Electron-induced dissociation devices and methods

Abstract

A polar electrode (150) is disclosed for use in ion reactors, such as electron-induced dissociation cells, to reduce fouling due to polymer buildup and increase the useful life of such electrodes. To reduce fouling, the novel polar electrode design includes an X-shaped aperture (160) instead of the traditional central circular aperture. The polar electrode is particularly useful in systems with multiple branch electrodes (152) that define a first axis for controlled passage of charged ions and a transverse axis for passage of an electron beam. The polar electrode is adapted for placement between the electron source and the branch electrodes, providing an aperture for passage of the electron beam while also preventing escape of ions and reaction products from the device. The X-shaped aperture eliminates or reduces the portion of the polar electrode surface most susceptible to fouling due to polymer buildup.

Description

[Technical field]

[0001] (Related U.S. Application) This application claims the benefit of priority from U.S. Provisional Application No. 62 / 908,773, filed October 1, 2019, the entire contents of which are incorporated herein by reference.

[0002] The teachings herein relate to inducing ion reactions for mass spectrometry, and more particularly, to methods and systems for performing electron induced dissociation (EID). [Background technology]

[0003] Ionic reactions typically involve the reaction of an ion, either positively or negatively charged, with another charged species, which may be another ion, positively or negatively charged, or an electron. In electron-induced dissociation (EID), for example, the charged species is an electron beam, and electron collisions on the ions result in fragmentation of the ions. EID has been used to dissociate biomolecules in mass spectrometry (MS), providing the ability to cover a wide range of potential applications, from conventional proteomics in liquid chromatography-mass spectrometry / mass spectrometry (LC-MS / MS), to top-down analysis (no digestion), de novo sequencing (discovery of unusual amino acid sequences), study of post-translational modifications (glycosylation, phosphorylation, etc.), protein-protein interactions (functional studies of proteins), and also identification of small molecules.

[0004] Mechanisms for EID can include, for example, electron capture dissociation (ECD), high temperature ECD (electrons with kinetic energies of 5-10 eV), and high energy electron ionization dissociation (HEEID) (electrons with kinetic energies above 13 eV), using electrons with kinetic energies between 0 and 3 eV. These electron induced dissociations are considered complementary to traditional collision induced or activated dissociation (CID or CAD) and are incorporated into advanced MS devices.

[0005] Hereinafter, use of the term "EID" in the present teachings should be understood to encompass all forms of electron-related dissociation techniques and is not limited to the use of electrons within any particular degree of kinetic energy.

[0006] In conventional MS systems, electrons are introduced as a transverse beam so that they collide with precursor positive ions as they pass axially through the instrument. For example, a mass spectrometer can include a branched RF ion trap structure in which an electron beam is orthogonally injected into the analytical ion beam with independent control of both the ion and electron beams. For further details, see PCT Application No. PCT / IB2014 / 00893, filed May 29, 2014, which is incorporated herein by reference in its entirety. Such devices can be operated in either a "flow" mode or a simultaneous trapping mode.

[0007] When a transverse beam of electrons is injected into an MS instrument, the electron beam must be controlled so that it is confined and directed into a region where the electrons can most efficiently interact (i.e., dissociate) with the ions passing through the instrument. Electron beam control is typically achieved by application of an electric field gradient, for example, by a series of positively biased electrodes that act as lenses to direct and focus the electron beam. The last of these electrodes is typically referred to as the "pole electrode" and is usually a positively biased metal plate with a central aperture through which the electron beam passes. The voltage on the pole electrode also acts as a confinement element to repel positively charged precursor and product ions and keep them within the instrument so that they can be extracted and analyzed.

[0008] It has been observed that the polar electrodes can become less effective at trapping ions over time. The degradation in function is believed to be the result of fouling due to the deposition of polymers on the polar electrode surface. The deposition is understood to be caused by vacuum residual gas molecules, typically hydrocarbons from low vacuum pumps, which are polymerized by stray electrons from the electron beam over time. Prolonged use makes the sticky polymer layer thicker. The polymer has little electrical conductivity, allowing additional electron accumulation on its surface, thus counteracting the applied positive voltage on the polar electrodes. This compromised potential gradually deteriorates the performance of the ion trap.

[0009] One conventional method for reducing this polymerization is to paint a graphite paste, such as AquaDAG®, on the polar electrode surface, but this is not a perfect solution because polymer buildup eventually occurs even on the rough graphite surface. Changing the composition of the polar electrode itself or coating the surface of the polar electrode with other metals such as gold, stainless steel, or molybdenum has also not proven effective.

[0010] Therefore, there is a need for a polar electrode design that is less susceptible to fouling so that frequent equipment maintenance can be avoided and the useful life time of polar electrodes and the like can be extended, and a method of reducing polymer build-up on polar electrodes that is better than graphite coatings. Summary of the Invention [Means for solving the problem]

[0011] According to the present teachings, a new pole electrode design is disclosed that can reduce fouling caused by polymer accumulation and increase the useful life time of such electrodes. In the case of quadrupole RF structures, it has been observed that polymer residues are most evident on some parts of the pole electrodes, i.e., along the gap regions between the underlying quadrupole electrodes. Without being bound by any theory or hypothesis, it is envisioned that stray electrons that cause polymerization mainly affect the pole electrode surface in these gap regions due to the combined effect of the quadrupole RF electric field and / or the parallel magnetic field. To reduce fouling, a new pole electrode design is disclosed that includes an X-shaped opening instead of the conventional central circular opening.

[0012] In one aspect of the present teachings, a pole electrode for use in an ion reactor is disclosed having a plurality of branched electrodes defining a first axis for controlled passage of charged ions and a transverse axis for passage of the electron beam, such that electron-induced dissociation of the ions by the electrons can occur in the intersection area, and an electron source for introduction of the electron beam along the transverse axis. The pole electrode of the present teachings is adapted for placement between the electron source and the branched electrodes, providing an opening for passage of the electron beam while also preventing escape of ions and reaction products of electron-induced dissociation. The X-shaped opening eliminates or reduces a portion of the pole electrode surface that is most susceptible to fouling by polymer buildup.

[0013] In particular, the novel polar electrode comprises a conductive plate, which can be charged to a desired potential, and an X-shaped opening. For example, the X-shaped opening can be formed from at least two intersecting rectangular openings in the conductive plate, preferably in an equidistant arrangement between two adjacent electrodes of the lateral electrodes. In some embodiments, the rectangular openings are fully cut-out openings in the conductive plate, while in other embodiments, the rectangular openings are partially cut-out recesses in the conductive plate.

[0014] The opening of the X-shaped aperture can have a width (narrower dimension) that is at least 1.5 times the diameter of the electron beam that it is designed to be used with. In some embodiments, the rectangular opening of the X-shaped aperture can have a width that is more than twice the diameter of the electron beam that it is designed to be used with. For example, the rectangular opening of the X-shaped aperture can have a width of more than about 1 millimeter, or a width of about 1 to about 5 millimeters, or a width of about 2 to about 4 millimeters.

