JP2004071470A - Atmospheric pressure plasma ionizing source mass spectrometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an atmospheric pressure plasma ionizing source mass spectrometer which has an ion deflection lens system that has a high ion transmission efficiency and a simple structure, and further, can be controlled easily. <P>SOLUTION: The atmospheric-pressure plasma ionizing source mass spectrometer has an ion deflection lens system which is made of an incident side plate-like electrode and an outgoing side plate-like electrode that have one aperture respectively and are opposed to each other and at least one cylindrical electrode arranged between the incident side plate-like electrode and the outgoing side plate-like electrode, and in which the incident side plate-like electrode and the outgoing side plate-like electrode are arranged so that the optical axis of each aperture may be mutually shifted, and the cylindrical electrode is arranged so that its center axis may be mutually shifted from the optical axis of at least incident side plate-like electrode. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an atmospheric pressure plasma ionization source mass spectrometer. More specifically, the present invention relates to an atmospheric pressure plasma ionization source mass spectrometer having an ion deflection lens system.
[0002]
[Prior art]
An analyzer, which uses atmospheric pressure plasma as an ionization source and a mass analyzer as a detector, such as a high-frequency inductively coupled plasma mass spectrometer (ICP-MS), has high sensitivity particularly in inorganic element analysis, and has an excellent detection limit. It is known that However, this type of analyzer requires a portion for separating target ions from neutral particles such as high-energy molecules or atoms, light that can be a noise source, and non-decomposed samples that can be a contamination source inside the device. The separation of neutral particles and target ions eliminates neutral particles that may be a noise source from the target ion stream, and prevents the inside of the vacuum chamber of the mass spectrometer from being contaminated by the ingress of non-decomposed samples. Adhesion of contaminants inside the vacuum chamber can significantly degrade signal stability, and the contamination can interfere with the signal.
[0003]
It is known to use a small disc called a photon stop placed on the optical axis and kept at a constant potential to separate neutral ions and a target ion stream. The neutral particles as described above collide with the photon stop disposed on the ion incident side of the second stage ion lens and are stopped. On the other hand, the target ions spread and enter, and a part thereof Without being stopped by the stop, it passes through the photon stop and is detected by the detector. The method using the photon stop is simple in structure and control, but has low ion transmission efficiency. In addition, there is a problem that ions are charged up to the non-decomposed sample deposited on the photon stop, and signal drift is likely to occur.
[0004]
In addition, a cylindrical member is divided into neutral particles and target ions by using an ion deflection lens which is divided into four in a direction parallel to the axis and a direction perpendicular to the axis, and the target ions are a kind of mass analyzer. It is known to lead to quadrupole mass filters. The use of two pairs of parallel plate electrodes as an ion deflection lens is disclosed in Japanese Utility Model Laid-Open No. 3-66145 entitled High Frequency Inductively Coupled Plasma Analyzer. These two methods have high ion permeation efficiency, and the signal adverse effect due to the deposition of the non-decomposed sample is smaller than when using the photon stop, but the structure and control are more complicated.
[0005]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide an atmospheric pressure plasma ionization source mass spectrometer having an ion deflecting lens system which has a high ion permeation efficiency, has a simple structure as compared with the conventional one, and can be easily controlled. And
[0006]
[Means for Solving the Problems]
An object of the present invention is to provide a mass spectrometer using an atmospheric pressure plasma as an ionization source and having an ion deflecting lens system, wherein each of the ion deflecting lens systems has one aperture and faces an incident side plate. The electrode and the output-side plate-shaped electrode, and at least one cylindrical electrode disposed between the incident-side plate-shaped electrode and the output-side plate-shaped electrode, the incident-side plate-shaped electrode and the output-side plate-shaped electrode, This problem is solved by arranging the optical axes of the respective apertures so as to be shifted from each other, and arranging the cylindrical electrodes such that their central axes are at least shifted from the optical axis of the incident side plate-shaped electrode.
[0007]
The ion deflecting lens system according to the invention has a very simple structure and, despite its simple control, ensures the entry of neutral particles which on the one hand can contaminate the mass analyzer and on the other hand a noise source. It is possible to shut off. The ion deflecting lens system according to the present invention has a simple structure, so that the types of voltages applied to the electrodes can be reduced as compared with the conventional lens system having the same purpose, and the ion deflecting lens system itself is compact. It becomes possible to design. This is very useful in a mass spectrometer using atmospheric pressure plasma as an ionization source.
[0008]
The cylindrical electrode may be a single electrode or may be composed of a plurality of cylindrical members. When the cylindrical electrode is composed of a plurality of cylindrical members, the cylindrical member can be formed by being divided by a plane perpendicular to the axis.
