Abstract
A mass spectrometry method comprises: (a) introducing ions and gas into a first electrode section of an ion transport apparatus along an axis, the ion transport apparatus further comprising a second electrode section including: a plurality of stacked, mutually parallel ring or plate electrodes; and an ion outlet aperture configured to receive the ions from the second electrode section and to transfer the ions to the vacuum chamber; (b) providing only non-oscillatory voltages to electrodes of the first electrode section of the ion transport apparatus that divert motion of the ions away from that axis and towards an entrance aperture of the second electrode section; (c) transporting the ions through the second electrode section to and through the ion outlet aperture to the vacuum chamber; and (d) removing a major portion of the gas through an exhaust port that is offset from the ion outlet aperture.
Claims
1. A method of introducing ions generated from an atmospheric ion source into a vacuum chamber of a mass spectrometer system, comprising: introducing the ions and gas into a first electrode section of an ion transport apparatus of the mass spectrometer system along an axis, wherein the ion transport apparatus further comprises a second electrode section that comprises: an ion inlet configured to receive the ions from the first electrode section; a plurality of electrodes to which radio frequency (RF) voltages are applied; and an ion outlet aperture configured to receive the ions from the second electrode section and to transfer the ions to the vacuum chamber; providing only non-oscillatory voltages to electrodes of the first electrode section of the ion transport apparatus, wherein the non-oscillatory voltages divert motion of the ions away from the axis and towards an entrance aperture of the second electrode section; transporting the ions through the second electrode section to and through the ion outlet aperture to the vacuum chamber; and removing a major portion of the gas through an exhaust port that is offset from the ion outlet aperture so that a major portion of the gas does not enter the ion inlet of the second electrode section.
2. A method as recited in claim 1, wherein the step of transporting the ions through the second electrode section to and through the ion outlet aperture to the vacuum chamber comprises transporting the ions past one or more sets of electrodes of an ion carpet device.
3. A method as recited in claim 1, wherein the step of transporting the ions through the second electrode section to and through the ion outlet aperture to the vacuum chamber comprises transporting the ions through a plurality of stacked, mutually parallel ring or plate electrodes.
4. A method as recited in claim 1, wherein the step of introducing the ions and gas into the first electrode section comprises introducing the ions and gas from an ion transfer tube into a space that is partially bounded by an electrode structure comprising one or more repeller electrodes and wherein the step of providing only non-oscillatory voltages to electrodes of the first electrode section of the ion transport apparatus comprises providing a common electrical potential, V.sub.1, to the ion transfer tube and to the repeller electrode or electrode structure.
5. A method as recited in claim 4, wherein the repeller electrode or electrode structure is L-shaped.
6. A method as recited in claim 4, wherein the space is additionally partially bounded by a radially-focusing electrode having a U-shaped inner surface and wherein the step of providing only non-oscillatory voltages to electrodes of the first electrode section of the ion transport apparatus comprises providing a second electrical potential, V.sub.2, to the radially-focusing electrode.
7. A method as recited in claim 6, wherein the radially-focusing electrode extends into the second electrode section.
8. A method as recited in claim 6, wherein the step of providing only non-oscillatory voltages to electrodes of the first electrode section of the ion transport apparatus comprises providing a third electrical potential, V.sub.3, to an entrance lens that is adjacent to or at an ion inlet of the second electrode section.
9. A method as recited in claim 3, wherein the step of transporting the ions through the second electrode section to and through the ion outlet aperture to the vacuum chamber comprises transporting the ions past a first subset of the stacked, mutually parallel ring or plate electrodes having outer respective surfaces that define concave cut-out areas.
10. A method as recited in claim 9, wherein the sizes of the concave cut-out areas progressively decrease along a direction towards the ion outlet aperture of the second electrode section.
11. A method as recited in claim 9, wherein the step of transporting the ions through the second electrode section to and through the ion outlet aperture to the vacuum chamber further comprises transporting the ions through apertures of electrodes of a second subset of the stacked, mutually parallel ring or plate electrodes, wherein the sizes of the apertures progressively decrease along a direction towards the ion outlet aperture of the second electrode section.
12. A method as recited in claim 11, wherein the shapes of the apertures are non-circular.
13. A method as recited in claim 2, wherein the step of transporting the ions through the second electrode section to and through the ion outlet aperture to the vacuum chamber comprises transporting the ions past ion carpet electrodes that are disposed on a substrate through which the ion outlet aperture passes.
14. A method as recited in claim 13, wherein at least a portion of the ion carpet electrodes surround the ion outlet aperture along non-circular paths.
15. An ion transport system for a mass spectrometer comprising: an ion inlet device; a first electrode section comprising: a repeller electrode or repeller electrode assembly configured to, in operation, deflect the trajectories of ions emitted from the ion inlet device; a second electrode section configured to, in operation, receive ions form the first electrode section and comprising: an ion carpet device comprising: a plurality of electrodes disposed upon a substrate, and an ion outlet aperture of the substrate configured to outlet the ions to a vacuum chamber; and one or more electrical power supplies electrically coupled to electrodes of the first and second electrode sections.
16. An ion transport system as recited in claim 15, further comprising a gas diverter structure that is configured to, in operation, deflect gas emitted from the ion inlet device away from the deflected trajectories of the ions.
17. An ion transport system as recited in claim 15, wherein the first electrode section further comprises a second ion carpet device configured to, in operation, prevent loss of the ions propagating along the deflected trajectories from the ion transport system.
18. An ion transport system as recited in claim 15, wherein the first electrode section further comprises a radially focusing electrode having a concave U-shaped surface and configured to, in operation, at least partially counteract the deflection of the ions generated by the repeller electrode.
