Electron capture dissociation (ECD) cell

Abstract

In some examples, an electron capture dissociation (ECD) cell may include a plurality of lenses. At least one lens of the plurality of lenses may be asymmetrically arranged about an axis that is orthogonal to a central axis of the ECD cell and intersects a central point along a length of the ECD cell defined along the central axis.

Description

Background Art

[0001] In tandem mass spectrometry, electron capture dissociation (ECD) can be implemented to fragment positively charged ions by capturing low-energy electrons for structural analysis. ECD can be used to analyze and sequence the structure of proteins and peptides. In collision-induced dissociation (CID), ion activation and dissociation can be achieved through collisions between ions and neutral buffer gas molecules. Both ECD and CID can be implemented in mass spectrometry. BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Features of the present disclosure are illustrated by way of example and not limitation in the following one or more figures, in which like reference numerals indicate like elements, and in which:

[0003] FIG1A is an isometric cutaway view of an asymmetric ECD cell according to an example of the present disclosure;

[0004] FIG1B is a schematic diagram of the asymmetric ECD cell of FIG1A according to examples of the present disclosure;

[0005] 1C illustrates the ECD operating mode for the asymmetric ECD cell of FIG. 1A , with centerline potential increasing with electron emission, according to examples of the present disclosure;

[0006] 2 illustrates the centerline potential as electron emission increases for the asymmetric ECD cell of FIG. 1A for operation with the filament off, according to an example of the present disclosure;

[0007] 3 illustrates the centerline potential as electron emission increases for the asymmetric ECD cell of FIG. 1A for operation with the filament on, according to an example of the present disclosure;

[0008] FIG4 is a schematic diagram of another asymmetric ECD cell according to examples of the present disclosure;

[0009] FIG5 is a schematic diagram of another asymmetric ECD cell according to examples of the present disclosure;

[0010] FIG6 is a schematic diagram of another asymmetric ECD cell according to examples of the present disclosure;

[0011] FIG7 is a schematic diagram of another asymmetric ECD cell according to examples of the present disclosure;

[0012] FIG8 is a schematic diagram of another asymmetric ECD cell according to examples of the present disclosure;

[0013] FIG9 is a schematic diagram of another asymmetric ECD cell according to examples of the present disclosure;

[0014] FIG10 is a schematic diagram of another asymmetric ECD cell according to examples of the present disclosure;

[0015] FIG11 is a schematic diagram of another asymmetric ECD cell according to examples of the present disclosure;

[0016] FIG12A is a schematic diagram of another asymmetric ECD cell according to examples of the present disclosure;

[0017] FIG. 12B illustrates the centerline potential as electron emission increases for the asymmetric ECD cell of FIG. 12A , according to examples of the present disclosure; and

[0018] 13 is a schematic diagram of another asymmetric ECD cell according to examples of the present disclosure. DETAILED DESCRIPTION

[0019] For the purpose of simplicity and illustration, the present disclosure is described primarily by reference to examples. In the following description, many specific details are set forth to provide a thorough understanding of the present disclosure. However, it will be readily apparent that the practice of the present disclosure may not be limited to these specific details. In other cases, some methods and structures are not described in detail to avoid unnecessarily obscuring the present disclosure.

[0020] Throughout this disclosure, the terms "a" and "an" are intended to mean at least one of a particular element. As used herein, the term "includes" means including but not limited to, and the term "comprising" means including but not limited to. The term "based on" means based at least in part on.

[0021] Electron capture dissociation (ECD) pond can comprise the filament of emitting electron and other components for constraining the electron emitted, thereby forming dense electron cloud. Constraint can be realized by annular magnet and electrostatic lens (for example, also expressed as electrode). In this respect, electron can orbit around the magnetic field line produced by annular magnet, and described magnetic field line can be roughly parallel to the ECD pond symmetry axis. In one example, magnetic field can be produced by two permanent annular magnets positioned at filament both sides. Axially, electron can be constrained under suitable electric potential by a group of electrostatic lens (for example, expressed as L1, L2, L3 ... Lx etc.). In one example, electrostatic lens can comprise L1, L2, L3 ... L7. High purity nitrogen (N2) can be introduced into ECD pond to prevent filament from burning out (for example, by excluding oxygen). N2 gas can also serve as buffer gas, to make electron energy thermalized by collision after electron emission, thereby maximizing reaction cross section (cross section) with positive ions. Electron energy can represent the important parameter that determines the fragmentation efficiency of ECD pond. In this regard, even moderately energetic electrons with a kinetic energy of 1 eV can have a capture cross section a thousand times lower than that of true hot electrons with a typical kinetic energy of the order of 0.1 eV. ECD efficiency can be defined as the ratio of the total abundance of fragmented ions to the total abundance of precursor ions in the absence of an electron cloud. In existing ECD cells, ECD efficiency can range from, for example, 10% to 20%.

