Source housing for a mass spectrometer, systems, and methods of use thereof

Abstract

A source housing for a mass spectrometer includes a first opening configured to couple with an off-axis probe substantially orthogonal to a central axis of an inlet to the mass spectrometer and a second opening configured to couple with an on-axis probe substantially coincident with the central axis, where the off-axis probe and the on-axis probe are in fluid communication with the inlet to the mass spectrometer and where the on-axis probe is configured to direct a fluid at an angle to the central axis. A system includes the source housing and a mass spectrometer. A method includes using the source housing or the system; flowing a calibrant fluid through the on-axis probe; and generating a calibration mass scale.

Description

Lathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCTSOURCE HOUSING FORA MASS SPECTROMETER, SYSTEMS, AND METHODS OF USE THEREOFRELATED APPLICATIONS

[0001] The present patent application claims the priority benefit of U.S. Provisional Patent Application Ser. No. 63 / 719,367, filed November 12, 2024, the content of which is hereby incorporated by reference in its entirety into this disclosure.BACKGROUND

[0002] Mass spectrometry (MS) is an analytical technique for measuring mass-to-charge ratios of molecules, with both qualitative and quantitative applications. MS can be useful for identifying unknown compounds, determining the structure of a particular compound by observing its fragmentation patterns, and quantifying the amount of a particular compound in a sample. Mass spectrometers separate and detect chemical entities as ions such that a conversion of the analytes to charged ions must occur prior to entering the mass spectrometer.

[0003] A variety of methods are known for ionizing chemical entities within a sample into charged ions suitable for detection with MS. One of the more common ionization methods is electrospray ionization (ESI). In a typical ESI process, a liquid sample is discharged into an ionization chamber via an electrically conductive needle, probe, electrospray electrode, or nozzle, while an electric potential difference between the electrospray electrode and a counter electrode generates a strong electric field within the ionization chamber that electrically charges the liquid sample. The electric field generated within the ionization chamber causes the liquid discharged from the electrospray electrode, probe, needle, or nozzle to disperse into a plurality of charged micro-droplets drawn toward the counter electrode if the charge imposed on the liquid's surface is strong enough to overcome the surface tension of the liquid. As solvent within the micro-droplets evaporates during desolvation in the ionization chamber, charged analyte ions can enter a sampling orifice of the counter electrode for subsequent mass spectrometric analysis.

[0004] In conventional ion sources, optimization of sensitivity performance requires the user to successfully adjust approximately seven interacting parameters, several of which involve physical adjustments within the source and others which can involve softwaresettable parameters such as temperature, electrical potential, and gas flows. These parametersLathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCTare highly dependent on the flow rate of a calibration or liquid sample stream. As an example, as flow rate increases the location of the probe tip relative to the inlet (entrance aperture) of the mass spectrometer is usually increased, ion source temperature is increased, electrospray ionization electrical potential is optimized differently, and nebulization and heat transfer gas flows are increased. Additionally, the protrusion of the emitter from the discharge end of the probe often requires adjustment, which in turn requires re-optimization of nebulization gas and ESI electrical potential. One or more optimal sets of parameters exists for each flow rate. When optimizing for sensitivity performance for a particular flow rate, each adjustment of the vertical position of the probe can trigger readjustment of ion source temperature, gas flows, and ESI electrical potential. Sensitivity performance optimization can be further complicated when the user attempts to determine optimal operational parameters for a mixture of compounds. In general, it is not possible to determine a single set of operational parameters that would produce optimal sensitivity for all compounds in a mixture, and the “optimal” parameters usually involve a performance compromise for a subset of the compounds in the mixture. As such, obtaining optimal performance with a conventional ion source is time consuming and can be difficult, even for experienced users.

[0005] Further, an ion probe of an ESI source can receive samples, for example, from an upstream liquid chromatography (LC) column, at flow rates within a particular range. If flow rates above or below that range are desired, the ion probe must be replaced with another probe that can accommodate the desired flow rates. Such replacement of probes can be, however, cumbersome and time consuming.

[0006] Accordingly, there is a need for enhanced ion sources for use in mass spectrometry that may provide improved ionization and ion sampling efficiency.BRIEF SUMMARY

[0007] Further and alternative aspects and features of the disclosed principles will be appreciated from the following detailed description. As will be appreciated, the compositions and methods disclosed herein are capable of being carried out and used in other and different embodiments, and capable of being modified in various respects. Accordingly, it is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and do not restrict the scope of the appended claims.

[0008] In one aspect, the disclosure features a source housing for a mass spectrometer including a first opening configured to couple with an off-axis probe substantially orthogonal to a central axis of an inlet to the mass spectrometer and a second opening configured toLathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCTcouple with an on-axis probe substantially coincident with the central axis, where the off-axis probe and the on-axis probe are in fluid communication with the inlet to the mass spectrometer and where the on-axis probe is configured to direct a fluid at an angle to the central axis.

