JP2015072775A - Time-of-flight mass spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately correct a mass-to-charge ratio error caused by a positional deviation of a sample plate surface in a direction along a flight trajectory, with a simple configuration to enable high-accuracy acquisition of a mass-to-charge ratio.SOLUTION: A range-finding part 6 using laser beam acquires ranging information on which a positional deviation of a sample plate immediately before or after mass spectrometry is reflected. A correction coefficient based on a relationship between a positional deviation of the sample plate surface and a mass-to-charge ratio error is previously stored in a deviation dealing correction information storage part 47, and a mass correction processing part 43 corrects a mass-to-charge ratio value calculated based on time of flight according to a calibration curve by using a positional deviation amount found from the ranging information and a correction coefficient. Thus, a mass-to-charge ratio in the state where the sample plate surface does not have a positional deviation is calculated. Further, a mechanism for moving a sample stage 11 at high accuracy in order to eliminate the mass-to-charge ratio error is unnecessary, and a cost increase can also be suppressed.

Description

  The present invention relates to a time-of-flight mass spectrometer (hereinafter referred to as “TOFMS”), and more particularly to a linear type TOFMS that allows ions to fly linearly from an ion source to a detector.

  In TOFMS, a certain length of energy is accelerated by applying a certain kinetic energy to ions derived from the substance to be measured generated by an ion source using the matrix-assisted laser desorption / ionization (MALDI) method. To fly in the flight space. Since the flight speed of each ion introduced into the flight space increases as the mass-to-charge ratio m / z decreases, the various ions emitted from the ion source simultaneously pass through the flight space in ascending order of the mass-to-charge ratio and reach the detector. That is, various ions are separated on the time axis according to the mass-to-charge ratio. Since the flight time of each ion derived from the substance to be measured has a predetermined relationship with the value of the mass-to-charge ratio, if the flight time is measured for each ion, the mass-to-charge ratio can be calculated from this measured value.

  In order to convert the time of flight of each ion into a mass-to-charge ratio as described above, that is, to perform mass calibration, usually a compound (standard substance) whose accurate mass-to-charge ratio (generally theoretical value) is known Calibration information (calibration curve) created from the relationship between the time of flight obtained by actually measuring and the precise value (theoretical value) of the mass-to-charge ratio is used.

  Mass calibration methods are roughly classified into an internal standard method and an external standard method. The internal standard method is a technique in which a standard substance is subjected to mass spectrometry simultaneously with a measurement target substance, and mass calibration is performed based on the result (see Patent Document 1). For example, in TOFMS using a MALDI ion source (hereinafter referred to as “MALDI-TOFMS”), a measurement target substance, a standard substance, and a matrix substance are mixed to prepare a sample on a sample plate. , And mass spectrometry is performed on the ions derived from the measurement target substance and the standard substance generated thereby. Therefore, the conditions of mass spectrometry for the measurement target substance and the standard substance are the same, and there is an advantage that calibration with high accuracy can be performed. However, in general, it is difficult for the internal standard method to select a standard substance and set analysis conditions (particularly ionization conditions such as laser beam intensity). This is because it is necessary to select a standard substance that has a mass-to-charge ratio different from that of ions derived from the substance to be measured and that can sufficiently obtain ionic strength under the same analysis conditions. Therefore, in some cases, an appropriate reference material may not be found. Further, when the measurement target substance is an unknown substance, that is, when the mass-to-charge ratio of the measurement target substance-derived ions is unknown, the internal standard method cannot be adopted.

  On the other hand, the external standard method is a technique in which mass spectrometry for a standard substance and mass spectrometry for a measurement target substance are separately performed, and mass calibration is performed based on the results. This technique is easy to set analysis conditions and has few restrictions on the standard substances as described above, so it is highly practical and widely used. However, there may be a case where the conditions that should originally be the same in the mass spectrometry for the measurement target substance and the mass spectrometry for the standard substance are not completely the same. For example, in MALDI-TOFMS, mass spectrometry is performed at different times on separate samples prepared at different locations on the sample plate. For this reason, for example, due to mechanical backlash of the sample stage holding the sample plate, inclination of the mounting surface of the sample stage, or unevenness of the sample forming surface of the sample plate, The distance between the sample surface and the extraction electrode for extracting ions from the vicinity of the sample changes during mass spectrometry with respect to the standard substance, and the kinetic energy imparted to the ions may be different or the flight distance may be different. This reduces time of flight reproducibility and can cause errors in mass calibration. For these reasons, the external standard method is generally less accurate in mass calibration than the internal standard method.

  In recent years, TOFMS has been frequently used for structural analysis and identification of biologically derived substances such as proteins and nucleic acids, and the mass accuracy required for such applications is increasing. In order to achieve high mass accuracy and mass reproducibility in TOFMS, it is necessary to increase the accuracy of mass calibration by the external standard method as described above.

  Patent Document 2 discloses a mass spectrometer that can reduce errors caused by the above-described misalignment of the sample plate. That is, this mass spectrometer includes a distance measuring unit that measures the distance between the surface of the sample to be ionized and the tip of the collection tube using a laser beam, and a distance measuring unit that measures the distance. A stage driving mechanism for moving a sample stage on which a sample is placed according to the distance result in a direction approaching the ion collecting unit or a direction moving away from the ion collecting unit. Even when the height of the sample placed on the sample stage changes, the position of the sample stage is adjusted so that the distance between the sample surface and the ion collector is always constant. . If this apparatus is applied to MALDI-TOFMS, for example, even if the sample plate has irregularities, the position of the sample surface at the time of mass analysis with respect to the measurement target substance is the same as the position of the sample surface at the time of mass analysis with respect to the standard substance The mass-to-charge ratio can be calculated with high accuracy from the mass analysis result obtained for the measurement target substance using the mass calibration information created using the standard substance.

  However, in the mass spectrometer described in Patent Document 2, a sample stage that is movable in two axial directions orthogonal to each other within the spread surface of the sample plate mounting surface is further accurately detected in the axial direction orthogonal to the two axes. A moving mechanism and a control circuit are required, and the cost of the apparatus is considerably higher than the case where such an error correction function is not added.

  In addition, in MALDI-TOFMS, not only the error in the position of the sample surface as described above, but also an error affecting the mass calibration, for example, a sample plate or the like for forming an electric field that extracts and accelerates ions from the vicinity of the sample. An error due to fluctuations in the voltage applied to the extraction electrode, etc., an error due to a deviation in the timing of the electric field change due to ion acceleration (that is, a temporal deviation in the change in applied voltage), or a flight space is formed in the interior. Errors in flight distance due to thermal expansion of the flight tube can occur simultaneously. The mass spectrometer described in Patent Document 2 does not correct the error due to such factors, and causes a mass error during mass calibration.

JP 2010-205460 A US Patent Publication No. 2010/000338 JP 2011-175898 A

  The present invention has been made to solve the above problems, and its main purpose is to improve the accuracy of mass calibration by the external standard method while reducing the cost of the apparatus and reducing the operator's work related to the measurement work, To provide a TOFMS capable of realizing high mass accuracy and mass reproducibility.

  Another object of the present invention is not only mass error due to inaccuracy of the sample surface position, but also mass accuracy due to various factors such as fluctuations in the voltage applied to the sample plate and extraction electrode, which can occur at the same time. Is to provide a TOFMS that can achieve high mass accuracy and mass reproducibility.

