JPH0357574B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an improvement of the double convergence mass spectrometer described in Japanese Patent Publication No. 57-31261, and particularly to a mass spectrometer with a wide measurement mass range and excellent sensitivity and resolution. [Prior Art] Recently, there has been a strong desire to analyze high-mass molecules in applied fields such as biochemistry. This is because advances in ionization methods such as primary ion bombardment or high-speed atom bombardment have made it possible to relatively easily create ions of high-mass molecules exceeding m/z=10,000. In order to analyze such high-mass molecular ions, an extremely large mass spectrometer is required, but large mass spectrometers are extremely expensive and cannot be easily used by anyone. Therefore, there is a need for a mass spectrometer that is relatively small and capable of analyzing high mass ranges, and the following ideas have been made, for example. That is, by using the electric field E and uniform fan-shaped magnetic field of a conventional commercially available mass spectrometer as shown in Figure 7a, the radius of rotation rm of the ion beam in the magnetic field is approximately doubled as shown in Figure 7b. In this method, the rotation angle φm is decreased to about 1/2, and the measurement mass range is expanded by about 4 times. In FIG. 7, S is an ion source and D is an ion detector. [Problems to be solved by the invention] Although this method does expand the measurement mass range, the ion trajectory becomes longer because φm becomes smaller, and higher-order aberrations occur due to the vertical spread of the ion beam. There is a tendency for resolution to decrease as the size increases, and this trend has been thought to be inevitable. Table 1 shows the first-order aberration coefficients Ax, Ay, Aβ and the second-order aberration coefficients Ax, Ay, Aβ and The values of the aberration coefficients A〓〓, A〓〓, A〓〓, A _yy , A _y 〓, A〓〓 are shown.

[Table] When the practically required resolution is 50,000 and the width of the ion beam at the ion source is around rm/300,
It is desirable that the second-order aberration coefficient is at least smaller than 0.8 to 1.0, but taking this value into consideration, the first
Looking at the secondary aberration coefficients in the table, it can be seen that the apparatus shown in Table 1 cannot provide a satisfactory resolution. By the way, the present inventor first arranged a quadrupole electrostatic lens QL between the electric field E and the magnetic field H, which gives the ion beam a divergent property in the horizontal direction and a convergent property in the vertical direction. A dual convergence mass spectrometer was proposed as Special Publication No. 57-31261. This proposed device has, for example, φe=70° to 95°, φm=
The angle was chosen to be 65.8° to 74.1° and re/rm = 1.27 to 1.357, making it possible to reduce all secondary aberrations and achieve high sensitivity and high resolution. In this proposed device, the aforementioned rm is increased by about twice and φm is reduced by about 1/2 (specifically, 30゜≦φm≦50゜, 0.4≦re/rm
≦0.8 range) If a method of expanding the measurement mass range is applied, it is fully expected that higher-order aberrations will increase and resolution will decrease. The present invention has been made in view of the above-mentioned points, and the φm and re/rm of the proposed device are set to 30°≦φm.
The purpose is to set the range of ≦50° and 0.4≦re/rm≦0.8 to provide conditions in which the resolution does not deteriorate even if the measurement mass range is expanded. [Means for solving the problem] In order to achieve this object, the double focusing mass spectrometer according to the present invention is arranged between an electric field and a magnetic field, and provides divergence in the lateral direction of the ion beam. In a double-focusing mass spectrometer equipped with a quadrupole electrostatic lens that provides convergence in the longitudinal direction of the ion beam, the rotation angle of the ion beam in the magnetic field is φm, and the radius of rotation of the ion beam in the magnetic field is rm. , the rotation radius of the ion beam in the electric field is re, the strength of the quadrupole electrostatic lens is Qk, the effective length of the quadrupole electrostatic lens in the ion beam direction is Ql,
When the convex curvature on the input end face of the magnetic field is ρ′ and the convex curvature on the output end face is ρ″, 30゜≦φm≦50゜0.4≦re／rm≦0.8 0.35≦Qk ² Qlre≦1.0 It is characterized by satisfying rm/ρ′+rm/ρ″<0. [Embodiment] FIG. 1 is a diagram showing the configuration of an apparatus showing an embodiment of the present invention. The ion source 1 has an ionization chamber 2 and a plurality of slits 3, and an accelerated ion beam IB is taken out from the slits 4 to the outside. This IB is transmitted through a cylindrical electric field 5 and a uniform fan-shaped magnetic field 7 through a quadrupole electrostatic lens 6.
The ion beams enter the ion detector 8, undergo dispersion according to the mass-to-charge ratio by the magnetic field 7, and those having a specific mass-to-charge ratio enter the ion detector 8 and are detected. The magnetic field 7 is configured so that its magnetic field strength can be repeatedly swept by a power source (not shown). Therefore, the mass-to-charge ratio of ions passing through the magnetic field 7 changes with the sweep, and a mass spectrum signal is obtained from the detector 8. Incidentally, the entrance and exit surfaces of the magnetic field 7 are provided with angles ε' and ε'' such that the ion beam enters and exits obliquely, and the entrance and exit end surfaces are given curvature radii of ρ' and ρ''. ing. FIG. 2 is a sectional view taken along the line AA of the quadrupole electrostatic lens 6, and a diagram showing the configuration of a power source 9 for applying a potential to the quadrupole electrostatic lens 6. The quadrupole electrostatic lens 6 consists of four cylindrical electrodes, which are arranged around the ion beam path O.
When analyzing positive ions, which are arranged symmetrically at 90° intervals, a positive potential is applied to opposing electrodes Py in the direction perpendicular to the orbital plane of the ion beam (y direction), and in the radial direction (x direction) of the ion beam. A negative potential is applied to the electrodes Px facing each other in the direction (direction). Therefore,
Positive ions receive a force in the convergence direction in the y direction, and a force in the divergence direction in the x direction. Table 2 shows a design example (*) of the proposed device and five design examples ((1) to (5)) of the device according to the present invention given appropriate dimensions.

