JPS62168328A - Mass spectrometer ion source - Google Patents

Abstract

PURPOSE:To heighten the sensitivity of measurement, by providing a magnetic field intensity controlling means, and switching the magnetic field intensity of source magnets corresponding to the mass number of an ion to be measured. CONSTITUTION:Source magnets 12 are electromagnets which are made by winding coils 13 around iron cores, and are disposed oppositely sandwiching an ionization chamber 1 outside a filament 7 and a trap 11. A power supply 14 which flows electric currents for the coil 13 is controlled by a CPU 15, and the output voltage thereof is changed corresponding to the molecular weight of a gas which is designated for an object to be measured by an instruction from a keyboard 16. Namely, in case of the measurement of a light gas such as hydrogen and helium, the voltage is switched for a low side, and in case of the measurement of other gases, it is switched for a high side, so that the intensity of the electromagnets can be changed by varying the electric currents which are flowed to the electromagnets.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an electromagnetic field kumquat mass spectrometer 4. method and chemical ionization method.

In the ion source VC of a mass spectrometer using these methods, a source magnet for collimating the entire electron beam incident on the ionization chamber is installed near the ionization chamber in order to increase the ionization efficiency.

This source magnet creates a magnetic field in the direction of electron incidence within the ionization chamber. Since the magnetic field lines are parallel to the electron flow, the incident electrons are prevented from spreading radially from the entrance hole, and the helical interlocking increases the probability of collision with gas molecules.

As a result, it acts as an agent to increase ionization efficiency.

I! →Problem to be solved by the invention In the above-mentioned ion source equipped with a source magnet i, ions of elements with small mass numbers such as hydrogen and helium are strongly influenced by the magnetic field and are deflected. There was a problem in that the efficiency of extraction from the sample was reduced and the sensitivity of the 9 analysis was reduced.

B) Means for Solving the Problems In the present invention, the magnetic field strength of the source magnet is switched depending on the mass number of the ions to be measured. A magnetic field strength control means is provided.

0 → When measuring ions with a small acting mass number, the magnetic field strength is weakened to increase extraction efficiency from the ion source, and for ions with a large mass number, the magnetic field strength is strengthened to increase ionization efficiency. Above all, the sensitivity of the measurement is increased in both cases.

(to) Mysterious practice FIG. 1 shows one embodiment of the ion source of the present invention.

Sample gas is introduced into the ionization chamber (1) through the sample introduction port (2), and adult ions are removed through the extraction port (3).
The ions pass through the ion focusing lens (4) and are extracted as an ion stream (5). An electron beam (6) for ionizing the gas in the ionization chamber is generated by a filament (7), introduced through a shield (extraction electrode) (8) and a hole (9), and passed through a hole α0) to a trap ( anode) α
captured by υ. In this example, the electron beam (6) fully collimated source magnet α is an electromagnet composed of a coil α3) wound around an iron core, and the ionization chamber (1) is sandwiched between the filament (71,) wrap. aυ
are placed facing each other on the outside.

The power supply αa that flows the coil (13) K current is controlled by the CPU Q, and is configured so that the output voltage of the iIf source (14) can be changed by instructions from the keyboard αQ, which is an input terminal for the CPU. . In this embodiment, all the output voltages on the power supply side from the keyboard are switched depending on the molecule # of the gas to be measured. In other words, when measuring light gases such as hydrogen and helium, the voltage is switched to the low side, and when measuring other gases, the voltage is switched to the high side, thereby changing the current ft flowing through the electromagnet and changing the strength of the electromagnet. .

In the second embodiment described below, the configuration of the ion source is almost the same as that in FIG. 1, but the method of controlling the magnetic field strength is different from the above. This second embodiment is used for mass chromatography or mass fragmentography KM in gas chromatography mass spectrometry (GC/MS),
After a preset time (chromatogram retention time) in the memory of the CPU constituting the magnetic field strength control means has elapsed, the magnetic field strength is automatically cut off. FIG. 2 illustrates the relationship between the mass chromatogram and the magnetic field strength. The upper graph in FIG. 2 shows a mass chromatogram.

The lower graph shows the magnetic field strength (power supply voltage of the electromagnet), and the horizontal axis shows the retention time 1R. As shown in Figure 2, the magnetic field strength is set low while gases with small mass numbers such as H2 are being output from the chromatograph, and the magnetic field strength is automatically set to normal before other gases begin to be output. can be switched to the value of

A variation of the embodiment described above is to reduce the magnetic field strength while the mass spectrometer is scanning the low mass number region.
It is also possible to increase the magnetic field strength while scanning other areas.

It is also possible to speed up such a switching operation and apply it to the case of mass fragmentography. In particular, in the case of mass fragmentography, it is also possible to perform swifting to obtain the optimum magnetic field strength according to the mass number.

Also, instead of using an electromagnet as the source magnet as shown in Figure 1, a permanent magnet is used.

A mechanically operated mechanism may be used as the magnetic field strength control means.

(G) Effects of the Invention According to the present invention, measurement sensitivity is improved in mass spectrometry of elements with small mass numbers such as hydrogen and helium, so it exhibits excellent effects particularly when used in trace gas analysis.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the ion source of the mass spectrometer of the present invention, and FIG. 2 is a diagram illustrating the timing of switching the magnetic field strength of the source magnet of the ion source of the present invention together with a mass chromatogram. It is. (1)...Ionization chamber (2)...Sample introduction port (3)...Ion extraction port (4)...Ion focusing lens (5)...Ion flow (6)
...electron beam (7) ...filamen) (8)
...Shield (9), 00)...hole
α1)...Trap Q3...Source magnet
0...Coil 04)...Power supply (19
・-CPUα0...Keyboard book ゛-"f'" Figure 1 Figure 2

Claims (1)

[Claims] (1) A source magnet for collimating electrons incident on the ionization chamber and a control means for controlling the magnetic field strength of the source magnet are provided, and the control means switches the magnetic field strength according to the mass number of ions to be measured. The ion source of the mass spectrometer.