The time-of-flight mass spectrometer according to the first aspect of the present invention, which has been made to solve the above-described problems, includes a sample holding unit that holds a sample plate, and a sample on the sample plate that is irradiated with laser light. An ion source for ionizing a target substance therein, an acceleration unit for accelerating ions derived from the target substance, a flight tube for forming a flight space for flying the accelerated ions, and detecting ions flying in the flight space In a time-of-flight mass spectrometer comprising an ion detector,
a) a position measuring unit for measuring a relative position of the sample surface or the sample plate surface in a direction along a flight trajectory of ions from the sample on the sample plate to the ion detector;
b) Data for correcting the flight time of ions derived from the target substance obtained by mass spectrometry or the mass-to-charge ratio obtained from the flight time based on the amount of deviation between the actual measurement position and the reference position measured by the position measurement unit A correction processing unit;
It is characterized by having.

  In the time-of-flight mass spectrometer according to the first aspect of the present invention, the position measurement unit can be, for example, a distance measurement unit using laser light or a distance measurement unit using capacitance.

  In the time-of-flight mass spectrometer according to the first aspect of the present invention, when performing mass analysis of a sample containing a substance to be measured, the position measurement unit can detect the relative position of the sample surface on the sample plate or the sample plate itself. Measure the relative position of the surface. In response to the measurement result, the data correction processing unit obtains the time of flight obtained by mass spectrometry for the ion derived from the measurement target substance based on the amount of deviation between the measured position based on the measurement result and the reference position stored in advance. Alternatively, the mass-to-charge ratio obtained from the flight time is corrected by arithmetic processing. Usually, most of various data processing for detection data obtained by digitizing a detection signal obtained by an ion detector is realized by operating predetermined software on a computer. Therefore, the data processing in the data correction processing unit can also be performed by operating predetermined software on the computer.

  For example, if mass calibration information that converts time-of-flight into a mass-to-charge ratio is obtained based on the result of mass spectrometry of a standard substance, calculation is performed by correcting the mass calibration information according to the amount of deviation. The mass-to-charge ratio value can be modified. Note that the reference position is determined based on the measurement value obtained by the position measurement unit when mass analysis is performed on a standard material for mass calibration, or commonly used for mass analysis of all materials. Any of those provided may be used.

When the data correction processing unit corrects, for example, the mass calibration information, the process is simple if the deviation amount based on the actual measurement value is applied to a predetermined correction formula.
Specifically, for example, the data correction processing unit sets the deviation amount of one deviation element as ΔPi (where i is an integer from 1 to the number of deviation elements), and the coefficient obtained in advance for the deviation element as pi. In this case, a correction formula obtained by assuming that the time of flight or the mass-to-charge ratio is shifted by a ratio of pi × ΔPi can be used. In other words, this is a correction that the time-of-flight or mass-to-charge ratio deviation to the deviation of one deviation element can be linearly approximated. A shift in the mass-to-charge ratio can be suppressed.

When it is desired to perform correction with higher accuracy, the data correction processing unit sets Δi as the deviation amount of one deviation element, pi1 as the first coefficient obtained for the deviation element, and pi2 as the second coefficient. and when, time of flight or mass to charge ratio can be made using the calculated correction formula as shifted by a rate of ^{pi1 × ΔPi × pi2 × ΔPi 2} . That is, this is a correction that the deviation of the flight time or mass-to-charge ratio with respect to the deviation of one deviation element can be approximated to a quadratic function. Of course, correction using a higher-order function of second order or higher is also possible.

  In a time-of-flight mass spectrometer, the relative position shift of the sample surface or sample plate surface to be analyzed is a major factor that affects the shift of the mass-to-charge ratio. This is not the only factor.

Therefore, in the time-of-flight mass spectrometer according to the first aspect of the present invention, preferably,
The acceleration unit includes a voltage application unit that applies an acceleration voltage to the sample plate and / or one or more acceleration electrodes, and a voltage applied from the voltage application unit to the sample plate and / or one or more acceleration electrodes. A voltage detector for detecting the value of
The data correction processing unit performs flight of ions derived from the target substance obtained by mass spectrometry based on at least the voltage value detected by the voltage detection unit in addition to the displacement amount of the position of the sample surface or the sample plate surface. The mass-to-charge ratio obtained from the time or the time of flight may be corrected.

  According to this configuration, not only the relative displacement of the sample surface or sample plate surface to be analyzed, but also the difference in the acceleration electric field due to the time-varying acceleration voltage applied to the sample plate or acceleration electrode. The time-of-flight and mass-to-charge ratio deviations caused by the problem can be eliminated.

In the time-of-flight mass spectrometer according to the first aspect of the present invention, more preferably,
The accelerating unit includes a voltage applying unit that applies an accelerating voltage to the sample plate and / or one or a plurality of accelerating electrodes, and from the voltage applying unit to start flight of ions derived from a target substance, the sample plate and / or A timing detector for detecting timing of change in voltage applied to one or a plurality of acceleration electrodes;
In addition to the amount of displacement of the position of the sample surface or sample plate surface, the data correction processing unit is configured to perform flight time of ions derived from the target substance obtained by mass spectrometry based on at least the timing detected by the timing detection unit. Alternatively, the mass-to-charge ratio obtained from the flight time may be corrected.

  In MALDI-TOFMS, an ion acceleration method called a delayed extraction method is conventionally known (see Patent Document 3). In the delayed extraction method, when a sample is irradiated with a laser beam to ionize a substance in the sample, a substantial acceleration electric field is not formed, and a sample plate or an acceleration electrode is delayed by a predetermined time after the generation of ions. This is a method of accelerating ions by forming an accelerating electric field by applying a predetermined voltage. When the delayed extraction method is used, not only the value of the voltage applied to the sample plate and the acceleration electrode to form the accelerating electric field, but also the timing of application (strictly speaking, the timing of changing the applied voltage) ) Also causes a difference in flight time and mass-to-charge ratio. On the other hand, according to the above configuration, not only the relative displacement of the sample surface or sample plate surface to be analyzed, but also the time of flight due to fluctuations in the timing of applying a voltage to the sample plate or acceleration electrode. And mass-to-charge ratio deviations can be eliminated.

In the time-of-flight mass spectrometer according to the first aspect of the present invention, more preferably,
A temperature detector for measuring the temperature of the flight tube;
In addition to the amount of displacement of the position of the sample surface or sample plate surface, the data correction processing unit is configured to perform flight time of ions derived from the target substance obtained by mass spectrometry based on at least the temperature detected by the temperature detection unit. Alternatively, the mass-to-charge ratio obtained from the flight time may be corrected.

  When the temperature of the flight tube changes due to the influence of ambient temperature fluctuations, etc., the flight distance changes due to the expansion and contraction of the tube, causing a deviation in flight time and mass-to-charge ratio. On the other hand, according to the above configuration, not only the relative position shift of the sample surface or sample plate surface to be analyzed, but also the time-of-flight and mass-to-charge ratio shift caused by the thermal expansion of the flight tube are eliminated. can do.

Further, in the time-of-flight mass spectrometer according to the first aspect of the present invention, in the configuration using the laser beam ranging unit, the ranging unit emits ions from the sample and passing through the flight space to the ion detector. A first reflecting mirror disposed at a position deviating from the flight path and directing the laser light emitted from the laser light source toward the sample or the sample plate, and the laser light reflected by the sample surface or the sample plate surface to the light detection unit The second reflecting mirror to be directed may be included.
In this configuration, the positions of the first and second reflecting mirrors may be fixed, but the positions need not prevent the passage of ions.

On the other hand, the distance measuring unit is configured to reflect the laser beam emitted from the laser light source toward the surface of the sample or the sample plate, and at the time of distance measurement, the reflecting mirror is emitted from the sample and passes through the flight space to the ion detector. A reflecting mirror moving unit that moves the reflecting mirror to a second position that is disposed at a predetermined first position on the flight trajectory of the ions to be moved, and at least when the mass analysis is performed, to retract the reflecting mirror to the second position off the flight trajectory. It is good also as a structure containing these.
In this configuration, a mechanism for moving the reflecting mirror and a control circuit therefor (only when moved by electrical control) are required. However, in general, distance measurement is performed by irradiating a laser beam in a direction perpendicular to the sample plate surface. Therefore, the accuracy of distance measurement is improved as compared with the case of irradiating the sample plate surface with laser light obliquely.

