Atmospheric pressure ionization in combination with electron ionization mass spectrometer

Abstract

An atmospheric pressure electron impact ionization mass spectrometer system includes an atmospheric pressure ionization component operating at atmospheric pressure. The electron impact ionization mass spectrometer includes an electron ionization source. The atmospheric pressure interface operates below about 10 Torr. The atmospheric pressure interface includes a source block for focusing a plurality of molecules and ions from the atmospheric pressure ionization component at atmospheric pressure into an electron ionization source operating at a pressure of less than about 10 <-3 > Torr.

Description

Cross - Reference to Related Applications

[0001] This application claims the benefit and priority of U.S. Non - Provisional 18 / 382,570, entitled "Atmospheric Pressure Ionization in Combination with an Electron Ionization Mass Spectrometer", filed on October 23, 2023, which claims the benefit of U.S. Provisional 63 / 423,190, entitled "Atmospheric Pressure Ionization in Combination with an Electron Ionization Mass Spectrometer", filed on November 7, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to mass spectrometry, and particularly to atmospheric pressure ionization techniques for use with electron ionization mass spectrometers. Background Art

[0003] Bioanalytical techniques for small molecule drug development typically utilize atmospheric pressure ionization techniques. Summary of the Invention

[0004] An atmospheric pressure electron impact ionization mass spectrometer system includes an atmospheric pressure ionization component operating at atmospheric pressure. The electron impact ionization mass spectrometer includes an electron ionization source. The atmospheric pressure interface operates at below about 10 Torr. The atmospheric pressure interface includes a source block for focusing a plurality of molecules and ions from the atmospheric pressure ionization component at atmospheric pressure into the electron ionization source, which operates at a pressure below about 10 -3 Torr.

[0005] The atmospheric pressure ionization component may include an electrospray ionization (ESI) component. The atmospheric pressure ionization component may include an atmospheric pressure chemical ionization (APCI) component. The atmospheric pressure ionization component may include an atmospheric pressure analysis probe (ASAP) component.

[0006] The atmospheric pressure electron impact ionization mass spectrometer system may further include a processor operatively coupled to at least the electron impact ionization mass spectrometer. The processor is configured and adapted to run a mass spectrometer analysis process. The electron ionization source may include a 70 eV electron ionization source, and the mass spectrometer analysis process may be configured to directly search an established 70 eV mass spectral library database. The electron ionization source may include a 40 eV electron ionization source.

[0007] The above and other aspects, features, and advantages of the present application will become more apparent from the following description and claims. Brief Description of the Drawings

[0008] The features of the present application can be better understood with reference to the drawings and claims described below. The drawings are not necessarily to scale, and emphasis is generally placed on illustrating the principles described herein. In the drawings, like numerals in the various views are used to indicate like components.

[0009] Figure 1is a diagram showing an exemplary 70 eV EI mass spectrometry identification of caffeine;

[0010] Figure 2 shows an exemplary API / EI (atmospheric pressure ionization / electron ionization) mass spectrometer system according to one or more illustrative embodiments of the present disclosure;

[0011] Figure 3 is a schematic diagram showing an exemplary API / EI mass spectrometer system according to one or more illustrative embodiments of the present disclosure;

[0012] Figure 4 is a flowchart showing a process for analyzing a sample according to one or more illustrative embodiments of the present disclosure; and

[0013] Figure 5 shows a distributed communication network according to one or more exemplary embodiments of the present disclosure. Detailed Description

[0014] Bioanalytical techniques for small molecule drug development (<2000 Daltons (Da)) typically utilize atmospheric pressure ionization techniques (such as including but not limited to electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI)), which require highly experienced technicians to interpret the data generated in the techniques and processes.

[0015] Analytes are typically detected as molecular ion adducts, such as [M+H]+, [M+Na]+, [M+K]+, [M+ACN]+, / M+MeOH]+, etc. Detecting analytes as molecular ion adducts results in very complex mass spectra. Fragmentation caused by collision-induced dissociation makes the mass spectra even more complex. These mass spectra cannot be searched in libraries, and there may be significant differences in the mass spectra of different instruments, different settings, and other parameters. For example, Figure 1 is a diagram showing an exemplary 70 eV EI mass spectrometry identification of caffeine.