19. An ion transport system as recited in claim 15, wherein the first electrode section further comprises an ion lens configured to direct the ions propagating along the deflected trajectories into the ion inlet aperture of the second electrode section.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0080] The above noted and various other aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings, not necessarily drawn to scale, in which:
[0081] FIG. 1A is a schematic depiction of a known mass spectrometer system comprising an ion funnel apparatus;
[0082] FIG. 1B is a schematic cross-sectional view of a known atmospheric-pressure-to-vacuum ion transport system comprising an ion funnel apparatus;
[0083] FIG. 1C is a schematic perspective view of a known slotted ion transfer tube as utilized in the ion transport system of FIG. 1B;
[0084] FIG. 1D is a schematic end view of the slotted ion transfer tube of FIG. 1B;
[0085] FIG. 2 is a depiction of a known ion transport device comprising conjoined ion guides;
[0086] FIG. 3 is a schematic longitudinal cross section of a first embodiment of an ion transport system including an ion transport apparatus in accordance with the present teachings;
[0087] FIG. 4 is a schematic depiction of an electrode plate of the ion transport apparatus of FIG. 3 as viewed on cross-section A-A′;
[0088] FIG. 5A is a schematic depiction of another electrode plate of the ion transport apparatus of FIG. 3 as viewed on cross-section B-Bʹ;
[0089] FIG. 5B is a schematic depiction of a ring electrode that may be used in place of the electrode plate of FIG. 5A;
[0090] FIG. 6 is a schematic depiction of yet another electrode plate of the ion transport apparatus of FIG. 3 as viewed on cross-section C-C';
[0091] FIG. 7 is a schematic longitudinal cross section of a second ion transport system including an ion transport apparatus in accordance with the present teachings;
[0092] FIG. 8 is a schematic depiction of a pair of electrode plates of the ion transport apparatus of FIG. 7 as viewed on cross-section D-D′;
[0093] FIG. 9A is a schematic depiction of another pair of electrode plates of the ion transport apparatus of FIG. 7 as viewed on cross-section E-E′;
[0094] FIG. 9B is a schematic depiction of an electrode structure comprising a pair of half-rings that may be used in place of the electrode plate of FIG. 9A;
[0095] FIG. 9C is an enlarged view of the electrode pair of FIG. 9A, highlighting the space between the pair of electrode plates;
[0096] FIG. 10 is a schematic depiction of yet another pair of electrode plates of the ion transport apparatus of FIG. 7 as viewed on cross-section F-F';
[0097] FIG. 11 is a schematic depiction of a pair of electrode plates of an ion transport apparatus that is a variant of the ion transport apparatus of FIG. 7;
[0098] FIG. 12 is a schematic depiction of another pair of electrode plates of the ion transport apparatus, as viewed on cross-section D-D′, that is a variant of the ion transport apparatus of FIG. 7;
[0099] FIG. 13A is a schematic longitudinal cross section of a third ion transport system including an ion transport apparatus in accordance with the present teachings;
[0100] FIG. 13B is a schematic longitudinal cross section of a fourth ion transport system including an ion transport apparatus in accordance with the present teachings;
[0101] FIG. 14 is a schematic longitudinal cross section of a fifth ion transport system including an ion transport apparatus in accordance with the present teachings;
[0102] FIG. 15A is a schematic longitudinal cross section of a sixth ion transport system including an ion transport apparatus in accordance with the present teachings;
[0103] FIG. 15B is a schematic transverse cross section of the ion transport apparatus of FIG. 15A, as viewed on cross-section G-G′;
[0104] FIG. 16A is a schematic longitudinal cross section of a seventh ion transport system including an ion transport apparatus in accordance with the present teachings;
[0105] FIG. 16B is a schematic transverse cross section of the ion transport apparatus of FIG. 16A, as viewed on cross-section H-H';
[0106] FIG. 17A is a schematic longitudinal cross section of an eighth ion transport system including an ion transport apparatus in accordance with the present teachings;
[0107] FIG. 17B is a schematic view of the ion transport apparatus of FIG. 17A, the view taken along the axis of the ion transport apparatus;
[0108] FIG. 18A is a schematic view of a representative example of a member of a first set of plate electrodes of the ion transport apparatus of FIG. 17A;
[0109] FIG. 18B is a schematic view of a representative example of a member of a second set of plate electrodes of the ion transport apparatus of FIG. 17A;
[0110] FIG. 18C is a schematic view of a representative example of a member of a third set of plate electrodes of the ion transport apparatus of FIG. 17A;
[0111] FIG. 19 is a schematic depiction of the general architecture of ion transport apparatus in accordance with the present teachings; and
[0112] FIG. 20 is a schematic illustration of a generalized mass spectrometer system on which methods in accordance with the present teachings may be practiced.
DETAILED DESCRIPTION
[0113] The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the described embodiments will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiments and examples shown but is to be accorded the widest possible scope in accordance with the features and principles shown and described. To fully appreciate the features of the present invention in greater detail, please refer to FIG. 1A-1D, 2-4, 5A-5B, 6-8, 9A-9C 10-12, 13A, 13B, 14, 15A, 15B, 16A, 16B, 17A, 17B, 18A-18C, 19, and 20 in conjunction with the following description.
[0114] In the description of the invention herein, it is understood that a word appearing in the singular encompasses its plural counterpart, and a word appearing in the plural encompasses its singular counterpart, unless implicitly or explicitly understood or stated otherwise. Furthermore, it is understood that, for any given component or embodiment described herein, any of the possible candidates or alternatives listed for that component may generally be used individually or in combination with one another, unless implicitly or explicitly understood or stated otherwise. Moreover, it is to be appreciated that the figures, as shown herein, are not necessarily drawn to scale, wherein some of the elements may be drawn merely for clarity of the invention. Also, reference numerals may be repeated among the various figures to show corresponding or analogous elements. Additionally, it will be understood that any list of candidates or alternatives is merely illustrative, not limiting, unless implicitly or explicitly understood or stated otherwise. As used herein, the term “DC”, when referring to a voltage applied to one or more electrodes of a mass spectrometer component (such as an ion funnel), does not necessarily imply the imposition of or the existence of an electrical current through those electrodes but is used only to indicate that the referred-to applied voltage either is static or, if non-static, is non-oscillatory and non-periodic. The term “DC” is thus used herein to distinguish the referred-to voltage(s) from applied periodic oscillatory voltages, which themselves may be referred to as either “RF” or “AC” voltages. As used herein, the term “major portion”, as used herein, refers to a portion that is greater than at least fifty percent. For example, if a major portion of gas flow is exhausted from a portion of a mass spectrometer apparatus through an exhaust port, then at least 50 percent of the gas flow is exhausted through the port. In many instances, it may be desirable or even necessary to exhaust a greater portion of gas flow through an exhaust port of a mass spectrometer apparatus, in order to prevent the gas from entering downstream high-vacuum chambers. Thus, the exhausting of a major portion of gas flow through an exhaust port may preferably, refer to exhausting a portion of the gas flow, through the exhaust port, that is greater than 60 percent, greater than 65 percent, greater than 70 percent, greater than 75 percent, greater than 80 percent, greater than 85 percent, greater than 90 percent, greater than 95 percent or greater than 99 percent of the original gas flow.
[0115] This document includes discussion of various ion conduit structures - referred to as “ion tunnels” and “ion funnels” - that permit ions to migrate through an internal volume of the conduit structure along a longitudinal direction while restricting ions from escaping from the internal volume along transverse or radial dimensions or directions. Because ions are prevented from escaping from the internal volume along certain dimensions or directions, the internal volume is also referred to as a “trapping volume”. As used herein, the terms “ion tunnel” and “ion funnel” refer to the combination of the physical conduit structure and the internal volume within which ions migrate longitudinally while being trapped transversely/radially. As used herein, the terms “ion tunnel section” and “ion funnel section” refer to an ion tunnel structure or ion funnel structure, respectively, that is a portion or component of a larger ion transport apparatus which, itself, may comprise one or more ion tunnel and/or ion funnel component portions or sections. As used herein, the term “ion funnel” refers to an ion conduit structure within which the cross-sectional area of the internal volume progressively decreases across the length of its central longitudinal axis or across a portion of the length of a central longitudinal axis of a containing ion transport structure. Likewise, as used herein, the term “ion tunnel” refers to an ion conduit structure that maintains a constant cross-sectional area across its central longitudinal axis or across a portion of a central longitudinal axis of a containing ion transport apparatus.
[0116] The use of the terms “ion tunnel” and “ion funnel” are not intended to restrict the cross-sectional shape of the internal volume of the referred to conduit structure to any particular shape. Thus, as the terms are used herein, an ion tunnel or ion funnel may comprise any regular or irregular cross-sectional shape, such as circular, rectangular, etc. If, in cross section, the trapping volume of an ion tunnel has radial symmetry or an n-fold axis of rotational symmetry, where n ≥ 2, then a central longitudinal axis is taken as the axis of radial or n-fold rotational symmetry. Otherwise, if, in cross section, the trapping volume has a single plane of mirror symmetry, the central longitudinal axis of the ion tunnel is taken as the intersection of the plane of mirror symmetry with the trapping volume. Otherwise, if, in cross section, the trapping volume is asymmetric, the central longitudinal axis is taken as the locus of the centers of mass, taken at all cross sections, of uniform-density laminae having the same shape as the shape of the respective trapping volume cross section.
[0117] The discussion in this document make reference to various as axes and planes that are defined with reference to geometric features of physical objects, such as slots, cutouts, apertures, etc. Such various axes and planes are to be understood as extending “to infinity” beyond the feature(s) of physical objects with respect to which they are defined. Accordingly, referred-to intersections of or geometric relationships between such axes and/or planes are not necessarily within the bounds of the defining features or physical objects. Further, as used herein, a statement that a first line or axis is coincident with a second line or axis means that all points of the second line or axis are also points of the first line or axis. Still further, as used herein, a statement that a line or axis is contained within a plane means that all points of the line are also points of the plane.
