JP2000097913A - Surface electrolytic dissociation-type ionization device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make easily changeable a surface electrolytic dissociation ionization (HSI) using supersonic molecular jet to normal surface electrolytic dissociation ionization (SI). SOLUTION: H2 gas with a small molecular weight and N2 gas with a large molecular weight are selected by a valve 3, are added to a sample gas as an auxiliary gas, and are introduced to a nozzle 6. Translation energy being obtained when a sample gas molecule jets out from a gas jet hole 7 depends on the amount of molecule of the auxiliary gas, thus accelerating a sample gas molecule to a supersonic region, and allowing the sample gas molecule to collide with an emitter 9 when the H2 gas is added. on the other hand, when the N2 gas is added, the sample gas molecule is brought into contact with the emitter 9 at a relatively slow speed without accelerating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ionization apparatus used as an ion source for ionizing a gas sample in a detector (including a mass spectrometer) for a gas chromatograph, for example. The present invention relates to a surface ionization type ionization apparatus.

[0002]

2. Description of the Related Art Various techniques for ionizing sample gas molecules, such as electron impact ionization (EI) and chemical ionization (CI), have been used. The surface ionization ionization method is one of the methods, in which a sample molecule or atom is brought into contact with an appropriately heated solid surface, and the sample molecule or atom is ionized by a surface ionization action. The surface ionization ionization method can be roughly classified into two types from the viewpoint of the speed of the sample molecule when it comes into contact with the solid surface.

That is, one of the methods is a method in which a sample molecule is accelerated to a supersonic range and collides with a solid surface by using a molecular acceleration method called a supersonic molecular flow method (hereinafter, referred to as a supersonic molecular flow method).
This method is called “HSI”). In this method, a sample gas molecule having a large molecular weight, which cannot be easily accelerated by itself, is mixed with an auxiliary gas having a low specific gravity, such as hydrogen or helium, and the mixed gas is forced from a gas outlet having a small diameter into a vacuum atmosphere. Squirt well. Then, the sample gas molecule is accelerated by repeating two-body collision with the auxiliary gas molecule, and reaches a speed in a supersonic region. By disposing the solid surface in such a supersonic molecular jet, the sample gas molecules collide with the solid surface vigorously and are ionized. (For details, see Japanese Patent Publication No. 5-12663).

[0004] Another method is to introduce sample gas molecules to a solid surface at a relatively low speed without performing molecular acceleration. This method is generally called a surface ionization ionization method (hereinafter, this method is referred to as “SI”).

[0005] In the HSI, since the sample gas molecules come into contact with the solid surface with extremely large kinetic energy, ionization is performed with high efficiency. On the other hand, ionization is performed irrespective of the magnitude of ionization energy,
It is difficult to ionize only specific molecules, that is, to obtain high selectivity. On the other hand, SI has a feature that it is difficult to ionize a molecule having a large ionization energy and the ionization efficiency is not high, but the selectivity is high.

[0006]

As described above, HSI and S
Since each has different characteristics from I, there is a demand to switch and use both methods as appropriate according to the purpose of analysis. When the sample gas molecules are ejected together with the auxiliary gas into the vacuum atmosphere to generate a molecular jet as described above, the kinetic energy obtained by the sample gas molecules depends on the diameter of the gas ejection hole. Becomes smaller. Therefore, conventionally, a method has been adopted in which, when performing SI, no nozzle is attached to the tip of a pipe that blows out gas, and when performing HSI, a nozzle having a gas ejection hole with a small diameter is attached to the tip of the pipe. I was

However, such a method requires a troublesome work of attaching and detaching the nozzle, and such a work must be performed while returning the pressure of the ionization chamber to the atmospheric pressure. Therefore, both ionization methods are switched during the analysis. I couldn't do that.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object to provide an HSI and an SI.
To provide a surface ionization type ionization apparatus capable of easily switching between the ionization apparatus and the ionization apparatus.

