Ion centrifuge ion separation equipment and mass spectrometer system

Abstract

An ion separation device comprises: (a) a first ion blanket and a second ion blanket, each of the first ion blanket and the second ion blanket comprising: a substrate having a first face and a second face; and a set of electrodes disposed on or below the first face, wherein a first plurality of electrodes in the set of electrodes are configured to define at least one set of circular sectors; (b) an ion exit aperture passing through one ion blanket; and (c) one or more power supplies configured to provide a radio frequency voltage to a first subset of the electrodes of each ion blanket, provide a potential difference across electrodes of the first subset of electrodes of each ion blanket, and provide a time-varying voltage to the first plurality of electrodes of each ion blanket that migrates through the sectors in the form of a traveling wave, wherein the ion blankets are disposed parallel to each other with a gap between them and the first faces facing each other across the gap.

Description

Technical Field

[0001] The present disclosure relates to mass spectrometry and, more particularly, to ion transport and separation devices for use as components of mass spectrometers.

[0002] Incorporated by Reference

[0003] All publications, patents, and patent applications mentioned in this specification are hereby incorporated herein by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference, except that in the event of any conflict between an incorporated reference and the present specification, the language of the present specification controls. Background Art

[0004] Most mass spectrometry devices employ at least one mass filter. Broadly speaking, a mass filter is a device capable of receiving an inlet ion stream comprising a plurality of different ion species and outputting an outlet ion stream, wherein the plurality of different ion species comprise different corresponding mass-to-charge (m / z) values ​​within a wide m / z range, and wherein the outlet ion stream consists of only a subset of the inlet ion species, wherein the subset of ion species comprises a much narrower m / z range. FIG1 schematically illustrates an example of a known use of a mass filter device 80. In this example, the mass filter device 80 is used to eliminate all ion species that do not comprise a desired m / z range from an ion stream generated by an atmospheric pressure ion source. As depicted in FIG1 , the mass filter device 80 comprises a quadrupole mass filter comprising a pair of X rod electrodes 83 and a pair of Y rod electrodes 81. In operation of the mass filter device 80, one or more power supplies (not shown) provide an oscillating radio frequency (RF) voltage waveform to the rod electrodes, wherein the RF phase applied to the Y rod electrode 81 is π radians out of phase with the RF phase applied to the X rod electrode 83. In a known manner, a DC offset voltage and / or an oscillating non-RF alternating current (AC) voltage may be applied to the rod electrodes in order to exclude ions that are not within the m / z range of interest.

[0005] In operation, an electrospray ion source (or other atmospheric pressure ion source) 44 within ion chamber 41 emits a plume 45 of ions, typically mixed with gas and / or solvent droplets. The ions include a large variety of ionic species with varying m / z values. Charged particles (ions and some droplets) are separated from the bulk of the gas by an electric field, which diverts them into an aperture within a partition 42 separating atmospheric pressure ion chamber 41 from an intermediate vacuum chamber 43. In the illustrated example, the aperture is the lumen of a heated ion transfer tube 47, which facilitates evaporation of most of the remaining droplets. The ions and remaining gas enter the evacuated chamber as a jet plume 71. A plasma focusing device 169, such as an ion funnel or other stacked annular ion guide, narrows the ion plume into a narrow ion beam 72, which is directed at the inlet end of a mass filter assembly 80 into the central axis of the assembly. An exit ion beam 75, exiting the assembly at its outlet, includes fewer ionic species than those contained in ion beam 72. Reduction in the number of ionic species is achieved by rejecting or neutralizing all ions that are not within the desired m / z range of interest before they are able to travel through the mass filter device to its outlet port.

[0006] Due to the above-mentioned ion rejection, the mass filter is not very efficient when considering overall ion usage. In order to improve the efficiency of ion usage, it is desirable to: (a) pre-separate each segment of the ions of the incoming ion beam 72 into a plurality of subsets, each of the plurality of subsets containing only a subset of the ion species of the ion beam 72, wherein each subset of the ion species includes an m / z range narrower than the m / z range of the ion beam 72; and (b) deliver the various ion subsets to the mass filter sequentially. This is a challenging problem because the ion pre-separation equipment must be tolerant to high ion beam intensities and, if the pre-separation equipment involves ion trapping, the pre-separation equipment must also be tolerant to high space-charge potentials. The device must also be able to eject ions with controlled energy so that the ions contribute to further mass isolation and activation in the mass filter 80. Conventionally, various types of ion mobility separation devices are used as pre-separation devices and ion delivery devices, which condition the ion beam before delivery to the mass filter device.

[0007] Radio frequency (RF) ion blankets have been used as focused ion guides and ion transport devices and have previously been used in high energy physics experiments. Very generally, an ion blanket is an ion transport device that includes a substrate on which a plurality of electrodes are disposed, with an oscillating radio frequency (RF) voltage applied to the electrodes, where the applied RF phase differs by π radians across each pair of adjacent electrodes. For example, Takamine et al. (“Space-charge effects in the catcher gas cell of a RF ion guide”, Review of Scientific Instruments, 76

[10] , pp. 103503-103503-6, 2005) and Schwarz (“RF ion carpets: The electric field, the effective potential, operational parameters and an analysis of stability”, International Journal of Mass Spectrometry, 299[2-3], pp. 71-77, 2011) have described the use of ion carpets for trapping high-energy particles in high-energy physics experiments.