  In particular, in a configuration using a laser beam ranging unit, a sample plate having at least one recess having a known depth is used, and at least not on the same plane on the sample plate including a point on the bottom surface of the recess. The flight time or mass-to-charge ratio of ions derived from the target substance may be corrected based on the distance measurement results for the two points. If the depth of one recess is known and its dimensional accuracy is high, the depth value can be used as an absolute reference. Thereby, the accuracy of the correction of the flight time and the mass to charge ratio can be further enhanced.

  In the time-of-flight mass spectrometer of the first aspect, the flight time and the mass-to-charge ratio deviation due to the sample and sample plate misalignment were corrected by data processing. It can also be performed by controlling the above.

That is, the time-of-flight mass spectrometer according to the second aspect of the present invention, which has been made to solve the above-mentioned problems, irradiates a sample holder that holds a sample plate and a sample on the sample plate with laser light. An ion source that ionizes a target substance in the sample, an acceleration unit that accelerates ions derived from the target substance, a flight tube that forms a flight space in which the accelerated ions fly, and ions that flew in the flight space In a time-of-flight mass spectrometer comprising an ion detector for detection,
a) a position measuring unit for measuring a relative position of the sample surface or the sample plate surface in a direction along a flight trajectory of ions from the sample on the sample plate to the ion detector;
b) Based on the amount of deviation between the actual measurement position and the reference position measured by the position measurement unit, conditions for ionization in the ion source or conditions for acceleration in the acceleration unit when performing mass analysis on the sample An analysis condition correction unit for correcting at least one of
It is characterized by having.

The time-of-flight mass spectrometer of this second aspect is, for example,
The acceleration unit includes a voltage application unit that applies an acceleration voltage to the sample plate and / or one or more acceleration electrodes,
The analysis condition correcting unit illuminates the storage unit storing voltage calibration information indicating the relationship between the position of the sample or the sample plate and the correction amount of the acceleration voltage, and the actual measurement position measured by the position measuring unit. A voltage adjustment control unit that obtains the correction amount of the acceleration voltage and adjusts the acceleration voltage by the voltage application unit according to the result.

  The position measuring unit in the second mode can have various configurations similar to the position measuring unit in the first mode.

  According to the time-of-flight mass spectrometer according to the present invention, if a device or unit capable of measuring the relative position of the sample surface or the sample plate surface, such as a range finder using a laser beam, is prepared, Except for the time of flight due to the relative displacement of the sample surface or the surface of the sample plate by processing on the obtained data or control during the execution of the analysis, i.e. without substantial provision of special hardware And the mass to charge ratio error can be corrected. Thereby, the accuracy and reproducibility of the flight time and mass-to-charge ratio obtained for the target substance can be improved while suppressing the increase in the cost of the apparatus. In particular, according to the time-of-flight mass spectrometer according to the present invention, the influence of the relative positional deviation of the sample surface or the sample plate surface in a plurality of mass analyzes performed at different times is finally calculated. Therefore, even if mass calibration is performed by an external standard method, high mass-to-charge ratio accuracy can be realized.

  Further, according to the time-of-flight mass spectrometer according to the present invention, the physical movement of the sample plate itself is not physically performed in order to correct the misalignment of the sample plate as in the prior art. Adjustment time is not required. Thereby, efficient measurement is possible without prolonging the measurement time. In general, such a mechanism for physical movement is likely to cause a failure, but according to the present invention, the failure is less likely to occur and the reliability of the apparatus can be improved. Furthermore, not only the error caused by the relative displacement of the sample surface or the sample plate surface, but also the error caused by other factors can be corrected. Accuracy and reproducibility can be further enhanced.

The schematic block diagram of TOFMS by 1st Example of this invention. Explanatory drawing of the difference in the electric field of this plate vicinity accompanying the difference in the position of a sample plate. Explanatory drawing of the difference in the flight time accompanying the difference in the position of a sample plate. Explanatory drawing of the difference in the flight time accompanying the difference in the potential of a sample plate. The figure which shows the simulation result about the correction effect of the mass to charge ratio error accompanying the position shift of the sample plate in TOFMS of 1st Example. The figure which shows the simulation result about the correction effect of the mass to charge ratio error accompanying the difference in the potential of the sample plate in the TOFMS of the first embodiment. The figure which shows an example of the mass calibration curve which shows the relationship between flight time and mass to charge ratio. The figure which shows the relationship between mass charge ratio when mass calibration is performed using the mass calibration curve shown in FIG. 7, and mass accuracy. When the mass-to-charge ratio is corrected using the multiple linear correction formula when the position of the sample plate, the applied voltage to the sample plate and the acceleration electrode, the timing of applying the acceleration voltage, and the flight tube temperature are all shifted The figure which shows the mass accuracy before and behind correction | amendment. The figure which shows the mass accuracy before and behind correction | amendment when correct | amending a mass to charge ratio using a multiple linear correction formula in the case where only the position of a sample plate and the applied voltage to a sample plate have shifted | deviated. The schematic block diagram of TOFMS by 2nd Example of this invention. Explanatory drawing of the example which correct | amends the difference in the flight time accompanying the difference in the position of a sample plate by adjustment of an acceleration voltage. FIG. 13 is a detailed view of a portion of FIG. 12. The figure which shows the relationship between the position shift of a sample plate and the adjustment voltage in TOFMS of 2nd Example. The figure which shows the mass accuracy before and after correction | amendment when only the position of a sample plate and the applied voltage to a sample plate have shifted | deviated, when mass-to-charge ratio is correct | amended by adjustment of acceleration voltage.

[First embodiment]
MALDI-TOFMS, which is one embodiment (first embodiment) of the present invention, will be described with reference to the accompanying drawings. FIG. 1 is a configuration diagram of a main part of the MALDI-TOFMS of this embodiment.

  The MALDI-TOFMS includes a MALDI ion source 1 that ionizes a target substance in a sample, a flight tube 2 that forms a flight space in which ions freely fly, an ion detector 3 that detects ions, and an ion detector. 3, a data processing unit 4 that digitizes and processes the signal obtained by 3, a voltage generation unit 5 that applies a predetermined DC voltage to each part including the sample stage 11 in the MALDI ion source 1, and a sample surface or sample plate surface A distance measuring unit 6 for determining the position of the sensor, a voltage detecting unit 7 for detecting an instantaneous value of the voltage actually applied to the sample stage 11 (more preferably, the sample plate 10), and a control for controlling the operation of each unit. Part 8.

  The MALDI ion source 1 includes a sample stage 11 that holds a sample plate 10, and a laser irradiation unit 16 that emits laser light that irradiates the sample 12 to ionize a target substance in the sample 12 formed on the sample plate 10. A reflecting mirror 17 that reflects the laser light and collects it on the sample 12; and an extraction electrode 13 that forms an electric field that extracts and accelerates ions derived from the target substance generated from the sample 12 between the sample plate 10 And an accelerating electrode 14 that forms an electric field for accelerating the extracted ions, and an ion lens 15 including three electrodes having a function of converging the ions.

