JP2000067809A - Quadrupole mass spectrometric device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a gas pressure by a single device regardless of the pressure of a measured gas and to improve detection sensitivity when the pressure of the measured gas is low. SOLUTION: A grid-like ionizing chamber 32 and a filament 33 are additionally arranged in an ionizing chamber 12, and when the pressure of a measured gas is high, ions are generated by turning on only a filament 13 and entering thermal electrons from it into the ionizing chamber 12 through an opening in a side wall of the ionizing chamber 12 and when the pressure of the measured gas is low, ions are generated by turning on only the filament 33 and entering thermal electrons from it into the ionizing chamber 32 through the grid-like side wall of the ionizing chamber 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quadrupole mass spectrometer for performing mass spectrometry, and more particularly to an improvement of a quadrupole mass spectrometer suitable for use as a gas monitor for analyzing and detecting process gas components.

[0002]

2. Description of the Related Art In a quadrupole mass spectrometer, two sets of elongated counter electrodes (quadrupole electrodes) having a surface whose cross-sectional shape is a hyperbola or an approximate shape thereof are arranged at 90 ° intervals. The DC voltage U and the high-frequency voltage Vco are applied between each pair which is different from each other by 90 ° after the opposing ones are equipotential.
A voltage in which sωt is superimposed is applied, the U / V ratio is made constant and V is changed, and ions incident on the counter electrode are selectively passed according to the (mass / charge number) ratio. It is.

More specifically, as shown in FIG. 12, an ion source 11 for ionizing a gas introduced into a vacuum vessel 10 evacuated by an evacuating system 19, and the ions are passed through a lens system 15 through a lens system 15. A quadrupole mass filter (quadrupole electrode) 16 to be incident, and an ion current detector 17 for detecting the current of ions passing through the quadrupole mass filter 16 are enclosed. The ion source 11 includes a filament 13 and an ionization chamber 12 including an electron reflecting plate 14 and the like. A gas to be measured is introduced into the ionization chamber 12 of the ion source 11 from a measurement system chamber 21 via a pipe 22 and a valve 23 inserted therein. Into the ionization chamber 12 into which the gas to be measured has been introduced, thermoelectrons emitted from the filament 13 are made to enter through an opening provided in the side wall of the ionization chamber 12, and the thermoelectrons cause ionization of the gas to be measured. Is generated. The ions are accelerated and converged by the lens system 15 and are incident on the quadrupole mass filter 16, and the current of the ions selectively passing therethrough is detected by the ion current detector 17. The detected ion current signal is sent to the controller 18.

[0004] The DC bias potential of the vacuum vessel 10 is set to V0 (reference value).
3, the DC bias potential of the ionization chamber 12 is V3, the DC bias potential of the first lens plate of the lens system 15 is V6, the DC bias potential of the second lens plate is V7, the quadrupole mass When the DC bias potential of the quadrupole electrode of the filter 16 is V8 and the DC bias potential of the ion current detector 17 is V9, these DC bias voltages are applied as shown in FIG.

In such a quadrupole mass spectrometer,
The quadrupole mass filter 16 is used to prevent the ions of the gas to be measured generated by the ion source 11 from colliding with the atmospheric gas while passing through the quadrupole mass filter 16 to reduce the resolution and sensitivity.
In general, the gas pressure in the part must be kept at 10 ⁻³ Pa or less. Therefore, when the pressure of the gas system to be measured is as high as 10 ^-1 Pa, the heat from the opening and the filament 13 in the ionization chamber 12 of the ion source 11 for allowing ions to enter the quadrupole mass filter 16. The aperture for introducing electrons is narrowed to reduce the conductance.

That is, as shown in the pressure diagram of FIG. 13A, the pressure of the chamber 21 to be measured is 10 ^-1.
Even in the case of the Pa unit, the pressure in the quadrupole mass filter 16 is set to be in the order of 10 ^-4 Pa by reducing the conductance of the opening of the ionization chamber 12 of the ion source 11. As can be seen from the relationship between (a) and (b) in FIG. 13, the differential pressure a is a differential pressure mainly generated by the measured gas introduction pipe 22 and the valve 23, and the differential pressure b
Is a pressure difference caused by narrowing an opening provided in the ionization chamber 12 of the ion source 11.

[0007]

However, the conventional quadrupole mass spectrometer as described above has a problem that the ion generation efficiency is low and the detection sensitivity is low.
That is, since the life of the filament is shortened when the filament is lit in an atmosphere having a high gas pressure, the filament must be disposed not in the ionization chamber 12 but in the outer space of the quadrupole mass filter 16 outside the ionization chamber. The thermoelectrons must enter the ionization chamber 12 only through the aperture narrowed as described above. That is, the thermoelectrons emitted from the filament 13 enter the ionization chamber 12 through a small-diameter hole (opening) having a small conductance, and the amount of the incident thermoelectrons is limited. The production efficiency decreases, and the detection sensitivity deteriorates. The deterioration of the detection sensitivity becomes remarkable because the amount of the gas to be measured drawn into the ionization chamber 12 is small when the gas pressure of the gas to be measured is low (10 ⁻³ Pa or less).