[0008] There is very little description of the use of ion blanket devices in mass spectrometry applications. For example, in commonly assigned U.S. Patent No. 8,829,463, Senko et al. describe an ion blanket ion transport device for use within a mass spectrometer to transport ions from one or more ion sources. Figure 2 is a schematic cross-sectional depiction of electrodes of one embodiment of an ion blanket ion transport device 10 as taught by Senko et al. In three dimensions, the device 10 is radially symmetric about a central axis 3. The device 10 includes a plurality of strip electrodes 4 disposed on a flat substrate 8. The width and spacing of the strip electrodes 4 vary from the periphery to the center of the device. Typically, the wider electrodes are positioned toward the outer edges—away from the central axis 3—and the electrode width gradually narrows toward the center. A generally cylindrical cage electrode 7 partially surrounds the plurality of strip electrodes 4, and an exit aperture 1 is preferably disposed inwardly from one or more innermost electrodes along the central axis 3. An extraction electrode 5 is disposed adjacent to the innermost strip electrodes and is supplied with a voltage to receive ions exiting the device 10 through the exit aperture 1. The extraction electrode 5 may comprise, for example, an ion transfer tube or any other form of ion transfer optical device or ion optical assembly for transferring ions collected by and from the ion blanket to another portion of an ion spectrometer (e.g., a mass spectrometer or an ion mobility spectrometer) of which the ion blanket device is a part. The extraction electrode may comprise a dedicated component of the ion blanket device.

[0009] During operation of the RF ion blanket device 10, an RF voltage generator (not shown in FIG. 2 ) is electrically coupled to each of the plurality of strip electrodes 4 and provides an oscillating voltage thereto, such that an RF phase difference of π radians exists between each pair of adjacent electrodes. For example, the plurality of strip electrodes 4 may be comprised of two electrode subsets: a first electrode subset 4a and a second electrode subset 4b, the two electrode subsets being indicated by different shading patterns, such that an RF phase difference of π radians exists between each pair of adjacent electrodes. Additionally, at least one direct current (DC) voltage generator (not shown) supplies a corresponding DC bias voltage to each of the plurality of strip electrodes 4. A DC voltage is also supplied to the cage electrode 7. The applied DC voltage generates an electric field that repels ions away from the cage electrode 7 and encourages ions to migrate away from the periphery and toward the central axis 3.

[0010] FIG2 further shows equipotential lines 2 calculated using a one-dimensional electrostatic model, wherein the width of the ion blanket device is set to 100 mm, the width of the exit aperture is set to 2 mm, the voltage in the cage electrode 7 is set to 10 V, the voltage on the extraction electrode 5 is set to −110 V, and the bias DC potential difference between each pair of adjacent strip electrodes 4 is set to 1 V. The model also uses a 750 kHz RF voltage with a peak amplitude of 200 V applied to each strip electrode. It is assumed that ions with mass-to-charge ratios (m / z) ranging from 100 to 1000 are generated from an ion source (not shown) located near the upper right corner of the device. The ion trajectories through the ion blanket device 10 are calculated using a SIMION® ionizer commercially available from Scientific Instrument Services of 1027 Old York Rd. Ringoes, N.J. 08551-1054 USA. TM The overall trajectory of the ion paths within the device 10 is indicated by the ion cloud 6, as calculated from the simulations described above.

[0011] Senko et al. showed that high efficiency transfer of ions from the edge of the device 10 to the central exit aperture is possible. There are only a few descriptions of the use of ion blanket devices or related devices as ion separation devices (e.g., U.S. Patent No. 5,572,035; U.S. Patent No. 7,365,317). Nevertheless, the potentially large area of ​​the surface adjacent to the ion blanket is suitable for temporarily storing and manipulating the large ion flux generated by the ion source. The distribution of ions throughout the spatial region of the surface area adjacent to the ion blanket can reduce the interfering effects of high space charge potentials that may be present in conventional mass spectrometer pre-separation equipment. In addition, it is known that in the presence of multiple non-cooperative forces, ion species with different corresponding m / z values ​​can be at least partially separated from each other. The inventors have recognized that one way to confine ions to a spatial region adjacent to the surface of the ion blanket is to balance inwardly directed radial electrostatic forces with outwardly directed radial "centrifugal forces." Summary of the Invention

[0012] To address the need for a more efficient ion pre-separation device for use upstream of a conventional mass filter, the inventors have developed an ion centrifuge apparatus employing a pair of ion blanket components. Specifically, an ion separation apparatus is provided, comprising: (a) a first ion blanket and a second ion blanket, each ion blanket comprising: a substrate having a first face and a second face; and a set of electrodes disposed on or below the first face, wherein a first plurality of electrodes in the set of electrodes are configured to define at least a set of circular sectors; an ion exit aperture passing through one of the ion blankets; and one or more power supplies configured to provide an oscillating radio frequency (RF) voltage to at least a first subset of the electrodes of each ion blanket, a non-oscillating direct current (DC) potential difference across at least the first subset of electrodes of the electrodes of each ion blanket, and a time-varying DC voltage that migrates across the sectors in a traveling wave manner to the first plurality of electrodes in the set of electrodes of each ion blanket, wherein the first ion blanket and the second ion blanket are disposed parallel to each other with a gap between the first ion blanket and the second ion blanket, wherein the first faces of the ion blankets face each other across the gap.

