JPH01281652A - Ion source for mass spectrometry - Google Patents

Abstract

PURPOSE:To achieve efficient extraction of generated ions by radiating an electron beam to a vaporized liquid sample that is ejected intensively out of an ion emission exit of a small aperture which is formed on the side wall of a closed chemical ionization box. CONSTITUTION:An aperture 27 for introducing electrons is formed along the periphery of a chemical ionization box 26 and an ion emission exit 28 is formed on the bottom thereof respectively, both of the aperture 27 and the ion emission exit 28 being formed small in their sizes with a view to keep the adequate pressure for chemical ionization in the chemical ionization box 26. Then a vaporized liquid sample is ejected out of the ion emission exit 28 and is ionized by an electron beam which passes through an electron bombardment ionization box 14, from an electron incident entrance 16 to an electron emission exit 17. At this time, a pass 31 is formed and the liquid sample vaporized therethrough is exhausted, and consequently with a reduced amount of ion ejected out of the ion emission exit 28, a decrease in the amount of ion is prevented. In this way, extraction of ions is executed efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an ion source for a mass spectrometer in which a liquid sample can be directly introduced into the ion source and ionized by chemical ionization or electron impact.

[Conventional technology]

Recently, progress has been made in the development of ion sources that ionize a sample liquid developed by a liquid chromatograph by directly introducing it into the ionization chamber of a mass spectrometer. As one of them, a transfer tube connected to a liquid chromatograph is guided into the ionization chamber, and a porous member, such as a filter (frit) made by sintering stainless steel powder, is attached to the tip of the transfer tube. A structure has been proposed in which the sample liquid passes through the member and oozes out from the surface thereof.

Further, methods for ionizing the sample liquid exuded onto the surface of the porous member include electron impact ionization (EI) and chemical ionization (CI).

Here, in the CI method, it is necessary to introduce an electron beam into the ionization chamber while the ionization chamber is sealed and maintained at a relatively high pressure atmosphere of, for example, about 1 Torr. On the other hand, in the EI method, the ionization chamber is not sealed, and the sample liquid is simply bombarded with an electron beam directly in a low-pressure atmosphere. Therefore, in the past, ion sources dedicated to CI and EI were prepared, and each time the device was disassembled to replace it with the desired ion source.
It was very difficult to handle.

In order to solve this problem, a CI-EIlji combined ion source as shown in FIG. 4 has recently been proposed.

This ion source has a small electron input for CI in an ionization box 3E equipped with a large electron entrance IE for EI and an electron exit 2 for CI! It has a structure in which the ionization box 3C that has been prepared is slidably inserted.

In addition, 4 is a transfer tube, 5 is a porous member, 6 is an electrode group, 7 is a mass spectrometer, 8 is a CI gas introduction bone tube 9 is a filament,
Reference numeral 10 denotes an ion exit port formed in the ionization box 3E.

In such a configuration, when used as a CI, the ionization box 3C is pushed into the ionization box 3E, the electron injection port IE and the IC are aligned, and the electron exit port 2 is blocked with the ionization box 3C. In a state where the airtightness is increased, CII gas is introduced from the tube 8, and the electron beam from the filament 9 is incident through the electron incidence ports IE and IC to ionize the CII gas, and then the CII gas is ionized through the porous member 12 by reaction with the CII gas. The introduced sample components are ionized.

Next, when using it as an EI, pull out the ionization box 3C until the dotted line position, that is, the right end of the ionization box 3c opens the entrance port IE, and stop the CII gas supply. Since the electron beam passes between the electron beam and the exit port 2, sample components are bombarded with electrons and are ionized.

[Problems to be Solved by the Invention] In this composite ion source, when the ionization i3c for CI is pulled out from the ionization fi3E for EI to set the EI mode, the right end of the ionization box 3c is open.
The sample components vaporized on the surface of the porous member are diffused into the ionization box 3E and are ionized by electron beam impact. As a result, ions are generated throughout the ionization w13E. Even if ions are generated throughout the entire area inside the ionization box 3E, these ions are not all taken out to the outside, but are generated in the area that is an extension of the ion exit (the area shown by diagonal lines in the figure). Since only the ions that have been removed are extracted, the amount of ions extracted is extremely small. Further, since the ion exit port 10 is formed as small as possible to improve airtightness during CI operation, the amount of ions extracted is further reduced.

