HK1185716B - Corona discharge device and ion mobility spectrometer with the same - Google Patents

Abstract

The invention provides a corona discharge device. The corona discharge device comprises a first electrode, wherein the first electrode comprises a general column-shaped first inner cavity part and a general cone-shaped second inner cavity part which is communicated with the first inner cavity part, and the cross section area of the second inner cavity part gradually enlarges on the direction far away the first inner cavity part. The invention further provides an ion mobility spectrometer with the corona discharge device. The ion mobility spectrometer comprises an ionization area and the corona discharge device arranged in the ionization area. The ion mobility spectrometer with the corona discharge device can be favorable for leading-out of ions and can prolong the service life of the electrode. Besides, the electrode is stored by focusing, and thus corona discharge pulse interference can be effectively shielded, and sample ions can be drawn and focused, a designed voltage control scheme is used for realizing migration distinguishing of the ions, meanwhile, ion number fluctuation caused by a corona pulse is shielded, and thus the effect of stable migration of spectral lines is achieved.

Description

Corona discharge device and ion mobility spectrometer with same

Technical Field

The present invention relates to a corona discharge device and an ion mobility spectrometer having the same.

Background

The ion mobility spectrometer realizes the resolution of ions according to the different drift speeds of different ions under a uniform weak electric field. The method has the advantages of high resolution speed, high sensitivity, no need of a vacuum environment and convenience for miniaturization, thereby being widely applied to the field of detection of drugs and explosives. A typical ion mobility spectrometer is generally comprised of a sample introduction portion, an ionization region, an ion gate, a mobility region, a collection region, readout circuitry, data acquisition and processing, a control portion, and the like. The main function of the ionization part is to convert sample molecules into ions for migration and separation, so the ionization effect has a very direct influence on the performance of the spectrometer. In the prior art, the most common and widely used ionizing assembly adopts a Ni63 radioactive source, which has the advantages of small volume, high stability and no need of an additional circuit, but also brings the problems of narrow linear range, low concentration of converted ions and radiation pollution. Especially, the problem of radiation pollution causes inconvenience in the operation, transportation and management of the equipment.

One solution to overcome this problem is to use corona discharge technology instead of radioactive source technology. Corona discharge is a phenomenon in which gas molecules are ionized in a spatially inhomogeneous electric field due to a locally strong electric field. Ions generated directly by the corona discharge, commonly referred to as reactant ions, are ionized by trapping the charge of the reactant ions as sample molecules having a higher proton or electron affinity pass through the ionization region. Generally, the corona discharge structure is simple, so the cost is low, and the concentration of the charges generated by the corona discharge is much higher than that of a radioactive source, so the sensitivity of the ion mobility spectrometer is favorably improved, and a larger dynamic range is obtained.

However, the application of corona discharge ionization has some disadvantages, except that a high-voltage power supply is needed for power supply, because corona discharge itself is in a pulse process (Trichel pulse), if ions directly enter an ion mobility spectrometer through an ion gate, spectral line disorder is caused, and a test result is seriously influenced; in addition, ions in a corona discharge region are accelerated by an electric field in the region and collide with a corona electrode to be lost, so that the improvement of the sensitivity of a mobility spectrometer is limited, and how to effectively pull the ions out of an ionization region is an important problem; in addition, because corona discharge oxidizes the corona electrode, extending the life of the electrode is also an important issue.

Disclosure of Invention

An object of the present invention is to provide a corona discharge device and an ion mobility spectrometer having the same, which are capable of structurally extending the life of an electrode.

It is another object of the present invention to provide an ion mobility spectrometer that can be structurally beneficial for extraction of ions.

It is a further object of the present invention to provide an ion mobility spectrometer that is capable of effectively shielding the interference of corona discharge pulses with a focused storage electrode.

According to an aspect of the present invention, there is provided a corona discharge device including: a first electrode, the first electrode comprising: a first generally cylindrical interior chamber portion, and a second generally conical interior chamber portion in communication with the first interior chamber portion, the second interior chamber portion having a cross-sectional area that gradually increases in a direction away from the first interior chamber portion.

