JPH04267045A - Electron impact type ion source - Google Patents

Abstract

PURPOSE:To increase the detection intensity of ions more than before with a relatively simple structure in an electron impact type ion source. CONSTITUTION:A collimation magnet is concurrently used for an ion source box 4 constituting an ionization chamber 2, then an electron beam generating filament 14, the incidence hole 8 of an electron beam, and an ion outgoing hole 6 are provided on the ion outgoing axis M respectively, and the direction of lines of magnetic force by the collimation magnet and the incidence axis direction of the electron beam from the filament are made to match the direction of the ion outgoing axis M.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron impact ion source installed in a gas chromatography mass spectrometer or the like.

0002

[Prior Art] Generally, in a gas chromatography mass spectrometer, a sample gas whose components have been separated by a gas chromatograph is ionized in an ion source, and then introduced into a mass spectrometer where the ions are mass-separated to perform qualitative and quantitative analysis of the sample. I do.

[0003] For such ionization of the sample gas, an electron impact type ion source is sometimes used, which ionizes the sample gas by directly bombarding the sample gas with an electron beam.

FIG. 2 shows the configuration of a conventional electron impact type ion source. In the figure, a is an ionization chamber, and b is a hollow ion source box constituting the ionization chamber a, not shown. It is placed inside a vacuum chamber.

A sample gas introduction tube c is inserted into this ion source box a, and this introduction tube c is also inserted into the ion source box a.
An entrance hole d and an exit hole f for the electron beam are respectively formed in a direction substantially perpendicular to the insertion direction (up and down in the figure), and an ion exit hole is formed perpendicular to the electron beam axis L connecting both holes d and f. An ion exit hole g is formed in the direction of the axis M (in the left-right direction in the figure).

At a position on the electron beam axis L outside the ion source box b, a filament h for generating thermionic electrons and a trap electrode i for monitoring the electron current contributing to ionization are arranged facing each other. , furthermore, the filament h
A pair of collimation magnets j is provided outside the trap electrode i.

On the other hand, an ion extraction electrode k is arranged coaxially with the ion emission axis M at a position outside the ion source box b on the side of the ion emission hole g.

In the above configuration, the electron beam generated from the filament h is distributed along the electron beam axis L with its divergence suppressed by the magnetic field of the collimation magnet j. In this state, when a sample gas is introduced from the introduction tube c into the ionization chamber a of the ion source box b, this sample gas is bombarded by the electron beam and ionized. The generated ions are then extracted to the outside of the ion source box b through the ion exit hole g by the ion extraction electrode k, focused into an ion beam by a converging lens (not shown), and supplied to the subsequent mass spectrometer. .

[0009]

[Problems to be Solved by the Invention] By the way, in the conventional electron impact ion source having the above configuration, the following two main problems are encountered:
One issue remains.

(2) Since the collimation magnet j is provided separately from the ion source box b, the overall structure becomes complicated.

(2) Since the electron beam from the filament h is distributed on the electron beam axis L, ions generated by being bombarded by this electron beam are also distributed on the electron beam axis L. Moreover, since the direction along the electron beam axis L and the direction of the magnetic field lines of the collimation magnet j coincide with each other, the generated ions are easily dissipated in the direction along the electron beam axis L, while the ions orthogonal to this are easily dissipated. It is not possible to sufficiently extract ions in the direction of the emission axis M, and therefore, in the conventional method, it has not been possible to sufficiently increase the ion detection intensity.

0012

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and has a relatively simple structure and is capable of increasing the detection intensity of ions. It is.

Therefore, the electron impact ion source of the present invention has a hollow ion source box constituting an ionization chamber, and this ion source box generates magnetic lines of force along the exit axis of ions taken out from the ionization chamber. It consists of a collimation magnet, and the ion source box has an electron beam entrance hole and an ion exit hole formed coaxially with the ion exit axis and facing each other with an ionization chamber in between.
Furthermore, a filament for generating thermoelectrons was arranged on the ion exit axis located on the side of the electron beam entrance hole outside the ion source box.

[0014]

[Operation] In the above structure, the direction of the magnetic lines of force of the collimation magnet coincides with the direction of incidence of the electron beam from the filament, and also coincides with the direction of the exit axis of ions generated by the impact of the electron beam.

Therefore, the electron beam is emitted along the direction of the ion emission axis and the sample gas is ionized, and the ions generated thereby are also distributed along the direction of the emission axis, and in the direction orthogonal to this. Dissipation into the air is suppressed. As a result, ions are efficiently drawn out of the ion source box, increasing the intensity of ion detection.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of an electron impact ion source according to an embodiment of the present invention.