[0009] In some embodiments, the on-axis probe is removable. In some embodiments, the on-axis probe includes an angled portion. In some embodiments, the angled portion is angled from about 1 degree to about 60 degrees from the central axis. In some embodiments, the on-axis probe is angled toward the off-axis probe, away from the off-axis probe, or any direction there between. In some embodiments, the on-axis probe includes a proximal end and a distal end and where the angled portion is from about 15 mm to about 50 mm from the distal end.

[0010] In some embodiments, the on-axis probe includes a proximal end and a distal end, where the proximal end is adjacent to the second opening and where the distal end includes a notch. In some embodiments, the notch includes an elongated portion and the elongated portion is from about 0.5 mm to about 20 mm. In some embodiments, the notch includes an angled notch and the angled notch is from about 0 to about 60 degrees. In some embodiments, the on-axis probe includes a fluid channel. In some embodiments, the fluid channel includes an angled portion. In some embodiments, the angled portion is angled from about 1 degree to about 60 degrees from the central axis and angled away from the elongated portion. In some embodiments, the angled portion is from about 0.5 mm to about 20 mm from a fluid channel outlet. In some embodiments, the notch is oriented toward the off-axis probe, away from the off-axis probe, or any direction there between.

[0011] In some embodiments, the fluid is a calibration fluid. In some embodiments, the calibration fluid has a flow rate of about 20 pl / min to about 200 pl / min. In some embodiments, the on-axis probe is configured to form a desolvated spray and more than 50%, 60%, 70%, 80%, 90%, 95%, 98%, or 99% of the desolvated spray impacts a curtain plate, which encircles the inlet to the mass spectrometer. In some embodiments, desolvated spray impacts the curtain plate from about 5 mm to about 50 mm radially away from the central axis of the inlet to the mass spectrometer. In some embodiments, the distal end of the on-axis probe is from about 0.5 mm to about 10 mm from the orthogonal sprayer axis.

[0012] In one aspect, the disclosure features a system including a source housing as described herein and a mass spectrometer. In some embodiments, the mass spectrometer is a sector, a single quadrupole, a triple quadrupole, a Qtof, a Tof, an ion trap, or a Fourier-transform ion cyclotron resonance mass spectrometer.Lathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCT

[0013] In one aspect, the disclosure features a method of calibrating a mass spectrometer, the method including using a source housing or a system described herein; flowing a calibrant fluid through the on-axis probe; and generating a calibration mass scale. In some embodiments, the method further includes flowing an analyte fluid through the off-axis probe before or after flowing the calibrant fluid through the on-axis probe. In some embodiments, the method further includes determining a mass of an analyte in the analyte fluid. In some embodiments, the flowing the calibrant fluid through the on-axis probe is scheduled to run via a software interface before, after, in between, or a combination thereof the flowing of the analyte fluid. In some embodiments, the inlet to the mass spectrometer is substantially clean from about 1 hour to after about 4, 5, or 6 months of use.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] An understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which :

[0015] FIG. 1 is a schematic perspective view of a source housing illustrating one embodiment of the disclosure.

[0016] FIG. 2 is an image illustrating a configuration of the interior of a source housing showing an off-axis probe, an on-axis probe, and an inlet of a mass spectrometer.

[0017] FIG. 3 is an image of one embodiment of an on-axis probe suitable for use in a source housing disclosed herein.

[0018] FIG. 4 is a schematic, cross-sectional view of another embodiment of an on-axis probe suitable for use in a source housing as disclosed herein.

[0019] FIGS. 5A and 5B are images illustrating the amount of build-up of residue on the interior of the inlet of the mass spectrometer using a conventional on-axis probe (FIG. 5A) compared to substantially no residue buildup on the interior of the inlet of the mass spectrometer using an on-axis probe as disclosed herein (FIG. 5B).

[0020] FIGS. 6A and 6B are images illustrating the amount of build-up of residue on the curtain plate (side view - FIG. 6A; front view - FIG. 6B) of the mass spectrometer using an on-axis probe configured with the angled portion of the on-axis probe angled toward the off-axis probe.

[0021] FIG. 7 is an image illustrating an on-axis probe configured with the angled portion of the on-axis probe angled away from the off-axis probe.Lathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCT

[0022] FIG. 8 is an image of three on-axis probes with different angled portions 0.

[0023] FIGS. 9A and 9B are images illustrating an on-axis probe with a notch. The on-axis probe is configured with the notch angled toward the off-axis probe (FIG. 9A) or angled away from the off-axis probe (FIG. 9B).DETAILED DESCRIPTIONI. Introduction

[0024] Current, state of the art ion sources are a multifunction part of a mass spectrometer. Typically, the multifunctionality offers the capability to switch between flow regimes and ionization types without the source being removed from the mass analyzer. The source can also accommodate multiple ion generating probes at its various ports. As a matter of efficiency in performance as well as in economy, it is desirable to keep the number of ports as low as possible (e.g., two). Increasing the number of ports and probes to three, four, or more can greatly increase the complexity of operation and negatively impact performance. The ports are used for multiple ionization / ion generating functions such as, for example, mass analysis of unknown samples and / or calibration and tuning. Generally, a port, on-axis with the sampling orifice of the mass spectrometer, is used for analysis of liquid analytes delivered at nano and micro flows so as not to overwhelm and contaminate the orifice, which could lead to carry-over issues. Whereas higher flowrates are typically accommodated by an off-axis port, such as a port located orthogonal to the mass spectrometer inlet axis. In certain applications, requiring high mass accuracy, a calibration on demand is useful while the (primary) orthogonal port / probe is generating ions from the sample and / or is useful in between unattended runs on the primary probe. In such a case, while analyzing samples delivered at higher flows, a calibration probe may be introduced into the on-axis port. This approach, with a standard calibration probe, is precluded by rapid contamination of the sampling orifice caused by the higher calibration flow rates. Calibration flow rates are higher than the nano / micro flows associated with the on-axis port. Lower flow rates for calibration is not possible due to the primary sprayer operation.