[0016] It has been recognized that atmospheric pressure ionization (API) can be combined with electron ionization (EI) as an API / EI mass spectrometer. The new API / EI combined mass spectrometer can generate an EI mass spectrum at 70 eV. The 70 eV EI mass spectrum can be used for library searches using NIST and Wiley libraries (e.g., searchable through the NIST Chemistry WebBook; NIST20: NIST Tandem and Electron Ionization Spectral Libraries). The NIST Chemistry WebBook provides users with easy access to chemical and physical property data of chemical substances via the Internet. The data on this website is from datasets maintained by the NIST Standard Reference Data Program and external contributors. The data in the WebBook system is organized by chemical species. The WebBook system allows users to search for chemical species in various ways. Once the desired species is identified, the system will display the data for that species.

[0017] To date, such API / EI mass spectrometry has not been achievable. It is believed that, according to the illustrative embodiments of the present invention, the new combination of API and EI for mass spectrometry enables this new synergy, which can revolutionize small molecule drug development in pharmaceuticals. The new API / EI mass spectrometer according to the illustrative embodiments can also be used in environmental applications, such as military and first responder applications, airport screening, in academia as a research and teaching tool, etc.

[0018] By using the new combination of API and EI in an API / EI mass spectrometer, the simplicity and speed of mass spectrometry interpretation substantially eliminate and minimize misunderstandings of mass spectra. In addition, the user no longer needs to be a mass spectrometry expert; the user only needs to click on the mass spectrum to display analyte ID matches.

[0019] Figure 2 FIG. is a diagram showing an exemplary API / EI mass spectrometer system 2000 according to one or more illustrative embodiments of the present invention. Atmospheric pressure ionization is performed by any suitable component, such as an electrospray ionization (ESI) device 2003a, an atmospheric pressure chemical ionization (APCI) device 2003b, or an atmospheric pressure analysis probe (ASAP) device 2003c. Sample molecules enter in liquid or solid form. The new atmospheric pressure interface 2001 focuses the molecules and ions from the atmospheric pressure ionization device (e.g., 2003a, 2003b, or 2003c) into the electron impact ion source 2005. The atmospheric pressure interface 2001 includes new aspects and structures in combination, including one or more inlet capillaries, orifices, intercepting lens apertures, and a turbopumping system with optimized gas flow dynamics.

[0020] The 70 eV products or fragments generated or produced by the electron impact ion source 2005 are analyzed by the mass analyzer 2007 and the detector 2009. Any suitable detector 2009 with an analog or digital output can be used. A photomultiplier tube (PMT) is an example of a suitable type of analog detector.

[0021] The processor 999 is operatively coupled to at least the mass analyzer 2007 and may optionally be coupled to any other components as Figure 2 shown. Any suitable components can be used for the electron impact source 2005. Any suitable processor 999 can be used. It should be understood that the processor 999 may include any suitable memory, computer interface, and optionally an instrument display ( Figure 2 not shown in).

[0022] It has been recognized that according to the illustrative embodiments of the present disclosure, a novel interface, such as the atmospheric pressure interface 2001, can be used to achieve a new combination of API / EI mass spectrometers. The new interface solves the problem of pressure drop while also focusing ions into the mass spectrometer. The atmospheric pressure interface 2001 provides a pressure gradient from atmospheric pressure ionization to the electron impact ion source 2005 as well as focusing (e.g., electrostatic focusing), and guides ions and molecules from the atmospheric pressure ionization devices 2003a, 2003b, 2003c into the electron impact ionization source 2005. The front-end fluid dynamics allows for atmospheric opening through differential pumping without flooding the system, while allowing the electron ionization source to operate at a relatively low pressure. In an exemplary embodiment, a system including at least the atmospheric pressure interface 2001 is capable of achieving differential pumping from atmospheric pressure to 2 mbar and then to 10 -4 mbar. The ions are focused into the electron impact ion source 2005 by one or more lenses and electrostatic fields.

[0023] In an embodiment, the API / EI mass spectrometer system includes Figure 2 one or more of the components shown in. In certain embodiments, the API / EI mass spectrometer system includes each component.

[0024] Example: Figure 3 A schematic diagram of a new API / EI spectrometer 3000 (with annotations) according to an illustrative embodiment of the present disclosure is shown. The figure includes an exemplary hardware interface and the above two figures, which illustrate ion focusing and the transition from the atmospheric pressure of the API to the vacuum of the EI mass spectrometer ionization source.

