Multi-reflection mass spectrometer

Abstract

A multi-reflection mass analyzer includes a pair of oppositely disposed ion optical mirrors linearly elongated along a longitudinal axis extending centrally through the mass analyzer while the ion optical mirrors are arranged substantially parallel to each other, and one or both of the ion optical mirrors are comprised of a series of spaced apart electrodes. Each electrode is elongated along a longitudinal axis. The series of electrodes extend in a direction transverse 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 respective linear edges of the adjacent electrodes. A second pair of adjacent electrodes is separated by a curved gap defined by respective curved edges of the adjacent electrodes.

Description

Technical Field

[0001] This invention relates to the field of mass spectrometry, and in particular to high-resolution time-of-flight mass spectrometry and electrostatic trap mass spectrometry that utilize multiple reflection techniques to extend the ion flight path. Background Technology

[0002] Figure 1A and Figure 1B This is a schematic diagram of a multireflection mass spectrometer comprising parallel ion optical mirrors linearly elongated along the drift length, illustrating a prior art analyzer as described in patent publication number SU1725289. Each ion optical mirror includes a series of electrodes, each linearly elongated along the drift length and separated by small gaps. Ions are incident from an ion source toward the opposing ion optical mirrors arranged parallel to each other. The ion line enters one mirror, is reflected, and then travels toward another mirror back, where it is reflected again and then travels back to the first mirror, and so on. In this way, ions follow a zigzag path through the mass analyzer, drifting relatively slowly from the ion source to the ion detector, where the ions collide with the ion detector and are detected. Although Figure 1A The ion source and ion detector are located within the volume defined by the mirror, but either or both of the ion source and detector may be located outside this volume.

[0003] The ion flight path varies depending on the angle of the specific ion incident mirror. Figure 1A Three different ion paths are shown, illustrating the diffusion of the ion beam along a mass analyzer that is not focused in the drift direction. It has been proposed to control this beam divergence along the drift length by providing mirrors between the mirrors, periodic modulation of the mirror structure itself, and individual mirrors. However, it is advantageous to allow ions to diffuse thus as they travel along the drift length, thereby reducing space charge interactions, provided they can be converged to a degree suitable for detection.

[0004] Figure 2 Another method for addressing ion beam divergence is shown, as described in patent publication US9136102. The mirrors are tilted at an angle θ, thus reducing the spacing between these mirrors in the drift direction away from the ion source. Ions are incident into the mirrors at an initial tilt angle, and with each oscillation (including two reflections), the mirrors converge the tilt angle θ, reducing the ion trajectory tilt angle by 2θ. Therefore, the ion's drift direction is eventually reversed, allowing the ion to travel back through the mirror electrodes and be detected by an ion detector placed in a nearby ion trap. The double passage through the mirrors lengthens the ion's flight path, which is desirable because it increases the ion's flight time interval, thus increasing the ability to distinguish small mass differences between ions in a time-of-flight (ToF) mass spectrometer.

[0005] However, tilting the mirror introduces Time-of-Flight (ToF) aberrations. This is because not all ions follow a common path through the mirror electrodes. The finite beam angle spread of ions incident on the mirror electrodes causes some ions to drift further down the mirror electrodes than others. Advantageously, these ions are spatially focused again when they return to the ion detector. However, a temporal aberration is introduced because the ion oscillation period decreases with distance along the drift direction due to the reduced spacing between the mirror electrodes.

[0006] These ToF aberrations are corrected by using strip electrodes to slow down ions as they pass between the mirror electrodes. The strip electrodes are shaped to generate an electric field with a voltage that varies with distance along the mirror, thereby mitigating the period shortening caused by the converging mirror electrodes.

[0007] Figure 3 This is a schematic diagram of a multi-reflection mass spectrometer with opposing ion optical mirrors, the mirrors having parabolic shapes and converging with each other along the drift direction away from the ion source. Such a mass spectrometer is described in US Patent Publication No. 9136102. As ions drift away from the ion source along the mirrors, they are reflected multiple times from one mirror to another, thus following a roughly zigzag path. The ion drift is opposite to the electric field generated by the converging mirrors, and the ions eventually reverse direction and travel back towards the ion source. An ion detector is located near the ion source and intercepts and detects the ions. Figure 3 Three ion paths are shown, representing the ion beam diffusion as it travels away from the ion source along the mirror. Ion beam diffusion is caused by the angular diffusion of ions incident on the mirror. Figure 3 It also shows that the ion paths converge as the ions travel through the mirror and return to the ion detector. Figure 3 The parabolic shape of a medium-ion mirror is advantageous because, even over a wide range of ion incidence angles, it causes ion trajectories to converge to a single point. Figure 2 The flat mirror in the system focuses the ion trajectory only within a relatively small incident angle interval.

[0008] The parabolic shape of the mirror causes parallel ion trajectory incident beams to converge into a single point after reflection, similar to an optical parabolic mirror. When an electric field is applied to the ion optical mirror, the parabolic mirror electrodes provide fully constrained ion motion. The isochronism of ion motion can be achieved by using strip electrodes with a parabolic shape.

[0009] As mentioned above, each ion optical mirror comprises a set of elongated electrodes. These electrodes are symmetrically positioned on either side of the ion beam propagation plane. Some electrodes carry accelerating voltages (negative voltages if the ions are anions), while others carry decelerating voltages (positive voltages for anions). The negatively voltaged electrodes generate an electric field that produces an ion optical focusing effect, while the positively voltaged electrodes generate an electric field that slows down the ions and reflects them back to the other mirror. The negative and positive voltage sets are optimized to provide isochronous dispersive reflection, meaning that the ion travel time is unaffected by changes in initial kinetic energy and small displacements around the plane of symmetry.