[0009]
The cross section perpendicular to the axis of the cylindrical electrode can be a circle, an ellipse, an ellipse, or a rectangle. From the viewpoint of ease of manufacture, it is preferable that the cross section is a circle and the electrode is a cylindrical electrode.
[0010]
As the ionization source of the atmospheric pressure plasma, a conventionally known source such as a microwave induction plasma (MIP) can be used, and a high frequency induction coupling plasma (ICP) is particularly preferable.
[0011]
An interface for the ion deflection lens system to introduce atmospheric pressure plasma into the high vacuum section, and an isolation for keeping the high vacuum section, which occupies most of the mass analysis section, airtight when the operation of the device is stopped It is preferably located between the valves. With this configuration, replacement or maintenance of the ion deflecting lens system can be performed while maintaining the vacuum in the high vacuum chamber after the isolation valve or in most of the high vacuum tanks, thereby improving work efficiency.
[0012]
In the configuration of the present invention, the same voltage can be applied to the pair of plate-shaped electrodes. For example, when one cylindrical electrode is used, the same voltage is applied to a pair of plate-shaped electrodes, so that two types of voltages may be applied to the entire ion deflecting lens system. Simple and easy.
[0013]
Both the optical axis of the aperture of the entrance-side plate-shaped electrode and the optical axis of the aperture of the exit-side plate-shaped electrode are in the same plane including the central axis of the cylindrical electrode, and are mutually central axes of the cylindrical electrode. From each other in substantially opposite directions. With this configuration, the ion deflection lens system has a simpler configuration, and can be operated with simpler control.
[0014]
Claim 7 is a modification of claim 1 independent of the modification from claim 2 to claim 6. The present invention is applied to a mass spectrometer using an atmospheric pressure plasma as an ionization source and having an ion deflecting lens, and using an ion guide as a part of an ion lens system. That is, according to a seventh aspect, the ion deflecting lens system is disposed between the entrance-side plate-like electrode and the exit-side plate-like electrode which are arranged so that the optical axes of the apertures are shifted from each other, and between these plate-like electrodes. At least one cylindrical electrode, the incident side plate electrode and the cylindrical electrode are arranged such that the optical axis of the aperture of the incident side plate electrode is shifted with respect to the center axis of the cylindrical electrode; It is characterized only by the fact that the deflecting lens system is arranged on the ion incidence side of the ion guide, and it is to be construed that there is no limitation in claims 2 to 6. Here, the ion incident side does not necessarily mean immediately adjacent to the incident side, and another lens may be inserted therebetween.
[0015]
In analyzers that use multipole ion guides such as quadrupoles, hexapoles, and octopoles as part of the ion lens system, such ion guides are more susceptible to contamination than ion lenses due to electrostatic fields. It is important that neutral particles do not enter the ion guide. In this configuration, since the ion deflecting lens system is disposed on the ion incident side of the ion guide, it is possible to effectively prevent neutral particles from entering the ion guide.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described in more detail with reference to the accompanying drawings. First, the ion deflection lens system is schematically shown in FIG. Arrow 1 in the drawing indicates the incident direction of ions. The ion deflecting lens shown here is composed of a pair of plate-like electrodes 26 and 28 and one cylindrical electrode 27 disposed therebetween, and the plate-like electrodes 26 and 28 are provided with apertures 46 and 48, respectively. Have been. The optical axes 56, 58 of the apertures 46, 48 pass through the centers of the apertures 46, 48, respectively, and extend in a direction perpendicular to the surface of the plate-shaped electrode. The optical axes 56 and 58 of the aperture are in the same plane including the central axis 40 which passes through the center of the opening surface of the cylindrical electrode 27 and extends in the direction perpendicular to the opening surface. With respect to axis 40, they are offset by the same distance in opposite directions. FIG. 2 is a diagram showing an example of a result of a trajectory simulation of ions passing through such an ion deflecting lens system obtained by calculation. Here, the cylindrical electrode 27 has an inner diameter of φ14 mm and a length of 16 mm, the entrance side aperture 46 and the exit side aperture 48 each have a diameter of φ3 mm, and the optical axes 56 and 58 of the apertures 46 and 48 respectively correspond to the cylindrical electrode 27. , A voltage of −50 V is applied to the entrance-side and exit-side plate-like electrodes, and a voltage of +10 V is applied to the cylindrical electrodes.
[0017]
FIG. 1 shows an example in which the optical axis 58 of the aperture 48 of the emission-side plate-like electrode 28 is shifted from the central axis 40 of the cylindrical electrode 27, but this configuration is not essential. Although the cylindrical electrode 27 having a circular cross section is used here, the cross section may be an ellipse, an ellipse, or a rectangle. In this case, the cross section is determined by the cross sectional shape and the driving voltage. The light-collecting characteristics in the two optical axis directions passing perpendicularly to the direction can be changed as appropriate.
