Time-of-flight mass spectrometer

Abstract

In one aspect, a time-of-flight (TOF) mass analyzer is disclosed, comprising: an inlet for receiving ions; a first ion acceleration region in which at least a portion of the ions received is accelerated to a first energy; a first field-free ion drift region positioned downstream of the first ion acceleration region for receiving the accelerated ions; a second ion acceleration region positioned downstream of the first field-free ion drift region for receiving ions exiting the first field-free ion drift region and accelerating the ions to a second energy; a second field-free ion drift region positioned downstream of the second ion acceleration region for receiving ions exiting the second ion acceleration region; and an ion detector for receiving ions passing through the second field-free ion drift region and generating ion detection data. The ion detection data may be analyzed to generate a mass spectrum of the detected ions.

Description

[0001] Related applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 590,600, filed October 16, 2023, entitled "Time of Flight Mass Spectrometer," the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] This disclosure generally relates to systems and methods for performing mass spectrometry analysis, and more particularly to such systems and methods utilizing time-of-flight (ToF) mass analyzers. Background Technology

[0004] This disclosure provides systems and methods for performing mass spectrometry analysis, and in particular, provides such systems and methods that allow for faster data acquisition with sufficient mass resolution.

[0005] Mass spectrometry (MS) is an analytical technique used to determine the structure of chemical substances for both qualitative and quantitative applications. MS can be used to identify unknown compounds, determine the elemental composition of molecules, determine the structure of compounds by observing their fragmentation, and quantify the amount of a specific chemical compound in a mixed sample. Mass spectrometry detects chemical entities as ions, necessitating the conversion of the analyte into charged ions.

[0006] Time-of-flight mass spectrometry (TOF-MS) relies on varying detection times to separate ions with different m / z ratios. In such a system, the mass analyzer accelerates the ions by passing them through a region where an electric field imparts kinetic energy to them. The accelerated ions then enter a field-free ion drift region, where they travel to the ion detector for detection. The time required for ions to travel through the drift region to reach the detector depends on their m / z ratio, thus allowing ion separation based on their m / z ratio. The longer the time required for ions to travel through the drift region to reach the ion detector, the higher the resolution of the mass measurement. However, a longer time for each measurement means fewer mass spectra per unit time, e.g., fewer mass spectra per second. In other words, higher mass resolution results in a lower duty cycle. Summary of the Invention

[0007] In one aspect, a time-of-flight (TOF) mass analyzer is disclosed, comprising: an inlet for receiving ions; a first ion acceleration region in which at least a portion of the received ions are accelerated to a first energy; a first fieldless ion drift region located downstream of the first ion acceleration region for receiving the accelerated ions; a second ion acceleration region located downstream of the first fieldless ion drift region for receiving ions leaving the first fieldless ion drift region and accelerating the ions to a second energy; a second fieldless ion drift region located downstream of the second ion acceleration region for receiving ions leaving the first fieldless ion drift region and accelerating the ions to a second energy; and an ion detector for receiving ions passing through the second fieldless ion drift region and generating ion detection data.

[0008] A TOF mass analyzer may include a first pair of electrodes, across which a first voltage difference (V1) is applied to generate an electric field (E1) in a first ion acceleration region. Furthermore, the TOF mass analyzer may include a second pair of electrodes, across which a second voltage difference (V3) is applied to generate an electric field (E2) in a second ion acceleration region. Additionally, the voltages applied to at least one electrode in the first pair and at least one electrode in the second pair are selected to result in an electric field approaching zero in a first fieldless ion drift region. In other words, no electric field exists in the first fieldless ion drift region. Similarly, no electric field exists in the second fieldless ion drift region. In some embodiments, an electric field may exist in either the first or second fieldless ion drift region, but at a low level such that it does not cause any substantial change to the trajectory of ions passing through those fieldless ion drift regions. For example, in various embodiments, the amplitude of such an electric field may be less than approximately 10 V / mm.

[0009] In some implementations, the TOF mass analyzer exhibits a mass resolution of at least approximately 3000. By way of example, the mass resolution exhibited by the TOF mass analyzer can range from approximately 3000 to approximately 20000.

[0010] In some implementations, the first voltage difference (V1) can be in the range of approximately 500 volts to approximately 3000 volts. Furthermore, the second voltage difference (V3) can be in the range of approximately 100 volts to approximately 20 kilovolts.

[0011] In some implementations, the mass analyzer may have an effective length equal to or less than approximately 2 meters. By way of example, the effective length of the mass analyzer can range from approximately 200 mm to approximately 2 meters. In some implementations, the first acceleration region may have an effective length (d1) such that a first voltage difference (V1) generates an electric field in the first ion acceleration region with an amplitude ranging from approximately 10 V / mm to approximately 250 V / mm. Typically, the electric field direction of each ion acceleration region is along the longitudinal axis of the linear TOF mass analyzer, for example, along a direction orthogonal to the surface of the deflector electrodes.

[0012] Furthermore, the second voltage difference (V3) can be in the range of approximately 100 volts to approximately 20,000 volts (20 kV). The second ion acceleration region can have a length (d3) such that the second voltage difference (V3) generates an electric field in the range of approximately 100 V / mm to 850 V / mm in the second ion acceleration region.

[0013] The quality analyzer may include at least one voltage source for applying either the first voltage difference or the second voltage difference to the first pair of electrodes and the second pair of electrodes, respectively.

[0014] At least one voltage source can be configured to apply a first voltage as a DC voltage, onto which multiple time-separated voltage pulses are superimposed. In some embodiments, by way of example, the voltage pulses can be applied at frequencies ranging from about 1000 Hz to about 200 kHz. Such voltage pulses can periodically guide ions (or at least a portion of ions) entering the mass analyzer to a first acceleration region.

