Ion guide including orthogonal merging pseudo-potential wells

Abstract

In some examples, an ion guide may include at least four rods spanning a portion of a circumference of the ion guide, and extending along a central axis of the ion guide. The ion guide may further include a plurality of electrodes. Each electrode of the plurality of electrodes may span a remaining portion of the circumference of the ion guide. Further, the plurality of electrodes may extend, in a side-by-side arrangement of electrodes of the plurality of electrodes, along the central axis of the ion guide.

Description

20230092-02 ION GUIDE INCLUDING ORTHOGONAL MERGING PSEUDO-POTENTIAL WELLS CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to U.S. Provisional Patent Application Serial Number 63 / 554,658, filed February 16, 2024, titled “ION GUIDE INCLUDING ORTHOGONAL MERGING PSEUDO-POTENTIAL WELLS”, which is incorporated by reference in its entirety. BACKGROUND

[0002] Operation of quadrupole-time-of-flight (QTOF) mass spectrometry may begin with selecting precursor ions in a quadrupole mass analyzer. The selected precursor ions may then be transferred to a collision cell and fragmented into product ions via collision- induced dissociation. Following fragmentation, the product ions may be transferred downstream to a time-of-flight (TOF) mass analyzer that distinguishes ions by the mass to charge ratio. Another function of the collision cell may include radially compressing the ion beam and cooling ions by collisional cooling. The resulting ion beam may be well- conditioned at the exit as required by downstream optics for achieving desired resolution and sensitivity.20230092-02 BRIEF DESCRIPTION OF DRAWINGS

[0003] Features of the present disclosure are illustrated by way of example and not limited in the following figure(s), in which like numerals indicate like elements, in which:

[0004] Figure 1 illustrates an isometric view of an ion guide including orthogonal merging pseudo-potential wells, where the ion guide includes a plurality of rods coated with resistive layers and a set of planar electrodes, in accordance with an example of the present disclosure;

[0005] Figure 2 illustrates fusion of two pseudo-potential wells on orthogonal R-planes for the ion guide including orthogonal merging pseudo-potential wells of Figure 1, in accordance with an example of the present disclosure;

[0006] Figure 3 illustrates fusion of two pseudo-potential wells on orthogonal R-Z planes for the ion guide including orthogonal merging pseudo-potential wells of Figure 1, in accordance with an example of the present disclosure;

[0007] Figure 4 illustrates elongation of the effective cooling distance to broaden mass range for the ion guide including orthogonal merging pseudo-potential wells of Figure 1, in accordance with an example of the present disclosure;

[0008] Figure 5 illustrates separation of charged droplets from ions to block charged droplets propagation for the ion guide including orthogonal merging pseudo-potential wells of Figure 1, in accordance with an example of the present disclosure;

[0009] Figure 6 illustrates separation of neutrals from ions to block neutrals propagation for the ion guide including orthogonal merging pseudo-potential wells of Figure 1, in accordance with an example of the present disclosure; and20230092-02

[0010] Figure 7 illustrates minimizing of ion loss in transmission through an inserted device for the ion guide including orthogonal merging pseudo-potential wells of Figure 1, in accordance with an example of the present disclosure.20230092-02 DETAILED DESCRIPTION

[0011] For simplicity and illustrative purposes, the present disclosure is described by referring mainly to examples. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be readily apparent however, that the present disclosure may be practiced without limitation to these specific details. In other instances, some methods and structures have not been described in detail so as not to unnecessarily obscure the present disclosure.

[0012] Throughout the present disclosure, the terms "a" and "an" are intended to denote at least one of a particular element. As used herein, the term "includes" means includes but not limited to, the term "including" means including but not limited to. The term "based on" means based at least in part on.

[0013] An ion guide including orthogonal merging pseudo-potential wells is disclosed herein, and provides a combination of two pseudopotential wells on orthogonal planes respectively within one ion guide. The pseudopotential wells enable shifting of the entrance and the exit off the axis of the ion guide in opposite directions.

