Mass spectrometer and setting method of analysis condition

Abstract

To improve the detection sensitivity of target ions while preventing interfering particles that become noise from being taken into a detector.SOLUTION: An ICP-MS includes a control device, a collision cell and a first electrode provided on an optical axis of plasma, a second electrode provided on a detection axis, a mass separator, and a detector. For an axis-shifting voltage applied to each of the first electrode and the second electrode, the control device sets an axis shift voltage in the gas mode to a voltage obtained by adding an offset determined according to the mass-to-charge ratio of the target ion to the initial voltage in the gas-free mode.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a mass spectrometer and a method for setting analysis conditions in the mass spectrometer. [Background technology]

[0002] ICP mass spectrometers (hereinafter referred to as "ICP-MS") using an inductively coupled plasma (ICP) ion source as an ion source are known. In an ICP-MS, a sample is ionized in an ion source, the ions are separated by mass-to-charge ratio in a mass separation section, and each ion separated by mass-to-charge ratio is detected by a detector. In an ICP-MS, the ion source is provided in an atmosphere at approximately atmospheric pressure. Ions generated by ionization in the ion source are taken into a vacuum chamber maintained in an approximately vacuum atmosphere, pass through a mass separation section provided in the vacuum chamber, and are detected by a detector.

[0003] In addition to the target ions to be measured, interfering particles that interfere with the measurement of the target ions are also introduced into the vacuum chamber. Interfering particles include, for example, those caused by gases such as argon (Ar) used to generate plasma in the ion source, those caused by impurities contained in the sample liquid, and those caused by additives added to the sample liquid. Various methods are used to remove such interfering particles.

[0004] For example, JP 2020-91988 A (Patent Document 1) discloses a method of separating and removing the interfering ions from the target ions by providing a collision cell to create a difference in kinetic energy between interfering ions, which are interfering particles, and the kinetic energy of the target ions, and forming an energy barrier at the exit of the collision cell.

[0005] Also, International Publication No. 2002 / 019382 (Patent Document 2) discloses an ICP-MS in which the aperture of a plate serving as the entrance of a collision cell is offset from the aperture of a plate serving as the intake port from an ion source to a vacuum region. According to the ICP-MS disclosed in Patent Document 2, the ion intake port and the entrance of the collision cell are arranged on different axes, thereby making it possible to prevent neutral particles, which are interfering particles, from entering the collision cell. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-91988 A [Patent Document 2] International Publication No. 2002 / 019382 Summary of the Invention [Problem to be solved by the invention]

[0007] Interfering particles such as neutral particles and photons can be removed by configuring the ion source entrance and the collision cell entrance so as to bend the ion traveling direction rather than arranging them on the same axis. However, if the two particle passage openings are arranged on different axes to remove some particles, there is a possibility that the ions to be detected will not be able to pass through one of the passage openings, reducing the total amount of target ions sent to the detector and lowering the detection sensitivity.

[0008] The present disclosure has been made to solve such problems, and aims to improve the detection sensitivity of target ions while preventing interfering particles that cause noise from being captured by the detector. [Means for solving the problem]

[0009] The mass spectrometer of the present disclosure includes an ion source for ionizing a sample, a sampling cone having an inlet formed on a first axis for taking in particles in an ionization chamber in which the ion source is arranged, a cell provided on the first axis for contacting the particles taken in from the sampling cone with a predetermined gas, a mass separator provided on a second axis parallel to the first axis for separating ions according to mass-to-charge ratios, a detector provided on the second axis for detecting each ion separated by the mass separator, a first electrode provided with a particle passage port on the first axis between the cell and the mass separator, a second electrode provided with a particle passage port on the second axis between the first electrode and the mass separator, and a control device. The control device is capable of controlling each part between a first mode for obtaining a detection result without introducing a predetermined gas into the cell and a second mode for obtaining a detection result by introducing a predetermined gas into the cell. The control device sets the electrode voltage in the second mode to a voltage obtained by adding an offset determined according to the mass-to-charge ratio of the target ion to be detected to an initial voltage set as the electrode voltage to be applied to each of the first electrode and the second electrode in the first mode.

[0010] The setting method of the present disclosure is a method for setting analysis conditions for a mass spectrometer. The mass spectrometer includes an ion source for ionizing a sample, a sampling cone having an inlet formed on a first axis for taking in particles in an ionization chamber in which the ion source is arranged, a cell provided on the first axis for contacting the particles taken in from the sampling cone with a predetermined gas, a mass separator provided on a second axis parallel to the first axis for separating ions according to mass-to-charge ratios, a detector provided on the second axis for detecting each ion separated by the mass separator, a first electrode provided with a particle passage port on the first axis between the cell and the mass separator, and a second electrode provided with a particle passage port on the second axis between the first electrode and the mass separator. The setting method includes a step of setting a first mode in which a detection result is obtained without introducing a predetermined gas into the cell, and a step of setting a second mode in which a detection result is obtained by introducing a predetermined gas into the cell. The setting method includes a step of setting, when the second mode is set, an initial voltage set as the electrode voltage to be applied to each of the first electrode and the second electrode in the first mode plus an offset determined according to the mass-to-charge ratio of the target ion to be detected, as the electrode voltage in the second mode. Effect of the Invention

