Mass analysis method and mass analysis device

Abstract

The mass analysis method of the present invention improves the detection sensitivity of ions with high molecular weight and high valence. The mass analysis method of one embodiment of the present invention causes ions to be analyzed to contact with cooling gas, for example, in an ion trap (2) and be cooled, and then kinetic energy is given to the ions, and the ions are introduced into the flight space of a multi-rotation time-of-flight mass separator (30) for separation based on mass-to-charge ratio to perform mass analysis. When the known or estimated valence of the ions to be analyzed is high, the amount of cooling gas supplied to the cooling part (ion trap (2)) for cooling the ions is reduced compared to when the valence is low.

Description

Technical Field

[0001] The present invention relates to a mass spectrometry method and a mass spectrometry apparatus, and more particularly to a mass spectrometry method and a mass spectrometry apparatus using a time-of-flight mass separator. Background Art

[0002] As disclosed in Patent Document 1, etc., an ion trap time-of-flight mass spectrometer is provided with an ion trap and a time-of-flight mass separator. In the ion trap time-of-flight mass spectrometer, various ions generated by a sample are temporarily captured inside the ion trap, and then the various ions are accelerated to be ejected from the ion trap and introduced into the time-of-flight mass separator. Each accelerated ion has a speed corresponding to its mass-to-charge ratio (strictly speaking, m / z in italic font, but in this specification, it is conventionally referred to as "mass-to-charge ratio"), so while the ions are flying in the flight space of the time-of-flight mass separator, the ions are separated according to the difference in mass-to-charge ratio and arrive at the detector for detection.

[0003] In a time-of-flight mass spectrometer (hereinafter sometimes referred to as "TOFMS" according to customary usage), the longer the distance that ions fly, the higher the mass resolution. Therefore, generally speaking, it is easier to obtain high mass resolution by a reflection type that makes ions fly back and forth, such as disclosed in Patent Document 1, than by a linear type that makes ions fly in a straight line.

[0004] In addition, Patent Documents 2 and 3 disclose a TOFMS that further extends the flight length by installing a reflectron that reflects ions two or more times. A TOFMS that extends the flight length of ions by reflecting two or more times is called a multi-reflection TOFMS.

[0005] In addition, a TOFMS is disclosed in patent document 4, and the TOFMS can further extend the flight length of the ions by making the ions orbit multiple times along roughly the same orbit. Further, there is disclosed in patent document 5 a TOFMS, the orbit of one week of the TOFMS is roughly circular, roughly elliptical or roughly 8-shaped, and can slightly deviate from the orbit by making the ions orbit each time they orbit, thereby avoiding the ions from flying along the same orbit while increasing the number of orbits and extending the flight length. A TOFMS that extends the flight length of the ions by orbiting multiple times like this is called a multi-transformation TOFMS. In particular, in the multi-transformation TOFMS, the flight length can be greatly extended without enlarging the device, and high mass resolution can be achieved while being small in size.

[0006] On the other hand, as an ion trap, in addition to the three-dimensional quadrupole ion trap disclosed in Patent Document 1 comprising one annular electrode and two pairs of end caps, there is also known a linear ion trap comprising four rod-shaped electrodes arranged parallel to the central axis in a manner surrounding the central axis, and a pair of end cap electrodes arranged in a manner clamping these rod-shaped electrodes.

[0007] For example, the ion trap device disclosed in Patent Document 6 has the following structure: cooling gas is introduced into the interior of a linear ion trap composed of a plurality of electrodes divided along the axial direction, ions are efficiently captured inside the ion trap, and the ions whose energy has been sufficiently reduced by cooling are ejected toward a time-of-flight mass separator.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: International Publication No. 2008 / 072377

[0011] Patent Document 2: U.S. Patent No. 9281175

[0012] Patent Document 3: U.S. Patent No. 6570152

[0013] Patent Document 4: International Publication No. 2010 / 049972

[0014] Patent Document 5: International Publication No. 2013 / 057505

[0015] Patent Document 6: U.S. Patent No. 10600631 Summary of the invention

[0016] Technical problem to be solved by the invention

[0017] As described above, in a mass spectrometer using a time-of-flight mass separator, although extending the flight distance of ions can improve mass resolution, on the other hand, there is a problem that the longer the flight distance is, the more the loss of ions in flight increases, and the amount of ions reaching the detector decreases, which reduces the detection sensitivity. One reason for the loss of ions in flight can be considered to be the ion escape caused by the collision with the gas remaining in the flight path. In order to suppress this situation as much as possible, the interior of the chamber equipped with the time-of-flight mass separator is usually maintained at a high vacuum.

[0018] In recent years, mass spectrometry has been frequently used to detect trace amounts of compounds contained in samples such as biological samples, and there is a strong demand for improved detector sensitivity. In addition, in MS, which uses methods such as collision-induced dissociation (CID) to dissociate and analyze ions from samples, n In the case of mass analysis, the amount of ions to be analyzed is often significantly less than the amount of the original compound, so higher detection sensitivity is required. Therefore, in TOFMS, more emphasis is placed than ever before on improving detection sensitivity by reducing the loss of ions to be analyzed.

[0019] The present invention is completed to solve such technical problems, and its purpose is to provide a mass analysis method and a mass analysis device that can reduce the loss of ions in the path from ions accelerated by an ion acceleration unit to ions reaching a detector, thereby improving detection sensitivity.

[0020] Solutions for solving the above technical problems

[0021] One scheme of the mass spectrometry method of the present invention completed in order to solve the above-mentioned technical problems is a mass spectrometry method, in which ions to be analyzed are exposed to a cooling gas for cooling, kinetic energy is given to the ions, and the ions are introduced into a flight space for separation according to mass-to-charge ratio for mass analysis. In this mass spectrometry method,

[0022] When the known or estimated valence of the ions to be analyzed is high, the amount of cooling gas supplied to the cooling unit that cools the ions is reduced compared to when the valence is low.

