Photoionization detectors and methods for gas sample analysis

Abstract

A photoionization detector (PID) is disclosed, comprising: an ionization chamber configured such that a flow of gas sample can pass through the ionization chamber, the ionization chamber defining an ionization region and a detection region; a photoionization source configured to generate ionizing radiation for irradiating the flow of gas sample in the ionization region; an electric field ionization source configured to apply an ionizing electric field inside the ionization chamber to intersect with the flow of gas sample in the ionization region, the ionizing radiation and the ionizing electric field being configured to ionize the gas sample; and an ion detector configured to detect an ionizing current generated by the ionized gas sample in the detection region. The PID may further include an optical window, made of, for example, a window material including sapphire, and configured such that at least a portion of the ionizing radiation can pass through the optical window before entering the ionization region.

Description

Technical Field

[0001] This technical field generally relates to gas detection, and more specifically to photoionization detectors for detecting chemical compounds in gas samples. Background Technology

[0002] Various types of gas detectors and detection techniques are known in the art. A photoionization detector (PID) is one type of gas detector. A PID is a broadband detector that responds to a wide range of organic compounds (such as volatile organic compounds (VOCs)) and some inorganic compounds. PIDs are widely used in gas chromatography (GC), as well as in a variety of other industrial and scientific applications for monitoring, detecting, and / or analyzing environmental and hazardous gases. A conventional PID typically comprises an ultraviolet (UV) radiation source, an ionization chamber optically coupled to the UV radiation source, and a pair of electrically biased collecting electrodes placed within the ionization chamber. The UV radiation source is typically a vacuum UV (VUV) lamp filled with a low-pressure inert gas (such as argon (Ar), xenon (Xe), or krypton (Kr)), configured to produce UV radiation with photon energies typically in the range of about 8.0 eV to about 12.0 eV. The UV radiation source has an optical window configured to allow UV radiation to pass through and enter the ionization chamber. Optical windows are typically made of fluoride salt crystals (such as BaF2, CaF2, MgF2, and LiF). The ionization chamber is configured to allow the gas sample to flow through it. UV radiation, generated by a UV radiation source, ionizes chemical compounds in the flowing gas sample with ionization energies equal to or less than the energy of a UV photon. This results in the removal of electrons from the chemical compounds and the formation of positively charged ions. A potential difference is applied between the collecting electrodes, creating an electric field within the ionization chamber. This electric field separates the ions from the electrons, allowing one electrode to collect ions and the other to collect electrons. This charge separation and collection process generates a current that can be measured and analyzed to provide quantitative and qualitative information about the composition of the gas sample.

[0003] PID controllers offer a variety of advantages, including, but not limited to, high sensitivity, wide dynamic range, versatility, ease of use, compact size, and non-destructive testing capabilities. However, PID controllers also have drawbacks and limitations. One drawback is that PID controllers tend to have a limited lifespan and are susceptible to performance degradation, especially at higher photon energies. Therefore, extending the lifespan of PID controllers to improve performance remains a challenge in the field. Summary of the Invention

[0004] This manual generally relates to photoionization detectors (PIDs) used in gas chromatography (GC) and other gas detection applications, and related operating methods.

[0005] According to one aspect, a PID is provided, which includes:

[0006] An ionization chamber is configured to allow a flow of gas sample to pass through it, and the ionization chamber defines an ionization region and a detection region.

[0007] A photoionization source is configured to generate ionizing radiation for irradiating a stream of gas sample in an ionization region.

[0008] An electric field ionization source is configured to apply an ionizing electric field inside an ionization chamber to intersect with a flow of gas sample in an ionization region, wherein ionizing radiation and the ionizing electric field are configured to ionize the gas sample into an ionized gas sample; and

[0009] An ion detector is configured to detect the ionization current generated by an ionized gas sample in a detection region.

[0010] The gaseous sample can be any gaseous substance known, expected, or suspected of containing the analyte, including gases, vaporized liquids, and vaporized solids. The analyte of interest can include volatile organic compounds (VOCs), and non-limiting examples of VOCs include (to name just a few): aromatics, alkenes, bromides and iodides, sulfides and thiols, organic amines, ketones, ethers, esters and acrylates, alcohols, aldehydes, alkanes, and alkyl halides.