[0015] In some embodiments, the effective length (d2) of the first field-free ion drift region and the effective length (d4) of the second field-free ion drift region simultaneously satisfy the following relationship:

[0016] Equation (1)

[0017] and

[0018] Equation (2)

[0019] in,

[0020] d1 represents the length of the first ion acceleration region.

[0021] d2 represents the length of the first field-free ion drift region.

[0022] d3 represents the length of the second ion acceleration region.

[0023] d4 represents the length of the second field-free ion drift region.

[0024] V1 represents the voltage across the first ion acceleration region, and

[0025] V3 represents the voltage across the second ion acceleration region, and

[0026] in,

[0027] d2 and d4 have real numbers (not imaginary numbers) and positive values.

[0028] In some implementations, the lengths (d2) of the first field-free ion drift region and (d4) of the second field-free ion drift region can be defined based on the amplitude of the electric field in the first and second ion acceleration regions and the length of the ion acceleration region. By way of example, lengths (d2) and (d4) can simultaneously satisfy the following relationship:

[0029] Equation (3)

[0030] and

[0031] Equation (4)

[0032] in,

[0033] d1 represents the length of the first ion acceleration region.

[0034] d2 represents the length of the first field-free ion drift region.

[0035] d3 represents the length of the second ion acceleration region.

[0036] d4 represents the length of the second field-free ion drift region.

[0037] E1 represents the magnitude of the electric field established across the first ion acceleration region, and

[0038] E3 represents the magnitude of the electric field established across the second ion acceleration region.

[0039] in,

[0040] d2 and d4 have real numbers (not imaginary numbers) and positive values.

[0041] By way of example, the first ion acceleration region can have a length in the range of approximately 2 mm to approximately 25 mm. Similarly, by way of example, the first field-free ion drift region can have a length in the range of approximately 0.5 mm to approximately 20 mm, the second ion acceleration region can have a length in the range of approximately 0.5 mm to approximately 20 mm, and the second field-free ion drift region can have a length in the range of approximately 200 mm to approximately 2 meters.

[0042] In a related aspect, a linear time-of-flight (TOF) mass analyzer is disclosed, comprising an inlet for receiving ions, at least two ion acceleration regions, at least two field-free ion drift regions, and an ion detector. One of the field-free ion drift regions is positioned between the two ion acceleration regions, and the other of the field-free ion drift regions is positioned between one of the acceleration regions and the ion detector.

[0043] In some implementations, the TOF mass analyzer can provide a mass resolution of at least about 3,000, for example, in the range of about 3,000 to about 20,000.

[0044] In some implementations, a field-free ion drift region located between the ion acceleration region and the ion detector can have a length equal to or less than approximately 2 meters.

[0045] In some implementations, the combined length associated with at least two ion acceleration regions and at least two field-free ion drift regions is equal to or less than about 2 meters, for example, in the range of about 200 mm to about 2 meters.

[0046] In some implementations, the TOF mass analyzer may include a first pair of electrodes and a second pair of electrodes, a first differential voltage may be applied across the first pair of electrodes to generate one of at least two ion acceleration regions, and a second differential voltage may be applied across the second pair of electrodes to generate the other of at least two ion acceleration regions.

[0047] In a related aspect, a mass spectrometer is disclosed, comprising: a mass filter for receiving a plurality of ions and allowing ions having an m / z ratio within its bandpass window to pass through; an ion dissociation device for receiving ions passing through the mass filter and dissociating at least a portion of them to generate a plurality of product ions; and a linear time-of-flight (TOF) mass analyzer positioned downstream of the ion dissociation device for receiving product ions and having an ion detector for detecting at least a portion of the product ions to generate ion detection data. The TOF mass analyzer may include a first ion acceleration region and a second ion acceleration region, as well as a first field-free ion drift region and a second field-free ion drift region, wherein the first field-free ion drift region is positioned between the first ion acceleration region and the second ion acceleration region, and the second field-free ion drift region is positioned between the second ion acceleration region and the detector of the TOF mass analyzer.

[0048] The mass spectrometer may also include an RF voltage source and a DC voltage source for applying RF and DC voltages to the mass filter to adjust the bandpass window of the mass filter. The mass spectrometer may also include a controller for controlling the DC and RF voltage sources. By way of example, the controller can be configured to send control signals to the DC and RF voltage sources to adjust the bandpass window of the mass filter for operation of the mass spectrometer in data-independent acquisition (DIA) mode.

[0049] In some embodiments, the mass spectrometer may also include a data processing module configured to receive ion detection data generated by the ion detector of the TOF mass analyzer and process the ion detection data to generate a mass spectrum of the product ions.

[0050] A further understanding of the various aspects of this teaching can be obtained by referring to the following detailed description in conjunction with the associated figures, which are briefly described below. Attached Figure Description

[0051] Figure 1A Various steps in an implementation of a method for performing mass spectrometry analysis according to this teaching are schematically depicted.

[0052] Figure 1B This is a schematic diagram of a ToF quality analyzer implemented according to this teaching.

[0053] Figure 1C yes Figure 1B A schematic diagram of another implementation of the ToF quality analyzer shown.

[0054] Figure 1D An example of how a ToF quality analyzer is implemented according to the embodiments of this teaching is illustrated schematically.

[0055] Figure 1E This is a partial unfolded view of a ToF mass analyzer, used to better illustrate the grid electrode used within it.

[0056] Figure 2 The simulated mass resolution, as a function of the ion path length associated with the last field-free ion drift region, is shown in an implementation of a TOF mass analyzer according to this teaching.

[0057] Figure 3 The diagram illustrates the expected potential difference in the first acceleration region as a function of the length of the second field-free region in a simulated implementation of a mass analyzer according to an embodiment of this teaching.

