JP4858614B2 - Laser desorption ionization mass spectrometer - Google Patents

Description

  The present invention relates to a laser desorption ionization mass spectrometer that performs mass spectrometry by irradiating a sample with laser light to ionize a target component in the sample.

  In a mass spectrometer, ions are detected in order to detect ions separated according to mass (more precisely, mass-to-charge ratio m / z) by a mass analyzer such as a quadrupole mass filter or a time-of-flight mass analyzer. An ion detector using a combination of a conversion dynode that converts to photoelectrons and a photomultiplier tube or a microchannel plate (MCP) is used. In order to increase measurement sensitivity in mass spectrometry, it is desirable to increase the gain of these ion detectors. On the other hand, if an excessive amount of ions are incident, the detection output will saturate and proper analysis cannot be performed. In other words, the detector may be damaged and the life may be shortened. Therefore, when the amount of ions generated in the ion source is too large, to reduce the gain of the ion detector (for example, the excitation voltage applied to the conversion dynode) or to reduce the ion amount itself introduced into the ion detector. For example, it is necessary to suppress the amount of ions generated in the ion source.

  In addition, in mass analyzers such as a quadrupole mass filter and a three-dimensional quadrupole ion trap, if the amount of ions introduced is too large, the mass separation performance deteriorates due to the effect of the space charge effect. May occur. Therefore, even in such a case, it is necessary to suppress, for example, the amount of ions generated in the ion source in order to reduce the amount of ions introduced into the mass analyzer.

  As a conventional technique, in the mass spectrometer described in Patent Literature 1, mass analysis of a sample is executed in advance, and the excitation voltage of the ion receptor (conversion dynode) is changed according to the detection output of the ion detector at that time. Adjust the gain with. Accordingly, when mass analysis of the sample is performed thereafter, the detection output can be prevented from being saturated even when a large amount of ions are incident.

  Moreover, in the time-of-flight mass spectrometer described in Patent Document 2, when the detection output of the ion detector exceeds a predetermined value, the amount of ions generated is reduced by reducing the irradiation power of the laser beam for ionizing the sample. Reduce. Thereby, the amount of ions reaching the ion detector is suppressed, and saturation of the output of the ion detector can be prevented.

  Further, in the three-dimensional quadrupole ion trap mass spectrometer described in Patent Document 3, ions generated by an ion source are passed through an ion trap to reach an ion detector to obtain a detection output (pre-measurement). Then, the amount of ions introduced into the ion trap is adjusted by determining the time for introducing the ions generated by the ion source into the ion trap according to the detection result, and an excessive amount of ions is trapped in the ion trap. This prevents the mass resolution from being reduced by the space charge effect.

  In any of the conventional techniques as described above, mass analysis is performed to obtain a detection output from the ion detector, and based on the detection output, adjustment of the gain of the ion detector or the amount of ion generation in the ion source is performed. In other words, since the gain of the ion detector is adjusted based on the ion detection result of the past ion detector, it is appropriate under the assumption that the amount of ions generated in the ion source is relatively stable. Adjustment is possible, but adjustment is difficult when the amount of ion generation varies each time the sample is ionized.

  For example, when a laser desorption ion source (LDI) typified by a matrix-assisted laser desorption ion source (MALDI) is used as the ion source, fluctuations in the amount of ions generated each time laser irradiation is performed even for the same sample. large. Therefore, even if the sensitivity is adjusted by adjusting the gain of the ion detector based on the ion detection result obtained in a certain measurement, the sensitivity is not always appropriate in the next measurement. In addition, when performing MS imaging for measuring a two-dimensional distribution of molecules of a sample such as a two-dimensionally spread biological sample, the amount of ion generation may vary greatly depending on the measurement site on the sample. Even if the sensitivity is appropriately adjusted in each measurement, the sensitivity is not always appropriate in the measurement of another measurement site. For this reason, a technique for adjusting the gain of the ion detector or controlling the amount of ion generation in the ion source using the detection results of past ions is not appropriate.