[0025] The source housing and probes disclosed herein offer a way to achieve calibration through the on-axis port. The source housing features a removable calibration probe that utilizes an angled nebulizer nozzle / electrode / tip assembly to produce spray that is angled from the sampling inlet axis. The off-axis direction ameliorates or prevents the inlet from being contaminated even at high calibration flow rates.Lathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCT

[0026] Generally, an esi probe forms a nebulizer assisted esi spray, which is an electrically charged mist of micro droplets. The droplets reduce in size while in flight through evaporation, a so called desolvation process. When the droplet reduction reaches a critical diameter, the surface charge mutual repulsion of the ions within the droplet overcomes the surface tension of the solvent, causing a Coulombic explosion releasing individual ions and ion clusters, ideal for mass spectrometer analysis. At higher flow rates, even with the addition of desolvation heaters, the spray is not fully desolvated and still contains charged micro droplets when it reaches the inlet, a wet spray, that adheres to the inlet edge. Upon extended operation the deposit grows significantly, reducing the sampling inlet size and hence performance. Off-axis probes aim the wet spray across a central axis coincident with the inlet such that the wet spray does not enter the inlet and only the ions and ion clusters that are fully desolvated enter the inlet of the mass spectrometer. Conventional on-axis probes launch the wet spray directly at the inlet.

[0027] Disclosed herein are on-axis ports and probes used for calibration. The on-axis port disclosed herein features a removable probe allowing dual functionality - mass analysis of samples and calibration. The on-axis probe in one aspect, features an angled portion that directs the spray at an angle to the central axis of the inlet.II. Definitions

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the methods described herein belong. Any reference to standard methods refers to the most recent available version of the method at the time of filing of this disclosure unless otherwise indicated.

[0029] For any method disclosed herein that includes discrete steps, the steps may be conducted in any feasible order. And, as appropriate, any combination of two or more steps may be conducted simultaneously.

[0030] All headings are for the convenience of the reader and should not be used to limit the meaning of the text that follows the heading, unless so specified.

[0031] The words "preferred" and "preferably" refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention.Lathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCT

[0032] The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Such terms will be understood to imply the inclusion of a stated step or element or group of steps or elements but not the exclusion of any other step or element or group of steps or elements.

[0033] The singular form "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. These articles refer to one or to more than one (i.e., to at least one). The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. As used herein, the term "or" is generally employed in its usual sense including "and / or" unless the content clearly dictates otherwise. The term "and / or" means any one or more of the items in the list joined by "and / or". As an example, "x and / or y" means any element of the three-element set {(x), (y), (x, y)}. In other words, "x and / or y" means "one or both of x and y". As another example, "x, y, and / or z" means any element of the seven-element set {(x), (y), (z), (x, y), (x, z), (y, z), (x, y, z)}. In other words, "x, y and / or z" means "one or more of x, y and z".

[0034] Where ranges are given, endpoints include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). Furthermore, unless otherwise indicated or otherwise evident from the context and understanding of one of ordinary skill in the art, values that are expressed as ranges can assume any specific value or subrange within the stated ranges in different embodiments of the disclosure, to the tenth of the unit of the lower limit of the range, unless the context clearly dictates otherwise. Herein, "up to" a number (for example, up to 50) includes the number (for example, 50). The term "in the range" or "within a range" (and similar statements) includes the endpoints of the stated range.

[0035] Reference throughout this specification to “one aspect (or embodiment),” “an aspect (or embodiment),” “certain aspects (or embodiments),” or “some aspects (or embodiments),” etc., means that a particular feature, configuration, composition, or characteristic described in connection with the aspect is included in at least one aspect of the disclosure. Thus, the appearances of such phrases in various places throughout this specification are not necessarily referring to the same embodiment of the disclosure.Furthermore, the particular features, configurations, compositions, or characteristics may be combined in any suitable manner in one or more aspects.Lathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCT

[0036] Unless otherwise indicated, all numbers expressing quantities of components, molecular weights, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about." As used herein in connection with a measured quantity, the term "about" refers to that variation in the measured quantity as would be expected by the skilled artisan making the measurement and exercising a level of care commensurate with the objective of the measurement and the precision of the measuring equipment used. The term "about" as used in connection with a numerical value throughout the specification and the claims denotes an interval of accuracy, familiar and acceptable to a person skilled in the art. In general, such interval of accuracy is + / -10%. Thus, "about" can be understood to be within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1 %, 0.5%, 0.1 %, 0.05%, 0.01 %, or 0.001 % greater or less than the stated value. Accordingly, unless otherwise indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0037] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. All numerical values, however, inherently contain a range necessarily resulting from the standard deviation found in their respective testing measurements.

