Mass spectrometer

Abstract

A mass spectrometer (1) capable of performing mass spectrometry by generating ions from a sample through a first ionization method and a second ionization method comprises: an ion transport optical system (211, 212, 221, 222, 231, 232) into which generated ions are introduced and which includes a plurality of electrodes arranged along a flight path of the ions; a mass spectrometry unit provided with mass separation parts (242, 252, 254, 255, 256) for separating the ions according to the mass-to-charge ratio ; a storage unit (51) in which information on a first applied voltage to be applied to the plurality of electrodes is stored; a second applied voltage generation unit (53) that, when the first applied voltage includes a value of a voltage that forms a rising gradient of a potential inside the ion transport optical system, changes the value of the voltage to generate a second applied voltage in which the rising gradient is suppressed; and an analysis execution unit (54) that applies the second applied voltage to the plurality of electrodes and performs mass spectrometry of ions generated through the second ionization method.

Description

mass spectrometer

[0001] The present invention relates to a mass spectrometer.

[0002] Mass spectrometers combining an atmospheric pressure MALDI (Matrix Assisted Laser Desorption / Ionization) source and a mass analyzer are used to perform imaging mass spectrometry to measure the distribution of target substances contained in a sample (see, for example, Patent Document 1). The atmospheric pressure MALDI source irradiates multiple measurement points set on the surface of a sample coated with a matrix substance with laser light, generating ions at each measurement point. The mass analyzer includes, in order from the ion source side, an ion transport optical system, a mass separator, and an ion detector. The ion transport optical system has multiple electrodes, and by applying appropriate voltages to these electrodes, ions are focused along the ion optical axis (the central axis of the ion flight direction) and transported to the mass separator. The mass separator also has multiple electrodes, and by applying appropriate voltages to these electrodes, ions are separated according to their mass-to-charge ratio. The ion detector detects the ions separated by the mass separator.

[0003] Some mass spectrometers like those mentioned above can replace the atmospheric pressure MALDI source with an ESI (Electrospray Ionization) source, allowing the use of both ion sources. This allows mass analysis to be performed selectively using either the MALDI method, in which ions are generated by irradiating multiple measurement points on the surface of a sample mixed with a matrix substance with a laser beam, or the ESI method, in which a liquid sample is ionized by spraying it while charging it.

[0004] Japanese Patent Application Laid-Open No. 2021-196303

[0005] With atmospheric-pressure MALDI sources, the nature of the ionization method—that is, ionization of samples via a matrix material—makes it difficult to continuously inject a constant amount of sample into the mass analyzer. Furthermore, variations in the amount of ions produced are likely to occur depending on factors such as ionization conditions and sample preparation. Therefore, in mass spectrometers capable of using both atmospheric-pressure MALDI and ESI sources, the voltage applied to each electrode in the mass analyzer is calibrated using the ESI source, which allows for continuous injection of a constant amount of standard sample. However, after calibrating the mass analyzer using the ESI source, replacing the ESI source with an atmospheric-pressure MALDI source and performing imaging mass spectrometry often results in blurred sample boundaries in the resulting images.

[0006] Here, as a specific example, the case of using an ionization method using an ESI source and an ionization method using an atmospheric pressure MALDI source has been described, but a similar situation can occur when using other ionization methods.

[0007] The problem to be solved by the present invention is to provide a technology that can improve analytical accuracy in a mass spectrometer that can perform mass analysis by generating ions from a sample using mutually different first and second ionization methods.

[0008] The present invention, which has been made to solve the above-mentioned problems, provides a mass spectrometer capable of generating ions from a sample by mutually different first and second ionization methods and performing mass analysis, comprising: a mass analysis unit including an ion transport optical system into which ions generated by the first ionization method or the second ionization method are introduced and including a plurality of electrodes arranged along the flight path of the ions; and a mass separation unit that separates the ions transported by the ion transport optical system according to their mass-to-charge ratios; a memory unit that stores information on first applied voltages, which are sets of voltage values ​​to be applied to each of the plurality of electrodes; a second applied voltage generation unit that, when the first applied voltages include a voltage value that forms a potential gradient inside the ion transport optical system, changes the value of the voltage to generate a second applied voltage that suppresses the gradient; and an analysis execution unit that applies the second applied voltage to the plurality of electrodes and performs mass analysis of ions generated by the second ionization method.

[0009] In a mass spectrometer according to the present invention, mass analysis is performed by generating ions from a sample using a first ionization method and a second ionization method, which are different from each other. The first ionization method is, for example, an ionization method that generates ions continuously during sample analysis. The second ionization method is, for example, an ionization method that generates ions discontinuously (intermittently) during sample analysis. Note that the first ionization method and the second ionization method are not limited to ionization methods using different ion sources, but may also include methods in which a sample is introduced into the same ion source in different forms.

[0010] The present inventors have found that when ions generated using the second ionization method are subjected to mass analysis, a decrease in analytical accuracy occurs, such as the boundary of the sample becoming unclear in an image obtained by imaging mass analysis. This is because an upward potential gradient formed inside the ion transport optical system causes ions to remain inside the ion transport optical system, resulting in a time delay.

