JPWO2008107931A1 - Mass spectrometer - Google Patents

Abstract

The present invention relates to a multi-round time-of-flight or Fourier transform type mass spectrometer. The complete time convergence condition was satisfied for each half-round unit from the point (S, T) to the point (T, S) by the four sets of main electrodes (11a), (12a), (13a), (14a). A circular orbit (C) is formed. Furthermore, electrostatic quadrupole lenses (15) and (16) comprising four rod electrodes are arranged in the final free flight space of the unit. The electric field formed by the electrostatic quadrupole lenses (15) and (16) has a characteristic that the potential distribution in the direction parallel to the plane including the linear ion optical axis is an even function with respect to the ion optical axis. Therefore, by adjusting the polarity and strength of the lens appropriately, the ion transmissivity can be improved by correcting the spatial ion trajectory while maintaining the time convergence of the circular trajectory (C). it can.

Description

  The present invention relates to a mass spectrometer, and more particularly, to a multi-round time-of-flight or Fourier transform type mass spectrometer equipped with an ion optical system for repeatedly flying ions along a closed orbit.

  In general, a time-of-flight mass spectrometer (TOF-MS) measures the time required to fly a certain distance based on the fact that ions accelerated with a constant energy have a flight speed corresponding to the mass. The mass of ions is calculated from the flight time. Therefore, it is particularly effective to increase the flight distance in order to improve the mass resolution. However, when trying to extend the flight distance linearly, it is inevitable that the device will be enlarged, so a mass spectrometer called a multi-turn time-of-flight mass spectrometer has been developed to extend the flight distance. (See, for example, Patent Document 1).

  In such a multi-round time-of-flight mass spectrometer, an eight-shaped closed orbit is formed by using 2 to 4 fan-shaped electric fields, and the ions are repeatedly circulated around the orbit by a number of times. The distance is effectively increased. According to such a configuration, the flight distance is not limited by the apparatus size, and the mass resolution can be improved every time the number of laps is increased.

  In the multi-round time-of-flight mass spectrometer as described above, it is necessary to prevent the sensitivity and resolution from deteriorating because ions having the same mass-to-charge ratio spread temporally and spatially during the round. Therefore, as a condition given to an ion optical system that forms a circular orbit (in the following description, an ion optical system that forms a circular orbit is simply referred to as an ion optical system), it simply has a closed orbit in terms of geometric structure. It is not sufficient, and it is required that the flight time peak width after the lap does not increase and that the ion beam after the lap does not diverge.

  In order to meet such a demand, for example, in the multi-round flight time mass spectrometer described in Patent Document 1, as the time convergence condition, the ion initial position, initial angle at the time when the flight time of the lap after the lap starts, and It is required not to depend on the initial energy, and further, as a spatial characteristic, it is required that the state of the position and angle of ions after circulation is the same as that before rotation. That is, this is a requirement that the complete convergence condition is satisfied so that the positions and directions (angles) of the ions are exactly the same before and after the turn except for the difference in the flight time due to the difference in the mass of the ions. .

  The design of the ion optical system as described above, specifically, the determination of parameters such as the shape and arrangement of the electrodes constituting the ion optical system, or the voltage applied to the electrodes, is subject to the constraints of various conditions including the convergence conditions described above. Below, it is carried out by simulating the flight trajectory of ions when the initial energy, position, angle and other variations are given to the ions incident on the orbit. As a result of such simulation, a procedure is generally adopted in which several candidates of the ion optical system are listed and a designer selects an appropriate one from them.

  However, some of the candidates satisfy the time convergence condition but have insufficient spatial trajectory stability. Conventionally, such an ion optical system cannot be adopted even if other conditions are preferable (for example, the device size is small, the electrode can be easily manufactured, etc.). There was a need to design.

  In addition, even for ion optical systems in which the stability of the orbit is ensured to some extent after satisfying the time convergence condition, the ion transmittance can be improved by further improving the stability of the spatial orbit. There is also a great demand to improve the analysis sensitivity. However, a method for improving only the spatial orbit stability while preserving the time convergence condition has not been known.

  The above-described problem is not limited to the configuration in which ions are circulated a predetermined number of times along the circular orbit, but also the ion non-destructive detector (or in the middle of circulating the ions along the circular orbit) (or A so-called Fourier transform type mass that is configured to calculate the mass-to-charge ratio of the ions by repeatedly detecting the ions with a detector that separates and detecting a part of the ions) and subjecting the detection signal obtained for each round to Fourier transform. The same applies to the analyzer (see, for example, Patent Document 2).

