Chemical ionization ion source and chemical ionization method

Abstract

The invention relates to a chemical ionization ion source for ionizing analytes in a sample into analyte ions by chemical ionization. The chemical ionization ion source comprises an irradiation chamber forming an irradiation chamber volume, a photoelectron emitting surface comprised in the irradiation chamber for emitting photoelectrons in the irradiation chamber volume upon being subjected to electromagnetic radiation, a source of electromagnetic radiation adapted to irradiate the photoelectron emitting surface with electromagnetic radiation, a reaction chamber defining a reaction chamber volume for ionizing analytes into analyte ions in the reaction chamber volume by bringing the analytes into contact with reagent ions, respectively, the reaction chamber further having an outlet, a chamber interface adapted to put the irradiation chamber volume in fluid communication with the reaction chamber volume, a collection electrode, a collection electrode voltage source for applying a voltage difference between the photoelectron emitting surface and the collection electrode, and a control unit. The invention further relates to a chemical ionization method for ionizing analytes in a sample into analyte ions by chemical ionization using a chemical ionization ion source.

Description

Technical Field

[0001] This invention relates to a chemical ionization ion source for ionizing analytes in a sample into analyte ions by chemical ionization, particularly for use in mass spectrometry. Furthermore, this invention relates to a chemical ionization method for ionizing analytes in a sample into analyte ions by chemical ionization using a chemical ionization ion source, particularly according to the present invention, particularly for chemical ionization methods used in mass spectrometry analysis. Background Technology

[0002] In chemical ionization, analytes are ionized in a reaction chamber through collisions between analytes and reagent ions. These reagent ions are sometimes referred to as primary ions. Reagent ions can be generated from reagents in solid, liquid, or gaseous states. Therefore, reagents can be ionized into reagent ions, for example, through electron ionization, electromagnetic radiation such as X-rays or UV radiation, or radioactive radiation.

[0003] Chemical ionization is considered a mild ionization technique used to generate analyte ions from a sample. During chemical ionization, analyte molecules in the sample react with reagent ions, which transfer their charge to the analyte molecules, thus ionizing them into analyte ions. These analyte ions can then be analyzed using mass analyzers known in the art.

[0004] In chemical ionization, the mild ionization of analyte molecules occurs in at least two steps. In the first step, reagent ions are formed from the reagent. These reagent ions can be generated under harsh conditions. In the final step, the reagent ions react with the analyte molecules in the sample. These analyte molecules are neutral in most cases. When the reagent ions react with the analyte molecules, the charge of the reagent ions is transferred to the analyte molecules, thus forming analyte ions. This subsequent final step is the chemical ionization reaction used to ionize analyte molecules into analyte ions. Other steps may also exist between the first and final steps. In one example of such other steps, there is an additional charge transfer step, where charge is transferred from primary reagent ions to lower-energy secondary reagent ions, thus mildly ionizing the secondary reagent into secondary reagent ions. Ultimately, the secondary reagent ions react with the analyte molecules in the sample, transferring the charge of the secondary reagent ions to the analyte molecules to form analyte ions. Therefore, reagent ions can be obtained using different ionization methods, such as corona discharge, plasma discharge, barrier discharge, electromagnetic radiation, electrospray ionization (ESI), electron ionization (EI), electron attachment ionization, or radioactive decay radiation.

[0005] Commonly used chemical ionization reactions in chemical ionization sources include protonation, deprotonation, formation of adducts with reagent ions or their fragments, or electron attachment or detachment. These processes are subject to gas-phase alkalinity (proton affinity) equilibrium, ionization potential equilibrium, electron affinity, dipole moment, or binding energy between reagent ions and analyte molecules.

[0006] In chemical ionization, reagent ions and analyte molecules interact directly. Therefore, within the reaction volume, reagent ions, analytes, and analyte ions undergo low-energy collisions, thus largely preserving the molecular structure of the analyte and preventing rearrangement or fragmentation of the analyte when it ionizes into analyte ions. Since the reaction volume is usually defined by the reaction chamber, it is sometimes referred to as the reaction chamber volume.

[0007] For the reasons mentioned above, chemical ionization has become a core analytical tool for analyzing volatile organic compounds in atmospheric chemistry and related fields (e.g., soil emissions, medical and food science, air quality monitoring), which require molecular-level species analysis.

[0008] CN109841491A describes an example of a chemical ionization source. This chemical ionization source includes a sealed chamber forming a chamber volume. A grid electrode is disposed within this sealed chamber, dividing the chamber volume into a photoionization region and a chemical ionization region. Furthermore, an ion repulsion electrode is disposed on the side of the photoionization region opposite to the chemical ionization region. Therefore, the ion repulsion electrode and the grid electrode are arranged alternately, opposite to each other, and parallel to each other. In addition, an ultraviolet light source is provided for irradiating at least a portion of the photoionization region with ultraviolet light.

[0009] In the operation of this chemical ionization source, a sample containing analytes to be ionized into analyte ions is inserted into the chemical ionization region. Additionally, a gaseous reagent composed of reagent molecules is inserted into the photoionization region through a reagent tube. In the photoionization region, ultraviolet light irradiates the electrodes to generate photoelectrons. These photoelectrons ionize the reagent molecules into reagent ions. The generated reagent ions are then transferred to the chemical ionization region. There, the reagent ions undergo an ion-molecule reaction with the analytes in the sample, causing the analytes to chemically ionize into analyte ions. Thus, by applying different DC and radio frequency voltages to the metal ring electrodes in the chemical ionization region, the ions in the chemical ionization region converge towards the outlet of the sealed chamber and exit from that outlet.

[0010] To transfer reagent ions from the photoionization region to the chemical ionization region, a voltage difference is applied between the ion-repelling electrode and the gate electrode, thereby generating an ion-repelling electric field in the axial direction between the ion-repelling electrode and the gate electrode. Therefore, driven by the ion-repelling voltage, the reagent ions generated in the photoionization region pass through the gate electrode and enter the chemical ionization region.

[0011] In this setup, photoelectrons generated in the photoionization region are accelerated toward the ion repulsion electrode, thus moving them away from the gate electrode. Therefore, this known chemical ionization source provides a very limited volume for reagent molecules to be ionized into reagent ions by photoelectrons. Furthermore, in this known chemical ionization source, the gate electrode allows analyte ions to move from the chemical ionization region to the photoionization region. In the photoionization region, the analyte undergoes photochemically induced rearrangement. Therefore, the ionization process in this chemical ionization source is not fully understood.

[0012] Due to these effects, known chemical ionization sources have the drawback that they only provide insufficient production of reagent ions, and therefore cannot efficiently ionize reactants into reactant ions, nor can they well confine the chemical ionization of reactants.

[0013] In this paper, the term "and / or" is sometimes used to connect two features. For example, in the expression "A and / or B", this term is used to connect feature A and feature B. This expression implies that at least feature A or feature B is implemented. In other words, the expression includes the options of "A and not B", "B and not A", and "A and B". Summary of the Invention

[0014] The purpose of this invention is to provide a chemical ionization source and a chemical ionization method for ionizing analytes in a sample into analyte ions through chemical ionization, which can more effectively and definitively ionize analytes into analyte ions.

[0015] The solution for which this invention aims is defined by the features of claim 1. According to the invention, the chemical ionization source comprises an irradiation chamber forming an irradiation chamber volume and having a reagent inlet for inserting a reagent comprising reagent molecules and / or reagent atoms into the irradiation chamber volume. Furthermore, the chemical ionization source comprises a photoelectron emitting surface contained within the irradiation chamber, the photoelectron emitting surface being used to emit photoelectrons within the irradiation chamber volume upon irradiation with electromagnetic radiation (especially ultraviolet light). The chemical ionization source also comprises an electromagnetic radiation source (especially an ultraviolet light source) adapted to irradiate the photoelectron emitting surface with electromagnetic radiation (especially ultraviolet light) for emitting photoelectrons from the photoelectron emitting surface. The chemical ionization source further comprises a reaction chamber defining a reaction chamber volume and having a sample inlet for inserting a sample comprising an analyte into the reaction chamber volume so as to ionize the analyte into analyte ions within the reaction chamber volume by contacting the analyte with reagent ions (i.e., ionized reagent molecules and / or reagent atoms), wherein the reaction chamber also has an outlet for discharging the analyte ions from the reaction chamber volume. The chemical ionization source further includes a chamber interface adapted to fluidly communicate an irradiation chamber volume with a reaction chamber volume for transferring the gaseous contents (especially gases, ions, and electrons, and corresponding reagent molecules and / or reagent atoms, reagent ions, and electrons, such as photoelectrons) of the irradiation chamber volume from the irradiation chamber volume to the reaction chamber volume. The chemical ionization source also includes a current collector. This current collector is disposed within the reaction chamber near the chamber interface, disposed at the chamber interface, or forming the chamber interface. The chemical ionization source further includes a current collector voltage source connected to at least one of the photoelectron emitting surface and the current collector, and for applying a voltage difference (especially a DC voltage difference) between the photoelectron emitting surface and the current collector, such that the potential of the current collector is higher than the potential of the photoelectron emitting surface, thereby driving negative charges from the photoelectron emitting surface to the current collector. Furthermore, the chemical ionization source includes a control unit adapted to control the current collector voltage source to apply a voltage difference between the photoelectron emitting surface and the current collector, such that the potential of the current collector is higher than the potential of the photoelectron emitting surface, thereby driving negative charges from the photoelectron emitting surface to the current collector.

[0016] As mentioned, a chemical ionization source includes an electromagnetic radiation source (especially an ultraviolet light source) adapted to irradiate a photoelectron emitting surface with electromagnetic radiation (especially ultraviolet light) for emitting photoelectrons from the photoelectron emitting surface. This electromagnetic radiation source can be, for example, an ultraviolet light source adapted to irradiate the photoelectron emitting surface with ultraviolet light for emitting photoelectrons from the photoelectron emitting surface, or, for example, an X-ray source adapted to irradiate the photoelectron emitting surface with X-ray radiation for emitting photoelectrons from the photoelectron emitting surface. The electromagnetic radiation source can be arranged inside or outside the irradiation chamber volume. In the first case, the electromagnetic radiation source is part of the irradiation chamber and can be arranged, for example, to directly irradiate the photoelectron emitting surface with electromagnetic radiation for emitting photoelectrons from the photoelectron emitting surface. In the second case, the electromagnetic radiation source can be, for example, part of the irradiation chamber or separate from the irradiation chamber. Thus, for example, the electromagnetic radiation source can be arranged in a volume adjacent to the irradiation chamber volume, wherein the two volumes are separated by a window transparent to the electromagnetic radiation emitted by the electromagnetic radiation source. In this case, ultraviolet light can be directed from the electromagnetic radiation source through a window to the photoelectron emitting surface for emitting photoelectrons from the photoelectron emitting surface.

[0017] As mentioned, the chemical ionization source includes a current collector, which is arranged within the reaction chamber near the chamber interface, at the chamber interface, or forming the chamber interface. In the case where the current collector is arranged within the reaction chamber near the chamber interface, the current collector can be located at the chamber interface or separate from it. In the case where the current collector is arranged at the chamber interface, the current collector can be located at the chamber interface within the reaction chamber, wholly or partially within the reaction chamber volume, or located within the reaction chamber but outside the reaction chamber volume, arranged within the irradiation chamber volume, or located inside the chamber interface and thus separate from both the reaction chamber volume and the irradiation chamber volume. In the latter case, i.e., when the current collector is arranged inside the chamber interface, the current collector can be covered by the chamber interface, providing a surface in contact with the reaction chamber volume, a surface in contact with the irradiation chamber volume, or both.

[0018] Therefore, the current collector can be arranged within the reaction chamber in the following ways: near the chamber interface, at the chamber interface, entirely or partially within the reaction chamber volume, or within the reaction chamber but outside its volume. In all these cases, the current collector is located within the reaction chamber. Thus, the current collector can be part of the reaction chamber or separate from it.

[0019] Regardless of its location, the current collector can consist of a single current collector element or two or more physically separate current collector elements. If the current collector consists of two or more physically separate current collector elements, each of these elements can be located within the reaction chamber near the chamber interface, at the chamber interface, or form the chamber interface, as described above. For example, if the current collector consists of two physically separate current collector elements, one of them can be located within the reaction chamber, while the other can form the chamber interface.