[0014] With respect to ion guides generally, in one example, a collision cell may employ three sections of hexapoles of different rod diameters. The first section may be a hexapole of the largest rod diameter corresponding to a large inscribed radius to facilitate capture of ions entering the collision cell. The second section may be an inwardly tilted hexapole of a smaller rod diameter than the first section. Each rod may be tilted inwardly to the axis, so that the inscribed radius is gradually reduced. The rods may be coated with resistive layers so that a potential difference can be established along the axis of the collision cell to move ions forward. The last section hexapole may be of the20230092-02 smallest rod diameter corresponding to an inscribed radius that matches the inscribed radius at the exit of the second section hexapole. This ion guide design may experience technical challenges with respect to blocking of neutral gas molecules and / or large droplets due to the presence of line of sight at the axis. Consequently, downstream optics are prone to contamination by such particles deposited on the surfaces. In addition, ion guides with the converging structure are also prone to contamination by the particles deposited on their surfaces. As a result, the longevity of the entire optics system may be decreased.

[0015] In another example, in order to eliminate the line of sight, a curved multipole may be utilized to separate the path of ions from the path of the neutral molecules. Alternatively, a curved ion funnel may be utilized to separate the path of ions and the path of the neutral molecules. In a yet further example, a curved ion guide may be implemented on two generally parallel surfaces with a tilted transition section. These ion guide designs separate the paths for ions and neutral particles by curving the mechanical structure of the ion guide for turning ions off the axis. As the confining field of ion guide is dependent on the mass-to-charge ratio (m / z), such curved structures can only make turns for ions of a limited m / z range.

[0016] In a further example, two parallel ion guides stacked side-by-side with an opening may be utilized to allow transferring ions from one ion guide to the other, so that one ion guide is used for the entrance and the other is used for the exit. Although this design addresses some of the aforementioned technical challenges, the side-by-side structure creates a pseudo-potential barrier at the interface of the two ion guides. As the height of the pseudo- potential barrier depends on the mass-to-charge ratio, ions are20230092-02 mass-to-charge ratio selectively transferred across the barrier by ramping the compensation direct current (DC) voltage difference between the two ion guides. This mass-to-charge ratio selective ion transfer may be useful for some of the applications when ions are transferred in pulses, but may present technical challenges when continuous ion flow is needed.

[0017] In order to address at least the aforementioned technical challenges, the ion guide including orthogonal merging pseudo-potential wells disclosed herein eliminates the line of sight through the collision cell for preventing contaminant particles (e.g., neutral gas molecules, large droplets) from prorogating to the downstream ion optics and the consequent contamination. Further, the ion guide including orthogonal merging pseudo- potential wells disclosed herein substantially reduces the probability of contaminant particles deposition on the surface of the ion guide inside the collision cell.

[0018] The ion guide including orthogonal merging pseudo-potential wells disclosed herein simultaneously transports ions of a broad range of mass-to-charge ratio (m / z). Further, the ion guide including orthogonal merging pseudo-potential wells disclosed herein simultaneously processes a large acceptance at the entrance and a tight convergence at the exit for ion transportation.

[0019] According to examples disclosed herein, an ion guide may include at least four rods spanning a portion of a circumference of the ion guide, and extending along a central axis of the ion guide. The ion guide may further include a plurality of electrodes. Each electrode of the plurality of electrodes may span a remaining portion of the circumference of the ion guide. Further, the plurality of electrodes may extend, in a side-by-side arrangement of electrodes of the plurality of electrodes, along the central axis of the ion20230092-02 guide.

[0020] According to examples of the ion guide disclosed herein, at least one rod of the at least four rods may include a circular cross-section.

[0021] According to examples of the ion guide disclosed herein, at least one rod of the at least four rods may include a non-circular cross-section (e.g., square, oval, etc.).

[0022] According to examples of the ion guide disclosed herein, the four rods may symmetrically span the portion of the circumference of the ion guide relative to the central axis of the ion guide.

