JP2004356073A - Ionic mobility sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ionic mobility sensorcapable of efficiently suppressing deterioration of time resolution. <P>SOLUTION: An ionic mobility sensor (IMS) has an ionizing chamber 1 and a drift chamber 21. On the other end side of a drift pipe 23 forming the drift chamber 21, a conductive substrate 43 is disposed. A collecting electrode 45 for collecting ionized sample molecules and a drift gas introducing pipe 47 for introducing drift gas into the drift chamber 21 are disposed on the substrate 43. The collecting electrode 45 is disposed so that its center axis is aligned with the center axis in a longitudinal direction of the drift chamber 21. An electric potential of the collecting electrode 45 is kept at the same as that of the substrate 43. An auxiliary electrode 55 at the same potential as the collecting electrode 45, arranged at an outer periphery side of the collecting electrode 45, has a plurality of through-holes 55a thereon and permeates the drift gas introduced from an introducing port 13 of the introducing pipe 47. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ion mobility detector.
[0002]
[Prior art]
As an ion mobility detector of this kind, an ionization chamber for ionizing sample molecules, a drift chamber for moving sample ions ionized in the ionization chamber in a longitudinal direction, and a collecting electrode for collecting ionized sample molecules are provided. And a grid electrode provided to face the collector electrode are known (for example, see Patent Document 1).
[0003]
The grid electrode is smaller than the area of the collector electrode so that ionized sample molecules that move in the vicinity of the longitudinal center axis of the drift chamber substantially perpendicular to the electric field formed in the drift chamber mainly reach the collector electrode. An aperture having an opening area is formed. As a result, ionized sample molecules dispersed in a direction intersecting the longitudinal center axis of the drift chamber during the movement and forming a trajectory apart from the longitudinal center axis of the drift chamber are prevented from reaching the collector electrode. In addition, a time delay component is prevented from being included in the output from the collector electrode, thereby suppressing deterioration in time resolution.
[0004]
[Patent Document 1]
US Pat. No. 4,714,008 [0005]
[Problems to be solved by the invention]
As a result of the research conducted by the present inventors, it has been found that the ion mobility detector described in Patent Document 1 still has a problem that the time resolution is deteriorated.
[0006]
Disturbance of the electric field occurs near the outer peripheral end of the collector electrode, and the disturbance of the electric field causes the ionized sample molecules that would not otherwise reach the collector electrode (the direction crossing the longitudinal central axis of the drift chamber during the movement). The ionized sample molecules that are dispersed in the drift chamber and form a trajectory distant from the longitudinal center axis of the drift chamber) may reach the collector electrode through the gap between the collector electrode and the grid electrode. There is. As described above, when the ionized sample molecules arrive around the collector electrode, the output from the collector electrode includes a time-delay component, so that the time resolution is deteriorated.
[0007]
An object of the present invention is to provide an ion mobility detector capable of effectively suppressing deterioration in time resolution.
[0008]
[Means for Solving the Problems]
An ion mobility detector according to the present invention includes: a drift chamber in which a sample molecule ionized in an ionization chamber moves in a longitudinal direction; and a collector electrode for collecting the ionized sample molecule. A detector, comprising: an auxiliary electrode provided on the outer peripheral side of the collector electrode and having the same potential as the collector electrode.
[0009]
In the ion mobility detector according to the present invention, since the auxiliary electrode having the same potential as the collector electrode is provided on the outer peripheral side of the collector electrode, the direction intersecting the longitudinal center axis of the drift chamber during the movement. The ionized sample molecules dispersed to form a trajectory distant from the central axis in the longitudinal direction are surely collected by the auxiliary electrode without being collected by the collector electrode. As a result, the output from the collecting electrode does not include a time delay component, and the deterioration of the time resolution can be effectively suppressed.
