Time-of-flight mass spectrometer and mass spectrometry analysis methods

Abstract

A time-of-flight (ToF) mass spectrometer comprises: a pulsed ion implanter for forming an ion beam traveling along an ion path; a detector for detecting ions in the ion beam, the ions occasionally arriving at the detector according to their m / z values; an ion focusing device, located between the ion implanter and the detector, for focusing the ion beam along at least one direction orthogonal to the ion path; and a variable voltage source for supplying at least one variable voltage to the ion focusing device, the variable voltage depending on the charge state and / or amount of at least one type of ions in the ion beam. A corresponding mass spectrometry method is provided. The charge state and / or the amount of ions can be obtained or predicted from a pre-scan. Tuning of the spectrometer based on the charge state and / or amount of at least one type of ions in the ion beam can be performed on the fly.

Description

Technical Field

[0001] The present disclosure relates to the field of time-of-flight mass spectrometry technology. Aspects of the present disclosure relate to a time-of-flight mass spectrometer and a method of time-of-flight mass spectrometry analysis. Background Art

[0002] Time-of-flight (ToF) mass spectrometers are widely used to determine the mass-to-charge ratio (m / z) of ions based on their flight time along a flight path. In a ToF mass spectrometer, short pulses of ions are generated by a pulsed ion implanter to form an ion beam, which is guided through a vacuum space along a prescribed ion flight path to an ion detector. These ions in each ion pulse are separated based on their flight time along the flight path, which depends on the m / z of the ion, and arrive at the detector in the form of short ion packets of different m / z separated by time. The detector detects the arrival time of the ions and the abundance of the arriving ions, and stores this data in a data acquisition system. A mass spectrum can be generated from the acquired ToF data.

[0003] Improved m / z resolution (also known as mass resolution) is an important attribute for the widespread use of mass spectrometers, especially in biological sciences such as proteomics and metabolomics. Assuming that the ion focusing properties remain constant, the mass resolution in a ToF mass spectrometer increases proportionally with the length of the ion flight path. Therefore, flight path extension within a ToF mass spectrometer is required to increase the flight separation time of the ions, thereby improving the ability to distinguish smaller m / z differences between ions.

[0004] Various arrangements are known which exploit single or multiple reflections of ions to extend the flight path of ions within a mass spectrometer without significantly increasing the overall size of the mass spectrometer. Examples are disclosed in US9136100, SU1725289, GB2478300, GB2403063, WO2008 / 047891 and US9136101.

[0005] Unfortunately, the distribution of ion energies and the interaction of space charge can cause ions to diffuse in flight, which in longer flight systems can cause ions to be lost from the analyzer or arrive at the detector with abnormal flight times.

[0006] Time-dependent lens voltage has been proposed in US8212209 and US2016 / 0111271A1 for ToF mass spectrometers to solve the problems of astigmatism focusing and ion beam expansion. Summary of the invention

[0007] Against the above background, the present disclosure is provided.

[0008] Aspects of the present disclosure address the problem that packets with multiple charged ions have less dispersion in flight and therefore may suffer from stronger space charge effects due to greater charge density. Similarly, ion packets consisting of a large number of ions may suffer from space charge effects due to greater charge density. Such space charge effects may reduce the mass resolution of a mass spectrometer and / or adversely affect ion transmission.

[0009] The present disclosure provides in one aspect a time-of-flight mass spectrometer according to claim 1. The present disclosure provides in another aspect a time-of-flight mass spectrometry method according to claim 24. Further aspects of the present disclosure are set out in the further claims and described below.

[0010] The present disclosure provides a time-of-flight mass spectrometer, comprising: a pulsed ion implanter for forming an ion beam traveling along an ion path; a detector for detecting ions in the ion beam, which ions arrive at the detector from time to time according to their m / z values; an ion focusing arrangement, which is located between the ion implanter and the detector, and is used to focus the ion beam along at least one direction orthogonal to the ion path; and a variable voltage source for providing at least one variable voltage to the ion focusing arrangement, wherein the at least one variable voltage depends on the charge state and / or amount of at least one type of ions in the ion beam.

[0011] A time-of-flight mass spectrometry analysis method provided by the present disclosure includes: forming an ion beam traveling along an ion path from a pulsed ion implanter; detecting ions in the ion beam, which arrive at a detector from time to time according to their m / z values; focusing the ion beam in at least one direction orthogonal to the ion path using an ion focusing arrangement located between the ion implanter and the detector; and supplying at least one variable voltage from a variable voltage source to the ion focusing arrangement, wherein the variable voltage depends on the charge state and / or amount of at least one type of ions in the ion beam.

[0012] The time-of-flight mass spectrometer of the present disclosure can be used to perform the method of the present disclosure. Therefore, the features of the time-of-flight mass spectrometer are also applicable to the method with appropriate changes.

[0013] According to the present disclosure, the voltage applied to the ion focusing arrangement can be optimized to the charge state and / or amount of ions of at least one ion type that is desired to be detected. Therefore, the applied voltage can be a function of the charge state and / or amount of ions of at least one ion type in the ion beam. The voltage can be a function of the charge state only, or a function of the ion amount only, or a function of both the charge state and amount of ions of at least one ion type. For example, if it is desired to detect multiply-charged ions that are less dispersed in flight, the voltage can be adjusted to a value that increases the spatial dispersion of ions in at least one direction orthogonal to the ion path, thereby reducing the influence of the spatial charge inherent in the multiply-charged ion packet. The term multiply-charged ion refers to ions with a charge state greater than 1, such as 2+, 3+, 4+... or 2-, 3-, 4-... etc. When the voltage applied to the ion focusing arrangement is optimized for detecting singly-charged ions, the variable voltage can increase the spatial dispersion of multiply-charged ions in the beam relative to the spatial dispersion of multiply-charged ions. Similarly, in order to optimize the detection of ion packets consisting of a large number of ions (i.e., high peak intensities in the mass spectrum), the voltage can be similarly adjusted to reduce the effects of space charge by increasing the spatial dispersion of the ion beam. In this way, mass resolution and / or ion transmission can be improved for one or more species with multiple charge states and / or a large number of ions. For example, if the charge state of an ion is higher than a threshold, such as at least 2 or 3 or 4 or 5 or 10 or 20 (e.g., +2 or +3 or +4 or +5... or +10 or greater than 10+), the variable voltage can be adjusted. For example, if the amount of a certain ion is higher than a threshold (e.g., the signal / noise (S / N) value or intensity of the peak is higher than a threshold, which may cause (preferably has been determined to cause) an undesirable space charge effect), the variable voltage can be adjusted.

[0014] The charge state of the ion species can be obtained in different ways. The charge state can be an approximate value or an exact value of the charge state. The charge state can be a predicted or measured charge state. The charge state of the ion can be predicted, for example, based on a priori knowledge of the sample type used to generate the ion. The charge state of the product ion in MS2 can be predicted based on the measured precursor charge state. The charge state of the ion can be measured, for example, by analyzing the mass spectrum obtained by the detector. Conventionally used algorithms (such as THRASH and advanced peak detection) can be used to determine the charge state of the ion from the spectrum. The charge state can be inferred from the mass spacing of different isotope species or the spacing of different charge states of the same ion. The ion amount of a certain ion can be obtained in different ways, for example, according to the peak intensity of the ion species measured in the mass spectrum obtained by the detector. Therefore, in some embodiments, a pre-scan (i.e., mass spectrum) is first obtained to obtain data on the charge state and / or amount of at least one type of ion of the ion in the ion beam. The data is then used to control the variable voltage power supply accordingly.

[0015] The time-of-flight mass spectrometer generally also includes a controller, which is configured to use data (referred to as charge state data and peak abundance data, respectively) about at least one charge state and / or amount of at least one ion species in the ion beam to control a variable voltage power supply. The controller generally uses a control signal to control the variable voltage power supply. The controller generally includes a computer. The computer is generally programmed to control the variable voltage supply according to data about at least one charge state and / or amount of at least one ion species in the ion beam. The controller can be configured to predict at least one charge state of the product ions in the MS2 analysis from at least one charge state of the parent ion obtained in the MS1 analysis. The charge state of the parent ion can be obtained in the MS1 analysis according to mass spectrometry, for example, using THRASH or advanced peak detection. For example, the charge state of the product ion can be predicted using fragmentation knowledge or rules about the fragmentation behavior of the parent ion. The controller, such as its computer, can be communicatively coupled to the detector so that the data about at least one charge state and / or amount of at least one ion species in the ion beam obtained by the detector can be used by the controller to control the variable voltage power supply.

[0016] The voltage source may be configured to vary the voltage supplied to the ion focusing arrangement based on charge state data and / or peak abundance data acquired by the detector and / or a charge measurement device for measuring charge in the ion beam. The charge measurement device is preferably located upstream of the ion focusing arrangement and may be located in or near the ion path. The charge measurement device may include, for example, a grid located in the ion path or an image current measurement device located near the ion path.

[0017] The voltage source may be configured to vary the voltage supplied to the ion focusing arrangement from one m / z scan of an ion pulse by the ion implanter to a subsequent scan of another ion pulse from the ion implanter. A scan includes detecting ions in a single pulse. That is, the voltage may vary between each scan.

[0018] The voltage source may be configured to vary the voltage supplied to the ion focusing arrangement within an m / z scan of an ion pulse from the ion implanter. That is, the voltage may be varied within a single scan. For example, the voltage may be varied synchronously with the arrival of ion species at the ion focusing arrangement.

[0019] The voltage source may be configured to vary the voltage supplied to the ion focusing arrangement based on charge state data and / or peak abundance data of ions in the ion beam acquired from a pre-scan of ion pulses from the ion implanter (ie a pre-scan of ions of the same sample).

[0020] The voltage source may be configured to vary a voltage supplied to the ion focusing arrangement based on data regarding the charge state and / or amount of at least one species of ions in an ion beam acquired from ions in flight during an m / z scan of an ion pulse from an ion implanter. The at least one variable voltage may be variable in a time-dependent manner that is related to arrival times of ions of different charge states and / or different spatial charges at the focusing arrangement.

[0021] The voltage applied based on the charge state and / or number of ions of at least one ion species can be determined by a calibration procedure. For example, one or more calibration mixtures can be ionized to provide one or more ion calibration mixtures that are mass analyzed by a spectrometer, i.e., detected by a detector based on m / z. The calibration mixture typically contains a known mixture of different molecular species that form ions of known m, z, and m / z. An example of a calibration mixture is available from Thermo Fisher Scientific TM Obtained Pierce TM FlexMix TM Calibration solution, which is a mixture of 16 high-purity ionizable components (mass range: 50 to 3000 m / z) designed for positive and negative ionization calibration, providing mainly singly charged ions. Calibration solutions for providing multiply charged ions can contain, for example, protein mixtures; proteins commonly used in calibration solutions include ubiquitin, myoglobin, cytochrome C, and / or carbonic anhydrase, but many other proteins and / or peptides can be used in calibration mixtures as needed. For example, Pierce TM The retention time calibration mixture comprises a mixture of 15 known peptides. The calibration mixture preferably comprises molecular species that produce ions with a range of different masses, charge states and abundances (peak intensities), in particular molecules that cover the range of most masses, charge states and ion abundances expected in the sample to be analyzed by the spectrometer. Thus, the ion calibration mixture comprises at least different charge states and / or ion amounts for at least two different types of ions, preferably at least five or at least 10 different types of ions.

[0022] The calibration procedure may include mass analysis (recording mass spectra) of one or more calibration mixtures of ions at different voltages applied to the ion focusing arrangement to determine the dependence of the m / z values ​​and peak intensities recorded in the spectrum on voltage changes at different ion masses (m), charge states (z) and peak intensities. A multidimensional data set is thus generated. The optimal voltage applied to the ion focusing arrangement for a given m, z and / or intensity of ions can be obtained. In some aspects of the present disclosure, additional or alternative calibration procedures using one or more calibration mixtures can be performed, wherein the dependence of the recorded m / z values ​​and peak intensities is determined for pressure and / or voltage changes in the ion implanter (ion trap). The aforementioned dependence can be approximated by a function (e.g., a smoothing function, such as a spline curve). A controller including a computer can determine such functions. These functions can be used to adjust variable voltages, etc. according to charge states, ion numbers, etc. Approximate functions can be used, for example, to correct the acquired mass spectrum before saving the spectrum. Preferably, the determined multidimensional dependence can be approximated by such a function (e.g., a spline) and used for online correction of the acquired mass spectrum before saving them.

