Ion trap for enhanced time-of-flight ion utilization

Abstract

In some examples, an ion trap may include an ion trap controller to apply a trapping potential and scanning voltage waveforms to at least one electrode to sequentially release higher mass-to-charge (m / z) ions before lower m / z ions. The ion trap may further include a linear configuration. Ion ejection from the ion trap may be perpendicular to an axis of the ion trap.

Description

20230186-02 ION TRAP FOR ENHANCED TIME-OF-FLIGHT ION UTILIZATION CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to U.S. Provisional Patent Application Serial Number 63 / 548,604, filed February 1, 2024, titled “ION TRAP FOR ENHANCED TIME- OF-FLIGHT ION UTILIZATION”, which is incorporated by reference in its entirety. BACKGROUND

[0002] An ion trap may be utilized to capture charged particles denoted ions. An ion trap may utilize electric and / or magnetic fields to capture the ions. Ion traps may include applications in various fields such as physics and chemistry. In one example, ion traps may be utilized in mass spectrometry.20230186-02 BRIEF DESCRIPTION OF DRAWINGS

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

[0004] Figure 1 illustrates an ion trap for enhanced time-of-flight ion utilization, in accordance with an example of the present disclosure;

[0005] Figure 2A illustrates undisturbed effective potentials in the absence of a scanning waveform, and Figure 2B illustrates combined potential in the presence of a scanning waveform, in accordance with an example of the present disclosure;

[0006] Figure 3 illustrates combined potentials in a quadrupolar trap with a slitted rod for ions with three different m / z ratios at different times during a scan, in accordance with an example of the present disclosure;

[0007] Figure 4A illustrates device (e.g., the ion trap) construction as a 3D ion trap, and Figures 4B – 4F illustrate device (e.g., the ion trap) construction as a linear ion trap with ejection of ions either between two adjacent rods (e.g., Figures 4D and 4F) or through a slit in one multipole rod (e.g., Figures 4B, 4C, and 4E), in accordance with an example of the present disclosure;

[0008] Figure 5 illustrates a quadrupole linear ion trap with slitted ejection rod in positive ion mode, in accordance with an example of the present disclosure;

[0009] Figure 6A illustrates ejection times of ions and their respective arrival times at mid- pulser after passing through the ion-optical transfer device, and Figure 6B illustrates kinetic energy of ions at the mid-pulser position, in accordance with an example of the present disclosure;20230186-02

[0010] Figure 7 illustrates orthogonal flow of ions to enter the ion trap of Figure 1, to exit the ion trap and to accelerate into a time-of-flight (TOF) mass analyzer, in accordance with an example of the present disclosure;

[0011] Figure 8 illustrates a number of RF cycles needed to bring a ratio between a standard deviation and mean kinetic energy of ions after passing the ion optical transfer device to acceptable values with respect to the ion trap of Figure 1, in accordance with an example of the present disclosure;

[0012] Figure 9 illustrates separate electrodes including electrodes used to apply scanning waveforms and electrodes used to apply RF waveforms, in accordance with an example of the present disclosure; and

[0013] Figure 10 illustrates further details of operation of the separate electrodes of Figure 9, in accordance with an example of the present disclosure.20230186-02 DETAILED DESCRIPTION

[0014] For simplicity and illustrative purposes, the present disclosure is described by referring mainly to examples. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be readily apparent however, that the present disclosure may be practiced without limitation to these specific details. In other instances, some methods and structures have not been described in detail so as not to unnecessarily obscure the present disclosure.

[0015] Throughout the present disclosure, the terms "a" and "an" are intended to denote at least one of a particular element. As used herein, the term "includes" means includes but not limited to, the term "including" means including but not limited to. The term "based on" means based at least in part on.

[0016] An ion trap for enhanced time-of-flight ion utilization, and a method for enhanced time-of-flight ion utilization are disclosed herein. The ion trap and the method disclosed herein provide for a fast scanning ion trap device to improve ion utilization in time-of-flight mass spectrometers.

[0017] Ion traps may include two general types (e.g., geometries) that use alternating radio frequency (RF) electric fields, suitable to produce harmonic effective potentials (also known as pseudo potentials) which can be utilized to generate mass-to-charge-specific spectra. An example of a geometry may include a three-dimensional (3D) ion trap, and a linear ion trap. Other geometries, such as hexapoles, octapoles, and non-hyperbolic quadrupoles, utilizing RF electric fields may be used as ion traps (e.g., with some rudimentary mass-analyzing capabilities), because these geometries do not generate harmonic potentials.20230186-02

[0018] The aforementioned 3D ion trap may include a ring electrode and two endcapelectrodes, which are shaped in such a way that a potential difference= + f( )applied between the endcap electrodes and the ring electrode generates a harmonic effectivepotential around the center of the device. For the potential difference 0 = + f( ),donates a constant (DC) voltage value, donates the amplitude of the RF waveform, f donates a 2-pi-periodic function (e.g., cosine), and donates the angular frequency of the RF waveform. The 3D ion trap may include two main modes of operation that include mass-to- charge-selective instability modes, and mass-to-charge-selective resonant excitation modes.