[0058] Figure 4 A mass spectrometer according to an embodiment of this teaching is schematically depicted.

[0059] Figure 5 The simulated mass peak of an ion with m / z of 829.5 is shown, generated using a simulated ToF mass analyzer according to an embodiment, wherein the liner has a length of 200 mm.

[0060] Figure 6 Another simulated peak of an ion with an m / z of 829.5 is shown, generated using a simulated ToF mass analyzer according to another embodiment, wherein the liner has a length of 500 mm.

[0061] Figure 7A The mass spectra of a group of ions with mass-to-charge ratios between 132 amu and 900 amu, obtained using a mass spectrometer with a TOF mass analyzer according to an embodiment of this teaching, are shown, wherein the second field-free ion drift region has a length of 1 meter.

[0062] Figure 7B It shows Figure 7A The spectrum depicted shows a narrow mass range and reveals isotopic peaks of the ALILTLVS peptide (m / z 829.539 amu).

[0063] Figure 8A The mass spectra of a group of ions with m / z ranging from 118 amu to 829.5 amu are shown, obtained using a mass spectrometer with a second field-free region of 500 mm according to another embodiment.

[0064] Figure 8B The isotopic peaks of the ALILTLVS peptide are shown, and

[0065] Figure 9 Theoretical ion utilization data for three types of TOF mass analyzers are presented. Detailed Implementation

[0066] It will be understood that, for clarity, the following discussion will set forth various aspects of the implementation of the applicant's teachings, while omitting certain specific details where convenient or appropriate. For example, the discussion of similar or analogous features in alternative implementations may be somewhat brief. For the sake of brevity, well-known ideas or concepts may also not be discussed in detail. Those skilled in the art will recognize that some implementations of the applicant's teachings may not require the details specifically described in each implementation, and that these details are set forth herein merely to provide a comprehensive understanding of the implementations. Similarly, it will be apparent that the described implementations may be readily modified or varied based on common general knowledge without departing from the scope of this disclosure. The following detailed description of the implementations should not be construed as limiting the scope of the applicant's teachings in any way.

[0067] As used herein, the terms “approximately” and “substantially equal” refer, for example, to variations in numerical quantities that may occur due to: real-world measurement or processing procedures; negligence or errors in such procedures; differences in the manufacture, origin, or purity of the reagent or ingredient; and so on. Generally, the terms “approximately” and “substantially” as used herein mean greater than or less than 10% of the complete condition or state or the value or range of the value. For example, a concentration value of approximately 30% or substantially equal to 30% could mean a concentration between 27% and 33%. These terms also refer to variations that are considered equivalent by those skilled in the art, provided that such variations do not contain values ​​known in prior art practice.

[0068] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items and may be abbreviated to “ / ”.

[0069] As used herein, the term "mass resolution" refers to a measure of a mass spectrometer's ability to distinguish between ions with very similar masses but different mass-to-charge ratios (m / z). By way of example, mass resolution can be expressed as a ratio (R) defined by the following relationship:

[0070] Equation (5)

[0071] in,

[0072] R represents the quality resolution.

[0073] m represents the mass of the ion of interest, and

[0074] Δm represents the smallest mass difference that a mass spectrometer can detect or resolve.

[0075] In the context of analytical equipment (including mass spectrometers), the term "sensitivity" refers to the ability of the equipment to detect minute changes or variations in the amount or concentration of an analyte in a sample being analyzed. For example, sensitivity can be defined as the ratio of a change in the equipment's response (e.g., the detection signal generated by the equipment) to a corresponding change in the amount or concentration of the analyte being measured. In other words, sensitivity can be determined by the analytical equipment's limit of detection (LoD), which is based on the minimum amount of analyte the equipment can detect (identify).

[0076] In the context of analytical equipment, the term "measurement cycle" refers to a series of steps or processes followed by the equipment to generate analytical data from a sample (or portion thereof) introduced into the equipment. In the context of an LC-MS system, a measurement cycle may include: introducing eluent leaving the LC column into an ion source to generate precursor ions; passing the precursor ions through a mass filter to select one or more precursor ions of interest; dissociating the selected precursor ions to generate product ions; and generating an ion detection signal corresponding to the product ions using a mass analyzer (e.g., a TOF mass analyzer). "Measurement cycle time" refers to the time required for the equipment to perform a measurement cycle.

[0077] The terms “measurement cycle frequency” and “cycle frequency” are used interchangeably and refer to the number of measurement cycles performed per unit of time (e.g., the number of measurement cycles per second).

[0078] The term "duty cycle" is the ratio of the number of ions detected to the total number of ions injected into a time-of-flight mass analyzer. In time-of-flight mass spectrometry, the duty cycle depends on the mass. Ions with low mass-to-charge ratios will have low duty cycles. Some ions with high mass-to-charge ratios can have 100% duty cycles.

[0079] The term "length" or "ion path length" is used herein to refer to the straight-line distance (i.e., physical path length) between the two electrodes of a mass analyzer or between an electrode and a detector. In various embodiments, the physical path length of the mass analyzer can be measured as the physical distance between the ion initiation position, such as the location of the deflector electrode, and the ion detector. In some cases, it may be useful to use an effective length associated with the final field-free ion drift region, such as the second field-free ion drift region discussed in the various embodiments herein, where the effective path length can be calculated by multiplying the ion flight time within the final field-free ion drift region by the ion velocity. By way of example, in some embodiments, such an effective length can be used as a metric for comparing TOF mass analyzers that include an ion mirror.

[0080] The term "field-free" indicates that there is no electric field in the region, or that any electric field that may exist is not strong enough to cause any substantial change in the trajectory of ions crossing the field-free region. By way of example, any electric field that may exist in a field-free region would have an amplitude of less than about 10 V / mm.