[0023] Therefore, on the one hand, the present disclosure provides a mass spectrometry method as described above, wherein the dependence of at least one variable voltage on the charge state and / or amount of at least one type of ions in the ion beam has been determined by calibration, wherein the calibration includes detecting one or more ion calibration mixtures having a varying voltage supplied to the ion focusing arrangement so as to determine the dependence of the m / z values ​​and / or peak intensities detected at different charge states and / or ion amounts on the variable voltage.

[0024] The charge state of at least one species of ions may include a multiply-charged state, and the voltage source may be configured to vary the voltage supplied to the ion focusing arrangement to normalize the spatial dispersion of the ions in the multiply-charged state to the spatial dispersion of the singly-charged ions. In other words, the voltage supplied to the ion focusing arrangement may be adjusted so that the spatial dispersion of the multiply-charged ion species is substantially the same as the average spatial dispersion for the singly-charged ions.

[0025] In some embodiments, at least one charge state may be the charge state of a single ion species. In some other embodiments, at least one charge state may be a plurality of charge states of different ion species. At least one charge state may include a representative charge state of a plurality of different ion species. For example, a representative charge state may be an average charge state of a plurality of different ion species with different charge states. In this way, the applied voltage may be a compromise between optimal voltages for many different ion species with different charge states. Similarly, in some embodiments, at least one amount of ions may be an amount of ions of a single ion species. In some other embodiments, at least one amount of ions may be a plurality of amounts of ions of different ion species. At least one amount of ions may include an amount of representative ions of a plurality of different ion species. For example, a representative amount of ions may be an average ion amount of a plurality of different ion species with different amounts of ions (different abundances) present in an ion beam. In this way, the applied voltage may be a compromise between optimal voltages for many different ion species with different abundances.

[0026] The ion beam can experience one or more reflections along the ion path, preferably multiple reflections. In some multiple reflection embodiments, the ion beam path can follow a zigzag path. The ion path can be located in a plane, and the focusing arrangement can focus the ion beam along the direction (orthogonal to the ion path) located in the plane and / or along the direction out of the plane. The time-of-flight mass spectrometer therefore preferably further includes at least one ion mirror, which is configured to reflect the ion beam along the ion path. The time-of-flight mass spectrometer also preferably includes a plurality of ion mirrors, which are configured to reflect the ion beam multiple times along the ion path. Therefore, the time-of-flight mass spectrometer can be a single reflection or multi-reflection time-of-flight mass spectrometer.

[0027] In some embodiments, a time-of-flight mass spectrometer may include two ion mirrors, the two ion mirrors being spaced apart from each other and opposite to each other in a direction X, each mirror being substantially elongated along a drift direction Y, the drift direction Y being orthogonal to the direction X, and being configured to provide a sawtooth ion path by reflecting the ion beam multiple times in the X direction between the ion mirrors while the ion beam drifts in the drift direction Y. Such spaced apart mirrors may be parallel or non-parallel (i.e. tilted) to each other. The ion path may be located in an XY plane, and a focusing arrangement may be used to focus the ion beam along a direction located in the XY plane and / or along an out-of-plane direction. A pulsed ion implanter may inject ion pulses into the space between the ion mirrors at a non-zero inclination angle with the X direction, and the ions are thereby formed along a sawtooth ion path and between the ion mirrors along the direction X undergoing an ion beam that is reflected N times, while drifting in the drift direction Y. N is an integer of at least 2. Therefore, the ion beam undergoes at least 2 reflections along the direction X between the ion mirrors, while drifting in the drift direction Y. Preferably, the number N of ion reflections in the ion mirror along the ion path from the ion implanter to the detector is at least 3, or at least 10, or at least 30, or at least 50, or at least 100. The number N of ion reflections in the ion mirror along the ion path from the ion implanter to the detector is 2 to 100, 3 to 100, or 10 to 100, or more than 100, such as one of the following groups: (i) 3 to 10; (ii) 10 to 30; (iii) 30 to 100; (iv) more than 100. The ions injected into the mass spectrometer are preferably repeatedly reflected back and forth between the ion mirrors in the X direction while the ions drift downward in the Y direction (in the +Y direction) along which the ion mirrors extend. In some embodiments, after multiple reflections (typically N / 2), the ions can reverse their drift velocity in the Y direction so that they are repeatedly reflected back and forth between the ion mirrors in the X direction while the ions drift backward in the Y direction (in the -Y direction) before being detected by the detector. Such an arrangement of ion mirrors is disclosed in US9136101, the entire contents of which are incorporated herein.

[0028] The ion focusing arrangement generally includes or is at least one ion focusing lens. Therefore, a voltage source is used to supply at least one variable voltage to at least one ion focusing lens. At least one ion focusing lens can be selected from the following types of lenses: trans-axial lens, Einzel lens and multipole lens. At least one ion focusing lens can be located before the first reflection in (one or more) ion mirrors. In such an embodiment, a time-of-flight mass spectrometer can have only a single ion mirror. More generally, in these types of embodiments, a spectrometer can include at least one ion mirror along an ion path configured to reflect an ion beam, wherein at least one ion focusing lens is located before the first reflection in at least one ion mirror. At least one ion focusing lens can be located after the first reflection in the ion mirror and before the fifth reflection. In such an embodiment, a time-of-flight mass spectrometer has a plurality of ion mirrors (e.g., two relative ion mirrors), and the plurality of ion mirrors are configured to reflect ion beams multiple times, so that these beams undergo multiple reflections in the ion mirrors, preferably five or more reflections.

[0029] Preferably, the ion focusing lens, or a lens having more than one focusing lens, comprises a transaxial lens, wherein the transaxial lens comprises a pair of relative lens electrodes, the pair of relative lens electrodes being positioned on either side of the beams, for example, on either side of the beams in direction Z, wherein Z is perpendicular to directions X and Y, and directions X and Y define the plane of the ion path. Preferably, each of the relative lens electrodes comprises a circular, elliptical, quasi-elliptical or arcuate electrode. In some embodiments, each of the pair of relative lens electrodes comprises an electrode array separated by a resistor chain to simulate the field curvature produced by electrodes with curved edges. In some embodiments, the relative lens electrodes are each placed in an electrically grounded assembly. In some embodiments, the lens electrodes are each placed in a deflector electrode but isolated from the deflector electrode. Each deflector electrode can be placed in an electrically grounded assembly. The deflector electrode can preferably have an external trapezoidal shape, which acts as a deflector for the ion beam. In some embodiments, the ion focusing lens comprises a multipole assembly. In some embodiments, the ion focusing lens comprises a single lens (a series of electrically biased holes).

[0030] In some preferred embodiments, the ion focusing arrangement may include more than one focusing lens. For example, the ion focusing arrangement may include a first focusing lens and a second focusing lens spaced apart from the first focusing lens. The first and second focusing lenses may have different variable voltages, which are applied to the first and second focusing lenses by a variable voltage source. For example, the first focusing lens may be a diverging lens in a direction orthogonal to the ion path, and the second focusing lens may be a converging lens in a direction orthogonal to the ion path, the second focusing lens being downstream of the first focusing lens. In some embodiments, the ion focusing arrangement includes: a first focusing lens, which is positioned before the first reflection in the ion mirror, in particular, wherein the first focusing lens is a diverging lens; and a second focusing lens, which is positioned after the first reflection in the ion mirror, for focusing the ion beam, wherein the second focusing lens is a converging lens (i.e., having a converging effect on the ion beam width, the ion beam width being orthogonal to the ion path).

[0031] The time-of-flight mass spectrometer may also include an ion fragmentation device, such as a collision induced dissociation (CID) cell or an electron transfer dissociation (ETD) cell or other dissociation cell, located upstream of the ion implanter, for performing an MS2 analysis of the ions, wherein the voltage source is configured to vary the voltage supplied to the ion focusing arrangement in the MS2 analysis based on data regarding the charge state and / or amount of at least one species of product ions, the data being derived from an MS1 ​​analysis of the ions performed prior to the MS2 analysis. In this way, adjustments to the focusing and ion beam spread in an MS2 (product ion) scan can be based on charge state or abundance data acquired from a previous MS1 (precursor ion) scan.

[0032] The pulsed ion implanter may include an ion trap with ion pulse emission, an orthogonal accelerator, a MALDI source, a secondary ion source (SIMS source) or other known pulsed ion implanters for a ToF mass spectrometer. Preferably, the ion implanter includes a pulsed ion trap, more preferably a linear ion trap, such as a linear ion trap or a curved linear ion trap (C-Trap).

[0033] Pulsed ion implanters typically receive ions from an ion source directly or indirectly via one or more ion optical devices (e.g., one or more of an ion guide, an ion lens, a mass filter, a collision cell, etc.). The ion source ionizes the sample to form ions. Suitable ion sources are well known in the art. In certain embodiments, the ion implanter itself can be an ion source (e.g., a MALDI source). The ion source can ionize multiple sample species to form ions, such as separated sample species from a chromatograph. These ions can be generated from a sample by any of the non-exhaustive list of ion sources: electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), atmospheric pressure gas chromatography (APGC) with glow discharge, AP-MALDI, laser desorption (LD), inlet ionization, electrospray desorption ionization DESI, laser ablation electrospray ionization (LAESI), inductively coupled plasma (ICP), laser ablation inductively coupled plasma (LA-ICP) source, etc. Any of these ion sources can be connected to any of the following non-exhaustive list of sample separations upstream of the ion source: liquid chromatography (LC), ion chromatography (IC), gas chromatography (GC), capillary zone electrophoresis (CZE), two-dimensional GC (GCxGC), two-dimensional LC (LCxLC), etc.

[0034] Pulsed ion implanters generate discrete ion pulses, i.e., inject discontinuous ion pulses rather than a continuous ion stream. As known in the art of ToF mass spectrometry, pulsed ion implanters form short ion pulses that include at least a portion of the ions from the sample / ion source. Typically, an accelerating voltage is applied to the ion implanter to implant the ions into the mirror, and the voltage may be several kV, such as 1 kV, 2 kV, 3 kV, 4 kV or 5 kV, or higher.

[0035] The ion focusing arrangement can be at least partially positioned between the relative ion mirrors. In certain embodiments, the ion focusing arrangement is positioned completely between the ion mirrors (that is, in the space between the ion mirrors), and in other embodiments, the ion focusing arrangement is positioned partially between the ion mirrors, and is partially positioned outside the space between the ion mirrors. For example, a lens of the ion focusing arrangement can be positioned outside the space between the ion mirrors, and another lens of the ion focusing arrangement is positioned between the ion mirrors.

[0036] The detector may comprise a suitable ion detector for ToF mass spectrometry known in the art. Examples include a secondary electron multiplier (SEM) detector or a microchannel plate (MCP) detector, or a detector containing a SEM or MCP in combination with a scintillator / photodetector.