[0038] The term "exemplary" means serving as a non-limiting example, instance, or illustration. As utilized herein, the terms "e.g.," and "for example" set off lists of one or more non-limiting aspects, examples, instances, or illustrations.

[0039] As used herein, the term "substantially" refers to the qualitative condition of exhibiting total or near-total extent or degree of a characteristic or property of interest.Biological and chemical phenomena rarely, if ever, go to completion and / or proceed to completeness or achieve or avoid an absolute result. The term "substantially" is therefore used herein to capture the potential lack of completeness inherent in many biological and chemical phenomena. For example, "substantially" may refer to being within at least about 20%, alternatively at least about 10%, alternatively at least about 5% of a characteristic or property of interest.Lathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCT

[0040] As used herein, the terms “nanoflow range” or “nanoflow regime” refer to flow rates less than about 1000 nanoliters / min, e.g., in a range of about 1 nanoliter / min to about 1000 nanoliters / min. As used herein, the terms “microflow range” or “microflow regime” refer to flow rates in a range of about 1 microliter / min to about 500 microliters / min. In some cases, the flow rate is even higher e.g., from about 500 microliters / min to about 3 ml / min).

[0041] As used herein, the term “fixedly positioned” as referring to an element indicates that the position of that element is not adjustable by a user.III. Source Housing and Probes for a Mass Spectrometer

[0042] The present disclosure is generally related to systems incorporating an electrospray ion source and methods for operating the same. In accordance with various aspects of the present disclosure, an ion source housing for use in a mass spectrometry system is disclosed in which a housing defining an ionization chamber provides at least a first opening for coupling to a first probe configured to discharge a liquid sample into the ionization chamber and a second opening for coupling to a second probe configured to discharge a liquid sample or calibration fluid into the ionization chamber and is disposed substantially on the central axis of the sampling inlet. In various aspects, the second probe is generally configured to spray a liquid sample or calibrant fluid at an angle to the central axis thereby to improve the calibration of the instrument before and / or during an experimental analysis of samples without contamination of the inlet of the mass spectrometer. For example, in various aspects, the second probe may be configured to alter the flow direction of the spray out of the second probe away from the inlet and toward a curtain plate encompassing the sampling inlet. Additionally or alternatively, the second probe can improve the detected signal intensity of the sample ions. Further, the second probe can improve the efficiency and confidence of the analysis by scheduling unattended calibration during an analytical experimental run that analyzes multiple samples.

[0043] The invention is defined in the claims. However, below is a non-exhaustive listing of non-limiting exemplary aspects. Any one or more of the features of these aspects may be combined with any one or more features of another example, embodiment, or aspect described herein.

[0044] FIG. 1 is an image showing a perspective view of an exemplary source housing 100 according to an embodiment of the present disclosure that includes an off-axis opening 120 and an on-axis opening 140, which may be coupled to a probe. Each openingLathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCTcan independently support various probes (e.g., an APCI probe, an ESI probe, a nanospray probe).

[0045] In one embodiment, both probes are ESI probes. Advantageously, one or both probes can be removed and replaced with a different ESI probe or different probe altogether (e.g., APCI or nanospray), allowing the source housing to operate in a variety of configurations, for example, depending on user preference or the experiments to be performed.

[0046] FIG. 2 is an image showing a side view of the inside of source housing 100 coupled to a mass spectrometer. Source housing 100 includes off-axis probe 124 extending from off-axis opening 120 and on-axis probe 144 extending from on-axis opening 140. At least a portion of on-axis probe 144 extends substantially coincident with a central axis 132a that extends coaxially to an inlet 136 of a mass spectrometer. Off-axis probe 124 extends substantially coincident with orthogonal sprayer axis 128b, which lies substantially orthogonal to central axis 132a. Off-axis probe 124 is configured to generate ions via electrospray ionization. Source housing 100 can be incorporated in a variety of different mass spectrometers for generating ions (e.g., a sector, a single quadrupole, a triple quadrupole, a Qtof, an ion trap, a Fourier-transform ion cyclotron resonance mass spectrometer). Further, source housing 100 is configured to accommodate different flow rates of samples to be ionized, including flow rates in the nanoflow, microflow, or higher flow ranges. By way of example, flow rates above the nanoflow range can be greater than about 1000 nanoliters / min to about 3 milliliters / min. In some embodiments, the flow range is from about 1 pl / min to about 500 pl / min, from about 5 pl / min to about 200 pl / min, or from about 10 pl / min to about 50 pl / min.

