Multiple reflection mass analyzer

Abstract

We provide a multiple reflection mass spectrometer. [Solution] The multiple reflection mass spectrometer comprises a pair of opposing ion optical mirrors that extend linearly along a longitudinal axis penetrating the mass spectrometer and are arranged substantially parallel to each other, with one or both ion optical mirrors each comprising a series of spaced electrodes. Each electrode extends along the longitudinal axis. The series of electrodes extends in a direction perpendicular to the longitudinal axis, and the electrodes are spaced apart by a series of gaps. The series of electrodes includes a first pair of adjacent electrodes and a second pair of adjacent electrodes. The first pair of adjacent electrodes is separated by a linear gap defined by the linear edges of each adjacent electrode. The second pair of adjacent electrodes is separated by a curved gap defined by the curved edges of each adjacent electrode.

Description

[Technical Field]

[0001] This invention relates to the field of mass spectrometry, particularly to high-mass-resolution time-of-flight mass spectrometry and electrostatic trapping mass spectrometry utilizing multiple reflection techniques to extend the flight paths of ions. [Background technology]

[0002] Figures 1A and 1B are schematic diagrams of a multiple reflection mass spectrometer with linearly elongated ion optical mirrors along the drift length, illustrating a prior art analyzer such as that described in Patent Document SU1725289. Each ion optical mirror contains a series of electrodes that extend linearly in the direction of the drift length and are separated by small gaps. Ions are injected from an ion source toward opposing ion optical mirrors arranged parallel to each other. The ions enter one mirror, are reflected and return toward the other mirror, where they are reflected again and return to the first mirror, and this process is repeated. In this way, the ions travel in a zigzag path within the mass spectrometer, drifting relatively slowly from the ion source to the ion detector, and finally colliding with the ion detector for detection. Figure 1A shows the ion source and ion detector arranged within a space surrounded by mirrors, but either or both of the ion source and / or ion detector may be located outside the space. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] SU1725289 [Patent Document 2] US9136102

[0004] The ion flight path changes depending on the angle at which a particular ion is injected into the mirror. Figure 1A shows three different ion paths, illustrating the spread of the ion beam as it drifts along the mass spectrometer when focusing is not performed in the drift direction. Lenses between mirrors, periodic modulation of the mirror structure itself, and the use of individual mirrors have been proposed as means of controlling this beam divergence along the drift length. However, if some degree of focusing is possible for detection, it is advantageous to allow the ions to spread as they move along the drift length and reduce space-charge interactions.

[0005] Figure 2 illustrates another technique for addressing ion beam divergence, as described in Patent Document US9136102. The mirrors are tilted by an angle θ, so that the mirror spacing decreases in the drift direction away from the ion source. Ions are injected into the mirrors at the initial tilt angle, and the ion trajectory tilt angle decreases by 2θ for each oscillation (including two reflections) due to the mirror's focusing tilt angle θ. As a result, the ion drift direction is eventually reversed, and the ions return through the mirror electrodes and are detected by an ion detector placed near the ion trap. Passing through the mirrors twice extends the ion flight path, which is desirable because it improves the ability of the time-of-flight (ToF) mass spectrometer to distinguish small mass differences between ions, thus increasing the separation of ion flight times. [Overview of the project] [Problems that the invention aims to solve]

[0006] However, tilting the mirror introduces ToF aberration. This is because not all ions follow a common path through the mirror electrodes. Due to the finite spread of the beam angle when ions are injected into the mirror electrodes, some ions drift further down the mirror electrodes than others. Advantageously, the ions are spatially focused again as they return to the ion detector. However, as the distance between the mirror electrodes decreases along the drift direction, the ion oscillation period shortens with distance, resulting in temporal aberration.

[0007] These ToF aberrations are corrected by using stripe electrodes to slow down ions as they traverse between the mirror electrodes. The stripe electrodes are designed to generate an electric field with a voltage that varies depending on the distance along the mirror, thereby mitigating the reduction in periodicity caused by the converging mirror electrodes.

[0008] Figure 3 is a schematic diagram of a multiple-reflection mass spectrometer equipped with opposing parabolic ion optical mirrors, where the mirrors converge on each other along the drift direction away from the ion source. Such a mass spectrometer is described in Patent Document US9136102. Ions are reflected multiple times from one mirror to the other, generally following a zigzag path, as they drift away from the ion source along the mirrors. The ion drift is suppressed by the electric field generated by the converging mirrors, and eventually the ions reverse direction and return towards the ion source. An ion detector is located near the ion source and captures and detects the ions. Figure 3 shows three ion paths to illustrate the spread of the ion beam as it travels away from the ion source along the mirrors. The spread of the ion beam is caused by the angular spread when the ions are injected into the mirrors. Figure 3 also shows how the ion paths converge as the ions return to the ion detector through the mirrors. The parabolic shape of the ion mirror in Figure 3 is advantageous because it can focus ion orbitals to a single point even over a wide range of ion implantation angles, whereas a linear mirror like the one in Figure 2 can only focus ion orbitals within a relatively narrow range of implantation angles.

[0009] The parabolic shape of the mirror, similar to that of an optical parabolic mirror, works to concentrate a bundle of parallel incident ion orbitals into a single point after reflection. When applied to the electric field of an ion optical mirror, the parabolic curved mirror electrode completely constrains the motion of the ions. Isochronism of ion motion can be achieved by using stripe electrodes with a parabolic shape.

[0010] As described above, each ion optical mirror is equipped with a pair of elongated electrodes. The mirror electrodes are arranged symmetrically on either side of the plane through which the ion beam propagates. Some electrodes have an accelerating voltage (a negative voltage assuming the ions are anions), while others have a decelerating voltage (a positive voltage in the case of anions). The electrode with the negative voltage generates an electric field that produces an ion optical focusing effect, while the electrode with the positive voltage generates an electric field that decelerates the ions and reflects them toward the other mirror. The combination of negative and positive voltages is optimized so that the chromatic aberration isochronism of the reflection, i.e., the variation in initial kinetic energy and the time of flight of the ions are independent of small displacements around the plane of symmetry.