[0022] In one example of a symmetrical ECD cell comprising electrostatic lenses L1, L2, L3, ..., L7, two ring magnets can generate a magnetic field having field lines generally parallel to the axis of the ECD cell. Lenses L1 and L7 can be arranged to optimize transmission to and from other functional elements of the instrument. Intermediate lenses L2 and L6 can be used to create valleys in the potential, thereby confining electrons axially. Further, lenses L3 and L5 can comprise permanent ring magnets with non-magnetic inserts.

[0023] With respect to the operation of the ECD cell, typically, electrons may be negatively charged and therefore attracted to positively charged electrodes (e.g., positive potential relative to the electron current). To direct the electron cloud away from the filament and into the magnet region, lenses L3 and L5 may need to be positively biased relative to the filament and lens L4. Several collisions with the nitrogen buffer gas may occur, thereby successively reducing the initial kinetic energy imparted to the electrons by the potential difference between the filament and lenses L3 and L5, respectively. Lenses L2 and L6 may be used to prevent the electrons from axially exiting the ECD cell.

[0024] The electron cloud can generate its own electrical potential, which can be expressed as a space charge potential. As the electron density becomes higher, the potential can deviate more and more from the original potential generated by the electrostatic lens. The space charge effect can facilitate the transport of ions through the ECD cell because the space charge exerts an attractive potential on positive ions along most of the length of the ECD cell around its axis.

[0025] In one example, the ECD cell can generate two electron clouds, one on each side of the filament. While this theoretically maximizes the overall ECD efficiency using a single filament, this symmetrical design can include various disadvantages. While electrons can be considered high-potential seekers, positive ions behave in the opposite manner and are therefore attracted to negative potentials. On one side of the ECD cell (e.g., the left side comprising lenses L1 to L4 and the filament), there is no conflict of these properties. In this regard, the positive ions can follow the overall gradient of the centerline potential "downhill," thereby overcoming the "valley" created by lens L2 and ultimately flying toward the filament. In one disadvantage of a symmetrical ECD cell, ions pass through the filament, but now they must overcome a second, wider potential wall between the filament and lens L5. The ECD cell can be tuned to transmit ions at an acceptable abundance, but the transmission efficiency is relatively sensitive to small changes in any potential on lenses L4 to L6, while the transmission efficiency is less sensitive to comparable voltage changes on lenses L1 to L4.

[0026] FIG1A is an isometric cutaway view of an asymmetric ECD cell 100 according to an example of the present disclosure. FIG1B is a schematic diagram of an asymmetric ECD cell 100 according to an example of the present disclosure. FIG1C illustrates an ECD operating mode for the asymmetric ECD cell 100 according to an example of the present disclosure, with the centerline potential increasing with electron emission. The ECD operating mode is similarly applicable to the asymmetric ECD cells disclosed herein with reference to FIG4-FIG13.

[0027] 1A-1C , an ECD cell 100 can include lenses (e.g., electrodes) L1, L2, L3, L6, and L7 configured as shown, and magnets M1 and M2 configured as shown. In a similar manner to that shown for the ECD cell 1200 of FIG. 12A , the lenses and magnets of the ECD cell 100 can be formed in an annular configuration around a central axis 102 and include an ion channel 104. As shown, a filament 106 can be disposed between lenses L3 and L6.

[0028] Typically, the ECD cell 100 can include a plurality of lenses, wherein at least one of the plurality of lenses (e.g., lens L3 in the examples of Figures 1A-1C, lens L3, L4, or L5 in the examples of Figure 4, lens L3 or L4 in the example of Figure 5, and other lenses as shown in the examples of Figures 6-11) can be asymmetrically arranged about an axis 120 that is orthogonal to the central axis 102 of the ECD cell and intersects a center point 122 along a length 124 defined along the central axis of the ECD cell. In this regard, at least one of the plurality of lenses can be asymmetrically arranged in the ECD cell 100 such that the centerline potential (e.g., as shown in Figures 1B-3) includes a predetermined gradient as electron emission increases. Further, at least one magnet (e.g., magnet M1 or M2 in the examples of Figures 1A-1C) includes at least one lens that can be at least partially disposed between the central axis and the at least one magnet. The filament 106 may be disposed between the at least one lens (eg, lens L3 in the example of FIG. 1A-1C ) and another lens (eg, lens L6 in the example of FIG. 1A-1C ) among the plurality of lenses.