[0020] As mentioned, the chemical ionization source includes a collector voltage source connected to at least one of the photoelectron emitting surface and the collector, and is used to apply a voltage difference between the photoelectron emitting surface and the collector such that the potential of the collector is higher than the potential of the photoelectron emitting surface, so as to drive negative charges from the photoelectron emitting surface to the collector.

[0021] As mentioned, the chemical ionization source includes a control unit adapted to control a collector voltage source to apply a voltage difference between the photoelectron emitting surface and the collector, such that the potential of the collector is higher than the potential of the photoelectron emitting surface, thereby driving negative charges from the photoelectron emitting surface to the collector. Therefore, the control unit can be any unit suitable for this purpose. For example, the control unit can be a hardwired circuit designed for this purpose. However, the control unit can also be any unit containing a processor programmed to control the collector voltage source to apply a voltage difference between the photoelectron emitting surface and the collector, such that the potential of the collector is higher than the potential of the photoelectron emitting surface, thereby driving negative charges from the photoelectron emitting surface to the collector. For example, the control unit can be a personal computer (PC), tablet computer, smartphone, or any other computer with software installed to control the collector voltage source to apply a voltage difference between the photoelectron emitting surface and the collector, such that the potential of the collector is higher than the potential of the photoelectron emitting surface, thereby driving negative charges from the photoelectron emitting surface to the collector.

[0022] In cases where a collector voltage source is connected to the collector to apply a voltage difference between the photoelectron emitting surface and the collector, this collector voltage source may or may not be connected to the photoelectron emitting surface. In either case, it is advantageous to apply a positive voltage to the collector via the collector voltage source to create a voltage difference between the photoelectron emitting surface and the collector. The advantage of this is that positively charged ions are repelled from the collector. Therefore, the collector can be used to push positively charged analyte ions from the reaction chamber volume towards the outlet, thereby causing the positively charged analyte ions to leave the reaction chamber volume. Since the collector is arranged within the reaction chamber volume near the chamber interface, or at the chamber interface, or forms the chamber interface, the above effect can be easily achieved simply by arranging the outlet within the reaction chamber opposite the collector. This allows the collector to push positively charged analyte ions through the reaction chamber to the outlet.

[0023] The solution to the objective of this invention is further defined by a chemical ionization method that uses a chemical ionization source, particularly the chemical ionization source according to the invention, to ionize an analyte in a sample into analyte ions via chemical ionization, especially for mass spectrometry analysis. The chemical ionization method comprises inserting a reagent, including reagent molecules and / or reagent atoms, into the irradiation chamber volume of the irradiation chamber through a reagent inlet of the irradiation chamber of the chemical ionization source, and irradiating a photoelectron emitting surface in the irradiation chamber volume with an electromagnetic radiation source of the chemical ionization source, particularly ultraviolet light from an ultraviolet light source, for emitting photoelectrons from the photoelectron emitting surface. The chemical ionization method further comprises applying a voltage difference, particularly a DC voltage difference, between the photoelectron emitting surface and the collector electrode of the chemical ionization source using a collector electrode voltage source of the chemical ionization source, such that the potential of the collector electrode is higher than the potential of the photoelectron emitting surface, so as to drive negative charges from the photoelectron emitting surface to the collector electrode, wherein the chemical ionization source provides a reaction chamber forming the reaction chamber volume. Therefore, the chemical ionization source provides a chamber interface adapted to fluidly communicate the irradiation chamber volume with the reaction chamber volume for transferring the gaseous contents (especially gases, ions, and electrons, and corresponding reagent molecules and / or reagent atoms, reagent ions, and electrons, such as photoelectrons) of the irradiation chamber volume from the irradiation chamber volume to the reaction chamber volume, wherein a collector electrode is arranged within the reaction chamber near the chamber interface, or arranged at the chamber interface, or forming the chamber interface. Thus, the chemical ionization method according to the invention comprises inserting a sample comprising an analyte into the reaction chamber volume through a sample inlet of the reaction chamber to ionize the analyte into analyte ions within the reaction chamber volume.

[0024] A voltage difference (especially a DC voltage difference) is applied between the photoelectron emitting surface and the collector electrode of the chemical ionization ion source using the collector voltage source of the chemical ionization ion source, so that the potential of the collector electrode is higher than that of the photoelectron emitting surface, so as to drive negative charges from the photoelectron emitting surface to the collector electrode. This operation is advantageously achieved by controlling the chemical ionization ion source with a control unit, which controls the collector voltage source to apply a voltage difference between the photoelectron emitting surface and the collector electrode, so that the potential of the collector electrode is higher than that of the photoelectron emitting surface, so as to drive negative charges from the photoelectron emitting surface to the collector electrode.

[0025] In cases where a collector voltage source is connected to the collector to apply a voltage difference between the photoelectron emitting surface and the collector, this voltage source may or may not be connected to the photoelectron emitting surface. In either case, the photoelectron emitting surface is preferably grounded, i.e., placed at ground potential. Alternatively, the photoelectron emitting surface is not grounded and thus remains at a floating potential. However, grounding the photoelectron emitting surface has the advantage that, in order to apply a voltage difference between the photoelectron emitting surface and the collector in a well-controlled manner, such that the potential of the collector is higher than that of the photoelectron emitting surface, so as to drive negative charges from the photoelectron emitting surface to the collector, only a positive voltage needs to be applied to the collector. In this case, where the outlet of the reaction chamber is positioned opposite the collector, the positive voltage applied to the collector can be used to push positively charged analyte ions in the reaction chamber volume from the collector to the outlet, thereby causing the positively charged analyte ions to be expelled from the reaction chamber volume.

[0026] Advantageously, the photoelectron emitting surface is a surface of the photoelectron emitting electrode. This photoelectron emitting electrode is advantageously part of a chemical ionization source. Therefore, a collector voltage source is advantageously connected to at least one of the photoelectron emitting electrode and the collector to apply a voltage difference between the photoelectron emitting surface and the collector, such that the potential of the collector is higher than the potential of the photoelectron emitting surface, so as to drive negative charges from the photoelectron emitting surface to the collector.

[0027] In cases where the photoelectron emitting surface is a surface of a photoelectron emitting electrode and the photoelectron emitting electrode is part of a chemical ionization source, the control unit is advantageously adapted to control the collector voltage source to apply a voltage difference between the photoelectron emitting electrode and the collector, such that the potential of the collector is higher than the potential of the photoelectron emitting surface, so as to drive negative charges from the photoelectron emitting surface to the collector.

[0028] As mentioned, a chemical ionization source is used to ionize an analyte in a sample into analyte ions by chemical ionization, while a chemical ionization method is used to ionize an analyte in a sample into analyte ions by chemical ionization. Therefore, a sample may contain only one analyte or more than one analyte. Even more specifically, a sample may contain multiple analytes. If a sample contains more than one analyte, a chemical ionization source is used to ionize these analytes in the sample into analyte ions by chemical ionization, while a chemical ionization method is used to ionize these analytes in the sample into analyte ions by chemical ionization. Therefore, the singular term "analyte" as used herein should be understood as "at least one analyte." It can be only one analyte or two or more analytes. Typically, multiple analytes are present in practice. Therefore, it can also be stated that a chemical ionization source is used to ionize at least one analyte in a sample into analyte ions by chemical ionization, while a chemical ionization method is used to ionize at least one analyte in a sample into analyte ions by chemical ionization.

[0029] The solution according to the present invention has the following advantages: due to the voltage difference between the photoelectron emitting surface and the collector, photoelectrons emitted from the photoelectron emitting surface are accelerated toward the chamber interface where the collector is located. Therefore, reagent ions for the chemical ionization of analytes can be generated more efficiently. Thus, analytes can be chemically ionized into analyte ions more efficiently and definitively.

[0030] Preferably, the chemical ionization source includes a magnet for generating a magnetic field within the irradiation chamber volume. This has the advantage of improving the efficiency of reagent ionization into reagent ions. Advantageously, the magnet is arranged such that the magnetic field is oriented substantially along an axis from the photoelectron emitting surface to the collector, such that electrons, particularly photoelectrons, driven from the photoelectron emitting surface to the collector by the voltage difference between the photoelectron emitting surface and the collector are driven along a spiral path towards the collector. In an advantageous variation, the magnet is a magnetic focusing ring. Examples of the design and arrangement of such magnets are detailed in Chinese Patent CN203690254U.

[0031] However, alternatively, the chemical ionization source may also exclude the magnet used to generate a magnetic field in the irradiation chamber volume.

[0032] Advantageously, the reagent is one or more of oxygen, water, ammonia, nitrogen, nitric oxide, and argon. In the case of oxygen, water, ammonia, nitrogen, or nitric oxide, the reagent comprises reagent molecules. In the case of argon, the reagent comprises reagent atoms, which are advantageously in gaseous form. However, alternatively, the reagent may be different from oxygen, water, ammonia, nitrogen, nitric oxide, and argon.

[0033] Advantageously, the voltage difference between the photoelectron emitting surface and the collector is between 100V and 2000V, particularly advantageously between 400V and 1000V, and most advantageously about 700V. This has the advantage that photoelectrons can be accelerated by the electrostatic field generated by the voltage difference between the photoelectron emitting surface and the collector, giving them sufficient kinetic energy to ionize reagent molecules and / or reagent atoms into reagent ions, thereby initiating photoelectron ionization. Therefore, photoelectron ionization can be tuned to occur only when the photoelectron emitting surface is irradiated by electromagnetic radiation from an electromagnetic radiation source, and thus only when the system receives photoelectrons emitted by the photoelectron emitting surface. Simultaneously, self-sustaining corona discharge and self-sustaining glow discharge can be avoided, which would otherwise be sustained by the voltage difference between the photoelectron emitting surface and the collector when the photoelectron emitting surface is not irradiated by electromagnetic radiation from an electromagnetic radiation source.

[0034] However, alternatively, the voltage difference between the photoelectron emitting surface and the collector can be less than or equal to 100V or greater than or equal to 2000V.

[0035] Advantageously, a chemical ionization source is provided in combination with a reagent. In the case of the chemical ionization source and reagent combination, the voltage difference between the photoelectron emitting surface and the collector is advantageously set such that photoelectrons emitted from the photoelectron emitting surface are accelerated by the voltage difference between the photoelectron emitting surface and the collector, resulting in kinetic energies high enough to ionize reagent molecules and / or reagent atoms into positively charged reagent ions and free secondary electrons, respectively. However, alternatively, the voltage difference between the photoelectron emitting surface and the collector can be chosen to be so low that photoelectrons emitted from the photoelectron emitting surface are accelerated by the voltage difference between the photoelectron emitting surface and the collector, but their kinetic energies are not high enough to ionize reagent molecules and / or reagent atoms into positively charged reagent ions and free secondary electrons, respectively. Thus, photoelectrons can bind to reagent molecules and / or reagent atoms to generate negatively charged reagent ions. In the reaction chamber volume, these negatively charged reagent ions can release electrons. The negatively charged reagent ions can be used to chemically ionize analytes into analyte ions.

[0036] Nevertheless, chemical ionization sources can exist without reagents. However, reagents are typically used when using such chemical ionization sources.

[0037] Regardless of whether the chemical ionization source is provided in conjunction with a reagent, in the chemical ionization source, the control unit is advantageously adapted to control the collector voltage source to apply a voltage difference between the photoelectron emitting surface and the collector, such that at least one of the current flowing through the photoelectron emitting surface and the current flowing through the collector is less than 100 µA, particularly less than 10 µA, more particularly less than 2 µA, or even less than 0.5 µA. Particularly advantageously, the control unit is adapted to control the collector voltage source to apply a voltage difference between the photoelectron emitting surface and the collector, such that both the current flowing through the photoelectron emitting surface and the current flowing through the collector are less than 100 µA, particularly less than 10 µA, more particularly less than 2 µA, or even less than 0.5 µA.

[0038] Accordingly, in the chemical ionization method, advantageously, at least one of the current flowing through the photoelectron emitting surface and the current flowing through the collector is less than 100 µA, particularly less than 10 µA, more especially less than 2 µA, or even less than 0.5 µA. Particularly advantageously, both the current flowing through the photoelectron emitting surface and the current flowing through the collector are less than 100 µA, particularly less than 10 µA, more especially less than 2 µA, or even less than 0.5 µA.

