JP2804676B2 - Mass spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for mass spectrometry by ionizing a sample, and more particularly to a technique for reducing background noise and removing contaminants due to photons and molecules emitted from an ionization source.

[0002]

2. Description of the Related Art Conventionally, there has been known a mass spectrometer in which a sample is ionized by an ionization source, and then the beam is accelerated into a beam and incident on a mass spectrometer.

As an ionization source, MIP (Microwave
Inducude Plasma), ICP
(Inductively Coupled Plasma) and other plasma ionization sources and API (Atomospheric Pressur)
e Ionization (atmospheric pressure ionization source) is used.

[0004] In the case of a plasma ionization source, photons emitted from the ionization source and non-ionized molecules are the main causes of background noise. On the other hand, in an atmospheric pressure ionization source used in a liquid chromatograph mass spectrometer, droplets are directly ionized by atomizing droplets, but molecules that have not been ionized cause background noise. Goes straight into the mass spectrometer and contaminates it, causing a decrease in resolution and sensitivity.

[0005] This problem will be described using a quadrupole mass spectrometer used in the mass spectrometer as an example.

[0006] In a quadrupole mass spectrometer composed of four columnar electrodes, opposing poles are electrically connected. Each pole has a DC voltage U and a high frequency (rf) voltage Vcosω
Positive and negative voltages with t superimposed are applied.

When ions generated by an ionization source are introduced into a quadrupole mass spectrometer, a certain m is determined according to U, V and ω.
Only ions of / z (ratio of mass to charge) pass through the gap while drawing a stable wavy trajectory, and are guided to the ion detector. Other m / z ions follow an unstable orbit of increasing amplitude and annihilate.

Now, A = 8 eU / mr ₀ ² ω ² , Q = 4 e
Assuming that V / mr ₀ ² ω ² and A and Q are coordinate axes, one point on the AQ plane corresponds to a certain m / z, and an m / z ion existing in a certain stable region passes through the quadrupole. . As described above, although it can be used with selectivity for m / z, as can be understood from the above equation, there is no selectivity for photons and molecular flows, and photons emitted from the ionization source are not selected. , The molecular flow goes straight on and hits the detector, increasing the background noise. That is, when photons and molecules enter the detector, secondary electrons are generated as in the case of ions, and noise current is generated.

Therefore, when plasma or the like is used as an ionization source, it is necessary to remove photons or the like.

For this reason, conventionally, focusing on the straightness of photons and the like, a photon stopper is attached between the ionization source and the mass spectrometer so that the progress of photons and the like generated by the plasma can be prevented.
Or block the, changing the trajectory of the ions by installing a deflector immediately after the mass analyzer, JP-2-29505
As disclosed in Japanese Patent Laid-Open Publication No. 5 (1994), various measures have been taken such as installing an ion beam deflection mechanism (electric field and magnetic field) in two stages before and after the mass spectrometer so that the orbit of photons and the like deviates from the orbit of ions. It has been done.

[0011]

However, in the above case, it is necessary to use a combination of ion lens systems that avoids the photon stopper, which makes it difficult to set the optimum lens voltage conditions for the ions to be measured, Many ion lenses must be used to avoid the stopper, and some of the ions adhere to the photon stopper.
To refocus the ions after passing through the photon stopper.
In this case, ions are greatly lost, and the sensitivity and resolution of the target ions are easily reduced.

In this case, the ion detector cannot completely eliminate the influence of the photons. In this case, it is considered that the photon and the like can be removed more because the ion beam deflecting mechanism is installed in two stages, but a part of the photon and the like is reflected and scattered by the electrode surface of the deflecting mechanism and is reflected on the detector. You need to take steps to get there. for that purpose,
As described in Japanese Patent Application Laid-Open No. 2-295055, a proposal has been made to make the electrodes of the deflection mechanism mesh, but in practice, the electrode surfaces need to be smooth to maintain the uniformity of the electric field. It is technically difficult to take such measures.

