The present disclosure relates generally to ion traps, and more particularly to ion traps that can allow spatial, mass and energy focusing of ions.
Ion traps are employed in a variety of different mass spectrometer systems. For example, in FT-ICR mass spectrometers, spatial, mass and energy focusing of ions is generally desired. However, such focusing poses a number of challenges. For example, when ions exhibit a kinetic energy spread, they can be spatially defocused after traveling from a trapping device to a downstream mass analyzer, which can adversely affect the performance of the mass analyzer.
In some conventional ion trapping devices, ions are extracted axially from the end of the trap. One disadvantage of such traps is that the extracted ions can experience spatial defocusing in length. To overcome such spatial defocusing, a trap commonly known as “C trap” employs radial extraction of ions from a curved linear ion trap, as shown schematically in
Accordingly, there is a need for enhanced systems and methods for trapping ions, e.g., in mass spectrometry applications.
In one aspect, an ion trap is disclosed, which includes a curved linear ion trap having a plurality of electrodes arranged around a central curved axis so as to provide a volume for trapping ions, said plurality of electrodes comprising at least one inner electrode (e.g., disposed radially inward from the curved central axis) and at least one outer electrode (e.g., disposed radially outward from the curved central axis) radially separated from said inner electrode. The ion trap further includes a pair of inner and outer ion guide electrodes that provide a volume therebetween for receiving ions ejected from said curved linear ion trap and that guide the ejected ions to one or more spatial locations along a focal line, said inner and outer ion guide electrodes being positioned external to said ion trapping volume and in proximity of the inner and outer electrodes of the curved ion trap, respectively, wherein a DC voltage is applied between said ion guide electrodes to provide an electric filed therebetween for guiding the ejected ions to said spatial locations along the focal line. In various aspects, the ion trap can include an exit aperture positioned in proximity of said spatial locations through which the ions converged on those spatial locations can exit, e.g., to propagate to components disposed downstream of the ion trap.
In some embodiments, the ion guide electrodes are configured to receive the ejected ions along directions substantially orthogonal to said curved central axis.
In some embodiments, each of the inner and the outer ion guide electrodes can be in the form of a truncated spherical surface (e.g., a section of a hemispherical surface). In some embodiments, the spherically-shaped surfaces can be positioned concentrically relative to one another, i.e., the centers of the corresponding spheres can be coincident. In some such embodiments, the focal line can be along a radial direction extending from the common centers of the spheres to the spherical surfaces.
The ion trap can further include a radiofrequency (RF) generator for applying one or more RF voltages to one or more electrodes of the curved linear ion trap for trapping ions therein. By way of non-limiting example, the RF voltages can have a frequency in a range of about 0.1 MHz to about 10 MHz and an amplitude in a range of about 10 V to about 10 kV.
In various aspects, the ion trap can also include a switchable DC voltage source for applying an extraction DC voltage to at least one electrode of the curved linear ion trap for ejecting at least a portion of trapped ions into the volume between the ion guide electrodes. By way of example, the applied extraction DC voltage can be in a range of about 0.1 volts to about 100 volts (e.g., so as to eject the ions from the trap between the inner and outer electrode).
In some aspects, the curved linear ion trap can be a curved quadrupole trap. In some aspects, the quadrupole trap can comprise eight elongated electrodes, with four pairs of the eight electrodes being electrically-connected (e.g., shorted) as in the form of a slotted quadrupole. For example, the quadrupole can include a pair of curved inner electrodes and a pair of curved outer electrodes radially separated from the pair of curved inner electrodes, a pair of curved bottom electrodes and a pair of curved top electrodes separated from one another along a vertical direction. In such embodiments, the two ion guide electrodes can be configured to receive the ejected ions along a vertical direction (e.g., along a direction substantially parallel to the focal line), for example, via passage through a gap between the upper electrodes of the quadrupole trap.
In some embodiments, the RF generator can be configured to apply at least one scanned RF voltage, e.g., in combination with a DC extraction voltage, to one or more electrodes of the curved ion trap for a selected time duration so as to achieve mass focusing of the ejected ions. By way of example, the duration of applied RF voltage scan can be in a range of about 0.1 ms to about 10 ms. In some embodiments, the scanned RF voltage can have a temporally-varying amplitude, e.g., an amplitude that changes from a maximum value (e.g., 1000 V) to a minimum value (e.g., 0 V) during the time period in which the scanned RF voltage is applied.
