Quality analysis equipment

Abstract

An aspect of a mass spectrometer according to the present invention comprises: a measurement unit (1, 2, 3, 4, ...) that performs a first measurement operation of repeatedly performing mass spectroscopy for an analysis range having a predetermined shape while moving the analysis range on a sample in a first predetermined direction and performs a second measurement operation of repeatedly performing mass spectroscopy for an analysis range having the same shape as said analysis range while moving the analysis range on the sample in a second direction which intersects with the first direction; and a computation unit (52) that calculates or infers mass-spectroscopic data in a region of a part where one analysis range in the first measurement operation and one analysis range in the second measurement operation by the measurement unit overlap on the sample, by using mass-spectroscopic data which is obtained in two analysis ranges each including the part where the overlap occurs and in another analysis range overlapping each of the two analysis ranges.

Description

[Technical field]

[0001] The present invention relates to a mass spectrometer, and more particularly to a mass spectrometer suitable for imaging mass spectrometry. [Background technology]

[0002] An imaging mass spectrometer is a device capable of visualizing the spatial distribution of compounds present in a sample such as a biological tissue slice. The imaging mass spectrometer disclosed in Patent Document 1 uses an ion source based on a matrix assisted laser desorption / ionization (MALDI) method.

[0003] In this imaging mass spectrometer, mass spectrum data over a predetermined range of mass-to-charge ratios (strictly speaking, this is the m / z in italics, but in this specification it is conventionally referred to as "mass-to-charge ratio" or simply "m / z") is collected for each micro-region that is finely divided into a grid-like pattern within a two-dimensional measurement region on the sample. From the mass spectrum data thus obtained, for example, the signal intensity values ​​at the m / z values ​​of ions derived from a specific compound are extracted, and an MS imaging image showing the distribution of the specific compound can be obtained by creating a heat map-like image by arranging the signal intensity values ​​according to the two-dimensional positions of each micro-region on the sample.

[0004] In the field of mass spectrometry, various ionization methods have been developed and put to practical use in order to ionize components contained in a sample. Imaging mass spectrometers that utilize various ionization methods other than the above-mentioned MALDI method are also known. One such ionization method is the Tapping mode Scanning Probe ElectroSpray Ionization (t-SPESI) method (tapping mode scanning probe electrospray ionization) described in Non-Patent Documents 1 and 2, etc. transformation (sometimes called the law) is known.

[0005] In the t-SPESI method, a solvent that has been charge-separated by applying a high voltage is passed through a channel of a cantilevered silica capillary probe (hereinafter simply referred to as a probe), and the probe is vibrated to intermittently bring the sample and the probe tip into contact. When the probe tip is in contact with the sample, a liquid bridge is formed between the two by the solvent, and the components in the sample are extracted into the solvent. When the probe tip is then separated from the sample, the solvent containing the sample components adhering to the probe tip breaks and scatters, generating an electrospray. The generated charged droplets are dried until they reach the entrance of an ion introduction tube arranged close to the probe tip and while passing through the ion introduction tube, generating gas-phase ions derived from the sample components.

[0006] In an imaging mass spectrometer using the above-mentioned t-SPESI method, mass spectrum data can be obtained at each micro-position within a two-dimensional area on the sample by moving either the sample or the probe, or both, two-dimensionally in a direction parallel to the measurement surface of the sample. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2011-191222 A [Non-patent literature]

[0008] [Non-Patent Document 1] Otsuka, "Direct Liquid Extraction Ionization for Capturing Diverse Molecular Environments in Biological Systems," Journal of the Japanese Society for Mass Spectrometry, Vol. 68, No. 5, 2020, pp. 59-74 [Non-Patent Document 2] Otsuka, "Development of a scanning probe electrospray ionization method using a capillary probe and nanovolume liquids," Journal of the Japanese Society for Mass Analysis, Vol. 68, No. 1, 2020, pp. 2-7 Summary of the Invention [Problem to be solved by the invention]

[0009] In an imaging mass spectrometer that uses the t-SPESI method (hereinafter, unless otherwise specified, an imaging mass spectrometer that uses the t-SPESI method will simply be referred to as an imaging mass spectrometer), if the vibration frequency of the probe is constant, the spatial resolution (resolution of the MS imaging image) in the scanning direction of the probe (the direction of movement relative to the sample) generally depends on the scanning speed. On the other hand, the spatial resolution in the direction perpendicular to the scanning direction generally depends on the size of the probe tip. Therefore, the spatial resolution in the scanning direction of the probe can be changed by adjusting the scanning speed, and the spatial resolution can be increased by slowing down the scanning speed.