[0011] In a mass spectrometer according to the present invention, information on first applied voltages, which is a set of voltage values ​​to be applied to each of a plurality of electrodes included in an ion transport optical system, is stored. This information on first applied voltages is determined, for example, by calibration using ions generated by a first ionization method and is primarily used when performing mass analysis of ions generated by the first ionization method. In a mass spectrometer according to the present invention, if the first applied voltage includes a voltage value that creates an upward potential gradient within the ion transport optical system, the second applied voltage generation unit changes the value of the first applied voltage to generate a second applied voltage that suppresses the upward potential gradient, and the analysis execution unit uses the second applied voltage to perform mass analysis of ions generated by the second ionization method. This suppresses ion retention in the ion transport optical system when generating ions using the second ionization method and performing mass analysis, thereby improving analysis accuracy compared to when the first applied voltage is used as is.

[0012] FIG. 1 is a diagram showing the configuration of the main parts of an embodiment of a mass spectrometer according to the present invention (when using an atmospheric pressure MALDI source). FIG. 2 is a diagram showing the configuration of the main parts near the ionization chamber of the mass spectrometer of this embodiment (when using an ESI source). The applied voltage obtained as a result of autotuning using an ESI source, used in Measurement Example 1, and voltages 1 to 5, which are differently modified versions of the applied voltage. Images obtained by imaging mass spectrometry using the AT voltage and voltages 1 to 5, along with optical microscope images, are shown. Five applied voltage values ​​with different rising gradients of the potential formed in the ion transport optical system, used in Measurement Example 2. Images obtained by imaging mass spectrometry using five different applied voltages, along with optical microscope images, are shown. Values ​​of the first and second applied voltages in Measurement Example 3. Images obtained by using the first applied voltage and the second applied voltage in an imaging mass spectrometer, along with optical microscope images, are shown. A mass spectrum obtained by using the first applied voltage in a mass spectrometer using an ESI source. A mass spectrum obtained by using the second applied voltage in a mass spectrometer using an ESI source. 10 shows an example of the first applied voltage and the second applied voltage when the measurement target is negative ions.

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A mass spectrometer according to an embodiment of the present invention will now be described with reference to the accompanying drawings.

[0014] <Configuration of Mass Spectrometer 1> Figure 1 shows the main components of a mass spectrometer 1 (using atmospheric pressure MALDI) according to this embodiment. This mass spectrometer 1 includes an ionization section with an atmospheric pressure MALDI source installed in an ionization chamber 11 at approximately atmospheric pressure, an ion transport optical system installed in a vacuum chamber 100 that transports ions generated in the ionization chamber 11 to a downstream stage, and a separation / detection section that separates and detects ions according to their mass-to-charge ratio. Furthermore, in this embodiment, the mass spectrometer 1 can use an ESI source (see Figure 2), which is also used in an atmospheric pressure environment, instead of the atmospheric pressure MALDI source. When the ESI source is installed, ions are generated from a sample using the ESI method (corresponding to the first ionization method in this invention). When the atmospheric pressure MALDI source is installed, ions are generated from a sample using the MALDI method (corresponding to the second ionization method in this invention).

[0015] The atmospheric pressure MALDI source includes a sample plate holder 13 on which a sample plate 12 is placed, and a moving mechanism 14 that moves the sample plate 12 between an observation position (the position indicated by the dashed line in FIG. 1 ) and a measurement position (the position indicated by the solid line in FIG. 1 ). It also includes an optical system, such as a laser light source 15, a mirror 16 that reflects light emitted from the laser light source 15 and irradiates it onto the sample plate 12 placed on the sample plate holder 13, and a lens 17 that focuses the laser light reflected by the mirror 16 onto a measurement point on the sample plate 12 at the measurement position. It also includes an optical microscope 18 for observing the surface of the sample on the sample plate 12 at the observation position.

[0016] 2 shows the configuration of the ionization chamber 11 equipped with an ESI source. The ESI source includes an electrospray ionization (ESI) probe 31 that imparts an electric charge to a liquid sample and sprays it. A liquid chromatograph (LC) 32, for example, is connected to the ESI probe 31, and a liquid sample containing sample components separated in a column of the liquid chromatograph 32 is introduced into the ESI probe 31. Alternatively, the liquid sample can be introduced directly into the ESI source.

[0017] A partition wall 80 is provided between the ionization chamber 11 and the vacuum chamber 100. An ion introduction tube 19 for introducing ions generated in the ionization chamber 11 into the first intermediate vacuum chamber 21 in the vacuum chamber 100 is inserted into the partition wall 80.