[0009]

Means for Solving the Problems A surface ionization type ionization apparatus according to the present invention which has been made to solve the above-mentioned problems comprises: a) a solid surface disposed in a vacuum chamber; A) a nozzle having a small-diameter gas ejection hole for ejecting a gas, c) a gas selection means for selecting and sending one of a plurality of auxiliary gases having different molecular weights, and d) a gas selection means selected by the gas selection means. And a pipe for mixing the auxiliary gas and a sample gas containing sample component molecules and feeding the mixed gas to the nozzle.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, sample component molecules are ejected from a gas ejection hole of a nozzle together with molecules of an auxiliary gas selected by a gas selection means, and come into contact with a solid surface located in front of the nozzle. The speed at which the sample component molecules come into contact with the solid surface depends on the molecular weight of the auxiliary gas, and the smaller the molecular weight, the higher the speed. Therefore, when an auxiliary gas having a relatively small molecular weight is used, the sample component molecules can be accelerated to a supersonic region and collide with a solid surface, while using an auxiliary gas having a relatively large molecular weight, The sample component molecules can be guided to the solid surface without acceleration.

【Example】

Hereinafter, an embodiment of the surface ionization type ionization apparatus according to the present invention will be described in detail with reference to the block diagram of FIG.

In FIG. 1, an auxiliary gas flow path 2 is connected to a sample gas flow path 1 to which a sample gas is supplied, and a distal end of the auxiliary gas flow path 2 has a small diameter gas ejection hole 7 having a diameter of about 1 to 150 μm. The formed nozzle 6 is mounted. The tip of the nozzle 6 is exposed inside the ionization chamber 11 that is evacuated by the vacuum pump 12, and an emitter 9 for causing a surface ionization is disposed in front of the gas ejection hole 7. When the sample component molecules become positive ions, the emitter 9 has a high work function. For example, a metal such as platinum, rhenium, and tungsten or a metal oxide thereof is used. A heater 8 is provided around the tip of the nozzle 6, and the nozzle 6 is heated to an appropriate temperature by a heating current supplied from a heating control unit (not shown). Also,
The emitter 9 is also heated to an appropriate temperature.

A collector 10 is provided in the traveling direction of ions generated in the vicinity of the emitter 9, and a minute ammeter 13 is provided for detecting an ion current flowing by the ions collected by the collector 10. The other end of the auxiliary gas passage 2 is connected to a common port of a three-way valve (3 ports, 2 positions) 3, and the other two ports are connected to a hydrogen gas passage 4 and a nitrogen gas passage 5. Therefore, the three-way valve 3
Is switched to hydrogen gas (H2) or nitrogen gas (N2)
Is selected and flows into the auxiliary gas flow path 2. The flow rates of the hydrogen gas and the nitrogen gas are appropriately adjusted by a flow controller (not shown) or a pressure valve.

When performing the analysis in the HSI mode, the three-way valve 3 is connected to a flow path indicated by a solid line in FIG. The sample gas flow path 1 is connected to, for example, an outlet end of a capillary column of a gas chromatograph device, and the sample gas flowing out of the column at the time of chromatographic analysis is supplied to the sample gas flow path 1.
And the hydrogen gas fed through the auxiliary gas flow path 2 is mixed and reaches the nozzle 6.

Since the gas ejection hole 7 has a small diameter and the gas is continuously supplied, the gas pressure in the nozzle 6 gradually increases. Since the inside of the ionization chamber 11 is in a vacuum atmosphere, a large pressure difference occurs between the inside and the outside of the gas ejection hole 7. As a result, the light hydrogen gas molecules squirt into the ionization chamber 11 vigorously, and the heavy sample component molecules also jump into the vacuum atmosphere riding on the squirt flow of the hydrogen gas. Then, the sample component molecules reach the velocity in the supersonic region while repeating two-body collision. The sample component molecules, which have become the supersonic free jet, vigorously collide with the emitter 9 and are ionized by the surface ionization.
The generated ions are collected by the collector 10, and the current according to the amount of the ions is measured by the microammeter 13 to sequentially detect the concentrations of the sample components.