[0010] On the other hand, the spatial resolution in the direction perpendicular to the scanning direction is physically determined, and usually cannot be increased beyond the determined resolution. Therefore, even if it is desired to increase the resolution of an MS imaging image, the resolution can only be increased in one direction, either the vertical or horizontal direction, of the image, resulting in a problem that it is not always possible to display a precise MS imaging image as expected by the user.

[0011] The present invention has been made to solve the above-mentioned problems, and a main object of the present invention is to provide a mass spectrometer that can obtain MS imaging images having a higher resolution than is limited by the size of the probe tip. [Means for solving the problem]

[0012] In order to solve the above problems, one aspect of the mass spectrometer according to the present invention is to a measurement unit that executes a first measurement operation in which mass analysis is repeatedly performed on an analysis range having a predetermined shape while moving the analysis range in a predetermined first direction on a sample, and a second measurement operation in which mass analysis is repeatedly performed on an analysis range having the same shape as the analysis range while moving the analysis range in a second direction intersecting the first direction on the sample; a calculation unit that calculates or estimates mass spectrometry data in a region of an overlapping portion between one analysis range in the first measurement operation by the measurement unit and one analysis range in the second measurement operation by the measurement unit, using mass spectrometry data obtained in two analysis ranges each including the overlapping portion and other analysis ranges each overlapping with the two analysis ranges; Equipped with.

[0013] The mass spectrometry data may be mass spectrum data over a predetermined m / z range, or may be signal intensity (ion intensity) data at one or more specific m / z values. In addition to data obtained by ordinary mass spectrometry, data obtained by MS / MS analysis or MS where n is 3 or more may also be used. n Analytical data is also included. Effect of the Invention

[0014] In the mass spectrometer according to the above aspect of the present invention, mass analysis data for a range (the overlapping portion) smaller than the size of the analysis range determined by various constraints in the ion source is calculated from mass analysis data obtained by measurements on a plurality of analysis ranges. As a result, the mass spectrometer according to the above aspect of the present invention can obtain an MS imaging image with a higher resolution than the resolution determined depending on the size of the probe tip in, for example, a t-SPESI ion source. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic diagram showing the configuration of an imaging mass spectrometer according to one embodiment of the present invention. [Figure 2A]FIG. 2 is an explanatory diagram of an example of a measurement procedure for a measurement region on a sample in the imaging mass spectrometer of this embodiment, showing an analysis range in a first series of measurements. [Figure 2B] FIG. 2 is an explanatory diagram of an example of a measurement procedure for a measurement region on a sample in the imaging mass spectrometer of this embodiment, showing an analysis range in a second series of measurements. [Diagram 3] FIG. 4 is a schematic diagram illustrating an example of data processing for an overlapping portion of two measurements in the imaging mass spectrometer of the present embodiment. [Figure 4] FIG. 11 is a schematic explanatory diagram of another example of data processing for an overlapping portion of two measurements in the imaging mass spectrometer of the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] An imaging mass spectrometer, which is one embodiment of a mass spectrometer according to the present invention, will be described with reference to the accompanying drawings. This imaging mass spectrometer is an imaging mass spectrometer using a t-SPESI ion source.

[0017] Fig. 1 is a schematic diagram of an imaging mass spectrometer according to this embodiment. For convenience of explanation, three mutually orthogonal axes, x, y, and z, are defined in space as shown in Fig. 1. Here, the surface of a sample S to be measured is parallel to the xy plane.

[0018] This imaging mass spectrometer has an ionization chamber 1, a first intermediate vacuum chamber 2, a second intermediate vacuum chamber 3, and an analysis chamber 4, each of which is approximately partitioned inside a chamber. The inside of the ionization chamber 1 is at approximately atmospheric pressure, and the inside of the analysis chamber 4 is maintained at a high vacuum atmosphere by evacuation using a vacuum pump (not shown). The first intermediate vacuum chamber 2 and the second intermediate vacuum chamber 3 are also evacuated by vacuum pumps (not shown), forming a multi-stage differential pumping system in which the degree of vacuum increases in stages from the ionization chamber 1 to the first intermediate vacuum chamber 2, the second intermediate vacuum chamber 3, and the analysis chamber 4 in that order.

[0019] A sample stage 14 is disposed in the ionization chamber 1, and this sample stage 14 is movable in two axial directions, the x-axis and the y-axis, and can freely rotate 90° around the z-axis (vertical axis) by a stage drive unit 17. A sample S, such as a slice of biological tissue, is set on the sample stage 14.