[0013] In some embodiments, the width of the gap is between 5 mm and 20 mm. In some embodiments, the gas pressure within the ion separation device is in the range of 1 mTorr to 10 Torr (0.13 Pa-1.3 kPa). In some embodiments, the first plurality of electrodes in the set of electrodes for each ion blanket define a first set of circular sectors and a second set of circular sectors, the first set of circular sectors being sectors of a first circle and the second set of circular sectors being sectors of a second circle located within the first circle, wherein the total number of sectors in the first set of sectors is different from the total number of sectors in the second set of sectors. In some embodiments, each electrode in the first plurality of electrodes in the set of electrodes for each ion blanket has the form of an arc segment of a circle, and each electrode in the first subset of electrodes for each ion blanket is an annular electrode having the form of a complete circle, wherein the circle of annular electrodes is concentric about a central axis of the ion separation device, the central axis being perpendicular to the face of the ion blanket and passing through the ion exit aperture. In some other embodiments, the first plurality of electrodes in the set of electrodes for each ion blanket is identical to the first subset of electrodes for each ion blanket. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and various other aspects of the invention will become apparent from the following description, given by way of example only and with reference to the accompanying drawings, which are not necessarily drawn to scale, in which:

[0015] FIG1 is a schematic depiction of a portion of a mass spectrometer apparatus including a mass filter that receives a flow of ions from an ion source;

[0016] FIG2 is a schematic cross-sectional depiction of electrodes of one embodiment of a known ion blanket ion transport device;

[0017] Figure 3A is a schematic perspective view of a first ion separation apparatus according to the teachings of the present invention;

[0018] Figure 3B yes Figure 3A a schematic cross-sectional view of the first ion separation apparatus depicted in , further illustrating an outer guard electrode structure;

[0019] Figure 3C yes Figure 3A a schematic cross-sectional view of a variant embodiment of the first ion separation apparatus depicted in ;

[0020] Figure 3D yes Figure 3A A schematic diagram of an electrode configuration of an ion blanket component of an ion separation device;

[0021] Figure 3E It is Figure 3A Schematic diagram of applying a series of inwardly monotonically decreasing potentials to the annular electrodes of the ion separation device and applying a series of rotating traveling wave potentials to the second set of electrodes of the ion separation device;

[0022] Figure 4 yes Figure 3A Schematic diagram of an alternative electrode configuration for an ion blanket component of an ion separation device;

[0023] Figure 5A is a schematic perspective view of a second ion separation apparatus according to the teachings of the present invention;

[0024] Figure 5B yes Figure 5A A schematic diagram of an electrode configuration of an ion blanket component of an ion separation device;

[0025] Figure 6A is a schematic diagram of the potential applied to the annular electrode of the ion separation device according to the teachings of the present invention;

[0026] Figure 6B is a schematic diagram of a rotating traveling wave potential of a set of paddle electrodes of an ion separation device according to the teachings of the present invention;

[0027] Figure 7 is a set of graphs showing the calculated ion separation resolution of an ion separation apparatus according to the teachings of the present invention as a function of the spacing between two ion blanket members and as a function of the mass-to-charge ratio of the ion outlet from the apparatus;

[0028] Figure 8 is a schematic diagram of a portion of a mass spectrometer system incorporating an ion separation apparatus according to the teachings of the present invention; and

[0029] Figure 9 is a flow chart of a method according to the teachings of the present invention. DETAILED DESCRIPTION

[0030] The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a specific application and its requirements. Various modifications to the described embodiments will be apparent to those skilled in the art, and the general principles herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments and examples shown, but should be consistent with the widest possible scope in accordance with the features and principles shown and described. In order to fully understand the features and advantages of the present invention in more detail, the reader is invited to refer to the following description in conjunction with the following description. Figures 3A-3E , 4, 5A, 5B, 6A, 6B and 7-9.

[0031] In the description of the present invention herein, it will be understood that, unless otherwise implicitly or explicitly understood or stated, words appearing in the singular encompass their plural counterparts, and words appearing in the plural encompass their singular counterparts. Furthermore, it will be understood that, unless otherwise implicitly or explicitly understood or stated, for any given component or embodiment described herein, any possible candidate or alternative listed for the component may generally be used individually or in combination with one another. It will be understood that, unless otherwise implicitly or explicitly understood or stated, any list of candidate or alternatives is merely illustrative and not restrictive. Furthermore, it will be understood that the drawings as shown herein are not necessarily drawn to scale, wherein only some elements may be drawn for clarity of the present invention. Furthermore, reference numerals may be repeated in the various figures to illustrate corresponding or similar elements.

[0032] As used herein, when the term "DC" refers to a voltage applied to one or more electrodes of a mass spectrometer component, it does not necessarily mean that a current is applied or exists through these electrodes, but is only used to indicate that the applied voltage in question is static, or if non-static, non-oscillating and non-periodic. Thus, the term "DC" is used herein to distinguish the voltage in question from an applied periodic oscillating voltage, which itself may be referred to as an "RF" or "AC" voltage. Similarly, when referring to an oscillating voltage applied to one or more electrodes of a mass spectrometer component, the terms "RF" and "AC" do not necessarily mean that a current is applied or exists through these electrodes.