[0011] According to the mass spectrometer and the method for setting analysis conditions of the present disclosure, it is possible to improve the detection sensitivity of target ions while preventing interfering particles from being captured by the detector. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing a schematic diagram of the overall configuration of an ICP-MS. [Diagram 2] FIG. 13 is an image diagram showing a method for determining incident energy. [Diagram 3] FIG. 1 is an image showing the effect of each function on a particle. [Figure 4] 10 is a flowchart showing a method for setting an axis shift voltage. [Diagram 5] 4 is a flowchart showing a method for determining an adjustment voltage. [Figure 6] FIG. 13 is a diagram showing the relationship between mass-to-charge ratio and tuning voltage. [Figure 7] FIG. 13 shows scan results obtained by changing the amount of standard sample sent. [Figure 8] FIG. 1 is an image diagram showing the movement of ions in an off-axis optical system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0014] [Overall configuration of ICP-MS] 1 is a diagram showing a schematic diagram of the overall configuration of an ICP-MS. The ICP-MS 100 includes an ion source 1, a collision cell 2, an axis shifting optical system 3, a mass separator 4, a detector 5, a voltage generator 6, and a controller 7. The ICP-MS 100 also includes an ionization chamber 10, a vacuum chamber 11 in which a sampling cone 14 is formed between the ionization chamber 10, a vacuum chamber 12 in which a skimmer 15 is formed between the vacuum chamber 11, and a vacuum chamber 13.

[0015] The ICP-MS 100 is configured such that the atmosphere inside the ionization chamber 10 is at atmospheric pressure, and the degree of vacuum increases in the order of vacuum chamber 11, vacuum chamber 12, and vacuum chamber 13 from the ionization chamber 10 side. The ion source 1 is disposed inside the ionization chamber 10, the collision cell 2 and the axis shifting optical system 3 are disposed inside the vacuum chamber 12, and the mass separator 4 and detector 5 are disposed inside the vacuum chamber 13.

[0016] The collision cell 2 is disposed on the optical axis A1 of the ion source 1. Meanwhile, the mass separator 4 and the detector 5 are disposed on the detection axis A2. The detection axis A2 is an axis parallel to the optical axis A1 and passes through a position shifted perpendicularly from the optical axis A1.

[0017] The ion source 1 is configured to ionize a sample by plasma, and includes an autosampler 1a and a plasma torch 1b. Although not shown, the ion source 1 further includes a nebulizer gas supply source for supplying various gases to the plasma torch 1b, a plasma gas supply source, and a cooling gas supply source.

[0018] The autosampler 1a introduces a sample into the plasma torch 1b, which converts argon gas into a plasma state by high-frequency inductive coupling, and ionizes the sample introduced by the autosampler 1a with the plasma.

[0019] Although not shown, the plasma torch 1b includes a sample tube through which a liquid sample atomized by a nebulizer gas flows, a plasma gas tube formed on the outer periphery of the sample tube, and a cooling gas tube formed on the outer periphery of the plasma gas tube. The plasma gas is, for example, argon (Ar) gas.

[0020] The vacuum chamber 11 is formed between the sampling cone 14 and the skimmer 15. The sampling cone 14 and the skimmer 15 are each substantially conical in shape, and have an opening at the apex of the cone that is configured to allow particles to pass through.

[0021] The sampling cone 14 is formed so that its opening is located on the optical axis A1 that passes through the tip of the plasma torch 1b. Particles such as ions generated by the plasma torch 1b and neutral particles generated during the plasma generation process are taken into the vacuum chamber 11 through the opening of the sampling cone 14.

[0022] The skimmer 15 is formed so that its opening is positioned on the optical axis A1. Particles in the vacuum chamber 11 are taken into the vacuum chamber 12 through the opening of the skimmer 15.

[0023] The vacuum chamber 12 is provided with a retraction electrode 16, an ion lens 17, a collision cell 2, a first electrode 31, and a second electrode 32. The retraction electrode 16, the ion lens 17, the first electrode 31, and the second electrode 32 are each a disk-shaped electrode with a substantially circular opening. The retraction electrode 16, the ion lens 17, and the first electrode 31 are each disposed in the vacuum chamber 12 such that the opening is positioned on the optical axis A1. The second electrode 32 is disposed in the vacuum chamber 12 such that the opening is positioned on the detection axis A2.

[0024] The collision cell 2 includes an entrance electrode 21, an exit electrode 22, and an ion guide 23. The entrance electrode 21 and the exit electrode 22 are each a disk-shaped electrode with a substantially circular opening. The opening formed in the entrance electrode 21 corresponds to the entrance of the collision cell 2, and the opening formed in the exit electrode 22 corresponds to the exit of the collision cell 2.

[0025] The collision cell 2 is disposed in the vacuum chamber 12 so that the opening of the entrance electrode 21 corresponding to the entrance and the opening of the exit electrode 22 corresponding to the exit are each located on the optical axis A1. The ion guide 23 is composed of a plurality of rod electrodes disposed parallel to the optical axis A1.

[0026] Particles in the vacuum chamber 11 pass through the opening of the skimmer 15 , the opening of the pull-in electrode 16 , the opening of the ion lens 17 , and the opening of the entrance electrode 21 in that order, and enter the collision cell 2 .

[0027] In addition to the target ions to be measured, interference ions and neutral particles that interfere with the measurement of the target ions are also taken into the vacuum chamber 12. The interference particles include those caused by gases such as Ar used to generate plasma in the ion source 1, and those caused by impurities and additives in the sample.

[0028] The collision cell 2 is for bringing the particles taken in from the inlet of the collision cell 2 into contact with a predetermined gas. The collision cell 2 separates the target ions from the interfering particles by bringing the particles into contact with the predetermined gas.

[0029] The predetermined gas is sent from the gas supply unit 8 to the collision cell 2, and an appropriate type of gas is selected depending on the purpose of observation. For example, when separating target ions from interfering particles by creating an energy difference between them, a low-reactivity inert gas called a collision gas is selected as the predetermined gas. On the other hand, when separating interfering particles from target ions by utilizing the difference in reactivity between them, a reactive gas called a reaction gas is selected as the predetermined gas.