[0018] The interior of the vacuum chamber 100 is partitioned into multiple sections (five in this embodiment), which are provided, in order from the side closest to the ionization chamber 11, with a first intermediate vacuum chamber 21, a second intermediate vacuum chamber 22, a third intermediate vacuum chamber 23, a first analysis chamber 24, and a second analysis chamber 25. The first intermediate vacuum chamber 21, the second intermediate vacuum chamber 22, the third intermediate vacuum chamber 23, the first analysis chamber 24, and the second analysis chamber 25 are evacuated to vacuum by vacuum pumps (not shown), and form a multi-stage differential pumping system in which the degree of vacuum increases in this order.

[0019] The first intermediate vacuum chamber 21 is provided with an ion guide (Qarray) 211, which is composed of a plurality of roughly rod-shaped electrodes arranged to surround the ion optical axis C, which is the central axis of the ion flight path, and which focuses ions in the vicinity of the ion optical axis C.

[0020] The first intermediate vacuum chamber 21 and the second intermediate vacuum chamber 22 are separated by a skimmer 212 having a small hole at the top. The second intermediate vacuum chamber 22 and the third intermediate vacuum chamber 23 are separated by a ring electrode (Multipole 1 Lens) 222 having a small hole for passing ions. The third intermediate vacuum chamber 23 and the first analysis chamber 24 are also separated by a ring electrode (Multipole 2 Lens) 232 having a small hole for passing ions. The second intermediate vacuum chamber 22 and the third intermediate vacuum chamber 23 are each equipped with an ion guide (Multipole 1) 221 and an ion guide (Multipole 2) 231, which are composed of multiple rod electrodes arranged to surround the ion optical axis C and focus ions near the ion optical axis C.

[0021] A predetermined DC voltage (bias voltage) is applied to each of the ion guide 211, skimmer 212, ion guide 221, ring electrode 222, ion guide 231, and ring electrode 232, which are located between the ionization chamber 11 and the first analysis chamber 24 (including grounding), and ions generated in the ionization chamber 11 are transported to the first analysis chamber 24 by an electric field formed by applying a voltage to each of these components. These components correspond to the ion transport optical system in the present invention. In the following description, these components will be collectively referred to as the ion transport optical system as appropriate. A radio frequency voltage is also applied to the ion guide 211, ion guide 221, and ion guide 231, which forms an electric field that focuses ions near the ion optical axis C.

[0022] The first analysis chamber 24 is equipped with a quadrupole mass filter 241, which is composed of four rod electrodes arranged along the ion optical axis C and includes a main rod electrode that separates ions according to their mass-to-charge ratio (m / z), a collision cell 242 that incorporates a multipole ion guide 243 composed of eight plate-shaped electrodes, and an ion transport electrode 244, which is composed of multiple ring-shaped electrodes and transports ions that have passed through the collision cell 242 to the subsequent stage.

[0023] A collision-induced dissociation (CID) gas supply source (not shown) is connected to the collision cell 242, and a CID gas (a predetermined type of inert gas) can be introduced at any timing depending on the purpose of the analysis.

[0024] The second analysis chamber 25 is equipped with an ion transport electrode 251 for transporting ions incident from the first analysis chamber 24, an orthogonal acceleration section 252 having a pair of pusher electrode 2521 and puller electrode 2522 arranged opposite each other across the ion optical axis C, a second acceleration section 253 for accelerating ions sent out into the flight space by the orthogonal acceleration section 252, a flight tube 254 for defining the outer edge of the ion flight space, a reflectron electrode 255 and a backplate electrode 256 for forming an electric field that causes ions to fly on a return trajectory in the flight space, and an ion detector 257 for detecting ions that have flown on the return trajectory. The quadrupole mass filter 241 arranged in the first analysis chamber 24 and the orthogonal acceleration section 252, flight tube 254, reflectron electrode 255, and backplate electrode 256 arranged in the second analysis chamber 25 correspond to the mass separation section in this invention.

[0025] The control and processing unit 5 includes a memory unit 51. The memory unit 51 stores a compound database that contains information on analytical conditions (measurement conditions, analysis methods, etc.) for various compounds, as well as information such as the voltages (first applied voltages) applied to each electrode included in the ion transport optical system. This information is, for example, based on the results of autotuning or the values ​​of voltages applied to each unit during past analyses.

[0026] The control / processing unit 5 also includes functional blocks, such as a tuning unit 52, a second applied voltage generator 53, and an analysis unit 54. The tuning unit 52 automatically optimizes (auto-tunes) the voltage values ​​applied to each component of the mass spectrometer based on user instructions. When the information about the first applied voltage stored in the memory unit 51 includes a voltage value that creates a potential gradient within the ion transport optical system, the second applied voltage generator 53 generates a second applied voltage that suppresses the gradient by changing the voltage value. The analysis unit 54 analyzes the sample based on the analysis conditions (including the first applied voltage or the second applied voltage) set by the user. The control / processing unit 5 is, for example, a general-purpose personal computer, and these functional blocks are realized by executing a dedicated mass analysis program pre-installed on the processor. The control / processing unit 5 is also connected to an input unit 61 through which the user can perform various input operations and a display unit 62 for displaying various information.