[0015] In addition, the rectangular opening of the X-shaped aperture has a length that is at least three times the diameter of the electron beam that it is designed to be used with. In some embodiments, the length of the rectangular opening can be more than four times the diameter of the electron beam that it is designed to be used with. For example, the rectangular opening of the X-shaped aperture can have a length of more than about 3 millimeters, or about 3 to about 8 millimeters, or about 4 to about 6 millimeters.

[0016] In an alternative embodiment, the X-shaped aperture of the polar electrode can be star-shaped. In the star-shaped alternative, the center of the star preferably forms an aperture that is at least 1.5 times, preferably at least twice, the width of the electron beam, with the distance between the two points being at least 5 millimeters, preferably 5 to 10 millimeters.

[0017] In another aspect of the present teachings, a method of reducing fouling due to polymer build-up and extending the useful life of a pole electrode is disclosed that includes providing an aperture in the pole electrode that is cross or star shaped with an opening extending from a central region of the aperture into a gap region between underlying pole electrodes.

[0018] The method of the present teachings can be used to perform electron-induced dissociation by at least partially introducing a plurality of ions into a first path extending along a first central axis and defined by a first plurality of electrodes, and introducing electrons into a second path extending along a second central axis via an electron source, the second path intersecting the first path at an intersection region such that the ions and electrons can interact. In the method of the present teachings, a pole electrode is deployed between the electron source and the intersection region, which provides an opening for the passage of the electron beam while also preventing the escape of ions and reaction products of electron-induced dissociation, the pole electrode comprising a conductive plate and an X-shaped opening that can be biased to a desired potential. Any of the pole electrodes described above can be used to practice the method of the present teachings.

[0019] In yet another aspect of the present teachings, a system for performing electron induced dissociation is disclosed that may include a first set of electrodes, at least a first segment of which is arranged in a quadrupole orientation about a first central axis, the first segment of the first set of electrodes extending axially along the first central axis from a proximal entrance end to a distal end to define a first portion of a first path extending along the first central axis, the proximal entrance end being configured to receive precursor ions from an ion source.

[0020] The system may further include a second set of electrodes arranged in a quadrupole orientation about a first central axis, at least a first segment of the second set of electrodes defining a second portion of a first path, the first segment of the second set of electrodes extending axially along the first central axis from a proximal end to a distal exit end, the proximal end of the second set of electrodes being spaced from the distal end of the first set of electrodes, such that a lateral path is formed between the proximal end of the second set of electrodes and the distal end of the first set of electrodes.

[0021] This lateral path (which will be used to introduce the electron beam) extends along a second central axis that is generally perpendicular to the first central axis and intersects the first path at an intersection region.

[0022] In this system, the electrodes of the first set of electrodes and the second set of electrodes are preferably bifurcated (L-shaped) electrodes having a vertical segment and a horizontal segment, the vertical segment of each electrode of the first set of electrodes and the second set of electrodes respectively defining a first segment of the first set of electrodes and the second set of electrodes, the horizontal segment of each electrode of the first set of electrodes and the second set of electrodes further defining a horizontal path, and two horizontal segments of the electrodes from the first set of electrodes and two horizontal segments of the electrodes from the second set of electrodes are oriented to define a set of horizontal electrodes arranged in a quadrupole orientation centered on the second central axis between a first axial end of the horizontal path and the intersection region.

[0023] The system may further include at least one electron source disposed proximate the lateral path to introduce a plurality of electrons along a second axis such that the electrons may travel through the lateral path toward the intersection region. (It should be understood that electron sources may be disposed at both ends of the lateral path due to the symmetry of the system, and in some embodiments, it may be advantageous to have two electron sources disposed at opposite ends of the lateral path.)

[0024] In addition, the system can include at least one pole electrode disposed between the electron source and the lateral electrode, the pole electrode having an outer side facing the electron source and an inner side facing the lateral electrode. In an embodiment, the pole electrode can include an aperture aligned with the second central axis to allow electrons to pass therethrough, with a portion of the pole electrode thickness centered around the periphery of the aperture at the outer side being removed into an X-shaped cutout, the X-shaped cutout including two strip-like openings, e.g., two generally rectangular openings intersecting the openings and at 90 degrees to each other, i.e., two openings oriented in the gap region above and between the lateral electrodes. In this embodiment, each strip opening is positioned in an equidistant arrangement between two adjacent electrodes of the lateral electrodes.

[0025] Of course, in MS instruments employing higher order multipole electrode designs, the cutouts would be modified accordingly. With a hexapole, an equivalent configuration of three intersecting stripes or star-shaped apertures could be employed, in an octapole design, four intersecting stripes or star-shaped apertures could be used, etc. Any of the polar electrodes described throughout this application can be used within the systems of the present teachings.

