JP2000036286A - Time-of-flight mass spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the convergence property relative to spatial expansion of ions in an ion reservoir in the optical axis direction, even in the case of using a triple-convergence spectral system, and to improve the ion yield. SOLUTION: An ion beam emitted from an outside ion source 1 is regulated by a beam regulation slit 2 and introduced into an ion reservoir 3, and expanded in the ion reservoir 3 in the optical axis direction (z-axis direction) with a range of r0. The ion beam in the ion reservoir 3 is pushed out in the optical axis direction by a voltage pulse V2 in this state. The expansion of the pushed- out ion beam is once time-focused on certain point (or a line) by a two-stage acceleration part 9, and a lag (aberration) of a flight time produced by the expansion of the ion beam is cancelled. Afterwards, the time-focused ion beam is space-focused by a triple-convergence TOFMS spectral part 7 in two directions (x, y-axis) directions) rectangular with the optical axis direction, and eventually space focusing in the x, y, z-axis direction is attained. Hereby, an ion yield of a time-of-flight mass spectrometer is improved and a resolution is raised.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of generating ions from a sample and accelerating the ions, thereby separating the ions of the sample into ions having a large mass and ions having a small mass and introducing the ions into an ion detector. And belongs to the technical field of a time-of-flight mass spectrometer that performs mass spectrometry of a sample. In particular, by combining a triple focusing spectroscopy system and a two-stage acceleration system, a high sensitivity and high resolution time-of-flight mass spectrometer is provided. It belongs to the technical field.

[0002]

2. Description of the Related Art Conventionally, as a mass spectrometer, ions generated from a sample are accelerated so that ions of the sample are separated into large ions and small ions and introduced into a mass spectrometer. A time-of-flight mass spectrometer (TOFMS) for mass spectrometry has been proposed. This time-of-flight mass spectrometer utilizes the fact that when the same kinetic energy is given to ions, the smaller the mass-to-charge ratio (M: mass number) of the ions, the sooner they reach the ion detector.

[0003] As such a time-of-flight mass spectrometer,
Conventionally, a vertical acceleration time-of-flight mass spectrometer (Orthogonal Accel
eration TOFMS (OA / TOF) has been proposed.

FIG. 4 is a diagram schematically showing an example of the OA / TOF. In the figure, 1 is an external ion source, 2 denotes a beam regulation slit, the ion reservoir length y ₀ 3, the ion extrusion plate 4, 5 first grid, the 6 second grid, 7 TOFM
The S spectroscopy unit 8 is an ion detector.

The external ion source 1 to which the voltage V ₁ is applied
Are introduced into the ion reservoir 3 through the ion regulating slit 2 with kinetic energy (eV ₁ ). And
With these ions filling the ion reservoir 3 of length y ₀ ,
A high-voltage pulse voltage (amplitude voltage = V) is applied to the ion extrusion plate 4.
_{When 2} ) is applied, the ions in the ion reservoir 3 are accelerated by the kinetic energy (eV ₂ ) in the direction perpendicular to the flight direction of the ions in the ion reservoir 3 (the direction of the optical axis of TOFMS) and ejected from the ion reservoir 3. You. Further, the ions discharged from the ion reservoir 3 enter the TOFMS spectroscopy unit 7 through the first and second grids 5 and 6, and fly through the TOFMS spectroscopy unit 7, and then reach the ion detector 8. It is supposed to.

[0006]

By the way, such a problem is solved.
In OA / TOF is, the larger the value of the mass number M of the ion, to lower the yield of ions, as directed to those mass detection ions is large, the length y ₀ is longer ion reservoir 3 Is required. The reason is as follows. The mass number of the ion is M, and the kinetic energy is U (= e
V), the flight velocity v of the ion is

[0007]

(Equation 2)

[0008] Also, this ion has a distance y
The flight time t _ion when flying is

[0009]

(Equation 3)