[0027] <Operation of Mass Spectrometer 1> Next, the operation of the mass spectrometer 1 of this embodiment will be described. Here, an example will be described in which the voltages applied to the various components of the mass spectrometer 1 are first autotuned using an ESI source, and then imaging mass spectrometry is performed using an atmospheric pressure MALDI source.

[0028] Before tuning the voltages applied to each component, the user installs an ESI source as an ion source in the vacuum chamber 100. With an atmospheric pressure MALDI source, due to the nature of the ionization method, in which the sample is ionized via a matrix material, it is difficult to continuously inject a constant amount of sample into the mass analyzer. Furthermore, the amount of ions generated is prone to variation depending on the ionization conditions and sample preparation. Therefore, when tuning the applied voltage, an ESI source capable of continuously injecting a constant amount of standard sample is used.

[0029] When the user issues an instruction to execute auto-tuning with the ESI source attached to the vacuum chamber 100, the tuning execution unit 52 continuously injects a predetermined amount of a preset standard sample, and during that time repeatedly measures ions of a predetermined mass-to-charge ratio by changing the voltage values ​​applied to each electrode, thereby determining a set of applied voltage values ​​that maximizes the measured intensity of the ions. Alternatively, the tuning execution unit 52 may determine a set of applied voltage values ​​that maximizes the score calculated using a predetermined formula or the like based on the measured ion intensity and mass resolution. The tuning execution unit 52 stores the set of applied voltage values ​​thus determined in the memory unit 51 as information on the first applied voltage.

[0030] The user then installs an atmospheric pressure MALDI source in place of the ESI source in the vacuum chamber 100, places a predetermined sample (for example, a sample with a predetermined matrix substance applied to its surface) on the sample plate 12, observes the surface with the optical microscope 18, and sets multiple measurement points.The user also selects measurement conditions for the target compound (such as the mass-to-charge ratio of ions generated from the target compound) from the compound database stored in the memory unit 51, and issues an instruction to execute the analysis.

[0031] When the user issues an instruction to perform analysis (mass analysis using atmospheric pressure MALDI, which is the second ionization method), the second applied voltage generator 53 reads out information about the first applied voltage stored in the memory unit 51. The second applied voltage generator 53 then determines whether the information about the first applied voltage includes a voltage value that creates an upward gradient of potential within the ion transport optical system. Specifically, when the ions to be measured are positive ions, the second applied voltage generator 53 determines whether there are any locations where the applied voltage value increases from the ionization chamber 11 toward the first analysis chamber 24, with respect to the values ​​of the voltages applied to the ion guide 211, skimmer 212, ion guide 221, ring electrode 222, ion guide 231, and ring electrode 232 that constitute the ion transport optical system. If there are any locations where the applied voltage value increases from the ionization chamber 11 toward the first analysis chamber 24, the second applied voltage generator 53 reduces the value of the applied voltage to the electrodes at those locations, thereby generating information about the second applied voltage that suppresses the upward gradient of potential. More preferably, at a location where the applied voltage increases from the ionization chamber 11 toward the first analysis chamber 24, the applied voltage to that electrode is changed to the same value (or a value lower than) the applied voltage to the electrode adjacent to the ionization chamber 11, thereby generating information on the second applied voltage that eliminates the upward gradient of the potential. In this case, if there are any electrodes in the ion transport optical system located downstream (on the first analysis chamber 24 side) of the electrode whose applied voltage value has been changed, the voltages applied to those electrodes should also be changed by the same value. This allows the shape of the potential formed downstream of the electrode whose applied voltage value has been changed to be the same as that during autotuning. When the ions to be measured are negative ions, the applied voltage to the electrode at the location where the upward gradient of the potential is formed in the ion traveling direction should be increased.

[0032] If the second applied voltage generation unit 53 determines that the information on the first applied voltage does not include a voltage value that forms an upward gradient of potential inside the ion transport optical system, it generates the information on the first applied voltage as information on the second applied voltage without modification.

[0033] When the second applied voltage generating unit 53 generates the information on the second applied voltage, the analysis executing unit 54 executes imaging mass spectrometry based on the analysis conditions including the information on the second applied voltage. Specifically, for example, the following analysis is executed.

[0034] The sample plate 12 is moved so that the first of multiple measurement points set on the sample is positioned at the laser beam irradiation position, and the laser light source 15 irradiates the first measurement point with laser light to generate ions. The ions generated at the measurement point enter the first intermediate vacuum chamber 21 through the ion introduction tube 19. The ions that enter the first intermediate vacuum chamber 21 pass through the ion guide 211, skimmer 212, ion guide 221, ring electrode 222, ion guide 231, and ring electrode 232 (ion transport optical system) in this order, which constitute the ion transport optical system, before being transported to the first analysis chamber 24. In the first analysis chamber 24, ions having a predetermined mass-to-charge ratio are selected as precursor ions by the quadrupole mass filter 241. CID gas is introduced into the collision cell 242, and product ions are generated from the precursor ions through collisions with the CID gas molecules. The generated product ions are focused by the ion transport electrode 244 and transported to the second analysis chamber 25. In the second analysis chamber 25, the flight direction of the product ions is deflected by the orthogonal acceleration unit 252, and after flying along a predetermined return trajectory, the product ions are detected by the ion detector 257. Output signals from the ion detector 257 are sequentially transmitted to the control and processing unit 5 and stored in the memory unit 51. The analysis execution unit 54 executes the above-described analysis at all measurement points in a predetermined order.

