JPS5914860B2 - Mass spectrometry tube pulse or AC modulation automatic correction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Conventionally, when measuring a mass spectrum, as shown in FIG. Generally, a modulation signal of several H2 to several KH2 is added from the modulation signal generator E, and a pulsed (or alternating current) ion current is obtained from the mass spectrometer tube and input to the electronic circuit D.

This is for the purpose of improving the S/N ratio, removing background components, that is, residual gas components, or compatibility when inputting the ion current to a pulse circuit or an alternating current circuit.
However, if the ion current is modulated by applying a modulation signal with a constant period to ion source A or mass analysis space B, etc., the phase and waveform of the modulated ion current signal coming out from mass analysis space B will change. It is affected by mass and energy, and an ion current signal with a constant phase and waveform determined by the modulation signal R shown in FIG. 2 Atl cannot be obtained.

That is, as the 5 mass M increases, the phase and waveform change greatly. (Figure 2B shows the ion current Ii when the mass M is small, and Figure 2C shows the ion current Ii when the mass is large.) Conversely, when the ion energy E1 of the mass M becomes smaller, the phase of the ion current signal And the waveform changes greatly by 10. This means that the speed of the ion passing through the mass analysis space is the ion mass,
It varies depending on the energy, so the higher the frequency, the more significant it is. For this reason, even if the ion current is modulated, the expected accurate mass spectrum cannot be measured.

The fifteenth invention aims to obtain a highly accurate mass spectrum by focusing on the above points, and modulates the ion current with a modulation signal to generate a pulsed or alternating current ion current from the mass spectrometer tube. In the method for measuring a mass spectrum, the phase and width of the modulation signal or the ion current exiting the analysis tube are automatically corrected by a signal corresponding to the mass and energy of ions incident on the mass analysis tube, It is characterized by an ionic current having a constant phase and width.
Embodiments of the present invention will be described below with reference to the drawings.

5. Figure 3 shows a block diagram of a mass spectrometer used in an embodiment of the present invention, where A, B, C, and D are the same as in Figure 1, F is an ion source control circuit, and G is a sweep control circuit. circuit,
H is a correction circuit. The 30 sweep signals supplied from the sweep control circuit G to the mass spectrometry space B change the magnetic field (sector type) or electric field (quadrupole type) in the mass spectrometer space B, and the ion current of each corresponding mass flows into the mass spectrometer tube. Since the current or voltage that is the sweep signal is the signal Q corresponding to the mass M, the ion current output from the ion source A is given kinetic energy by the voltage of the ion accelerating electrode. , the voltage corresponding to the voltage of the electrode taken out from the ion source control circuit F is a signal P corresponding to the ion energy Ei at that time.

Therefore, a signal P corresponding to the energy of this ion and a signal Q corresponding to the mass of the ion are supplied to a correction circuit H which operates as detailed below, and a corrected modulation signal k is extracted from the circuit H. and supply it to ion source A or mass analysis space B. The influence of the mass M on the phase and waveform of the modulated ion current is, as described above, when the mass is small, as shown in Figure 2B, the phase delay is small and the pulse width is large; As a result, the phase is greatly delayed and the pulse width is narrowed as shown in FIG. 2C.

Therefore, in order to always obtain an ion current with a constant phase and pulse width regardless of the mass size, it is necessary to
When the mass M produces an ion current as shown in FIG.
If correction is made using the correction circuit H so that The pulse always has a constant phase and waveform regardless of the size of the mass. Therefore, the correction circuit H is composed of, for example, a delay circuit and a monostable multivibrator, and the delay circuit and monostable multivibrator are controlled by a signal corresponding to a large mass taken out from the sweep control circuit G. The phase and pulse width are corrected to the modulated signal w shown in FIG. 2D. When this modulation signal w is supplied to the ion source A or the sweep control circuit B, a pulsed ion current having the phase and waveform shown in FIG. 2E is obtained from the mass spectrometer tube. next,
Similarly, the delay circuit and the monostable multivibrator are controlled by the signal corresponding to the small mass, and the phase and pulse width of the modulation signal R are changed to the modulation signal w with the phase and pulse width shown in FIG. 2A.
If the current is corrected, a pulsed ion current 11 having the phase and waveform shown in FIG. 2B can be obtained from the mass spectrometer tube.

