JP6160472B2 - Time-of-flight mass spectrometer - Google Patents

Description

  The present invention relates to a time-of-flight mass spectrometer (hereinafter abbreviated as “TOFMS”), and more particularly to an orthogonal acceleration (OA) type TOFMS.

  In TOFMS, a constant kinetic energy is applied to ions derived from a sample component to fly in a space of a fixed distance, the time required for the flight is measured, and the mass-to-charge ratio of the ions is obtained from the flight time. Therefore, when accelerating ions and starting flight, if there are variations in the position of the ions and the initial energy of the ions, the flight time of ions with the same mass-to-charge ratio will vary, resulting in mass resolution and mass accuracy. It leads to decline. As a technique for solving such a problem, orthogonal acceleration (also called “vertical acceleration”, “orthogonal extraction”, etc.) type TOFMS is known.

  In the orthogonal acceleration method TOFMS, a sample-derived ion beam is accelerated in a pulse direction in a direction orthogonal to the traveling direction thereof, and an ion packet generated thereby is sent into a flight space for mass analysis. By suppressing the variation of the initial velocity of ions in the acceleration direction by accelerating in the orthogonal direction, the turnaround time that occurs during the acceleration of ions can be greatly reduced, thereby improving the mass resolution. Can do. The so-called Q-TOF device, which is equipped with a quadrupole mass filter with excellent ion selectivity, with a collision cell in front of the orthogonal acceleration method TOFMS having such high mass resolution and mass accuracy, has high accuracy and high resolution. MS / MS analysis is possible, and in recent years, it has been widely used for proteome analysis and the like.

FIG. 4 is a schematic configuration diagram of the orthogonal acceleration unit of the conventional orthogonal acceleration type TOFMS.
The orthogonal acceleration unit 1 includes a flat extrusion electrode 11 arranged in parallel with the traveling direction (X-axis direction) of the introduced ion beam, and an extraction electrode arranged opposite to the extrusion electrode 11 with the ion beam interposed therebetween. 12 and a plurality of acceleration electrodes 13 (13a, 13b) forming an acceleration region for accelerating ions extracted by the extrusion electrode 11 and the extraction electrode 12. Among these, the extraction electrode 12 and the acceleration electrode 13b at the final stage of the acceleration region are grid electrodes in which a conductive grid is stretched in an opening through which ions pass (see Non-Patent Document 1).

  In the orthogonal acceleration unit 1, the ion beam derived from the sample component is introduced into the extraction region between the extraction electrode 11 and the extraction electrode 12 in the X-axis direction as shown in FIG. 4. At this time, the electrodes 11 and 12 are at the same potential (for example, both are ground potential), and there is no electric field in the extraction region and the acceleration region. At a predetermined point in time when a sufficient amount of ions are introduced, a high voltage pulse having the same polarity as the ions is applied to the extrusion electrode 11, and the extraction electrode 12 and the acceleration electrode 13 are accelerated along the Z-axis direction. A voltage for each is applied. A part of the ion beam is pushed out from the extraction region to the acceleration region by the electric field formed by the voltage applied in this way, and further, a large kinetic energy is given by the acceleration electric field, and the grid of the final stage acceleration electrode 13b. It passes through the opening and is emitted as an ion packet. The acceleration direction of ions by the acceleration electric field is the Z-axis direction, but since the ions have an initial velocity in the X-axis direction (drift direction), the actual flight start direction is the direction of the white arrow in FIG. Become.

  The grid electrode is used for the extraction electrode 12 and the acceleration electrode 13b. The boundary electrode is defined while allowing ions to pass with a predetermined transmittance, and a uniform acceleration electric field is formed in the acceleration region. It is to do. However, when ions pass through the grid electrode, a certain percentage of the ions come into contact with the grid and disappear, and thus the signal sensitivity is inevitably lowered. In addition, since the diverging lens action occurs due to the leakage of the electric field through the fine openings in the grid, some of the diverged ions do not enter the detector, causing further sensitivity deterioration, or when the detector reaches the detector. There is a risk that the ion optical characteristics such as time convergence will deteriorate and the resolution and accuracy will decrease.