[0037] (One or more) ion mirrors may include any known type of elongated ion mirrors. (One or more) ion mirrors are or are typically electrostatic ion mirrors. (One or more) mirrors may be gridded, or (one or more) mirrors may be gridless. Preferably, (one or more) mirrors are gridless. (One or more) ion mirrors are typically (one or more) planar ion mirrors, in particular (one or more) electrostatic planar ion mirrors. In some embodiments, two planar ion mirrors are parallel to each other over most or all of the lengths in, for example, drift direction Y. In some embodiments, the ion mirrors may not be parallel over a shorter length in drift direction Y (e.g., as described in US 2018-0138026 A, at the inlet end closest to the ion implanter). The ion mirrors typically have substantially the same length in drift direction Y. Preferably, the ion mirrors are separated by a spatial region without an electric field. The ion optical mirrors are relative to each other. Relative mirrors mean that the mirrors are oriented so that ions directed to the first mirror are reflected from the first mirror to the second mirror, and ions entering the second mirror are reflected from the second mirror to the first mirror. Therefore, the relative mirrors have electric field components that are generally oriented in opposite directions and relative to each other. Each plane mirror is preferably made of a plurality of parallel elongated strip electrodes, which are usually elongated in the Y direction. This structure of the mirror is known in the art, such as described in SU172528 or US2015 / 0028197. The elongated electrodes of the ion mirror can be set to metal tracks on an installed metal strip or PCB base. The elongated electrodes can be made of a metal with a low thermal expansion coefficient, such as Invar, so that the flight time can resist changes in temperature in the instrument. The electrode shape of the ion mirror can be accurately processed or obtained by wire corrosion manufacturing. The ion mirror length (the total length of the first and second stages) is not particularly limited in the present invention, but the total length of the preferred practical embodiment is in the range of 300-500mm, more preferably in the range of 350-450mm.

[0038] Both ion mirrors can be elongated primarily in one direction Y. The elongation can be linear (i.e., straight), or the elongation can be non-linear (e.g., curved or comprising a series of small steps approximating a curve), as will be further described. The elongated shape of each ion mirror can be the same or different. Preferably, the elongated shape of each mirror is the same. Preferably, the mirrors are a pair of symmetrical mirrors. In the case where the elongation is linear, the mirrors can be parallel to each other, but in some embodiments, the mirrors may not be parallel to each other.

[0039] As described herein, the two mirrors are aligned with each other so that they are located in the XY plane and so that the elongated dimensions of the two mirrors are substantially located in the drift direction Y. These mirrors are spaced apart in the X direction and are opposite to each other. The distance or gap between the ion mirrors can be conveniently set to be constant according to the drift distance, that is, constant according to Y (the elongated dimension of the mirror). In this way, the ion mirrors are arranged parallel to each other. However, in some embodiments, the distance or gap between the mirrors can be set to vary according to the drift distance, that is, vary according to Y, and the elongated dimensions of the two mirrors will not be precisely located in the Y direction, for which these mirrors are described as being elongated substantially along the drift direction Y. Therefore, elongating substantially along the drift direction Y can be understood as elongating primarily or substantially along the drift direction Y. In some embodiments of the present invention, the elongated dimension of at least one mirror can be angled with the direction Y over at least a portion of its length.

[0040] Under superficial inspection, the mechanical structure of the ion mirror itself may appear to maintain a constant X distance (varying according to Y), while the average reflective surface may actually be located at a different X distance (varying according to Y). For example, one or more relative ion mirrors may be formed by conductive traces disposed on an insulating coil frame (such as a printed circuit board), and the coil frame of one such ion mirror may maintain a constant distance from the relative ion mirror along the entire drift length, while the distance between the conductive traces disposed on the coil frame and the electrodes in the relative ion mirror may not be constant. Even if the electrodes of the two ion mirrors are arranged to be spaced a constant distance apart along the entire drift length, different electrodes within one or both ion mirrors may be biased with different potentials along the drift length, causing the distance between the relative average reflective surfaces of the mirrors to vary along the drift length. Therefore, the distance in the X direction between the relative ion optical mirrors varies in the drift direction along at least a portion of the mirror length.

[0041] In some embodiments, the mass spectrometer of the present invention includes one or more compensation electrodes in the space between the ion mirrors to minimize the effects of time-of-flight aberrations caused, for example, by alignment errors of the mirrors, such as described in US9136102, the entire contents of which are incorporated herein. The compensation electrode extends along at least a portion of the drift direction in or near the space between the ion mirrors. In some embodiments, the compensation electrode generates an electric field component that is opposite to the ion motion in the +Y direction along at least a portion of the length of the ion optical mirror in the drift direction. When the ions move along the drift direction, these components of the electric field preferably provide or contribute a return force to these ions. Relative to the ion mirrors of the multi-reflection mass spectrometer, one or more compensation electrodes can have any shape and size. In a preferred embodiment, one or more compensation electrodes include an extended surface parallel to the XY plane facing the ion beam, and the electrode deviates from the ion beam flight path displacement on + / -Z, that is, each one or more electrodes preferably have a surface substantially parallel to the XY plane, and preferably, there are two such electrodes located on either side of the space extending between the relative ion mirrors. In another preferred embodiment, one or more compensation electrodes are elongated in the Y direction along a substantial portion of the drift length, each electrode being located on either side of the space extending between the opposing ion mirrors. In this embodiment, preferably, one or more compensation electrodes are elongated in the Y direction along a substantial portion, the substantial portion being at least one or more of the following: 1 / 10; 1 / 5; 1 / 4; 1 / 3; 1 / 2; 3 / 4. In some embodiments, one or more compensation electrodes include two compensation electrodes elongated in the Y direction along a substantial portion of the drift length, the substantial portion being at least one or more of the following: 1 / 10; 1 / 5; 1 / 4; 1 / 3; 1 / 2; 3 / 4 of the total drift length, one electrode being displaced in the +Z direction away from the ion beam flight path, the other electrode being displaced in the -Z direction away from the ion beam flight path, so that the two electrodes are located on either side of the space extending between the opposing ion mirrors. However, other geometries are contemplated. Preferably, the compensation electrodes are electrically biased in use so that the total flight time of the ions is substantially independent of the incident angle of the ions. Since the total drift length traveled by an ion depends on the angle of incidence of the ion, the total flight time of the ion is essentially independent of the drift length traveled.

[0042] The compensation electrode can be biased by an electric potential. In the case of using a pair of compensation electrodes, each electrode in the pair of electrodes can be applied with the same electric potential, or the two electrodes can be applied with different electric potentials. Preferably, in the presence of two electrodes, the electrodes are symmetrically located on either side of the space extending between the relative ion mirrors, and both electrodes are electrically biased with substantially equal electric potentials. In some embodiments, each electrode in a pair of one or more pairs of compensation electrodes is biased with the same electric potential, and the electric potential can be zero volt relative to the electric potential referred to as the analyzer reference potential herein. Typically, the analyzer reference potential will be the ground potential, but it should be understood that the potential of the analyzer can be arbitrarily increased, that is, the potential of the entire analyzer can float up and down relative to the ground. As used herein, zero potential or zero volts is used to represent a zero potential difference relative to the analyzer reference potential, and the term non-zero potential is used to represent a non-zero potential difference relative to the analyzer reference potential. Typically, an analyser reference potential is applied, for example, to a shield such as an electrode used to terminate an ion mirror, and as defined herein is the potential in the drift space between opposing ion optical mirrors in the absence of all electrodes other than those constituting the ion mirror.

[0043] In some embodiments, two or more pairs of relative compensation electrodes are provided. In such embodiments, multiple pairs of compensation electrodes in which each electrode is biased at zero volts are further referred to as non-biased compensation electrodes, and other pairs of compensation electrodes to which non-zero potential is applied are further referred to as biased compensation electrodes. Typically, the non-biased compensation electrodes terminate the field from the biased compensation electrodes. In one embodiment, the surface of at least one pair of compensation electrodes has a profile in the XY plane so that the distance that the surface extends toward each mirror in the region near one or both ends of the mirror is greater than the distance it extends in the central region between these ends. In another embodiment, at least one pair of compensation electrodes has a surface with a profile in the XY plane so that the distance that the surface extends toward each mirror in the region near one or both ends of the mirror is less than the distance it extends in the central region between these ends. In such embodiments, one or more pairs of compensation electrodes preferably extend along the drift direction Y from the region adjacent to the ion implanter at one end of the elongated mirror, and the length of the compensation electrode in the drift direction is substantially the same as the length of the extended mirror, and the compensation electrode is positioned on either side of the space between the mirrors. In alternative embodiments, the compensation electrode surface as described above can be composed of a plurality of discrete electrodes.

[0044] Preferably, in all embodiments of the invention, the compensation electrode does not comprise an ion-optical mirror in which the ion beam encounters a potential barrier at least as large as the kinetic energy of the ions in the drift direction. However, as already stated and will be further described, the compensation electrode preferably generates an electric field component that opposes the motion of the ions in the +Y direction along at least a portion of the length of the ion-optical mirror in the drift direction.

[0045] Preferably, one or more compensation electrodes are electrically biased in use to compensate for at least some of the time-of-flight aberrations produced by the relative ion mirrors. Where there is more than one compensation electrode, the compensation electrodes may be biased at the same potential, or may be biased at different potentials. Where there is more than one compensation electrode, one or more compensation electrodes may be biased at a non-zero potential, while other compensation electrodes may be maintained at another potential, which may be zero potential. In use, some compensation electrodes may be used to limit the spatial extent of the electric field of other compensation electrodes.

[0046] In some embodiments, one or more compensation electrodes may include a plate coated with a resistive material, to which different potentials are applied at different ends of the plate along the Y direction, thereby producing an electrode whose surface has a potential that varies with the drift direction Y. Therefore, the electrically biased compensation electrode can be kept at a constant potential. Preferably, one or more compensation electrodes are electrically biased during use to compensate for the flight time offset in the drift direction due to alignment errors or manufacturing tolerances of the relative ion mirrors, and to make the total flight time offset of the system substantially independent of such misalignment or manufacturing.

[0047] The electric potential applied to the compensation electrode can remain constant or can vary over time. Preferably, the electric potential applied to the compensation electrode remains constant in time while the ions travel through the multi-reflection mass spectrometer. The electric bias applied to the compensation electrode can cause the ions to pass near the compensation electrode, thereby being biased to decelerate or accelerate, and the shape of the compensation electrode therefore changes accordingly, and this example will be further described. As described herein, the term "width" applied to the compensation electrode refers to the physical dimensions of the biased compensation electrode in the + / -X direction. It should be understood that when the ion mirror and / or the compensation electrode are electrically biased respectively, there is an electric potential (i.e., electric potential) and an electric field provided by the ion mirror and / or an electric potential and an electric field provided by the compensation electrode.

[0048] A bias compensation electrode positioned in or near the space between the ion mirrors may be located between two or more non-bias (ground) electrodes in the XY plane, the non-bias electrodes also being positioned in or near the space between the ion mirrors. The shape of the non-bias electrode may be complementary to the shape of the bias compensation electrode.

[0049] In some preferred embodiments, the space between opposing ion-optical mirrors is open in the XZ plane at each end of the drift length.Open in the XZ plane means that the mirrors are not constrained by electrodes in the XZ plane that fully or substantially span the gap between the mirrors. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A time-of-flight mass spectrometer according to an embodiment of the present disclosure is schematically shown.

[0051] Figure 2 An embodiment of an ion implanter in the form of an extraction ion trap is schematically shown.

[0052] Figure 3 An embodiment of an ion implantation optics layout is schematically shown.

[0053] Figure 4 The ion mirror electrode configuration and applied voltages are shown schematically.

[0054] Figure 5 Schematically shown are shaped ion focusing lenses with circular (A) and elliptical (B) shapes, as well as lenses integrated in a prismatic deflector (C).

[0055] Figure 6 Alternative structures of ion focusing lenses are schematically shown.

[0056] Figure 7 The voltage variation of the ion focusing lens in different dispersion energy ranges is shown.

[0057] Figure 8 The variation of the optimum lens voltage for different ion charge states is shown.

[0058] Fig. 9A A flow chart schematically representing a method of mass spectrometry in which predicted or measured data regarding the charge state and / or number of ions of at least one ion species is used to adjust an ion focusing lens voltage.

[0059] Fig. 9B A flow chart schematically representing tandem (MS2) mass spectrometry analysis is shown, in which the charge state of the product ions is predicted from the charge state of the precursor ions from the MS1 scan, and the lens voltages are adjusted in MS2 for the product ion charge state.

[0060] Fig.10 The relationship between the product ion modal charge states and the precursor ion charge states for a number of different proteins is shown.

[0061] Fig.11 A single reflection time-of-flight mass spectrometer with an intermediate ion focusing lens is schematically shown.