  On the other hand, using the result of detecting some ions by the detector during the transport of ions by the ion transport optical system, or using the current flowing by the ions colliding with the aperture electrode or the like, as described above. In addition, a method for adjusting the gain of the ion detector has been proposed. For example, in the time-of-flight mass spectrometers described in Patent Documents 4 and 5, an auxiliary ion detector for detecting a part of ions in the middle until ions reach the ion detector is prepared separately. The gain of the ion detector that finally detects ions is adjusted based on the ion detection result obtained by a typical ion detector. In other words, in this configuration, the amount of incident ions can be determined before ions to be analyzed reach the ion detector, and the gain of the ion detector can be appropriately set according to the amount of incident ions.

  However, in order to do so, it is necessary to branch some ions on the way and detect them with a highly sensitive ion detector. In addition, when the amount of ions generated in the ion source is originally small, the amount of ions reaching the final ion detector is reduced by separating some ions in order to detect ions on the way, and the detection sensitivity is improved. There is a risk of lowering. Further, in the method using the current flowing by ions colliding with the aperture electrode as described above, appropriate sensitivity adjustment cannot be performed unless the amount of ions generated in the ion source is large.

Japanese Patent Laid-Open No. 9-45278 JP 2005-25946 A JP 9-306419 A JP 2000-323089 A JP 2001-15061 A

  For the above reasons, mass spectrometers using laser desorption ion sources adaptively detect ions according to the amount of ions actually generated by laser light irradiation rather than past ion detection results. It is desirable to adjust the gain of the analyzer and limit the amount of ions to the mass analyzer. However, in order to avoid cost reduction, downsizing of the apparatus, etc., and reduction in sensitivity, it is not preferable to branch a part of the generated ions and detect them with another ion detector.

  The present invention has been made in view of these points, and an object of the present invention is to perform appropriate sensitivity adjustment according to the amount of ions actually generated in the ion source while suppressing an increase in the cost of the apparatus. It is an object of the present invention to provide a laser desorption ionization mass spectrometer capable of improving the dynamic range of measurement.

The present invention, which has been made to solve the above-mentioned problems, comprises a laser beam irradiation means for irradiating a sample with a laser beam in order to ionize component molecules in the sample, and transports generated ions to a subsequent stage or temporarily. An ion transport optical system that transports ions to the subsequent stage after being accumulated, a mass analyzer that separates the transported ions according to the mass, and an ion detector that detects the ions separated according to the mass In a laser desorption ionization mass spectrometer,
a) a conductive sample plate holding the sample to be analyzed;
b) detection means for detecting a change in potential of the sample plate corresponding to laser light irradiation by the laser light irradiation means;
And the amount of ion generation from the sample corresponding to the irradiation of the laser beam is estimated based on the amount of potential change detected by the detection means.

  In the matrix-assisted laser desorption / ionization mass spectrometer, the sample plate is a metal sample plate on which a sample mixed, coated or sprayed with a matrix is placed.

  In the laser desorption ionization mass spectrometer according to the present invention, when a sample placed on a sample plate is irradiated with laser light for a short time and ionized as the sample molecules are vaporized, electrons are sampled if they are positive ions. Is applied to the sample plate, and if it is a negative ion, electrons are applied from the sample plate to the sample. In any case, the potential of the sample plate changes due to the movement of electrons, and the amount of potential change depends on the amount of ions generated. Therefore, the amount of ions generated corresponding to the laser beam irradiation can be estimated with high accuracy based on the amount of change in potential detected by the detection means.

  The estimation of the amount of ion generation in the ion source as described above can be performed almost simultaneously with the generation of ions by laser light irradiation, that is, almost in real time. Adjustment and control is possible.

  That is, as one aspect of the laser desorption ionization mass spectrometer according to the present invention, the number of irradiation times, the irradiation time, or the irradiation output of the laser beam by the laser beam irradiation unit according to the amount of potential change detected by the detection unit. It is preferable to further include a control means for adjusting at least one of the above.

  When the ion generation amount estimated from the potential change amount is small, the control means may increase the number of laser light irradiations, increase the irradiation time, or increase the irradiation output. As a result, the amount of ions generated within a predetermined time increases accordingly, so that the analysis sensitivity can be improved by increasing the amount of ions used for mass analysis. In general, in a laser desorption ionization mass spectrometer, laser irradiation is repeatedly performed a plurality of times in a time much shorter than the time required for ions emitted from an ion source to be introduced into a mass analyzer. Since it is possible, ions generated from the sample by multiple times of laser beam irradiation can be introduced into the mass spectrometer almost simultaneously. Of course, if the ion transport optical system is configured to temporarily capture and accumulate ions, even if it takes a certain amount of time to repeat the laser beam irradiation, the ions generated by such multiple laser beam irradiations can be detected. Can be collected and introduced into the mass analyzer.