According to an aspect of the invention, the first electrode further comprises: a generally cylindrical first portion defining the first interior cavity portion; and a generally tapered second portion connected to the first portion, the second portion defining the second interior cavity portion.

According to an aspect of the invention, the first inner cavity portion has a substantially cylindrical shape and the second inner cavity portion has a substantially conical shape, and the first inner cavity portion is arranged substantially coaxially with the second inner cavity portion.

According to an aspect of the invention, the first electrode further has an opening through a wall of the first electrode; and the corona discharge device further comprises: and a second electrode inserted into the first electrode from the outside of the first electrode through the opening of the first electrode, the second electrode having a needle-like shape.

According to an aspect of the invention, the second electrode is inserted into the first lumen portion.

According to an aspect of the present invention, the needle-shaped second electrodes are at least one pair of needle-shaped second electrodes that are oppositely disposed and extend substantially on the same straight line.

According to an aspect of the present invention, there is provided an ion mobility spectrometer comprising: an ionization region; and the corona discharge device is arranged in the ionization region and is the corona discharge device.

According to an aspect of the invention, the ion mobility spectrometer further comprises: a focus storage electrode having a substantially tapered barrel portion, at least a portion of which is inserted into the second inner cavity portion of the first electrode.

According to another aspect of the invention, the barrel portion has a generally conical shape.

According to another aspect of the invention, the first interior cavity portion has a generally cylindrical shape, and a diameter of an end of the barrel portion abutting the corona discharge device is smaller than a diameter of the first interior cavity portion.

According to another aspect of the present invention, the ion mobility spectrometer further comprises: a first grid electrically connected to an end of the barrel portion of the focused storage electrode distal from the corona discharge device.

According to another aspect of the present invention, the ion mobility spectrometer further comprises: a second gate spaced a predetermined distance from the first gate.

According to another aspect of the invention, the first electrode and the focus storage electrode are arranged substantially coaxially.

According to another aspect of the invention, the carrier gas flows in said first electrode substantially in the axial direction of said first electrode.

According to a further aspect of the present invention, there is provided an ion mobility spectrometer comprising: an ionization region; a corona discharge device disposed in the ionization region, one cylindrical electrode of the corona discharge device having an inner cavity portion; and a focus storage electrode having a substantially tapered cylindrical portion, at least a part of which is inserted into the inner cavity portion of the electrode.

According to another aspect of the invention, the barrel portion has a generally conical shape.

According to another aspect of the invention, the inner cavity portion has a substantially cylindrical shape, and a diameter of an end of the cylinder portion abutting the corona discharge device is smaller than a diameter of the inner cavity portion.

According to another aspect of the present invention, the ion mobility spectrometer further comprises: a first grid electrically connected to an end of the barrel portion of the focused storage electrode distal from the corona discharge device.

According to another aspect of the present invention, the ion mobility spectrometer further comprises: a second gate spaced a predetermined distance from the first gate.

According to another aspect of the invention, the electrode and the focus storage electrode are arranged substantially coaxially.

According to another aspect of the invention, the carrier gas flows in the electrode substantially in the axial direction of the electrode.

With some embodiments of the present invention, extraction of ions and extension of electrode life may be structurally facilitated. In addition, by using the focusing storage electrode, the interference of corona discharge pulses can be effectively shielded, and sample ions can be pulled and focused. The designed voltage control scheme is utilized to realize the migration resolution of ions, and simultaneously, the fluctuation of the ion quantity caused by corona pulse is shielded, so that the effect of stabilizing the migration spectral line is achieved.

Drawings

FIG. 1 is a schematic diagram of an ion mobility spectrometer according to an embodiment of the present invention.

Figure 2 is a schematic cross-sectional view of a corona discharge device according to an embodiment of the invention.

Figure 3 is a schematic left side view of a corona discharge device according to an embodiment of the invention.

Figure 4 is a schematic perspective view of a corona discharge device according to an embodiment of the invention.

Fig. 5 is a schematic cross-sectional view of a focusing storage electrode according to an embodiment of the present invention.

FIG. 6 is a schematic right side view of a focused storage electrode according to an embodiment of the invention.

