JP4259371B2 - Time-of-flight mass spectrometer - Google Patents

Description

  The present invention relates to a time-of-flight mass spectrometer having a reflectron for reflecting ions.

  In a time-of-flight mass spectrometer, ions generated by an ion source are accelerated by a predetermined acceleration voltage and fly in a non-electric field space of a predetermined length called a flight tube. The time for flying this predetermined distance varies depending on the initial velocity of ions, and this initial velocity depends on the mass number (mass / charge number) of ions. That is, the smaller the mass number, the larger the initial velocity obtained with the same acceleration voltage, and the larger the mass number, the smaller the initial velocity obtained with the same acceleration voltage. Therefore, the mass spectrum of ions generated in the ion source can be obtained by continuously measuring the ion detection amount with an ion detector provided at the end of the flight tube.

  In practice, however, each ion has a different initial kinetic energy when it is generated by the ion source, so that even the ions having the same mass number have variations in flight time.

  In order to solve such problems, a mass spectrometer has been developed in which a reflectron that reflects ions is provided at the end of a flight tube to compensate for differences in initial energy of ions having the same mass number.

  An example of a time-of-flight mass spectrometer having a reflectron is shown in FIG. Ions generated in the ion source 11 are given kinetic energy by a predetermined acceleration voltage in the accelerator 12 and introduced into the flight tube 13. The ions enter the reflectron 14 after flying through the non-electric field drift space in the flight tube 13. A gradient electric field is formed inside the reflectron 14, and ions are reflected in a direction slightly inclined from the incident direction by the gradient electric field, and return to the flight tube 13 to be detected by the ion detector 15.

  Here, even if the ions have the same mass number, ions having a large initial energy enter deep into the reflectron 14, and thus the flight time in the reflectron 14 becomes long. On the other hand, even with the same mass number, ions having a small initial energy enter only to the vicinity of the entrance of the reflectron 14, so that the flight time in the reflectron 14 is shortened. Therefore, by appropriately setting the gradient electric field in the reflectron 14, it is possible to set so that ions of the same mass number can reach the detector 15 at the same time by compensating for the difference in these initial energies.

  As shown in FIG. 2A, the reflectron 14 generally has a structure in which a large number of electrode plates (ion lenses) 21 are arranged along the ion traveling direction. As shown in FIG. 2 (b), a hole 22 through which ions pass is provided at the center of each ion lens 21, and by applying a slightly different voltage to each ion lens 21, a number of ion lenses can be obtained. A gradient electric field that repels incoming ions is formed inside the reflection space formed by the envelope surface of the edge of the center hole 22 of 21.

JP 2003-151487 A

As shown in FIG. 2 (a), the reflectron 14 includes a rod 24 implanted in an adapter 23 fixed to a flight tube of a time-of-flight mass spectrometer, and a large number of ion lenses 21 via insulating spacers 25. Have a configuration arranged. The ion lens 21 and the spacer 25 are tightened by a nut 27 via a back plate 26 at the end.
Since each ion lens 21 is a thin metal plate having a center hole 22, it is relatively light weight. However, it is arranged in a large number such as several tens, and is supported at the end of the flight tube 28 in a cantilever manner. Since the spacer 25 is interposed between the ion lenses 21 and the whole is relatively long, when the time-of-flight mass spectrometer is installed horizontally, as shown in FIG. 3, deflection occurs due to gravity at the end. As a result, the electric field distribution inside the reflectron deviates from the design value, which has a problem of adversely affecting the ion resolution of the mass spectrometer.

  The present invention has been made to solve such problems, and the object of the present invention is to provide a resolution due to the influence of gravity in a time-of-flight mass spectrometer having a reflectron held substantially horizontally. It is to solve the problem of decrease in the number.

The present invention was made in order to solve the above described problems is the time-of-flight mass spectrometer equipped with a reflectron having the structure held in a substantially horizontal direction a plurality of ion lens by cantilevered rods, each ion lens gravity In order to compensate for the downward displacement from the axis perpendicular to the fixed end, the center of each ion lens is mounted so as to be displaced upward with respect to the rod .

Here, the “gravity state” means a state where there is no gravity acting on the reflectron when the reflectron is held in a substantially horizontal direction, and “upward” means a state where the reflectron is held in a substantially horizontal direction. The direction above the reflectron.
The downward displacement due to the gravity of each ion lens is such that the center axis of each ion lens is aligned with the axis perpendicular to the fixed end, and the reflectron is actually assembled and held horizontally to move below each ion lens. Can be obtained by actually measuring the displacement.

各イオンレンズにおける下方への変位の量も、同様の計算から求めることができる。 Further, the entire reflectron can be regarded as a cantilever beam with a distributed load, and can also be obtained by calculation of structural mechanics. That is, if the total length of the reflectron is L, the distributed load by the ion lens is w, the concentrated load by the back plate at the free end is W, the elastic modulus of the rod is E, and the secondary moment of inertia of the rod is I, the deflection at the free end The quantity y _max can be obtained from equation (1).

The amount of downward displacement in each ion lens can also be obtained from the same calculation.

  When assembling the reflectron, support each ion lens from the bottom and keep the ion lens upward by a distance corresponding to the gravitational displacement of each ion lens obtained as described above in a state where gravity does not work (non-gravity state). And fix the position with a rod.

  When assembling the reflectron, it is troublesome to displace a large number of ion lenses individually by a predetermined distance. Therefore, it is possible to easily assemble the reflectron according to the present invention by preparing an assembly jig having a shape corresponding to those displacements, placing each ion lens on the jig and fastening with a rod. become able to.

