JPS5914859B2 - Fast measurement method for mass spectra - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for rapidly measuring mass spectra of a plurality of discontinuous masses.

As shown in Figure 1, a mass spectrum is generated by combining a microcurrent amplifier D into a mass spectrometer tube consisting of an ion source A) a mass analysis space B and an ion collector (or secondary electron multiplier tube) C.
Connect the ion collector (or Ion current Ii obtained with secondary electron multiplier) C
It is measured by amplifying it with a microcurrent amplifier D and recording it with a recorder H or the like.

Since the microcurrent amplifier D itself has a capacitance and a high input resistance, its response speed ranges from several microseconds to several seconds or more, and therefore an input signal faster than this response time is added, the disadvantage is that the output cannot follow the input.

Therefore, when measuring a mass spectrum using such a measurement method, the sweep speed is slowed down to a speed at which the minute current amplifier D can respond. However, the discontinuous mass MA
, MB, MC... When sweeping at a uniform slow speed, the measurement time becomes long and the amount of information is too large, which is inconvenient for processing. As shown in , the discrete masses to be measured MA, M
B, MCo sweep m, , m2, m3 are minute current amplifiers D
The mass Mx that does not need to be measured is carried out at a speed that can respond to
, MY, between mass MA and mass MB including M2 and mass MB
51, 52, etc. (including cases where the sweep speed is faster than the sweep speed at masses MA, MB, and Mc). However, after the skip is completed, even if the sweep speed is slowed down at masses MA, MB, ..., the ion current peaks Ii at masses Mx, MY, and M2 between masses MA and MB during skipping (Fig. 3A)
is microcurrent amplifier D! 0, and due to the response delay, the output current 10 of the microcurrent amplifier D is input to the third
As shown in Figure B, the true ion current value corresponding to the mass MB is not shown (the shaded area in Figure 3B is the signal input to the microcurrent amplifier D during skipping). Therefore this '5
The number of ions with mass MB cannot be determined accurately from the ion current peak. Therefore, as shown in FIG. 4, conventionally, after skip S ends, wait until the ion currents of masses Mx, MY, and M2 between masses MA and MB output from minute signal amplifier D become almost zero a. , then the next sweep of mass MB had to be performed. The purpose of the present invention is to improve measurement speed or accuracy by eliminating or reducing the time (tw) after skipping in the conventional mass spectrum measurement method. In a method for measuring mass spectra of discontinuous multiple masses in which multiple masses are swept stepwise with skips, an ion current blocking signal is applied to the mass spectrometer tube during the skip to eliminate unnecessary signals during the skip. The feature is that the current is not input to the microcurrent amplifier.

An embodiment of the present invention will be described below with reference to the drawings. Fifth
The figure shows a block diagram of an example of a mass spectrometer used to carry out the method of the present invention, and FIG. 6 shows a block diagram of the sweep signal generator 1 in the mass spectrometer of FIG. In Figure 6,
1 is a first multiplexer; 2A, 2B, and 2C are voltage generators corresponding to the masses MA, MB, and Mc, respectively; for ease of understanding, the generated voltages are, for example, 1V16V120V.
shall be.

3 is a mass sweep voltage generator, 4 is a first addition circuit, 5 is a hold circuit, and the above 1, 2A, 2B, 2C, 3, 4
, 5 constitute a sweep voltage generation circuit for the masses MA, MB, and MC.

6 is an integrating circuit that generates a ramp voltage for skipping, 7 is a second addition circuit, 8 is a second multiplexer,
9 is a comparator, and 10 is a flip-flop.

First, the selection signal S,a of the voltage A voltage generator 2A having mass M is applied to the first multiplexer 1, and the voltage is output from its output terminal to IV.
At the same time or a little later, a start signal S2 is applied to the mass sweep voltage generator 3 to output the maximum ramp voltage of 1 from its output terminal, and these two voltages are added to the first adding circuit. 4 and its output K is applied to the first multiplexer 8.

This second multiplexer 3 has a flip-flop 10
Since the output K is selected by the off signal, a sweep voltage of the mass MA from 1V to 2V, which is the output K, is output from the output terminal 11. This highest 2V is held in the hold circuit 5, and this voltage (2V) is transferred to the second summing circuit 7 together with the ramp voltage of the integrating circuit activated by the input signal S3.
This added voltage L is added to the second multiplexer 8.
is applied to At this time, the second multiplexer 8
Flip-flop 10 set by input signal S3
Since the signal L is selected by the ON signal of
1 to output L of the second adder circuit 7.