  In order to overcome such drawbacks in the case of using a grid electrode, an orthogonal acceleration type TOFMS that does not use a grid electrode has also been proposed (see Patent Documents 1 and 2). However, such a device requires additional hardware and sophisticated and complicated control, such as adding an electrode that is driven in a pulse manner at a predetermined timing, and a considerable increase in cost is inevitable.

  In addition, in order to be able to use a detector with a small ion detection surface by compressing ion packets in the drift direction, a device with a focusing electrode arranged in the extraction region sandwiched between the extrusion electrode and extraction electrode is also proposed. (See Patent Document 3). However, in this apparatus, as in the prior art, a grid electrode is used at the final stage of the extraction electrode and the acceleration electrode, so that it is difficult to achieve a high ion transmittance. Further, it is necessary to newly add a focusing electrode, and it is actually difficult to provide a focusing electrode so that an electric field acts sufficiently in a narrow extraction region between the extrusion electrode and the extraction electrode.

British Patent No. 2386751 International Publication No. 2001/011660 Japanese Patent No. 4649234

M. Guilhaus and two others, “Orthogonal Acceleration Time-of-flight Mass Spectrometry”, Mass Spectrom. Review Rev.), Vol.19, 2000, p.65-107 Kato, “Introduction to Electron Optics-For Understanding Electron Spectroscopy (4th Journal of Surface Analysis Vol.12 No.1 (2005) pp.24-45)”, [Searched on December 6, 2013 ] Internet <URL: http://www.sasj.jp/JSA/CONTENTS/vol.12_1/Vol.12%20No.1/Vol.12%20No.1%2024-45.pdf>

  The present invention has been made to solve the above-mentioned problems, and its main purpose is to realize high ion permeability by a simple electrode configuration and control, thereby avoiding an increase in cost and high sensitivity and high performance. An object of the present invention is to provide an orthogonal acceleration type time-of-flight mass spectrometer capable of measuring accuracy.

  Another object of the present invention is to provide high-resolution measurement that emphasizes mass resolution while ensuring sufficient sensitivity and high sensitivity that particularly emphasizes measurement sensitivity while ensuring sufficient resolution, depending on the purpose of analysis. An object of the present invention is to provide an orthogonal acceleration type time-of-flight mass spectrometer that can be switched between sensitivity measurement.

The present invention made to solve the above-mentioned problems is an orthogonal acceleration type time-of-flight mass spectrometer having an orthogonal acceleration unit that accelerates introduced ions in a direction orthogonal to the optical axis of the ion beam. The orthogonal acceleration unit is
a) an extrusion electrode arranged parallel to the optical axis of the ion beam;
b) an extraction electrode which is a grid electrode arranged opposite to the extrusion electrode across the ion beam;
c) a circle that forms an accelerating electric field for accelerating ions that have passed through the grid of the extraction electrode by an electric field formed between the extrusion electrode and the extraction electrode in a direction perpendicular to the optical axis of the ion beam; A plurality of accelerating electrodes that are annular or cylindrical;
d) An electric field in which the descending gradient of the potential distribution on the central axis of the plurality of acceleration electrodes gradually increases in the direction of ion travel to cause at least one of the acceleration electric fields to cause a convergence effect on the ions in a direction orthogonal to the acceleration direction. A voltage application unit configured to apply a voltage determined to be formed by a unit to each of the plurality of acceleration electrodes;
It is characterized by having.

  In the conventional general orthogonal acceleration method TOFMS, the applied voltage to the acceleration electrode is set so that the axial potential distribution in the direction of ion travel in the acceleration electric field of the orthogonal acceleration portion has a linear downward gradient. Has been. That is, in this case, the accelerating electric field is a uniform electric field, and ions are not subjected to radial force (direction perpendicular to the accelerating direction) in the accelerating electric field.