In the figure, reference numeral 1 indicates the entire electron impact type ion source, 2 is an ionization chamber, and 4 is a hollow ion source box constituting the ionization chamber.

This ion source box 4 has an ionization chamber 2.
It consists of a main body part 4a made of a collimation magnet that generates magnetic lines of force (indicated by broken lines in the figure) along the exit axis M of the ions extracted from the main body part 4a, and an electron incidence electrode 4b made of a non-magnetic material fixed to the side surface of the main part 4a. ing.

The main body 4a of the ion source box 4 has an ion exit hole 6, and an electron entrance electrode 4.
In b, the electron beam entrance hole 6 is aligned with the ion exit axis M.
As a result, both holes 6 and 8 face each other with the ionization chamber 2 in between. Furthermore, a sample gas introduction tube 10 that opens into the ionization chamber 2 in a direction substantially perpendicular to the ion emission axis M is inserted into the ion source box 4 .

Inside the ionization chamber 2, a hollow repeller electrode 12 for pushing out ions is disposed coaxially with the ion exit axis M, while a hollow repeller electrode 12 for pushing out ions is arranged coaxially with the ion exit axis M. A filament 14 for generating thermoelectrons is arranged on the emission axis M, and an ion extraction electrode 16 is arranged coaxially with the ion emission axis M on the ion emission hole 6 side.

A potential difference of, for example, about 70 V is applied between the ion source box 4 and the filament 14 in order to accelerate the thermoelectrons inside the ionization chamber 2, and the repeller electrode 12 A higher potential than the ion source box 4 is applied to push the ions toward the exit hole 6 side.

In the above configuration, the thermoelectrons generated from the filament 14 are accelerated by the potential difference with the ion source box 4 and become an electron beam, which is incident into the ionization chamber 2 through the entrance hole 8 and further into the repeller electrode 12. passes through the central hole. In this case, the direction of the magnetic lines of force produced by the collimation magnet coincides with the direction of the incident axis of the electron beam, so that divergence of the electron beam in a direction perpendicular to this direction is suppressed.

On the other hand, since the sample gas is introduced into the ionization chamber 2 through the introduction pipe 10, this sample gas is ionized by the electron beam. Therefore, the ions generated in this case are along the ion emission axis M direction,
In addition, the electron beam is distributed in a region with a spread similar to the diameter of the electron beam, and dissipation in a direction perpendicular to this region is suppressed.

Then, the generated ions are pushed out toward the ion exit hole 6 by the repeller electrode 12, and further passed through the ion exit hole 6 to the outside due to the potential difference between the ion extraction electrode k and the ion source box 4. The ion beam is extracted into an ion beam, focused into an ion beam by a converging lens (not shown), and supplied to a subsequent mass spectrometer.

In this way, in the above configuration, the direction of the magnetic field lines, the direction of the incident axis of the electron beam, and the direction of the exit axis of the ions are all the same, so that the sample gas is efficiently ionized and the generated The removed ions are also efficiently drawn out of the ion source box, increasing the ion detection intensity.

In order to control the amount of hot electrons generated from the filament 14, instead of providing a conventional trap electrode, the electron current emitted from the filament 14 may be directly monitored, or the ion source box 4 may be This can be done by monitoring the flowing electron current.

[0027]

According to the present invention, the structure is simplified because the collimation magnet that generates the magnetic field also serves as the ion source box.

Furthermore, since the direction of the ion exit axis and the direction of the incident axis of the magnetic field line and electron beam coincide, the sample gas is efficiently ionized, and the ions thus generated are also efficiently transported outside the ion source box. Therefore, it is possible to increase the detection strength compared to the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an electron impact ion source according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a conventional electron impact ion source.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Electron impact ion source, 2... Ionization chamber, 4... Ion source box, 6... Ion exit hole, 8... Electron incidence hole, 14
...Filament, M...Ion exit axis.

Claims (1)

[Claims] Claim 1: A hollow ion source box (4) constituting an ionization chamber (2);
4) consists of a collimation magnet that generates magnetic lines of force along the exit axis (M) of ions taken out from the ionization chamber (2), and the ion source box (4) has an electron beam entrance hole (8) and an electron beam entrance hole (8). Ion exit holes (6) are formed coaxially with the ion exit axis (M) and facing each other with the ionization chamber (2) in between, and an electron beam incident outside of the ion source box (4) is formed. An electron impact ion source characterized in that a filament (14) for generating thermionic electrons is disposed on the ion emission axis (M) located on the hole (8) side.