[0029] The at least two additional lenses (e.g., lenses L1 and L7 in the examples of Figures 1A-1C, lenses L1 and L7 in Figure 4, etc.) may include first and second additional lenses disposed at opposite ends of the ECD cell. Further, the at least two additional lenses (e.g., lenses L2 and L6 in the examples of Figures 1A-1C, lenses L2 and L6 in Figure 4, etc.) may include third and fourth additional lenses disposed between the first and second additional lenses and the at least one lens. A magnet (e.g., M1 and M2 in the examples of Figures 1A-1C) may be disposed between the first and second additional lenses.

[0030] For the ECD cell 100, the magnet can be configured to radially confine the electrons emitted from the filament. The magnet can be positioned so that the magnetic field lines are roughly parallel to the ECD cell axis in the region between lenses L2 and L7. In this regard, the magnetic field lines may need to be roughly parallel between lens L2 and the filament. However, in the example of Figures 1A-1C, the magnetic field lines are also roughly parallel between the filament and lens L7. The magnet can also be represented as an electromagnet.

[0031] For the ECD cell 100, lenses L2 and L6 can represent electrostatic lenses that axially confine electrons. Lenses L1 and L7 can optionally be connected to the instrument interface. Further, lenses L3 and L5 can shape the electron cloud between lens L2 and the filament.

[0032] In ECD mode, one goal of the ECD cell 100 can include generating an electron cloud between the lens L2 and the filament 106. The electrons may need to be confined long enough so that a significant number of the electrons have kinetic energies below 1 eV, preferably below 0.1 eV, and generally preferably close to thermal kinetic energy. The electron density may need to be as high as possible, preferably close to the space charge limit. In this regard, a high density of low-energy electrons can lead to electron capture and subsequent dissociation.

[0033] An example of an electrostatic lens setup for achieving ECD mode is as follows: F: is defined as 0 volts Lens L6: below F: Electrons are repelled from lens L6 and head towards lens L3 Lens L3: higher than F; attracts electrons away from F Lens L2: lower than F; prevents the initial electrons from emitting toward lens L1 Lens L1: Provides reference interface potential (upstream) Lens L7: Provides reference interface potential (downstream)

[0034] With respect to ECD cell 100, the presence of electrons can lower the centerline potential to a point where electrons emitted by the filament are no longer effectively extracted into the region including lens L3, as shown at 108. In this regard, the centerline potential without electrons is shown at 110, and the centerline potential with electrons is shown at 112.

[0035] FIG2 illustrates the centerline potential as electron emission increases for an asymmetric ECD cell 100 with the filament 106 turned off for an MS1 ​​mode of operation and / or an MS2 mode of operation (with fragmentation such as CID) according to an example of the present disclosure. The MS1 mode of operation and / or the MS2 mode of operation (with fragmentation such as CID) are similarly applicable to the asymmetric ECD cells disclosed herein with reference to FIG4-FIG13.

[0036] With respect to the MS1 mode of operation and / or the MS2 mode of operation (with fragmentation such as CID), with the filament 106 turned off, no electrons are present in the ECD cell 100. A goal of the ECD cell 100 may include transmitting ions with minimal loss. With the filament 106 turned off, the possibility of undesirable ECD in this mode can be eliminated. However, the filament warm-up may take some time (e.g., several seconds to several minutes).

[0037] A typical electrostatic lens setup to achieve MS1 with the filament 106 off (e.g., denoted herein as Mode 2A) may include the following specifications: F: is defined as 0 volts Lens L6: Below F: Positive ions are attracted towards the exit (lens L7) Lens L3: Set between lens L2 and filament F (continuous gradient towards the exit) Lens L2: Set between lens L1 and lens L3 (continuous gradient towards the exit) Lens L1: Provides reference interface potential (upstream) Lens L7: Provides reference interface potential (downstream)

[0038] As shown at 114, all lenses may be arranged to achieve a negative gradient across the ECD cell 100 to direct positive ions toward the exit.

[0039] FIG3 illustrates the centerline potential as electron emission increases for an asymmetric ECD cell 100 with the filament 106 on for an MS1 ​​mode of operation and / or an MS2 mode of operation (with fragmentation such as CID) according to an example of the present disclosure. The MS1 mode of operation and / or the MS2 mode of operation (with fragmentation such as CID) are similarly applicable to the asymmetric ECD cells disclosed herein with reference to FIG4-FIG13.