The present invention has been made in view of the above points, and an object of the present invention is to effectively remove noise elements such as photons generated from an ionization source and contaminant elements such as non-ionized molecules and droplets by a simple method. It is to improve measurement sensitivity and resolution of mass spectrometry.

[0014]

In order to achieve the above object, the present invention basically proposes the following means for solving the problems. The reference numerals in the components refer to those in FIG.

That is, according to the present invention, the sample is ionized by the plasma ionization source 6 and then drawn out to the mass spectrometer 3.
In the leading mass spectrometer, the plasma ionization source 6
Reflection to change the trajectory of ions extracted from
Comprising an ion reflector electrodes 1 forming an electric field, the ion counter
The working electrode 1 is a working space for ion incidence and ion reflection.
Through hole 1A is provided, and the ion reflection electrode 1
Is the intersection of the ion incidence direction and the ion reflection direction.
The vertical plane B perpendicular to the ion incidence axis at the position
And the plasma ionization source side with respect to the vertical plane B.
Angle between the ion incident direction and the ion reflection direction
Is set to an acute angle, b based on the ion-reflective electrode 1
Ions converge at the positions that are on the incident side and the ion reflection side
The ion lenses 7, 8 to secure the ion orbit
A stage after the ion lens 8 disposed on the ion reflection side
The deflector 2 changes the orbit of the ion again,
The mass spectrometer 3 and the ion detector 4 are disposed,
The ion whose orbit has been changed by the deflector 2
The configuration is such that it is guided to the detector 4.

Further, as the invention accompanying the above invention,
From the ion reflection electrode 1 to the plasma ionization source 6
When the direction is defined as forward, after the ion reflecting electrode 1
The light absorbing element at a position on the extension of the ion incidence axis
A proposal in which the child 17 is arranged is proposed.

Further , the deflector 2 is provided with the ion counter.
Between the ion lens 8 provided on the launch side and the mass spectrometer 3
And the deflector 2 and the mass spectrometer 3
Between which a differential exhaust slit 14 is interposed,
When the analysis unit 3 is a sector type, the ion acceleration
Since the pressure is set to be swept, this ion acceleration
When the voltage of the ion reflection electrode 1 is variable in synchronization with the voltage,
We also propose a mass spectrometer and the like set to be as follows.

[0018]

According to the basic structure of the present invention, the following functions are provided.
Is made. (A) Sample ion extracted from plasma ionization source 6
The ion beam is converged by the ion lens 7 and
One of the through holes 1A. The incident ions are through-hole 1
A is reflected by the action of the reflected electric field formed at A. this
The direction of ion reflection at the ion reflection electrode 1 is the direction of ion incidence.
The ion incidence axis at the intersection of the ion direction and the ion reflection direction
With respect to the vertical plane B that intersects vertically,
Since it is tilted to the plasma ionization source 6 side, ion reflection
Turns into a V-shape at an acute angle to the ion incidence axis
Reflection mode. Therefore, the ion orbit is
It is bent 90 ° or more at the position of the reflective electrode 1. Ion reflection
The ions reflected by the electrode 1 are re-
It is converged and reaches the ion detector 4 via the mass spectrometer 3.
Before reaching the ion detector 4 (the
Before or after the deflector 2)
Then, it is led to the ion detector 4.

(B) As described above, plasma ions
Orbit 13 from the source 6 to the mass spectrometer 3
Incident side and ion reflecting side with respect to the ion reflection electrode 1
Both sides (ion orbit) take into account the installation length of the ion lens
And these two sides intersect in an acute V-shape.
Orbit on the ion reflection side.
The portion has a track shape bent by the deflector 2.

(C) Such an ion trajectory is formed
As a result, the removal rate of noise such as photons is increased as follows.
Confuse.

That is, the ion trajectory corresponds to the ion reflecting electrode 1
Bend more than 90 ° at the position, while photons and ions
Most of the molecules that are not converted to
1A, go straight ahead, and place the ion reflection electrode 1
Greatly deviate from the ion trajectory at the position
Can be blocked.