[0062] Fig.12 Shown in 1x10 -3 Simulated collisional cooling of ions of different m / z in mbar N2 buffer gas for different times.

[0063] Fig.13 The variation of the best focus lens voltage over time for ion implantation is shown.

[0064] Fig.14 The simulated m / z dependence of the optimum voltage for an out-of-plane lens is shown.

[0065] Fig.15 The voltage applied to the out-of-plane lens is shown as a function of time during ion implantation. DETAILED DESCRIPTION

[0066] Various embodiments of mass spectrometers and mass spectrometry methods according to various aspects of the present disclosure will now be described with reference to the accompanying drawings. These embodiments are intended to illustrate various features of the present disclosure, but are not intended to limit the scope of the present disclosure. It should be understood that changes may be made to these embodiments, but these changes still fall within the scope of the appended claims.

[0067] There is a commercial need for an extended flight path in a time-of-flight analyzer to provide high quality resolution (e.g., >50K) while maintaining high ion transmission, mass range, and tolerance to space charge. One problem in achieving space charge tolerance is controlling the divergence of the ion beam in the analyzer, which varies with the number of ions (ion amount) and the charge state of the ions, because heavy multiply-charged ions have a lower velocity in a direction orthogonal to the electron beam direction under the action of thermal energy compared to light single-charged ions of the same mass / charge ratio. Therefore, the velocity distribution of multiply-charged ions in the orthogonal drift dimension is lower than that of light single-charged ions of the same m / z. The out-of-plane velocity dispersion is also different. The out-of-plane velocity dispersion can be at least partially controlled by an out-of-plane lens. The dispersion of the beam may also vary with changes in m / z, specifically affected by RF ion source conditions and ion cooling limitations, especially when the time in the ion source is limited or gas pressure can be used to heat higher quality ions.

[0068] The present disclosure provides charge state correction of ion beam characteristics on the one hand. One element of the present disclosure is a mass spectrometer, which is combined with an ion focusing arrangement to correct the changes in ion beam characteristics caused by the difference in charge state. This can be achieved by applying a variable voltage to the ion focusing arrangement or the ion source. Another element is a method for controlling the ion focusing arrangement to optimize the different charge state distributions that a mass spectrometer may encounter. Before ion analysis, information about the charge state distribution of sample ions is needed to optimize the voltage setting. In some cases, this information can be easily inferred by understanding the sample and / or application, for example, when the spectrometer is used with one or more charge state filters (e.g., ion mobility separators), so that only ion states of known charge are transmitted to the mass spectrometer. In some cases, the mass spectrometer can perform a pre-scan to determine the ion charge state, and then use the charge state information to perform a more optimized analysis to change the focusing voltage to one or more optimal values ​​to obtain a mass spectrum under conditions optimized for one or more different charge states.

[0069] One problem caused by multiply charged ions is that thermal energy produces much lower ion velocities than singly charged ions. This naturally results in reduced ion beam divergence in a time-of-flight analyzer, which, while superficially attractive, can make space charge effects more severe for multiply charged ions. The effects of low beam emission exacerbate negative space charge effects that occur as the number of charges per ion increases.

[0070] For the converging mirror time-of-flight mass analyzer disclosed by Grinfeld et al. in US9136101B2, the beam divergence is most critical in the drift direction along the length of the relative ion mirror. Here, in one embodiment, it is proposed to add an ion focusing arrangement, which includes an ion focusing lens, also called a drift focusing lens, to control the beam divergence in this dimension.

[0071] Figure 1 A multi-reflection mass spectrometer 2 according to an embodiment of the present disclosure is schematically shown in FIG. A certain amount of ions generated from an ion source (e.g., an electrospray ion source or other ion source) not shown is guided and captured in a pulsed ion implanter 4. In some embodiments, the ions can be mass selected before the pulsed ion implanter 4, for example, using an upstream quadrupole mass filter. An ion beam along a path 5 is formed by extracting a pulse of trapped hot ions from the pulsed ion implanter 4. The beam has a width of less than 0.5 mm, for example, in direction Y (the so-called drift direction). By applying an appropriate extraction voltage to the electrodes (e.g., pull / push electrodes) of the ion implanter 4 to accelerate the ions out of the ion trap, the ion pulses are injected into the space between two opposing elongated mirrors 6 and 8 at high energy (e.g., 4 kV in the present embodiment).

[0072] In this embodiment, the pulsed ion implanter 4 is an ion trap. In particular, the ion trap is a linear ion trap, such as a straight line ion trap (R-Trap) or a curved linear ion trap (C-trap). The ion trap is also a quadrupole ion trap. Figure 2 An embodiment of a linear ion trap suitable for use as an ion implanter 4 is shown. The ion trap is a linear quadrupole ion trap that can receive ions generated by an ion source (not shown) and delivered by an interface ion optical arrangement (e.g., including one or more ion guides, etc.), as is known in the art. The ion trap is composed of a quadrupole electrode set. The inscribed circle has a radius of 2 mm. The ion trap is formed by applying to the opposing elongated quadrupole electrode pairs 41, 42 and 44, 44, respectively. / The ions are radially confined by a reverse RF voltage (1000 V at 4 MHz) on the ion trap; and axially confined by a small DC voltage (+5 V) on each of the DC aperture electrodes (46, 48). The ions are introduced into the ion trap through the holes in the DC aperture electrode 46 and are separated by the background gas (<5x10 -3 The ions are thermalized by collision cooling at 400 mbar. Before the cooled ions are extracted into the ion mirror of the mass spectrometer, the trap potential is raised to 4 kV and then an extraction field is applied by applying -1000 V to the pull electrode 42 and +1000 V to the push electrode (41), causing the positive ions to be discharged into the analyzer through the slit (47) on the pull electrode in the direction shown by the arrow A. Alternatively, the straight quadrupole ion trap shown can be replaced by a curved linear ion trap (C-trap) known in the art.

[0073] In addition to the ion trap 4, there are preferably a number of further ion optical elements ("injection optics") to control the injection of ions into the ion mirrors 6, 8. Such ion injection optics may be considered as part of the ion focusing arrangement. Figure 1In the illustrated embodiment, out-of-plane focusing lenses 54, 58 (i.e., focusing in a direction outside the XY plane, in other words, focusing in the Z direction) are positioned along the ion path between the ion implanter 4 and the first mirror 6. Such out-of-plane focusing lenses may include elongated holes and improve the transmission of ions to the ion mirror. Secondly, when the ion beam enters the ion mirror, a portion (e.g., half) of the incident angle of the ion beam in the X direction may be provided by the angle of the ion trap relative to the X direction, and the remainder (e.g., the other half) of the angle may be provided by the deflection caused by at least one deflector 56 (the so-called injection deflector) positioned in front of the implanter 4. In this embodiment, out-of-plane focusing lenses 54, 58 are located before and after the injection deflector 56. The injection deflector is usually positioned before the first reflection in the ion mirror. The injection deflector may include at least one injection deflector electrode (e.g., a pair of electrodes positioned above and below the ion beam). In this way, the isochronous plane of the ion will be correctly aligned with the analyzer without being misaligned by, for example, 2 degrees due to the corresponding flight time error. This method is described in detail in US 9,136,101. The injection deflector 56 may be Figure 5 Prism-type deflector of the type shown in C, with or without a drift focus lens.

[0074] In some embodiments, all or a majority of the injection angle may be provided by the injection deflector 56. Additionally, it will be appreciated that more than one injection deflector may be used (e.g., in series) to achieve the desired injection angle (i.e., it will be appreciated that the system may include at least one injection deflector, optionally two or more injection deflectors). Figure 3 An example embodiment of the injection optical scheme and a suitable applied voltage are schematically shown. The ion implanter 4 is a linear ion trap, and the above-mentioned +1000V push voltage and -1000V pull voltage are applied to the 4kV trap to extract the ion beam. The ion beam indicated by the arrow then passes through the ion optical device in sequence, which includes a first ground electrode 52, a first lens 54 maintained at +1800V, a prism-type ion deflector 56 (+70V), a second lens 58 maintained at +1200V, and a last ground electrode 60. The first lens 54 and the second lens 58 are aperture lenses (rectangular single lenses) for providing out-of-plane focusing. The deflector 56 provides an inclination angle of the ion beam relative to the X-axis.

[0075] Two ion mirrors 6, 8 are spaced apart from each other and opposite to each other in the X direction, and each mirror is usually elongated along the drift direction Y, which is orthogonal to the X direction. As described above, the pulsed ion beam is injected into the space between the relative ion mirrors 6, 8 at an angle inclined relative to the X direction, so that the ions have a velocity component in the Y direction. Thus, the ion beam is along the ion path 5 that is jagged due to multiple reflections between the ion mirrors in the X direction, and the ion beam drifts in the drift direction Y (+Y direction). The ion mirrors 6, 8 are not absolutely parallel but slightly at an angle to each other (that is, they converge along the drift direction Y), so that after a certain number of reflections (usually N / 2, where N is the total number of reflections between ion injection and detection), the ions drift backward along the Y direction (-Y direction) in the reverse direction of their drift velocity, while continuing to reflect back and forth between the mirrors along the X direction before being detected by the detector 14 located near the ion implanter 4. This arrangement of the converging ion mirror is disclosed in US9136101, the entire contents of which are incorporated herein. With this type of mass spectrometer, total flight paths of 10 meters or more can in practice be obtained. The so-called compensation electrodes described in US9136101 for compensating time-of-flight aberrations are preferably connected to Figure 1 The embodiments shown are used together (but not shown in the figures for clarity).

[0076] Preferably, the ToF mass spectrometer is a high-resolution mass spectrometer. For example, the mass resolution of the high-resolution mass spectrometer at m / z 400 may be greater than 50,000, 70,000 or 100,000. The ToF mass spectrometer preferably has a high mass accuracy, for example, its accuracy is less than 5ppm, or 3ppm under external calibration.

[0077] When different ion species in the ion beam travel from the ion implanter 4 to the ion detector 14, these different ion species are separated according to their m / z so that they arrive at the detector in ascending order of their m / z. The detector is preferably a fast time response detector, such as a multi-channel plate (MCP) or a dynode electron multiplier with magnetic and electric fields for electron focusing. The ion detector 14 detects the arrival of ion species of different m / z and provides a signal proportional to the number of ions of each species. A data acquisition system (DAQ) 30 (including a computer with at least one processor (not shown)) is connected to the detector 14 to receive signals from the detector and is able to determine the flight time of the ions, thereby determining the mass frequency to be generated. The DAQ 30 may include a data storage unit (memory) for storing data from the detector, mass spectra, etc.

[0078] Suitable ion mirrors (such as 6 and 8) are known in the art (eg US 9136101). Figure 4An example of a configuration of an ion mirror is schematically shown in FIG, wherein the ion mirror 6 comprises a mirror of a plurality of pairs of opposing elongated electrodes (e.g., five pairs of elongated electrodes) spaced apart in the X direction, and a first pair of electrodes 6a of the ion mirror is set to ground potential. In each pair of electrodes, one electrode is positioned above the ion beam and the other electrode is positioned below the ion beam (i.e., in the Z direction, so that only one electrode of each pair of electrodes is visible in the figure). Figure 4 An example of a voltage for providing a reflection potential with time focusing for an electrode group (6a-6e) is shown in , where the applied voltage is suitable for focusing 4keV positive ions. For negative ions, the polarity can be reversed. When the ion beam enters the first mirror 6, it is focused on the out-of-plane dimension by the lens effect produced by the first electrode pair 6a of the mirror 6, and is reflected to the time focus by the remaining electrodes 6b-6e of the mirror. As an example, the available space between the mirrors (i.e., the distance in the X direction between the first electrodes (6a, 8a) of each mirror) is 300mm, and the total effective width of the analyzer (i.e., the effective distance in the X direction between the average turning points of the ions in the mirror) is ~650mm. The total length (i.e., in the Y direction) is 550mm to form a suitably compact analyzer.