[0023] According to examples of the ion guide disclosed herein, alternating current (AC) voltage applied to each rod of the at least four rods is maintained at an opposite phase relative to an adjacent rod to form a pseudo-potential well on a cross-sectional plane perpendicular to the central axis.

[0024] According to examples of the ion guide disclosed herein, AC voltages applied to neighboring electrodes of the plurality of electrodes are maintained at 180° out of phase relative to each other to form a further pseudo-potential well on a transverse plane through the central axis.

[0025] According to examples of the ion guide disclosed herein, alternating current (AC) voltages applied to neighboring electrodes of the plurality of electrodes are maintained at 180° out of phase relative to each other to form a pseudo-potential well on a transverse plane through the central axis.

[0026] According to examples of the ion guide disclosed herein, each electrode of the plurality of electrodes may include a planar configuration that spans greater than one-half20230092-02 of the circumference of the ion guide.

[0027] According to examples disclosed herein, a method may include supplying ions at a radial location relative to a central axis of an ion guide. The method may further include staggering, by the ion guide, the supplied ions such that ions exiting the ion guide exit at a different radial location relative to the central axis of the ion guide.

[0028] According to examples disclosed herein, an ion guide may include a plurality of rods spanning a portion of a perimeter of the ion guide, and extending along an axis of the ion guide. The ion guide may further include a plurality of electrodes. Each electrode of the plurality of electrodes may span a remaining portion of the perimeter of the ion guide. Further, the plurality of electrodes may extend, in a side-by-side arrangement of electrodes of the plurality of electrodes, along the axis of the ion guide. Thus, the ion guide may include a circular or non-circular configuration, where, for the circular configuration, the perimeter of the ion guide may represent the circumference of the ion guide, and for a non-circular configuration, the perimeter of the ion guide may represent a measure along the outer surface or inner surface of the ion guide.

[0029] Figure 1 illustrates an isometric view of an ion guide including orthogonal merging pseudo-potential wells, hereinafter referred to as “ion guide 100”, in accordance with an example of the present disclosure.

[0030] Referring to Figure 1, ion guide 100 may include at least four rods (e.g., rods 102, 104, 106, and 108) spanning a portion (e.g., as shown at 118) of a circumference of the ion guide 100, and extending along a central axis 112 of the ion guide 100. The ion guide may further include a plurality of electrodes 110. Each electrode of the plurality of electrodes 110 may span a remaining portion (e.g., 120) of the circumference of the ion20230092-02 guide 100. Further, the plurality of electrodes 110 may extend, in a side-by-side arrangement of electrodes of the plurality of electrodes, along the central axis 112 of the ion guide 100.

[0031] According to examples of the ion guide 100 disclosed herein, at least one rod of the at least four rods (e.g., rods 102, 104, 106, and 108) may include a circular cross- section. Alternatively, at least one rod of the at least four rods may include a non-circular cross-section (e.g., square, oval, etc.).

[0032] According to examples of the ion guide 100 disclosed herein, the four rods (e.g., rods 102, 104, 106, and 108) may symmetrically span the portion of the circumference of the ion guide relative to the central axis 112 of the ion guide 100. For example, as shown in Figure 1, rods 102 and 104 are symmetrical about a vertical axis in the orientation of Figure 1 relative to rods 106 and 108.

[0033] According to examples of the ion guide 100 disclosed herein, each electrode of the plurality of electrodes 110 may include a planar configuration (e.g., see flat configuration shown in Figure 1) that spans greater than one-half of the circumference of the ion guide 100.

[0034] With continued reference to Figure 1, the ion guide 100 may provide a longitudinal conduit of a circular cross-sectional area along which ions are transported. The cross-sectional area of the conduit may be circular as shown, or include other shapes such as oval, convex, etc. The plurality of rods 102, 104, 106, and 108 may be coated with resistive layers. The set of rods 102, 104, 106, and 108 may be arranged circumferentially about central axis 112 of the ion guide 100 in parallel, with an inscribed diameter equal to the diameter of the conduit (e.g., 2xR0). The ion guide 100 is illustrated20230092-02at 114 in the R- plane, and at 116 in the R-Z plane.