[0047] Off-axis probe 124 is positioned relative to an aperture (inlet 136) of a mass spectrometer in which at least some of the ions generated by off-axis probe 124 would pass through inlet 136 to reach the downstream components of a mass spectrometer, such as downstream mass separators and detectors. Off-axis probe 124 is positioned such that its longitudinal axis 128b is substantially orthogonal to the inlet's central axis 132a. Though a variety of sample flow rates may be accommodated (e.g., in the nanoflow range or higher), off-axis probe 124 is most beneficially utilized for sample flow rates higher than the nanoflow range as the orthogonal positioning of off-axis probe 124 relative to inlet 136 of the mass spectrometer can help ensure that a sufficient number of ions enter inlet 136 while minimizing, and preferably eliminating, the passage of a large number of incompletely desolvated ions. It will be appreciated that by reducing the entry of partially desolvated ionsLathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCTthrough inlet 136, contamination of the downstream components of the mass spectrometer can be ameliorated and / or prevented. Additionally, many samples can include endogenous and excipient compounds that will be discharged from off-axis probe 124. By reducing the entry of these components, interference with the analytes of interest during MS analysis may be reduced.

[0048] FIG. 3 is an image showing a side view of an exemplary on-axis probe 244, which includes proximal end 252 and distal end 256. On-axis probe 244 is configured to be inserted into the on-axis opening of the source housing. Upon insertion, proximal end 252 lies adjacent to the on-axis opening of the source housing and distal end 256 extends toward the inlet of the mass spectrometer. On-axis probe 244 also includes angled portion 248, which angles distal end 256, 0 degrees away from central axis 232a. In some embodiments, 0 is from about 1 to about 60 degrees. In some embodiments, 0 is from about 2 to about 15 degrees. In some embodiments, 0 is about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 11, about 12, about 13, or about 14 degrees. The on-axis probe can be positioned (e.g., rotated) to be angled toward the off-axis probe, away from the off-axis probe, or angled any direction there between. In other words, while angled portion 248 is fixedly positioned or angled 0 degrees relative to central axis 232a for a given probe and similarly the distance from distal end 256 to the inlet of the mass spectrometer is fixedly positioned, the distance from distal end 256 to a distal end of the off-axis probe can be changed by rotating on-axis probe 244 within the on-axis opening of the source housing.

[0049] The distance between angled portion 248 and distal end 256 is from about 15 mm to about 50 mm. In some embodiments, the distance between angled portion 248 and distal end 256 is from about 20 mm to about 45 mm, from about 25 mm to about 40 mm, or from about 30 mm to about 35 mm. In some embodiments, the distance between angled portion 248 and distal end 256 is about 25 mm, about 26 mm, about 27 mm, about 28 mm, about 29 mm, 30 mm, about 31 mm, about 32 mm, about 33 mm, about 34 mm, about 35 mm, about 36 mm, about 37 mm, about 38 mm, about 39 mm, 40 mm, about 41 mm, about 42 mm, about 43 mm, about 44 mm, or about 45 mm.

[0050] FIG. 4 is a schematic showing a cross-sectional view of on-axis probe 344, which includes a proximal end (not shown in FIG. 4) and distal end 356. On-axis probe 344 also includes notch 360. A portion of distal end 356 of on-axis probe 344 has been removed to form notch 360 having an elongated portion 364, which is the distance from distal end 356 to the end of notch 360. Elongated portion 364 is from about 0.5 mm to about 20 mm in length. In some embodiments, elongated portion 364 is from about 2 mm to about 18 mm, fromLathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCTabout 4 mm to about 16 mm, from about 6 mm to about 14 mm, or from about 8 mm to about 12 mm. In some embodiments, elongated portion 364 is about 1 mm, about 2 mm, about 3 mm, about 4 mm, about 5 mm, about 6 mm, about 7 mm, about 8 mm, about 9 mm, about 10 mm, about 11 mm, about 12 mm, about 13 mm, about 14 mm, about 15 mm, about 16 mm, about 17 mm, about 18 mm, or about 19 mm. In some embodiments, notch 360 defines a cross-sectional plane that is substantially co-planar with central axis 332a. The notch depth can vary from a range of about 0.1mm to the full diameter of the probe less about 0.1 mm.

[0051] Notch 360 includes angled notch a, which is from about 90 degrees to about 150 degrees relative to central axis 332a. In some embodiments, angled notch a is from about 95 degrees to about 145 degrees, from about 100 degrees to about 140 degrees, from about 105 degrees to about 135 degrees, from about 110 degrees to about 130 degrees, or from about 115 degrees to about 125 degrees.

[0052] On-axis probe 344 also includes fluid channel 368 that is circumferentially axial to central axis 332a. Fluid channel 368 includes angled portion 348, which angles fluid channel 368, p degrees away from central axis 232a. In some embodiments, is from about 1 to about 60 degrees. In some embodiments, p is from about 2 to about 15 degrees. In some embodiments, p is about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 11, about 12, about 13, or about 14 degrees. The on-axis probe can be positioned (e.g., rotated) such that angled portion 348 or notch 360 is angled toward the off-axis probe, away from the off-axis probe, or angled in any direction therebetween. In other words, while angled portion p is fixedly positioned relative to central axis 232a for a given probe and similarly the distance from an outlet of fluid channel 368 to the inlet of the mass spectrometer is fixedly positioned, the distance from an outlet of fluid channel 368 to a distal end of the off-axis probe can be changed by rotating on-axis probe 344 within the on-axis opening of the source housing.