[0019] With respect to the mass-to-charge-selective instability modes, ion trajectories in such a device can be calculated and grouped into two categories that include stable and unstable trajectories. Whether a trajectory is stable (e.g., an ion stays confined within thephysical boundaries of the device) may depend on its mass-to-charge ratio, U, V,and theinscribed radius r0of the device. Stable and unstable trajectories may be visualized as area plots using reduced variables a (depending on U, m / z, r0and ) and q (depending on V, m / z, r0and ). It is possible to initially choose a set of variables which results in stable trajectories for ions of interest within a certain m / z-range and subsequently scan one or more of these variables as a function of time to sequentially bring certain m / z-ranges fromunstable to stable trajectories. Furthermore, one can choose which dimension of ionmotion should become unstable and ions with specific m / z values can be released from the trap through openings in either one or both endcap electrodes. The ions exiting the trap may either be detected or guided to another device (e.g., an ion guide within a mass spectrometer).

[0020] With respect to the mass-to-charge-selective resonant excitation modes, an20230186-02 additional RF signal may be applied on one or more electrodes while all ions of interest are in stable regions, e.g., trapped. This technique exploits the fact that the effective potential well depth is mass-to-charge dependent, and therefore ions of different mass- to-charge values have different resonant frequencies within the trap. By applying an additional RF signal (e.g., with a frequency lower than the main trapping RF frequency) matching the resonant frequency (i.e., a resonant excitation waveform) of a particular mass-to-charge ratio, otherwise stable ion trajectories can be manipulated, leading to increasing spatial amplitudes of ions until they are eventually ejected through openings in the endcap electrode(s).

[0021] The aforementioned linear ion trap (LIT) may include four hyperbolic quadrupole rods, producing a harmonic 2D effective potential along the LIT axis when a potentialdifference of 0 = + f( ) is applied between each adjacent rod. Confinement in theremaining dimension (e.g., along the axis) may need to be accomplished through endcap electrodes or quadrupole segments, or the device may be used as a flow-through device, referred to as a quadrupole mass filter.

[0022] Similarly to the 3D ion trap, for the LIT, ions can be ejected, handed off to another device, or detected using mass-to-charge-dependent instability modes or resonant ejection modes. In the resonant ejection mode, ions of specific mass-to-charge ratios can be ejected through slits in one or more electrodes or between electrodes. When used as a flow- through mass filter, no trapping with end caps or quadrupole segments is required and ions with stable trajectories can pass through the device, while ions with unstable mass-to-charge values cannot, since they either hit electrodes or are ejected between rods.

[0023] The instability modes can be disadvantageous in that ions exit the trap with a20230186-02 wide distribution of kinetic energies, depending on the RF-phase at which they are ejected (which itself depends on initial conditions of the trapped ions which are impractical to control). The kinetic energy distribution may be wider than an acceptable energy distribution for a pulser in a time-of-flight mass spectrometer. Furthermore, low mass-to- charge ions may be ejected first during a mass scan when scanned in such a way that other (higher) mass-to-charge ratios would be still on stable trajectories and therefore preserved during the scan.

[0024] The mass-selective resonant excitation modes can be disadvantageous in that while these modes allow ejection of mass-to-charge ratios in any order, resonant frequencies typically are in the range of up to 200 kHz, limited by the maximum effective potential well depth achievable with stable ion trajectories. The time difference between the lowest mass-to-charge ratio ion (e.g., m / z = 100) and the highest one (e.g., m / z = 3000) utilized, for example, by the ion trap for enhanced time-of-flight ion utilization disclosed herein is on the order of 100 us. Therefore, a maximum of 20 excitation waveform cycles can be ‘fitted’ into the available scan time, which leads to the necessity of higher amplitudes of the resonant excitation waveform. Higher amplitudes on the order of 1 V or higher may lead to wider ejected ion kinetic energy distributions, which is higher than acceptable for orthogonal acceleration time-of-flight mass spectrometers.

