A lensed ion transfer tube

Abstract

This invention discloses a lens-type ion mobility tube. An ion optical lens with radial divergence and then radial convergence of the ion beam is disposed within the ionization region of the ion mobility tube. This increases the probability of contact between the reactant ions generated by the ion source and neutral sample molecules, thereby enabling a sufficient ion-molecule reaction to generate high-abundance sample product ions and improving the detection sensitivity of the ion mobility tube. This ion mobility tube technology organically combines increasing the ion-molecule contact probability to improve the ion-molecule reaction yield with radial convergence of the ion beam to improve the ion number density, providing a novel approach to enhancing the detection sensitivity of ion mobility spectrometry. This technology does not require modification of the existing ion mobility tube structure; it can be achieved simply by changing the voltage applied between adjacent electrodes within the ionization region, facilitating its widespread application in the field of ion mobility spectrometry.

Description

Technical Field

[0001] This invention relates to the ion migration tube, a core component of ion mobility spectrometers, and more specifically, to a lens-type ion migration tube with the function of first diverging and then converging ion beams. Background Technology

[0002] Ion mobility spectrometry (IMS) is an ion separation and detection technique operating at atmospheric pressure. Efficient ionization of the analyte is a prerequisite for highly sensitive detection of target analytes using IMS. IMS typically employs an ion source to pre-generate reagent ions and introduce them into the ionization region. Then, a sample gas stream is used to introduce the sample carrier into the ionization region, where it reacts with the reagent ions to generate sample product ions. In their previous studies, Li Mei, Xiao Yao, and others (Sensor Actuat. B-Chem., 2021, 330:129365; Sensor Actuat. B-Chem., 2022, 350:130844) found that the gas flow pattern inside the ion mobility spectrometer is mainly laminar. In addition, the gas diffusion rate is slow under atmospheric pressure. After the sample molecules enter the ionization region with the sample gas, they mainly exist near the inner wall of the circumference of the ionization region. The neutral sample molecules do not come into sufficient contact with the reaction reagent ions before flowing out of the ion mobility tube through the gas outlet, which is an important reason for the low response sensitivity of the target analyte in the sample.

[0003] In 2021, Chen et al. (ZL202111410919.4) used an optical diverging lens to expand the ultraviolet light beam of the photoionization source of an ion migration tube, increasing the probability of ultraviolet light contacting and ionizing neutral molecules in the sample, thus effectively improving the detection sensitivity of the photoionization ion migration tube. Furthermore, Zhou Qinghua, Ni Kai et al. (DOi: 10.1038 / srep10659; Anal.Chem., 2018, 90:4514) verified that the isopotential line distribution of a unidirectional outward convex configuration can manipulate the radial convergence or radial divergence of ion clusters under atmospheric pressure, changing the radial spatial distribution size of the ion clusters.

[0004] These previous studies inspired us to design a lens-type ion migration tube that uses ion-molecule reactions to ionize the sample. By setting an ion optical lens with the function of radial divergence and radial convergence of the ion beam in the ionization region, we can improve the sensitivity of ion mobility spectrometry detection by combining the increase in the probability of ion-molecule contact to improve the yield of ion-molecule reaction and the increase in ion number density by radial convergence of ion beam. Summary of the Invention

[0005] This invention discloses a lens-type ion migration tube, which combines the two functions of increasing the probability of ion-molecule contact and thus improving the ion-molecule reaction yield and increasing the ion number density by setting an ion optical lens with the function of radial divergence and then radial convergence of ion beam in the ionization region, thereby improving the detection sensitivity of ion migration spectrum.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A lens-type ion migration tube, comprising an ion source, an ionization region, an ion gate, a migration region, and an ion receiving electrode arranged coaxially from left to right;

[0008] The ionization region is a cylindrical body composed of M+1 annular insulators with through holes in the middle and M annular electrodes with through holes in the middle, which are coaxially and alternately stacked from left to right. The inner diameter of the through hole in the middle of the annular insulator is larger than the inner diameter of the through hole in the middle of the annular electrode. The annular electrode serves as a lens electrode.