[0081] In one aspect, this disclosure provides systems and methods for performing high-resolution mass spectrometry analyses, which can acquire spectra at high rates, such as at least about 1,000 spectra per second (e.g., in the range of about 1,000 to about 100,000 spectra per second), at an acceptable mass resolution level (e.g., 10,000). More particularly, in various embodiments, a time-of-flight (TOF) mass analyzer is disclosed, comprising at least two accelerating regions and at least two field-free ion drift regions arranged relative to each other such that ions received by the TOF mass analyzer, after passing through a final field-free ion drift region, alternately pass through the ion accelerating regions and the field-free ion drift regions to reach the ion detector. In various embodiments, the TOF mass analyzer according to this teaching is a linear mass analyzer that does not include any ion mirror.

[0082] Figure 1A This is a flowchart depicting various steps of a method for performing mass spectrometry analysis according to an embodiment, wherein multiple ions are introduced into a time-of-flight (ToF) mass analyzer. The ions are accelerated to a first kinetic energy in a first ion acceleration region of the ToF mass analyzer. The accelerated ions are then introduced into a first field-free ion drift region. After passing through the first field-free ion drift region, the ions are accelerated to a second kinetic energy in a second ion acceleration region. Subsequently, the ions are introduced into a second field-free ion drift region. After passing through the second field-free ion drift region, the ions are detected by an ion detector of the mass analyzer, which generates ion detection data. The ion detection data can be processed to generate a mass spectrum of the ions. As discussed in more detail below, in various embodiments, the lengths of the ion acceleration region and the field-free ion drift region are selected to achieve the desired mass resolution while allowing for rapid acquisition of ion detection data.

[0083] Figure 1BA linear ToF mass analyzer 100 according to an embodiment of this teaching is schematically depicted, comprising an inlet 101 for receiving a plurality of ions propagating along the transverse axis (TA) and a deflector electrode 102 to which voltage pulses can be applied. Each voltage pulse can deflect a portion of the ions arriving at the TOF mass analyzer in an orthogonal direction along the longitudinal axis (LA), into a first ion acceleration region 104 established between the deflector electrode 102 and a downstream grid electrode 106. More specifically, an electric field E1 can be generated in the region between the deflector electrode 102 and the grid electrode 106 by a voltage difference (V1) applied between the deflector electrode 102 and the downstream grid electrode 106 via a pulsed voltage source 105 operating under the control of a controller 107, thereby establishing a first ion acceleration region 104 in which ions can be accelerated to a first kinetic energy (KE1) under the influence of the electric field E1.

[0084] The linear TOF mass analyzer 100 also includes another grid electrode 110 positioned downstream of grid electrode 106 and maintained at the same potential as grid electrode 106 (in this embodiment, both grid electrodes 106 and 110 are maintained at ground potential) to establish a first field-free ion drift region 108 between the two grid electrodes 106 and 110. Since no electric field is applied to the ions as they travel across the field-free ion drift region 108, ions with the same charge but different masses undergo a degree of spatial separation before leaving the first field-free ion drift region. In other words, because the ions entering the first field-free ion drift region have the same kinetic energy (KE1), ions with different masses will have different velocities, which determines the time required for the ions to traverse the field-free ion drift region.

[0085] The second ion acceleration region 112 is located downstream of and adjacent to the first fieldless ion drift region 108. The second ion acceleration region 112 is established by applying a voltage difference between the gate electrode 110 and the downstream gate electrode 114. More specifically, a DC power supply device 115, also operating under the control of the controller 107, applies a voltage difference (V2) across the gate electrodes 110 and 114, which causes an electric field E3 to be generated in the region between the two gate electrodes 110 and 114. Ions leaving the fieldless drift region 108 enter the second ion acceleration region 112 established between the gate electrodes 110 and 114 and are accelerated under the influence of the electric field in this region to achieve a kinetic energy KE2 greater than KE1.

[0086] The linear TOF mass analyzer also includes a second field-free ion drift region 116, positioned downstream of the second ion acceleration region 112 and enclosed within a housing 117 (also referred to herein as a liner), which maintains the same potential as the grid electrode 114. More specifically, the second field-free ion drift region 116 extends from the grid electrode 114 to an ion detector 118, which detects ions passing through the second field-free ion drift region 116 and generates ion detection data. This ion detection data can then be received by a digital data processing module 120 (also referred to herein as a computer data system), which processes the ion detection data to generate a mass spectrum correlated with the ions detected by the mass analyzer.

[0087] Figure 1C Another implementation of the ToF mass analyzer 100 (referred to herein as ToF mass analyzer 100') is schematically depicted, wherein electrically connected grid electrodes 106 / 110 are in electrical communication with a pulse voltage source 105'a (also referred to herein as a master pulse generator), and deflector electrode 102 is in electrical communication with a pulse voltage source 105'b (also referred to herein as a floating pulse generator), enabling the generation of electric field pulses within a first ion acceleration region while the region between the grid electrodes 106 / 110 remains field-free. Furthermore, in this implementation, the liner 117 is held electrically grounded. Similar to the previous implementation, ion detector 118 receives ions that have passed through a second field-free ion drift region and generates ion detection data (also referred to herein as an ion detection signal) in response to the detection of ions. The ion detection data can be analyzed via computer data system 120 to generate a mass spectrum of the ions.