[0033] Figure 3Ais a schematic perspective view of a first ion separation device 50 according to the teachings of the present invention. The ion separation device 50 includes two ion blanket components 51a, 51b, each of which includes an electrically insulating substrate (substrate plate or substrate board) 18a and 18b arranged parallel to each other and separated by an inter-ion blanket gap 53 of width D. Each of the ion blanket components includes a first set of electrodes 54 and a second set of electrodes 55 arranged on or under the surface of the respective substrate, wherein the surfaces having the electrodes on or at the respective substrate face each other across the gap. In a preferred embodiment, the ion blanket components can be manufactured as a conventional printed circuit board, wherein the substrates 18a, 18b include layered fiber reinforced plastic and the electrodes 54, 55 include interlayer copper traces. However, the substrates may include any suitable rigid insulating material, and the electrodes may be any suitable conductive material in any form, such as embedded or attached wires or printed or deposited metal films or foils. Due to Figure 3A , the electrodes of the ion blanket member 51a are not visible in the drawing.

[0034] One of the ion blanket members ( Figure 3A The ion blanket member 51a in the apparatus 50 has an ion exit aperture 52 that extends completely through the ion blanket member. During operation of the apparatus 50, separated ion species exit the ion exit aperture 52 at different times depending on their respective mass-to-charge ratio (m / z) values. An extraction electrode (not shown) can be positioned adjacent to or within the ion exit aperture 52. A central axis 13 of the apparatus 50, which is perpendicular to a parallel plane of the ion blanket member, passes through the center of the exit aperture 52. A repeller electrode can also be positioned on or within the opposing ion blanket member 51b. In operation, one or more voltages applied to the extraction electrode and / or the repeller electrode can help to encourage ions to exit through the aperture.

[0035] Figure 3B yes Figure 3A The ion separation device 50 depicted in FIG. Figure 3D Schematic cross-sectional view taken along the cross section AA' is shown. As shown, the surfaces of the two ion blanket members 51a, 51b having electrodes 54, 55 thereon or therein face each other and define an inter-ion blanket gap 53 between the two ion blanket members. Figure 3AAlthough not explicitly shown in the figures, the ion separation device 50 may also include one or more guard electrodes 17 that further limit the gap 53 and, during operation, help confine the ions within the gap by preventing them from being ejected radially out of the gap. In an embodiment, the device 50 may include only a single guard electrode 17 surrounding the periphery of the two ion blanket members 51a, 51b. If the ion blanket members are circular in plan view, such a single guard electrode may take the form of a right circular cylinder. The one or more guard electrodes (if present) have one or more ion inlet apertures 19 therein or therebetween, which, during operation of the device 50, are used to introduce ions into the inter-ion blanket gap 53.

[0036] Also like Figure 3B As shown, the two ion blanket members 51a, 51b include a first region 58 through which the central axis 13 passes and in which the second electrode 55 is absent. The first region is surrounded by a second region 56a in which both the first electrode 54 and the second electrode 55 are present. The first electrode 54 is present in both regions 58, 56a.

[0037] Figure 3C is a schematic cross-sectional view of an ion separation device 250 according to the teachings of the present invention. The device 250 is Figures 3A-3B . Ion separation device 250 differs from ion separation device 50 in that one of the ion blanket members is replaced by a simple plate electrode 254, which preferably includes a flat electrode surface parallel to the remaining ion blanket members (e.g., ion blanket member 51a) and facing the ion blanket member across gap 53. The configuration of the electrodes of the remaining ion blanket members remains unchanged from the above configuration. Although Figure 3C The plate electrode 254 is depicted as a single, unitary piece, but the plate electrode 254 may alternatively be provided as a conductive coating, film, or foil disposed on or within a non-conductive substrate.

[0038] Replacing one ion blanket member with its patterned electrode structure with a single plate electrode does not change the basic function of the device, which depends on the voltage distribution applied to the electrodes of at least one ion blanket member. As is known, the so-called "pseudopotential field" generated by applying an RF voltage to the electrodes on the surface of the ion blanket device effectively repels ions of both polarities away from the surface. If a simple plate electrode with a voltage that repels ions of a given polarity is placed parallel to the ion blanket device and spaced apart from the ion blanket device, such as Figure 3CAs shown, the combination of the ion blanket and the plate electrode is also an ion confinement device for ions of a given polarity. In this case, the ions are pushed into the gap 53 by both the ion blanket and the plate electrode.

[0039] Returning to the discussion of the first ion separation device 50, Figure 3D is a schematic plan view representation of an ion blanket member 51b of the apparatus as viewed directly toward its electrode-bearing surface. Another ion blanket member 51a is generally similar to ion blanket member 51b, except that ion blanket member 51a has an ion exit aperture at its center. Electrode 54 comprises a set of concentric circular rings and is therefore referred to herein as a ring electrode. The geometric circle defined by the ring electrodes of ion blanket members 51a, 51b is concentric about the ion exit aperture. Furthermore, the projection of the ion exit aperture onto ion blanket member 51b is substantially the common center of the circle defined by ring electrodes 54. It should be noted that while the ring electrodes of ion blanket members 51a, 51b are substantially circular in form, the substrates 18a, 18b on which the electrodes are mounted need not be circular in plan view and may be formed in any shape.