[0025] Atmospheric pressure ionization is performed by the ionization device 3100 (e.g., Figure 2is performed by ESI, APCI, or ASAP). The atmospheric pressure interface 3300 (an example of the atmospheric pressure interface 2001) includes a source block 3310, such as an optical block for guiding ion and molecule focusing. In an embodiment, Figure 3 The exemplary atmospheric pressure interface 3300 includes a source block 3310 having an electrostatic plate 3315 and a conical intercepting lens 3330 (schematically shown). The atmospheric pressure interface 3300 implements a pressure conversion from the atmospheric pressure of the atmospheric pressure ionization device 3100 to a pressure of about 2 millibars (mbar) within the atmospheric pressure interface 330. Ions and molecules are received into the tube / capillary 3320 and can be adjusted up or down as indicated by the vertical arrow "v" to be set at an optimized position. This position can be set by any suitable continuous or ratchet structure and adjusted by any appropriate manual or electric technique (e.g., by a stepper motor). The optical electrostatic plate 3310 of the atmospheric pressure interface 3300 orthogonally focuses molecules and ions into the intercepting lens 3330. The tube / capillary can be set and optimized to about +200V; the source block can be set to and optimized to about +50V; the intercepting lens 3330 can be set to and optimized to about +10V, thereby providing an electrostatic potential gradient to focus ions into the electron ionization source 3500.

[0026] The atmospheric pressure interface 3300 focuses molecules and ions into the closed ion source (CIS) 3520 at a vacuum of 10 -4 mbar, where the ions and molecules are exposed to 70 eV of electron ionization. The 70 eV ionized molecules and ions from the ionization source 3500 are further focused into the mass spectrometer through the focusing lens stack 3530 and the quadrupole mass filter 3700.

[0027] Exemplary voltage gradient variations from the atmospheric pressure ionization device 3100 to the ionization source 3500 include but are not limited to the following. The exemplary operating voltage at the atmospheric pressure ionization device 3100 is about 3500V to 5000V. The voltage at the entrance of the atmospheric pressure interface 3300 is about 200V, and the plate voltage in the source block optics is about 50V. The electrostatic plate 3310 of the source block optics is about +50V. The voltage at the intercepting lens 3330 (the conical entrance where ions enter the electron ionization source 3500) is about 10V. The voltages referred to above are the lens voltages for focusing ions into the electron ionization source.

[0028] Exemplary progress of the pressure drop from the atmospheric pressure to the vacuum below the voltage gradient line includes but is not limited to the following. Depending on the atmospheric pressure of the atmospheric pressure ionization device 3100, the entrance of the atmospheric pressure interface 3300 and the atmospheric pressure interface 3300 are both at a pressure of about 2 millibars. The pressure of the ionization source 3500 is about 2x10 -4 torr (~10 -4 mbar).

[0029] The differential pumping region can be maintained by any suitable vacuum pump, typically a turbomolecular pump, in combination with a narrow aperture capillary, an orifice, and an intercept lens aperture. The inlet capillary allows the first stage pressure to drop from ATM to about 2 mbar, and the combination of the orifice and the intercept lens aperture allows the second stage pressure to drop from 2 mbar to 10 -4 mbar.

[0030] An atmospheric pressure electron impact ionization mass spectrometer system according to an exemplary embodiment of the present disclosure preferably operates with electron ionization at 70 eV to directly use the NIST or Wiley databases. However, an atmospheric pressure electron impact ionization mass spectrometer system according to an exemplary embodiment of the present invention can also operate at 40 eV electron ionization using a 40 eV electron ionization source. The softer ionization with a lower emission of 40 eV can be compatible with standard 40 eV analysis, which is common in some semiconductor manufacturing applications.

[0031] An electrospray ionization (ESI) probe (e.g., FIG. 22003a) can be used for single-charged and multi-charged molecules (targeting acidic and basic molecules). Atmospheric pressure chemical ionization (APCI) (e.g., FIG. 22003b) or atmospheric pressure analysis probe (ASAP) (e.g., FIG. 22003c) can be used for single-charged molecules (targeting neutral and non-polar molecules). 70 eV EI can be used together with an electron multiplier (EM) detector heated inlet (>100°C). The turbo bypass can evacuate the API (e.g., FIGS. 22001, 3300) to about 2 mbar, for example, by ultrasonic expansion, while optimizing the sampling of the Mach disk region ion optics. There can be independent voltage control on the atmospheric pressure interface (API) lens (e.g., FIG. 33330), for example, by modifying the front end to allow separate voltages / gradients.