[0010] As an example, the flight speed v ₁ of an ion in which the voltage applied to the external ion source 1 is V ₁ = 20 volts and the mass number of the ions is M = 500 is obtained from Equation 1 as v ₁ = 2.78 × 10 ³ m / s. In addition, the length y ₀ of the ion reservoir 3 is generally several cm. If the length is now y ₀ = 3 cm, the ion retention time of ions flying in the ion reservoir 3 is given by , T _ion
= 10.8 μs. On the other hand, ion extrusion plate 4 at an accelerated by the kinetic energy of the ions ejected from the ion reservoir 3 (U ₂₎ is _{U 2 = 3000eV (V 2 =} 3000
V) If the maximum ion mass number is M = 1000 and the flight distance of the TOFMS spectroscopic unit 7 is 1 m, the ion flight time in the TOFMS spectroscopic unit 7 is t _ion = 41.6 μs from Equation 3. That is, the ion yield is about 26% (10.6 ÷).
41.6 × 100). Therefore, as the mass number M of the ions increases, the yield of the ions decreases.
The ion reservoir 3 having a longer length y ₀ is required.

However, when the length y ₀ of the ion reservoir 3 is increased, not only the ion reservoir 3 becomes large, but also the TOFM
The advantages of S such as simultaneous detection and broad mass range are lost. For this reason, the length y ₀ of the ion reservoir 3 is limited, and when the mass number M of the ions is large, the improvement of the ion yield is also limited.

On the other hand, the kinetic energy of ions generated by the continuous ionization method is substantially constant without depending on the mass number (M) of the ions. When this continuous ionization method is used, ions discharged from the ion reservoir 3 are subjected to TOFM as shown in FIG.
The S spectroscope 7 flies at an angle θ with respect to the optical axis. When the kinetic energy of the ions accelerated by the voltage V ₁ is U ₁ and the kinetic energy of the ions accelerated by the voltage V ₂ is U ₂ ,

[0013]

(Equation 4)

Is given by For example, U ₁ (= eV ₁ ) =
Assuming that 20 eV and U ₂ (= eV ₂ ) = 3000 eV, ions fly in the TOFMS spectroscopy unit 7 at an angle of θ = 0.08 radian. At this time, the ions reach a position 8 cm away from the optical axis of the TOFMS spectroscopy unit 7.

For this reason, the flight trajectory of the ions in the TOFMS spectroscopic section 7 is greatly different, and after the ions have flown 1 m,
Each ion of M = 10 and M = 500 is TOFM
Since the light arrives at the centers 2.8 cm and 20 cm away from the optical axis of S, a flight time shift (aberration) occurs, which deteriorates the time convergence, and lowers the resolution and sensitivity of the obtained spectrum.

As means for solving this problem,
Conventionally, a triple focusing spectroscopy system using a fan-shaped electric or magnetic field has already been known. This triple focusing spectroscopy system has the simultaneous convergence of three terms of space, emission angle and energy with respect to time.

FIG. 5 is a diagram showing coordinate axes taken by such a triple focusing spectral system.

In this triple convergent spectroscopy system, as shown in FIG. 5, a plane perpendicular to the optical axis (z-axis) of the TOFMS spectroscopy unit 7 (a plane composed of the x-axis and the y-axis). It converges on the spread. In other words, this 3
The double focusing spectroscopy has no convergence for the spatial spread of ions in the optical axis direction (z-axis direction) in the ion reservoir 3. Therefore, the resolution and sensitivity of the obtained spectrum are reduced.

The present invention has been made in view of such circumstances, and has as its object to reduce the spatial spread of ions in the direction of the optical axis in an ion reservoir even when a triple focusing spectroscopy system is used. An object of the present invention is to provide a time-of-flight mass spectrometer having convergence and capable of improving the ion yield.

[0020]

According to a first aspect of the present invention, there is provided an ion source for emitting ions, and an ion source for introducing the ions and for accelerating and releasing the ions. A reservoir, a two-stage accelerating unit for accelerating ions from the ion reservoir to converge the spatial spread of the ions in the direction of the optical axis in the ion reservoir, and
A triple convergence spectrometer for simultaneously converging the space in the direction orthogonal to the optical axis direction, the emission angle of ions and the energy of ions, and an ion detector for detecting ions from the triple convergence spectrometer. It is characterized by.