[0088] Reference Figure 1D and Figure 1E Various ion acceleration regions of the ToF mass analyzer 200 can be implemented by employing a stack of electrodes, to which a voltage is applied to generate a desired electric field within the region. For example, the first ion acceleration region (d1) of the ToF mass analyzer 200 includes, for example, a pulsed electrode 202 in the form of a solid conductive planar element for deflecting ions received by the ToF mass analyzer in an orthogonal direction, and a stack of electrodes 204, 206, for example, in the form of a solid conductive planar element with a central opening through which ions can pass. Various voltages can be applied to electrodes 204 and 206 to establish a desired electric field within the first acceleration region (d1).

[0089] Multiple spacers 203a and 203b separate electrodes 202 / 204 and 204 / 206 from each other, respectively. The thickness of the spacers can be selected to achieve the desired length of the first acceleration region (d1).

[0090] The mass analyzer 200 also includes a second ion acceleration region (d3) and a first field-free ion drift region (d2) separating the first and second ion acceleration regions. The second ion acceleration region (d3) includes conductive electrodes 208, 210, 212, 214, 216, 218, and 220, each in a planar form with a central opening through which ions can pass, stacked relative to each other and separated in pairs via multiple electrically insulating separators 207, 209, 211, and 213. A voltage applied to the conductive electrodes can establish an electric field within the second ion acceleration region. The thickness of the insulating separators can be selected to achieve the desired effective length of the second ion acceleration region.

[0091] Continue to refer to Figure 1D and Figure 1E Referring now to the first field-free ion drift region (d2), two grid electrodes 300 and 302 are electrically contacted with electrodes 206 and 208, respectively. These grid electrodes provide openings through which ions can pass. To establish the field-free ion drift region, electrodes 206 and 208, as well as the corresponding grid electrodes 300 and 302, are maintained at the same voltage. In various embodiments, the grid electrodes can facilitate the formation of a sharp transition in the amplitude of the electric field between the ion acceleration region and the adjacent field-free ion drift region.

[0092] The second fieldless ion drift region (d4) extends from the second ion acceleration region (d3) to the ion detector 118. Ions leaving the second ion acceleration region (d3) pass through the grid electrode 304 to propagate through the final fieldless ion drift region, thereby reaching the ion detector 118. The voltage applied to the grid electrode positioned between the second ion acceleration region (d3) and the second fieldless ion drift region (d4) is the same as the voltage applied to the liner of the second fieldless ion drift region, and in various embodiments, it can create a distinct and abrupt transition between the second ion acceleration region and the second fieldless ion drift region. The second fieldless ion drift region is surrounded by a liner, which can be maintained, for example, at a ground potential or a floating voltage.

[0093] It has been found that a combination of fast data acquisition rate and excellent quality resolution can be achieved by selecting the lengths associated with the two ion acceleration regions and the two field-free ion drift regions, as well as the voltages V1 and V3 applied across the first and second ion acceleration regions, respectively. By way of example, and not limitation, in various embodiments, a data acquisition rate of at least 1 kHz and a quality resolution of at least 3000 can be obtained.

[0094] exist Figure 1BIn the described mass analyzer configuration, the time of flight (FT) of ions with a mass-to-charge ratio expressed in m / z through the mass analyzer can be obtained using the following relationship:

[0095] Equation (6)

[0096] in,

[0097] y represents the ion position in the first acceleration region, where y = 0 is the position adjacent to the first electrode (i.e., the deflector electrode), and y = d1 coincides with the exit grid of the first acceleration region.

[0098] d1 represents the length of the first ion acceleration region.

[0099] d2 represents the length of the first field-free ion drift region.

[0100] d3 represents the length of the second ion acceleration region.

[0101] d4 represents the length of the second field-free ion drift region.

[0102] V1 represents the voltage applied across the first ion acceleration region, and

[0103] V3 represents the voltage applied across the second ion acceleration region.

[0104] In various embodiments, by setting the ion path length (d1) associated with the first ion acceleration region and the ion path length (d3) associated with the second ion acceleration region, as well as the values ​​of the voltages V1 and V3 applied across the first and second ion acceleration regions, the values ​​of the lengths associated with the first fieldless ion drift region and the second fieldless ion drift region can be obtained using the above relationships, which are obtained by solving (d2) and (d4) in the above equations (3) and (4).

[0105] In other words, in some implementations, the size of each region of the mass analyzer 100 can be determined by selecting the dimensions of the two regions of the mass analyzer and the voltage applied across the two ion acceleration regions, and using the relationship described above.

[0106] In various embodiments, the desired resolution can be obtained by selecting the ion path length through the mass analyzer (i.e., the path length of ions from deflector electrode 102 to ion detector 118) and the voltage applied across the two ion acceleration regions. The pulse generator rate (i.e., the rate at which voltage is applied to the deflector electrode) can then be adjusted to provide the maximum possible pulse generator frequency for the desired length and resolution configuration. Generally, the selection of d1-d4 lengths and voltage can affect the overall resolution and the limitation on the maximum available pulse generator frequency, but does not directly change the pulse generator frequency. In particular, in various embodiments, the acquisition rate can be changed only by changing the frequency of the pulse generator itself. More generally, by selecting the values ​​of four of the parameters described above, the values ​​of the other two parameters can be derived from the relationships described above (equations (3) and (4)).

[0107] There is a trade-off between the path length of ions through the mass analyzer and the mass resolution provided by the mass analyzer. Generally, a longer ion path length results in a higher mass resolution. This is illustrated graphically. Figure 2 The simulated mass resolution is shown as a function of the ion path length associated with the last field-free ion drift region in the mass analyzer 100 described above. The mass resolution data show that the mass resolution increases with the length of the last field-free ion drift region, although the rate of change decreases. The m / z of the ion used in the simulation is 829.5 amu.

[0108] Table 1 below provides the voltages applied across the first and second ion acceleration regions, the lengths of the ion acceleration regions and the fieldless ion drift regions, and the resulting simulated mass resolution and ion flight time through the TOF mass analyzer. Note that Leff represents the product of the ion velocity and ion flight time in the second fieldless ion drift region: .

