivity and resolution of the ion mobility spectrometer. The field correction ion mobility spectrometer used in this embodiment is composed of an ionization source 1, an ionization region 2, a reaction region 3, a correction grid 4, an ion gate 5, a migration region 6, a signal detector 7, and the like.

[0022] ​As shown in Fig. 2(a), when the ionization region 2 or the reaction region 3 is not inserted with the correction grid 4, the electric field near the ionization region 2 or even the reaction region 3 is distorted due to the voltage at the position of the ionization source 1 being higher than the voltage on the electrodes of the downstream ionization region 2 and the reaction region 3, and the electric field lines are distorted. In this case, as shown in Fig. 2(b), the ion motion trajectory simulation shows that the ions move towards the wall of the drift tube during the migration, and even some ions will hit the wall of the drift tube and be annihilated, and the radial distribution of the ions in the drift tube is more dispersed. At this time, as shown in Fig. 2(c), in the negative ion detection mode of the ion mobility spectrometer, the signal of the reaction ions is investigated by taking clean air as the detection object, and it is found that the signal intensity I0 of the ion mobility spectrum is 204.44, and the ion mobility spectrum resolution R0 calculated from the migration time is 34 (where t is the migration time of the ions, and w is the half-width of the signal peak). Figure 4

[0023] When the correction grid 4 is inserted at a position 6.5 mm downstream of the ionization source 1, as shown in Fig. 3(a), although the voltage at the position of the ionization source 1 is still higher than the voltage on the electrodes of the downstream ionization region 2 and the reaction region 3, the distorted electric field is greatly improved, and the distortion of the electric field lines is also greatly improved. As shown in Fig. 3(b), the ion motion trajectory simulation shows that in this case, most of the ions are constrained near the axis of the drift tube during the migration, and the radial distribution of the ions in the drift tube is more concentrated. As shown in Fig. 3(c), under the same experimental conditions as above, when the correction grid 4 is not inserted, the signal intensity I1 of the ion mobility spectrum is 411.39, and the ion mobility spectrum resolution R1 calculated from the migration time is 38. Further calculation shows that Figure 4 This indicates that when the correction grid 4 is inserted in the ionization region 2, the signal intensity and the resolution of the ion mobility spectrometer are both enhanced.

[0024] The position of the insertion of the correction grid 4 depends on the region of the distorted electric field of the ionization region 2 and the reaction region 3, and in the actual process, the position needs to be optimized. In addition, as the position of the insertion of the correction grid 4 changes, the ions also exhibit different distribution characteristics at the front end of the ion gate 5. Therefore, when optimizing the position of the correction grid 4, in order to obtain an ion mobility spectrum with better sensitivity and resolution, the closing voltage of the ion gate 5 also needs to be further optimized. In the above example, the optimized closing voltage of the ion gate 5 is 460 V.

[0025] ​​​​​The correction grid 4 is composed of a metal electrode 8, a metal grid 9 and a nest plate 10. The metal electrode 8 is matched with the inner diameter of the migration ring in the migration tube, and is used to fix the metal grid 9. The metal electrode 8 and the metal grid 9 are installed in the nest plate 10 made of insulating material, and form the correction grid 4. When the voltage of the ionization source 1 is higher than the ionization zone 2 and the reaction zone 3, the non-uniform electric field existing near the ionization zone 2 and the reaction zone 3 will push the ions in the area to the wall of the migration tube, thus affecting the trajectory and distribution of the ions, and reducing the detection performance of the ion mobility spectrometer. When the correction grid 4 is inserted into the ionization zone 2 and the reaction zone 3, the non-uniform electric field in the above-mentioned areas can be corrected, and the ions migrating to the wall of the migration tube are restrained to the direction of the center of the migration tube, thus increasing the number density of the ions in front of the ion gate 5. The distance between the correction grid 4 and the ionization source 1 is 0.2 cm to 4 cm.