On the other hand, in the TOFMS according to the present invention, the potential distribution on the central axis Z of the acceleration electrode, that is, the axial potential distribution φ is ∂ ² φ / ∂Z ² <0 in at least a part of the acceleration electric field. Thus, the voltage applied to each acceleration electrode is set. This is an axial potential distribution in which the downward gradient gradually increases. As is well known, if the spatial potential distribution is defined by the Laplace equation, the provisions of the Laplace equation in axisymmetric coordinate system is ∂ ² φ / ∂Z ² <0, the potential There is a positive component in the radial direction orthogonal to the central axis Z so as to cancel the change in distribution. Therefore, the electric field at this time exerts a force toward the central axis Z in the radial direction with respect to ions located at a position off the central axis Z. As a result, the ion packet passing through the accelerating electric field receives at least a part of the accelerating electric field toward the center, that is, a force that converges the ion spread, and the ion trajectory is converged toward the center. It is injected towards the flight space.

  In other words, the TOFMS according to the present invention can be regarded as having a lens function for converging ions on the acceleration electrode itself for accelerating ions in the orthogonal acceleration unit. This allows ions to fly efficiently without the need to provide a grid electrode, which was previously provided at the final stage of a plurality of acceleration electrodes, and without adding a lens electrode or voltage source for additional convergence. To reach the detector.

When the grid electrode is not used in the final stage of the accelerating electrode, an axial potential such that ∂ ² φ / ∂Z ² > 0 is generated in the vicinity of the injection opening due to electric field leakage. Therefore, in this region, a lens action for diverging ions occurs. However, as long as the axial potential distribution is adjusted so as to give a larger convergence effect than the diverging action in the acceleration region where ions reach that area, the overall convergence effect is superior and the ion packet is reduced. it can be compressed into (the traveling direction of the ion beam is introduced between the repeller electrode and the extraction electrode) that drift direction.

As described above, by converging ions in the accelerating electric field, the amount of ions reaching the detector increases, but the flight distance slightly changes depending on the initial position of the ions, which may reduce the mass resolution and the like.
Therefore, in the time-of-flight mass spectrometer according to the present invention, preferably, the voltage applied to each of the plurality of acceleration electrodes is adjusted in order to adjust the action of converging ions in the acceleration electric field in a direction orthogonal to the acceleration direction. It is preferable to further include a control unit that controls the voltage application unit so as to be changed.

  In the time-of-flight mass spectrometer according to the present invention, more preferably, a high-resolution measurement mode that prioritizes mass resolution and a high-sensitivity measurement mode that prioritizes sensitivity can be switched. When a mode is specified, a plurality of acceleration voltages are generated so that an electric field in which a descending gradient of potential distribution on the central axes of a plurality of acceleration electrodes gradually increases in the ion traveling direction is formed in at least a part of the acceleration electric field. When a high-resolution measurement mode is specified by applying to each of the electrodes, a voltage that provides an electric field with a uniform potential gradient of the potential distribution may be applied to each of the plurality of acceleration electrodes.

  In this configuration, when the high sensitivity measurement mode is designated, the ion packet is converged in the acceleration region as described above, and the ions reach the detector with a small loss. Thereby, a particularly sensitive measurement is possible. On the other hand, when the high resolution measurement mode is designated, a uniform accelerating electric field is formed in the acceleration region as usual. As a result, the ions ejected from the orthogonal acceleration unit travel while spreading, so that some ions do not reach the detector and the sensitivity is lower than in the high sensitivity measurement mode. On the other hand, since the lengths of the flight distances of the same ion species reaching the detector are uniform, higher resolution can be achieved than in the high sensitivity measurement mode.

  According to this configuration, since the high sensitivity measurement mode and the high resolution measurement mode can be switched in a short time by the control by the control unit, for example, a specific component separated by a liquid chromatograph is introduced. It is also possible to switch between high-resolution measurement and high-sensitivity measurement during a relatively short period of time, and obtain the results (mass spectrum) for each measurement.

  According to the time-of-flight mass spectrometer according to the present invention, it is not necessary to use the grid electrode provided at the final stage of the plurality of acceleration electrodes. Can be incident on the detector. In addition, since it is not necessary to newly add a lens electrode for focusing or its voltage source in order to focus ions, it is possible to increase the sensitivity of measurement while suppressing an increase in the cost of the apparatus. Further, since the width of the ion packet can be compressed and incident on the detector, the size of the ion detection surface required for obtaining the same measurement sensitivity can be reduced. Thereby, not only the cost of the detector can be suppressed, but also a detector with better performance such as time response can be used.