[0040] The electrodes 54 of the ion separation device 50 are similar to the electrodes 4 of the known device 10 ( FIG. 2 ). In operation of the device 50, an RF power supply supplies an oscillating voltage to each of the plurality of annular electrodes 54, such that there is an RF phase difference of π radians between each annular electrode 54 and its nearest adjacent annular electrode 54. In addition, a direct current (DC) voltage generator (not shown) supplies a corresponding DC bias voltage to each of the plurality of annular electrodes 54. The pseudopotential generated by the oscillating RF voltage applied to the annular electrodes 54 of the ion blanket members 51 a, 51 b serves to confine ions within the gaps between the ion blanket members. The DC voltage applied to these identical annular electrodes generates a DC electric field that acts to push ions inward toward the common center of the annular electrodes.

[0041] The ion blanket members 51a, 51b further include a second set of electrodes 55 disposed between at least some of the pairs of ring electrodes 54, such as Figure 3D These second electrodes are referred to herein as "paddle electrodes" because, in operation, their function is to propel ion packets along a circular path through the ion separation apparatus in a partially geometric manner similar to the way the wooden or metal paddles of a water wheel carry packets of water along a partially circular path. As shown, the paddle electrodes may be provided in the form of geometric arcs that are segments of a circle concentric with the circle defined by the ring electrode 54. Figure 3DIn the example shown, the paddle electrodes are organized into and define an integer number n of identical sectors (i.e., "pie slices") of the geometric circle defined by the outermost ring electrode 54. Thus, each paddle electrode is a member of and occupies a portion of only one of the sectors. Figure 3D In the hypothetical example shown in , there are eight such sectors of the circle (ie, n=8), three of which are labeled sectors 59a, 59b, and 59c. According to some embodiments, no paddle electrodes are positioned between the subset of ring electrodes 54 closest to the center of the circle.

[0042] For the sake of clarity of the drawing, Figure 3D The depiction of the ion blanket member 51b in FIG is limited to eight circular sectors as defined by the alignment of the paddle electrodes 55. Preferably, the ion blanket member includes a significantly greater number of circular sectors, such as Figure 3E 48 circular sectors are indicated in FIG, wherein the first twelve circular sectors are marked as circular sectors 59.1 to 59.12 and the last two circular sectors are marked as circular sectors 59.47 and 59.48. Figure 3E The separate ring and paddle electrodes are not depicted. Figure 3E as well as Figure 4 Only the ion blanket member 51b is shown, but Figure 4 The discussion also relates to the unillustrated ion blanket member 51a of the apparatus 50. The central region 58 of the ion blanket member 51b is the region where the paddle electrodes are absent (see Figure 3D The remaining annular region 56a of the ion blanket member is where the paddle electrode 55 is located.

[0043] By a mechanism described in more detail below, DC potentials are sequentially applied to the paddle electrodes 55 so that, in operation of the ion separation apparatus 50, the ions are caused to move in a manner such as that indicated by the surrounding Figure 3E The arcuate arrows shown schematically around the perimeter of the representation of ion blanket member 51b in the annular region 56a schematically illustrate the centrifugal-like circular motion experienced within the device. For example, an ion packet residing within the potential well at sector 59.11, formed by the paddle potential applied to sector 59.12 during a first incremental time period, is caused to migrate to the potential well at sector 59.10 during a second incremental time period in which the paddle potential is applied to sector 59.11. During subsequent incremental time periods, the same ion packet is caused to migrate to sectors 59.10 and 59.9, and so on. Simultaneously, there may be several other ion packets, as indicated by the shaded sectors, undergoing similar sector-to-sector migration in other portions of annular region 56a.

[0044] While the ion packets are circling around the center of the device in response to the potential applied to the paddle electrode 55, another DC potential is applied to the ring electrode 54, the gradient of which causes the ions to migrate towards the center of the device, as shown in FIG. Figure 3E The DC potential applied to the ring electrodes is superimposed on the oscillating RF potential described previously.

[0045] In a first approximation, ions must experience an inward-pointing radial acceleration that is proportional to the square of the velocity and inversely proportional to the radius in order to follow a stable circular path within the device. This inward-pointing radial acceleration is stimulated by the radial electric field generated by a DC potential applied to the annular electrode. If, at a particular radial distance r1 from the center of the device, the radial force from the DC field is too weak to maintain an ion species in a stable circular orbit, ions of that species will migrate outward to a larger radial distance r2, where they will require a greater inward-pointing radial acceleration to remain stable. Consequently, the paths of these ions will become unstable, leading to ion ejection from the periphery of the device. To prevent this ejection of ions, a DC potential that repels ions back toward the center of the device can be applied to the guard electrode 17, thereby stabilizing the ion orbits under the influence of the radial electric field generated by the paddle electrodes.

[0046] The generation of an inwardly directed radial electric field caused by the application of a potential difference to the annular electrode 54 produces a centripetal acceleration that depends on m / z. If the radial field is tilted upward, at some point the inward force will exceed the outward force, and the ions will migrate towards the central axis 13 of the device in an m / z-dependent manner.

