JP2798425B2 - Mass spectrometer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an analyzer suitable for specifying a substance based on a charge-to-mass ratio of particles.

(Prior art) For example, in a mass spectrometer for analyzing components separated by gas chromatography, a particle ionization means is provided close to a column outlet, and a quadrupole is disposed on the discharge side of the means. The discharged components are separated by the ratio of the mass to the charge amount, and the separated components are detected by a particle detector.

By the way, in such an analyzer, the number of particles incident on the detector per unit time is reduced due to the separation of the particles based on the ratio E / M of the charge E to the mass M. Not only does the output become smaller and the signal-to-noise ratio becomes lower, but also there is a problem that high processing accuracy is required in the production of the quadrupole.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a particle analyzer having a high signal-to-noise ratio while simplifying the structure.

(Means for Solving the Problem) In order to solve such a problem, in the present invention,
A particle ionizing means for ionizing particles, first and second grid electrodes arranged at a fixed distance in a moving direction of charged particles discharged from the means, an accelerating electrode for accelerating the charged particles, and a second Particle detection means disposed outside the grid electrode; pulse voltage generation means for supplying a positive potential pulse voltage whose repetition frequency f changes while maintaining a constant duty ratio to the first and second grid electrodes; A measuring signal analyzing means for spectrum-analyzing a detection signal from the particle detecting means based on a frequency f of the pulse voltage from the pulse voltage generating means.

(Function) The particles are accelerated by a constant acceleration voltage, and the particles are sieved at a speed depending on the ratio E / M of the charge amount E to the mass M, and the pulse voltage applied to the first and second grid electrodes is reduced. Based on the change in the repetition frequency and the output level from the particle detection means, the velocity of the particles, that is, the ratio of the charge amount E to the mass M
Detect E / M and its number.

(Embodiment) Therefore, the details of the present invention will be described below based on an illustrated embodiment.

FIG. 1 shows an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a particle ionization device disposed at a position where particles to be analyzed are discharged. An electron irradiator 3, a grid electrode 4, and a particle extraction electrode 5 are arranged in this order from the particle incident direction, in addition to an electron irradiating means 2 such as a filament for irradiating the particles.

Reference numeral 10 denotes a mass spectrometer characterized by the present invention, in which grid-like electrodes 11 and 12 are provided at both ends of a cylindrical body made of a conductive material having openings formed in the moving direction of particles, and a flight tube 13 is provided. And a first grid electrode 14 serving as an electrostatic shutter upstream of the flight tube 13 on the incident side, a second grid electrode 15 serving as an electrostatic shutter downstream of the discharge side, and further, these grid electrodes 14. , 15 are provided with a grid-shaped first shield electrode 16 and a second shield electrode 17, and a particle detector 18 is disposed on a particle passage R downstream of the second shield electrode 17. Has been established. Thereby, the distance L between the first grid electrode 14 and the second grid electrode 15 is
The flight space can be secured without being affected by the external electric field.

Numeral 20 denotes an accelerating voltage generator for supplying a particle accelerating voltage to the flight tube 13 or the grid-shaped electrodes 11, 12, and a negative constant potential capable of accelerating the particles to a speed at which the variation in energy in the particle ionizer 1 can be ignored. (For example, minus 500 to minus 200 volts).

Reference numeral 21 denotes a pulse voltage generation circuit for supplying a positive potential for blocking particles to the first and second grid electrodes 14 and 15. The pulse voltage generation circuit 21 discharges the charged particles from the particle ionization apparatus 1 to the first grid electrode 14.
And outputs a pulse of a positive potential (for example, 10 to 15 volts) at a constant duty ratio, for example, one-to-one, which can prevent charged particles flying in the cylindrical body 13 by the second grid electrode 15. At the same time, as shown in FIG. 2, the repetition frequency f is configured to be changed continuously, for example, up to 10 MHz while maintaining a fixed time (for example, 1 millisecond).

Reference numeral 22 denotes a measurement signal analysis circuit which receives signals from the particle detector 18 and the pulse voltage generation circuit 21 and receives a pulse voltage frequency f
Is configured to perform spectral analysis, for example, cosine Fourier transform, on the detection signal from the particle detector 18 according to the flight time or flight speed of the particle based on the following equation.

Reference numeral 19 in the figure denotes an electrostatic lens for converging particles, which is disposed between the particle ionization apparatus 1 and the shield electrode 16.
Reference numeral 23 denotes a vacuum container for accommodating the particle ionizer 1, the analyzer 10, and the particle detector 18, respectively.

Next, the operation of the thus configured device will be described.

When particles emitted from a particle generation source (not shown), for example, a gas chromatograph, are guided to the particle ionization apparatus 1, the particles are ionized by the impact of electrons from the electron generation means 2. The ionized particles are pulled by the potential of the extraction electrode 6 and discharged in the direction of the analyzer 10, are drawn by the acceleration potential of the flight tube 13 and subsequently enter the electrostatic lens 19, where they are converged. It moves toward the first grid electrode 14.

At this time, if a positive potential pulse voltage is applied to the first and second grid electrodes 14 and 15, the charged particles are repelled electrostatically by the first grid electrode 14 and enter the flight tube 13. Will be blocked.

Now, in order to simplify the explanation, the ratio of the charge amount E to the mass M will be described.
Let us first consider only particles with a constant E / M, that is, at a constant velocity Va.