[0010] To obtain the precise electric field required for high-resolution mass spectrometry, mirror electrodes must be manufactured within extremely tight tolerances. These stringent requirements stem from the fact that adjacent mirror electrodes carry a voltage difference of several kilovolts, and therefore, even micrometer-level shape errors can cause significant errors in the resulting electrostatic field distribution. For example, the mechanical tolerance of the mirror electrode might be a maximum of 10–20 micrometers over the entire length of the mirror (potentially around 1 meter). Achieving this level of precision is much easier for straight electrodes, as manufacturing techniques such as precision milling and wire cutting can be used. For curved surfaces (such as those present in parabolic electrodes), achieving this level of precision is much more difficult. Therefore, while parabolic mirrors theoretically offer excellent resolution, achieving this resolution is both difficult and expensive due to the difficulty in manufacturing electrodes to the necessary tolerances. Summary of the Invention

[0011] This invention introduces an ion optical mirror whose ion optical properties are substantially similar to those of a reflecting mirror comprising parabolic electrodes and parabolic compensation strips. Furthermore, the majority of the electrodes in the ion optical mirror of this invention are straight electrodes, with only a few being curved electrodes. Obviously, any adjacent electrodes with high voltages have flat surfaces facing each other, which facilitates their precise manufacturing. The few curved electrodes have relatively small voltage differences, which significantly reduces tolerance requirements.

[0012] Obviously, the effective curvature and isochronism of the ion optical mirror of this invention are modulated and adjusted by variations in the relatively small voltage difference between the curved electrodes. This advantage is due to the fact that all electrodes are parabolic in shape and their focusing intensity is determined by manufacturing and cannot be adjusted electrically. Figure 4 Concave ion optical mirrors create contrast.

[0013] A first aspect of the invention relates to a multi-reflection mass analyzer comprising a pair of opposing ion optical mirrors. These ion optical mirrors are elongated along a centrally extending longitudinal axis through the mass analyzer. The ion optical mirrors are arranged parallel to or substantially parallel to each other. One or both of the ion optical mirrors include a series of spaced-apart electrodes, wherein:

[0014] (i) Each electrode is elongated along the longitudinal axis;

[0015] (ii) The series of electrodes extends in a direction transverse to the longitudinal axis and is separated by a series of gaps;

[0016] (iii) The series of electrodes includes a first pair of adjacent electrodes and a second pair of adjacent electrodes;

[0017] (iv) The first pair of adjacent electrodes are separated by a straight gap defined by the corresponding straight edges of the adjacent electrodes; and

[0018] (v) The second pair of adjacent electrodes are separated by a curved gap defined by the corresponding curved edges of the adjacent electrodes.

[0019] The first pair of electrodes (with a straight gap) can be used to reflect ions in a direction transverse to the longitudinal axis, so that the ions oscillate between the ion mirrors. This requires a relatively high potential difference between adjacent electrodes, which in turn imposes relatively high tolerance requirements on the straight edges of the first pair of adjacent electrodes. Furthermore, the second pair of adjacent electrodes (with a curved gap) can be used to deflect ions in a direction aligned with the longitudinal axis, so that the ions can reverse their drift direction after multiple reflections in the ion mirrors. For this purpose, a relatively weak electric field and therefore a relatively small potential difference (relative to the relatively large potential difference between the first pair of adjacent electrodes) are required between the second pair of adjacent electrodes, which in turn imposes lenient tolerance requirements on the curved edges of the second pair of adjacent electrodes. Therefore, this solves the difficulties encountered in machining curved electrodes to a high precision.

[0020] For example, the straight edges of the first pair of electrodes can be formed within a tolerance range of less than 10 micrometers, and the curved edges of the second pair of electrodes can be formed within a tolerance range of greater than 10 micrometers. Alternatively, the straight edges of the first pair of electrodes can be formed within a tolerance range at least one order of magnitude smaller than the tolerance of the curved edges of the second pair of electrodes.

[0021] The curved edges of the second pair of adjacent electrodes can be defined by a function corresponding to the logarithm of a quadratic polynomial. The edges of the first and / or second pair of adjacent electrodes can have corresponding shapes, such that the gap between them has a constant width along the longitudinal axis. The straight edges of the first pair of electrodes are preferably manufactured by metal cutting along a straight line, and the curved edges of the second pair of electrodes are manufactured by metal cutting along a curve defined by a formula. Optionally, the second pair of electrodes separated by the curved surface gap is the outermost electrode pair relative to the longitudinal axis.

[0022] The multi-reflection quality analyzer may further include a controller configured to apply a potential to a series of electrodes such that the potential difference between the first pair of adjacent electrodes (with straight edges) is relatively high compared to the potential difference between the second pair of adjacent electrodes (with curved straight edges). For example, the potential difference between the first pair of adjacent electrodes (with straight edges) may be at least ten times, at least one hundred times, or at least one thousand times higher than the potential difference between the second pair of adjacent electrodes (with curved straight edges).

[0023] Optionally, the vertical axis of the mass analyzer defines the y-axis of a Cartesian coordinate system, and a series of electrodes extends at right angles relative to the y-axis to define the z-axis. Each mirror then includes first and second series of corresponding electrodes arranged opposite to each other and spaced apart along the x-axis.

[0024] The controller can be further configured to provide an accelerating potential to accelerate ions along the mass analyzer. The controller can be configured to provide accelerating and / or decelerating potentials on the electrodes of the ion optical mirror. The outermost electrode of the ion optical mirror can receive a decelerating potential higher than the accelerating potential, thereby stopping the ions at a point inside each ion optical mirror and reflecting the ions back to another ion optical mirror. Thus, before and after each reflection, ions pass through some electrodes whose potential is lower than the accelerating potential (“traversed electrodes”), while ions cannot reach other electrodes whose voltage is higher than the accelerating potential (“non-traversed electrodes”), but the potential in the non-traversed electrodes affects the ion movement near the reflection point.

