阅读说明：本技术 离子检测装置及质谱分析装置 (Ion detection device and mass spectrometry device ) 是由 西口克 于 2017-05-17 设计创作，主要内容包括：离子检测器(4)在孔板(41)与转换打拿极(43)之间具备屏蔽电极(42)。屏蔽电极(42)具有位于四极杆滤质器(3)的中心轴(C)的延长线(C’)上的直行粒子阻挡壁(42a)、以及相对于该延长线(C’)倾斜规定角度θ(锐角)的离子诱导电场调整壁(42b),在离子诱导电场调整壁形成有离子通过开口(42c)。从四极杆滤质器(3)出来的中性粒子等直行粒子被直行粒子阻挡壁(42a)阻断,因此由直行粒子引起的噪音降低。另一方面,离子诱导电场调整壁(42b)的电位被设为与由转换打拿极(43)形成的强电场的等电位面相应的电位,因此,强电场的状态与没有屏蔽电极(42)的情况相比变化不大。由此,发挥强电场对离子的引入作用,能够维持高的离子检测效率。(The ion detector (4) is provided with a shield electrode (42) between the aperture plate (41) and the conversion dynode (43). The shield electrode (42) has a straight particle blocking wall (42a) positioned on an extension line (C ') of a central axis (C) of the quadrupole mass filter (3), and an ion-induced electric field adjustment wall (42b) inclined at a predetermined angle theta (acute angle) with respect to the extension line (C'), and an ion passage opening (42C) is formed in the ion-induced electric field adjustment wall. Straight particles such as neutral particles coming out of the quadrupole mass filter (3) are blocked by the straight particle blocking wall (42a), and therefore, noise caused by the straight particles is reduced. On the other hand, the potential of the ion-inducing electric field adjustment wall (42b) is set to a potential corresponding to the equipotential surface of the strong electric field formed by the conversion dynode (43), and therefore the state of the strong electric field does not change much compared with the case where the shield electrode (42) is not provided. This allows a strong electric field to act on the ions, thereby maintaining high ion detection efficiency.)

1. An ion detection device that detects ions that have passed through an ion separation unit that separates ions according to their mass or mobility, or ions that have been emitted from the ion separation unit, the ion detection device comprising:

a) a conversion dynode which is disposed at a position deviated from an extension of a central axis of the incident ion flow sent from the ion separating unit and converts ions attracted by an electric field formed by the conversion dynode itself into electrons;

b) an electron detection unit which is disposed opposite to the conversion dynode with an extension line of a central axis of the incident ion flow interposed therebetween, and which amplifies and detects electrons emitted from the conversion dynode;

c) a shield electrode disposed between an incident position of the incident ion flow and the conversion dynode and the electron detection unit, the shield electrode including: c1) a blocking wall located on an extension of a central axis of the incident ion flow, blocking passage of particles; and c2) an electric field adjustment wall connected to the blocking wall, the electric field adjustment wall being planar, curved, or polyhedral, the electric field adjustment wall having an opening for passage of ions going to the conversion dynode or having a portion through which the ions pass, wherein the plane includes a straight line having an acute angle with a central axis of the incident ion flow on a plane including both the central axis of the incident ion flow and a central axis of an ion collision surface of the conversion dynode when viewed from an incident position of the incident ion flow, the curved surface includes a curve having the straight line as an approximate straight line, and the polyhedral is approximate to the curved surface; and

d) and a voltage applying unit that applies a predetermined direct current voltage to the shield electrode.

2. The ion detection apparatus of claim 1,

the ion separator further includes an aperture electrode that shields an electric field generated by the ion separator and allows ions to pass therethrough, at an incident position of the ion flow sent from the ion separator, and the shield electrode is disposed between the aperture electrode, the conversion dynode, and the electron detector.

3. The ion detection apparatus of claim 2,

the electric field adjustment wall has a wall surface surrounding an opening for passage of ions going to the conversion dynode.

4. The ion detection apparatus of claim 3,

the opening provided in the electric field adjustment wall is located outside a cylindrical space virtually formed when the ion passage opening of the aperture electrode is moved in the extending direction of the central axis of the incident ion flow.

5. The ion detection apparatus of claim 3,

the blocking wall is parallel to a plane substantially orthogonal to the central axis of the incident ion flow, and the shield electrode has an electric field auxiliary adjustment wall connected to the electric field adjustment wall and parallel to the blocking wall on the side opposite to the blocking wall with the electric field adjustment wall interposed therebetween.