[0020] A probe 11 is disposed above the sample stage 14, the base of which is supported by a probe holder 13 in a cantilevered manner. The probe 11 is a silica capillary probe, as described in, for example, Non-Patent Documents 1 and 2, and is flexible. A flow path is formed inside the probe 11, which continues from the base to the tip, and a solvent is supplied to this flow path by a syringe pump (not shown). A high voltage generated by a high voltage generator 16 is applied to the solvent at the probe holder 13. An excitation unit 12 such as a piezoelectric actuator is attached to the probe 11. When a drive signal is supplied from the probe driver 15 to the excitation unit 12, the probe 11 oscillates in a pendulum-like manner at a predetermined frequency in the approximately vertical direction, as shown by the double-headed arrow in FIG. 1.

[0021] In the ionization chamber 1, the components in the sample S are ionized mainly as follows. The height of the sample stage 14 is appropriately adjusted so that the tip of the probe 11 intermittently contacts the sample S when the probe 11 is excited. In this state, when the tip of the probe 11 contacts the surface of the sample S, a liquid bridge of the solvent (solvent with charge separation) flowing out from the tip of the probe 11 is formed between the tip of the probe 11 and the sample S. The components (compounds) contained in the sample S are extracted into the solvent, and when the probe 11 is separated from the sample S, the solvent containing the sample components is scattered upward to form minute charged droplets. The charged droplets come into contact with surrounding gas molecules and are broken down into fine particles, and the solvent in the droplets evaporates. In the process, gas-phase ions derived from the sample components are generated from the charged droplets.

[0022] The ionization chamber 1 and the first intermediate vacuum chamber 2 are in communication with each other through a thin-diameter desolvation tube 21 that is heated to a predetermined temperature. Ions derived from the sample components generated in the ionization chamber 1 and fine charged droplets containing the component molecules are drawn into the desolvation tube 21 and sent to the first intermediate vacuum chamber 2 by the action of a gas flow formed by the difference between the pressure in the ionization chamber 1 (approximately atmospheric pressure) and the pressure in the first intermediate vacuum chamber 2, and an electric field formed by a voltage applied to the ion introduction port of the desolvation tube 21. Vaporization of the solvent from the charged droplets is promoted even while passing through the desolvation tube 21, promoting the generation of ions derived from the sample components.

[0023] A multipole ion guide 22 is disposed in the first intermediate vacuum chamber 2, and ions introduced into the first intermediate vacuum chamber 2 are focused near the ion optical axis C by the electric field formed by the ion guide 22, and enter the second intermediate vacuum chamber 3 through a hole at the top of the skimmer 23. A multipole ion guide 31 is also disposed in the second intermediate vacuum chamber 3, and ions are sent from the second intermediate vacuum chamber 3 to the analysis chamber 4 while being focused by the electric field formed by the ion guide 31.

[0024] In the analysis chamber 4, a mass separator 41 that separates ions according to m / z and an ion detector 42 are arranged. The type of the mass separator 41 is not particularly limited, and for example, a quadrupole mass filter, a time-of-flight mass separator, an ion trap, or the like can be used. When the mass separator 41 is a quadrupole mass filter, for example, the quadrupole mass filter is driven so that the m / z of the ions passing through it changes sequentially over a predetermined m / z range. The ions that have passed through the quadrupole mass filter reach the ion detector 42, which outputs an ion intensity signal according to the number of ions that have reached it. The mass separator 41 may be configured to generate product ions using a collision cell or ion trap that dissociates ions by collision induced dissociation or the like, and to perform mass analysis on the product ions.

[0025] The data processing unit 5 which receives the output signal of the ion detector 42 includes, as functional blocks, a data storage unit 51, an arithmetic processing unit 52, an MS imaging image generating unit 53, and the like. The control unit 6 performs imaging mass spectrometry by controlling the high voltage generating unit 16, the probe driving unit 15, the stage driving unit 17, the voltage generating unit 7, etc. An input unit 8 and a display unit 9 serving as a user interface are connected to the control unit 6.

[0026] Although the control unit 6 and the data processing unit 5 can be configured by hardware, they are usually implemented as general-purpose computers such as personal computers. The functions of the functional blocks in the control unit 6 and the data processing unit 5 described above can be achieved by executing dedicated control and processing software installed in the computer.

[0027] An example of a characteristic analysis operation in the imaging mass spectrometer of this embodiment will be described with reference to Figures 2 to 4. Figures 2 to 4 all show the top surface (a surface parallel to the xy plane) of the sample S as viewed from above.

