JPH042034A - Method and device for mass-analysis - Google Patents

Abstract

PURPOSE:To have easy setting of the electrode voltage at a plurality of levels by making scan for the voltages impressed on a plurality of electrode, and providing automatic voltage setting to the specified value on the basis of the ion sensing output obtained through these scans. CONSTITUTION:Initial voltage setting is made for electrodes A and B during mass spectral measurement of N<15>. The voltage of electrode A is scanned, and when the max. peak value is obtained, setting of the voltage VPA1 of the electrode A at the time is made. This is followed by voltage scan for the electrode B, and when the max. peak value is obtained, setting of the voltage VPB1 of the electrode B at the time is made. Then comparative judgement is made between the max. peak value PA1 and max. peak value PA2. In case the former is greater than the latter, the setting voltage of the electrode A remains at VPA1, and in the opposite case, the voltage of the electrode A is set anew to VPA2. As for how to consider about voltage setting, the same applies to the case with three or more electrodes as the case with two electrodes, provided that steps increase according to the number of electrodes.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method and apparatus for mass spectrometry, particularly a mass spectrometer characterized by voltage settings of a plurality of electrodes used to guide generated ions to a mass spectrometer. METHODS AND APPARATUS.

[Conventional technology]

When the sample is atomized and introduced into the ionization section along with an inert gas such as nitrogen gas or argon and microwave energy is applied, the sample and gas are ionized and a plasma is generated. Attempts are being made to guide the ions in the plasma to a mass spectrometer for mass analysis.

In such microwave plasma ion mass spectrometry, it is desirable to guide the generated ions in a focused state at a certain predetermined position, and then introduce the ions into the mass spectrometer. Furthermore, in order to guide ions in the plasma in a focused manner to a certain predetermined position, it is desirable to arrange a plurality of electrodes between the plasma generation section and the certain predetermined position.

Plasma is also generated by ionizing the sample and the inert gas by introducing the sample into an ionization section together with an inert gas such as argon in atomized form and exposing it to a high-frequency magnetic field.

Therefore, mass spectrometry can be similarly performed by extracting ions from this plasma and introducing them into the mass spectrometer. This is known as inductively coupled high-frequency plasma ion mass spectrometry, and is disclosed in, for example, JP-A-62-20231 (corresponding specification of U.S. Pat. No. 4,740,696) and U.S. Pat. No. 4,804,838. It is stated in the specification etc.

Even in the case of such inductively coupled high-frequency plasma ion mass spectrometry, it is desirable to guide the ions in the plasma in a focused state at a certain predetermined position and then introduce them into the mass spectrometer. It is desirable to arrange a plurality of electrodes between and the certain predetermined position to guide ions in a focused state to that position.

[Problem to be solved by the invention]

Generally, different voltages are applied to multiple electrodes, but it is not easy to set these voltages to optimal values.

Therefore, one object of the present invention is to provide a mass spectrometry method and apparatus in which it is easy to set a plurality of electrode voltages.

Another object of the present invention is to provide a mass spectrometry method and apparatus suitable for allowing accurate setting of multiple electrode voltages.

Another object of the present invention is to provide a mass spectrometry method and apparatus suitable for preventing changes in sensitivity due to drift of multiple electrode voltages.

Yet another object of the present invention is to provide a mass spectrometry method and apparatus suitable for preventing erroneous voltage settings due to saturation of ion detection output.

Still another object of the present invention is to provide a mass spectrometry method and apparatus that enable high counting efficiency.

Still another object of the present invention is to provide a mass spectrometry method and apparatus that can clarify mass number errors, if any.

[Means to solve the problem]

In the present invention, the voltages applied to the plurality of electrodes are each scanned and automatically set to a predetermined value based on the ion detection output obtained through the scanning.

According to one aspect of the invention, the mass number scans are performed repeatedly, and the voltage scan is performed prior to each mass number scan.