[0039] The advantage of ensuring that the current flowing through the photoelectron emitting surface and the current flowing through the collector are both less than 100 µA, especially less than 10 µA, even more particularly less than 2 µA, or even less than 0.5 µA, is that corona discharge ionization and glow discharge ionization can be avoided within the irradiation chamber volume and the reaction chamber volume. Therefore, self-sustaining ionization within the irradiation chamber volume and the reaction chamber volume is avoided, and the ionization process can be easily and very effectively controlled by turning the electromagnetic radiation source on and off. This enables optimal control of the chemical ionization method and the chemical ionization ion source. Furthermore, avoiding corona discharge ionization and glow discharge ionization within the irradiation chamber volume and the reaction chamber volume also has the advantage of preventing the degradation of the irradiation chamber and reaction chamber materials due to discharge effects.

[0040] Regardless of whether the current flowing through the photoelectron emitting surface, the current flowing through the collector, or both the current flowing through the photoelectron emitting surface and the collector is less than 100 µA, especially less than 10 µA, more particularly less than 2 µA, or even less than 0.5 µA, the photoelectron emitting surface is advantageously arranged inside the irradiation chamber volume. In the first example, the photoelectron emitting surface is the surface of an element arranged inside the irradiation chamber volume. In the second example, the photoelectron emitting surface is the surface defining the irradiation chamber volume and facing the irradiation chamber wall. In either example, in an advantageous variation, the photoelectron emitting surface is arranged inside the irradiation chamber volume and located opposite the chamber interface. Since the collector is arranged inside the reaction chamber near the chamber interface, or arranged at the chamber interface, or forming the chamber interface, the photoelectron emitting surface arranged inside the irradiation chamber volume and opposite the chamber interface has the advantage that photoelectrons emitted by the photoelectron emitting surface are driven toward the chamber interface and enter the volume between the photoelectron emitting surface and the chamber interface. Within this volume, photoelectrons can individually strike reagent molecules and / or reagent atoms, ionizing them into reagent ions. These ions then combine with the reagent molecules and / or atoms to form reagent ions, or are further driven through the chamber interface into the reaction chamber volume. However, the photoelectron emitting surface can also be arranged inside the irradiation chamber volume, but not opposite the chamber interface.

[0041] Advantageously, the distance between the photoelectron emitting surface and the collector is less than 20 mm, and particularly advantageously less than 15 mm. This arrangement allows for a relatively high electric field strength between the photoelectron emitting surface and the collector for a given voltage difference.

[0042] However, alternatively, the distance between the photoelectron emitting surface and the collector is 20 mm or more.

[0043] Particularly advantageously, the photoelectron emitting surface is the surface of a cone arranged within the irradiation chamber volume, with the tip of the cone extending into the irradiation chamber volume and facing the chamber interface. This structure offers the advantage of providing a high photoelectron density near the chamber interface between the photoelectron emitting surface and the chamber interface during operation of the chemical ionization source.

[0044] However, instead, the photoelectron emitting surface is not arranged on the surface of a cone inside the irradiation chamber volume.

[0045] Preferably, the volume of the irradiation chamber is greater than 1 cm³. 3 Preferably, the diameter is greater than 3cm. 3 The optimal value is greater than 7cm. 3 Therefore, in an advantageous variant, the volume of the irradiation chamber is less than 20 cm³. 3 Especially those smaller than 10cm3 .

[0046] However, the volume of the irradiation chamber can be 20 cm³. 3 The above can also be 1cm. 3 the following.

[0047] Preferably, the volume of the reaction chamber is greater than 10 cm³. 3 Preferably, it should be greater than 20cm. 3 The optimal value is greater than 30cm. 3 Therefore, in an advantageous variation, the volume of the reaction chamber is less than 100 cm³. 3 Especially those less than 50cm 3 .

[0048] However, the volume of the reaction chamber can be either 100 cm³ or... 3 The above can also be 10cm. 3 the following.

[0049] Preferably, the length of the reaction chamber volume measured from the chamber inlet to the outlet is greater than 2 cm, particularly preferably greater than 5 cm, and most preferably greater than 8 cm. Therefore, in an advantageous variation, the length of the reaction chamber volume measured from the chamber inlet to the outlet is less than 25 cm, and especially less than 15 cm.

[0050] Alternatively, the length of the reaction chamber volume measured from the chamber interface to the outlet is 25 cm or more, or 2 cm or less.

[0051] Chemical ionization ion sources advantageously include ion transfer devices adapted to transfer analyte ions from the reaction chamber volume to an outlet. Particularly advantageously, the ion transfer devices are also adapted to transfer analyte ions out of the reaction chamber volume via the outlet. However, the ion transfer devices may not be adapted to transfer analyte ions out of the reaction chamber volume via the outlet. In the latter case, since the gas pressure inside the reaction chamber volume is higher than the gas pressure outside the outlet, the analyte ions can be transferred out of the reaction chamber volume, for example, by a gas flow through the outlet. This is the case in one example when the mass analyzer for receiving analyte ions is arranged outside the outlet, wherein the operating gas pressure of the mass analyzer is lower than the gas pressure inside the reaction chamber volume. This is, for example, when the chemical ionization ion source is part of a mass spectrometer. In this case, the mass spectrometer advantageously includes a chemical ionization ion source and a mass analyzer for mass analysis of the analyte ions.

[0052] Advantageously, the chemical ionization method includes an ion transfer device operating a chemical ionization ion source for transferring analyte ions from the reaction chamber volume to the outlet of the reaction chamber, thereby removing the analyte ions from the reaction chamber volume. This can be achieved, for example, by applying a voltage to at least one transfer electrode of the ion transfer device to generate an electric field.

[0053] The ion transfer device can be arranged inside the reaction chamber volume, outside the reaction chamber volume, or partially inside and partially outside the reaction chamber volume. In the first case, the ion transfer device is part of the reaction chamber. In the second and third cases, the ion transfer device can be part of the reaction chamber or separate from the reaction chamber.

[0054] Preferably, the ion transfer device includes at least one transfer electrode for generating an electric field when a voltage is applied thereto. In one example, the at least one transfer electrode is a DC electrode for generating an electrostatic field along the reaction chamber volume to transfer ions inside the reaction chamber volume to an outlet and out of the reaction chamber volume through the outlet. Thus, the DC electrode can also act as a current collector. In this case, the current collector is one of at least one transfer electrode of the ion transfer device. In this example, the reaction chamber can be formed, for example, by an ion guiding chamber as described by Tofwerk AG in EP1968100A1. In this case, the ion guiding chamber comprises a tube made of a resistive material (i.e., lead-doped silicate glass), wherein the resistive regions at the two longitudinal ends of the tube are connected to opposite poles of a DC voltage generator, thereby applying a voltage to the tube to accelerate the movement of positive charges along the tube toward the outlet. Thus, the longitudinal end of the tube opposite the outlet can be formed by a current collector. In either of these examples, the ion transfer device may also include at least one confinement electrode for applying an electric field when transferring ions in the reaction chamber volume along the reaction chamber volume to an outlet to confine the ions within the reaction chamber volume. The design and operation of the at least one constraint electrode are described, for example, in paragraphs 43 and 44 of Tofwerk AG's EP1968100A1 patent. In this example, the constraint electrode is referred to as a rod electrode.

[0055] Alternatively, a chemical ionization source may not have an ion transfer device, and a chemical ionization method may also not operate the ion transfer device of the chemical ionization source, which is originally used to transfer analyte ions in the reaction chamber volume to the outlet of the reaction chamber, thereby allowing the analyte ions to exit the reaction chamber volume.

[0056] Regardless of the presence of such an ion transfer device or whether it is part of a chemical ionization source, and regardless of the design of such an ion transfer device, the electromagnetic radiation advantageously consists of photons with energies in the range of 2 eV to 100 keV, and particularly advantageously in the range of 2 eV to 200 eV. If the electromagnetic radiation source is a green light source, the electromagnetic radiation consists of photons with energies in the range of approximately 2.2 eV to approximately 2.5 eV. If the electromagnetic radiation source is an X-ray source, the electromagnetic radiation consists of photons with energies in the range of approximately 100 eV to approximately 150 keV. If the electromagnetic radiation is ultraviolet light, the ultraviolet light advantageously consists of photons with energies in the range of 3 eV to 20 eV, particularly advantageously in the range of 3 eV to 15 eV, and most advantageously in the range of 4 eV to 11 eV.

[0057] However, alternatively, the photon energy of ultraviolet light can be less than 3 eV or greater than 20 eV. Even more alternatively, the photon energy of electromagnetic radiation can be less than 2 eV or greater than 100 keV.

[0058] Preferably, the electromagnetic radiation source is an ultraviolet light source for emitting ultraviolet light. Particularly preferably, the ultraviolet light source includes a vacuum ultraviolet (VUV) light source, especially an inert gas lamp, for emitting ultraviolet light, especially for irradiating a photoelectron emitting surface, for emitting photoelectrons from the photoelectron emitting surface.

[0059] The advantage of a vacuum ultraviolet light source is that it can provide 10 times per second. 13 Up to 10 15 The photon intensity is on the order of 10^-10^-10. This allows for the emission of a large number of photoelectrons. Assuming an idealized vacuum ultraviolet light source with a photon intensity of 10^- ... 13 On the order of magnitude, where all photons are directed to the photoelectron emitting surface, and each photon causes the surface to emit one photoelectron, then 10-1 photoelectrons will be emitted per second. 13 One photoelectron per second. 10 per second 13 Each photoelectron corresponds to a current of approximately 1.6 µA.

[0060] Examples of vacuum ultraviolet (VUV) light sources include photoionized krypton lamps, electron beam-pumped argon excimer lasers, and Nd:YAG lasers with a ninth harmonic generation VUV cavity. Photoionized krypton lamps primarily emit photons in the vacuum UV range at wavelengths of 124 nm and 117 nm, corresponding to photon energies of 10 eV and 10.6 eV, respectively. Electron beam-pumped argon excimer lasers emit photons in the vacuum UV range at wavelength of 126 nm, corresponding to a photon energy of 9.8 eV. Nd:YAG lasers with a ninth harmonic generation VUV cavity emit photons in the vacuum UV range at wavelength of 118 nm, corresponding to a photon energy of 10.5 eV.

[0061] Alternatively, ultraviolet light can be provided by a photon source different from that of a vacuum ultraviolet (VUV) source. Therefore, the ultraviolet source can include a photon source different from that of a VUV source to provide ultraviolet light for irradiating a photoelectron emitting surface, from which photoelectrons are emitted. For example, the ultraviolet light can be provided by an ultraviolet light-emitting diode (UV-LED). In this variation, the ultraviolet source includes a UV-LED for providing ultraviolet light for irradiating a photoelectron emitting surface, from which photoelectrons are emitted.

[0062] Alternatively, the electromagnetic radiation source may differ from an ultraviolet light source. For example, the electromagnetic radiation source may be an X-ray radiation source used to emit X-ray radiation.

[0063] Regardless of the type of electromagnetic radiation source used, advantageously, the chamber interface is adapted to fluidly communicate the irradiation chamber volume and the reaction chamber volume for transferring the gaseous contents of the irradiation chamber volume from the irradiation chamber volume to the reaction chamber volume along the contents transfer direction. Advantageously, the electromagnetic radiation source is arranged such that, in order to irradiate the photoelectron emitting surface with electromagnetic radiation for the emission of photoelectrons from the photoelectron emitting surface, the electromagnetic radiation is directed onto the photoelectron emitting surface at an angle greater than 10°, more advantageously greater than 45°, and most advantageously substantially perpendicular to the contents transfer direction. This has the advantage of effectively preventing electromagnetic radiation from entering the reaction chamber volume from the irradiation chamber volume. Therefore, photochemically induced analyte rearrangement can be avoided, thereby more precisely defining the chemical ionization of analytes into analyte ions.

[0064] However, alternatively, the electromagnetic radiation source is arranged such that, in order to irradiate the photoelectron emitting surface with electromagnetic radiation, and to emit photoelectrons from the photoelectron emitting surface, the electromagnetic radiation is directed onto the photoelectron emitting surface at an angle of less than 10° relative to the direction of content transfer.