[0028] First, the operation during measurement for collecting MS imaging data in the imaging mass spectrometer of this embodiment will be described with reference to FIGS. 2A and 2B.

[0029] In the imaging mass spectrometer of this embodiment, it is necessary to obtain mass spectrum data for each of a large number of micro-regions in a predetermined measurement region on a sample, which is designated in advance by, for example, a user. As an example, the measurement region 100 on the sample S is assumed to be rectangular in top view as shown in Figs. 2A and 2B. In a typical scanning type (not a so-called projection type) imaging mass spectrometer, mass analysis is performed sequentially on each of the multiple micro-regions in the measurement region 100, thereby obtaining mass spectrum data for all of the micro-regions. In contrast, in this imaging mass spectrometer, measurement (repetition of mass analysis) is performed twice for one measurement region 100 as follows. FIG. 2A is a diagram showing an analysis range 101A of each mass analysis in the first measurement, and FIG. 2B is a diagram showing an analysis range 101B of each mass analysis in the second measurement.

[0030] As described above, in a mass spectrometer using a t-SPESI ion source, the probe 11 is vibrated at a predetermined frequency (usually a frequency close to the resonance frequency of the probe 11 itself) while the sample S (or the probe 11 itself) is moved linearly in the same direction as the extension direction of the probe 11 in a top view (the x-axis direction in FIG. 1), so that mass analysis of a predetermined analysis range is repeatedly performed along the movement direction. When the movement speed of the sample S, that is, the scanning speed, is increased, the movement distance in the scanning direction during the time when the tip of the probe 11 is in contact with the sample S becomes longer, so that the analysis range 101A becomes wider in the scanning direction. Conversely, when the movement speed of the sample S is decreased, the movement distance in the scanning direction during the time when the tip of the probe 11 is in contact with the sample S becomes shorter, so that the analysis range 101A becomes narrower in the scanning direction. On the other hand, the size of the analysis range 101A in the direction perpendicular to the scanning direction on the sample S is determined by the size of the tip of the probe 11.

[0031] That is, regarding the size of the analysis range 101A, which is the smallest unit on the sample S from which mass spectrum data over a predetermined m / z range can be obtained, the size in the direction perpendicular to the scanning direction (y-axis direction) is structurally determined, and the size in the scanning direction (x-axis direction) is variable depending on the scanning speed. Therefore, in the example shown in Figures 2A and 2B, the scanning speed is adjusted so that the size of the analysis ranges 101A and 101B in the scanning direction is about 1 / 3 of the size in the direction perpendicular to it. Here, the length of one side of the analysis ranges 101A and 101B, which is determined depending on the size of the tip of the probe 11, is L, and the length of the other side, which is determined depending on the excitation frequency and scanning speed, is L / 3.

[0032] For the first measurement, the control unit 6 controls each unit to repeat mass analysis by vibrating the probe 11 while moving the sample S in the x-axis direction. As a result, mass analysis is performed for each of n analysis ranges 101A arranged in one row in the X-direction (which coincides with the x-axis direction at this time) of the measurement area 100, as shown in FIG. 2A. When the tip of the probe 11 reaches the boundary of the measurement area 100 (the right end in FIG. 2A), the sample S is moved in the y-axis direction by a distance equivalent to L, and the sample S is moved so that the tip of the probe 11 comes to the left end of the measurement area 100. Then, the sample S is moved again in the x-axis direction from the left end of the measurement area 100, while vibrating the probe 11, to repeat mass analysis. This operation is repeated until the analysis range 101A covers the entire measurement area 100. That is, the sample S is moved so that the tip of the probe 11 raster scans the sample S in the X-direction.

[0033] When the first measurement is completed, the control unit 6 rotates the sample stage 14 by the stage driving unit 17 so as to rotate the sample S by 90° around the z-axis. In this state, when the sample S is moved in the x-axis direction while vibrating the probe 11 in the same manner as in the first measurement, the scanning direction becomes the Y-direction of the measurement area 100 as shown in FIG. 2B. As in the first measurement, the mass analysis is repeated while moving the sample S in the x-axis direction, and when the tip of the probe 11 reaches the boundary of the measurement area 100 (the lower end in FIG. 2B), the sample S is moved in the y-axis direction by a distance equivalent to L. Then, the sample S is moved again in the x-axis direction from the upper end of the measurement area 100, while vibrating the probe 11, and the mass analysis is repeated. This operation is repeated until the analysis range 101B covers the entire measurement area 100. This is the second measurement.