In addition, noise elements such as photons
There are some which reflect irregularly on the reflective electrode 1 and the ion path.
Since the on-orbit was bent more than 90 °, the amount of diffused light
Of which, it is possible to reduce the ratio of going to the orbit on the ion reflection side.
Wear.

Further, irregularly reflected light traveling in the ion reflection direction
(Photons) from plasma ionization source 6
The trajectory length of the ion beam up to between the ON detectors 4 is described above.
The ion lens 7 on the ion incidence side and the ion lens on the ion reflection side
Can be longer than before due to the presence of lens 8
Therefore, the light between the plasma ionization source 6 and the ion detector 4
Increase the damping rate. That is, in the present invention, the ion reflection
Pole 1 as relay point and ion reflection side in addition to ion incidence side
The ion lens 8 is also placed on the
This ion lens reflects ions to converge
If it is arranged also on the side, the ion reflection electrode 1 and the ion detector 4
Without reducing the distance between them (in other words, ion reflection
Ion lens on the ion reflection side between electrode 1 and ion detector 4
(Even if the distance is increased by 8 minutes),
Since it can be guided without spreading to the output device 4,
The trajectory of the ion beam has been greatly increased
To increase the attenuation of scattered reflected light and promote noise removal.
You. Note that the ion reflection electrode 1 is used as a relay point (reference).
The ion lenses located on the ON incident side and the reflective side
V corresponds to the sharp V-shaped ion orbit as described above.
The ion orbital length
Even if the length is longer, the whole device is reduced to a simple compact shape.
Can be stopped. Further, in the present invention, the mass spectrometer
Noise element such as photons toward the ion detector 3 and the ion detector 4
Ion trajectory that makes it longer even if it exists
And then deflector 2
Higher noise reduction rate for photons etc.
Confuse.

The advantages of the above-described constituent elements of the invention are described below.
The points are as follows.

The last part of the ion reflection electrode 1 or the reflection electrode
If a light absorbing element 17 is provided after the
Reflection scattering can be further prevented.

The deflector 2 is placed on the ion reflection side.
Between the ion lens 8 provided and the mass spectrometer 3.
Difference between the deflector 2 and the mass spectrometer 3
When the dynamic exhaust slit 14 is interposed, the differential exhaust slot
Photons (such as those that are mainly scattered and reflected) and contaminants
Etc. from entering the mass spectrometer, and light scattering at the mass spectrometer.
Diffuse reflection can be prevented, and contamination of the mass spectrometer can be prevented.
Can be.

Further , in synchronization with the ion acceleration voltage,
If the voltage of the ON reflection electrode 1 is set to be variable,
Ion acceleration voltage changes by sweep like sector type
Even so, always the optimal ion reflection according to the accelerating voltage
It is possible to create an electric field.

The present invention relates to a mass spectrometer for a plasma ionization source.
This is particularly useful for applications.

However, as described above, in addition to photons,
Contaminants such as molecules and droplets that are not turned on are also sent to the mass spectrometer.
To prevent contamination of the mass spectrometer and ion detector.
Prevent dyeing. Therefore, in addition to the plasma ionization source,
Applied to a mass spectrometer using an atmospheric pressure ionization source
It is effective.

[0030]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 is a configuration diagram according to a first embodiment of the present invention.

In this embodiment, a mass spectrometer using the plasma ionization source 6 will be exemplified.

The plasma ionization source 6 is, for example, an IC
Ru P and MIP der.

The sample introduced from the capillary is ionized by the plasma torch 5 of the plasma ionization source 6, accelerated by the acceleration voltage of the ionization source, and evacuated by the vacuum pump 9 via the sampling cone 10 and the skimmer cone 11. It is drawn into the vacuum section 12 which is in
You .

In the vacuum section 12, sample ions are focused on the ion reflection electrode 1 by the ion lens system 7.