6. The ion detection apparatus of claim 1,

the electric field adjustment wall has a plane having the same potential, which is similar to a curved equipotential surface in the vicinity of the position where the shield electrode is disposed in the electric field formed by the conversion dynode in the state where the shield electrode is not disposed.

7. A mass spectrometry device is characterized by comprising:

the ion detection device of claim 1;

an ion source that ionizes a compound in a sample; and

a quadrupole mass filter that selectively passes ions having a particular mass-to-charge ratio among the ions generated by the ion source,

wherein the mass spectrometer introduces ions that have passed through the quadrupole mass filter into the ion detector and detects the ions.

8. A mass spectrometry device is characterized by comprising:

the ion detection device of claim 1;

an ion source that ionizes a compound in a sample;

a front stage quadrupole mass filter that selectively passes ions having a specific mass-to-charge ratio among the ions generated by the ion source;

an ion splitting unit that splits ions that have passed through the front stage quadrupole mass filter; and

a post-stage quadrupole mass filter for selectively passing ions having a specific mass-to-charge ratio among product ions generated by fragmentation in the ion fragmentation section,

wherein the mass spectrometer introduces ions that have passed through the post-stage quadrupole mass filter into the ion detector and detects the ions.

9. A mass spectrometry device is characterized by comprising:

the ion detection device of claim 1;

an ion source that ionizes a compound in a sample; and

an ion trap that separates and sequentially emits ions according to a mass-to-charge ratio after temporarily capturing the ions generated by the ion source or other ions derived from the ions,

wherein the mass spectrometer introduces ions emitted from the ion trap into the ion detector and detects the ions.

Technical Field

The present invention relates to an ion detection device for detecting ions in a mass spectrometer and a mass spectrometer using the same.

Background

In the field of mass spectrometry, in recent years, it has been required to detect an extremely small amount of a compound contained in a sample, and high sensitivity of a mass spectrometer has become an increasingly important issue. In order to cope with such problems, efforts have been made to improve the sensitivity of each component such as the ion source, the mass separator, and the ion detector.

Fig. 9 is a schematic configuration diagram of a conventional ion detector in a quadrupole rod type mass spectrometer which is most widely used. Fig. 9 also shows simulation results of trajectories of ions and electrons.

The ion detector 4 mainly includes: an aperture electrode 41 for shielding a quadrupole electric field formed by the quadrupole mass filter 3 of the preceding stage; a conversion dynode 43 for converting ions into electrons; and a secondary electron multiplier 44 which detects electrons with high sensitivity. The hole electrode 41 is usually set to a ground potential (0V), and a dc high voltage having a polarity opposite to that of the ion to be observed is applied to the conversion dynode 43. Ions that have reached the vicinity of the opening of the aperture electrode 41 through the quadrupole mass filter 3 are efficiently introduced to the conversion dynode 43 by the electrostatic field generated by the applied voltage, and accelerated. Thus, the ions have large energy and collide with the conversion dynode 43, and therefore electrons are discharged at the conversion dynode 43 with high efficiency. The electrons emitted from the conversion dynode 43 are incident on a secondary electron multiplier 44 disposed to face each other with an extension line C' of the central axis (ion optical axis) C of the quadrupole mass filter 3 interposed therebetween. The secondary electron multiplier 44 multiplies the incident electrons, and outputs a current signal corresponding to the amount of the electrons as a detection signal.

In the ion detector 4, the neutral particles are not affected by the electric field, and therefore, pass through the quadrupole mass filter 3 and then go straight. In a mass spectrometer using an ion source based on an Electron Ionization (EI) method, a Chemical Ionization (CI) method, or the like, a carrier gas such as helium, a carrier gas in a metastable (metastable) state, an unionized compound molecule, a reagent gas used in the CI method, or the like may become neutral particles. In a mass spectrometer using an ion source based on an electrospray ionization (ESI) method, an Atmospheric Pressure Chemical Ionization (APCI) method, or the like, droplets in which a solvent is not sufficiently evaporated (unionized droplets) or the like may become neutral particles. In a mass spectrometer using a collision cell such as a triple quadrupole mass spectrometer, a collision gas such as argon, helium, and nitrogen may be used as neutral particles. In addition, in mass spectrometry devices, there is a possibility of unexpected and varied neutral particles. In the mass spectrometer using the ESI ion source, charged droplets in which the solvent is not sufficiently evaporated but neutral particles are sometimes introduced into the quadrupole mass filter 3, but the charged droplets are very heavy compared to ions and are therefore hardly affected by the electric field, and travel straight after passing through the quadrupole mass filter 3 as they are, like the neutral particles. In the following, the particles that have passed through the quadrupole mass filter 3 and then have gone straight without being affected by the electric field generated by the dynode 43 are referred to as straight particles.