[0030] In addition, when a reaction gas is used as the specified gas, the collision cell 2 may be called a "reaction cell", but in this specification, it is referred to as a collision cell even when a reaction gas is used.

[0031] The axis shifting optical system 3 is provided between the collision cell 2 and the mass separator 4. The axis shifting optical system 3 is configured to bend the direction of movement of charged ions among particles emitted from the opening of the exit electrode 22, which is the exit of the collision cell 2, and send the ions to the mass separator 4 arranged on the detection axis A2.

[0032] The off-axis optical system 3 includes a first electrode 31 and a second electrode 32. The first electrode 31 and the second electrode 32 each have an opening formed therein, which is a passage port for particles. The first electrode 31 is disposed in the vacuum chamber 12 such that the opening is positioned on the optical axis A1. The second electrode 32 is disposed in the vacuum chamber 12 such that the opening is positioned on the detection axis A2.

[0033] A deflection electric field is formed by offsetting the center position of the lens aperture (opening) of the second electrode 32 with respect to the center position of the lens aperture (opening) of the first electrode 31. The ion trajectory of the ions emitted from the opening of the first electrode 31 is bent under the influence of this deflection electric field. On the other hand, particles that do not have a charge, such as photons and neutral particles, are not affected by the deflection electric field and proceed along the optical axis A1 without bending. As a result, the ions pass through the opening of the second electrode 32 and are sent to the mass separator 4 arranged at the rear of the axis shifting optical system 3. On the other hand, particles that do not have a charge, such as photons and neutral particles, cannot pass through the opening of the second electrode 32 and are not sent to the mass separator 4. This makes it possible to prevent photons and neutral particles, which are types of interfering particles, from being captured by the detector 5.

[0034] An opening is formed in the vacuum chamber 13 at a position facing the opening of the second electrode 32. In the vacuum chamber 13, a mass separator 4 and a detector 5 are arranged on a detection axis A2.

[0035] The mass separator 4 is, for example, a quadrupole mass filter, and includes a pre-rod electrode 41 and a main rod electrode 42. Ions having a mass-to-charge ratio according to the voltage applied to the mass separator 4 pass through the mass separator 4 and reach the detector 5. Therefore, by changing the voltage of the mass separator 4, the ions incident on the mass separator 4 are separated according to their mass-to-charge ratio.

[0036] The detector 5 is, for example, a secondary electron multiplier, which generates a detection signal according to the amount of ions that reach the detector 5 and sends the signal to a control device 7 .

[0037] The control device 7 includes a CPU 71 (Central Processing Unit) which is a calculation section, and a storage device 72. In addition, an input device 73 and a display device 74 are connected to the control device 7.

[0038] The CPU 71 reads out and executes a program stored in the storage device 72 to control the operation of each part of the ICP-MS 100. For example, the CPU 71 executes the program to control the voltage generating unit 6 to control the voltage applied to each part. Note that while the example in Fig. 1 illustrates a configuration in which there is a single CPU 71, the ICP-MS 100 may also be configured to have multiple CPUs.

[0039] The storage device 72 is realized by a non-volatile storage device such as a ROM (Read Only Memory) or a hard disk. The storage device 72 stores a program executed by the CPU 71, data used by the CPU 71, etc. The program may be stored in a non-transitory computer-readable medium.

[0040] The input device 73 is typically a mouse, a keyboard, various buttons, a touch panel, etc. The input device 73 receives information necessary for controlling the operation of the ICP-MS 100, information necessary for the processing performed by the control device 7, etc., through user operations.

[0041] Display device 74 is typically a liquid crystal monitor or the like, and displays information input by the user via input device 73, as well as analysis results, analysis conditions, etc. Display device 74 may be configured with a printer and paper, and may display analysis conditions, etc. by printing analysis results, etc. on paper.

[0042] [Analysis mode type] The ICP-MS100 according to this embodiment can analyze a sample in a plurality of analysis modes that are different in analysis technique. The types of analysis modes are explained below. The input device 73 inputs, as an analysis condition, which analysis mode is to be used to analyze the sample to the control device 7 according to the user's operation.

[0043] The analysis modes include a gas-free mode in which detection results are obtained without supplying gas to the collision cell 2, and a gas-present mode in which detection results are obtained by supplying gas to the collision cell 2.

[0044] In the gas-free mode, detection results are obtained without supplying gas to the collision cell 2, that is, without bringing the particles taken in from the sampling cone 14 and sent into the collision cell 2 into contact with a predetermined gas.

[0045] In the gas-present mode, gas is supplied to the collision cell 2, and the particles sent into the collision cell 2 are brought into contact with a predetermined gas, causing collision and / or reaction to obtain a detection result. Note that in the gas-present mode, the control device 7 may control the voltage generating unit 6 to accelerate ions in the collision cell 2 or form an energy barrier at the exit of the collision cell 2.

[0046] The target ions may be extremely decelerated due to collision or reaction of the target ions and interfering particles with a specific gas. If the target ions are extremely decelerated, it may take a long time for the ions to reach the detector 5, which may increase the time required for measurement, or the target ions may not reach the exit of the collision cell 2. Therefore, in the gas-present mode, the control device 7 may control the voltage generating unit 6 to accelerate the ions in the collision cell 2.

[0047] When accelerating ions in the collision cell 2, the control device 7 controls the voltage generating unit 6 to offset each electrode subsequent to the ion guide 23 with respect to the ion traveling direction by a cell voltage for accelerating the ions.