For this reason, especially when the gas pressure of the gas to be measured is low (10 ⁻³ Pa or less), a quadrupole mass spectrometer having a nude type ion source 41 as shown in FIG. There is also. The nude ion source 41 includes a lattice ionization chamber 42, a filament 43 provided outside the ionization chamber 42, and an electron reflector 44. In this case, the detection sensitivity can be improved by about two orders of magnitude as compared with the above, but it cannot be used when the gas pressure of the measured gas system is high (10 ^-3 Pa or more).
That is, since the ionization chamber 42 is formed in a lattice shape,
This is because if the conductance of the opening is large and the gas pressure of the measured gas system is high, it is impossible to realize a pressure diagram as shown in FIG.

In view of the above, the present invention has improved a quadrupole mass to improve detection sensitivity without sacrificing the life of the filament regardless of whether the gas pressure of the gas system to be measured is high or low. An object of the present invention is to provide an analyzer.

[0010]

According to the present invention, an ion source for ionizing an introduced gas to be measured, a quadrupole mass filter into which the ions are incident, and In a quadrupole mass spectrometer including an ion current detector that detects the current of ions that have passed through the quadrupole mass filter, and a vacuum container that stores these,
The ion source emits thermoelectrons through a first ionization chamber, a grid-like second ionization chamber formed therein, and a relatively small opening into the first ionization chamber;
A first filament provided outside the first ionization chamber, and a second filament provided inside the first ionization chamber, which emits thermoelectrons into the second ionization chamber through the grid-like second ionization chamber. And two filaments.

When the gas pressure of the measured gas system is low, the second
Only the filament is turned on, and thermions are emitted from this. Then, in this case, the thermoelectrons are emitted into the second ionization chamber through the grid-like second ionization chamber, so that the amount of the incident thermoelectrons is not limited, and the generation of ions is prevented. Increases efficiency. as a result,
The detection sensitivity when the gas pressure of the measured gas system is low is improved. The second filament turned on is the first filament.
In this case, since the gas pressure of the gas system to be measured is low and the inside of the first ionization chamber is also low, the life is not shortened.

When the gas pressure of the gas system to be measured is high, only the first filament is turned on to emit thermoelectrons therefrom. The thermoelectrons enter the first ionization chamber through a relatively small opening provided in the first ionization chamber. Therefore, the amount of thermoelectrons incident on the first ionization chamber is limited. In this case, since the gas pressure of the gas system to be measured is high, a large amount of the gas to be measured is introduced into the first ionization chamber. Therefore, the ion generation efficiency does not deteriorate so much. The first filament that is turned on is located outside the first ionization chamber where the gas pressure is high and is placed under the same gas pressure as the space in which the quadrupole mass filter is located, so that the life span is reduced. Is never shortened.

[0013]

Next, embodiments of the present invention will be described in detail with reference to the drawings. In FIG. 1, an ion source 11 for ionizing introduced gas and a quadrupole mass filter (quadruple) into which the ions are incident via a lens system 15 are placed in a vacuum vessel 10 evacuated by an evacuation system 19. (Electrode) 16 and an ion current detector 17 for detecting the current of ions passing therethrough are enclosed. A detected current signal is sent to the controller 18, and the space between the vacuum vessel 10 and the system chamber 21 is measured. Is similar to FIG. 12 in that a pipe 22 having a valve 23 is connected.

Here, the ion source 11 is provided with an ionization chamber and a filament doubly. The ionization chamber 12
As in FIG. 12 described above, a filament 13 and an electron reflecting plate 14 are provided, and a narrowed opening for introducing thermoelectrons from the filament 13 is provided on the side wall. Inside the ionization chamber 12, another lattice-like ionization chamber 32 and a filament 33 are arranged. The filament 33 is located inside the ionization chamber 12 but outside the ionization chamber 32.

When the gas pressure of the gas system to be measured is high, only the filament 13 is turned on, and the thermoelectrons are passed through a narrowed opening provided on the side wall of the ionization chamber 12 as shown in FIG.
It is drawn into the ionization chamber 12. At this time, the DC bias voltages V0 to V9 of each section are set as schematically shown in FIG. As shown in FIG. 2, V0 is a potential of the vacuum container 10 serving as a reference, and includes an electron reflecting plate 14, a filament 13, an ionization chamber 12, a filament 33, a lattice ionization chamber 32, and a first lens plate of the lens system 15. , Second lens plate, quadrupole electrode of quadrupole mass filter 16, ion current detector 17
DC bias potentials are V1, V2, V3, V
4, V5, V6, V7, V8, and V9.

In this case, since the amount of the thermoelectrons is introduced into the ionization chamber 12 through the narrowed opening, the amount thereof is limited. However, since the gas pressure of the gas to be measured in the ionization chamber 12 is high, The ion generation efficiency is not bad. The turned-on filament 13 is disposed outside the ionization chamber 12 having a high gas pressure, that is, in the space having the same low gas pressure as the space in which the quadrupole mass filter 16 is disposed. Will not occur.