  The sample 12 is prepared by mixing a target substance (measurement target substance, standard substance for mass calibration, etc.) and an appropriate matrix. When a laser beam having a short time width is emitted from the laser irradiation unit 16 under the control of the control unit 8, the laser beam is reflected by the reflecting mirror 17 and irradiated near the surface of the sample 12. Due to the energy of the laser light, the matrix and the target substance in the sample 12 are evaporated, and the target substance is ionized in the process. The sample plate 10 has conductivity, and a predetermined DC voltage is applied to the sample stage 11, the extraction electrode 13, the acceleration electrode 14, and the ion lens 15 from the voltage generator 5. Therefore, an electric field for extracting ions derived from the target substance is formed in the space between the sample 12 and the extraction electrode 13, and the extracted ions are accelerated in the space between the extraction electrode 13 and the acceleration electrode 14. An electric field is formed. Due to the action of the electric field in two steps, ions derived from the target substance are accelerated substantially simultaneously after being extracted from the vicinity of the surface of the sample 12 in the right direction in FIG. The accelerated ions are converged by the ion lens 15. It should be noted that delayed extraction of ions is achieved by switching the voltage applied to the acceleration electrode 14 so that a substantial acceleration electric field is formed after a predetermined time from the point of time when ions are generated by laser light irradiation.

  The flight tube 2 forms a flight space in which no electric or magnetic field exists. As described above, various ions accelerated in the MALDI ion source 1 are introduced into the flight space in the flight tube 2 and fly at the respective flight speeds. Ideally, in the MALDI ion source 1, each ion receives a constant kinetic energy regardless of the mass-to-charge ratio, and the flight speed of each ion depends on the mass-to-charge ratio. Specifically, since ions having a smaller mass-to-charge ratio have a higher flight speed and are introduced into the flight space, they pass through the flight space in order of increasing mass-to-charge ratio and reach the ion detector 3.

  The ion detector 3 uses, for example, a combination of a conversion dynode and a secondary electron multiplier or a combination of a microchannel plate and a photomultiplier, and outputs a detection signal having an intensity corresponding to the number of incident ions. To do. Ideally, since the start of flight of various ions derived from the target substance can be regarded as simultaneous, for example, when performing delayed extraction, a predetermined acceleration voltage is applied to the acceleration electrode 14 in order to accelerate the ions all at once. The time (flight time) until the ion reaches the ion detector 3 from the time point is measured. The flight time and the mass-to-charge ratio of each ion have a predetermined relationship with the kinetic energy and flight distance received by the acceleration electric field as parameters. The flight distance is a structurally determined parameter, and the kinetic energy received by the acceleration electric field is applied to the sample plate 10 through the sample stage 11, the voltage applied to the extraction electrode 13, and the acceleration electrode 14. This parameter is determined by the voltage to be determined.

  Ideally, the position of the surface of the sample plate 10 is always the same in the direction of the X axis (that is, the central axis of the ion flight trajectory) in FIG. However, the position of the surface of the sample plate 10 slightly shifts in the X-axis direction due to factors such as rattling and tilting of the sample stage 11 and uneven thickness of the sample plate 10 (in the following description, Unless otherwise stated, “deviation” may mean deviation in the X-axis direction). When the position of the surface of the sample plate 10 is shifted, the distance between the sample plate 10 and the extraction electrode 13 and the acceleration electrode 14 changes, and the intensity of the electric field near the sample 12 substantially varies. As a result, the kinetic energy imparted to the ions changes, resulting in fluctuations in the flight time, and errors in the mass-to-charge ratio.

FIG. 2 shows a case where the surface of the sample plate 10 is in an ideal position (x ₀ = −2.0 [mm]) and a position (x ₀ + Δx ₀ = −1) shifted by 0.1 [mm] therefrom. .9 [mm]) is a diagram for explaining the difference in the electric field (acceleration electric field) generated near the surface of the sample plate 10. FIG. 2 shows an applied voltage E ₁ = 18000 [V] to the sample plate 10, an applied voltage E ₂ = 18660 [V] to the extraction electrode 13, and E _2p = −1260 [V] (where E ₂ is a laser) The central axis of the ion flight trajectory when the voltage E _2p is applied to the extraction electrode 13 under the condition of the applied voltage at the time of light irradiation, E _2p is an acceleration voltage applied after a predetermined delay time from the time of laser light irradiation) This is a simulation calculation of the electric field strength along the line. The electric field strength in the very vicinity of the sample plate 10 is 0.9 [V / mm] to 5.2 [V / mm] just by shifting the surface of the sample plate 10 toward the extraction electrode 13 by 0.1 [mm]. To increase. Thereby, the kinetic energy acting on the ions generated from the sample increases, and the flight speed increases even if the mass-to-charge ratio is the same.

FIG. 3 is a diagram showing the result of simulating the flight time of ions having the same mass-to-charge ratio (1000 [Da]) when the position of the sample plate surface is in the two states described in FIG. FIG. 3 shows that the flight time is shifted by 0.018 to 0.019 [μsec] because the position of the surface of the sample plate 10 is shifted by 0.1 [mm]. When the sample plate surface is at an ideal position (x ₀ = -2.0 [mm]), calibration information that converts the flight time to the mass-to-charge ratio is acquired, and the actual flight time is calculated based on this calibration information. When converted to the mass-to-charge ratio, when the sample plate surface is shifted by 0.1 [mm] (x ₀ + Δx ₀ = -1.9 [mm]), the mass-to-charge ratio is 998.321 [Da]. As a result, a large mass error of about 1.68 [Da] occurs. From this error, when the mass deviation amount Δm / m per positional deviation amount Δx ₀ is calculated, (Δm / m) / Δx ₀ = 17 [ppm / μm] is obtained.

  In addition, when the voltage value itself of the DC voltage applied to the sample plate 10 from the voltage generator 5 through the sample stage 11 varies (that is, the potential of the sample plate 10 deviates from an ideal state), The electric field strength in the very vicinity of the sample plate 10 varies. As a result, the flight time of ions having the same mass-to-charge ratio changes as well as the positional deviation of the sample plate surface, causing a mass error.

FIG. 4 is a diagram showing a result of simulating the flight time of ions having the same mass-to-charge ratio (1000 [Da]) when the potential E ₁ of the sample plate is shifted. The flight time when the deviation amount ΔV of the potential E ₁ of the sample plate is changed in 2 [V] steps within the range of −10 [V] to 10 [V] is approximately 21.833 to 21.903 [μsec]. Calibration information for converting the flight time to the mass-to-charge ratio when the sample plate potential is ideal (ΔV = 0) is obtained, and the actual flight time is calculated based on this calibration information. If converted to, the apparent mass-to-charge ratio is 999.073 to 1000.944 [Da]. That is, a mass error of about ± 1 [Da] occurs.

In the MALDI-TOFMS of this embodiment, in order to reduce the mass-to-charge ratio error due to the positional deviation of the sample plate 10 and the potential deviation of the sample plate 10 as described above, a characteristic configuration and a characteristic are provided. Is executing various controls and processes.
That is, for this purpose, the MALDI-TOFMS of this embodiment includes a distance measuring unit 6 and a voltage detecting unit 7. Although not shown, the distance measuring unit 6 includes a laser emitting unit that emits a pulsed laser beam for distance measurement, a detector that detects the reflected laser beam, and a direction (angle) of light incident on the detector. A signal processing unit that recognizes with high accuracy and calculates the distance to the sample plate 10 on the X-axis by a triangulation method. The reflecting mirror 60 inserted into the ion flight trajectory is also a part of the distance measuring unit 6. The reflecting mirror 60 can be moved by a driving mechanism (not shown) between a position in the ion flight trajectory and a position outside the trajectory, that is, a position that does not hinder the flight of ions. In FIG. 1, the state where the reflecting mirror 60 is located in the ion flight trajectory is indicated by a dotted line.