[0040] With respect to the MS1 mode of operation and / or the MS2 mode of operation (with fragmentation such as CID), with the filament 106 on, electrons are present in the ECD cell 100, but electron capture is not desired. The goal of the MS1 mode can include transmitting ions with minimal loss with the filament on. In this regard, ECD can depend on the kinetic energy of the electrons (e.g., the lower the more efficient) and the electron density. This mode can ensure that the electron cloud is confined to exist between lens L6 and lens L7, having high kinetic energy and low density (e.g., due to a short lifetime). This mode can achieve relatively fast switching between MS1 ​​(and / or MS2) and ECD modes because no warm-up time for the filament 106 is required.

[0041] A typical electrostatic lens setup to achieve MS1 with the filament 106 on (e.g., denoted herein as Mode 2B) may include the following specifications: F: is defined as 0 volts Lens L6: Above F: Positive ions are attracted towards this lens. Electrons hit lens L6, have a short lifetime and therefore low density → Minimized ECD Lens L3: Set below F - repels electrons towards lens L6 Lens L2: Set between lens L1 and lens L3 (continuous gradient towards the exit) Lens L1: Provides reference interface potential (upstream) Lens L7: Provides reference interface potential (downstream)

[0042] For the example of FIG. 3 , the electron cloud 116 may cause the centerline potential at 118 to decrease.

[0043] For the example of Figures 1A-3, all lenses except lens L6 can be configured to achieve a negative gradient throughout the ECD cell 100 to direct positive ions toward the exit. The ions can contain sufficient kinetic energy (e.g., from lenses L1 and L2) to overcome the hump. Therefore, the distances between the filament F and lens L6, and between lens L6 and lens L7, are relatively short.

[0044] Therefore the asymmetric design of ECD pool 100 can avoid aforementioned polarity conflict, as shown in Figure 1B.Therefore, for example, in the use case (for example, single-stage mass spectrum, MS1 or collision induced dissociation mode) that does not expect ECD, ECD efficiency and ease of use and transmission efficiency can be realized.When avoiding aforementioned polarity conflict, the tuning of ECD pool 100 can be relatively efficient, because do not need the compromise between ion transmission (for example, from left to right) and electron capture.ECD pool 100 can also include robust operation, because optimal voltage is set and combination is less sensitive to potential contamination and other (unknown) variations.Therefore, ECD pool 100 can be operated near optimal setting with less intermittent retuning process, and can realize and / or carry out possible retuning process (for example, automated or completed by user) efficiently.

[0045] FIG4 is a schematic diagram of another asymmetric ECD cell 400 according to examples of the present disclosure.

[0046] 4 , an ECD cell 400 may include lenses (e.g., electrodes) L1, L2, L3, L4, L5, L6, and L7 configured as shown, and a magnet M1 configured as shown. In a similar manner to that shown for the ECD cell 1200 of FIG. 12A , the lenses and magnets of the ECD cell 400 may be formed in an annular configuration around a central axis 402 and include an ion channel 404. As shown, a filament 406 may be disposed between lenses L5 and L6. Alternatively, the filament 406 may be disposed between lenses L2 and L3 (not shown).

[0047] FIG5 is a schematic diagram of another asymmetric ECD cell 500 according to examples of the present disclosure.

[0048] 5 , an ECD cell 500 can include lenses (e.g., electrodes) L1, L2, L3, L4, L6, and L7 configured as shown, and a magnet M1 configured as shown. In a similar manner to that shown for the ECD cell 1200 of FIG. 12A , the lenses and magnets of the ECD cell 500 can be formed in an annular configuration around a central axis 502 and include an ion channel 504. As shown, a filament 506 can be disposed between lenses L4 and L6. Alternatively, the filament 506 can be disposed between lenses L2 and L3 (not shown).

[0049] FIG6 is a schematic diagram of another asymmetric ECD cell 600 according to examples of the present disclosure.

[0050] 6 , an ECD cell 600 can include lenses (e.g., electrodes) L1, L2, L3, L6, and L7 configured as shown, and a magnet M1 configured as shown. In a similar manner to that shown for the ECD cell 1200 of FIG. 12A , the lenses and magnets of the ECD cell 600 can be formed in an annular configuration around a central axis 602 and include an ion channel 604. As shown, a filament 606 can be disposed between lenses L3 and L6. Alternatively, the filament 606 can be disposed between lenses L2 and L3 (not shown).