[0011] To achieve the precise electric field required for high-resolution mass spectrometry, mirror electrodes must be manufactured within extremely tight tolerances. This stringent requirement stems from the fact that even micron-level errors in shape can cause significant errors in the resulting electrostatic field distribution due to the voltage difference of several kilovolts between adjacent mirror electrodes. For example, the mechanical tolerance of a mirror electrode can be as high as 10-20 micrometers for a mirror approximately 1 meter in length. This level of precision is far easier to achieve for straight electrodes using manufacturing techniques such as precision milling or wire electrical discharge machining. This level of precision is far more difficult to achieve for curved surfaces, such as those found in parabolic electrodes. Therefore, while parabolic mirrors theoretically offer superior resolution, achieving this resolution is difficult and costly due to the difficulty of manufacturing electrodes with the required tolerances. [Means for solving the problem]

[0012] This invention introduces an ion-optical mirror whose ion-optical properties are essentially similar to those of a mirror with parabolic electrodes and parabolic compensation stripes. Simultaneously, most of the electrodes in the ion-optical mirror of this invention are linear, with only a few being curved. In particular, adjacent electrodes with high voltages between them have linear faces, which facilitates their precise fabrication. The few curved electrodes have relatively small voltage differences, which significantly relaxes tolerance requirements.

[0013] In particular, the effective curvature and isochronism of the ion optical mirror of the present invention are adjusted and controlled by changing the relatively small voltage difference between the curved electrodes. This advantage is in contrast to the concave ion optical mirror shown in Figure 4, where all electrodes are parabolic, and their focusing intensity is determined by fabrication and cannot be electrically changed.

[0014] A first aspect of the present invention relates to a multiple reflection mass spectrometer comprising a pair of opposing ion optical mirrors. The mirrors extend along a longitudinal axis that runs through the center of the mass spectrometer. The ion optical mirrors are arranged parallel or substantially parallel to each other. One or both ion optical mirrors are provided with a series of spaced electrodes having the following characteristics: (i) Each electrode extends along the longitudinal axis, (ii) The series of electrodes extends in a direction perpendicular to the longitudinal axis, and the electrodes are spaced apart by a series of gaps, (iii) The series of electrodes includes a first pair of adjacent electrodes and a second pair of adjacent electrodes, (iv) The first pair of adjacent electrodes are separated by a linear gap defined by the linear edges of each of the adjacent electrodes, (v) The second pair of adjacent electrodes are separated by a curved gap defined by the curved edges of each of the adjacent electrodes.

[0015] A first pair of electrodes with a linear gap can be used to reflect ions laterally with respect to the longitudinal axis, causing the ions to vibrate between the mirrors. This requires a relatively large potential difference between adjacent electrodes, resulting in relatively strict tolerance requirements for the linear edges of the adjacent electrodes in the first pair of electrodes. Alternatively, a second pair of adjacent electrodes with a curved gap can be used to deflect ions along the longitudinal axis, allowing the ions to reverse their drift direction after multiple reflections within the mirrors. For this purpose, a relatively weak electric field, i.e., a relatively small potential difference, is required between the adjacent electrodes of the second pair of electrodes (compared to the relatively large potential difference between adjacent electrodes in the first pair of electrodes), resulting in looser tolerance requirements for the curved edges of the adjacent electrodes in the second pair of electrodes. This thus eliminates the difficulties encountered when machining curved electrodes with high precision.

[0016] For example, the straight edges of the first electrode pair may be formed within a tolerance of less than 10 micrometers, while the curved edges of the second electrode pair may be formed within a tolerance of more than 10 micrometers. Alternatively, the straight edges of the first electrode pair may be formed within a tolerance at least one order of magnitude smaller than that of the curved edges of the second electrode pair.

[0017] The curved edges of the second adjacent electrode pair may be defined based on a function corresponding to the logarithm of a quadratic polynomial. The adjacent electrode edges of the first and / or second electrode pairs may have corresponding shapes such that the gap width is constant along the longitudinal axis. The straight edges of the first electrode pair are preferably fabricated by metal cutting along a straight line, and the curved edges of the second electrode pair are fabricated by metal cutting along the curve defined by the formula. Alternatively, the second electrode pair separated by the curved gap may be the outermost electrode pair with respect to the longitudinal axis.

[0018] A multiple reflection mass spectrometer may further include a controller configured to apply potential to a series of electrodes such that the potential difference between adjacent electrodes of a first electrode pair (with linear edges) is relatively larger than the potential difference between adjacent electrodes of a second electrode pair (with curved edges). For example, the potential difference between adjacent electrodes of the first electrode pair (with linear edges) may be at least 10 times, at least 100 times, or at least 1000 times higher than the potential difference between adjacent electrodes of the second electrode pair (with curved edges).

[0019] Alternatively, the longitudinal axis of the mass spectrometer may define the y-axis of the Cartesian coordinate system, and a series of electrodes may extend perpendicular to the y-axis to define the z-axis. In this case, each mirror may comprise a first and second series of corresponding electrodes facing each other and spaced apart in the x-axis direction.

[0020] The controller may also be configured to provide an acceleration potential to accelerate ions along the mass spectrometer. The controller may also be configured to provide acceleration and / or deceleration potentials to the electrodes of the ion optical mirrors. The outermost electrodes of the ion optical mirrors may receive a deceleration potential higher than the acceleration potential, which causes the ions to stop at a certain position within each ion optical mirror and reflect outwards toward the other ion optical mirror. Thus, some electrodes with a potential lower than the acceleration potential are passed by the ions before and after each reflection ("pass electrodes"), while other electrodes with a potential higher than the acceleration potential do not reach the ions ("non-pass electrodes"), although the potential at the non-pass electrodes affects the motion of the ions near the reflection point.

[0021] Therefore, the electrodes of the mirror may belong to one of two groups: (1) through electrodes, and (2) non-through electrodes positioned beyond the reflection point.