[0023] Furthermore, one aspect of the mass spectrometer of the present invention completed in order to solve the above-mentioned problems comprises:

[0024] A cooling unit that cools ions to be analyzed by contacting them with a cooling gas;

[0025] An ion acceleration section that imparts kinetic energy to the cooled ions;

[0026] A time-of-flight mass separation section for separating ions according to mass-to-charge ratio, comprising a flight space for introducing ions given kinetic energy in the ion acceleration section;

[0027] A detection unit that detects the ions separated in the time-of-flight mass separation unit;

[0028] The supply amount adjusting unit adjusts the supply amount of the cooling gas supplied to the cooling unit, and changes the supply amount according to the known or estimated valence of the ion to be analyzed.

[0029] In an ion trap time-of-flight mass spectrometer, generally speaking, when ions are temporarily captured in an ion trap as described above, cooling (Cooling) using a cooling gas (generally an inert gas such as Ar, He, N2, etc.) is performed. In addition, in a time-of-flight mass spectrometer that does not use an orthogonal acceleration method using an ion trap, there are also cases where cooling is performed in order to suppress the speed of ions incident on the orthogonal acceleration section or to facilitate the ion convergence near the axis. For example, in an ion trap time-of-flight mass spectrometer, by using cooling to reduce the kinetic energy of the ions, the ions become easier to gather near the center of the ion trap, thereby reducing the deviation of the ion position, the deviation of the velocity, the deviation of the emission angle (direction), etc. caused by acceleration when the ions are ejected, thereby improving the mass accuracy or mass resolution.

[0030] However, part of the cooling gas supplied to the cooling part of the ion trap or the like may flow into the ion introduction path or the flight space until the ejected ions enter the flight space, and may collide with the ions as residual gas, thus becoming a cause of ion loss. The larger the collision cross-sectional area of ​​the ion, the higher the possibility of the ion colliding with the residual gas. Therefore, the inventors have conducted various discussions on the collision cross-sectional area of ​​the ions and found that the valence of the ions and the collision cross-sectional area are highly correlated, especially in polymer compounds. Based on this understanding, it can be inferred that the collision cross-sectional area of ​​ions with high valence is larger than that of ions with low valence, and therefore the possibility of collision with residual gas is relatively high, and the loss of ions is also increased.

[0031] Therefore, in one embodiment of the mass spectrometry method and mass spectrometry device of the present invention, when the valence of the ion to be analyzed is known in advance or estimated, the cooling gas supply amount is changed according to its valence. Specifically, compared with the case where the valence of the ion to be analyzed is low, the cooling gas supply amount is reduced when the valence of the ion to be analyzed is high or estimated to be high. As a result, the amount of gas flowing from the cooling unit into the above-mentioned ion introduction path or flight space is reduced, and the amount of residual gas in the path of these ions can be reduced. As a result, high-valence ions with a large collision cross-sectional area also become difficult to collide with residual gas, which can reduce ion loss caused by collision.

[0032] Effects of the Invention

[0033] According to one aspect of the mass spectrometry method and mass spectrometry device of the present invention, it is particularly possible to reduce the loss of ions with large molecular weight and high valence, which are easily lost due to collision with residual gas due to their large collision cross-sectional area. Thus, the detection sensitivity of ions with large molecular weight and high valence can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic block diagram of MT-TOFMS which is one embodiment of the mass spectrometer of the present invention.

[0035] Figure 2 It is a longitudinal cross-sectional view (A) and a top view (B) of the MT type mass separation section in the MT-TOFMS of this embodiment.

[0036] Figure 3 It is shown Figure 2 A top view of the trajectories of ions in an MT-type mass separation section is shown.

[0037] Figure 4 This is a basic block diagram of the mass spectrometer of the present invention.

[0038] Figure 5 This is a diagram showing the relationship between the valence of ions and the collision cross-sectional area.

[0039] Figure 6 It is a diagram showing the measurement sequence when the measurement is repeated. DETAILED DESCRIPTION

[0040] [Principle of the mass analysis method of the present invention]

[0041] First, the causes of the technical problems to be solved by the present invention and the principles of the analytical method thereof are explained.

[0042] Figure 4 This is a very schematic diagram of the structure of a general mass spectrometer. Figure 4 (A) is a device equipped with an ion trap such as an ion trap TOFMS. Figure 4 (B) is a device that does not have an ion trap, such as an orthogonal acceleration TOFMS.

[0043] exist Figure 4In (A), the ion source 1 ionizes the compound contained in the sample. The various ions generated are introduced into the ion trap 2 composed of multiple electrodes and temporarily captured. At this time, a cooling gas such as He is supplied to the inside of the ion trap 2, and the kinetic energy of the ions is weakened by causing the ions to collide with the gas. That is, the ions are cooled. After that, a predetermined voltage is applied to the electrodes constituting the ion trap 2, so that the captured ions are given kinetic energy at the same time, and the ions are ejected from the ion trap 2 and sent to the time-of-flight mass separator (TOF unit) 3. During the flight of the ions in the flight space of the TOF unit 3, they are separated according to different mass-to-charge ratios, and the ion detection unit 4 detects the separated ions in turn and outputs a detection signal of an intensity corresponding to the amount of ions. The flight time of the ions in the flight space of the TOF unit 3 depends on the mass-to-charge ratio of the ions. Thus, the mass spectrum showing the relationship between the mass-to-charge ratio and the signal intensity can be obtained based on the flight time spectrum showing the relationship between the time and the signal intensity obtained by the ion detection unit 4.