[0009] Along the direction from left to right from the ion source to the ion receiver, the annular electrodes inside the ionization region are, in sequence, the first lens electrode, the second lens electrode, ..., the (M-1)th lens electrode and the Mth lens electrode. The first lens electrode is circumferentially sealed to the ion source located to its left through an annular insulator, and the Mth lens electrode is circumferentially sealed to the ion gate located to its right through an annular insulator. The first lens electrode, the second lens electrode, ..., the (M-1)th lens electrode and the Mth lens electrode constitute an ion optical lens, where M is a positive integer greater than or equal to 4.

[0010] The inner diameter of the first lens electrode and the Mth lens electrode is the same as d1, and the inner diameter of the second lens electrode, ..., the M-2th lens electrode and the M-1th lens electrode is the same as d2, where d2 is greater than or equal to d1, and preferably d2 is 2 to 3 times d1;

[0011] A voltage V1 is applied between the ionization source and the first lens electrode, a voltage V2 is applied between the first lens electrode and the second lens electrode, a voltage V3 is applied between adjacent electrodes from the second lens electrode to the (M-1)th lens electrode, a voltage V2 is applied between the (M-1)th lens electrode and the Mth lens electrode, and a voltage V1 is applied between the Mth lens electrode and the ion gate. The voltage V1 is controlled to be greater than or equal to the voltage V2, and the voltage V2 is greater than or equal to the voltage V3. Preferably, V2 is 5 to 10 times V3. This forms a spindle-shaped electric field line distribution characteristic along the ion migration tube axis inside the ion optical lens.

[0012] The reactant ions generated by the ion source migrate along the direction from the ion source to the ion receiving electrode to form a continuous cylindrical ion flow. During the process of the ion flow flowing into the ion optical lens through the first lens electrode and then flowing out of the ion optical lens through the Mth lens electrode, the radial diameter of the ion flow first diverges and increases and then converges and decreases. It also comes into full contact with the neutral sample molecules inside the ion optical lens to generate ion-molecule reactions and produce high abundance of sample product ions. After the ion flow carrying the sample product ions flows out of the ion optical lens, it migrates towards the region adjacent to the ion gate in the ionization region under the drive of the electric field.

[0013] A sample gas inlet is provided on the circumferential sidewall of the ionization region adjacent to the ion source, an outlet is provided on the circumferential sidewall of the ionization region adjacent to the ion gate, and a drift gas inlet is provided on the circumferential sidewall of the migration region adjacent to the ion receiving electrode.

[0014] When the ion migration tube is working, a sample gas enters the ion optical lens inside the ionization region through the sample gas inlet. Neutral sample molecules react with the reagent ions in the ion flow to generate sample product ions. The sample product ions migrate with the ion flow towards the region of the ionization region adjacent to the ion gate.

[0015] The ion gate, which opens briefly in a periodic manner, injects the ion flow in the ionization region into the migration region in the form of pulsed ion clusters. Driven by a uniform DC electric field, the ions reach the ion receiving electrode in sequence to achieve separation and detection, and are converted into two-dimensional spectrum information of current intensity versus time for output.

[0016] The drifting gas enters the migration zone through the drifting gas inlet and flows out of the migration zone in the opposite direction to the ion flight direction. Finally, it flows out of the ion migration tube through the outlet (9) together with the gas inside the ionization zone.

[0017] The gas used for drifting is any one of the following gases, including O2, N2, CO2, H2, Ar, or a mixture of two or more gases; the gas used for sample gas is any one of the following gases, including O2, N2, CO2, H2, Ar, or a mixture of two or more gases.

[0018] The migration region is a cylindrical body composed of N+1 annular insulators with through holes in the middle and N annular electrodes with through holes in the middle, which are coaxially and alternately stacked from left to right. The inner diameter of the through hole in the middle of the annular insulator is larger than the inner diameter of the through hole in the middle of the annular electrode; N is a positive integer greater than or equal to 2.

[0019] The advantages of this invention are:

[0020] The lens-type ion migration tube disclosed in this invention does not require any improvement to the structure of existing ion migration tubes. It can form an ion optical lens with the function of radial divergence and radial convergence of ion beams in the ionization region by simply changing the voltage applied between adjacent electrodes inside the ionization region. This organically combines the increase in the probability of ion-molecule contact to improve the ion-molecule reaction yield with the radial convergence of ion beams to improve the ion number density, thereby improving the sensitivity of ion mobility spectrum detection.