[0118] FIG. 3 is a schematic longitudinal cross section of a first embodiment of an ion transport system 100 including an ion transport apparatus 120 in accordance with the present teachings. In FIG. 3 as well as in subsequent drawings, the dashed line 101 schematically depicts the outline of a cross-sectional view of a hollow interior volume of the ion funnel 100, where the cross section is taken to include the apparatus' central longitudinal axis 47. In similarity to conventional ion funnels, the ion funnel 100 comprises a set of stacked parallel plate electrodes 142, each such electrode comprising at least one aperture. In known fashion, Radio Frequency (RF) oscillatory voltage waveforms are applied to the electrode plates, with waveforms of immediately adjacent plates being out of phase by π radians. FIGS. 4, 5A and 6 show schematic depictions of individual plate electrodes located at transverse cross sections A-A′, B-B', and C-C', respectively. These figures show the locations of apertures 153, 154, 155a and 155b which are defined below.
[0119] Collectively, the apertures of the plate electrodes 142 define the hollow interior volume of the ion funnel 120 which may be considered as being composed of sub-volumes 143, 144 and 145a-145b. Gas and/or ions from an ionized sample are delivered into the sub-volume 143 by means of an ion transfer tube 17. The ion transfer tube may comprise a conventional round bore or lumen for transporting the gas and/or ions. Alternatively, as taught in U.S. Pat. No. 8,309,916, which is hereby incorporated herein in its entirety, the ion transfer tube 17 may comprise a slot or may comprises multiple straight or curved slots or may comprise one or more bores or channels having cross sections that comprise one or more obround or slot-shaped lobes. All such bore configurations fulfil the function of transmitting high gas flow and hence more ions, but at the same time providing good heat transfer to ions within the tube that permits efficient desolvation. Optionally, an auxiliary transfer tube 19 may be provided to supply an auxiliary gas flow that optionally includes ions of a calibrant material into the sub-volume 43. The small dotted circle and oval in each of FIGS. 3, 7, 13A, 13B, 14 and 15A represent projections, parallel to the axis 47, of the locations of the lumens of the transfer tubes 19 and 17, onto the plane of the depicted electrode plate. In a preferred embodiment, the slotted-bore ion transfer tube 17 has a bore in the form of a single straight slot, as depicted in FIGS. 1C-1D.
[0120] As previously described, the ion transfer tube 17 delivers an aerosol into the sub-volume 143 of the ion funnel 120 that includes a mixture of neutral gas molecules, charged solvent droplets and ions derived from a sample. The position of the slotted-bore ion transfer tube 17 is schematically indicated by an elongated slot that indicates that the long dimension of the slot (corresponding to the length, s, depicted in FIG. 1D) is aligned parallel to the x-z plane (i.e., the plane of the printed page) of the funnel 120. Accordingly, the slot plane 39 (see FIG. 1C) of the slotted-bore ion transfer tube 17 is parallel to the plane of the printed drawing page with regard to each of FIGS. 3, 7, 13A, 13B, 14 and 15A. The longitudinal axis of the slotted-bore ion transfer tube 17 may be tilted within the slot plane, at an angle β (0 ≤ β ≤ π/4), relative to the central longitudinal axis 47 of the funnel apparatus 120. The auxiliary transfer tube 19, if present, has a conventional round bore, the axis of which is preferably aligned parallel to the central longitudinal axis 47 of the funnel. The auxiliary transfer tube 19, if present, may be employed to deliver, into the sub-volume 43, either a flow of neutral gas or a flow of a second aerosol comprising gas molecules, charged solvent droplets and ions derived from a calibrant material.
[0121] In contrast to conventional ion funnels, the ion funnel 120 comprises two outlet apertures. A first ion outlet aperture 46 receives ions and a small proportion of the inlet gas from funnel sub-volume 145a and delivers the ions and gas to intermediate vacuum chamber 26 via an aperture 48 in inter-chamber partition 15. A second outlet aperture 51 receives a greater proportion of the inlet gas as well as some ions from funnel sub-volume 145b and exhausts the gas and ions as exhaust flow 112 via a gas exhaust port 110. The exhaust port 110 may be coupled to a vacuum pump. Exhausting a major portion introduced gas flow through the exhaust port 110 is necessary to prevent excessive gas from entering the intermediate-vacuum and high-vacuum chambers 26, 27 (FIGS. 1A, 3, 13A-13B, 14, 15A, 16A).
[0122] FIGS. 4, 5A and 6 illustrate how the apertures of plate electrodes 142 vary in progression through the apparatus 120 from its inlet to its outlets. The apertures 153 of the plate electrodes in electrode section 149a define the ion tunnel shape of sub-volume 143. Accordingly, the plate electrodes and their apertures in electrode section 149a define an ion tunnel section of the apparatus 120. Axis 47, which is a central longitudinal axis of the apparatus 120 is also a central longitudinal axis of the ion tunnel section as well as of the adjacent truncated funnel section of the apparatus, the latter section being defined by the electrodes and apertures of electrode section 149b. The apertures of the electrodes of section 149a all have the same aperture diameter θ.sub.T as shown in FIG. 4. The length of the section 149a is sufficient to generate a desired amount of adiabatic cooling of the ions. The diameter θ.sub.T is sufficiently large to substantially contain the expansion plume of gas and ions that emerges at high velocity from the ion transfer tube 17 as well as from the auxiliary transfer tube 19, if present. However, because of the orientation of the slot of the ion transfer tube 17, within the x-z plane (i.e., the plane of the drawing), the velocity and quantity of gas lateral expansion is greater parallel to the apparatus y-axis (i.e., perpendicular to the plane of the drawing) than are the lateral expansion velocity and quantity parallel to the x-axis (i.e., vertically within the drawing). Whereas gas undergoes expansion, RF voltages applied to the plates in known fashion cause ions to migrate towards and so as to become concentrated near the central axis 47, residing in a pseudopotential well within the sub-volumes 143 and 144. The apertures 154 of the plate electrodes of section 149b (FIG. 5A) define the shape of the truncated ion funnel sub-volume 144 of the hollow interior volume. The plate electrodes of section 149b have variable diameters, θ, that progressively decrease with increasing distance from the entrance aperture. In similarity to conventional ion funnel apparatuses, the decreasing aperture diameters cause progressive focusing of the flow of ions around the central longitudinal axis 47. Accordingly, ion transport through the apparatus to the mass spectrometer intermediate-vacuum chamber 26 occurs through sub-volumes 143, 144 and 145a, which are thus referred to in this document as “ion transport” volumes.
[0123] Each electrode plate of section 149c comprises two separate apertures, shown as apertures 155a and 155b in FIG. 6. The collection of apertures 155a define the apparatus sub-volume 145a and the collection of apertures 155b define the sub-volume 145b. The centers of the apertures 155a are co-axial and define an axis 119 of the funnel-shaped sub-volume 145a of apparatus 120. Likewise, the centers of the apertures 155b are co-axial and define a central longitudinal axis 119 of the funnel-shaped sub-volume 145b. Accordingly, the electrodes of the electrode plate section 149c, together with their apertures, define first and second ion funnel sections of the apparatus 120, which correspond to the sub-volumes 145a and 145b, respectively. Longitudinal funnel-section axes 119 and 117 correspond to the first and second ion funnel sections, respectively. According to the apparatus configuration shown in FIG. 3, the three axes 119, 47 and 117 are all parallel to one another but do not coincide with one another. The axis 119 indicates the orientation of a pseudopotential well within the sub-volume 145a; likewise, the axis 117 is the location of a pseudopotential well within the sub-volume 145b.