The ionization source 6 and the mass analysis unit 3 are arranged on a non-linear line, and the ion reflection electrode 1 is arranged between the ionization source 6 and the mass analysis unit 3. In this embodiment, as an example, the ionization source 6 and the sampling cone 1 are used.
0, a skimmer cone 11, an ion lens system 7, an ion reflection electrode 1, an ion lens system 8, a deflector 2, a differential exhaust slit 14, and a mass spectrometry unit 15, which are located between the ionization source 6 and the mass spectrometry unit 3. The ion reflection electrode 1 and the deflector 2 function to bend (change) the trajectory of ions.

The ion reflecting electrode 1 is composed of a plurality of electrodes placed on an ion trajectory ,
Creates a reflected electric field that gives repulsion, as if it were a mirror
Has the function of reflecting ions. That is, the electrode closest to the ionization source 6 side is a ground potential slit, and the voltage of the electrode placed behind the electrode is set so as to gradually increase. The voltage applied to the last electrode is the ion acceleration voltage of the sample ions. Somewhat higher (ion acceleration voltage V + α)
Is set to For example, assuming that the ion acceleration voltage of the ionization source is 100 V and three ion reflecting electrodes 1 are used, these are arranged at equal intervals on each of the reflecting electrodes.
In terms of voltage, the foremost one (first sheet) near the ionization source is set to ground potential, the second sheet is set to 50 V, and the third sheet is set to 110 V.

In this manner, 100 from the ionization source
If the sample ions 13 emitted at an ion accelerating voltage of V enter the ion reflection electrode 1, the ground potential slit
(Through hole) At the position of 1A , the light is incident while maintaining the speed accelerated by the ion acceleration voltage of 100 V, but the potential is 50 V
At the position, the speed is halved, and at the position where the potential is 100 V (slightly forward of the third electrode), the speed of the sample ions becomes zero. The sample ions having a speed of 0 are re-emitted to the 50 V electrode and the ground potential electrode perpendicularly to the angle of the ion reflection electrode 1 under the action of the voltage applied to the ion reflection electrode 1. .

On the other hand, photons and non-ionized molecules are provided with through holes 1A in each electrode plate of the ion reflection electrode 1 (the holes are provided at positions coincident with the ion incident axis). Go straight without being reflected by
The light is absorbed by the light absorbing element 17 provided behind the ion reflection electrode 1.

As described above, the beam trajectory of the ions 13 is bent at the position of the ion reflection electrode 1 to change the trajectory.
The ion reflector electrodes 1, reflection direction ion lens 8,
Since the angle is set so as to coincide with the deflector 2, the ions 13 reflected by the ion reflection electrode 1 are re-orbited by the deflector 2 while being converged by the ion lens 8, and then pass through the differential exhaust slit 14. Mass spectrometry section 3
And the ions subjected to mass spectrometry are converted to the ion detector 4
Is detected.

The through hole 1A of the ion reflecting electrode 1
It is an operating space for incidence and ion reflection. Ion reflection electrode 1
The ion reflection direction is the ion incident direction and the ion reflection direction
Plane perpendicular to the ion incidence axis at the point of intersection
B with respect to the plasma ion
Between the ion incidence direction and the ion reflection direction
The angle is set to an acute angle. Ion reflection direction as above
By setting to, as shown in FIG.
Turn into a V-shape at an acute angle to the ion incidence axis
It becomes a reflection mode. Therefore, the ion orbit is reflected by the ion
It is bent by 90 ° or more at the position of the electrode 1. Ion reflection electrode
Positions on the ion incidence side and ion reflection side with reference to 1.
Ion lenses 7 and 8 to secure ion orbits
It placed Ru. Therefore, the light is reflected by the ion reflection electrode 1.
The ions are refocused by the ion lens 8 and
To the ion detector 4 via the analyzer 3,
Before reaching the output unit 4, the deflector 2
The trajectory is further bent and guided to the ion detector 4. The mass spectrometer 3 and the ion detector 4 are connected to a vacuum pump 16
Is arranged in a vacuum chamber 15 which is in a high vacuum state.

The mass spectrometer 3 may be a quadrupole analyzer,
It may be a sector type or another type.