[0026] These and other features of the applicants' teachings are described herein. The present invention provides, for example, the following: (Item 1) A pole electrode for use in an ion reactor having an RF electrode and an electron source for introduction of an electron beam along an axis defined by the RF electrode such that electron induced dissociation of ions by electrons may occur, the pole electrode adapted for placement between the electron source and the RF electrode and providing an aperture for the passage of the electron beam while also preventing escape of ions and reaction products of the electron induced dissociation, the pole electrode comprising: a conductive plate capable of being biased to a desired potential; an X-shaped opening formed in the conductive plate; A pole electrode. (Item 2) 2. The polar electrode of claim 1, wherein the X-shaped opening is preferably formed from at least two intersecting rectangular openings in the conductive plate in an equidistant arrangement between two adjacent electrodes. (Item 3) 3. The polar electrode of claim 2, wherein the rectangular opening is a completely cut opening in the conductive plate. (Item 4) 3. The polar electrode of claim 2, wherein the rectangular opening is a partially cut-out recess in the conductive plate. (Item 5) 3. The polar electrode of claim 2, wherein the rectangular opening of the X-shaped aperture has a width at least 1.5 times the diameter of the electron beam it is designed to be used with. (Item 6) 3. The pole electrode of claim 2, wherein the rectangular opening of the X-shaped aperture has a width that is greater than twice the diameter of the electron beam with which it is designed to be used. (Item 7) 3. The polar electrode of claim 2, wherein the rectangular opening of the X-shaped aperture has a width greater than 1 millimeter. (Item 8) 3. The polar electrode according to item 2, wherein the rectangular opening of the X-shaped aperture has a width of 1 to 5 millimeters. (Item 9) 3. The polar electrode according to item 2, wherein the rectangular opening of the X-shaped aperture has a width of 2 to 4 millimeters. (Item 10) 3. The polar electrode of claim 2, wherein the rectangular opening of the X-shaped aperture has a length at least three times the diameter of the electron beam with which it is designed to be used. (Item 11) 3. The polar electrode of claim 2, wherein the rectangular opening of the X-shaped aperture has a length that is greater than four times the diameter of the electron beam with which it is designed to be used. (Item 12) 3. The polar electrode of claim 2, wherein the rectangular opening of the X-shaped aperture has a length greater than 3 millimeters. (Item 13) 3. The polar electrode according to item 2, wherein the rectangular opening of the X-shaped aperture has a width of 3 to 8 millimeters. (Item 14) 3. The polar electrode according to item 2, wherein the rectangular opening of the X-shaped aperture has a width of 4 to 6 millimeters. (Item 15) 3. The polar electrode of claim 2, wherein the X-shaped opening is star-shaped. (Item 16) 1. A method for conducting an ionic reaction, comprising: introducing a plurality of ions into a first pathway, the first pathway extending at least in part along a first central axis and defined by a first plurality of electrodes; introducing electrons into a second path via an electron source, the second path extending along a second central axis, the second path intersecting the first path at an intersection region such that the ions and electrons may interact; providing a pole electrode between the electron source and the intersection region that provides an aperture for the passage of the electron beam while also preventing escape of the ions and reaction products of electron induced dissociation, the pole electrode comprising a conductive plate that can be biased to a desired potential and an X-shaped aperture; A method comprising: (Item 17) Item 17. The method of item 16, wherein the step of providing a pole electrode having an X-shaped opening further comprises the step of providing a pole electrode having an X-shaped opening formed from at least two intersecting rectangular openings in the conductive plate. (Item 18) Item 18. The method of item 17, wherein the step of providing a pole electrode having an X-shaped opening further comprises the step of providing a pole electrode having an X-shaped opening with a rectangular opening that is a completely cut opening in the conductive plate. (Item 19) Item 18. The method of item 17, wherein the step of providing a pole electrode having an X-shaped opening further comprises the step of providing a pole electrode having an X-shaped opening with a rectangular opening that is a partially cut-out recess in the conductive plate. (Item 20) Item 18. The method of item 17, wherein the rectangular opening of the X-shaped aperture has a width at least 1.5 times the diameter of the electron beam it is designed to be used with. (Item 21) Item 18. The method of item 17, wherein the rectangular opening of the X-shaped aperture has a width that is greater than twice the diameter of the electron beam it is designed to be used with. (Item 22) Item 18. The method of item 17, wherein the rectangular opening of the X-shaped aperture has a width greater than 1 millimeter. (Item 23) Item 18. The method of item 17, wherein the rectangular opening of the X-shaped aperture has a width of 1 to 5 millimeters. (Item 24) Item 18. The method of item 17, wherein the rectangular opening of the X-shaped aperture has a width of 2 to 4 millimeters. (Item 25) Item 18. The method of item 17, wherein the rectangular opening of the X-shaped aperture has a length at least three times the diameter of the electron beam it is designed to be used with. (Item 26) Item 18. The method of item 17, wherein the rectangular opening of the X-shaped aperture has a length that is greater than four times the diameter of the electron beam it is designed to be used with. (Item 27) Item 18. The method of item 17, wherein the rectangular opening of the X-shaped aperture has a length greater than 3 millimeters. (Item 28) Item 18. The method of item 17, wherein the rectangular opening of the X-shaped aperture has a width of 3 to 8 millimeters. (Item 29) Item 18. The method of item 17, wherein the rectangular opening of the X-shaped aperture has a width of 4 to 6 millimeters. (Item 30) Item 18. The method of item 17, wherein the X-shaped opening is star-shaped. (Item 31) 1. A system for performing electron induced dissociation, comprising: a first set of electrodes, at least a first segment of the first set of electrodes arranged in a quadrupole orientation about a first central axis, the first segment of the first set of electrodes extending axially along the first central axis from a proximal inlet end to a distal end to define a first portion of a first path extending along the first central axis, the proximal inlet end for receiving precursor ions from an ion source; a second set of electrodes arranged in a quadrupolar orientation about the first central axis such that at least a first segment of the second set of electrodes defines a second portion of the first path, the first segment of the second set of electrodes extending axially along the first central axis from a proximal end to a distal exit end, the proximal end of the second set of electrodes being spaced from the distal end of the first set of electrodes such that a lateral path extends between the proximal end of the second set of electrodes and the distal end of the first set of electrodes, the lateral path extending from a first axial end to a second axial end along a second central axis that is substantially perpendicular to the first central axis and intersects the first path at an intersection region; a second set of electrodes, the electrodes of the first set of electrodes and the second set of electrodes being L-shaped electrodes having a vertical segment and a horizontal segment, the vertical segment of each electrode of the first set of electrodes and the second set of electrodes respectively defining a first segment of the first set of electrodes and the second set of electrodes, the horizontal segment of each electrode of the first set of electrodes and the second set of electrodes defining the horizontal path, and two horizontal segments of the electrodes from the first set of electrodes and two horizontal segments of the electrodes from the second set of electrodes being oriented to define a set of horizontal electrodes arranged in a quadrupole orientation about the second central axis between a first axial end of the horizontal path and the intersection region; an electron source disposed proximate a first axial end of the lateral path to introduce a plurality of electrons along the second central axis such that the electrons travel through the lateral path in a first lateral direction toward the intersection region; a pole electrode disposed between the electron source and the lateral electrode, the pole electrode having an outer side facing the electron source and an inner side facing the lateral electrode, the pole electrode including an opening aligned with the second central axis for allowing electrons to pass therethrough, a portion of the thickness of the pole electrode centered around the periphery of the opening on the outer side being removed to form an X-shaped opening; A system comprising: (Item 32) Item 32. The system of item 31, wherein the X-shaped apertures preferably comprise at least two rectangular openings intersecting at 90 degrees to each other in an equidistant arrangement between two adjacent ones of the lateral electrodes. (Item 33) Item 33. The system of item 32, wherein the rectangular opening is a completely cut opening in the conductive plate. (Item 34) Item 33. The system of item 32, wherein the rectangular opening is a partially cut-out recess in a conductive plate. (Item 35) Item 33. The system of item 32, wherein the rectangular opening of the X-shaped aperture has a width at least 1.5 times the diameter of the electron beam it is designed to be used with. (Item 36) Item 33. The system of item 32, wherein the rectangular opening of the X-shaped aperture has a width that is greater than twice the diameter of the electron beam it is designed to be used with. (Item 37) Item 33. The system of item 32, wherein the rectangular opening of the X-shaped aperture has a width greater than 1 millimeter. (Item 38) Item 33. The system of item 32, wherein the rectangular opening of the X-shaped aperture has a width of 1 to 5 millimeters. (Item 39) Item 33. The system of item 32, wherein the rectangular opening of the X-shaped aperture has a width of 2 to 4 millimeters. (Item 40) Item 33. The system of item 32, wherein the rectangular opening of the X-shaped aperture has a length at least three times the diameter of the electron beam it is designed to be used with. (Item 41) Item 33. The system of item 32, wherein the rectangular opening of the X-shaped aperture has a length that is greater than four times the diameter of the electron beam it is designed to be used with. (Item 42) Item 33. The system of item 32, wherein the rectangular opening of the X-shaped aperture has a length greater than 3 millimeters. (Item 43) Item 33. The system of item 32, wherein the rectangular opening of the X-shaped aperture has a width of 3 to 8 millimeters. (Item 44) Item 33. The system of item 32, wherein the rectangular opening of the X-shaped aperture has a width of 4 to 6 millimeters. (Item 45) Item 33. The system of item 32, wherein the X-shaped opening is star-shaped. [Brief description of the drawings]

[0027] Those skilled in the art will understand that the drawings, described below, are for illustration purposes only and are not intended to limit the scope of the applicant's teachings in any way.