  In addition to the spectrum data collection unit 40, mass calibration information storage unit 41, mass calibration processing unit 42, and mass spectrum creation unit 44, the data processing unit 4 includes a mass correction processing unit 43, It includes functional blocks such as a position variation calculation unit 45, a potential variation calculation unit 46, and a deviation correspondence correction information storage unit 47. The mass calibration information storage unit 41 is created based on the result of mass analysis of a sample including a standard material for mass calibration (a substance whose precise mass-to-charge ratio value is known, such as a theoretical mass-to-charge ratio value). Mass calibration information such as a calibration curve indicating the relationship between the time of flight and the mass-to-charge ratio is stored. The spectrum data collection unit 40 digitizes the ion intensity signals sequentially obtained from the ion detector 3 as described above when performing mass analysis, and collects so-called time-of-flight spectrum data. The mass calibration processing unit 42 detects a significant peak in the flight time spectrum data, obtains a flight time corresponding to the detected peak, and based on the mass calibration information stored in the mass calibration information storage unit 41. Is converted into a mass-to-charge ratio.

  In a conventional apparatus, a mass spectrum is created using a mass-to-charge ratio value converted from time of flight based on mass calibration information. On the other hand, in the MALDI-TOFMS of the present embodiment, the mass correction processing unit 43 outputs the position variation calculation unit 45 and the potential variation calculation unit 46, and the correction stored in the deviation correspondence correction information storage unit 47. Using the information, the mass-to-charge ratio value obtained by the mass calibration processing unit 42 is further corrected. This correction information includes the above-described information for correcting the error of the mass-to-charge ratio caused by the positional deviation of the sample plate surface and the information for correcting the error of the mass-to-charge ratio caused by the deviation of the potential of the sample plate. .

  For example, immediately before or after performing a mass analysis of a certain sample 12 containing a measurement target substance, the distance measuring unit 6 under the control of the control unit 8 determines the distance to the surface of the sample plate 10 in the immediate vicinity of the sample 12. Measure. That is, the reflecting mirror 60 is moved to the position indicated by the dotted line in FIG. 1, and pulsed laser light is emitted from the laser light emitting unit. Laser light hits the surface of the sample plate 10 through the reflecting mirror 60, and the reflected light returns to the detector of the distance measuring unit 6. The distance measuring unit 6 calculates a distance reflecting the positional deviation of the sample plate 10 in the X-axis direction based on the angle of the reflected light at that time.

In the data processing unit 4, the position fluctuation amount calculation unit 45 calculates the positional deviation amount of the sample plate 10 surface at that time based on the distance information obtained by the distance measurement unit 6. Specifically, for example, the distance measured when the standard substance is subjected to mass spectrometry is stored as a reference distance under the condition that the surface of the sample plate 10 is not misaligned (that is, Δx = 0). The amount of positional deviation is obtained by calculating the difference between the distance obtained by the above and the reference distance.
On the other hand, the voltage detection unit 7 detects the potential of the sample plate 10 through the sample stage 11 when the sample is irradiated with laser light in order to perform mass analysis of the sample containing the measurement target substance. Based on the voltage value obtained by the voltage detector 7, the potential fluctuation amount calculator 46 calculates the potential deviation amount of the sample plate 10 at that time. Specifically, for example, as in the case of the above-described positional deviation, the voltage value detected when the standard substance is mass-analyzed is the reference potential under the condition that there is no potential deviation of the sample plate 10 (that is, ΔV = 0). And the difference between the potential obtained by actual measurement and the reference potential is calculated to obtain the potential deviation amount.

According to the study of the present inventor, the amount of displacement of the sample plate surface and the amount of displacement of the sample plate potential and the mass-to-charge ratio error due to the effect of such displacement, that is, the mass-to-charge ratio value obtained when there is an effect of such displacement. And the difference from the accurate mass-to-charge ratio value obtained in an ideal state without the influence of such a deviation is almost proportional.
FIG. 5 is a diagram showing the relationship between the displacement amount Δx of the sample plate surface and the mass-to-charge ratio error obtained by simulation calculation, and FIG. 6 shows the relationship between the displacement amount ΔV of the sample plate potential and the mass-to-charge ratio error. It is a figure which shows the result calculated | required by simulation calculation. Now, when the plot points of “no correction” and the line connecting them are seen in both figures, it can be seen that both are almost straight lines. Thus, a mass-to-charge ratio value m _e of the actual measurement when there is the influence of such deviation of the positional deviation and sample plate potential of the sample plate surface, such displacement effect is not ideal state is long when obtained exact mass charge The ratio value m ₀ can be approximated by a linear form represented by the following equation.
m ₀ = m _e (1 + p _i · ΔP _i ) (1)

In the equation (1), ΔP _i is a deviation amount from a nominal value (value in an ideal state) of a certain parameter P _i , and p _i is a correction coefficient for the parameter P _i . Here, since the parameter P _i is two, that is, the positional deviation of the surface of the sample plate and the potential deviation of the sample plate, i = 1 and 2, and the expression (1) becomes the following expression (2).
m ₀ = _me (1 + p ₁ · ΔP ₁ ) (1 + p ₂ · ΔP ₂ ) (2)
Here, ΔP ₁ is a positional deviation amount Δx on the surface of the sample plate, that is, a value calculated by the positional fluctuation amount calculation unit 45. ΔP ₂ is a potential deviation amount ΔV of the sample plate, that is, a value calculated by the potential fluctuation calculation unit 46.

On the other hand, the two correction coefficients p ₁ and p _{2 in the} equation (2) are derived in advance by computer simulation modeling the MALDI-TOFMS of this embodiment, or a substance having a known mass-to-charge ratio (for example, mass It can be derived on the basis of preliminary measurements using calibration standards. Not only computer simulation but also preliminary measurement, this can be performed by the manufacturer of the apparatus before shipping the product and need not be performed by the user. Therefore, the manufacturer of this apparatus uses a computer simulation and / or preliminary measurement, or both, to calculate the correction coefficient p ₁ related to the position of the sample plate surface and the correction coefficient p ₂ related to the potential deviation of the sample plate, respectively. It may be obtained and stored in the correction information storage unit 47 corresponding to the deviation as correction information.

As described above, when the sample 12 containing the measurement target substance is actually subjected to mass spectrometry, the mass correction processing unit 43 corrects the correction coefficients p ₁ and p ₂ stored in the shift correspondence correction information storage unit 47 as described above. Is read. Then, the mass correction processing unit 43 uses the positional deviation amount Δx input from the positional fluctuation amount calculation unit 45, the potential deviation amount ΔV input from the potential fluctuation amount calculation unit 46, and the correction coefficients p ₁ and p ₂ . According to the equation (2), the mass-to-charge ratio value m _exp based on the actual measurement given from the mass calibration processing unit 42 is corrected. As a result, a mass-to-charge ratio value in which an error in the mass-to-charge ratio caused by the positional deviation of the sample plate surface and the deviation of the sample plate potential is corrected is obtained with reference to the state at the time of measuring the sample including the standard substance. The mass correction processing unit 43 corrects the mass-to-charge ratio value obtained by conversion based on the mass calibration information for each significant peak detected on the time-of-flight spectrum. The mass spectrum creation unit 44 creates a mass spectrum based on the mass-to-charge ratio value thus corrected and the intensity value of each peak.

FIG. 5 also shows the mass-to-charge ratio error when the mass-to-charge ratio is corrected with the correction coefficient p ₁ = 1.752 × 10 ⁻⁵ [μm ⁻¹ ]. FIG. 6 also shows the mass-to-charge ratio error when the mass-to-charge ratio is corrected with the correction coefficient p ₂ = 9.317 × 10 ⁻⁵ [V ⁻¹ ]. From these results, by using the linear correction formula shown in Equation (2), it is possible to accurately correct even a large range of fluctuations in both the position deviation of the sample plate surface and the deviation of the sample plate potential. It can be confirmed that the mass-to-charge ratio error is almost zero. The correction results shown in FIG. 5 and FIG. 6 are obtained by executing two correction processes for the positional deviation and the potential deviation, respectively, but these deviations occur completely independently and can be corrected independently. Thus, it is clear that the mass-to-charge ratio error is almost zero even if the two correction processes are executed simultaneously.