[0051] FIG7 is a schematic diagram of another asymmetric ECD cell 700 according to examples of the present disclosure.

[0052] 7 , the ECD cell 700 can include lenses (e.g., electrodes) L1, L2, L3, L4, L5, L6, and L7 configured as shown, and magnets M1 and M2 configured as shown. In a similar manner to that shown for the ECD cell 1200 of FIG. 12A , the lenses and magnets of the ECD cell 700 can be formed in an annular configuration around a central axis 702 and include an ion channel 704. As shown, a filament 706 can be disposed between lenses L5 and L6. With respect to the first and second lenses disclosed herein, a magnet (e.g., M1 and M2 of FIG. 7 ) can be disposed between a third and fourth additional lens (e.g., lenses L2 and L6 of FIG. 7 ). Alternatively, a filament 706 can be disposed between lenses L2 and L3 (not shown).

[0053] FIG8 is a schematic diagram of another asymmetric ECD cell 800 according to examples of the present disclosure.

[0054] 8 , an ECD cell 800 can include lenses (e.g., electrodes) L1, L2, L3, L4, L6, and L7 configured as shown, and magnets M1 and M2 configured as shown. In a similar manner to that shown for the ECD cell 1200 of FIG. 12A , the lenses and magnets of the ECD cell 800 can be formed in an annular configuration around a central axis 802 and include an ion channel 804. As shown, a filament 806 can be disposed between lenses L4 and L6. Alternatively, the filament 806 can be disposed between lenses L2 and L3 (not shown).

[0055] FIG9 is a schematic diagram of another asymmetric ECD cell 900 according to examples of the present disclosure.

[0056] 9 , an ECD cell 900 may include lenses (e.g., electrodes) L1, L2, L3, L6, and L7 configured as shown, and magnets M1 and M2 configured as shown. In a similar manner to that shown for the ECD cell 1200 of FIG. 12A , the lenses and magnets of the ECD cell 900 may be formed in an annular configuration around a central axis 902 and include an ion channel 904. As shown, a filament 906 may be disposed between lenses L3 and L6. Alternatively, the filament 906 may be disposed between lenses L2 and L3 (not shown).

[0057] FIG10 is a schematic diagram of another asymmetric ECD cell 1000 according to examples of the present disclosure.

[0058] With reference to Figure 10, ECD pool 1000 can comprise lens (for example, electrode) L1, L2, L3, L4, L5, L6 and L7 configured as shown, and magnet M1 and M2 configured as shown.In a similar manner with shown in the ECD pool 1200 for Figure 12 A, the lens and magnet of ECD pool 1000 can be formed with annular configuration around central axis 1002, and include ion channel 1004.As shown, filament 1006 can be arranged between lens L5 and L6.Alternatively, filament 1006 can be arranged between lens L2 and L3 (not shown).For the example of Figure 10, magnet (for example, M1 and M2) can be arranged at the opposite end of ECD pool.

[0059] FIG. 11 is a schematic diagram of another asymmetric ECD cell 1100 according to examples of the present disclosure.

[0060] 11 , an ECD cell 1100 can include lenses (e.g., electrodes) L1, L2, L3, L4, L6, and L7 configured as shown, and magnets M1, M2, and M3 configured as shown. In a similar manner to that shown for the ECD cell 1200 of FIG. 12A , the lenses and magnets of the ECD cell 1100 can be formed in an annular configuration around a central axis 1102 and include an ion channel 1104. As shown, a filament 1106 can be disposed between lenses L4 and L6. Alternatively, the filament 1106 can be disposed between lenses L1 and L2 (not shown).

[0061] Figure 12A is a schematic diagram of another asymmetric ECD cell 1200 according to an example of the present disclosure. Figure 12B shows the centerline potential as electron emission increases for the asymmetric ECD cell 1200 according to an example of the present disclosure.

[0062] 12A and 12B , the ECD cell 1200 can include lenses (e.g., electrodes) L1, L2, L3, L4, L5, and L6 configured as shown, and magnets M1 and M2 configured as shown. The lenses and magnets of the ECD cell 1200 can be formed in an annular configuration around a central axis 1202 and include an ion channel 1204. As shown, the filament 1206 can be primarily disposed within the lens L5. For example, the filament 1206 can be disposed within a cavity 1208 of at least one lens (e.g., lens L5). As shown in FIG12A , at least one magnet (e.g., M2) includes at least one lens (e.g., lens L5) that can be disposed adjacent to the at least one magnet.