[0025] For the ion trap for enhanced time-of-flight ion utilization disclosed herein, in a typical orthogonal acceleration time-of-flight mass spectrometer, ions may be pulsed and accelerated orthogonally to the incoming ion beam and their arrival time may be detected at the detector, often after one or more ion mirrors to extend the flight time and distance for better performance (e.g., resolution). The maximum pulse frequency may depend on the20230186-02 highest mass-to-charge ratio which should be detectable in a mass spectrum. Depending on the final time-of-flight energy of ions (e.g., 5 keV) and the path length, a new pulse may be fired after the slowest (e.g., highest mass-to-charge ratio) ion arrived at the detector.

[0026] The axial kinetic energy and the time-of-flight kinetic energy orthogonal to the incoming ion beams’ axis may form an angle, such that the ions hit the detector at its given position. The axial kinetic energy is, to the first degree, not changed and therefore preserved. The technical challenge with respect to pulsing a continuous incoming ion beam is that only a mass-dependent fraction of the beam may be pulsed, while ions not encountering a pulse are not accelerated and therefore not detected. This may be referred to as the duty cycle (DC) and a measure of ion utilization. In any orthogonal acceleration time-of-flight mass spectrometer pulsing from a continuous ion beam, the maximum duty cycle (e.g., for the highest mass-to-charge ratio to be detected) is equal to the ratios between the detector width (or accelerator width, whichever is smaller) and the distance between accelerator and detector. Examples of values for the duty cycle (orion utilization) of the highest mass-to-charge ratio ( ) may range from 10 % to < 50% in single reflectron time-of-flight (TOF) mass spectrometers and relatively smaller for multi-reflectron TOFs if no ion trapping scheme is used prior to pulsing. The duty cycles for lower mass-to-charge ratios may decrease as follows:In this regard, the ion trap for enhanced time-of-flight ion utilization disclosed herein increases the duty cycle to approximately 100% for all mass-to-charge ratios of interest, therefore increasing an instrument’s performance (e.g., sensitivity) significantly.20230186-02

[0027] According to examples disclosed herein, the ion trap for enhanced time-of- flight ion utilization disclosed herein avoids ion losses arising from orthogonal extraction of a continuous ion beam in a time-of-flight mass spectrometer.

[0028] According to examples disclosed herein, the ion trap for enhanced time-of- flight ion utilization disclosed herein improves ion beam characteristics such as primarily radial energy distribution (e.g., potentially improving resolution), as well as axial energy distribution (e.g., avoiding ion loss due to ions missing the detector).

[0029] According to examples disclosed herein, the ion trap for enhanced time-of- flight ion utilization disclosed herein allows for efficient scanning through ions of different mass-to-charge ratios.

[0030] According to examples disclosed herein, an ion trap may include at least one rod and an ion trap controller to apply a trapping potential and scanning voltage waveforms to at least one electrode operatively connected to the at least one rod to sequentially release higher mass-to-charge (m / z) ions before lower m / z ions. The ion trap may further include a linear configuration. The ion ejection from the ion trap may be perpendicular to an axis of the ion trap. The ion trap controller may be executed by at least one hardware processor. Alternatively, the ion trap controller may be an field- programmable gate array (FPGA).

[0031] According to examples disclosed herein, the ions may include an m / z range of 100 to 3000.

[0032] According to examples disclosed herein, the linear configuration may include a linear quadrupole configuration. The at least one rod may include a slitted rod. The at20230186-02 least one rod may include four rods including the slitted rod with RF trapping potential applied to the four rods.

[0033] According to examples disclosed herein, the linear configuration may include a linear quadrupole configuration. The at least one rod may include a slitted rod. The at least one rod may include four rods including the slitted rod with RF trapping potential applied to two rods.

[0034] According to examples disclosed herein, the linear configuration may include a linear quadrupole configuration. The at least one rod may include two rods for ion ejection between the two rods.

[0035] According to examples disclosed herein, the linear configuration may include a linear hexapole configuration. The at least one rod may include a slitted exit rod.

[0036] According to examples disclosed herein, the linear configuration may include a linear hexapole configuration. The at least one rod may include two rods for ion ejection between the two rods.

[0037] According to examples disclosed herein, the at least one rod may include a slitted rod with a scanning voltage waveform applied to the slitted rod. Further, the at least one rod may include a first set of rods including a slitted rod with a first radio frequency (RF) waveform applied to the first set of rods, and the at least one rod may include a second set of rods with a second RF waveform applied to the second set of rods.

[0038] According to examples disclosed herein, the slitted rod to which the first RF waveform is applied may represent an inner slitted rod, and the slitted rod to which the20230186-02 scanning voltage waveform is applied may be disposed behind the inner slitted rod relative to a center of the ion trap to pull ions from the center of the ion trap.