[0065] In a first preferred variant, the chamber interface is made of a conductor, particularly a metal. In this first variant, the collector is advantageously formed within the chamber interface. This has the advantage of requiring fewer components for the chemical ionization source and therefore allowing for simpler construction. Nevertheless, the chamber interface can still be made of metal, while the collector is separate from the chamber interface.

[0066] In a second preferred variant, the chamber interface is made of an insulating material, such as ceramic. The advantage of using an insulating material for the chamber interface is that a higher voltage difference can be applied between the photoelectron emitting surface and the collector without the risk of corona discharge or glow discharge between the photoelectron emitting surface and the collector.

[0067] Instead of the first and second preferred variants, the chamber interface is made of a material different from the conductor or insulating material.

[0068] Advantageously, the chamber interface provides an opening with an aperture for fluid communication between the irradiation chamber volume and the reaction chamber volume, for transferring the gaseous contents (especially gases, ions, and electrons, and corresponding reagent molecules and / or reagent atoms, reagent ions, and electrons) of the irradiation chamber volume from the irradiation chamber volume to the reaction chamber volume, wherein the aperture is 0.01 mm. 2 Up to 5000mm 2 Within a range, particularly advantageously within 1mm 2 Up to 100mm 2 Within the range.

[0069] Advantageously, the chamber interface has a funnel-shaped recess on the side facing the irradiation chamber volume, which leads from the irradiation chamber volume to the opening of the chamber interface. This has the advantage of more efficiently transferring the gaseous contents of the irradiation chamber volume from the irradiation chamber volume to the reaction chamber volume. However, in an alternative, this funnel-shaped recess is not present at the chamber interface.

[0070] Preferably, the chamber interface is provided with a cone on the side facing the reaction chamber volume, the tip of which extends into the reaction chamber volume, wherein an opening with an aperture for fluidly communicating the irradiation chamber volume and the reaction chamber volume to transfer the gaseous contents of the irradiation chamber volume from the irradiation chamber volume to the reaction chamber volume is located at the tip of the cone for introducing the gaseous contents of the irradiation chamber volume into the reaction chamber volume.

[0071] Advantageously, the cone extends from its base into the interior of the reaction chamber volume by at least 2 mm, particularly advantageously at least 4 mm.

[0072] Regardless of the depth to which the tip of the cone extends into the reaction chamber volume, the collector is advantageously positioned between the tip of the cone and the irradiation chamber volume. This has the advantage of allowing a higher voltage differential to be applied between the photoelectron emitting surface and the collector without the risk of corona discharge or glow discharge between the photoelectron emitting surface and the collector. Therefore, it is particularly advantageous that the cone is made of an insulating material, and most advantageously, the chamber interface is made of an insulating material.

[0073] Alternatively, the side of the chamber interface facing the reaction chamber volume does not have a cone extending into the reaction chamber volume.

[0074] Advantageously, the sample inlet for inserting the sample into the reaction chamber volume is arranged between the chamber interface and the outlet.

[0075] In a case where a cone is provided on the side of the chamber interface facing the reaction chamber volume, and the tip of the cone extends into the reaction chamber volume, an opening with an aperture for fluid communication between the irradiation chamber volume and the reaction chamber volume to transfer the gaseous contents of the irradiation chamber volume from the irradiation chamber volume to the reaction chamber volume is located at the tip of the cone to introduce the gaseous contents of the irradiation chamber volume into the reaction chamber volume. A sample inlet for inserting a sample into the reaction chamber volume is then arranged between the tip and the outlet of the cone. Therefore, it is particularly advantageous that the sample inlet for inserting a sample into the reaction chamber volume is arranged between the tip and the outlet of the cone, and the distance between it and the cone tip is less than 15 mm, particularly less than 10 mm. However, the sample inlet for inserting a sample into the reaction chamber volume can also be arranged between the tip and the outlet of the cone, and the distance between it and the cone tip is 15 mm or more.

[0076] In an advantageous variation, a cone is provided on the side of the chamber interface facing the reaction chamber volume, with the tip of the cone extending into the reaction chamber volume. The sample inlet is formed by one end of a sample tube extending into the reaction chamber volume through the tip of the cone. Furthermore, in the case where the photoelectron emitting surface is the surface of a cone arranged within the irradiation chamber volume, with the tip of the cone extending into the irradiation chamber volume towards the chamber interface, the sample inlet is advantageously formed by one end of a sample tube that passes through the tip of the cone arranged within the irradiation chamber volume and further extends into the reaction chamber volume through the tip of the cone.

[0077] However, as an alternative to these variations, the sample inlet for inserting the sample into the reaction chamber volume is not located between the chamber interface and the outlet. For example, the chamber interface could be located between the sample inlet and the outlet.

[0078] Advantageously, the reaction chamber is provided with a vacuum port for reducing the gas pressure within the reaction chamber volume to below atmospheric pressure. This allows the reaction chamber to operate efficiently at sub-atmospheric pressures.

[0079] Advantageously, the reaction chamber vacuum port can be connected to or is already connected to a vacuum pump or built-in vacuum system within the building. Such built-in vacuum systems are typically provided in laboratory buildings. In these buildings, each room provides a vacuum port that connects to a vacuum pump within the building. In cases where the reaction chamber vacuum port can be connected to or is already connected to a vacuum pump, the vacuum pump can be part of or separate from a chemical ionization source.

[0080] Instead of or attached to the vacuum port of the reaction chamber, the irradiation chamber may provide an irradiation chamber vacuum port for reducing the gas pressure within the irradiation chamber volume to below atmospheric pressure. Advantageously, the irradiation chamber vacuum port may be connected to or has been connected to a vacuum pump or vacuum system typically installed in the laboratory building.

[0081] In cases where the irradiation chamber provides an irradiation chamber vacuum port for reducing the gas pressure within the irradiation chamber volume, but the reaction chamber does not provide a reaction chamber vacuum port for reducing the gas pressure within the reaction chamber volume to below atmospheric pressure, the gas pressure within the reaction chamber volume can be reduced via the chamber interface, through the irradiation chamber volume, and through the irradiation chamber vacuum port.

[0082] In cases where the reaction chamber provides a vacuum port for reducing the gas pressure within its volume, while the irradiation chamber does not provide a vacuum port for reducing the gas pressure within its volume to below atmospheric pressure, the gas pressure within the irradiation chamber volume can be reduced via the chamber interface, through the reaction chamber volume, and through the vacuum port. However, regardless of whether the irradiation chamber provides a vacuum port for reducing the gas pressure within its volume, providing a vacuum port for reducing the gas pressure within the reaction chamber volume to below atmospheric pressure offers the advantage that by reducing the gas pressure within the reaction chamber volume to below the gas pressure within the irradiation chamber volume via the vacuum port, the gaseous contents within the irradiation chamber volume can flow to the reaction chamber volume via the chamber interface. This allows the gaseous contents within the irradiation chamber volume (especially gases, ions, and electrons, as well as corresponding reagent molecules and / or reagent atoms, reagent ions, and electrons, such as photoelectrons) to transfer from the irradiation chamber volume to the reaction chamber volume. In particular, even if a voltage difference is applied between the photoelectron emitting surface and the collector, such that the potential of the collector is higher than that of the photoelectron emitting surface to drive negative charges from the photoelectron emitting surface to the collector, positively charged reagent ions can still be transferred from the irradiation chamber volume to the reaction chamber volume through the chamber interface by the flow of gaseous contents within the irradiation chamber volume from the irradiation chamber volume to the reaction chamber volume via the chamber interface, thereby driving positively charged and thus positively charged reagent ions toward the photoelectron emitting surface.

[0083] Instead of these variations, the irradiation chamber lacks an irradiation chamber vacuum port, and the reaction chamber lacks a reaction chamber vacuum port. In this case, both the reaction chamber volume and the irradiation chamber volume can operate at gas pressures below atmospheric pressure. To achieve this, for example, a reduced gas pressure can be maintained upstream of the outlet, outside the chemical ionization source. This could be, for example, a case where the chemical ionization source is part of a mass spectrometer, where a region of reduced gas pressure is provided downstream of the reaction chamber outlet.

[0084] Preferably, the chemical ionization method involves reducing the gas pressure within the reaction chamber volume to below atmospheric pressure, particularly advantageously via a reaction chamber vacuum port or via an outlet. Therefore, it is particularly advantageous that the reaction chamber provides a reaction chamber vacuum port connected to a vacuum pump or built-in vacuum system in the building for reducing the gas pressure within the reaction chamber volume.

[0085] Instead of reducing the gas pressure within the reaction chamber volume to below atmospheric pressure via a reaction chamber vacuum port or via the reaction chamber outlet, chemical ionization methods advantageously include reducing the gas pressure within the irradiation chamber volume to below atmospheric pressure via an irradiation chamber vacuum port. In this case, the irradiation chamber vacuum port is advantageously connected to a vacuum pump or built-in vacuum system in the building for reducing the gas pressure within the irradiation chamber volume.

[0086] Regardless of whether the gas pressure within the irradiation chamber volume is reduced to below atmospheric pressure via the outlet or the irradiation chamber vacuum port, it is particularly advantageous that the gas pressure within the reaction chamber volume is reduced to below the gas pressure within the irradiation chamber volume via the outlet or the reaction chamber vacuum port, thereby causing the gaseous contents of the irradiation chamber volume to flow through the chamber interface and subsequently transfer to the reaction chamber volume. This flow has the advantage that even when a voltage difference is applied between the photoelectron emitting surface and the collector, such that the potential of the collector is higher than that of the photoelectron emitting surface to drive negative charges from the photoelectron emitting surface to the collector, positively charged reagent ions can still be transferred from the irradiation chamber vacuum volume to the reaction chamber volume via the chamber interface, thereby driving positive charges and thus positively charged reagent ions toward the photoelectron emitting surface.

[0087] Advantageously, the irradiation chamber is adapted to operate with a gas pressure within its volume ranging from 0.01 mbar to 100 mbar, particularly advantageously from 0.1 mbar to 10 mbar, and most advantageously from 1 mbar to 4 mbar. Advantageously, the reaction chamber is adapted to operate with a gas pressure within its volume ranging from 0.01 mbar to 100 mbar, particularly advantageously from 0.1 mbar to 10 mbar, and most advantageously from 1 mbar to 4 mbar.

[0088] Advantageously, in the chemical ionization method, the gas pressure within the irradiation chamber volume is in the range of 0.01 mbar to 100 mbar, particularly advantageously in the range of 0.1 mbar to 10 mbar, and most advantageously in the range of 1 mbar to 4 mbar. Advantageously, in the chemical ionization method, the gas pressure within the reaction chamber volume is in the range of 0.01 mbar to 100 mbar, particularly advantageously in the range of 0.1 mbar to 10 mbar, and most advantageously in the range of 1 mbar to 4 mbar.

[0089] Advantageously, the voltage difference between the photoelectron emitting surface and the collector is between 100V and 2000V. When the irradiation chamber volume and the reaction chamber volume are operated at pressures ranging from 1 mbar to 4 mbar, the voltage difference between the photoelectron emitting surface and the collector is advantageously between 400V and 1000V. When the irradiation chamber volume and the reaction chamber volume are operated at pressures of approximately 3 mbar, the voltage difference between the photoelectron emitting surface and the collector is advantageously approximately 700V.

[0090] However, in one variant, the voltage difference between the photoelectron emitting surface and the collector is either less than 100V or more than 2000V.

[0091] However, as alternatives to these variations, the irradiation chamber is suitable for operation with a gas pressure of 0.01 mbar or less or 100 mbar or more within its volume, whereas in the chemical ionization method, the irradiation chamber operates with a gas pressure of 0.01 mbar or less or 100 mbar or more within its volume. Furthermore, instead of the aforementioned variations, the reaction chamber is suitable for operation with a gas pressure of 0.01 mbar or less or 100 mbar or more within its volume, whereas in the chemical ionization method, the reaction chamber operates with a gas pressure of 0.01 mbar or less or 100 mbar or more within its volume.

[0092] The chemical ionization method advantageously includes maintaining the flow rate of the gaseous contents of the irradiation chamber volume, which enters the reaction chamber volume from the irradiation chamber volume via the chamber interface, in the range of 0.1 sccm to 500 sccm, particularly preferably in the range of 1 sccm to 300 sccm, and most preferably in the range of 5 sccm to 20 sccm.