According to another aspect of the invention, the voltages applied to the plurality of electrodes are scanned in a predetermined order and are automatically set based on the ion detection output obtained through the scan. Subsequently, the voltage of at least one selected electrode of the plurality of electrodes is scanned, and the voltage of the selected electrode is automatically checked and reset based on the ion detection output obtained through the scanning. Ru.

[Effect]

In the present invention, the voltage applied to the plurality of electrodes is scanned, and is automatically set to a predetermined value based on the ion detection output obtained through the scanning, which facilitates the setting. .

According to one aspect of the present invention, since mass number scans are performed repeatedly and electrode voltage scans are performed prior to each mass number scan, sensitivity changes due to electrode voltage drifts that occur during mass spectrometry can be avoided. This will help prevent this.

According to another aspect of the invention, after scanning the plurality of electrode voltages, at least one selected one of them is scanned again, so that the electrode voltage can be brought closer to the appropriate value. Become. That is, it is possible to more accurately set the electrode voltage.

〔Example〕

Referring to FIG.
Microwave power is supplied to the plasma generation section through.

At this time, a sample 4 is atomized by a nebulizer 5 and introduced into a plasma generation section together with a N (nitrogen) discharge gas 3 to generate plasma.

Ions in the plasma are guided to a mass spectrometer 6 in vacuum. That is, ions are focused by an ion lens system 6A, further subjected to mass analysis by a quadrupole mass filter 6B, which is a mass spectrometer, and the ions subjected to mass analysis are detected by an ion detector 7.

The output of the detector 7 is amplified by a pulse amplifier 8 and introduced into a discriminator 9. The discriminator 9 has a discrimination level automatically set by the master CPU 29, and only pulse signals above this level enter the gate circuit 12.

On the other hand, from the user via the personal computer 31,
Information on setting analysis conditions enters the master CPU 29 via the interface 30, and this CPU converts the information signal into a command signal in the register 28 and transfers it to the slave CPU 20. The slave CPU 20 can store voltage data corresponding to the mass number to be scanned in the scan memory 18 for mass number scanning by the quadrupole mass filter 6B of the ion mass spectrometer according to the command signal of the register 28. It has become. Therefore, slave CPU2
0 temporarily stores the address signal in the latch circuit 16 and further passes it through the up/down counter 17 to the scan memory 1.
Set the address to 8. The scan data (mass number) corresponding to the address is stored in the scan memory 18 through the buffer 19. By repeating this operation, a series of scanned mass number data is stored in the scan memory 18.

After that, when the personal computer 31 executes the start of measurement, the slave CPU 20 sends a start signal to the scan timing circuit 15, and this circuit 15 opens the gate of the gate circuit 12 according to the scan mode.

At the same time, a clock pulse signal is input to the up/down counter 17, the counter of the up/down counter 17 is incremented, the memory address of the memory 18 is scanned, the mass number data is output, and the latch circuit 2
The data is input to the D/A converter 23 while being temporarily stored in the D/A converter 23. The D/A converter 23 drives the high frequency power supply 24 to step-scan the quadrupole mass filter 6B. That is, mass number scanning is performed. The ion pulses within the time of that step are counted by the pulse counter 13 through the gate circuit 12, and sent to the latch circuit 14.
The count value for each step scan is stored in the memory section in U20. This scanning is repeated several times, and the average value of each ion count corresponding to the scanning position, so-called mass number, is determined by the master CPU 29, and a spectrum is calculated and displayed on the screen of the personal computer 31. Furthermore, buffer 2
Scan memory data from 1 to slave CPU at the same time
20 and displays the mass number on the horizontal axis of the screen of the personal computer 31 while comparing the mass number currently being scanned with the mass number stored in advance.

If the two do not match, a mismatch display is displayed on the screen of the personal computer 31.

Furthermore, the master CPU 29 has a function of controlling the D/A converter 11 and setting the voltage of the ion detector high voltage generator 1.0 to a position where its multiplication sensitivity is favorable.