[0047] In order to facilitate the extraction of ions from the device through the centrally located ion exit aperture 52 (according to the ion's m / z ratio), it is necessary to eliminate the forces exerted by the paddle electrodes. For this reason, as previously described, no paddle electrodes are present in the central region 58 of the device. The elimination of these forces allows the ions to cool and fall cleanly into the ion exit aperture. Ions reaching the boundary of the central region 58 are pulled directly into the central region and toward the central axis 13, driven by the DC potential gradient caused by the different DC potentials applied to the annular electrodes in the region. Upon reaching the central axis, one or more potentials applied to the extraction electrode 57 adjacent to or within the exit aperture 52 and / or to the repeller electrode on the ion blanket member 51b cause the ions to exit the device through the aperture. Simulations also indicate that the elimination of paddle electrode forces within the central region 58 provides the additional benefit of better m / z resolution when extracting ions. The reduction or elimination of the electric field produced by the voltage applied to the paddle electrode 55 may be accompanied by an increase in the radially inwardly directed field produced by the voltage applied to the ring electrode 54, which may be configured in one or more annular regions as further described below.

[0048] As mentioned above Figure 3D and Figure 3E As described above, the individual sectors of each ion blanket member of the ion separation device 50 are defined by the presence and configuration of the paddle electrodes 55 . Figures 3D-3E A configuration is shown in which the paddle electrodes define forty-eight identical sectors (ie, sectors 59.1-59.12 and others indicated) occupying annular region 56a. In another example, Figure 4 A variation of the sector configuration is shown, wherein the number and angular width of the sectors on the ion blanket member vary with radial distance from the central axis 13, thereby defining three paddle electrode carrying annular regions 56a, 56b, 56c in addition to a central paddle electrode-free region 58. The sectors within each annular region are identical to one another, but the number of sectors within each annular region is different. In addition, the orbital frequency f r And / or the form of the paddle electrode waveform profile may vary between different annular regions.

[0049] Figures 5A-5B A second ion separation apparatus, apparatus 150 , is referred to in accordance with the teachings of the present invention. Figure 5A is a schematic perspective view of the ion separation device 150, and Figure 5B is a schematic diagram of the electrode configuration of the ion blanket component of the ion separation device 150. As previously described with respect to the ion separation device 50 (e.g., Figure 3A ), ion separation device 150 includes two ion blanket components, designated as ion blanket component 151a and ion blanket component 151b, each including an electrically insulating substrate. The two substrates are positioned parallel to each other and separated by an inter-ion blanket gap having a distance D. Each of the ion blanket components includes a corresponding set of electrodes 154 positioned on or within a corresponding substrate on one side of the corresponding ion blanket component. The sides having the electrodes thereon face each other across the gap. The ion blanket components can be manufactured as discussed above with respect to device 50. One of the ion blanket components 151a has an ion exit aperture extending through the substrate of the ion exit aperture 152. In other respects, the two ion blanket components 151a, 151b are generally similar to each other. A central axis 13, perpendicular to the plane of the parallel ion blanket components, passes through the center of the ion exit aperture 152.

[0050] Ion separation device 150 ( Figures 5A-5B ) is generally similar to the ion separation device 50 (e.g., Figures 3A-3D), in addition to the configuration of electrodes on the mutually facing surfaces of the ion blanket members. Specifically, although the facing surfaces of the ion blanket members 51a, 51b of the ion separation device 50 include two sets of electrodes: a set of ring electrodes and a set of arc-shaped paddle electrodes, the ion blanket members 151a, 151b of the ion transmission device 150 each have only a set of single electrodes, referred to herein as segmented ring electrodes 154. The individual segmented ring electrodes are all arranged on each substrate along concentric circles centered on the central axis 13. In addition, the segmented ring electrodes 154, which are preferably arc-shaped in shape, are configured to define a group of multiple identical circular sectors. For example, as Figure 5B As depicted in FIG, ion transfer member 151b includes eight such sectors. Figure 5B Three such sectors 159a, 159b and 159c are specifically indicated in FIG. Figure 5B Eight sectors are depicted in FIG, but the ion blanket members 151a, 151b may include any number of sectors. As previously described herein, one of the ion blanket members 151a, 151b may be replaced by a simple plate electrode.

[0051] In operation of the ion separation device 150, one or more power supplies (not shown) supply the electrodes 154 with: (a) an oscillating RF voltage having the same amplitude, such that all electrodes 154 of a single electrode ring receive the same RF phase and such that the RF phase applied to each electrode ring differs by π radians from the RF phase applied to each of the one or two other electrode rings closest to the electrode ring; (b) a first DC offset voltage that increases or decreases inwardly between each electrode ring; and (c) a traveling DC voltage waveform that migrates around the sector in a clockwise or counterclockwise manner. Thus, in operation of the device 150, the segmented annular electrodes 154 of the ion separation device 150 provide the combined ion guiding force provided by the two sets of electrodes of the device 50.

[0052] Figure 6A and 6B is a schematic "topography" diagram of the potentials applied to the ring and paddle electrodes of an ion separation apparatus constructed according to the above reference. Figures 3A-3D A general discussion of the configuration is provided. Figure 6A and Figure 6B The dashed schematic equipotential "contours" in FIG. 5 depict the general shape of the potential surfaces generated within the ion separation apparatus in response to controlled voltages applied to the ring electrode 54 and the paddle electrode 55, respectively, as shown in FIG. Figure 3D These surfaces are drawn assuming that positively charged ionic species undergo separation within the device.