[0093] This can be achieved, for example, by controlling at least one of the following: a vacuum pump, connected to the vacuum port of the reaction chamber, for reducing the gas pressure within the reaction chamber volume to below atmospheric pressure; an irradiation chamber valve for controlling the gas flow rate entering the irradiation chamber volume; and a reaction chamber valve for controlling the gas flow rate entering the reaction chamber volume, thereby maintaining the flow rate of the gaseous contents of the irradiation chamber volume entering the reaction chamber volume from the irradiation chamber volume via the chamber interface within the range of 0.1 sccm to 500 sccm, particularly preferably within the range of 1 sccm to 300 sccm, and most preferably within the range of 5 sccm to 20 sccm. This can also be achieved, for example, by adapting the control unit of the chemical ionization source to control at least one of the vacuum pump, irradiation chamber valve, and reaction chamber valve included in the chemical ionization source, thereby maintaining the flow rate of the gaseous contents of the irradiation chamber volume entering the reaction chamber volume from the irradiation chamber volume via the chamber interface within the irradiation chamber volume within the range of 0.1 sccm to 500 sccm, particularly preferably within the range of 1 sccm to 300 sccm, and most preferably within the range of 5 sccm to 20 sccm.

[0094] Therefore, the chemical ionization source advantageously includes at least one of the following: a vacuum pump connected to a reaction chamber vacuum port for reducing the gas pressure within the reaction chamber volume to below atmospheric pressure; an irradiation chamber valve for controlling the gas flow rate entering the irradiation chamber volume; and a reaction chamber valve for controlling the gas flow rate entering the reaction chamber volume. Thus, the control unit is advantageously adapted to control at least one of the vacuum pump, irradiation chamber valve, and reaction chamber valve included in the chemical ionization source, thereby maintaining the flow rate of the gaseous contents of the irradiation chamber volume entering the reaction chamber volume from the irradiation chamber volume via the chamber interface within the range of 0.1 sccm to 500 sccm, particularly preferably within the range of 1 sccm to 300 sccm, and most preferably within the range of 5 sccm to 20 sccm.

[0095] Instead of these variations, the flow rate of the gaseous contents of the irradiation chamber volume entering the reaction chamber volume from the irradiation chamber volume via the chamber interface can be maintained at less than 0.1 sccm or more than 500 sccm. Furthermore, the chemical ionization method can be performed without any control over the flow rate of the gaseous contents of the irradiation chamber volume entering the reaction chamber volume from the irradiation chamber volume via the chamber interface. Accordingly, the control unit can be adapted to control at least one of the vacuum pump, irradiation chamber valve, and reaction chamber valve included in the chemical ionization source, thereby maintaining the flow rate of the gaseous contents of the irradiation chamber volume entering the reaction chamber volume from the irradiation chamber volume via the chamber interface at 0.1 sccm or less or more than 500 sccm; alternatively, the control unit may not be adapted to control at least one of the vacuum pump, irradiation chamber valve, and reaction chamber valve included in the chemical ionization source, thereby maintaining the flow rate of the gaseous contents of the irradiation chamber volume entering the reaction chamber volume from the irradiation chamber volume via the chamber interface at a specific value.

[0096] A chemical ionization ion source is advantageously part of a mass spectrometer, and a chemical ionization method is advantageously part of a mass analysis method for mass analysis of analytes in a sample. Therefore, the mass spectrometer advantageously includes a chemical ionization ion source. Consequently, the mass spectrometer advantageously includes a mass analyzer for mass analysis of analyte ions provided by the chemical ionization ionization method. This mass analyzer is advantageously adapted to receive analyte ions exiting from the outlet of the reaction chamber volume of the chemical ionization ion source. Accordingly, the mass analysis method for mass analysis of analytes in a sample includes a chemical ionization method. Therefore, the mass analysis method advantageously includes ionizing analytes in the sample into analyte ions and performing mass analysis of the analyte ions using a mass analyzer.

[0097] However, alternatively, the chemical ionization source is not part of the mass spectrometer, and the chemical ionization method is used separately from the mass analysis method.

[0098] Other advantageous embodiments and combinations of features of the invention are derived from the exemplary embodiments described below and throughout the patent claims. Attached Figure Description

[0099] The following figures illustrate exemplary embodiments: Figure 1 A simplified schematic diagram of a mass spectrometer including a chemical ionization ion source and a mass analyzer according to the present invention; Figure 2 When water vapor is used as a reagent, the following is adopted: Figure 1 The mass spectrum shown is obtained by a mass spectrometer that includes a chemical ionization source and a mass analyzer. Figure 3 When water vapor is used as a reagent, the following is adopted: Figure 1The mass spectrum shown is of a calibration gas mixture diluted in clean air, obtained by a mass spectrometer including a chemical ionization source and a mass analyzer. Figure 4 Is adopted Figure 1 The graph shown illustrates the change in total ion signal over time obtained by a mass spectrometer, including a chemical ionization ion source and a mass analyzer, to demonstrate the effect of the DC voltage difference between the photoelectron emitting surface and the collector on the efficiency of the chemical ionization source; and Figure 5 Is adopted Figure 1 The two-week long-term measurement performed by a mass spectrometer, including a chemical ionization source and a mass analyzer, illustrates the long-term stability of the chemical ionization source and the chemical ionization method according to the invention.

[0100] Typically, the same parts in the accompanying drawings use the same reference numerals. Detailed Implementation

[0101] Figure 1 A simplified schematic diagram of a mass spectrometer 100 comprising a chemical ionization source 1 and a mass analyzer 95 according to the invention is shown. Using the chemical ionization source 1, analytes in a sample can be ionized into analyte ions by the chemical ionization method according to the invention. The analyte ions are then transferred to the mass analyzer 95, where mass analysis is performed in accordance with methods known in the art. As data output, a mass spectrum is obtained in accordance with methods known in the art.

[0102] In one variant, the chemical ionization source 1 is a separate unit, rather than part of the mass spectrometer.

[0103] Figure 1 The entire mass spectrometer 100 is shown in the diagram. The chemical ionization ion source 1 is thus shown in a partial cross-sectional view. Therefore, the internal components of the chemical ionization ion source 1 are visible. It is evident that the chemical ionization ion source 1 comprises an irradiation chamber 2 and a reaction chamber 3. The irradiation chamber 2 forms an irradiation chamber volume 21 and has a reagent inlet 22 for inserting a reagent, comprising reagent molecules and / or reagent atoms, into the irradiation chamber volume 21. The reagent may be, for example, one of oxygen, water, ammonia, nitrogen, nitric oxide, and argon. The volume of the irradiation chamber volume 21 is 8 cm³. 3 On the other hand, the reaction chamber 3 includes a glass tube 34 defining the reaction chamber volume 31. Therefore, the glass tube 34 is made of a resistive material (i.e., lead-doped silicate glass). The volume of the reaction chamber 31 is 31 cm³. 3The total length of the glass tube 34 along its length direction is 10 cm. The reaction chamber 3 also has a sample inlet 32 ​​for inserting a sample containing the analyte into the reaction chamber volume 31, so that the analyte is ionized into analyte ions within the reaction chamber volume 31 by contacting the analyte with reagent ions formed by the ionization of reagent molecules and / or reagent atoms. Furthermore, the reaction chamber 3 has an outlet 33 for discharging the analyte ions from the reaction chamber volume 31. The outlet 33 is located at the end of the glass tube 34. In the mass spectrometer 100, a mass analyzer 95 is arranged downstream of the outlet 33 for receiving analyte ions generated by the chemical ionization source 1.

[0104] To transfer analyte ions from reaction chamber volume 31 to outlet 33, reaction chamber 3 and thus chemical ionization source 1 include ion transfer device 36. Ion transfer device 36 is adapted to transfer analyte ions from reaction chamber volume 31 to outlet 33. Ion transfer device 36 includes several confinement electrodes 35. These confinement electrodes 35 are arranged on the outside of glass tube 34, distributed circumferentially around glass tube 34. During operation of chemical ionization source 1, these confinement electrodes 35 are subjected to radio frequency AC voltage. These radio frequency AC voltages can be provided by any radio frequency AC voltage source, which can be part of or independent of chemical ionization source 1. In one example, these radio frequency AC voltages are provided by collector voltage source 7, as described below. Regardless of the design of the RF AC voltage source, and regardless of whether the collector voltage source 7 also functions as an RF AC voltage source, the RF AC voltage applied to the confinement electrode 35 generates an RF electromagnetic field within the glass tube 34. This RF electromagnetic field drives the positive and negative charges within the reaction chamber volume 31, and consequently the ions containing reagent ions and analyte ions, toward the central length axis of the glass tube 34 and thus toward the central length axis of the reaction chamber volume 31. Therefore, the analyte ions are confined by the confinement electrode 35 along the central length axis of the reaction chamber volume 31.

[0105] The ion transfer device 36 further includes a transfer electrode for pushing analyte ions within the reaction chamber volume 31 toward and out of the reaction chamber volume 31 through the outlet 33. This transfer electrode is disposed on a glass tube 34 opposite the end of the glass tube 34 where the outlet 33 is located. A positive voltage is applied to this transfer electrode to push the analyte ions through the reaction chamber volume 31 and out through the outlet 33. Figure 1In the chemical ionization source 1 shown, the transfer electrode is also the current collector 6 (hereinafter referred to as the current collector 6), and it is in direct electrical contact with the resistance region 61 at the longitudinal end of the glass tube 34 adjacent to the current collector 6. However, in a variant, the transfer electrode is an electrode independent of the current collector 6 (hereinafter referred to as the current collector 6). In one variant, the ion transfer device 36 includes several transfer electrodes (e.g., five or ten transfer electrodes) for pushing analyte ions within the reaction chamber volume 31 to the outlet 33 and out of the reaction chamber volume 31 through the outlet 33. In this variant, these transfer electrodes are arranged sequentially along the glass tube 34. The first of these transfer electrodes is... Figure 1 The current collector 6 is shown. Starting with the first of these transfer electrodes, the remaining transfer electrodes are arranged sequentially in the direction toward the outlet 33, with the last transfer electrode located at the outlet. During operation, a corresponding DC voltage is applied to each transfer electrode in a manner known in the art to push the analyte ions in the reaction chamber volume 31 along the reaction chamber volume 31 to the outlet 33 and out of the reaction chamber volume 31 through the outlet 33.

[0106] exist Figure 1 In the embodiment shown, the glass tube 34 and the confinement electrode 35 are designed as the glass tube and four cylindrical rod-shaped electrodes described in Tofwerk AG EP1 968 100 A1, respectively. Thus, the collector 6 contacts one of the resistance regions 61 at one of the two longitudinal ends of the glass tube 34, while the outlet 33 is arranged at the longitudinal end of the glass tube opposite to the collector 6.

[0107] However, the ion transfer device 36 can also be designed differently.

[0108] The chemical ionization source 1 includes a photoelectron emitting electrode 23 having a photoelectron emitting surface 24. The photoelectron emitting surface 24 is located inside the irradiation chamber 2 and is used to emit photoelectrons in the irradiation chamber volume 21 when irradiated with ultraviolet light.

[0109] To acquire ultraviolet light, the chemical ionization source 1 also includes an ultraviolet light source 5, which is adapted to irradiate the photoelectron emitting surface 24 with ultraviolet light for emitting photoelectrons from the photoelectron emitting surface 24. The ultraviolet light source 5 includes a photoionization krypton lamp. The photoionization krypton lamp is a vacuum ultraviolet (VUV) light source, providing ultraviolet light with photon energies of approximately 10 eV and 10.6 eV. The ultraviolet light source 5 is arranged outside the irradiation chamber volume 21, but is still part of the irradiation chamber 2. Thus, the ultraviolet light source 5 is arranged within a volume adjacent to the irradiation chamber volume 21, separated from it by a window 25 that allows ultraviolet light to pass through. Ultraviolet light from the ultraviolet light source 5 is directed through the window 25 to the photoelectron emitting surface 24 for emitting photoelectrons from the photoelectron emitting surface 24.