[0022] The controller may further be configured to apply an acceleration or deceleration potential to the curved electrode among the through electrodes. The curved edge of this through electrode may generate an electrostatic field having a component along the longitudinal axis, deflecting ions in this axial direction. The following equation The parabolic edges according to JPEG2026052675000002.jpg6170 generate a non-uniform longitudinal electrostatic field component with a focusing effect similar to that of a parabolic concave (convex) mirror. By configuring the controller to apply a predetermined potential difference between adjacent electrode pairs having parabolic curved edges, it becomes possible to change the focusing effect on ions, and therefore to change the effective focal length of the ion optical mirror. The time-of-flight effect at the passing curved electrode arises from the deceleration or acceleration of ions as they pass through this electrode. The time-of-flight effect at the passing curved electrode is not substantially zero, and a mirror having only curved passing electrodes becomes substantially non-isochronous.

[0023] The controller may also be configured to apply a potential exceeding the accelerating voltage to one of the curved non-pass electrodes, i.e., electrodes positioned beyond the ion reflection point. Nevertheless, the potential applied to the non-pass curved electrode will, due to the penetration effect of the electric field proportional to the exponential, reach the reflection point z R It affects nearby ions. JPEG2026052675000003.jpg11170z R is the z-coordinate of the reflection, and s(y)>z R is the z-coordinate of the curved edge, and 2H is the x-axis distance between the planes on either side of the central plane of the ion optical mirror where the electrodes are positioned. Because the edge shape s(y) is not constant along the longitudinal axis, applying a potential difference between a non-transmissive curved electrode pair with a curved gap results in non-uniform effects on ion deflection and reflection time in the longitudinal y-direction.

[0024] To generate deflection and time-of-flight effects that parabolically depend on the ion orbital as a quadratic function of the longitudinal coordinate, the curved edge of the non-pass electrode may follow a logarithmic parabolic shape (i.e., it may be defined based on a function corresponding to the logarithm of a quadratic polynomial). The logarithmic parabolic shape may be defined by the following equation: JPEG2026052675000004.jpg10170 Here, s0 and k are constants.

[0025] The time-of-flight effect in non-pass electrodes is due to a slight shift in the reflection point in the z-axis direction. Applying a larger deceleration potential to a non-pass electrode shortens the ion path within the ion optical mirror, reducing the time of flight per reflection. Conversely, applying a smaller (less deceleration) potential lengthens the ion path, resulting in a longer reflection time. The time-of-flight effect in non-pass electrodes appears at the inverse rate of the time-of-flight effect in pass electrodes. Therefore, by combining a parabolic passing curved electrode with a logarithmic parabolic non-pass curved electrode, it is possible to mutually compensate for the time-of-flight effects of both. Ion optical mirrors with such curved electrodes are isochronous, meaning that the time-of-flight aberration is zero for ions, which means that the reflection time does not depend on the y-coordinate of the reflection point.

[0026] Accordingly, the present invention can provide an isochronous ion optical mirror comprising at least one parabolic passing curved electrode and at least one logarithmic parabolic non-passing curved electrode. The controller may be configured to apply a potential of a relative magnitude to the curved electrodes that compensates for longitudinal time-of-flight aberrations.

[0027] Therefore, the series of electrodes may further include a third pair of adjacent electrodes. The third pair of adjacent electrodes may be separated by a curved gap defined by the parabolic edges of each third pair of adjacent electrodes. The third pair of adjacent electrodes may have parabolic edges of corresponding shapes such that the gap is of a constant width. Such an arrangement is advantageous because it can further contribute to reflecting ions along the longitudinal axis and reversing the direction of drift of ions within the mirror.

[0028] The controller may be configured to apply a potential to a series of electrodes such that the potential difference between adjacent electrodes of a first electrode pair (with linear edges) is relatively larger than the potential difference between adjacent electrodes of a third electrode pair (with parabolic curved edges). For example, the potential difference between adjacent electrodes of the first electrode pair (with linear edges) may be at least 10 times, at least 100 times, or at least 1000 times higher than the potential difference between adjacent electrodes of the third electrode pair (with parabolic curved edges). This difference in electric field strength is possible because the reflection effect is mainly realized in the "z" direction by the electric field between the linear edges, while the electric field between the curved edges is intended to control the relatively slow motion of ions in the longitudinal direction "y". The kinetic energy component of the ion in the y direction is relative to the kinetic energy component in the z direction. Ky / Kz=tan 2 It is represented by θ, where θ is the angle of incidence of the ion, and is preferably 5 degrees or less. Therefore, the drift energy component is at least 1 / 100th of the z component.

[0029] The relatively small potential difference between adjacent electrodes of the third electrode pair (which has a parabolic curved edge) allows for relatively lenient tolerance requirements for its curved edge, thereby eliminating the difficulties encountered when machining the curved electrode with high precision. For example, the straight edges of adjacent electrodes of the first electrode pair may be formed within a tolerance of less than 10 micrometers, while the parabolic edges of adjacent electrodes of the third electrode pair may be formed within a tolerance of more than 10 micrometers. Alternatively, the straight edges of adjacent electrodes of the first electrode pair may be formed within a tolerance at least one order of magnitude smaller than that of the parabolic edges of adjacent electrodes of the third electrode pair.

[0030] The third pair of adjacent electrodes (having parabolic curved edges) may be the innermost pair of electrodes with respect to the longitudinal axis. The controller may be configured to apply a potential to the adjacent electrodes of the third pair of adjacent electrodes (having parabolic curved edges) so that the innermost electrode is grounded.

[0031] The curved gaps between the second and third adjacent electrode pairs introduce variations in the time of flight of ions passing through the ion optical mirror. Advantageously, by using a parabolic gap between the third adjacent electrode pair (which may be the passing electrode) and a logarithmic parabolic gap between the second adjacent electrode pair (which may be the non-passing electrode), the variations in time of flight act in opposite directions (i.e., one increases the time of flight, and the other decreases it). This allows the second and third adjacent electrode pairs (the passing electrode and the non-passing electrode, respectively) to be shaped such that the time of flight variations they produce cancel each other out or are substantially canceled out.