[0053] The distance from angled portion 348 to an outlet of fluid channel 368 is from about 0.5 mm to about 20 mm in length. In some embodiments, the distance is from about 2 mm to about 18 mm, from about 4 mm to about 16 mm, from about 6 mm to about 14 mm, or from about 8 mm to about 12 mm. In some embodiments, the distance is about 1 mm, about 2 mm, about 3 mm, about 4 mm, about 5 mm, about 6 mm, about 7 mm, about 8 mm, about 9 mm, about 10 mm, about 11 mm, about 12 mm, about 13 mm, about 14 mm, about 15 mm, about 16 mm, about 17 mm, about 18 mm, or about 19 mm.

[0054] Both on-axis probes 244 and 344 can be fixedly positioned in the source housing and their distal ends 256 and 356, respectively, can be from about 0.5 mm to about 20 mmLathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCTaway from the inlet of the mass spectrometer. In some embodiments, the distance is from about 2 mm to about 18 mm, from about 4 mm to about 16 mm, from about 6 mm to about 14 mm, or from about 8 mm to about 12 mm. In some embodiments, the distance is about 1 mm, about 2 mm, about 3 mm, about 4 mm, about 5 mm, about 6 mm, about 7 mm, about 8 mm, about 9 mm, about 10 mm, about 11 mm, about 12 mm, about 13 mm, about 14 mm, about 15 mm, about 16 mm, about 17 mm, about 18 mm, or about 19 mm.

[0055] The probes disclosed herein can be any suitable probe known in the art or hereafter developed that can be used for electrospray ionization (ESI) and modified according to the present teachings. Such suitable ESI probes include, for example, a probe with an emitter in which the position of the electrospray emitter may be extended or adjusted relative to the discharge end of the probe as in conventional ESI. In some embodiments, the emitter of the probe may extend out of the probe body at the discharge end by a fixed amount (z.e., by a distance which is not adjustable by a user), thereby eliminating the need for some physical adjustment of the length of the emitter, which is often the most difficult and time-consuming aspects of ion source optimization. By way of example, in some exemplary aspects, the probe can include an emitter that extends by a fixed amount beyond the distal end of the probe. In some embodiments, the probe includes a fluid channel that extends from the proximal end to the distal end and in which an emitter can be installed. The fluid channel may include at least a portion of the fluid channel formed of a polymer, such as poly ether ether ketone (PEEK) while another portion of the fluid channel may be formed of stainless steel. In some embodiments, the emitter extends beyond the distal end of the probe by a fixed (non-adjustable) amount (D). The emitter may include an emitter channel (e.g., a microchannel) that extends from an entrance end to an ionization discharge end of the emitter. The ionization discharge end of the emitter may extend out of the probe by a fixed (non-adjustable) amount D relative to the distal end of the probe. The fixed distance D can be, for example, in a range of about 0.1 mm to about 2 mm. By way of non-limiting example, the fixed distance D for a probe accommodating sample flow rates in the nanoflow range can be about 0.9 mm, and the fixed distance D for the probe accommodating sample flow rates above the nanoflow range can be about 1.0 mm.

[0056] Generally, the distal ends of the probes include an electrically conductive electrode for generating an electric field adjacent the inlet of the mass spectrometer when coupled to a power source, though in some aspects, additional portions of the probe may also be electrically conductive e.g., formed of stainless steel), such that the entire portion disposed within the ionization chamber functions as an electrode for adjusting the electricLathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCTfield generated between the discharge end of the probe and the curtain plate. Though not shown, it will be appreciated that an electric potential may be applied to the probe and its distal end by coupling to one or more power sources (not shown). In some embodiments, the electrode of the on-axis probe may be maintained at substantially the same potential as that applied to the off-axis probe, and indeed, may in some aspects be coupled to the same power supply to reduce costs, for example. By way of non-limiting example, the discharge end of the on-axis probe and the distal end of the off-axis probe can be maintained in a range of about 2000 V to about 6000 V (e.g., about 5 kV).

[0057] The source housing can further include one or more heaters that are coupled to the source housing and are configured to heat the ionization chamber to assist in the desolvation of the ions generated by the probes, for example, before those ions reach the inlet of the mass spectrometer. In some embodiments, the source housing includes one, two, three, four, or more heaters that are disposed non-coaxially relative to the probes. Alternatively, the heaters can also be utilized as a gas source to provide temperature control over the path taken by the sample. The heaters can act as a simple gas source for cooling or a heated gas source for heating of the distal ends of the probes (e.g., the discharge tips of the emitters), the sample path and the curtain plate. It will be appreciated that the location and orientation of the heater(s) may vary to accommodate different source geometries and sample flow regimes to achieve a desired level of thermal control over the environment to which the sample is exposed prior to its entry to the inlet of the mass spectrometer.

[0058] The fluid channel may be coupled to a gas source, such that a nebulizer gas can be provided from the distal end of the probes (with or without the emitter) so as to shape and / or contain the spray discharged from the emitter (e.g., direct the spray toward the inlet) or may shape the sample plume generated by the probes to further assist in ion transport to the inlet.