JP-A-11-195398 JP-A-2005-79037

  The present invention has been made in view of the above problems, and its main object is to provide a time-of-flight or Fourier transform-type mass spectrometer having multiple orbits while satisfying the time convergence condition and spatial. Provided is a mass spectrometer capable of ensuring or improving the stability of a spatial orbit without breaking the time convergence condition for an ion optical system in which orbital stability is not ensured or insufficient. That is.

The mass spectrometer according to the present invention, which has been made to solve the above-described problems, causes ions to have a mass-to-charge ratio by repeatedly flying ions along a circular orbit closed by the action of an electric field including a plurality of electric fields. A multi-round time-of-flight or Fourier transform type mass spectrometer that separates according to
a) a plurality of main electrodes each generating a sectoral electric field to fly ions so as to satisfy a time convergence condition in units of one round or 1 / n (n is an integer of 2 or more);
b) An auxiliary electrode arranged in the final free flight space that is not affected by the electric sector in the unit and forming an auxiliary electric field that corrects the spatial trajectory of ions without affecting the time convergence. When,
It is characterized by having.

  The time convergence condition is satisfied when the ion flight time does not depend on the initial position, initial angle, and initial energy of the ion, that is, if the ion mass is the same even if these conditions vary. It is in a state where the flight time is the same.

  The free flight space is a space where ions travel almost straight without being affected by the sectoral electric field to form a circular orbit, and the “final free flight space” in the “unit” is the unit's It refers to the free flight space in front of and close to the end point.

  In the mass spectrometer according to the present invention, an ion orbit is formed by a plurality of main electrodes, and at least the time convergence condition is guaranteed for each unit in the orbit. On the other hand, the spatial convergence condition for each unit is not satisfied, or the theoretical spatial convergence condition is satisfied for the time being, but it is close to the boundary condition for ensuring orbital stability, and factors such as manufacturing variations Considering the above, the track may be unstable. The additional auxiliary electrode acts to achieve or increase the stability of the spatial trajectory by spatially modifying the ion trajectory without breaking the time convergence condition of the periodic trajectory. To do. That is, in the conventional multi-orbit flight time type or Fourier transform type mass spectrometer, ions fly almost linearly in the free flight space in the orbit, but in the mass spectrometer according to the present invention, the free flight space Among them, in the final free flight space, when the ions pass through the auxiliary electric field, the trajectory is corrected by being slightly bent by the influence of the electric field.

In order to improve the orbital stability without breaking the time convergence condition, the auxiliary electrode needs to satisfy the following three conditions.
(1) The ion optical axis is linear.
(2) Only an electric field is generated (no magnetic field is generated).
(3) An electric field in which a potential distribution in a direction parallel to a plane including the ion optical axis is an even function with respect to the ion optical axis is generated.

  Here, as a matter of course, the above-described characteristics may be realized by a set of auxiliary electrodes arranged in one final free flight space. Thus, the above-described characteristics may be realized by a plurality of sets of auxiliary electrodes arranged along the direction of the ion optical axis. In this case, a plurality of sets of auxiliary electrodes arranged in one final free flight space must satisfy the above conditions (1) and (2) for each set, but for each set (3) It is not necessary to satisfy the condition (3) as long as the condition (3) is satisfied by combining the auxiliary electric fields formed by a plurality of sets of auxiliary electrodes.

  As a specific embodiment of the mass spectrometer according to the present invention, the auxiliary electrode may be an electrostatic quadrupole lens. The configuration of a typical electrostatic quadrupole lens is parallel to each other so that four rod electrodes whose inner surfaces are cylindrically curved or hyperboloid are inscribed in a cylindrical peripheral surface centered on a linear ion optical axis. And spaced apart by an angle of 90 ° around the ion optical axis. In addition, a multipole lens having a larger number of rod electrodes can be used.