The following techniques are known: although the straight traveling particles do not reach the conversion dynode 43 because they are hardly or completely not affected by the electric field as described above, noise in the detection signal is caused when the straight traveling particles enter the strong electric field formed by the conversion dynode 43 or when the straight traveling particles pass in the electron current going from the conversion dynode 43 to the secondary electron multiplier 44. The mechanism of this noise generation has not been sufficiently elucidated, but reduction of noise caused by straight particles is one of the major problems in increasing the sensitivity of an ion detector.

As one method for reducing such noise, an ion detector described in patent document 1 has been known. In the ion detector described in patent document 1, a deflection electrode (a "bending pole" in patent document 1) for deflecting the trajectory of ions from the central axis of the quadrupole mass filter is disposed between the aperture electrode and the conversion dynode, and the central axis of the ion collision surface of the conversion dynode is offset so as not to intersect the central axis of the quadrupole mass filter. The ion passing through the aperture electrode is deflected by the electric field generated by the deflection electrode and enters the conversion dynode. On the other hand, since the straight particles travel substantially straight after passing through the hole electrodes, they pass through a strong electric field formed by the conversion dynode or go to a position other than the electron current of the secondary electron multiplier tube from the conversion dynode.

The conventional ion detector described above is effective in preventing the straight particles from entering a strong electric field region or an electron current formed by the conversion dynode, and is considered effective in reducing noise caused by the straight particles. However, since the conversion dynode is disposed so as to avoid the intersection of the central axis of the ion collision surface of the conversion dynode and the central axis of the quadrupole mass filter, the effect of the strong electric field formed by the conversion dynode on the introduction of ions from the quadrupole mass filter cannot be sufficiently exhibited. Therefore, the proportion of ions that reach the conversion dynode among the ions that have passed through the aperture electrode decreases, and there is a fear that the level of the ion intensity signal itself decreases. That is, in the conventional ion detector, although noise due to the straight particles is reduced, the level of the ion intensity signal itself is also reduced, and therefore, there is a problem that the SN ratio of the detection signal is not necessarily improved.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an ion detector and a mass spectrometer using the same, which can achieve a high SN ratio and high sensitivity by sufficiently securing the amount of ions incident on a conversion dynode and reducing noise caused by straight particles.

Means for solving the problems

An ion detection device according to the present invention for solving the above-described problems detects ions that have passed through an ion separation unit that separates ions according to mass or mobility, or ions that have been emitted from the ion separation unit, and includes:

a) a conversion dynode which is disposed at a position deviated from an extension of a central axis of the incident ion flow sent from the ion separating unit and converts ions attracted by an electric field formed by the conversion dynode itself into electrons;

b) an electron detection unit which is disposed opposite to the conversion dynode with an extension line of a central axis of the incident ion flow interposed therebetween, and which amplifies and detects electrons emitted from the conversion dynode;

c) a shield electrode disposed between an incident position of the incident ion flow and the conversion dynode and the electron detection unit, the shield electrode including: c1) a blocking wall located on an extension of a central axis of the incident ion flow, blocking passage of particles; and c2) an electric field adjustment wall connected to the blocking wall, the electric field adjustment wall being planar, curved, or polyhedral, the electric field adjustment wall having an opening for passage of ions going to the conversion dynode or having a portion through which the ions pass, wherein the plane includes a straight line having an acute angle with a central axis of the incident ion flow on a plane including both the central axis of the incident ion flow and a central axis of an ion collision surface of the conversion dynode when viewed from an incident position of the incident ion flow, the curved surface includes a curve having the straight line as an approximate straight line, and the polyhedral is approximate to the curved surface;

d) and a voltage applying unit that applies a predetermined direct current voltage to the shield electrode.

In the ion detection device according to the present invention, the ion separation unit is typically a quadrupole mass filter or an ion trap (three-dimensional quadrupole rod type or linear type), as will be described later.

In, for example, a quadrupole mass filter, the central axis of the ion flow through the quadrupole mass filter coincides with the central axis of the quadrupole mass filter. When neutral particles such as compound molecules pass through the quadrupole mass filter together with ions and enter the ion detection device according to the present invention, the neutral particles travel substantially straight without being affected by the electric field and collide with the barrier wall of the shield electrode located in front of the travel of the neutral particles. In addition, in the case of using an electrospray ion source as an ion source, there is a possibility that charged droplets may come through a quadrupole mass filter, but since the charged droplets have a large mass and are hardly affected by an electric field, they travel substantially straight like neutral particles and collide with a barrier wall of a shield electrode. Thus, the neutral particles and the straight particles such as the charged liquid droplets do not enter the space between the conversion dynode and the electron detection unit. That is, the straight particles do not enter the strong electric field formed by the conversion dynode, and do not pass through the electron current from the conversion dynode to the electron detection unit. This can reduce noise caused by the straight particles.