[0011] In some embodiments, the ionization chamber includes a chamber body, a sample inlet configured to receive a gaseous sample into the chamber body, and a sample outlet configured to discharge the gaseous sample from the chamber body. The chamber body may enclose an internal volume defining an ionization region and a detection region. The chamber body may also provide a sample flow path that allows the gaseous sample to flow sequentially from the sample inlet through the ionization region and the detection region to the sample outlet.

[0012] In some embodiments, the photoionization source is configured to emit ionizing radiation in the ultraviolet (UV) region of the electromagnetic spectrum, such as in the vacuum UV (VUV) sub-region, and more specifically in the wavelength range of about 150 nm to about 100 nm, which corresponds approximately to photon energies between about 8.0 eV and about 12.0 eV. Such photon energies can enable the ionization of various analytes of interest without the ionization of a typical carrier gas, or with little or negligible ionization of the typical carrier gas. While the various embodiments disclosed herein use ionizing radiation in the UV range, some embodiments may use ionizing radiation in other regions of the electromagnetic spectrum, such as the visible range.

[0013] In some embodiments, the PID includes an optical window configured such that at least a portion of the ionizing radiation can pass through the optical window before entering the ionization region of the ionization chamber. Depending on the application, the optical window may be provided as a component of a photoionization source or an ionization chamber, or as a separate component of the PID. The ionizing radiation generated by the photoionization source comprises high-energy photons capable of ionizing one or more analytes of interest in a gas sample, either alone or in conjunction with an ionizing electric field applied by an electric field ionization source. In some embodiments, the flow of the gas sample, the ionizing electric field, and the surface orthogonal to the optical window are perpendicular to each other. In some embodiments, the optical window is made of a window material including lithium fluoride (LiF), magnesium fluoride (MgF2), calcium fluoride (CaF2), barium fluoride (BaF2), strontium fluoride (SrF2), sodium fluoride (NaF), sapphire (Al2O3), or quartz (SiO2), or combinations thereof.

[0014] In some embodiments, the photoionization source includes at least one UV lamp in optical communication with the ionization chamber. The UV lamp may include a lamp body that encloses an internal volume defining a discharge region configured to receive discharge gas within the discharge region. The UV lamp may also include or be coupled to a lamp power supply and associated electronic circuitry, the lamp power supply being configured to excite the discharge gas within the discharge region into plasma that generates ionizing radiation. The UV lamp may also include an optical window mounted to the lamp body and configured such that at least a portion of the ionizing radiation generated within the discharge region can pass through the optical window and enter the ionization chamber. In some embodiments, at least one UV lamp includes a pair of UV lamps positioned on opposite sides of the ionization chamber.

[0015] The discharge gas can be any gas or combination of gases capable of producing a plasma accompanied by radiation emission (e.g., UV radiation). The energy of the UV photons emitted by the gas discharge plasma can depend on the type of discharge gas used to fill the discharge region. Non-limiting examples of discharge gases include (to name just a few): argon (Ar), xenon (Xe), krypton (Kr), neon (Ne), helium (He), hydrogen (H2), oxygen (O2), nitrogen (N2), or combinations thereof.

[0016] The optical window can be removably mounted to the lamp body. In this case, the optical window can be removed for inspection, cleaning, repair, replacement, and / or any other suitable maintenance operations. The optical window can be made of a material with high UV transmittance in certain spectral ranges. The optical window can serve as a cutoff filter that determines the spectrum of ionizing radiation generated in the discharge region, which exits the UV lamp into the ionization chamber to irradiate a gas sample in the ionization region. The optical window can be characterized by a high cutoff photon energy, beyond which the transmittance of the optical window decreases significantly, becoming very low or negligible from a practical standpoint. Non-limiting examples of window materials include (to name just a few): crystalline materials (such as lithium fluoride (LiF), magnesium fluoride (MgF2), calcium fluoride (CaF2), barium fluoride (BaF2), strontium fluoride (SrF2), sodium fluoride (NaF), sapphire (Al2O3), quartz (SiO2), and combinations thereof) and any suitable current or future window materials. Since different window materials have different transmission spectra, the highest energy photons transmitted into the ionization chamber can be controlled by selecting the window material.