FIG. 2 shows the electrode arrangement of the ion lens system of FIG. 1. Ions in the plasma are extracted by the extraction electrode 50 through the sampling cone electrode 50', and further accelerated by the acceleration electrode 51 through the extraction electrode 50 and the acceleration electrode 51. The ions thus accelerated pass through the gap between the collecting electrodes 54, which consist of a central electrode element 52 disposed on the center line of the lens system and peripheral electrode elements 53 disposed around it. The ions that have passed through in this manner are focused by the focusing electrode 55 through the differential aperture electrode 56 to the position of the slit electrode 57,
The focused ions enter the quadrupole mass filter 6B through the slit electrode 57 and are subjected to mass analysis.

When plasma is generated, light is emitted, and the emitted light is blocked by the center electrode element 52.

The sampling cone electrode 50', the extraction electrode 50, and the slit electrode 57 are grounded, whereas the accelerating electrode 51. Collection electrode 54. Focusing electrode 55 and differential aperture electrode 56 each have a voltage of -350 volts;
Voltages of +8 volts, +31 volts and +20 volts are applied.

These voltages should be determined so that the output of the ion detector 7 is maximized, but adjustment thereof is difficult in practice. Therefore, in the present invention, the adjustment is automatically performed to facilitate the adjustment.

For ease of understanding, FIG. 3 shows the accelerating electrode 51 to which a voltage is applied. Collection electrode 54. A flow for automatically adjusting and setting the voltage applied to only arbitrary two electrodes of the focusing electrode 55 and the differential aperture electrode 56 is shown. Here, 5 the selected two electrodes are A and B.
shall be.

In this voltage adjustment, mass number scanning of the quadrupole mass filter is not performed, but voltage adjustment is performed with the mass number fixed at a certain mass number. - As an example, a voltage adjustment method using the mass number of nitrogen N15 isotope ions in the discharge gas will be explained.

Referring to FIG. 3, first, the mass spectrum of N15 is measured. During this measurement, the initial voltages of electrodes A and B are set. Subsequently, n=1 is set, the voltage of electrode A is scanned, and it is determined whether the ion detector output at that time is the maximum. This decision step is repeated until the maximum peak value is obtained. When the maximum peak value is obtained, the voltage vp^1 of the electrode A at that time is set.

Next, a determination is made as to whether n=1. Since n; 1 has been set, it is determined that n = 1 is correct in this step, and the process then proceeds to voltage scanning of electrode B. Through this voltage scanning, it is determined whether the output signal obtained from the ion detector is the maximum. This determination is repeated until the maximum peak value is obtained. When the maximum peak value is obtained, the voltage VPBI of electrode B at that time is set. After this, a determination is made as to whether n=1, but since n=1 is correct in this case, a determination is then made as to whether n=2. Obviously, n=2, so in this case the value of n is incremented by "1". That is, n=2 is set. In this state, voltage scanning of electrode A is performed again. Then, it is determined whether n=1 is correct, but in this case n=2, so n=
1 is judged to be incorrect, and it is judged whether the voltage Vp^2 of electrode A when the ion detector output obtained through the second IB scan is the maximum is equal to the first set voltage Vp^. be done. If they are equal, the voltage of electrode A remains set to Vp^1, but if they are not equal, the maximum peak value P^1 of the output of the first ion detector and the voltage of the second ion detector 8 are changed. A comparative judgment is made on the maximum peak value P^2 of the force. If the former is larger than the latter, the set voltage of electrode A remains Vp^1, but in the opposite case, the voltage of electrode A is reset to VP^2.

The voltage setting of electrode B is also performed in the same manner as shown in the flowchart of FIG. Finally, it is determined whether n=2, but since n=2 is correct in this case, the voltage setting adjustment for electrodes A and B is completed.

When there are three or more electrodes, the voltage setting concept is exactly the same as when there are two electrodes, except that the number of steps increases by the number of electrodes.

The plurality of electrodes can be considered to constitute one lens. Since voltage adjustment is performed for each electrode, this causes a voltage change between the electrodes, which affects the ion detector output as a whole. Therefore, by adjusting each electrode voltage multiple times, it is possible to bring each electrode voltage closer to the optimal voltage value that provides the maximum ion detection output as a whole.

