Time-of-flight mass spectrometer

Abstract

A metallic plate holder 3 is directly placed on a flat bottom plate 1a of a sample chamber. A linear guide 21 extending in x-direction is located below the bottom plate. Another linear guide 22 extending in y-direction is fixed to a movable part 21a of the linear guide 21. A magnet 23, fixed to a movable part 22a of the linear guide 22, magnetically attracts the plate holder across the bottom plate. When the magnet is two-dimensionally driven by the linear guides, the plate holder follows it and moves two-dimensionally. The flat bottom plate limits the z-position of the plate holder, thereby reducing the fluctuation in the level of the sample on a sample plate 2 due to the movement. Thus, the variation in the level at different positions on the sample plate is reduced, so that the number of times of a calibrant measurement can be decreased.

Claims

1. A time-of-flight mass spectrometer comprising: a base plate having a flat obverse surface on which a sample plate made of a metallic material or a plate holder which is made of a metallic material and configured to hold the sample plate is to be placed; an orthogonal driver located on a reverse side of the base plate, the orthogonal driver being capable of transferring a moving part in two axial directions orthogonal to each other in a plane substantially parallel to the obverse surface of the base plate; and a magnet integrally formed in or attached to the movable part, for attracting, across the base plate, the sample plate or the plate holder, wherein: ions are generated from a sample provided on the sample plate by irradiating the sample with a laser beam or particle beam; the ions are accelerated and introduced into a flight space to separate from each other according to mass-to-charge ratios of the ions within the flight space and to individually detect the ions; and a reverse surface of the sample plate or the plate holder has a planar surface slidable on the obverse surface while keeping in direct contact with the obverse surface.

2. The time-of-flight mass spectrometer according to claim 1, wherein: the base plate is a bottom plate of a sample chamber in which a sample is to be contained.

3. A time-of-flight mass spectrometer configured to generate ions from a sample held by a sample holder by irradiating the sample with a laser beam or particle beam, as well as accelerate and introduce the generated ions into a flight space to separate the ions from each other according to mass-to-charge ratios of the ions within the flight space and individually detect the ions, the time-of-flight mass spectrometer comprising: a) a base plate having a flat obverse surface; b) a first driver for pushing and pulling a side surface of the sample holder placed on the obverse surface of the base plate in one direction in a plane substantially parallel to the obverse surface of the base plate; and c) a second driver for pushing and pulling a side surface of the sample holder placed on the obverse surface of the base plate, in a direction which is orthogonal to the direction in which the first driver pushes and pulls the side surface of the sample holder in the plane substantially parallel to the obverse surface of the base plate.

4. The time-of-flight mass spectrometer according to claim 3, wherein: the base plate is a bottom plate of a sample chamber in which a sample is to be contained.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic configuration diagram of a MALDI-TOFMS as one embodiment of the present invention.

(2) FIGS. 2A-2C are schematic configuration diagrams of a plate-holder drive mechanism in the MALDI-TOFMS according to the present embodiment, where FIG. 2A is a front view, FIG. 2B is a side view, and FIG. 2C is a top view.

(3) FIGS. 3A-3C are schematic configuration diagrams of a plate-holder drive mechanism in an MALDI-TOFMS according to another embodiment of the present invention, where FIG. 3A is a front view, FIG. 33 is a side view, and FIG. 3C is a top view.

(4) FIG. 4 is a top view showing a schematic configuration of a modified example of the drive mechanism shown in FIGS. 3A-3C.

(5) FIGS. 5A-5C are schematic configuration diagrams of a plate-holder drive mechanism in a conventional MALDI-TOFMS, where FIG. 5A is a front view, FIG. 5B is a side view, and FIG. 5C is a top view.

(6) FIG. 6 is a chart showing the result of a measurement of the amount of change in the level of the sample plate at each position of the sample wells arrayed in one direction on the sample plate in a conventional MALDI-TOFMS.

DESCRIPTION OF EMBODIMENTS

(7) A MALDI-TOFMS as one embodiment of the present invention is hereinafter described with reference to the attached drawings. FIG. 1 is a schematic configuration diagram of the MALDI-TOFMS according to the present embodiment. FIGS. 2A-2C are schematic configuration diagrams of a plate-holder drive mechanism in the MALDI-TOFMS according to the present embodiment. Similar to FIGS. 5A-5C, FIG. 2A is a front view, FIG. 2B is a side view, and FIG. 2C is a top view.

(8) As shown in FIG. 1, a sample plate 2, which is a flat metallic plate, is attached to a plate holder 3 made of a metallic material. This holder is directly placed on a bottom plate 1a within a sample chamber 1. An X-Y drive mechanism 20 for two-dimensionally driving the plate holder 3 on the bottom plate 1.a is located below the sample chamber 1. A vacuum chamber 10 communicating with the inside of the sample chamber 1 is located above the sample chamber 1. The vacuum chamber 10 contains an extraction electrode 11, acceleration electrode 12, reflecting mirror 14, flight tube 15 and detector 16 vertically arranged from the bottom end. A laser irradiation unit 13 is provided on the outside of a window 10a formed in the vacuum chamber 10.

