JPH0228227B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion detector used in mass spectrometers and the like, and particularly to an ion detector using a secondary electron multiplier.

Conventionally, in order to detect positive and negative ions, an ion-ion converter was installed in front of the first dynode of the secondary electron multiplier, and when positive ions were detected, a negative voltage was applied to the converter. Positive ions are made to enter the converter, and when negative ions are detected, a positive voltage is applied to the converter to make negative ions enter the converter. During positive ion detection, when positive ions enter the ion-ion converter, electrons are mainly emitted from the converter and enter the first dynode of the secondary electron multiplier; during negative ion detection, negative ions When the positive ions are incident on the ion-ion converter, positive ions are emitted from the converter and made incident on the first dynode of the secondary electron multiplier.

In the conventional positive and negative ion detection methods described above, it is necessary to switch the voltage applied to the ion-ion converter according to the polarity of the ions to be detected, which makes the power supply for the ion-ion converter complicated. In addition, a mechanism for switching the applied voltage is required, and operation is troublesome.

The present invention was made with the object of solving the above-mentioned difficulties of the conventional method when attempting to detect both positive and negative ions with an ion detector using a secondary electron multiplier. The present invention will be explained below with reference to Examples.

FIG. 1 shows an embodiment of the present invention.
1 is a deflection electrode and an ion-ion converter (hereinafter simply referred to as an ion-ion converter or converter); 2 is a first dynode of a secondary electron multiplier; hereinafter, a plurality of stages of dynodes 3, 3... and an anode 4
A secondary electron multiplier tube P is constructed by the following. 5
is the power supply for the voltage applied to the dynode, and a voltage of -0.7KV to -3.5KV can be applied to the first stage dynode, and by changing this voltage, the gain is changed. The ion-ion converter 1 emits positive ions when negative ions are incident.The incident negative ions cause metal atoms or adsorbed molecules on the converter surface to sputter as positive ions, or the incident negative ions cleave and release positive ions. Depending on the mechanism of generation or incident negative ions stealing electrons and becoming positive ions, it is possible to use the same material as the first-stage dynode of the secondary electron multiplier. Reference numeral 6 denotes a power source for applying voltage to the ion-ion converter 1, which is capable of applying a voltage of 0 to +3.5 KV to the converter 1. The present invention is characterized in that the polarity of the voltage applied to the converter is constant (positive). Ions to be detected enter the ion-ion converter 1 from the left as shown by the arrow. Considering the case of detecting positive ions, the incoming positive ions are repelled because a positive voltage is applied to the converter 1, and their trajectory is deflected toward the first dynode 2 of the secondary electron multiplier, and the power source When the voltage of 6 is adjusted appropriately, the positive ions to be detected that fly in are transferred to the first dynode 2.
is incident on the dynode, causing secondary electrons to be emitted from the first dynode. When detecting negative ions, since a positive voltage is applied to the converter 1 as described above, the negative ions to be detected enter the converter 1, and as described above, positive ions are emitted from the converter 1.
Since the converter 1 has a positive voltage and the first dynode 2 has a negative voltage, these positive ions are accelerated toward the first dynode, enter the first dynode 2, and emit secondary electrons.

As described above, the secondary electron multiplier can detect both positive and negative ions while applying a positive voltage to the ion converter 1.

When a negative voltage is applied to the ion-ion converter 1 when positive ions are detected in the configuration shown in FIG. 1, the state is the same as the positive ion detection mode in a conventional positive and negative ion detector. FIG. 2 is an example of a performance comparison between the present invention device and a conventional device in detecting positive ions. The horizontal axis is the applied voltage to the ion-ion converter 1. The case where a negative voltage is applied is shown to the left of the center of the figure, and the case where a positive voltage is applied to the converter 1 is shown to the right of the center of the figure. As mentioned above, the case where a negative voltage is applied to the converter 1 corresponds to the conventional device, and the case where a positive voltage is applied shows the performance of the device of the present invention. The vertical axis is the ion detection sensitivity (relative value), the curve connecting black circles is when the initial stage dynode voltage is -1.65KV (low sensitivity), and the curve connecting white squares is when the dynode voltage is -2.55KV. (high sensitivity), the left and right curves in the figure are approximately symmetrical to each other, and when the dynode voltage is increased (in the negative direction), the present invention tends to have higher sensitivity than the conventional example.

In the above embodiment, the ion-ion converter 1 has a curved shape similar to a dynode, but
Of course, this may be in the form of a flat plate. However, if anything, the curved shape is more efficient both as a deflection electrode for positive ions and as an ion-ion converter for negative ions. Furthermore, in the above embodiment, the deflection electrode and ion-ion converter 1 described above is separately provided in front of the secondary electron multiplier, but the first stage dynode and second stage dynode of the secondary electron multiplier are connected separately. If the structure is such that the electrical insulation voltage is sufficiently large by electrically separating the two electrodes, the first stage dynode can be used as the above-mentioned deflection electrode and ion-ion converter.

The ion detector of the present invention has the above-mentioned configuration,
Both positive and negative ions can be detected without switching operations.
The device becomes simpler in terms of power supply and switching mechanism.
In particular, when switching between positive and negative ions at high speed and detecting them, switching between positive and negative ion-ion converter power supplies is extremely complicated in conventional devices, and the present invention is particularly advantageous.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a device according to an embodiment of the present invention;
The figure is a graph comparing the performance of the present invention and a conventional example. 1... Deflection electrode and ion-ion converter,
2, 3...dynode, 4...anode, 5...
Dynode power supply, 6... Power supply for the ion-ion converter 1.

Claims (1)

[Claims] 1. Place an electrode with the characteristics of an ion-ion converter in front of the secondary electron multiplier tube, apply a voltage of a constant polarity to this electrode, and apply the same polarity to the electrode for ions of the same polarity as this voltage. The electrode acts as a deflection electrode that allows ions to enter the secondary electron multiplier, and for ions of opposite polarity to the voltage, the electrode acts as an ion-ion converter, and the ions emitted from the electrode are converted into secondary electrons. An ion detector whose light is incident on an electron multiplier tube.