The degree of influence of each electrode voltage on the ion detection output is not necessarily the same, and some electrode voltages may have a much smaller influence on the ion detection output than other electrode voltages. In this case, it is advisable to adjust the electrode voltages that have a large influence. Further, the electrode voltage, which has a very small influence, may only need to be checked once.

FIGS. 4 to 6 are flowcharts for adjusting and setting three electrode voltages with n=3. However, although the first and second electrode voltage checks are performed three times, the third electrode voltage check is performed twice. The three electrodes will be described as A, B and C, respectively.

First, NIB spectrum measurement is performed. Through this measurement, initial voltage settings for electrodes A, B, and C are performed.

Thereafter, n=1 is set, and voltage scanning of electrode A is performed in this state. This scan is repeated until the ion detector output gives the maximum peak value. When the output reaches its maximum peak, the voltage VPA1 of electrode A at that time is set. After that, a judgment is made whether n=1 or not,
In this case, since n=1 is correct, the next step is to check and set the voltage of electrode B (FIG. 5). This check.

The setting is done in a similar way to that of the voltage of electrode A.

After that, it is determined whether n = 1, but n = 1
is correct, so first check the voltage of electrode C.

Proceed to settings (Figure 6). This check and setting are also the same as those for the voltage of electrode A. Finally, it is determined whether n=3, but in this case n=3 is incorrect, so check the voltage of electrode A again.

Return to settings. That is, the value of n is incremented by 1.The checking and setting method is the same as the first time.

Next, it is determined whether n=1, but since n=2 is correct, it is then determined whether n=2.

In this case, since n=2 is correct, the second voltage Vp^2 of the electrode A and the first voltage V P A 1 are then compared and judged. If they are equal, VPAI is not changed, but if they are not equal, a comparison is made between the first ion detector output P^1 and the second ion detector output P^2. If the former is greater than the latter, no change in VPAI is made, but in the opposite case, the voltage at electrode A becomes VPAI.
It is reset to Vp^2 instead of I.

Exactly the same is then carried out for electrodes B and C. Finally, it is determined whether n=3, but since n=2, the process returns to checking the voltage of electrode A once again. That is, n is further incremented by rlJ. As a result, the voltage of electrode A is checked and set again. The method is the same as the first and second rounds. After that, a judgment is made as to whether n = 1, but since n = = 1, n = 2 on the subsequent page.
A judgment will be made as to whether Of course, since n=3 instead of n;2, this time the voltage Vp of electrode A for the third time
3 is equal to the second setting voltage vPAi or VpAx. If they are equal, the voltage setting of electrode A is not changed, but if they are not equal, the judgment of the magnitude of the third ion detector output P^8 and the second ion detection output FAI or P^2 is made. will be done. Of course, if the former is small, the voltage of electrode A is not changed, but in the opposite case, the voltage of electrode A is reset to VpAs.

Thereafter, the process moves to the third checking and setting step of the voltage of electrode B (FIG. 5). The procedure is the same as that for electrode A. When this is completed, a determination is made as to whether n;3. Of course, since n=3, this completes the adjustment and setting of the voltages of all electrodes.

The above adjustment and setting of the electrode voltage is performed for each mass number scan prior to that scan. In other words, the scanning of the high frequency of the high frequency power supply 24, and therefore the scanning of the mass number, is performed in the 78th (b)
If the procedure is performed as shown in Figure 7(c), the mass spectrum will be obtained as shown in Figure 7(c), so the adjustment and setting of the electrode voltage should be repeated during the previous stage T of mass number scanning (see Figure 7(a)). be exposed. This reduces sensitivity changes due to electrode voltage drift.8 Nitrogen gas has an isotope abundance ratio of N14 of 99.6% and 0.9%.
There is 37% N14. When N14 ions are used to adjust and set the electrode voltage, the ion detection output may become saturated at a certain voltage or when the sample concentration is high. This problem can be solved by using N1B ions, which have a low abundance ratio.