[0048] Furthermore, when kinetic energy discrimination (KED) is performed by colliding or reacting the particles sent into the collision cell 2 with a predetermined gas, the control device 7 controls the voltage generating unit 6 to form an energy barrier. The energy of ions originating from the plasma gas generated in the ion source 1 is generally significantly reduced by colliding with the predetermined gas compared to the energy of the target ions. By providing an energy barrier at the outlet of the collision cell 2, the ions originating from the plasma gas cannot cross the energy barrier, whereas the target ions can cross the energy barrier, making it possible to separate the target ions from the interfering particles.

[0049] When forming an energy barrier, the control device 7 controls the voltage generating unit 6 to offset each electrode after the exit electrode 22 by an energy filter (hereinafter referred to as "EF") voltage for the energy barrier with respect to the traveling direction of the ions.

[0050] As described above, the control device 7 controls each part of the ICP-MS 100 in the gas-present mode or the gas-absent mode, and in the gas-present mode, may offset the cell voltage and / or the EF voltage.

[0051] [Function as a bandpass filter for off-axis optical systems] The present inventors have found that the off-axis optical system 3 functions as a bandpass filter. First, the present inventors have determined the incident energy of ions incident on the mass separator 4 by the following method.

[0052] FIG. 2 is an image diagram showing a method for determining the incident energy. A bias voltage, which is a DC voltage that does not contribute to ion separation, is applied to each of the pre-rod electrode 41 and the main rod electrode 42 of the mass separator 4. When the target ions are detected by changing this bias voltage, the graph shown on the left side of FIG. 2 is obtained. Ions enter the mass separator 4 with an energy distribution. At this time, among the ions entering the mass separator 4, ions having a lower energy compared to the bias voltage applied to the main rod electrode 42 cannot overcome the energy barrier due to the bias voltage. Therefore, the bias voltage at which the slope of the rate of change of the detection intensity is maximum is considered to correspond to the incident energy of the ions entering the mass separator 4. Therefore, the graph shown on the left side of FIG. 2 showing the relationship between the bias voltage and the detection intensity was differentiated to obtain the graph shown on the right side of FIG. 2, and the bias voltage at the peak position of the graph shown on the right side of FIG. 2 was extracted. The extracted bias voltage corresponds to the incident energy of the ions.

[0053] The inventor changed the axis shifting voltage, which is the voltage applied to each of the first electrode 31 and the second electrode 32 included in the axis shifting optical system 3, and applied each axis shifting voltage to determine the incident energy of ions entering the mass separator 4 using the above-mentioned method.

[0054] As a result, it was found that changing the axis shifting voltage also changes the incident energy of ions entering the mass separator 4. This shows that changing the axis shifting voltage changes the energy range that can pass through the axis shifting optical system 3, and that the axis shifting optical system 3 functions as a band-pass filter.

[0055] Figure 3 is an image diagram showing the effect of each function on the particle. The image diagram shown in Figure 3 is an image diagram when an EF voltage for an energy barrier is applied in a gas-present mode. Figure 3 shows the effect of each function on the particle by showing how the energy distribution of the particle changes due to each function.

[0056] Particles in the ionization chamber 10 taken in from the sampling cone 14 come into contact with a specific gas in the collision cell 2. For example, consider the case where KED is performed by colliding particles with a specific gas. In this case, the kinetic energy of particles with a large collision area is greatly reduced compared to the kinetic energy of particles with a small collision area. As a result, the energy distribution of the particles in the collision cell 2 becomes wider.

[0057] As described above, the axis-shifting optical system 3 functions as a band-pass filter, so that when a group of particles with a broad energy distribution enters the axis-shifting optical system 3, only particles having a specific energy pass through the axis-shifting optical system 3.

[0058] In addition, when an EF voltage is applied to the electrodes subsequent to the exit electrode 22, only high-energy particles among the particle group with a broad energy distribution can cross the energy barrier and are detected by the detector 5.

[0059] In this way, the axis shifting optical system 3 functions as a band pass filter, and therefore it is necessary for it to function as a band pass filter according to the energy of the target ions to be detected when they exit the collision cell 2. For this reason, it is necessary to set the axis shifting voltage to an appropriate voltage.

[0060] [How to set the axis shift voltage] The ICP-MS100 includes an off-axis optical system 3. The off-axis optical system 3 prevents neutral particles, which are interfering particles, from being captured by the detector 5 by arranging the electrodes such that the opening of the first electrode 31 and the opening of the second electrode 32 are located on different axes. If the ion path is thus bent to prevent some particles from being captured by the detector 5, there is a possibility that even the target ions to be detected will not be captured by the detector 5.

[0061] In fact, the off-axis optical system 3 functions as a band-pass filter. Therefore, it is necessary to set the voltages applied to the first electrode 31 and the second electrode 32 included in the off-axis optical system 3 so as to improve the transmission rate of the target ions through the off-axis optical system 3.

[0062] A method for setting the axis shift voltage will be described with reference to Fig. 4. Fig. 4 is a flowchart showing the method for setting the axis shift voltage. In the following, steps will be simply abbreviated as "S". Each step shown in Fig. 4 is executed by the control device 7.

[0063] In S1, the control device 7 applies an initial voltage V according to the mass-to-charge ratio of the target ion. i Determine whether the initial voltage V i is the set value set in the gas-free mode. Initial voltage V i When it is determined that the initial voltage V is not stored in the storage device 72 (NO in S1), the control device 7 advances the process to S1a. i is stored in the storage device 72 (YES in S1), the control device 7 advances the process to S2 without executing S1a.

