JPS6148214B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a mass spectrometer using a quadrupole mass spectrometer. Various types of mass spectrometry paths have been considered in the past. A quadrupole mass spectrometer is one of them. A quadrupole mass spectrometer belongs to an electric field mass spectrometer, and has the characteristics of being smaller, lighter, and less expensive than, for example, a magnetic field mass spectrometer. However, on the other hand, it had the following drawbacks compared to the magnetic field type. In other words, in the case of a magnetic field type mass spectrometer, for example, when the strength of the magnetic field is set to a value corresponding to the mass number M in order to quantitatively analyze a substance containing a nuclide with the mass number M, The waveform of the collector output when
It is almost trapezoidal as shown by the solid line. It is extremely difficult to keep the strength of the magnetic field constant, and small fluctuations cannot be avoided. Now, when the strength of the magnetic field changes from a value corresponding to the mass number M to a value corresponding to a very slightly larger mass number M', the collector output becomes as shown by the broken line in FIG. 1a. As mentioned above, the waveform of the collector output is approximately trapezoidal, so even if it changes from M to M', which is extremely slightly larger, the peak value does not change. Therefore, in the case of a magnetic field type mass spectrometer, even slight fluctuations in the strength of the magnetic field do not cause errors in measurement. On the other hand, in the case of a quadrupole mass spectrometer, for example, if the scanning voltage is set to a value corresponding to the mass number M as described above, the waveform of the collector output will be as shown by the solid line in Figure 1b. The top becomes sharply pointed. In this case as well, it is difficult to keep the scanning voltage constant and slight fluctuations are inevitable. Now, when the magnitude of the scanning voltage changes from a value corresponding to the mass number M to a value corresponding to a very slightly larger mass number M', the collector output changes significantly as shown by the broken line in the figure. In other words, in the case of a quadrupole mass spectrometer, even if the scanning voltage varies slightly, the peak value of the collector output varies significantly. Therefore, it cannot be used in cases where the same mass peak is measured over a long period of time, such as in isotope ratio measurements, because accurate retention of the mass peak is required. Conventionally, when using a quadrupole mass spectrometer, a method of averaging the output obtained by repeatedly scanning a narrow range centered around the target mass number or a method of averaging the output obtained from a considerably wide scanning range has been used. Methods have been adopted in which an electrical output proportional to the peak area is obtained and the peak value is determined from this, but in either case, it takes time and the influence of adjacent peaks appears, and it is difficult to obtain a highly accurate method. There was a drawback that it could not be measured. The present invention has been made in view of the above circumstances, and its purpose is to substantially prevent fluctuations in the scanning voltage corresponding to the nuclide to be measured, and to perform highly accurate mass spectrometry. An object of the present invention is to provide a mass spectrometer using a quadrupole mass spectrometer. The details of the present invention will be explained below with reference to the illustrated embodiments. The figure shows an example in which a sample containing two types of isotopes A and B can be analyzed and the isotope ratio B/A can be measured at the same time. FIG. 2 shows the overall structure of the device of the present invention, which is roughly divided into a quadrupole mass spectrometer 1 ,
A scanning power supply 2 that applies a scanning voltage to the quadrupole of the quadrupole mass spectrometer 1 , and a control signal generator 3 that switches the output voltage of the scanning power supply 2 to three levels at predetermined time intervals and repeats this . , a processing system 4 that processes the collector output of the quadrupole mass spectrometer 1 , and a comparison amplifier 5 that controls the output level of the control signal generator 3 according to the collector output of the quadrupole mass spectrometer 1. It is made up of. The quadrupole mass spectrometer 1 has a well-known structure, and includes a vacuum insulating container 11 and the container 1.
Introduction system 12 that ionizes and introduces the sample into 1.
and an exhaust system 13 that evacuates the inside of the container 11.
and four electrodes 14a provided in the container 11,
14b, 14c, 14d (however, 14c and 14d are omitted) and a collector electrode 15. Note that the electrodes 14a, 14b, 14c, 1
4d are equally distributed in the circumferential direction, and every other one is commonly connected. The electrodes divided into two groups are connected to the output end of the scanning power source 2 via lead wires 16a and 16b provided to hermetically penetrate the vacuum insulating container 11. The scanning power supply 2 has a DC voltage E and an AC voltage e _cps.