On the other hand, when the gas pressure of the measured gas system is low, only the filament 33 is turned on, and the thermoelectrons from this filament 33 are drawn into the ionization chamber 32 as shown in FIG. Therefore, the potentials V0,
V1, V2, V3, V4, V5, V6, V7, V8, V
9 is set as schematically shown in FIG. At this time, since the thermoelectrons from the filament 33 are drawn into the ionization chamber 32 through the lattice-shaped side walls of the ionization chamber 32, the quantity of the thermoelectrons becomes sufficient, and the ion generation efficiency increases, and as a result, In addition, the detection sensitivity of the gas to be measured is improved.
At this time, the filament 33 which is turned on is
Is disposed in the ionization chamber 12, but the gas pressure in the ionization chamber 12 is low because the gas pressure of the gas system to be measured is low, so that the life of the filament 33 is not shortened.

The above description relates to one embodiment of the present invention, and the specific structure and the like can be variously changed without departing from the gist of the present invention. For example, the fixing of the lattice ionization chamber 32 may be supported by the insulating support body 34 on the lens system 15 side as shown in FIG. 6, or conversely, as shown in FIG. You may make it support with the insulating support body 35.

Further, the number of lens plates constituting the lens system 15 is two in the above description, but may be one as shown in FIGS. FIG. 8 shows the case where the lattice ionization chamber 32 is supported by the insulating support 34 on the lens system 15 side, and FIG. 9 shows the case where the lattice ionization chamber 32 is supported on the gas introduction side by the insulating support 3.
5 is a case where the support is performed. The number of lens plates constituting the lens system 15 is not limited to these.

The filaments 13 and 33 are shown in FIG.
0, two opposing filaments 13, 13
And 33, 33. Further, as shown in FIG. 11, the filament 13 may be constituted by a pair of filaments 13, 13 facing each other, and the filament 33 may be formed in a shape surrounding the ionization chamber 32. Even if the filament 33 is formed in this way, it is possible for the thermoelectrons to enter the ionization chamber 32 because the ionization chamber 32 has a lattice shape, and by doing so, the thermoelectrons from the entire surroundings enter the ionization chamber 32. Since the light is incident, the incident efficiency is improved, the ion generation efficiency is increased, and the detection sensitivity is improved. 10 and 11 are schematic views of the ionization chambers 12 and 32 taken along a plane perpendicular to the central axis and viewed in the direction of the central axis.

[0021]

As described above, according to the quadrupole mass spectrometer of the present invention, even when the gas pressure to be measured is high even when the gas pressure to be measured is low, it can be measured with a single device and the gas pressure to be measured is low. In this case, the detection sensitivity can be improved, and the life of the filament is not shortened.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

FIG. 2 is a schematic view of a part of a vacuum vessel for explaining an operation when a measured gas pressure is high.

FIG. 3 is a graph showing a DC bias voltage of each part when a measured gas pressure is high.

FIG. 4 is a schematic view of a part of a vacuum vessel for explaining an operation when a measured gas pressure is low.

FIG. 5 is a graph showing a DC bias voltage of each part when a measured gas pressure is low.

FIG. 6 is a schematic view showing a modified example of fixing the lattice ionization chamber.

FIG. 7 is a schematic view showing another modification example of fixing the lattice ionization chamber.

FIG. 8 is a schematic diagram showing a modified example in which a single lens system lens plate is used.

FIG. 9 is a schematic view showing another modification in which one lens plate of the lens system is used.

FIG. 10 is a schematic view showing a modified example of a filament.

FIG. 11 is a schematic view showing another modification of the filament.

FIG. 12 is a schematic view showing a conventional example.

FIG. 13 is a diagram showing the pressure of each part when introducing a gas to be measured having a high gas pressure and the corresponding parts.

FIG. 14 is a schematic diagram for explaining the operation of the conventional example.

FIG. 15 is a graph showing a DC bias voltage of each part during operation of the conventional example.

FIG. 16 is a schematic diagram showing a conventional example having a nude ion source.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Vacuum container 11 Ion source 12 Ionization chamber 13, 33, 43 Filament 14, 44 Electron reflector 15 Lens system 16 Quadrupole mass filter 17 Ion current detector 18 Controller 19 Vacuum exhaust system 21 System chamber to be measured 22 Gas to be measured Introducing pipe 23 Valve 32, 42 Grid ionization chamber 41 Nude type ion source

Claims (1)

[Claims] An ion source for ionizing an introduced gas to be measured, a quadrupole mass filter to which the ions are incident, and an ion current detector for detecting a current of ions passing through the quadrupole mass filter And a vacuum vessel for accommodating them, wherein the ion source comprises a first ionization chamber, a grid-like second ionization chamber formed therein, and the first ionization chamber. In the ionization chamber of
The first, which emits thermoelectrons through a relatively small aperture.
A first filament provided outside the ionization chamber, and a second filament provided inside the first ionization chamber, which emits thermoelectrons into the second ionization chamber through the grid-like second ionization chamber. And a quadrupole mass spectrometer.