[0017] Depending on the application, various methods can be used to excite the discharge gas inside a UV lamp and generate a gas discharge plasma that emits UV radiation. Non-limiting examples of excitation methods include (to name just a few): continuous direct current (DC) discharge, pulsed DC discharge, alternating current (AC) discharge, dielectric barrier discharge (DBD), corona discharge, radio frequency (RF) discharge, microwave (MW) discharge, hollow cathode (HC) discharge, inductively coupled plasma (ICP) discharge, and capacitively coupled plasma (CCP) discharge.

[0018] In some embodiments, the UV lamp can be configured to operate according to a DBD-based excitation method. In this case, the UV lamp may include a pair of discharge electrodes and a pair of dielectric barriers, the discharge electrodes being spaced apart and positioned on opposite sides of the lamp body to define a discharge gap in the discharge region, the dielectric barriers being positioned within the discharge gap, each dielectric barrier extending along and adjacent to a corresponding one of the discharge electrodes. In some embodiments, the lamp body includes a pair of opposing sidewalls providing the dielectric barriers. The lamp power supply can be configured to excite the discharge gas into plasma by applying a discharge drive signal to the discharge electrodes to generate a discharge electric field across the discharge gap, wherein the discharge electric field is configured to establish and maintain plasma emitting UV radiation in the discharge region.

[0019] In some embodiments, the UV lamp includes one or more gas ports formed through the lamp body to provide gas communication between the discharge region and the outside of the lamp body. The one or more gas ports may include a discharge gas inlet and a discharge gas outlet, the discharge gas inlet being configured to receive discharge gas into the discharge region and the discharge gas outlet being configured to discharge discharge gas from the discharge region. The discharge gas inlet and discharge gas outlet may be configured to connect to a gas flow system. The gas flow system may be configured to continuously or intermittently allow a flow of discharge gas from the discharge gas inlet through the discharge region to the discharge gas outlet. Allowing the discharge gas to flow through the interior of the UV lamp during operation can be useful, for example, for removing contaminants formed during plasma discharge and / or for removing heat from the UV lamp. The gas flow system may be configured to be able to select between different types of gases and gas mixtures that may include doped gases as the discharge gas in the UV lamp.

[0020] In some embodiments, the PID may include an optical window made of a window material whose highest energy transmitted photons have lower energies than those of common fluoride crystal materials (such as CaF2, MgF2, and LiF), while enabling the detection of analytes over a fairly wide range of ionization energies. This is because the ionization of a gas sample can be achieved through a combination of ionizing radiation generated by a photoionization source and an ionizing electric field applied by an electric field ionization source. For example, the optical window may be made of sapphire, which exhibits high mechanical strength, high chemical resistance, and high thermal stability. However, sapphire has a lower high cutoff photon energy than CaF2, MgF2, and LiF. By using field-assisted photoionization, the PID can benefit from the enhanced robustness and durability of the sapphire optical window compared to common fluoride crystal windows, without being limited by the narrowing range of detectable analytes caused by the lower photon energies emitted by the sapphire UV lamp.

[0021] In some embodiments, the electric field ionization source may include a pair of ionizing electrodes arranged relative to the ionization region, for example, positioned on opposite sides of the ionization chamber outside the chamber in a spaced-apart relationship. The electric field ionization source may also include or be coupled to an ionization power supply and associated electronic circuitry, the power supply being configured to apply an ionization drive signal to the ionizing electrodes to generate an ionizing electric field in the ionization region. In some embodiments, the ionization drive signal may be a DC signal, which may be a continuous DC signal or a pulsed DC signal. Specifically, the DC signal may have a constant amplitude or may vary abruptly or gradually over time, making various types of DC waveforms possible, including fully rectified and partially rectified waveforms. In other embodiments, the ionization drive signal used to generate the ionizing electric field may be a low-intensity AC signal and / or a low-frequency AC signal. In some embodiments, the ionization power supply may be configured to control the amplitude of the ionizing electric field to increase the upper limit of the range of ionization energies of detectable analytes in the gas sample by an amount from about 1 eV to about 4 eV.