[0035] The set of planar electrodes 110 may be an array of evenly spaced planar electrodes of open-ring geometry. The planar electrodes 110 may be arranged in parallel with a plane perpendicular to the central axis 112. The inner diameter of the ring geometry of the planar electrodes 110 may represent the diameter of the conduit.

[0036] As shown at 118 and discussed above, the set of rods 102, 104, 106, and 108 may span over a portion of the circumference of the conduit in the azimuthal dimension. In this regard, as shown at 120, the planar electrodes 110 may cover the rest of circumference of the conduit in the cross-sectional plane.

[0037] Figure 2 illustrates fusion of two pseudo-potential wells on orthogonal R-planes for the ion guide 100, in accordance with an example of the present disclosure.

[0038] Referring to Figure 2, as shown at 200, a first alternating current (AC) voltage supply may be utilized to apply an AC voltage to the set of rods 102, 104, 106, and 108 with two opposite phases (e.g., RF+, RF-, RF+, RF-) on interdigitating rods to form a first pseudo-potential well 202 on the cross-sectional plane perpendicular to the central axis 112. In this regard, the corresponding electric field is shown generally at 206. Thus, referring to Figures 1 and 2, each rod of the at least four rods (e.g., rods 102, 104, 106, and 108) may be maintained at an opposite phase relative to neighboring rods to form the pseudo-potential well 202 on a cross-sectional plane perpendicular to the central axis 112.

[0039] With continued reference to Figure 2, normalized potential on the R- plane isshown at 204 for different radius (R) values (e.g., 25%R0, 50%R0, and 75%R0). In this20230092-02 regard, normalized potential U based on an analytical solution may be specified as follows:In this regard, U represents the potential, represents the azimuthal angle, and represents the order of harmonics. As shown at 204, the normalized potential U determined based on the numerical solution from the electric field at 206 shows a close match to the analytical solution.

[0040] Figure 3 illustrates fusion of two pseudo-potential wells on orthogonal R-Z planes for the ion guide 100, in accordance with an example of the present disclosure.

[0041] Referring to Figure 3, as shown at 300, a second AC voltage supply may be utilized to apply an AC voltage to the array of planar electrodes 110 with neighboring electrodes 180° out of phase from one another as shown at 302. Thus, a second pseudo- potential well 308 may be formed on the transverse plane through the central axis 112. In this regard, the corresponding electric field is shown generally at 312. Thus, neighboring electrodes of the plurality of electrodes may be maintained at 180° out of phase relative to each other to form the further pseudo-potential well 308 on a transverse plane through the central axis 112.

[0042] With continued reference to Figure 3, normalized potential on the R-Z plane is shown at 310 for different radius (R) values (e.g., 25%R0, 50%R0, and 75%R0). In this regard, normalized potential U based on an analytical solution may be specified as follows:20230092-02In this regard, U represents the potential, L represents the pitch of stacked planar electrodes, z represents the axial displacement, and Inrepresents the modified Bessel function of the first kind of order n. As shown at 310, the normalized potential U determined based on the numerical solution from the electric field at 312 shows a close match to the analytical solution.

[0043] For the ion guide 100, a first DC voltage supply (not shown) may be utilized to apply a DC voltage gradient along the rods 102, 104, 106, and 108 with a common DC bias. Further, a second (optional) DC voltage supply (not shown) may be utilized to apply an axial DC voltage gradient along the stack of planar electrodes in the longitudinal dimension with a common DC bias.