[0110] Therefore, the ultraviolet light source 5, suitable for irradiating the photoelectron emitting surface 24 with ultraviolet light to emit photoelectrons from the photoelectron emitting surface 24, is also an electromagnetic radiation source suitable for irradiating the photoelectron emitting surface with electromagnetic radiation to emit photoelectrons from the photoelectron emitting surface. In a variation, the chemical ionization source 1 may comprise an electromagnetic radiation source of a different type than the ultraviolet light source 5. For example, the electromagnetic radiation source may be an X-ray radiation source. In such an example, the X-ray radiation source is suitable for irradiating the photoelectron emitting surface with X-ray radiation to emit photoelectrons from the photoelectron emitting surface.

[0111] Between the irradiation chamber 2 and the reaction chamber 3, the chemical ionization source 1 includes a chamber interface 4 adapted to fluidly connect the irradiation chamber volume 21 to the reaction chamber volume 31, for transferring gaseous contents within the irradiation chamber volume 21 to the reaction chamber volume 31. Figure 1 In the variant shown, the chamber interface 4 is made of ceramic, i.e., an insulating material. However, in other variants, the chamber interface can be made of other materials, or even of conductors such as metals.

[0112] The chamber interface 4 provides an opening 41 for fluid communication between the irradiation chamber volume 21 and the reaction chamber volume 31, for transferring gaseous contents (particularly gases, ions, and electrons, and consequently corresponding reagent molecules and / or reagent atoms, reagent ions, and electrons) from the irradiation chamber volume 21 to the reaction chamber volume 31. Therefore, a funnel-shaped recess 42 is provided on the side of the chamber interface 4 facing the irradiation chamber volume 21, which opens from the irradiation chamber volume 21 into the aperture of the opening 41 of the chamber interface 4. Furthermore, a cone 43 is provided on the side of the chamber interface 4 facing the reaction chamber volume 31, the tip of which extends into the reaction chamber volume 31. Therefore, an opening 41 is arranged at the top of the cone 43, the opening having an aperture for fluidly communicating the irradiation chamber volume 21 to the reaction chamber volume 31, for transferring the gaseous contents of the irradiation chamber volume 21 from the irradiation chamber volume 21 to the reaction chamber volume 31, and for introducing the gaseous contents of the irradiation chamber volume 21 into the reaction chamber volume 31.

[0113] With this arrangement, the chamber interface 4 is adapted to fluidly connect the irradiation chamber volume 21 to the reaction chamber volume 31, for transferring gaseous contents from the irradiation chamber volume 21 to the reaction chamber volume 31 in the contents transfer direction. Therefore, the ultraviolet light source 5 is arranged such that, in order to irradiate the photoelectron emitting surface 24 with ultraviolet light to emit photoelectrons from the photoelectron emitting surface 24, the ultraviolet light is directed towards the photoelectron emitting surface 24 in a direction perpendicular to the contents transfer direction. Therefore, ultraviolet light cannot reach the reaction chamber volume 31 from the irradiation chamber volume 21. Thus, photochemically induced analyte rearrangement is avoided, thereby more precisely defining the chemical ionization of analytes into analyte ions.

[0114] exist Figure 1 In the illustrated embodiment, chamber interface 4 forms a small chamber interface volume within cone 43. In one variation, chamber interface 4 does not have such a small chamber interface volume. In yet another variation, chamber interface 4 has a larger chamber interface volume. Whether the chamber interface forms one or more chamber interface volumes or simply provides an opening for forming a channel, the chamber interface is adapted to fluidly communicate irradiation chamber volume 21 to reaction chamber volume 31 for transferring gaseous contents within irradiation chamber volume 21 to reaction chamber volume 31 in the contents transfer direction.

[0115] exist Figure 1 In the illustrated embodiment, the photoelectron emitting surface 24 is disposed within the irradiation chamber volume 21 opposite to the chamber interface 4. Therefore, the photoelectron emitting surface 24 is a conical surface 26 disposed inside the irradiation chamber volume 21, with its tip extending into the irradiation chamber volume 21 towards the chamber interface 4. Since the collector 6 is disposed within the reaction chamber 3 close to the chamber interface 4, arranging the photoelectron emitting surface 24 opposite to the chamber interface 4 within the irradiation chamber volume 21 has the advantage that photoelectrons emitted by the photoelectron emitting surface 24 are driven toward the chamber interface 4 and enter the volume between the photoelectron emitting surface 24 and the chamber interface 4. However, in a variant, the photoelectron emitting surface 24 is disposed within the irradiation chamber volume 21 but not opposite to the chamber interface 4. Figure 1 In the variant shown, the photoelectron emitting surface 24 is located at a distance of less than 15 mm from the collector electrode 6.

[0116] The sample inlet 32 ​​for inserting the sample into the reaction chamber volume 31 is formed at the end of the sample tube 37, which extends into the reaction chamber volume 31 through the tip of the cone 26 arranged in the irradiation chamber volume 21 and the tip of the cone 43 of the chamber interface 4. Therefore, the sample inlet 32 ​​for inserting the sample into the reaction chamber volume 31 is located inside the reaction chamber volume 31, between the tip of the cone 43 and the outlet 33, and approximately 10 mm away from the tip of the cone 43.

[0117] Since the sample tube 37 passes through the tip of the cone 43 of the chamber interface 4, the effective aperture of the opening 41 of the chamber interface 4 is 3 mm. 2 This aperture allows the gaseous contents within the irradiation chamber volume 21 to flow from the irradiation chamber volume 21 to the reaction chamber volume 31. In variations, this aperture may be greater than or less than 3 mm. 2 For example, the aperture is 1 mm. 2 Up to 100mm 2 Within this range. In another example, the aperture is 0.01 mm. 2 Up to 5000mm 2 Within the range.

[0118] As briefly mentioned, the chemical ionization source 1 includes a current collector 6, which is also one of at least one transfer electrode, and therefore part of the aforementioned ion transfer device 36. Figure 1 In the illustrated embodiment, the collector 6 is arranged within the reaction chamber 3 near the chamber interface 4 and partially extends into the reaction chamber volume 31. Therefore, the collector 6 is located at the chamber interface 4. In a variation of this particular embodiment, the collector 6 is arranged at the chamber interface 4, or forms the chamber interface 4.

[0119] In addition, the chemical ionization source 1 includes the aforementioned collector voltage source 7 and control unit 8.

[0120] A collector voltage source 7 is connected to at least one of the photoelectron emitting surface 24 and the collector 6, for applying a DC voltage difference between the photoelectron emitting surface 24 and the collector 6, such that the potential of the collector 6 is higher than the potential of the photoelectron emitting surface 24, thereby driving negative charges from the photoelectron emitting surface 24 toward the collector 6. Therefore, the control unit 8 is adapted to control the collector voltage source 7 to apply a DC voltage difference between the photoelectron emitting surface 24 and the collector 6, such that the potential of the collector 6 is higher than the potential of the photoelectron emitting surface 24, thereby driving negative charges from the photoelectron emitting surface 24 toward the collector 6. More specifically, in Figure 1 In the illustrated embodiment, the photoelectron emitting electrode 23 with photoelectron emitting surface 24 is grounded, and the collector voltage source 7 is connected to the collector electrode 6 and used to apply a DC voltage difference between the photoelectron emitting surface 24 and the collector electrode 6. During operation, the control unit 8 controls the collector voltage source 7 to apply a positive voltage to the collector electrode 6 so as to apply a DC voltage difference between the photoelectron emitting surface 24 and the collector electrode 6. Therefore, positively charged ions are repelled away from the collector electrode 6. Since the outlet 33 is arranged opposite the collector electrode 6 in the reaction chamber 3, the positive voltage applied to the collector electrode 6 pushes the positively charged analyte ions in the reaction chamber volume 31 from the collector electrode 6 to the outlet 33, thereby causing the positively charged analyte ions to leave the reaction chamber volume 31. Furthermore, since the collector electrode 6 is arranged close to the chamber interface 4 in the reaction chamber 3, the positive voltage applied to the collector electrode 6 pushes the positively charged analyte ions in the reaction chamber volume 31 through the reaction chamber volume 31 to the outlet 33.

[0121] When the chemical ionization source 1 is running, the DC voltage difference between the photoelectron emitting surface 24 and the collector 6 is between 100V and 2000V, especially between 400V and 1000V, or even about 700V.

[0122] exist Figure 1In the illustrated chemical ionization source 1, the reaction chamber 3 provides a reaction chamber vacuum port 38 for reducing the gas pressure within the reaction chamber volume 31 to below atmospheric pressure. During operation of the chemical ionization source 1, this reaction chamber vacuum port 38 is connected to a vacuum pump or built-in vacuum system in the building. In one example, the chemical ionization source 1 includes a vacuum pump 9 connected to the reaction chamber vacuum port 38. This vacuum pump 9 is controlled by a control unit 8 of the chemical ionization source 1.

[0123] When the chemical ionization source 1 is operating, the gas pressure within the reaction chamber volume 31 is reduced to below atmospheric pressure by the vacuum pump 9. Alternatively, the gas pressure within the irradiation chamber volume 21 can be reduced to below atmospheric pressure via the reaction chamber vacuum port 38, the reaction chamber volume 31, and the chamber interface 4. Thus, the irradiation chamber 2 and the reaction chamber 3 operate at gas pressures of 0.01 mbar to 100 mbar, particularly 0.1 mbar to 10 mbar, within the irradiation chamber volume 21 and the reaction chamber volume 31, respectively. Therefore, the vacuum pump 9 is controlled by the control unit 8 to maintain the flow rate of the gaseous contents of the irradiation chamber volume 21, which enters the reaction chamber volume 31 from the irradiation chamber volume 21 through the chamber interface 4, within the range of 0.1 sccm to 500 sccm, particularly preferably within the range of 1 sccm to 300 sccm, or even within the range of 5 sccm to 20 sccm. Attached to or replacing the reaction chamber vacuum port 38, the chemical ionization source 1 may further include an irradiation chamber valve 27 for controlling the flow rate of gas entering the irradiation chamber volume 21, and / or a reaction chamber valve 39 for controlling the flow rate of gas entering the reaction chamber volume 31. In this variant, the control unit 8 is adapted to control at least one of the vacuum pump 9, the irradiation chamber valve 27, and the reaction chamber valve 39 included in the chemical ionization source 1, thereby maintaining the flow rate of the gaseous contents of the irradiation chamber volume 21 entering the reaction chamber volume 31 from the irradiation chamber volume 21 via the chamber interface 4 in the range of 0.1 sccm to 500 sccm, particularly preferably in the range of 1 sccm to 300 sccm, or even in the range of 5 sccm to 20 sccm. Taking the irradiation chamber valve 27 as an example, the irradiation chamber valve 27 can be used to control the flow rate of reagent flowing into the irradiation chamber volume 21 through the reagent inlet 22. The irradiation chamber valve 27 controls the flow rate of reagent flowing into the irradiation chamber volume 21 through the reagent inlet 22. It can control the flow rate of gaseous contents of the irradiation chamber volume 21 entering the reaction chamber volume 31 from the irradiation chamber volume 21 through the chamber interface 4 when the gas pressure in the reaction chamber volume 31 is reduced through the outlet 33 or through the reaction chamber vacuum port 38.

[0124] When performing the chemical ionization method according to the invention, in which the analyte in the sample is ionized into analyte ions by chemical ionization using the chemical ionization source 1, the reagent 11, comprising reagent molecules and / or reagent atoms, is inserted into the irradiation chamber volume 21 through the reagent inlet 22 of the irradiation chamber 2. To supply the reagent 11, the chemical ionization source 1 may include a reagent reservoir 10 containing the reagent 11, or a separate reagent supply device may be provided for supplying the reagent 11. In either case, the chemical ionization source 1 itself may not contain the reagent 11. However, to perform the chemical ionization method, the chemical ionization source 1 is combined with the reagent 11 to form a combination of the chemical ionization source 1 and the reagent 11.