  In addition, according to the time-of-flight mass spectrometer having a preferred configuration according to the present invention, when high sensitivity measurement with an emphasis on measurement sensitivity is desired, such as quantitative analysis of trace components, although mass resolution is low, mass resolution is emphasized. Measurement can be performed with sufficiently high sensitivity compared to the high resolution measurement. On the other hand, if you want to perform high-resolution measurement with an emphasis on mass resolution, such as qualitative analysis of components with a relatively high content, the sensitivity is low, but the measurement should be performed with sufficiently high mass resolution compared to high-sensitivity measurement. Can do. As described above, since it is possible to clearly switch the measurement with emphasis on sensitivity or mass resolution, it is possible to obtain an accurate result according to the analysis purpose.

1 is an overall configuration diagram of an orthogonal acceleration TOFMS that is an embodiment of the present invention. FIG. The block diagram of the orthogonal acceleration part in the orthogonal acceleration type TOFMS of a present Example. Schematic which shows the comparison of the voltage respectively applied to the several acceleration electrode of an orthogonal acceleration part by the orthogonal acceleration type TOFMS of a present Example, and the conventional orthogonal acceleration type TOFMS. The block diagram of the orthogonal acceleration part in the conventional orthogonal acceleration type TOFMS. The figure which shows the electrode model for the simulation of ion trajectory (a), the figure which shows the axial potential distribution in the orthogonal acceleration part of orthogonal acceleration type TOFMS of this execution example (b), the orthogonal acceleration part of conventional orthogonal acceleration type TOFMS The figure which shows the axial potential distribution in (c). The figure (a) which shows the simulation result of the ion orbit in the orthogonal acceleration type TOFMS of a present Example, and the figure (b) which shows the simulation result of the ion orbit in the orthogonal acceleration part of the conventional orthogonal acceleration type TOFMS.

  An orthogonal acceleration type TOFMS which is an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is an overall configuration diagram of the orthogonal acceleration type TOFMS of this embodiment, and FIG. 2 is a configuration diagram of an orthogonal acceleration unit in the orthogonal acceleration type TOFMS of this embodiment. 1 and 2, the same reference numerals are given to the same components as those already described in FIG. 4.

  The orthogonal acceleration method TOFMS of the present embodiment includes an ion source 4 that ionizes components in a target sample, a TOF analyzer 2 that includes a flight space 21 and a reflector 22, and an orthogonal that accelerates ions and sends them to the TOF analyzer 2. Accelerator 1, ion guide 5 that guides ions emitted from ion source 4, detector 3 that detects ions flying in flight space 21 of TOF analyzer 2, and detection signal from detector 3 The data processing unit 6 that receives the received data and creates a mass spectrum, the orthogonal acceleration power source unit 7 that applies a predetermined voltage to each of the plurality of electrodes included in the orthogonal acceleration unit 1, the orthogonal acceleration power source unit 7 and the like The control part 8 which controls this, and the input part 9 which performs input setting are provided. The control unit 8 includes a mode switching unit 81 as a functional block. In addition, although the component which applies a voltage to the ion guide 5, the reflector 22, etc. also exists naturally, these description is abbreviate | omitted in FIG.

  As shown in FIG. 2, the orthogonal acceleration unit 1 includes an extrusion electrode 11 arranged in parallel to the X-axis direction that is also an ion beam incident direction, an extraction electrode 12 arranged substantially parallel to the extrusion electrode 11, and a Z-axis. A plurality of acceleration electrodes 13 arranged in the direction are included. The acceleration electrode 13 has an annular shape or a flat cylindrical shape that is rotationally symmetric about a central axis C1 extending in the Z-axis direction. In the conventional orthogonal acceleration unit 1 shown in FIG. 4, the final stage acceleration electrode 13 is the grid electrode 13b. However, in the configuration of this embodiment, the final stage acceleration electrode has the same shape as the other acceleration electrodes. It is not a grid electrode.