  As described above, in the MALDI-TOFMS of the present embodiment, the positional deviation in the X-axis direction of the sample plate 10 between the execution of the mass analysis of the sample containing the standard substance and the execution of the mass analysis of the sample containing the measurement target substance. Even if there is a shift in the potential of the plate due to the voltage applied to the sample plate 10 via the sample stage 11, the data processing in the data processing unit 4 performs correction to reduce the influence, An accurate mass-to-charge ratio value can be obtained. In addition, this makes it possible to obtain a mass spectrum with high mass accuracy.

  In the MALDI-TOFMS of this example, the mass-to-charge ratio error due to only the positional deviation of the sample plate surface and the deviation of the sample plate potential was corrected, but the mass-to-charge ratio error due to other factors is the same. It can be corrected by a technique. Other factors that may cause a mass-to-charge ratio error include a shift in timing of a step change in voltage applied to the acceleration electrode 14 during delay extraction (delay in delay time) and a change in ambient temperature of the apparatus. There is a deviation in flight distance (or deviation from the reference temperature of the temperature of the flight tube 2 itself or in the vicinity thereof) due to the expansion and contraction of the flight tube 2 (usually only thermal expansion). Further, since a potential shift other than the sample plate 10 also affects the flight time, a potential shift of the acceleration electrode 14 due to a voltage applied to the acceleration electrode 14 and a potential of the ion lens 15 due to a voltage applied to the ion lens 15. The deviation is also a factor of mass-to-charge ratio error.

  For example, in order to correct a mass-to-charge ratio error caused by a shift in timing of a step change in voltage applied to the acceleration electrode 14 during delayed extraction (delay in delay time), the potential of the acceleration electrode 14 is detected in real time. And detecting a deviation amount of the delay time with respect to a reference delay time based on a detection result by the detection unit. In addition, in order to correct the mass-to-charge ratio error caused by the flight distance shift due to the thermal expansion of the flight tube 2, a temperature sensor is attached to the flight tube 2, and the temperature shift with respect to the reference temperature in the detection result by the temperature sensor. The deviation of the flight distance calculated from the quantity or the deviation is obtained. Then, using the correction coefficient obtained in advance (usually by the manufacturer) for each shift element, the mass-to-charge ratio obtained by mass calibration may be corrected according to the equation (1).

Now, assuming that ΔP ₃ is the delay time deviation amount Δτ, ΔP ₄ is the flight distance deviation amount Δx _d due to temperature change, and the respective correction coefficients are p ₃ and p ₄ , the correction equation is as follows: 3)
m ₀ = _me (1 + p ₁ · ΔP ₁ ) (1 + p ₂ · ΔP ₂ ) (1 + p ₃ · ΔP ₃ ) (1 + p ₄ · ΔP ₄ ) (3)
Furthermore, when correcting other shift factors in the same manner, an extended or generalized correction formula may be used as follows.
m ₀ = _me (1 + p ₁ · ΔP ₁ ) (1 + p ₂ · ΔP ₂ ) (1 + p ₃ · ΔP ₃ ) (1 + p _n · ΔP _n ) (4)
As a result, it is possible to correct a shift caused by n different shift factors (n is an integer of 1 or more) and obtain a mass-to-charge ratio with high accuracy.

A specific example of the effect of correcting the mass-to-charge ratio error in the mass-to-charge ratio range m / z 1000 to 2500 [Da] when the above method is used will be described.
FIG. 7 is an example of a mass calibration curve for converting time of flight to mass-to-charge ratio. In this example, the mass-to-charge ratio is m ₁ (= 1046.5423 [Da]), m ₂ (= 12966.653 [Da]), m ₃ (= 1570.6774 [Da]), m ₄ (= 1800. 9637 [Da]), m ₅ (= 2093.0867 [Da]), and m ₆ (= 2465.1989 [Da]), the flight time is obtained by simulation calculation, of which m ₁ and m as the two plotted points indicating the relationship between the flight time and mass-to-charge ratio values at ₆ which, fitting to four plotted points indicating the relationship between the flight time and mass-to-charge ratio values of the other m ₂ ~m ₅ A two-point calibration curve was created by doing so. This two-point calibration curve is the following equation (5).
m _exp = 2.21241 × (t−0.63316) ² (5)
The ions having a mass-to-charge ratio of m _{1 to} m ₆ are angiotensin II (Ang2), angiotensin I (Ang1), glucose fibrinogen (Glufib), renin, and adrenocorticotropic hormone 1-17 (ACTH1- 17) Ion derived from adrenocorticotropic hormone 18-39 (ACTH18-39).

FIG. 8 shows a case where the time-of-flight t obtained by the simulation calculation is converted into the mass-to-charge ratio by using the calibration curve shown in the equation (5) for the ions having the mass-to-charge ratio of m _{1 to} m ₆ described above. It is a figure which shows a mass to charge ratio error. Of course, since the data points for ions with mass to charge ratios m ₁ and m ₆ are on the calibration curve, the mass to charge ratio error for these ions is zero. The mass-to-charge ratio error of the ions m ₃ farthest from m ₁ and m ₆ is the largest, but the error is still 160 [ppm]. This error is a mass-to-charge ratio error that inevitably occurs with mass calibration, and can be said to be a mass-to-charge ratio error in an ideal state.

(A) of FIG. 9 is a simulation calculation result of the mass-to-charge ratio error in the six types of ions when assuming various parameter deviations such as positional deviation of the sample plate surface, and (b) shows various assumed simulations. The parameter value and the amount of deviation. Here, as described above, x ₀ , E ₁ , E ₂ , and E _2p are the positions on the x-axis of the surface of the sample plate 10, the potential of the sample plate 10, the applied voltage at the time of laser beam irradiation, and the laser beam, respectively. The acceleration voltage is applied after a predetermined delay time from the irradiation time point, τ is the delay time, E ₃ is the potential of the ion lens 15, and x _d is the flight distance. In the mass-to-charge ratio range of 1000 to 2500 [Da] when such various shifts occur simultaneously from the plot points indicated as “before correction” in FIG. 9A and the line connecting them, 2700 to 3100 [ It can be seen that a mass to charge ratio error of [ppm] has occurred.

  On the other hand, when all of the deviations of the seven parameters shown in FIG. 9B are corrected using the correction formula shown in equation (4), the plot shown as “after correction” in FIG. Like the dots and the lines connecting them, the mass-to-charge ratio error is greatly reduced to -400 to 12.8 [ppm] in the mass-to-charge ratio range of 1000 to 2500 [Da], and the above-mentioned mass-to-charge ratio error in the ideal state. It can be said that it is quite close to. From this result, according to the technique employed in the MALDI-TOFMS of this embodiment, it is possible to accurately correct the mass-to-charge ratio error due to various deviation factors of the apparatus itself and to obtain an accurate mass-to-charge ratio. I understand.

  FIG. 10 (a) focuses on only the positional deviation of the sample plate surface and the deviation of the sample plate potential, and shows the mass-to-charge ratio error of the above six types of ions when it is assumed that there is no deviation of other parameters. It is a simulation calculation result, (b) is the values of various parameters and the amount of deviation. In this case, the mass to charge ratio error before correction is 1800 to 1941 [ppm] in the mass to charge ratio range of 1000 to 2500 [Da]. In other words, about two-thirds of the mass-to-charge ratio error caused by the deviation of the seven types of parameters including the deviation of the two types of parameters, the positional deviation of the sample plate surface and the deviation of the potential of the sample plate. I understand. From this, it can be said that the deviation of these two kinds of parameters is the main factor of the mass-to-charge ratio error.