Fig. 7 is a potential diagram of various components of an ion mobility spectrometer in positive ion mode according to an embodiment of the present invention.

Detailed Description

The ion mobility spectrometer of the present invention can operate in either the positive or negative ion mode, and for the sake of convenience, the following description will be made only in the positive ion mode.

Fig. 1 is a schematic diagram of an ion mobility spectrometer 100 according to an embodiment of the present invention. As shown in fig. 1, the ion mobility spectrometer 10 includes: a housing 20, a sample introduction section 22, an ionization region 24, a focusing storage electrode 14, a migration region 28, a collection region 30, a readout circuit 40, a data acquisition and processing device, a control section, and the like. The sample introduction section 22 includes an inlet 221 for introducing a carrier gas and a sample. In addition, the ion mobility spectrometer 100 further includes an air outlet 201 and a migration gas inlet 202. The ion mobility spectrometer 10 further includes: a corona discharge device 50 disposed in the ionization region 24; the drift electrodes 16 are arranged in the migration region 28, and the drift electrodes 16 are coaxial circular rings arranged at equal intervals; a faraday plate 18 disposed in the collection region 30, and a suppressor grid 17 disposed between the drift electrode 16 and the faraday plate 18 for suppressing the ions from generating electrostatically induced charges in the faraday plate 18. The suppressor grid 17 is a single grid. The faraday plate 18 is a circular flat plate and is coupled to a charge sensitive amplifier for reading ion signals.

As shown in fig. 2 to 4, the corona discharge device includes: a first electrode 12, the first electrode 12 comprising: a first generally cylindrical interior cavity portion 530, and a second generally conical interior cavity portion 550 in communication with the first interior cavity portion 530, the second interior cavity portion 550 having a gradually increasing cross-sectional area in a direction away from the first interior cavity portion 530. The first electrode 12 has a substantially cylindrical shape. The first electrode 12 further comprises: a generally cylindrical first portion 53, said first portion 53 defining said first interior cavity portion 530; and a generally tapered second portion 55 connected to the first portion 53, the second portion 55 defining the second interior cavity portion 550.

As shown in fig. 1-4, the first inner chamber portion 530 may have a generally cylindrical shape and the second inner chamber portion 550 may have a generally conical shape and the first inner chamber portion 530 is disposed generally coaxially with the second inner chamber portion 550. The first portion 53 may have a substantially cylindrical surface shape and the second portion 55 may have a substantially conical surface shape, and the first portion 53 and the second portion 55 may be substantially coaxially arranged. The first inner cavity portion 530, the second inner cavity portion 550, the first portion 53, and the second portion 55 can also have other suitable shapes.

As shown in fig. 2 to 4, the first electrode 12 also has an opening 51 through the wall of the first electrode 12. The opening 51 may pass through a wall of the first portion 53 or the second portion 55. The corona discharge device further includes: and a second electrode 11 inserted into the first electrode 12 from the outside of the first electrode 12 through the opening 51 of the first electrode 12, wherein the second electrode 11 has a needle-like shape. The second electrode may be inserted into the first lumen portion 530 or the second lumen portion 550.

As shown in fig. 2 to 4, the second electrodes 11 are at least one pair (e.g., one pair, two pairs, three pairs or more) of second electrodes 11 that are oppositely disposed and extend substantially on the same straight line. Alternatively, each pair of second electrodes 11 may be disposed in a staggered manner, rather than in an opposed manner. The second electrode 11 may be referred to as a corona needle and the first electrode 12 may be referred to as a corona target.

As shown in fig. 2 to 4, the needle-like second electrode 11 may be connected to the first portion 53 through the cylindrical insulating block 13. The second electrode 11 may extend in a radial direction of the cylindrical first portion 53, and a length inserted into the first inner cavity portion 530 may be adjustable. The second electrode 11 is made of an oxidation-resistant metal such as stainless steel, tungsten, nickel, platinum, or the like. The first electrode 12 may be formed by plating a nickel on a common metal surface.