On the other hand, an electric field adjustment wall of the shield electrode is present between the incident position of the incident ion flow and the conversion dynode, but the electric field adjustment wall is disposed so as to be inclined with respect to the central axis of the ion flow as a whole. Further, the electric field adjusting wall is set to a predetermined potential by the voltage applied to the shield electrode by the voltage applying unit. Therefore, the electric field adjusting wall can form a wall having a potential closer to the equipotential surface of the electric field formed between the conversion dynode and the incident position of the incident ion flow in the state where the shield electrode is not present, and the electric field in the space between the electric field adjusting wall and the incident position of the incident ion flow can be brought into a state close to the state where the shield electrode is not present. By the action of the electric field, ions reaching the vicinity of the incident position of the ion flow can be induced to the conversion dynode. The induced ions are accelerated directly through the openings or missing portions of the electric field adjustment walls to the conversion dynode. That is, the ions can reach the conversion dynode through almost the same trajectory as in the state where the shielding electrode is not present. Therefore, even if the shield electrode having a function of blocking the straight particles is provided, the loss of ions caused by the shield electrode can be minimized, and the detection efficiency of ions can be almost the same as that in the state where the shield electrode is not present.

In the ion detection device according to the present invention, it is preferable that: the ion separator further includes an aperture electrode that shields an electric field generated by the ion separator and allows ions to pass therethrough, at an incident position of the ion flow sent from the ion separator, and the shield electrode is disposed between the aperture electrode, the conversion dynode, and the electron detector.

In a quadrupole mass filter or an ion trap plasma separation unit, a high-frequency electric field is used in many cases to separate ions, but when the high-frequency electric field wave reaches an ion passage region in an ion detection device, the trajectory of the ions is affected. In contrast, when a hole electrode is provided at the incident position of the ion current, that is, outside the outlet of the quadrupole mass filter plasma separator, to substantially shield the high-frequency electric field formed by the ion separator, the trajectory of the ions going to the conversion dynode is stable, and the ions can reach the conversion dynode with high efficiency.

In the ion detection device having the above configuration according to the present invention, it is preferable that: the electric field adjustment wall has a wall surface surrounding an opening for passage of ions going to the conversion dynode.

According to this configuration, since the electric field in the entire space surrounding the ion flow going to the conversion dynode through the opening of the via electrode is in a state close to the state where the shield electrode is not present, the trajectory of the ion is not easily deviated, and it is convenient in terms of improving the ion detection efficiency.

In the ion detection device having the above configuration according to the present invention, it is preferable that: the opening provided in the electric field adjustment wall is located outside a cylindrical space virtually formed when the ion passage opening of the aperture electrode is moved in the extending direction of the central axis of the incident ion flow.

As described above, the straight particles passing through the quadrupole mass filter travel substantially parallel to the central axis of the quadrupole mass filter, i.e., the central axis of the incident ion flow. Therefore, in the case where the orifice electrode is provided outside the outlet of the quadrupole mass filter, the spatial spread (spread in the radial direction) of the particle flow of the straight particles is substantially limited to the size of the ion passage opening of the orifice electrode. Therefore, according to the above configuration, it is possible to substantially avoid the straight particles from passing through the opening provided in the electric field adjustment wall, and it is possible to more reliably reduce noise caused by the straight particles.

In the ion detection device having the above configuration according to the present invention, it is preferable that: the blocking wall is parallel to a plane substantially orthogonal to the central axis of the incident ion flow, and the shield electrode has an electric field auxiliary adjustment wall connected to the electric field adjustment wall and parallel to the blocking wall on the side opposite to the blocking wall with the electric field adjustment wall interposed therebetween.

According to this configuration, since the potential at the position of the electric field auxiliary adjustment wall is fixed, it is possible to more reliably suppress disturbance of the electric field due to the provision of the shield electrode.

The electric field adjustment wall may be planar, curved, or polyhedral with a combination of a plurality of planes, but when the electric field adjustment wall is curved or polyhedral, the processing takes time and labor, which increases the cost. Therefore, in the ion detection device according to the present invention, it is preferable that the electric field adjustment wall has a plane having the same potential, the plane being approximate to a curved equipotential surface in the vicinity of the position where the shield electrode is disposed in the electric field formed by the convertible dynode in the state where the shield electrode is not disposed.