  According to the mass spectrometer according to the present invention, the stability of the ion's spatial trajectory can be increased by the additional auxiliary electrode, so that the main electrode forming the circular trajectory satisfies the full time convergence condition. The degree of freedom in designing the ion optical system is wider than before. In addition, with respect to an ion optical system that forms a circular orbit in which a certain degree of spatial orbital stability is ensured, the ion orbital stability can be further improved and the ion transmittance can be improved. Analysis sensitivity can be increased. Furthermore, since the high ion permeability means that a sufficient amount of ions can reach the detector even if the number of ions is increased, the mass resolution can be improved.

1 is a schematic top view of an ion optical system of a multi-turn time-of-flight mass spectrometer according to an embodiment of the present invention. The schematic perspective view of the quadrupole lens which is an auxiliary electrode in the multi-turn time-of-flight mass spectrometer of a present Example. The figure which drew the flight trajectory for 1 round of the ion from which an initial position, an initial angle, and initial energy differ by simulation. The figure which shows the simulation result of the relationship between the frequency | count of circulation and ion transmittance. The figure for demonstrating the expression method of an ion orbit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ion optical system 11, 12, 13, 14 ... Main electrode E1, E2, E3, E4 ... Toroidal sector electric field 11a, 12a, 13a, 14a ... Outer electrode 11b, 12b, 13b, 14b ... Inner electrode 15, 16 ... Electrostatic quadrupole lens (auxiliary electrode)
15 a, 15 b, 15 c, 15 d, 16 a, 16 b, 16 c, 16 d... Rod electrode C.

First, an expression method of ion trajectories used in the following description will be described with reference to FIG. Assume that ions are incident from the incident surface, transported by an arbitrary ion optical system including a sector electric field, and emitted from the exit surface. For convenience, the central trajectory of ions is drawn linearly in FIG. The traveling direction of these ions is taken as the Z direction. Further, an ion having specific energy passing through the central trajectory and having a specific mass-to-charge ratio is determined as a reference ion. With respect to position, angle (flight direction) and kinetic energy, the ions that depart from the entrance surface with initial values deviated from the reference ions have spatial deviation and temporal variation with respect to the ions that have traveled the central trajectory on the exit surface. The deviation is expressed by the following first-order approximation expression based on the well-known theory of the ion optical system.
x = (x | x) x ₀ + (x | α) α ₀ + (x | δ) δ (1)
α = (α | x) x ₀ + (α | α) α ₀ + (α | δ) δ (2)
y = (y | y) y ₀ + (y | β) β ₀ (3)
β = (β | y) y ₀ + (β | β) β ₀ (4)
t = (t | x) x ₀ + (t | α) α ₀ + (t | δ) δ (5)

Here, x ₀ and α ₀ are the position in the direction orthogonal to the center orbit (X direction in FIG. 5) and the angle (flight direction) deviation amount in the circular orbit plane on the incident surface. y ₀ and β ₀ are the position in the direction perpendicular to the center orbit in the plane perpendicular to the circular orbit surface on the incident surface and the amount of deviation of the angle with respect to the center orbit. x and α are a position in the direction orthogonal to the center orbit (X direction in FIG. 5) and a displacement amount of an angle with respect to the center orbit in the circular orbit surface on the exit surface. y and β are the position in the direction perpendicular to the center orbit (Y direction in FIG. 5) in the plane perpendicular to the circular orbit surface on the exit surface and the amount of displacement of the angle with respect to the center orbit. δ is an energy shift amount on the incident surface. t represents a deviation (in other words, advance or delay) of a flight distance in a direction parallel to the central trajectory of an arbitrary ion with respect to a reference ion, and corresponds to a deviation in flight time with respect to the reference ion. (X | x), (x | α), (x | δ), (α | x), (α | α), (α | δ), (y | y), (y | β), (Β | y), (β | β), (t | x), (t | α), (t | δ) are coefficients (primary coefficients) determined by elements of the symbols in parentheses in the ion optical system. is there.