Referring to fig. 1 to 4, the interior of the first electrode 12 serves as a gas path through which carrier gas entering the ion mobility spectrometer 10 from the carrier gas and sample inlet 221 flows. The carrier gas flows in the first electrode 12 substantially in the axial direction of the first electrode 12. I.e. the direction of the flow a of the spectrometer carrier gas inlet is substantially parallel to the axial direction of the first electrode 12. The second electrode 11 enters the gas path. The direction of the electric field generated by the first electrode 12 and the second electrode 11 is orthogonal to the flow direction a of the carrier gas in the first electrode 12, so that the electric field can be prevented from interfering with the electric field area downstream in the gas path.

As shown in fig. 1 and 5, the focus storage electrode 14 has a substantially tapered cylindrical portion 141, and the cylindrical portion 141 may have a substantially conical surface shape. At least a portion of the tapered barrel portion 141 is inserted into the second interior portion 550 of the first electrode 12. The cylindrical portion 141 is not in contact with the first electrode 12. In the case of using an existing first electrode having an inner cavity, at least a portion of the tapered barrel portion 141 may be similarly inserted into the inner cavity of the existing first electrode. The second portion 55 may facilitate the barrel portion 141 of the focus storage electrode 14 to be as close as possible to the corona region and form a focused electric field with the focus storage electrode 14. The diameter of the end 143 of the cylindrical portion 141 abutting the corona discharge device 50 is smaller than the diameter of the first inner cavity portion 530 of the first portion 53 of the first electrode 12. For example, the diameter of the end 143 of the cylindrical portion 141 abutting the corona discharge device 50 is about 1 to 3mm smaller than the diameter of the first inner cavity portion 530 of the first portion 53 of the first electrode 12.

Alternatively, the first electrode 12 may include only: a first inner cavity portion 530 that is generally cylindrical, without a second inner cavity portion 550 that is generally conical. At this time, at least a portion of the barrel portion 141 of the focus storage electrode 14 may be inserted into the first inner cavity portion 530 of the first electrode 12.

The focus storage electrode 14 may have only the barrel portion 141. Alternatively, the focus storage electrode 14 may further include a flange 145, the flange 145 being formed at the larger diameter end 147 of the tapered cylinder portion 141. The first electrode 12 and the focus storage electrode 14 may be arranged substantially coaxially.

As shown in fig. 1, the ion mobility spectrometer 10 further includes: a first grid 145, the first grid 145 being electrically connected to an end 147 of the barrel 141 of the focusing storage electrode 14 distal from the corona discharge device 50. The first grid 145 contacts an end 147 of the barrel portion 141 of the focus storage electrode 14 distal from the corona discharge device 50 or a flange 149 of the focus storage electrode 14. The first gate electrode 145 has a mesh shape, and the mesh may have various shapes such as a hexagon shape, a rectangle shape, and the like. A substantially equipotential region is formed in the vicinity of the end 147 or the inside of the first grid 145 of the cylindrical portion 141, and this region is used for ion storage.

As shown in fig. 1, the ion mobility spectrometer 10 further includes: a second gate 15, the second gate 15 being spaced apart from the first gate by a predetermined distance. The second grid 15 has a grid network shape, and the grid may have various shapes such as a hexagon and a rectangle.

The first grid electrode 145 and the second grid electrode 15 constitute an ion gate, and a voltage applied between the first grid electrode 145 and the second grid electrode 15 forms a periodically varying and forward or reverse electric field that forms "on" and "off" states of the ion gate.

Referring to fig. 1 and 7, fig. 7 is a potential diagram of various components of an ion mobility spectrometer 10 in a positive ion mode according to an embodiment of the present invention. In fig. 7, the horizontal axis P represents the position of each component, the vertical axis V represents the potential of each component, reference numeral 110 represents the potential of the second electrode 11, reference numeral 120 represents the potential of the first electrode 12, reference numeral 140 represents the potentials of the focus storage electrode 14 and the first gate electrode 145, reference numeral 150 represents the potential of the second gate electrode 15, reference numeral 160 represents the potential of the drift electrode 16, reference numeral 170 represents the potential of the suppression gate 17, and reference numeral 180 represents the potential of the faraday disk 18.