[0034] The entire measurement area 100 is measured approximately twice by the first measurement and the second measurement. In Fig. 2A and Fig. 2B, the rectangular analysis ranges 101A (or 101B) are spread over the entire measurement area 100 on the sample S, but in reality, the sample S moves even while the tip of the probe 11 is separated from the sample S and ionization by electrospray is being performed, so the analysis ranges 101A (or 101B) are not spread completely in the scanning direction (x-axis direction), and a gap where substantially no analysis is performed may be formed between one analysis range 101A (or 101B) and an analysis range 101A (or 101B) adjacent to it in the scanning direction.

[0035] The size of one analysis range 101A or 101B is approximately L×(L / 3). Therefore, for example, in the upper left part of the measurement region 100 shown in Fig. 2A, there is a substantially square area of ​​size L×L in which three analysis ranges 101A from the first measurement and three analysis ranges 101B from the second measurement overlap, as shown in Fig. 3. Here, the area including the three analysis ranges 101A aligned in the X direction and the three analysis ranges 101B aligned in the Y direction in such a measurement region 100 is referred to as analysis range 102.

[0036] As shown in FIG. 3, one analysis range 102 is apparently divided into nine square microregions 103 each having a length and width of L / 3. If mass spectrum data is obtained for each of these microregions 103, the spatial resolution (resolution) is three times that of the mass spectrum data obtained for each analysis range 101A (or 101B) by the first or second measurement. However, what is obtained by actual measurement is mass spectrum data for each of the analysis ranges 101A and 101B. Therefore, in the imaging mass spectrometer of this embodiment, mass spectrum data for nine microregions 103 included in one analysis range 102 is calculated from mass spectrum data for a total of six analysis ranges, including three analysis ranges 101A arranged in the X direction and three analysis ranges 101B arranged in the Y direction, which are included in the analysis range 102.

[0037] Before considering the example shown in FIG. 3, let us consider a simpler case in which one analysis range 102 can be divided into four 2×2 microregions 103 as shown in FIG. 4. In this case, the mass spectrum data for the four microregions P11, P12, P21, and P22 are unknown values, and the known values ​​are the mass spectrum data for two analysis ranges 101A (X1, X2) arranged in the X direction and two analysis ranges 101B (Y1, Y2) arranged in the Y direction. The signal intensity of a certain m / z value in the mass spectrum data for one analysis range 101A, 101B should be the sum of the signal intensities of the m / z value in the mass spectrum data for multiple microregions 103 included in the analysis ranges 101A, 101B. Therefore, a simultaneous equation including the following four equations is established. <p11> + <p12> = <x1> <p21> + <p22> = <x2> <p11> + <p21> = <y1> <p12> + <p22> = <y2> Here, <*> indicates the signal intensity of each m / z value obtained in the analysis range 101A, 101B or the minute region 103, and the addition symbol + indicates the addition for each m / z value.

[0038] That is, in the example of FIG. 4, the number of unknowns is the same as the number of equations, so in this case, the calculation processing unit 52 solves the above simultaneous equations to obtain four unknowns. <p11> 、 <p12> 、 <p21> 、 <p22>It is possible to obtain accurate values ​​for the spatial resolution. The improvement in spatial resolution is twice the original spatial resolution, and by measuring one measurement region 100 twice, the effect of improving the spatial resolution by two times is obtained. Although the effect of improving the spatial resolution is not necessarily high, there is a sufficient advantage in that the spatial resolution can be improved without reducing the size of the tip of the probe 11.

[0039] Next, consider a case where one analysis range 102 is divided into nine 3 x 3 micro regions 103 as shown in Figure 3. In this case, the mass spectrum data for the nine micro regions P11, P12, P13, P21, P22, P23, P31, P32, and P33 are unknown values, and the known values ​​are the mass spectrum data for three analysis ranges 101A (X1, X2, and X3) aligned in the X direction and three analysis ranges 101B (Y1, Y2, and Y3) aligned in the Y direction. Therefore, the following six equations hold: <p11> + <p12> + <p13> = <x1> <p21> + <p22> + <p23> = <x2> <p31> + <p32> + <p33> = <x3> <p11> + <p21> + <p31> = <y1> <p12> + <p22> + <p32> = <y2> <p13> + <p23> + <p33> = <y3>

[0040] In this case, since there are more unknowns than equations, it is not possible to find a correct solution by solving the simultaneous equations as described above. Therefore, the calculation processing unit 52 finds an approximate solution by using a well-known multiple regression analysis method such as partial least squares. A simple linear regression model can be used as the regression. The partial least squares method and other solution methods used here are included in general numerical analysis software and are well known, so a detailed explanation will be omitted. In this case, the improvement in spatial resolution is three times that of the original spatial resolution.

