JPS6342814B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dual focus mass spectrometer. A double convergence mass spectrometer conventionally consists of an energy analysis section using a cylindrical electrode and a mass analysis section using a magnetic field. In this configuration, the ion flux can be focused when the ion trajectory lies only on one plane (horizontal plane), but the ions ejected from the ion source have a velocity component in the direction perpendicular to the plane. In this case, there is no focusing effect in the direction perpendicular to the plane, so the ion transmittance is low. By creating an ion optical arrangement consisting of a toroidal electrode with an appropriate curvature for the energy analysis section and a mass analysis section that takes into account the shape of the entrance end face, the ion flux three-dimensionally ejected from one point can be adjusted to the vertical direction ( A configuration that converges to a single point, including the vertical) direction, has come to be adopted. However, even in this configuration, the ion flux emitted from one point is actually focused on a single point only by the paraxial ion flux using ion optics, and in reality, the ion source has a spread and the ion source is located at the end of the ion source. The point is quite far from the ion optical optical axis, and the divergence angle of the ion flux emitted from one point of the ion source has a certain range of values, so in a high-resolution mass spectrometer, the aberration in the image of the ion source is Can't be ignored. Among these aberrations, secondary aberration is particularly problematic, and in order to reduce this, the entrance and exit surfaces of the toroidal electrode are made concave, and the ion entrance and exit ends of the magnetic field for mass spectrometry are used to direct the ion flux. However, it has been proposed to make it diagonal. As mentioned above, if the entrance and exit surfaces of the toroidal electrode are made concave so that ions enter and exit the magnetic field obliquely, a mass spectrometer that first performs energy selection of the ions and then performs mass dispersion A device with relatively good ion permeability and high resolution can be obtained. However, with this type, if the direction of ion travel is reversed so that mass dispersion by a magnetic field is first performed and energy analysis is then performed, aberrations are large. However, recently, an analysis method called the collision activation method has been developed, which requires an apparatus configuration in which the ion flux is first passed through an analysis magnetic field and then input into an energy analysis section. The proposed structure described above is not effective against such requirements. Therefore, it is an object of the present invention to provide an ion optical system with little aberration suitable for a mass spectrometer that first performs mass dispersion using a magnetic field and then performs energy analysis using a toroidal electrode. The purpose of this design was to provide an ion optical system with little aberration, in which the aberrations hardly change even when In a double-focusing mass spectrometer, there are a large number of factors that determine the aberrations of the ion optical system, so first we start by combining appropriate values for each factor, and then calculate the aberrations caused by slightly changing the values of each factor. The value of each factor is determined by calculating the change tendency of the state of , thereby assuming the range of change in the value of each factor so that the aberration state changes in the desired direction, and then the new value of each factor is determined. By repeating the procedure of performing the same calculation operations as above as a starting point, a combination of values of each factor that minimizes the aberration is reached. The present invention is a double focusing mass spectrometer having a toroidal electrode, in which the outer end surface of the magnetic field for mass analysis is concave, and the inner end edge is inclined with respect to the center line of ion flux. Here, the outer end face of the mass dispersion magnetic field is the end face on the far side from the toroidal electrode, and the inner end face is the end face facing the toroidal electrode. The present invention will be explained below with reference to Examples. FIG. 1 is a plan view of an ion optical system in an apparatus according to an embodiment of the present invention. 1 is a magnetic field for mass dispersion,
2 and 2' are double toroidal electrodes, and S1 and S2 are slits. The slit extends perpendicular to the plane of the drawing. In the case of a magnetic field advance type mass spectrometer (equipment for Collision Activation method belongs to this), S1 is the ion entrance slit, 3 is the ion generator, and S2 is the ion exit slit, 4 is the ion generator.
becomes an ion detector. On the other hand, in the case of electric field leading type,
4 is the ion generation part, S2 is the ion incidence slit,
S1 is an ion exit slit, and 3 is an ion detector. am is the radius of curvature of the optical axis of the ion optical system in the magnetic field 1 for mass spectrometry, φm is the angle between the intersection of both end surfaces of the magnetic field 1 and the ion optical optical axis with respect to the center of curvature of the radius of curvature am, and E2 is the inner end of the magnetic field. The inclination angle of the edge with respect to the ion optical axis, RM1 is the radius of curvature of the concave surface of the outer edge of the magnetic field, and D1 is the distance between the center of the outer edge of the magnetic field and the slit S.
1. ae, φe, D3, RE1,
RE2 has the meaning shown in the figure, ae is the radius of curvature of the optical axis of the ion optical system in the toroidal electrodes 2 and 2', and so on. The specific values of each of the above factors am and φm are shown in the table below. Electric field radius ae vs. magnetic field radius am: 0.75ae/am0.9 Electric field deflection angle φe: 85゜φe95゜Magnetic field deflection angle φm: 85゜φm95゜Magnetic field outer end surface radius of curvature RM1: -amRM1-
0.5am Inclination angle E2 of the magnetic field inner end face: −14.0°E2−6.0° Electric field inner end face radius of curvature RE1: −aeRE1ae Electric field outer end face radius of curvature RE2: −2aeRE20.6ae Toroidal electric field constant D1: 0.85amD11.25am C1: 0.45C10 .55 Here, the positive and negative radii of curvature are negative for both the magnetic field end face and the electric field end face. Also, the sign of the angle is E in Figure 1.
2 is defined as negative. Also, the toroidal electric field constant C
1 is the radius of curvature ae of the ion optical axis of the toroidal electrode
The ratio of ae/ce to the radius of curvature ce of the equipotential surface between the electrodes in the cross section of a plane perpendicular to the plane of the figure and including one radius of curvature ae.For a spherical electric field, C1=ae/ce=1
It is. FIG. 2 shows the ion optical system of a double focusing mass spectrometer developed in a straight line, with the optical axis direction as the Z axis, the horizontal direction as the x axis, and the vertical direction as the y axis. S is the entrance slit, and considering an ion beam that is spaced apart from the optical axis by αo in the horizontal direction and βo in the vertical direction as shown in the figure at the height of the upper end yo of this slit center line, the output slit surface at point yo is Let the ideal image be yo′,
The intersection of the above ion beam with the exit slit surface is
yo''. What is related to the resolution is the horizontal distance Δ between yo'' and yo'. Δ is calculated using six second-order aberration coefficients, Δ=am[|Aαα・αo ² |+|Aαδ・αo・δo| +|Aδδ・δo ² |+|Ayy(yo/am) ² | +| Ayβ(yo／am)βo｜＋｜Aββ・βo ² ｜
... is given by (1). In the above equation, δo is the energy width of the ion beam. In order to brighten the mass spectrometer, it is desirable to be able to increase the slit height. For this purpose, the slit height yo in the aberration coefficient is relevant.
It is good that Ayy, Ayβ especially Ayy is small. The results of calculating the aberration coefficients by specifically determining the values of each of the above factors are shown below.

