JPH0477415B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a mass spectrometer including a quadrupole electrostatic lens as a component.

[Prior Art] FIG. 5 schematically shows a mass spectrometer introduced in Japanese Patent Application Laid-Open No. 160949/1983. In this mass spectrometer, an ion source S, a uniform fan-shaped magnetic field H, a cylindrical electric field C, and an ion detector D are arranged in this order. Two quadrupole electrostatic lenses Q1 and Q2 are arranged to provide focusing in the direction perpendicular to the plane and divergence in the radial direction of the ion beam, and further between the uniform fan-shaped magnetic field H and the cylindrical electric field C. A third beam that provides focusing in the direction perpendicular to the orbital plane of the ion beam passing through the
It is characterized by arranging a quadrupole electrostatic lens Q3.

Figure 6 shows an example of this quadrupole electrostatic lens, which is composed of four cylindrical electrodes arranged parallel to the ion beam traveling direction (z direction) on the same circumference at 90° intervals. A positive potential is applied to electrodes facing each other in the direction perpendicular to the orbital plane (y direction), and a negative potential is applied to electrodes facing each other in the radial direction (x direction) of the ion beam.

In such a proposed device, a quadrupole electrostatic lens Q
Since the width of the ion beam is widened by Q1 and Q2, the image magnification, which is a parameter of the mass spectrometry system, can be reduced, and the resolution can be improved. Furthermore, since the ion beam is focused in a direction perpendicular to the orbital plane by the third quadrupole electrostatic lens Q3, the efficiency of passing the ion beam through the mass spectrometry system is improved, and the sensitivity can also be improved.

[Problems to be Solved by the Invention] However, according to studies by the present inventor, extremely large fifth-order aberration occurs in a mass spectrometry system using such a quadrupole electrostatic lens. Therefore, the resolution and sensitivity may not reach the desired values.

The present invention has been made in view of this point, and is a mass spectrometer that can cancel out the fifth-order aberration caused by the quadrupole electrostatic lens by arranging the electrostatic 12-pole lens in the mass spectrometry system. The purpose is to provide equipment.

[Structure of the Invention] To achieve this object, the present invention provides an ion source and a mass spectrometry system into which ions generated by the ion source are introduced, wherein the magnetic field and the direction perpendicular to the orbital plane of the ion beam are a mass spectrometer comprising at least first and second quadrupole electrostatic lenses arranged at a distance from each other in front of the magnetic field to provide convergence to the ion beam and divergence in the radial direction of the ion beam; and an ion detector into which ions selected in the mass spectrometry system are incident, in which a 12-pole electrostatic It is characterized by the arrangement of lenses.

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

[Example] FIG. 1 is a diagram showing the configuration of a device showing an example of the present invention. The difference from the proposed device shown in FIG. The 12-pole electrostatic lens T has been newly inserted and arranged.

Figure 2 shows a cross-sectional view of this 12-pole electrostatic lens T, in which 12 cylindrical electrodes P1 to P12 are arranged on the same circumference at 30° intervals, and each electrode is alternately connected to +V and -V potentials are applied.

Figure 3 shows the 12 generated by these 12 electrodes.
Shows the heavy pole electric field.

By the way, a quadrupole electrostatic lens having a structure as shown in FIG. 6 ideally generates an electric field expressed by the following equation.

V (x, y, z) = {K (z) / 2} { (x ² − y ² ) + {K (z)″ / 24} { (x ⁴ − y ⁴ )} ...(1) Here where K(z) is a coefficient related to the strength of the quadrupole field.

The first term in equation (1) is a function indicating the quadrupole field, and this term is the only one when the field inside the lens is uniform in the z direction. The second term is a term that occurs when the potential is not uniform in the z direction at the entrance and exit of the lens.

At the entrance and exit of the quadrupole electrostatic lens, a potential also exists at the part exiting the lens, and this potential can be expressed as follows by approximation up to the sixth order due to symmetry.

V (x, y, z) = {K (z) / 2} { (x ² − y ² ) + {
K
(z)″／24}{x ⁴ −y ⁴ )}+a(x ⁶ −15x ⁴ y ² +15x ² y ⁴
−y ⁶ ) ...(2) Here, a is a coefficient related to the strength of the decaphatic field.

