JPH10283984A - Flight time type mass spectrograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct mass spectrometry correctly regardless of a velocity component of ions in the lateral direction by providing an ion convergence optical system in which an ion strike point is set to be an object point and an ion incident face of an ion detector is set to be an image point on an ion flight path. SOLUTION: Ions struck from an aperture 34 are accelerated by an electric field formed through a plate, and fly in an (x) direction obtaining velocities corresponding to respective masses. On the way the ions are steered by a steering plate, and enter an ion detector 29 after unnecessary ions such as Ar and the like are excluded by a deflection plate. The incident ions are detected by the ion detector 29, and are amplified by an amplifier. The output signal of the amplifier 31 is sent to a signal processing portion, and is arithmetic- processed so as to obtain the spectrometric value of an element to be measured in a sample. An ion flight path is converged to an intermediate point 48 by the convergence action of a lens 42, and the ions diverging from a real image at the intermediate point 48 are converged into the ion detector 29 by a lens 44.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a time-of-flight mass spectrometer, and more particularly to a time-of-flight mass spectrometer in which an optical system of an ion flight path is improved.

[0002]

2. Description of the Related Art A time-of-flight mass spectrometer utilizes the fact that the flight speed of ions in an electric field varies depending on the mass of an element, and the time required to fly a certain distance, that is, the time of flight (TOF). Specifies the type of element.

In this apparatus, a packet of ions is launched from one side of a chamber by a pulsar, accelerated by an electric field, and incident on an ion detector at a predetermined distance. The time from ejection of ions to generation of a detection signal indicates the type of element, and the intensity of the detection signal indicates the concentration of the element.

[0004]

The ions ejected from the pulsar have a potential depending on the element due to the plasma ion source used for ion generation.
The direction (lateral direction) perpendicular to the flight direction also has a different velocity component depending on the element. For this reason, the flight path of each ion deviates in the horizontal direction according to the respective velocity components, and some of the ions do not enter the ion detector. In that case, ions that do not enter the ion detector cannot be detected, so that correct mass analysis cannot be performed.

The present invention has been made to solve the above problems, and an object of the present invention is to realize a time-of-flight mass spectrometer that performs mass spectrometry correctly regardless of the lateral velocity component of ions. is there.

[0006]

[Means for Solving the Problems]

[1] The invention according to claim 1, which solves the above problem, is a time-of-flight mass spectrometer that performs mass spectrometry based on the time of flight of ions in an electric field.
An ion focusing optical system having an ion launch point as an object point and an ion incident surface of an ion detector as an image point is provided.

According to the first aspect of the present invention, the real image of the ion packet at the launch point is formed on the ion incident surface of the ion detector by the ion focusing optical system. Therefore, all ions within the aperture range of the ion focusing optical system are incident on the ion detector. This makes it possible to realize a time-of-flight mass spectrometry that performs mass spectrometry correctly regardless of the ion velocity component in the lateral direction.

[2] According to a second aspect of the present invention for solving the above-mentioned problems, in the first aspect of the present invention, the ion focusing optical system has an image magnification of 1 or less. According to the second aspect of the invention, the ion focusing optical system forms a real image of the ion packet at the launch point at a magnification equal to or less than the same size on the ion incident surface. For this reason, the ion detector can have a small ion incident surface area.

[3] According to a third aspect of the present invention, which solves the above-mentioned problems, in the first or second aspect of the present invention, the ion focusing optical system includes an ion launching point and an ion incident surface of the ion detector. And two ion focusing lenses arranged equidistant from each other.

According to the third aspect of the present invention, since the objective side lens is close to the ion emission point, the solid angle from the emission point to the opening of the objective lens becomes large. As a result, the trapping rate of ions by the lens is increased.

[4] According to a fourth aspect of the present invention, there is provided an image forming apparatus according to the third aspect, wherein the two ion focusing lenses are supplied with a voltage from a common voltage source. Features.

According to the fourth aspect of the present invention, the two ion focusing lenses are controlled by a common voltage source. Thereby, the configuration of the control unit of the ion focusing lens can be simplified.

[5] According to a fifth aspect of the present invention, which solves the above-mentioned problem, in the invention according to any one of the first to fourth aspects, the time-of-flight mass spectrometer is of an orthogonal type. It is characterized by.

According to a fifth aspect of the present invention, in the orthogonal type time-of-flight mass spectrometer, a real image of the ion packet at the launch point is formed on the ion incident surface of the ion detector by the ion focusing optical system. Therefore, it is possible to realize an orthogonal type time-of-flight mass spectrometer that performs mass spectrometry correctly regardless of the lateral velocity component of ions.

[6] According to a sixth aspect of the present invention, which solves the above problem, in the fifth aspect of the present invention, the ions are generated by high frequency inductively coupled plasma.