(9) When a measurement is performed, a pulsed laser beam is emitted from the laser irradiation unit 13. After passing through the window 10a and being reflected by the reflecting mirror 14, the laser beam falls onto one of the samples on the sample plate 2 which is set at a predetermined laser irradiation point, whereby the components contained in the sample are ionized. The laser irradiation point is fixed, whereas the position of the sample plate 2 can be changed by appropriately driving the plate holder 3 through the X-Y drive mechanism 20. Thus, a sample at any position on the sample plate 2 can be irradiated with the laser beam to perform the measurement.

(10) Predetermined voltages are respectively applied from a voltage generator (not shown) to the extraction electrode 11 and the acceleration electrode 12 located above the sample plate 2. Another predetermined voltage is also applied to the sample plate 2 via the plate holder 3. Due to the electric field created between the extraction electrode 11 and the sample, the ions generated from the sample irradiated with the laser beam in the previously described manner are extracted upward from an area near the site at which the ions have been generated. The extracted ions receive acceleration energy from the accelerating electric field created by the acceleration electrode 12. Thus, the ions begin to fly upward (in the z-axis direction). After flying through the field-free flight space formed within the flight tube 15, the ions reach the detector 16. Within the flight space, an ion having a smaller mass-to-charge ratio has a higher flight speed. Therefore, the various kinds of ions which have almost simultaneously begun to fly will sequentially reach the detector 16 in ascending order of mass-to-charge ratio. The detector 16 produces a detection signal according to the amount of incident ions.

(11) The MALDI-TOFMS in the present embodiment is a linear TOFMS in which ions are made to fly linearly. Understandably, the present invention may also be applied in a reflectron TOFMS including a reflectron for reversing the flight path of the ions, or a multiturn TOFMS in which ions are made to repeatedly fly in a loop path.

(12) A detailed description is hereinafter given of the X-Y drive mechanism 20 used in the MALDI-TOFMS according to the present embodiment to two-dimensionally drive the plate holder 3 which corresponds to the sample holder in the present invention.

(13) As already described, the plate holder 3 is placed on the flat bottom plate 1a which corresponds to the base plate in the present invention. This bottom plate is made of a material that is insusceptible to magnetic force, such as non-magnetic stainless steel. Its upper surface should preferably have a high degree of flatness as well as a high degree of smoothness. To this end, the upper surface of the bottom plate 1a may be finished by an appropriate surface-machining or surface-treating process.

(14) As shown in FIGS. 2A and 2B, the X-Y drive mechanism 20 includes two linear guides 21 and 22, which are similar to the linear guides 51 and 52 in the conventional device shown in FIGS. 5A-5C, as the elements corresponding to the orthogonal driver in the present invention. That is to say, the first linear guide 21 extending in the x-axis direction is fixed to a bottom plate of the casing (not shown) of the X-Y drive mechanism 20, while the second linear guide 22 extending in the y-axis direction is fixed to the movable part 21a of the first linear guide 21. A magnet 23 is fixed to the movable part 22a of the second linear guide 22. The upper surface of the magnet 23 is substantially in contact with the lower surface of the bottom plate 1a or in close proximity to the latter surface with a slight gap in between. The movable parts 21a and 22a of the two linear guides 21 and 22 can be driven in the x-axis and y-axis directions, respectively, by the power of a motor or similar driving device (not shown). With such a mechanism, the magnet 23 can be transferred to a desired two-dimensional position in a substantially horizontal plane (i.e. the plane of the x-axis and the y-axis) underneath the bottom plate 1a.

(15) The magnetic force of the magnet 23 penetrates the bottom plate 1a and reaches the plate holder 3 which is placed above the magnet. When the magnet 23 is two-dimensionally transferred to a desired position in the substantially horizontal plane in the previously described manner, the plate holder 3, being attracted by the magnet 23, follows the magnet 23 and changes its two-dimensional position on the bottom plate 1a. During the two-dimensional movement of the magnet 23, the width of the gap between the upper surface of the magnet 23 and the lower surface of the bottom plate 1a may possibly change to a certain extent. However, this does not hinder the sliding movement of the plate holder 3 on the bottom plate 1a as long as the plate holder 3 is within reach of the magnetic force of the magnet 23. This means that the entire upper surface of the bottom plate 1a functions as a guide which limits the position of the lower surface of the plate holder 3 in the z-axis direction during the two-dimensional movement of the same holder. Therefore, if the upper surface of the bottom plate 1a is extremely flat, the change in the position of the plate holder 3 in the z-axis direction during its movement will be extremely small. Thus, as compared to a conventional device, the present device will dramatically reduce the change in the level of the sample on the sample plate 2 at the laser irradiation point.