[0079] After the first reflection in the first ion mirror 6, the ion beam arrives at the ion focusing arrangement in the form of a focusing lens 12, which focuses the ion beam in the drift direction Y, i.e., substantially orthogonal to the ion path. Therefore, in this embodiment, the focusing lens 12 can be referred to as a drift focusing lens. The focusing lens 12 is located in the center of the space between the mirrors, i.e., in the middle between the mirrors in the direction X, preferably focusing in time. The focusing lens 12 in this embodiment is a transaxial lens comprising a pair of relative lens electrodes, and the pair of relative lens electrodes are positioned on either side of the ion beam in the direction Z (perpendicular to the directions X and Y). Specifically, the focusing lens 12 includes a pair of aligned elliptical plates 12a, 12b positioned above and below the ion beam. The lens can be a button-shaped lens. In this embodiment, the plate is 7mm wide (X direction) and 24mm long (Y direction). In various embodiments, a pair of relative lens electrodes can include circular, elliptical, quasi-elliptical or arc-shaped electrodes. The focusing lens 12 can have a converging or diverging effect on the spatial dispersion of the ion beam according to the voltage applied thereto, i.e., applied to the lens electrodes 12a, 12b. The voltage is applied to the focusing lens 12, i.e., to a pair of electrodes forming the focusing lens 12, by a variable DC voltage source 32 controlled by a controller 34. The controller 34 includes a computer and associated control electronics. The computer of the DAQ 30 and the computer of the controller 34 can use the same computer, or different computers can be used. The computer of the controller 34 runs a computer program that, when executed by one or more processors of the computer, enables the computer (and associated control electronics) to control the mass spectrometer to perform the method according to the present invention. The computer program is stored on a computer readable medium. The controller 34 (e.g., its computer) is further communicatively connected to the data acquisition system 30. As described above, the computer of the data acquisition system 30 and the computer of the controller 34 can use the same computer.

[0080] The idea of ​​placing button-shaped electrodes (e.g., circular, flat, elliptical or quasi-elliptical) above and below the ion beam to produce drift focus in a multi-turn ToF instrument, albeit in a periodic manner and constructed within an orbital geometry, is described in US 2014 / 175274A, the contents of which are incorporated herein by reference in their entirety. Such a lens is a form of "trans-axis lens" (see PW Hawkes and E Kasper, Principles of Electron Optics, Vol. 2, Academic Press, London, 1989, the contents of which are incorporated herein by reference in their entirety). Such a lens has the advantage of having a wide spatial acceptance, which is important for controlling elongated ion beams.

[0081] The lens must be wide enough to accommodate the ion beam and so that 3D field disturbances on the sides of the lens do not damage the focusing characteristics. The space between the electrodes of the through-axis lens should also be a compromise between minimizing these 3D disturbances and accommodating the height of the ion beam. In practice, a distance of 4-8mm between the lens electrodes may be sufficient. It is possible to vary the lens curvature from a circular (button) lens to a narrow elliptical lens. Quasi-elliptical structures with short arcs reduce flight time aberrations compared to wider arcs or full circles because the path through them is shorter, but the quasi-elliptical structures require stronger voltages and in extreme cases will begin to cause considerable out-of-plane lenses. This effect can be used to control some combination of drift and out-of-plane dispersion in a single lens, but will limit the range of control over each property. As an aid, areas where strong fields have been applied (such as the ion extraction region of the ion trap 4) can be used to cause or limit drift divergence of the ion beam by the curvature of the ion trap pull / push electrodes. An example of this is the commercial curved linear ion trap (C-trap) described in US 2011-284737 A, the contents of which are incorporated herein by reference in their entirety, in which an elongated ion beam is focused to a point to facilitate injection into an orbitrap. TM In mass spectrometer.

[0082] Figure 5 Different embodiments (A, B) of drift focusing lenses are shown, which include a circular lens plate (electrode) 20 and a quasi-elliptical lens plate 22, and a grounded surrounding electrode 24 for each plate. The lens electrodes 20, 22 are insulated from the grounded surrounding electrode 24. Also shown (C) is the integration of the lens 22 (in this case, a quasi-elliptical (elliptical or near-elliptical), but it can also be circular, etc.) into the deflector, which in this embodiment includes a trapezoidal prismatic electrode structure 26 arranged above and below the ion beam, which acts as a deflector by presenting the incident ions with a constant field angle rather than a curve. The deflector structure includes a trapezoidal or prismatic electrode arranged above the ion beam and another trapezoidal or prismatic electrode arranged below the ion beam. The lens electrode 22 is insulated from the deflector (i.e., the trapezoidal prismatic electrode), which is positioned in the deflector and then insulated from the grounded surrounding electrode 24. Placing the lens within a deflector structure with a wide spatial acceptance is a space-saving design.

[0083] Figure 6Other possible embodiments of suitable lenses are shown in , such as: an array of mounted electrodes 30 (e.g., mounted on a printed circuit board (PCB) 32) (A) separated by resistor chains to simulate the field curvature produced by shaped electrodes; a multipole rod assembly for producing a quadrupole or quasi-quadrupole field (B), such as a 12-rod based lens with a quasi-quadrupole configuration and showing relative rod voltages (V); and an aperture-based lens, such as a conventional aperture single lens structure (C). Figure 5 and Figure 6 This embodiment of the focusing lens shown can be applied to all embodiments of the ToF mass spectrometer.

[0084] The best position of the focusing lens 12 may be after the first reflection but before the fourth or fifth reflection in the ion reflection system, i.e., it is located relatively early in the system, which has >20 reflections. The best position of the focusing lens may be after the first reflection but before the second or third reflection (particularly before the second).

[0085] Figure 1 The configuration of a converging mirror ToF mass spectrometer is shown, in which the focusing lens 12 is located after the first ion reflection, in this case being incorporated into the drift energy reducing deflector 16. It may be preferred that the focusing lens 12 installed after the first reflection also incorporates the ion deflector 16, e.g. Figure 5 The ion deflector of the prism type shown (Example C). The deflector can be tuned to adjust the injection angle to the desired level and / or correct any ion beam deflection caused by mechanical deviations in the ion mirrors. In addition, errors in the mirror manufacturing or installation process will cause small flight time errors at each reflection because ions on one side of the ion beam have a shorter flight path than ions on the other side, and these ions are preferably corrected by adding two compensations in the space between the ion mirrors as described above.

[0086] In some embodiments, it has been found useful to use an additional focusing lens mounted between the ion implanter 4 and the first reflector and operating in a divergent manner (focusing in the same drift (Y) direction as the focusing lens 12) because it provides some control over the ion beam divergence before the ion beam reaches the focusing lens 12. Such an additional focusing lens may be mounted within the ion implantation deflector 56 as described above and may be mounted within the ion implantation deflector 56. Figure 3is shown in the injection optical scheme. Therefore, in some embodiments, the ion focusing arrangement may include: a first focusing lens, which is positioned before the first reflection in the ion mirror, for focusing the ion beam in the drift direction Y, wherein the first focusing lens is preferably a divergent lens; and a second focusing lens 12, which is positioned after the first reflection in the ion mirror, for focusing the ion beam in the drift direction Y, and the divergence of the second focusing lens on the beam may be smaller than that of the first focusing lens or may be positively converging. The additional drift focusing lens may be constructed in the same manner as the focusing lens 12, for example, as Figure 5 A through-axis lens having a circular, elliptical or quasi-elliptical shape as shown, or Figure 6 However, the additional focusing lens will typically have a different voltage applied to it than the focusing lens 12 because it acts on a different ion beam width and provides different focusing characteristics.

[0087] The ion beam is focused in an out-of-plane (out-of-XY plane) dimension by a pair of lenses 54, 58 and is directed into the first ion mirror 6 of two opposing ion mirrors 6, 8. After the first reflection, the ions encounter the combined deflector / focusing lenses 12, 16, whereby the deflector 16 minimizes the injection angle (to maximize the number of ion reflections within the mirror length) and the lens 12 focuses the ion beam in the Y (drift) direction. The lens 12 can adjust the focus of the ion beam based on the charge state of at least one species of ions in the ion beam that is desired to be accurately detected. The lens 12 preferably normalizes the beam spatial dispersion of multiply charged ions to the beam spatial dispersion of singly charged ions. After passing through the focusing lens 12, the beam then enters the second ion mirror 8, after which the ions pass back and forth between the two mirrors after multiple reflections as they move down the drift length. Finally, the converging mirror (and Figure 1 The additional ToF compensation electrode (not shown) in the ion implanter 4 reflects the ions back in the drift direction and finally focuses the ions on the ion detector 14 located near the ion implanter 4.

[0088] Figure 1 Simulations of the system shown in show that at the point of maximum beam width divergence, i.e. at the reflection point in the drift direction Y, the width of singly charged ions in the drift direction Y reaches 28 mm of full width at half maximum (FWHM), but the width of 10+ ions is only 7 mm; this results in a significantly reduced space charge tolerance. This can be corrected by applying +70 V to the electrodes of the focusing lens 12, and 0 V for singly charged ions, assuming that the analyzer characteristics without lenses are tuned by design to the singly charged thermal distribution of the ions, so that the space charge tolerance can be preserved.

[0089] Thus, the present disclosure provides for tuning the voltage of the focusing lens 12 in a manner that depends on the charge state of the analyte. For example, for relatively higher charge states (multiple charge states), the magnitude of the voltage applied to the converging focusing lens can be reduced (convergence voltage), or the voltage on the diverging focusing lens can be increased (divergence voltage) compared to relatively lower charge states (e.g., single charge states) so that the beam remains at an optimal or near-optimal divergence state for ions having the higher charge state. Variations in the voltage applied to the out-of-plane focusing lenses 54, 58 will also have values ​​that maintain optimal ion beam dispersion orthogonal to the drift direction. However, for Figure 1 In the system shown in , focusing in this dimension is less critical, where the dispersion in this plane is relatively narrow, but may be potentially significant. Therefore, a variable voltage may be applied to an ion focusing arrangement that focuses the ion beam in one or two directions orthogonal to the ion path. Since ion beam dispersion in a time-of-flight spectrometer is determined by lenses (e.g., Figure 1 The drift control lens 12 and the out-of-plane lenses 54, 58 are controlled, so it is beneficial to change the voltages on these lenses to optimally correct for changes in these properties.

[0090] right Figure 1 The mass spectrometer shown in FIG. 1 is modeled (using MASIM 3D simulation software), and ion trajectories with varying dispersion energies are simulated. For a series of different dispersion energies, the voltage of the ion drift focusing lens 12 is tuned to the optimal value, and the results are shown in FIG. Figure 7 (optimum lens voltage on the vertical axis versus the dispersion velocity for thermalized singly charged positive ions on the horizontal axis). In this model, a range of about 2 times the velocity is correctable (4 times the thermal energy), but there is a limit when the width of the highly dispersed beam at the lens exceeds the spatial acceptance of the lens. Since the charge state of the ion corresponds directly to the dispersion velocity, the variation of the optimum lens voltage for different charge states can be roughly determined, and the variation of this lens voltage (vertical axis) with the charge state of the ion (horizontal axis) is in Figure 8 In practice, it is preferable to calibrate the lens voltages on the spectrometer itself rather than using values ​​derived from simulations.

[0091] The present disclosure enables the control and optimization of ion focusing for different charge states that may be present in the charge state distribution that the analyzer may encounter. Before optimizing the ion focusing settings, it is necessary to have some knowledge of the ion charge state distribution of the sample prior to ion analysis. In some cases, this can be inferred or predicted based on knowledge of the type of sample and / or application or the mass spectrometer (where it includes a charge state filter, such as an ion migration device upstream of a pulsed ion implanter) so that only ions of known charge state are delivered to the ToF mass spectrometer, or a pre-scan is performed to determine the ion charge state before performing one or more analytical scans.