[0022] In some embodiments, the use of field-assisted photoionization can enable the embodiments of the PID disclosed herein to employ more durable but lower-energy UV lamps (such as UV lamps with sapphire windows), but can respond to compounds having an ionization energy range comparable to that provided by higher-energy UV lamps (such as UV lamps based on CaF2, MgF2, LiF and other fluoride crystals).

[0023] In some embodiments, the strength of the ionizing electric field can be varied during or between operations to adjust the selectivity of the PID according to the range of ionization energies of the detectable analyte, which is typically inversely proportional to the electric field strength.

[0024] In some embodiments, the ion detector may include a pair of detection electrodes arranged relative to a detection region, for example, spaced apart and positioned on opposite sides of the ionization chamber outside the chamber. The ion detector may also include or be coupled to a detection power supply and associated electronic circuitry, the detection power supply being configured to establish and maintain a bias voltage between the detection electrodes to generate a detection electric field in the detection region. The detection electric field is configured to deflect and separate ions and electrons from the ionized gas sample onto a corresponding one of the detection electrodes for collection. The ion detector may also include detection circuitry configured to measure an ionization current based on the ions and electrons collected by the detection electrodes and output a detection signal representing the measured ionization current.

[0025] In some embodiments, the PID may include a control and processing unit. The control and processing unit may be configured to control, monitor, and / or coordinate the function and operation of various components of the PID, such as an ionization chamber, photoionization source, electric field ionization source, and ion detector. The control and processing unit may also be configured to receive a detection signal representing an ionization current from the ion detector and determine analyte information about an analyte in the gas sample based on the detection signal. The analyte information may be determined based on calibration with a known standard gas. The analyte information may be the presence or absence of an analyte in the gas sample, or the amount of an analyte in the gas sample, or both the presence or absence of an analyte in the gas sample and the amount of an analyte in the gas sample. The control and processing unit may include a processor and a memory.

[0026] According to another aspect, a PID is provided, which includes:

[0027] An ionization chamber is configured to receive a gas sample and defines an ionization area and a detection area.

[0028] A UV radiation source is configured to generate UV radiation. The UV radiation source includes an optical window configured to transmit at least a portion of the UV radiation into an ionization chamber to irradiate a gas sample in the ionization region. The optical window is made of a window material including sapphire (Al2O3).

[0029] An electric field ionization source is configured to apply an ionizing electric field to a gas sample in an ionization region, wherein the ionizing electric field is configured to combine with transmitted UV radiation to ionize the gas sample into an ionized gas sample; and

[0030] An ion detector is configured to detect the ionization current generated by an ionized gas sample in a detection region.

[0031] In some embodiments, the optical window is configured to substantially prevent the transmission of UV photons with photon energies greater than about 8.5 eV, and wherein the transmitted UV radiation and ionizing electric field are configured to ionize analytes in the gas sample with ionization energies greater than about 10 eV.

[0032] In some embodiments, the UV radiation source is configured to generate dielectric barrier discharge plasma and to generate UV radiation from the dielectric barrier discharge plasma.

[0033] In some embodiments, the electric field ionization source includes a pair of ionizing electrodes and an ionizing power source. The pair of ionizing electrodes are positioned on opposite sides of the ionization chamber outside the ionization chamber in a spaced-apart relationship. The ionizing power source is configured to apply an ionization drive signal to the ionizing electrodes to generate an ionizing electric field in the ionization region.

[0034] According to another aspect, a method for analyzing a gas sample is provided, the method comprising:

[0035] The gas sample is passed through an ionization chamber that includes an ionization region and a detection region;

[0036] In the ionization region, the gas sample is subjected to ionizing radiation and an ionizing electric field to ionize the gas sample into an ionized gas sample; and

[0037] The ionization current generated by the ionized gas sample is detected in the detection area to generate a detection signal that transmits information about the gas sample.