【table】

[Table] Value of Δ αo = 1/250 radian, δo = 1/2000, yo = 1mm,
Assuming βo = 1/1000 radian, substitute the values in the above table into equation (1), Δ = 0.115μm

[Table] Value of Δ As in the case of section B, Δ=1.022 μm In order to clarify the effects of the present invention, calculation results for the conventional example are shown below. This example is designed to be optimal as an electric field leading type, and the magnetic field outer end face is a plane (RM1 = ∞) and obliquely intersects the ion flux at an angle E1 = 35°.

【table】

[Table] Value of Δ αo etc. are the same as in the above embodiment of the present invention, Δ=0.681μm

[Table] Value of Δ 18.729 μm Looking at the results of this conventional example, Δ when used as an electric field leading type is 0.681 μm, which is better than Δ = 1.022 μm when using the example of the present invention as an electric field leading type. On the other hand, when using the magnetic field leading type, the result was very poor, Δ=18.729 μm. In contrast, in the present invention, when using the magnetic field leading type, Δ = 0.115 μm, which is extremely good, and even when using the electric field leading type,
Since the diameter is 1.022 μm, good results can be obtained using either type. The cause of these effects is that in the conventional example, Ayy, Ayβ, and Aββ are significantly different when the electric field precedes type and when the magnetic field precedes type. In addition, a comparison with the conventional example shows that the main reason for the effect of the present invention is that the outer end surface of the magnetic field for mass spectrometry is made concave (there is no large difference in the values of each factor).
It is clear from this. As is clear from the above calculation results, according to the present invention, by making the outer end surface of the magnetic field for mass spectrometry concave, the difference in aberration, especially the change in Ayy and Ayβ, is small no matter which side the ion beam passes through. , and the respective values are found to be small, and a mass spectrometer that provides good resolution and brightness can be obtained as either an electric field leading type or a magnetic field leading type.

[Brief explanation of drawings]

FIG. 1 is a plan view of an apparatus according to an embodiment of the present invention, and FIG.
The figure is a perspective view of the ion optical system of the double focusing mass spectrometer. 1... Magnetic field for mass dispersion, 2, 2'... Toroidal electrode, S1, S2... Slit, 3, 4... Ion source and ion detector.

Claims (1)

[Claims] 1. An energy analysis section with a deflection angle φe of 85° to 95° using a toroidal electrode and a mass spectrometer section with a deflection angle φm of 85° to 95° using a uniform magnetic field are connected to each other by an ion optical system. The optical axes are made to coincide and face each other, an entrance slit and an exit slit are arranged at both ends of the optical axis of the ion optical system, an ion source is arranged behind the entrance slit, an ion detector is arranged behind the exit slit, and the toroidal The radius of curvature of the optical axis of the ion optical system of the electrode is ae,
Using the plane that includes the entire optical axis of the ion optical system as a reference plane, the radius of curvature in the cross section of the inner end surface by a plane perpendicular to the reference plane and tangent to the optical axis of the ion optical system is RE1,
The radius of curvature in the cross section by the plane perpendicular to the reference plane of the outer end surface and tangent to the optical axis of the ion optical system is RE2, and the curvature of the center line between the electrodes in the cross section by the plane perpendicular to the optical axis of the ion optical system and including the radius of curvature ae. The radius is ce, the radius of the optical axis of the ion optical system of the magnetic field forming the mass spectrometer is am, the inclination angle within the reference plane from the plane perpendicular to the ion optical system of the inner end face is E2, and the reference plane of the outer end face is When the radius of curvature in the cross section is RM1, and the distance between the center of the outer edge of the magnetic and electric fields and each slit behind it is D, then 0.75<ae/am<0.9 −am<RM1<−0.5am −ae<RE1 A double convergence mass spectrometer characterized in that <ae −2ae<RE2<0.6ae 0.85am<D<1.25am 0.45<ae/ce<0.55 −14°<E2<−6°. However, the radius of curvature of the electric field and magnetic field end faces is positive for convex surfaces, and the slope E2 is negative for the direction in which the side near the center of curvature of the optical axis of the ion optical system in the magnetic field of the end face moves away from the opposing electric field end face.