[0035] In a mass spectrometer configured so that an atmospheric pressure MALDI source or an ESI source can be selectively attached to the vacuum chamber 100 as described above, the voltages applied to each part of the mass spectrometer have conventionally been autotuned using a configuration equipped with an ESI source, and the tuning results have been used as is when performing mass analysis using a configuration equipped with an atmospheric pressure MALDI source.

[0036] However, when imaging mass spectrometry was performed using an atmospheric pressure MALDI source with the applied voltage determined by autotuning using an ESI source, the boundaries of the sample were sometimes blurred in the resulting images.

[0037] The inventors discovered that the cause of this problem is the formation of an upward potential gradient within the ion transport optical system due to the set of applied voltages determined by autotuning using an ESI source, resulting in ion retention there. More specifically, they discovered that some ions generated at a certain measurement point stagnate within the ion transport optical system and pass through the ion transport optical system with a time delay, resulting in temporal carryover. As a result, the ions are detected as measurement data from a measurement point later than the measurement point at which they were generated, causing blurring at the boundary of the sample in images acquired by imaging mass spectrometry. In typical mass spectrometry using an ESI source, a large number of ions are continuously generated from the sample over time during mass analysis. In such cases, a large number of ions also continuously flow into the ion transport optical system, forming a continuous ion flow from the ionization chamber 11 to the first analysis chamber 24. Therefore, even if a potential gradient with a slight upward gradient exists within the ion transport optical system, ions do not stagnate at that point but are instead swept away by the ion flow to subsequent stages. On the other hand, when ions are generated intermittently (discontinuously in time) from the sample and the amount of ions is small, such an ion flow does not form. Therefore, if there is a place inside the ion transport optical system where an upward potential gradient is formed, ions tend to stagnate there.

[0038] Therefore, in the above embodiment, if the information on the first applied voltage obtained as a result of autotuning using the ESI source includes a voltage value that forms an upward gradient of potential inside the ion transport optical system, a second applied voltage is generated that suppresses (preferably eliminates) the upward gradient. In this embodiment, by using the second applied voltage in mass spectrometry imaging using an atmospheric pressure MALDI source, it is possible to suppress ion retention inside the ion transport optical system and cause temporal carryover, thereby making it possible to acquire clearer image data with higher resolution than conventional methods.

[0039] When mass spectrometry using an ESI source is performed in the mass spectrometer 1 of this embodiment, the applied voltage (first applied voltage) obtained by autotuning using the ESI source can be used as is.

[0040] <Measurement Example> A measurement example will be described in which the inventors confirmed that ions were retained in the ion transport optical system when performing imaging mass spectrometry using an atmospheric pressure MALDI ion source using an applied voltage obtained by autotuning using an ESI source.

[0041] <Measurement Example 1> In the mass spectrometer 1 of this embodiment, the applied voltage for measuring positive ions (AT voltage) obtained by autotuning using the ESI source formed a slight upward gradient of about 0.8 V between the ion guide (Multipole 1) 221 and the ring electrode (Multipole 1 Lens) 222. Therefore, first, a set of applied voltages (Voltage 1, Voltage 2) was created in which the voltage applied to the ring electrode (Multipole 1 Lens) 222 was changed to 0 V. Furthermore, taking into consideration the possibility that ions were retained due to an insufficient downward gradient of the potential at each electrode of the ion transport optical system, sets of applied voltages (Voltage 3 to 5) were also created in which the potential difference was increased (the downward gradient of the potential was increased) at each electrode position. If the blurring of the sample boundary in the image acquired by imaging mass spectrometry improves at voltages 1 and 2, then the presence of an upward potential gradient is the cause of ion retention. If the blurring of the sample boundary improves at voltages 1 and 2 at voltages 3 to 5, then the cause of ion retention is insufficient potential difference at the electrode position where the downward potential gradient is increased.

[0042] 3 shows the AT voltage and voltages 1 to 5. Voltage 3 increases the downward gradient of the potential in the ring electrode (Multipole 1 Lens) 222, voltage 4 increases the downward gradient of the potential in the ion guide (Multipole 2) 231, and voltage 5 increases the downward gradient of the potential in the ring electrode (Multipole 2 Lens) 232.