The ion detection device according to the present invention can be used for various types of mass spectrometry devices.

For example, a mass spectrometer according to a first aspect of the present invention includes:

the ion detector according to the present invention described above;

an ion source that ionizes a compound in a sample; and

a quadrupole mass filter that selectively passes ions having a particular mass-to-charge ratio among the ions generated by the ion source,

wherein the mass spectrometer introduces ions that have passed through the quadrupole mass filter into the ion detector and detects the ions.

The mass spectrometer of the first embodiment is a single-type quadrupole rod-type mass spectrometer. Furthermore, it goes without saying that ion sources of different ionization methods are used depending on which of a liquid sample and a gas sample (sample gas) the sample is.

A mass spectrometer according to a second aspect of the present invention includes:

the ion detector according to the present invention described above;

an ion source that ionizes a compound in a sample;

a front stage quadrupole mass filter that selectively passes ions having a specific mass-to-charge ratio among the ions generated by the ion source;

an ion splitting unit that splits ions that have passed through the front stage quadrupole mass filter; and

a post-stage quadrupole mass filter for selectively passing ions having a specific mass-to-charge ratio among product ions generated by fragmentation in the ion fragmentation section,

wherein the mass spectrometer introduces ions that have passed through the post-stage quadrupole mass filter into the ion detector and detects the ions.

As the ion dissociation part, a collision cell that cleaves ions by Collision Induction Dissociation (CID), for example, can be used. The mass spectrometer of the second embodiment is a triple quadrupole mass spectrometer.

A mass spectrometer according to a third aspect of the present invention includes:

the ion detector according to the present invention described above;

an ion source that ionizes a compound in a sample; and

an ion trap that separates and sequentially emits ions according to a mass-to-charge ratio after temporarily capturing the ions generated by the ion source or other ions derived from the ions,

wherein the mass spectrometer introduces ions emitted from the ion trap into the ion detector and detects the ions.

The mass spectrometer of the third aspect is an ion trap mass spectrometer. The ion trap may be any one of a three-dimensional quadrupole rod type and a linear type.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the ion detection device of the present invention, the drawing action of the strong electric field formed by the voltage applied to the conversion dynode on the ions is effectively utilized, whereby the amount of the ions incident on the conversion dynode can be sufficiently ensured, and on the other hand, the noise caused by the particles traveling straight without being affected by the electric field can be reduced. Thus, according to the ion detection device and the mass spectrometer of the present invention, a high SN ratio and a high detection sensitivity can be realized as compared with the conventional ion detection device and the mass spectrometer using the same.

Drawings

Fig. 1 is a schematic overall configuration diagram of a mass spectrometer equipped with an ion detector as an embodiment of the present invention.

Fig. 2 is a diagram showing a simulation result of ion trajectories in the ion detector of the present embodiment.

Fig. 3 is an explanatory diagram of a method for determining the shape of the shield electrode based on the simulation result of the equipotential surface in the electric field formed by the conversion dynode in the ion detector of the present embodiment.

Fig. 4 is an external perspective view of the shield electrode in the ion detector of the present embodiment.

Fig. 5 is a graph showing the effect of improving the SN ratio and the effect of reducing the noise level in the ion detector of the present embodiment.

Fig. 6 is an external perspective view showing a modification of the shield electrode.

Fig. 7 is a schematic plan view showing a further modification of the shield electrode.

Fig. 8 is a schematic overall configuration diagram of another example of a mass spectrometer including an ion detector as an embodiment of the present invention.

Fig. 9 is a schematic configuration diagram of an ion detector in a conventional quadrupole mass spectrometer.

Detailed Description

A mass spectrometer including an ion detector according to an embodiment of the present invention will be described with reference to the drawings.

Fig. 1 is a schematic overall configuration diagram of the mass spectrometer, fig. 2 is a diagram showing a simulation result of an ion trajectory in the ion detector 4 in fig. 1, fig. 3 is an explanatory diagram of a method for determining a shape of a shield electrode in the ion detector 4 based on a simulation result of an equipotential surface in an electric field formed by a conversion dynode, and fig. 4 is an external perspective view of the shield electrode 42 in the ion detector 4. The mass spectrometer ionizes a compound in a liquid sample and performs mass spectrometry, and typically a liquid chromatograph is connected to a stage preceding the mass spectrometer.