  As another aspect of the laser desorption ionization mass spectrometer according to the present invention, the ion transport optical system is used to change the ion passage efficiency by the ion transport optical system in accordance with the potential change detected by the detection means. It is preferable to further include control means for adjusting the voltage applied to the electrodes constituting the system.

  In general, since it is preferable that the ion passing efficiency by the ion transport optical system is high, the applied voltage is set so that the ion passing efficiency is as high as possible. However, when an excessive amount of ions is introduced into the mass analyzer when the amount of ions generated in the ion source is excessive, mass separation of the ions may be deteriorated due to the space charge effect of the ions. Therefore, the control means adjusts the applied voltage so as to reduce the ion passage efficiency of the ion transport optical system when the amount of ions generated estimated by the potential change amount is too large. This moderately reduces the amount of ions subjected to mass analysis and reduces the effects of space charge effects in mass analyzers such as quadrupole mass filters and ion traps. As a result, ions can be appropriately separated according to mass to achieve high mass resolution.

  As another aspect of the laser desorption / ionization mass spectrometer according to the present invention, the laser desorption / ionization mass spectrometer further includes a control unit that changes the gain of the ion detector according to the potential change amount detected by the detection unit. You can also.

  When the amount of ions generated in the ion source is too large and the amount of ions introduced into the ion detector may be excessive, the control means lowers the gain of the ion detector. Specifically, for example, when the ion detector is a combination of a conversion dynode and a photomultiplier tube, the gain can be lowered by lowering the excitation voltage applied to the conversion dynode. As a result, saturation of the detection output at the ion detector can be prevented, and damage caused by an excessive amount of electrons entering, for example, a photomultiplier tube or a microchannel plate can be prevented. It is possible to extend the service life and reduce the analysis cost.

  As yet another aspect of the laser desorption / ionization mass spectrometer according to the present invention, a signal processing means for calculating the result of mass spectrometry as a ratio to the ion generation amount estimated from the potential change amount is further provided. You may make it output a result to a display means. In particular, such a configuration has an imaging function for performing mass analysis on a plurality of minute regions set two-dimensionally on the sample and measuring the spatial distribution of specific molecules in the sample based on the result of the mass analysis. It is suitable for a laser desorption ionization mass spectrometer.

  In such a mass spectrometer, the correlation between the molecular weight and intensity (concentration) of a specific molecule contained in each micro area and the position of the micro area is obtained based on the mass analysis result obtained from each micro area on the sample. In this case, the intensity value normalized by the amount of ion generation can be used as the intensity of the specific molecule. When ionization is performed by the MALDI method, the amount of ions generated is affected by the density of the matrix to be applied or sprayed even if the molecules have the same strength, but according to the above configuration, the molecular strength is Since it is standardized by the generation amount, it is possible to output a result in which the influence of the non-uniformity of the matrix adhesion is reduced.

The block diagram of the principal part of the atmospheric pressure matrix assistance laser desorption ionization mass spectrometer (AP-MALDI-MS) by one Example of this invention. Explanatory drawing of operation | movement of AP-MALDI-MS by a present Example. The flowchart which shows the characteristic control and processing operation of AP-MALDI-MS by a present Example. Explanatory drawing of operation | movement of AP-MALDI-MS by the other Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ionization chamber 2 ... Sample plate 3 ... Sample 4 ... Laser light source 5 ... Reflective mirror 6 ... Condensing lens 7 ... Heating capillary 10 ... First intermediate vacuum chamber 11 ... First ion lens 12 ... Skimmer 13 ... Orifice 14 ... First 2 Intermediate vacuum chamber 15 ... second ion lens 16 ... partition wall 17 ... analysis chamber 18 ... quadrupole mass filter 19 ... ion detector 20 ... A / D converter 21 ... data processing part 22 ... lens voltage generation part 23 ... excitation Voltage generator 24 ... Laser light irradiation control unit 25 ... Control unit 30 ... Resistance 31 ... DC power supply 32 ... Capacitor 34 ... A / D converter 35 ... Ion amount estimation unit

  An atmospheric pressure matrix-assisted laser desorption / ionization mass spectrometer (AP-MALDI-MS), which is an embodiment of a laser desorption / ionization mass spectrometer according to the present invention, will be described with reference to the drawings. FIG. 1 is a configuration diagram of a main part of the AP-MALDI-MS according to the present embodiment.