[0010]
In addition, the apparatus further includes a drift gas introduction unit that introduces the drift gas into the drift chamber from the front of the collector electrode when viewed in the moving direction of the ionized sample molecules in the drift chamber, and the auxiliary electrode transmits the drift gas. Is preferred. With this configuration, the neutralized sample molecules present in the vicinity of the collecting electrode are removed by the drift gas introduced from the front of the collecting electrode when viewed in the direction of movement of the ionized sample molecules. As a result, the arrival of the ionized sample molecules to the collector electrode is not delayed by the neutralized sample molecules existing near the collector electrode, and the deterioration of the time resolution can be further suppressed. Since the auxiliary electrode transmits the drift gas, it does not hinder the flow of the drift gas.
[0011]
Further, the auxiliary electrode is preferably formed in a mesh shape. With such a configuration, it is possible to easily and at low cost provide an auxiliary electrode having a configuration capable of reliably transmitting the drift gas.
[0012]
Preferably, the auxiliary electrode is made of a plate-like member having a through hole. With such a configuration, it is possible to easily and at low cost provide an auxiliary electrode having a configuration capable of reliably transmitting the drift gas.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
An ion mobility detector according to an embodiment of the present invention will be described with reference to the drawings. In the description, the same elements or elements having the same functions will be denoted by the same reference symbols, without redundant description.
[0014]
FIG. 1 is a schematic perspective view for explaining the configuration of the ion mobility detector according to the present embodiment. FIG. 2 is a longitudinal sectional view showing the ion mobility detector according to the present embodiment. FIG. 3 is a sectional view taken along line III-III in FIG. FIG. 4 is a sectional view taken along the line IV-IV in FIG. The ion mobility detector IMS has an ionization chamber 1 and a drift chamber 21 as shown in FIG. The pressure in the ionization chamber 1 and the drift chamber 21 is equivalent to the atmospheric pressure. The ion mobility detector IMS according to the present embodiment cationizes a sample molecule and detects the ion mobility of the cationized sample molecule.
[0015]
As shown in FIGS. 2 to 4, the ionization chamber 1 is a cylindrical member 3 having openings 3 a and 3 b at both ends (in the present embodiment, a rectangular tube whose inner and outer cross-sectional shapes are rectangular). Is a region in which the sample molecules are ionized. The tubular member 3 is made of an electrically insulating material. The ionization chamber 1 (the internal space of the cylindrical member 3) communicates with the drift chamber 21 through one opening 3a of the cylindrical member 3. The tubular member 3 is provided with a sample introduction tube 5 and a vacuum ultraviolet lamp 7.
[0016]
The sample introduction tube 5 is connected to a carrier gas supply source 9 for supplying a carrier gas and a sample molecule supply source 11 for supplying a sample molecule, and is connected to an ionization chamber 1 through an inlet 13 formed at one end of the sample introduction tube 5. Is in communication with The carrier gas supplied from the carrier gas supply source 9 and the sample molecules supplied from the sample molecule supply source 11 are introduced into the ionization chamber 1 through the sample introduction tube 5 in a mixed state. Here, the sample introduction tube 5 functions as a sample molecule introduction unit that introduces a sample molecule into the ionization chamber 1. In the present embodiment, the carrier gas supply source 9 and the sample molecule supply source 11 are connected in series to the sample introduction tube 5, but may be connected in parallel.
[0017]
The vacuum ultraviolet lamp 7 irradiates the sample molecules introduced into the ionization chamber 1 through the sample introduction tube 5 with vacuum ultraviolet light. The sample molecules irradiated with the vacuum ultraviolet light are ionized. Here, the vacuum ultraviolet lamp 7 functions as an energy beam irradiation unit that irradiates the sample molecules introduced into the ionization chamber 1 with energy beams. As the vacuum ultraviolet lamp 7, an excimer lamp using a rare gas or the like, a capillary discharge tube, or a hydrogen discharge lamp can be used. Instead of the vacuum ultraviolet lamp 7, a D2 lamp that emits ultraviolet rays or X-rays, a soft X-ray tube, or a UV laser that can be ionized by multiphoton absorption can be used.