[0018]
FIG. 3 schematically shows a main part of a high-frequency inductively coupled plasma mass spectrometer incorporating the ion deflection lens system shown in FIG. In this method, a sample is ionized using a high frequency inductively coupled plasma (ICP) 17, and the generated ions are guided to a mass spectrometer through an interface section including a sampling cone 22 and a skimmer cone 23, and are electrically detected. By precisely measuring the ion amount, the element to be measured in the sample is analyzed with high accuracy. In the present embodiment, when the operation of the apparatus is stopped, an isolation valve 30 is provided to maintain the airtightness of a high vacuum portion that occupies most of the mass analysis unit. Is disposed between the interface section and the isolation valve.
[0019]
The sample ions, which are ionized by the ICP 17 and passed through the sampling cone 22 and the skimmer cone 23 and introduced into the second stage maintained in a high vacuum, are arranged on the ion emission side by the first lens 25. It is adjusted to go to the ion deflection lens system. The ions first pass through the aperture 46 of the incident-side plate electrode 26. At this time, neutral particles that are not desired to enter the mass analyzer also pass through the aperture 46 of the incident-side plate-like electrode 26 together with target ions. In the ion deflecting lens system, the neutral particles are not affected by the electric field and go straight, collide with the emission-side plate-like electrode 28, do not enter any further downstream, and do not reach the detector 38. On the other hand, ions are generated by the electric field in the ion deflecting lens system despite the optical axes 56 and 58 of the apertures 46 and 48 provided on the entrance plate electrode 26 and the exit plate electrode 28, respectively. As a result, the path is deflected and passes through the aperture 48 of the emission-side plate-like electrode 28. Thereafter, the ions are condensed by an ion lens 32, further separated by a mass analyzer 36 according to a mass-to-charge ratio (m / z value), and detected by a detector 38.
[0020]
Next, the operation of the ICP-MS according to the present invention will be described in detail with reference to FIG. The apparatus shown in this embodiment is a quadrupole mass filter type ICP-MS using an octopole ion guide as a part of the ion lens system.
[0021]
The sample 11 is sent to a nebulizer 13 by a known liquid sending pump 12, where it is converted into an aerosol by argon gas passing through a nebulizer Ar gas tube 19, and sent to a plasma torch 15 via a connecting pipe 14. A high frequency electric field is applied to the coil 16 by the RF power supply 21, and the energy is transmitted by inductively discharging the argon gas supplied by the Ar gas supply device 18 to form a high frequency inductively coupled plasma (ICP) 17. You. The sample aerosol is introduced into this plasma, evaporates, decomposes and, for most elements, is converted to virtually 100% ions. These ions are introduced into the inside of the high vacuum chamber of the second stage having the ion lens via the interface section including the sampling cone 22 and the skimmer cone 23. The apparatus shown here uses a vacuum evacuation system called three-stage differential evacuation. The three vacuum chambers connected by small conductances are evacuated by a rotary pump 24, a turbo molecular pump 31, and a turbo molecular pump 35, respectively. Enables the introduction of ions from the atmospheric pressure at which plasma is generated into the final high vacuum chamber. At this time, the three vacuum chambers are also referred to as a first stage, a second stage, and a third stage, respectively, from the atmospheric pressure side.
[0022]
The ions appropriately collected by the first lens 25 are reflected by the ion deflecting lens system disposed between the interface and the isolation valve on the ion incident side of the isolation valve 30 as shown by a dotted line 51 in the figure. You can bend your course. In the example shown in FIG. 4, the ion deflecting lens system includes an incident-side plate-like electrode 26, a cylindrical electrode 27, and an emission-side plate-like electrode 28, and an optical axis 56 of an aperture 46 of the incident-side plate-like electrode 26. The optical axis 58 of the aperture 48 of the emission-side plate-like electrode 28 is offset from the center axis 40 of the cylindrical electrode 27 by the same distance and in the opposite direction. The ions efficiently pass through the aperture 48 of the emission-side plate-like electrode 28 by this deflection lens system, and are introduced into the next-stage octupole ion guide 32 '. On the other hand, the neutral particles such as the non-decomposed sample and plasma light introduced through the skimmer cone together with the ions are not deflected by the deflecting lens, but proceed straight as indicated by the solid line 52 in the figure, and collide with the emission-side plate-like electrode. Can be stopped. Therefore, the ion guide 32 'is not contaminated by the non-decomposed sample, and can maintain a stable operation. Further, it is possible to completely prevent light from the plasma from entering the detector 38, and it is possible to completely eliminate noise due to light. On the other hand, as the calculation example in FIG. 2 shows, the ion transmission efficiency of the deflecting lens is close to 100%, which contributes to the high sensitivity of the device.