  In this AP-MALDI-MS, a partition wall is provided between the ionization chamber 1 which is an atmospheric atmosphere and the analysis chamber 17 where the quadrupole mass filter 18 and the ion detector 19 are installed. The first intermediate vacuum chamber 10 and the second intermediate vacuum chamber 14 are provided. The ionization chamber 1 and the first intermediate vacuum chamber 10 communicate with each other via a small heating capillary 7, and the first intermediate vacuum chamber 10 and the second intermediate vacuum chamber 14 are connected to the top of the skimmer 12. Communication is made through a formed through hole (orifice) 13 having a very small diameter.

The inside of the ionization chamber 1 that is an ion source is in an atmospheric pressure atmosphere (about 10 ⁵ [Pa]), and the inside of the first intermediate vacuum chamber 10 in the next stage is reduced to about 10 ² [Pa] by a rotary pump (not shown). It is evacuated to a vacuum state. Further, the inside of the second intermediate vacuum chamber 14 at the next stage is evacuated to a medium vacuum state of about 10 ⁻¹ to 10 ⁻² [Pa] by a turbo molecular pump (not shown), and the inside of the analysis chamber 17 at the final stage is illustrated. It is evacuated to a high vacuum state of about 10 ⁻³ to 10 ⁻⁴ [Pa] by another turbo molecular pump that does not. That is, in this MS, the inside of the analysis chamber 17 in the final stage is subjected to a high vacuum by adopting a configuration of a multistage differential exhaust system in which the degree of vacuum is increased stepwise from the ionization chamber 1 toward the analysis chamber 17. I try to keep it in a state.

  In the ionization chamber 1, a metal sample plate 2 (conductive sample plate in the present invention) 2 on which a sample 3 in which a matrix is mixed with a sample to be analyzed is placed. When the laser beam emitted from the laser light source 4 in a pulse shape under the control of the laser light irradiation control unit 24 is irradiated to the sample 3 through the reflecting mirror 5 and the condenser lens 6, the matrix in the sample 3 rapidly It is heated and vaporizes with the desired sample components. At this time, the sample components are ionized. Due to the differential pressure between the ionization chamber 1 and the first intermediate vacuum chamber 10, the atmosphere in the ionization chamber 1 flows into the first intermediate vacuum chamber 10 through the heating capillary 7, so that the ions generated in the ionization chamber 1 as described above. Also, the air flow is drawn into the heating capillary 7 and discharged into the first intermediate vacuum chamber 10.

  A first ion lens 11 whose applied voltage is controlled by a lens voltage generator 22 is provided in the first intermediate vacuum chamber 10, and the electric field formed by the first ion lens 11 is transmitted through the heating capillary 7. While helping the drawing of ions, it has the effect of converging the ions in the vicinity of the orifice 13 of the skimmer 12. The ions that have passed through the orifice 13 and introduced into the second intermediate vacuum chamber 14 are converged by an octopole-type second ion lens 15 constituted by eight cylindrical rod electrodes, and are drilled in the partition wall 16. It is sent to the analysis chamber 17 through the opened opening.

  In the analysis chamber 17, only ions having a specific mass (strictly, mass-to-charge ratio m / z) pass through the space in the long axis direction of the quadrupole mass filter 18, and ions having other masses are on the way. Diverge. That is, ions are selected based on mass. Then, the ions that have passed through the quadrupole mass filter 18 reach the ion detector 19, and the ion detector 19 outputs an ion intensity signal corresponding to the amount of ions reached as a detection signal. The ion detector 19 includes, for example, a conversion dynode that converts introduced ions into photoelectrons and a photomultiplier that multiplies and detects the converted photoelectrons. The conversion efficiency of the conversion dynode, that is, the gain as an ion detector is controlled by the voltage applied to the.