[0018]
As shown in FIG. 1, the irradiation direction of the vacuum ultraviolet light by the vacuum ultraviolet lamp 7 and the introduction direction of the sample molecules through the sample introduction tube 5 cross each other (in the present embodiment, orthogonally). The direction is set to intersect (orthogonal in the present embodiment) the longitudinal center axis L of the drift chamber 21. In the present embodiment, the irradiation direction of the vacuum ultraviolet light from the vacuum ultraviolet lamp 7, the direction of introduction of the sample molecules through the sample introduction tube 5, and the longitudinal center axis L of the drift chamber 21 intersect at one point. I have.
[0019]
An outlet 15 for discharging the introduced sample molecules is formed in the cylindrical member 3 at a position facing the inlet 13 when viewed in the direction of introducing the sample molecules through the sample introduction tube 5. The ionization chamber 1 communicates with the external space through the outlet 15.
[0020]
The other opening 3 b of the cylindrical member 3 is closed by the electron collecting electrode 17. The electron collecting electrode 17 is for collecting electrons generated when the sample molecules are ionized, and is applied with a predetermined positive potential. The electron collecting electrode 17 has a protruding portion 19 inserted into the other opening 3 b of the cylindrical member 3.
[0021]
The drift chamber 21 is formed in the drift tube 23 as shown in FIGS. 2 to 4, and has one end communicating with the ionization chamber 1, and sample molecules ionized in the ionization chamber 1 in the longitudinal direction. The area to move. The drift tube 23 includes a plurality of ring-shaped electrodes 25 and a plurality of ring-shaped electric insulators 27, and has a configuration in which the electrodes 25 and the electric insulators 27 are alternately stacked. That is, the electric insulator 27 is arranged between the electrodes 25, and the electrodes 25 are electrically insulated by the electric insulator 27. The electrode 25 and the electric insulator 27 function as electric field forming means for forming an electric field for moving the ionized sample molecules into the drift chamber 21.
[0022]
A gate electrode 31 as a gate shutter is provided at one end of the drift tube 23. As the gate electrode 31, a Bradbury-Nielsen shutter can be used. The gate electrode 31 allows a sample molecule ionized by a change in applied potential to pass therethrough, and includes a pair of electrodes 31a and a frame member 32 having electrical insulation. Each of the electrodes 31a has a comb-teeth shape having a base portion and a plurality of branch portions extending in a direction intersecting from the base portion, and is arranged so as to mesh with the frame member 32. By setting the potential difference between the pair of electrodes 31a to 0, the passage of ionized sample molecules is allowed. By setting the potential difference to a predetermined value larger than 0, the passage of ionized sample molecules is prohibited. You. Therefore, by supplying a pulse signal to the gate electrode 31 and setting the potential difference between the pair of electrodes 31 a to 0 for a predetermined time, the sample molecules ionized for the predetermined time pass through the gate electrode 31. It becomes. The gate electrode 31 separates the ionization chamber 1 from the drift chamber 21. The gate electrode 31 is provided with a lead 33 for applying a potential, which protrudes in the radial direction of the drift tube 23.
[0023]
A substantially disk-shaped electrode 35 is arranged between the gate electrode 31 and the cylindrical member 3. The electrode 35 has an outer peripheral portion 37 having the same shape as the electrode 25 constituting the drift tube 23, and a base 39 extending inward from the outer peripheral portion 37. The base 39 has an opening 39a communicating with one opening 3a of the tubular member 3, and a gas outlet 39b formed at a position near the outer periphery of the opening 39a. A gas outlet 37a is also formed in the outer peripheral portion 37. The drift chamber 21 (the internal space of the drift tube 23) communicates with the ionization chamber 1 through an opening 39 a formed in the base 39 of the electrode 35 and one opening 3 a of the tubular member 3. In addition, the drift chamber 21 (the internal space of the drift tube 23) communicates with the external space through the gas discharge ports 37a and 39b.
[0024]
A conductive substrate 43 is provided on the other end side of the drift tube 23, as shown in FIG. A collecting electrode 45 (which functions as an anode in the present embodiment) for collecting ionized sample molecules and a drift gas introducing pipe 47 for introducing a drift gas into the drift chamber 21 are arranged on the substrate 43. Have been. FIG. 5 is a cross-sectional view showing the periphery of the substrate included in the ion mobility detector according to the present embodiment.