After a predetermined period of time has elapsed, the first multiplexer 1 selects and outputs the voltage 6V of the mass MB according to the selection signal Slb, and applies it to the first adder circuit 4 together with the output voltage of the single mass sweep voltage generator 3 that has been restarted. be done. When 6V is output from the first multiplexer 1, this voltage M is applied to the comparator circuit 9, so that the output voltage L of the second adder circuit 7
When M is equal to but greater than the voltage M, the comparator circuit 9 generates an output voltage which causes the integrator circuit 6 and the flip-flop 10 to be stopped or reset. Thus, again from the second multiplexer 8, a mass MB of 6V to 7
A sweep voltage K is output. From then on, as above, the highest 7
V is held by the hold circuit 5, and is again applied to the input signal S3. The output voltage L of the second adding circuit 7 is added together with the lamp voltage of the integrating circuit 6 which is activated by the second adding circuit 7, and the output voltage L of the second adding circuit 7 is selected from the output terminal 11 of the second multiplexer 8 and outputted. A sweep voltage for the mass Mc is also generated as described above. Selection signals Sla, S of the first multiplexer 1
lb, SlO switching, start signal S2, integration circuit 6
Each application of the input signal S3 is performed by sequence control and computer control.

The sweep signals output from the output terminal 11 of the sweep signal generator 1 in the time relationship shown in FIG. 2B are inputted to the sweep control circuit F as shown in FIG. Change the electric or magnetic field in space.

On the other hand, an on signal generated from the flip-flop 10 of the sweep signal generator 1 during the skip period of the sweep is applied to the ion source control circuit E as the ion current blocking signal X1. When the ion source A is an electron impact type, the voltage applied to the electron accelerating electrode is zero or significantly reduced by applying the ion current blocking signal X1 to the ion source control circuit E, thereby reducing the electron energy to zero or significantly. Alternatively, the ion current is blocked by stopping the generation of electrons, or changing the voltage applied to the ion accelerating electrode from negative to positive or zero to stop the acceleration of ions.

For other types, the ion current blocking signal can be used in the same way to prevent the generation of ion current.〇The ion current blocking signal X2 is swept and controlled without using the ion current blocking signal X1. In the case of a quadrupole type circuit, the ratio of the DC voltage and radio frequency voltage applied to the poles is changed by an ion current blocking signal to prevent the ion current from reaching the ion collector, etc. C. Good too,
Alternatively, a voltage as an ion current blocking signal X3 may be applied to the ion collector etc. C so that the ion current does not flow through the ion collector etc. C.

Which of the above ion current blocking signals Xl, X2, X3 is 1
Of course, it is also possible to apply two or more at the same time.

Fig. γ shows the ion current blocking signal X1 (Xl, X2, X3
) is applied to a mass spectrometer tube or the like, and the waveforms of the ion current 1i and the output current o of the microcurrent amplifier D are shown.

Although the method for measuring a mass spectrum of the present invention has been described using hardware, it may also be implemented using software.

In this way, according to the present invention, the ion current is blocked by the signal generated when the sweep is skipped, and unnecessary ion current during the skip is prevented from being input to the microcurrent amplifier that amplifies the ion current. This method has the effect of increasing the measurement speed and accuracy compared to the method of measuring mass spectra of a plurality of discontinuous masses.

[Brief explanation of the drawings] Figure 1 is a block diagram of a mass spectrometer used to carry out a conventional mass spectrum measurement method, and Figure 2A is a diagram of the sweep voltage Vf (or current 1f) and ion current. Relationship diagram, Figure 2B is a relationship diagram between sweep voltage (or current) and time, Figure 3
Figures A and 4A are time vs. ion current characteristic diagrams when the conventional measurement method is carried out, Figures 3B and 4B are output current diagrams of the microcurrent amplifier at that time, and Figure 5 is the current characteristic diagram of the current measurement method. A block diagram of an example of a mass spectrometer used when carrying out the method of the invention, Fig. 6 is a block diagram of a sweep signal generator in the apparatus, and Fig. 7 shows a block diagram of each part when carrying out the method of the invention. A variant diagram is shown. A: Ion source, B: Mass analysis space, C: Ion collector (or secondary electron amplifier), D: Microcurrent amplifier, E...
・Ion source control circuit, F...Sweep control circuit, G...Ion collector or secondary electron multiplier control circuit, H...Recorder, 1... ...Sweep signal generator, 1,8...Multiplexer, 2A,
2B, 2C... Mass voltage generator, 3...
・One-mass sweep voltage generator, 4, 7...Addition circuit, 9...Comparator, 10...Flip-flop.

Claims (1)

[Claims] 1. In a method for measuring mass spectra of a plurality of discontinuous masses in which the discontinuous masses are skipped and swept in a stepwise manner, the ion current is blocked by the signal generated during the skip, and the unnecessary 1. A high-speed mass spectrum measurement method, characterized in that a large ion current is not input to a minute current amplifier that amplifies the ion current.