  The detection signal is converted into a digital value by the A / D converter 20 and input to the data processing unit 21. Normally, a voltage obtained by superimposing a high-frequency voltage on a DC voltage is applied to the quadrupole mass filter 18, and the mass of ions passing through the quadrupole mass filter 18 is scanned by changing the voltage value. be able to. Therefore, by scanning the voltage, the mass is scanned in a predetermined range, and the data processor 21 can create a mass spectrum in the predetermined mass range based on the data obtained at that time.

  In order to perform MALDI ionization as described above, a predetermined DC voltage V is applied to the sample plate 2 from the DC power supply 31 via the resistor 30. The AC potential change of the sample plate 2 is taken out through the capacitor 32, converted into a digital value by the A / D converter 34, and input to the ion amount estimation unit 35. The ion amount estimation unit 35 reads the potential change digitized by the A / D converter 34 in synchronization with the laser drive pulse signal given to the laser light source 4 from the laser beam irradiation control unit 24, and thereby the laser beam irradiation Thus, the amount of ions generated from the sample 3 is estimated and the result is sent to the control unit 25. As will be described later, the control unit 25 controls at least one of the laser light irradiation control unit 24, the lens voltage generation unit 22, and the excitation voltage generation unit 23 in accordance with the estimated ion generation amount.

  Next, characteristic control operations in the AP-MALDI-MS of the present embodiment will be described in more detail.

  As described above, when the sample 3 is irradiated with the laser beam and is positively ionized when the sample molecule is vaporized, the electrons jumping out from the molecule flow to the ground point through the sample plate 2. On the other hand, when the sample molecule is negatively ionized, the ions take electrons from the sample plate 2, so that the electrons flow into the sample plate 2. In any case, as the amount of ions generated from the sample 3 increases, the amount of potential change extracted through the capacitor 32 increases.

  If the amount of ions introduced into the quadrupole mass filter 18 is too small, the sensitivity is lowered, and if too much, the mass resolution is lowered. In addition, the gain of the ion detector 19 has an appropriate range in which the sensitivity is the best depending on the amount of incident ions. Therefore, the ion generation amount in the ionization chamber 1, that is, the potential change amount of the sample plate 2 at the time of laser light irradiation, and the first ion lens 11 so that the performance such as ion detection sensitivity and mass resolution is optimized. The relationship between the applied voltage and the gain of the ion detector 19 is examined in advance, and calibration data based on the relationship is stored in a memory provided in the control unit 25. Such a calibration data acquisition operation may be performed by a manufacturer that manufactures the apparatus before shipment, but may be performed by a user using a calibration sample or the like.

  The operation when actually measuring an arbitrary sample will be described with reference to FIGS. When the analysis is started and the control unit 25 gives a command to the laser beam irradiation control unit 24 to generate the laser driving pulse, the laser beam irradiation control unit 24 generates the laser driving pulse as shown in FIG. (Step S1). In response to this, the laser light source 4 emits laser light for a short time, and this laser light strikes the sample 3 to generate ions. As the ions are generated, the potential of the sample plate 2 changes as shown in FIG. The ion amount estimation unit 35 detects, for example, the maximum potential change amount ΔV within a predetermined time after the appearance of the laser drive pulse, and estimates the ion generation amount from this value ΔV. The control unit 25 reads the estimated value (step S2), and integrates the estimated value of the ion generation amount for each mass analysis (step S3). When an estimated value of the amount of ion generation is obtained corresponding to the first laser beam irradiation in a certain mass analysis, since the past integrated value is zero, the obtained estimated value becomes the integrated value as it is. .

  Next, the control unit 25 determines whether or not the integrated value of the ion generation amount is less than a predetermined value (step S4). If the integrated value is less than the predetermined value, the control unit 25 returns to step S1 and performs ionization again. Therefore, a command is given to the laser light irradiation control unit 24 so as to generate a laser driving pulse. On the other hand, if the integrated value of the ion generation amount is equal to or greater than the specified value, no further laser beam irradiation is performed, and then the amount of integrated value overrun from the specified value is calculated (step S5). For example, if the estimated value of the ion generation amount exceeds a specified value by one laser beam irradiation, the process proceeds to step S5 without performing the second laser beam irradiation. On the contrary, when the amount of ions obtained for one laser irradiation is too small, the processes of steps S1 to S4 are repeated, and laser light irradiation is performed a plurality of times. The sample molecules are ionized.