[0043] Figure 4 shows the images (MS images) obtained by imaging mass spectrometry using each of the above voltages, along with optical microscope images. The MS images are a mapping of the detection intensity of an ion with a mass-to-charge ratio (m / z) of +478.3200. As can be seen from Figure 4, the sample boundaries in the MS images are clearer at all voltages 1 to 5 than when the voltage obtained by autotuning using the ESI source was used. Furthermore, there is no significant difference between the MS images obtained at voltages 1 and 2 and those obtained at voltages 3 to 5. From these results, the inventors concluded that the presence of an upward potential gradient in the ion transport optics causes ion retention, resulting in temporal carryover as the ions pass through the ion transport optics with a time delay, which causes the blurring of the sample boundaries in the MS images.

[0044] <Measurement Example 2> In Measurement Example 2, five sets of applied voltages were set by increasing or decreasing the applied voltage to the ring electrode (Multipole 1 Lens) 222 electrode, on which an upward potential gradient was formed, using the applied voltage (first applied voltage) obtained by autotuning using the ESI source, and imaging mass spectrometry was performed using each of the five sets of applied voltages.

[0045] Figure 5 shows the values ​​of five applied voltages (voltages A to E). Of these, voltage B is the applied voltage (first applied voltage) obtained by autotuning using an ESI source, voltage A suppresses the rising gradient of the potential formed by the first applied voltage, and voltages C to E increase the rising gradient of the potential formed by the first applied voltage. Voltage A (which suppresses the rising gradient of the potential) is one aspect of the present invention.

[0046] Figure 6 shows the measurement results for each applied voltage. The top row in Figure 6 is an optical microscope image of the analysis area on the sample surface, and the bottom row is an image acquired by imaging mass spectrometry (MS image). This MS image also maps the detection intensity of an ion with a mass-to-charge ratio (m / z) of +478.3200. Comparing the five images acquired by imaging mass spectrometry, it can be seen that the sample boundary becomes less clear in the image as the potential gradient increases. This is thought to be because the greater the potential gradient, the more ions become trapped in the ion transport optical system, and these trapped ions are detected as ions generated at later measurement points.

[0047] <Measurement Example 3> The inventors actually determined the voltages applied to each component of the ion transport optical system by autotuning using an ESI source, and performed imaging mass spectrometry using an atmospheric pressure MALDI source using the applied voltages (first applied voltage) as is (Comparative Example), and also performed imaging mass spectrometry using an atmospheric pressure MALDI source using an applied voltage (second applied voltage) obtained by changing the value of the voltage applied to the ring electrode (Multipole 1 Lens) 222 that forms an upward gradient potential inside the ion transport optical system, thereby eliminating the upward gradient (Example).

[0048] 7 shows the values ​​of the first applied voltage (the applied voltage obtained as a result of autotuning) and the second applied voltage (the applied voltage obtained by eliminating the upward gradient of the potential from the first applied voltage). This example is for measuring a positive ion (mass-to-charge ratio m / z = +478.3200). In this example, the value of the first applied voltage applied to the ring electrode (Multipole 1 Lens) 222 is greater than the value of the voltage applied to the ion guide (Multipole 1) 221 located upstream, resulting in an upward gradient of the potential at the position of the ring electrode (Multipole 1 Lens) 222.

[0049] For the second applied voltage, the value of the voltage applied to the ring electrode (Multipole 1 Lens) 222 of the first applied voltage was changed to the same value as the value of the voltage applied to the ion guide (Multipole 1) 221 located further upstream (changed from 0.8 V to 0 V), and the voltages applied to the ion guide (Multipole 2) 231 and ring electrode (Multipole 2 Lens) 232 located downstream (towards the first analysis chamber 24) of the ring electrode (Multipole 1 Lens) 222 were also changed by the same value (-0.8 V).

[0050] Figure 8 shows the results of a comparative example and an example. The top row of Figure 8 is an optical microscope image of the analysis region on the surface of the sample, and the bottom row of Figure 8 is an image obtained by imaging mass spectrometry (MS image). This MS image also maps the detection intensity of an ion with a mass-to-charge ratio m / z of +478.3200. In the comparative example shown on the left side of Figure 8, the boundary of the sample shown in the optical microscope image is difficult to distinguish in the image obtained by imaging mass spectrometry. On the other hand, in the example shown on the right side of Figure 8, it can be seen that the boundary of the sample in the image obtained by imaging mass spectrometry is clearer than in the comparative example.

[0051] <Measurement Example 4> The present inventors obtained mass spectra using the first applied voltage and the second applied voltage described above in mass analysis using an ESI source (mass analysis using the first ionization method), and the mass spectra shown in Figure 9 (first applied voltage) and Figure 10 (second applied voltage) were obtained. Comparing these mass spectra, it can be seen that there is no significant difference in the detection intensity of each ion in the mass spectrum. Therefore, it can be seen that when performing mass analysis using the first ionization method, it is sufficient to use the first applied voltage as is. However, this does not negate the use of the second applied voltage in mass analysis using the first ionization method.

[0052] The above-described embodiments and examples are merely examples and can be modified as appropriate in accordance with the spirit of the present invention.

[0053] In the above-described embodiments and examples, the ion transport optical system includes the ion guide 211, the skimmer 212, the ion guide 221, the ring electrode 222, the ion guide 231, and the ring electrode 232. However, the ion transport optical system may be configured as appropriate as long as it receives ions generated by the first ionization method or the second ionization method in the ion source and transports the ions to a subsequent stage.