[0032] Preferably, one set of electrodes is shaped to form a gap of a certain width between a straight electrode and a curved electrode. The gap between the two curved electrodes has a curved shape. The gap between the curved electrodes through which the electrode passes is preferably parabolic in shape according to the following equation. JPEG2026052675000005.jpg6170 The gap between non-pass electrodes is shaped according to the equation of a logarithmic parabola. In that case, the values ​​of s0, s0', k and k' and the potential difference across the gap may be set such that the time-of-flight variation caused to ions by the third adjacent electrode pair (through electrodes) is canceled out or substantially canceled out by the time-of-flight variation caused by the second adjacent electrode pair (non-through electrodes).

[0033] Alternatively, the series of electrodes may include a further number of adjacent electrode pairs separated by linear gaps defined by the linear edges of adjacent electrodes. The innermost adjacent electrode pair may form a third adjacent electrode pair (with a parabolic gap between them), and the outermost adjacent electrode pair may form a second adjacent electrode pair (with a logarithmic parabolic gap between them). The series of electrodes may include seven electrodes, where the first and second electrodes, counting outward from the longitudinal axis, form a third adjacent electrode pair (with a parabolic gap), the second to sixth electrodes are separated by linear gaps (each of these adjacent electrode pairs corresponds to the first electrode pair described above), and the sixth and seventh electrodes may form a second adjacent electrode pair (with a logarithmic parabolic gap).

[0034] Alternatively, the ion optical mirrors may be symmetrical about their longitudinal axis. In such an arrangement, both ion optical mirrors deflect the ions in the longitudinal direction (drift direction), ultimately reversing the direction of ion drift. Alternatively, one ion optical mirror may have a curved electrode as described in any of the above configurations, while the other ion optical mirror may have a series of linear edge electrodes, with each adjacent electrode pair separated by a linear gap. In such an arrangement, only one ion optical mirror deflects the ions in the longitudinal direction (drift direction).

[0035] A multiple reflection mass spectrometer may further include an ion source located at one end of an ion optical mirror and an ion optical system capable of injecting ions generated by the ion source into the ion optical mirror. An ion detector may be located at the same end as the ion source of the ion optical mirror. The ion detector may be capable of detecting ions reflected by the ion optical mirror.

[0036] The present invention also relates to a method for operating any of the above-described multiple reflection mass spectrometers, the method comprising a controller applying a potential to a series of electrodes such that the potential difference between adjacent electrodes of a first pair of adjacent electrodes is relatively larger than the potential difference between adjacent electrodes of a second pair of adjacent electrodes.

[0037] If the second adjacent electrode pair is the outermost electrode pair with respect to the longitudinal axis, the method may include the controller providing an acceleration potential for ions to pass through the mass spectrometer and applying a potential higher than the acceleration potential to the adjacent electrode of the second adjacent electrode pair.

[0038] If the series of electrodes further includes a third pair of adjacent electrodes, and the third pair of adjacent electrodes is separated by a curved gap defined by the parabolic edges of the adjacent electrodes, the method may include a controller applying a potential to the series of electrodes such that the potential difference between adjacent electrodes of the first pair of adjacent electrodes is relatively larger than the potential difference between adjacent electrodes of the third pair of adjacent electrodes. [Brief explanation of the drawing]

[0039] [Figure 1A] The first conventional mass spectrometer is shown. [Figure 1B] The first conventional mass spectrometer is shown. [Figure 2] The second conventional mass spectrometer is shown. [Figure 3] A third conventional mass spectrometer is shown. [Figure 4] This shows the parabolic ion optical mirror of a mass spectrometer. [Figure 5] This shows a quasi-parabolic mirror used in the mass spectrometer according to the present invention. [Figure 6] This shows another quasi-parabolic mirror used in the mass spectrometer according to the present invention, and the electric field strength within the mirror. [Figure 7] This shows the action integral and time-of-flight perturbation depending on the gap position between the electrodes of the mirror. [Figure 8] Another quasi-parabolic mirror used in the mass spectrometer according to the present invention is shown. [Figure 9] This shows a mass spectrometer equipped with opposing quasi-parabolic mirrors. [Modes for carrying out the invention]

[0040] As described above, Figures 1A and 1B are schematic diagrams of a conventional multiple reflection mass spectrometer equipped with parallel ion optical mirrors extending linearly along the drift length. Figure 1A shows the spectrometer in the yz plane, and Figure 1B shows the same spectrometer in the xz plane. Opposing ion optical mirrors 11 and 12 extend along the drift direction y and are arranged parallel to each other. Ions are injected from the ion source 14 with an average angle θ relative to the z axis and have an angular divergence δθ in the yz plane. Three ion flight paths 20a, 20b, and 20c are drawn to illustrate several different paths resulting from the angular divergence δθ. Ions 20 move along the zigzag flight path and drift relatively slowly along the drift direction y. After multiple reflections by mirrors 11 and 12, ions 20 reach the ion detector 16.

[0041] Figure 2 shows a conventional multiple reflection time-of-flight mass spectrometer with mirrors 11 and 12 tilted by an angle θ such that the spacing in the z direction decreases as they extend along the drift direction y. Ions are supplied from an ion trap 14 and form an ion beam 20 controlled and shaped by electrodes 18 and 19. The ions in the ion beam 20 oscillate in the y direction between the opposing mirrors 11 and 12. The ion drift is reversed by the focusing tilt angle θ of the mirrors, and the ions 20 return through the mirrors 11 and 12 and are detected by an ion detector 16. This detector 16 is located adjacent to the ion trap 14. As described above, the time-of-flight aberration caused by the tilted mirrors 11 and 12 is corrected by using a stripe electrode 24 to decelerate the ions 20 as they pass between the mirror electrodes 11 and 12.