[0025]
The collector electrode 45 is a disk-shaped member, and is disposed on the substrate 43 by being screwed to a support member provided on the substrate 43 via a ring-shaped member 46 having electrical insulation. Means for electrically insulating the collector electrode 45 from the substrate 43 other than the ring-shaped member 46 include sealing the lead portion of the collector electrode 45 with an electrically insulating material such as glass, or stopping the O-ring. Is also good. As the collecting electrode 45, a Faraday cup or the like can be used. The collector electrode 45 is provided such that the central axis thereof coincides with the longitudinal central axis L of the drift chamber 21. The potential of the collecting electrode 45 is kept at the same potential as the substrate 43.
[0026]
The drift gas introduction pipe 47 is connected to a drift gas supply source 51 that supplies a drift gas, and communicates with the other end of the drift chamber 21 through an introduction port 49 formed at one end of the drift gas introduction pipe 47. . The drift gas supplied from the drift gas supply source 51 passes through the drift gas introduction pipe 47 and is introduced into the drift chamber 21 from the front of the collector electrode 45 when viewed in the moving direction of the ionized sample molecules in the drift chamber 21. You. That is, the collector electrode 45 is located downstream of the inlet 49 of the drift gas inlet pipe 47 when viewed in the drift gas flow direction. The drift gas introduced into the drift chamber 21 flows in the drift chamber 21 toward the ionization chamber 1 and is discharged from the gas discharge ports 37a and 39b to the outside. The flow direction of the drift gas in the drift chamber 21 and the moving direction of the ionized sample molecules are opposite to each other.
[0027]
A grid electrode 53 having a mesh shape is provided on the other end side of the drift chamber 21 so as to face the collector electrode 45. The grid electrode 53 is electrically connected to the electrode 25 closest to the substrate 43 among the electrodes 25 and has the same potential as the electrode. The grid electrode 53 suppresses the electric field formed in the drift chamber 21 from fluctuating due to a pulse-like change in the potential at the gate electrode 31.
[0028]
An auxiliary electrode 55 is arranged on the outer peripheral side of the collector electrode 45. As shown in FIG. 6, the auxiliary electrode 55 is made of a plate-like member, and has an opening 57 having an inner diameter slightly larger than the diameter of the collector electrode 45 at the center. The auxiliary electrode 55 is provided on the same plane as the collecting electrode 45 so that the collecting electrode 45 is located in the opening 57. The outer peripheral portion of the auxiliary electrode 55 is in contact with the substrate 43 and is electrically connected to the substrate 43. Thus, the potential of the auxiliary electrode 55 is maintained at the same potential as the substrate 43. The potential of the auxiliary electrode 55 is the same as the potential of the collecting electrode 45.
[0029]
The auxiliary electrode 55 has a plurality of through holes 55a. The drift gas introduced from the introduction port 49 of the drift gas introduction pipe 47 first flows into a space defined by the substrate 43, the auxiliary electrode 55, and the collector electrode 45. Thereafter, the drift gas flows through the drift chamber 21 through the through hole 55 a formed in the auxiliary electrode 55 and the gap between the inner circumference of the auxiliary electrode 55 and the outer circumference of the collector electrode 45. The space defined by the substrate 43, the auxiliary electrode 55, and the collector electrode 45 functions as a drift gas buffer region.
[0030]
The auxiliary electrode 55 may be a mesh member as shown in FIG. 7 in addition to the plate member having the through-hole 55a.
[0031]
The electrodes 25 and 35, the electrical insulator 27, the gate electrode 31, the tubular member 3, and the electron collecting electrode 17 are sandwiched between the substrate 43 and the holding plate 59. The holding plate 59 is screwed to the other end of the column 61 having one end fixed to the substrate 43 in a state where the electrode 25, the electric insulator 27, the gate electrode 31, the cylindrical member 3, and the electron collecting electrode 17 are sandwiched. Is fixed to the substrate 43 by a nut 63. The electron collecting electrode 17 is screwed to the holding plate 59.