In some aspects, the ion trap can further include a DC focusing lens disposed between the curved linear ion trap and said inner and outer ion guide electrodes so as to focus the ejected ions into the volume between the ion guide electrodes. For example, the DC focusing lens can include a stack of a plurality of electrode pairs, wherein each of said electrode pairs comprises two electrodes spaced from one another so as to provide a gap therebetween for passage of the ejected ions. In some embodiments, a DC voltage differential can be applied between the electrode pairs of the DC focusing lens, e.g., a DC voltage differential in a range of about −10V to about +10V, for generating a field suitable for focusing the ejected ions into the volume between the inner and the outer ion guide electrodes.
In accordance with various aspects of the present teachings, an ion trap device is disclosed, which includes a linear curved ion trap comprising a plurality of curved electrodes arranged to provide a volume therebetween for storing ions, and a DC ion guide comprising a plurality of spherically-shaped electrodes coupled to the linear curved ion trap so as to receive ions ejected from the linear curved ion trap and to guide said ions onto one or more spatial locations along a focal line. In some embodiments, the spherically-shaped electrodes can be concentrically positioned so as to have a common center of curvature. In some such embodiments, the focal line can be along a radial line extending from the common center of the spherical electrodes to those electrodes.
In accordance with various aspects of the present teachings, a method of trapping ions is disclosed, which includes injecting a plurality of ions into a curved linear ion trap, applying at least one RF voltage to said curved linear ion trap so as to trap said ions, and applying a DC extraction voltage to said curved linear ion trap so as to eject at least a portion of said trapped ions into a volume between two spherically-shaped DC-biased electrodes coupled to said curved linear ion trap so as to guide the ions to one or more spatial locations within the volume.
Further understanding of the various aspects of the invention can be obtained by reference to the following detailed description in conjunction with the associated drawings, which are described briefly below. These and other features of the applicant's teachings are set forth herein.
The skilled person in the art will understand that the drawings, described below, are for illustration purposes only. The drawings are not intended to limit the scope of the applicant's teachings in any way.
The present teachings relate generally to an ion trap device that includes a curved linear ion trap for storing ions and a DC ion guide that can receive ions ejected from the curved linear ion trap and guide those ions to spatial locations along a focal line for transmission to other components in communication with the ion trap. In various aspects, an ion trap according to the present teachings can be incorporated in a mass spectrometer system.
Various terms are used herein consistent with their ordinary meanings in the art. In particular, the term “ion trap” as used herein refers to a device that can store ions by employing magnetic and/or electric fields. The term “spherically-shaped” as used herein refers to a surface that forms at least a portion of a sphere. The term “scanned RF voltage” refers to a radiofrequency voltage, e.g., with a frequency in a range of about 0.1 MHz to about 10 MHz, the amplitude of which monotonically increases or decreases over a given time period, e.g., over a time period in a range of about 0.1 ms to about 10 ms. The term “about” as used herein denotes a variation of at most 10% around a numerical value. The term “substantially” as used herein denotes a deviation of less than 5% from a complete state or condition.
As is generally known in the art and modified in accordance with the present teachings, an RF voltage generator 1112 can apply one or more voltages to the electrodes 1008, (e.g., an RF voltage to the various electrodes 1008 such that adjacent pairs of electrodes exhibit the opposite phase to the adjacent pair) to provide trapping electromagnetic fields so as to store the received ions within the ion trapping volume 1110. For example, one or more RF voltages, e.g., at a frequency in a range of about 0.1 MHz to about 10 MHz and an amplitude in a range of about 10 V to about 10 kV, can be applied to one or more of the electrodes 1008 to confine ions within the trapping volume 1110. In some embodiments, the curved linear ion trap 1002 may include an endcap electrode at its proximal and distal ends to which a DC voltage can be applied to assist with axial confinement of the ions within the curved linear ion trap 1002. The trapping of the ions by the curved linear ion trap 1002 can be used for a variety of different purposes. For example, the trapped ions can undergo translational cooling or collision-induced dissociation to generate ion fragments, which can be detected and analyzed via downstream components, such as a mass analyzer.