[0042] Figure 3 is a schematic diagram of a multiple reflection mass spectrometer equipped with opposing parabolic ion optical mirrors 11 and 12 that converge on each other along the drift direction away from the ion source 14. As already described, ions 20 move along a zigzag path between mirrors 11 and 12, and as their drift direction reverses, ions 20 return towards the detector 16. Compared to the arrangement in Figure 2, the parabolic ion optical mirrors in Figure 3 offer superior spatial focusing of ion orbitals, but the fabrication of curved electrodes is difficult due to strict tolerance requirements.

[0043] Figure 4 is a schematic diagram of a single parabolic mirror 12 to illustrate its operation. The mirror 12 consists of five electrodes 121-125 separated by a parabolic gap. Electrode 121 is the innermost electrode closest to the central axis of the mass spectrometer 10, and electrode 125 is the outermost electrode. The other electrodes are numbered 122-124 in order. The main ionic optical property of the mirror is that, upon reflection, it imparts a predetermined tilt angle θ(y) to each ion 20, depending on the incident point y along the y-axis. In the mirror 12, all electrodes 121-125 are quadratic function Δ(y)=y 2bent according to / 2R, where R is the radius of curvature and is common to all electrodes 121 to 125. The action integral in the path of the ions is from the plane z0 to the flight direction reversal point z m (y) and back to the plane z0 again, JPEG2026052675000007.jpg16170 where m, q, and u are the mass, charge, and acceleration voltage of the ions, respectively. It is more convenient to use the action normalized by the momentum p z =√2mqu of the incident ions. This value is described by an integral having the dimension of a length independent of mass JPEG2026052675000008.jpg16170

[0044] From the action integral shown in Equation (1), two main characteristics of the electrostatic mirror 12 acting on the reflected ions 20 can be derived. The deflection angle and the flight time are obtained as functions of the incident point y. The deflected ions 20 acquire a momentum component Δp y =∂I / ∂y in the y direction, and thus the deflection angle is JPEG2026052675000009.jpg10170The difference in flight time in reflection is the derivative with respect to the ion energy of the action, [[ID=1�]] JPEG2026052675000010.jpg16170

[0045] The ideal electrostatic parabolic ion mirror 12 focuses all incoming parallel trajectories to a single point located at the focal length f, so that the deflection angle θ(y)=-y / f The action integral in the electrostatic mirror 12 of FIG. 4 is different from the action integral calculated at the midpoint y = 0 when calculated at the point y, and the difference is the length Δz = y 2 / 2R of the free flight section doubled. This quantity Δz is removed from the integral by the radius of curvature R. As a result, according to Equation (1), J(y,u)-J(0,u)=-y 2 / R and θ(y)=-2y / R, which corresponds to an ideal focusing with a focal length f = R / 2

[0046] The time-of-flight characteristics of mirror 12 in Figure 4 are not isochronous, and unlike optical mirrors to which Fermat's principle applies, the concave electrostatic mirror 12 does not simultaneously focus ions at the focal point. T(y) ≠ constant.

[0047] Figure 5 shows a quasi-parabolic mirror 112. This mirror has five main electrodes 1121-1125. Generally, voltages similar to or similar to those applied to the corresponding electrodes 121-125 of the mass spectrometer in Figure 4 can be applied to electrodes 1121-1125. However, two of the main electrodes 1121-1125 each have two sub-electrodes 112 1A and 112 1B , and 112 5A and 112 5B It is divided into two parts. The voltage difference between the main electrodes 1121 and 1125 is relatively large. Therefore, the linear gap between the main electrodes 1121 and 1125 is advantageous because the manufacturing tolerance of the linear edge can be well secured to a few microns by known precision machining methods such as wire electrical discharge machining. For electrodes with curved edges separated by a curved gap, it is impossible to achieve the same level of manufacturing precision, and they cannot be considered equivalent.

[0048] The innermost main electrode 1121 is separated by a curved gap 1251 from an electrically insulated partial electrode 112 1A and 112 1B It is divided into. Similarly, the outermost main electrode 1125 is separated by a curved gap 1255 from an electrically insulated partial electrode 112 5A and 112 5B It is divided into two parts. Each pair has two partial electrodes 112 1A and 112 1B , and 112 5A and 112 5B Different voltages are applied to each pair of partial electrodes, 112 1A and 112 1B , and 112 5A and 112 5BThe potential difference across the gaps 1251 and 1255 is set to be relatively small. The potential difference may be, for example, a few percent of the ion acceleration voltage u. This significantly reduced potential difference allows the partial electrodes 112 that define the curved gaps 1251 and 1255. 1A and 112 1B , and 112 5A and 112 5B The requirements for the shape accuracy of the curved edges are relaxed, allowing them to be manufactured without significantly affecting the operation of the mirror. Generally, the effect of insufficient mechanical precision of an electrode on the generated electrostatic field is proportional to the potential difference between adjacent electrodes. The potential difference across the curved gaps 1251 and 1255 is, for example, about 1 / 100th of the potential difference across the straight gap separating the main electrodes 1121-1125. Therefore, the mechanical tolerances of the curved gaps 1251 and 1255 are much looser, ranging from tens to hundreds of microns. This is compatible with many conventional methods for manufacturing curved electrodes, such as milling.

[0049] The optimal shapes of the curved gaps 1251 and 1255 are defined such that they generate an action integral (2) such that the deflection angle θ(y) = -2y / R is a linear function of coordinate y and the isochronism property T(y) = constant is satisfied.

[0050] Using the following considerations, the optimal shapes of the curved gaps 1251 and 1255 can be determined, which makes the quasi-parabolic ion mirror 112 equivalent to an ideal parabolic ion mirror with focal length f=R / 2, resulting in a flat time of flight (i.e., ions incident on mirror 112 simultaneously are reflected simultaneously and reach the focal position).