[0124] In operation of the apparatus 120, a flow of ions through the apparatus is divided into two unequal flow portions at the boundary between electrode plate sections 149b and 149c. Most of the flow of ions that is emitted from the ion transfer tube 17 is deflected generally away from the axis 117 by an electric field that is generated by voltages that are applied to repeller electrode 162 and to attractor electrode 163 and/or to the tube 17. This electric field causes most of the emitted ions to flow generally towards the central longitudinal axis 47 and longitudinal funnel-section axes 119. This first portion of the ions passes through the sub-volume 145a to ion outlet aperture 46 and a second portion of the ions passing through the sub-volume 145b to outlet aperture 51. The first portion of the ions passes into mass spectrometer intermediate-vacuum chamber 26. A second, lesser portion of the emitted ion flux is either neutralized or lost through gas exhaust port 110.
[0125] Additionally, the inventors have discovered that, provided that the flow rates from and relative positions of inlets 17, 19 are chosen so as to optimally reduce turbulence, as may be determined from gas dynamics calculations, there is little cross flow of gas between the fluxes from the two transfer tubes. In other words, under such conditions, most of the gas flux, Q.sub.1, emitted from the slotted-bore ion transfer tube 17 does not cross the axis 47 into sub-volume 145a and, likewise, most of the smaller gas flux, Q.sub.2, emitted from the auxiliary transfer tube 19, if present and utilized, does not cross into the sub-volume 145b. Thus, most of the gas and droplets emitted from the ion transfer tube 17 are exhausted from the apparatus, either through gas exhaust port 110 or by escape through the gaps between the plate electrodes. The smaller gas flow from the auxiliary transfer tube 19 is either exhausted from the apparatus through gaps between plates or else remains as a small residual gas flow that propels the ions through the ion outlet aperture 46.
[0126] The vertical orientation of the dotted oval representing the slot of the slotted ion transfer tube 17 in FIG. 3 and other drawings is a representation that the long dimension of the slot is oriented parallel to the denoted x-axis. Such an orientation is advantageous because the velocity of gas emitted from the slot is greater parallel to the y-axis (i.e., into and out of the page of the drawing of FIG. 3) than is the velocity parallel to the x-axis. Thus, the depicted slot orientation aids in directing most of the gas flow away from the ion outlet aperture 46 in the y-direction, meanwhile allowing a reduction in the distance between the ion transfer tube and the aperture 46 along the x-direction. More generally, the slotted-bore ion transfer tube 17 may be advantageously oriented such that the central longitudinal axis 47 of the apparatus is contained within the slot plane 39 of the slotted-bore ion transfer tube 17.
[0127] In operation of the funnel 120, sample-derived ions, together with un-ionized gas and charged droplets, are emitted into the sub-volume 143 from the slotted-bore ion transfer tube 17. As taught in US Pat. No. 9,761,427, gas jet expansion emerging from the slotted-bore ion transfer tube 17 into the funnel apparatus is anisotropic, with greater gas expansion and velocity occurring perpendicular to the slot plane 39. Within the funnel apparatus 120, the slot of the ion transfer tube 17 is oriented parallel to the x-axis, as indicated on the drawing. Accordingly, most of the expansion of gas that is inlet to the sub-volume 143 from the ion transfer tube is perpendicular to the plane of the drawing and only a minor proportion of the gas expansion occurs parallel to the x-axis. Therefore, most neutral gas molecules and residual droplets follow the general gas flow into sub-volume 145b and are exhausted from the apparatus at outlet aperture 51. At the same time, ions are urged by DC fields to migrate towards axes 47, 119 and beyond towards electrodes 149c. Thus, it is preferable that the central longitudinal axis 47 is contained within the slot plane 39 of the slotted-bore ion transfer tube 17. In this fashion, ions may migrate from the outlet of the slotted-bore ion transfer tube 17 towards the pseudopotential well near electrodes 149c with minimal deflection caused by gas flow. Thus, the probability that ions will enter the sub-volume 145a is much higher than the probability that the ions will enter the sub-volume 145b. Accordingly, employment of the funnel apparatus 120 significantly reduces the proportion of neutral molecules relative to ions that are transferred into the downstream intermediate-vacuum chamber 26.
[0128] During operation of the funnel apparatus 120, the auxiliary transfer tube 19, if present, may be employed according to one of three different auxiliary tube operational modes: an inactive mode in which no gas or ions are inlet to the sub-volume 143; a calibration mode in which a flow of calibrant ions and other particles are introduced into the sub-volume 143 from a secondary electrospray ion source; and an auxiliary gas flow mode in which a flow of neutral gas molecules only is introduced into the sub-volume 43. As noted above, gas dynamics calculations indicate that, in all such operational modes, a large proportion of the gas flow emitted from the slotted-bore ion transfer tube 17 is exhausted through the gas exhaust port 110. Neutral gas molecules and residual droplets are thereby advantageously prevented from passing into the intermediate-vacuum chamber 26. However, the calculations also indicate that, when the auxiliary transfer tube 19 is inactive during operation of the system 100, a significant amount of gas turbulence may develop in the portion of the hollow interior volume that is disposed between the auxiliary transfer tube 19 and the ion outlet aperture 46. This turbulence is believed to interfere with the migration of ions out into the intermediate-vacuum chamber through the ion outlet aperture 46 when the auxiliary transfer tube 19 is inactive. The gas dynamics calculations indicate that this turbulence is suppressed by a relatively small auxiliary gas flow that is provided by the auxiliary transfer tube 19 when it is operated in either the calibration mode or the auxiliary gas flow mode.
[0129] FIG. 7 is a schematic longitudinal cross section of a second ion transport system 200 including an ion transport apparatus 220 in accordance with the present teachings. The ion transport apparatus 220 of FIG. 7 differs from the ion transport apparatus 120 of FIG. 3 in that each individual plate electrode 142 of the apparatus 120 is replaced, in the apparatus 220, by a pair of half-electrode plates 242a, 242b that are preferably co-planar with one another. FIGS. 8, 9A and 10 show schematic depictions of such plate-electrode pairs located at cross sections D-D′, E-E′, and F-F', respectively. The cross-section of the hollow interior volume of the ion transport apparatus 220, as taken along a plane the incudes the central axis 47 and as depicted by dashed line 101, is essentially identical to the cross section depicted in FIG. 3. However, as shown in FIGS. 8, 9A and 10, the hollow interior volume is partially defined by cutout surfaces 253a, 254a and aperture surface 255a of electrodes 242a and partially defined by cutout surfaces 253b, 254b and aperture surface 255b of electrodes 242b. These surfaces define an ion tunnel electrode section 249a of the electrode pairs, a truncated ion funnel electrode section 249b of the electrode pairs and a third section 249c of the electrode pairs that corresponds to first and second ion funnel sections of the apparatus 220, the first of which outlets ions and a small proportion of the inlet gas to ion outlet aperture 46 and the second of which outlets a major portion of the inlet gas and a lesser quantity of ions to second outlet aperture 51.
[0130] As shown in FIG. 8, the cutout surfaces 253a and 253b of electrode pairs within electrode section 249a oppose one another across the position of the central axis 47, with each of the two opposing surfaces 253a, 253b outlining and defining a cutout within an edge of the respective plate electrode. Each cutout surface approximates a semicircle and the two semicircles together define an approximately circular aperture having a constant apparent diameter of θ.sub.T throughout the ion tunnel section of the apparatus. Likewise, as shown in FIG. 9A, the cutout surfaces 254a and 254b of electrode pairs within the truncated funnel electrode section 249b oppose one another across the position of the central axis 47, with each of the two opposing surfaces approximating a semicircle and the two semicircles together defining an approximately circular aperture having a variable apparent diameter of θ. Within the section 249c, the aperture surfaces 255a and the surfaces 255b (FIG. 10) define separate circular apertures within electrodes 242a and 242b, respectively. Taken together, the three sections of the two sets of electrodes define six sub-volumes of the hollow interior of the apparatus 220. As denoted in FIG. 7, these are referred to as sub-volumes 243a-243b, 244a-244b and 245a-245b.
