JPS61237360A - Mass spectrometer - Google Patents

Abstract

PURPOSE:To bring only the target ions to the ion collector by constructing a slit with a central electrode for slit and auxiliary electrodes thereby arranging the slit without disturbing the electrical field. CONSTITUTION:Ions having specific mass mo will arrive to the ion collector 8 but those having different mass are deflected differently through the magnetic field 6 and never arrive to the ion collector 8. But they may arrive to the ion collector 8 through collision against gas or reflection from the electrode and provide background noise which can be removed through a slit 9. Since the ion focus point is in the electrostatic field 7, insertion of slit having simple structure may cause disturbance of electrical field thereby such slit structure as comprising a central electrode 10 for slit and the auxiliary electrodes 11, 12 at the incident and outlet sides arranged through insulators 13 in front and rear of said electrode 10 is employed. Consequently, background noise in conventional mass spectrograph can be reduced considerably.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a magnetic field dispersion type double focusing mass spectrometer, and particularly to a mass spectrometer that reduces background and allows only target ions to reach a collector. The present invention relates to a mass spectrometer designed to achieve

[Background of the invention]

With the development of the life science field, mass spectrometers are being used as a means of measuring the molecular weight and molecular structure of substances related to living organisms. In this field, extremely small amounts of samples are often handled, and there is a desire to develop instruments with high sensitivity and high mass resolution.

An ion optical system that satisfies this requirement consists of an ion source, a magnetic field, and an electrostatic field arranged in this order, and a quadrupole lens incorporated therein.
ss Spectrometry Reviews)
19g3゜2, Pp, 299-325. has been proposed. As shown in FIG. 5, this ion optical system is magnetic field-first, and guides the ion beam exiting the ion source 1 to a magnetic field 6 via a quadrupole lens 2.3 and an octupole lens 5. After mass dispersing the ions in step 6, the quadrupole lens 4
, and the electrostatic field 7 created by the electric field sectors 7a and 7b, the ions are focused on the ion collector 8. In addition, Figure 5 (
FIG. 3A is a diagram showing the configuration, and FIGS. 3B and 3C are diagrams showing ion trajectories in the horizontal and vertical directions, respectively. With the above configuration, ions other than the target ion will deviate from the central orbit due to magnetic field dispersion, but ions that deviate from the central orbit may hit the sector electrode and be reflected, or after colliding with gas, the quadrupole It is often collected by lenses, electrostatic fields, etc., and reaches the collector. These are inconvenient for trace measurement because they give a background signal.

In a normal double focus mass spectrometer, an ion convergence point is located in an electric field-free region between a magnetic field and an electrostatic field, and by providing a slit here, unnecessary ions can be removed. However, in an ion optical system where the ion convergence point is within the electric field sector.

There was a drawback in that it was not possible to simply provide a slit within the electric field sector for reasons such as disturbing the electric field.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned difficulties and to provide a mass spectrometer having a configuration in which a slit is inserted into an electric field sector and capable of measuring a spectrum with a good signal-to-noise ratio.

[Summary of the invention]

A feature of the present invention is that a slit is provided at the ion convergence point in the electrostatic field of the mass spectrometer to restrict the passage of ions. , the central electrode for the slit,
The configuration consists of auxiliary electrodes that are electrically insulated from the center electrode so that potentials can be applied independently to the front and rear positions (ion incidence and exit sides) of the center electrode. It's about hiring.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1(a) is a configuration diagram of the optical system of the embodiment, and the difference from FIG. 5(a) is that a slit 9 is provided at the ion convergence point within the electrostatic field 7, and (b) (c) is a diagram showing ion trajectories in the horizontal direction and in the vertical direction. The ion beam exiting the ion source 1 sequentially passes through the quadrupole lenses 2 and 3 and the octupole lens 5, and is diverged horizontally as shown in (b) and vertically as shown in (c). It converges and enters the magnetic field 6. In the magnetic field 6, the ion beam is configured to pass through a narrow analysis tube in the vertical direction, that is, it is an ion optical system that limits the spread of the ion beam in the vertical direction. A certain mass m of the beam leaving the magnetic field 6. The ions waiting for
, 7b, the ions are focused by the electrostatic field 7 and reach the ion collector 8. The mass is m. Since different ions have different deflection angles in the magnetic field 6, they will not be on the ion optical axis within the quadrupole lens 4 and the electrostatic field 7, and will not normally reach the ion collector 8.