  In addition, instead of increasing the number of times of laser light irradiation, the output of the laser light may be increased or the irradiation time of one time of the laser light may be lengthened, but particularly in the case of a heat-sensitive sample such as a biological sample. If a laser beam with a strong output is continuously applied to the same part, the temperature may become too high and the sample may be severely damaged. In order to avoid such a risk, it is preferable to repeat laser irradiation for a short time multiple times.

  Normally, it is preferable to maximize the passage efficiency of ions in the first ion lens 11 during mass analysis. However, when the amount of ions generated in the ionization chamber 1 is too large as described above, an excessive amount of ions is generated by a quadrupole. It is necessary to suppress introduction into the mass filter 18. Therefore, for example, when the over amount of the integrated value of the ion generation amount exceeds a certain amount, the control unit 25 should reduce the ion passage efficiency in the first ion lens 10 according to the over amount. The lens voltage generator 22 is controlled so as to adjust the lens voltage (step S6). Here, the calibration data as described above is used to obtain the adjustment amount of the lens voltage from the over amount. That is, the calibration data may be created so that the relationship between the ion generation amount over-range and the lens voltage adjustment amount is expressed in a table format, for example.

  Further, the control unit 25 adjusts the ion passage efficiency in the first ion lens 11 as described above, and corresponds to the amount of ions predicted to be introduced into the quadrupole mass filter 18. The excitation voltage generator 23 is controlled to adjust the gain of the ion detector 19 so as to obtain a sensitivity close to that (step S7).

  As described above, even when one laser light irradiation is repeated a plurality of times, the time duration of one irradiation is very short, and the repetition interval of the laser light irradiation is sufficiently shorter than the ion movement time. Therefore, ions generated by multiple times of laser light irradiation are introduced into the analysis chamber 17 almost simultaneously and subjected to mass spectrometry.

  As described above, in the AP-MALDI-MS of the above-described embodiment, ions used for mass spectrometry can be obtained by increasing the number of times of laser light irradiation even when the amount of ions generated by one time of laser light irradiation in the atmospheric pressure MALDI ion source is small. The analysis sensitivity can be increased by increasing the amount. Even when the amount of ions generated in the ion source is excessive, the amount of ions provided for mass analysis can be adjusted by the first ion lens 10 to reduce the adverse effect of the space charge effect. The gain of 19 can also be adjusted appropriately to avoid problems such as detection output saturation and photomultiplier tube damage.

In the above embodiment, the ion source is atmospheric MALDI, but the present invention can also be applied to a MALDI under vacuum atmosphere or a laser desorption ionization method that does not use a matrix. . The mass analyzer is not limited to a quadrupole mass filter, and may be configured to use, for example, a time-of-flight mass analyzer or a three-dimensional quadrupole ion trap. As an ion transport optical system for adjusting the amount of ions used for mass spectrometry, not only an ion lens and an ion guide but also a three-dimensional quadrupole ion trap that temporarily accumulates ions can be considered.

  For example, atmospheric pressure MALDI or MALDI is used as an ion source, and ions generated by this ion source are temporarily accumulated in a three-dimensional quadrupole ion trap (in some cases, selection of precursor ions and In the configuration (MALDI-IT-TOFMS) in which ions extracted simultaneously from the ion trap are introduced into a time-of-flight mass spectrometer and separated and detected by an ion detector (1 to 1) Introduced and accumulated in the ion trap for each of the multiple times of laser light irradiation, and if there is a possibility that the amount of ions introduced will be excessive, adjust the amount of introduction according to the introduction time, for example. That's fine.

  Next, the configuration and operation of an AP-MALDI-MS according to another embodiment of the present invention will be described with reference to FIG. Although the basic configuration is the same as the apparatus shown in FIG. 1, the apparatus of this embodiment can image the spatial distribution of molecules contained in the sample 3 with respect to the sample 3 having a two-dimensional extent. It has such an imaging function. For this purpose, the sample plate 2 on which the sample 3 is placed can be moved by a stage moving mechanism (not shown) in a predetermined range in the two axial directions x and y as shown in FIG. The light irradiation position, that is, the part on the sample 3 to be subjected to mass spectrometry moves two-dimensionally. In FIG. 4, the site | part which is a unit in which mass spectrometry is performed is shown with the micro area | region divided into the grid | lattice form.