[0025] Therefore, the electrodes of the reflector may belong to one of the following two groups: (1) through electrodes and (2) non-through electrodes located outside the reflection point.

[0026] The controller can be further configured to provide an accelerating or decelerating potential to a curved through-electrode. The curved edge of this through-electrode generates an electrostatic field with a component along the longitudinal axis, deflecting ions along that axis. It has a parabolic edge according to the following formula.

[0027] s′(y)=s′0+k′y 2

[0028] The focusing effect is similar to the non-uniform longitudinal electrostatic field component of a concave (convex) mirror. The controller is configured to provide a potential difference across a pair of adjacent electrodes with parabolic curved edges, which can adjust the focusing effect on ions and thus the effective focal length of the ion optical mirror. The time-of-flight effect of the traveling, curved electrodes lies in the deceleration or acceleration of ions as they travel through these electrodes. The time-of-flight effect of the traveling, curved electrodes is essentially non-zero, making mirrors with only curved traveling electrodes substantially non-uniform.

[0029] The controller can be further configured to apply a potential higher than the accelerating voltage on a curved, non-penetrating electrode (i.e., an electrode located outside the ion reflection point). However, the potential applied to the non-penetrating curved electrode affects the ion reflection point z. R The nearby ions are due to the fact that they are proportional to the exponent.

[0030] The field penetration effect, where z R The z-coordinate of the reflection is s(y) > z. R Let s(y) be the z-coordinate of the curved edge, and 2H be the x-axis interval between the planes on either side of the central plane of the ion mirror. Since the edge shape s(y) is not constant along the y-axis, applying a potential difference between a pair of non-penetrating curved electrodes (with a curved gap between them) non-uniformly affects ion deflection and reflection time along the y-axis.

[0031] To generate deflection and time-of-flight effects on ion trajectories that are parabolic and dependent on the ordinate (as a quadratic function), the curved edges of the non-penetrating electrode can follow a logarithmic parabolic shape (i.e., defined according to a function corresponding to the logarithm of a quadratic polynomial). The logarithmic parabolic shape can be defined by the following formula:

[0032]

[0033] Where s0 and k are constants.

[0034] The time-of-flight effect of non-passing electrodes arises from a small offset of the reflection point on the z-axis. Applying a more significant deceleration potential to a non-passing electrode shortens the ion path in the ion mirror and reduces the time of flight for each reflection. Conversely, applying a smaller (less significant deceleration) potential lengthens the ion path and therefore increases the reflection time. The time-of-flight effect of non-passing electrodes is inversely proportional to that of passing electrodes. Therefore, a combination of a passing curved electrode with a parabolic shape and a non-passing curved electrode with a logarithmic parabolic shape can have mutually compensating time-of-flight effects. Ion mirrors with such curved electrodes are isochronous and provide zero time-of-flight aberration for ions, meaning that the reflection time is independent of the y-coordinate of the reflection point.

[0035] Therefore, the present invention provides an isochronous ion optical mirror comprising at least one traveling curved electrode having a parabolic shape and at least one non-traveling curved electrode having a logarithmic parabolic shape. A controller can be configured to provide a relative magnitude of the potential on the curved electrode to compensate for time-of-flight aberrations to a certain extent in the longitudinal direction.

[0036] Therefore, this 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 corresponding parabolic edges of the third pair of adjacent electrodes. The third pair of adjacent electrodes may have parabolic edges of such a corresponding shape that the gap separating the third pair of adjacent electrodes has a constant width. This configuration is advantageous because it allows for further reflection of ions in a direction aligned with the longitudinal axis, thereby causing the ions to reverse their drift direction as they pass through the mirror.

[0037] The controller can be configured to apply a potential to a series of electrodes such that the potential difference between the first pair of adjacent electrodes (with straight edges) is relatively high compared to the potential difference between the third pair of adjacent electrodes (with parabolic curved edges). For example, the potential difference between the first pair of adjacent electrodes (with straight edges) can be at least ten times, at least a hundred times, or at least a thousand times higher than the potential difference between the third pair of adjacent electrodes (with parabolic curved edges). This difference in electric field strength is possible because the reflection effect of the mirror in the 'z' direction is mainly achieved through the electric field between the straight edges, while the electric field between the curved edges is intended to control the relatively slow ion movement in the longitudinal 'y' direction. The kinetic energy component of the ion along the 'y' direction is related to the kinetic energy component along the 'z' direction as follows: in The angle of incidence of the ions is preferably less than five degrees. Therefore, the drift energy component is at least 100 times less than the z component.

[0038] The relatively small potential difference between the third pair of adjacent electrodes (with parabolic curved edges) allows for relatively low tolerance requirements on their curved edges, thus solving the difficulties encountered in machining curved electrodes to high precision. For example, the straight edges of the first pair of adjacent electrodes can be formed within a tolerance range of less than 10 micrometers, and the parabolic edges of the third pair of adjacent electrodes can be formed within a tolerance range of greater than 10 micrometers. Alternatively, the straight edges of the first pair of adjacent electrodes can be formed within a tolerance range at least one order of magnitude smaller than the tolerance of the parabolic edges of the third pair of adjacent electrodes.

[0039] The third pair of adjacent electrodes (the parabolic curved edge) can be the innermost electrode relative to the longitudinal axis. The controller can be configured to apply a potential to the third pair of adjacent electrodes (the parabolic curved edge) such that the innermost electrode is grounded.