Also, the isotope abundance ratio of argon, which is an inert gas, is 0.
．． 337% Ar36.0.063% Ar3899
．． There is 6% Ar40. Therefore, when using argon for micro liquid plasma generation, it is preferable to use Ar'' or Ar5g, which has a low abundance ratio.

Note that when gas ions for generating microwave plasma are used to adjust and set the electrode voltage, there is also the advantage that there is no need to prepare a special standard sample.

FIG. 8 is an example of a display screen displayed when adjusting the electrode voltage. The voltage values of electrodes A, B, C, and D are displayed, and the count value of the ion detector output pulses for the N'' spectrum is shown in bar graph form overlaid for each electrode voltage.

This allows you to visually check the adjustment and setting status of the electrode voltage.

FIG. 9 is a block diagram for setting the discrimination level of the discriminator. The output ion signal from the ion detector 7 is amplified by the pulse amplifier 8 and input to the discriminator 9. The master CPU controls the D/A converter 11' and sets the discrimination level of the discriminator 9. At this time, the first
As shown in FIG. 0, before plasma generation, the noise N is counted by a pulse counter 13 as the number of pulse counters at each equally spaced point within the pulse height value adjustment range LDL-HDL.

It is stored in the memory 32. Next, a plasma is generated and Nl”
The ions are measured, the number of signals S at the same point is counted, and the master CPU 29 calculates the S/N ratio at each point. Then, the maximum peak value DL of the S/N curve is determined, and the discrimination level of the discriminator 9 is set at this position. This increases pulse counting efficiency and increases detection sensitivity.

The horizontal axis in Fig. 10 is the pulse height value, which is the 11th
The vertical axis of the figure represents the magnitude of the pulse.

〔Effect of the invention〕

According to the present invention, the following effects can be expected.

(1) It is easy to set a plurality of electrode voltages.

(2) It is possible to accurately set the electrode voltage.

(3) Sensitivity changes due to electrode voltage drift can be prevented.

(4) Erroneous voltage setting based on saturation of ion detection output can be prevented.

(5) High counting efficiency is achieved.

(6) Mass number errors can be confirmed.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a mass spectrometer showing an embodiment of the present invention, FIG. 2 is a layout diagram of the lens system in FIG. 1, and FIG. 3 is an adjustment of the electrode voltage according to the present invention. A flow diagram of a setting example, FIGS. 4 to 6 are a flow diagram of another adjustment of the electrode voltage according to the present invention, a flow diagram of a setting example, and FIG. 7 is a flow diagram of the adjustment and setting of mass number scanning and electrode voltage according to the present invention. FIG. 8 is an example of the screen display during adjustment of the electrode voltage according to the present invention, FIG. 9 is the discriminator circuit diagram of FIG. 1, and FIG. An explanatory diagram for setting the discrimination level, FIG. 11 is a diagram for explaining the horizontal axis of FIG. 10. Mass spectrometry section, 9...Discriminator,...Scan memory, 20...Slave CPU, Figure CR7 screen → Time Figure 11 Figure Screen

Claims (1)

