JPS5823157A - Mass spectrograph - Google Patents

Abstract

PURPOSE:To detect ions with different masses with the maximum sensitivities, and to reduce the variation of the detection sensitivities caused according to the masses by providing a cylindrical or circular-hole electrode coaxially with an ion-introducing hole, and applying voluntary voltages independently to an ion- discharging hole and the cylindrical or circular-hole electrode. CONSTITUTION:A cylindrical electrode (CP) is placed between an ion-discharging hole plate (P1) and an ion-introducing hole plate (P2), and is located coaxially with an ion-introducing hole (En). The inner diameter of the electrode (CP) is adjusted so that it includes both an ion-discharging hole (Ex) and the hole (En). The hole plates (P1) and (P2) and the electrode (CP) can be earthed independently, and voluntary voltages can be applied to them. Ions, after passing through the hole (Ex), are deflected toward the center of a cylindrical electric field, and receive a divergence-suppressing effect existing within the above electric field before becoming incident upon the hole (En). As a result, since ion beams can be deflected while suppressing the divergence of ions, the transmittance of ions is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a four-electrode mass spectrometer. In a four-electrode mass spectrometer, the electric field created at both ends of the electrodes of the four-electrode (hereinafter abbreviated as Q and P) mass spectrometer section, that is, the edge electric field, is one of the factors that determines the performance of the mass spectrometer. The present invention aims to improve the influence of the electric field on the ion exit side of the above-mentioned edge electric field. In addition, in QP mass spectrometers, in order to prevent light emitted from the ion source from entering the ion detector and causing noise, off-axis P mass spectrometry is performed by shifting the center axis of the QP and the center axis of the ion detector. This invention relates to improving the influence of the edge electric field on the ion exit side of the device.

FIG. 1 shows an example of the configuration of a conventional QP mass spectrometer from the ion exit end of the QP electrode to the ion detector. R
1 and R2 are a pair of electrode rods in Q and P, PI is an ion exit hole plate, and Ex is an ion exit hole. P2 is an ion entrance hole plate, and En is an ion entrance hole into the ion detector. EMP is an electron multiplier placed after the ion entrance hole En. As shown in the figure, the central axis of the ion injection hole Kn is shifted laterally from the central axis Ax of the Q, P mass spectrometer. Df is the ion exit hole plate P
An appropriate voltage is applied by an ion deflection electrode disposed between the ion injection aperture plate P2 and the ion injection aperture plate P2, thereby deflecting the ions emitted from the ion emission aperture Ex toward the ion injection aperture En. In this case, a voltage having the same sign as that of the ion heavy gun is applied to the deflection electrode Df, thereby deflecting the ions toward the entrance hole En. Ions that have passed between the QP electrodes in a stable orbit are diverged into ion beams due to the action of the edge electric field formed at the ends of the QP electrodes, reducing the efficiency of incidence into the ion detector. The extent of this effect depends on the time the ions spend in the edge field. Therefore, it depends on the edge field length, ion mass, and ion implantation voltage. Although the deflection electrode Df improves the efficiency of ion injection into the ion detector to some extent by deflecting the ion beam toward the ion injection hole En, it does not have the effect of improving the injection efficiency against the above-mentioned divergence of the ion beam. As mentioned above, the effect of this edge field increases as the ion mass increases. Figure 2 shows this relationship. Figure 2 shows the ion detection intensity using the ion mass as a parameter when changing the voltage of the deflection electrode Df in the configuration shown in Figure 1.The optimum deflection electrode voltage that maximizes the ion detection intensity is the ion mass. The ion detection intensity also differs depending on the mass, and the detection sensitivity is lower for ions with larger masses. In other words, the conventional configuration shown in FIG. 1 has a problem in that the ion transmission chamber of the entire mass spectrometer is poor and the sensitivity is low, and the sensitivity is not the same depending on the mass.

The present invention aims to improve such problems.