The coefficient appearing in the equations (1) to (4) is a spatial aberration coefficient affecting the spatial orbital stability, and the coefficient appearing in the equation (5) is a temporal aberration coefficient affecting the time convergence. In general, it is known that the perfect time convergence condition is given by the following equation for the first-order time aberration coefficient.
(T | x) = (t | α) = (t | δ) = 0 (6)

On the other hand, with regard to the spatial aberration coefficient, it has been clarified by the inventors that the following conditions are effective for the stability of the orbit (Japanese Patent Application No. 2006-197626). reference)
-2 <(x | x) + (α | α) <2 (7)
-2 <(y | y) + (β | β) <2 (8)
| (X | δ) | <1 (9)
| (Α | δ) | <1 (10)

By the way, in the case where ions sequentially pass through a plurality of ion optical elements (usually electrodes that form an electric field), each aberration coefficient after passing through the nth ion optical element is as follows according to the theory of ion optics: Calculated.
(X | x) _n = (x | x) (x | x) _n−1 + (x | α) (α | x) _n−1 (11)
(Α | α) _n = (α | x) (x | α) _n−1 + (α | α) (α | α) _n−1 (12)
(Y | y) _n = (y | y) (y | y) _n−1 + (y | β) (β | y) _n−1 (13)
(Β | β) _n = (β | y) (y | β) _n−1 + (β | β) (β | β) _n−1 (14)
(T | x) _n = (t | x) (x | x) _n−1 + (t | α) (α | x) _n−1 + (t | x) _n−1 (15)
(T | α) _n = (t | x) (x | α) _n−1 + (t | α) (α | α) _n−1 + (t | α) _n−1 (16)
(T | δ) _n = (t | x) (x | δ) _n−1 + (t | α) (α | δ) _n−1 + (t | δ) _n−1 + (t | δ) (17)

  The aberration coefficient to which a subscript index (for example, n−1) is attached in the above formulas (11) to (17) represents an aberration coefficient after sequentially passing through the number of ion optical elements indicated by the index. The index aberration coefficient represents the aberration coefficient of the nth ion optical element alone. Regarding the spatial aberration coefficient, four typical examples are shown in the above equations (11) to (14). For the purpose of correcting the trajectory to increase the spatial trajectory stability, changing the spatial aberration coefficient up to n-1 on the right side of Equations (11) and (12) generally results in Equation (15). The time aberration coefficient in the expression (17) also changes. In other words, in an ion optical system in which complete time convergence is achieved, the time convergence condition is broken if an attempt is made to increase the spatial orbital stability by adjusting the parameters of the ion optical element.

  Therefore, in the mass spectrometer according to the present invention, the trajectory is corrected to a predetermined position along the orbit without changing the basic ion optical system that forms the orbit that satisfies the time convergence condition. By separately adding an ion optical system for this purpose, only the spatial trajectory stability is improved without breaking the original time convergence condition. Next, a multi-turn time-of-flight mass spectrometer that is an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic top view of an ion optical system 1 for making multiple circulations of ions in the mass spectrometer according to the present embodiment. In the ion optical system 1, four main electrodes each having a pair of an outer electrode and an inner electrode are arranged, and an approximately 8-shaped circuit is formed by the action of an electrostatic field formed by a DC voltage applied to the main electrodes. A trajectory C is formed. That is, the first toroidal electric field E1 is between the outer electrode 11a and the inner electrode 11b of the first main electrode 11, and the second toroidal electric field is between the outer electrode 12a and the inner electrode 12b of the second main electrode 12. E2, a third toroidal electric field E3 between the outer electrode 13a and the inner electrode 13b of the third main electrode 13, and a fourth toroidal electric field between the outer electrode 14a and the inner electrode 14b of the fourth main electrode 14. E4 is formed, and when passing through these toroidal sector electric fields E1 to E4, the ions are greatly bent in a circular arc shape, and the ions travel almost straight in a free flight space where the electric field does not reach, so that the circular orbit C as shown in the figure. Is formed. That is, in FIG. 1, the plane parallel to the paper surface is the XZ plane (circular orbit surface in FIG. 5).

  In this orbit C, the midpoint between the exit end face of the fourth main electrode 14 and the entrance end face of the first main electrode 11 is the start point (and end point of one turn) S. The midpoint between the exit end face of the second main electrode 12 and the entrance end face of the third main electrode 13 is a half-circumference start point (and a half-circumference end point) T. Here, the half circle from point S to point T and the half circle from point T to point S are units in which the complete time convergence condition is satisfied. That is, this example is an example in the case of n = 2 in the present invention. Although not shown, an entrance gate electrode and an exit gate electrode are disposed at the position of point S, and ions generated outside are introduced into the orbit C by the entrance gate electrode, and on the other hand, along the orbit C Circulated ions deviate from the orbit C on the exit gate electrode and are guided to an ion detector (not shown). Further, the exit gate electrode may deviate from the orbit C from the point T.