[0044] exist Figure 4 In the device shown in (A), cooling operation and ion acceleration operation are performed in the ion trap 2. On the other hand, Figure 4 In the device shown in (B), the ion cooling unit 2A and the ion accelerating unit 2B are separated. The ions introduced into the ion cooling unit 2A move while contacting the cooling gas and reducing the kinetic energy, and are introduced into the ion accelerating unit 2B while being accumulated to a certain extent. The ion accelerating unit 2B accelerates the introduced ions together and sends them to the TOF unit 3 in a packet shape.

[0045] exist Figure 4 (A) Figure 4 In any of the configurations of (B), the TOF unit 3 is usually arranged in a chamber that maintains a particularly high vacuum degree. However, since it is not completely separated from the ion trap 2 or ion cooling unit 2A of the preceding stage, a portion of the cooling gas flows into the flight space of the TOF unit 3. In addition, even if it does not flow into the flight space, a portion of the cooling gas will exist in the ion introduction path from the ion acceleration position in the ion trap 2 or the ion acceleration unit 2B to the incident position into the flight space. If ions come into contact with residual gas originating from such cooling gas, they will escape and cause ion loss. Although it is also possible to consider reducing the supply amount of the cooling gas itself in order to reduce the residual gas, this may reduce the cooling effect, and the improvement effect of the mass accuracy or mass resolution brought about by the cooling will be weakened.

[0046] Therefore, the inventors focused on the collision cross-sectional area of ​​ions, because both the cooling effect of ions and the ion loss caused by contact with residual gas depend on the contact between ions and gas, and the probability of this contact should depend on the collision cross-sectional area of ​​ions.

[0047] The present inventors have derived the relationship between the valence of ions and the collision cross-sectional area for various polymer compounds based on various literature values. Figure 5 The following is a graph summarizing the results. Figure 5 In the figure, BSA is bovine serum albumin, MAB is monoclonal antibody, and AT2 is angiotensin II. In addition, CID in the brackets means Collision-Induced Dissociation, DT means Drift Tube, and Twave means Traveling wave, which are the values ​​of CID, flying in a constant electric field, and moving in a traveling wave tube, respectively.

[0048] Figure 5 Among the compounds described, the more the right side of the compound has a larger molecular weight, and the larger the molecular weight, the higher the valence. In addition, even for the same compound, there is a tendency that the higher the valence, the larger the collision cross-sectional area. This can be inferred that the higher the valence, the more the ions diffuse due to the electrostatic repulsion of the ions themselves, and the larger the size.

[0049] Compared with ions with smaller collision cross-sectional areas, ions with larger collision cross-sectional areas have a higher probability of contacting with cooling gas, so the cooling effect is relatively high, but on the other hand, they are also prone to contact with residual gas, so they are easily dissipated during flight and are prone to reduced sensitivity. In previous mass spectrometers, the reduction in detection sensitivity caused by cooling gas was not taken into account, and of course, no improvement plan for this problem was tried. In contrast, in the mass spectrometry method and mass spectrometer of the present invention, the correlation between the valence of ions and the collision cross-sectional area is used to reduce the supply of cooling gas when analyzing ions with high valence compared to ions with low valence, thereby suppressing the amount of cooling gas flowing into the ion introduction path or flight space. As a result, the collision frequency between ions generated during the period from the time when ions are ejected from the ion trap 2 or the ion acceleration unit 2B to the time when they enter the flight space, and during the flight of the TOF unit 3, and the residual gas from the cooling gas is reduced, thereby suppressing the loss of ions.

[0050] On the other hand, since the collision cross-sectional area of ​​ions is large, even if the supply of cooling gas is reduced, the contact opportunity between ions and cooling gas in the ion trap 2 or the ion cooling unit 2A will not be reduced accordingly, and a sufficient cooling effect can be obtained. Of course, in order to more reliably maintain the cooling effect even when the supply of cooling gas is reduced, the cooling time can be extended compared to the case where the supply of cooling gas is large.

[0051] In addition, as described above, the cooling gas supply amount is changed according to the valence of the ion of the analysis object, and the valence of the ion of the analysis object needs to be known in advance or can be estimated. In addition, the ions of the analysis object can be multiple, but whether the type of compound is one or multiple, the valence of the multiple ions is required to be similar (i.e., high-valence ions and low-valence ions are not mixed). Therefore, it is difficult to apply the method of the present invention when analyzing completely unknown compounds. In the case where the compound contained in the sample is unknown, or the type of the compound is known but the valence cannot be estimated, the valence of the ion as the analysis object can be investigated or estimated by performing a preliminary mass analysis in advance.

[0052] Of course, even if the valence of the ion to be analyzed is unknown, it is possible to perform the analysis by assuming that the valence is high and relatively reducing the cooling gas supply, and then perform the analysis by assuming that the valence is low and relatively increasing the cooling gas supply. In this way, the same ion type can be analyzed multiple times under different cooling gas supply amounts and their results can be compared.

[0053] [Configuration and Operation of MT-TOFMS According to One Embodiment]

[0054] Next, one embodiment of the mass spectrometer of the present invention will be described with reference to the drawings.

[0055] Figure 1 This is a schematic diagram of the configuration of a multi-transformation TOFMS (hereinafter referred to as "MT-TOFMS") according to the present embodiment. Figure 2 It is a longitudinal cross-sectional view (A) and a top view (B) of the MT type mass separation section in the MT-TOFMS of this embodiment. Figure 3 It is shown Figure 2 A top view of the trajectories of ions in an MT-type mass separation section is shown.