[0054] In the above embodiments and examples, the case where the measurement target is a positive ion has been described, but when the measurement target is a negative ion, the upward gradient of the potential can be suppressed or eliminated in the same way as when measuring positive ions by increasing the value of the voltage applied to the electrode at the location where the upward gradient of the potential is formed in the direction of ion travel. Fig. 11 shows an example of the first applied voltage and the second applied voltage when the measurement target ion is a negative ion.

[0055] In the above embodiment, the first ionization method is ESI and the second ionization method is atmospheric pressure MALDI. However, one or both of the first and second ionization methods may be different ionization methods. As described in the above embodiment, the first ionization method typically generates a large amount of ions continuously over time from the sample during mass spectrometry, forming a continuous ion flow within the ion transport optical system. In contrast, the second ionization method generates ions discontinuously (intermittently) from the sample, or generates a smaller amount of ions than the first ionization method, making it difficult to form a continuous ion flow within the ion transport optical system. Note that the first and second ionization methods do not necessarily have to be performed using different ion sources, and may be performed using the same ion source. For example, the scope of the present invention also includes a configuration in which a liquid sample is continuously introduced into an ESI source to continuously generate a large amount of ions from the sample, and a second ionization method is intermittently introduced into the ESI source to generate a small amount of ions from the sample. Furthermore, the first ionization method and the second ionization method are not limited to atmospheric pressure ionization, but may be vacuum ionization. Even when ions are generated and analyzed by vacuum ionization, the same effects as those of the above-described embodiment and example can be obtained by suppressing (preferably eliminating) the upward gradient in the ion transport optical system.

[0056] In the above embodiment, the first applied voltage was determined by performing autotuning using the ESI source and stored in the storage unit 51. However, the first applied voltage stored in the storage unit 51 may be a different voltage. For example, it may be an applied voltage used in a previous mass analysis or an initial applied voltage set when the mass spectrometer was installed. Note that in the above embodiment, the first applied voltage was determined by autotuning, and therefore it was assumed that the first applied voltage could be used when performing mass analysis using the ESI source. However, if the first applied voltage was used in a previous mass analysis or was initially set when the device was installed, the second applied voltage may be used in mass analysis using the ESI source (mass analysis using the first ionization method).

[0057] Aspects It will be apparent to those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0058] (Item 1) One aspect of the present invention is a mass spectrometer capable of generating ions from a sample by mutually different first and second ionization methods to perform mass analysis, comprising: a mass analysis unit including an ion transport optical system into which ions generated by the first ionization method or the second ionization method are introduced and including a plurality of electrodes arranged along the flight path of the ions; and a mass separation unit that separates ions transported by the ion transport optical system according to their mass-to-charge ratios; a memory unit that stores information on first applied voltages, which are sets of voltage values ​​to be applied to each of the plurality of electrodes; a second applied voltage generation unit that, when the first applied voltages include a voltage value that forms a potential upward gradient inside the ion transport optical system, changes the value of the voltage to generate a second applied voltage that suppresses the upward gradient; and an analysis execution unit that applies the second applied voltage to the plurality of electrodes to perform mass analysis of ions generated by the second ionization method.

[0059] (Clause 2) The mass spectrometer according to clause 2 is the mass spectrometer according to clause 1, wherein the first ionization method is an ionization method that continuously generates ions from the sample, and the second ionization method is an ionization method that intermittently generates ions from the sample.

[0060] (Clause 3) The mass spectrometer according to clause 3 is the mass spectrometer according to clause 1 or 2, wherein the first ionization method is ESI, APCI, EI, or CI, and the second ionization method is atmospheric pressure MALDI, vacuum MALDI, or LDI.

[0061] The mass spectrometer according to paragraph 1 performs mass analysis by generating ions from a sample using a first ionization method and a second ionization method, which are different from each other. The first ionization method is, for example, an ionization method that generates ions continuously during sample analysis, as described in paragraph 2. The second ionization method is, for example, an ionization method that generates ions discontinuously (intermittently) during sample analysis, as described in paragraph 2. Note that the first ionization method and the second ionization method are not limited to ionization methods using different ion sources, but may also include methods in which the sample is introduced into the same ion source in different forms. As with the mass spectrometer according to paragraph 3, typical first ionization methods are ESI, APCI, EI, or CI, and typical second ionization methods are atmospheric pressure MALDI, vacuum MALDI, or LDI.

[0062] The present inventors have found that when ions generated using the second ionization method are subjected to mass analysis, a decrease in analytical accuracy occurs, such as the boundary of the sample becoming unclear in an image obtained by imaging mass analysis. This is because an upward potential gradient formed inside the ion transport optical system causes ions to remain inside the ion transport optical system, resulting in a time delay.