[0051] In the mirror 112 of Figure 5, the innermost main electrode 1121 is connected to two complementary partial electrodes 112 1A and 112 1B It is divided into two parts. Generally, one partial electrode is grounded, and a small bias is applied to the other partial electrode. For example, partial electrode 112 1A A positive bias voltage Δv1 is applied to generate a focusing effect on the cations 20. Partial electrode 1121A The shape change in the y-axis direction is represented by a width s1(y) that depends on y. The bias voltage Δv1 is small compared to the ion acceleration voltage u. For example, u is approximately 4000V, |Δv1|≦40V is also acceptable. Partial electrode 112 1A The ion 20 passes through the mirror 112 twice for each vibration, and once before and after each reflection. Both passes cause a perturbation in the action integral. Due to the small bias voltage Δv1, this perturbation can be approximated linearly. JPEG2026052675000011.jpg15170 JPEG2026052675000012.jpg14170

[0052] A positive bias voltage Δv1 > 0 (assuming ion 20 is a positive ion and slowing it down) produces a positive time lag ΔT1, and it should be noted that this time lag is larger for ion 20, which is furthest from the z axis in both y directions. ΔJ1 and ΔT1 are proportional to each other, and therefore the partial electrode 112 1A and 112 1B The spatial focusing of the curved gap 1251 between them inevitably causes time-of-flight variations in the ions 20 that depend on the incident point y.

[0053] However, this time-of-flight variation can be corrected by splitting one of the other main electrodes 1122-1125. In the embodiment shown in Figure 5, the outermost electrode 1125 is a partial electrode 112 5A and 112 5B It is divided into two parts. This main electrode 1125 is the electrode with the most positive electrical bias. The pair of inner partial electrodes 112 5A The change in shape along the y-axis is represented by a width s5(y) that depends on y.

[0054] Partial electrode 112 5A A voltage v5 is applied to the partial electrode 112 5B Voltage v 5BA voltage of =v5+Δv5 is applied, where Δv5 is small compared to the ion acceleration voltage u. In a conventional mass spectrometer 10, the voltage v5 exceeds the acceleration voltage u, and the ions 20 are reflected near the interface of the main electrodes 124 and 125. In the mirror 112 of Figure 5, the voltage v5 set on the partial electrode 1125 also exceeds the acceleration voltage u, and therefore the ions 20 are reflected near the electrode 112 5B It does not pass through completely. Nevertheless, partial electrode 112 5B The voltage difference applied to the ion's reflection coordinate z m Vary (y) and the action integral during reflection.

[0055] Generally, partial electrode 112 5B There is no analytical solution for the perturbation of the action caused by the voltage ΔV5 applied to the partial electrode 112 5A The dependence of on the width s5(y) is expected to be exponential, as it follows the propagation of voltage perturbations between two conductive plates separated by a gap H, and is represented by the attenuation coefficient exp(-πs5 / 2H). The effects on the action integral and reflection time are proportional to the voltage bias ΔV5 and the attenuation coefficient. JPEG2026052675000013.jpg11170 JPEG2026052675000014.jpg9170 Here, A[mm] and B[μs] are constants determined by numerical simulation. Note that the positive voltage ΔV5 reverses the flight direction of ion 20 (anion) at a smaller z-coordinate, so both the action and time perturbations are negative. Therefore, coefficients A and B are both negative. Biased partial electrode 112 1B The contributions ΔJ1 and ΔT1 resulting from this have opposite signs, whereas the partial electrode 112 5B The bias ΔV5 in generates contributions ΔJ5 and ΔT5 of the same sign. Therefore, partial electrode 112 1A and 112 1B Curved gap 1251 and partial electrode 112 5A and 112 5BBy using the curved gap 1255 between them, a subtractive combination becomes possible such that the contribution ΔJ1+ΔJ5 to the action integral increases while the contribution of flight time is canceled out, resulting in ΔT1+ΔT5=0. That is, JPEG2026052675000015.jpg11170 JPEG2026052675000016.jpg14170 Since both the deflection angle and the time-of-flight difference are expressed by the derivatives of equations (5) and (6), these equations are described with precision for insignificant constants. When the perturbation ΔJ of the action is differentiated with respect to y to find the deflection angle θ(y), the constant c1 is eliminated. Also, the constant c2 is a time-of-flight shift common to all ions and is therefore not important in the operation of a time-of-flight mass spectrometer.

[0056] According to equations (5) and (6), the partial electrode 112 1B and 112 5A The shape functions s1(y) and s5(y) take on specific shapes. JPEG2026052675000017.jpg6170 JPEG2026052675000018.jpg10170 Here, s 10 [mm], k1[mm -1 ] and s 50 [mm], k5[mm] -1 ] is a coefficient that can be selected with a certain degree of freedom. Substitute equations (7) and (8) into equations (5) and (6), and y 2 By connecting the coefficients with an equality, we obtain equations for ΔV1 and ΔV5. JPEG2026052675000019.jpg19170 JPEG2026052675000020.jpg14170

[0057] Equation (10) defines the proportional relationship between ΔV1 and ΔV5 for the mirror to be isochronous with respect to variations in the y-position of the incident ions, and equation (9) sets the desired focal length.

[0058] The advantage of the quasi-parabolic ion mirror 112 is that, unlike mirror 12 in which electrodes 121-125 are physically curved, the effective radius of curvature can be electrically changed by applying different biases ΔV1 and ΔV5. As an example of such a quasi-parabolic stripe, consider an ion optical mirror 112 having five main electrodes 1121-1125 similar to that shown in Figure 5.

[0059] Figure 6 is a side view of such a quasi-periodic electrostatic mirror 112, where the first and last main electrodes 1121 and 1125 are each two sub-electrodes 112 1A and 112 1B , as well as 1125A and 112 5B It is divided into: Partial electrode 112 1B and 112 5B These are complementary partial electrodes 112 1A and 112 5A A bias of voltages ΔV1 and ΔV5 is applied to it.