[0040] The curved gaps between the second and third pairs of adjacent electrodes introduce a time-of-flight difference to the ions passing through the ion optical mirror. Advantageously, using a parabolic gap between the third pair of adjacent electrodes (which may be through electrodes) and a logarithmic parabolic gap between the second pair of adjacent electrodes (which may be non-through electrodes) means that the time-of-flight difference acts in opposite ways (i.e., one leads to an increase in time of flight, while the other leads to a decrease in time of flight). This allows the second and third pairs of adjacent electrodes (through electrodes and non-through electrodes, respectively) to be shaped so that the time-of-flight differences introduced by them cancel each other out or substantially cancel each other out.

[0041] The electrode assembly is preferably shaped to form a uniformly wide gap between the straight electrode and the curved electrode. The gap between two curved electrodes has a curved shape. The gap between the curved electrodes is preferably shaped according to the formula...

[0042] s′(y)=s′0+k′y 2

[0043] Shaped parabolically, and the gap between the non-penetrating electrodes has a shape according to the following logarithmic parabolic formula.

[0044]

[0045] Then, the values ​​of s0, s'0, k, and k', as well as the potential difference across the gap, can be set such that the time-of-flight difference introduced into the ion by the third pair of adjacent electrodes (through-passing) is offset or substantially offset by the time-of-flight difference introduced into the ion by the second pair of adjacent electrodes (non-through-passing).

[0046] Optionally, the series of electrodes includes additional pairs of adjacent electrodes separated by linear gaps defined by the corresponding linear edges of the adjacent electrodes. The innermost pair of adjacent electrodes may form a third pair of adjacent electrodes (with parabolic gaps between them), and the outermost pair of adjacent electrodes may form a second pair of adjacent electrodes (with logarithmic parabolic gaps between them). The series of electrodes may include seven electrodes, with electrode one and electrode two (counting outwards from the longitudinal axis) forming a third pair (with parabolic gaps), electrodes two through six each separated by linear gaps (so that any adjacent pair corresponds to the first pair of electrodes as described above), and electrodes six through seven forming a second pair (with logarithmic parabolic gaps).

[0047] Optionally, the ion optical mirrors are symmetrical about the longitudinal axis. In this configuration, both ion optical mirrors function to deflect ions in a direction aligned with the longitudinal axis (drift direction) and ultimately reverse the ion drift direction. Alternatively, only one ion optical mirror may include curved electrodes as described in any of the above arrangements, while the other ion optical mirror may include a series of straight electrodes, such that each pair of adjacent electrodes is separated by a straight gap. In this configuration, only one ion optical mirror functions to deflect ions in a direction aligned with the longitudinal axis (drift direction).

[0048] The multi-reflection mass analyzer may further include an ion source located at one end of an ion optical mirror and an ion optical device operatively used to incident ions generated by the ion source into the ion optical mirror. An ion detector may be located at the same end of the ion optical mirror as the ion source. The ion detector is operatively used to detect ions reflected by the ion optical mirror.

[0049] The invention also relates to a method of operating any of the above-described multi-reflection mass analyzers, the method comprising a controller that applies a potential to a series of electrodes such that the potential difference between a first pair of adjacent electrodes is relatively high compared to the potential difference between a second pair of adjacent electrodes.

[0050] In the case where the second pair of adjacent electrodes is the outermost electrode relative to the longitudinal axis, the method may include a controller that provides an accelerating potential to accelerate ions passing through the mass analyzer and applies a potential higher than the accelerating potential to the second pair of adjacent electrodes.

[0051] When 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 respective parabolic edges of the adjacent electrodes, the method may include a controller that applies a potential to the series of electrodes such that the potential difference between the first pair of adjacent electrodes is relatively high compared to the potential difference between the third pair of adjacent electrodes. Attached Figure Description

[0052] Figure 1A and Figure 1B This demonstrates a quality analyzer of the first prior art.

[0053] Figure 2 This displays a second type of existing technology quality analyzer.

[0054] Figure 3 This displays a quality analyzer using the third existing technology.

[0055] Figure 4 The parabolic ion optical mirror of the display mass analyzer.

[0056] Figure 5This shows a quasi-parabolic reflector that can be used in the mass analyzer of this invention.

[0057] Figure 6 This displays another quasi-parabolic reflector that can be used in the mass analyzer of this invention, along with the electric field strength inside the reflector.

[0058] Figure 7 This displays the integral perturbation of the action and the time-of-flight perturbation as the position of the gap between the reflector electrodes changes.

[0059] Figure 8 This invention shows another quasi-parabolic reflector that can be used in the mass analyzer of this invention.

[0060] Figure 9 The display includes a mass analyzer featuring a quasi-parabolic reflector with relative orientation. Detailed Implementation

[0061] As mentioned above, Figure 1A and Figure 1B This is a schematic diagram of a prior art multi-reflection mass analyzer, which includes a parallel ion optical mirror linearly elongated along the drift length. Figure 1A The analyzer is displayed on the yz plane, while Figure 1B The same analyzer is displayed in the xz plane. Ion optical mirrors 11 and 12, positioned opposite each other, are elongated along the drift direction y and arranged parallel to each other. Ions are drawn from ion source 14 at an average angle relative to the z-axis. and angular divergence in the yz plane Upper incidence. Three ion flight paths were plotted at 20a, 20b, and 20c to illustrate the effect of this angular divergence. Several different paths are generated. Ion 20 follows a zigzag ion flight path, drifting relatively slowly in the drift direction y. After multiple reflections in mirrors 11 and 12, ion 20 reaches ion detector 16.