[0021] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0022] Figure 1 This is a specific structural diagram of a lens-type ion migration tube disclosed in this invention; wherein: 1, ion source; 2, ionization region; 3, ion gate; 4, migration region; 5, ion receiving electrode; 6, ion optical lens; 6-1, first lens electrode; 6-2, second lens electrode; 6-3, third lens electrode; 6-4, fourth lens electrode; 6-5, fifth lens electrode; 7, drift gas inlet; 8, sample gas inlet; 9, gas outlet;

[0023] Figure 2 The diagram shows the distribution of (a) isopotential lines, (b) electric field lines, and (c) changes in the shape of the ion beam within the ion optical lens when the lens-type ion migration tube is operating in ion beam modulation mode (i.e., when the voltage applied between adjacent lens electrodes is different).

[0024] Figure 3 The diagram shows the distribution of (a) isopotential lines, (b) electric field lines, and (c) changes in the shape of the ion beam within the ion optical lens when the lens-type ion migration tube is operating in non-ion beam modulation mode (i.e., when the voltage applied between adjacent lens electrodes is the same).

[0025] Figure 4 The detection spectra of 10 ppb monochlorobenzene obtained by the lens-type ion migration tube operating in (a) ion beam modulation mode and (b) non-ion beam modulation mode. Detailed Implementation

[0026] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way. The invention will now be described in further detail with reference to the accompanying drawings.

[0027] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0028] Example 1

[0029] Figure 1 This is a specific structural diagram of a lens-type ion migration tube disclosed in this invention. In the diagram, 1 is the ion source, 2 is the ionization region, 3 is the ion gate, 4 is the migration region, 5 is the ion receiving electrode, 6 is the ion optical lens, 6-1 is the first lens electrode, 6-2 is the second lens electrode, 6-3 is the third lens electrode, 6-4 is the fourth lens electrode, 6-5 is the fifth lens electrode, 7 is the drift gas inlet, 8 is the sample gas inlet, and 9 is the gas outlet.

[0030] Ion source 1 is a single-ended closed metal cylinder with an axial length of 10 mm, an outer diameter of 12 mm, and an inner diameter of 10 mm. The inner surface of the cylinder is equipped with radioactive materials. 63The Ni coating has its open end welded to a ring-shaped metal electrode with an axial length of 2 mm, an outer diameter of 30 mm, and an inner diameter of 12 mm. Ionization region 2 is composed of six ring-shaped PTFE insulators with an axial length of 3 mm, an outer diameter of 30 mm, and an inner diameter of 26 mm, and five metal conductive rings with an axial length of 2 mm and an outer diameter of 30 mm, coaxially and alternately stacked from left to right. Along the direction from ion source 1 to ion receiver 5, the first conductive ring is the first lens electrode 6-1 with an inner diameter of 10 mm; the second conductive ring is the second lens electrode 6-2 with an inner diameter of 22 mm; the third conductive ring is the third lens electrode 6-3 with an inner diameter of 22 mm; the fourth conductive ring is the fourth lens electrode 6-4 with an inner diameter of 22 mm; and the fifth conductive ring is the fifth lens electrode 6-5 with an inner diameter of 10 mm. mm; the first lens electrode 6-1, the second lens electrode 6-2, the third lens electrode 6-3, the fourth lens electrode 6-4, and the fifth lens electrode 6-5 constitute the ion optical lens 6; the ion gate 3 is a BN type ion gate with two sets of coplanar metal wires, the metal wire diameter is 0.1 mm, and the spacing between adjacent wires is 0.5 mm; the migration region 4 is composed of an annular PTFE insulator with an axial length of 3 mm, an outer diameter of 30 mm, and an inner diameter of 26 mm, and a metal conductive ring with an axial length of 2 mm, an outer diameter of 30 mm, and an inner diameter of 10 mm, which are coaxially and alternately stacked from left to right, and the axial length of the migration region 4 is 60 mm; the ion receiving electrode 5 is a Faraday disk with an axial length of 1 mm and an outer diameter of 6 mm, which is insulated and sealed on a metal shielding cylinder with an outer diameter of 30 mm and a thickness of 5 mm;

[0031] When the ion migration tube is working, the electric field strength of migration region 4 is maintained at 500 V / cm, and the closing voltage of ion gate 3 is maintained at ±50V. Purified air filtered through 13X molecular sieve, silica gel, and activated carbon is used as bleaching gas and enters the ion migration tube through bleaching gas inlet 7 at a flow rate of 200 mL / min. Purified air filtered through 13X molecular sieve, silica gel, and activated carbon is used as sample gas carrier to carry the target analyte into the ion migration tube through sample gas inlet 8 at a flow rate of 100 mL / min.