[0059] The distal end of the probes can have a variety of configurations, but is generally configured to physically interact with the sample plume generated by the probes and / or the electric field generated thereby to improve the desolvation of the sample plume and the transport of ions ejected from the sample plume into the inlet. The electrically conductive distal end can have a variety of shapes and sizes.

[0060] The probes disclosed herein can support various flow rates. In some embodiments, the probes have sample flow rates in the nanoflow range. In some embodiments, the probes have sample or calibrant flow rates higher than the nanoflow range. Advantageously, the on-axis probes disclosed herein can support, for example, calibrant flow rates from about 1 pl / min to about 3 ml / min without contaminating the inlet or down stream components of theLathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCTmass spectrometer. In some embodiments, the calibrant flow rates are from about 2 pl / min to about 500 pl / min without contaminating the inlet or down stream components of the mass spectrometer. In some embodiments, the calibrant flow rates are from about 10 pl / min to about 50 pl / min without contaminating the inlet or down stream components of the mass spectrometer.

[0061] The on-axis probes disclosed herein angles or diverts the incomplete desolvated spray away from the central axis of the inlet of the mass spectrometer. The incomplete desolvated spray can impact a curtain plate that circumferentially surrounds the inlet of the mass spectrometer. In some cases, the incomplete desolvated spray remains captured, trapped, or immobilized on the curtain plate. In some embodiments, more than about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, about 98%, or about 99% of the incomplete desolvated spray impacts a curtain plate. In some embodiments, the incomplete desolvated spray impacts the curtain plate from about 5 mm to about 50 mm away from the inlet to the mass spectrometer. In some embodiments, the incomplete desolvated spray impacts the curtain plate from about 10 mm to about 45 mm, about 15 mm to about 40 mm, about 20 mm to about 35 mm, or about 25 mm to about 30 mm away from the inlet to the mass spectrometer.

[0062] An on-axis probe as disclosed herein can be used to calibrate the mass spectrometer on-demand or in a scheduled manner. Advantageously, the on-axis probe can be used to calibrate the mass spectrometer while the off-axis probe is dedicated to running analytical samples without changing probes or configuration of the probes within the source housing. This can improve the mass accuracy of the mass spectrometer throughout the entire analytical run of multiple samples. In some cases, the number of samples are from 2 to 10,000 or more samples. Scheduling calibration in between sample analyses can mitigate some potential errors generated during the running of multiple samples (e.g., instrument drift).

[0063] Briefly, calibration occurs by introducing ions in a calibrant fluid with known mass to charge ratios into the mass spectrometer, which separates the ions based on their mass to charge ratios. The instrument responses associated with the detected ions are associated with the known masses, generating a mass scale. Unknown samples or analyte fluids containing analytes can then be introduced into the mass spectrometer and the instrument response is recorded. The detected unknown ions are then interpolated or extrapolated by comparing the recorded responses to the mass scale, facilitating the determination of the unknown ions mass to charge ratios. The calibration can occur before,Lathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCTafter, and / or in between the analysis of the samples or analyte fluids. In some embodiments, the calibration is carried out at the beginning, at the end, and periodically during the analysis of multiple samples.EXAMPLESExample 1

[0064] A mass spectrometer was calibrated repeatedly using an on-axis conventional probe or an on-axis probe that angles the spray away from the center axis as disclosed herein.FIGS. 5A and 5B are images of inlet 436 of a mass spectrometer viewed from the front (orthogonal to central axis 432a). As shown in FIG. 5A, inlet 436 of the mass spectrometer accumulates incomplete desolvated spray 438 along the edges of inlet 436 over time using a conventional on-axis probe. The calibration was repeated to simulate typical usage of the mass spectrometer over approximately five months. As shown in FIG. 5B, no substantial amount of incomplete desolvated spray accumulated along the edges of inlet 436 run under the same conditions for the same duration of time using an on-axis probe as disclosed herein.Example 2

[0065] A mass spectrometer was calibrated repeatedly using an on-axis probe that angles the spray away from the center axis as disclosed herein. FIGS. 6A and 6B are images showing a side view of the interior of the source housing and a front-view of the inlet to the mass spectrometer, respectively. FIG. 6A shows off-axis probe 524, on-axis probe 544 configured with angled portion 0 angled toward off-axis probe 544, curtain plate 534, and inlet 536. Also shown in FIG. 6A is incomplete desolvated spray 538 that accumulated on curtain plate 534 over time. FIG. 6B shows inlet 536, curtain plate 534, and incomplete desolvated spray 538 that accumulated on curtain plate 534 over time. Advantageously, incomplete desolvated spray 538 accumulated on curtain plate 534 and not in inlet 536, allowing for more instrument uptime without sacrificing performance, resulting in less maintenance, and resulting in fewer calibrant carry-over issues. FIG. 7 is an image showing a side view of the interior of the source housing. FIG. 7 shows off-axis probe 524, on-axis probe 544 configured with angled portion 0 angled away from off-axis probe 544, curtain plate 534, and inlet 536.Lathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCTExample 3