Comparing equations (1) and (2), it can be seen that the third term in equation (2) is newly generated. This third term does not occur if the boundary condition at the entrance and exit of the quadrupole electrostatic lens satisfies the condition given by equation (1). however,
In order to satisfy the condition of equation (1), a complicated electrode structure and potential distribution are required, and it must be said that it is impossible in reality. Therefore, the third term above usually occurs. However, this third term has not been considered in the past, and appears as a fifth-order aberration in actual ion optical systems, and although its magnitude is not necessarily clear, it is It can be seen that the optical system includes the possibility of large fifth-order aberrations occurring.

On the other hand, the 12-pole electrostatic lens shown in FIG. 1 generates a dode dipole electric field φ(x, y) expressed by the following equation.

φ(x, y) = Vo(x ⁶ −15x ⁴ y ² +15x ² y ⁴ −y ⁶ )
...(3) Vo is a coefficient related to the strength of the dipole electric field and is determined by the potential applied to the lens electrode.

Equation (3) has the same form as the third term of equation (2), and generates fifth-order aberration. Therefore, this 12-pole electrostatic lens,
By inserting a quadrupole electrostatic lens into a mass spectrometry system (within an ion optical system) that has a component and setting its strength appropriately, at least one term of the fifth-order aberration caused by the quadrupole electrostatic lens can be resolved. It is possible to cancel it.

Further, by arranging a plurality of 12-pole electrostatic lenses, it is possible to cancel out even more terms of the fifth-order aberration.

It is desirable to use the 12-pole electrostatic lens at a location where ions pass away from the center orbit of the ion beam, that is, at a location where the width of the ion beam is widened. In the embodiment shown in FIG. 1, between the quadrupole electrostatic lens Q2, where the width of the ion beam is widened the most by the quadrupole electrostatic lenses Q1 and Q2, and the uniform fan-shaped magnetic field H, it is also connected to the magnetic field H. located nearby.

This 12-pole electrostatic lens has no effect on fourth-order or lower aberrations.

The 12-pole electrostatic lens actually used is (3)
Any device that can approximately generate the double dipole electric field expressed by the equation may be used. The easiest method to realize this is to use a cylindrical electrode as shown in FIG. 1, but it is also possible to use a cylindrical electrode as shown in FIG. 4, for example.

[Effect] As detailed above, according to the present invention, in order to provide convergence in the direction perpendicular to the magnetic field and the orbital plane of the ion beam, and to provide divergence in the radial direction of the ion beam, the magnetic field is In a mass spectrometer equipped with a mass spectrometry system including at least first and second quadrupole electrostatic lenses arranged at a distance from each other, by arranging a dodecapole electrostatic lens near the magnetic field, A mass spectrometer capable of reducing order aberrations is realized.

[Brief explanation of the drawing]

FIG. 1 is a device configuration diagram showing an embodiment of the present invention;
Figure 2 is a cross-sectional view of the 12-pole electrostatic lens in the embodiment shown in Figure 1, Figure 3 is a diagram showing the 12-dipole electric field generated in the 12-pole electrostatic lens, and Figure 4 is a diagram showing the 12-pole electrostatic field generated in the 12-pole electrostatic lens. FIG. 5 is a diagram showing the configuration of a conventional device, and FIG. 6 is a sectional view of a quadrupole electrostatic lens. S: ion source, H: uniform fan-shaped magnetic field, C: cylindrical electric field, D: ion detector, Q1 to Q3: 4-pole electrostatic lens, T: 12-pole electrostatic lens, P1 to P12: cylindrical electrode.

Claims (1)

[Claims] 1 A mass spectrometry system into which an ion source and ions generated by the ion source are introduced, which provides convergence in the direction perpendicular to the magnetic field and the orbital plane of the ion beam and divergence in the radial direction of the ion beam. a mass spectrometry system including at least first and second quadrupole electrostatic lenses arranged at a distance from each other in front of the magnetic field to provide a magnetic field; and ions selected by the mass spectrometry system are incident. A mass spectrometer equipped with an ion detector, characterized in that a 12-pole electrostatic lens is disposed near the magnetic field where the width of the ion beam is widened within the mass spectrometry system. .