The basic analysis operation in the orthogonal acceleration type TOFMS of this embodiment will be briefly described.
Various ions generated in the ion source 4 are introduced into the orthogonal acceleration unit 1 in the X-axis direction while being converged by the ion guide 5. When ions are introduced into the orthogonal acceleration unit 1, an acceleration electric field is not formed in the orthogonal acceleration unit 1, and when a sufficient amount of ions are introduced into the orthogonal acceleration unit 1, the orthogonal acceleration power supply unit By applying a predetermined voltage from 7 to the extrusion electrode 11, the extraction electrode 12, and the plurality of acceleration electrodes 13, an extraction electric field and an acceleration electric field are formed. Ions are sent from the extraction region to the acceleration region by the action of the extraction electric field, and further, the ions are given kinetic energy in the Z-axis direction by the action of the acceleration electric field and are sent to the flight space 21 of the TOF analyzer 2.

  As indicated by a two-dot chain line in FIG. 1, ions that have started flying from the acceleration region of the orthogonal acceleration unit 1 are folded back by the reflected electric field formed by the reflector 22 and finally reach the detector 3. The detector 3 sequentially generates detection signals according to the amount of ions that have reached with time. The data processing unit 6 obtains the time-of-flight spectrum from the detection signal starting from the ion injection time point, and further obtains the mass spectrum by converting the flight time to the mass-to-charge ratio m / z.

  When performing the analysis as described above, the orthogonal acceleration power supply unit 7 applies a predetermined voltage to the extrusion electrode 11, the extraction electrode 12, and the plurality of acceleration electrodes 13 in a pulse manner at a predetermined timing. FIG. 3 is a schematic diagram showing a comparison of voltages applied to a plurality of acceleration electrodes of the orthogonal acceleration unit in the orthogonal acceleration type TOFMS of the present embodiment and the conventional orthogonal acceleration type TOFMS. This is an example when the analysis target is a positive ion.

As shown in FIG. 3, conventionally, an acceleration voltage having a linear downward gradient in the acceleration direction (that is, the Z-axis direction) is applied to each acceleration electrode 13 provided at equal intervals. The potential distribution (axial potential distribution) on the central axis C1 of the accelerating electric field formed by such an accelerating voltage also has a downward slope linearly in the acceleration direction. That is, the axial potential distribution φ is ∂ ² φ / ∂Z ² = 0 in principle, and the accelerating electric field is a uniform electric field with no change in acceleration.

In contrast, in the orthogonal acceleration type TOFMS of the present embodiment, an acceleration voltage that gradually increases the downward gradient in the acceleration direction is applied to each acceleration electrode 13 provided at equal intervals. Therefore, the axial potential distribution φ of the accelerating electric field is ∂ ² φ / ∂Z ² <0. The behavior of ions in such an accelerating electric field can be explained by using a Laplace equation that is commonly used to obtain a potential distribution of a spatial electrostatic field. Since it is well known in theory (see, for example, Non-Patent Document 2 etc.), a detailed description will be omitted, and the description will be made schematically. Here, since the acceleration region has a cylindrical shape, the cylindrical coordinates are considered.

In an electrostatic acceleration electric field formed by the acceleration electrode 13, the potential distribution needs to satisfy the following Laplace equation.
(1 / r) {∂ / ∂r (r∂φ / ∂r)} + ∂ ² φ / ∂Z ² = 0 (1)
Here, r is a position in the radial direction of the cylindrical coordinates, and Z is a position on the central axis C1.
When ∂ ² φ / ∂ Z ² = 0, equation (1) is
(1 / r) {∂ / ∂r (r∂φ / ∂r)} = 0 (2)
It becomes. Since this does not depend on Z, it means that the radial potential distribution is the same at any position on the central axis C1. Therefore, no force acts on the ions passing through the acceleration electric field in the radial direction r. That is, no force is generated in the accelerating electric field to converge or diverge the ions.