[Table] The undefined symbols used in Table 2 are as follows. Qk: Strength of the electrostatic quadrupole lens Ql: Length of the electrostatic quadrupole lens le′: Distance between the main slit and the electric field lm′: Distance between the collector slit and the magnetic field deq: Distance between the electric field and the quadrupole electrostatic lens dqm : Distance between the quadrupole electrostatic lens and the magnetic field Note that all lengths in Table 2 are based on the radius of rotation of the magnetic field rm in the design example (*) of the proposed device.
is normalized to 1, and Qk is normalized to the acceleration voltage of the ion beam. In the design examples (1) to (5) above, the secondary aberration coefficients are all much smaller than 1, and it is clear that high resolution that could not be achieved with the conventional equipment shown in Table 1 can be obtained. Ru. By the way, the values of Qk ² Qlre are shown in Table 2, but the inventor of this application believes that these values represent secondary aberrations and ion transmission, Ay and Aβ (the smaller the value, the better the transmission). It was found that there is a close connection between Figure 3 shows the sum of the absolute values of the second-order aberration coefficients I, Ay, and Aβ depending on the value of Qk ⁵ Qlre for the above design example (1).
The results of investigating how the sum of the absolute values of Ay and Aβ change are shown. FIGS. 4 and 5 show the results of similar investigations for the above design examples (4) and (5), respectively. Usually, if the value of I exceeds 4 to 5, practically sufficient resolution cannot be obtained, so it is necessary to keep it below that value. Furthermore, if the sum of Ay and Aβ absolute value exceeds 10, sufficient sensitivity cannot be obtained, so it is necessary to keep it below that value. Looking at Figures 3 to 5 based on these two conditions, from the condition of I, Qk ² Qlre can be changed from 0.35 to 1.0.
It is necessary to set Qk ² Qlre in the range of 0.4 to 0.9, and also considering the sensitivity. Along with the value of Qk ² Qlre above, the curvatures ρ' and ρ'' applied to the magnetic field entrance and exit surfaces have a large influence on the second-order aberration.In the above design examples (1) to (5), the magnetic field exit end surface does not have a curvature, but according to the conditions found by the inventor of this application, in such a case, it is necessary to give the input end face a negative curvature (in the direction in which the end face is concave).Actually, Since the curvature is approximately equivalent whether it is applied to the input end face of the magnetic field or the output end face, it is necessary to take it as the value of rm/ρ′+rm/ρ″. Figure 6 shows rm/ρ′+rm/ for the above design example (1).
Given several values of ρ'', we show the results of investigating what value the sum I of the absolute values of the second-order aberration coefficients takes depending on the value.Based on this figure, the value of I can be calculated as follows. 4～
Considering that it is not possible to obtain a practically sufficient resolution if it exceeds 5, it is necessary that at least rm/ρ′+rm/ρ″ takes a negative value in order to suppress the value of I below that value. Furthermore, rm/ρ′+rm/
It is desirable to set ρ'' in the range of −0.3 to −1.5. Furthermore, in the present invention, since the rotation angle of the magnetic field becomes smaller, it is inevitable that the convergence effect of the magnetic field becomes weaker, and the proposed device in Table 2 If the magnetic field input end face is tilted (ε') by -15 degrees as in the design example (*), the distance between the magnetic field and the ion detector becomes long, which is a problem for practical devices.
Therefore, it is necessary to set the magnetic field output end face with an inclination (ε″) of -15° or more. However, if the inclination is increased too much, aberrations will increase, so in practice, the limit for both ε′ and ε″ is about -30°. It is. [Effects of the Invention] As detailed above, according to the present invention, the ion beam is disposed between an electric field and a magnetic field, and provides divergence in the lateral direction of the ion beam, and convergence in the longitudinal direction of the ion beam. In a double focusing mass spectrometer equipped with a quadrupole electrostatic lens, φm is
Even if a mass spectrometer with a wide measurement mass range is obtained by setting re/rm in the range of 30°≦φm≦50° and 0.4≦re/rm≦0.8, a device with high resolution can be obtained.