As shown in fig. 1, an ionization chamber 11, a first intermediate vacuum chamber 12, a second intermediate vacuum chamber 13, and a high vacuum chamber 14 are provided in a chamber 10. The ionization chamber 11 is substantially in an atmospheric pressure environment, and has a multistage differential exhaust system in which the degree of vacuum is increased stepwise from the ionization chamber 11 to the high vacuum chamber 14. The liquid sample is sprayed from the electrospray ionization nozzle 21 into the ionization chamber 11, and the compound in the charged droplets generated by the spraying is ionized in the process of droplet splitting and solvent evaporation. The generated various ions are sent to the first intermediate vacuum chamber 12 through the heated capillary 22, focused by the ion guide 23, and sent to the second intermediate vacuum chamber 13 through the separator 24. The ions are focused by the ion guide 25, sent to the high vacuum chamber 14, and introduced into the quadrupole mass filter 3.

A predetermined voltage (voltage obtained by adding a dc voltage to a high-frequency voltage) is applied to the 4 rod electrodes constituting the quadrupole mass filter 3, and only ions having a mass-to-charge ratio according to the voltage are introduced into the ion detector 4 through the quadrupole mass filter 3. The ion detector 4 generates a detection signal according to the amount of the introduced ions. Here, the central axis C of the quadrupole mass filter 3 is the optical axis (central axis) of the ion flow passing through the quadrupole mass filter 3.

The ion detector 4 includes an aperture electrode 41, a shielding electrode 42, a conversion dynode 43, and a secondary electron multiplier 44. The orifice electrode 41 is disposed in the vicinity of the outer side of the outlet of the quadrupole mass filter 3, and has a substantially disk-like shape with a circular opening centered on the central axis C of the quadrupole mass filter 3. The conversion dynode 43 has a substantially disk-shaped ion collision surface 43a, and is disposed so that the central axis B of the ion collision surface 43a is substantially orthogonal to the extension line C' of the central axis C of the quadrupole mass filter 3. The secondary electron multiplier 44 is disposed at a position substantially opposed to the ion collision surface 43a of the conversion dynode 43 with an extension line C' of the central axis C of the quadrupole mass filter 3 interposed therebetween.

The hole electrode 41 is grounded, and a predetermined direct current voltage is applied to the shield electrode 42, the conversion dynode 43, and the secondary electron multiplier 44 by the SE power supply unit 6, the CD power supply unit 7, and the SEM power supply unit 8, respectively. This voltage is controlled by the control unit 5. It is to be noted that, of course, predetermined voltages are applied to the quadrupole mass filter 3 and the ion guides 23 and 25, respectively, and a circuit block for applying voltages to components other than the ion detector 4 is not described here.

For convenience of explanation, the extending direction of the central axis C of the quadrupole mass filter 3 (lateral direction in fig. 1 to 3) is defined as the Z direction, the extending direction of the central axis of the ion collision surface 43a of the conversion dynode 43 (vertical direction in fig. 1 to 3) orthogonal to the Z direction is defined as the Y direction, and the direction orthogonal to both the Z direction and the Y direction (direction orthogonal to the paper surface in fig. 1 to 3) is defined as the X direction.

In the ion detector 4, the aperture electrode 41, the conversion dynode 43, and the secondary electron multiplier 44 are basically the same as those of the conventional ion detector shown in fig. 8. A characteristic constituent element is a shield electrode 42 disposed between the hole electrode 41 and the conversion dynode 43.

As shown in fig. 4, the shield electrode 42 is formed by, for example, bending 1 metal (or other conductive) plate member in 2 lines extending in the X direction, and the straight particle blocking wall 42a, the ion-induced electric field adjustment wall 42b, and the electric field auxiliary adjustment wall 42d are connected. The straight particle blocking wall 42a and the electric field auxiliary adjustment wall 42d are parallel to the X-Y plane. The ion-inducing electric field-adjusting wall 42b is a surface inclined at a predetermined angle θ (where θ is an acute angle) with respect to an X-Z plane including a straight line (in fig. 4, the central axis C of the ion flow or an extension C thereof) perpendicular to the straight particle blocking wall 42 a. A circular ion passage opening 42c is formed at a predetermined position of the ion-inducing electric field adjustment wall 42 b.

As shown in fig. 1 to 3, the shield electrode 42 having the above-described shape is arranged as follows: the straight particle barrier wall 42a is orthogonal to the central axis C of the quadrupole mass filter 3, and the electric field auxiliary adjustment wall 42d is located closer to the aperture electrode 41 than the straight particle barrier wall 42a, and the electric field auxiliary adjustment wall 42d is located between the aperture electrode 41 and the conversion dynode 43. Here, a method of determining the inclination angle θ of the ion-induced electric field adjustment wall 42b and the applied voltage applied to the shield electrode 42 will be described.