On the other hand, if ∂ ² φ / ∂Z ² ≠ 0 due to the constraint of equation (1), the potential distribution in the radial direction is also relative to the acceleration direction (Z-axis direction) so as to cancel out this potential change. Need to change. And when ∂ ² φ / ∂ Z ² <0,
(1 / r) {∂ / ∂r (r∂φ / ∂r)} = − ∂ ² φ / ∂Z ² > 0 (3)
And the component in the radial direction r is always positive.
It is clear from the following formula that the force in the radial direction r acts in the central direction. That is, from the Laplace equation,
(1 / r) {∂ / ∂r (r∂φ / ∂r)} = c (> 0) (4)
Then, taking into account that ∂φ / ∂r = 0 at r = 0 from the symmetry of the system, the following equation (5) is obtained by integrating equation (4).
∂φ / ∂r = c'r (5)
Since the electric field in the radial direction is E (r) = − ∂φ / ∂r, equation (6) is obtained.
E (r) = − c′r (6)
This equation (6) shows that a force toward the center is applied in the radial direction. An equivalent expression can be obtained from approximation up to the second order of Expression (20) shown in Non-Patent Document 2.
As described above, the accelerating electric field at this time is an electric field in which a force that always pushes toward the central axis Z acts on ions existing at a position away from the central axis C1 in the radial direction r. Therefore, the ions accelerated by the accelerating electric field are converged in the X-axis direction, that is, the drift direction as a whole.

An ion trajectory simulation performed to confirm the ion focusing action will be described. 5A is a diagram showing an electrode model for ion orbit simulation, FIG. 5B is a diagram showing an on-axis potential distribution in the orthogonal acceleration portion of the orthogonal acceleration method TOFMS of the present embodiment, and FIG. It is a figure which shows the axial potential distribution in the orthogonal acceleration part of the conventional orthogonal acceleration type TOFMS. 6A is a diagram illustrating a simulation result of the ion trajectory in the orthogonal acceleration method TOFMS of the present embodiment, and FIG. 6B is a diagram illustrating a simulation result of the ion trajectory in the orthogonal acceleration unit of the conventional orthogonal acceleration method TOFMS. is there.
In addition, since the exact simulation in a grid electrode is complicated, in this simulation, the grid electrode is replaced by the boundary with no thickness only of the role which defines an equipotential surface. Therefore, the diverging lens action by the grid electrode is not considered.

As shown in FIG. 5A, in the simulation calculation, the acceleration electrode 13 is a five-stage cylindrical electrode, the entire length in the Z-axis direction is 0.1 [m], and the inner diameter is 0.05 [m]. It is. In the orthogonal acceleration type TOFMS of this embodiment, the voltages applied to the extrusion electrode 11, the extraction electrode 12, and the five-stage acceleration electrode 13 are 9100, 4900, 4900, 4116, 3136, 1764, and 0 [V], respectively. At this time, as shown in FIG. 5B, the axial potential distribution is ∂ ² φ / 加速 Z ² <0 over almost the entire acceleration region. On the other hand, in the conventional orthogonal acceleration type TOFMS to be compared, the voltages applied to the extrusion electrode 11, the extraction electrode 12, and the five-stage acceleration electrode 13 are 9100, 4900, 3920, 2940, 1960, 980, 0 [V, respectively. ]. At this time, the axial potential distribution is ∂ ² φ / ∂Z ² = 0 over almost the entire acceleration region. However, in any case, since no grid electrode is provided at the exit opening from the acceleration region, ∂ ² φ / ∂Z ² > 0 in the vicinity of the region.

In the simulation calculation, it is assumed that ions continuously enter a region between the extrusion electrode 11 and the extraction electrode 12 with a predetermined energy, and an initial packet width of 30 [mm] from an ion beam extending in the X-axis direction is assumed. The ion packet was cut out and accelerated after being extracted from the extraction region to the acceleration region.
Under the conventional voltage condition where the accelerating electric field is uniform, as shown in FIG. 6 (b), an ion packet with a width of 30 [mm] in the initial drift direction becomes large when flying 60 [cm]. You can see that it diverges. When ions diverge in this way, the ratio of ions that cannot reach the ion detection surface of the detector becomes considerably large, and thus a large sensitivity reduction cannot be avoided. In order to capture as many diverged ions as possible, a detector having a large ion detection surface is required, and the cost of the detector is greatly increased.