[Brief explanation of drawings]

FIG. 1 is a device configuration diagram showing an embodiment of the present invention;
Figure 2 is a sectional view taken along line A-A of the quadrupole electrostatic lens and the configuration of the power supply for applying potential to it.
Figures 5 to 5 are for design examples (1), (4), and (5).
Figure 6 shows the results of investigating how the sum of the absolute values of the secondary aberration coefficients I and Ay, Aβ and the sum of the absolute values of Ay and Aβ change depending on the value of Qk ² Qlre. We give several values of rm/ρ'+rm/ρ'' for design example (1), and show the results of investigating what value the sum I of the absolute values of the second-order aberration coefficients takes depending on the values. 7 are diagrams for explaining the conventional apparatus. 1: ion source, 2: ionization chamber, 3, 4: slit, 5: cylindrical electric field, 6: quadrupole electrostatic lens, 7:
Uniform sector magnetic field, 8: ion detector.

Claims (1)

[Claims] 1. A quadrupole electrostatic lens disposed between an electric field and a magnetic field, which provides divergence in the lateral direction of the ion beam and convergence in the longitudinal direction of the ion beam. In a dual-focusing mass spectrometer, the rotation angle of the ion beam in the magnetic field is φm, and the radius of rotation of the ion beam in the magnetic field is
rm, the radius of rotation of the ion beam in the electric field is re,
The strength of the quadrupole electrostatic lens is Qk, the effective length of the quadrupole electrostatic lens in the ion beam direction is Ql, the convex curvature on the input end face of the magnetic field is ρ′, and the convex curvature on the output end face is ρ″. 30°≦φm≦50°0.4≦re/rm≦0.8 0.35≦Qk ² Qlre≦1.0 rm/ρ′+rm/ρ″<0. .