Fig. 3 shows the equipotential surfaces (strictly speaking, the equipotential lines in a cross section containing the central axis C) of the electric field formed by the voltage applied to the conversion dynode 43 (here, -10kV) in the absence of the shielding electrode 42. The equipotential line between the conversion dynode 43 and the aperture electrode 41 is curved as shown in the drawing, and the trajectory of the ion emitted from the quadrupole mass filter 3 and traveling in the Z direction is gently curved by the potential gradient conforming to the equipotential surface, so that the ion reaches the ion collision surface 43a of the conversion dynode 43.

When the shield electrode 42 is provided between the aperture electrode 41 and the conversion dynode 43, it is desirable to prevent the trajectory of ions from the quadrupole mass filter 3 to the conversion dynode 43 from changing with respect to a state where the shield electrode 42 is not provided, as much as possible, in order to maintain the ion detection efficiency. For this reason, it is desirable to avoid the electric field in the ion passage region, that is, the state of the equipotential surface, from changing as much as possible even when the shield electrode 42 is disposed. Therefore, equipotential lines in a curved shape as shown in fig. 3 in the electric field in the vicinity of the ion passage region are approximated by straight lines, and the inclination angle θ of the ion-inducing electric field adjustment wall 42b of the shield electrode 42 is determined based on the angle of the approximated straight lines with respect to the central axis C.

In the example of fig. 3, the shield electrode shape indicated by reference numeral 420 in the drawing is obtained based on the approximate straight line of the equipotential lines of the region indicated by reference numeral a in the drawing. The voltage applied to the shield electrode 42 is determined based on the potential of the equipotential line in the vicinity of the intersection of the ion-induced electric field adjustment wall 42b of the shield electrode 42 and the ion trajectory center. However, even if the equipotential surfaces are determined by simulation as shown in fig. 3, it is impossible to avoid the occurrence of a deviation in the equipotential surfaces in the actual apparatus. In addition, there are ions and straight particles that do not exhibit ideal behavior. Further, the behavior of ions is slightly different depending on the mass-to-charge ratio of the ions to be observed. Therefore, in practice, it is desirable to find the optimum state while adjusting the shape of the shield electrode and the applied voltage so as to obtain the highest ion detection efficiency.

Fig. 2 is a graph showing the results of simulation of the trajectories of ions and electrons, and it is understood that the ions passing through the aperture electrode 41 pass through the ion passage opening 42c and hardly collide with the ion-induced electric field adjustment wall 42b of the shield electrode 42. On the other hand, most of the straight particles such as neutral particles collide with the particle blocking wall 42a, bounce, and are discharged to the outside by vacuum evacuation. Thus, the straight particles hardly enter the space between the conversion dynode 43 and the secondary electron multiplier 44, and noise caused by the straight particles can be greatly suppressed. On the other hand, since the ions are hardly affected by the provision of the shield electrode 42, high ion detection efficiency can be achieved.

Fig. 5 is a graph showing results obtained by experimentally investigating SN ratios of the case where the shield electrode is provided and the case where the shield electrode is not present, and noise levels derived from straight particles. From the results, it was found that the provision of the shield electrode blocked the straight particles, and the noise level caused by the blocking was reduced, and the SN ratio was also improved. This makes it possible to confirm the effectiveness of the shield electrode.

The shape of the shield electrode is not limited to the shape shown in fig. 4 and the like. It is important to be able to block the straight particles and to avoid that the state of the electric field formed between the aperture electrode 41 and the conversion dynode 43 changes significantly with respect to when no shielding electrode is provided. For the former, the straight particle blocking wall 42a is required, and for the latter, the ion induced electric field adjusting wall 42b connected to the straight particle blocking wall 42a is required. The ion-inducing electric field adjustment wall 42b may be short, for example, as shown in fig. 6, and the ion-inducing electric field adjustment wall 42b may be short up to a position where the ion passage opening 42c is provided in the shield electrode 42 shown in fig. 4.

Fig. 7 shows an example of a shield electrode having another shape. Fig. 7 is a side view of the shield electrode, fig. 7 (a) is the shield electrode 42 shown in fig. 4, and fig. 7 (B) is the shield electrode 42B shown in fig. 6. In these shield electrodes 42 and 42B, the ion-inducing electric field adjustment wall 42B is planar. On the other hand, in the shield electrode 42C shown in fig. 7 (C), the ion-inducing electric field adjustment wall 42b is formed to be bent in the middle. In the shield electrode 42D shown in fig. 7 (D), the ion-inducing electric field adjustment wall 42b is curved. It is apparent that the same effect as that of the ion detector 4 in the above embodiment can be obtained with this configuration.