Specifications of the basic ion optical system formed by the main electrodes 11 to 14 excluding the electrostatic quadrupole lens described later are DL1 = 80.2 mm, R = 50 mm, W = 157.35 mm, C = 0. 025, G1 = 10 mm, DL2 = 107.8 mm. DL1 is the distance from the point S to the entrance end face of the first main electrode 11, R is the center orbit radius of the toroidal electric fields E1 to E4, W is the length of the main electrodes 11 to 14 in the direction perpendicular to the plane of FIG. C is the center trajectory radius r _0, and a radius of curvature of the equipotential surfaces in the plane perpendicular to the central orbit was _{R, C = r 0 / R} , in being defined C value, G1 is main electrodes 11 ˜14 of the distance between the outer electrodes 11a to 14a and the inner electrodes 11b to 14b (distance between the ion optical axes), DL2 is the outlet end face of the first main electrode 11 and the inlet end face of the second main electrode 12; This is a half value of the distance between the outlet end face of the third main electrode 13 and the inlet end face of the fourth main electrode 14.

In this basic ion optical system, the aberration coefficient for half a circle (that is, one unit) and the aberration coefficient for one circle (that is, two units) are as shown in the following Tables 1 and 2, respectively.

  Since the half-circumference is an ion optical system that is a unit of complete time convergence, the primary time aberration coefficients (t | x), (t | α), and (t | δ) are zero for both the half-circumference and the one-round. On the other hand, focusing on the spatial aberration coefficient after one round, the sum of (x | x) and (α | α) is −1.97. Although this is within the range of the orbit stabilization condition given by the above equation (7), it is not preferable because it is close to the boundary value (−2). This is because the equation (7) considers only the first-order aberration, so there is a risk that the orbital stability condition may be substantially deviated due to the influence of the second-order or higher-order aberration coefficient. This is because the tolerances such as the dimensional accuracy and the placement accuracy of each component are extremely small, and there is a possibility that sufficient trajectory stability cannot be secured even with a small error.

  Therefore, in the mass spectrometer of the present embodiment, an electrostatic quadrupole lens serving as an auxiliary electrode in the present invention in the free flight space at the final stage of the time convergence unit with respect to the basic ion optical system including the main electrodes 11 to 14. 15 and 16 are inserted. As described above, in the basic ion optical system, the half circumference is a unit for complete time convergence. Therefore, the free flight space of the last stage of the time convergence unit of the half circumference from the point T to the point S is from the exit end face of the fourth main electrode 14 to the point S. Therefore, the electrostatic quadrupole lens 15 is inserted here. Further, the free flight space of the last stage of the time convergence unit of the half circumference from the point S to the point T is from the exit end face of the second main electrode 12 to the point T. Therefore, another electrostatic quadrupole lens 16 is inserted here. In addition, if it is in the free flight space of the last stage, the insertion position of the electrostatic quadrupole lenses 15 and 16 can be suitably shifted along the circular orbit C.

  FIG. 2 is a schematic perspective view of the electrostatic quadrupole lens 15. The other electrostatic quadrupole lens 16 is exactly the same. The electrostatic quadrupole lens 15 includes four cylindrical rod electrodes 15a, 15b, 15c, and 15d arranged in parallel to each other so as to be inscribed in a cylindrical circumferential surface centered on the ion optical axis. The centers of the electrodes 15a and 15c are arranged so as to face each other on the Y axis, and the centers of the rod electrodes 15b and 15d are arranged so as to face each other on the X axis. The same DC voltage is applied to the two rod electrodes (15a and 15c, 15b and 15d) facing each other across the ion optical axis, and the rod electrodes adjacent in the circumferential direction have the same absolute value but only the opposite polarity. DC voltage is applied. The electrostatic quadrupole lens 15 (or 16) is a concave lens or convex lens in the X direction with respect to the ion flow by appropriately determining the polarity of the DC voltage applied to each of the rod electrodes 15a to 15d according to the polarity of ions passing therethrough. Act as either. Further, by adjusting the value of the applied voltage, the lens characteristics (that is, the ion current focusing or diffusing property) change.

Aberration coefficients for a simple free flight space and a case where an electrostatic quadrupole lens is inserted in the free space will be described. Table 3 shows aberration coefficients of the free flight space and the electrostatic quadrupole lens. L in Table 3 is the length in the ion optical axis direction.