[0032]
Incidentally, the substrate 43, the electrodes 25 and 35, and the electron collecting electrode 17 are electrically connected to each other by a voltage dividing resistor (not shown). The voltage dividing resistor is a thin film resistor formed on the bleeder circuit board 65, and is electrically connected to the substrate 43, the electrodes 25 and 35, and the electron collecting electrode 17 through a conductive screw 67. The screw 67 also has a function of fixing the bleeder circuit board 65. Then, as described above, when a predetermined positive potential is applied to the electron collecting electrode 17 and the substrate 43 is grounded, an electric field is formed from the ionization chamber 1 to the drift chamber 21 as shown in FIG. . The sample molecules ionized by this electric field move from the ionization chamber 1 to the drift chamber 21, and move inside the drift chamber 21 toward the collector electrode 45. FIG. 8 is a diagram showing the electric field distribution in the ionization chamber and the drift chamber and the movement trajectory of the ionized sample molecules. In FIG. 8, the solid line indicates the movement trajectory of the ionized sample molecule, and the dashed line indicates the equipotential surface of the electric field in the ionization chamber 1 and the drift chamber 21. The potentials (+) set for the electrodes 25 and the like are respectively
Electron collecting electrode 17: 2.1 kV
Electrode 35: 1.67 kV
Gate electrode 31: 1.57 kV
Electrode 25 next to gate electrode 31: 1.512 kV
…
Electrode 25 next to electrode 25 to which grid electrode 53 is electrically connected: 215 V
Electrode 25 to which grid electrode 53 is electrically connected: 53 V
Substrate 43: 0V
It is.
[0033]
A mesh electrode 69 is arranged between the tubular member 3 and the electrode 35. The mesh electrode 69 is sandwiched between the tubular member 3 and the electrode 35, and has the same potential as the electrode 35. The mesh electrode 69 is located in the vicinity of the one opening 3 a of the tubular member 3, and suppresses the electric field formed in the ionization chamber 1 from fluctuating due to a pulse-like change in the potential of the gate electrode 31. .
[0034]
Next, the measurement principle of the ion mobility detector IMS having the above-described configuration will be briefly described. The sample molecules (hereinafter simply referred to as ions) ionized in the ionization chamber 1 are introduced into the drift chamber 21 by applying a pulsed voltage to the gate electrode 31 to change the potential. The pulse-like ions introduced into the drift chamber 21 move with a time delay due to the influence of the molecules of the drift gas introduced from the drift gas introduction pipe 47 and are formed in the drift chamber 21. It reaches the collecting electrode 45 along a substantially uniform electric field. The ion group that has reached the collecting electrode 45 is output as a pulsed electric signal, and based on the electric signal, the time of arrival from the gate electrode 31 to the collecting electrode 45 (time of flight (TOF), The amount of the group is detected, etc. The ion mobility can be obtained from the above-mentioned arrival time, thereby enabling the identification of the sample molecule, and the quantification of the sample molecule from the integrated value or peak value of the response waveform of the electric signal. Becomes possible.
[0035]
As described above, in the present embodiment, since the auxiliary electrode 55 having the same potential as that of the collector electrode 45 is provided on the outer peripheral side of the collector electrode 45, the central axis of the drift chamber 21 in the longitudinal direction during the movement is provided. The ionized sample molecules dispersed in the direction intersecting L and forming a trajectory apart from the longitudinal center axis L are surely collected by the auxiliary electrode 55 without being collected by the collector electrode 45. Become. As a result, the output from the collecting electrode 45 does not include a time delay component, and it is possible to effectively suppress deterioration in the time resolution of the ion mobility detector IMS.