With continued reference to
Though the inner guide electrode 1004a is depicted in the form of a truncated spherical shell and is positioned external to the ion trapping volume 1110 of the curved linear ion trap 1002 in proximity of the inner electrode pair 1008a/1008b, it will be appreciated that the inner shell can exhibit a variety of geometries that include, by way of non-limiting example, a portion of an ellipsoid, spheroid, ovoid, or sphere. Likewise the outer guide electrode 1004b can have a variety of configurations but is depicted in
In various aspects, the spherically-shaped inner and outer shells 1004a/1004b can be concentric, i.e., they have a common center (C). Further, in some aspects, the focal line can extend along a radial direction (R) extending from the common center (C) to the spherically-shaped shells. The radius of curvature of the inner and the spherical shells forming the inner and the outer guide electrodes can be selected based, for example, on types of ions and/or a particular application for which the ion trap is intended. By way of non-limiting example, in some embodiments, the truncated spherical shell forming the inner ion guide electrode 1004a can have a radius of curvature in a range of about 50 mm to about 500 mm and the truncated spherical shell forming the outer ion guide electrode 1004b can have a radius of curvature in a range of about 50 mm to about 500 mm.
In accordance with various aspects of the present teachings, a DC voltage generator 1116 can apply a DC voltage differential between the inner and outer ion guide electrodes 1004a/1004b so as to generate an electric field in the space between those electrodes, where the electric field is effective to guide the ions received from the curved linear ion trap onto one or more spatial point(s) along the focal line 1114. It will be appreciated in light of the present teachings that the polarity of the applied DC voltage differential can be selected based on the charge of the ions (i.e., whether positive or negative) such that the electric field causes the received ions to converge onto spatial locations along the focal line 1114. By way of example, in some embodiments, a DC voltage differential in a range of about 0 volts to about 50 volts can be applied between the inner and the outer guide electrodes 1004a/1004b.
With reference to
In such aspects, the DC voltage generator 1116 can apply voltage differentials between the electrode pairs 1120/1122/1124 so as to generate an electric field within the passageway 1126 suitable for focusing the ions into the space between the ion guide electrodes 1004a and 1004b. By way of non-limiting example, the center electrode pair 1122 can be biased positively relative to the bottom and top electrode pairs 1120/1124 so as to focus the ions passing through the gaps between the electrodes of each pair into the space between the ion guide electrodes 1004a and 1004b. In some embodiments, the bias voltage applied to the center electrode pair 1122 can be in a range of about −20 volts to about +20 volts, though other voltages can also be employed depending, for example, on the type of ions and a particular application for which the ion trap is employed.
With continued reference to
The ion trap 1000 further includes an exit aperture 1132 through which ions focused on the spatial location(s) along the focal line 1114 can exit the trap, e.g., toward downstream component(s) in a mass spectrometer in which the ion trap 1000 is incorporated.
In use, ions are injected into the curved linear ion trap 1002 to be stored within the ion trapping volume 1110 provided between the electrodes 1008. In various aspects, ions received within the curved linear ion trap 1002 may be trapped within the ion trapping volume 1110 for a period of time (e.g., of the order of milliseconds) sufficient for cooling of the translational motion of the ions. Subsequently, the ions can be ejected, via application of the ejection voltage to the lower and the upper electrode pairs of the curved linear ion trap 1002, along a vertical direction (i.e., along directions substantially orthogonal to the center axis (CA)) into the space between the spherically-shaped ion guide electrodes 1004a and 1004b. As noted above, during the ejection of the ions from the linear ion trap, the RF voltage(s) applied to the electrodes of the linear ion trap can be reduced or set to zero. By way of example, for positive ions, the bottom pair of electrodes 1008e/1008f can be biased positively compared to the top electrode pair 1008g/1008h, and for negative ions, the polarity can be reversed.