[0062] Figure 2 This demonstrates existing multi-reflection time-of-flight quality analyzers, including those using angle-based... The mirrors 11 and 12 are tilted, such that the spacing between them in the z-direction decreases as they extend in the drift direction y. Ions are supplied from the ion trap 14 to form an ion beam 20 guided and shaped by electrodes 18 and 19. Ions in the ion beam 20 oscillate in the Y-direction between the opposing mirrors 11 and 12. The mirrors converge at an angle of tilt. This causes the ion drift to reverse, so that ion 20 travels back through mirrors 11 and 12 to be detected by ion detector 16, which is positioned adjacent to ion trap 14. As described above, the time-of-flight aberration introduced by the tilted mirrors 11 and 12 is corrected by using strip electrode 24 to slow down ion 20 as it travels between mirror electrodes 11 and 12.

[0063] Figure 3 This is a schematic diagram of a multiple reflectance mass spectrometer, which includes parabolic ion mirrors 11 and 12 arranged opposite each other, the ion mirrors converging on each other in the drift direction away from the ion source 14. As already described, ions 20 follow a zigzag path through mirrors 11 and 12, and their drift directions are thus reversed, causing ions 20 to travel back towards detector 16. Figure 2 Compared to the layout, Figure 3 The parabolic ion mirror provides excellent spatial focusing of ion trajectories; however, the stringent tolerance requirements hinder the fabrication of curved electrodes.

[0064] Figure 4 A schematic diagram of a single parabolic reflector 12 is provided to illustrate its operation. Reflector 12 is defined by five electrodes 121-125, separated by parabolic gaps. Electrode 121 is the innermost electrode closest to the central axis of the mass analyzer 10, while electrode 125 is the outermost electrode. The other electrodes are labeled 122-124 sequentially. The primary ion optical characteristic of the reflector lies in providing a tilt angle θ(y) for each ion 20 upon reflection, which depends on the incident point y along the y-axis. Reflector 12 has a quadratic function Δ(y) = y 2 / 2R represents the curvature of all electrodes 121-125, where R is the radius of curvature. The same principle applies to all electrodes 121-125. From plane z0 to the flight reversal point z... m (y) and return the action integral on the ion path in plane z0.

[0065]

[0066] Where m, q, and u represent the ion's mass, charge, and accelerating voltage, respectively. More conveniently, this is expressed in terms of the incident ion's momentum p. z =√2mqu normalized action. This value is described by the following mass-independent integral with a length dimension.

[0067]

[0068] The action integral given by formula (1) allows for the derivation of two key characteristics of the electrostatic reflector 12 acting on the reflected ion 20: the deflection angle and the time of flight as a function of the incident point y. The deflected ion 20 gains momentum. The y-component, therefore the deflection angle is...

[0069]

[0070] And the time-of-flight difference of the reflection is the action derivative with respect to the ion energy.

[0071]

[0072] An ideal electrostatic parabolic ion reflector 12 should focus each incident parallel trajectory to a point located at focal length f, thus deflecting it by an angle of θ(y)-y / f. Figure 4 The integral of the action of the electrostatic reflector 12 calculated at point y differs from the integral calculated at the midpoint y = O by a length Δz = y. 2 / 2R is twice the free flight interval. This quantity Δz disappears from the integral due to the radius of curvature R. Therefore, according to formula (1), J(y,u)-J(0,u)=-y 2 / R and θ(y) = -2y / R correspond to ideal focusing with a focal length of f = R / 2.

[0073] Figure 4 The time-of-flight characteristic of the reflector 12 is non-uniform: unlike optical mirrors that utilize Fermat's principle, the concave electrostatic reflector 12 does not simultaneously bring ions to the focal point: T(y) ≠ const.

[0074] Quasi-parabolic mirror 112 is shown Figure 5 It includes five main electrodes 1121-1125. Generally speaking, it can be determined according to... Figure 4 The corresponding electrodes 121-125 of the quality analyzer apply the same or similar voltage to electrodes 1121-1125. However, the two main electrodes 1121-1125 are divided into two part-electrodes 112. 1A With 112 1B and 112 5A With 112 5B The voltage difference between the main electrodes 1121-1125 is relatively high. Therefore, a straight gap between the main electrodes 1121-1125 is advantageous because known precision machining methods (such as wire EDM) allow for manufacturing tolerances of a few micrometers for straight edges. This is not the case for electrodes with curved edges separated by curved gaps, in which case the same level of manufacturing precision is impossible.

[0075] The innermost main electrode 1121 is divided into electrically isolated electrode portions 112 separated by curved surface gaps 1251. 1A and 112 1B This also applies to the outermost main electrode 1125, which is divided into electrically isolated electrode portions 112 separated by curved gaps 1255.5A and 112 5B Different voltages are applied to the two electrode portions 112 of each pair. 1A With 112 1B and 112 5A With 112 5B However, by setting the voltage in this way, the voltage is distributed in 112 portions per pair of electrodes. 1A With 112 1B and 112 5A With 112 5B The voltage difference between gaps 1251 and 1255 is relatively small. For example, the voltage difference may only account for a few percent of the ion accelerating voltage u. This significantly reduced voltage difference relaxes the electrode portion 112. 1A With 112 1B and 112 5A With 112 5B The required precision is achieved when forming the curved edges of the defined surface gaps 1251 and 1255, without significantly affecting the operation of the mirror. Generally, the mechanical inaccuracies of the electrodes affect the electrostatic field they generate in proportion to the voltage difference between adjacent electrodes. Because the voltage difference across the surface gaps 1251 and 1255 is small—for example, at most 100 times smaller than the voltage difference across the straight gap separating the main electrodes 1121-1125—the mechanical tolerances for the surface gaps 1251 and 1255 are much more lenient, potentially reaching tens or even hundreds of micrometers. This is compatible with many conventional methods for fabricating curved electrode surfaces, such as milling.

[0076] The optimal shapes of the surface gaps 1251 and 1255 are defined to generate the action integral (2) in such a way that the deflection angle is obtained. It is a linear function of the coordinate y, and also satisfies the isochronous property T(y) = const.