[0131] In operation of the system 200, the members of each pair of “half” electrodes are preferably supplied with an identical RF voltage amplitude and phase. Further, the RF phase supplied to each electrode pair is out of phase with the RF phase supplied to each immediately adjacent pair of electrodes. Thus, a pseudopotential well is generated within the apparatus 220 in the same manner that a similar pseudopotential well is generated in the apparatus 120 of FIG. 3. However, in contrast to the operation of the apparatus 120, the operation of the apparatus 220 includes providing a constant DC potential difference between the electrodes 242a and the electrodes 242b. The sign of the DC potential difference is such as to pull sample-derived ions emitted from the slotted ion transfer tube 17 out of the sub-volumes 243b and 245b and into the sub-volumes 243a, 244a and 245a. These sample-derived ions then exit the apparatus 220 through ion outlet aperture 46 and are subsequently transferred into intermediate-vacuum chamber 26. The provision of the DC potential difference, which is made possible by the replacement of each electrode plate 142 (e.g., as in FIG. 3) by a pair of half-electrode plates 242a, 242b, assists in urging the migration of sample ions towards and through the exit port 46. Accordingly, it may be seen that sub-volumes 243b, 243a, 244a and 245a are ion transport volumes through the apparatus 220.
[0132] At the same time that ions are being transported towards and through the exit port 46, the flow 112 of neutral gas molecules and residual droplets is predominantly directed out of the apparatus through gas exhaust port 110 or between the gaps in the electrode plates as described above with regard to the apparatus 120. Because the opposing electrode surfaces of electrode pairs that define the sub-volumes 243a-243b and 244a-244b complement one another (i.e., by approximating a set of circular apertures) no pseudopotential barrier (which would otherwise be centered about the central longitudinal axis 47) is created between the electrodes 242a and 242b. Because a fully-enclosed pseudopotential barrier between the electrodes 242a and 242b segments does not exist along the entire axial length of the device, each such set of electrodes 242a, 242b of the apparatus 220 cannot function as an independently-controllable ion guide as is described, for instance, in US Pat. No. 8,581,181. The auxiliary transfer tube 19, if present, may be employed according to any one of the “inactive”, “calibration” and “auxiliary gas flow” operational modes with results similar to those describe with regard to the apparatus 120. In particular, the latter two modes are preferred.
[0133] FIGS. 11-12 are schematic depictions, taken at the cross-sectional locations D-D′ and E-E′, of plate electrode pairs of a variant embodiment of an ion transport apparatus in accordance with the present teachings. The variant embodiment is generally similar to the apparatus 220 shown in FIG. 7. However, in cross section, the cutout-defining surfaces, 253a-253b and 254a-254b of each pair of electrodes of the variant embodiment are portions of separate circles (e.g., FIGS. 11-12) instead of portions of a single circle centered on the central longitudinal axis 47 (e.g., FIG. 8-9A).
[0134] FIG. 13A is a longitudinal cross section of another embodiment of an ion transport system 300 including an ion transport apparatus 320 in accordance with the present teachings. The ion transport apparatus 320 is generally similar to the ion transport system 200 (FIG. 7) except that all or a portion of the electrodes 242b whose apertures would otherwise define the sub-volume 245b are replaced by an enlargement of the gas exhaust port 110 and/or deeper extension of the exhaust port 110 into the interior of the funnel apparatus. The depiction of the exhaust port in FIG. 13A is highly schematic and other shapes may be envisioned for the purpose of efficiently purging the gas flow from the funnel. For example, the interior of the gas collection end of the gas exhaust port 110 may be funnel shaped, thereby replacing the defining boundaries of the sub-volume 245b. The enlarged exhaust port may be accompanied by an enlarged or re-configured inter-chamber partition 315 that replaces the conventional partition 15. Many or all of the replaced electrodes may be un-necessary since ion guiding is generally not required for any ions that flow into the sub-volume 245b. Alternatively, the configuration depicted in FIG. 13B as ion transport system 350 may be adopted. The ion transport apparatus 320b of the system 350 comprises the same physical structure as the ion transport system 200 of FIG. 7. The ion transport apparatus 320b differs from the ion transport system 200 only through the replacement of all or a portion of the electrodes 242b that define the sub-volume 245b by apertured plates 352. No RF voltages are provided to the apertured plates 352. However, a DC offset voltage may be applied to the apertured plates 352 in order to prevent loss of ions through the gas exhaust port.
[0135] FIG. 14 is a schematic longitudinal cross section of another embodiment of an ion transport system 400 including an ion transport apparatus 420 in accordance with the present teachings. The ion transport apparatus 420 is generally similar to the ion transport system 200 (FIG. 7) except that the set of electrodes 242b are replaced by a set of electrodes 442 that are oriented differently from the orientation of the electrodes 242b. Although the individual electrodes 242b and 442 are all planar in form, the electrodes 242b (as well as the electrodes 242a) are oriented (see FIG. 7) with their planes (e.g., the planes of the faces of the plate electrodes) substantially perpendicular to the central longitudinal axis 47. However, in the apparatus 420, each electrode 442 is oriented with the normal to its plane disposed at an angle to the axis 47. The slant angle is provided in a direction such that the flow of gas and/or residual droplets emitted from the slotted ion transfer tube 17 are directed away from the ion outlet aperture 46. The slant angle of the electrodes thus aids in the separation of gas and/or residual droplets from sample-derived ions, which are urged away from the flow of gas by the DC potential difference applied between the electrodes 242a and the electrodes 442. In a variant embodiment of the apparatus 420, a portion of the electrodes 442 may be replaced by an enlargement of the gas exhaust port 110 and/or deeper extension of the exhaust port into the interior of the funnel apparatus, as depicted in FIG. 13A.
[0136] FIG. 15A and FIG. 15B are schematic longitudinal and transverse cross sections, respectively, of another embodiment of an ion transport system 500 including an ion transport apparatus 520 in accordance with the present teachings. The view shown in FIG. 15B is taken at the cross-sectional location G-G′. Although the ion transport apparatus 520 includes the set of electrodes 242a of the system 200 (FIG. 7), the second set of electrodes 242b are replaced by one or more repeller electrodes, depicted as the three repeller electrodes 562a, 562b and 562c. Accordingly, in contrast to the other embodiments of herein-taught ion transport apparatuses, the apertures of the electrodes 242a of the apparatus 520 define only a single ion funnel section that corresponds to the funnel-shaped sub-volume 245a. The funnel-shaped sub-volume 245b of the apparatus 350 (FIG. 13B) is replaced, in the apparatus 520, by a channeled structure 515, which may be a portion of a wall or housing, that comprises the gas exhaust port 110.
[0137] Although three repeller electrode plates are shown in FIG. 15B, it should be kept in mind that that the entire electrode depicted in FIGS. 15A-15B could alternatively be formed of a single integrated piece. Although the depicted repeller electrodes are illustrated in the form of flat plates, it should be kept in mind that the one or more repeller electrodes may comprise curved surfaces of various shapes such as, without limitation, segments or arcs of tubes. In operation of the apparatus 520, a constant DC electrical potential difference is applied between the repeller electrodes and the set of plate electrodes 242a. The shape of the repeller electrode(s) and the sign of the DC potential difference are such that sample-derived ions are urged away from the repeller electrodes 562a-562c and towards the sub-volumes 243a and 244a. As shown in FIG. 16B, the sub-volume 243b, which receives ions and gas from the ion transfer tube 17, is defined within the confines of the repeller electrodes 562a-562c.