  In the time-of-flight mass spectrometer according to the present invention, each ion lens of the reflectron is assembled so as to compensate for the deflection caused by gravity (self-weight) generated when the reflectron is installed substantially horizontally. Yes. For this reason, when the reflectron is actually held in a cantilevered manner, each ion lens constituting the reflectron hangs down due to gravity (self-weight), and as a result, is held in an accurate position with respect to the ion travel axis. Become so. Thereby, in the time-of-flight mass spectrometer having such a horizontal holding reflectron, an intended resolution can be obtained.

  A reflective time-of-flight mass spectrometer that is an embodiment of the present invention will be described. The basic structure of the reflection-type time-of-flight mass spectrometer of this embodiment is the same as that of the conventional one shown in FIG. 1, and the reflectron 14 is located at the end opposite to the ion source toward the ion detector 15. It is installed with a slight inclination.

  The basic configuration of the reflectron 14 used in the reflective time-of-flight mass spectrometer of the present embodiment is almost the same as the conventional apparatus shown in FIG. That is, four rods 24 are implanted in the adapter 23 fixed to the end of the flight tube 28 of the time-of-flight mass spectrometer, and the ion lenses 21 and the insulating spacers 25 are alternately inserted into the rods 24. A back plate 26 made of an insulating plate is inserted into and tightened with a nut 27. However, here, if the centers of the center holes 22 of all the ion lenses 21 are fixed in alignment with the axis c perpendicular to the adapter 23, the back plate 26 side is caused by the weight of the ion lens 21 and the like as shown in FIG. The center of each ion lens 21 is displaced downward from the axis c on the end (free end) side.

  Therefore, in the reflectron 30 used in the reflection type time-of-flight mass spectrometer of the present embodiment, the ion lens 31 is displaced and fixed upward so as to compensate in advance for such downward displacement. Specifically, it is convenient to use an ion lens fixing jig 32 as shown in FIG. The upper surface of the jig 32 is raised by an amount by which each ion lens 31 should be displaced upward toward the free end. By laying the jig 32 underneath and inserting the ion lens 31 and the spacer 33 sequentially into the rod 34 so that the ion lens 31 is placed thereon, each ion lens 31 is automatically moved upward by a predetermined distance. It is displaced to. The state in which the ion lens 31 is placed on the upper surface of the jig 32 in this way is the above “gravity-free state”.

  Since the upward displacement amount of each ion lens 31 is different for each ion lens 31, as shown in FIG. 5, the rod hole 35 of all the ion lenses has a length obtained by adding the maximum upward displacement amount ymax to the rod diameter d, or It is convenient to make it a long hole slightly longer than that. Instead of such a long hole, it may be a circular hole having a diameter slightly larger than d + ymax. Alternatively, the rod holes of the individual ion lenses may be a set of ion lenses provided by gradually shifting downward from the adapter 36 side to the back plate 37 side.

After all the ion lenses 31 have been inserted, the back plate 37 is inserted, and the back plate 37 is tightened with the nut 38 while pulling the rod 34 with a predetermined force. Thereafter, when the tensile force of the rod 34 is released, the ion lens 31 and the spacer 33 are firmly fixed.
Thereafter, when the jig 32 is removed, as shown in FIG. 6, each ion lens is displaced downward by a predetermined amount due to its own weight, and the center of the center hole 39 of each ion lens is placed on the axis c. As a result, the electric field inside the reflectron has an intended shape, and high-resolution mass spectrometry can be performed.

The schematic block diagram of a reflection type time-of-flight mass spectrometer. The side view (a) of the reflectron used with a reflection type time-of-flight mass spectrometer, and the top view (b) of an ion lens. The side view showing the mode of a deflection | deviation at the time of installing a reflectron in the cantilever and horizontal. The side view showing a mode that a reflectron is assembled using the jig for ion lens fixation. The top view of the ion lens by which the rod hole was made into the long hole. The side view showing a mode at the time of fixing a reflectron horizontally to the edge of a flight tube.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Ion source 12 ... Accelerator 13, 28 ... Flight tube 14, 30 ... Reflectron 15 ... Detector 21, 31 ... Ion lens 22, 39 ... Center hole 23, 36 ... Adapter 24, 34 ... Rod 25, 33 ... Spacer 26 ... Back plates 27, 38 ... Nuts 32 ... Ion lens fixing jig 35 ... Rod hole 37 ... Back plate

Claims (4)

In a time-of-flight mass spectrometer equipped with a reflectron having a configuration in which a plurality of ion lenses are held in a substantially horizontal direction by cantilever rods , downward from an axis perpendicular to the fixed end of each ion lens by gravity A time-of-flight mass spectrometer, wherein the center of each ion lens is mounted so as to be displaced upward with respect to the rod in order to compensate for the displacement .   In a method of manufacturing a time-of-flight mass spectrometer equipped with a reflectron having a configuration in which a plurality of ion lenses are held in a substantially horizontal direction by cantilever rods, the gravity lens is separated from an axis perpendicular to the fixed end of each ion lens A method of manufacturing a time-of-flight mass spectrometer, characterized in that the center of each ion lens is displaced upward relative to the rod in order to compensate for downward displacement. 2. The time-of-flight mass spectrometer according to claim 1, wherein the vertical dimension of the hole for penetrating the rod provided in the ion lens is a length obtained by adding the maximum upward displacement to the rod diameter . Have a shape corresponding to the upward displacement of the ion lens of claim 2, for mounting by displacing the ion lens upward in the manufacturing method of the time-of-flight mass spectrometer according to claim 2 Reflectron assembly jig for time-of-flight mass spectrometer used .

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