The electric field between the inner and the outer spherically-shaped guide electrodes 1004a/1004b can have a spherical configuration that causes the ions to travel along curved paths in the space 1004c between the two electrodes and converge on one or more spatial location(s) identified by the focal line 1114. By way of example, to obtain a curved travelling path in the space between the spherically-shaped ion guide electrodes 1004a/1004b as depicted in
Moreover, the spherical electric field configuration between the inner and the outer guide electrodes 1004a/1004b can in some aspects provide for energy focusing—a feature not realized in prior art C traps. In other words, the spherical electric field between the ion guide electrodes 1004a/1004b can ensure that ejected ions having different energies, e.g., ions with an energy spread in a range of about 1 eV and 2 eV, arrive substantially concurrently at the focal line 1114. In particular, ions having lower kinetic energies can travel along trajectories between the ion guide electrodes 1004a/1004b characterized by smaller radii while ions having higher kinetic energies travel along trajectories characterized by larger radii. In this manner, the shorter trajectory for ions of lower kinetic energy can compensate for the lower velocity of such ions and the longer ion trajectory for ions of higher kinetic energy can compensate for the higher velocity of those ions such that all ions entering the space between the ion guide electrodes substantially at the same time arrive substantially concurrently at the spatial locations along the focal line 1114. Hence, the ion guide electrodes 1004a/1004b can be used to realize energy focusing, i.e., the ion arrival time at focal point(s) along the focal line 1114 exhibits reduced dependence on the kinetic energy of the ejected ions so long as the ions have the same mass-to-charge ratios (i.e., the same m/z). It will therefore be appreciated by those skilled in the art, that ion traps according to various aspects of the present teachings can therefore provide both spatial as well as energy focusing.
By way of illustration,
In various aspects, a combination of a DC extraction field and a scanned RF field can also be employed to achieve mass focusing of the ions ejected from the curved ion trap 1002. In particular, it has been discovered that by adjusting the time duration of an applied scanned RF voltage having an amplitude that decreases or increases, typically monotonically, over that duration, mass focusing of the ions ejected from the curved linear ion trap can be achieved. In other words, adjusting the time duration of the applied scanned RF voltage can additionally result in ions having different m/z ratios nonetheless being focused on the focal line 1114.
By way of example,
By way of illustration,
Although the above-described curved linear ion trap includes four electrically-connected pairs of electrodes 1008 (e.g., slotted electrodes) providing a quadrupolar field for trapping ions, it will be appreciated that other configurations of curved linear ion traps can be employed. By way of example,
An ion trap according to the present teachings comprising a curved linear ion trap and a DC ion guide, which can be formed, e.g., of two spherically-shaped electrodes, can be incorporated in a variety of different mass spectrometers, for example, a time-of-flight (ToF), an FT-ICR or an orbitrap mass spectrometer, as well as in other types of ion handling devices that require fine focusing.
As shown schematically in the exemplary embodiment depicted in
As shown in
The ionization chamber 14, within which analytes contained within the fluid sample discharged from the ion source 104 can be ionized, is separated from a gas curtain chamber by a curtain plate 30 defining a curtain plate aperture in fluid communication with the upstream section via the sampling orifice of an orifice plate 32. In accordance with various aspects of the present teachings, a curtain gas supply can provide a curtain gas flow (e.g., of N2) between the curtain plate 30 and orifice plate 32 to aid in keeping the downstream section of the mass spectrometer system clean by declustering and evacuating large neutral particles. By way of example, a portion of the curtain gas can flow out of the curtain plate aperture into the ionization chamber 14, thereby preventing the entry of droplets through the curtain plate aperture.
As discussed below, the mass spectrometer system 100 also includes a power supply (not shown) and controller 20 that can be coupled to the various components so as to operate the mass spectrometer system 100 in accordance with various aspects of the present teachings.
As shown, the depicted system 100 includes a sample source 102 configured to provide a fluid sample to the ion source 104. The sample source 102 can be any suitable sample inlet system known to one of skill in the art and can be configured to contain and/or introduce a sample (e.g., a liquid sample containing or suspected of containing an analyte of interest) to the ion source 104. The sample source 102 can be fluidly coupled to the ion source so as to transmit a liquid sample to the ion source 102 (e.g., through one or more conduits, channels, tubing, pipes, capillary tubes, etc.) from a reservoir of the sample to be analyzed, from an in-line liquid chromatography (LC) column, from a capillary electrophoresis (CE) instrument, or an input port through which the sample can be injected, all by way of non-limiting examples. In some aspects, the sample source 102 can comprise an infusion pump (e.g., a syringe or LC pump) for continuously flowing a liquid carrier to the ion source 104, while a plug of sample can be intermittently injected into the liquid carrier.