According to the sixth aspect of the present invention, ions generated by the high-frequency inductively coupled plasma are injected into an orthogonal type time-of-flight mass spectrometer. These ions are ejected in the orthogonal direction in an orthogonal type time-of-flight mass spectrometer, and are converged by an ion focusing optical system and incident on an ion detector. Therefore, it is possible to realize an orthogonal time-of-flight mass spectrometer that performs mass spectrometry correctly irrespective of the lateral velocity component of the ions ejected in the orthogonal direction.

The high-frequency inductively coupled plasma (ICP) is one of the most excellent ion sources at present. However, since the potential varies depending on the element, the coupling with the orthogonal type time-of-flight mass spectrometer is actually performed for the above-mentioned reason. Was not the target.

On the other hand, in the invention of claim 6, the use of the ion focusing optical system makes it possible to effectively combine the ICP with the orthogonal type time-of-flight mass spectrometer.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiment.

[Configuration] FIG. 1 shows a schematic configuration of an orthogonal type time-of-flight mass spectrometer. This device is an example of an embodiment of the present invention. An example of an embodiment relating to the device of the present invention is shown by the configuration of the present device.

The configuration of the present apparatus will be described. In FIG.
Reference numeral 2 denotes a plasma torch, which is, for example, a quartz tube into which an aerosol or the like is introduced. FIG. 2 shows a more detailed configuration of this plasma torch. In FIG. 2, reference numeral 4 denotes a plasma torch 2
A high frequency induction coil for generating a high frequency magnetic field, which is wound around, a high frequency power supply 6 for supplying high frequency power to the high frequency induction coil 2, an impedance matching circuit 8,
Is a shield plate provided between the plasma torch 2 and the high frequency coil 4, and 40 is a high frequency inductively coupled plasma.

Returning to FIG. 1, reference numeral 30 is a nozzle, 32 is a skimmer, and 32 'is a second skimmer provided at the back of the skimmer 32. 18 is suctioned by, for example, a vacuum pump or the like.
Fore chamber 20 is evacuated and the inside is maintained at, for example, 1 torr. 20 is a center chamber which is sucked and evacuated by, for example, a first hydraulic diffusion pump and the inside is maintained at, for example, 1 × 10 ^-4 torr. The inside is, for example, 1 × 10
A rear chamber 24 maintained at ^-6 torr. Is a lens system for converging the ion beam. A slit 241 allows the ion beam focused by the lens system 24 to pass therethrough.

Reference numeral 25 denotes a pulser, into which the ion beam passing through the slit 241 is injected. The pulser 25 is supplied with a pulse voltage from a driving unit (not shown). With this pulse voltage, the pulser 25
Are ejected from the aperture 34 as ion packets.

Reference numeral 35 denotes a plate to which a voltage is applied from a voltage source (not shown) to form an electric field for ion acceleration. The ions ejected from the aperture 34 are accelerated by the electric field, fly at right speeds in the figure with speeds corresponding to their masses. That is, the ions injected into the pulsar 25 change their directions at right angles (orthogonal) and fly.

Reference numeral 37 denotes a steering plate to which a voltage is applied from a voltage source (not shown) to perform steering in the flight direction of ions. Reference numeral 39 denotes a deflection plate to which a voltage is applied from a voltage source (not shown) to remove unnecessary ions such as Ar from the flight path.

Reference numeral 29 denotes an ion detector comprising, for example, a macro channel plate or the like. The ion detector 29 is an example of an embodiment of the ion detector according to the present invention. 31
Is an amplifier for amplifying the detection signal of the ion detector 29. The output signal of the amplifier 31 is sent to a signal processing unit (not shown) and is subjected to arithmetic processing to obtain an analysis value of the element to be measured in the sample.

Numerals 42 and 44 converge the ion beam.
It is a pair of lenses. A lens 42 is disposed near the steering plate 37, and the lens 42 is
Is disposed in the vicinity of. The lenses 42 and 44 are an example of the embodiment of the ion focusing lens in the present invention. 1
The ion focusing optical system formed by the pair of lenses 42 and 44 is an example of an embodiment of the ion focusing optical system in the present invention.

FIG. 3 is a schematic diagram of an ion focusing optical system formed by the pair of lenses 42 and 44. As shown in the figure, the lens 42 includes a center plate 421 and side plates 422 and 423 disposed on both sides thereof. The voltage of the voltage source 46 is applied to the center plate 421. Side plate 422,
423 is connected to the common.

The lens 44 includes a center plate 441 and side plates 442 and 443 disposed on both sides of the center plate 441. The voltage of the voltage source 46 is applied to the center plate 441. Side plate 4
42 and 443 are connected to the common.