[0028] [Figure 1] FIG. 1 depicts a general schematic of an ion reaction cell.

[0029] [Diagram 2] FIG. 2 depicts a cross-sectional view according to one embodiment of the present invention.

[0030] [Figure 3A] FIG. 3A depicts a cross-sectional view of FIG. 2 along line II.

[0031] [Figure 3B] FIG. 3B depicts a cross-sectional view of FIG. 2 along line II-II.

[0032] [Figure 4] FIG. 4 depicts a simplified side view of an example of electron injection, according to an embodiment of the present invention.

[0033] [Diagram 5] FIG. 5 depicts a simplified side view of the focusing and defocusing effects of an electron beam, according to one embodiment of the present invention.

[0034] [Figure 6] FIG. 6 depicts the injection and trapping of ions into the device according to one embodiment of the present invention.

[0035] [Figure 7] FIG. 7 depicts the ejection of ions or reaction products of an ionic reaction from the device, according to one embodiment of the invention.

[0036] [Figure 8] FIG. 8 depicts a sustained mode operation of an embodiment of the present invention in which ions and electrons are continuously injected and the stream of product ions as a result of ion-electron interactions is continuously ejected.

[0037] [Figure 9] FIG. 9 depicts a cross-sectional view of an embodiment of the present invention illustrating the orientation of the magnetic field.

[0038] [Figure 10] FIG. 10 depicts a front view of a conventional quadrupole electrode for use with a transverse quadrupole RF electrode.

[0039] [Figure 11] FIG. 11 depicts a quadrupole electrode for use with a transverse quadrupole RF electrode in accordance with the present teachings.

[0040] [Figure 12] FIG. 12 depicts an alternative polar electrode design in accordance with the present teachings for use with a transverse quadrupole RF electrode.

[0041] [Figure 13] FIG. 13 depicts another alternative polar electrode design in accordance with the present teachings for use with a transverse quadrupole RF electrode.

[0042] [Figure 14] FIG. 14 depicts a polar electrode for use with a transverse hexapole RF electrode in accordance with the present teachings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] Detailed Description For clarity, it should be understood that the following discussion, while detailing various aspects of the embodiments of the applicant's teachings, will omit certain specific details whenever it is convenient or appropriate to do so. For example, discussion of similar or similar features in alternative embodiments may be somewhat abbreviated. Well-known concepts or ideas may also not be discussed in detail for the sake of brevity. Those skilled in the art will recognize that some embodiments of the applicant's teachings may not require some of the details specifically described in every implementation described herein only to provide a thorough understanding of the embodiments. Similarly, it will be apparent that the described embodiments may be susceptible to modification or alteration according to common general knowledge without departing from the scope of the present disclosure. The detailed description of the embodiments below should not be considered as limiting the scope of the applicant's teachings in any way.

[0044] Referring to FIG. 1, a general schematic diagram of an embodiment of the present invention is depicted. An ion reaction cell 1 accepts as input a series of reactants, which are ions 2 and charged species 3. Optionally, energy is added, in the form of photons or light 4. The light 4 can be obtained from a laser source, preferably any light in the ultraviolet or infrared spectrum. The ions 2 can be any ions, positively (cations) or negatively (anions). The charged species 3 can be electrons or ions, either positively or negatively charged. As will be explained in more detail below, in a preferred embodiment, the charged species is a beam of electrons, which is transmitted laterally to the ions 2 and passes through the reaction cell 1, inducing collisions and reactions. When the charged species is electrons, the electron source can be a filament, such as a tungsten or thorium-treated tungsten filament, or other electron source, such as a Y2O3 cathode. The reaction device can also include cooling gases, such as helium (He) and nitrogen (N2). Typical pressures for cooling gas are 10 -2 ~10 -4 It can be Tor.

[0045] Filament electron sources are typically used because they are inexpensive, but are less robust in the presence of oxygen residual gas. On the other hand, cathodes made of Y2O3 are more expensive electron sources, but are more robust in oxygen and therefore can be useful for de novo sequencing using radical-oxygen reactions. In operation, a current of 1-3 amps is typically applied to heat the electron source, which generates a thermal power of 1-10 watts. A heat sink system for the electron source can be arranged to keep the temperature of the magnet, if one is utilized, below its Curie temperature, at which the magnetization of the permanent magnet is lost. Other known methods of cooling the magnet can also be utilized.

[0046] Inside the ion reaction cell 1, the ions 2 and charged species 3 all interact with each other along with the optional addition of photons 4. Depending on the nature of the reactants utilized, the interaction can give rise to several phenomena that result in the formation of product ions 5, which can then be extracted or ejected from the ion reaction cell 1, potentially along with other unreacted ions 2 and / or possibly charged species 3, depending on the circumstances.

[0047] When ion 2 is a cation and charged species 3 is an electron, the cation may undergo electron capture dissociation, where the cation captures an electron and the interaction between ion 2 and charged species 3 results in the formation of product ion 5, a fragment of the original ion 2. When ion 2 is a cation and charged species 3 is an anion, the interaction between ion 2 and charged species 3 may be electron transfer dissociation, where an electron is transferred from charged species 3 to ion 2, which causes ion 2 to fragment. The stream of species ejected from the ion reaction cell may consist of one or more of ion 2 and / or its fragments, or a mixture thereof.

[0048] In addition, for electron-related fragmentation, high-temperature ECD, high-energy electron ionization dissociation (HEEID), active ion ECD (AI-ECD), electron impact excitation of ions from organics (EIEIO), electron detachment dissociation (EDD), negative ETD, and negative ECD can be implemented. For example, when ion 2 is a cation, ECD, ETD, and high-temperature ECD can be implemented, while EID can be used when ion 2 is an anion. Proton transfer reactions can also be implemented if the charged species 3 is appropriately selected.

[0049] 2, a side view of an ion reactor 10 is depicted in accordance with an aspect of an embodiment of the present invention. Shown as a cutaway cross section, an outer cylindrical housing 29 and an inner cylindrical housing 30 surround a first passage 11 having a first central axis 12, a first axial end 13, and a second axial end 14. The passage provides a path for ions 2 to enter into the ion reactor 10.

[0050] At each end of the first path 11, a gate electrode (15, 16) is mounted. The gate electrode 15 allows ions 20 to enter the device 10, and the gate electrode 16 controls the exit of unreacted ions 2 or product ions 5 from the device 10. The gate electrodes need not be mounted directly at the axial ends, but can be mounted just outside and adjacent to the axial ends. As will be appreciated, due to the symmetrical nature of the device, the direction of the ions can be reversed, with ions 2 entering through gate electrode 16 and exiting through gate electrode 15, if the surrounding ion transport devices are appropriately configured.