[0038] In some embodiments, ionizing radiation includes UV radiation.

[0039] In some embodiments, the method includes: generating ionizing radiation and supplying the ionizing radiation to an ionization region. In some embodiments, generating ionizing radiation includes: exciting a discharge gas into a plasma and generating ionizing radiation from the plasma. In some embodiments, the plasma is a dielectric barrier discharge plasma. In some embodiments, generating ionizing radiation includes: operating a pair of UV lamps arranged relative to the ionization chamber. In some embodiments, supplying ionizing radiation to the ionization region includes: transmitting the ionizing radiation through an optical window. In some embodiments, the optical window is made of a window material including lithium fluoride (LiF), magnesium fluoride (MgF2), calcium fluoride (CaF2), barium fluoride (BaF2), strontium fluoride (SrF2), sodium fluoride (NaF), sapphire (Al2O3), or quartz (SiO2), or combinations thereof.

[0040] In some embodiments, the method further includes: providing a pair of ionizing electrodes and applying an ionization driving signal to the ionizing electrodes to generate an ionizing electric field in the ionization region.

[0041] In some embodiments, detecting the ionization current includes: providing a pair of detection electrodes; biasing the detection electrodes to generate a detection electric field in a detection region to deflect ions and electrons in an ionized gas sample onto a corresponding one of the detection electrodes for collection by the detection electrode; and measuring the ionization current based on the ions and electrons collected by the detection electrode.

[0042] According to another aspect, a GC system is provided, which includes a PID as described herein. For example, the GC system may include a sample processing unit and a chromatographic separation unit (e.g., a chromatographic column), the sample processing unit being configured to process a gas sample, and the chromatographic separation unit being configured to receive a sample from the gas sample processing unit and perform chromatographic separation of the gas sample. The PID may be configured to detect the chromatographically separated sample and generate a detection signal from the chromatographically separated sample. The GC system may also include a control and processing unit configured to receive the detection signal from the PID and obtain a chromatogram of the sample from the detection signal. The sample processing unit may include a sample collector, a sample conditioner, and a sample injector, the sample collector being configured to collect or receive the gas sample, the sample conditioner being configured to process the gas sample to make the gas sample suitable for GC analysis, and the sample injector being configured to meter and inject the processed gas sample as part of the mobile phase into the chromatographic separation unit.

[0043] It should be noted that other methods and process steps may be performed before, during, or after the steps described herein. The order of one or more steps may also differ, and some steps may be omitted, repeated, and / or combined depending on the application. It should also be noted that various data processing techniques may be used to perform some methods and processing steps, and these data processing techniques may be implemented in hardware, software, firmware, or any combination thereof.

[0044] Other objects, features, and advantages of this specification will become more apparent when reading the following non-limiting description of specific embodiments of this specification, which are given by way of example only with reference to the accompanying drawings. Although the specific features described in the above overview and the following detailed description may be described with respect to specific embodiments or aspects, it should be noted that these specific features may be combined with each other unless otherwise stated. Attached Figure Description

[0045] Figure 1 This is a perspective view of the PID according to an embodiment.

[0046] Figure 2 for Figure 1 A partial cross-sectional perspective view of the PID.

[0047] Figure 3 For along Figure 1 Section line 3-3 is cut from Figure 1 A cross-sectional perspective view of the PID.

[0048] Figure 4 This is a flowchart illustrating an embodiment of a method for analyzing gas samples. Detailed Implementation

[0049] In this specification, similar features in the accompanying drawings are given similar reference numerals. To avoid confusion in some figures, elements that have already been identified in preceding figures may not be indicated. It should be understood that the elements in the drawings are not necessarily drawn to scale, as the focus is on clearly illustrating the structure and operation of this embodiment. Furthermore, for simplicity and clarity of description, positional descriptors are used herein to indicate the position and / or orientation of one element relative to another element. Unless otherwise stated, these positional descriptors should be used in the context of the drawings and should not be considered limiting. It should be understood that in the use or operation of this embodiment, such spatial relative terms are intended to encompass different orientations in addition to those illustrated in the drawings.

