JPH0366778B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dual focus mass spectrometer. A double focusing mass spectrometer usually consists of an energy analysis section using a concentric electric field and a mass analysis section using a deflection magnetic field. When concentric electric fields are considered only within a cross section perpendicular to their common axis, they have a convergence effect on energy (ion beams emitted from one point with the same energy converge at one point), but in the cross section just considered, On the other hand, since it does not have a focusing effect on the spread of the beam in the vertical direction, it does not have sufficient sensitivity as a mass spectrometer. Therefore, it was proposed to use a toroidal electric field in the energy analysis section in order to improve sensitivity and resolution (reduce ion optical aberrations). The present invention relates to an improvement of a mass spectrometer using a toroidal electric field in the energy analysis section. Figure 1 schematically shows the configuration of a mass spectrometer using a toroidal electric field in the energy analysis section. A, B
is a toroidal electrode, and FIG. 2 shows a perspective view thereof. Reference numeral 1 denotes an ion source slit, which serves as an ion source in terms of ion optics. The ion beam is deflected approximately at right angles by the electric field within the toroidal electric field (simply referred to as the toroidal electric field), and the ions with a certain energy converge at point 2. The ion beam is further bent at a substantially right angle by the deflecting magnetic field M, and ions having a certain mass are focused onto the exit slit 3. Various studies have already been conducted on this type of double convergence mass spectrometer, and the basic configuration has been approximately determined. As shown in Figure 1, the ion beam is deflected at right angles in each of the energy analyzer and mass analyzer.
The shape of the deflection magnetic field is determined so that the ion beam enters and exits the deflection magnetic field obliquely, and the entrance and exit surfaces of the toroidal electric field are concavely curved in a plane perpendicular to the plane of the figure. It is becoming. Such a configuration is recognized as a type that can provide a mass spectrometer with high sensitivity and high resolution. However, even if the configuration shown in FIG. 1 is adopted, when actually designing a mass spectrometer, it is necessary to determine the values of a large number of ion optical factors. For this reason, for example, Japanese Patent Laid-Open No. 51-93279 proposes a combination of numerical values that provides guidelines for determining these factors. Now, the ion optical factors that should be determined in the design of the configuration shown in Figure 1 can be determined by using an electronic computer to trace ion trajectories for all combinations of numerical values with appropriate jumps in each factor. Therefore, the optimal combination of numerical values for each factor can be determined within a certain range. Furthermore, since the aberration of the ion image on the slit 3 is not a single aberration but a mixture of various aberrations, what is the best convergence state (more specifically, which of the various aberrations is minimized? Various choices are possible depending on whether it should be done or not. Therefore, even if the configuration shown in FIG. 1 is a basic model that yields good results,
Many guidelines are still required for specific design, and the aforementioned Japanese Patent Application Laid-Open No. 51-93279 is one such guideline. This provides one guideline when designing an analytical device. In Figure 3, 01 is the center of the ion source on the ion optics and the center of slit 1 in Figure 1, and 03 is the center of the slit 1 in Figure 1.
The center of the exit slit 3 in the figure is shown, and Z is the optical axis of the ion optical system in the configuration of FIG. 1, which is straightened for convenience. Both slits 1 and 3 extend in the y-axis direction in the figure. The width of the slit 1 is narrow, and the ion source can actually be thought of as a straight line along the y-axis. The ideal image point on the slit 3 by the paraxial ion beam at the y point on the slit 1 is y', and the y' point is the intersection y'' of the single ion trajectory exiting the y point with the plane including the slit 3. Let Δ be any direction in the x direction from It can be expressed as: Δrm{|Aαα・α ² |+|Aαδ・α×δ| +|Aδδ・δ ² |+|Ayy(y+ym) ² | +|Ayβ(yo/rm)β|+|Aββ・β ² |} In the above formula, rm: radius of curvature of the ion optical axis in the deflection magnetic field rm in Figure 1 α: deflection angle in the x-axis direction at the y-point of the ion trajectory β: deflection in the y-axis direction at the y-point of the ion trajectory Angle δ: deviation from the central value of ion energy Also, each A with a subscript at the bottom right is a secondary aberration coefficient. For example, Aαα is the aberration amount Δ of the spread angle of the ion beam in the x direction (in the horizontal plane) at the ion source. This gives a contribution of The configuration shown in FIG. 1, in which the incidence and exit of the deflection magnetic field is oblique incidence and exit, is to reduce the above-mentioned aberration coefficients overall.
The numerical combinations of each ion optical factor proposed in No. 93279 are different from those in which only the entrance surface of the toroidal electric field is concave (the exit surface is flat), and Aαα, Aαδ, Aββ
is getting smaller. This means that the degree of divergence of the ion beam emitted from the ion source can be relatively large (because the aberration coefficient related to the beam spread angles α and β is small). The main purpose of the present invention is to increase the height of the slit 1 in FIG. 1 by reducing Ayy, Ayβ, and Aββ among the above-mentioned aberration coefficients. The sensitivity of mass spectrometry can be increased by obtaining a high amount of light. In the present invention, regarding each ion optical factor shown in FIG. The following ranges are proposed: 32°≦Ep1≦36° −10°≦Ep2≦−8° 0.9rm≦le′≦1.2rm re/Re0.5. In addition, le″, lm′,
lm'' is determined from trajectory calculation once the above factors are determined. The table below shows one embodiment of the present invention.

[Table] The aberration coefficient values when using each value above are shown below. Aαα=−0.002 Aαδ=−0.021 Aδδ=−0.033 Ayy=−0.011 Ayβ=0.125 Aββ=−1.799 Comparing this with that of JP-A No. 51-93279, it can be seen that there is a significant improvement in Ayy and Ayβ. In the above embodiment, if α=1/300 (radian), β=1/1000 (radian), δ=0.1%, y=1 mm, and the width of slit 1 is 1 μ, the calculated value of Δ is 0.56 μ. A numerical comparison of the above embodiment of the present invention with two other examples in which the values of each factor are known is shown below.

【table】

[Table] In the first example above, the shape of the magnetic field is largely different from that of the present invention; Ayy is approximately 5 times larger, and △ is 1.4 times larger. In example 2, Ep1 is even smaller than in case 1 (approximately 30° in the present invention, 10° in case 1), Ayy is approximately 18 times, and Δ is
It has increased by 2.3 times. According to the invention, as described above, the entrance slit 1
Since the magnitude of aberration is small when the height is increased, a double convergence mass spectrometer with high resolution and high sensitivity can be obtained.

[Brief explanation of drawings]

Fig. 1 is a plan view of a double focusing mass spectrometer, Fig. 2 is a perspective view of the concentric double toroidal electrode in the above device, and Fig. 3 is a perspective view showing the coordinate axes of the ion optical system of the above mass spectrometer. be. 1...Incidence slit as ion source, A, B
...Toroidal electrode, 3...Ion exit slit.

Claims (1)

[Claims] 1. A toroidal electric field that deflects the ion beam between 85° and 92°, and a toroidal electric field that deflects the ion beam after leaving the same electric field.
A uniform deflection magnetic field is used to deflect the beam from 85° to 92°, and the ion beam enters and exits obliquely with respect to the deflection magnetic field, and the dimensional ratios and angles of each part are set within the following ranges. Double convergence mass spectrometer. 0.9≦re／rm≦1.2 0.8≦RE1／re≦2.0 0.5≦RE2／re≦1.2 32°≦Ep1≦36° −10°≦Ep2≦−8° 0.9rm≦le′≦1.2rm re／Re0.5