[0051] The apparatus 10 comprises a first set 17 of quadrupole electrodes mounted on an inner cylindrical housing 30, the electrodes 17 being arranged around a first central axis 12 in a quadrupole type arrangement. Although quadrupoles are specifically embodied here, any multipole arrangement may also be utilized, including hexapoles, octopoles, etc. In the figure, only two of the four quadrupole electrodes are depicted, the other two electrodes being directly behind the depicted electrodes. For the two electrodes depicted within the quadrupole electrodes 17, the electrodes have opposite polarities. These first set 17 of quadrupole electrodes are connected to an RF voltage source and controller (not shown) that serves to provide RF voltage to the electrodes to generate an RF field that can induce ions 2 towards the first central axis 12, which is the midpoint of the quadrupole.

[0052] Also mounted on the inner cylindrical housing 30 is a second set of quadrupole electrodes 18 (only two are depicted, the other two directly behind), which are mounted a short distance away from the first set of quadrupole electrodes 17, which distance forms a generally cylindrically shaped gap 19 between the first 17 and second 18 sets of electrodes. The first 17 and second 18 quadrupoles share the same central axis 12, and the rods of the first 17 set of quadrupoles are aligned with the second 18 set of quadrupoles. Although depicted as cylindrical in shape, it should be understood that the shape of this gap is not critical, rather, there is a gap between the first 17 and second 18 sets of quadrupoles. For example, this shape could also be described as being a rectangular box shape, even though the quadrupoles have the same configuration. This second set of quadrupole electrodes 18 is also attached to an RF voltage source and controller (not shown) that serves to provide an RF voltage to the electrodes to generate an RF field that may serve to guide the ions 2 and / or product ions 5 toward a central axis 12, which is the midpoint of the second set of quadrupole electrodes 18.

[0053] The inner and outer cylindrical housings have cutouts for the insertion of a second passageway 20 having a second central axis 21 with a first axial end 22 and a second axial end 23. This second passageway 20 provides a passageway for transport of the charged species 3 into the device 10. The first and second passageways are generally perpendicular to one another and meet at an intersection 24, which is along the first central axis 12 and the second central axis 21. As more readily depicted in Figures 3A and 3B, which are cross-sectional views taken at lines II and II-II, respectively, in Figure 2, each of the four electrodes in the first set of quadrupole electrodes 17 can be paired with one of the four electrodes in the second set of electrodes 18, e.g., each electrode (25a, 25b) in each electrode pair has an opposite polarity and is directly across the intersection of the other electrode (25b, 25a) in the electrode pair. A similar relationship exists with respect to the electrode pair involving electrodes (26a, 26b).

[0054] The same relationship applies to the two remaining electrodes in the first set of electrodes 17, which are paired with the two remaining electrodes in the second set of electrodes 18. This orientation of the electrodes results in the RF field generated between the node 24 and the first axial end 22 of the second path 20 being in anti-phase with respect to the RF field generated between the node 24 and the second axial end 23 of the second path 20. Due to this configuration of the electrodes, essentially no RF field is present on the central axis 21.

[0055] The first axial end 22 of the second path 20 contains or has in close proximity to an electron filament 27 to be used to generate electrons for transmission into the second path 2 toward the intersection 24. The first axial end 22 may also contain or have in close proximity to one or more suitable electrode gates 28 for controlling the entrance of electrons into the device 10. A magnetic field source (not shown), such as a permanent magnet, is configured to implement a magnetic field that is parallel to the second path 20. This magnetic field is useful when ECD, high temperature ECD, HEEID, EDD, and negative ECD are implemented when the charged species are electrons. When the charged species are reagent anions, including scenarios where the reaction occurring is an ETD reaction, for example, a magnetic field source and magnetic field are not required.

[0056] The presence of a gap can lead to leakage of ions through the side of the cell, where the quadrupole RF field is weaker in the gap area. This can be mitigated by the use of "pole" electrodes, which are typically flat plate electrodes positioned to prevent this leakage. The pole electrodes are vertically aligned and spaced apart from the other electrodes. The positive charge on the pole electrodes serves to repel such charged ions and reaction products from the aperture. As will be appreciated, the pole electrodes are electrically connected to a suitable voltage source.

[0057] In accordance with the present teachings, an improved pole electrode design is disclosed. Figure 10 illustrates a conventional prior art pole electrode 150 configured to be deployed between an electron source (not shown) and a branched quadrupole electrode 152 (shown in phantom) that defines a lateral passage for introducing electrons into a reaction cell. The pole electrode 150 is an essentially conductive plate that can be charged to a desired potential. This conventional design includes a circular central aperture 154 for the passage of the electron beam.

[0058] FIG. 11 illustrates one embodiment of a quadrupole electrode 150A according to the present teachings, in which an X-shaped aperture 160 replaces the circular aperture of the prior art (FIG. 10). The X-shaped aperture in FIG. 11 is formed from two intersecting rectangular cutout openings that intersect on the horizontal axis. The rectangular cutouts are mounted between the underlying quadrupole electrodes 152, and the narrower dimension of each rectangle is preferably wider than the electron beam, for example, more than 1.5 times the width of the electron beam or at least 2 times the width of the beam. The length (longer dimension) of each rectangular cutout is preferably at least 3 times the width of the electron beam, and more preferably at least 4 times the width of the beam. In an exemplary embodiment, the width (narrower dimension) of each rectangular cutout can be greater than 1.5 mm, or at least 2 mm. In an embodiment, the length can be greater than 3 mm, or greater than 4 mm.

[0059] 12 depicts an alternative pole electrode 150B in accordance with the present teachings for use with a transverse quadrupole RF electrode in which the conventional circular aperture (as shown in FIG. 10) is replaced by a star-shaped aperture 162 mounted between the underlying quadrupole electrodes. At its center, the star-shaped aperture 162 is preferably wider than the electron beam, e.g., more than 1.5 times the width of the electron beam or at least twice the width of the beam. The length (longer dimension) of each star (point to point) is preferably at least three times the width of the electron beam, and more preferably at least four times the width of the beam.

[0060] FIG. 13 depicts another alternative polar electrode 150C according to the present teachings for use with a transverse quadrupole RF electrode, in which a central aperture and an X-shaped partially cut-out opening (recess) replace the circular aperture of the prior art (FIG. 10). In a manner similar to the embodiment of FIG. 11, the X-shaped partially cut-out opening of FIG. 13 is formed from two rectangular recesses intersecting at the transverse axis. The rectangular recesses are similarly mounted between the underlying quadrupole electrodes 152, with the narrower dimension of each rectangle preferably being wider than the electron beam, for example, more than 1.5 times the width of the electron beam or at least twice the width of the beam. The length (longer dimension) of each rectangular cutout is preferably at least three times the width of the electron beam, more preferably at least four times the width of the beam. In an exemplary embodiment, the width (narrower dimension) of each rectangular cutout can be greater than 1.5 mm, or at least 2 mm. The length can be greater than 3 mm, or greater than 4 mm.