The control signal generating device 3 is configured to _output a voltage e ₀ = _E +e _cps
The configuration is such that the magnitudes of E and e change in accordance with the magnitude of the output signal of E/e=constant. The control signal generator 3 is configured as follows. That is, the output voltage of the DC stabilized power supply 17 is supplied to three voltage dividers 18, 19, and 20, and the three types of voltages with different magnitudes obtained by these voltage dividers 18, 19, and 20 are transferred to the changeover switch 21 and the amplifier. 22, it is configured to be applied as a control signal to the scanning power supply 2 . Note that the changeover switch 21 is switched so that the output voltages of the voltage dividers 18, 19, and 20 are sequentially output for a certain period of time,
It is configured to repeat this process. On the other hand, the collector output of the quadrupole mass spectrometer 1 is input to the signal discriminator 23 of the processing system 4 .
This signal discriminator 23 performs signal discrimination in synchronization with the changeover switch 21. That is, when the changeover switch 21 is passing the output of the voltage divider 18, the current collector output is output to the terminal 24, and when the changeover switch 21 is passing the output of the voltage divider 19, the current collector output is output to the terminal 25. output,
Further, when the output of the voltage divider 20 is being passed through, the collector output at that time is outputted to the terminal 26. The output signal of the signal discriminator 23 is then introduced into the calculation display 27. This calculation display 27 is configured to display the level of the signals sent out from the terminals 24 and 25, and also to display the ratio between the magnitude of the signal sent out from the terminal 25 and the magnitude of the signal sent out from the terminal 24. has been done. Therefore, the terminals 24, 2 of the signal discriminator 23
The signal sent to 6 is introduced into the comparison amplifier 5 . This comparison amplifier 5 has the terminal 24
When a signal is sent out to the terminal 26, this signal is delayed so as to coincide with the signal sent out from the terminal 26 in time, and the signal sent out from the terminal 26 is multiplied by a fixed amount, and this multiplied signal and the terminal 24 are It is configured to output the difference between the signal sent from the The difference signal is provided as an output level adjustment signal of the DC stabilized power supply 17. Next, a case will be described in which a sample containing isotopes A and B is analyzed using the apparatus of the present invention configured as described above. First, the output voltage of the DC stabilized power supply 17 is set to V ₀ , and the output voltages of the voltage dividers 18, 19, and 20 are set as follows. That is, the scanning voltage V corresponding to the mass number of the isotope A is applied from the scanning power source 2 .
Set the output voltage of the voltage divider 18 so that _A is sent out, set the output voltage of the voltage divider 19 so that the scanning voltage V _B corresponding to the mass number of the isotope B is sent out from the scanning power supply 2 , Also, isotope A is supplied from the scanning power source 2.
The scanning voltage V _C corresponds to a mass number that is, for example, slightly larger than
The output voltage of voltage divider 20 is set so that . Next, the introduction system 12 of the quadrupole mass spectrometer 1 is activated to ionize the sample, and in this state, the changeover switch 21 is activated. When the changeover switch 21 operates, the outputs of the voltage dividers 18, 19, and 20 are introduced into the scanning power supply 2 in the above order for a fixed period of time, so that the scanning voltages V _A , V _B , and V _C are supplied from the scanning power supply 2 in the above order. This voltage is applied to the quadrupole mass spectrometer 1 divided into two sets of electrodes 14a, 14.