[0056] The MT-TOFMS of this embodiment includes an ion source 1, an ion trap 2, a TOF unit 3, an ion detection unit 4, a voltage generating unit 5, a control unit 6, a gas supply unit 7, a flow rate adjustment unit 8, and an input unit 9. Although the ion trap 2, the TOF unit 3, and the ion detection unit 4 are not shown in the figure, they are arranged in a chamber that is evacuated by a vacuum pump. In addition, depending on the type of ionization method, the ion source 1 may be arranged in a vacuum-evacuated chamber or in an ionization chamber at approximately atmospheric pressure.

[0057] The ion trap 2 is a linear ion trap, and includes four main electrodes 21, 22, 23, and 24 arranged rotationally symmetrically around a linear ion optical axis 20, and end cap electrodes 25 and 26 arranged at both ends of the main electrodes 21 to 24 in a manner of sandwiching the main electrodes 21 to 24. Here, like the main electrodes 21 to 24, the end cap electrodes 25 and 26 are also four electrodes arranged rotationally symmetrically around the ion optical axis 20. That is, the main electrodes 21 to 24 and the end cap electrodes 25 and 26 are formed by dividing four rod-shaped electrodes extending in the same direction as the ion optical axis 20 in the axial direction.

[0058] The TOF unit 3 includes a main electrode 31 having an outer electrode 311 in the shape of a rotational ellipsoid and an inner electrode 312 in the shape of a substantially rotational ellipsoid provided inside the outer electrode 311 . Figure 2 (A) is an end view (longitudinal end view) of the main electrode 31 in the ZX plane, which is a plane including the Z axis as the rotation axis in the approximate rotating ellipsoid of the outer electrode 311 and the inner electrode 312, and the X axis as an axis in a direction perpendicular to the Z axis. When the main electrode 31 is cut on a plane including the Z axis, it does not depend on the azimuth angle (angle around the Z axis) of the cross section, and presents Figure 2 The shape is roughly the same as shown in (A). Figure 2 (B) is a plan view of the main electrode 31 as viewed from the positive direction of the Z axis. An axis perpendicular to the Z axis and the X axis is referred to as the Y axis, and a plane including the X axis and the Y axis is referred to as the XY plane.

[0059] The outer electrode 311 and the inner electrode 312 are composed of the following electrode pairs: that is, three groups of partial electrode pairs S1, S2 and S3 that are curved electrodes facing each other in the ZX plane, and four groups of partial electrode pairs L1, L2, L3 and L4 that are straight electrodes facing each other in the ZX plane. The partial electrode pair S2 is arranged at both ends of the main electrode 21 in the X-axis direction in the ZX plane, and has a shape that is linearly symmetrical with respect to the X-axis. The partial electrode pair S1 is arranged on the positive side of the Z-axis direction that is closer to the partial electrode pair S2. The partial electrode pair S3 is arranged on the negative side of the Z-axis direction that is closer to the partial electrode pair S2 so as to be linearly symmetrical with the partial electrode pair S1 with respect to the X-axis. The partial electrode pair L2 is arranged between the partial electrode pairs S1 and S2. The partial electrode pair L3 is arranged between the partial electrode pairs S2 and S3, and has a shape that is linearly symmetrical with the partial electrode pair L2 with respect to the X-axis. The partial electrode pair L1 has an annular plate shape perpendicular to the Z axis and is arranged on the positive side of the Z axis direction and inside the partial electrode pair S1 in the XY plane. The partial electrode pair L4 is arranged on the negative side of the Z axis direction and is line symmetrical with the partial electrode pair L1 with respect to the X axis.

[0060] By the combination of these multiple partial electrode pairs, the outer electrode 311 and the inner electrode 312 present the shape of an approximate rotating ellipsoid as a whole. The size of the outer shape of the outer electrode 311 is, for example, 500mm in the major axis direction (X-axis direction and Y-axis direction) and 300mm in the minor axis direction (Z-axis direction). In addition, the interval between the outer electrode 311 and the inner electrode 312 is, for example, 20mm. By reducing the size of the outer electrode 311 and the inner electrode 312 as a whole, the MT-TOFMS can be miniaturized as a whole. Of course, these sizes are only an example and are not limited to this.

[0061] A voltage that can form an electric field from the outer electrode 311 toward the inner electrode 312 is applied from the voltage generating unit 5 to the curved partial electrode pairs S1, S2, and S3 in the ZX plane. On the other hand, a voltage that can make the outer electrode 311 and the inner electrode 312 have the same potential is applied from the voltage generating unit 5 to the linear partial electrode pairs L1, L2, L3, and L4 in the ZX plane. As a result, a surrounding electric field that causes ions to surround in the space between the outer electrode 311 and the inner electrode 312 is formed. Here, this space is referred to as a surrounding space 319.

[0062] An ion introduction port 34 for introducing ions ejected from the ion trap 2 into the surrounding space 319 is provided on the outer electrode 311 of the partial electrode pair S1. The ion introduction port 34 is provided at a position slightly biased toward the positive side of the Y-axis direction relative to the XY plane, so as to be configured so that the ions are incident from the ion trap 2 approximately parallel to the X-axis. The ions are subjected to the centripetal force from the surrounding electric field generated by the partial electrode pair S1 at the position just after they are incident into the surrounding space 319 from the ion introduction port 34. In addition, as described above, since the ion introduction port 34 is biased toward the positive side of the Y-axis direction relative to the XY plane, the ions are subjected to a force in the direction of the XY plane. As a result, the ions orbit in the surrounding space 319 along an approximately elliptical orbit, and fly in an orbit 318 that moves in a counterclockwise direction when the orbit is observed from the positive side of the Y-axis direction for each revolution (refer to Figure 3 ).exist Figure 3 , the trajectory 318 of the ions is shown by a top view of the XY plane.