[0064] In S1a, the control device 7 determines the initial voltage V i In the determination process, the control device 7 analyzes a standard sample corresponding to the mass-to-charge ratio of the target ion in a gas-free mode by changing the axis shift voltage, and determines the axis shift voltage at which the highest detection intensity is obtained as the detection result as the initial voltage V i The determination process is performed using the obtained initial voltage V i may include a step of storing the mass-to-charge ratio in the storage device 72 in association with the mass-to-charge ratio.

[0065] In S2, the control device 7 determines whether the analysis mode is the gas-free mode based on the analysis conditions input via the input device 73. If the analysis mode is determined to be the gas-free mode (YES in S2), the control device 7 sets the initial voltage V i The process is terminated with the above set value. The voltages applied to the pull-in electrode 16, the ion lens 17, the entrance electrode 21, the exit electrode 22, and the ion guide 23, and the bias voltages applied to the pre-rod electrode 41 and the main rod electrode 42 are set to the voltages that provide the highest detection intensity as the detection result, similar to the axis shift voltage.

[0066] When it is determined that the analysis mode is not the gas-free mode (NO in S2), that is, when it is determined that the analysis mode is the gas-present mode, the control device 7 advances the process to S3. In S3 and after, the control device 7 determines the setting value of the axis shift voltage in the gas-present mode. In the gas-present mode, the control device 7 sets the offset, which is set according to the mass-to-charge ratio of the target ions, to the initial voltage V i The voltage applied to is the set value of the axis shift voltage.

[0067] In S3, the control device 7 detects the cell voltage V C Whether or not the cell voltage V C is a voltage for accelerating ions in the collision cell 2, and is a voltage applied to each electrode after the ion guide 23 in the direction of ion travel. C When it is determined that the cell voltage V is set (YES in S3), the control device 7 advances the process to S4. C If it is determined that the setting is not set (NO in S3), the control device 7 advances the process to S5 without executing S4.

[0068] In S4, the control device 7 offsets the cell voltage V C Add the cell voltage V Cis predetermined regardless of the mass-to-charge ratio of the target ions. As described above, the cell voltage V C is a voltage applied to each electrode subsequent to the ion guide 23 in the ion traveling direction, and is therefore also applied to each of the first electrode 31 and the second electrode 32. Therefore, the control device 7 controls the cell voltage V C is set, it is necessary to offset each of the first electrode 31 and the second electrode 32 by the cell voltage.

[0069] In S5, the control device 7 controls the EF voltage V EF Whether or not the EF voltage V is set is determined based on the analysis conditions input via the input device 73. As described above, EF is the voltage applied to form an energy barrier when performing KED. EF voltage V EF When it is determined that the EF voltage V is set (YES in S5), the control device 7 advances the process to S6. EF If it is determined that the setting has not been made (NO in S5), the control device 7 advances the process to S7 without executing S6.

[0070] In S6, the control device 7 sets the EF voltage V EF Add EF voltage V EF is predetermined regardless of the mass-to-charge ratio of the target ions. As described above, the EF voltage V EF Since EF voltage V is a voltage applied to each electrode subsequent to the exit electrode 22 in the direction of ion travel, it is also applied to the first electrode 31 and the second electrode 32. EF When this is set, it is necessary to offset each of the first electrode 31 and the second electrode 32 by the EF voltage.

[0071] In S7, the control device 7 adjusts the adjustment voltage V according to the mass-to-charge ratio of the target ions. ad Determine whether the regulated voltage V is stored in the memory device 72. ad is the cell voltage V, which is set uniformly regardless of the mass-to-charge ratio. Cand EF voltage V EF Unlike the above, the voltage is determined according to the mass-to-charge ratio of the target ion and is stored in the storage device 72 in association with the mass-to-charge ratio. The mass-to-charge ratio of the target ion is included in the analysis conditions input by the user via the input device 73, for example.

[0072] Adjustment voltage V ad When it is determined that the regulated voltage V is not stored in the storage device 72 (NO in S7), the control device 7 determines in S70 that the regulated voltage V ad A decision process is performed to determine the regulated voltage V ad The process for determining the regulated voltage V will be described later with reference to FIG. ad is stored in the storage device 72 (YES in S7), the control device 7 advances the process to S8.

[0073] In S8, the control device 7 applies an adjustment voltage V according to the mass-to-charge ratio of the target ion to the offset. ad Add.

[0074] In S9, the control device 7 sets the initial voltage V i The set value is the voltage obtained by adding an offset to the mass-to-charge ratio. In other words, the offset is determined by at least the adjustment voltage V ad cell voltage V C and / or EF voltage V EF may include.

[0075] As described above, the control device 7 controls the initial voltage V i The offset voltage is set to the voltage obtained by adding an offset to the voltage V. As shown in S7 to S8, the offset is set to an adjustment voltage V according to the mass-to-charge ratio of the target ion regardless of the analysis conditions. ad Therefore, it can be said that the mass-to-charge ratio is determined according to the mass-to-charge ratio of the target ion.

[0076] That is, in the gas-present mode, the control device 7 sets the initial voltage V iThe set value of the axis shift voltage is determined by adding an offset determined according to the mass-to-charge ratio of the target ion to the voltage above.

[0077] [How to determine the regulated voltage] Fig. 5 is a flowchart showing a method for determining an adjustment voltage. The flowchart shown in Fig. 5 corresponds to the determination process executed in S70 in Fig. 4. Each step shown in Fig. 5 is executed by the control device 7.