[0125] When performing a chemical ionization method using the chemical ionization source 1, ultraviolet light from the ultraviolet light source 5 is used to irradiate the photoelectron emitting surface 24 in the irradiation chamber volume 21, causing the photoelectron emitting surface 24 to emit photoelectrons. Furthermore, a DC voltage difference is applied between the photoelectron emitting surface 24 and the collector electrode 6 by the collector voltage source 7, making the potential of the collector electrode 6 higher than that of the photoelectron emitting surface 24, thereby driving negative charges from the photoelectron emitting surface 24 toward the collector electrode 6. To achieve this, the collector voltage source 7 is controlled by the control unit 8 to apply a voltage difference between the photoelectron emitting surface 24 and the collector electrode 6. Thus, while a positive voltage is applied to the collector electrode 6, the photoelectron emitting surface 24 is grounded. In particular, a positive voltage between 100V and 2000V, especially between 400V and 1000V, or even approximately 700V, is applied to the collector electrode 6. Furthermore, the current flowing through the photoelectron emitting surface 24 and the current flowing through the collector 6 are less than 100 μA, or in one variation less than 10 μA, in another variation even less than 2 μA, and in yet another variation even less than 0.5 μA. Accordingly, the control unit 8 is adapted to control the collector voltage source 7 to apply a voltage difference between the photoelectron emitting surface 24 and the collector 6, such that the current flowing through the photoelectron emitting surface 24 and the current flowing through the collector 6 are less than 100 μA, or in one variation less than 10 μA, in another variation even less than 2 μA, and in yet another variation less than 0.5 μA.

[0126] Furthermore, when performing the chemical ionization method, a sample including the analyte is inserted into the reaction chamber volume 31 through the sample inlet 32 ​​of the reaction chamber 3, so that the analyte is ionized into analyte ions within the reaction chamber volume 31. Additionally, the ion transfer device 36 operates as follows: a radio frequency AC voltage is applied to the confinement electrode 35 as described above to confine the ions in the reaction chamber volume 31 to the central length axis of the reaction chamber volume 31, while a positively voltaged current collector 6 serves as one of at least one transfer electrode of the ion transfer device 36 to push positive analyte ions through the reaction chamber volume 31 to the outlet 33 and out of the outlet 33. Therefore, in Figure 1 In the mass spectrometer 100, the analyte ions exiting the outlet 33 are fed into the mass analyzer 95 for mass analysis. Therefore, the chemical ionization method according to the present invention is used in a mass analysis method for mass analysis of analytes in a sample.

[0127] When performing the chemical ionization method, the vacuum pump 9, controlled by the control unit 8, reduces the gas pressure within the reaction chamber volume 31 to below atmospheric pressure via the reaction chamber vacuum port 38 connected to the vacuum pump 9. Therefore, the gas pressure within the irradiation chamber volume 21 can also be reduced to below atmospheric pressure via the reaction chamber vacuum port 38, the reaction chamber volume 31, and the chamber interface 4. Thus, the irradiation chamber 2 and the reaction chamber 3 operate under gas pressures of 0.01 mbar to 100 mbar, particularly 0.1 mbar to 10 mbar, respectively, within the irradiation chamber volume 21 and the reaction chamber volume 31. Therefore, the flow rate of the gaseous contents of the irradiation chamber volume 21 entering the reaction chamber volume 31 from the irradiation chamber volume 21 via the chamber interface 4 is maintained in the range of 0.1 sccm to 500 sccm, particularly preferably in the range of 1 sccm to 300 sccm, or even in the range of 5 sccm to 20 sccm.

[0128] Figure 1 The illustrated chemical ionization source 1 may further include one or more heating units for heating the irradiation chamber 2 and its volume 21 and / or the reaction chamber 3 and its volume 31 to a specific temperature, and for maintaining the irradiation chamber 2 and its volume 21 and / or the reaction chamber 3 and its volume 31 at that specific temperature. Such heating units may be based on resistive elements. Thus, a resistive element may, for example, be arranged around the irradiation chamber volume 21 in the irradiation chamber 2. Another resistive element may be arranged around the reaction chamber volume 31 in the reaction chamber 3. This arrangement of the heating units is known in the field of chemical ionization sources for creating optimal temperatures within the chemical ionization source to provide optimal operating conditions for the chemical ionization source.

[0129] Figure 2 To adopt Figure 1 The mass spectrum shown is obtained by a mass spectrometer 100 including a chemical ionization source 1 and a mass analyzer 95. This mass spectrum is obtained when water is used as reagent 11, and more specifically, when water vapor is used as the reagent gas. Figure 2 During the measurement of the mass spectrum shown, clean air was introduced as a sample through sample inlet 32. The clean air was laboratory air from which all volatile organic compounds (VOCs) had been removed by a platinum catalyst trap. The total VOC concentration in this clean air was estimated to be less than 10 ppb. Therefore, Figure 2 The mass spectrum shown primarily displays the reagent ion H3O.+ and H3O + (H2O). The 32nd peak is O2. + It is introduced along with the clean air used as a sample.

[0130] To obtain Figure 2 The mass spectrum was obtained, a positive DC voltage of 950V was applied to the collector electrode 6, and water vapor at a flow rate of 15 sccm was introduced as reagent 11 into the irradiation chamber volume 21 through the reagent inlet 22, and the ultraviolet light source 5 was turned on. Therefore, the gas pressure in the reaction chamber volume 31 was maintained at a constant 3 mbar. Thus, the constant flow rate of 15 sccm from the irradiation chamber volume 21 to the reaction chamber volume 31 through the opening 41 of the chamber interface 4 was maintained. As mentioned, the aperture of the opening 41 of the chamber interface 4 is 3 mm. 2 This aperture allows the gaseous contents within the irradiation chamber volume 21 to flow from the irradiation chamber volume 21 to the reaction chamber volume 31. Figure 2 This demonstrates how chemically ionized ion source 1 can be used in conjunction with water vapor as reagent 11 to produce H3O that can be used for proton transfer reaction (PTR) mass spectrometry. + and H3O + (H2O) reagent ion.

[0131] Figure 3 To adopt Figure 1 The image shows another mass spectrum obtained by a mass spectrometer 100, which includes a chemical ionization source 1 and a mass analyzer 95. This mass spectrum was also obtained using water vapor as reagent 11.

[0132] Therefore, a calibration gas mixture diluted in clean air to a concentration of 20 ppb for each compound was introduced into reaction chamber volume 31 via sample inlet 32 ​​as a sample. This calibration gas mixture contained acetone, 2-butanone, benzene, toluene, xylene, trimethylbenzene, and α-pinene. The clean air was also laboratory air from which all volatile organic compounds (VOCs) had been removed via a platinum catalyst trap. The total VOC concentration in this clean air was estimated to be less than 10 ppb.

[0133] To obtain Figure 3 The mass spectrum was obtained, and a positive DC voltage of 850V was applied to the collector electrode 6. Water vapor at a flow rate of 20 sccm was introduced as reagent 11 into the irradiation chamber volume 21 through the reagent inlet 22, and the ultraviolet light source 5 was turned on. Therefore, the gas pressure in the reaction chamber volume 31 was maintained at a constant 3.8 mbar. Thus, a constant flow rate of 20 sccm from the irradiation chamber volume 21 to the reaction chamber volume 31 through the opening 41 of the chamber interface 4 was maintained. As mentioned, the aperture of the opening 41 of the chamber interface 4 is 3 mm. 2This is to allow the gaseous contents within the irradiation chamber volume 21 to flow from the irradiation chamber volume 21 to the reaction chamber volume 31.

[0134] Figure 4 To adopt Figure 1 The graph shown is a curve of the total ion signal changing over time obtained by a mass spectrometer 100, which includes a chemical ionization source 1 and a mass analyzer 95.

[0135] Figure 4 The chemical ionization source 1 is shown to operate advantageously with a DC voltage applied to the current collector 6, which is below the threshold for the generation of self-sustaining plasma in one or both of the irradiation chamber volume 21 and the reaction chamber volume 31. Similarly, in carrying out the method of the invention, the DC voltage applied to the current collector 6 is advantageously below the threshold for the generation of self-sustaining plasma in one or both of the irradiation chamber volume 21 and the reaction chamber volume 31.

[0136] To obtain Figure 4 The data shown indicates that a water vapor stream at a flow rate of 12 sccm was introduced as reagent 11 into the irradiation chamber volume 21 through reagent inlet 22. Additionally, clean air was introduced as a sample into the reaction chamber volume 31 through sample inlet 32. This clean air was also laboratory air from which all volatile organic compounds (VOCs) had been removed by a platinum catalyst trap. The total VOC concentration in this clean air was estimated to be less than 10 ppb. The gas pressure within the reaction chamber volume 31 was maintained at a constant 1 mbar. Therefore, a constant flow rate of 12 sccm from the irradiation chamber volume 21 to the reaction chamber volume 31 through the opening 41 of the chamber interface 4 was maintained. As mentioned, the orifice diameter of the opening 41 of the chamber interface 4 is 3 mm. 2 This is to allow the gaseous contents within the irradiation chamber volume 21 to flow from the irradiation chamber volume 21 to the reaction chamber volume 31.

[0137] In obtaining Figure 4 When the data is shown, an initial positive DC voltage of 850V is continuously applied to the collector 6. After 45 seconds, the ultraviolet light source 5 is turned on, illuminating the photoelectron emitting surface 24 with ultraviolet light. With the ultraviolet light source 5 turned on, for 90 seconds while the ultraviolet light source 5 remains on, the ion signal detected by the mass analyzer 95, which is set on a time scale of less than one second, is maintained at approximately 6 × 10⁻⁶. 6 The count rate is above 1 / second. During this period, the current flowing through the photoelectron emitting surface 24 does not exceed 0.1 μA, while the current flowing through the collector 6 is 0.2 μA to 0.3 μA. After the ultraviolet light source 5 is turned off, the ion signal detected by the mass analyzer 95 disappears in less than one second.

[0138] Ultimately, under the condition of applying a positive DC voltage of 850V to the collector electrode 6, reagent molecules and / or reagent atoms are each photo-ionized by ultraviolet light to form reagent ions within the chemical ionization source 1. When the DC voltage applied to the collector electrode 6 is 850V, no self-sustaining plasma is generated in the irradiation chamber volume 21 and / or the reaction chamber volume 31.

[0139] During the same measurement process, 195 seconds after the start, the positive DC voltage applied to collector 6 was increased to 1050V, while the ultraviolet light source 5 remained off. Less than one second after increasing the positive DC voltage at collector 6, an ion signal reappeared at mass analyzer 95. However, the intensity of this ion signal was only about 5 × 10⁻⁶. 6 The count was 1 / second, and then rapidly decreased to 4 × 10⁻⁶ in the following seconds. 6 The count / second was below 1050V. Approximately 90 seconds after the positive DC voltage applied to collector 6 increased to 1050V, the positive DC voltage applied to collector 6 dropped back to 850V. The ion signal detected by mass analyzer 95 then disappeared in less than one second. Approximately 60 seconds later, the UV light source 5 was turned on again. As a result, the ion signal detected by mass analyzer 95, which was again set to a timescale of less than one second, remained substantially constant at 6 × 10⁻⁶ during the period the UV light source 5 remained on. 6 Counts per second or more. Similarly, during this period, the current flowing through the photoelectron emitting surface 24 does not exceed 0.1 μA, while the current flowing through the collector 6 is 0.2 μA to 0.3 μA.

[0140] from Figure 4 It is clearly evident that when a positive DC voltage of 1050V is applied to the collector electrode 6, a self-sustaining plasma is generated in the irradiation chamber volume 21 and / or the reaction chamber volume 31. However, in this state, the yield of reagent ions is not very high. More importantly, the yield of reagent ions is unstable and rapidly decays after reaching an initial maximum value. In contrast, when a positive DC voltage of 850V is applied to the collector electrode 6 and ultraviolet light-driven photoelectron ionization is implemented, the yield of reagent ions in the chemical ionization source 1 is higher and quite stable. Therefore, the chemical ionization source 1 according to the present invention and the chemical ionization method according to the present invention can achieve a surprisingly efficient and stable yield of reagent ions suitable for chemical ionization.

[0141] Based on this result, the inventors hypothesize that when the chemical ionization source 1 is operating, photoelectrons within the irradiation chamber volume 21 strike reagent molecules and / or reagent atoms, respectively, ionizing them into reagent ions, or combining with them to form reagent ions, or being further driven through the chamber interface 4 into the reaction chamber volume 31. In the latter case, photoelectrons within the reaction chamber volume 31 strike reagent molecules and / or reagent atoms, respectively, ionizing them into reagent ions, or combining with them to form reagent ions. Regardless of the specific process, the inventors have observed that this scheme can achieve unexpectedly high efficiency and stable reagent ion production, which can react with the analytes in the sample within the reaction chamber volume 31, ionizing the analytes into analyte ions.