[0109] Table 1 (Performance and voltage requirements as a function of d4 length)

[0110]

[0111] In many practical implementations of the linear TOF mass analyzer 100, the increase in analyzer mass resolution as a function of ion path length is expected to plateau at a specific ion path length, for example, around 1 meter. Without being bound by any particular theory, such plateauing of mass resolution may be partly due to the need to reduce, for long ion path lengths, the voltage across the first ion acceleration region below a threshold, which would lead to thermal effects in the ion velocity distribution, thus contributing to the reduction in mass resolution.

[0112] By way of examples Figure 3 The expected potential difference in the first acceleration region is shown as a function of the length of the second field-free region of the mass analyzer 100, where the aforementioned values ​​of other parameters are used. Figure 3 The trend shown illustrates that when the length of the second field-free region increases beyond a certain threshold, the optimized analyzer defined by the solutions of d2 and d4 will require a small potential difference approaching zero in the first acceleration region.

[0113] The linear TOF mass analyzer described in this teaching can be incorporated into various mass spectrometers. This is done by way of example, not limitation. Figure 4 An LC-MS spectrometry system 400 is schematically depicted, comprising a liquid chromatography (LC) column (not shown) capable of receiving a sample and an ion source (not shown) connected to the LC column to receive the eluent exiting the LC column. The ion source can ionize one or more analytes in the received eluent to generate multiple ions that can be received by an ion director QJet via orifice 402 of the mass spectrometer. The QJet ion director includes a set of bars 401 arranged in a quadrupole configuration, two of which, 401a / 401b, are visible in the figure, and a combination of gas dynamics and a radio frequency field is used to induce ion focusing. Ions exiting the QJet ion director are focused by the ion lens IQ0 into the ion director Q0, which includes a set of quadrupoles 404, two of which, 404a / 404b, are visible in the figure. An RF voltage can be applied to this set of quadrupoles 404 to cause radial confinement of the ions and generate an ion beam, which is then received by the ion mass filter Q1. The ion directors QJet and Q0, and the mass filter Q1, are housed in a differential pump chamber maintained at a gradually decreasing pressure.

[0114] The ion lens IQ1 focuses ions exiting the ion guide Q0 into the mass filter Q1. The mass filter Q1 includes a short, thick lens 406 formed by a set of quadrupoles (two 406a / 406b of the set of quadrupoles are visible in the figure), to which an RF voltage can be applied to induce ion focusing. The mass filter Q1 also includes a set of quadrupoles 410, two 410a / 410b of the set of quadrupoles 410 are visible in the figure, to which a combination of RF and DC voltages can be applied to the set of quadrupoles 410 to allow selection of one or more precursor ions, for example, all precursor ions of interest having an m / z ratio within the target m / z range when the mass spectrometer is operating in DIA mode, for transmission via the ion lens IQ2 to the downstream ion dissociation device Q2, such as the collision chamber in this example.

[0115] More specifically, the DC voltage source 426 and RF voltage source 428, operating under the control of the controller 430, can apply RF and DC voltages to the quality filter Q1 in a manner known in the art, and configure the bandpass window of the quality filter as described in this teaching. By way of example, and not limitation, the RF voltage applied to the rod of the Q1 quality filter can have a frequency in the range of approximately 200 kHz to approximately 12 MHz and a peak-to-peak amplitude (V) in the range of approximately 100 volts to approximately 10 kilovolts (kV). pp ).

[0116] In this embodiment, the collision chamber Q2 includes a set of rods 417, two of which, 417a / 417b, are visible in the figure. The set of rods 417 is arranged in a quadrupole configuration and pressurized by introducing nitrogen gas to allow the collision chamber Q2 to fragment upon impact. The RF frequency applied to the rods in the Q2 collision chamber can, for example, be in the range of approximately 1 MHz to approximately 5 MHz. In various embodiments, the Q2 chamber can be used for collision focusing, where a higher RF frequency, such as 5 MHz, can be employed.

[0117] A set of ion-focusing optics 415 focuses ions exiting the Q2 chamber onto a time-of-flight (TOF) mass analyzer 418 according to various embodiments of this teaching, such as the TOF mass analyzer 100 described above. The mass analyzer 418 includes an ion detector 420 that generates ion detection data in response to detecting ions incident thereon. A data processing module 425 can be used to process the ion detection signal generated by the ion detector to generate a mass spectrum of the product ions.

[0118] The TOF mass analyzer based on this teaching offers significant advantages. As mentioned above, it allows for the acquisition of mass data at high sensitivity and high rate. Furthermore, it provides a simpler geometry compared to TOF mass analyzers that utilize ion mirrors to extend the ion path length and subsequently improve ion focusing. In various embodiments, the duty cycle can be high enough that an ion trap is not required upstream of the TOF mass analyzer.

[0119] The following implementation methods are provided to further illustrate various aspects of this teaching, rather than to indicate the best way to practice this teaching and / or the best results that can be obtained.

[0120] Example

[0121] Example 1

[0122] Figure 5The simulated mass peak of the ALILTLVS peptide (m / z = 829.5 amu) is shown, calculated based on a simulated linear TOF mass analyzer according to an embodiment of this teaching. The following parameters were used to perform the simulation: V1 (voltage applied across the first ion acceleration region) = 1600 V, V3 (voltage applied across the second ion acceleration region) = -7095 V, d1 (effective length of the first ion acceleration region) = 12 mm, d2 (effective length of the first field-free ion drift region) = 1.5 mm, d3 (effective length of the second ion acceleration region) = 24, d4 (effective length of the second field-free ion drift region (i.e., the effective length of the liner)) = 200 mm. The m / z ratio of the ion is 829.5 amu.