[0066] Four on-axis probes that angle the spray away from the center axis at different angles were tested (three of the probes are shown in FIG. 8 and the results are reported in TABLE 1). All four showed a signal gain for all ions introduced through the off-axis probe as compared to the signal obtained for ions using the off-axis probe without the on-axis probe in the on-axis opening of the source housing. The 0 degrees of the angled portion of the on-axis probes are reported in TABLE 1 as 0 angle. The ions used for the sensitiveity gain comparison were those of a calibration solution. Advantageously, multiply charged ionsshowed greater gains than the singly charged ions.TABLE 1Example 4

[0067] FIGS. 9A and 9B are images showing a side view of the interior of the source housing. FIG. 9A shows notched probe 644 configured with the notch angled toward the off-axis probe. FIG. 9B shows notched probe 644 configured with the notch angled away from the off-axis probe.

[0068] All references, including publications, patent applications, and patents, citedherein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0069] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications andLathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCTequivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

Lathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCTWhat is claimed is:

1. A source housing for a mass spectrometer, the source housing comprising: a first opening configured to couple with an off-axis probe substantially orthogonal to a central axis of an inlet to the mass spectrometer and a second opening configured to couple with an on-axis probe substantially coincident with the central axis, wherein the off-axis probe and the on-axis probe are in fluid communication with the inlet to the mass spectrometer and wherein the on-axis probe is configured to direct a fluid at an angle to the central axis.

2. The source housing of claim 1, wherein the on-axis probe is removable.

3. The source housing of claim 1 or claim 2, wherein the on-axis probe comprises an angled portion.

4. The source housing of claim 3, wherein the angled portion is angled from about 1 degree to about 60 degrees from the central axis.

5. The source housing of claim 3 or claim 4, wherein the on-axis probe is angled toward the off-axis probe, away from the off-axis probe, or any direction there between.

6. The source housing of any one of claims 3 to 5, wherein the on-axis probe comprises a proximal end and a distal end and wherein the angled portion is from about 15 mm to about 50 mm from the distal end.

7. The source housing of claim 1 or claim 2, wherein the on-axis probe comprises a proximal end and a distal end, wherein the proximal end is adjacent to the second opening and wherein the distal end comprises a notch.

8. The source housing of claim 7, wherein the notch comprises an elongated portion and the elongated portion is from about 0.5 mm to about 20 mm.

9. The source housing of claim 7 or claim 8, wherein the notch comprises an angled notch and the angled notch is from about 90 to about 150 degrees.

10. The source housing of any one of claims 7 to 9, wherein the on-axis probe comprises a fluid channel.Lathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCT11. The source housing of claim 10, wherein the fluid channel comprises an angled portion.

12. The source housing of claim 11, wherein the angled portion is angled from about 1 degree to about 60 degrees from the central axis and angled away from the elongated portion.

13. The source housing of claim 10 or claim 11, wherein the angled portion is from about 0.5 mm to about 20 mm from a fluid channel outlet.

14. The source housing of any one of claims 7 to 13, wherein the notch is oriented toward the off-axis probe, away from the off-axis probe, or any direction there between.

15. The source housing of any one of claims 1 to 14, wherein the fluid is a calibration fluid.

16. The source housing of claim 15, wherein the calibration fluid has a flow rate of about 20 pl / min to about 200 pl / min.

17. The source housing of any one of claims 1 to 16, wherein the on-axis probe is configured to form a desolvated spray and more than about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, about 98%, or about 99% of the desolvated spray impacts a curtain plate, which encircles the inlet to the mass spectrometer.

18. The source housing of any one of claims 1 to 17, wherein desolvated spray impacts the curtain plate from about 5 mm to about 50 mm radially away from the central axis of the inlet to the mass spectrometer.

19. The source housing of any one of claims 6 to 18, wherein the distal end of the on-axis probe is from about 0.5 mm to about 20 mm from the orthogonal sprayer axis.

20. A system comprising the source housing of any one of claims 1 to 19 and a mass spectrometer.

21. The system of claim 20, wherein the mass spectrometer is a sector, a single quadrupole, a triple quadrupole, a Qtof, a Tof, an ion trap, or a Fourier-transform ion cyclotron resonance mass spectrometer.Lathrop Ref. No. 770144: DASC-876PC Sciex Ref. No. 2024-25005 -PCT22. A method of calibrating a mass spectrometer, the method comprising using the source housing of any one of claims 1 to 19 or the system of claim 20 or claim 21; flowing a calibrant fluid through the on-axis probe; and generating a calibration mass scale.

23. The method of claim 22 further comprising flowing an analyte fluid through the off- axis probe before or after flowing the calibrant fluid through the on-axis probe.

24. The method of claim 23 further comprising determining a mass of an analyte in the analyte fluid.

25. The method of any one of claims 22 to 24, wherein the flowing the calibrant fluid through the on-axis probe is scheduled to run via a software interface before, after, in between, or a combination thereof the flowing of the analyte fluid.

26. The method of any one of claims 22 to 24, wherein the inlet to the mass spectrometer is substantially clean from about 1 hour to after about 4, about 5, or about 6 months of use.

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