[0041] As described above, mass spectrum data for each microregion 103 included in the measurement region 100 can be obtained by performing a calculation to solve the above-mentioned simultaneous equations for the signal intensity value for each m / z value or a calculation of an approximation by multiple regression analysis. The data calculated in this manner is stored in a data storage unit in association with information (coordinate information) indicating the position of each microregion 103 in the measurement region 100.

[0042] When the user specifies an m / z value to be observed on the input unit 8 and issues an instruction to display an image, the MS imaging image creation unit 53 then reads out the signal intensity values ​​at the specified m / z value for each specified microregion from the data storage unit 51. The signal intensity values ​​are then arranged two-dimensionally, and an MS imaging image is created by converting the signal intensity values ​​into colors according to, for example, a predetermined color scale. This image is then displayed on the screen of the display unit 9. It is possible to display an MS imaging image with a higher spatial resolution than the spatial resolution during measurement.

[0043] Of course, the imaging mass spectrometer of the above embodiment can be modified to further increase the spatial resolution. Specifically, the first and second measurements are performed so that one analysis range 102, which is a substantially square shape, is divided into 16 microregions 103 of 4×4. In this case, the number of unknown values ​​is 16, the number of known values ​​is 8, and eight equations are established. As described above, the more the number of unknown values ​​deviates from the number of known values, the lower the accuracy of the approximation by the multiple regression analysis (i.e., the larger the error becomes), so that although the spatial resolution of the MS imaging image is improved, the accuracy of the signal intensity of each microregion is reduced, and the accuracy of the distribution of the target component is reduced. Therefore, although in principle it is possible to divide one analysis range 102 into even finer regions, in practice it is preferable to divide one analysis range 102 into about 9 microregions 103 of 3×3 or 16 microregions 103 of 4×4.

[0044] In the above description, the mass spectrum data obtained in the first measurement and the mass spectrum data obtained in the second measurement for the same measurement area 100 are treated substantially equally, but depending on the type of sample S, in many cases, many of the components present on the surface of the sample S are extracted in the first measurement, so that the amount of components remaining on the surface of the sample S in the second measurement is significantly reduced compared to the first measurement. Therefore, it is unavoidable that the signal intensity is generally reduced in the second measurement compared to the first measurement. Therefore, when deriving a solution by setting up simultaneous equations and solving them or by using multiple regression analysis as described above, it is advisable to perform a process to correct the reduction in signal intensity in the second measurement.

[0045] Specifically, for example, when formulating the simultaneous equations, the signal intensity values ​​collected in the second measurement can be multiplied by a correction coefficient that is an appropriate value equal to or greater than 1. This correction coefficient can be determined, for example, experimentally. As a result, even if the sensitivity decreases during the second measurement when the same portion within the same measurement region 100 is measured twice, the effect can be reduced and the calculation accuracy of the mass spectral data in each microregion can be improved.

[0046] Although the imaging mass spectrometer of the above embodiment uses a t-SPESI ion source, the ion source is not limited to this, and as described above, any ion source that can perform mass analysis repeatedly such that an analysis range of a rectangular shape or another predetermined shape is aligned in one direction on the sample can be used. For example, a desorption electrospray ionization (DESI) method can be used.

[0047] In principle, the scanning direction of the first measurement and the scanning direction of the second measurement for the same measurement region do not have to be perpendicular to each other, and the planar shape of one analysis range does not have to be rectangular. However, in such a case, the calculation of mass spectrum data for each minute region becomes complicated, so in practice, it is better to make the planar shape of one analysis range rectangular and make the scanning direction of the first measurement and the scanning direction of the second measurement perpendicular to each other, as in the above example.

[0048] Furthermore, the above embodiment and modifications are merely examples of the present invention, and it is clear that any appropriate modifications, amendments, and additions made within the spirit of the present invention will also be encompassed within the scope of the claims of this application.

[0049] [Various aspects] It will be apparent to those skilled in the art that the above-described exemplary embodiments are illustrative of the following aspects.