b, 14c, and 14d. Therefore, when the scanning voltage V _A is applied, the signal discriminator 23 sends out the signal X shown in FIG. 3a to the terminal 24,
When the scanning voltage V _B is applied, a signal Y shown in FIG. 3B is sent to the terminal 25, and when the scanning voltage V _C is applied, the signal Z shown in FIG. 3C is sent to the terminal 26. The peak value of the signal X is proportional to the total weight of isotopes with mass number A, and the peak value of signal Y is proportional to the total weight of isotopes with mass number B. Furthermore, since the scanning voltage V _C is set to a value slightly larger than the scanning voltage V _A , the peak value of the signal Z is determined by the scanning voltage on the waveform of the signal X obtained by the scanning voltage V _A. It is equal to the value at the point where it intersects the line shifted to V _B. That is, it becomes the value indicated by P on the slope line of the X signal indicated by the broken line in FIG. 3c. The calculation display 27 displays the peak value levels of the signals X and Y, and also displays the ratio Y/X of both peak values. Therefore, the isotope ratio B/A in the sample can be immediately determined from the above ratio. By the way, as described above, if the scanning voltage of the quadrupole mass spectrometer 1 fluctuates, a large error will be included in the measured value. When the scanning voltage fluctuates in this way, the following operation is performed to prevent the voltage fluctuation. That is, if the output voltage V ₀ of the DC stabilized power supply 17 is now constant, the difference between the peak value of the signal X and the peak value of the signal Z should be constant. output voltage
When V ₀ fluctuates, the above-mentioned difference will not be constant because the signals X and Z have non-linear parts, but will change. Therefore, it is only necessary to control the output voltage of the DC stabilized power supply 17 so that the above-mentioned difference becomes constant. Although the above explanation assumes that V ₀ fluctuates, it is still possible to adjust V ₀ even when the scanning voltage fluctuates. Therefore, in this embodiment, as a means for detecting fluctuations in the scanning voltage, the signal X and the signal Z are introduced into the comparator amplifier 5 , and the signal is determined from the difference in the peak values of the two signals X and Z. For example, V ₀ is adjusted so that the output is always zero. Therefore, even if the scanning voltage V _A attempts to fluctuate, it will not fluctuate for the above-mentioned reason, so that the set peak value of the mass number will always be maintained after all. Note that it is advantageous to set the scanning voltage V _C so that it matches the slope portion of the signal X that changes relatively linearly, because it is easier to set, and a large difference signal can be obtained when the scanning voltage fluctuates. It is. In this way, since the scanning voltage can always be maintained at the set value, the obtained collector output does not fluctuate, and as a result, isotope ratios can be measured immediately, making it possible to obtain something that is very easy to use. Note that in the embodiment described above, fluctuations in the scanning voltage are prevented using the signal X as a reference;
It is also possible to prevent fluctuations in the scanning voltage based on .
Further, in the above embodiment, two types of nuclides with mass numbers are measured at the same time, but three or more types of nuclides may be measured simultaneously. Also,
The voltage divider may be fixed, and the output voltage of the DC stabilized power source may be varied depending on the nuclide to be measured. As described in detail above, according to the present invention, it is possible to provide a mass spectrometer that can maximize the characteristics of a quadrupole mass spectrometer.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the problems of the conventional device, FIG. 2 is a diagram for explaining the configuration of an embodiment of the present invention, and FIG. 3 is a diagram for explaining the operation of the embodiment. 1 ...quadrupole mass spectrometer, 2 ...scanning power supply,
3 ...control signal generator, 4 ...processing system, 5 ...
Comparison amplifier, 17... DC stabilized power supply, 23...
signal discriminator.

Claims (1)

[Claims] 1 has a quadrupole mass spectrometer, a scanning power source that applies a scanning voltage to the quadrupole of the quadrupole mass spectrometer and changes the scanning voltage according to an input level signal, and a reference signal source, which outputs the reference signal. From the output of the source, the scanning power source generates a level signal capable of transmitting a scanning voltage corresponding to the mass number of a plurality of nuclides to be measured and a scanning voltage in the vicinity of a specific scanning voltage selected from these scanning voltages. means for sequentially inputting these level signals to the scanning power supply at fixed time intervals; means for detecting collector outputs corresponding to each scanning voltage of the quadrupole mass spectrometer; means for determining the difference between the collector output and the collector output when a scanning voltage near the scanning voltage is applied; and an output level of the reference signal source so that the difference determined by the means is always constant. A mass spectrometer characterized by comprising: means for controlling.