FIG. 3 shows the configuration of the portion from the ion exit end of the QP to the ion detector in an embodiment of the present invention. R1, R2
are a pair of electrode rods of QP, Pl is an ion exit hole plate, P2 is an ion entrance hole plate, Ex is an ion exit hole, En is an ion entrance hole, and EMI) is an electron multiplier. The arrangement of the above parts is the same as the conventional example shown in FIG. In this embodiment, instead of the deflection electrode Df in the conventional example shown in FIG. 1, a cylindrical electrode cp is arranged coaxially with the ion entrance hole En between the ion exit aperture plate P1 and the ion entrance aperture plate P2. There are characteristics. Instead of the cylindrical electrode cp, the electrode plate with a circular hole is arranged so that the central axis of the circular hole is the ion incidence hole, K
It may be arranged so as to coincide with the axis of n. The inner diameter of this cylindrical electrode CP (the diameter of the circular hole in the case of a circular hole electrode) is set so that both the ion exit hole Ex and the ion entrance hole En are included within the inner diameter of the CP. Ion exit hole plate 2 cylinder electrodes.

The ion entrance aperture plates can be grounded independently of each other or can be applied with any voltage.

The cylindrical electrode applies a potential of the same sign as the ions, but the electric field is affected by the potential of the ion exit aperture plate and the dynode of the electron multiplier. In particular, the vicinity of the central axis of the cylindrical electrode is almost dependent on the dynode potential (with the opposite sign of the ion) of the ion exit aperture plate and the electron multiplier.

The ions that have passed through Ex are deflected toward the center because the center of the cylindrical electric field is shifted from the center of the cylindrical electric field, and are incident on En due to the effect of suppressing the divergence in this electric field. In this way, since the ion beam can be deflected while suppressing ion divergence, ion transmittance can be improved.

Furthermore, the following effects can be obtained in the present invention. Figure 4 shows the ion detection intensity using the ion mass as a parameter when the cylindrical electrode voltage is kept constant and the voltage of the ion exit aperture plate P1 is varied. From this figure, it can be seen that the optimum voltage of the ion exit aperture plate P1 that provides maximum sensitivity is approximately the same regardless of the ion mass.Figure 5 shows the voltage of the deflection electrode Df in the configuration of Figure 1. The relationship between the ion detection intensity when the voltage of the ion exit aperture plate P1 is changed while keeping the ion exit aperture plate P1 constant is shown, and the voltage of the ion exit aperture plate P1 that provides the maximum sensitivity differs depending on the mass number. The effect that the optimal voltage of the ion exit aperture plate PI does not change depending on the ion mass when using the configuration shown in FIG. By setting the configuration appropriately, ions of different masses can be detected with maximum sensitivity, and the difference in sensitivity due to the amount of condensate, in which ions of different masses are detected with maximum sensitivity, is also smaller than in the conventional configuration.

[Brief Description of the Drawings] Fig. 1 is a side view of the main part of the conventional example, Fig. 2 is a graph showing the relationship between the deflection electrode voltage and ion detection intensity in the conventional example, and Fig. 3 is an embodiment of the present invention. Example: Main part side view of the device, No. 4
The figure is a graph showing the relationship between the voltage of the ion exit aperture plate PI and the ion detection intensity in the same embodiment, and FIG. 5 is a graph showing the same relationship in the conventional example. R1, R2...QP electrode rod, Ex...ion exit hole, Pl...ion exit hole plate, En...ion entrance hole, P2...ion entrance hole plate, KMP...electron multi Pliers, CP...Cylindrical electrode. Agent Patent Attorney Kosuke Agata

Claims (1)

[Claims] In an arrangement where the center of the ion entrance hole of the ion detector is shifted from the central axis of the quadrupole field, the ion A mass spectrometer in which a cylindrical or circular hole electrode is provided coaxially with an entrance hole, and a voltage can be arbitrarily applied independently to the ion exit hole and the cylindrical or circular hole electrode.