[0050] (Item 1) One aspect of the mass spectrometer according to the present invention is a measurement unit that executes a first measurement operation in which mass analysis is repeatedly performed on an analysis range having a predetermined shape while moving the analysis range in a predetermined first direction on a sample, and a second measurement operation in which mass analysis is repeatedly performed on an analysis range having the same shape as the analysis range while moving the analysis range in a second direction intersecting with the first direction on the sample; a calculation unit that calculates or estimates mass spectrometry data in a region of an overlapping portion between one analysis range in the first measurement operation by the measurement unit and one analysis range in the second measurement operation by the measurement unit, using mass spectrometry data obtained in two analysis ranges each including the overlapping portion and other analysis ranges each overlapping with the two analysis ranges; Equipped with.

[0051] In the mass spectrometer described in paragraph 1, the predetermined shape is not particularly limited, but can typically be a substantially rectangular shape. The angle at which the first direction and the second direction intersect is also not particularly limited, but can typically be 90°, that is, the first direction and the second direction are perpendicular to each other. When the predetermined shape is substantially rectangular and the first direction and the second direction are perpendicular to each other, the first direction can be a direction along one side of the substantially rectangular analysis range, and the second direction can be a direction along the other side of the analysis range.

[0052] In the mass spectrometer described in paragraph 1, one analytical range that is the subject of mass analysis in the first measurement operation and one analytical range that is the subject of mass analysis in the second measurement operation overlap at least in a certain portion. The area of ​​the overlapping portion is smaller than either of the two analytical ranges that include the overlapping portion. The calculation unit obtains mass spectrum data in the area of ​​the overlapping portion using mass spectrum data obtained in two analytical ranges that each include the overlapping portion and in other analytical ranges that overlap the two analytical ranges. As a result, the mass spectrometer described in paragraph 1 can obtain an MS imaging image with a resolution higher than the resolution determined depending on the size of the probe tip in, for example, a t-SPESI ion source.

[0053] (2) In the mass spectrometer according to the first aspect, the analysis range is a substantially rectangular range, 1 way The direction is the direction in which one side of the analysis range extends, 2 ways The direction may be the direction in which the other side of the analysis range extends.

[0054] (Item 3) In the mass spectrometer according to item 2, the length of one side of the rectangular analysis range is 1 / n (n is an integer of 2 or more) of the length of the other side, and the measurement unit is 1 way The n analysis ranges arranged in the direction are all set to a substantially square range, and the first analysis range to be mass analyzed in the second measurement operation is set to the substantially square range. 2 ways The first measurement operation and the second measurement operation may be performed so that n analysis ranges aligned in the same direction overlap.

[0055] According to the mass spectrometer described in the second and third aspects, the first mass spectrometer to be mass analyzed in the first measurement operation is 1 way The n analytical ranges arranged in the same direction are treated as one analytical range, and the mass spectrometry data obtained for each analytical range are treated as known values, the first 1 way One of the n analysis ranges arranged in the direction 2 ways It is possible to easily formulate simultaneous equations consisting of multiple equations, in which the mass analysis data in the portion where the n analytical ranges arranged in the direction overlap with one of the n analytical ranges arranged in the direction is taken as an unknown value. This simplifies the calculation using the mass analysis data in the calculation unit, and makes it possible to quickly obtain the mass analysis data for each target micro-region.

[0056] (4) In the mass spectrometer according to the third aspect, the calculation unit converts the mass analysis data obtained for the analysis range into a known value, 1 way One analytical range arranged in the direction and a second analytical range to be mass analyzed in the second measurement operation 2 ways The mass spectrometry data for a region overlapping with one of the analytical ranges arranged in the opposite direction can be set as unknown values, and simultaneous equations in which the number of unknowns is greater than the number of equations can be formulated, and the unknown values ​​can be obtained as approximate solutions from the simultaneous equations.

[0057] (Item 5) In the mass spectrometer as described in item 4, the calculation unit may obtain the approximate solution by a linear approximation method.

[0058] In the mass spectrometer described in paragraph 3, the spatial resolution improves as the value of n increases. However, the value of n has calculation constraints. For example, when n=2, the number of simultaneous equations is 4 and the number of unknown values ​​is 4, so the simultaneous equations can be solved to obtain true values ​​(not estimated values). On the other hand, when n is 3 or more, the number of unknown values ​​is greater than the number of simultaneous equations, so the simultaneous equations cannot be solved as is. In contrast, in the mass spectrometer described in paragraph 4 or 5, the unknown values ​​are calculated by finding an approximate solution from the simultaneous equations, so that although the unknown values ​​are not true values, values ​​relatively close to the true values ​​can be obtained, and thus a generally accurate two-dimensional distribution image of the compound can be created.