Further, in the invention according to claim 2, a first grid is provided in an ion emitting portion of the ion reservoir, and a second grid is provided in an ion introducing portion of the two-stage accelerator. The distance α from the second grid to the spatial convergence point in the two-stage acceleration unit is 2s ₀ for the width of the ion reservoir, d for the distance between the first grid and the second grid, and the acceleration voltage of ions in the ion reservoir. Is V _a , and the acceleration voltage of ions in the two-stage acceleration unit is V _b ,

[0022]

(Equation 5)

It is characterized by being set to:
Further, the invention according to claim 3 is characterized in that the triple convergence spectroscopy unit comprises a predetermined number of cylindrical electric fields.

[0024]

In the time-of-flight mass spectrometer of the present invention having the above-described structure, the spread of the ion beam in the ion reservoir in the optical axis direction (z-axis direction) is at a point (line) due to the two-stage acceleration unit. ) Above. Thereby, the deviation (aberration) of the flight time caused by the spread of the ion beam in the ion reservoir is eliminated.

The time-focused ion beam is spatially converged in two directions (x, y-axis directions) orthogonal to the optical axis by the triple focusing spectroscope, and finally in two directions orthogonal to the optical axis. (X, y axis direction) and optical axis direction (z axis direction)
Spatial convergence in the directions (x, y, z axis directions) is achieved. This improves the ion yield of the time-of-flight mass spectrometer,
Higher resolution. In particular, by using a predetermined number of cylindrical electric fields in the triple focusing spectroscopy system, an ion beam that is long in the longitudinal direction (y-axis direction) of the ion reservoir can be triple focused.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically illustrating an example of an embodiment of a time-of-flight mass spectrometer according to the present invention.
The same components as those shown in FIG.
The detailed description thereof will be omitted by giving the same reference numerals.

In the OA / TOF shown in FIG.
TOFMS so that the entrance of the S spectroscopy unit 7 is on the second grid 6
Although the spectroscopy unit 7 is installed, as shown in FIG. 1, in the time-of-flight mass spectrometer of this example, the TOFMS spectroscopy unit 7 is used.
Is installed such that its entrance is separated from the second grid 6 by a predetermined distance α. And these second grids 6
A predetermined voltage _VL is applied between the TOFMS spectroscopy unit 7 and.

When the predetermined distance α is reached, the ions having a spatial expanse which are simultaneously emitted from the ion reservoir 3 arrive at the same time on the same line at the entrance of the TOFMS spectroscopic section 7, that is, the ions from the ion reservoir 3 It is set to converge spatially. Therefore, at the entrance of the TOFMS spectroscopy unit 7, a spatial convergence point D of ions is set. The predetermined distance α is a distance d between the first and second grids 5 and 6, a width of the ion reservoir 3 is 2s ₀ , and a distance from the center position of the ion beam in the ion reservoir 3 to the first grid 5. Is s ₀ ,

[0029]

(Equation 6)

Is given by FIG. 2 is a diagram showing an example of the spatial convergence of ions obtained by the ion trajectory calculation program (SIMION) using Expression 6.
“·” Indicates the same time. As is apparent from FIG. 2, when the predetermined distance α is set by Expression 6, the ions having a spatial spread and emitted from the ion reservoir 3 at the same time at the space convergence point D on the same line at the same time. It can be seen that it reaches.

FIG. 3 is a plan view showing a (x, z) plane of a spectral system using a cylindrical electric field, which constitutes a triple focusing TOFMS spectral unit of the time-of-flight mass spectrometer of this example. As shown in FIG. 3, the triple convergence TOFMS spectral portion 7 in this example, at a rotation angle of the electric field phi _e, with two cylindrical electric field 9, 10 turning radius is r _e of the electric field is arranged , Three triple convergence points D, E, F
Are formed. Then, the triple convergence point D shown in FIG. 2 is made to coincide with the first triple convergence point D in the triple convergence TOFMS spectroscopy unit 7 so that FIG. 2 is perpendicular to FIG. Therefore, the width of the ions shown in FIG. 3 is a width in the direction perpendicular to the drawing of FIG. 2 (in FIG. 2, it is represented by a straight line). In this case, even if the ion beam spreads to r ₀ = 2.0 mm and θ = _{0 to} 0.2 radian as described above, the cylindrical electric fields 9 and 10 and the y
By setting the length in the direction as long as necessary, it becomes possible to detect all ions that have time-converged to the second or third triple convergence points E and F.

