JPS5935146B2 - mass spectrometer - Google Patents

Description

[Detailed description of the invention] The present invention relates to a dual focus mass spectrometer.

In a mass spectrometer, the ions generated by the ion source have a certain initial velocity distribution, and a single focusing mass spectrometer only has the function of converging ion beams of the same velocity with a certain aperture angle to one point. Therefore, the mass spectral lines are slightly broadened due to the unevenness of the ion velocities due to the width of the initial ion velocity distribution, making it impossible to obtain high resolution. In the case of a double convergence type, it has the function of converging ion beams with an aperture angle and the same velocity to one point, and converging beams within a certain velocity distribution width to the same point (the mass number is the same), so the mass spectrum The lines become extremely thin and have high resolution. An object of the present invention is to further improve the speed and reproducibility of mass number scanning in the above-mentioned double focus mass spectrometer.

If you use a method of changing the magnetic field strength to perform mass number scanning with a magnetic field deflection type mass spectrometer, it is difficult to change the magnetic field at high speed, and the reproducibility of the mass number decreases due to hysteresis of the iron core. Since this is low, various methods have been proposed in which mass number scanning is performed while keeping the deflection magnetic field constant.

However, these are aimed at single-focus mass spectrometers, and despite various efforts, there are limits to improving resolution. Therefore, it is of great significance that a means for high-speed scanning be developed in a dual-focus mass spectrometer.
FIG. 1 illustrates the principle of the invention.

In the figure, H is a deflection magnetic field. In a normal mass spectrometer, S
is fixed as the entrance side slit, and a mass spectrum is obtained on line JK. Here, reverse the direction of ion movement and
When an ion point source is placed on the K line and moved along the JK line to detect ions behind the fixed slit S, ions with a specific mass number are detected at a specific position as the source moves. . If the ion point source on the JK line is moved ion-optically, high-speed mass number scanning becomes possible, and since the magnetic field is constant, the reproducibility is also very good. If such an ion optical system is used, it is clear that the same objective can be achieved even if the ions are moved backwards. The present invention will be explained below with reference to Examples. In Figure 2, I is the ion source, S is the ion source slit, L is the converging lens, D1 and D2 are the first and second deflectors, H is the deflection magnetic field, E is the converging electrode, Sc is the detection slit, and T is the detector.

Ions travel from I toward T, but in order to first explain the double convergence of this configuration, the direction of ion travel is reversed and T is considered an ion source. Slits Sc
is located at the focal point of the convergence electrode E, and E is a part of a concentric cylinder cut out, and an electric field is formed in the radial direction of the cylinder. Ions incident perpendicularly to the incident surface draw an arc centered on the center of curvature of the cylindrical electrode E, regardless of their mass number. Since Sc is at the focal point of the electrode E, the ion beam with the opening angle α that exits Sc is deflected by the angle φe and becomes a parallel beam a, which is incident perpendicularly on the left end face of the magnetic field H. If this beam consists of ions with a constant mass number, the beam will be
It is deflected by .degree. and converges, for example, at point P1. However, since the ions exiting from T have variations in initial velocity, ions of a certain mass number exiting from Sc have variations in velocity as well as α in the direction. Therefore, an ion beam whose velocity is larger by v than the above-mentioned ion beam (opening angle is α)
Considering this, this beam draws an arc larger than the intermediate curvature of the electrode E, and the deflection angle is slightly smaller than φe, which also becomes a parallel beam b and enters the magnetic field H. This beam is incident on the left end face of the magnetic field H at an angle slightly inclined from perpendicular, but its convergence point eventually becomes point P1. In this way, ions with the same mass number but varying initial velocities are converged to one point, and when the mass numbers are different, the JK line is inclined at 45 degrees with respect to the left end face of the convergence point locus force crucible. is easily understood since it is a 9σ deflection. This configuration is known as a Pine Turbo-Hertz Oak double convergence system. The present invention uses this configuration in the opposite direction. The optical axes of the ion source 11, the slit S1, and the lens L3 are in a straight line and in a direction inclined with respect to the exit end surface (left end surface) of the deflection magnetic field H.

Ions exiting the slit S are immediately accelerated by a constant accelerating electric field. The deflection directions of the first deflector D1 and the second deflector D2 are opposite to each other, and the deflection angle of D2 is larger than that of D1.The beam exiting D2 becomes parallel to the exit end surface of the magnetic field H.
The beam exiting D2 is translated in parallel by changing the deflection angle in conjunction with the relationship that the deflection angle is larger in D2 than in D1. The intensity of the lens L is changed in conjunction with the deflection signals applied to Dl and D2 so that the beam converges on the JK line no matter where it is located. Thus ion source 1
The ion beam emitted from the ion beam converges on the JK line and scans the JK line. For example, when converging on point P1, only ions of a certain mass number converge on the slit Sc and are detected. Therefore, mass spectrometry can be performed by swinging the ion beam on the JK line. Now we will discuss the convergence of the ion optical system from the ion source 1 to the JK line.

If both the lens and deflector are electric field type, when the accelerating voltage is constant, the focal length of the lens L, Dl, regardless of the mass number,
The deflection angles of D2 are the same. When ions have an initial velocity distribution, lens L becomes a long focal point for high-speed ions, so
Although the ion convergence point shifts in the optical axis direction of the optical system on the JK line, this point can be ignored by appropriately increasing the distance from L to the JK line due to the depth of focus of L. The deflection angle of the deflector D1 is smaller for ions with higher initial velocity. The distribution width of the initial velocity of the ion is v, the difference in the deflection angle of D1 due to the difference of only this v is d1, and that of D2 is D.
2, since Dl and d2 are proportional to the deflection angle of each deflector, D2>d1, and by appropriately setting the distance between Dl and D2 and the distance from D2 to the JK line, ions with different initial velocities can be The beams can be converged to the same point on the JK line. At this time, the direction of incidence on the JK line differs between those with high and low initial velocities, but this difference is consistent with the difference in the direction of ion beams with different initial velocities due to double convergence in the mass spectrometer. ing. The present invention satisfies the double convergence condition with the above-mentioned configuration, has high resolution, does not change the deflection magnetic field during scanning, and is excellent in high-speed scanning and reproducibility.
Compared to conventional electric field scanning type or quadrapol type mass spectrometers, the characteristics in the high mass range are particularly excellent.

Although the above embodiment utilizes the configuration of a Matsuturbo-Hertz-Oak type mass spectrometer, any configuration that satisfies the double convergence condition may be used, and the JK line may be a curved line instead of a straight line. Nor does the direction need to be parallel in the scanning range. These can be done as required by the conditions of double convergence. It goes without saying that in the above example, the ions may be caused to move backwards.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the principle of the scanning method in the present invention,
FIG. 2 is a plan view of one embodiment of the present invention. H...Magnetic field for deflection, I...Ion source, T...Ion detector, Dl, D2...
・Scanning deflector.

Claims (1)

[Claims] 1. A magnetic field for mass analysis with a fixed magnetic field strength, an ion lens system that forms an image of a mass spectrum image formed by the magnetic field, and a mass spectrum image formed by the magnetic field and the lens. An image of an arbitrary point on the mass spectral surface formed by the magnetic field, which is placed between the image of the mass spectral image surface formed by the ion lens system, is the image of the lens. A mass spectrometer that consists of an ion trajectory deflecting electric field that deflects ion trajectories so that they come to a fixed point on a surface.