  The constant k appearing in the aberration coefficient of the electrostatic quadrupole lens in Table 3 is a constant determined by the intensity of the quadrupole electric field and the like, and can be changed by the voltage applied to the rod electrode. Here, the aberration coefficient of the electrostatic quadrupole lens is expressed using a trigonometric function, but depending on the value of k, a modification such as using a hyperbolic function is required. As is clear from Table 3, the aberration coefficient existing on the right side of Equations (11) and (12) differs between free flight space and electrostatic quadrupole lenses. It can be seen that the right side of equations (11) and (12) can be adjusted by replacing with a multipole lens, and the position and angle of the ion trajectory can be corrected.

  The important thing here is that the spatial aberration coefficient is different between free flight space and electrostatic quadrupole lens, but the temporal aberration coefficient is exactly the same between free space and electrostatic quadrupole lens. is there. It should be further noted that (t | x) and (t | α) are both zero among the temporal aberration coefficients. In this case, from the equations (15) and (16), the free flight space and the electrostatic quadrupole lens do not depend on the spatial aberration coefficient with respect to (t | x) and (t | α), and the ion optical element in the previous stage It can be seen that the time aberration coefficient until is preserved. Similarly, from equation (16), it can be seen that (t | δ) does not depend on the spatial aberration coefficient and is a value obtained by adding its own aberration coefficient to the temporal aberration coefficient up to the previous stage. From these facts, it can be concluded that even if the free flight space is replaced with an electrostatic quadrupole lens having a length equal to the ion optical axis direction, the time aberration coefficient up to that point does not change. On the other hand, between the point where the electrostatic quadrupole lens is inserted and the end point, the spatial aberration coefficient changes unless it is composed of only optical elements in which both (t | x) and (t | α) are zero. Therefore, it can be easily understood that the time aberration coefficient as a whole is not preserved. Therefore, it is important to arrange the electrostatic quadrupole lens in the free flight space at the final stage of the basic ion optical system.

  Specifications relating to the electrostatic quadrupole lenses 15 and 16 in this embodiment are DL3 = 10 mm, QK = −20, QL = 10 mm, and G2 = 10 mm. Here, DL3 is the distance between the exit end faces of the fourth main electrode 14 and the second main electrode 12 and the incident end faces of the electrostatic quadrupole lenses 15 and 16, QK is an index value indicating the strength of the lens, and QL is The length of the electrostatic quadrupole lenses 15 and 16 (rod electrodes) in the ion optical axis direction, and G2 is the distance between the inner surfaces of the electrostatic quadrupole lenses 15 and 16 and the ion optical axis. Here, QK is a negative value, which means that the electrostatic quadrupole lenses 15 and 16 act as concave lenses in the X direction.

Tables 4 and 5 show the aberration coefficient for half a circle (that is, 1 unit) and the aberration coefficient for one circle (that is, 2 units) when the electrostatic quadrupole lens is added to the basic ion optical system.

  It can be seen that the temporal aberration coefficient maintains the same value as when no electrostatic quadrupole lens is inserted, and the state of complete time convergence is preserved. On the other hand, with respect to the spatial aberration coefficient, the sum of (x | x) and (α | α) is −0.532 after a half turn, and −1.717 after a round, both of which are given by equation (7) It can be seen that the margin for the boundary is increased as compared with the case where the above condition is satisfied and the electrostatic quadrupole lens is not inserted. That is, the spatial orbit stability is improved without destroying the time convergence.

  FIG. 3 is a diagram showing the result of simulating the orbital expansion in the X direction for one round (from the point S in FIG. 1 until returning to the point S), (a) is a basic ion optical system, (b ) Shows the result when an electrostatic quadrupole lens is added to the basic ion optical system. When starting from the point S, the trajectory followed by the ions when there is a predetermined amount of X-direction positional deviation, angular deviation, and energy deviation is calculated. As can be seen from FIG. 3A, in the basic ion optical system, the angular deviation and the energy deviation are almost converged after one round, whereas the initial position deviation is further spread after one round. I understand. It can also be seen that the track vibrates greatly during one round. For this reason, when the number of times of ion circulation is increased, the influence of the initial positional deviation expands, for example, disappears in contact with the main electrodes 11 to 14 or diverges without being accepted by the main electrodes 11 to 14. There is a fear.