[0044] During operation of the ion guide 100, ions may enter the ion guide off-axis near the side of planar electrodes at 306. Ions may be first confined by the pseudopotential well of the stacked planar electrodes 110. Then, the axial DC gradient on the rods 102, 104, 106, and 108 may attract ions to the rods and drag them downward to the exit in the longitudinal dimension. As ions approach to the rods 102, 104, 106, and 108, the ion beam diameter may be increasingly reduced due to the convergence of the pseudopotential well generated by the rods. Eventually, ions exit off-axis (e.g., at 304) at the opposite side of the ion guide 100. As a result, axes for entrance (e.g., at 306) and exit (e.g., at 304) are staggered to eliminate the line of sight through the collision cell.

[0045] Figure 4 illustrates elongation of the effective cooling distance to broaden mass range for the ion guide 100, in accordance with an example of the present disclosure.20230092-02

[0046] Referring to Figure 4, with respect to elongation of the effective cooling distance to broaden mass range, the DC potential profile applied to the electrodes 110 is illustrated by the curve 400, and the DC potential profile applied to the rods 102, 104, 106, and 108 is illustrated by the curve 402. In this regard, different masses with the same m / z (and same V, which represents the potential difference at the entrance between the preceding optics and the ion guide 100) will penetrate differently as shown at 404. This effect allows for elongation of the effective cooling distance to broaden mass range.

[0047] Figure 5 illustrates separation of charged droplets from ions to block charged droplets propagation for the ion guide 100, in accordance with an example of the present disclosure.

[0048] Referring to Figure 5, with respect to separation of charged droplets from ions to block charged droplets propagation for the ion guide 100, the DC potential profile applied to the electrodes 110 is illustrated by the curve 500, and the DC potential profile applied to the rods 102, 104, 106, and 108 is illustrated by the curve 502. In this regard, separation of charged droplets from ions to block charged droplets propagation occurs as shown at 504.

[0049] Figure 6 illustrates separation of neutrals from ions to block neutrals propagation for the ion guide 100, in accordance with an example of the present disclosure.

[0050] Referring to Figure 6, the single unit (e.g., single ion guide 100) at 600 shows that the entrance and exit of ions does not include the same line of site. For example, ions enter at 602 and exit at 604. This allows neutrals at 606 to be separated from the20230092-02 ions of interest.

[0051] The arrangement at 608 shows an ion guide 610 and a 180° rotated ion guide 612. An aperture lens 614 may be disposed between the ion guides 610 and 612. Ions entering at 616 may exit the ion guide 610 via aperture 618 and may further exit the ion guide 612 via exit 620, where the entrance at 616 and the exit at 620 are at the same line of site. Moreover, neutrals may be effectively eliminated as they exit at 618.

[0052] Figure 7 illustrates minimizing of ion loss in transmission through an inserted device for the ion guide 100, in accordance with an example of the present disclosure.

[0053] Referring to Figure 7, in a similar manner as disclosed herein for Figure 6 for the arrangement at 608 that shows an ion guide 610 and a 180° rotated ion guide 612, the arrangement at 700 shows an ion guide 702 and a 180° rotated ion guide 704. A device, such as an ECD device 706, may be inserted between the ion guides 702 and 704. The ECD device 706 may further increase the ion collection capacity at 708.

[0054] What has been described and illustrated herein is an example along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration only and are not meant as limitations. Many variations are possible within the spirit and scope of the subject matter, which is intended to be defined by the following claims -- and their equivalents -- in which all terms are meant in their broadest reasonable sense unless otherwise indicated.

Claims

20230092-02 What is claimed is:

1. An ion guide comprising: at least four rods spanning a portion of a circumference of the ion guide, and extending along a central axis of the ion guide; and a plurality of electrodes, wherein each electrode of the plurality of electrodes spans a remaining portion of the circumference of the ion guide, and wherein the plurality of electrodes extend, in a side-by-side arrangement of electrodes of the plurality of electrodes, along the central axis of the ion guide.

2. The ion guide according to claim 1, wherein at least one rod of the at least four rods includes a circular cross-section.

3. The ion guide according to claim 1, wherein at least one rod of the at least four rods includes a non-circular cross-section.