[0078] In S71, the control device 7 instructs the user to analyze the standard sample. Specifically, the control device 7 displays instruction information on the display device 74 to set the standard sample in the autosampler 1a. Here, the standard sample is a sample consisting of a specific component. The specific component is appropriately selected according to the target ion to be measured. The specific component may be a component that becomes a target ion when ionized, or may be a component that becomes an ion having a mass-to-charge ratio that is the same as or very close to that of the target ion when ionized. Note that the standard sample does not need to contain any component that becomes an interfering particle when measuring the specific component, and may contain components other than the specific component.

[0079] In S72, the control device 7 determines whether or not a standard sample has been set. As an example, the control device 7 determines whether or not a standard sample has been set based on information input by the user via the input device 73. When it is determined that a standard sample has been set (YES in S72), the control device 7 advances the process to S73.

[0080] In S73, the control device 7 sets a reference voltage. The reference voltage is a voltage set according to the analysis conditions, and is an initial voltage V i The voltage set by the analysis conditions, regardless of the mass-to-charge ratio of the target ions, is the cell voltage V C and EF voltage V EF It is.

[0081] In S74, the control device 7 varies the off-axis voltage around the reference voltage to obtain the detection result of the standard sample and obtain a scan result of the off-axis voltage. The detection result of the standard sample is obtained by detecting specific ions obtained by ionizing specific components contained in the standard sample with the detector 5. The scan result of the off-axis voltage is the relationship between the off-axis voltage and the detection intensity of the specific ions.

[0082] In S75, the control device 7 extracts the peak voltage at which the detected intensity is the greatest from the scan result.

[0083] In S76, the control device 7 calculates the adjusted voltage V ad The fact that the detection intensity is highest when the peak voltage is set means that more specific ions can pass through the off-axis optical system 3 by setting the peak voltage. Therefore, the control device 7 adjusts the adjustment voltage V so that the peak voltage becomes the off-axis voltage in the gas-present mode. ad More specifically, the control device 7 determines the fluctuation value from the reference voltage set in S73 to the peak voltage as the adjustment voltage V ad The initial voltage V i The variation from the peak voltage corresponds to the offset.

[0084] In S77, the control device 7 determines the regulated voltage V ad The determined adjustment voltage V is stored in the storage device 72 in association with the mass-to-charge ratio of the specific ion, and the process ends. ad By storing the mass-to-charge ratio of a specific ion in association with the voltage V, when analyzing a target ion under the same analytical conditions, the voltage V can be adjusted again. ad Therefore, it is not necessary to execute a determination process for determining the axis shift voltage, and the axis shift voltage can be set efficiently.

[0085] As described above, the control device 7 analyzes a standard sample of a specific ion to adjust the adjustment voltage V ad Determine.

[0086] FIG. 6 is a diagram showing the relationship between the mass-to-charge ratio and the adjustment voltage. ad The relationship between the mass-to-charge ratio and the tuning voltage V ad The offset information indicating the relationship between the above is stored in, for example, the storage device 72. Thus, the control device 7 is configured to be able to acquire the offset information. The offset information may be stored in a server configured to be able to communicate with the control device 7 via a network.

[0087] In addition, the adjustment voltage V ad is the cell voltage V C Whether to apply EF voltage V EF Therefore, the offset information depends on whether the cell voltage V C and EF voltage V EF It is preferable that the offset information is set according to the analysis conditions regarding the mass-to-charge ratio and the adjustment voltage V ad The relationship between the adjustment voltage V ad Cell voltage V C and / or EF voltage V EF and the mass-to-charge ratio.

[0088] In steps S7 and S8 of FIG. 4, the control device 7 adjusts the adjustment voltage V according to the input mass-to-charge ratio based on the offset information. ad The control device 7 may determine the adjustment voltage V corresponding to the input mass-to-charge ratio. ad Even if the offset information does not include the mass-to-charge ratio adjustment voltage V ad The adjustment voltage V according to the input mass-to-charge ratio ad It may be determined as:

[0089] FIG. 7 shows the scan results obtained by changing the amount of standard sample sent. The plots shown by black circles in FIG. 7 are the scan results obtained when the standard sample is sent to the plasma torch 1b by the autosampler 1a at a first flow rate. The plots shown by black triangles in FIG. 7 are the scan results obtained when the standard sample is sent to the plasma torch 1b by the autosampler 1a at a second flow rate that is smaller than the first flow rate. The horizontal axis of the graph shown in FIG. 7 is the axis shift voltage when the reference voltage is set to 0.

[0090] As shown in FIG. 7, the peak voltage does not change regardless of the flow rate sent to the plasma torch 1b. Therefore, the control device 7 adjusts the adjustment voltage V ad can be set.

[0091] As shown in FIG. 7, the intensity fluctuation is relatively small around the peak voltage. Therefore, the adjustment voltage V ad By determining the above, it is possible to reduce the fluctuation range of the detection intensity when the voltage value of the set axis shift voltage fluctuates, and it is possible to obtain stable detection results.

[0092] [Movement of ions in an off-axis optical system] Figure 8 is an image diagram showing the movement of ions in an off-axis optical system. The length of the arrow in Figure 8 indicates the speed of the ions, and the longer the arrow, the faster the speed.

[0093] If the mass is the same, the energy of an ion and the speed of the ion are proportional to each other. Therefore, if the speed of an ion is too fast, the energy of the ion is large, so the ion does not bend significantly as shown in FIG. 8, and the ion cannot pass through the opening of the second electrode 32 and cannot reach the mass separator 4. On the other hand, if the speed of an ion is too slow, the energy of the ion is small, so the ion bends too much as shown in FIG. 8, and the ion cannot pass through the opening of the second electrode 32 and cannot reach the mass separator 4. Therefore, it is necessary to set the axis shift voltage so that the speed of the ion when passing through the first electrode 31, i.e., the energy of the ion, is appropriate.