[0059] (Item 6) In the mass spectrometer described in any one of items 1 to 5, the calculation unit may perform processing to correct a difference in detection sensitivity between the first measurement operation and the second measurement operation.

[0060] Regardless of the ionization method, when the same part on a sample is subjected to mass spectrometry multiple times, the amount of the target sample component is reduced and the detection sensitivity is reduced. In contrast, the mass spectrometer described in paragraph 6 corrects the data obtained by the second mass spectrometry for the same part, thereby reducing the effect of the reduction in detection sensitivity and enabling more accurate calculation of mass spectrometry data for parts where multiple analysis ranges overlap.

[0061] (Item 7) In the mass spectrometer according to any one of items 1 to 6, the measurement unit is a tapping mode scanning probe electrospray ion spectrometer. transformation The mass spectrometer may be an ion source using a t-SPESI (t-SPESI) method.

[0062] In an ion source based on the t-SPESI method, the size of the analysis range in the movement direction can be adjusted by adjusting the relative movement speed (scanning speed) between the probe and the sample. It is also possible to make the shape of the analysis range approximately rectangular. For these reasons, a mass spectrometer having an ion source based on the t-SPESI method is one of the mass spectrometers suitable for the present invention. [Explanation of symbols]

[0063] 1…Ionization chamber 11…Probe 12...Excitation section 13…Probe holder 14...Sample stage 15...Probe drive unit 16…High voltage generator 17…Stage drive unit 2, 3...Intermediate vacuum chamber 21...Desolvation tube 22, 31…Ion Guide 23...Skimmer 4…Analysis room 41...Mass separator 42…Ion detector 5. Data processing section 51...Data storage section 52...Calculation processing unit 53…MS Imaging Department 6...Control section 7…Voltage generation section 8...Input section 9…Display section C…Ion optical axis < / p33> < / p23> < / p13> < / y2> < / p32> < / p22> < / p12> < / y1> < / p31> < / p21> < / p11> < / x3> < / p33> < / p32> < / p31> < / x2> < / p23> < / p22> < / p21> < / x1> < / p13> < / p12> < / p11> < / p21> < / p12> < / p11> < / p22> < / p12> < / y1> < / p21> < / p11> < / x2> < / p22> < / p21> < / x1> < / p12> < / p11>

Claims

1. a measurement unit that executes a first measurement operation in which mass analysis is repeatedly performed on an analysis range having a predetermined shape while moving the analysis range in a predetermined first direction on a sample, and a second measurement operation in which mass analysis is repeatedly performed on an analysis range having the same shape as the analysis range while moving the analysis range in a second direction intersecting the first direction on the sample; a calculation unit that calculates or estimates mass spectrometry data in a region of an overlapping portion between one analysis range in the first measurement operation by the measurement unit and one analysis range in the second measurement operation by the measurement unit, using mass spectrometry data obtained in two analysis ranges each including the overlapping portion and other analysis ranges each overlapping with the two analysis ranges; A mass spectrometer comprising:

2. 2. The mass spectrometer of claim 1, wherein the analysis range is a substantially rectangular range, the first direction is a direction in which one side of the analysis range extends, and the second direction is a direction in which the other side of the analysis range extends.

3. 3. The mass spectrometer of claim 2, wherein the length of one side of the rectangular analysis range is 1 / n (n is an integer greater than or equal to 2) of the length of the other side, and the measurement unit performs the first measurement operation and the second measurement operation such that the entire n analysis ranges lined up in a first direction to be mass analyzed in the first measurement operation form an approximately square-shaped range, and the n analysis ranges lined up in a second direction to be mass analyzed in the second measurement operation overlap this approximately square-shaped range.

4. 4. The mass spectrometer according to claim 3, wherein the calculation unit sets up simultaneous equations in which the number of unknowns is greater than the number of equations, using mass analysis data obtained for an analysis range as known values ​​and mass analysis data for a region where one analysis range aligned in a first direction that is mass analyzed in the first measurement operation overlaps with one analysis range aligned in a second direction that is mass analyzed in the second measurement operation as unknown values, and determines the unknown values ​​as approximate solutions from the simultaneous equations.

5. The mass spectrometer according to claim 4 , wherein the calculation unit determines the approximate solution by a linear approximation method.

6. The mass spectrometer according to claim 1 , wherein the calculation unit performs a process for correcting a difference in detection sensitivity between the first measurement operation and the second measurement operation.

7. 2. The mass spectrometer according to claim 1, wherein the measurement unit is a mass spectrometer having an ion source using a tapping mode scanning probe electrospray ionization method.

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