[Claims] 1. Generate ions, guide the ions in a focused manner to a predetermined position using a plurality of electrodes, and guide the guided ions to a mass spectrometer for mass spectrometry; A mass spectrometry method for detecting the mass-analyzed ions, in which voltages applied to the plurality of electrodes are each scanned, and the voltages are automatically set based on the ion detection output obtained through the scanning. Mass spectrometry. 2. The mass spectrometry method according to claim 1, wherein each of the voltages to be set has a value when the ion detection output is substantially maximum. 3. The mass spectrometry method according to claim 1, wherein said ions are microwave plasma ions. 4. The mass spectrometry method according to claim 3, wherein said ions are ions of an isotope with a lower abundance ratio among isotopes. 5. The ion detection output is applied to a discriminator having a discrimination level set to a substantially maximum value of the ratio of the ion detection output when the plasma ions are generated to the noise component of the ion detection output when the plasma is not generated. A mass spectrometry method according to claim 3, characterized in that it leads to: 6. Generate ions, guide the ions in a focused state at a predetermined position using a plurality of electrodes, guide the guided ions to a mass spectrometer and perform mass analysis while performing mass number scanning, A mass spectrometry method for detecting the mass-analyzed ions, in which voltages applied to the plurality of electrodes are each scanned, and the voltages are automatically set based on the ion detection output obtained through the scanning. Mass spectrometry. 7. The mass number of the ions to be scanned is stored in advance in a storage device, and when scanning the mass number in order to perform the mass analysis, the mass number during this scanning is used as the stored mass number. 8. A mass spectrometry method according to claim 7, characterized in that an error in the mass number during the scan is checked by successive comparison with the mass number. 8. Generate ions, focus and guide the ions to a predetermined position using multiple electrodes, guide the guided ions to a mass spectrometer, and perform mass analysis while repeating mass number scanning. , a mass spectrometry method for detecting the mass-analyzed ions, in which the voltages applied to the plurality of electrodes are scanned prior to each mass number scan, and the ions obtained through the scan are A mass spectrometry method in which the voltage is automatically set based on the detection output. 9. The mass spectrometry method according to claim 8, wherein each of the voltages to be set has a value when the ion detection output is substantially maximum. 10. Generate ions, guide the ions in a focused manner to a predetermined position using multiple electrodes, guide the guided ions to a mass spectrometer for mass analysis, and collect the mass-analyzed ions. A mass spectrometry method for detecting
Each of the voltages is automatically set based on the ion detection output obtained through the scanning, and then the voltage of at least one electrode selected from the plurality of electrodes is scanned, and the voltage is obtained through the scanning. A mass spectrometry method characterized in that the voltage of the selected electrode is automatically checked and reset based on the ion detection output. 11. A mass spectrometry method, characterized in that the mass number of the ions is scanned multiple times for the mass spectrometry, and voltages of the plurality of electrodes are set prior to each scan. 12. A means for generating ions, a plurality of electrodes for guiding the generated ions in a focused state at a predetermined position, a means for applying a voltage to each of these electrodes, and mass spectrometry for the guided ions. means for repeatedly performing mass number scanning so as to perform mass number scanning; means for detecting mass-analyzed ions; and means for scanning voltages applied to the plurality of electrodes prior to each mass number scanning; and means for automatically setting the voltage based on the output of the ion detection means obtained through the ion detection means. 13. The mass spectrometer according to claim 12, wherein each of the voltages to be set has a value when the ion detection output is substantially maximum. 14. The mass spectrometer according to claim 12, wherein said ion generating means includes a microwave plasma ion source. 15. The mass spectrometer according to claim 14, wherein said ions are ions of an isotope with a lower abundance ratio among isotopes. 16. A discriminator is provided for discriminating the ion detection output, and the discrimination level of this discriminator is the ratio of the ion detection output when the plasma ions are generated to the ion detection output noise component when the plasma is not generated. 16. A mass spectrometer according to claim 15, wherein the mass spectrometer is set to a substantially maximum value. 17. A means for storing in advance the mass number to be scanned of the ions, and when scanning the mass number for the mass analysis, successively comparing the mass number during this scanning with the stored mass number. 13. A mass spectrometer according to claim 12, wherein the mass spectrometer is configured to check for mass number errors during its scanning. 18. A means for generating ions, a plurality of electrodes that guide the generated ions in a focused state at a predetermined position, a means for applying a voltage to each of these electrodes, and mass spectrometry for the guided ions. means for repeatedly performing mass number scanning so as to perform mass number scanning; and prior to each mass number scanning, sequentially scanning the voltages of the plurality of electrodes, based on the output of the ion detection means obtained through the scanning. The voltage of each electrode is set, and then the voltage of at least one preselected electrode is scanned, and the voltage of the selected electrode is determined based on the output of the ion detection means obtained through the scanning. and means for adjusting said voltage applying means to check and set the voltage. 19. The mass spectrometer according to claim 18, wherein each of the set voltages is set to a value that substantially maximizes the output of the ion detection means obtained through the scan.