When the ion energy changes, a voltage corresponding to the voltage applied to the ion accelerating electrode of the ion source A is extracted from the ion source control circuit F, and is added to the correction circuit H as a signal P corresponding to the ion energy, and the above-mentioned mass In the same way as when the ion energy changes, the modulation signal w corrected according to the change in ion energy is extracted from the correction circuit H, the ion current is modulated, and the ion current is output from the mass spectrometer tube with a constant phase and waveform regardless of the change in ion energy. The pulsed ion current is extracted.

Note that when the ion energy is large, the ion velocity is large, so the phase delay of the modulated pulsed ion current is small, so the relationship is inverse to the mass, and the amount of correction of the modulation signal is small, and the ion energy is When the correction amount is small, the correction amount becomes large.

FIG. 4 is a block diagram of a mass spectrometer used in another embodiment of the present invention, and FIG. 5 is a block diagram of an example of the correction circuit J shown in FIG. This example shows that the mass of the ion,
By passing a modulated ion current whose phase and waveform have changed depending on the energy through a correction circuit J, a modulated ion current that is independent of the mass and energy of the ions is supplied to the electronic circuit D, as shown in Fig. 3. The same symbols indicate the same things, K and M are first and second delay circuits controlled by a signal P corresponding to the ion energy and a signal Q corresponding to the mass of the ions, and N is an adder circuit.

When the ion cage flow 11 taken out from the ion collector or the secondary electron multiplier C is input to the first delay circuit K of the correction circuit J, this ion current i is converted into a signal P corresponding to the ion energy and/or the ion A delay phase corresponding to the signals P and Q is generated by the signal Q corresponding to the mass of the electronic circuit D. An ion current with a constant phase and waveform is always input regardless of the energy and mass of the ions. The above description is for the case where the ion current is pulse modulated, but it can also be applied to the case of AC modulation in which the ion current is modulated with an AC wave, and the operation is the same as in the case of pulse modulation. , the explanation is omitted.

Further, in order to use the method of the present invention, hardware was used in the above embodiments, but it goes without saying that the process can be performed by resoftware on a computer.

In this way, according to the present invention, the modulation signal or the phase and waveform of the output ion current of the mass spectrometer tube are automatically corrected by signals corresponding to the mass and energy of the ions incident on the mass spectrometer tube, and the phase and waveform of the output ion current of the mass spectrometer tube are automatically corrected. Since the phase and waveform of the ion current are modulated, a highly accurate mass spectrum can be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an example of a mass spectrometer for performing conventional mass spectrometry measurements, Fig. 2 is an operational diagram, and Figs. 3 and 4 are used in different embodiments of the present invention. FIG. 5 shows a block diagram of a correction circuit J in the apparatus shown in FIG. 4. A...Ion source, B...Mass analysis space, C...Ion collector (or secondary electron multiplier), D...Electronic circuit, E...Modulation signal generator, F...Ion source control circuit, G
...Sweep control circuit, H, J...Correction circuit, K, M...Delay circuit, N...Addition circuit.

Claims (1)

[Claims] 1 In a mass spectrum measurement method in which an ion current is modulated by a modulation signal to obtain a pulsed or alternating current ion current from a mass spectrometer tube, a signal corresponding to the mass and energy of ions incident on the mass spectrometer tube A method for automatically correcting pulse or alternating current modulation of a mass spectrometer tube, characterized in that the phase and width of a modulation signal or an output ion current of an analysis tube are automatically corrected to obtain an ion current having a constant phase and width. .