[0138] Taken together, the ion-repulsive potential applied to the repeller electrodes of the apparatus 520 and the ion-repulsive pseudopotential that is caused by application of alternately out-of-phase RF voltage waveforms to the electrodes 242a combine to create a pseudopotential well within the sub-volumes 243a, 244a. This pseudopotential well is generally near to the funnel axis 119 within the sub-volumes 243a, 244a. However, the pseudopotential may not be precisely centered about the funnel axis 119 as a result of the cross-sectional asymmetry of the apparatus 520 (e.g., see FIG. 15B). For good results, it is preferable that the slotted-bore ion transfer tube 17 is oriented such that ions may migrate from the outlet of the ion transfer tube and towards the pseudopotential well that is near the funnel axis 119 with minimal disturbance caused by gas flow. To achieve this goal, it is advantageous to orient the slotted-bore ion transfer tube 17 such that the funnel axis 119 is contained within the slot plane 39 of the ion transfer tube. Such a configuration causes most ions to be directed by an applied DC field away from the exhaust port and generally towards the towards the sub-volumes 243a, 244a, 245a and the ion outlet aperture 46. Accordingly, sub-volumes 243b, 243a, 244a, 245a are ion transport volumes within the apparatus 520. At the same time that ions are being transported to the ion outlet aperture 46 through the ion transport volumes, the asymmetric jet expansion of gas that emanates from the slotted ion transfer tube 17 causes most neutral gas molecules and residual droplets to be directed towards the exhaust port 110. The asymmetry of the jet expansion permits the width of the repeller electrode or electrode structure to be greater than the distance of this electrode or electrode structure from the jet axis 17a. As a result, the required DC electrical potential difference between the repeller electrodes and the set of electrodes 242a advantageously remains well below the 300-350 V threshold for initiation of undesired Paschen discharge.
[0139] FIGS. 16A and 16B are a schematic side-elevational view and a schematic transverse cross section, respectively, of another embodiment of another ion transport system 600 including an ion transport apparatus 620 in accordance with the present teachings. The ion transport apparatus 620 is a modified and simplified version of the funnel apparatus 520 in which the exhaust port 110 is replaced by a gas exhaust channel 610 that is defined by a gap between a repeller electrode assembly 662 and a gas diverter surface 617 of a gas diverter structure 615, the latter of which may comprise a portion of a wall or housing of the apparatus. The repeller electrode assembly 662 may comprise a box-like structure as depicted in the transverse cross-sectional view of the system provided in FIG. 16B. As shown in FIG. 16B, the repeller electrode assembly 662 may be comprise two wall sections 662a, 662b and a basal section 662b that define an internal gas channel that guides gas and droplets that emerge from the slotted-bore ion transfer tube 17 to the exhaust channel 610. The wall and basal sections may be formed as a single integral piece, as shown in FIG. 16B or, alternatively, may be separate from one another.
[0140] In similarity to other ion transport apparatuses described herein, the funnel apparatus 620 comprises a plurality of apertured plate electrodes 342, the apertures of which define a funnel-shaped volume 645 that corresponds to a funnel section of the apparatus and, possibly, a short tunnel-shaped volume 644 having a longitudinal axis 119. In order to allow free flow of gas into the exhaust channel 610, a portion of the apertured electrodes are absent from a region of the apparatus that is upstream from the ion funnel and/or ion tunnel volumes and that is downstream from the secondary transfer tube 19, if present. These “missing” electrodes are replaced by an optional set of ion carpet electrodes 359 that are configured to receive oscillatory RF voltages in similar fashion to the manner in which such oscillatory RF voltages are received by the plurality of apertured plate electrodes 342. When energized with such RF voltages, the ion carpet electrodes 359 prevent loss of ions through the side of the apparatus along which the ion carpet electrodes are disposed. Accordingly, a pseudopotential well is formed in the vicinity of central longitudinal axis 47 and, as discussed above with reference to FIG. 3, it is preferable to orient the slotted-bore ion transfer tube 17 such that the central longitudinal axis 47 is contained within the slot plane 39 of the ion transfer tube. Ion carpets are well known to those of ordinary skill in the art. As illustrated in FIG. 16A, the axis 121 of the funnel-shaped volume 645 of the funnel apparatus 620 may be disposed at an angle to the overall central longitudinal axis 47 (or to a central longitudinal axis of an upstream ion tunnel section). Preferably, the angle of the axis 121 is such that the ion outlet aperture 46 is disposed along a projection line 49, that is taken parallel to the central longitudinal axis 47 of the ion outlet of the slotted-bore ion transfer tube 17. This funnel configuration reduces the overall size of the funnel apparatus, allows upgrading of existing mass spectrometer systems without a drastic change of their layout and assists in elimination of most neutral gas molecules and droplets that may enter the funnel-shaped volume 645.
[0141] Because a major portion of gas is exhausted from the apparatus 600 through the exhaust channel 600 (FIG. 16A), that gas flow is not available to propel ions within the tunnel-shaped volume 644 and the funnel-shaped volume 645. Therefore, it is generally necessary to generate a DC field within the tunnel-shaped volume 644 and the funnel-shaped volume 645 that urges the ions forward towards the ion outlet aperture 46 and, ultimately, into the intermediate-vacuum chamber 26. Such a DC field may be generated, in known fashion, by proportionally dividing an applied DC electrical potential difference across the various apertured plate electrodes 342 whose apertures define the tunnel-shaped and funnel-shaped volumes.
[0142] FIG. 17A is a schematic longitudinal cross section of an eighth ion transport system 700 including an ion inlet (e.g., ion transfer tube 17) and an ion transport apparatus 720 in accordance with the present teachings. In general operation, the ion transport apparatus receives an inlet flow comprising a mixture of sample-derived ions and neutral gas molecules from the ion transfer tube 17, substantially spatially separates the flow of ions from the flow of gas, focuses the flow of ions into a spatially constrained beam and delivers the focused beam of ions to an evacuated chamber 706 through an ion outlet 705 while simultaneously exhausting the separated flow of gas through an exhaust port 712. Ions of the ion beam may be urged into the vacuum chamber by an electric field generated, in part, by an electrical potential applied to ion lens 702 which may be adjacent to or integral with a gas-restricting partition between ion transport apparatus 720 and the vacuum chamber 706. The vacuum chamber 706 generally comprises additional ion optics (e.g., ion guide 704, shown in phantom) that are not part of the ion transport apparatus.
[0143] In similarity to other ion transport apparatuses described herein, the ion transport apparatus 720 comprises a first electrode section and a second electrode section (see FIG. 19), where the second section comprises a set of stacked plate/ring electrodes 742 where the body of each plate and/or ring defines a respective plane and all of the so-defined planes are essentially parallel to one another. In the ion transport apparatus 720, the electrodes 742 are generally configured as three subsets of electrodes 749a, 749b, 749c, as defined by the basic shapes of the internal apertures or areas, 743.1, 743.2, 743.3 (FIGS. 18A, 18B and 18C) that are proximal to a sub-region or sub-volume 745 of the ion transport apparatus through which ions pass under normal operation. Individual electrodes of the subset 749a are referred to herein as electrodes 742.1 that are defined by concave re-entrant cutout areas of the type 743.1. Similarly, individual electrodes of the subset 749b referred to herein as electrodes 742.2, and are defined by inner non-circular apertures of the type 743.2. Finally, individual electrodes of the subset 749c are referred to herein as electrodes 742.3 that are defined by generally circular apertures of the type 743.3. It should be noted that dotted lines 749p in FIG. 17A represent the full sizes of the electrodes 749a, as projected onto the cross section of FIG. 17A, and indicate the lower open-ended terminus of these electrodes at hypothetical plane 749s (see also FIG. 17B and FIG. 18A).