The ion source 104 can have a variety of configurations but is generally configured to generate ions from analytes contained within a sample (e.g., a fluid sample that is received from the sample source 102). In the exemplary embodiment depicted in
In some embodiments, upon passing through the orifice plate 32, the ions can traverse one or more additional vacuum chambers and/or quadrupoles (e.g., a QJet® quadrupole) to provide additional focusing of and finer control over the ion beam using a combination of gas dynamics and radio frequency fields prior to being transmitted into the downstream high-vacuum section 18. In accordance with various aspects of the present teachings, it will also be appreciated that the exemplary ion guides described herein can be disposed in a variety of front-end locations of mass spectrometer systems. By way of non-limiting example, the ion guide 108 can serve in the conventional role of a QJet® ion guide (e.g., operated at a pressure of about 1-10 Torr), as a conventional Q0 focusing ion guide (e.g., operated at a pressure of about 3-15 mTorr) preceded by a QJet® ion guide, as a combined Q0 focusing ion guide and QJet® ion guide (e.g., operated at a pressure of about 3-15 mTorr), or as an intermediate device between a the QJet® ion guide and Q0 (e.g., operated at a pressure in the 100s of mTorrs, at a pressure between a typical QJet® ion guide and a typical Q0 focusing ion guide).
As shown, the upstream section 16 of system 100 is separated from the curtain chamber via orifice plate 32 and generally comprises a first RF ion guide 106 (e.g., Qjet® of SCIEX) and a second RF guide 108 (e.g., Q0). In some exemplary aspects, the first RF ion guide 106 can be used to capture and focus ions using a combination of gas dynamics and radio frequency fields. By way of example, ions can be transmitted through the sampling orifice, where a vacuum expansion occurs as a result of the pressure differential between the chambers on either side of the orifice plate 32. By way of non-limiting example, the pressure in the region of the first RF ion guide can be maintained at about 2.5 Torr pressure. The Qjet 106 transfers ions received thereby to subsequent ion optics such as the Q0 RF ion guide 108 through the ion lens IQ0107 disposed therebetween. The Q0 RF ion guide 108 transports ions through an intermediate pressure region (e.g., in a range of about 1 mTorr to about 10 mTorr) and delivers ions through the IQ1 lens 109 to the downstream section 18 of system 100.
The downstream section 18 of system 10 generally comprises a high vacuum chamber containing the one or more mass analyzers for further processing of the ions transmitted from the upstream section 16. As shown in
As will be appreciated by a person skilled in the art, the ion trap 114 can be operated at a decreased operating pressure relative to that of q2, for example, less than about 1×10−4 Torr (e.g., about 5×10−5 Torr), though other pressures can be used for this or for other purposes. It will also be appreciated by those skilled in the art that the downstream section 18 can additionally include additional ion optics, including RF-only stubby ion guides (which can serve as a Brubaker lens) as schematically depicted. Typical ion guides of ion guide regions Q0, Q1, and q2 and stubbies ST1, ST2 and ST3 in the present teachings, can include at least one electrode as generally known in the art, in addition to ancillary components generally required for structural support. For convenience, the mass analyzer 110 and collision cell 112 are generally referred to herein as quadrupoles (that is, they have four rods), though the elongated rod sets can be any other suitable multipole configurations, for example, hexapoles, octapoles, etc. It will also be appreciated that the one or more mass analyzers can be any of triple quadrupoles, single quadrupoles, time of flights, linear ion traps, quadrupole time of flights, Orbitrap or other Fourier transform mass spectrometers, all by way of non-limiting example.
Following processing or transmission through the ion trap 114, the ions can be focused into a ToF detector 118 (or trap analyzer as depicted in
By way of further illustration,
The section headings used herein are for organizational purposes only and are not to be construed as limiting. While the applicant's teachings are described in conjunction with various embodiments, it is not intended that the applicant's teachings be limited to such embodiments. On the contrary, the applicant's teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those of skill in the art.
This application claims priority to U.S. provisional application No. 62/420,900, filed on Nov. 11, 2016, entitled “Spatial, Mass and Energy Focused Ion Injection Method and Device,” which is incorporated herein by reference in its entirety.
Filing Document | Filing Date | Country | Kind |
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PCT/IB2017/056819 | 11/2/2017 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2018/087634 | 5/17/2018 | WO | A |
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