[0077] The following considerations are used to determine the optimal shapes of the surface gaps 1251 and 1255, which make the quasi-parabolic ion mirror 112 equivalent to an ideal parabolic ion mirror in terms of focal length f = R / 2 and flatness dependence on time of flight (i.e., so that ions entering the mirror 112 simultaneously are reflected and reach the focal position simultaneously).

[0078] exist Figure 5 In the reflector 112, the innermost main electrode 1121 is divided into two complementary electrode portions 112. 1A and 112 1B Generally, one electrode section is grounded, while the other electrode section receives a small bias voltage. For example, electrode 112... 1A A positive bias voltage Δv1 is applied to focus cation 20. Electrodes can be distributed in 112. 1AThe shape variation along the y-axis is described as a y-dependent width s1(y). The bias voltage Δv1 is small compared to the accelerating voltage u of the ions. For example, u might be approximately 4000V and / Δv1 / ≤ 40V. Ions 20 pass through electrode section 112 during each oscillation within mirror 112. 1A The event occurs twice, once before each reflection and once after each reflection, and both passes cause an integral perturbation in the action. A small bias voltage Δv1 allows for a linearized approximation of this perturbation.

[0079]

[0080] Note that the forward bias voltage Δv1 > 0 (assuming ion 20 is a cation, which is decelerated) produces a positive time shift ΔT1, and the time shift is greater for ions 20 that are furthest from the z-axis in both y-directions. ΔJ1 and ΔT1 are proportional to each other, and therefore, at electrode section 112 1A Between 112 1B The spatial focusing of the curved surface gap 1251 inevitably produces time-of-flight differences manifested by the dependence of time-of-flight on the incident point y of ion 20.

[0081] However, this difference in flight time can be corrected by separating another main electrode 1122-1125. Figure 5 In the embodiment shown, the outermost electrode 1125 is divided into electrode portions 112. 5A and 112 5B The main electrode 1125 is the electrode with the maximum forward bias voltage. The inner electrodes of this pair can be divided into 112 sections. 5A The shape variation along the y-axis is described as a y-dependent width s5(y).

[0082] Electrode section 112 5A With voltage V5 applied as a bias, electrode distribution 112 5B With voltage v 5B =v5 + Δv5 (bias voltage applied), where Δv5 is smaller than the ion accelerating voltage u. In the conventional mass analyzer 10, voltage v5 exceeds the accelerating voltage u, and ions 20 are reflected near the interface between the main electrodes 124 and 125. Figure 5 In the reflector 112, the voltage v5 set on the electrode section 1125 also exceeds the accelerating voltage u, so the ions 20 do not completely pass through the electrode 112. 5B Nevertheless, applied to electrode section 112 5B The voltage difference adjusted the ion reflection coordinate z. m (y) and the integral of the effect of reflection.

[0083] Generally, for the electrode portion 112 5BThe disturbance of the action caused by the voltage Δv5 has no analytical solution. Nevertheless, for electrode section 112 5A The dependence of the s5(y) width is expected to be exponential as the voltage disturbance propagates between the two conductive plates separated by a distance H, which is determined by the attenuation coefficient exp(-πs5 / 2H). The effects on the action integral and reflection time are proportional to the bias voltage Δv5 and the attenuation coefficient:

[0084]

[0085] Where A[mm] and B[μs] are constants to be determined through numerical simulation. Note that the positive voltage Δv5 causes ion 20 (anion) to reverse its flight direction at a smaller z-coordinate, thus making both the action and time perturbations negative. Therefore, coefficients A and B are both less than zero. This contrasts with the bias electrode section 112, which has the opposite sign. 1B The resulting contributions ΔJ1 and ΔT1 are different, and the electrode distribution is 112. 5B The bias voltage Δv5 generates contributions ΔJ5 and ΔT5 with the same sign. Therefore, using the electrode portion 112... 1A With 112 1B and 112 5A With 112 5B The surface gaps 1251 and 1255 between the two surfaces may increase the summation contribution to the action integral ΔJ1+ΔJ5, while simultaneously causing the subtractive combination to be eliminated, thus ΔT1+ΔT5=0. That is...

[0086]

[0087] The accuracy is reduced to non-essential constants because both the deflection angle and the time-of-flight difference are expressed by the derivatives of (5) and (6). When the action perturbation ΔJ is differentiated with respect to y to find the deflection angle θ(y), the constant c1 disappears; and the constant c2 is the same time-of-flight offset for all ions and is therefore not essential for operating the time-of-flight mass analyzer.

[0088] According to equations (5) and (6), electrode section 112 1B and 112 5A The shape functions s1(y) and s5(y) take a specific form

[0089] s1(y)=s 10 +k1y 2 (7)

[0090]

[0091] Where s 10 [mm]、k1[mm -1 ] and s 50[mm]、k5[mm -1 ] is a coefficient that can be chosen with a certain degree of freedom. Substitute (7) and (8) into (5) and (6), and make y 2 With the previous coefficients equal, we obtain the equations for Δv1 and Δv5.

[0092]

[0093] Equation (10) establishes the proportional relationship between Δv1 and Δv5, where the diffusion of the mirror relative to the incident ion at the y position is isochronous, and Equation (9) sets the desired focal length.

[0094] The advantage of the quasi-parabolic ion reflector 112 is that its effective radius of curvature can be electrically varied by applying different bias voltages Δv1 and Δv5, which is impossible for a reflector 12 whose electrodes 121-125 are physically curved. As an example of implementing such a quasi-parabolic stripe, we consider a structure with similar... Figure 5 The five main electrodes 1121-1125 shown are ion optical mirrors 112.