[0123] Figure 5 The simulated mass peak depicted exhibits a mass resolution of approximately 6800. The simulated flight time of the ions through the mass analyzer is 6.8 microseconds. A lens is used to manipulate and prepare the ions for injection into the TOF accelerator. This lens is adjusted to minimize the ratio of the base peak width to the half-peak width (5% peak height / 50% peak height). The peak shown is the result of simulating approximately one million different ion trajectories through the collision chamber, transport optics, and TOF analyzer.

[0124] Simulation data show that even with ion flight times of less than 7 µs (corresponding to measurement cycle frequencies greater than 140 kHz), the calculated mass resolution is greater than the typical mass resolution exhibited by a quadrupole mass filter. Furthermore, the cycle frequency is greater than that achievable via any TOF mass analyzer with an ion mirror (it is approximately 10 times higher).

[0125] Example 2

[0126] Figure 6 The simulated mass peak for the ALILTLVS peptide ion (m / z = 829.5 amu) with a path length of 470 mm is shown through a simulated TOF mass analyzer according to an embodiment. The following parameters were used for the simulation: V1 = 1209 V, V3 = -10,000 V, d1 = 12 mm, d2 = 2.1 mm, d3 = 36 mm, and d4 = 500 mm.

[0127] and Figure 5 Compared to the simulated quality peaks depicted, Figure 6 The simulated mass peak depicted exhibits greater mass resolution but a longer flight time. The analyzer's measurement cycle frequency was calculated to be approximately 76 kHz. Similar to the previous example, a FOR lens was chosen to minimize the width ratio.

[0128] Example 3

[0129] Figure 7A MS mass spectra of ion mixtures covering masses between 100 m / z and 1000 m / z, obtained using a mass spectrometer with a TOF mass analyzer according to an embodiment of this teaching, are shown. More specifically, the TOF mass analyzer includes two ion acceleration regions separated by a field-free ion drift region. A second field-free ion drift region extends from the second ion acceleration region to the ion detector. The length of the second field-free ion drift region is 1000 mm, and this data was acquired at 30 kHz. Figure 7B Showing from Figure 7A The spectrum of the ALILTLVS peptide ion (m / z = 829.5 amu) in the spectrum.

[0130] Example 4

[0131] Figure 8A MS mass spectra of ion mixtures covering masses between 100 m / z and 1000 m / z, obtained using a mass spectrometer with a TOF mass analyzer according to an embodiment of this teaching, are shown. More specifically, the TOF mass analyzer includes two ion acceleration regions separated by a field-free ion drift region. A second field-free ion drift region extends from the second ion acceleration region to the ion detector. The length of the second field-free ion drift region is 500 mm, and data are acquired at 45 kHz. Figure 8B Showing from Figure 8A The spectrum of the ALILTLVS peptide ion (m / z = 829.5 amu) in the spectrum.

[0132] Example 5

[0133] Figure 9 Theoretical ion utilization (duty cycle) is provided for each of three types of TOF mass analyzers based on specific operating voltage values ​​and analyzer size as a function of different m / z ratios in the range of approximately 50 to 1000. More specifically, Figure 9 The duty cycles exhibited by linear TOF mass analyzers (LTOF), TOF mass analyzers with a single ion mirror (VTOF), and TOF mass analyzers with two ion mirrors (NTOF) are provided.

[0134] This data indicates that the LTOF analyzer exhibits a higher duty cycle than both the VTOF and NTOF mass analyzers, with the VTOF mass analyzer showing a higher duty cycle than the NTOF mass analyzer.

[0135] Pairwise comparisons of duty cycle ratios at different masses show that these ratios are constant, meaning they are independent of the mass-to-charge ratio. By way of example, regardless of the mass-to-charge ratio, the duty cycle ratio of the LTOF mass analyzer to the VTOF mass analyzer is approximately 4.3, and the corresponding ratio of the LTOF mass analyzer's duty cycle to the NTOF mass analyzer is approximately 7.6.

[0136] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items and may be abbreviated as " / ". Although some aspects have been described in the context of apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or device corresponds to a method step or feature of a method step. Similarly, aspects described in the context of method steps also represent a description of a corresponding block or item or feature of a corresponding apparatus. Some or all of the method steps may be performed by (or using) hardware devices such as processors, microprocessors, programmable computers, or electronic circuits. In some embodiments, one or more of the most important method steps may be performed by such devices.

[0137] Depending on the specific implementation requirements, embodiments of the present invention can be implemented in hardware and / or software. This implementation can be executed using a non-transitory storage medium, such as a digital storage medium like a floppy disk, DVD, Blu-ray, CD, ROM, PROM, EPROM, EEPROM, or flash memory, which stores electronically readable control signals thereon, and cooperates with (or is capable of cooperating with) a programmable computer system to perform the corresponding method. Therefore, the digital storage medium can be computer-readable.

[0138] While various embodiments have been detailed and described in the accompanying drawings and foregoing description, such descriptions should be considered illustrative or exemplary, not restrictive; the embodiments of this disclosure are not limited to those disclosed. Based on a study of the drawings, the disclosure, and the appended claims, those skilled in the art will understand and implement other variations of the disclosed embodiments in practicing the embodiments of this disclosure.

[0139] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. A single processor or other processing unit can perform the functions of several items listed in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used advantageously. Any reference numerals in the claims should not be construed as limiting the scope.

[0140] Those skilled in the art will understand that various changes can be made to the above embodiments without departing from the scope of this teaching.