[0039] According to examples disclosed herein, an ion trap may include a three- dimension quadrupole configuration including two endcap electrodes. One endcap electrode of the endcap electrodes may include an entrance opening and another endcap electrode of the endcap electrodes may include an exit opening. The three-dimension quadrupole configuration may further include a central ring electrode. The ion trap may further include an ion trap controller to apply a trapping potential and scanning voltage waveforms to at least one electrode of the endcap electrodes and the central ring electrode to sequentially release higher mass-to-charge (m / z) ions before lower m / z ions.

[0040] According to examples disclosed herein, an assembly may include an ion trap including a three-dimension quadrupole configuration or a linear configuration to sequentially release higher mass-to-charge (m / z) ions before lower m / z ions. The assembly may further include an ion-optical transfer device to transfer the sequentially released ions to an ion accelerator. Further, the ion accelerator may accelerate ions from the ion-optical transfer device.

[0041] According to examples disclosed herein, for the assembly described above, the ion accelerator may be part of a time-of-flight (TOF) mass analyzer (not shown).

[0042] According to examples disclosed herein, for the assembly described above, the ion accelerator may accelerate the ions from the ion-optical transfer device in a direction that is perpendicular to an ion beam entering the ion trap, and is further perpendicular to an ion beam direction in the ion-optical transfer device. In this regard, this double turn of the ion beam reduces detector noise as well as achieves ultimate20230186-02 vacuum in the TOF mass analyzer.

[0043] According to examples disclosed herein, an ion trap may include a gap between a slitted rod and the beginning of the ion-optical transfer device. The ion trap may avoid a sudden transition from RF rod fields to ion optics transfer fields to thus eliminate much of the RF phase dependent kinetic energy spread. In this regard, the gap between the slitted rod and the beginning of the ion optical transfer device may be similarto the R0 (e.g.,inscribed radius) as disclosed herein, but may also be dependent onfactors such as the rod and lens geometry, the ion velocities, and the RF frequency.

[0044] According to examples disclosed herein, for the ion trap disclosed herein, another criteria that may be applied to the ion trap is a minimum number of RF cycles experienced by the ions as they transition from the exit of the slit to the entrance of the ion-optical transfer device (or the ion accelerator if there are no ion-optical transfer device). In this regard, too short of a gap (e.g., between a slitted rod and the beginning of the ion-optical transfer device) may cause the kinetic energy to be dependent on the RF phase as the ions transition between the devices. Too great of a spacing may cause too much radial beam dispersion.

[0045] According to examples disclosed herein, for the ion trap disclosed herein, the ion-optical transfer device, or the ion accelerator without the ion-optical transfer device, may be separated from the slit by a distance allowing the electric RF field amplitude to gradually decay to a sufficiently low value compared to its maximum value, such that an ion passing through this distance experiences a sufficiently high number of RF cycles (e.g., 20), and such that the kinetic energy spread of ions arriving at the accelerator is low enough (e.g., standard deviation of kinetic energies lower than 3% of the mean of kinetic20230186-02 energies).

[0046] For the ion trap disclosed herein, a controller of the ion trap (e.g., ion trap controller) disclosed herein may be any combination of hardware and programming to implement the functionalities of respective elements of the ion trap and / or an assembly as disclosed herein. In some examples described herein, the combinations of hardware and programming may be implemented in a number of different ways. For example, the programming for the elements may be processor executable instructions stored on a non- transitory machine-readable storage medium and the hardware for the elements may include a processing resource to execute those instructions. In these examples, a computing device implementing such elements may include the machine-readable storage medium storing the instructions and the processing resource to execute the instructions, or the machine-readable storage medium may be separately stored and accessible by the computing device and the processing resource. In some examples, some elements may be implemented in circuitry.

[0047] Figure 1 illustrates an ion trap for enhanced time-of-flight ion utilization, hereinafter referred to as “ion trap 100”, in accordance with an example of the present disclosure.

[0048] Referring to Figure 1, the ion trap 100 may store ions with a broad mass-to- charge (m / z) range for a period of time and then release those ions sequentially, for example, the high mass-to-charge ratios first, and the low mass-to-charge ratios subsequently. Furthermore, all ions may have narrow kinetic energy distributions with ideally identical mean values for all mass-to-charge ratios. The delays between certain m / z ratios should be in such a manner that all ions within the mass-to-charge ratio of20230186-02 interest arrive at a certain point in space downstream of the ion trap 100 at the same time after passing through an ion-optical transfer device 102 (e.g., an ion-optical guide), in order to be, for example, pulsed by an ion accelerator 104 (e.g., pulser) in an orthogonal- acceleration time-of-flight mass spectrometer.