Therefore, the present invention has been made in view of this point, and it is an object of the present invention to provide an ion source that can increase the amount of ions extracted in the EI mode in a CI-EI composite ion source. .

[Means for Solving the Problems] In order to achieve the above object, the ion source of the present invention includes an EI ionization box having an electron entrance, and an electron beam introduced into the EI ionization chamber through the electron entrance. an electron beam generating means that generates an electron beam, and a C that is movably inserted into the EI ionization area and has an electron introduction opening and an ion exit opening.
a sample introduction probe with the Cl ionization box attached to its tip;
a transfer tube for transferring a sample liquid into the Cl ionization box, and a porous member placed in the Cl ionization box and attached to seal the tip of the transfer tube; When ionizing a sample liquid by chemical ionization, the above E
1. Introducing an electron beam into the Cl ionization box by aligning the electron incidence port of the ionization box with the opening of the Cl ionization box, and
When the sample liquid is ionized by electron impact, the C! It is characterized in that the ionization box is pulled out from the EI ionization box and electrons are made to collide with the sample ejected from the ion exit port of the CI ionization box.

Hereinafter, embodiments of the present invention will be explained in detail based on the drawings.

[Example] FIG. 1 is a sectional view showing an example in which the ion source of the present invention is used in CI mode, and FIG. 2 is an enlarged view taken along the line BB in FIG. 1.

In the figure, 11 is an ion source 2 in the entire analyzer.
The body maintains a high vacuum inside. 12 is the lid body;
13 is an ion source block, 14 is an EI ionization box, 15
16 and 17 are the electron entrance and exit ports formed to face the outer periphery of the EI ionization box 14, and 18 are the ions generated in the previous EI ionization box 14. ■Take out 1 to the outside,
There are seven electrode groups that perform acceleration and focusing, and the left electrode 18a in this electrode group is fixed to the end of the EI ionization box 14 and serves as a lid. A hole 19 is provided for use. Furthermore, these electrode groups, the ion source block 13, and the EI ionization sheath box 14 are fixed to the ion source housing 11.

20 has one end passed through the ion source block 13 and E.
I is a cylindrical sample introduction probe that is detachably inserted into the ionization box 14, and the other end passes through a cylindrical guide body 21 provided at approximately the center of the lid body 12 and is taken out to the outside. A knob 22 is provided at the tip. Further, a transfer tube 23 is inserted into the probe in an airtight manner.

For example, a fused silica tube with an inner diameter of about 40 μm is used as this transfer tube, and one end of the transfer tube is taken out into the atmosphere and connected to a liquid chromatograph (not shown). Furthermore, the other end of the transfer tube (EI ionization box 1
4 side), a porous member 24 is attached via a set screw 25 so as to close the opening.

Reference numeral 26 denotes a cylindrical CI ionization box with a bottom attached to the tip of the probe 20 so as to accommodate the porous member 24, and an opening 27 for introducing electrons is provided on the outer periphery of the CI ionization box. An ion exit port 28 is formed in each of the holes. The opening 27 and the ion exit port 28 are formed small in order to maintain a relatively high pressure suitable for the CI ionization sheath box 26CI.

As shown in FIG. 2, 29 is a stepped guide groove provided at the open end of the guide body 21, and is for regulating the position of the probe 20. A pin 30 implanted in 20 is fitted.

Although not shown, a heater is built into the ion source block 13, and an air lock valve is provided at the guide body 21 portion of the lid body 12, so that the ion source block 13 can be heated without breaking the vacuum inside the ion source housing 11. , the probe 20 can be inserted and removed.

In the state shown in FIG. 1, the pin 30 is located in the guide groove 29 as shown by the solid line.
The CI ionization sheath box 26 is inserted to the bottom (electrode 18a) of the EI ionization box 14.

As a result, the electron incidence port 16 of the EI ionization box 14 and the CI
Since the opening 27 of the ionization sheath box 26 coincides with the opening 27 of the CI ionization sheath box 26, the electron beam generated by energizing the filament 15 is introduced into the CI ionization sheath box 26. In this state, if the sample liquid developed by the liquid chromatograph is guided into the CI ionization box 26 via the transfer pipe 23 and the porous member 24,
Ionization is performed using the solvent in the sample liquid as a reactive gas.