As shown in fig. 1 and 7, when the ion mobility spectrometer 10 is operated, the potential 110 of the second electrode 11 is higher than the potential 120 of the first electrode 12 by about 700V to 3000V (depending on the radius of the tip of the second electrode 11 and the length of the second electrode 11, different corona-starting voltages may occur for different geometric dimensions), so that ions are generated by corona, the potential 140 of the focusing storage electrode 14 is periodically transited, the focusing storage electrode 14 is in a storage state when the focusing storage electrode 14 is at a low potential (as shown by a solid line indicated by reference numeral 140 in fig. 7), and the focusing storage electrode 14 is in a storage state traction state when the focusing storage electrode 14 is at a high potential (as shown by a broken line indicated by reference numeral 140 in fig. 7). When the focusing storage electrode 14 is in a storage state, the potential 140 of the focusing storage electrode 14 is lower than the potential 120 of the first electrode 12 by 60V-150V and lower than the potential 150 of the second grid 15 by about 5V-60V, the ions are subjected to a weaker electric field force after entering the focusing storage electrode 14, and mainly do thermal motion in the cavity of the focusing storage electrode 14, after a certain time, the ions in the focusing storage electrode 14 are accumulated to a certain number, the potential of the focusing storage electrode 14 jumps to a traction state, the ions generated by corona discharge at the first electrode 12 stop entering the focusing storage electrode 14, and the fluctuation of the number of ions in the focusing storage electrode 14 due to a corona pulse is prevented, and the ions in the focusing storage electrode 14 rapidly enter the drift electrode 16 through the second grid 15 under the action of the electric field force between the focusing storage electrode 14 and the second grid 15. In the drift electrode 16, the ions reach a state of uniform motion under the combined action of the electric field traction and the moving gas flow in the opposite direction, and after a longer moving distance, the ions with different mobilities are separated due to the difference of the velocities, and finally are received by the faraday 18 after passing through the suppression grid 17.

As shown in fig. 1 and 7, the focusing storage electrode 14 and the first grid 145 of the ion gate form a combined electrode, the potential 140 of which is periodically stepped, and the focusing storage electrode 14 and the first grid 145 of the ion gate can be in a storage state and a traction state according to the difference of the potential 140. When in the storage state (as shown by the solid line indicated by reference numeral 140 in fig. 7), the electric field between the first grid 145 of the focusing storage electrode 14 and ion gate and the first electrode 12 is in the same direction as the ion movement, and since the diameter of the end 143 of the focusing storage electrode 14 is smaller than the diameter of the first inner cavity portion 530 of the first electrode 12, a traveling focusing electric field region is formed, effectively pulling the corona-generated ions away from the corona region and focusing them into smaller beam spots into the focusing storage electrode 14. After the ions enter the focusing storage electrode 14 for a certain distance, due to the fact that the focusing storage electrode 14 and the first grid 145 of the ion gate are at the same potential, the internal electric field of the focusing storage electrode 14 is weaker, and due to the fact that the focusing storage electrode 14 and the weak reverse electric field applied between the focusing storage electrode 14 and the first grid 145 and the second grid 15 of the ion gate are combined, a roughly equipotential region is formed at least in the focusing storage electrode 14 near the first grid 145 of the ion gate, the ions do not have the electric field effect in the region and mainly act as thermal motion, and the large cavity at the end 147 of the focusing storage electrode 14 also ensures the thermal motion of the ions without colliding with the focusing storage electrode 14 and being lost. When the thermally moved ions are accumulated to a certain amount, the potential of the focusing storage electrode 14 jumps to a "transition state" (as indicated by a dotted line indicated by reference numeral 140 in fig. 7), the electric field between the focusing storage electrode 14 and the first electrode 12 is opposite to the ion moving direction, ions generated by corona are prevented from entering the focusing storage electrode 14, and at the same time, the electric field between the focusing storage electrode 14 and the ion gate first grid 145 and the ion gate second grid 15 becomes identical to the ion moving direction. The equipotential varying potential 160 of the ring electrode 16 of the transition region 28 creates a pulling electric field. Ions accumulated in the focused storage electrode 14 are rapidly drawn into the mobility region 28 by applying a strong forward electric field through the ion gate, causing the ions to move through the suppression grid 17 having an electric potential 170 towards the faraday disk 18 having an electric potential 180. Therefore, the influence of fluctuation of the ion quantity caused by the corona discharge pulse on the migration spectral line is weakened in the ion accumulation process in front of the ion gate, so that the migration spectral line can be basically kept stable under the corona discharge pulse.