[0049] The ion trap 100 may include a linear quadrupole geometry with ions being ejected orthogonally with respect to an ion trap axis. Ejection may be achieved using a slitted rod, or between two rods. For the ion trap 100, a mode of operation of the ion trap 100 may allow a scan speed to be fast enough and the ejected ion energies narrow enough to be utilized as an ion storage device placed in front of the ion accelerator 104 (e.g., the pulser) used in time-of-flight mass spectrometers. Other geometries, such as a 3D ion trap, may also be implemented.

[0050] In order to orthogonally accelerate ions originating from a continuous source within a mass-to-charge range of interest (e.g., m / z = 100 to 3000), ions may need to be trapped and released sequentially such that all ions arrive at the accelerator 104 (e.g., pulser) at the same time after passing the ion-optical transfer device 102. Ion optical devices may be DC and ions therefore may have nominally the same kinetic energy. Higher m / z ions move slower than ions with lower m / z. Releasing higher m / z ions earlier than the lower m / z ions in a well-defined manner may ensure that ions arrive at the same time close to the center of the desired acceleration region. In one example, the ion-optical transfer device 102 may be on the order of 10 to 100 mm, with axial ion energies spanning 3 to 30 eV. As a result, the required delay time between an ion with m / z = 3000 and an ion of m / z = 100 may be on the order of 100 microseconds.

[0051] With respect to mass spectrometry, if the ion trap 100 is utilized as a mass-20230186-02 selecting device, the scan speed is preferably on the order of 2E7 Thompson per second. Alternatively, the mass resolving power may not need to be high if the accelerator region is sufficiently large (e.g., within practical limits), where a mass resolving power on theorder of 10 (m / m) is sufficient.

[0052] The ion trap 100 may include an ion trap controller 106 (that is executed by at least one hardware processor) to apply a trapping potential and scanning voltage waveforms to at least one electrode operatively connected to the at least one rod to sequentially release higher mass-to-charge (m / z) ions before lower m / z ions. In this regard, the ion trap 100 may provide for a relatively high scanning speed. Further, for the ion trap 100, the scanning voltage may be monotonically increasing / decreasing, as opposed to being periodic.

[0053] With respect to the ion trap controller 106, the ion trap 100 may utilize a combination of a trapping potential and scanning voltage waveforms applied to one or more electrodes. The trapping potential (also denoted effective potential or pseudo-potential) may be created by oscillating electric fields, where the scanning waveform ( )is a monotonic function used to deform the effective potential. Initially, the scanningwaveform is zero and ions are allowed to accumulate in the center of the ion trap 100 ( =0). With increasing values of the scanning waveform ( ), the local minimum of the combinedpotential (e.g., effective potential and potential created by the scanning waveform) issteered towards an exit of the ion trap 100 ( = 0) and ions are finally ejected from the iontrap 100. Since the depth of the effective potential created by oscillating electric fields is m / z- dependent and higher m / z ions have lower effective potential depths, higher m / z ions are released before lower m / z ions. Thus the combined potential transitions from a shape20230186-02 having a local minimum to a shape lacking a local minimum at certain (e.g., m / z dependent) scanning voltages.

[0054] Figure 2A illustrates undisturbed effective potentials in the absence of a scanning waveform, and Figure 2B illustrates combined potential in the presence of a scanning waveform, in accordance with an example of the present disclosure.

[0055] Referring to Figure 2A, undisturbed effective potentials in the absence ofscanning waveform (U( = 0) = 0) are shown at 200. Further, referring to Figure 2B,combined potential in the presence of a scanning waveform (U( > 0) > 0) is shown at 202.The potential for m / z = 3000 lacks a local minimum and ions of this m / z-ratio will be ejected from the trap, while ions with m / z = 300 are still confined near the local potential minimum.

[0056] Figure 3 illustrates combined potentials in a quadrupolar trap with a slitted rod for ions with three different m / z ratios at different times during a scan, in accordance with an example of the present disclosure.

[0057] Referring to Figure 3, combined potentials in a quadrupolar trap with a slitted rod for ions with three different m / z ratios at different times during a typical scan are shown at300. For Figure 3, U donates the scanning voltage 3( ) 1( ) in Figure 4B. The diamondshape at 302 indicates the position of ions close to the local minimum of the combined potential. High-m / z-ions are trapped in shallower effective potentials at the beginning of thescan ( V=0), and their potential is deformed early on using moderate voltages. Withdecreasing m / z values, the effective potential increases and higher Vs are needed to significantly deform the potential such that the local minimum shifts towards the slitted exit rod.20230186-02

[0058] Different scanning parameters or a combination thereof may be utilized to mass- selectively deform the effective potential. For example, scanning the RF frequency using a constant offset voltage, scanning the RF amplitude, using a non-sinusoidal waveform (e.g., a square wave), a combination of duty-cycles, and / or amplitude and frequency may be utilized.