[0063] In the mass spectrometer according to paragraph 1, information on first applied voltages, which is a set of voltage values ​​to be applied to each of a plurality of electrodes included in the ion transport optical system, is stored. This information on the first applied voltages is determined, for example, by calibration using ions generated by a first ionization method and is primarily used when performing mass analysis of ions generated by the first ionization method. In the mass spectrometer according to paragraph 1, if the first applied voltage includes a voltage value that forms an upward gradient of potential within the ion transport optical system, the second applied voltage generation unit changes the value of the first applied voltage to generate a second applied voltage that suppresses the upward gradient, and the analysis execution unit uses the second applied voltage to perform mass analysis of ions generated by the second ionization method. This suppresses ion retention in the ion transport optical system when generating ions using the second ionization method and performing mass analysis, thereby improving analysis accuracy compared to when the first applied voltage is used as is.

[0064] (4) A mass spectrometer according to 4 is the mass spectrometer according to any one of 1 to 3, wherein the second applied voltage generating unit eliminates the upward gradient by changing the value of the first applied voltage.

[0065] In the mass spectrometer according to the fourth aspect, the upward gradient of the potential is eliminated, thereby further reducing the retention of ions in the ion transport optical system, and further improving the analytical accuracy.

[0066] (Clause 5) A mass spectrometer according to clause 5 is the mass spectrometer according to any one of clauses 1 to 4, wherein the second applied voltage generating unit changes the voltage applied to the electrode where the upward gradient of the potential is formed and the electrode located downstream of the electrode by the same value.

[0067] (Clause 6) A mass spectrometer according to clause 6 is the mass spectrometer according to any one of clauses 1 to 5, wherein the first applied voltage is a value of an applied voltage obtained by tuning using the first ionization method.

[0068] In the mass spectrometer according to paragraph 5, it is possible to generate a second applied voltage that suppresses or eliminates the upward gradient of the potential while maintaining the shape of the potential formed by the first applied voltage in other locations. This is particularly effective when the first applied voltage has been optimized by tuning, as in the mass spectrometer according to paragraph 6.

[0069] REFERENCE SIGNS LIST 1...Mass spectrometer 100...Vacuum chamber 11...Ionization chamber 12...Sample plate 13...Sample plate holder 14...Moving mechanism 15...Laser light source 16...Mirror 17...Lens 18...Optical microscope 19...Ion introduction tube 21...First intermediate vacuum chamber 211...Ion guide (Qarray) 212...Skimmer 22...Second intermediate vacuum chamber 221...Ion guide (Multipole 1) 222...Ring electrode (Multipole 1 Lens) 23...Third intermediate vacuum chamber 231...Ion guide (Multipole 2) 232...Ring electrode (Multipole 2 Lens) 24...First analysis chamber 241...Quadrupole mass filter 242...Collision cell 243...Multipole ion guide 244...Ion transport electrode 25...Second analysis chamber 251...Ion transport electrode 252...Orthogonal acceleration section 2521...Pushing electrode 2522...Pulling electrode 253...Second acceleration section 254...Flight tube 255...Reflectron electrode 256...Back plate electrode 257...Ion detector 31...ESI probe 32...Liquid chromatograph 5...Control and processing section 51...Memory section 52...Tuning execution section 53...Second applied voltage generation section 54...Analysis execution section 61...Input section 62...Display section 80...Bulkhead C...Ion optical axis

Claims

1. A mass spectrometer capable of generating ions from a sample by different first and second ionization methods and performing mass spectrometry, the mass spectrometer comprising: an ion transport optical system into which ions generated by the first ionization method or the second ionization method are introduced and which includes a plurality of electrodes arranged along the flight path of the ions; a mass separation unit that separates the ions transported by the ion transport optical system according to the mass-to-charge ratio; a storage unit that stores information on a first applied voltage that is a set of values of voltages applied to each of the plurality of electrodes; a second applied voltage generation unit that, when the first applied voltage includes a value of a voltage that forms an upward gradient of potential inside the ion transport optical system, changes the value of the voltage to generate a second applied voltage that suppresses the upward gradient; and an analysis execution unit that applies the second applied voltage to the plurality of electrodes to perform mass spectrometry on the ions generated by the second ionization method.

2. The mass spectrometer according to claim 1, wherein the first ionization method is an ionization method that continuously generates ions from the sample, and the second ionization method is an ionization method that intermittently generates ions from the sample.

3. The mass spectrometer according to claim 1, wherein the first ionization method is an ESI method, an APCI method, an EI method, or a CI method, and the second ionization method is an atmospheric pressure MALDI method, a vacuum MALDI method, or an LDI method.

4. The mass spectrometer according to claim 1, wherein the second applied voltage generation unit eliminates the upward gradient by changing the value of the first applied voltage.

5. The mass spectrometer according to claim 1, wherein the second applied voltage generation unit changes the voltages applied to the electrode where the upward gradient of potential is formed and the electrode located downstream of the electrode by the same amount.

6. The mass spectrometer according to claim 1, wherein the first applied voltage is a value of an applied voltage obtained by tuning using the first ionization method.

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