Claims

1. A time-of-flight (TOF) quality analyzer, comprising: An inlet for receiving ions. In a first ion acceleration region, at least a portion of the ions received in the first ion acceleration region are accelerated to a first energy. A first field-free ion drift region, located downstream of the first ion acceleration region, is used to receive accelerated ions. A second ion acceleration region is located downstream of the first field-free ion drift region, which is used to receive ions leaving the first field-free ion drift region and accelerate the ions to a second energy. A second field-free ion drift region, located downstream of the second ion acceleration region, is used to receive the ions leaving the second ion acceleration region. An ion detector is used to receive ions passing through the second field-free ion drift region and generate ion detection data.

2. The TOF mass analyzer of claim 1 further includes a first pair of electrodes, across which a first voltage difference (V1) is applied to generate an electric field (E1) in the first ion acceleration region.

3. The TOF mass analyzer according to claim 2 further includes a second pair of electrodes, across which a second voltage difference (V3) is applied to generate an electric field (E3) in the second ion acceleration region.

4. The TOF mass analyzer according to claim 3, wherein, The first voltage difference and the second voltage difference applied across the first pair of electrodes and the second pair of electrodes result in an electric field approaching zero in the first field-free ion drift region.

5. The TOF mass analyzer according to any one of claims 1 to 4, wherein, The TOF mass analyzer exhibits a mass resolution of at least 3000, and optionally, the mass resolution is in the range of approximately 3000 to approximately 20000.

6. The TOF mass analyzer according to any one of claims 1 to 4, wherein, The length of the mass analyzer is equal to or less than approximately 2 meters, and optionally, the length is in the range of approximately 200 mm to approximately 2 meters.

7. The TOF mass analyzer according to claim 2, wherein, The first voltage difference (V1) is in the range of approximately 500 volts to approximately 3000 volts.

8. The TOF mass analyzer according to claim 6, wherein, The first acceleration region has a length (d1) such that the voltage difference (V1) generates an electric field in the first ion acceleration region in the range of approximately 10 V / mm to approximately 250 V / mm.

9. The TOF mass analyzer according to claim 3, wherein, The second voltage difference (V3) is in the range of approximately 1,000 volts to approximately 20,000 volts.

10. The TOF mass analyzer according to claim 7, wherein, The second ion acceleration region has a length (d2) such that the second voltage difference (V3) generates an electric field in the range of approximately 100 V / mm to 850 V / mm.

11. The TOF quality analyzer of claim 3, further comprising at least one voltage source for applying either the first voltage difference or the second voltage difference to the first pair of electrodes and the second pair of electrodes, respectively.

12. The TOF mass analyzer according to claim 11, wherein, The at least one voltage source is configured to apply the first voltage as a plurality of time-separated voltage pulses.

13. The TOF mass analyzer according to claim 12, wherein, The at least one voltage source is configured to apply the voltage pulse at a frequency in the range of about 1000 Hz to about 200 kHz, wherein, optionally, the frequency is greater than about 20 kHz, or greater than about 50 kHz, or greater than about 75 kHz.

14. The TOF mass analyzer according to claim 3, wherein, The lengths (d2) of the first field-free ion drift region and the lengths (d4) of the second field-free ion drift region simultaneously satisfy the following relationship: as well as in, d1 represents the effective length of the first ion acceleration region. d2 represents the effective length of the first field-free ion drift region. d3 represents the effective length of the second ion acceleration region. d4 represents the effective length of the second field-free ion drift region. V1 represents the voltage across the first ion acceleration region, and V3 represents the voltage across the second ion acceleration region, and in, d2 and d4 have real numbers (not imaginary numbers) and positive values.

15. The TOF mass analyzer according to claim 1, wherein, The first ion acceleration region has a length in the range of approximately 2 mm to 25 mm, the first field-free ion drift region has a length in the range of approximately 0.5 mm to 20 mm, the second ion acceleration region has a length in the range of approximately 2 mm to 100 mm, and the second field-free ion drift region has a length in the range of approximately 200 mm to 2 meters.

16. A linear time-of-flight (TOF) mass analyzer, comprising: An inlet for receiving ions. At least two ion acceleration regions, At least two field-free ion drift regions, and Ion detector, One of the field-free ion drift regions is located between the two acceleration regions, and the other of the field-free ion drift regions is located between one of the acceleration regions and the ion detector.

17. The linear TOF mass analyzer according to claim 16, wherein, The TOF mass analyzer provides a mass resolution of at least 3000.

18. The linear TOF mass analyzer according to any one of claims 16 and 17, wherein, The field-free region located between the ion acceleration region and the ion detector has a length equal to or less than 2 meters, and wherein, optionally, the combined length associated with the at least two ion acceleration regions and the at least two field-free ion drift regions is equal to or less than about 2 meters, and wherein, optionally, the combined length is in the range of about 200 mm to about 2 meters.

19. The linear TOF mass analyzer of claim 16, further comprising a first pair of electrodes and a second pair of electrodes, capable of applying a first differential voltage across the first pair of electrodes to generate one of the at least two ion acceleration regions, and capable of applying a second differential voltage across the second pair of electrodes to generate the other of the at least two ion acceleration regions.

20. A mass spectrometer, comprising: A mass filter, used to receive multiple ions and allow ions with an m / z ratio within its bandpass window to pass through. An ion dissociation device for receiving the ions passing through the mass filter and dissociating at least a portion of them to generate a plurality of product ions. A linear time-of-flight (TOF) mass analyzer is positioned downstream of the ion dissociation device. It receives the product ions and has an ion detector for detecting at least a portion of the product ions to generate ion detection data. The TOF mass analyzer includes: First ion acceleration region and second ion acceleration region. First field-free ion drift region and second field-free ion drift region The first field-free ion drift region is located between the first ion acceleration region and the second ion acceleration region, and the second field-free ion drift region is located between the detector of the TOF mass analyzer and the second ion acceleration region.

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