[0053] According to the above assumptions, Figure 6AThe potential surface 161 is a potential well that tends to encourage positively charged ions to be pushed toward the center of the device. Although the potential surface is shown as a general parabola of revolution, the potential surface may alternatively be configured as a surface having a non-parabolic cross-section. The exact form of the potential surface can be produced by a combination of the choice of voltage applied to the annular electrodes and the choice of the spacing between the annular electrodes. Still assuming the separation of positively charged ionic species, the individual paddle electrode potential surfaces 163a-163f include a plurality of potential peaks that tend to encourage the ions to move tangentially to the circle of the annular electrodes. The full potential surface also contains intermediate potential wells between the individual potential peaks. The periodicity of the DC potential applied to the individual paddle electrodes causes the peaks and valleys to rotate about the central axis of the device in either a clockwise or counterclockwise manner, the latter being determined by Figure 6B In operation, the resulting potential surface at any time is Figure 6A The potential surface 161, Figure 6B The paddle electrode potential surfaces 163a-163f are a complex superposition of the time-varying potential surfaces provided by the RF voltage applied to the ring electrodes.

[0054] Figure 7 The present invention provides a set of graphs showing the calculated ion separation resolution of an ion separation apparatus according to the teachings of the present invention as a function of the spacing between two ion blanket members and as a function of the mass-to-charge ratio of the ion exit from the apparatus, as determined by simulations of the ion trajectory. The simulated extraction of ions involved ramping an inwardly directed radial field using an RF amplitude applied to a 200 V annular electrode at a frequency of 1 MHz, a paddle electrode voltage amplitude of 50 V applied at an annular frequency of 4 kHz, and a helium pressure of 0.075 Torr (10 Pa).

[0055] Figure 8 is a schematic diagram of a portion of a mass spectrometer system incorporating an ion separation device according to the teachings of the present invention. Specifically, Figure 8 An ion separation device 50 as taught herein is depicted fluidically coupled to a mass filter device, such as a quadrupole mass filter 80. Figure 8 Shown in Figures 3A-3D ion separation device 50, but it can be as Figures 5A-5B The ion separation device 150 shown may be replaced or replaced by virtually any ion separation device modified according to the teachings of the present invention or operated according to the principles of operation taught herein. The ion separation device and mass filter device are components of a mass spectrometer system, which may include many other components not shown, such as an ion source, a mass analyzer, an ion detector, a fragmentation cell, various ion optical components, one or more power supplies, etc.

[0056] exist Figure 8In the example shown, the ion separation device 50 receives an ion stream 72 comprising a plurality of different ion species having various m / z values. The ions of the ion stream 72 originate from an ion source within the ionization chamber 41 shown in FIG1 , such as an electrospray ionization source, an atmospheric pressure chemical ionization source, an electron ionization source, or the like. The ion stream preferably comprises a focused or collimated ion beam, such as that obtained by an ion optical assembly ( Figure 8 The focused or collimated ion beam, formed by a central region 58 (not shown), is introduced into the gap between two ion blanket members 51a, 51b of the ion separation device 50. The ion packets or pulses of ion flow 72 are preferably introduced into the gap along a preferred direction relative to the ion separation device (e.g., tangentially to the arc of the ring electrode or segmented ring electrode). According to operation of the ion separation device as taught herein, the ion species of the original ion packet are generally urged toward the ion exit aperture 52 within the gap between the ion blanket members 51a, 51b according to their respective m / z values. Ions that reach the outer boundary of the central region 58 are then pulled directly toward the ion exit aperture 52 under the influence of the electric field generated by the DC voltage applied to the ring electrodes within the region. As a result of these processes, the exit ion beam 73 from the aperture 52 is temporally graded with respect to the range of m / z values ​​of the ion species present. At any instant, the range of m / z values ​​of the ions present is less than the full range of m / z values ​​of the input ion packet, with the average m / z value of the ions present increasing over time. Therefore, the primary function of the ion separation device 50 is to partially separate the initial input ion species.

[0057] The partially separated ions of the exit ion beam 73 pass through holes in a partition 85 that separates the intermediate vacuum chamber 43, which houses the ion separation device 50, from the high vacuum chamber 87, which houses the mass filter. The intermediate vacuum chamber 43 is maintained at a pressure of 1 mTorr to 10 Torr (0.13 Pa to 1.3 kPa), which is required to cool the thermal energy of the ions to a level that can induce the ions to undergo a centrifugal-like circular motion within the ion separation device 50, 150. The pressure of the high vacuum chamber 87 can be maintained at a sub-mitorr pressure.

[0058] Figure 9 2 is a flow chart of a method 200 for separating and transmitting ions received from an input ion stream according to the teachings of the present invention. Execution of the method 200 may begin at step 202a involving ion separation by an apparatus comprising two ion blanket components (see Figure 3B ), or begins with step 202b involving ion separation by an apparatus comprising a single ion blanket member disposed parallel to a plate electrode (see Figure 3CIn step 202a of method 200, a portion of the ion flow is directed into an outermost segment of a gap between separated ion blanket members of an ion separation apparatus, wherein electrode-bearing surfaces of the parallel ion blanket members face each other across the gap, wherein the electrode configurations of the two facing surfaces are identical to each other, and wherein each electrode configuration in the outermost segment includes a first set of electrodes that generate an electric field that pulls ions inward toward a central axis of the apparatus that is perpendicular to the parallel plates, and further includes a second set of electrodes that generate a time-varying electric field that causes ions to circulate about the central axis within the outermost segment of the apparatus gap. In an alternative initial step 202b of method 200, the portion of the ion flow is directed into an outermost segment of a gap between an ion blanket member and a plate electrode of an ion separation device, wherein an electrode-bearing surface of the ion blanket member faces the gap, wherein the electrode configuration of the ion blanket member in the outermost segment includes a first set of electrodes that generates an electric field that pulls ions inwardly toward a central axis of the device perpendicular to the ion blanket member, and further includes a second set of electrodes that generates a time-varying electric field that causes the ions to circulate about the central axis within the outermost segment of the device gap. The ion circulation about the central axis includes sequential transfer of the ions through a first plurality of identical circular sectors defined by the configuration of the second set of electrodes. The sequential transfer of the ions through the sectors is caused by a traveling potential wave generated by the time-varying electric field.

