JPS6182651A - Time-of-flight type mass spectrometer - Google Patents

Abstract

PURPOSE:To facilitate a measurement a mass number in a region of higher masses by applying between an ionizing chamber and a lead electrode, voltage of a shorter pulse width than the time of arrival of an ion of a minimum mass number to be observed to a drift tube. CONSTITUTION:A time-of-flight type mass spectrometer includes an ionizing chamber 2, a lead electrode 3, a drift tube 4 for forming a space with no electric field, and an ion detector 5. In addition, pulse voltage generator means 6 is connected between the ionizing chamber 2 and the lead electrode 3, said pulse voltage generator means 6 generating pulsed voltage of a shorter pulse width than the time of arrival of an ion of a minimum mass number to be observed to the drift tube 4, said pulsed voltage serving to accelerate all ions by an equal momentum. Thus, since the ions in concern are accelerated by the equal momentum, the time, of flight of any ion gets proportional to the mass thereof, whereby a measurement of a mass number in a region of higher masses is facilitated to improve resolution of the spectrometer.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a time-of-flight mass spectrometer, and particularly to an ion acceleration method thereof.

(b) Conventional technology In conventional time-of-flight mass spectrometers, a DC voltage is applied between the ionization chamber and the extraction electrode, and ions are generated in the ionization chamber in a pulsed manner, or ions are generated steadily. A well-known method is to use pulsed voltage to extract ions from the ionization chamber. Both of these methods apply equal energy to ions of all mass to accelerate them (equal-energetic acceleration).

In other words, considering an ion with mass m, 1/2 mvo
2=eVo=constant----(1-1') holds true. Here, vO is the velocity obtained by the ions, Vo is the extraction voltage, and e is the amount of charge.

Now, if the distance in the field-free space to the ion detector is L, then the flight time T of the ion is T = L / v o = L (i / r) go (1-2), and the flight time T is the mass of the ion. It is proportional to the square root i, and therefore, the difference in flight time T is used to distinguish the mass m.

However, in isoenergetic acceleration, the time of flight T is proportional to the square root f of the mass, so as the mass m increases, the difference ΔT in the time of flight T for a certain mass number difference Δm decreases, and in the high mass range This makes mass number measurement difficult.

(c) Purpose This invention was developed in view of the above circumstances, and it is an object of the present invention to provide a time-of-flight mass spectrometer that can easily measure mass numbers in a high mass range and has good resolution.

(d) Configuration and this invention has a configuration in which a pulse voltage is applied between an ionization chamber and an extraction electrode by a pulse voltage generation means. In a time-of-flight mass spectrometer equipped with a drift tube, which is a path through which ions fly, an ion detector, and an extraction electrode located between the ionization chamber and the drift tube, all ions are A flight characterized by electrically connecting and providing a pulse voltage generating means for accelerating by a uniform momentum and generating a pulse voltage having a pulse width shorter than the time it takes for ions of the minimum mass number to be observed to reach the drift tube. It is a time-based mass spectrometer.

(e) Examples Examples of the present invention will be described in detail below with reference to the drawings, but the invention is not limited to the following examples.

In FIG. 1, the time-of-flight mass spectrometer of the present invention (
The structure of 1) will be explained.

(2) is an ionization chamber in which ions are constantly generated by irradiating a target material with a laser beam or an electron beam. (3) is an extraction electrode located near the end of the drift tube (4) on the ionization chamber side that forms an electric field-free space. An ion detector (
5) is provided. (6) is a pulse voltage generating means, which is connected to the ionization chamber (2) and the extraction electrode (3). As shown in FIG. 2, the pulse voltage generating means (6)
Pulse voltage ■0 with a pulse width Δt shorter than the time for ions with the minimum mass number to be observed to reach the extraction electrode (3)
It is something that generates.

Next, the operation of the time-of-flight mass spectrometer (1) of the present invention will be explained with reference to FIG.

Let us now consider monovalent ions.

The distance between the ionization chamber (2) and the extraction electrode (3) is D1, the mass of the ions is m, and the flight direction of the ions is 2. Assuming that the amount of charge of the ion is e and the pulse voltage output by the pulse voltage generating means (6) is V (t), the equation of motion of this ion is: where E (t) is the electric field generated by the pulse voltage V (t). It is.

becomes. The velocity V of this ion at time t is then. In other words, this ion is the distance! i! When it is accelerated by a pulse voltage ■o with a pulse width Δm shorter than the time it takes to fly ItD, its speed V is ■=2■0Δt...
・(2-3)D, which shows that all ions have the same momentum of eVoΔt/D.

That is, when ions are accelerated with a pulse voltage Vo having a pulse width Δt, the ions are uniformly accelerated. Therefore, the time T for this ion to fly the distance to the ion detector (5) is given by, and it can be seen that the flight time T is proportional to the quality im of the ion. This is because, as shown in FIG. 3, the flight time T and the ion mass m are in a straight line (A) relationship, which facilitates the conversion of the flight time T to the quality 1 m.

Next, when the mass resolution R is determined from the equation (2-4), MT is obtained. However, Δm is the mass number difference centered on the mass m, and the mass resolution R increases in proportion to the mass number. Further, the ratio between the mass number difference Δm and the flight time difference Δ is as follows, which is a constant value that does not depend on the mass m. As can be seen from Figure 3, in the curve (B) showing the relationship between mass and flight time due to conventional isoenergetic acceleration, the higher the mass, the smaller ΔT/Δm, making it difficult to determine the quality (Jm). However, in this invention, (2-
Since it is expressed by equation 6), it is easy to determine the mass m from a low mass range to a high mass range.

Note that in the above embodiment, the second pulse voltage waveform is
I used an ideal square wave as shown in the figure, but (2-2)
As is clear from the equation, the time integral value of the pulse voltage V (t) is related to the flight time T, so the waveform does not necessarily have to be a rectangular waveform.

Furthermore, regarding the generation of ions in the ionization chamber, although the above embodiment described the steady generation of ions, the generation of ions may be performed in a pulsed manner (for example, using a pulsed laser beam or a pulsed
A similar effect can be expected if uniform momentum acceleration is performed as in the embodiment after ion generation (by using secondary ions, pulsed neutral particles, etc.).

(C) Effects According to the present invention, since the ions are accelerated with uniform momentum, the flight time becomes proportional to the mass, and a time-of-flight mass spectrometer that can easily measure mass numbers in a high mass range can be obtained. . Further, since the flight time is proportional to the amount of W, it is easy to convert the mass from the flight time, and the mass resolution is also proportional to the mass, so the resolution in the high mass range is improved. Furthermore, since the flight time difference with respect to the mass number difference is constant regardless of the mass, it becomes easy to determine the mass number in a high mass range.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the configuration of an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the waveform of a pulse voltage, and FIG. 3 is a graph showing the relationship between flight time and mass. (2)...Ionization chamber, (3)...Extraction electrode, (4)...Drift tube, (5)...Ion detector, (6)...Pulse voltage generation means. Representative Patent Attorney Shinta Nogawa-r7 4
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Claims (1)

[Claims] 1. Flight time that includes an ionization chamber that ionizes the sample, a drift tube that is a path for ions extracted from the ionization chamber to fly, an ion detector, and an extraction electrode located between the ionization chamber and the drift tube. A pulse that generates a pulse voltage between the ionization chamber and the extraction electrode in a type mass spectrometer that accelerates all ions with uniform momentum and has a pulse width shorter than the time it takes for ions with the minimum mass number to be observed to reach the drift tube. A time-of-flight mass spectrometer characterized in that a voltage generating means is electrically connected and provided.