  On the other hand, as shown in FIG. 6 (a), in the orthogonal acceleration type TOFMS according to the present invention, an ion packet having a width of 30 [mm] in the initial drift direction has a width of 60 [cm] at the time of flight. It turns out that it is compressed to 20 [mm]. From this, it can be confirmed that ion focusing is effectively performed in the acceleration region. By making the converged ions enter the detector, the ions can efficiently reach the ion detection surface of the detector, which is very effective in improving sensitivity. In addition, since the ion detection surface of the detector is small, the cost of the detector can be suppressed.

  As is clear from the trajectory simulation results, when an accelerating voltage is applied to each accelerating electrode 13 so that the downward gradient gradually increases in the accelerating direction, the ion packets converged in the accelerating region enter the flying space 21. Since it is ejected, the amount of ions incident on the detector 3 is increased as compared with the case where such convergence is not performed. Thereby, highly sensitive measurement is possible. However, if convergence is performed in the acceleration region, naturally, the flight trajectory of many ions changes slightly, and the flight distance also changes accordingly. The change in the flight distance is initially larger for ions located farther from the central axis C1, and the width of the flight distance change amount for ions having the same mass-to-charge ratio causes a decrease in mass resolution. That is, the improvement in measurement sensitivity due to ion convergence as described above may cause a decrease in mass resolution.

  Therefore, the orthogonal acceleration type TOFMS of this embodiment does not always perform the ion convergence as described above, but improves the sensitivity by converging the ions according to the selection of the user when the measurement is particularly important. I try to figure it out. Therefore, in the orthogonal acceleration method TOFMS of the present embodiment, a high-sensitivity measurement mode and a high-resolution measurement mode are prepared as measurement modes, and in any measurement mode according to a user instruction via the input unit 9. Measurement is possible. In addition, when the analysis is automatically performed according to the method file in which the analysis conditions are set in advance, the measurement can be performed while automatically switching between the high sensitivity measurement mode and the high resolution measurement mode.

  In any case, the mode switching unit 81 in the control unit 8 instructs the orthogonal acceleration power supply unit 7 to select the measurement mode, and in the high sensitivity measurement mode, the orthogonal acceleration power supply unit 7 converges ions in the acceleration electric field as described above. A voltage (voltage in which the downward gradient gradually increases in the acceleration direction) is applied to each acceleration electrode 13, and in the high resolution measurement mode, the orthogonal acceleration power supply unit 7 does not converge ions in the acceleration electric field (downward in the acceleration direction). Is applied to each accelerating electrode 13. Thereby, in the high sensitivity measurement mode, a larger amount of ions reaches the detector 3 than in the high resolution measurement mode, so that high measurement sensitivity can be realized. On the other hand, in the high resolution measurement mode, although the amount of ions reaching the detector 3 is reduced as compared with the high sensitivity measurement mode, the flight distances of ions having the same mass-to-charge ratio are uniform, so that high resolution can be realized. .

  Since the degree of ion convergence varies depending on the axial potential distribution in the acceleration region, not only the switching of the measurement mode as described above, but also the axial potential distribution is appropriately determined according to the TOF analyzer 2 and the detector 3 to be used. The applied voltage may be set so as to be adjusted. Thereby, in the orthogonal acceleration TOFMS having various configurations, it is possible to ensure mass resolution and mass accuracy while increasing the measurement sensitivity as much as possible.

In the above embodiment, an electric field is formed such that the axial potential distribution φ is ∂ ² φ / ∂Z ² <0 in almost all the central axis C of the acceleration region. An electric field is formed such that the on-axis potential distribution φ is ∂ ² φ / ∂Z ² <0 at least in part, and the on-axis potential distribution φ is ∂ ² φ / ∂Z ² = 0 in other parts. May be an electric field. Of course, it is apparent from the above description that the ion focusing action in the acceleration region needs to exceed the ion divergence that occurs when the final stage of the acceleration region is not a grid electrode.

  Moreover, although the said Example introduced the ion produced | generated with the ion source 4 to the orthogonal acceleration part 1 through the ion guide 5, the ion discharged from the ion trap, the ion dissociated with the collision cell, etc. are orthogonal acceleration part. 1 may be introduced. Further, the orthogonal acceleration type TOFMS according to the present invention can be used in various apparatuses.