[0059] In optional step 204, ions are transferred inwardly from the outermost section of the gap to a second section of the gap within the device, wherein each electrode configuration in the second section includes the first set of electrodes as described above and includes a third set of electrodes instead of the second set of electrodes. The third set of electrodes generates a time-varying electric field that causes the ions to circulate around the central axis within the second section of the device gap. The ion circulation around the central axis includes sequentially transferring the ions through a second plurality of identical circular sectors defined by the configuration of the third set of electrodes within the second section. The sequential transfer of the ions through the sectors is caused by a traveling potential wave generated by the time-varying electric field. Various operating parameters and configuration parameters can be varied between the outermost section and the second section of the gap. Such operating parameters include, but are not limited to: the number of sectors; the electric field strength between the sectors; and the speed of the traveling wave.

[0060] In step 206 of method 200, the ion flow is discharged from the device through the ion exit hole in one of the plates, and the ion flow is partially spatially separated according to its corresponding mass-to-charge ratio by traversing the device laterally. The execution of step 206 may include transferring the ions to a central section of the device, the central section including the first set of electrodes but not including the second or third set of electrodes. The ions are discharged from the device ion in a direction perpendicular to the plane of the parallel plates. By applying a voltage to an extraction electrode arranged adjacent to the hole or in the hole and / or by applying a voltage to a repeller electrode arranged on an electrode bearing surface of the ion blanket that does not have a hole, the ions can be forced to pass through the hole and leave the ion separation device. Finally, in an optional step 208, the discharged ions can be transferred to a mass filter for further separation.

[0061] It will be appreciated that those skilled in the art will recognize that many simple or minor modifications may be made to the above-described apparatus and method without changing the basic function of the apparatus or the results of the method. It will be appreciated that while the present invention has been described in conjunction with the description of various embodiments thereof, the foregoing description is intended to illustrate and not to limit the scope of the invention. The scope of the invention is defined solely by the appended claims.

Claims

1. An ion separation device comprising: A first ion blanket and a second ion blanket, each ion blanket comprising: a substrate having a first side and a second side; and a set of electrodes disposed on or below the first face, wherein a first plurality of electrodes in the set of electrodes are configured to define at least one set of circular sectors; an ion exit aperture extending through one of the ion blankets; and one or more power supplies configured to provide an oscillating radio frequency (RF) voltage to at least a first subset of the set of electrodes of each ion blanket, provide a non-oscillating direct current (DC) potential difference across electrodes of at least the first subset of the electrodes of each ion blanket, and provide a time-varying DC voltage to the first plurality of electrodes of the set of electrodes of each ion blanket that migrates across the sector in the form of a traveling wave, The first ion blanket and the second ion blanket are arranged parallel to each other with a gap therebetween, and the first surfaces face each other across the gap.

2. The ion separation device of claim 1 , wherein each electrode of the first plurality of electrodes in the set of electrodes of each ion blanket has the form of an arc segment of a circle, wherein each electrode in the first subset of the electrodes of each ion blanket is an annular electrode having the form of a complete circle, and wherein the circle of the annular electrodes is concentric around a central axis of the ion separation device, the central axis being perpendicular to the first face of the ion blanket and passing through the ion exit aperture. 3 . The ion separation device according to claim 1 , wherein the gas pressure within the ion separation device is in the range of 0.13 Pa to 1.3 kPa. The ion separation apparatus of claim 1 , wherein the width of the gap is between 5 mm and 20 mm.

5. The ion separation device according to claim 1, further comprising: a central axis of the ion separation device, the central axis being perpendicular to the first face of the ion blanket and passing through the ion exit aperture; as well as Each ion blanket has a corresponding region around the central axis within which no electrode of the first plurality of electrodes exists.

6. The ion separation device according to claim 1, wherein the first plurality of electrodes in the set of electrodes of each ion blanket define a first set of circular sectors and a second set of circular sectors, the first set of circular sectors being sectors of a first circle and the second set of circular sectors being sectors of a second circle located within the first circle, The total number of sectors in the first group of sectors is different from the total number of sectors in the second group of sectors.

7. A method for separating ionic species in an ion group, the ionic species comprising a range of mass-to-charge ratios, the method comprising: introducing the set of ions into a device where the ions are exposed to time-varying electrostatic forces that cause the ions to circulate about a central axis and to time-invariant electrostatic forces directed toward the axis; as well as Each of a plurality of subsets of the set of ions is transferred from a respective annular region around the central axis to an ion exit aperture centered on the central axis, each subset comprising a respective subset of mass-to-charge ratio ranges.

8. The method of claim 7, further comprising introducing each of the plurality of subsets of the set of ions into a quadrupole mass filter device.

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