[0063] 1B and 12A , in contrast to the ECD cell 1200, which does not include gaps between the magnets and the lenses (e.g., at 1210), the ECD cell 100 includes gaps between the magnets and the lenses (e.g., at 126), which may or may not be present. For example, in the example of FIG12A , lenses L3 and L4 are aligned with the magnets surrounding them and can be press-fit together so that electrical connections can be provided from outside the ECD cell 1200. In the ECD cell 100 of FIG1B (and the ECD cells of FIG4-11 ), gaps can be included to prevent electrical shorting between the lenses and the magnets.

[0064] FIG. 13 is a schematic diagram of another asymmetric ECD cell 1300 according to examples of the present disclosure.

[0065] 13 , an ECD cell 1300 can include lenses (e.g., electrodes) L1, L2, L3, L4, L5, L6, and L7 configured as shown, and a magnet M1 configured as shown. In a similar manner to that shown for the ECD cell 1200 of FIG12A , the lenses and magnets of the ECD cell 1300 can be formed in an annular configuration about a central axis 1302 and include an ion channel 1304. As shown, a filament 1306 can be disposed between lenses L2 and L3.

[0066] What has been described and illustrated herein are examples and some of their variations. The terms, descriptions, and figures used herein are set forth by way of illustration only and are not meant to be limiting. Many variations are possible within the spirit and scope of the present invention, which are intended to be covered by the appended claims and their equivalents. Unless otherwise indicated, all terms are given their broadest reasonable meanings understand.

Claims

1. An electron capture dissociation (ECD) cell comprising: A plurality of lenses, wherein at least one lens of the plurality of lenses is asymmetrically arranged about an axis that is orthogonal to a central axis of the ECD cell and intersects a center point along a length of the ECD cell defined along the central axis.

2. The ECD cell of claim 1 , further comprising: At least one magnet includes the at least one lens at least partially disposed between the central axis and the at least one magnet.

3. The ECD cell of claim 1 , further comprising: At least one magnet includes the at least one lens disposed adjacent to the at least one magnet.

4. The ECD cell of claim 1 , further comprising: A filament is disposed between the at least one lens and another lens of the plurality of lenses.

5. The ECD cell of claim 1 , further comprising: A filament is disposed within a cavity of the at least one lens.

6. The ECD cell of claim 1 , wherein the plurality of lenses comprises: At least two additional lenses include first and second additional lenses disposed at opposite ends of the ECD cell.

7. The ECD cell of claim 6, wherein the plurality of lenses comprises: At least two further lenses, the at least two further lenses comprising third and fourth further lenses arranged between the first and second further lenses and the at least one lens.

8. The ECD cell of claim 7, further comprising: A magnet is disposed between the third and fourth further lenses.

9. The ECD cell of claim 6, further comprising: A magnet is disposed between the first and second further lenses.

10. The ECD cell of claim 1, further comprising: Magnets are positioned at opposite ends of the ECD cell.

11. An electron capture dissociation (ECD) cell comprising: A plurality of lenses, wherein at least one lens of the plurality of lenses is asymmetrically arranged along a length of the ECD cell defined along a central axis.

12. The ECD cell of claim 11, further comprising: At least one magnet includes the at least one lens at least partially disposed between the central axis and the at least one magnet.

13. The ECD cell of claim 11, further comprising: A filament is disposed between the at least one lens and another lens of the plurality of lenses.

14. An electron capture dissociation (ECD) cell comprising: A plurality of lenses, wherein at least one lens of the plurality of lenses is asymmetrically arranged in the ECD cell such that a centerline potential that increases with electron emission includes a predetermined gradient.

15. The ECD cell of claim 14, further comprising: At least one magnet includes the at least one lens disposed at least partially between a central axis of the ECD cell and the at least one magnet.

16. The ECD cell of claim 14, wherein the plurality of lenses comprises: At least two additional lenses include first and second additional lenses disposed at opposite ends of the ECD cell.

17. The ECD cell of claim 16, wherein the plurality of lenses comprises: At least two further lenses, the at least two further lenses comprising third and fourth further lenses arranged between the first and second further lenses and the at least one lens.

18. The ECD cell of claim 17, further comprising: A magnet is disposed between the third and fourth further lenses.

19. The ECD cell of claim 16, further comprising: A magnet is disposed between the first and second further lenses.

20. The ECD cell of claim 14, further comprising: Magnets are positioned at opposite ends of the ECD cell.

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