[0144] Taken together, the three subsets of electrodes 749a, 749b, 749c of the second section of the ion transport apparatus 720 may comprise and may be operated as a stacked ring ion guide and/or an ion funnel apparatus and/or an ion tunnel apparatus as described above herein. The sub-region or sub-volume 745 comprises an ion inlet end 741 through which ions pass into the sub-region or sub-volume 745, the ion inlet end either having or being adjacent to an entrance lens that, with application of an appropriate electrical potential, attracts ions into the sub-volume 745. According to some embodiments, the entrance lens may be identical to or coincident with a first one of the electrodes 742. The sub-region or sub-volume 745 also comprises an ion outlet 705 that is defined by an aperture 743.3 (FIG. 18C) in a last one of the electrodes 742.3 and that is adjacent to a gap or aperture 748 of an outlet/exit lens 702. DC voltage distribution along electrodes 742 preferably creates an axial field to transport ions to the ion outlet 705.
[0145] In a different implementation, the three subsets of electrodes 749a, 749b, 749c of the second section of the ion transport apparatus may comprise and may be operated as an ion carpet. When used in reference to the ion transport apparatus 720 shown in FIG. 17A, the drawing of FIG. 17B is to be viewed as a projection, onto the plane of the drawing, of the plurality of plate electrodes 742 as if viewed along a viewing direction perpendicular to the plates. However, when used in reference to an analogous apparatus in which the plurality of plate electrodes are replaced by electrodes of an ion carpet, the appearance will be the same as in FIG. 17B, but all of the electrodes 749a, 749b, 749c will be now formed by wires or tracks which are preferably arranged on a single planar substrate, such as a printed circuit board, and these wires or tracks are represented by the various dashed lines in FIG. 17B. By inspection of FIG. 17B, some such wires or tracks may be configured in the shape of a letter “U”. Other such wires or tracks surround an aperture in the planar substrate, with most of the surrounding wires or tracks being non-circular in shape.
[0146] In operation of such an ion carpet apparatus, ions are directed towards the substrate, with its electrodes, by a DC potential difference between an inlet electrode (not shown) and the plurality of wire or track electrodes of the ion carpet. Pseudopotential forces created by additional oscillatory RF voltage waveforms applied to the plurality of ion carpet electrodes prevent the ions from making physical contact with the ion carpet. At the same time, DC potential gradients between individual wire or track electrodes cause inwardly directed radial migration of the ions towards an ion outlet aperture of the substrate.
[0147] The following discussion pertains specifically to an ion transport apparatus 720 (FIG. 17A) that includes an ion funnel portion having plate or ring electrodes 742. The view of the ion transport apparatus 720 that is shown in FIG. 17B is constructed as if looking into the sub-region or sub-volume 745 from a viewing point on the upright section of an electrode or electrode structure 762. As illustrated in FIGS. 17A and 17B, each of the first 749a and second 749b subsets of the electrodes comprises a respective plurality of electrodes. In contrast, the third subset 749c may consist of only a single electrode. As further illustrated in FIG. 17B and FIGS. 18A-18C, each one of the electrodes 742 of the second 749b and third 749c subsets has a respective aperture therethrough, with the apertures generally decreasing in cross sectional area in a general direction away from the ion inlet 741 and towards the ion outlet aperture 743.3. Thus, the electrodes 742 of the second 749b and third 749c subsets of electrodes generally resemble a conventional ion funnel. However, the arrangement of electrodes 742 shown in FIGS. 17A-17B and FIGS. 18A-18C differs from a conventional ion funnel in that, with the possible exception of the electrode(s) of the third subset 749c, the apertures (e.g., apertures 743.2) are not circular in shape and further in that the geometric centers of the apertures 743.2, 743.3 are not necessarily coincident with an axis that is perpendicular to planes that are defined by the bodies of the ring or plate electrodes 742. Instead, the apertures of at least the electrodes of subset 749b have bilaterally symmetric deformed elliptical shapes (e.g., see aperture 743.2 of representative electrode 742.2 of FIG. 18B), the inner surface 753.2 of each aperture having a basal portion 754 that is flat or substantially flat, the collection of all the basal portions being aligned or substantially aligned with one another (e.g., aligned along plane 721 as shown in FIG. 17A. The plane 721 may also be coincident with a point on the surface of a circular aperture (e.g., circular aperture 743.3 of representative electrode 742.3 as shown in FIG. 18C) of an electrode of the third electrode subset 749c.
[0148] As illustrated in FIG. 18A, each electrode 742.1 of the first subset 749a of the electrodes 742 does not comprise an enclosed aperture that perforates the body of the electrode. Instead, a concave surface portion 753.1 of an outer surface of the body of each electrode 742.1 defines a re-entrant cutout cross-sectional area 743.1 through which ions are caused to pass during the application of normal operating voltages to the various electrodes of the apparatus 720. As shown, the re-entrant cutout cross-sectional area 743.1 may be essentially U-shaped. The bounds of the cutout area may be defined as the area between the concave surface portion 753.1 and the projection of plane 749s (see FIG. 17A), which coincides with the open end of the cutout, onto the plane of the drawing. The cutout areas generally decrease in magnitude in the general direction away from the ion inlet aperture 741. The collection of the re-entrant areas 743.1 define a portion of the sub-region or sub-volume 745 (see FIG. 17A) through which the ions pass under the application of the normal operating voltages. It should be appreciated that, although portions of the outermost perimeters 755 of the electrodes 742.1, 742.2 and 742.3 (FIGS. 18A-18C) are illustrated as comprising arcs of circles, the outermost perimeters of the electrodes (defined here as excluding the concave surface portion 753.1) may comprise any shape (e.g., comprising straight edges) that is convenient for manufacture and that fits within available space of the ion transport apparatus 720. The non-arcuate portions of the outermost perimeters 755 of the electrodes are depicted as straight or flat surfaces, a shape which, although not necessarily required, may be preferable as a result of the proximity of the electrodes to a gas diverter structure 715 (FIG. 17A).
[0149] The ion transport apparatus 720 further comprises (FIG. 17A) a first electrode section that includes one or more repeller electrodes 762 that comprise in electrode structure that is preferably formed in the shape of the letter “L” so as to divert the general migration pathway of the ions along or towards the diverted pathway 718. The first electrode section may also optionally include a radially-focusing electrode 765 (FIGS. 17A-17B) that comprises an inner electrode surface that is generally in the form of the letter “U”. In FIG. 17A, the dotted line 765p represents the approximate projection of the full extent of the radially-focusing electrode onto the plane of the drawing. The radially-focusing electrode may optionally extend into the second electrode section as indicated by the dotted lines 765e. In addition to facilitating focusing of ions, the electrode 765 effectively electrically isolates the various electric fields within the apparatus 720 from perturbations that may arise from electric fields generated from electrical circuits that are external to the apparatus. The one or more repeller electrodes comprise or define an aperture or opening 763 through which an ion transfer tube 17 passes.
[0150] In operation, a mixture of ions and neutral molecules (i.e., gas) are introduced, in the general direction of axis or path 717, into the ion transport apparatus 700 from ion transfer tube 17. At the same time, a common electrical potential, V.sub.1, is applied to both the ion transfer tube 17 and the L-shaped repeller electrode 762 while a second electrical potential, V.sub.2, may be applied to the U-shaped radial-focusing electrode 720, a third electrical potential, V.sub.3, may be applied to the entrance lens that is at or near the ion inlet 741 and a fourth electrical potential, V.sub.4, may be applied to the outlet/exit lens 702. At the same time, RF voltages that confine ions to the sub-region or sub-volume 745 are applied to the electrodes 742 in known fashion.