[0060] Figure 7 (top) shows the curved partial electrode 112 1B and 112 5B This shows the perturbation ΔJ of the action integral and the perturbation of the time of flight, normalized by the incident momentum of the ion, caused by the applied bias ΔV1 / u = ΔV5 / u = 1V / 4000V. Figure 7 (bottom) shows the change in time ΔT corresponding to an ion with a mass-to-charge ratio m / z = 1000Da. Both the action integral ΔJ and the time difference ΔT are shown as functions of the corresponding gap positions s1 and s5.

[0061] As predicted by theory, the action integral ΔJ and the time perturbation ΔT are linear with respect to s1 and exponential with respect to s5. The damping constant is π / 2H, where H=24mm is the half-interval in the x-axis direction between electrodes 1111~1115 and 1121~1125 (these distances are equal because electrodes 111 and 112 are located on the same plane parallel to the yz plane). Ion optics simulations (using MASIM 3D software) revealed the following: JPEG2026052675000021.jpg6170 Here, the prior constants A and B of the exponential function were found to be A = -16.676 mm and B = -15.6287 μs, respectively (when m / z = 1000 Th).

[0062] Based on this information, the solutions for the geometric constants in equations (7) and (8) that realize the flat dependence of T(y) can be obtained as simple algebraic calculations. The solutions are not unique, and one solution that satisfies reasonable mechanical constraints is as follows: JPEG2026052675000022.jpg6170 JPEG2026052675000023.jpg6170

[0063] Solving equations (9) and (10) for Δv1 and Δv5, assuming the focal length of the mirror f = 10m, The result is JPEG2026052675000024.jpg7170. These voltage differences are indeed small compared to the ion acceleration voltage u, justifying the assumptions used when deriving the approximate formulas for action and time-of-flight variations.

[0064] Figure 8 shows the partial electrode 112 based on the parameters described above. 1A and 112 1B , and 112 5A and 112 5B The structure of the quasi-parabolic mirror 112 with a gap in between is shown. Electrode 112 1A and 112 1B The gap s1(y) separating them is parabolic, and electrode 112 5A and 112 5B The gap s5(y) separating them is logarithmic parabolic (i.e., defined based on a function corresponding to the logarithm of a quadratic polynomial).

[0065] Figure 9 shows a time-of-flight mass spectrometer 110 equipped with a pair of quasi-parabolic mirrors 111 and 112. Both mirrors 111 and 112 are complementary parabolic partial electrodes 111 according to equation (8). 1A and 111 1B , 112 1Aand 112 1B and the complementary logarithmic parabolic partial electrodes 111 according to formula (8) 5A and 111 5B and 112 5A and 112 5B and includes 112. The other main electrodes 1112 to 1114 and 1122 to 1124 have straight edges and are parallel to each other, so high-precision manufacturing is easy.

[0066] The ion beam 20 generated from the ion source 14 vibrates multiple times between the mirrors 111 and 112 and finally reaches the ion detector 16. In this embodiment, the partial electrodes 111 1B and 112 1B are grounded, and a voltage bias ΔV1 is applied to the partial electrodes 111 1A and 112 1A . A voltage v5 exceeding the acceleration voltage u of the ions is applied to the partial electrodes 111 5A and 112 5A , whereby the ions 20 are reversed near the interfaces of the electrodes 1114 and 111 5A , and 1124 and 112 5A . The partial electrodes 111 5B and 112 5B are further biased with a voltage difference Δv5 with respect to the partial electrodes 111 5A and 112 5A , whereby the reflection point z of the ions m changes according to the y direction along the mirrors 111 and 112. The biases Δv1 and Δv5 can be set so that the oscillation time of the ions 20 is constant for all oscillations regardless of the incident angle to the mirrors 111 and 112 and the positions on the mirrors 111 and 112 along the drift (y) direction.

[0067] In other embodiments, a voltage bias ΔV1 is applied to the parabolic stripe electrode 24 similar to that shown in FIG. 2. The biased stripe arranged in front of the ion optical mirrors 111 and 112 can be regarded as a functional part of this mirror.

[0068] The present invention is not limited to the embodiments shown, and it should be understood by those skilled in the art that many additions and modifications are possible without departing from the scope of the invention.

Claims

1. A multiple reflection mass spectrometer comprising a pair of opposing ion optical mirrors extending linearly along a longitudinal axis penetrating the mass spectrometer and arranged substantially parallel to each other, and a series of electrodes spaced apart from one or both of the ion optical mirrors, Each of the electrodes extends along the longitudinal axis, The series of electrodes extends in a direction perpendicular to the longitudinal axis, and the electrodes are spaced apart by a series of gaps. The series of electrodes includes a first pair of adjacent electrodes and a second pair of adjacent electrodes. The first pair of adjacent electrodes is separated by a linear gap defined by the linear edges of each adjacent electrode, and A multiple reflection mass spectrometer in which the second pair of adjacent electrodes are separated by a curved gap defined by the curved edges of each adjacent electrode.

2. The multiple reflection mass spectrometer according to claim 1, wherein the curved edge of the second adjacent electrode pair is defined according to a function corresponding to the logarithm of a quadratic polynomial.

3. The longitudinal axis of the mass spectrometer defines the y-axis of the Cartesian coordinate system, and the series of electrodes extends orthogonally to the y-axis, defining the z-axis. One or both of the ion optical mirrors comprises a first and second series of corresponding electrode sets arranged opposite each other and spaced apart in the x-axis direction, The adjacent electrode of the second pair of adjacent electrodes has a width in the z-axis direction that corresponds to the equation of a logarithmic parabola, depending on its position y along the y-axis direction. Here, H represents the semi-separation distance in the x-axis direction between the electrode and the corresponding electrode, and s 0 The multiple reflection mass spectrometer according to claim 2, wherein k is the minimum width of the electrode and k is a constant.

4. The linear edges of the adjacent electrodes in the first pair of adjacent electrodes are formed within a tolerance of less than 10 microns, and the logarithmic parabolic edges of the adjacent electrodes in the second pair of adjacent electrodes are formed within a tolerance of more than 10 microns, and / or The multiple reflection mass spectrometer according to any one of claims 1 to 3, wherein the linear edges of the adjacent electrodes of the first pair of adjacent electrodes are formed within a tolerance that is at least one order of magnitude smaller than that of the curved edges of the adjacent electrodes of the second pair of adjacent electrodes.