When performing quantitative analysis using a sector type mass spectrometer, the response of the magnetic field is slow. Therefore, the magnetic field is fixed at a certain strength, and mass spectrometry, ie, measurement, is performed while sweeping the ion acceleration voltage. Since the target ions are detected, if the voltage of the ion reflection electrode 1 is also changed in synchronization with the ion acceleration voltage so as to maintain the above-mentioned voltage relationship, the mirror reflection operation of the ion reflection electrode 1 can be performed.

According to the present embodiment, the plasma ionization source 6
Trajectory 13 from to the mass spectrometer 3 is ion reflection
Two sides on the ion incidence side and ion reflection side with respect to electrode 1
(Ion trajectory) takes into account ion lens installation length
Orbit where these two sides intersect at an acute V-shape
And part of the ion trajectory on the ion reflection side is
The orbit is bent by the reflector 2. Such an ion trajectory is 90 ° or more at the position of the ion reflection electrode 1.
Bent, while photons, non-ionized molecules, etc.
Many pass through the through-hole 1A of the ion reflection electrode 1 and
Go straight on from the ion orbit at the position of the ion reflective electrode 1.
It can be largely prevented from becoming a noise element. Ma
In addition, the ion reflection electrode 1 and the
Some diffusely reflect in the on path, but the ion trajectory is 90
°, the ion reflection of the irregularly reflected light
The proportion going to the side trajectory can be reduced. In addition
There is irregularly reflected light (photon) going in the ON reflection direction
Also, between the plasma ionization source 6 and the ion detector 4
The ion beam trajectory length is set to
The presence of the lens 7 and the ion lens 8 on the ion reflection side
Longer than before, so plasma ion
The light attenuation between the ionization source 6 and the ion detector 4
It helps remove noise such as noise. Relay the ion reflection electrode 1
Placed on the ion incidence side and reflection side as a point (reference)
The ion lens is a sharp V-shaped ion lens as described above.
Are provided in a V- shaped arrangement corresponding to the
Even if the total track length is longer than before,
It can be put together in a compact shape. In addition,
In the description, the focus toward the mass spectrometer 3 and the ion detector 4 will be described.
Even if there are noise elements such as tons,
After being attenuated by the extended ion orbit,
The trajectory is changed by the rectifier 2.
Further increase the noise removal rate. As described above, in the ion detector, photons and contaminants can be completely removed, and a shield such as a conventional photon stopper is arranged in the ion trajectory by using an ion reflection electrode. Since there is no need to perform the above, noise can be eliminated by a simple optical structure to enable high-sensitivity, high-resolution mass spectrometry.

Further, the ion reflection electrode eliminates the complicated voltage setting of the ion lens system, which is a problem when a photon stopper is provided, and is simple in structure, so that the simplicity and low cost can be achieved. Can be achieved. In addition, since ions can be reflected without colliding with the last electrode of the ion reflection electrode, loss of sample ions is eliminated,
Further, the measurement accuracy of ions can be improved.

Although the above embodiment has exemplified the mass spectrometer using the plasma ionization source, this embodiment can be applied to a mass spectrometer using an atmospheric pressure ionization source. There are the following advantages.

That is, in a liquid chromatograph mass spectrometer, droplets are atomized and ionized using an atmospheric pressure ionization source, but non-ionized molecules, droplets, and the like are reflected by an ion reflection electrode. By deviating from the ion trajectory, the sensitivity and resolution of the apparatus are greatly improved, and the contamination is extremely reduced, so that the stability is increased and the life of the apparatus is prolonged.

In the above embodiment, the ion reflection electrode 1 is provided between the ionization source 6 and the mass spectrometer 3. However, as shown in FIG. However, it is possible to prevent noise elements such as photons and contaminants from entering the ion detector 4, thereby improving the sensitivity and resolution of this type of device. However, FIG.
Since the ion lens 8 is not disposed on the ion reflection side as in the embodiment, the ion orbit cannot be lengthened as shown in FIG.