Referring to fig. 1 and 7, in the corona discharge device 50 as a corona discharge ion source, a voltage of about 700V to 3000V may be generally applied between the first electrode 12 and the second electrode 11 to generate corona discharge, that is, a potential difference between the potential 110 of the second electrode 11 and the potential 120 of the first electrode 12 may be generally about 700V to 3000V. Since the second electrode 11 is inserted into the first electrode 12 perpendicularly to the carrier gas flow direction a, the corona electric field is perpendicular to the gas path in the first electrode 12, which reduces the interference of the corona electric field on the electric field of the subsequent component (especially the pulse interference). In addition, a plurality of second electrodes 11 are inserted to increase the ion concentration, and when one of the second electrodes 11 is degraded due to oxidation, the ionization performance is not significantly degraded. The first portion 53 of the first electrode 12 may be cylindrical to enable electrical discharge with the second electrode 11, and the second portion 55 of the first electrode 12 may be flared to allow the focus storage electrode 14 to be closer to the corona ionization region and to form a focus electric field with the focus storage electrode 14. The potential difference between the second electrode 11 and the first electrode 12 is maintained near the corona onset voltage to reduce the ionization region energy density, avoid the generation of large amounts of sample molecular fragments, and extend the life of the second electrode 11.

Claims (12)

1. An ion mobility spectrometer comprising:

an ionization region; and

a corona discharge device disposed in the ionization region,

the corona discharge device includes:

a first electrode, the first electrode comprising: a first generally cylindrical interior chamber portion, and a second generally conical interior chamber portion in communication with the first interior chamber portion, the second interior chamber portion having a gradually increasing cross-sectional area in a direction away from the first interior chamber portion,

the ion mobility spectrometer further comprises:

a focus storage electrode having a substantially tapered barrel portion, at least a portion of which is inserted into the second inner cavity portion of the first electrode.

2. The ion mobility spectrometer of claim 1, wherein:

the first electrode further comprises: a generally cylindrical first portion defining the first interior cavity portion; and a generally tapered second portion connected to the first portion, the second portion defining the second interior cavity portion.

3. The ion mobility spectrometer of claim 2, wherein:

the first inner chamber portion has a generally cylindrical shape and the second inner chamber portion has a generally conical shape, and the first inner chamber portion is disposed generally coaxially with the second inner chamber portion.

4. The ion mobility spectrometer of claim 1, wherein: the first electrode further having an opening through a wall of the first electrode; and the corona discharge device further comprises: and a second electrode inserted into the first electrode from the outside of the first electrode through the opening of the first electrode, the second electrode having a needle-like shape.

5. The ion mobility spectrometer of claim 4, wherein:

the second electrode is inserted into the first lumen portion.

6. The ion mobility spectrometer of claim 4, wherein:

the needle-shaped second electrodes are at least one pair of needle-shaped second electrodes which are oppositely arranged and extend on the same straight line.

7. The ion mobility spectrometer of claim 1, wherein:

the barrel portion has a substantially conical shape.

8. The ion mobility spectrometer of claim 7, wherein:

the first interior cavity portion has a generally cylindrical shape, and

the diameter of the end of the barrel abutting the corona discharge device is smaller than the diameter of the first inner cavity portion.

9. The ion mobility spectrometer of claim 1, further comprising:

a first grid electrically connected to an end of the barrel portion of the focused storage electrode distal from the corona discharge device.

10. The ion mobility spectrometer of claim 9, further comprising:

a second gate spaced a predetermined distance from the first gate.

11. The ion mobility spectrometer of claim 8, wherein:

the first electrode and the focus storage electrode are arranged substantially coaxially.

12. The ion mobility spectrometer of claim 8, wherein:

the carrier gas flows in the first electrode substantially in an axial direction of the first electrode.