[0092] exist Fig. 9A A flow chart of an embodiment of the method according to the present disclosure is shown in FIG. Figure 1 In the illustrated mass spectrometer embodiment, the controller 34 uses data regarding the charge state and / or amount of at least one species of ions in the ion beam to control the variable voltage source 32 and select a voltage to be applied to the ion focusing lens 12. The charge state of the various ions can be obtained in different ways. The charge state can be an approximate value or an exact value of the charge state. The charge state of the ions can be predicted, for example, based on a priori knowledge of the type of sample used to generate the ions. Thus, a user can input information into the controller (i.e., into the controller computer through a user interface) based on one or more charge states of ions to be generated from a particular sample, or the type of sample (e.g., sample source (e.g., blood), molecular species (e.g., metabolites), molecular class (e.g., protein), etc.), so that the controller can predict the expected charge state based on the sample type. Thus, in Fig. 9A In the step 90 shown, the controller obtains the predicted charge state data. Alternatively, one or more charge states of the ions can be measured in the pre-scan, for example, by analyzing one or more mass spectra acquired by the detector and the data acquisition system 30. The data acquisition system 30 can use conventionally used algorithms such as THRASH and advanced peak detection to determine the charge state of the ions from the mass spectrum generated by the data acquired by the detector. The controller therefore obtains the measured charge state data in step 92. The measured charge state data can be obtained alternatively or additionally to predict the charge state data, for example to verify or modify the predicted charge state data. The ion quantity of the ion species can be obtained in different ways, for example, by obtaining the amount of the ion from the peak intensity of the ion species measured in one or more mass spectra acquired from the detector in the pre-scan by the data acquisition system 30. Therefore, in some embodiments, the pre-scan (i.e., preliminary mass spectrum) is first acquired by the detector and the data acquisition system to obtain data on the charge state and / or quantity of at least one type of ions in the ion beam in step 92.

[0093] The controller 34 is communicatively connected to the data acquisition system 30 so that in step 94 the controller can use the acquired data about the charge state and / or ion abundance to control the variable voltage source 32. Additionally or alternatively, in this step, the controller can use user input data about the charge state and / or ion abundance to control the variable voltage source 32. The controller 34 uses a control signal to control the variable voltage source 32. The controller includes a computer that is programmed to control the variable voltage supply based on data about at least one charge state and / or amount of at least one ion species in the ion beam. For example, in some embodiments, when the data about the charge state indicates that only singly charged ions are present and / or a mass spectrum should be acquired using ion beam conditions optimized for singly charged ions, the controller 34 controls the variable voltage source 32 to apply a first voltage (V1) to the ion focusing lens 12 according to the program. When the data about the charge state indicates the presence of multiply charged ions and / or that a mass spectrum should be acquired using ion beam conditions optimized for multiply charged ions, the controller 34 controls the variable voltage source 32 to change the voltage applied to the focusing lens 12 from a first voltage (V1) to a second voltage (V2) different from V1.

[0094] In this way, depending on one or more charge states of the ions in the ion beam, a plurality of different voltages may be applied to the focusing lens from the variable voltage source 32. For example, a first voltage (V1) may be applied to the focusing lens 12 for singly charged ions, a second voltage (V2) may be applied for multiply charged ions of charge +2 to +5, a third voltage (V3) may be applied for multiply charged ions of charge +6 to +10, and so on. In some embodiments, a different voltage may be applied for each different charge state, such as voltage V1 for charge +1, voltage V2 for charge +2, voltage V3 for charge +3, ... and so on. In some embodiments, different voltages may be applied for different charge state ranges, such as voltage V1 for charge state +1, voltage V2 for charge +2 to +4, voltage V3 for charge +5 to +7, ... and so on.

[0095] In addition to the effects caused by higher charge states, strong ion peaks or adjacent strong ion peaks will cause space charge effects within the spectrometer which increase the ion beam dispersion and can therefore also be at least partially corrected by voltage changes on the ion focusing lenses, especially the drift focusing lens. Just as the voltage changes with charge state, it is necessary to have advance knowledge of the strong ion peaks (data packets) or clusters of peaks as they approach the associated focusing lenses so that the voltage can be adjusted. As described above, this can be accomplished by a prescan or, in some embodiments, can be accomplished using an inductive charge or current detection device having electrodes which are preferably positioned near the ion beam upstream of the focusing lens, preferably near the ion source where the ions are first focused, as this maximizes the resolution and signal strength of the detection device. Figure 1 In the spectrometer shown, this electrode is preferably placed between the ion implanter 4 and the first out-of-plane lens 54, because the first focus is located here and the time available for detection and voltage response is maximized. As an example, a strong ion peak or packet (e.g., about 100-1000s ions) will induce a detectable current on the charge detector, thereby generating a signal that can trigger a change in the lens voltage to correct for the space charge of the ion packet.

[0096] Therefore, in some embodiments, when the data on the number of ions of the ion species indicates that the number is below a first threshold value set by a computer program and / or that the ion beam conditions optimized for the ions of the ion species should be used to acquire a mass spectrum, the controller 34 controls the variable voltage source 32 to apply a first voltage (V1) to the ion focusing lens 12 according to the program. When the data on the number of ions of the ion species indicates that the number is above the first threshold value and / or that the ion beam conditions optimized for the ions of the ion species should be used to acquire a mass spectrum, the controller 34 controls the variable voltage source 32 to change the voltage applied to the focusing lens 12 from the first voltage (V1) to a second voltage (V2) different from V1. When the data on the number of ions of the ion species indicates that the number is above the first threshold value and / or that the ion beam conditions optimized for the ions of the ion species should be used to acquire a mass spectrum, the controller 34 controls the variable voltage source 32 to change the voltage applied to the focusing lens 12 from the first voltage (V1) to a second voltage (V2) different from V1. In some embodiments, different voltages may be applied for different ranges of ion numbers, for example, voltage V1 may be applied for ion numbers in the range of I1 to I2, voltage V2 may be applied for ion numbers above I2 to I3, voltage V3 may be applied for ion numbers above I3 to I4, and so on.

[0097] The voltage applied to the ion focusing lens by the variable voltage source 32 may be a function of the charge state and amount of ions of at least one ion species in the ion beam. Thus, the voltage V applied to the lens may be given by V=f(z, I), where f(z, I) is a function that depends on the terms z and I, where the terms z and I represent the charge state (z) and the amount of ions (I), respectively.

[0098] The voltage value applied based on the charge state and / or number of ions of at least one ion species in the ion beam can be determined by a calibration procedure. In one embodiment, one or more calibration mixtures can be ionized to provide one or more ion calibration mixtures, which are mass analyzed by a spectrometer. The calibration mixtures contain molecules that form ions, typically known by their m / z. Examples of calibration mixtures are available from Thermo Fisher Scientific TM Obtained Pierce TM FlexMix TM Calibration solution, which is a mixture of 16 high purity ionizable components (mass range: 50 to 3000 m / z) designed for positive and negative ionization calibration, providing mainly singly charged ions. Calibration solutions for providing multiply charged ions can contain, for example, protein mixtures; proteins commonly used in calibration solutions include ubiquitin, myoglobin, cytochrome C and / or carbonic anhydrase, but many other proteins and / or peptides can be used in calibration mixtures as needed. For example, Pierce TM The retention time calibration mixture contains a mixture of 15 known peptides. During the calibration process, one or more ion calibration mixtures are mass analyzed (mass spectra are recorded) at different voltages applied to the ion focusing arrangement 12 to determine the dependence of the recorded m / z values ​​and peak intensities on voltage changes for different ion masses (m), charge states (z) and peak intensities. Therefore, for a given m, z and / or peak intensity (number of ions), the optimal voltage to be applied to the ion focusing arrangement 12 can be determined. In some aspects of the present disclosure, an additional or alternative calibration procedure using one or more calibration mixtures can be performed, wherein the dependence of the recorded m / z values ​​and peak intensities is determined for pressure and / or voltage changes in the ion injector (ion trap) 4. This dependence of the recorded m / z values ​​and peak intensities (on the ion focusing arrangement voltage, the injector pressure and / or the injector voltage) can be approximated by a function (e.g., a smoothing function, such as a spline). The approximation function can also be used, for example, to perform post-acquisition corrections on the acquired mass spectrum before saving the spectrum. Preferably, the determined multidimensional dependencies can be approximated by such functions (eg splines) and used for on-line correction of the acquired mass spectra before saving them.

[0099] Using the adjusted optimized voltage on the ion focusing lens, a mass spectrum can be obtained under optimal ion beam conditions for a specific charge state and / or number of at least one type of ion for which the voltage is set, such as Fig. 9A After acquiring the desired number of mass spectra using the optimized voltages, if further optimized mass spectra need to be acquired, rather than optimizing for other charge states and / or numbers of at least one species of ions in the ion beam, the controller can return to step 94 to adjust the voltage applied to the ion focusing lens to a different value to optimize the ion beam conditions for the specific other charge states and / or numbers of ions, and one or more additional mass spectra can be acquired, etc. When no additional spectra are needed, the method ends.

[0100] In another embodiment, if Figure 1 As generally shown in , the mass spectrometer also includes an ion fragmentation device, such as a collision induced dissociation (CID) cell or other dissociation cell, located upstream of the ion injector 4 to enable MS2 analysis of ions. A mass filter (such as a quadrupole mass filter) is also located upstream of the ion fragmentation device for selecting ions of a specific m / z to be fragmented. In MS2, the controller 34 can be configured to control a voltage source to change the voltage supplied to the ion focusing arrangement based on data on the charge state and / or amount of at least one type of product ions obtained from the MS1 analysis of ions performed before the MS2 analysis. In this way, the adjustment of focusing and ion beam dispersion in the MS2 (product ion) scan can be based on the charge state and / or abundance data obtained from the previous MS1 (precursor ion) scan. The controller computer can be configured to, for example, use fragmentation knowledge or rules about the fragmentation behavior of parent ions to predict at least one charge state of the product ions in the MS2 analysis according to at least one charge state of the parent ions obtained in the MS1 analysis.

[0101] Thus, in certain embodiments, the present disclosure provides a method for tandem (MS2) mass spectrometry analysis, wherein the charge state of the parent ion is determined during an MS1 ​​scan, as routinely performed by algorithms such as THRASH and advanced peak detection. For an MS2 scan, the charge state of the product ion will depend on the charge state of the parent ion, as well as other factors such as the dissociation method and conditions (normalized collision energy, gas selection, etc.). A broad relationship can be used to help infer the likely product ion charge state, and to set the focusing lens voltage accordingly to correct for the charge state. A simple flow chart of this method is shown in FIG. Fig. 9BAs shown in . In step 110, an MS1 ​​scan of the precursor ions is performed. The MS1 scan is analyzed using a charge state detection algorithm to determine the charge state distribution that exists between the precursor ions. In step 120, the mass spectrometer then uses a mass filter to select a specific precursor ion species for MS2 analysis. Based on the charge state of the determined precursor ions, in step 130, the computer of the controller predicts the charge state of the product ions, i.e., the charge state distribution, and in step 140, the controller adjusts the voltage applied to the ion focusing arrangement (charge state correction device) by the variable voltage supply to an optimal value, which is determined for the charge state distribution of the product ions. In step 150, the mass spectrometer uses the voltage setting of the ion focusing arrangement set in the previous step 140 to acquire an MS2 scan. Then in step 160, a decision is made by the computer of the controller so that if there are other precursors that need to be analyzed by MS2 analysis, another precursor is selected, and the method is performed again from step 120, and if there are no remaining precursors to be analyzed by MS2, the method terminates or returns to step 110 to prepare for acquiring a new MS1 mass spectrum.

[0102] It is not always easy to predict the charge state relationship between precursor ions and product (fragmented) ions. Obviously, only highly charged precursors can produce highly charged fragmented ions, and intuitively, the greater the charge of the precursor, the higher the charge of the fragmented ions. Madsen et al. (Anal. Chem., 2009, 81(21), pp. 8677-8686) showed that as the charge state of the precursor increases, the product ions both increase the modal charge state and expand the charge state distribution. However, this trend was observed to vary with different protein ions, such as Fig.10 The protein ions shown are for ubiquitin, myoglobin, cytochrome C, and carbonic anhydrase. However, it may be beneficial to simply tune the ion focusing arrangement as a simple function of the charge state of the precursor ions. For example, based on Fig.10 For the data in , a linear trend of 0.45x will fit. However, it is ideal to optimize the function for your specific samples and conditions.