[0063] On the other hand, the outer electrode 311 of the partial electrode pair S3 is provided with an ion outlet 35 for extracting ions from the surrounding space 319 after circling multiple times (tens of times) in the surrounding space 319. The ions extracted from the ion outlet 35 fly in a linear track. The ion detection unit 4 is arranged on the linear track.

[0064] With the above configuration, ions with various mass-to-charge ratios ejected from the ion trap 2 fly in the surrounding space 319 within the main electrode 31. During the flight, the ions are spatially separated according to their mass-to-charge ratios and arrive at the detection unit 4 with time differences. In the TOF unit 3, since the trajectory 318 of the ion is determined independently of the mass-to-charge ratio of the ion, the flight distance is the same for all ions. Figure 3 As shown, since the orbit of the ions deviates slightly every time, the problem of ion overtaking that would otherwise occur if the ions were orbiting the same orbit can be avoided.

[0065] An example of a typical measurement operation in the MT-TOFMS of this embodiment will be described.

[0066] The ion source 1 ionizes the compounds contained in the introduced sample. The generated ions are introduced into the internal space of the ion trap 2 through the ion entrance opening 251. At this time, under the control of the control unit 6, the voltage generating unit 5 applies a specified high-frequency voltage to each of the four main electrodes 21 to 24, and applies a specified DC voltage to each of the end cap electrodes 25 and 26. The electric field thus formed is used to capture the ions into the internal space of the ion trap 2. In addition, the flow adjustment unit 8 supplies the cooling gas (for example, He) supplied by the supply unit 7 to the ion trap 2 at a specified flow rate. The ions introduced into the internal space of the ion trap 2 come into contact with the cooling gas, thereby reducing the kinetic energy of the ions. Therefore, the ions become easier to be captured by the high-frequency electric field and also easier to converge near the ion optical axis 20.

[0067] After the ion cooling is performed for a predetermined time so that the ions are sufficiently focused near the ion optical axis 20, a predetermined ejection voltage is applied from the voltage generating unit 5 to the main electrodes 21 to 24. As a result, the ions are given kinetic energy in a direction perpendicular to the ion optical axis 20, that is, accelerated, and ejected from the ion trap 2 at once through the ejection port 211 formed in the main electrode 21. The ejected ions are introduced into the surrounding space 319 of the TOF unit 3 through the ion introduction path and the ion introduction port 34.

[0068] As described above, the ions orbiting and flying in the surrounding space 319 are taken out of the surrounding space 319 through the ion outlet 35 and incident on the ion detection unit 4. Since each ion has a speed depending on its mass-to-charge ratio when ejected from the ion trap 2, ion species with different mass-to-charge ratios are separated during the flight in the surrounding space 319 and are incident on the ion detection unit 4 with a time difference. The ion detection unit 4 outputs a detection signal corresponding to the amount of the incident ions. Figure 1 Although not described in the literature, the detection signal of the ion detection unit 4 is input to the data processing unit, which converts the flight time starting from the ion emission time point into a mass-to-charge ratio and generates a mass spectrum showing the relationship between the mass-to-charge ratio and the ion intensity.

[0069] Alternatively, a collision cell may be provided between the ion source 1 and the ion trap 2 for dissociating ions using other mass separators such as a quadrupole mass spectrometer filter and methods such as CID, and product ions generated by dissociating precursor ions having a specific mass-to-charge ratio may be introduced into the ion trap 2 for mass analysis as described above. Furthermore, after ions are captured in the internal space of the ion trap 2, the mass separation function of the ion trap 2 may be used to select specific precursor ions, and mass analysis may be performed on the product ions generated by dissociating the precursor ions using methods such as CID. In this way, MS / MS analysis or MS n analyze.

[0070] The shape of the track in the TOF unit 3 or the configuration and structure of the electrodes forming the TOF unit 3 are not limited to Figure 1 as well as Figure 2 The present invention can also adopt various well-known structures and configurations.

[0071] exist Figure 1 The MT-TOFMS shown is connected to a liquid chromatograph (LC) at the front stage, and when a sample containing various compounds separated in the chromatographic column of the liquid chromatograph is introduced into the ion source 1 for mass analysis, or when the introduced sample is mass analyzed by flow injection analysis without using a chromatographic column, it is necessary to repeatedly measure the sample continuously introduced into the ion source 1 in the MT-TOFMS. Figure 6 : is a diagram showing the measurement procedure in this case.

[0072] exist Figure 6 In (A), ions are introduced into the ion trap 2 during the "accumulation" period, and the newly introduced ions are cooled during the next "cooling" period. The ions are ejected from the ion trap 2 during the extremely short "ejection" period, and the ions are made to fly in the surround space 319 of the TOF unit 3 and detected during the "surrounding and detecting" period. While the ions introduced into the ion trap 2 are being cooled, further introduction of ions is prohibited, and immediately after the cooled ions are ejected from the ion trap 2, the ions of the next analysis object are introduced into the ion trap 2 and accumulated. Figure 6 In the example of (A), the “cooling” time in the ion trap 2 is t1.

[0073] In the MT-TOFMS of this embodiment, the control unit 6 controls the operation of the flow rate adjustment unit 8 based on the user's instructions provided by the input unit 9 or automatic judgment according to the built-in program, thereby appropriately adjusting the flow rate of the cooling gas supplied to the ion trap 2 .