Due to the convergence of the ion beam by the lens 42, the ion packets diverging from the aperture 34 are converged at the intermediate point 48 between the lenses 42 and 44. The ion packet diverging from the intermediate point 48 is converged on the ion incident surface of the ion detector 29 by the convergence action of the lens 44. That is, the lenses 42 and 44 constitute an ion focusing optical system in which the position of the aperture 34 is the object point and the position of the ion incident surface of the ion detector 29 is the image point. The object point and the image point have a conjugate relationship with respect to the lenses 42 and 44.

[Operation] The operation of the present apparatus will be described. As shown in FIG. 2, the plasma gas and the auxiliary gas
And, for example, an argon (Ar) gas as a carrier gas is supplied to the plasma torch 2.
In addition, the impedance matching circuit 8
A high-frequency current is supplied to the high-frequency coil 4 via the interface, and a high-frequency magnetic field is formed around the high-frequency coil 6. When electrons or ions are implanted in the Ar gas near such a high-frequency magnetic field, the high-frequency inductively coupled plasma 40 is instantaneously generated by the action of the high-frequency magnetic field.

In this state, when the aerosol in which the sample is atomized is conveyed to the carrier gas and supplied into the plasma torch 2, the aerosol is supplied to the high frequency inductively coupled plasma 4.
Ionized by 0. The ions in the high-frequency induction plasma 40 generated in this manner pass through the nozzle 30, the skimmer 32 and the second skimmer 32 ', and pass through the lens system 2.
4 and is injected into the pulsar 25 through the slit 241. These ions are ejected by the pulsar 25 through the aperture 34 to the right in the drawing.

The ions ejected from the aperture 34 are accelerated by the electric field formed by the plate 35 and fly rightward in the figure with a velocity corresponding to their mass. On the way, the steering is performed by the steering plate 37, and unnecessary ions such as Ar are removed by the deflection plate 39 and incident on the ion detector 29. Incident ions are detected by the ion detector 29. The detection signal is amplified by the amplifier 31. The output signal of the amplifier 31 is sent to a signal processing unit (not shown) and is subjected to arithmetic processing to obtain an analysis value of the element to be measured in the sample.

In an orthogonal type time-of-flight mass spectrometer, ions injected into the pulsar 25 are ejected in a right angle direction, so that the ions have a velocity component in a transverse direction with respect to the flight direction. Therefore, aperture 3
The ions ejected into the rear chamber 22 from 4 are:
As shown in FIG. 3, a velocity component Vy also exists in the y direction perpendicular to the flight direction x, that is, in the lateral direction, and this velocity component differs for each element. Therefore, the flight path of the ions that fly out of the aperture 34 diverges, for example, as illustrated.

The flight path of such ions is the lens 42
Is converged to the intermediate point 48 by the convergence action of. As a result, a real image of the ion packet at the aperture 34 is formed at the intermediate point 48. The flight path of the ions diverging from the real image at the intermediate point 48 is converged on the ion incident surface of the ion detector 29 by the lens 44. As a result, a real image of the ion packet in the aperture 34 is eventually formed on the ion incident surface of the ion detector 29.

The magnification of the real image of the ion packet formed on the ion incident surface of the ion detector 29 is 1 or less. Thus, the area of the ion incident surface of the ion detector 29 can be made equal to or less than the area of the aperture 34, and the ion detector 29 can be downsized.

When the focal lengths of the lenses 42 and 44 are the same to form an ion focusing optical system having an image magnification of 1, the focal length of one lens is the distance from the aperture 34 to the ion incidence surface of the ion detector 29. Is L
f = L / 8. That is, 1 / the flight distance of the ion
A lens with a focal length of 8 is used.

As a result, the lens 42 is disposed at a position very close to the aperture 34. Since the distance from the aperture 34 to the lens 42 is short, even if the aperture of the lens 42 is relatively small, the solid angle for viewing the aperture from the aperture 34 is sufficiently large, so that all ions diverging from the aperture 34 can be easily placed in the aperture. Can be included. If the number of lenses is three or more, the objective lens can be further brought closer to the aperture 34, and a lens with a smaller aperture can be used.

On the other hand, when the ion focusing optical system is constituted by a single lens, the lens is located at the intermediate point between the aperture 34 and the ion detector 29, so that the solid angle of the aperture viewed from the aperture 34 is reduced. To achieve the same level, it is necessary to use a lens having a large aperture, which is difficult to realize.
When the aperture is set to a common sense value, the aperture 34
There is a possibility that the solid angle as viewed from the side becomes small, so that all the diverging ions cannot be covered.

The focal length of the lenses 42 and 44 is
Is controlled by the voltage of Supplying the voltage from the common voltage source 46 in this way is preferable in that the configurations of the lenses 42 and 44 are the same and the control unit is simplified. Of course, the lenses 42 and 44 may be configured separately and controlled by separate voltage sources. In that case, it is preferable that the lenses 42 and 44 each have an optimum configuration independently and are controlled optimally. It is also preferable in that the image magnification is individually adjusted or the influence of another optical system on the flight path of ions is individually corrected.