[0061] FIG. 14 depicts a hexapole electrode 150D for use with a hexapole RF electrode 166 according to the present teachings. The X-shaped aperture in FIG. 14 is formed from three rectangular cutouts intersecting at a horizontal axis. The rectangular cutouts are mounted between the underlying hexapole electrodes 166, and the narrower dimension of each rectangle is again preferably wider than the electron beam, for example, more than 1.5 times the width of the electron beam or at least 2 times the width of the beam. The length (longer dimension) of each rectangular cutout is preferably at least 3 times the width of the electron beam, more preferably at least 4 times the width of the beam. In an exemplary embodiment, the width (narrower dimension) of each rectangular cutout can be greater than 1.5 mm, or at least 2 mm. The length can be greater than 3 mm, or greater than 4 mm.

[0062] It will be appreciated that the design of FIG. 14 for a hexapole instrument may be further modified to apply to higher order multipoles, e.g., octapole instruments, and that such designs may also be modified to employ star-shaped or partially truncated apertures in higher order multipole instruments similar to those illustrated in FIGS. 12 and 13 for quadrupole configurations.

[0063] The term "X-shaped," as used herein to describe openings in polar electrodes, is intended to encompass the full and / or partially truncated cross- or star-shaped openings illustrated in FIGS. 11-14, and other shaped structures that provide similar protection from fouling by preventing polymer buildup on the polar electrodes.

[0064] The pole electrodes of the present teachings can be used in conjunction with an anti-fouling coating, such as a graphite paste, for example, AquaDAG®, on the remaining portion of the pole electrode surface.

[0065] Referring again to FIG. 2, in one embodiment, the RF frequency applied to the quadrupole is in the range of approximately 400 kHz to 1.2 MHz, and preferably the RF frequency is approximately 800 kHz.

[0066] Referring now to FIG. 4, a depiction of another embodiment in a side view of an ion reaction device 40 is shown, where only charged species 3, specifically electrons, are injected. The ion reaction device 40 contains a first passage 41 having a first central axis 42, the passage 41 having a first axial end 43 and a second axial end 44. At each end of the first passage 41, an electrode gate (45, 46) is mounted, which allows the control of the entry and exit of ions from the ion reaction device 40. The device 41 comprises a first set 47 of quadrupole electrodes, which are generally L-shaped and arranged around the first central axis 42. In the figure, only two of the four quadrupole electrodes are depicted, the other two electrodes are directly behind the depicted electrodes. For the two electrodes depicted in the quadrupole electrodes 47, the electrodes have opposite polarities. A second set of quadrupole electrodes 48 (only two are depicted, the other two are directly behind), which are also generally L-shaped, are mounted a small distance away from the first set of quadrupole electrodes 47, which distance forms a sturdy, generally cylindrically shaped gap 49 between the first and second sets of electrodes 47, 48.

[0067] For the two electrodes depicted in quadrupole electrodes 48, the electrodes have opposite polarities. The electrodes depicted at the top in each of the first and second sets 47 and 48 of quadrupole electrodes are opposite in polarity to each other. As would be understood by one of ordinary skill in the art, the two electrodes not shown in each set of quadrupole electrodes would have a polarity consistent with the polarity of the quadrupole electrodes, such as the configurations shown in Figures 3A and 3B.

[0068] The second pathway 50 has a second central axis 51 having a first axial end 52 and a second axial end 53. This second pathway provides a passage for transport of charged species into the device 40. This orientation of the electrodes results in the RF field generated between the intersection (of the first pathway 41 and the second pathway 50) and the first axial end 52 of the second pathway 50 being in anti-phase with the RF field generated between the intersection (of the first pathway 41 and the second pathway 50) and the second axial end 53 of the second pathway 50. The first axial end 52 of the second pathway 50 contains or is mounted adjacent to an electron filament 57 to be used to generate electrons 60 for transmission into the second pathway 50. The first axial end 52 can also contain, and be mounted near and adjacent to a suitable electrode gate 63 that serves to direct electrons into the device along the second pathway.

[0069] The polar electrode 58 also serves to control the entry of the electrons 60 into the device 40 and also to block the ions and reaction products from escaping. Another polar electrode 59 is installed at or near the second axial end 53 of the second path 50. A magnetic field generator (not shown) is positioned and oriented in such a way that it generates a magnetic field parallel to the second path. The direction of the magnetic field can be either from the first axial end 52 to the second axial end 53 or vice versa. This magnetic field is useful when ECD, high temperature ECD, HEEID, EIEIO, EDD, and negative ECD are implemented, where the charged species is electrons. A grid 61 can be positioned to act as a gate to switch the electrons 60 near or in close proximity to the electron filament 57. The RF field causes the electrons 60, which are focused as they enter the device 40, to become defocused as they approach the intersection of the first path 41 and the second path 50. As the electrons 60 pass through the intersection, a reversal of the polarity of the RF field causes the electrons 60 to become refocused. This results in a more uniform distribution of electrons normal to the first path, increasing the chances of ion-electron interactions within the device 40, which can also result in better sensitivity. The electron beam creates a local attractive potential.

[0070] A clearer view of the electron defocusing effect is depicted in FIG. 5, where device 70 is configured in a manner similar to device 40 with a first set of quadrupole electrodes 71 and a second set of quadrupole electrodes 72. In an embodiment, electron lenses with a potential of +1V are placed at the entrance and exit of the electron beam path, which are used to assist in focusing the electron beam. Other parts are not repeated for the sake of brevity. It can be seen that the flow of electrons 60 into device 70 defocuses as they approach center point 74, but is refocused as they pass the center point. A 0.1T magnetic field (not shown) is aligned parallel to and along the path of the electron direction. Again, this magnetic field is useful when ECD, high temperature ECD, HEEID, EIEIO, EDD, and negative ECD are implemented, where the charged species is electrons. The RF field can be of maximum amplitude 100V, and the electron beam energy can be 0.2eV at the center.