[0074] As an example, when the user knows the molecular weight of the compound to be analyzed or the valence of the ion as a priori information in advance, or when such information can be estimated by the method described later, the user inputs the molecular weight or valence information from the input unit 9. The control unit 6 uses the input molecular weight and valence information, or only the valence information, to determine whether the collision cross-sectional area of ​​the ion estimated thereby is above a predetermined threshold value, and selects the "high sensitivity mode" when the collision cross-sectional area of ​​the ion is above the predetermined threshold value, and selects the "high resolution mode" when it is not above the predetermined threshold value. Compared with the "high resolution mode", the supply amount of cooling gas is reduced in the "high sensitivity mode". That is, when the ion of the analysis object is of high valence and has a large collision cross-sectional area, the supply amount of cooling gas is reduced to suppress the amount of gas flowing into the TOF unit 3. As a result, as described above, the ions ejected from the ion trap 2 become difficult to contact the residual gas when passing through the ion introduction path or orbiting the orbit, and the loss of ions can be suppressed, thereby improving the detection sensitivity.

[0075] In addition, the "high sensitivity mode" suitable for the analysis of high molecular weight, high valence ions and the "high resolution mode" suitable for the analysis of other general compound ions can be selected in advance by operating the input unit 9, and the user can select any mode. Of course, the name of the mode is not limited to this, as long as any one of the multiple modes with different cooling gas supply amounts can be selected.

[0076] In the absence of prior information on the molecular weight of the compound to be analyzed or the valence of the ion, a preliminary measurement is performed using the present device or another mass spectrometer to obtain a mass spectrum in which a peak of the ion to be analyzed is observed. Figure 5 In the compound mainly derived from organisms as shown in FIG. , not only a monoisotopic peak (monoisotopic peak) but also multiple isotopic peaks are observed, and the interval between the monoisotopic peak and the isotopic peak and the interval between the isotopic peaks depend on the valence of the ion. Therefore, the valence of the ion can be roughly estimated from the peak interval in an isotopic peak group. In addition, the molecular weight can be roughly estimated based on the mass-to-charge ratio of the monoisotopic peak and the valence of the ion.

[0077] In addition, the cooling gas supply amount may not be adjusted based on the user's instructions or settings, but after performing a preliminary measurement as described above to estimate the molecular weight and valence of the compound to be analyzed, the present measurement may be performed in a state where the cooling gas supply amount is adjusted based on the result. Alternatively, the cooling gas supply amount may be changed in two stages for the same compound and two measurements may be performed separately. In this case, since two mass spectra can be obtained for the same compound, the two mass spectra can be displayed (output), or the two mass spectra can be merged to generate one mass spectrum. When merging, it is sufficient to select either side of the corresponding peaks in the two mass spectra based on a prescribed reference.

[0078] Even when the cooling gas supply is reduced due to the high valence of the ions as described above, a sufficient cooling effect can be obtained in the ion trap 2 due to the relatively large collision cross-sectional area of ​​the ions. However, in order to obtain a more reliable cooling effect, the cooling time can be extended when the cooling gas supply is small compared to when the supply is large.

[0079] Generally speaking, compared to low-valence ions with a valence of about 20 or less, high-valence ions with a valence of more than 20 to 30 have a significantly larger molecular weight. Therefore, ions with a higher valence also have a relatively larger mass-to-charge ratio. Such high-molecular-weight, high-valence ions have a slow flight speed and a long flight time when flying the same flight distance. Therefore, in the case of repeated measurements, such as Figure 6 As shown in (B), compared with low molecular weight, low valence ions, the "surrounding and detecting" period needs to be extended. Since the "surrounding and detecting" period is extended as described above, the extended period can be allocated to the cooling time to extend the cooling time (in Figure 6 In the example t1→t2=t1+Δt).

[0080] As described above, in the MT-TOFMS of this embodiment, when the collision cross-sectional area of ​​the ions to be analyzed is large, the supply amount of cooling gas is relatively reduced, thereby ensuring the cooling effect while suppressing the amount of gas flowing into the TOF unit 3 side. As a result, it is not necessary to increase the performance of the vacuum pump that performs vacuum exhaust in the chamber in which the TOF unit 3 is configured to be high vacuum, thereby reducing the loss of ions caused by collision with residual gas. As a result, it is possible to reduce the cost of the vacuum pump and use a smaller and lighter vacuum pump.

[0081] In addition, in the MT-TOFMS of the above-mentioned embodiment, the cooling gas is directly introduced into the internal space of the ion trap 2, but, for example, it is also possible to configure the cooling gas to be introduced into a chamber in which the ion trap 2 is arranged or into a space inside a pool surrounding the ion trap and outside the ion trap. Of course, it is also possible to configure the cooling gas to be introduced into both the interior of the ion trap and the space outside the ion trap, so that the supply amount of either or both sides can be adjusted.

[0082] Furthermore, by adjusting the supply amount of the cooling gas as described above, not only can the leakage of the cooling gas from the cooling part such as the ion trap 2 to the TOF part 3 etc. be suppressed as much as possible, but other countermeasures can also be used in combination, which is effective for increasing the vacuum degree in the chamber equipped with the TOF part 3 (or other time-of-flight mass separator).

[0083] Specifically, for example, the following measures can be used in combination.

[0084] (1) A turbomolecular pump is provided to evacuate the chamber in which the TOF unit 3 is arranged. In addition, when the chamber is evacuated by a plurality of turbomolecular pumps, a turbomolecular pump is provided in the main electrode 31 forming the surrounding space 319 in the TOF unit 3 so that the main electrode 31 is evacuated from the outside of the electrode having a relatively large surface area (in the vicinity of the main electrode 31). Figure 1 In the example, the upper and lower parts are vacuum-exhausted. This is because it is easy to release the gas from the surface of the metal main electrode 31. As a result, the vacuum degree in the chamber can be improved, and the loss of ions can be further reduced.