[0050] In this specification, the terms “a” and “an” are defined as “at least one”, meaning that, unless otherwise stated, these terms do not exclude multiple elements.

[0051] Terms (such as "substantially," "usually," and "about") used to modify the values, conditions, or characteristics of features in exemplary embodiments should be understood to mean that the value, condition, or characteristic is limited to acceptable tolerances for correct operation of the exemplary embodiment in its intended application, or to tolerances falling within an acceptable range of experimental error. In particular, the term "about" generally refers to a range of numbers that a person skilled in the art would consider equivalent to the value (e.g., having the same or equivalent function or result). In some cases, the term "about" refers to a variation of ±10% of the value. Note that unless otherwise stated, all numerical values ​​used herein are assumed to be modified by the term "about."

[0052] The terms “matched,” “matching,” and “matched” are intended to refer to the condition that two elements are identical or within a predetermined tolerance of each other. That is, these terms refer not only to matching two elements “exactly” or “identically,” but also to matching two elements “substantially,” “approximately,” or “subjectively,” and to providing a higher or better match among multiple matching possibilities.

[0053] Unless otherwise stated, the terms “connection,” “linkage,” and their derivatives and variations refer to any direct or indirect connection or linkage between two or more elements. Connections or linkages between elements can be, for example, mechanical, optical, electrical, thermal, chemical, fluid, magnetic, logical, operational, or any combination thereof.

[0054] In this specification, the term "simultaneously" refers to two processes that occur during overlapping or concurrent time periods. The term "simultaneously" does not necessarily mean complete synchronization, but encompasses a variety of situations, including: the two processes occurring at the same time or concurrently; the occurrence of a first process that begins and ends during the duration of the second process; and the occurrence of a first process that begins during the duration of the second process but ends after the completion of the second process.

[0055] This specification generally relates to photoionization detectors (PIDs) for detecting analytes in gas samples and related methods of use. Depending on the application, the PIDs disclosed herein may be suitable for use in laboratory environments, such as in high-performance GC applications, or in other fields. The disclosed PIDs may be stationary, portable, or handheld instruments, and may be externally powered or battery-powered.

[0056] A PID (Polyionized Analyzer) is a gas detection device in which a gas sample is typically ionized by high-energy photons in the VUV range. A conventional PID usually includes a high-energy photon source, an ionization chamber, and a collection electrode. High-energy photons are directed into the ionization chamber to ionize the gas sample, and a potential difference is applied to the collection electrode to collect the ions and electrons present in the ionized gas sample. The collected ions and electrons generate an electric current that conveys information related to the gas sample, such as the concentration of analytes in the gas sample. It should be understood that the theory, instrumentation, operation, and applications of PIDs are generally known in the art and need not be described in detail herein except to facilitate understanding of the technique.

[0057] In this specification, the terms "light" and "optics," and their variations and derivatives, are intended to refer to radiation in any suitable region of the electromagnetic spectrum. These terms are not limited to visible light but also include the invisible regions of the electromagnetic spectrum, such as UV radiation. The spectrum of UV radiation is typically defined in the range of about 400 nm to about 10 nm and can be further subdivided into many sub-regions. Conventional PIDs typically operate with VUV radiation in the wavelength range of about 150 nm to about 100 nm, which roughly corresponds to photon energies in the range of about 8.0 eV to about 12.0 eV. VUV sub-regions are typically defined as containing wavelengths in the range of 200 nm to 10 nm. It should be understood that the spectral range definitions of different UV sub-regions and the boundaries between different UV sub-regions can vary depending on the field of study considered and are not intended to limit the scope of application of this technology. It should also be understood that while this technology can be implemented or used in PIDs using UV radiation sources, other embodiments may additionally or alternatively operate in other regions of the electromagnetic spectrum (e.g., in the visible range).