[0049]

As described above, according to the present invention, the ion reflecting electrode, the ion lens provided on the ion incident side and the reflecting side with reference to the ion reflecting electrode, and the ion reflecting electrode provided on the subsequent stage of the ion reflecting side ion lens are provided. The ion trajectory peculiar to the present application can be formed by a simple means such as a deflector (ie,
Mass spectrometry section from plasma ionization source and then ion detection
The ion trajectory to the detector is based on the ion reflection electrode.
Both sides (ion orbit) of the ON incident side and the ion reflection side are both
It has a length that takes into account the installation length of the ion lens.
The trajectory intersects with the V-shape whose side is acute.
Part of the ion trajectory on the reflection side is bent by the deflector
Orbital shape), thereby effectively removing noise elements such as photons generated from an ionization source, and contaminant elements such as non-ionized molecules and droplets, thereby improving the measurement sensitivity and resolution of mass spectrometry. . Also, photons
Even if the ion orbit is lengthened due to attenuation of
With the electrode as the relay point (reference) on the ion incidence side and reflection side
The ion lens to be arranged has an acute angle V as described above.
It is provided in a V-shaped arrangement corresponding to the
The whole device can be put together in a simple compact shape.
it can.

[Brief description of the drawings]

FIG. 1 is a configuration diagram according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram according to a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ion reflection electrode, 2 ... Deflector, 3 ... Mass spectrometer, 4 ... Ion detector, 5 ... Plasma torch, 6 ... Plasma ionization source, 7, 8 ... Ion lens, 13 ... Ion beam, 14 ... Differential exhaust slit.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenichi Shizukuishi 832-2 Nagakubo, Horiguchi, Katsuta-shi, Ibaraki Prefecture Within Hitachi Measurement Engineering Co., Ltd. (72) Inventor Akira Yoneya 832-2 Nagakubo, Horiguchi, Katsuta-shi, Ibaraki Hitachi Measurement Engineering (56) References JP-A-2-295055 (JP, A) JP-A-62-40150 (JP, A) JP-A-64-39371 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01J 49/26-49/42 H01J 49/06

Claims (4)

(57) [Claims] 1. A mass spectrometer which leads to the mass analyzer pull after ionized plasma ionization source of the sample, the trajectories of ions extracted from the plasma ionization source
Ion reflection electrode that forms an ion reflection electric field for changing
The ion reflection electrode has a movement of ion incidence and ion reflection.
Through holes to be created space is provided, ion reflection direction of the ion reflective electrode, ion incidence side
The ion incidence axis at the intersection of the ion direction and the ion reflection direction
With reference to the vertical plane that intersects vertically,
Ion incidence direction and ions tilted toward the plasma ionization source
The angle between the reflection directions is set to an acute angle , and the ion incident side and the ion
Focus the ion to the position that is the reflection side of the ion and confirm the ion trajectory.
An ion lens for keeping the ion is arranged, and an ion gauge is provided at a stage subsequent to the ion lens on the ion reflection side.
A deflector for changing the path again, the mass spectrometer,
An ion detector is arranged, and the rail is deflected by the deflector.
Configuration in which ions whose path has been changed are guided to the ion detector
Mass spectrometer, characterized in that the the. 2. The plasma reflecting device according to claim 1, wherein
If the direction toward the on-source is defined as forward, the ion
A position on the extension of the ion incidence axis behind the reflective electrode
The mass spectrometer according to claim 1, wherein a light absorbing element is disposed in the device. 3. The deflector is provided on the ion reflection side.
Provided between the provided ion lens and the mass spectrometer.
Between the deflector and the mass spectrometer.
3. An exhaust slit according to claim 1 or 2, wherein an exhaust slit is interposed.
Mass spectrometer of. 4. The mass spectrometer according to claim 1, wherein said mass spectrometer is a sector type.
Is set to sweep the acceleration voltage.
The voltage of the ion reflection electrode is synchronized with the ion acceleration voltage.
4. The method according to claim 1, wherein the setting is changed.
The mass spectrometer according to any one of the above .