[0151] Preferably, the electrical potentials, V.sub.1, V.sub.2, V.sub.3, and V.sub.4 are all independently adjustable and may be adjusted depending on: (a) the polarity of the analyte ions; and (b) the m/z values of the analyte ions. Under application of the appropriate electrical potentials to the electrodes, ions that emerge into the ion transport apparatus 720 from ion transfer tube 17 are caused to migrate towards or along the generalized ion pathway 718, which is essentially perpendicular to iso-potential lines as primarily determined by the electrical potentials V.sub.1 and V.sub.3.
[0152] As the ions migrate along the generalized ion path 718, they come under progressively greater influence of ion beam focusing effects of the DC voltage V.sub.2, applied to the U-shaped electrode 765 and of pseudopotential wells generated by application of RF voltages the horseshoe-shaped electrodes 749a. Accordingly, under the appropriate selection of the magnitudes of the various voltages, ions may be captured into the sub-region or sub-volume 745. In comparison to conventional ring-shaped electrodes, the illustrated mirror-symmetric horseshoe shaped electrode 742.1 of the first subset 749a of the electrodes 742 features a more open structure for off-axis ion beam introduction and therefore favors wider acceptance area for the entering ion beam compared to a ring-shaped entrance area of a stacked ring ion guide. One may note that the general trajectory or pathway 718 of ions that are delivered to the second section of the ion transport apparatus is not parallel to a hypothetical line that connects the center of the ion inlet aperture 741 to the center of the ion outlet aperture 705. One of ordinary skill in the art will appreciate that the horseshoe-shaped electrode structure, similar to the structure of electrodes 742.1, may be effective at capturing ions into any stacked-ring ion guide transporting or ion guiding apparatus in situations in which a first hypothetical line that connects the center of the ion emitting device (e.g., ion transfer tube 17) to the center of the ion inlet aperture of the stacked ring ion guide apparatus is at an angle to a second hypothetical line that connects the center of the ion inlet aperture of the apparatus to the center of the ion outlet aperture of the apparatus. Once the ions have been captured within the sub-region or sub-volume 745, the ions may be urged through the sub-volume 745 to the ion outlet 705 of the ion transport apparatus by an internal axial electric field, which may be generated by a difference between the electrical potential, V.sub.3, applied to the entrance lens 741 and the electrical potential, V.sub.4, applied to the outlet/exit lens 702.
[0153] At the same time that ions are diverted into the sub-region or sub-volume 745 of the ion transport apparatus along generalized ion path 718, the various neutral molecules of the introduced gas, which are not affected by the electric field, continue along trajectories that causes the flow of the gas to generally proceed through the apparatus along straight path 717 so as to ultimately be diverted to exhaust path 712 by deflection surface 716 of the gas diverter structure 715. Preferably, the exhaust path 712 is fluidically coupled to a gas evacuation system (not shown) comprising one or more vacuum pumps.
[0154] FIG. 20 schematically illustrates a generalized mass spectrometer system 90 on which methods in accordance with the present teachings may be practiced. The mass spectrometer system includes a set of various hardware components, e.g., ion source(s) 91, an ion transport apparatus and other ion optical components 92 as taught herein, one or more mass filters, ion traps and/or mass analyzers 93, one or more vacuum pumps 94 and one or more power supplies 95. Various of the hardware components 91-95 comprise electrodes, electrical components or motors and may comprise various sensors and detectors, such as temperature sensors, pressure sensors, current sensors, ion detectors, etc. The various electrodes, other electrical components, motors and sensors are electrically or electronically coupled to a computer or other digital-logic controller processor apparatus 96. The electrical or electronic couplings, illustrated by dashed arrows in FIG. 20, convey control signals to the various hardware components 91-94 and may also convey data from the hardware components to the computer or controller 96. The computer or controller is also coupled to one or more data storage devices 97, various user input devices 98 such as keyboards, terminals, etc. and various user output devices 99.
[0155] In the context of the present teachings, the controller 96 may transmit control signals to the ion source(s) 91 to generate and provide ions of sample and/or calibrant materials to and through the ion funnel and other ion optical components. The ion funnel may comprise various of the features, possibly in combination, described in the above descriptions and accompanying drawings. The controller 96 may also transmit control signals to the one or more vacuum pumps 94 to evacuate the ion funnel and other mass spectrometer components. Pressure and temperature sensors within the ion funnel and/or other mass spectrometer components may transmit data back to the controller that is used by the controller to determine when the ion funnel and other mass spectrometer components are available and ready to measure data. Similarly, voltage sensors or ion current sensors within or associated with the ion funnel may transmit data to the controller that is used by the controller to control RF and DC voltages applied to plate electrodes, repeller electrodes, focusing electrodes or other lens electrodes of the funnel in order to optimize ion transmission through the funnel to downstream mass spectrometer components. Various sensor data, operational configuration data and experimental data may be stored in the information storage device 97.
[0156] The discussion included in this application is intended to serve as a basic description. The present invention is not intended to be limited in scope by the specific embodiments described herein, which are intended as single illustrations of individual aspects of the invention. Functionally equivalent methods and components are within the scope of the invention. Various other modifications of the invention, in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and accompanying drawings.
[0157] Not all of the various illustrated technical features and components are depicted and described for all possible embodiments. Features or components described for fewer than all of the illustrated embodiments are considered to be applicable to other embodiments, provided that they are not incompatible with those other embodiments. For example, the enlarged and expanded exhaust port 110 shown in the illustration of system 300 in FIG. 13A could be similarly employed in the system 100 (FIG. 3), or the system 400 (FIG. 14). Similarly, the alternative aperture shapes shown in FIGS. 11-12 with reference to the system 200 (FIG. 7) could likewise be employed within a portion of the system 300 (FIG. 13A) or the system 400 (FIG. 14). More generally, although electrode apertures are illustrated as circular or partially circular in shape, other aperture shapes, such as oval shapes, are possible.
[0158] Further, the electrodes themselves need not be formed as square or rectangular metal plates. For example, FIG. 5B and FIG. 9B are alternative electrode forms in which the square plate electrodes 142 of FIG. 5A are replaced by ring electrodes 642 and the rectangular plate electrodes of 242a, 242b of FIG. 9A are replaced by half-ring electrodes 842a and 842b, respectively. In alternative embodiments, both plate and ring electrodes may be replaced by flat planar or ring-like films, foils or coatings that are supported on a rigid backing substrate, such as printed circuit board material.
[0159] FIG. 9C is an enlarged version of FIG. 9A in which the spaced-apart electrodes 242a, 242b are outlined in phantom, using dashed lines. If the electrodes are in the form of rigid plates, then, the term “space between electrode pairs”, as used herein, includes the entire shaded area, including the strip-like space 262 as well as the semi-circular spaces 264a, 264b. This statement applies to all embodiments taught herein that include pairs of rigid plate electrodes or ring electrodes wherein the two electrodes of each pair are oppositely disposed from one another across or relative to a central longitudinal axis 47. Upon introduction into an interior volume of an ion transport apparatus, gas and ions may occupy both the semi-circular spaces 264a, 264b as well as the portions of the strip 262 that are not within the circular space that is defined by the semi-circular spaces 264a, 264b. However, as ions migrate through the funnel apparatus, the ions will essentially become concentrated in a pseudopotential well zone surrounding the axis. With regard to embodiments in which the electrodes are not rigid plates but, instead, are films, coatings or foils disposed upon a rigid substrate, then the term “space between electrode pairs” only includes the space within the shaded area that is outlined by an aperture (or apertures) in the substrate, unless otherwise stated.
[0160] Any patents, patent applications, patent application publications or other literature mentioned herein are hereby incorporated by reference herein in their respective entirety as if fully set forth herein, except that, in the event of any conflict between the incorporated reference and the present specification, the language of the present specification will control.