[0094] In the gas-present mode, the energy of the ions emitted from the collision cell 2 changes from the energy they had when they were taken in from the sampling cone 14 by coming into contact with a specific gas in the collision cell 2. In addition, the effect of the specific gas on the ions differs depending on the type of ion.

[0095] That is, the amount of change in the energy of an ion due to contact with a specific gas varies depending on the type of ion. Therefore, in the gas-free mode, the initial voltage V i Set the initial voltage V i If a uniform offset is applied to the ions regardless of their mass-to-charge ratio, the ions will not have an appropriate energy when passing through the first electrode 31.

[0096] In this embodiment, the control device 7 controls the initial voltage V i The offset voltage in the gas-present mode is set to a voltage obtained by adding an offset determined according to the mass-to-charge ratio of the target ion to the above voltage. This allows the ion energy to be set to an appropriate value when passing through the first electrode 31, improving the transmission rate of the target ion through the axis-shifting optical system 3 and, as a result, increasing the detection sensitivity.

[0097] [Aspects] It will be understood by those skilled in the art that the above-described embodiments are illustrative of the following aspects.

[0098] (Item 1) A mass spectrometer according to one embodiment includes an ion source for ionizing a sample, a sampling cone having an inlet formed on a first axis for taking in particles in an ionization chamber in which the ion source is arranged, a cell provided on the first axis for contacting the particles taken in from the sampling cone with a predetermined gas, a mass separator provided on a second axis parallel to the first axis for separating ions according to mass-to-charge ratios, a detector provided on the second axis for detecting each ion separated by the mass separator, a first electrode provided with a particle passage port on the first axis between the cell and the mass separator, a second electrode provided with a particle passage port on the second axis between the first electrode and the mass separator, and a control device. The control device is capable of controlling each part between a first mode for obtaining a detection result without introducing a predetermined gas into the cell and a second mode for obtaining a detection result by introducing a predetermined gas into the cell. The control device sets the electrode voltage in the second mode to a voltage obtained by adding an offset determined according to the mass-to-charge ratio of the target ion to be detected to an initial voltage set as the electrode voltage to be applied to each of the first electrode and the second electrode in the first mode.

[0099] According to the mass spectrometer described in paragraph 1, the passage opening of the first electrode and the passage opening of the second electrode are located on different axes, so that it is possible to prevent interfering particles such as photons and neutral particles from passing through the passage opening of the second electrode and being taken into the mass separator and detected by the detector. Furthermore, the electrode voltage set in the second mode includes an offset determined according to the mass-to-charge ratio of the target ions, so that an appropriate electrode voltage can be set according to the target ions, and the detection sensitivity of the target ions can be improved.

[0100] (Item 2) In the mass spectrometer described in item 1, the control device can execute a determination process for determining an offset when a first ion having a first mass-to-charge ratio is a target ion by analyzing a first standard sample consisting of a first component having a first mass-to-charge ratio when ionized in a second mode. The determination process includes the steps of detecting the first ion by changing an electrode voltage and obtaining a scan result showing a relationship between the detection intensity of the first ion and the electrode voltage, and extracting a peak voltage at which the detection intensity is the largest from the scan result and determining an offset when the first ion is a target ion based on the peak voltage.

[0101] According to the mass spectrometer described in paragraph 2, the offset is determined based on the peak voltage at which the detection intensity is greatest, and therefore, by performing analysis under an electrode voltage set according to the determined offset, the detection sensitivity of the target ion can be improved.

[0102] (Item 3) In the mass spectrometer according to item 2, the control device stores the relationship between the determined offset and the mass-to-charge ratio in a memory unit.

[0103] According to the mass spectrometer described in paragraph 3, by storing the relationship between the determined offset and the mass-to-charge ratio in the memory unit, the electrode voltage can be set efficiently when analyzing target ions under similar analysis conditions.

[0104] (Item 4) In the mass spectrometer according to any one of items 1 to 3, the offset includes a voltage for an energy barrier that is determined in advance regardless of the mass-to-charge ratio.

[0105] According to the mass spectrometer described in item 4, when energy discrimination is carried out by contacting a predetermined gas in the cell, the target ions can be separated from interfering substances by an energy barrier.

[0106] (5) In the mass spectrometer according to any one of paragraphs 1 to 4, the control device sets a predetermined cell voltage, regardless of the mass-to-charge ratio, as a voltage to be applied to the ion guide of the cell in the second mode. The offset includes the cell voltage.

[0107] According to the mass spectrometer described in paragraph 5, even if the velocity of the target ions is extremely reduced due to contact with a specific gas in the cell, the target ions can be accelerated and emitted from the outlet of the cell.

[0108] (Item 6) In the mass spectrometer described in any one of Items 1 to 5, the control device is configured to be able to acquire offset information indicating the relationship between a mass-to-charge ratio and an offset when an ion having that mass-to-charge ratio is treated as a target ion, and when an input of a mass-to-charge ratio of the target ion is received, an offset corresponding to the input mass-to-charge ratio is determined based on the offset information.