The above is an example of an orthogonal type time-of-flight mass spectrometer. The ion focusing optical system including the lenses 42 and 44 uses the ion detector 29 from the plasma torch 2.
The present invention can also be applied to a so-called on-axis time-of-flight mass spectrometer in which the path of ions to the ion beam is straight. This will be described below.

FIG. 4 shows a schematic configuration of an on-axis time-of-flight mass spectrometer. In this figure, the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. 28
Is an ion detector including, for example, a photomultiplier tube. The ion detector 28 is an example of an embodiment of the ion detector according to the present invention.

In this apparatus, the high-frequency induction plasma 40
Are focused through the lens system 24 via the nozzle 30 and the skimmer 32 and the aperture 34
Through the rear chamber 22.

The ions ejected from the aperture 34 fly in the rear chamber 22 and travel to the ion detector 28.
Incident on. At this time, the spread of the ion beam based on the ion energy distribution is converged by the converging optical system formed by the lenses 42 and 44. Thus, ion loss due to the spread of the ion beam can be eliminated. Incident ions are detected by the ion detector 29. The detection signal is sent to a signal processing unit (not shown) and is subjected to arithmetic processing to obtain an analysis value of the element to be measured in the sample.

[0045]

As described above in detail, according to the first aspect of the present invention, the real image of the ion packet at the launch point is formed on the ion incident surface of the ion detector by the ion focusing optical system. All ions within the aperture range of the ion focusing optical system are incident on the ion detector. This makes it possible to realize a time-of-flight mass spectrometry that performs mass spectrometry correctly regardless of the ion velocity component in the lateral direction.

According to the second aspect of the present invention, since the ion focusing optical system forms a real image of an ion packet at a launch point equal to or less than the same size on the ion incident surface,
The ion detector requires only a small area of the ion incident surface.

According to the third aspect of the present invention, since the lens on the objective side is close to the ion emission point and the solid angle at which the aperture of the objective lens is seen from the emission point is increased, the ion capture rate by the lens is increased. .

According to the fourth aspect of the present invention, since the two ion focusing lenses are controlled by the common voltage source, the configuration of the control unit of the ion focusing lens can be simplified.

According to a fifth aspect of the present invention, in the orthogonal type time-of-flight mass spectrometer, the real image of the ion packet at the launch point is formed on the ion incident surface of the ion detector by the ion focusing optical system. Therefore, it is possible to realize an orthogonal time-of-flight mass spectrometer that performs mass spectrometry correctly regardless of the lateral velocity component of ions.

According to the invention of claim 6, ions generated by high frequency inductively coupled plasma (ICP) are injected into an orthogonal type time-of-flight mass spectrometer, and the ions are injected into the orthogonal type time-of-flight type mass spectrometer. In the orthogonal direction, the ion beam is focused by the ion focusing optical system and made incident on the ion detector. ICP time-of-flight mass spectrometer can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an apparatus according to an example of an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a plasma torch in an apparatus according to an example of an embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of an ion focusing optical system in an apparatus according to an example of an embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of an apparatus according to an example of an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 2 Plasma torch 4 High frequency induction coil 6 High frequency power supply 8 Impedance matching circuit 10 Shield plate 18 Fore chamber 20 Center chamber 22 Rear chamber 24 Lens system 28 Ion detector 30 Nozzle 32 Skimmer 34 Aperture 36 Partition wall 38 Cooling water channel 40 High frequency induction coupling plasma 42 , 44 lenses 421, 441 Center plate 422, 423, 442, 443 Side plate 32 'Second skimmer 241 Slit 25 Pulser 35 Plate 37 Steering plate 39 Deflection plate 29 Ion detector 31 Amplifier

Claims (6)

[Claims] 1. A time-of-flight mass spectrometer for performing mass spectrometry based on the flight time of ions in an electric field, wherein an ion launch surface is an object point on an ion flight path and an ion incidence surface of an ion detector is imaged. A time-of-flight mass spectrometer comprising an ion focusing optical system serving as a point. 2. The time-of-flight mass spectrometer according to claim 1, wherein the ion focusing optical system has an image magnification of 1 or less. 3. The ion focusing optical system according to claim 1, wherein the ion focusing optical system comprises two ion focusing lenses arranged at an equal distance from the ion launch point and an ion incidence surface of the ion detector. 3. The time-of-flight mass spectrometer according to 2. 4. The time-of-flight mass spectrometer according to claim 3, wherein the two ion focusing lenses are supplied with a voltage from a common voltage source. 5. The time-of-flight mass spectrometer according to claim 1, wherein the time-of-flight mass spectrometer is an orthogonal type. 6. The time-of-flight mass spectrometer according to claim 5, wherein the ions are generated by high frequency inductively coupled plasma.