[0026] The ion gate 5 can be a Tyndall-Powell type or a Bradbury-Nielsen type ion gate. When the correction grid 4 is inserted into the ionization zone 2 and the reaction zone 3 at the appropriate position, more ions will gather in the area near the ion gate 5 at the center of the migration tube under the action of the electric field of the correction grid 4 during the closing of the ion gate 5. When the ion gate 5 is opened, the number of ions entering the migration zone 6 of the migration tube increases, and the sensitivity of the ion mobility spectrometer is enhanced. Based on the above reasons, most of the ions entering the migration zone 6 converge near the center of the migration tube, the spatial diffusion is small, and the time distribution of the ions reaching the signal detector 7 is more concentrated, that is, the signal resolution of the ion mobility spectrum is improved. The voltage value of the ion gate 5 needs to be adjusted and optimized according to the position of the correction grid; the voltage value of the Tyndall-Powell gate is 100 V to 600 V, and the voltage value of the Bradbury-Nielsen gate is 80 V to 400 V.

[0027] The specific embodiments described in the present application are only examples of the present application. Those skilled in the art of the technical field to which the present application belongs can make various modifications or supplements to the described specific embodiments or use similar ways to replace them, without deviating from the spirit of the present application or exceeding the scope defined by the appended claims. Some parts of the specification of the present application are not described in detail, which belongs to the commonly known technology in the art.

Claims

1. A field-calibrated ion mobility spectrometer, which improves detection sensitivity and resolution by correcting the non-uniform electric field in the ionization and reaction regions, characterized in that: It includes an ionization source (1), an ionization region (2), a reaction region (3), a correction grid (4), an ion gate (5), a migration region (6), and a signal detector (7). By adjusting the position of the correction grid (4) in the ionization region (2) and the reaction region (3), and combining the changes in signal intensity and sensitivity, the non-uniform electric field of the ionization region (2) and the reaction region (3) is corrected, thereby constraining the spatial diffusion of ions in the ionization region (2) and the reaction region (3), and improving the detection sensitivity and resolution of the ion mobility spectrometer. The correction grid (4) consists of a metal electrode (8), a metal mesh (9), and a nested plate (10); wherein the metal electrode (8) is matched with the inner diameter of the migration ring in the ionization region (2) and the reaction region (3) to fix the metal mesh (9), and the assembly consisting of the metal electrode (8) and the metal mesh (9) is installed in the nested plate (10) made of insulating material, and the three together constitute the correction grid (4), and the correction grid (4) is 0.2 cm to 4 cm away from the ionization source (1).

2. The field-corrected ion mobility spectrometer according to claim 1, characterized in that: The voltage at the ionization source (1) is higher than the voltage at the electrode in the downstream ionization region (2), resulting in a non-uniform electric field between them.

3. The field-corrected ion mobility spectrometer according to claim 1, characterized in that: The voltage at the ionization source (1) is even higher than the voltage at the electrode in the reaction zone (3), and a non-uniform electric field is generated between the two.

4. The field-corrected ion mobility spectrometer according to claim 3, characterized in that: The position of the metal mesh (9) relative to the ionization source in the ionization zone (2) and the reaction zone (3) is changed by altering the fixed position of the nested plate (10) in the ionization zone (2) and the reaction zone (3); the nested plate (10) has an adjustable bracket or screw for precise positioning; after adjusting the nested plate (10), the position of the metal mesh (9) relative to the ionization source (1) is remeasured to ensure that it reaches the target position; the accuracy of the position adjustment is confirmed by using precision measuring tools such as vernier calipers, micrometers, or laser rangefinders.

5. The field-corrected ion mobility spectrometer according to claim 1, characterized in that: The ion gate (5) is either a Tyndall-Powell type or a Bradbury-Nielsen type ion gate; the closing voltage value of the ion gate (5) needs to be adjusted and optimized according to the position of the calibration grid (4), and the optimization index is the detection sensitivity and resolution of the instrument; among them, the closing voltage value of the Tyndall-Powell type ion gate is 100 V to 600 V, and the closing voltage value of the Bradbury-Nielsen type ion gate is 80 V to 400 V.

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