JPS5910019B2 - Ion source device in mass spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion source device in a mass spectrometer, and aims to improve ion extraction efficiency.

Chemical ionization■
(abbreviated as Cl), a reagent gas such as methane, isobutane, or ammonia is constantly flowed through the ion source to maintain the internal pressure of the ion source.

Reagent gas molecules are ionized to generate reactive ions by electron impact ionization and ion-molecule reactions while maintaining a force of about 1 Torr. The sample is introduced into the ion source in this state, and the sample molecules are ionized by the ion-molecule reaction between the reactant ions and the sample molecules.This method has the advantage of making it easy to obtain information on the molecular weight of the sample, and is widely used. . FIG. 1 shows a schematic diagram of a conventional chemical ionization ion source and a part of an analysis section.

A reagent gas is flowed from the gas supply pipe 1 to the ion filter box 2, and the pressure inside the box is maintained at about 1 Torr. The box is provided with an electron entrance hole A and an ion exit hole B.
A thermal filament 3 made of rhenium, tungsten, etc. is installed as an electron source outside the box on the axis of the electron entrance hole A.
is placed, and the thermal electrons emitted from the box are accelerated to several tens of eV to several hundreds of eV and enter the box to ionize the reagent gas molecules. Furthermore, reactive ions are generated by an ionic-molecule reaction between the generated ions and reagent gas molecules. When a sample is introduced here, the sample molecules are ionized by an ion-molecule reaction between the reactant ions and the sample molecules. The generated sample ions are extracted from the ion exit hole B and are made to enter the analysis section T through the opening c provided in the partition wall 6.

4 is an ion extraction electrode, and 5 is a converging lens electrode.

In order to ensure the practical life of the wall filament 3, the external area of the ion source box has a degree of vacuum better than 10-4 Torr.

The analysis section uses 10-5To to obtain good mass separation characteristics.
Make the degree of vacuum better than rr. For this reason, the ion source section and the analysis section are vacuum isolated by a partition wall 6, and are evacuated by vacuum pumps 8 and 9 independently.

Inside the ion source box (~1 Torr), outside (<10T0
The ion source box is required to be highly airtight in order to maintain the pressure difference of rr).

(2) Because of c, it is unavoidable that both the electron entrance hole and the iodine exit hole are too small. Generally, the conductance of the ion source box is approximately 1 to 5 x 10-21/S in practical use.
Since the ion source box has a highly airtight structure, there are the following problems. An ion extraction electrode is installed after the ion exit hole, but the ion exit hole restricts the penetration of the extraction electric field created by this electrode into the ion source box, resulting in a low extraction efficiency for generated ions. This is one of the limiting factors for the sensitivity of mass spectrometers. In addition, since the internal pressure of the ion source box is as high as 1T0rr, the equation 1
The fact that ionization by electrons of 0 eV to several 100 eV is limited to the vicinity of the electron entrance hole is also a limiting factor for extraction efficiency. The present invention solves this problem and provides a highly sensitive mass spectrometer by improving ion extraction efficiency.

That is, a voltage is applied between the front and rear walls of the ion source box to form an ion accelerating electric field within the box from the rear wall to the center of the front wall, thereby directing the ions generated within the box to the ion exit hole. An extruded ion source box is provided. FIG. 2 shows an embodiment of the present invention.

The ion source box is composed of a cylinder 10 having flanges 11, 12 and a conical hollow part 2. flange 11,
12 is made of stainless steel, and a DC voltage of several volts is applied between both flanges. The cylinder 10 is made of a semiconductor material, and when a voltage is applied, a constant current flows, and an equipotential surface distribution shown by dotted lines in the figure is obtained in the conical hollow region. The generated ions travel in a direction perpendicular to the equipotential surface, that is, toward the ion exit hole B, while being focused by this electric field.
That is, all ions generated at any point within the ion source box gather at the ion exit hole and are extracted. By locating the hot filament 3 as an electron source on the central axis, extraction efficiency can be improved. The cylinder 10 can be formed by coating the glass surface with a semiconductor, using ferrite, or by using zinc titanate ceramic or barium titanate ceramic, which are used in continuous dynode electron multiplier tubes.

This semiconductor ceramic is particularly suitable for use up to about 300°C. It is also easy to extract both positive and negative ions by switching the polarity of the DC voltage applied between the flanges 11 and 12. Although the present invention is effectively applied to a CI ion source, it can also be applied to an electron impact ion source, so it can also be used to configure an ion source for both electron impact ionization and chemical ionization. FIG. 3 shows another embodiment of the present invention, in which the peripheral side wall 10 of the ion source box is formed of an insulator, and the front wall 12 and the rear wall 11 are
is a conductor, the front wall 12 is made smaller in area than the rear wall 11, and the equipotential surface inside the box is shaped close to a concentric spherical surface.

Note that by making the rear wall 11 a concave spherical surface as shown in the figure,
A more desirable electric field is formed. Other parts corresponding to those in FIG. 2 are given the same reference numerals. Note that in this embodiment as well, the side wall 10 may be formed of a high-resistance material. The ion source device of the present invention has the above-described configuration and forms an electric field in the ion source box that accelerates ions toward the ion exit hole, so the ion exit effect is high and the detection sensitivity is increased. This is highly effective in CI ion source devices, where it is necessary to keep the gas pressure higher than the outside and to make the ion exit hole smaller.

[Brief explanation of the drawing]

FIG. 1 is a schematic longitudinal sectional view of a conventional example, and FIGS. 2 and 3 are longitudinal sectional side views of different embodiments of the present invention. 10... Circumference side wall of ion source box, 11...
...Flange forming the rear wall of the ion source box, 12
．． ．． ．． ...Flange forming the front wall of the ion source box,
A: Electron entrance hole, B: Ion exit hole, 3: Filament.

Claims (1)

[Claims] 1. The peripheral side wall of the ion source box is formed of an electric resistor or an insulator, and a voltage is applied between the front wall and the rear wall of the box, and an ion exit hole is formed in the box. An ion source in a mass spectrometer, characterized by forming a directed ion focusing electric field. 2. An ion source device in a mass spectrometer according to claim 1, wherein the electron entrance hole is provided on the same axis as the ion exit hole in the rear wall of the ion source box.