[0059] Figure 4A illustrates device (e.g., the ion trap 100) construction as a 3D ion trap, and Figures 4B – 4F illustrate device (e.g., the ion trap 100) construction as a linear ion trap with ejection of ions either between two adjacent rods (e.g., Figures 4D and 4F) or through a slit in one multipole rod (e.g., Figures 4B, 4C, and 4E), in accordance with an example of the present disclosure.

[0060] Referring to Figure 4A, the ion trap 100 may be constructed either as a 3D ion trap as shown at 400, or as a linear ion trap (e.g., at 402, 404, 406, 408, and 410) with ejection of ions either between two adjacent rods (e.g., Figures 4D and 4F) or through a slit in one multipole rod (e.g., Figures 4B, 4C, and 4E). Even higher order multipoles (e.g., in the case of a linear ion trap) such as hexapoles (e.g., Figures 4E and 4F) or octapoles may be utilized due to the low requirements in mass resolving power.

[0061] Referring again to Figures 4A-4F, Figure 4A illustrates the ion trap 100 as a 3D quadrupole ion trap including two endcap electrodes 412 and 414 with an entrance (e.g., left side of Figure 4A) and exit openings (e.g., right side of Figure 4A) and a central ring electrode 416. Figure 4B illustrates the ion trap 100 as a linear quadrupole ion trap with a slitted rod 418 and with RF trapping potential applied to all four rods (e.g., 418, 420, 422, and 424). Figure 4C illustrates the ion trap 100 as a linear quadrupole ion trap with a slitted rod 426, and RF trapping potential applied on two rods (e.g., 428 and 430) with20230186-02 twice the amplitude (e.g., resulting in the same RF trapping potential depth as the example of Figure 4B). Figure 4D illustrates the ion trap 100 as a linear quadrupole ion trap with ejection between two rods (e.g., at 432). Figure 4E illustrates the ion trap 100 as a linear hexapole ion trap with a slitted exit rod 434. Figure 4F illustrates the ion trap 100 as a linear hexapole ion trap with ion ejection (e.g., at 436) between two rods. For Figures 4A-4F, 0denotes a constant offset voltage common to all electrodes, ( ) denotes a 2 periodicfunction, such as a sinusoidal function, 0 denotes the RF amplitude, and ( ) are thescanning waveforms used to scan ions out of the trap in a m / z-specific manner.

[0062] Figure 5 illustrates a quadrupole linear ion trap with slitted ejection rod in positive ion mode, in accordance with an example of the present disclosure.

[0063] For the example of Figure 5, the ion trap 100 may be a quadrupole linear ion trap as shown at 500 with a slitted ejection rod in positive ion mode. For Figure 5, for0= 10 , 1( ) may be used to pull ions towards the exit slit. In this regard, since ions exitwith some kinetic energy through the slit, the final kinetic energy of 12 EV in this exampleis slightly higher than U0. For 2( ) = 0, 3( ) may be used to push ions towards the exitslit. The push-pull mechanism using two identical waveforms (but scaled differently) may ensure that the instantaneous ion kinetic energy of an ion ejected, and the instantaneous potential energy of the slotted rod, combined, result in the desired kinetic energy (e.g., 12 eV in this case) at the mid-pulser position as shown in Figure 6B.

[0064] With respect to the example of Figure 5, the functionality disclosed herein with respect to Figure 5 may be performed by having U3(t) and U1(t) and V0 constant but scanning omega (e.g., ). Alternatively, the functionality disclosed herein with respect to Figure 5 may be performed by having U3(t) and U1(t) and omega constant, but scanning20230186-02 V0.

[0065] Figure 6A illustrates ejection times of ions and their respective arrival times at mid- pulser after passing through the ion-optical transfer device, and Figure 6B illustrates kinetic energy of ions at the mid-pulser position, in accordance with an example of the present disclosure.

[0066] Referring to Figure 6A, Figure 6A illustrates ejection times of ions (e.g., , time ions pass the slit) and their respective arrival times at 600 at mid-pulser after passing through the ion-optical transfer device. Figure 6B illustrates kinetic energy of ions at 602 at the mid-pulser position. In this regard, the kinetic energy distribution in Figure 6B is not total kinetic energy, but rather energy in the vector perpendicular to the acceleration force vector (e.g., the kinetic energy which creates the natural angle of the TOF and which determines if the ions will hit the TOF detector).

[0067] Figure 7 illustrates orthogonal flow of ions to enter the ion trap 100, to exit the ion trap and to accelerate into a TOF mass analyzer, in accordance with an example of the present disclosure.

[0068] Referring to Figure 7, incoming ions to the ion trap 100 are shown at 700, the direction of ions within the ion-optical transfer device 102 is shown at 702, and the acceleration direction within a TOF mass analyzer (not shown) is shown at 704.