The straight particle blocking wall 42a may not be completely orthogonal to the extension line C' of the central axis C of the quadrupole mass filter 3. The same applies to the electric field auxiliary adjustment wall 42 d.

Next, an example will be described in which the ion detector 4 in the above-described embodiment is applied to a mass spectrometer for ionizing a compound in a sample gas and performing mass spectrometry. Fig. 8 is a schematic overall configuration diagram of the mass spectrometer, and components identical or corresponding to those in the mass spectrometer shown in fig. 1 are given the same reference numerals, and detailed description thereof is omitted. A gas chromatograph is often connected to the mass spectrometer at a stage preceding the mass spectrometer.

In this mass spectrometer, an ion source 110, a lens electrode 120, a quadrupole mass filter 3, and an ion detector 4 are disposed in a chamber 100 evacuated by a vacuum pump not shown. Here, the ion source 110 is an EI-based ion source, and includes an ionization chamber 111, a filament 112 for generating thermal electrons, a trapping electrode 113 for trapping thermal electrons, and a sample gas introduction pipe 114 for introducing a sample gas into the ionization chamber 111. Further, although not shown, a repulsion electrode is disposed in the ionization chamber 111.

A sample gas is introduced into the ionization chamber 111 through the sample gas introduction pipe 114, and compounds in the sample gas are ionized by contacting with thermal electrons generated from the filament 112 and going to the trapping electrode 113. The generated ions are pushed out of the ionization chamber 111 by an electric field formed by a repulsive electrode, or are extracted from the ionization chamber 111 by an electric field formed by a lens electrode 120, focused by the lens electrode 120, and introduced into the quadrupole mass filter 3. The behavior of the ions introduced into the quadrupole mass filter 3 and thereafter is the same as in the above example described with reference to fig. 1 to 4. In this mass spectrometer, most of the sample gas is a carrier gas used in a preceding gas chromatograph, and molecules of the carrier gas or metastable molecules obtained by the metastable conversion thereof are easily introduced into the quadrupole mass filter 3 as neutral particles. The straight particles as such neutral particles are blocked by the particle blocking wall 42a of the shield electrode 42 as described above, and can be prevented from becoming a noise source.

In addition, when the ion source 110 is not an EI ion source but a CI ion source, a reagent gas is introduced into the ionization chamber for ionization, and the reagent gas also becomes straight particles. Such neutral particles are also blocked by the particle blocking wall 42a of the shield electrode 42, and can be prevented from becoming a noise source.

In addition, although the mass spectrometer shown in fig. 1 and 8 is a single quadrupole rod type mass spectrometer, the ion detector 4 of the above-described embodiment can also be used as an ion detector of a triple quadrupole rod type mass spectrometer. In addition, the ion trap type mass spectrometer can also be used as an ion detector of the ion trap type mass spectrometer. In this case, the ion trap may be either a linear type or a three-dimensional quadrupole type, and the ion detector 4 may be disposed such that the aperture electrode 41 is positioned outside the ion exit from which ions are emitted from the ion trap.

In the ion detector 4 of the above embodiment, the aperture electrode 41 is not essential, but in the case where the aperture electrode 41 is not provided, the ion detector 4 needs to be disposed so as to be apart from the quadrupole mass filter 3 (or the ion trap). This causes a large loss of ions sent from the quadrupole mass filter 3, which is disadvantageous in terms of ion detection efficiency. Thus, although the hole electrode 41 is not essential, it is practically desirable to provide a hole electrode.

The above-described embodiments and various modifications thereof are merely examples of the present invention, and it is needless to say that the present invention is included in the scope of the claims of the present application even if appropriately changed, modified, or added within the scope of the present invention.

Description of the reference numerals

10: a chamber; 11: an ionization chamber; 12: a first intermediate vacuum chamber; 13: a second intermediate vacuum chamber; 14: a high vacuum chamber; 21: an electrospray ionization nozzle; 22: heating the capillary tube; 23. 25: an ion guide; 24: a separator; 3: a quadrupole rod mass filter; 4: an ion detector; 41: a hole electrode; 42. 42B, 42C, 42D: a shield electrode; 42 a: a straight particle blocking wall; 42 b: an ion-induced electric field adjustment wall; 42 c: ions pass through the opening; 42 d: an electric field assisted adjustment wall; 43: converting the dynode; 43 a: an ion collision surface; 44: a secondary electron multiplier tube; 5: a control unit; 6: an SE power supply unit; 7: a CD power supply unit; 8: an SEM power supply unit; 110: an ion source; 111: an ionization chamber; 112: silk; 113: a capture electrode; 114: a sample gas introduction pipe; 120: and a lens electrode.