  On the other hand, when the deviation of the two types of parameters shown in FIG. 10B is corrected using the correction formula shown in the expression (2), as shown as “after correction” in FIG. The mass to charge ratio error is greatly reduced to −180 to −40 [ppm] in the mass to charge ratio range of 1000 to 2500 [Da]. From this result, according to the method adopted in the MALDI-TOFMS of this embodiment, the mass-to-charge ratio error due to the main factors, ie, the positional deviation of the surface of the sample plate and the deviation of the potential of the sample plate is accurately corrected, and the accuracy is improved. It can be seen that a good mass to charge ratio can be determined.

[Second Embodiment]
MALDI-TOFMS, which is another embodiment (second embodiment) of the present invention, will be described with reference to the accompanying drawings. FIG. 11 is a configuration diagram of the main part of the MALDI-TOFMS of the second embodiment. The same components as those in the MALDI-TOFMS of the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted unless particularly required.

  In the MALDI-TOFMS of the first embodiment, a mass-to-charge ratio error due to a shift factor such as an electric circuit including the structure of the apparatus and control, such as a position shift on the surface of the sample plate and a sample plate potential, is calculated by a calculation process in the data processing unit 4. It was corrected. On the other hand, in the MALDI-TOFMS of the second embodiment, the mass charge is adjusted by adjusting a parameter which is one of the analysis conditions when actually performing the mass analysis, instead of performing correction by the data processing unit 4. The ratio error is corrected. That is, in the MALDI-TOMS shown in FIG. 11, the control unit 8 includes an analysis condition correction unit 81 that is characteristic of the present embodiment, and the analysis condition correction unit 81 detects distance information and voltage detected by the distance measurement unit 6. Based on the voltage information obtained by the unit 7, the value of the DC voltage applied to the ion lens 15 for converging the ions generated from the sample 12 is adjusted.

FIG. 14 is a diagram showing the relationship between the amount of deviation Δx on the surface of the sample plate and the amount of adjustment ΔE ₃ of the ion lens voltage when correcting the mass-to-charge ratio error due to the displacement on the surface of the sample plate. In the MALDI-TOFMS of the first embodiment, the adjustment amount ΔE ₃ of the ion lens voltage is zero even if the sample plate surface is displaced, but in the MALDI-TOFMS of the second embodiment, as shown in FIG. The relationship is acquired and stored in advance, and when the actual mass analysis is performed on the sample containing the measurement target substance, it corresponds to the sample plate surface position shift amount based on the distance information obtained by the distance measuring unit 6. An ion lens voltage adjustment amount ΔE ₃ is obtained. Then, a voltage increased or decreased by the ion lens voltage adjustment amount ΔE ₃ is applied to the ion lens 15.

FIG. 12 shows the time of flight of ions having the same mass-to-charge ratio (1000 [Da]) when there is no displacement on the surface of the sample plate (Δx = 0) and when there is a displacement of Δx = 60 [μm]. It is a figure which shows the result of having simulated. From this figure, it can be seen that the flight time is shifted by about 0.011 [μsec] because the surface position of the sample plate 10 is shifted by 60 [μm]. If the mass to charge ratio is calculated from the time of flight according to the calibration curve at this time, it becomes 998.937 [Da], and a mass to charge ratio error of 1.063 [Da] occurs. At this time, the ion lens voltage E ₃ is 5000 [V].

On the other hand, when the ion lens voltage is increased by the ion lens voltage adjustment amount ΔE ₃ = 292 [V] calculated using the relationship shown in FIG. 14, and E ₃ + ΔE ₃ = 5292 [V], The flight time is almost equal to the state without misalignment. FIG. 13 is a partial detail view of FIG. 12, and it can be seen that the flight time is substantially equal to the state in which there is no position shift by adjusting the ion lens voltage. As a result, the mass-to-charge ratio error due to the displacement of the sample plate surface can be corrected almost completely, and a highly accurate mass-to-charge ratio can be calculated.
This is an example in which only the mass-to-charge ratio error due to the positional deviation of the sample plate surface is corrected, but in the same way, the mass-to-charge ratio error caused by other factors, such as the deviation of the sample plate potential, can also be corrected. it can.

FIG. 15 shows a positional deviation on the surface of the sample plate (however, in the example of FIG. 10, the deviation amount Δx = 0.1 [mm], whereas in this example, the deviation amount Δx = 60). [μm]) and the deviation of the sample plate potential. This is a simulation calculation result of the mass-to-charge ratio error in the six types of ions when correction is attempted by adjusting the ion lens voltage. In this case, the mass-to-charge ratio error before correction is 874 to 1056 [ppm] in the mass-to-charge ratio range of 1000 to 2500 [Da], but by adjusting the ion lens voltage, the mass-to-charge ratio error is −145 to It is greatly reduced to 11 [ppm].
As described above, according to the MALDI-TOFMS of the second embodiment, as in the MALDI-TOFMS of the first embodiment, the mass-to-charge ratio error due to various factors can be corrected to obtain a highly accurate mass-to-charge ratio. it can.

Further, the MALDI-TOFMS of the above embodiment can be modified into various forms.
For example, in the above embodiment, as shown in the equations (1) to (4), the primary correction equation is used assuming that the relationship between the deviation amount of one deviation element and the mass-to-charge ratio error is approximately linear. It was. Although this is a sufficiently reasonable approximation as shown in FIGS. 5 and 6, a second-order or higher-order correction equation may be used in order to perform correction with higher accuracy.
Specifically, for example, when the deviation amount of one deviation element is ΔP _i and the two correction coefficients for the deviation element are p _i1 and p _i2 , the following correction equation (6) can be used. it can.
m ₀ = _me (1 + p ₁₁ , ΔP ₁ , p ₁₂ , ΔP ₁ ² ) (1 + p ₂₁ , ΔP ₂ , p ₂₂ , ΔP ₂ ² ) (1 + p ₃₁ , ΔP ₃ , p ₃₂ , ΔP ₃ ² ) (1 + p _{i1 · ΔP i · p i2 ·} ΔP i 2) ... (6)

  In the above embodiment, the distance measuring unit 6 uses laser light. However, if the distance measuring unit 6 can accurately measure the position of the surface of the sample plate 10 or the surface of the sample 12 on the X-axis, The configuration is not limited. For example, a distance measuring unit using capacitance provided near the sample plate 10 may be used.

  Moreover, in the said Example, when using what used a laser beam as the ranging part 6, the structure of the ranging part 6 can also be changed suitably. For example, instead of using a movable reflecting mirror, a first reflecting mirror that is arranged at a position off the flight path and bends the laser light emitted from the laser light source toward the sample plate 10 is also off the flight path. It is good also as a structure provided with the 2nd reflective mirror which is arrange | positioned in the position and directs the laser beam reflected on the sample 12 surface or the sample plate 10 surface to a photon detection part.

  In general, the position of the surface of the sample plate 10 when the sample containing the measurement target substance is subjected to mass spectrometry with reference to the position of the surface of the sample plate 10 when the sample containing the standard substance for mass calibration is subjected to mass spectrometry. If the amount of deviation is calculated, that is, if the relative amount of positional deviation is obtained, the mass-to-charge ratio error can be corrected sufficiently, but in order to obtain the amount of positional deviation more strictly, the absolute dimension must be set. It may be corrected using the result measured by the distance measuring unit 6. For this purpose, for example, a sample plate having a recess having a known depth is used, and distance measurement is performed on at least two points on the sample plate including the point on the bottom surface of the recess and not on the same plane. Based on the distance result, the flight time or mass-to-charge ratio of ions derived from the target substance may be corrected, or the flight time or mass-to-charge ratio of ions derived from the target substance may be obtained after correcting the amount of positional deviation.