[0023]
This deflecting lens is composed of two plate-shaped electrodes 26 and 28 and one cylindrical electrode 27, and can be configured simply and compactly, and can be provided outside the isolation valve 30 and on the ion incident side as shown in the figure. It is possible. Therefore, cleaning of the emission-side plate-like electrode 28 that receives dirt can be easily performed while the isolation valve 30 is closed when the apparatus is not operating. Conventionally, such a dirt receiving lens is often located inside the isolation valve on the ion emission side. In this case, it is necessary to break the vacuum of the entire apparatus in order to perform the cleaning, and it takes a long time to recover the lens. Time was needed.
[0024]
The deflection lens can be controlled by two voltages, and its optimization is simple. The ions sent to the ion guide 32 'pass through an orifice 34 for differential evacuation, and are separated by a quadrupole mass filter 36' according to the mass-to-charge ratio (m / z value). It is detected at 38. The multipole ion guide used in this embodiment has an advantage that, for example, the number of control variables is small and optimization is easy, as compared with a general electrostatic lens, but is generally susceptible to contamination. Therefore, stopping the non-decomposed sample which causes contamination before the ion guide greatly contributes to the stable operation of the apparatus.
[0025]
In the present embodiment, the octopole ion guide of the multipole ion guide is used as a part of the ion lens. However, a quadrupole or hexapole ion guide may be used. Needless to say, an ion lens using an electrostatic field can be used. Although not shown in the figure, the octopole ion guide controller 33, the quadrupole mass filter controller 37, the detector preamplifier 39, the RF power supply 21, the Ar gas supply device 18, and the like are connected via a main board on the device. Can be controlled.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an ion deflection lens system used in the present invention.
FIG. 2 is a diagram showing an example of an ion trajectory passing through the ion deflecting lens system shown in FIG. 1 obtained by calculation.
FIG. 3 is a schematic diagram of an atmospheric pressure plasma ionization source mass spectrometer according to the present invention incorporating the ion deflection lens system of FIG. 1;
FIG. 4 is a schematic diagram illustrating an operation of an ICP-MS according to the present invention.
[Explanation of symbols]
1: Ion incident direction 11: Sample solution 12: Liquid sending pump 13: Nebulizer 14: Connecting tube 15: Plasma torch 16: RF coil 17: Plasma 18: Ar gas supply device 19: Ar gas tube (for nebulizer)
20: Ar gas tube (for plasma torch)
Reference numeral 21: RF power supply 22: Sampling cone 23: Skimmer cone 24: Rotary pump 25: First lens 26: Incident side plate electrode 27: Cylindrical electrode 28: Exit side plate electrode 29: Lens power supply 30: Isolation valve 31: Turbo molecular pump 32: Ion lens 32 ': Octopole ion guide 33: Octopole ion guide controller 34: Orifice 35: Turbo molecular pump 36: Mass analyzer 36': Quadrupole mass filter 37: Quadrupole mass Filter controller 38: Ion detector 39: Detector preamplifier 40: Cylindrical electrode central axis 46: Incident side plate electrode aperture 48: Outgoing side plate electrode aperture 51: Ion path 52: Neutral particle path 56: Incident Optical axis 58 of side plate electrode aperture: outgoing The optical axis of the plate-shaped electrode aperture

Claims (7)

A mass spectrometer using an atmospheric pressure plasma as an ionization source, which has an ion deflection lens system,
The ion deflection lens system,
An incident side plate-shaped electrode and an exit side plate-shaped electrode each having one aperture and facing each other,
And at least one cylindrical electrode disposed between the incident-side plate-shaped electrode and the emission-side plate-shaped electrode,
The incident side plate-shaped electrode and the emission side plate-shaped electrode are arranged such that the optical axes of the respective apertures are shifted from each other,
An analyzer wherein the cylindrical electrode is arranged so that its central axis is at least shifted from the optical axis of the incident-side plate-shaped electrode. The analyzer according to claim 1, wherein the cylindrical electrode has a cylindrical shape. The analyzer according to claim 2, wherein the ionization source is a high-frequency inductively coupled plasma. 4. The analyzer according to claim 3, wherein the ion deflection lens system is disposed between the interface unit and the isolation valve. The analyzer according to claim 4, wherein the same voltage is applied to the incident side plate-shaped electrode and the output side plate-shaped electrode. 6. The optical axis of each of the apertures of the incident-side plate-shaped electrode and the output-side plate-shaped electrode is substantially the same distance from the central axis of the cylindrical electrode, and is shifted from each other in opposite directions. The analysis device as described. Has an ion guide as part of the ion lens,
The analyzer according to claim 1, wherein the ion deflection lens system is arranged on an ion incidence side of the ion guide.

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