[0109] According to the mass spectrometer described in item 6, the electrode voltage can be set efficiently. (Item 7) A setting method according to one aspect is a method for setting analysis conditions for a mass spectrometer. The mass spectrometer includes an ion source for ionizing a sample, a sampling cone having an inlet formed on a first axis for taking in particles in an ionization chamber in which the ion source is arranged, a cell provided on the first axis for contacting the particles taken in from the sampling cone with a predetermined gas, a mass separator provided on a second axis parallel to the first axis for separating ions according to mass-to-charge ratios, a detector provided on the second axis for detecting each ion separated by the mass separator, a first electrode provided on the first axis between the cell and the mass separator with a particle passage port, and a second electrode provided on the second axis between the first electrode and the mass separator with a particle passage port. The setting method includes a step of setting a first mode for obtaining a detection result without introducing a predetermined gas into the cell, and a step of setting a second mode for obtaining a detection result by introducing a predetermined gas into the cell. The setting method also includes a step of, when the second mode is set, setting the electrode voltage in the second mode to a voltage obtained by adding an offset determined according to the mass-to-charge ratio of the target ion to be detected to an initial voltage set as the electrode voltage to be applied to each of the first electrode and the second electrode in the first mode.

[0110] According to the setting method described in paragraph 7, since the passage opening of the first electrode and the passage opening of the second electrode are located on different axes, it is possible to prevent interfering particles such as photons and neutral particles from passing through the passage opening of the second electrode and being taken into the mass separator and detected by the detector. Furthermore, since the electrode voltage set in the second mode includes an offset determined according to the mass-to-charge ratio of the target ions, it is possible to set an appropriate electrode voltage according to the target ions, and it is possible to improve the detection sensitivity of the target ions.

[0111] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not by the description of the embodiments described above, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0112] 1 ion source, 1a autosampler, 1b plasma torch, 2 collision cell, 3 axis shifting optical system, 4 mass separator, 5 detector, 6 voltage generator, 7 control device, 8 gas supply device, 10 ionization chamber, 11-13 vacuum chamber, 14 sampling cone, 15 skimmer, 16 lead-in electrode, 17 ion lens, 21 entrance electrode, 22 exit electrode, 23 ion guide, 31 first electrode, 32 second electrode, 41 pre-rod electrode, 42 main rod electrode, 72 storage device, 73 input device, 74 display device, 100 ICP-MS, A1 optical axis, A2 detection axis.

Claims

1. an ion source for ionizing the sample; a sampling cone having an inlet formed on a first axis for taking in particles in an ionization chamber in which the ion source is disposed; a cell provided on the first axis for contacting the particles taken in from the sampling cone with a predetermined gas; a mass separator arranged on a second axis parallel to the first axis, the mass separator separating ions according to their mass-to-charge ratio; a detector provided on the second axis for detecting each ion separated by the mass separator; a first electrode having a particle passage opening on the first axis between the cell and the mass separator; a second electrode having a particle passage opening on the second axis between the first electrode and the mass separator; a control device; The control device includes: Each part can be controlled in a first mode in which a detection result is obtained without putting the predetermined gas into the cell, and in a second mode in which a detection result is obtained by putting the predetermined gas into the cell, a mass spectrometer that sets the electrode voltage in the second mode to a voltage obtained by adding an offset determined according to the mass-to-charge ratio of a target ion to be detected to an initial voltage that is set as the electrode voltage to be applied to each of the first electrode and the second electrode in the first mode.

2. the control device is capable of performing a determination process for determining the offset when a first ion having a first mass-to-charge ratio is set as the target ion by analyzing a first standard sample made of a first component having a first mass-to-charge ratio when ionized in the second mode; The determination process includes: detecting the first ions by varying the electrode voltage, and obtaining a scan result indicating a relationship between a detection intensity of the first ions and the electrode voltage; 2. The mass spectrometer according to claim 1, further comprising a step of extracting a peak voltage at which a detection intensity is maximized from the scan result, and determining the offset when the first ion is the target ion based on the peak voltage.

3. The mass spectrometer according to claim 2 , wherein the control device stores the determined relationship between the offset and the mass-to-charge ratio in a storage unit.

4. 4. The mass spectrometer according to claim 1, wherein the offset includes a predetermined energy barrier voltage regardless of the mass-to-charge ratio.

5. the control device, in the second mode, sets a predetermined cell voltage as a voltage to be applied to an ion guide included in the cell, regardless of a mass-to-charge ratio; The mass spectrometer according to claim 1 , wherein the offset includes the cell voltage.

6. The control device includes: The offset information indicating a relationship between a mass-to-charge ratio and the offset when an ion having the mass-to-charge ratio is regarded as the target ion is obtained, 4. The mass spectrometer according to claim 1, wherein, when an input of a mass-to-charge ratio of the target ion is received, the offset corresponding to the input mass-to-charge ratio is determined based on the offset information.

7. A method for setting analysis conditions for a mass spectrometer, comprising the steps of: The mass spectrometer is an ion source for ionizing the sample; a sampling cone having an inlet formed on a first axis for taking in particles in an ionization chamber in which the ion source is disposed; a cell provided on the first axis for contacting the particles taken in from the sampling cone with a predetermined gas; a mass separator arranged on a second axis parallel to the first axis, the mass separator separating ions according to their mass-to-charge ratio; a detector provided on the second axis for detecting each ion separated by the mass separator; a first electrode having a particle passage opening on the first axis between the cell and the mass separator; a second electrode having a particle passage opening on the second axis between the first electrode and the mass separator; The setting method includes: setting the cell to a first mode in which a detection result is obtained without introducing the predetermined gas into the cell; a step of setting a second mode in which the predetermined gas is introduced into the cell to obtain a detection result; and when the second mode is set, setting a voltage obtained by adding an offset determined according to the mass-to-charge ratio of a target ion to be detected to an initial voltage set as an electrode voltage to be applied to each of the first electrode and the second electrode in the first mode as the electrode voltage in the second mode.

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