  In addition, since each of the above embodiments is an example of the present invention, any modifications, corrections, and additions may be made as appropriate within the scope of the present invention other than the above various modifications. It is natural to be done.

DESCRIPTION OF SYMBOLS 1 ... MALDI ion source 10 ... Sample plate 11 ... Sample stage 12 ... Sample 13 ... Extraction electrode 14 ... Acceleration electrode 15 ... Ion lens 16 ... Laser irradiation part 17 ... Reflector 2 ... Flight tube 3 ... Ion detector 4 ... Data processing Unit 40 ... Spectrum data collection unit 41 ... Mass calibration information storage unit 42 ... Mass calibration processing unit 43 ... Mass correction processing unit 44 ... Mass spectrum creation unit 45 ... Position variation calculation unit 46 ... Potential variation calculation unit 47 ... Correction information storage unit 5 ... Voltage generation unit 6 ... Distance measurement unit 60 ... Reflector 7 ... Voltage detection unit 8 ... Control unit 81 ... Analysis condition correction unit

Claims (13)

A sample holder for holding a sample plate; an ion source for irradiating a sample on the sample plate with laser light to ionize a target substance in the sample; an acceleration part for accelerating ions derived from the target substance; and an acceleration A time-of-flight mass spectrometer comprising: a flight tube that forms a flight space for flying the generated ions; and an ion detector that detects ions flying in the flight space;
a) a position measuring unit for measuring a relative position of the sample surface or the sample plate surface in a direction along a flight trajectory of ions from the sample on the sample plate to the ion detector;
b) Data for correcting the flight time of ions derived from the target substance obtained by mass spectrometry or the mass-to-charge ratio obtained from the flight time based on the amount of deviation between the actual measurement position and the reference position measured by the position measurement unit A correction processing unit;
A time-of-flight mass spectrometer. The time-of-flight mass spectrometer according to claim 1,
The acceleration unit includes a voltage application unit that applies an acceleration voltage to the sample plate and / or one or more acceleration electrodes, and a voltage applied from the voltage application unit to the sample plate and / or one or more acceleration electrodes. A voltage detector for detecting the value of
The data correction processing unit performs flight of ions derived from the target substance obtained by mass spectrometry based on at least the voltage value detected by the voltage detection unit in addition to the displacement amount of the position of the sample surface or the sample plate surface. A time-of-flight mass spectrometer that corrects the time or the mass-to-charge ratio determined from the time of flight. The time-of-flight mass spectrometer according to claim 1 or 2,
The accelerating unit includes a voltage applying unit that applies an accelerating voltage to the sample plate and / or one or a plurality of accelerating electrodes, and from the voltage applying unit to start flight of ions derived from a target substance, the sample plate and / or A timing detector for detecting timing of change in voltage applied to one or a plurality of acceleration electrodes;
In addition to the amount of displacement of the position of the sample surface or sample plate surface, the data correction processing unit is configured to perform flight time of ions derived from the target substance obtained by mass spectrometry based on at least the timing detected by the timing detection unit. Alternatively, a time-of-flight mass spectrometer that corrects a mass-to-charge ratio determined from the time of flight. The time-of-flight mass spectrometer according to any one of claims 1 to 3,
A temperature detector for measuring the temperature of the flight tube;
In addition to the amount of displacement of the position of the sample surface or sample plate surface, the data correction processing unit is configured to perform flight time of ions derived from the target substance obtained by mass spectrometry based on at least the temperature detected by the temperature detection unit. Alternatively, a time-of-flight mass spectrometer that corrects a mass-to-charge ratio determined from the time of flight. A time-of-flight mass spectrometer according to any one of claims 1 to 4,
When the shift amount of one shift element is ΔP _i (where i is an integer from 1 to the number of shift elements) and the coefficient obtained in advance for the shift element is p _i , A time-of-flight mass analysis characterized by correcting an actual flight time or a mass-to-charge ratio obtained from the flight time using a correction formula obtained by assuming that the flight time or mass-to-charge ratio is shifted by a ratio of p _i × ΔP _i apparatus. A time-of-flight mass spectrometer according to any one of claims 1 to 4,
The data correction processing unit sets the shift amount of one shift element to ΔP _i (where i is an integer from 1 to the number of shift elements), the first coefficient previously determined for the shift element is p _i1 , When the coefficient is p _i2 , the actual flight time or the flight time is calculated using a correction formula obtained by assuming that the flight time or mass-to-charge ratio is shifted by the ratio of p _i1 × ΔP _i × p _i2 × ΔP _i ^2. A time-of-flight mass spectrometer characterized by correcting a mass-to-charge ratio obtained from In the time-of-flight mass spectrometer according to any one of claims 1 to 6,
A time-of-flight mass spectrometer characterized in that the position measuring unit is a distance measuring unit using a laser. In the time-of-flight mass spectrometer according to any one of claims 1 to 6,
A time-of-flight mass spectrometer characterized in that the position measuring unit is a distance measuring unit using a capacitance. The time-of-flight mass spectrometer according to claim 7,
The distance measuring unit is configured to emit laser light emitted from a laser light source, which is arranged at a position deviating from a flight trajectory of ions emitted from the sample and passing through the flight space to the ion detector. A time-of-flight mass spectrometer comprising: a first reflecting mirror directed toward the surface; and a second reflecting mirror directing laser light reflected by the sample surface or sample plate surface toward the light detection unit. The time-of-flight mass spectrometer according to claim 7,
The distance measuring unit includes a reflecting mirror that directs laser light emitted from a laser light source toward the sample or the sample plate, and the reflecting mirror is emitted from the sample at the time of distance measurement to the ion detector through the flight space. A reflecting mirror moving unit that moves the reflecting mirror to a second position that is disposed at a predetermined first position on the flight trajectory of the ions to be moved, and at least when the mass analysis is performed, to retract the reflecting mirror to the second position off the flight trajectory. When,
A time-of-flight mass spectrometer. The time-of-flight mass spectrometer according to any one of claims 1 to 10,
Using a sample plate having at least one recess with a known depth and derived from the target substance based on the distance measurement results for at least two points on the sample plate including the point on the bottom surface of the recess A time-of-flight mass spectrometer that corrects the time-of-flight or mass-to-charge ratio of ions. A sample holder for holding a sample plate; an ion source for irradiating a sample on the sample plate with laser light to ionize a target substance in the sample; an acceleration part for accelerating ions derived from the target substance; and an acceleration A time-of-flight mass spectrometer comprising: a flight tube that forms a flight space for flying the generated ions; and an ion detector that detects ions flying in the flight space;
a) a position measuring unit for measuring a relative position of the sample surface or the sample plate surface in a direction along a flight trajectory of ions from the sample on the sample plate to the ion detector;
b) Based on the amount of deviation between the actual measurement position and the reference position measured by the position measurement unit, conditions for ionization in the ion source or conditions for acceleration in the acceleration unit when performing mass analysis on the sample An analysis condition correction unit for correcting at least one of
A time-of-flight mass spectrometer. The time-of-flight mass spectrometer according to claim 12,
The acceleration unit includes a voltage application unit that applies an acceleration voltage to the sample plate and / or one or more acceleration electrodes,
The analysis condition correcting unit illuminates the storage unit storing voltage calibration information indicating the relationship between the position of the sample or the sample plate and the correction amount of the acceleration voltage, and the actual measurement position measured by the position measuring unit. A time-of-flight mass spectrometer comprising: a voltage adjustment control unit that obtains an acceleration voltage correction amount and adjusts the acceleration voltage by the voltage application unit according to the result.

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