[0085] (2) The ion trap 2 or ion acceleration unit 2B for emitting ions, the ion optical system for focusing the emitted ions, and the TOF unit 3 are housed in different chambers respectively, and the conductivity of the ion passage between adjacent chambers is reduced. Then, multi-stage differential exhaust is performed by vacuum exhausting each chamber with an independent vacuum pump. As a result, the cooling gas used in the ion trap or ion cooling unit is difficult to leak into the subsequent ion optical system or TOF unit 3, which can improve the vacuum degree in the ion optical system or TOF unit 3 and further reduce the loss of ions.

[0086] (3) Not only the electrodes included in the TOF unit 3 can become the emission source of gas, but all the various components arranged in the chamber or the components of the chamber itself can become the emission source of gas. In particular, electronic parts such as resistors or cables provided to supply power to the electrodes included in the TOF unit 3 generate heat when energized and become the main source of gas emission. Therefore, such electronic parts or wiring parts, electrodes, insulators, etc. can be baked in advance in an oven or the like during the manufacturing process of the device to reduce the emission of gas in advance. In addition, the entire units can be baked after assembly instead of before assembly. Furthermore, the emission of gas itself can be reduced by electrolytic grinding, chemical grinding, or Ni plating on the surface of such electrodes or the inner surface of the chamber.

[0087] In addition, when baking is performed after assembly, it is necessary to discharge the gas released from the electrode or insulator smoothly to the outside and prevent re-adsorption. Therefore, for example, a degassing opening can be provided at an appropriate position of the main electrode so that the gas released from the inside of the main electrode can be discharged smoothly and quickly. Among them, the opening can be set as a mesh structure so that the degassing opening does not affect the electric field for making the ions fly. In addition, especially when a notch is formed on the electrode in a large range, the notch portion can be set as a double mesh structure to reduce the disorder of the electric field.

[0088] In addition, when the above-mentioned baking is performed, the electrodes constituting the TOF unit 3 expand thermally. Therefore, in the case where a plurality of positioning pins are provided to prevent damage or deformation of the electrode or the insulator, the position of one of the positioning pins can be completely fixed, and the other positioning pins can slide along the long hole to absorb the position deviation caused by the thermal expansion. In this case, the size of the long hole can be determined based on the thermal expansion coefficient of the material used for the electrode and the temperature at which the baking is performed.

[0089] In addition, as described above, in the MT-TOFMS of the above embodiment, the flight distance is the same for all ions, but the longer the flight distance, the greater the chance of collision with residual gas. Therefore, an auxiliary detector that can detect ions can be set in the middle of the orbit, and a mode in which the auxiliary detector detects ions can be selected for ions that require high sensitivity. Thus, since the flight distance of the ions to be analyzed can be shortened, the probability of collision with residual gas can be reduced, suppressing the loss of ions. For ions that attach more importance to mass resolution than sensitivity, it is sufficient to extend the flight distance and use the original ion detection unit for detection.

[0090] Furthermore, even if the components are baked in the manufacturing process of the device as described above, there is also the possibility of gas or moisture adsorption on the surface by exposing those components to the atmosphere when the device is assembled. Thus, the assembly operation of the device, particularly the assembly work of the TOF part 3, can be implemented in a roughly closed space that is separated from the outside by a vinyl sheet, etc. and continuously supplied with nitrogen or dry air, etc. Thus, the adsorption of gas or moisture on the surface of each component of the device can be suppressed, and the generation of useless residual gas can be prevented. In addition, by such a countermeasure, the time until the desired vacuum degree is reached can also be shortened when the device is used.

[0091] In addition, when the vacuum state in the chamber is restored to the atmospheric pressure state after the device is used, pure gas with a moisture content of ppm is introduced into the chamber and the chamber is filled with pure gas instead of introducing the normal atmosphere into the chamber. In this way, it is possible to prevent moisture from adhering to the various components arranged in the chamber again. In addition, by providing a dehumidification pipe in the leakage valve used to introduce pure gas into the chamber, the moisture content in the pure gas can be further reduced, and the adsorption of moisture can be suppressed. In this way, the vacuum degree can be quickly increased to the desired state when vacuum exhaust is performed next, and the residual gas that causes ion loss can be further reduced.

[0092] The above-mentioned embodiment applies the present invention to MT-TOFMS, and it is self-evident that the present invention can also be applied to linear, reflective, or multi-transformation TOFMS. However, the longer the flight distance, the greater the impact of ion loss caused by the collision between ions and residual gas. Therefore, in the case of a short flight distance such as a linear type, the adverse effect of reduced mass accuracy or mass resolution caused by reduced cooling effect may be more obvious than the effect of improved detection sensitivity caused by reduced cooling gas.

[0093] The above-described embodiment and the above-described modified examples are examples of the present invention, and it goes without saying that appropriate modifications, changes, or additions within the scope of the gist of the present invention are also included in the scope of the claims of the present application.

[0094] [Various options]

[0095] Those skilled in the art will appreciate that the above exemplary embodiments are specific examples of the following schemes.

[0096] (Item 1) One aspect of the mass spectrometry method of the present invention is a mass spectrometry method, in which ions to be analyzed are exposed to a cooling gas to be cooled, kinetic energy is imparted to the ions, and the ions are introduced into a flight space for separation based on a mass-to-charge ratio to perform mass analysis. In this mass spectrometry method,

[0097] When the known or estimated valence of the ions to be analyzed is high, the amount of cooling gas supplied to a cooling unit for cooling the ions is reduced compared to when the valence is low.

