JPH0450700B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of a quadrupole electrostatic lens used in mass spectrometers and the like.

[Prior art] Figure 2 shows an example of a quadrupole electrostatic lens conventionally used in mass spectrometers, and Figure 3 shows its A.
-A sectional view. The 4-pole electrostatic lens aligns the ion beam in the traveling direction (z direction) at 90° intervals on the same circumference.
It is composed of four lens electrodes 1 to 4 and shield plates 5 and 6 arranged in parallel to each other. The lens electrode is originally a hyperbolic electrode (the cut end is a hyperbola), but a cylindrical electrode can also be used approximately as shown in the figure. A positive potential is applied to the lens electrodes 1 and 3 facing in the direction perpendicular to the orbital plane of the ion beam (y direction), and the electrodes 2 and 4 facing in the radial direction (x direction) of the ion beam are applied with a positive potential. A negative potential is applied to the lens electrode, and a hyperbolic electric field is formed in the space surrounded by the lens electrode.

[Problem to be solved by the invention] The potential φ(x, y, z) in the edge field of a quadrupole electrostatic lens is determined by Matsuda et al., where K(z) is a coefficient related to the strength of the quadrupole field. As, φ=(x,y,z) ={K(z)/2}{(x ² +y ² ) +{K(z)″/24}{(x ⁴ −y ⁴ )} …(1) It is assumed that calculations are based on this equation when designing ion optical systems.Equation (1) ignores higher-order terms that occur outside of hyperbolic electrodes.

However, in the quadrupole electrostatic lens with the structure shown in Figure 2, the shield plate and the space before and after it are free spaces, and therefore the space created by the hyperbolic electrode shown in equation (1) It is thought that it is far out of place. Therefore, in the ion optical system designed based on equation (1), it may happen that the desired resolution and sensitivity cannot be obtained.

The present invention has been made in view of this point,
4 that can generate an edge field according to equation (1) above.
The purpose is to provide a polar electrostatic lens.

[Means for Solving the Problems] To achieve this objective, the present invention provides a quadrupole electrostatic lens in which four lens electrodes are arranged rotationally symmetrically around the trajectory of charged particles. The present invention is characterized in that a shield electrode having a cross-sectional shape approximately equal to that of the electrode is disposed close to the extension of the end portions of the four lens electrodes, and the shield electrode is grounded.

Hereinafter, one embodiment of the present invention will be explained in detail using the drawings.

[Embodiment] FIG. 1 is a configuration diagram showing an embodiment of the present invention, in which shield electrodes 7 having the same diameter as the lens electrodes are placed at both ends of four lens electrodes 1 to 4 via insulating spacers 8. It is attached by screws 9.

In a quadrupole electrostatic lens with such a configuration, a hyperbolic electrode (shield electrode) is also present in the edge field portion of the lens entrance and exit, and the electric field in this portion is regulated by this hyperbolic electrode (shield electrode). Therefore, a field that can be well approximated by the above equation (1) is formed. Therefore, if the quadrupole electrostatic lens having such a configuration is used as a component and the ion optical system is designed based on equation (1), a mass spectrometer that can obtain the designed resolution and sensitivity can be realized.

Note that it is desirable that the shield electrode be as long as possible, and that the insulating spacer be as thin as possible. As a rough guide, it is desirable that the length of the shield electrode be at least the diameter of the circle inscribed in the four lens electrodes, and that the thickness of the insulating spacer be 1/10 or less of the diameter of the inscribed circle.

In the above embodiment, the shield electrode was attached to the lens electrode, but if the shield electrode can be supported from the outside, it is not necessarily necessary to attach it to the lens electrode, and if the shield electrode can be placed close to the lens electrode while maintaining insulation, it is possible to Spacers are also not required.

[Effects] As described in detail above, the present invention provides a quadrupole electrostatic lens that can generate an edge field that can be well approximated by the above equation (1). Therefore, using this quadrupole electrostatic lens as a component, we can design an ion optical system.
If the calculation is performed based on equation (1), a mass spectrometer that can obtain the designed resolution and sensitivity can be realized.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure shows an example of a quadrupole electrostatic lens conventionally used in mass spectrometers, and Figure 3 shows its A-A.
FIG. 1 to 4: lens electrode, 5, 6: shield plate,
7: Shield electrode, 8: Insulating spacer, 9: Screw.

Claims (1)

[Claims] 1. In a quadrupole electrostatic lens in which four lens electrodes are arranged rotationally symmetrically around the trajectory of charged particles, a shield electrode having a cross-sectional shape substantially equal to that of the four lens electrodes, A quadrupole electrostatic lens, characterized in that the four lens electrodes are disposed close to each other on extensions of end portions thereof, and the shield electrode is grounded. 2. The quadrupole electrostatic lens according to claim 1, wherein the shield electrode is attached to an end of the lens electrode via an insulating spacer.