  For example, an LC-TOFMS apparatus can be obtained by connecting a liquid chromatograph to the front stage of the orthogonal acceleration type TOFMS, and a GC-TOFMS apparatus can be obtained by connecting a gas chromatograph to the front stage of the orthogonal acceleration type TOFMS. Can do. Further, a LC-IMS-TOFMS apparatus can be obtained by connecting a liquid chromatograph to the front stage of the orthogonal acceleration type TOFMS and providing an ion mobility meter between the ion source 4 and the orthogonal acceleration unit 1. Furthermore, a LC-Q-TOFMS apparatus is provided by connecting a liquid chromatograph to the front stage of the orthogonal acceleration type TOFMS and providing a quadrupole mass filter and a collision cell between the ion source 4 and the orthogonal acceleration unit 1. By connecting a gas chromatograph to the front stage of this orthogonal acceleration type TOFMS and providing a quadrupole mass filter and a collision cell between the ion source 4 and the orthogonal acceleration unit 1, GC-Q- It can be a TOFMS device.

  Furthermore, in the above embodiment, the TOF analyzer is a reflectron type TOF analyzer, but it goes without saying that a TOF analyzer having another configuration such as a linear type or a circular type (multi-turn type) may be used. It is.

  The above-described embodiments and the above-described various modifications are merely examples of the present invention, and appropriate changes, modifications, additions, etc. within the scope of the present invention are included in the scope of the claims of the present application. It is clear.

DESCRIPTION OF SYMBOLS 1 ... Orthogonal acceleration part 11 ... Extrusion electrode 12 ... Extraction electrode 13 ... Acceleration electrode 2 ... TOF analyzer 21 ... Flight space 22 ... Reflector 3 ... Detector 4 ... Ion source 5 ... Ion guide 6 ... Data processing part 7 ... Orthogonal Acceleration power supply unit 8 ... control unit 81 ... mode switching unit 9 ... input unit

Claims (3)

In the orthogonal acceleration type time-of-flight mass spectrometer having an orthogonal acceleration unit that accelerates the introduced ions in a direction orthogonal to the optical axis of the ion beam, the orthogonal acceleration unit includes:
a) an extrusion electrode arranged parallel to the optical axis of the ion beam;
b) an extraction electrode which is a grid electrode arranged opposite to the extrusion electrode across the ion beam;
c) a circle that forms an accelerating electric field for accelerating ions that have passed through the grid of the extraction electrode by an electric field formed between the extrusion electrode and the extraction electrode in a direction perpendicular to the optical axis of the ion beam; A plurality of accelerating electrodes that are annular or cylindrical;
d) An electric field in which the descending gradient of the potential distribution on the central axis of the plurality of acceleration electrodes gradually increases in the direction of ion travel to cause at least one of the acceleration electric fields to cause a convergence effect on the ions in a direction orthogonal to the acceleration direction. A voltage application unit configured to apply a voltage determined to be formed by a unit to each of the plurality of acceleration electrodes;
A time-of-flight mass spectrometer. The time-of-flight mass spectrometer according to claim 1,
In order to adjust the action of converging ions in the acceleration electric field in a direction orthogonal to the acceleration direction, the apparatus further includes a control unit that controls the voltage application unit so as to change a voltage applied to each of the plurality of acceleration electrodes. A time-of-flight mass spectrometer. The time-of-flight mass spectrometer according to claim 2,
A high-resolution measurement mode that prioritizes mass resolution and a high-sensitivity measurement mode that prioritizes sensitivity can be switched, and when the high-sensitivity measurement mode is designated, the control unit is arranged on the central axes of a plurality of acceleration electrodes. When a voltage is applied to each of the plurality of accelerating electrodes such that an electric field in which the descending slope of the potential distribution gradually increases in the ion traveling direction is formed in at least a part of the accelerating electric field, and a high resolution measurement mode is designated, A time-of-flight mass spectrometer characterized in that a voltage that produces an electric field with a uniform potential gradient of the potential distribution is applied to each of a plurality of acceleration electrodes.

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