[0071] 6 and 7 depict side views of an ion trapping effect produced by an apparatus 100 in accordance with an embodiment of the present invention in a batch mode. A first path 101 with a first axial end 103 and a second axial end 104 provides a flow path for ions to be injected from the first axial end 103. A second path 110 with a first axial end 112 and a second axial end 113 also provides a path for an electron beam generated by a filament 114. A set of quadrupole electrodes 107 (only two are depicted, the other two are directly behind), attached to an appropriate set of RF voltage sources, are oriented and serve to guide ions to a midpoint within the quadrupole electrodes 107 to the central axis 102. The second set of quadrupole electrodes 108 (only two are depicted, the other two are directly behind) are mounted a small distance away from the first set of quadrupole electrodes 107, the distance between the first set of quadrupole electrodes 107 and the second set of quadrupole electrodes 108 forming a gap 109 between the sets of electrodes. This second set of quadrupole electrodes 108 serves to direct ions to a midpoint between the quadrupole electrodes 108 and the central axis 102. For the two electrodes depicted in the quadrupole electrodes 107, the electrodes have opposite polarities. For the two electrodes depicted in the quadrupole electrodes 108, the electrodes have opposite polarities. The electrodes depicted at the top in each of the first set of quadrupole electrodes 107 and the second set of quadrupole electrodes 108 are opposite in polarity to each other. As would be understood by one skilled in the art, the two electrodes not shown of each set of quadrupole electrodes would have a polarity consistent with that of the quadrupole electrodes, such as the configuration shown in Figures 3A and 3B. A magnetic field generator (not shown) generates a magnetic field oriented parallel to the direction of the second path and aligned with the second central axis 111. Again, this magnetic field is useful when ECD, high temperature ECD, EIEIO, HEEID, EDD, and negative ECD are implemented, where the charged species are electrons. The entrance gate electrode 105 and the exit lens gate electrode 106 control the flow of ions into and out of the device 100, respectively.In this embodiment, the entrance lens gate electrode 105 is set to a potential that allows the flow of ions into the device 100, while the exit lens gate electrode 106 has a sufficiently high potential to temporarily prevent the flow of ions out of the device.

[0072] The second path also contains or is mounted adjacent to positively biased polar electrodes 115, 116 that prevent the escape of ions through the axial ends 112, 113 of the second path 110. In this embodiment, as ions are injected, the filament 114 is initially turned off and charged species do not enter the device 100 via the second path 110. In this manner, the device 100 functions as an ion trap where injected ions are accumulated at the intersection between the first path 101 and the second path 110.

[0073] When enough ions have accumulated, the potential of the gate electrode 105 is increased to prevent the inflow of ions into the device 100, thereby preventing the entry and exit of ions. The filament 114 can then be turned on to allow electrons to pass into the device 100 through the opening in the pole electrode 115. In response, the electrons can interact with the ions and undergo EID, resulting in fragmentation into product ions. Once sufficient fragmentation has occurred, the filament 114 can be turned off, the potential of the gate electrode 105 can be increased, and the potential of the gate electrode 106 can be lowered to allow the exit of the product ions through the second axial end 104, as depicted in FIG. 7. For example, a cooling gas, such as helium or nitrogen gas, may be introduced into the device 100 to obtain a more efficient trap. Each of the electrodes from the first quadrupole 107 and the second quadrupole 108 has a first portion of the electrode oriented substantially parallel to the first central axis 102, while the second portion is oriented substantially parallel to the second central axis. Because each portion of each electrode has the same polarity for a given electrode, the electrodes can collectively act as a trap that directs ions in both the central axis 102 and the central axis 111. In this manner, the device 100 acts as a two-dimensional trap, or more precisely, a linear trap in two directions. Although depicted in FIG. 6 as having a smooth rounded transition between the first and second portions, other configurations such as sharp corners can also be utilized. Shown below the device in each of FIGS. 6 and 7 are graphs of the space potential for positive ions in the horizontal direction within the device along the central axis 102.

[0074] In Figure 6, the potential at the inlet is approximately equal to that of the incoming isolated ions, thus allowing the ions to pass and enter the device, and the potential present at the outlet is higher than that of the isolated ions entering the device, thus the ions do not exit through the right side of the device but become trapped. In Figure 7, the inlet potential is higher, thereby preventing the ions from exiting back through the inlet, while the potential at the outlet is lower than that of the product ions, thereby allowing the ions to exit the device.

[0075] FIG. 8 depicts a side view of the operation of the device 100 in a semi-persistent mode, where ions continually enter through the gate 105 and electrons 117 continually enter through the aperture into the pole electrode 115. The interaction between the ions and the electrons 117 can cause EID, resulting in fragmentation and the formation of product ions. These product ions and unreacted ions are extracted from the device through the gate electrode 106 in a semi-persistent manner, where the gate electrode 106 switches between an open and a closed position. When in the closed position, the potential placed within the gate electrode is higher than that of the ions contained within the device, thereby allowing the ions to accumulate and increase residence and reaction time so that an EID reaction can occur. Once the ions are to be extracted, the gate electrode 106 is opened by lowering the potential within the gate, allowing the product ions to be removed. Shown below the apparatus 100 in FIG. 8 is a horizontal spatial representation of the potential for positive ions, showing the exit potential oscillating between high and low potentials representing the closed and open positions of the gate 106.

[0076] Referring now to FIG. 9, another system 200 according to the present teachings is depicted in side view inserted between two quadrupole filters in series. A quadrupole filter Q1 with quadrupole rods 218 is mounted upstream of the device 200 and serves to trap / guide / etc. ions and provide an ion source at the inlet of the device 200. A quadrupole Q2 with quadrupole rods 219 is mounted downstream of the device 200 and serves to receive product ions and unreacted ions and to trap / guide / etc. these species in the quadrupole for further analysis or processing. This device is similar to the devices described above and will not be described in detail for the sake of brevity. The device 200 has a first path 201 and a second path 210. The device 200 contains two filaments, each one located at either the first axial end 212 or the second axial end 213 of the second path 210. This configuration allows for independent operation of the filaments such that if one filament is being used and suddenly becomes inoperable, the other filament can be used as a spare and activated with no or minimal downtime.

[0077] Although the use of an additional quadrupole is specifically illustrated, it should be understood that other types of devices can be installed either before or after the apparatus according to the present teachings. For example, the device can include various ion guides, filters, traps, ion mobility devices, including differential mobility and field asymmetric ion mobility analyzers, and other mass analysis devices such as time-of-flight mass analyzers. In various embodiments, the electron control optics and the ion control optics are completely separated, so that independent operation for both charged particles is possible. For electrons, the electron energy can be controlled by the potential difference between the electron source and the intersection between the ion path and the charged species path. The charged species path can be controlled in an on / off manner by the use of a gate electrode. A lens can be positioned at or near the axial end of either of the second paths, and when biased positively, focuses the charged species when such species are electrons. Ions introduced through the other path are stable in the vicinity of the lens because they are biased positively. It should also be appreciated that the design of the present invention is also applicable to higher order multipole structures such as hexapole or octapole RF electrode structures.

[0078] For additional teachings regarding electron induced dissociation, see U.S. Patent Application Publication No. 20180005810, filed December 21, 2015, and entitled "Electron Induced Dissociation Devices and Methods," PCT Application No. PCT / IB2014 / 00893, filed May 29, 2014, and entitled "Inline Ion Reaction Device Cell And Method of Operation," and PCT Application No. PCT / IB2012 / 002621, filed December 6, 2012, and entitled "Ion Extraction Method For Ion Trap Mass Spectrometry," each of which is incorporated herein by reference in its entirety.