However, when these ions collide with the gas or are reflected by the electrodes, the quadrupole lens 4 and the electrostatic field 7
may reach the ion collector 8 by passing through the ion collector 8. These usually do not pass through the ion focus point within the electrostatic field 7;
The ion beam passes through a position off the ion optical axis and reaches the ion collector. These give background noise, but since most of them do not pass through the ion focus point, they can be removed by placing a slit 9 as shown in FIG. 2 at the ion focus point.

Since this ion convergence point is within the electrostatic field 7, inserting a slit with a simple configuration will cause disturbance of the electric field. In order to prevent this, in the first embodiment of the present invention, a slit 9 having a cross-sectional structure shown in FIG. 2 is used.

That is, the slit central electrode 10 and this central electrode 1
An auxiliary electrode 11 on the incident side and an auxiliary electrode on the output side are provided at positions before and after 0 via insulating insulators 13, respectively).
It has a slit structure consisting of 2. The illustrated arrow 14 indicates the direction of ion incidence. Each auxiliary electrode 11.12 is
A potential is applied to each independently. The slit central electrode 10 is normally at zero potential, but is insulated from the ground potential so that it can be given a potential if necessary.

In the embodiment, the interval between the two opposing auxiliary electrodes 11 and 12 was set to be 1 inch or more. These auxiliary electrodes 11 , 12 can be fixed to the central electrode 10 or can be attached to the electric field sector 7 .
A, 7b may be fixed, but as in the embodiment shown in FIG.
This is preferable in order to obtain optimal passage conditions.

According to the configuration of this embodiment, a slit is provided at the position of the ion convergence point in the electrostatic field 7 so as not to disturb the electric field at the center, thereby eliminating background noise, which is a problem in conventional mass spectrometers. It becomes possible to significantly reduce the amount.

FIG. 3 is a cross-sectional view showing another embodiment of the slit, and it is the same as the embodiment in FIG. , the structure of the auxiliary electrode is different. That is, in the embodiment shown in FIG. 3, the structure is such that the outer electrode 17 is attached to the outer periphery of the auxiliary electrode, and the inner electrode 18 is attached to the center of the auxiliary electrode.
Resistive coating 15.1 between outer electrode 17 and inner electrode 18
6, respectively. Thereby, the uniformity of the electric field can be maintained well.

FIG. 4 is a cross-sectional view showing still another embodiment of the slit, in which ions other than the target ions are absorbed into the gap between the inner wall surfaces of the electric field sectors 7a and 7b and the outer circumference of the slit 9. In order to prevent the ions from passing through, a shielding plate or folded electrode 19 is provided on the inner wall surface of the electric field sector near the slit on the ion incidence side. This results in
This prevents ions from passing through areas other than the center of the slit and exiting toward the ion collector, making it possible to more reliably reduce background noise.

〔Effect of the invention〕

As described above, according to the present invention, a slit is provided at the ion convergence point in the electrostatic field of the mass spectrometer without disturbing the electric field, and the slit removes stray ions and ionizes only the target ions. It can reach the collector. To give a numerical example, compared to the case where the slit of the present invention is not inserted.

It was confirmed that the background noise was reduced to -(1/3 to 115) several minutes.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining one embodiment of the present invention, in which (a) is an overall configuration diagram, (b) is an ion trajectory diagram in the horizontal direction, (c) is an ion trajectory diagram in the vertical direction, and FIG. 3 and 4 are cross-sectional views showing other embodiments of the slit in the present invention, and FIG. 5 is a diagram illustrating a conventional mass spectrometer (a). ) is a configuration diagram, (
b) is an ion trajectory diagram in the horizontal direction, and (c) is an ion trajectory diagram in the vertical direction. Explanation of symbols 1... Ion source 2.3.4... Quadrupole lens 5... Octupole lens 6... Magnetic field 7... Electrostatic field 7a, 7b... Electric field sector 8...・Ion collector 9...Slit 10...Central electrode for slit

Claims (3)

[Claims] (1) A mass spectrometer comprising at least an ion source, a magnetic field, an electrostatic field, and an ion collector, characterized in that a slit for restricting passage of ions is provided at an ion convergence point within the electrostatic field. (2) A patent claim characterized in that the slit is a slit consisting of a central electrode for the slit, and auxiliary electrodes provided at front and rear positions sandwiching the central electrode and electrically insulated from the central electrode. The mass spectrometer according to item 1. (3) The slit is a slit equipped with a shielding plate or a pleated electrode that prevents ions from passing between the inner wall surface of the electric field sector creating the electrostatic field and the outer periphery of the slit. A mass spectrometer according to claim 1.