[0095] Figure 6 A side view of this quasi-periodic electrostatic reflector 112 is shown, wherein the first and last main electrodes 1121 and 1125 are divided into two electrode portions 112. 1A With 112 1B and 112 5A With 112 5B Electrode section 112 1B and 112 5B With respect to its complementary electrode portion 112 1A and 112 5A Bias voltages Δv1 and Δv5 are applied.

[0096] Figure 7 (Upper part) shows the perturbation of the action integral ΔJ with respect to the normalization of ion incident momentum and the curve electrode section 112. 1B and 112 5B The time-of-flight disturbance is generated by the bias voltage Δv1 / u=Δv5 / u=1V / 4000V. Figure 7 (Lower section) shows the corresponding time shift ΔT for ions with m / z = 1000 Da. The action integral ΔJ and time difference ΔT are expressed as functions of the corresponding interstitial positions s1 and s5.

[0097] As predicted by theory, the action integral ΔJ and the time perturbation ΔT are linearly related to s1 and exponentially related to s5, with a decay constant of π / 2H, where H = 24 mm is half the distance along the X-axis between electrodes 1111-1115 and 1121-1125 (these distances are equal since electrodes 111 and 112 lie on the same plane parallel to the yz plane). This was found in ion optical simulations (using the MASIM 3D software package).

[0098] ΔJ≈Aexp(-πs5 / 2H)andΔT≈B exp(-πs5 / 2H)

[0099] The exponential constants A and B are A = -16.676 mm and B = -15.6287 μs (for m / z = 1000 Th).

[0100] Based on this information, the solution for the geometric constant that realizes the flatness dependency T(y) in formulas (7) and (8) can be obtained through simple algebraic operations. This is not unique; a solution with reasonable mechanical constraints is...

[0101] s 10 =s1(0)=10mm, k1=0.003mm -1

[0102] s 50 =1.75mm, k5 =1.72×10 -4 mm -1

[0103] Solving equations (9) and (10) for Δv1 and Δv5, while assuming the focal length of the mirror is f = 10m, we obtain Δv1 ≈ 64.2V; Δv5 ≈ -61.8V. These voltage differences are indeed small compared to the ion acceleration voltage u, which proves that the assumptions for deriving approximate formulas for the difference in action and time of flight are reasonable.

[0104] Figure 8 This shows the parameters determined above, in electrode section 112 1A With 112 1B and 112 5A With 112 5B The structure of the quasi-parabolic mirror 112 with gaps between them. Separating electrodes 112 1A and 112 1B The gap s1(y) is parabolic, and electrode 112 5A With 112 5B The gap s5(y) is logarithmically parabolic (according to the function definition corresponding to the logarithm of a quadratic polynomial).

[0105] Figure 9A time-of-flight mass analyzer 110 is shown, comprising a pair of parabolic mirrors 111 and 112. Each mirror 111 and 112 includes an electrode portion 111 having a complementary parabolic shape according to equation (8). 1A With 111 1B and 112 1A With 112 1B And the electrode portion 111 with a complementary logarithmic parabolic shape according to equation (8). 5A With 111 5B and 112 5A With 112 5B The other main electrodes 1112-1114 and 1122-1124 have straight edges and are parallel to each other, which is beneficial for their high-precision manufacturing.

[0106] The ion beam 20 originating from ion source 14 oscillates multiple times between mirrors 111 and 112 before finally impacting ion detector 16. In this embodiment, electrode portion 111 1B and 112 1B All are grounded and the electrode distribution is 111 1A and 112 1A It has a bias voltage Δv1. Electrode section 111 5A and 112 5A A voltage v5 higher than the ion acceleration voltage u causes ions 20 to be present at electrodes 1114 and 111. 5A and 1124 and 112 5A Turn back near the interface between them. Electrode section 111 5B and 112 5B Further relative to electrode portion 111 5A and 112 5A Applying a bias voltage with a voltage difference Δv5 causes the ion reflection point z to be affected. m The bias voltage Δ can be set by varying along the y-direction along mirrors 111 and 112. v1 And Δv5 ensures that the oscillation time of ion 20 is constant in all oscillations, regardless of its incident angle in mirrors 111 and 112 or its position in the drift (y) direction along mirrors 111 and 112.

[0107] In other embodiments, a bias voltage Δv1 is applied to a voltage having a similar value to... Figure 2 The parabolic strip electrode 24 shown is a biased strip located in front of the ion optical mirrors 111 and 112. This biased strip can be considered a functional part of the mirror.

[0108] Those skilled in the art will understand that the present invention is not limited to the embodiments shown, and many additions and modifications can be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A multi-reflection mass analyzer, comprising a pair of opposing ion optical mirrors, the ion optical mirrors being linearly elongated along a centrally extending longitudinal axis through the mass analyzer, the ion optical mirrors being arranged substantially parallel to each other, and one or both ion optical mirrors comprising a series of spaced-apart electrodes, wherein: Each electrode is elongated along the longitudinal axis; The series of electrodes extends in a direction transverse to the longitudinal axis, and the electrodes are separated 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 are separated by a straight gap defined by the corresponding straight edges of the adjacent electrodes; and The second pair of adjacent electrodes are separated by a curved gap defined by the corresponding curved edges of the adjacent electrodes.

2. The multi-reflection quality analyzer according to claim 1, wherein the curved edges of the second pair of adjacent electrodes are defined according to a function corresponding to the logarithm of a quadratic polynomial.

3. The multi-reflection quality analyzer according to claim 2, wherein: The vertical axis of the mass analyzer defines the y-axis of the Cartesian coordinate system, and a series of electrodes extend at right angles relative to the y-axis to define the z-axis. One or two ion optical mirrors include first and second series of corresponding electrodes arranged opposite to each other and spaced apart along the x-axis; and The second pair of adjacent electrodes has a width in the z-axis direction, which varies with the position y along the y-axis according to the logarithmic parabolic formula: Where H is the half-space between the corresponding electrode and its corresponding electrode in the x-axis direction, s0 is the minimum width of the corresponding electrode, and k is a constant.