It is known that when the molecular acceleration is performed as described above, the translational kinetic energy E obtained by the sample component molecules ejected from the gas ejection holes 7 can be approximated by the following equation (1). E = {(2/5) · (Mh / M1) · k · TN} · {1-exp (−δ · P0 · d)} (1) where Mh: mass of sample component molecule [g] , M1: mass of auxiliary gas molecules [g], TN: nozzle temperature [K], P0:
Nozzle internal pressure [Torr], d: diameter of gas ejection hole [cm],
k and δ are constants. Therefore, the smaller the molecular weight of the auxiliary gas molecule, the larger the above-mentioned translational kinetic energy E. If hydrogen gas, helium or the like is used as the auxiliary gas, the sample component molecules can be given a large translational kinetic energy and accelerated to the supersonic range. .

On the other hand, when performing the SI mode analysis, the three-way valve 3 is connected to the flow path shown by the dotted line in FIG.
Then, nitrogen gas is sent into the auxiliary gas flow path 2, and the sample gas and the nitrogen gas are mixed and reach the nozzle 6. The molecular weight of the nitrogen gas is at least 10 times the molecular weight of the hydrogen gas. Therefore, according to the above equation (1), the translational kinetic energy obtained by the sample component molecules is only 1/10 or less of the above case. In practice, if only such a small translational kinetic energy is obtained, the sample component molecules ejected from the gas ejection holes 7 are hardly accelerated and collide with the residual gas molecules in the ionization chamber 11 to form a thermal kinetic flow. It reaches the emitter 9. And it is ionized in contact with the emitter 9.

As described above, in the configuration of the present embodiment, the HSI mode and the SI
By switching between the modes, it is possible to perform analysis utilizing the characteristics of both modes, that is, high sensitivity and high selectivity. Switching in such a short time is useful, for example, in the following case. If it is known in advance that there is partial interference of the contaminant component during a series of chromatographic analyses, the three-way valve 3 is switched only during the period in which the interference occurs, and nitrogen gas is supplied as an auxiliary gas. Then, the selectivity of ionization is increased only for that period, and analysis excluding contaminant component molecules becomes possible.

The above embodiment is merely an example, and it is apparent that changes and modifications can be made within the spirit of the present invention.

[0020]

As described above, in the surface ionization type ionization apparatus according to the present invention, HSI and SI can be switched and executed by switching the type of auxiliary gas mixed with the sample gas. A troublesome operation such as replacement of a nozzle is not required as in the related art, and efficient analysis can be performed. In addition, since switching can be performed while maintaining the vacuum state of the ionization chamber, the HSI / SI mode can be temporarily switched during chromatographic analysis to utilize the features of high sensitivity of HSI and high selectivity of SI. can do.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a surface ionization type ionization apparatus according to one embodiment of the present invention.

[Description of Signs] 1 ... Sample gas flow path 2 ... Auxiliary gas flow path 3 ... Three-way valve 4 ... Hydrogen gas flow path 5 ... Nitrogen gas flow path 6 ... Nozzle 7 ... Gas ejection hole 9 ... Emitter 10 ... Collector 11 ... Ionization Room

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideyuki Uegaki 1-chome, Kuwabaracho, Nishinokyo, Nakagyo-ku, Kyoto Inside Shimadzu Corporation Sanjo Plant (72) Inventor Toshihiro Fujii 16-2 Onogawa, Tsukuba City National Institute for Environmental Studies F Term (reference) 5C038 GG13 GH04 GH08

Claims (1)

[Claims] 1. a) a solid surface disposed in a vacuum chamber; b) a nozzle having a small-diameter gas ejection hole for ejecting a gas toward the solid surface; c) a plurality of assists having different molecular weights. Gas selecting means for selecting and sending one of the gases; d) a pipe for mixing the auxiliary gas selected by the gas selecting means with a sample gas containing sample component molecules and sending the mixed gas to the nozzle; A surface ionization type ionization apparatus comprising: