Mass spectrometer and calibration method for mass spectrometer

Abstract

A mass spectrometer 100 comprises: an ion source 101 that ionizes a sample; a detection unit 105 that has a photomultiplier tube 105a and that analyzes the mass of the sample ionized by the ion source 101; a vacuum chamber 102 that achieves communication between the ion source 101 and the detection unit 105; a vacuum gauge 106 that measures the degree of vacuum inside the vacuum chamber 102; and a data analysis unit 112 and analysis control unit 113 that use electrons emitted from the vacuum gauge 106 to calibrate a setting of the photomultiplier tube 105a.

Description

Mass spectrometer and method for calibrating mass spectrometer

[0001] The present invention relates to a mass spectrometer and a method for calibrating a mass spectrometer.

[0002] Patent document 1 describes a mass spectrometer having a gas inlet adapted to supply a sample gas to be ionized to an ionization region of the mass spectrometer, a calibration unit adapted to supply a calibration gas to be ionized to the ionization region, and an ionization unit adapted to ionize the sample gas and / or the calibration gas in the ionization region, wherein the calibration unit includes at least one evaporation source that generates the calibration gas by evaporating a raw material.

[0003] Special Publication No. 2022-553543

[0004] A mass spectrometer includes an ion source that ionizes compounds in a sample, a mass analysis unit such as a mass filter that separates ions derived from the compounds according to their mass-to-charge ratio (m / z), and a detector that detects the separated ions.

[0005] Patent Document 1 describes a mass spectrometer equipped with a vacuum chamber that connects an ion source and a mass spectrometer, which is equipped with an ionization-type vacuum gauge that measures the degree of vacuum inside the vacuum chamber, and which operates the vacuum gauge when no measurements are being made in the mass spectrometer to calibrate the detector of the mass spectrometer using a calibration gas.

[0006] Thus, to calibrate the detector of a mass spectrometer, the sample must be ionized before being introduced. However, because the sample must be ionized when calibrating the detector, a technology that allows for more efficient calibration has been awaited.

[0007] The present invention provides a mass spectrometer that allows calibration to be performed more easily than in the past, and a method for calibrating a mass spectrometer.

[0008] The present invention includes a plurality of means for solving the above-described problems, and one example thereof includes an ion source that ionizes a sample, a mass analysis unit having a photomultiplier tube and analyzing the mass of the sample ionized by the ion source, a vacuum chamber that connects the ion source and the mass analysis unit, a vacuum gauge that measures the degree of vacuum inside the vacuum chamber, and a calibration unit that calibrates the settings of the photomultiplier tube using electrons emitted from the vacuum gauge.

[0009] According to the present invention, calibration can be performed more easily than in the past. Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments.

[0010] A diagram showing the overall configuration of a mass spectrometer. A flowchart of voltage adjustment of a photomultiplier tube. A sequence diagram of the voltage adjustment set of a photomultiplier tube. A sequence diagram of voltage adjustment of a photomultiplier tube. A diagram showing an example of a display of a software GUI screen for voltage adjustment of a photomultiplier tube.

[0011] An embodiment of a mass spectrometer and a method for calibrating a mass spectrometer of the present invention will be described with reference to Figures 1 to 5. In the drawings used in this specification, identical or corresponding components are designated by the same or similar reference numerals, and repeated description of these components may be omitted.

[0012] First, the overall configuration of the mass spectrometer will be described with reference to Fig. 1. Fig. 1 is a diagram showing the overall configuration of the mass spectrometer.

[0013] The mass spectrometer 100 shown in FIG. 1 includes an ion source 101, a vacuum chamber 102 having an ion transport section 103, a mass separation section 104, and a detection section 105, a vacuum gauge 106, an A / D conversion section 111, a data analysis section 112, an analysis control section 113, a display device 114, and the like.

[0014] The ion source 101 is a part that ionizes a sample.

[0015] The inside of the vacuum chamber 102 is evacuated by a pump to transport the sample ionized by the ion source 101 to the detection section 105, and an ion transport section 103, a mass separation section 104, a detection section 105, and a vacuum gauge 106 are arranged inside the vacuum chamber 102.

[0016] The ion transport section 103 is a section that transports ions that have been ionized by the ion source 101 and introduced into the vacuum chamber 102 toward the mass separation section 104 and detection section 105 on the downstream side.

[0017] The mass separation unit 104 is a device such as a mass filter that separates compounds in the ionized sample according to their mass-to-charge ratio (m / z).

[0018] The detection unit 105 is a part that analyzes the mass of a sample by detecting ions separated into only those of a predetermined mass in the mass separation unit 104, and includes conversion dynodes (CD1, CD2), a scintillator, a photomultiplier tube 105a (photomultiplier tube), etc.

[0019] The vacuum gauge 106 is an ionization vacuum gauge for measuring the degree of vacuum inside the vacuum chamber 102, and may be, for example, a cold cathode ionization vacuum gauge.

[0020] The analysis control unit 113 is electrically connected to each mechanism within the mass spectrometer 100 and controls their operation. In this embodiment, it calibrates the settings of the photomultiplier tube 105a using electrons emitted from the vacuum gauge 106.

[0021] The analysis control unit 113 can be configured as a computer having, for example, a display device 114 configured by a liquid crystal display or the like, a memory configured by a hard disk memory or an external memory, an A / D conversion unit 111 that converts the detection signal from analog to digital, an interface, an input device such as a keyboard for inputting operation commands, etc., a data analysis unit 112, etc., and may be configured as a single computer or as separate computers, and is not particularly limited.

[0022] The data analysis unit 112 sends commands to the analysis control unit 113 and the like to control the operation of each mechanism. Furthermore, A / D converted data (photometric values) obtained from the detection unit 105 via the A / D conversion unit 111 is taken into the data analysis unit 112. The data analysis unit 112 performs arithmetic processing using the taken-in data (photometric values). In other words, the data analysis unit 112 can control each mechanism of the detection unit 105 via the analysis control unit 113, and can also perform arithmetic processing of the data.

[0023] The analysis control unit 113 controls the operation of each device based on various programs stored in a storage device. The control processes for the operations executed by the analysis control unit 113 may be integrated into a single program, or may be separated into multiple programs, or a combination thereof. Some or all of the programs may be implemented using dedicated hardware or may be modularized.

[0024] The display device 114 is a user interface such as a touch panel display, and outputs information to the user and accepts various inputs from the user. In this embodiment, it displays a screen for setting conditions for calibration. Details will be described later.

[0025] The drive voltage (hereinafter referred to as PMT voltage) of the photomultiplier tube 105a mounted in the detection unit 105 and the offset voltage (hereinafter referred to as base voltage) of the signal input to the A / D conversion unit 111 can be adjusted by changing the settings from the A / D conversion unit 111 of the detection unit 105.

[0026] Because the optimal base voltage and PMT voltage differ for each mass spectrometer 100 and the photomultiplier tube 105a therein, optimization is required when setting up the device after assembly and when replacing new parts. Therefore, the parameters of the A / D converter 111 are mainly adjusted when the device is assembled. In addition, adjustment of the parameters must be performed when a problem occurs during actual use, such as after replacing parts due to a malfunction of the A / D converter 111 or the photomultiplier tube 105a.

[0027] In the mass spectrometer 100, the PMT voltage has conventionally been adjusted by introducing a sample consisting mainly of positive ions, but this is time-consuming. Therefore, in this embodiment, the idea is to use electrons to adjust the PMT voltage, which has conventionally been done using ions.

[0028] Next, the flow of PMT voltage adjustment and an example of device operation will be described with reference to Figures 2 to 5. Figure 2 shows a flowchart of PMT voltage adjustment. Figure 3 is a sequence diagram of the voltage adjustment set, Figure 4 is a sequence diagram of voltage adjustment, and Figure 5 is a diagram showing an example of a software GUI screen display for voltage adjustment.

[0029] First, the flow of preparation will be described with reference to Fig. 2. In this embodiment, the data analysis unit 112 and the analysis control unit 113 perform calibration at a timing when analysis is not being performed by the detection unit 105, but the timing of voltage adjustment is not limited to this timing.

[0030] First, when the PMT voltage adjustment process is started (S101), the analysis control unit 113 executes PMT voltage adjustment set (S102). This PMT voltage adjustment set is a pre-operation for PMT voltage adjustment, and is an operation for turning on various power sources. For example, it can be executed when it is recognized that the user has selected and pressed a voltage adjustment set button 114a1 on a PMT voltage adjustment setting screen 114a displayed on the display device 114 as shown in FIG. 5.

[0031] Next, the analysis control unit 113 adjusts the PMT voltage (S103). For example, this can be done when it recognizes that the user has selected and pressed a PMT voltage adjustment button 114a2 in a PMT voltage adjustment setting screen 114a displayed on the display device 114 as shown in FIG.

[0032] In this embodiment, since calibration is preferably performed using electrons emitted from the vacuum gauge 106, it is desirable that the data analysis unit 112 and the analysis control unit 113 set the detection unit 105 to measure negative ions during calibration.

[0033] Specifically, when the PMT voltage adjustment button 114a2 is pressed, the analysis control unit 113 specifies the conversion dynodes (CD1, CD2), scintillator, and PMT voltage to the detection unit 105 in the order shown in the time chart of FIG.

[0034] For example, the various parameters of the adjustment software include the following "target value," "allowable error (tolerance)," "Acoff (software adjustment step value)," and "maximum number of trials (upper limit of repetition)."

[0035] 3, when the user presses the PMT voltage adjustment button 114a2, the analysis control unit 113 sets the voltages of the measurement conditions of the conversion dynode, scintillator, and photomultiplier tube 105a to specified voltages and turns each electrode "ON" so that electrons are introduced into the detection unit 105. Next, the vacuum gauge 106 is turned ON to start emitting electrons.

[0036] As a result, as shown in FIG. 4, the analysis control unit 113 instructs the detection unit 105 to start measurement.

[0037] After reading the software operation parameters for the screen settings sent from the analysis control unit 113, the detection unit 105 repeats the measurement processing flow, average area value calculation, and target value comparison until the target value of the setting parameters is within ± the allowable error, or the number of repetitions reaches the maximum number of attempts.

[0038] The emitted electrons are detected as counts (analog data) by the photomultiplier tube 105a via the conversion dynodes (CD1, CD2) and scintillator according to the parameter settings for negative ion detection in the detection unit 105. The detected data is converted from analog to digital data by the A / D conversion unit 111 and then read into the data analysis unit 112, where a pulse width histogram is created and the average pulse area is calculated, which is compared with a target value and evaluated.

[0039] Here, the average area value can be calculated using the following formula (1): Average value of ion amount in grams = Σ (frequency × pulse area) / number of pulses (1)

[0040] Furthermore, the obtained average value of the ion amount in grams is compared with a target value, and if the calculation result obtained by the average value calculation satisfies the target value ± allowable error (target value - allowable error ≦ average value ≦ target value + allowable error), the repeating operation is stopped and "OK" is displayed on the PMT voltage adjustment setting screen 114a.

[0041] On the other hand, even if the maximum number of attempts set by the software operation parameter maximum attempt count setting button 114a4 is reached, if the target value ± allowable error (target value - allowable error ≦ average value ≦ target value + allowable error) is not met, the repeated operation will stop and an "error" will be displayed on the PMT voltage adjustment setting screen 114a.

[0042] 2 to 4, the analysis control unit 113 then prompts the user to determine whether the PMT voltage determination is satisfactory (S104). For example, the measurement results and / or determination results may be displayed on a display device 114 as shown in FIG. 5, prompting the user to make a determination.

[0043] For example, when the repeated operation ends with the above conditions being met, the result of pass / fail judgment is output to the display device 114. The judgment results are categorized as follows.

[0044] "OK": The post-adjustment processing button 114a3 is enabled, the adjusted PMT voltage is displayed on the display device 114, the PMT voltage in the voltage status frame of the PMT voltage button 114a8 in Figure 5 is updated, and the analysis control unit 113 specifies this to the detection unit 105 (S106 described below).

[0045] "Error": The post-adjustment process button 114a3 remains inoperable, and a message is displayed stating "Please adjust the PMT voltage again" (S105, described later).

[0046] If it is determined in S104 that there is a problem, the process proceeds to S105, where the analysis control unit 113 makes adjustments based on the software operation parameters (PMT voltage) input by the user (S105).

[0047] 5, this can be done by changing the set values ​​of the conversion dynode (CD1, CD2) voltage, scintillator voltage, and PMT voltage in the CD1 voltage button 114a5, CD2 voltage button 114a6, scintillator voltage button 114a7, and PMT voltage button 114a8 in the PMT voltage adjustment setting screen 114a displayed on the display device 114, or by changing the set values ​​by input. Thereafter, the process returns to step S103.

[0048] On the other hand, if it is determined in S104 that there is no problem, the process proceeds to S106, and the analysis control unit 113 executes the PMT voltage post-adjustment process (S106).

[0049] For example, it can be executed when it is recognized that the user has selected and pressed the post-adjustment process button 114a3 in the PMT voltage adjustment setting screen 114a displayed on the display device 114 as shown in FIG.

[0050] Here, it is desirable that the analysis control unit 113 disables the post-adjustment processing button 114a3 unless the voltage adjustment set button 114a1 and the PMT voltage adjustment button 114a2 are in the "OK" state, i.e., both the PMT voltage adjustment set and PMT voltage adjustment operations are in the "OK" state.

[0051] Thereafter, the analysis control unit 113 completes the PMT voltage adjustment (S107).

[0052] Next, the effects of this embodiment will be described.

[0053] The above-described mass spectrometer 100 includes an ion source 101 that ionizes a sample, a detection unit 105 that has a photomultiplier tube 105 a and analyzes the mass of the sample ionized by the ion source 101, a vacuum chamber 102 that connects the ion source 101 and the detection unit 105, a vacuum gauge 106 that measures the degree of vacuum inside the vacuum chamber 102, a data analysis unit 112 that calibrates the settings of the photomultiplier tube 105 a using electrons emitted from the vacuum gauge 106, and an analysis control unit 113.

[0054] Therefore, since the vacuum gauge 106 originally provided in the mass spectrometer 100 can be used, calibration can be performed without introducing a sample separately, making calibration easier than before.

[0055] Furthermore, since the vacuum gauge 106 is an ionization type, stable electrons are emitted reliably and stably, allowing calibration work to be carried out more smoothly.

[0056] Furthermore, the data analysis unit 112 and the analysis control unit 113 perform calibration at a time when analysis is not being performed by the detection unit 105, thereby ensuring that the calibration work is carried out without being hindered by other work.

[0057] Furthermore, the data analysis unit 112 and the analysis control unit 113 can use the conventional settings by setting the detection unit 105 at the time of calibration to the settings for measuring negative ions, which makes the design easier.

[0058] Furthermore, by further providing a display device 114 that displays a screen for setting conditions during calibration, the user can easily change the setting conditions and understand the status of the calibration.

[0059] <Others> The present invention is not limited to the above-described embodiments, and various modifications and applications are possible. The above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those having all of the described configurations.

[0060] DESCRIPTION OF SYMBOLS 100...Mass spectrometer 101...Ion source 102...Vacuum chamber 103...Ion transport section 104...Mass separation section 105...Detection section (mass analysis section) 105a...Photomultiplier tube 106...Vacuum gauge 111...A / D conversion section 112...Data analysis section (calibration section) 113...Analysis control section (calibration section) 114...Display device 114a...PMT voltage adjustment setting screen 114a1...Voltage adjustment set button 114a2...PMT voltage adjustment button 114a3...Post-adjustment processing button 114a4...Software operation parameter maximum trial count setting button 114a5...CD1 voltage button 114a6...CD2 voltage button 114a7...Scintillator voltage button 114a8...PMT voltage button

Claims

1. A mass spectrometer comprising: an ion source that ionizes a sample; a mass analysis unit having a photomultiplier tube and analyzing the mass of the sample ionized by the ion source; a vacuum chamber that communicates between the ion source and the mass analysis unit; a vacuum gauge that measures the degree of vacuum inside the vacuum chamber; and a calibration unit that calibrates the settings of the photomultiplier tube using electrons emitted from the vacuum gauge.

2. A mass spectrometer according to claim 1, wherein said vacuum gauge is of the ionization type.

3. A mass spectrometer according to claim 1, wherein the calibration unit performs calibration at a timing when analysis is not being performed in the mass spectrometer.

4. A mass spectrometer according to claim 1, wherein the calibration section sets the settings of the mass spectrometer during the calibration to measurements of negative ions.

5. A mass spectrometer according to claim 1, further comprising a display device for displaying a screen for setting conditions for said calibration.

6. A method for calibrating a mass spectrometer comprising: an ion source for ionizing a sample; a mass analysis section having a photomultiplier tube and analyzing the mass of the sample ionized by the ion source; a vacuum chamber connecting the ion source and the mass analysis section; and a vacuum gauge for measuring the degree of vacuum inside the vacuum chamber, wherein the setting of the photomultiplier tube is calibrated using electrons emitted from the vacuum gauge.