  On the other hand, when the electrostatic quadrupole lenses 15 and 16 are inserted, since the electrostatic quadrupole lenses 15 and 16 function as concave lenses in the X direction, ions are generated in the next toroidal sector electric field. The incident angle at the time of incidence is corrected. As a result, the vibration of the track in the latter half of the period due to the influence of the initial position shift is suppressed, and the spread (position shift) of the track after one round is also smaller than the initial position shift. For this reason, even if the number of laps is increased, ions are not easily lost or diverged, that is, the stability of the orbit is increased. The lens polarities and lens strengths of the electrostatic quadrupole lenses 15 and 16 are appropriately determined and adjusted according to the state of the orbit by the basic ion optical system so as to suppress the divergence of the orbit as much as possible. Is desirable. As a policy for correcting the trajectory at that time, it is effective to satisfy the equations (7) to (10) and to keep them as far as possible from the boundary conditions. However, depending on the case, it may be possible to perform optimization according to the purpose, such as adjusting the value of a specific aberration coefficient to improve the convergence.

  In addition, in order to verify the effect of inserting an electrostatic quadrupole lens, each of the basic ion optical system and the case where an electrostatic quadrupole lens is added to the basic ion optical system is used. The change of the ion transmittance when the number of times was increased was obtained by simulation. The result is shown in FIG. As is apparent from this, the ion transmittance is improved by about 10% by inserting an electrostatic quadrupole lens. Thereby, the amount of ions finally introduced into the ion detector can be increased, and the analysis sensitivity can be increased. In addition, it was confirmed that there is no difference in the first-order time aberration coefficient between the case of only the basic ion optical system and the case of adding an electrostatic quadrupole lens to the basic ion optical system at all the number of rotations.

  In the above embodiment, an electrostatic quadrupole lens is used as an example of the auxiliary electrode. However, the auxiliary electrode generates only an electric field, its ion optical axis is a straight line, and the potential distribution in the X direction is the ion optical axis. In theory, the temporal aberration coefficients (t | x) and (t | α) are zero. On the other hand, as shown in Table 3, when the length of the free flight space in the ion optical axis direction is L, the time aberration coefficient (t | δ) is not zero, −L / 2. If the time aberration coefficient (t | δ) is not zero, for example, parameters such as the length L can be adjusted as appropriate to match (t | δ) in the free flight space. Therefore, an auxiliary electrode other than the electrostatic quadrupole lens can be used as long as the optical system satisfies such conditions.

  In addition, for example, even when a certain set of auxiliary electrodes cannot form an electric field in which the potential distribution in the X direction is an even function with respect to the ion optical axis, the above-described tandem connection of a plurality of electric fields causes As long as the conditions can be satisfied, the same action and effect can be achieved by arranging a plurality of sets of auxiliary electrodes in one final free flight space. Further, it is not always necessary to insert an auxiliary electrode for each unit for which time convergence is guaranteed. For example, when there are a plurality of units in one circuit, the auxiliary electrode is inserted into one of the units. When it is possible to correct the trajectory for one round, there may be a unit in which the auxiliary electrode is not provided.

  Furthermore, the mass spectrometer according to the present invention can also be applied to a Fourier transform mass spectrometer that provides an ion non-destructive detector in the middle of the orbit C and acquires a detection signal for each revolution.

Claims (3)

A multi-round time-of-flight or Fourier transform type mass spectrometer that separates ions according to their mass-to-charge ratio by repeatedly flying ions along a circular orbit closed by the action of an electric field including a plurality of sector electric fields. And
a) a plurality of main electrode portions each generating a sectoral electric field to fly ions so as to satisfy a time convergence condition in units of one round or 1 / n (n is an integer of 2 or more);
b) An auxiliary electrode arranged in the final free flight space that is not affected by the electric sector in the unit and forming an auxiliary electric field that corrects the spatial trajectory of ions without affecting the time convergence. When,
A mass spectrometer comprising:   The auxiliary electrode forms an electrostatic field in which a potential distribution in a direction parallel to a plane including a linear ion optical axis is an even function with respect to the ion optical axis. Item 2. The mass spectrometer according to Item 1.   The mass spectrometer according to claim 2, wherein the auxiliary electrode is an electrostatic quadrupole lens.

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