JP2000311649A - Ion detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong a life until replacement is required by providing a plurality of conversion dynodes, and providing a switching means selecting to which conversion dynode a high voltage should be applied. SOLUTION: A transfer switch 7 selects a conversion dynode 6a side to be applied with a high voltage, and it is applied with the negative high voltage of -5 kV through -20 kV from a high-voltage generating circuit. Converged ions passing through an aperture electrode 3 are attracted by the negative high voltage and reach the conversion dynode 6a. Secondary electrons are generated by the collision with the conversion dynode 6a, the generated secondary electrons collide with the initial stage electrode 8a of a secondary electron multiplier tube 8 then collide with electrodes 8b, 8c... and the final stage electrode 8f successively, and electrons are multiplied and outputted. When the ion collision face of the conversion dynode 6a is deteriorated and conversion efficiency is reduced after use for a long period, the conversion dynode to be applied with the high voltage is changed to the conversion dynode 6b side by the selector switch 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion detector used for detecting ions in a mass spectrometer or the like.

[0002]

2. Description of the Related Art An ion detector using a conversion dynode is sometimes used for ion detection in a mass spectrometer or the like. FIG. 1 shows an example of an ion detector used in a mass spectrometer. After passing through the aperture electrode 3, the ions 2 separated by mass in the mass analyzer 4 are incident on a conversion dynode 6 to which a high voltage (several kV to several tens kV) of an opposite charge to the ions is applied and converted. . That is, a high negative voltage is applied to the conversion dynode when positive ions are detected, and a high positive voltage is applied to the conversion dynode when negative ions are detected. Secondary electrons (positive ions) generated by the collision of positive ions (negative ions) with the dynode
Is guided to the secondary electron multiplier 18, and is amplified and output as an electron current. The output of the secondary electron multiplier 18 is the amplifier 2
At 0, the signal is further amplified and detected as an output.

[0003]

The output of the ion detector as described above is set by the voltage applied to the conversion dynode and the gain of the amplifier. As long as these are kept constant, measurement can be performed under stable and constant conditions. It should be possible. However, the output fluctuates due to continuous use in spite of the fact that the setting is kept constant. This is presumably because the position at which the ions collide with the conversion dynode is always the same, and the state of the conversion dynode changes. Therefore, if the ion detector is used for a long time, the state changes and the conversion dynode deteriorates, the detection sensitivity drops, and finally the entire detector needs to be replaced.

The ion detector itself is expensive, and it is desired that each ion detector can be used for as long as possible. Therefore, an object of the present invention is to provide an ion detector that extends the life until the ion detector needs to be replaced.

[0005]

The ion detector of the present invention amplifies charged particles generated by applying a high voltage having a polarity opposite to that of ions to be detected to a conversion dynode and causing the ions to collide with the conversion dynode. The ion detector includes a plurality of conversion dynodes and switching means for selecting which conversion dynode is to be applied with a high voltage.

In this ion detector, since a high voltage is applied to the conversion dynode selected by the switching means, the ion detector continues to be used by the selected conversion dynode. When the conversion dynode eventually deteriorates and high-sensitivity measurement cannot be performed, switching is performed by the switching unit so that a high voltage is applied to another conversion dynode. Thereby, the conversion dynode can be easily replaced without replacing the entire ion detector, and high-sensitivity measurement can be performed again.

[0007]

FIG. 2 is a diagram showing a configuration of a mass spectrometer using an ion detector according to one embodiment of the present invention.
In the figure, 2 is an ion to be detected, 3 is a ring-shaped aperture electrode, and 4 is a quadrupole mass separator. In this mass spectrometer, the ions 2 having a value of the mass / charge number determined by the setting of the voltage applied to the quadrupole mass separator 4 can pass through the mass separator 4. The passed ions 2 are made to converge by an aperture electrode 3 provided at a subsequent stage. 6
a and 6b are conversion dynodes, which have the same shape. 7 is a changeover switch, which is a conversion dynode 6
a, 6b so that a high voltage can be applied to any of the selected conversion dynodes. Reference numeral 18 denotes a secondary electron multiplier, which is arranged such that the first-stage electrode 8a to the second-stage electrode 8b, the third-stage electrodes 8c,... A resistor is interposed between the electrodes, and when a high voltage is applied to the first-stage electrode 8a, a voltage changed by a voltage drop due to the resistance is applied to each of the electrodes 8b, 8c,. It is like that. The conversion dynodes 6a and 6b are both arranged so as to face the first-stage electrode 8a, and the conversion dynodes 6a and 6b are adjacent to each other.

Next, the operation of the ion detector will be described. The case where positive ions are measured is taken as an example. The changeover switch 7 is selected so that a high voltage is applied to the conversion dynode 6a, and a negative high voltage (−5 to −2) from the high voltage generation circuit is selected.
0 kV). Then, the focused ions that have passed through the ring-shaped electrode 3 are pulled to a negative high voltage, and
to a. Secondary electrons are generated by colliding with the conversion dynode 6a. The generated secondary electrons collide with the first-stage electrode 8a of the secondary electron multiplier 18, and thereafter, 8b,
The electrons are multiplied and output by successively colliding with 8c,..., 8f. As a result, electrons in proportion to the amount of ions transmitted through the mass separator 4 are output, so that high-sensitivity measurement can be performed. However, after long-term use, the ion collision surface of the conversion dynode 6a is deteriorated, and conversion efficiency is reduced. When the voltage drops, the conversion dynode to which the high voltage is applied by the changeover switch 7 is changed to the 6b side. After the switching, the positive ions proceed as shown by the broken line, and collide with the conversion dynode 6b having a new surface, thereby recovering the conversion efficiency.

Although the above embodiment is directed to the case of positive ions, the same applies to the case of negative ions, and the polarity of the applied voltage may be reversed. Although the changeover switch is used in the embodiment,
Two terminals may be prepared so that the cord from the power supply can be switched by hand. In the embodiment, two conversion dynodes are switched, but three or more conversion dynodes may be used. However, as the number of conversion dynodes increases, the area of the conversion dynodes decreases. Therefore, if the number of conversion dynodes is increased excessively, some measure must be taken to converge ions.

[0010]

As described above, the ion detector of the present invention has a plurality of conversion dynodes and switching means for selecting which conversion dynode is to be applied with a high voltage. Even if is deteriorated, conversion efficiency can be recovered by switching to another conversion dynode.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a conventional mass spectrometer using an ion detector.

FIG. 2 is a configuration diagram of a mass spectrometer using an ion detector according to one embodiment of the present invention.

[Explanation of symbols]

 2: Electron 3: Aperture electrode 4: Mass separator 6a, 6b: Conversion dynode 7: Changeover switch 8: Secondary electron multiplier 8a: First stage electrode, 8f: Last stage electrode 10: Amplifier

Claims (1)

[Claims] An ion detector for applying a high voltage having a polarity opposite to that of ions to be detected to a conversion dynode and amplifying and detecting charged particles generated by colliding the ions with the conversion dynode. An ion detector comprising a dynode and switching means for selecting which of the conversion dynodes applies a high voltage.