[0098] If the amount of cooling gas supplied to the cooling unit is reduced, the amount of gas flowing from the cooling unit to the flight space of the subsequent stage or the ion introduction path for guiding ions to the flight space can be reduced accordingly. Therefore, according to the mass spectrometry method described in item 1, the loss of ions with large molecular weight and high valence, which are prone to collision with residual gas due to the large collision cross-sectional area, can be reduced. As a result, the detection sensitivity of ions with large molecular weight and high valence can be improved.

[0099] (Item 5) In addition, one aspect of the mass spectrometer of the present invention is a mass spectrometer for implementing the mass spectrometry method described in Item 1, comprising:

[0100] A cooling unit that cools ions to be analyzed by contacting them with a cooling gas;

[0101] An ion acceleration section that imparts kinetic energy to the cooled ions;

[0102] A time-of-flight mass separation section for separating ions according to mass-to-charge ratio, comprising a flight space for introducing ions given kinetic energy in the ion acceleration section;

[0103] A detection unit that detects the ions separated in the time-of-flight mass separation unit;

[0104] The supply amount adjusting unit adjusts the supply amount of the cooling gas supplied to the cooling unit, and changes the supply amount according to the known or estimated valence of the ion to be analyzed.

[0105] In the mass spectrometer described in item 5, the supply amount of cooling gas can be relatively reduced when analyzing ions with large molecular weight and high valence. In particular, the loss of ions with large molecular weight and high valence, which are easily lost due to collision with residual gas due to their large collision cross-sectional area, can be reduced, thereby improving the detection sensitivity.

[0106] (Item 2) In the mass spectrometry method described in Item 1, the cooling unit is an ion trap that captures and accumulates ions, and can cool the ions in the ion trap and then impart kinetic energy to the ions and eject them.

[0107] Here, the ion trap can be configured to capture ions by the action of an electric field, and can be configured to have, for example, a three-dimensional quadrupole or linear structure.

[0108] According to the mass spectrometry method described in item 2, since the ions in the space confined in the ion trap are cooled by contacting the cooling gas, a high cooling effect can be obtained. In addition, when the supply amount of the cooling gas is reduced, it is easy to adjust the cooling effect such as extending the cooling time.

[0109] (Item 3) In the mass spectrometry method described in Item 1 or Item 2, the flight space can be set as a flight space of a multi-rotation time-of-flight mass separator.

[0110] In the multi-turn type, since the flight distance of ions is long, the chances of ions contacting with residual gas are increased, and the loss of ions caused by contact with residual gas has a greater impact. In this regard, according to the mass analysis method described in item 3, since the amount of cooling gas flowing into the flight space of the multi-turn time-of-flight mass separator can be reduced, the loss of ions can be reduced, and the improvement effect of detection sensitivity can be fully obtained.

[0111] (Item 4) In the mass spectrometry method described in Item 3, a mode can be implemented in which the ions are detected using a detector provided in the middle of an orbit in which the ions orbit in the flight space.

[0112] According to the mass analysis method described in item 4, even when a multi-rotation time-of-flight mass separator is used, the flight distance of the ions to be analyzed can be shortened. Thus, the loss of ions can be suppressed by reducing the probability of collision between ions and residual gas, thereby improving the analytical sensitivity. In addition, when mass resolution is more important than analytical sensitivity, it is not necessary to detect ions in the middle of the track, and the ions can be detected by the original detector after the ions have flown a sufficiently long distance.

[0113] Description of Reference Numerals

[0114] 1 Ion source

[0115] 2 Ion trap

[0116] 20 Ion optical axis

[0117] 21~24 Main electrode

[0118] 211 ejection port

[0119] 25, 26 End cap electrode

[0120] 251 Ion entrance opening

[0121] 2A Ion cooling unit

[0122] 2B Ion Acceleration Unit

[0123] 3 TOF Department

[0124] 31 Main electrode

[0125] 311 Outer electrode

[0126] 312 Medial Electrode

[0127] 318 Track

[0128] 319 Surrounding Space

[0129] 34 Ion introduction port

[0130] 35 Ion export port

[0131] 4 Ion detection unit

[0132] 5 Voltage generating unit

[0133] 6 Control Unit

[0134] 7 Gas supply unit

[0135] 8 Flow adjustment unit

[0136] 9 Input section.

Claims

1. A mass analysis method, wherein ions to be analyzed are cooled by contacting a cooling gas, kinetic energy is imparted to the ions, and the ions are introduced into a flight space for separation according to mass-to-charge ratio to perform mass analysis, wherein: When the known or estimated valence of the ions to be analyzed is high, the amount of cooling gas supplied to the cooling unit for cooling the ions is reduced compared to when the valence of the ions to be analyzed is low.

2. The mass analysis method according to claim 1, characterized in that The cooling unit cools ions to be analyzed by contacting them with a cooling gas, and after cooling the ions in the ion trap, imparts kinetic energy to the ions and ejects them.

3. The mass analysis method according to claim 1 or claim 2, characterized in that: The flight space is the flight space of a multi-rotation time-of-flight mass separator.

4. The mass analysis method according to claim 3, characterized in that: The pattern of the ions is detected by an auxiliary detector disposed in the middle of the orbit of the ions in the flight space.

5. A mass analysis device, characterized in that: have: A cooling unit that cools ions to be analyzed by contacting them with a cooling gas; An ion acceleration section that imparts kinetic energy to the cooled ions; A time-of-flight mass separation section for separating ions according to mass-to-charge ratio, comprising a flight space for introducing ions given kinetic energy in the ion acceleration section; A detection unit that detects the ions separated in the time-of-flight mass separation unit; a supply amount adjusting unit for adjusting a supply amount of cooling gas supplied to the cooling unit; a control unit, controlling the supply amount adjustment unit, The supply amount is changed by the control unit according to the known or estimated valence of the ion to be analyzed.

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