[0058] In this specification, the term "gas sample" is intended to refer to any gaseous substance known, expected, or suspected of containing an analyte. Gas samples can be broadly classified as organic, inorganic, or biological gas samples. Gas samples may include mixtures of analytes and non-analytes. The term "analyte" is intended herein to refer to any component of interest in a gas sample that can be detected by a PID according to this technique, while the term "non-analyte" is intended to refer to any sample component that does not require detection in a given application. Non-limiting examples of non-analytes may include (to name only a few): water, oil, solvents, and other media in which analytes can be found, as well as various impurities and contaminants. In some cases, terms such as "component," "compound," "ingredient," and "species" may be used interchangeably with the term "analyte." The analyte of interest may include volatile organic compounds (VOCs). VOCs are organic chemical substances that readily vaporize at ambient temperatures and are therefore emitted in gaseous form from certain solids or liquids. VOCs include both man-made and naturally occurring chemical compounds. Non-limiting examples of VOCs include (to name just a few): aromatics, alkenes, bromides and iodides, sulfides and thiols, organic amines, ketones, ethers, esters and acrylates, alcohols, aldehydes, alkanes and alkyl halides. However, it should be understood that this technique can also be used to detect certain volatile inorganic compounds and semi-volatile organic compounds. In some embodiments, the measurable gas concentration can be in the range of about 1 ppb to about 10,000 ppm, although concentrations outside this range can be measured in other embodiments.

[0059] This technology can be used or implemented in a variety of fields that can benefit from enhanced photoionization detectors. Non-limiting examples of fields include (to name just a few): including breath analysis in medicine, pharmaceuticals, food analysis, environment, petrochemicals, toxicology, forensics, industrial hygiene, chemical process control, hazardous waste monitoring, soil remediation, indoor air quality testing, and gas leak detection.

[0060] The various embodiments disclosed herein can be used as detectors in gas chromatography (GC) applications. The term "gas chromatography" herein refers to an analytical or processing technique used to separate a gaseous sample or mixture into its individual components and for qualitative and / or quantitative analysis of the separated sample components. In most GC applications, the sample is delivered in a carrier gas to form a mobile phase. The mobile phase is then carried through a stationary phase located in a column or another separation device. The mobile and stationary phases are selected such that the components of the gaseous sample delivered in the mobile phase exhibit different interaction strengths with the stationary phase. This difference in interaction strength results in different sample components having different retention times in the system. Sample components that interact strongly with the stationary phase move more slowly with the flow of the mobile phase and elute from the column later than sample components that interact weakly with the stationary phase. As the sample components separate, they elute from the column and enter the detector. The detector (such as a PID) is configured to generate a detection signal (e.g., an electrical signal) whenever the presence of a sample component is detected. The measurement data can be processed by a computer to obtain a chromatogram, which is a time series representing the peaks as the sample component elutes from the column. The retention time of each peak indicates the composition of the corresponding eluent, while the peak height or peak area conveys information about the amount or concentration of the eluent. However, it should be understood that various other embodiments disclosed herein can be used in fields other than GC. Non-limiting examples of such fields include (to name just a few): gas purification systems, gas leak detection systems, and online gas analyzers without chromatographic separation.

[0061] Now refer to Figures 1 to 3 Describes various possible implementations of this technology. Figures 1 to 3 Several views of possible embodiments of the PID 100 for analyzing gas sample 102 are shown.

[0062] Gas sample 102 may include any gaseous substance known, expected, or suspected of containing analytes that can be ionized and detected using this technique. These gaseous substances include gases, vaporized liquids, and vaporized solids. For example, gas sample 102 may include a mixture of analytes 104 (such as VOCs) flowing in a carrier gas 106. Non-limiting examples of carrier gases include (to name just a few): helium, nitrogen, argon, air, oxygen, and hydrogen. The ionization energy of the analyte 104 of interest may be less than the ionization energy of the carrier gas 106. In some embodiments, gas sample 102 may originate from a GC column. In this case, gas sample 102 may be a stream of analytes entrained in the carrier gas stream, where different analytes are eluted from the GC column and arrive at PID 100 at different times. PID 100 may sequentially detect the different analytes and may output an electrical signal representing the analyte measurement. The electrical signal may be processed to produce a chromatogram. However, as described above, PID 100 can be used to analyze gas samples in a variety of applications other than GC.