[0069] Figure 8 illustrates a number of RF cycles needed to bring a ratio between a standard deviation and mean kinetic energy of ions after passing the ion optical transfer device to acceptable values with respect to the ion trap 100, in accordance with an example of the present disclosure.20230186-02

[0070] Referring to Figure 8, the simulation illustrates a number of RF cycles needed to bring a ratio between a standard deviation and mean kinetic energy of ions after passing the ion optical transfer device to acceptable values (e.g., 3%). In this regard, the number of RF cycles in Figure 8 is defined as the number of RF cycles an ion experiences between its maximum electric field RF amplitude (e.g., 300 V / mm shortly after passing the slit) and the point where the electric field amplitude has decayed to 1 / e of its maximum.

[0071] Figure 9 illustrates separate electrodes including at least one electrode used to apply a scanning waveform (e.g., “scanning lens” or “Lens 1”) and electrodes used to apply RF waveforms, in accordance with an example of the present disclosure.

[0072] The example of Figure 5 includes adding the scanning waveform U1(t) and the RF waveform V(t)*cos(wt), and applying the summed waveform to the slitted rod. In this regard, the example of Figure 9 includes a scanning technique that avoids the summation of U1(t) and the RF waveform via an electric circuit, for example, by using separate electrodes. In addition, the example of Figure 9 includes a variable amplitude of the RF waveform V(t). For example, one electrode 900 (also designated as “rod”) includes the application of the scanning waveforms (e.g., ”scanning lens”), and another set of electrodes 902A, 902B and 904A, 904B includes the application of RF waveforms. This example of Figure 9 may utilize field penetration from the scanning lens through a slit as shown at 906 in the RF-carrying electrodes to the center of the device. Additionally, as shown at 908, RF amplitude ramping (V(t)) may be performed during the scanout to avoid fragmentation for low masses.

[0073] Thus, the example of Figure 9 may include at least one rod including a slitted rod (e.g., electrode 900) with a scanning voltage waveform applied to the slitted rod.20230186-02 Further, the at least one rod may include a first set of rods (e.g., electrodes 902A and 902B) including a slitted rod (e.g., electrode 902B) with a first RF waveform applied to the first set of rods. Further, the at least one rod may include a second set of rods (e.g., electrodes 904A and 904B) with a second RF waveform applied to the second set of rods.

[0074] Further, the slitted rod (e.g., electrode 902B) to which the first RF waveform is applied may represent an inner slitted rod. The slitted rod (e.g., electrode 900) to which the scanning voltage waveform is applied may be disposed behind the inner slitted rod relative to a center of the ion trap to pull ions from the center of the ion trap.

[0075] Thus, the configuration of Figure 9 may include at least one slit in the RF- carrying “inner” electrode 902B and the scanning electrode 900 “behind” the slitted RF electrode where the scanning voltage is applied. This configuration enables ions to be pulled out of the center of the ion trap. Alternatively, ions out may be pushed from the other side of the ion trap, for example, by replacing electrode 902A with a RF-carrying electrode and a scanning electrode in front the slitted RF electrode where the scanning voltage is applied. Yet further, the ion trap may include a push / pull configuration, where ions are pushed from the other side of the ion trap with electrode 902A replaced as discussed above and electrodes 900 and 902B disposed as shown.

[0076] Figure 10 illustrates further details of operation of the separate electrodes of Figure 9, in accordance with an example of the present disclosure.

[0077] Referring to Figure 10, the sum of effective potentials for three different mass- to-charge ratios (m / z = 300 Th shown at 1000, m / z = 1000 Th shown at 1002, and m / z = 3000 Th shown at 1004) and the potentials resulting from applying a set of different scanning voltages to the scanning lens is shown. For higher mass-to-charge ratios, lower20230186-02 scanning voltages may be utilized in order to achieve a total potential without a local minimum. Therefore, if the scanning voltage is applied in a ramp going from low scanning voltages to high scanning voltages, higher mass-to-charge ratios will be ejected through the slit in electrode 900 before lower mass-to-charge ratios.

[0078] What has been described and illustrated herein is an example along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration only and are not meant as limitations. Many variations are possible within the spirit and scope of the subject matter, which is intended to be defined by the following claims -- and their equivalents -- in which all terms are meant in their broadest reasonable sense unless otherwise indicated.

Claims

20230186-02 What is claimed is:

1. An ion trap comprising: an ion trap controller to apply a trapping potential and scanning voltage waveforms to at least one electrode to sequentially release higher mass-to-charge (m / z) ions before lower m / z ions, wherein the ion trap includes a linear configuration, and wherein ion ejection from the ion trap is perpendicular to an axis of the ion trap.