[0103] The variable voltage source together with the controller can be configured to change the voltage supplied to the ion focusing arrangement from one m / z scan to a subsequent m / z scan (i.e., between scanning one ion pulse and subsequently scanning another ion pulse). In this way, an earlier scan can be used to derive charge state and / or abundance data of at least one species of ions, which is used to control the voltage applied to the ion focusing arrangement in a later scan. The earlier scan may be the immediately preceding scan to the later scan, or may be two, three or more earlier scans. In one method, the voltage source is configured to change the voltage supplied to the ion focusing arrangement based on charge state data and / or spatial charge data (data about the number of ions of different species) of ions in the ion beam obtained by pre-scanning the ion pulses from the ion implanter.

[0104] The variable voltage source together with the controller can be configured to change the voltage supplied to the ion focusing arrangement based on the data of the charge state and / or amount of at least one kind of ions in the ion beam acquired by the detector and / or in some embodiments using a charge measuring device for measuring the charge in the ion beam. The charge measuring device can be located upstream of the ion focusing arrangement and can be located in or near the ion path. The charge measuring device can include, for example, a grid located in the ion path or an image current measuring device located near the ion path. Therefore, the voltage source can be configured to change the voltage supplied to the ion focusing arrangement within the m / z scan of a single ion pulse from the ion implanter. In other words, the voltage source can be configured to change the voltage supplied to the ion focusing arrangement based on the data of the charge state and / or amount of at least one kind of ions in the ion beam acquired from the ions in flight during the m / z scan of the ion pulse from the ion implanter. The data of a given ion type in the ion beam is acquired by upstream charge measurement, and the data is provided to the controller to adjust the voltage supplied to the ion focusing arrangement by the variable voltage source when the ions of the given ion type arrive at the ion focusing arrangement. Thus, at least one variable voltage may be variable in a time-dependent manner related to the arrival times of ions with different charge states and / or different space charges at the ion focusing arrangement, i.e. varies synchronously with the arrival of different ion species at the ion focusing arrangement.

[0105] The voltage applied to the ion focusing arrangement for at least one species having a multiply charged state may be such that the spatial dispersion of the ions in the multiply charged state is normalized to the spatial dispersion of the singly charged ions. In other words, the voltage supplied to the ion focusing arrangement may be adjusted so that the spatial dispersion of the multiply charged ion species is substantially the same as the average spatial dispersion for the singly charged ions.

[0106] The variable voltage source together with the controller can be configured to apply voltage to the ion focusing arrangement based on the charge state of a single ion species in the ion beam. In some other embodiments, the variable voltage source together with the controller can be configured to apply voltage based on multiple charge states of different ion species in the ion beam, such as based on the representative charge state values ​​of multiple different ion species of different charge states. For example, the representative charge state can be the average charge state of multiple different ion species with different charge states. In this way, the applied voltage can be a compromise between the optimal voltages of many different ion species with different charge states. Similarly, in some embodiments, where the variable voltage source together with the controller is configured to apply voltage to the ion focusing arrangement based on at least one amount of ions, at least one amount of ions can be the amount of ions of a single ion species. In some other embodiments, at least one amount of ions can be multiple amounts of ions of different ion species. At least one amount of ions can include the amount of representative ions of multiple different ion species. For example, the representative amount of ions can be the average ion amount of multiple different ion species with different amounts of ions (different abundances) in the ion beam. In this way, the applied voltage can be a compromise between the optimal voltages for many different ion species with different abundances.

[0107] It should be understood that Figure 1 The mass spectrometer design shown is only one example of a time-of-flight mass spectrometer, and the teachings of the present disclosure can be used with time-of-flight mass spectrometers. In general, the present disclosure is broadly applicable to other types, including more common or simpler time-of-flight instruments, as long as they include at least one ion focusing lens. For example, the present disclosure is applicable to Fig.11 A single reflection time-of-flight mass spectrometer is schematically shown in and disclosed in US9136100. A pulsed ion source 200 generates ions, and the ion beam passes through two intermediate lenses 202 located between the ion source 200 and an ion mirror 204 (in addition to the lens close to the ion source) for controlling the ion beam dispersion in the y and z directions orthogonal to the ion beam path. After reflection in the ion mirror, the ions are detected by an ion detector 206. The lenses 202 can have a voltage supplied by a variable voltage source so that they can be adjusted as described herein to optimize the ion beam performance based on the charge state and / or number of ions of at least one ion species, or in fact generally to optimize the ion beam performance based on space charge, temperature, m / z, etc. The through-axis focusing lenses described herein are particularly suitable for use in Figure 1 Converging mirror mass spectrometer shown. For a common single-cycle time-of-flight mass spectrometer, a single lens (eg, an Einzel lens) as described in US9136100 may be used to provide adjustment of the electron beam divergence depending on the charge state and / or number of ions of the ion species.

[0108] In some mass spectrometers, the total beam divergence may be determined at least in part by the initial spatial distribution of ions in the ion implanter, which initial spatial distribution is also typically a function of charge state and may be controlled by, for example, varying the trap conditions, such as adjusting the trapping voltage to vary the axial potential in accordance with one or more charge states of the ions present. For example, one or more trapping voltages may be varied in a manner that depends on different charge states. Thus, variations of the above applications are based on the recognition that space charge effects in an RF ion trap used as an ion implanter may also be a factor that may require control of the focusing voltage to achieve optimal beam characteristics because the size and effective temperature of the initial ion cloud in the ion trap vary. However, for time-of-flight mass analysers, it is generally preferred that this not be a factor because allowing the ion cloud to expand affects resolution by increasing the turnover time of the ion trap. The initial axial distribution of ions in a linear trap depends on the axial DC potential of the well. For Figure 2 The linear ion trap shown in , which is controlled by a DC voltage applied to the end hole. Since multiply charged ions are more affected by the DC potential well than singly charged ions, they are subjected to greater compression and thus suffer greater space charge effects in the ion trap. Therefore, in another aspect of the present disclosure, the ion implanter for forming an ion beam is an RF ion trap having a DC potential well to capture ions provided by one or more electrodes, and a variable voltage source can provide at least one voltage to the one or more electrodes, which voltage depends on the charge state of at least one species of ions in the ion trap, thereby finely adjusting the DC potential according to the expected ion charge state.

[0109] Another variation of the above application of the ion focusing lens is to control the voltage applied to the lens to compensate for changes in ion energy caused by the fact that higher mass ions are not properly cooled in the ion trap injector 4 compared to lower mass ions. Conventionally, ions are heated in an ion trap used as an ion injector by collision cooling in the ion trap before being extracted into the mass analyzer. However, effective cooling of higher m / z ions requires high background gas pressures, which may produce excessive pressure in the analyzer itself, thereby hindering ion transmission, or causing fragmentation of analyte ions due to high-energy collisions extracted from the trap. Higher m / z ions may encounter further difficulties because their larger size increases the probability of accidental collisions in flight. In instruments operating at scan frequencies >100 Hz, the long cooling times required for ideal low-pressure cooling are not actually available at all. If there is not enough time or pressure to heat the ions in the required mass range, the dispersion of ions in this mass range will change. However, being able to change the focusing lens voltage to compensate for changes in dispersion is very useful for maintaining performance over the entire required mass range. Controlling the focusing lens voltage with ion mass can also allow shorter cooling times to be used, allowing faster instrument operation. Thus, the voltage applied by the variable voltage source to the ion focusing arrangement may be varied in a time-dependent manner that is related to the arrival times of ions of varying m / z. Such adjustment of the focusing lens voltage may be applied, i.e. in addition to an adjustment of the focusing voltage suggested for the charge state distribution and / or number of ions of at least one ion species in the beam. Thus, the adjustment of the focusing voltage may be a function of the charge state and / or number of at least one ion species, and the ion mass (arrival time at the ion focusing arrangement).

[0110] In the simulation example, the ion trap is arranged with 1x10 -3 mbar of nitrogen buffer gas and the ions were injected at 1 eV. The cooling time was longer than 1 millisecond (ms) as Fig.12 If the ions are subsequently extracted from the trap after cooling for 1 ms, the mass range m / z 100-2000 will reach the drift control lens within 7-30 μs. Applying the simulated drift mirror optimum versus energy with respect to the ion arrival time gives a time-dependent voltage of Fig.13 . In practical cases, it is reasonable to use an approximate voltage with a linear trend, as the most efficient way to produce such rapid voltage changes is to switch between 2 voltage levels (0 to -50V in this case) using a transistor-based switch and appropriate resistors and capacitors to control the rise time to about 25μs. Alternatively, a function generator can be used to provide a better calibration fit. The timing and gradient of this dynamic voltage can also be changed to fit the expected ionic charge state distribution.

[0111] In an RF ion trap, ions at the low m / z end of the stable m / z range occupy a smaller volume than high m / z ions. Therefore, ideally, the optimal voltage applied to the focusing lens of the mass spectrometer will have some m / z dependence related to the initial spatial distribution, as shown. Figure 1 In the ToF mass spectrometer shown, the ion injector 4 is a linear RF ion trap in which ions are trapped along the long axis by a DC potential well that is aligned with the drift direction Y in the mass spectrometer. This means that there should not be much initial spatial variation in m / z along this drift direction (beyond the m / z-dependent charge state distribution of small molecules), so there is little benefit in applying correction voltages to the drift control electrodes. However, the out-of-plane lenses 54, 58 have considerable m / z dependence in their optimum voltage from the ion trap source, and simulation results show that the m / z dependence of the ion trap source is 0.0447°. Fig.14 Based on this, the voltage function applied to the second out-of-plane lens 58 is as follows: Fig.15 Again, for practical electronic design reasons, it is preferred to keep this approximately linear, with the voltage being switched between two levels with an appropriate time constant.

[0112] The following numbered clauses define various embodiments of the invention.

[0113] 1. A time-of-flight mass spectrometer, comprising:

[0114] a pulsed ion implanter for forming an ion beam that travels along an ion path;

[0115] a detector for detecting ions in the ion beam, the ions arriving at the detector from time to time according to their m / z values;

[0116] an ion focusing arrangement located between the ion implanter and the detector for focusing the ion beam in at least one direction orthogonal to the ion path; and

[0117] A variable voltage source for supplying at least one variable voltage to the ion focusing arrangement, the at least one variable voltage being dependent on the charge state and / or amount of at least one species of ions in the ion beam.

[0118] 2. A time-of-flight mass spectrometer according to claim 2, wherein the voltage source is configured to change the voltage supplied to the ion focusing arrangement based on data about the charge state and / or amount of at least one type of ions in the ion beam acquired by the detector and / or a charge measurement device for measuring the charge in the ion beam.

[0119] 3. A time-of-flight mass spectrometer according to clause 1 or 2, further comprising a controller configured to control the voltage supply using data regarding the charge state and / or amount of at least one type of ions in the ion beam.

[0120] 4. A time-of-flight mass spectrometer according to clause 3, wherein the controller is configured to predict at least one charge state of the product ions in the MS2 analysis from at least one charge state of the parent ions obtained in the MS1 analysis.

[0121] 5. A time-of-flight mass spectrometer according to any preceding clause, wherein the variable voltage source is configured to vary the variable voltage supplied to the ion focusing arrangement from one m / z scan of an ion pulse from the ion implanter to a subsequent scan of another ion pulse from the ion implanter.

[0122] 6. A time-of-flight mass spectrometer according to any preceding clause, wherein the variable voltage source is configured to vary the variable voltage supplied to the ion focusing arrangement based on data regarding the charge state and / or quantity of ions in the ion beam acquired by a pre-scan of ion pulses from the ion implanter.

[0123] 7. A time-of-flight mass spectrometer according to any preceding clause, wherein the variable voltage source is configured to vary the variable voltage supplied to the ion focusing arrangement within an m / z scan of ion pulses from the ion implanter.

[0124] 8. A time-of-flight mass spectrometer according to claim 7, wherein the variable voltage source is configured to vary the voltage supplied to the ion focusing arrangement based on data regarding the charge state and / or quantity of at least one species of ions in the ion beam acquired from ions in flight during an m / z scan of an ion pulse from the ion implanter.