The repetition frequency f of the pulse voltage is sufficiently small, that is, the time during which the ions move from the first grid electrode 14 to the second grid electrode 15 (t = L / Va, where L is the first grid electrode).
When the distance between the first grid electrode 14 and the second grid electrode 15) is sufficiently smaller than the reciprocal 1 / f of the repetition frequency f, the first grid electrode 14 is moved as shown in FIG. Most of the passed ions Nf ₁ are Nf ₁ ′ in the second grid electrode
You will pass 15. As the repetition frequency f of the pulse voltage increases, the ratio of ions Nf ₂ ′ / Nf ₂ and Nf ₃ ′ / Nf ₃ that can pass through the second grid electrode 15 decreases (II, III). And the reciprocal 1 / f of the repetition frequency f
Is equal to 1/2 of the flight time t = L / Va of the ions, the ions cannot pass through the second grid electrode 15 (IV). However, when the repetition frequency f of the pulse voltage further increases from this state, the pulse voltage can pass through the second grid electrode 15 again, and the ratio Nf ₅ ′ / Nf
_{5, and} the reciprocal 1 / f of the repetition frequency becomes maximum when the ion movement time t = L / Va coincides. Hereinafter, the output from the particle detector 18 becomes the lowest when the repetition frequency f of the pulse voltage matches (Va / L) × (n + 1/2) (where n = 0, 1, 2,...) It changes in a triangular wave shape as shown in FIG. 3 so that it becomes the highest when it matches (Va / L) × n.

Therefore, when observing particles A, B, and C having different ratios E / M of the charge amount E to the mass M, the output of the particle detector 18 for each particle is represented by a triangle as shown in FIGS. 3, I, II, and III. In this example, the number of particles of the ions A, B, and C is set to 2: 1: 1. That is, the velocities of the particles A, B, and C are Va, Vb, and Vb, respectively.
Vc, the frequency f of the pulse voltage is (Va / L) × (n +
1/2), (Vb / L) × (n + 1/2), (Vc / L) × (n + 1 /
It becomes the lowest when 2), and (Va / L) × n, (Vb / L) ×
The triangular wave signal which becomes the maximum when n, (Vc / L) × n is output from the particle detector 18.

Therefore, when analysis is performed on ions containing these three types of particles, the signal from the particle detector 18 is
Since the waveform shown in FIG. 4 obtained by adding the signal of each particle alone is periodically repeated, the ratio E / M of the charge E to the mass M is obtained by performing an orthogonal transformation such as a cosine Fourier transformation. It can be separated into M and its number can be detected. In the process of such orthogonal transformation, 1 / f = L / V
an odd multiple of i (where Vi represents the flight speed of each particle) 3 x L / V
False peaks of i.times.5.times.L / Vi, 7.times.L / Vi... are generated, but these can be removed by mathematical processing, so that there is no practical problem.

In this embodiment, a cylindrical flight tube is used to stabilize the electric field in the region where the particles fly, but when the electric field is not affected from the outside, a grid shape for acceleration is used. Obviously, the same operation is achieved even if the electrodes (11 and 12 in FIG. 1) are provided.

(Effects of the Invention) As described above, in the present invention, the particle ionization means for ionizing particles, and the first ionization means disposed at a fixed distance in the moving direction of the charged particles discharged from the means.
And a second grid electrode; an accelerating electrode for accelerating the charged particles; a particle detecting means disposed outside the second grid electrode; and a first and a second grid electrode repeatedly maintaining a constant duty ratio. Pulse voltage generating means for supplying a positive potential pulse voltage whose frequency changes, and means for detecting the correlation between the signal level from the particle detector and the frequency are provided, so that all of the particles incident on the ionization means Since it is targeted for detection, the signal-to-noise ratio can be increased and reliable analysis can be performed. In addition, since it can be composed of two grid electrodes and an accelerating electrode for blocking particles, a quadrupole This eliminates the need for such high-precision processing, reduces manufacturing costs, and enables the industrial use of a multi-type particle analyzer that performs multiple analyzes simultaneously. It made.

[Brief description of the drawings]

FIG. 1 is a block diagram of a device showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing an output voltage from a pulse voltage generating circuit in the above device, and FIGS. Explanatory diagram showing the operation of the above device, FIGS. 4 (I) to (IV)
4 is a waveform chart showing a signal from a particle detector in the same device. DESCRIPTION OF SYMBOLS 1 ... Particle ionization apparatus 10 ... Analyzer 11, 12 ... Grid electrode 13 ... Flight tube 14, 15 ... 1st and 2nd grid electrode for electrostatic shutters 18 ... Particle detector

Claims (1)

(57) [Claims] An ionizing means for ionizing particles, first and second grid electrodes arranged at a fixed distance in a moving direction of charged particles discharged from the means, and an acceleration for accelerating the charged particles An electrode; a particle detecting means disposed outside the second grid electrode; and a pulse supplying a positive potential pulse voltage whose repetition frequency f changes while maintaining a constant duty ratio to the first and second grid electrodes. A mass spectrometer comprising: a voltage generator; and a measurement signal analyzer that performs a spectrum analysis of a detection signal from the particle detector based on a frequency f of the pulse voltage from the pulse voltage generator.