2. The ion trap according to claim 1, wherein the ions include an m / z range of 100 to 3000.

3. The ion trap according to claim 1, wherein the linear configuration includes a linear quadrupole configuration, wherein the ion trap includes at least one rod comprising a slit, and wherein the at least one rod includes four rods including the at least one rod comprising the slit with radio frequency (RF) trapping potential applied to the four rods.

4. The ion trap according to claim 1, wherein the linear configuration includes a linear quadrupole configuration,20230186-02 wherein the ion trap includes at least one rod comprising a slit, and wherein the at least one rod includes four rods including the at least one rod comprising the slit with radio frequency (RF) trapping potential applied to two rods.

5. The ion trap according to claim 1, wherein the linear configuration includes a linear quadrupole configuration, and wherein the ion trap includes at least one rod comprising two rods for ion ejection between the two rods.

6. The ion trap according to claim 1, wherein the linear configuration includes a linear hexapole configuration, and wherein the ion trap includes at least one rod comprising a slitted exit rod.

7. The ion trap according to claim 1, wherein the linear configuration includes a linear hexapole configuration, and wherein the ion trap includes at least one rod comprising two rods for ion ejection between the two rods.

8. The ion trap according to claim 1, wherein the ion trap includes at least one rod comprising a slitted rod with a scanning20230186-02 voltage waveform applied to the slitted rod, wherein the at least one rod includes a first set of rods including a slitted rod with a first radio frequency (RF) waveform applied to the first set of rods, and wherein the at least one rod includes a second set of rods with a second RF waveform applied to the second set of rods.

9. The ion trap according to claim 8, wherein the slitted rod to which the first RF waveform is applied represents an inner slitted rod, and wherein the slitted rod to which the scanning voltage waveform is applied is disposed behind the inner slitted rod relative to a center of the ion trap to pull ions from the center of the ion trap.

10. An ion trap comprising: a three-dimension quadrupole configuration including two endcap electrodes, one endcap electrode of the endcap electrodes including an entrance opening and another endcap electrode of the endcap electrodes including an exit opening, wherein the three- dimension quadrupole configuration further includes a central ring electrode; and an ion trap controller to apply a trapping potential and scanning voltage waveforms to at least one electrode of the endcap electrodes and the central ring electrode to sequentially release higher mass-to-charge (m / z) ions before lower m / z ions.20230186-02 11. The ion trap according to claim 10, wherein the ions include an m / z range of 100 to 3000.

12. An assembly comprising: an ion trap including a three-dimension quadrupole configuration or a linear configuration to sequentially release higher mass-to-charge (m / z) ions before lower m / z ions; and an ion-optical transfer device to transfer the sequentially released ions to an ion accelerator, wherein the ion accelerator is to accelerate ions from the ion-optical transfer device.

13. The assembly according to claim 12, wherein the linear configuration includes a linear quadrupole configuration, wherein the linear configuration includes at least one rod including a slitted rod, and wherein the at least one rod includes four rods including the slitted rod with radio frequency (RF) trapping potential applied to the four rods.

14. The assembly according to claim 12, wherein the linear configuration includes a linear quadrupole configuration,20230186-02 wherein the linear configuration includes at least one rod including a slitted rod, and wherein the at least one rod includes four rods including the slitted rod with radio frequency (RF) trapping potential applied to two rods.

15. The assembly according to claim 12, wherein the linear configuration includes a linear quadrupole configuration, and wherein the linear configuration includes at least one rod including two rods for ion ejection between the two rods.

16. The assembly according to claim 12, wherein the linear configuration includes a linear hexapole configuration, and wherein the linear configuration includes at least one rod including a slitted exit rod.

17. The assembly according to claim 12, wherein the linear configuration includes a linear hexapole configuration, and wherein the linear configuration includes at least one rod including two rods for ion ejection between the two rods.

18. The assembly according to claim 12, wherein the three-dimension quadrupole configuration includes two endcap20230186-02 electrodes, one endcap electrode of the endcap electrodes including an entrance opening and another endcap electrode of the endcap electrodes including an exit opening, and wherein the three-dimension quadrupole configuration further includes a central ring electrode.

19. The assembly according to claim 12, wherein the ion trap further comprises an ion trap controller to apply a trapping potential and scanning voltage waveforms to at least one electrode operatively connected to at least one rod to sequentially release higher m / z ions before lower m / z ions.

20. The assembly according to claim 12, wherein the ion accelerator is to accelerate the ions from the ion-optical transfer device in a direction that is perpendicular to an ion beam entering the ion trap, and is further perpendicular to an ion beam direction in the ion-optical transfer device.

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