[0032] Figure 2This diagram illustrates the distribution of isopotential lines, electric field lines, and ion beam shape within the ion optical lens 6 when the lens-type ion migration tube operates in ion beam modulation mode. In this mode, the voltage between ion source 1 and the first lens electrode 6-1 is 400V, the voltage between the first lens electrode 6-1 and the second lens electrode 6-2 is 400V, the voltage between the second lens electrode 6-2 and the third lens electrode 6-3 is 50V, the voltage between the third lens electrode 6-3 and the fourth lens electrode 6-4 is 50V, the voltage between the fourth lens electrode 6-4 and the fifth lens electrode 6-5 is 400V, and the voltage between the fifth lens electrode 6-5 and the ion gate 3 is 400V. Inside the ion optical lens 6, the isopotential lines exhibit a distribution characteristic of being dense at both ends and sparse in the middle. Figure 2 a), further forming an electric field line distribution characteristic that varies in a spindle shape along the axial direction of the ion migration tube ( Figure 2 (b) When the ion beam passes through the ion optical lens 6, the radial diameter of the ion beam first diverges and increases, then converges and decreases. Figure 2 c).

[0033] Comparative Example 1

[0034] Based on the lens-type ion migration tube disclosed in Example 1, the isopotential line distribution, electric field line distribution, and ion beam shape changes inside the ion optical lens 6 when the ion migration tube operates in a non-ion beam modulation mode were further obtained, such as... Figure 3 As shown. The difference from Example 1 is that, in this mode, the voltage between the ion source 1 and the first lens electrode 6-1 is 400V, the voltage between the first lens electrode 6-1 and the second lens electrode 6-2 is 400V, the voltage between the second lens electrode 6-2 and the third lens electrode 6-3 is 400V, the voltage between the third lens electrode 6-3 and the fourth lens electrode 6-4 is 400V, the voltage between the fourth lens electrode 6-4 and the fifth lens electrode 6-5 is 400V, and the voltage between the fifth lens electrode 6-5 and the ion gate 3 is 400V. Inside the ion optical lens 6, the isopotential lines exhibit a uniform distribution characteristic (…). Figure 3 a), further forming an electric field line distribution characteristic parallel to the ion migration tube axis ( Figure 3 (b) When the ion beam passes through the ion optical lens 6, the radial diameter of the ion beam remains essentially unchanged. Figure 3 c).

[0035] Comparative Example 2

[0036] Based on the lens-type ion migration tube disclosed in Example 1, the response of 10 ppb monochlorobenzene in both ion beam modulation and non-ion beam modulation modes was further obtained. Figure 4a is the response spectrum of the ion migration tube operating in ion beam modulation mode. It can be seen that the ion peak intensity of 10 ppb monochlorobenzene is 554 pA. Figure 4 b shows the response spectrum of the ion migration tube operating in non-ion beam modulation mode. It can be seen that the ion peak intensity of 10 ppb monochlorobenzene is 279 pA. Clearly, when the ion migration tube operates in ion beam modulation mode, the response signal intensity of monochlorobenzene increases by nearly two times.