4. The multi-reflection mass analyzer according to any of the preceding claims, wherein: The straight edges of the first pair of adjacent electrodes are formed within a tolerance of less than 10 micrometers, and the logarithmic parabolic edges of the second pair of adjacent electrodes are formed within a tolerance of greater than 10 micrometers; and / or The straight edges of the first pair of adjacent electrodes are formed within a tolerance range that is at least an order of magnitude smaller than the tolerance of the curved edges of the second pair of adjacent electrodes.

5. The multi-reflection quality analyzer according to any of the preceding claims, further comprising a controller configured to apply a potential to a series of electrodes such that the potential difference between the first pair of adjacent electrodes is relatively high compared to the potential difference between the second pair of adjacent electrodes.

6. The multi-reflection mass analyzer according to claim 5, wherein the second pair of adjacent electrodes are the outermost electrodes relative to the longitudinal axis.

7. The multi-reflection mass analyzer of claim 6, wherein the controller is further configured to provide an accelerating potential to accelerate ions passing through the mass analyzer, and the controller is configured to apply a potential higher than the accelerating potential to the second pair of adjacent electrodes.

8. The multi-reflection quality analyzer according to any one of claims 5 to 7, wherein the series of electrodes further comprises a third pair of adjacent electrodes, and the third pair of adjacent electrodes is separated by a curved gap defined by the respective curved edges of the adjacent electrodes.

9. The multi-reflection quality analyzer according to claim 8, wherein the curved edges of the third pair of adjacent electrodes have a parabolic shape defined by a quadratic polynomial according to coordinate y.

10. The multi-reflection quality analyzer according to claim 8 or 9, wherein the series of electrodes further comprises pairs of adjacent electrodes separated by a linear gap defined according to the respective linear edges of adjacent electrodes.

11. The multi-reflection quality analyzer of claim 10, wherein the innermost adjacent electrode pair forms a third pair, the outermost adjacent electrode pair forms a second pair, and all other adjacent electrode pairs correspond to the first pair or other adjacent electrode pairs.

12. The multi-reflection quality analyzer according to any one of claims 8 to 11, wherein: The second and third pairs of adjacent electrodes are shaped such that the time-of-flight difference introduced into the ions by the third pair of adjacent electrodes is offset or substantially offset by the time-of-flight difference introduced into the ions by the second pair of adjacent electrodes.

13. The multi-reflection mass analyzer according to any one of claims 8 to 12, wherein the controller is configured to apply a potential to a series of electrodes such that the potential difference between the first pair of adjacent electrodes is relatively high compared to the potential difference between the third pair of adjacent electrodes.

14. The multi-reflection quality analyzer according to claim 13, wherein the third pair of adjacent electrodes are the innermost electrodes relative to the longitudinal axis.

15. The multi-reflection quality analyzer of claim 14, wherein the controller is configured to apply a potential to adjacent electrodes of the third pair of electrodes such that one of the electrodes of the third pair is grounded.

16. The multi-reflection quality analyzer according to any one of claims 8 to 15, wherein: The straight edges of the first pair of adjacent electrodes are formed within a tolerance of less than 10 micrometers, and the parabolic edges of the third pair of adjacent electrodes are formed within a tolerance of greater than 10 micrometers; and / or The straight edges of the first pair of adjacent electrodes are formed within a tolerance range that is at least an order of magnitude smaller than the parabolic edges of the third pair of adjacent electrodes.

17. The multi-reflection quality analyzer according to any one of claims 8 to 16, wherein: The vertical axis of the mass analyzer defines the y-axis of the Cartesian coordinate system, and a series of electrodes extend at right angles relative to the y-axis to define the z-axis. One or two ion optical mirrors include first and second series of corresponding electrodes arranged opposite to each other and spaced apart along the x-axis; The second pair of adjacent electrodes has a width in the z-axis direction, which varies with the position y along the y-axis direction according to the following formula: Where H is the distance between the corresponding electrode and its corresponding electrode in the x-axis direction, s0 is the minimum width of the corresponding electrode, and k is a constant. The width of the third pair of electrodes in the z-axis direction varies with the position y along the y-axis according to the formula: s′(y)=s′0+k′y 2 Where s'0 is the minimum width of the electrode, and k' is a constant.

18. The multi-reflection mass analyzer of claim 17, wherein s0, s'0, k, k and k' are configured such that the time-of-flight difference introduced into the ions by the third pair of adjacent electrodes is offset or substantially offset by the time-of-flight difference introduced into the ions by the second pair of adjacent electrodes.

19. The multi-reflection quality analyzer according to any of the preceding claims, wherein the mirrors are symmetrical about the longitudinal axis.

20. The multi-reflection quality analyzer according to any of the preceding claims, further comprising: An ion source located at one end of the mirror; An ion optical device operable to direct ions generated by an ion source into a mirror; and An ion detector, located at the same end of a mirror as the ion source, is operable to detect ions reflected by the mirror.

21. A multi-reflection mass analyzer according to any preceding claim, the method comprising: A controller that applies a potential to a series of electrodes such that the potential difference between the first pair of adjacent electrodes is relatively high compared to the potential difference between the second pair of adjacent electrodes.

22. The method of claim 12, wherein the second pair of adjacent electrodes are the outermost electrodes relative to the longitudinal axis and the method includes a controller that provides an accelerating potential to accelerate ions passing through the mass analyzer and applies a potential higher than the accelerating potential to the second pair of adjacent electrodes.

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

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