(16) In the MALDI-TOFMS according to the present embodiment, the magnet 23 does not need to be a permanent magnet; it may also be an electromagnet. It is also possible to directly drive the sample plate 2 by magnetic force without using the plate holder 3. A sample stage consisting of a simple metallic plate on which a sample can be placed may be used in place of the plate holder 3 for holding the sample plate 2.

(17) Hereinafter, a plate-holder drive mechanism in a MALDI-TOFMS according to another (second) embodiment of the present invention is described. FIGS. 3A-3C are schematic configuration diagrams of the present drive mechanism. Similar to FIGS. 2A-2C, FIG. 3A is a front view, FIG. 3B is a side view, and FIG. 3C is a top view. The same components as shown in FIGS. 2A-2C are denoted by the same reference signs.

(18) Unlike the drive mechanism in the previous embodiment in which a magnet is used to two-dimensionally drive the plate holder 3 in a contactless manner, the drive mechanism in the present embodiment is configured to two-dimensionally drive the plate holder 3 on the bottom plate 1a by means of two pairs of arms which are arranged so that the plate holder 3 is sandwiched between each pair of arms. More specifically, as shown in FIGS. 3A-3C, the plate holder 3 is sandwiched between two arms 31a and 31b extending in the y-axis direction as well as between two arms 33a and 33b extending in the x-axis direction. The pair of arms 31a and 31b can be driven by an x-directional driver 32 in the x-axis direction without changing their distance. Similarly, the other pair of arms 33a and 33b can be driven by a y-directional driver 34 in the y-axis direction without changing their distance. For example, when the pair of arms 31a and 31h are driven leftward in FIG. 3A, the arm 31b pushes the right side of the plate holder 3, making the plate holder 3 slide leftward on the bottom plate 1a.

(19) With the x-directional driver 32 and the y-directional driver 34, the present mechanism allows the first pair of arms 31a and 31b and the second pair of arms 33a and 33h to be independently driven so as to transfer the plate holder 3 to a desired position on the bottom plate 1a. As in the previous embodiment, the entire upper surface of the bottom plate 1a functions as a guide which limits the position of the lower surface of the plate holder 3 in the z-axis direction during the two-dimensional movement of the same holder. Therefore, if the upper surface of the bottom plate 1a is extremely flat, the change in the position of the plate holder 3 in the z-axis direction during its movement will be extremely small, and the fluctuation in the level of the sample depending on the position on the sample plate 2 will also be reduced.

(20) In the example of FIGS. 3A-3C, the transfer of the plate holder 3 is achieved by pushing the circumferential surface (side surface) of the plate holder 3 from behind with one of the arms 31a, 31b, 33a and 33b. FIG. 4 shows a modified example, in which two arms 41 and 43, each of which has a gripping part for holding the plate holder 3, are respectively driven by the x-directional driver 42 and the y-directional driver 44. It is evident that any mechanism configured to drive the plate holder 3 on the bottom plate 1a by pushing or pulling it from its circumferential surface (side surface) can produce the same effects as described in the previous embodiment.

(21) In any of the previous embodiments, the bottom plate 1a is horizontally set. It is evident that this plate does not always need to be horizontal but may be inclined or vertically set. In the case where the bottom plate 1a in the second embodiment is vertically set, the plate holder 3 needs to be prevented from falling off the bottom plate 1a. This can be achieved, for example, by magnetically attracting the plate holder 3 onto the bottom plate 1a.

(22) The previous embodiment is an application of the present invention in a MALDI-TOFMS, It is evident that the present invention is generally applicable in any type of time-of-flight mass spectrometer including an ion source in which the components in a sample formed on a sample plate 2 or placed on a sample stage are ionized by irradiating the sample with a laser beam or any other kind of thin particle beam, such as an ion beam, electron beam or neutral atomic beam. Examples of such an ion source include SALDI, SIMS, DIOS, ELM and FAB.

(23) It should be noted that the previously described embodiments are mere examples of the present invention, and any change, modification or addition appropriately made within the spirit of the present invention will evidently fall within the scope of claims of the present application.

REFERENCE SIGNS LIST

(24) 1 . . . Sample Chamber 1a . . . Bottom Plate 2 . . . Sample Plate 3 . . . Plate Holder 10 . . . Vacuum Chamber 10a . . . Window 11 . . . Extraction Electrode 12 . . . Acceleration Electrode 13 . . . Laser irradiation Unit 14 . . . Reflecting Mirror 15 . . . Flight Tube 16 . . . Detector 20 . . . X-Y Drive Mechanism 21, 22 . . . Linear Guide 21a, 22a . . . Movable Part 23 . . . Magnet 31a, 31b, 33a, 33b, 41, 43 . . . Arm 32, 42 . . . x-Directional Driver 34, 44 . . . y-Directional Driver