[0142] Figure 5 Long-term measurements over a period of two weeks are shown, illustrating the long-term stability of the chemical ionization source and the chemical ionization method according to the invention. Figure 5 The data shown is obtained using Figure 1 The mass spectrometer 100 shown includes a chemical ionization source 1 and a mass analyzer 95.

[0143] In this long-term measurement, both water vapor and oxygen are used as reagent 11. Therefore, reagent inlet 22 is connected to two different reagent sources, one for water vapor and the other for oxygen. Thus, reagent 11 is switched between the two every ten seconds. For example, water vapor is used as reagent 11 for 10 seconds, followed by oxygen for another 10 seconds. This process is repeated, with water vapor used again. When water vapor is used as reagent 11, a flow rate of 14 sccm is introduced into the irradiation chamber volume 21 via reagent inlet 22. When oxygen is used as reagent 11, a flow rate of 20 sccm is introduced into the irradiation chamber volume 21 via reagent inlet 22. Each time reagent is switched, data acquired within three seconds is discarded to purge the chemical ionization source 1 and mass analyzer 95 using the newly adopted reagent. Data acquired within the next seven seconds is retained until the next reagent switch.

[0144] Throughout the two weeks, the UV light source 5 remained on, applying a positive DC voltage of 900V to the collector 6 while maintaining the gas pressure within reaction chamber volume 31 at approximately 3.5 mbar. Ambient air was sampled into the chemical ionization source 1 and analyzed. To demonstrate the long-term stability of the chemical ionization source 1, ambient air sampling was paused for 10 to 30 minutes every few days for equipment calibration. During calibration, benzene (C6H6) diluted to 20 ppbv in clean air was used instead of ambient air and introduced into reaction chamber volume 31 via sample inlet 32. As explained earlier, during these calibrations, the reagents were switched between water and oxygen every 10 seconds.

[0145] The clean air used to dilute benzene during calibration was laboratory air with all volatile organic compounds (VOCs) removed via a platinum catalyst trap. The total VOC concentration in this clean air was estimated to be less than 10 ppb. Using this clean air, a 1 ppmv benzene calibration standard gas was diluted to 20 ppbv.

[0146] Figure 5 The data points corresponding to benzene ionized in water and oxygen, respectively, measured using a mass analyzer 95 during calibration are shown. Therefore, the data points are normalized to counts per second per ppbv (parts per billion of volume) of benzene. Since the data points remained stable over the two-week measurement period, it is clearly demonstrated that the chemical ionization source and chemical ionization method according to the invention can achieve surprisingly stable ionization of samples even during extended operation.

[0147] In summary, this invention provides a chemical ionization source and a chemical ionization method for ionizing analytes in a sample into analyte ions through chemical ionization, thereby enabling analytes to be chemically ionized into analyte ions more efficiently and definitively.

[0148] List of reference numerals 1. Chemical ionization source 2 Irradiation Chamber 3. Reaction Chamber 4. Chamber Interface 5. Ultraviolet light source 6 collectors 7 Collector Voltage Source 8 Control Unit 9. Vacuum pump 10. Reagent storage container 11 Reagents 21 Irradiation chamber volume 22 Reagent Inlet 23 Photoelectron Emission Electrode 24 Photoelectron emitting surface 25 windows 26 cones 27 Irradiation Chamber Valves 31. Reaction chamber volume 32 Sample Inlet 33 Exports 34 Glass tubes 35 Constrained Electrodes 36 Ion transfer device 37 Sample tubes 38 Vacuum port of the reaction chamber 39. Reaction chamber valves 41 Opening 42 Funnel-shaped depression 43 Cones 61 Resistance Region 95 Quality Analyzer 100 mass spectrometer

Claims

1. A chemical ionization ion source (1) for ionizing an analyte in a sample into analyte ions by chemical ionization, said chemical ionization ion source (1) comprising: a) an irradiation chamber (2) forming an irradiation chamber volume (21) and having a reagent inlet (22) for inserting a reagent comprising reagent molecules and / or reagent atoms into the irradiation chamber volume (21). b) Photoelectron emitting surface (24), which is contained in the irradiation chamber (2) for emitting photoelectrons from the photoelectron emitting surface in the volume (21) of the irradiation chamber when irradiated by electromagnetic radiation; c) An electromagnetic radiation source, the electromagnetic radiation source being adapted to irradiate the photoelectron emitting surface (24) with electromagnetic radiation so that the photoelectron emitting surface (24) emits photoelectrons; d) A reaction chamber (3) defining a reaction chamber volume (31) and having a sample inlet (32) for inserting the sample comprising the analyte into the reaction chamber volume (31) to ionize the analyte into analyte ions in the reaction chamber volume (31) by contacting the analyte with reagent ions that are ionized reagent molecules and / or reagent atoms, respectively, wherein, The reaction chamber (3) also has an outlet (33) for discharging the analyte ions from the reaction chamber volume (31). e) Chamber interface (4), the chamber interface being adapted to fluidly communicate the irradiation chamber volume (21) and the reaction chamber volume (31) for transferring the gaseous contents of the irradiation chamber volume (21) from the irradiation chamber volume (21) to the reaction chamber volume (31). f) Collector (6), wherein the collector (6) is arranged in the reaction chamber (3) near the chamber interface (4), arranged at the chamber interface (4), or forming the chamber interface (4). g) A collector voltage source (7) connected to at least one of the photoelectron emitting surface (24) and the collector (6), and used to apply a voltage difference between the photoelectron emitting surface (24) and the collector (6), such that the potential of the collector (6) is higher than the potential of the photoelectron emitting surface (24), so as to drive negative charges from the photoelectron emitting surface (24) to the collector (6); and h) Control unit (8), the control unit being adapted to control the collector voltage source (7) to apply the voltage difference between the photoelectron emitting surface (24) and the collector (6), such that the potential of the collector (6) is higher than the potential of the photoelectron emitting surface (24), so as to drive negative charge from the photoelectron emitting surface (24) to the collector (6).

2. The chemical ionization ion source (1) according to claim 1, characterized in that, The voltage difference between the photoelectron emitting surface (24) and the collector (6) is between 100V and 2000V.

3. The chemical ionization ion source (1) according to claim 1, characterized in that, The control unit (8) is adapted to control the collector voltage source (7) to apply the voltage difference between the photoelectron emitting surface (24) and the collector (6) such that at least one of the current flowing through the photoelectron emitting surface (24) and the current flowing through the collector (6) is less than 100µA.

4. The chemical ionization ion source (1) according to claim 1, characterized in that, The chemical ionization source (1) includes an ion transfer device (36) adapted to transfer the analyte ions in the reaction chamber volume (31) to the outlet (33).

5. The chemical ionization ion source (1) according to claim 1, characterized in that, The electromagnetic radiation source is an ultraviolet light source (5), which includes a vacuum ultraviolet (VUV) light source for emitting ultraviolet light.

6. The chemical ionization ion source (1) according to claim 1, characterized in that, The chamber interface (4) provides an opening (41) with an aperture for fluid communication between the irradiation chamber volume (21) and the reaction chamber volume (31), for transferring the gaseous contents of the irradiation chamber volume (21) from the irradiation chamber volume (21) to the reaction chamber volume (31), wherein the aperture is 0.01 mm. 2 Up to 5000mm 2 Within the range.

7. The chemical ionization ion source (1) according to claim 1, characterized in that, The reaction chamber (3) provides a reaction chamber vacuum port (38) for reducing the gas pressure in the reaction chamber volume (31) to below atmospheric pressure.

8. The chemical ionization ion source (1) according to claim 7, characterized in that, The chemical ionization source (1) includes at least one of the following: - A vacuum pump (9), connected to the vacuum port (38) of the reaction chamber, is used to reduce the gas pressure within the volume (31) of the reaction chamber to below atmospheric pressure. - Irradiation chamber valve (27), used to control the gas flow rate entering the irradiation chamber volume (21), and -Reaction chamber valve (38), used to control the gas flow rate entering the reaction chamber volume (31), The control unit (8) is adapted to control at least one of the vacuum pump (9), the irradiation chamber valve (27), and the reaction chamber valve (39) contained in the chemical ionization source (1) to maintain the flow rate of the gaseous contents of the irradiation chamber volume (21) entering the reaction chamber volume (31) from the irradiation chamber volume (21) through the chamber interface (4) in the range of 0.1 sccm to 500 sccm.

9. The chemical ionization ion source (1) according to claim 1, characterized in that, The electromagnetic radiation source is an ultraviolet light source.

10. The chemical ionization ion source (1) according to claim 1, characterized in that, The electromagnetic radiation is ultraviolet light.

11. The chemical ionization ion source (1) according to claim 2, characterized in that, The voltage difference between the photoelectron emitting surface and the collector is between 400V and 1000V.

12. The chemical ionization ion source (1) according to claim 5, characterized in that, The vacuum ultraviolet (VUV) light source is an inert gas lamp.

13. The chemical ionization ion source (1) according to claim 6, characterized in that, The aperture is 1 mm 2 Up to 100mm 2 Within the range.

14. A mass spectrometer (100) comprising a chemical ionization source (1) according to claim 1.

15. A chemical ionization method that uses a chemical ionization ion source to ionize analytes in a sample into analyte ions via chemical ionization. in, The chemical ionization method comprises: inserting a reagent, including reagent molecules and / or reagent atoms, into the irradiation chamber volume (21) of the irradiation chamber (2) of the chemical ionization ion source (1) through the reagent inlet (22); and irradiating the photoelectron emitting surface (24) in the irradiation chamber volume (21) with the electromagnetic radiation source of the chemical ionization ion source (1), particularly with ultraviolet light from the ultraviolet light source (5), so that the photoelectron emitting surface (24) emits photoelectrons. The chemical ionization method includes: applying a voltage difference between the photoelectron emitting surface (24) and the collector electrode (6) of the chemical ionization ion source (1) using a collector electrode voltage source (7), such that the potential of the collector electrode (6) is higher than the potential of the photoelectron emitting surface (24), so as to drive negative charges from the photoelectron emitting surface (24) to the collector electrode (6), wherein the chemical ionization ion source (1) provides a reaction chamber (3) forming a reaction chamber volume (31), wherein the chemical ionization ion source (1) provides a chamber interface (4), the chamber interface being adapted to allow the irradiation chamber volume (31) to be transferred to the reaction chamber. 21) Fluidly connected to the reaction chamber volume (31), for transferring the gaseous contents of the irradiation chamber volume (21) from the irradiation chamber volume (21) to the reaction chamber volume (31), wherein the current collector (6) is arranged in the reaction chamber (3) near the chamber interface (4), arranged at the chamber interface (4), or forming the chamber interface (4), wherein the chemical ionization method comprises: inserting the sample including the analyte into the reaction chamber volume (31) through the sample inlet (32) of the reaction chamber (3) so as to ionize the analyte into the analyte ions in the reaction chamber volume (31).

16. The chemical ionization method according to claim 15, characterized in that, At least one of the current flowing through the photoelectron emitting surface (24) and the current flowing through the collector (6) is less than 100µA.

17. The chemical ionization method according to claim 15, characterized in that, The chemical ionization method includes: an ion transfer device (36) operating the chemical ionization ion source (1) for transferring the analyte ions in the reaction chamber volume (31) to the outlet (33) of the reaction chamber (3) so that the analyte ions are discharged from the reaction chamber volume (31).

18. The chemical ionization method according to claim 15, characterized in that, The chemical ionization method includes reducing the gas pressure in the reaction chamber (31) to below atmospheric pressure via the outlet (33) or via the reaction chamber vacuum port (38) of the reaction chamber (3).

19. The chemical ionization method according to claim 15, characterized in that, The chemical ionization method comprises maintaining the flow rate of the gaseous contents of the irradiation chamber volume (21) into the reaction chamber volume (31) from the irradiation chamber volume (21) through the chamber interface (4) in the range of 0.1 sccm to 500 sccm.

20. The chemical ionization method according to claim 17, characterized in that, The chemical ionization method comprises: operating the ion transfer device (36) of the chemical ionization ion source (1) by applying a voltage to a transfer electrode (6) in at least one transfer electrode (6) of the ion transfer device (36) to generate an electric field, for transferring the analyte ions in the reaction chamber volume (31) to the outlet (33) of the reaction chamber (3) so that the analyte ions are discharged from the reaction chamber volume (31).

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