  That is, basically, each time a laser beam is irradiated to a minute region and ions correspondingly generated are subjected to mass analysis, the sample plate 2 is moved so that the laser beam strikes the next minute region. . Then, by repeating the movement of the sample plate 2 and the laser beam irradiation / mass analysis, mass analysis results for the entire sample 3 or for each minute region within a predetermined range on the sample 3 are obtained. By performing qualitative processing and quantitative processing based on the mass analysis result (mass spectrum), the type and intensity (concentration) of molecules present in the minute region can be obtained, so the spatial distribution of molecules present on the sample 3 Can be created as a two-dimensional image.

  In the apparatus of this embodiment, the amount of potential change occurring in the sample plate 2 in response to laser light irradiation is detected as in the above embodiment, and the amount of ion generation is estimated from this, and the estimated value is used as position information of the minute region. Store in association with each other. However, the number of times of laser light irradiation and the lens voltage are not controlled based on the estimated value of the ion generation amount. Then, when creating the spatial distribution of molecules as described above during data processing, the intensity is divided by the estimated value of ion generation instead of the intensity information of the molecules of each micro area, that is, the ion generation of each micro area This is converted into the intensity standardized by the estimated value of the quantity and used. For example, when analyzing a biological sample such as a section excised from a biological tissue, the matrix is attached to the sample by applying or spraying the matrix to the sample. Even if they are the same, there is a large difference in the amount of ion production. On the other hand, the intensity value normalized by the amount of ion generation as described above is used when creating a spatial distribution image of molecules, thereby reducing the inaccuracy of intensity information due to non-uniformity of matrix adhesion. can do.

  As described above, the potential change that occurs in the sample plate 2 with respect to the laser beam irradiation reflects the amount of ions generated with high accuracy. Therefore, the amount of ion generation estimated based on this amount of potential change is simply that of each part. It can be used not only for control but also for data processing.

  It should be noted that the above embodiment is an example of the present invention, and it is obvious that modifications, corrections, and additions are appropriately included in the scope of the present application within the scope of the present invention.

Claims (6)

A laser beam irradiation means for irradiating the sample with a laser beam in a pulsed manner to ionize component molecules in the sample; and an ion transport optical system for transporting the generated ions to the subsequent stage or transporting the generated ions to the subsequent stage after being temporarily accumulated In a laser desorption ionization mass spectrometer comprising: a mass analyzer that separates transported ions according to mass; and an ion detector that detects ions separated according to mass;
a) a conductive sample plate holding the sample to be analyzed;
b) detection means for detecting a change in potential of the sample plate corresponding to the laser light irradiation by the laser light irradiation means;
And a desorption ionization mass spectrometer that estimates the amount of ions generated from the sample corresponding to the irradiation of the laser beam based on the amount of potential change detected by the detection means.   The apparatus further comprises a control unit that adjusts at least one of the number of times of laser irradiation by the laser beam irradiation unit, the irradiation time, or the irradiation output according to the amount of potential change detected by the detection unit. 2. The laser desorption ionization mass spectrometer according to 1.   The apparatus further comprises control means for adjusting a voltage applied to the electrodes constituting the ion transport optical system in order to change the passage efficiency of ions by the ion transport optical system according to the potential change amount detected by the detection means. The laser desorption / ionization mass spectrometer according to claim 1.   2. The laser desorption ionization mass spectrometer according to claim 1, further comprising a control unit that changes a gain of the ion detector in accordance with a potential change amount detected by the detection unit.   2. The laser desorption ionization mass spectrometer according to claim 1, further comprising a signal processing unit that calculates a result of mass spectrometry as a ratio to an ion generation amount estimated from the potential change amount.   It has an imaging function for performing mass analysis on a plurality of minute regions set two-dimensionally on a sample and measuring the spatial distribution of specific molecules in the sample based on the result of the mass analysis. The laser desorption / ionization mass spectrometer according to claim 5.

Images