[0032] Mass spectrometry process - The mass spectrometry process can include tuning and mass calibration of the API-EI MS by controlling various voltages, pneumatic valves, vacuum pump systems, detection optics, and signal amplification and digitization. The process can also operably incorporate and control the conversion of analog-to-digital (ADC) (e.g., the analog output from one or more detectors), and plot the mass spectrum on a user interface, for example, by a processor and / or any suitable computer (desktop, laptop, notebook, tablet, etc.), allowing the user to seamlessly search a library mass spectrometry database as described above.

[0033] The above describes a novel atmospheric pressure ionization / liquid chromatography separation technique (electrospray ionization ESI, atmospheric pressure chemical ionization APCI) combined with an electron impact ionization mass spectrometer. The atmospheric pressure ionization / solid analysis technique (atmospheric solids analysis probe ASAP) can be connected to an electron impact ionization mass spectrometer. An electrospray ionization probe voltage of 1 - 5 kV (constant voltage, variable current) can use fused silica or stainless steel capillary tubes. By using fused silica or stainless steel capillary tubes, the atmospheric pressure ionization current can be about 1 to 5 mA (constant current, variable voltage). A pneumatically operated atmospheric pressure ionization source (ESI, APCI, ASAP) can operate within a pressure range of about 30 to 150 psi. Suitable pneumatic gases include, for example, N2, O2, air, inert gases (He, Ne, Ar, Kr, Xe), their single gases or gas combinations. Suitable coaxial pneumatic heated desolvation gases (50 - 400 °C) include, for example, N2, O2, air, inert gases (He, Ne, Ar, Kr, Xe), their single gases or gas combinations. Nanoelectrospray can use, for example, microcapillaries, chips (silicon wafers, glass or combinations of both) and / or electrophoresis separation techniques combined with an electron impact ionization mass spectrometer. The range of electron ionization energy can be from about 10 eV to 100 eV. Any suitable narrow-bore capillary, orifice or combination of both can be used to differentially pump the mass spectrometer from about 760 Torr (atmospheric pressure) to 2 Torr. Any suitable heated inlet / interface / interstage component can be used within a temperature range of about 50 °C to 250 °C. The mass spectrometer can be differentially pumped within a pressure range of about 760 Torr to < 2 Torr. The mass spectrometer can be differentially pumped from 760 Torr to < 1x10 -3 Torr. The mass spectrometer can be differentially pumped from 760 Torr to < 1x10 -6 Torr. Any suitable type of mass spectrometer can be used, including, for example, single quadrupole, time-of-flight, ion trap and tandem and hybrid instruments. The mass spectrometer can be equipped with, for example, a Faraday cup, electron multiplier, high energy conversion dynode or any combination thereof. The mass range of the mass spectrometer is about m / z 1 to 5000. It is possible to turn off EI to provide ESI, APCI or only ASAP mass spectra. It is possible to generate single-charge and multi-charge ion species. The processor can assemble API / EI mass spectra into a library format. There can be quadrupole, hexapole or octapole ion focusing (e.g., only RF from about 300 to 1000 kHz, scan amplitude or fixed amplitude) for ion transport to facilitate collisional cooling of ions before entering the mass analysis component.

[0034] Figure 4It is a flowchart showing a process for analyzing sample molecules according to some embodiments of the present disclosure. In step 4002, for example, sample molecules are introduced into the atmospheric pressure ionization devices 2003a, 2003b, 2003c, and corresponding ionization processes are performed to form sample molecule ions. In step 4004, the sample ions are transferred to the atmospheric pressure interface 2001, where, through a pressure difference including the use of one or more lenses, capillaries, and / or electrostatic voltages, the sample ions are focused into the electron impact source 2005. In step 4006, the sample ions and / or molecules undergo an electron ionization process under vacuum, for example, 70 eV electron ionization through the electron impact source 2005, to generate fragment ions, which are analyzed and detected by the mass analyzer 2007 and the detector 2009 to generate a mass spectrum (step 4008). The generated mass spectrum can be presented visually on a screen associated with the processor 999. The generated mass spectrum is compared with a mass spectrometry library database associated with or communicating with the processor (step 4010). The determination or percentage probability library match of the identified analyte is communicated to the user (step 4012).

[0035] Any software and / or firmware including a mass spectrometry analysis process for an API / EI collision ionization mass spectrometer system according to illustrative embodiments of the present disclosure can be provided on a computer-readable non-transitory storage medium. A computer-readable non-transitory storage medium for non-transient data storage includes any data stored in a non-transitory manner on any suitable medium. Such data storage includes any suitable computer-readable non-transitory storage medium, including but not limited to hard disk drives, non-volatile RAM, SSD devices, CDs, DVDs, etc.