5. The multiple reflection mass spectrometer according to any one of claims 1 to 4, further comprising a controller configured to apply a potential to the series of electrodes such that the potential difference between adjacent electrodes of the first pair of adjacent electrodes is relatively larger than the potential difference between adjacent electrodes of the second pair of adjacent electrodes.

6. The multiple reflection mass spectrometer according to claim 5, wherein the second adjacent electrode pair is the outermost electrode with respect to the longitudinal axis.

7. The multiple reflection mass spectrometer according to claim 6, wherein the controller is configured to further supply an accelerating potential for accelerating ions through the mass spectrometer, and the controller is configured to apply a potential higher than the accelerating potential to the adjacent electrode of the second adjacent electrode pair.

8. The multiple reflection mass spectrometer according to any one of claims 5 to 7, wherein the series of electrodes further includes a third pair of adjacent electrodes, the third pair of adjacent electrodes being separated by a curved gap defined by the curved edges of each of the third adjacent electrodes.

9. The multiple reflection mass spectrometer according to claim 8, wherein the curved edge of the third adjacent electrode pair is a parabolic shape defined based on a quadratic polynomial of coordinate y.

10. The multiple reflection mass spectrometer according to claim 8 or 9, wherein the series of electrodes further includes a plurality of pairs of adjacent electrodes separated by linear gaps defined by the linear edges of each of the adjacent electrodes.

11. The multiple reflection mass spectrometer according to claim 10, wherein the innermost adjacent electrode pair forms the third adjacent electrode pair, the outermost adjacent electrode pair forms the second adjacent electrode pair, and all other adjacent electrode pairs correspond to either the first adjacent electrode pair or the further adjacent electrode pairs.

12. The multiple reflection mass spectrometer according to any one of claims 8 to 11, wherein the second and third adjacent electrode pairs are formed such that the time-of-flight variation introduced into the ions by the third adjacent electrode pair is canceled out or substantially canceled out by the time-of-flight variation introduced into the ions by the second adjacent electrode pair.

13. The multiple reflection mass spectrometer according to any one of claims 8 to 12, wherein the controller is configured to apply a potential to the series of electrodes such that the potential difference between the adjacent electrodes of the first pair of adjacent electrodes is relatively larger than the potential difference between the third pair of adjacent electrodes.

14. The multiple reflection mass spectrometer according to claim 13, wherein the third adjacent electrode pair is the innermost electrode with respect to the longitudinal axis.

15. The multiple reflection mass spectrometer according to claim 14, wherein the controller is configured to apply a potential to the adjacent electrode of the third adjacent electrode pair such that one electrode of the third adjacent electrode pair is grounded.

16. The linear edges of the adjacent electrodes in the first pair of adjacent electrodes are formed within a tolerance of less than 10 microns, and the parabolic edges of the adjacent electrodes in the third pair of adjacent electrodes are formed within a tolerance of more than 10 microns, and / or The multiple reflection mass spectrometer according to any one of claims 8 to 15, wherein the linear edge of the adjacent electrode of the first pair of adjacent electrodes is formed within a tolerance that is at least one order of magnitude smaller than the parabolic edge of the adjacent electrode of the third pair of adjacent electrodes.

17. The longitudinal axis of the mass spectrometer defines the y-axis of the Cartesian coordinate system, and the series of electrodes extends orthogonally to the y-axis, defining the z-axis. The system comprises first and second corresponding electrode series in which one or both of the ion optical mirrors are arranged opposite each other and spaced apart in the x-axis direction, The adjacent electrode of the second pair of adjacent electrodes changes in width in the z-axis direction according to the following equation, with respect to the position y in the y-axis direction: Here, H is the distance in the x-axis direction between the electrode in question and the corresponding electrode, and s 0 is the minimum width of the electrode, and k is a constant. Furthermore, the width of the electrode in the z-axis direction changes according to the position y in the y-axis direction according to the following equation: Here, s 0 The multiple reflection mass spectrometer according to any one of claims 8 to 16, wherein ' is the minimum width of the electrode and k' is a constant.

18. s 0 s 0 The multiple reflection mass spectrometer according to claim 17, wherein the values ​​of ', k and k' are set such that the time-of-flight variation introduced into the ion by the third adjacent electrode pair is canceled out or substantially canceled out by the time-of-flight variation introduced into the ion by the second adjacent electrode pair.

19. The multiple reflection mass spectrometer according to any one of claims 1 to 18, wherein the mirror is symmetrical with respect to the longitudinal axis.

20. An ion source positioned at one end of the mirror, An ion optical element capable of implanting ions generated by the ion source into the mirror, and The multiple reflectance mass spectrometer according to any one of claims 1 to 19, further comprising an ion detector positioned at the same end of the mirror as the ion source and capable of detecting ions reflected by the mirror.

21. A method for operating a multiple reflection mass spectrometer according to any one of claims 1 to 20, A method comprising the controller applying potential to a series of electrodes such that the potential difference between the adjacent electrodes of the first pair of adjacent electrodes is relatively larger than the potential difference between the adjacent electrodes of the second pair of adjacent electrodes.

22. The method according to claim 21, wherein the second pair of adjacent electrodes is the outermost electrode with respect to the longitudinal axis, and the method comprises the controller supplying an accelerating potential for accelerating ions through the mass spectrometer, and applying a potential higher than the accelerating potential to the adjacent electrode of the second pair of adjacent electrodes.

23. The method according to claim 21 or 22, wherein the series of electrodes further includes a third pair of adjacent electrodes, the third pair of adjacent electrodes separated by a curved gap defined by the respective parabolic edges of the adjacent electrodes, and the method comprises the controller applying a potential to the series of electrodes such that the potential difference between the adjacent electrodes of the first pair of adjacent electrodes is relatively larger than the potential difference between the adjacent electrodes of the third pair of adjacent electrodes.

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