4. The ion guide according to claim 1, wherein the at least four rods symmetrically span the portion of the circumference of the ion guide relative to the central axis of the ion guide.

5. The ion guide according to claim 1, wherein alternating current (AC) voltage applied20230092-02 to each rod of the at least four rods is maintained at an opposite phase relative to an adjacent rod to form a pseudo-potential well on a cross-sectional plane perpendicular to the central axis.

6. The ion guide according to claim 5, wherein AC voltages applied to neighboring electrodes of the plurality of electrodes are maintained at 180° out of phase relative to each other to form a further pseudo-potential well on a transverse plane through the central axis.

7. The ion guide according to claim 1, wherein alternating current (AC) voltages applied to neighboring electrodes of the plurality of electrodes are maintained at 180° out of phase relative to each other to form a pseudo-potential well on a transverse plane through the central axis.

8. The ion guide according to claim 1, wherein each electrode of the plurality of electrodes includes a planar configuration that spans greater than one-half of the circumference of the ion guide.

9. A method comprising: supplying ions at a radial location relative to a central axis of an ion guide; and staggering, by the ion guide, the supplied ions such that ions exiting the ion guide20230092-02 exit at a different radial location relative to the central axis of the ion guide.

10. The method according to claim 9, wherein the ion guide comprises: at least four rods spanning a portion of a circumference of the ion guide, and extending along the central axis of the ion guide; and a plurality of electrodes, wherein each electrode of the plurality of electrodes spans a remaining portion of the circumference of the ion guide, and wherein the plurality of electrodes extend, in a side-by-side arrangement of electrodes of the plurality of electrodes, along the central axis of the ion guide.

11. The method according to claim 9, wherein the ion guide is a first ion guide, further comprising: staggering, by a second ion guide that is disposed adjacent to an exit of the first ion guide and rotated 180° relative to the first ion guide, the supplied ions such that the ions exiting the first and the second ion guides exit at a same radial location relative to the central axis of the first ion guide.

12. The method according to claim 9, wherein the ion guide is a first ion guide, further comprising: staggering, by a second ion guide that is disposed adjacent to an exit of the first ion guide and rotated 180° relative to the first ion guide, the supplied ions such that the ions20230092-02 exiting the first ion guide, through a device disposed between the exit of the first ion guide and an entrance of the second ion guide, and through an exit of the second ion guide, exit at a same radial location relative to the central axis of the first ion guide.

13. An ion guide comprising: a plurality of rods spanning a portion of a perimeter of the ion guide, and extending along an axis of the ion guide; and a plurality of electrodes, wherein each electrode of the plurality of electrodes spans a remaining portion of the perimeter of the ion guide, and wherein the plurality of electrodes extend, in a side-by-side arrangement of electrodes of the plurality of electrodes, along the axis of the ion guide.

14. The ion guide according to claim 13, wherein the plurality of rods includes four rods.

15. The ion guide according to claim 13, wherein at least one rod of the plurality of rods includes a circular cross-section.

16. The ion guide according to claim 13, wherein at least one rod of the plurality of rods includes a non-circular cross-section.

17. The ion guide according to claim 14, wherein the four rods symmetrically span the20230092-02 portion of the perimeter of the ion guide relative to the axis of the ion guide.

18. The ion guide according to claim 14, wherein alternating current (AC) voltage applied to each rod of the plurality of rods is maintained at an opposite phase relative to an adjacent rod to form a pseudo-potential well on a cross-sectional plane perpendicular to the axis.

19. The ion guide according to claim 18, wherein AC voltages applied to neighboring electrodes of the plurality of electrodes are maintained at 180° out of phase relative to each other to form a further pseudo-potential well on a transverse plane through the axis.

20. The ion guide according to claim 13, wherein alternating current (AC) voltages applied to neighboring electrodes of the plurality of electrodes are maintained at 180° out of phase relative to each other to form a pseudo-potential well on a transverse plane through the axis.

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