[0036] Figure 5A computing / communication system according to one or more embodiments of the present disclosure is shown. In an exemplary embodiment, the computing / communication system 5000 includes atmospheric pressure electron impact ionization mass spectrometer systems 2000, 3000, a processor 999, and a display 5002. The processor 999 and the display 5002 may or may not be incorporated into the atmospheric pressure electron impact ionization mass spectrometer systems 2000, 3000. One or more computing devices 5004 (e.g., smartphones, tablets, portable computers, iPhones, etc.) (hereinafter referred to as PCDs) communicate with at least one of the processors 999 of the atmospheric pressure electron impact ionization mass and / or spectrometer systems 2000, 3000 via a network 5006. The network 5006 may include, for example, a global computer network such as the Internet, a wide area network (WAN), a local area network (LAN), a satellite network, a telephone or wired network, or various portions or combinations of these and other types of networks (including wired and / or wireless networks). In an exemplary embodiment, the computing system 5000 may be a LAN-based environment where all processing and analysis may be performed by one or more computing devices locally coupled to the LAN. In one or more embodiments, the computing system environment employs a cloud computing platform, where "cloud" refers to the collective computing infrastructure that enables the cloud computing paradigm. The processor 999 and / or the atmospheric pressure electron impact ionization mass spectrometer systems 2000, 3000 communicate with a spectral library database 5008 via, for example, the network 5006. The spectral library database 5008 may be remote from the processor 999 and they are connected via a network. In an exemplary embodiment, one or more of the computing devices 5004 may include the processor 999. In other embodiments, one or more of the computing devices 5004 communicate with the processor 999 and / or the atmospheric pressure electron impact ionization mass spectrometer systems 2000, 3000 such that according to Figure 4 the state and / or operation results of the system of the process can be continuously monitored and / or displayed on one or more of the computing devices 5004. In some embodiments, the state and / or results of the process may be visualized on the display 5002 associated with the processor 999 to present results associated with the mass spectrum. Other arrangements are also contemplated.

[0037] It should be understood that the variations and other features and functions, or alternatives thereof, disclosed above may be combined into many other different systems or applications. Those skilled in the art may subsequently make various currently unforeseen or unexpected alternatives, modifications, variations, or improvements thereto, which are also intended to be covered by the appended claims.

Claims

1. An atmospheric pressure electron impact ionization mass spectrometer system, comprising: a. An atmospheric pressure ionization component operating at atmospheric pressure; b. An electron impact ionization mass spectrometer component, which includes an electron ionization source; and c. An atmospheric pressure interface component operating below about 10 Torr, said atmospheric pressure interface assembly including a source block for focusing a plurality of molecules and ions from an atmospheric pressure ionization component at atmospheric pressure into an electron ionization source, said electron ionization source operating at a pressure below about 10 -3 Torr.

2. The atmospheric pressure electron impact ionization mass spectrometer system according to claim 1, wherein the atmospheric pressure ionization component includes an electrospray ionization (ESI) component.

3. The atmospheric pressure electron impact ionization mass spectrometer system according to claim 1, wherein the atmospheric pressure ionization component includes an atmospheric pressure chemical ionization (APCI) component.

4. The atmospheric pressure electron impact ionization mass spectrometer system according to claim 1, wherein the atmospheric pressure ionization component includes an atmospheric pressure analysis probe (ASAP) component.

5. The atmospheric pressure electron impact ionization mass spectrometer system according to claim 1, further comprising a processor operably coupled to at least the electron impact ionization spectrometer assembly, the processor being configured to perform a mass spectrometer analysis process.

6. The atmospheric pressure electron impact ionization mass spectrometer system according to claim 5, wherein the electron ionization source includes a 70 eV electron ionization source.

7. The atmospheric pressure electron impact ionization mass spectrometer system according to claim 6, wherein the processor communicates with a 70 eV mass spectral library database.

8. The atmospheric pressure electron impact ionization mass spectrometer system according to claim 1, wherein the electron ionization source includes a 40 eV electron ionization source.

9. The atmospheric pressure electron impact ionization mass spectrometer system according to claim 1, wherein the source block optics includes at least one of an electrostatic plate and an extraction lens, and the extraction lens is one or more.

10. The atmospheric pressure electron impact ionization mass spectrometer system according to claim 1, including a pump configured to generate a differential pumping region.

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