[0125] 9. A time-of-flight mass spectrometer according to clause 7 or 8, wherein the at least one variable voltage is variable in a time-dependent manner, which is related to the arrival time of ions of different charge states and / or different spatial charges at the focusing arrangement.

[0126] 10. A time-of-flight mass spectrometer according to any of the preceding clauses, wherein the charge state of the ions includes multiple charge states, and the variable voltage source is configured to vary the variable voltage supplied to the ion focusing arrangement to normalize the spatial dispersion of the ions in the multiple charge states to the spatial dispersion of the singly charged ions.

[0127] 11. A time-of-flight mass spectrometer according to any preceding clause, wherein the at least one charge state is a charge state of a single ion species.

[0128] 12. A time-of-flight mass spectrometer according to any one of clauses 1 to 10, wherein the at least one charge state is a plurality of charge states of different ion species.

[0129] 13. A time-of-flight mass spectrometer according to any preceding clause, wherein the at least one charge state is a representative charge state of a plurality of different ion species.

[0130] 14. A time-of-flight mass spectrometer according to clause 13, wherein the representative charge state is an average charge state of the plurality of different ion species.

[0131] 15. A time-of-flight mass spectrometer according to any preceding clause, further comprising at least one ion mirror configured to reflect the ion beam along the ion path.

[0132] 16. A time-of-flight mass spectrometer according to clause 15, further comprising a plurality of ion mirrors configured to reflect the ion beam multiple times along the ion path.

[0133] 17. The time-of-flight mass spectrometer according to claim 16 further includes two ion mirrors, which are spaced apart and opposite to each other in direction X, each mirror being substantially elongated along a drift direction Y, which is orthogonal to the direction X, and configured to provide a zigzag ion path by reflecting the ion beam multiple times in the X direction between the ion mirrors while the ion beam drifts along the drift direction Y.

[0134] 18. A time-of-flight mass spectrometer according to any preceding clause, wherein the ion path lies in a plane and the ion focusing arrangement is used to focus the ion beam along a direction within the plane.

[0135] 19. A time-of-flight mass spectrometer according to any preceding clause, wherein the ion path lies in a plane and the ion focusing arrangement is used to focus the ion beam in an out-of-plane direction.

[0136] 20. A time-of-flight mass spectrometer according to any of the preceding clauses, wherein the ion focusing arrangement comprises at least one ion focusing lens, and the voltage source is used to supply at least one variable voltage to the at least one ion focusing lens, wherein the at least one ion focusing lens is selected from the following items: a transaxial lens, a single lens and a multipole lens.

[0137] 21. A time-of-flight mass spectrometer according to any preceding clause, comprising at least one ion mirror along the ion path, the ion mirror being configured to reflect the ion beam, wherein the at least one ion focusing lens is located before a first reflection in the at least one ion mirror.

[0138] 22. A time-of-flight mass spectrometer according to clause 21, comprising a plurality of ion mirrors configured to reflect the ion beam multiple times, wherein at least one ion focusing lens of the ion focusing arrangement is located after a first reflection and before a fifth reflection in the ion mirror.

[0139] 23. A time-of-flight mass spectrometer according to any of the preceding clauses, further comprising an ion fragmentation device upstream of the ion injector for performing MS2 analysis of ions, wherein the voltage source is configured to change the voltage supplied to the ion focusing arrangement in the MS2 analysis based on data regarding the charge state of at least one species of product ions, the data being derived from an MS1 ​​analysis of the ions performed prior to the MS2 analysis.

[0140] 24. A mass spectrometry analysis method, comprising:

[0141] forming an ion beam from a pulsed ion implanter that travels along an ion path;

[0142] detecting ions in the ion beam, the ions arriving at a detector from time to time according to their m / z values;

[0143] focusing the ion beam in at least one direction orthogonal to the ion path using an ion focusing arrangement between the ion implanter and the detector; and

[0144] At least one variable voltage is supplied to the ion focusing arrangement from a variable voltage source, wherein the variable voltage depends on the charge state and / or amount of at least one species of ions in the ion beam.

[0145] 25. A mass spectrometry method according to claim 24, wherein the dependence of the at least one variable voltage on the charge state and / or amount of at least one type of ions in the ion beam has been determined by calibration, wherein the calibration comprises detecting one or more ion calibration mixtures having a varying voltage supplied to the ion focusing arrangement so as to determine the dependence of the m / z values ​​and / or peak intensities detected under different charge states and / or different amounts of ions on the variable voltage.

[0146] The terms mass and m / z are used interchangeably herein, so reference to one includes reference to the other.

[0147] As used herein (including in the claims), unless the context indicates otherwise, the singular forms of the terms herein should be construed to include the plural forms, and vice versa. For example, unless the context indicates otherwise, the singular forms herein (including in the claims), such as "a" or "an", mean "one or more".

[0148] Throughout the description and claims of this specification, the words “comprise,” “including,” “having,” and “contain” and variations of these words (e.g., “comprising, comprises,” etc.) mean “including (but not limited to),” and are not intended to (and do not) exclude other components.

[0149] It should be understood that the foregoing embodiments of the present invention may be modified without falling within the scope of the present invention as defined by the claims. Unless otherwise specified, each feature disclosed in this specification may be replaced with an alternative feature for the same, equivalent or similar purpose. Therefore, unless otherwise specified, each feature disclosed is only an example of a series of equivalent or similar attribute features.

[0150] Unless otherwise stated, the use of any and all examples or exemplary language ("for example", "such as", "for example" and similar language) provided herein is intended only to better illustrate the present invention and is not intended to limit the scope of the present invention. No language in the specification should be construed as indicating that any non-claimed element is essential to the practice of the present invention.

Claims

1. A time-of-flight mass spectrometer, comprising: a pulsed ion implanter for forming an ion beam that travels along an ion path; a detector for detecting ions in the ion beam, wherein the ions arrive at the detector at corresponding times according to their mass-to-charge ratio m / z values; an ion focusing arrangement located between the ion implanter and the detector for focusing the ion beam in at least one direction orthogonal to the ion path; and A variable voltage source for supplying at least one variable voltage to the ion focusing arrangement, the at least one variable voltage being dependent on the charge state of at least one species of ions in the ion beam.

2. The time-of-flight mass spectrometer according to claim 1, wherein: The voltage source is configured to vary a voltage supplied to the ion focusing arrangement based on data regarding the charge state of at least one species of ions in the ion beam acquired by the detector and / or a charge measurement device for measuring charge in the ion beam.

3. A time-of-flight mass spectrometer according to claim 1 or 2, further comprising a controller configured to control the voltage supply using data on the charge state of at least one species of ions in the ion beam.

4. The time-of-flight mass spectrometer according to claim 3, wherein: The controller is configured to predict at least one charge state of product ions in the MS2 analysis from at least one charge state of precursor ions obtained in the MS1 analysis.

5. The time-of-flight mass spectrometer according to claim 1 or 2, wherein: The variable voltage source is configured to vary the variable voltage supplied to the ion focusing arrangement from one m / z scan of an ion pulse by the ion implanter to a subsequent scan of another ion pulse by the ion implanter.

6. The time-of-flight mass spectrometer according to claim 1 or 2, wherein: The variable voltage source is configured to vary the variable voltage supplied to the ion focusing arrangement based on charge state data of ions in the ion beam acquired from a pre-scan of ion pulses from the ion implanter.

7. The time-of-flight mass spectrometer according to claim 1 or 2, wherein: The variable voltage source is configured to vary the variable voltage supplied to the ion focusing arrangement within an m / z scan of ion pulses from the ion implanter.

8. The time-of-flight mass spectrometer according to claim 7, wherein: The variable voltage source is configured to vary a voltage supplied to the ion focusing arrangement based on data regarding a charge state of at least one species of ions in the ion beam acquired from ions in flight during an m / z scan of ion pulses from the ion implanter.

9. The time-of-flight mass spectrometer according to claim 7, wherein: The at least one variable voltage is variable in a time-dependent manner that is related to the arrival times of ions of different charge states at the focusing device.

10. The time-of-flight mass spectrometer according to claim 1 or 2, wherein: The charge state of the ions comprises a multiple charge state, and the variable voltage source is configured to vary a variable voltage supplied to the ion focusing arrangement to normalize the spatial dispersion of the ions in the multiple charge state to the spatial dispersion of the singly charged ions.

11. The time-of-flight mass spectrometer according to claim 1 or 2, wherein: The charge state of the at least one species of ions is a charge state of a single ion species.

12. The time-of-flight mass spectrometer according to claim 1 or 2, wherein: The charge state of the at least one species of ions is a plurality of charge states of different ion species.

13. The time-of-flight mass spectrometer according to claim 1 or 2, wherein: The charge state of the at least one species of ions is representative of charge states of a plurality of different ion species.

14. The time-of-flight mass spectrometer according to claim 13, wherein: The representative charge state is an average charge state of the plurality of different ionic species.

15. The time-of-flight mass spectrometer of claim 1 or 2, further comprising at least one ion mirror configured to reflect the ion beam along the ion path.

16. The time-of-flight mass spectrometer of claim 15, further comprising a plurality of ion mirrors configured to reflect the ion beam multiple times along the ion path.

17. The time-of-flight mass spectrometer according to claim 16 further includes two ion mirrors, which are spaced apart from and opposite to each other in direction X, each ion mirror is substantially elongated along a drift direction Y, and the drift direction Y is orthogonal to the direction X, and the ion mirrors are configured to provide a zigzag ion path by reflecting the ion beam multiple times in the direction X between the ion mirrors while the ion beam drifts along the drift direction Y.

18. The time-of-flight mass spectrometer according to claim 1 or 2, wherein: The ion path lies in a plane, and the ion focusing arrangement is used to focus the ion beam along a direction in the plane.

19. The time-of-flight mass spectrometer according to claim 1 or 2, wherein: The ion path lies in a plane, and the ion focusing arrangement is used to focus the ion beam in a direction away from the plane.

20. The time-of-flight mass spectrometer according to claim 1 or 2, wherein: The ion focusing arrangement comprises at least one ion focusing lens, and the voltage source is used to supply at least one variable voltage to the at least one ion focusing lens, wherein the at least one ion focusing lens is selected from the following: a trans-axis lens, a single lens and a multipole lens.

21. A time-of-flight mass spectrometer according to claim 20, comprising at least one ion mirror along the ion path, the ion mirror being configured to reflect the ion beam, wherein the at least one ion focusing lens is located before a first reflection in the at least one ion mirror.

22. A time-of-flight mass spectrometer according to claim 21, comprising a plurality of ion mirrors, which are configured to reflect the ion beam multiple times, wherein at least one ion focusing lens of the ion focusing arrangement is located after the first reflection and before the fifth reflection in the ion mirror.

23. The time-of-flight mass spectrometer according to claim 1 or 2, further comprising an ion fragmentation device upstream of the ion implanter for performing MS2 analysis of ions, wherein: The voltage source is configured to vary a voltage supplied to the ion focusing arrangement in an MS2 analysis based on data regarding the charge state of at least one species of ions of product ions, the data originating from an MS1 ​​analysis of ions performed prior to the MS2 analysis.

24. A mass spectrometry analysis method, comprising: forming an ion beam from a pulsed ion implanter that travels along an ion path; Detecting ions in the ion beam, the ions arriving at the detector at corresponding times according to their mass-to-charge ratio m / z values; focusing the ion beam in at least one direction orthogonal to the ion path using an ion focusing arrangement between the ion implanter and the detector; as well as At least one variable voltage is supplied to the ion focusing arrangement from a variable voltage source, wherein the variable voltage depends on a charge state of at least one species of ions in the ion beam.

25. The mass spectrometry method according to claim 24, wherein: The dependence of the at least one variable voltage on the charge state of at least one type of ions in the ion beam has been determined by calibration, wherein the calibration includes detecting one or more ion calibration mixtures having a varying voltage supplied to the ion focusing arrangement so as to determine the dependence of the m / z values ​​and / or peak intensities detected in different charge states on the variable voltage.

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