Claims

1. A lens-type ion migration tube, wherein the ion migration tube comprises an ion source (1), an ionization region (2), an ion gate (3), a migration region (4), and an ion receiving electrode (5) arranged coaxially from left to right, characterized in that: The ionization region (2) is a cylinder formed by M+1 annular insulators with through holes in the middle and M annular electrodes with through holes in the middle, which are coaxially and alternately stacked from left to right. The inner diameter of the through hole in the middle of the annular insulator is larger than the inner diameter of the through hole in the middle of the annular electrode. The annular electrode serves as a lens electrode. Along the left-to-right direction from the ion source (1) to the ion receiving electrode (5), the annular electrodes inside the ionization region (2) are, in sequence, the first lens electrode (6-1), the second lens electrode (6-2), ..., the (M-1)th lens electrode (6-M-1) and the Mth lens electrode (6-M). The first lens electrode (6-1) is circumferentially sealed to the ion source (1) located to its left through an annular insulator. The Mth lens electrode (6-M) is circumferentially sealed to the ion gate (3) located to its right through an annular insulator. The first lens electrode (6-1), the second lens electrode (6-2), ..., the (M-1)th lens electrode (6-M-1) and the Mth lens electrode (6-M) constitute an ion optical lens (6), where M is a positive integer greater than or equal to 4. The inner diameters of the first lens electrode (6-1) and the Mth lens electrode (6-M) are the same, d1. The inner diameters of the second lens electrode (6-2), ..., the M-2nd lens electrode (6-M-2) and the M-1st lens electrode (6-M-1) are the same, d2, and d2 is greater than or equal to d1. A voltage V1 is applied between the ionization source (1) and the first lens electrode (6-1), a voltage V2 is applied between the first lens electrode (6-1) and the second lens electrode (6-2), a voltage V3 is applied between the second lens electrode (6-2) and the adjacent electrodes of the M-1 lens electrode (6-M-1), a voltage V2 is applied between the M-1 lens electrode (6-M-1) and the M lens electrode (6-M), and a voltage V1 is applied between the M lens electrode (6-M) and the ion gate (3). The voltage V1 is controlled to be greater than or equal to the voltage V2, and the voltage V2 is greater than or equal to the voltage V3. Thus, an electric field line distribution feature with a spindle shape along the ion migration tube axis is formed inside the ion optical lens (6). The reaction reagent ions generated by the ion source (1) migrate along the direction from the ion source (1) to the ion receiving electrode (5) to form a cylindrical continuous ion flow. The ion flow flows into the ion optical lens (6) through the first lens electrode (6-1) and then flows out of the ion optical lens (6) through the M lens electrode (6-M). During this process, the radial diameter of the ion flow first diverges and increases and then converges and decreases. It fully contacts the neutral sample molecules inside the ion optical lens (6) to generate a high abundance of sample product ions through an ion-molecule reaction. After the ion flow carrying the sample product ions flows out of the ion optical lens (6), it migrates towards the region adjacent to the ion gate (3) in the ionization region (2) under the drive of the electric field.

2. The lens-type ion migration tube according to claim 1, characterized in that: A sample gas inlet (8) is provided on the circumferential sidewall of the ionization region (2) adjacent to the ion source (1), an outlet (9) is provided on the circumferential sidewall of the ionization region (2) adjacent to the ion gate (3), and a drift gas inlet (7) is provided on the circumferential sidewall of the migration region (4) adjacent to the ion receiving electrode (5).

3. The lens-type ion migration tube according to claim 2, characterized in that: When the ion migration tube is working, a sample gas enters the ion optical lens (6) inside the ionization region (2) through the sample gas inlet (8). Neutral sample molecules react with the reagent ions in the ion flow to generate sample product ions. The sample product ions migrate with the ion flow to the region of the ionization region (2) adjacent to the ion gate (3). The ion gate (3) that is opened briefly in a periodic period injects the ion flow in the ionization region (2) into the migration region (4) in the form of pulsed ion clusters. Driven by a uniform DC electric field, the ion flow reaches the ion receiving electrode (5) in sequence to achieve separation and detection, and is converted into a two-dimensional spectrum of current intensity versus time for output. The drifting gas enters the migration zone (4) through the drifting gas inlet (7) and flows out of the migration zone (4) in the opposite direction to the ion flight direction. Finally, it flows out of the ion migration tube through the outlet (9) together with the gas inside the ionization zone (2).

4. The lens-type ion migration tube according to claim 3, characterized in that: The bleaching gas is any one of the following gases, including O2, N2, CO2, H2, Ar, or a mixture of two or more gases; the sample gas is any one of the following gases, including O2, N2, CO2, H2, Ar, or a mixture of two or more gases.

5. The lens-type ion migration tube according to claim 1, characterized in that: The migration zone (4) is a cylindrical body composed of N+1 annular insulators with through holes in the middle and N annular electrodes with through holes in the middle, which are coaxially and alternately stacked from left to right. The inner diameter of the through hole in the middle of the annular insulator is larger than the inner diameter of the through hole in the middle of the annular electrode; N is a positive integer greater than or equal to 2.

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