[0079] It should be understood that numerous changes can be made to the disclosed embodiments without departing from the scope of the present teachings. Although the foregoing figures and examples refer to specific elements, this is present only as an example and illustration, and is not intended to be limiting. It should be understood by those skilled in the art that various changes can be made in the form and details of the disclosed embodiments without departing from the scope of the teachings encompassed by the appended claims.

Claims

1. 1. A method for performing an ionic reaction, comprising: introducing a plurality of ions into a first path, the first path extending at least partially along a first central axis and defined by a first plurality of electrodes; introducing a plurality of electrons into a second path via an electron source for introducing an electron beam, the second path extending along a second central axis, the second path intersecting the first path at an intersection region such that the plurality of ions and the plurality of electrons may interact; providing a pole electrode between the electron source and the intersection region, the pole electrode providing an opening for the electron beam to pass through while also preventing the plurality of ions and reaction products of electron induced dissociation from escaping, the pole electrode comprising a conductive plate capable of being biased to a desired potential and an X-shaped opening; The method includes:

2. 2. The method of claim 1, wherein providing a pole electrode having an X-shaped opening further comprises providing a pole electrode having an X-shaped opening formed from at least two intersecting rectangular openings in the conductive plate.

3. 3. The method of claim 2, wherein providing a pole electrode with an X-shaped opening further comprises providing a pole electrode with an X-shaped opening having a rectangular opening that is a completely cut-out opening in the conductive plate.

4. 3. The method of claim 2, wherein providing a pole electrode with an X-shaped opening further comprises providing a pole electrode with an X-shaped opening having a rectangular opening that is a partially cut-out recess in the conductive plate.

5. The method of claim 2 , wherein the rectangular opening of the X-shaped aperture has a width at least 1.5 times the diameter of the electron beam it is designed to be used with.

6. The method of claim 2 , wherein the rectangular opening of the X-shaped aperture has a width that is greater than twice the diameter of the electron beam it is designed to be used with.

7. The method of claim 2 , wherein the rectangular opening of the X-shaped aperture has a width greater than 1 millimeter.

8. The method of claim 2 , wherein the rectangular opening of the X-shaped aperture has a width between 1 millimeter and 5 millimeters.

9. The method of claim 2 , wherein the rectangular opening of the X-shaped aperture has a width between 2 millimeters and 4 millimeters.

10. The method of claim 2 , wherein the rectangular opening of the X-shaped aperture has a length at least three times the diameter of the electron beam it is designed to be used with.

11. The method of claim 2 , wherein the rectangular opening of the X-shaped aperture has a length that is greater than four times the diameter of the electron beam it is designed to be used with.

12. The method of claim 2 , wherein the rectangular opening of the X-shaped aperture has a length greater than 3 millimeters.

13. The method of claim 2 , wherein the rectangular opening of the X-shaped aperture has a width between 3 millimeters and 8 millimeters.

14. The method of claim 2 , wherein the rectangular opening of the X-shaped aperture has a width between 4 millimeters and 6 millimeters.

15. The method of claim 2 , wherein the rectangular opening of the X-shaped aperture is tapered in shape.

16. 1. A system for performing electron induced dissociation, comprising: a first set of electrodes, at least a first segment of the first set of electrodes arranged in a quadrupole orientation about a first central axis, the first segment of the first set of electrodes extending axially along the first central axis from a proximal entrance end to a distal end to define a first portion of a first path extending along the first central axis, the proximal entrance end for receiving precursor ions from an ion source; a second set of electrodes, at least a first segment of the second set of electrodes arranged in a quadrupolar orientation about the first central axis to define a second portion of the first path, the first segment of the second set of electrodes extending axially along the first central axis from a proximal end to a distal exit end, the proximal end of the second set of electrodes spaced from the distal end of the first set of electrodes such that a lateral path extends between the proximal end of the second set of electrodes and the distal end of the first set of electrodes, the lateral path extending along the second central axis from a first axial end to a second axial end, the second central axis being substantially perpendicular to the first central axis and intersecting the first path at an intersection region, a second set of electrodes, the electrodes of the first set of electrodes and the second set of electrodes being L-shaped electrodes having a vertical segment and a horizontal segment, the vertical segment of each electrode of the first set of electrodes and the second set of electrodes respectively defining the first segment of the first set of electrodes and the second set of electrodes, the horizontal segment of each electrode of the first set of electrodes and the second set of electrodes defining the horizontal path, and two horizontal segments of the electrodes from the first set of electrodes and two horizontal segments of the electrodes from the second set of electrodes being oriented to define a set of horizontal electrodes arranged in a quadrupole orientation about the second central axis between a first axial end of the horizontal path and the intersection region; an electron source disposed proximate the first axial end of the lateral path for introducing the plurality of electrons along the second central axis such that the plurality of electrons travel in a first lateral direction through the lateral path toward the intersection region; a pole electrode disposed between the electron source and the lateral electrode, the pole electrode having an outer surface facing the electron source and an inner surface facing the lateral electrode, the pole electrode including an aperture, the aperture being aligned with the second central axis to allow electrons to pass through the aperture, and a portion of the thickness of the pole electrode centered around the periphery of the aperture at the outer surface being removed to form an X-shaped aperture; A system comprising:

17. The system of claim 16 , wherein the X-shaped opening comprises at least two rectangular openings intersecting at 90 degrees relative to one another.

18. The system described in claim 17, wherein the X-shaped openings are an equidistant arrangement between two adjacent ones of the lateral electrodes.

19. 20. The system of claim 17, wherein the rectangular opening is a completely cut opening in a conductive plate.

20. The system of claim 17 , wherein the rectangular opening is a partially cut-out recess in a conductive plate.

21. 20. The system of claim 17, wherein the rectangular opening of the X-shaped aperture has a width at least 1.5 times a diameter of the beam of electrons it is designed to use in combination.

22. 20. The system of claim 17, wherein the rectangular opening of the X-shaped aperture has a width greater than twice the diameter of the beam of electrons it is designed to use with.

23. 20. The system of claim 17, wherein the rectangular opening of the X-shaped aperture has a width greater than 1 millimeter.

24. The system of claim 17, wherein the rectangular opening of the X-shaped aperture has a width between 1 millimeter and 5 millimeters.

25. The system of claim 17, wherein the rectangular opening of the X-shaped aperture has a width between 2 millimeters and 4 millimeters.

26. 20. The system of claim 17, wherein the rectangular opening of the X-shaped aperture has a length at least three times a diameter of the beam of electrons it is designed to use in combination.

27. 20. The system of claim 17, wherein the rectangular opening of the X-shaped aperture has a length greater than four times a diameter of the beam of electrons it is designed to use in combination.

28. 20. The system of claim 17, wherein the rectangular opening of the X-shaped aperture has a length greater than 3 millimeters.

29. The system of claim 17, wherein the rectangular opening of the X-shaped aperture has a width between 3 millimeters and 8 millimeters.

30. The system of claim 17, wherein the rectangular opening of the X-shaped aperture has a width between 4 millimeters and 6 millimeters.

31. The system of claim 17 , wherein the rectangular opening of the X-shaped aperture is tapered in shape.

Images