In the triple focusing TOFMS spectroscopy unit 7 of this example, three triple convergence points are formed by using two cylindrical electric fields, but n + 1 by using n cylindrical electric fields. It is also possible to form three triple convergence points and use these triple convergence points.

As described above, in the time-of-flight mass spectrometer of this example, the spread of the ion beam in the ion reservoir 3 in the optical axis direction (z-axis direction) is made at a certain point (or Line), the flight time deviation (aberration) caused by the spread of the ion beam in the ion reservoir 3 is eliminated, and then the time-focused ion beam is triple-focused by the TOFMS spectroscope. 7, spatial convergence in two directions (x, y-axis directions) orthogonal to the optical axis direction (z-axis direction) is performed, so that spatial convergence in three directions (x, y, z-axis directions) is finally achieved. Can be achieved. Thereby, the ion yield of the time-of-flight mass spectrometer can be improved, and therefore the resolution can be increased.

[0034]

As is clear from the above description, according to the time-of-flight mass spectrometer of the present invention, the spread of the ion beam in the ion reservoir in the optical axis direction (z-axis direction) is accelerated by two steps. After the time is once converged by the section, this ion beam is
Since the double convergence spectroscopy unit performs spatial convergence in two directions (x, y axis directions) orthogonal to the optical axis direction (z axis direction), spatial convergence in three directions (x, y, z axis directions) Can be reliably achieved. Thereby, regardless of the magnitude of the mass number of ions, the ion yield of the ion yield time-of-flight mass spectrometer can be improved, and at the same time, the resolution can be increased. In addition, since the ion yield is improved, the length of the ion reservoir does not need to be so large, and the apparatus can be made compact.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating an example of an embodiment of a time-of-flight mass spectrometer according to the present invention.

FIG. 2 shows a time-of-flight mass spectrometer shown in FIG.
It is a figure which shows an example of the spatial convergence of the ion calculated | required by the ion trajectory calculation program (SIMION).

FIG. 3 is a plan view showing an example of a triple focusing TOFMS spectroscopic section of the time-of-flight mass spectrometer of the example shown in FIG. 1, and showing a (x, z) plane of a spectroscopic system using a cylindrical electric field. .

FIG. 4 is a diagram schematically showing a conventional triple convergent TOFMS.

5 is a diagram illustrating spatial convergence in two directions (x, y-axis directions) orthogonal to the optical axis direction (z-axis direction) in the triple convergence TOFMS shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... External ion source, 2 ... Beam regulation slit, 3 ... Ion pool, 4 ... Ion extrusion plate, 5 ... 1st grid, 6
... Second grid, 7: TOFMS spectroscopy unit, 8: Ion detector, 9: Two-stage acceleration unit, D: Spatial convergence point

Claims (3)

[Claims] 1. An ion source for emitting ions, an ion reservoir for introducing the ions and accelerating and releasing the ions, and an optical axis in the ion reservoir for accelerating the ions from the ion reservoir. A two-stage accelerating unit for converging the spatial spread of ions in the direction, and a triple focusing spectroscopic unit for simultaneously converging the space in the direction orthogonal to the optical axis direction, the emission angle of the ions, and the energy of the ions with respect to time. A time-of-flight mass spectrometer comprising: an ion detector for detecting ions from the triple focusing spectroscopy unit. 2. A first grid is provided in an ion discharge section of the ion reservoir, and a second grid is provided in an ion introduction section of the two-stage acceleration section. the distance α to the spatial focusing points in the acceleration section, the ion reservoir 2s ₀ the width of the distance between the first grid second grid d, the acceleration voltage of ions in the ion reservoir V _a, the 2-stage When the accelerating voltage of the ions in the accelerating unit is _Vb , The time-of-flight mass spectrometer according to claim 1, wherein the mass spectrometer is set to: 3. The time-of-flight mass spectrometer according to claim 1, wherein the triple convergence spectrometer comprises a predetermined number of cylindrical electric fields.