That is, the solvent (reactive gas) vaporized on the surface of the porous member 24 is first ionized by the electrons incident from the electron entrance port 16 and the opening 27, and then the vaporized sample component is ionized by a chemical reaction with the solvent ions. The generated ions 1 are sent to the ion exit port 28. Since the light is sent to a mass spectrometer (not shown) through the hole 19, mass spectrometry using CI ionization can be performed.

Next, if the knob 22 is moved in the direction of arrow C and the pin 30 is moved to the position indicated by the dotted line a in the guide groove 29, the probe 20 will pass through the CI ionization box 26EI ionization box 14.
As shown in FIG. 3, the CI ionization box 26 is stopped just before the EI ionization seedling box 14 closes the electron entrance port 16. In this state, if a sample liquid from the liquid chromatograph is introduced into the CI ionization sheath box 26 via the transfer tube 23 and the porous member 24, the vaporized sample liquid will be ejected from the ion exit port 28, and the ejected sample will be The liquid is ionized by the impact of the electron beam passing through the EI ionization box 14 from the electron entrance 16 toward the electron exit 17. Since the generated ions (2) are sent to the LQ analysis section through one hole, mass spectrometry using electron impact ionization can be performed.

At this time, a large amount of vaporized sample liquid is released from the ion exit port 28.
Since it is introduced into the EI ionization box 14, the pressure inside the EI ionization box may become too high than the pressure suitable for ionization by electron impact, unless the pumping speed within the EI ionization box is selected appropriately. If the pressure inside the EI ionization box becomes too high as described above, the proportion of ions generated by chemical reactions will increase, which is undesirable, and the pressure at the electrode group 18 will also increase, reducing the rate of ion passage and removing the ions. The amount of ions will decrease.

In such a case, as shown by the dotted line in FIG. 3, the ion source housing 11 (
or a vacuum pump), forming a passage 31 that communicates with the
By exhausting the vaporized sample liquid into the CI ionization box through this passage, the amount of vaporized sample liquid ejected from the ion exit port 28 can be reduced, so that the pressure in the EI ionization box 14 can be reduced to EI. It is possible to set the pressure to a low level suitable for this, and also to lower the pressure at the electrode group 18 portion. Therefore, the proportion of ions generated by CI is significantly reduced, making it possible to obtain a chromatogram based on accurate ionization by electron impact, and preventing a decrease in the amount of ions, thereby improving sensitivity.

It should be noted that the above description is an example of the present invention, and many modifications can be made in implementing the present invention. For example, in the above example, EI
Although the ionization box was provided with an electron exit port, this exit port is not necessarily required.

[Effects] As detailed above, according to the present invention, since the ion exit port with a small diameter is formed in the side wall of the sealed CI ionization box, the electron beam is not ejected into the vaporized sample liquid that is ejected in a concentrated manner. It can be irradiated. As a result, the generated ions can be generated only in a certain area without being generated in the metal region within the EI ionization box as in the conventional case, so that the generated ions can be extracted efficiently. Also,
Since the EI ionization box is sealed, the ion passage holes provided in the EI ionization box can be made larger, so that ions can be taken out more efficiently.

[Brief explanation of the drawing]

1 to 3 are diagrams each showing the configuration of an embodiment of the present invention, and FIG. 4 is a diagram for explaining a conventional example. 11: Ion source housing 14: EI ionization box 15: Filament 16: Electron entrance port 17: Electron exit port 19: Ion passage hole 20: Sample introduction probe 23: Transfer tube 24: Porous member 26: CI ionization box 27 : Opening 28: Ion exit port

Claims (1)

[Claims] an EI ionization box having an electron entrance; an electron beam generating means for generating an electron beam to be introduced into the EI ionization box through the electron entrance; A CI ionization box having an electron introduction opening and an ion exit port, a sample introduction probe having the CI ionization box attached to its tip, and a transfer tube for transferring a sample liquid into the CI ionization box through the inside of the probe. , a porous member placed in the CI ionization box and attached to seal the tip of the transfer tube, and when ionizing the sample liquid by chemical ionization, the electron incidence port of the EI ionization box is provided. The electron beam is introduced into the CI ionization box by aligning the opening of the CI ionization box with the opening of the CI ionization box, and when the sample liquid is ionized by electron impact, the electron beam is introduced into the EI ionization box through the electron incidence port. An ion source for a mass spectrometer, characterized in that the CI ionization box is pulled out from the EI ionization box as far as possible, and electrons are caused to collide with the sample ejected from the ion exit port of the CI ionization box.