[0036]
Further, in the present embodiment, there is further provided a drift gas introduction pipe 47 for introducing the drift gas into the drift chamber 21 from the front of the collector electrode 45 when viewed in the moving direction of the ionized sample molecules in the drift chamber 21. Thus, the auxiliary electrode 55 transmits the drift gas. Thus, the neutralized sample molecules existing near the collecting electrode 45 are removed by the drift gas introduced from the front of the collecting electrode 45 when viewed in the direction of movement of the ionized sample molecules. As a result, the arrival of the ionized sample molecules to the collector electrode 45 is not delayed by the neutralized sample molecules existing near the collector electrode 45, and the degradation of the ion mobility detector IMS time resolution is more reduced. It can be further suppressed. Since the auxiliary electrode 55 transmits the drift gas, it does not hinder the flow of the drift gas.
[0037]
In the present embodiment, the auxiliary electrode 55 has a mesh shape. Thus, the auxiliary electrode 55 having a configuration that can surely transmit the drift gas can be realized simply and at low cost.
[0038]
In the present embodiment, the auxiliary electrode 55 is formed of a plate-like member having a through hole 55a. Thus, the auxiliary electrode 55 having a configuration that can surely transmit the drift gas can be realized simply and at low cost.
[0039]
The present invention is not limited to the embodiments described above. For example, the means for ionizing the sample molecules introduced into the ionization chamber 1 is not limited to the energy beam irradiation means such as the vacuum ultraviolet lamp 7 described above, but may be any as long as it gives ionization energy to the sample molecules.
[0040]
In the present embodiment, the present invention is applied to an ion mobility detector IMS that cationizes a sample molecule and detects the ion mobility of the cationized sample molecule, but is not limited thereto. The present invention can also be applied to an ion mobility detector that anionizes sample molecules and detects the ion mobility of the anionized sample molecules. In the case of an ion mobility detector for detecting the ion mobility of an anionized sample molecule, the potential arrangement has a relationship opposite to the potential arrangement of the ion mobility detector IMS. The position of GND (ground) can be set arbitrarily.
[0041]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide an ion mobility detector capable of effectively suppressing deterioration in time resolution.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view for explaining a configuration of an ion mobility detector according to an embodiment.
FIG. 2 is a longitudinal sectional view showing the ion mobility detector according to the embodiment.
FIG. 3 is a sectional view taken along line III-III in FIG. 2;
FIG. 4 is a sectional view taken along the line IV-IV in FIG. 3;
FIG. 5 is a cross-sectional view showing the periphery of a substrate included in the ion mobility detector according to the embodiment.
FIG. 6 is a perspective view illustrating an example of an auxiliary electrode included in the ion mobility detector according to the embodiment.
FIG. 7 is a perspective view illustrating an example of an auxiliary electrode included in the ion mobility detector according to the embodiment.
FIG. 8 is a diagram showing an electric field distribution in an ionization chamber and a drift chamber and a movement locus of ionized sample molecules.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Ionization chamber, 3 ... cylindrical member, 5 ... Sample introduction tube, 7 ... Vacuum ultraviolet lamp, 17 ... Electron collection electrode, 21 ... Drift chamber, 23 ... Drift tube, 25 ... Electrode, 27 ... Electric insulator, 31 ... gate electrode, 35 ... electrode, 43 ... substrate, 45 ... collector electrode, 47 ... drift gas inlet tube, 53 ... grid electrode, 55 ... auxiliary electrode, 55a ... through hole, 65 ... bleeder circuit board, 69 ... mesh shape Electrode, IMS: ion mobility detector, L: longitudinal axis of drift chamber.

Claims (4)

A drift chamber in which sample molecules ionized in the ionization chamber move in the longitudinal direction, and a collector electrode for collecting the ionized sample molecules, an ion mobility detector,
An ion mobility detector comprising an auxiliary electrode provided on an outer peripheral side of the collector electrode and having the same potential as the collector electrode. Drift gas introduction means for introducing a drift gas into the drift chamber from the front of the collector electrode when viewed in the direction of movement of the ionized sample molecules in the drift chamber,
The ion mobility detector according to claim 1, wherein the auxiliary electrode transmits the drift gas. The ion mobility detector according to claim 2, wherein the auxiliary electrode has a mesh shape. The ion mobility detector according to claim 2, wherein the auxiliary electrode is formed of a plate-like member having a through hole.

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