[0063] Figures 1 to 3 The illustrated PID 100 typically includes an ionization chamber 108, a photoionization source 110, an electric field ionization source 112, and an ion detector 114. The ionization chamber 108 is configured such that a gas sample 102 can flow through it along a longitudinal flow axis 116. The ionization chamber 108 defines an ionization region 118 and a detection region 120. The detection region 120 is located downstream of the flow of the gas sample 102 relative to the ionization region 118. The photoionization source 110, which may be a UV radiation source, is configured to generate ionizing radiation 122 for irradiating the flow of gas sample 102 in the ionization region 118. The photoionization source 110 may include one or more optical windows 124 configured to transmit at least a portion of the generated ionizing radiation 122 into the ionization chamber 108 to irradiate the flow of gas sample 102 in the ionization region 118. An electric field ionization source 112 is configured to apply an ionizing electric field 126 inside the ionization chamber 108. The ionizing electric field 126 is configured to intersect with the flow of gas sample 102 in the ionization region 118. Ionizing radiation 122 and ionizing electric field 126 combine to ionize gas sample 102 into an ionized gas sample. An ion detector 114 is configured to measure the ionization current generated by the ionized gas sample 102 in the detection region 120. Note that the gas sample will be indicated by reference numeral 102 before and after ionization. The structure and operation of these and other possible components of the PID 100 are described in more detail below.

[0064] In this specification, the term "ionization" generally refers to the ability to remove one or more electrons from a neutral atom or molecule to form a positively charged particle called an ion and one or more free electrons. Specifically, the term "ionizing radiation" refers to any electromagnetic radiation capable of producing ions and free electrons on its own (referred to herein as "pure photoionization," or simply "photoionization") or with the assistance of an applied electric field (referred to herein as "field-assisted photoionization"). In this specification, the applied electric field used in conjunction with ionizing radiation to achieve field-assisted photoionization is referred to as an "ionizing electric field." Furthermore, the term "ionized gas sample" is intended to encompass both fully ionized gas samples and partially ionized gases.

[0065] It should be understood that Figures 1 to 3 Simplified schematic diagrams are provided to illustrate several basic components of the PID 100, so that additional components and features that may be useful or necessary for the actual operation of the PID 100 may not be specifically shown. Non-limiting examples of such additional features and components may include (to name just a few): power supplies, electrical connections, gas sources, gas supply lines (e.g., conduits, such as pipes or tubes), pressure and flow control devices (e.g., pumps, valves, regulators, limiters), and other types of hardware and equipment.

[0066] Ionization chamber 108 is configured to receive a gas sample 102 to be analyzed. In the illustrated embodiment, ionization chamber 108 typically includes a chamber body 128, a sample inlet 130 configured to receive the gas sample 102 into the chamber body 128, and a sample outlet 132 configured to discharge the gas sample 102 from the chamber body 128. For example, in GC applications, sample inlet 130 may receive the gas sample 102 from a GC column or an upstream GC detector, while sample outlet 132 may discharge the gas sample 102 to a downstream GC detector, other downstream equipment, or the atmosphere.

[0067] The chamber body 128 encloses and defines the internal volume of the ionization region 118 and the detection region 120. The internal volume also provides a sample flow path 134 extending along a longitudinal flow axis 116, allowing the gas sample 102 to flow sequentially from the sample inlet 130 through the ionization region 118 and the detection region 120 to the sample outlet 132. For illustrative purposes, the chamber body 128 is shown as a longitudinally elongated tubular shell with a square cross-section (e.g., side lengths ranging from about 0.1 mm to about 2 mm) and a length ranging from about 5 mm to about 30 mm. However, it should be understood that the shape, size, and construction of the ionization chamber 108 can vary depending on the application. The chamber body 128 can be made of a variety of materials, including but not limited to dielectric materials (such as polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK)) and other synthetic polymer materials.

[0068] In some embodiments, a pressure control system (not shown) may be provided to control the operating pressure inside the ionization chamber 108. For example, in some embodiments, the gas pressure inside the ionization chamber 108 may be in the range of about 10 Pa to about 200 kPa, although other pressure ranges may be used in other embodiments.

[0069] Still refer to Figures 1 to 3 The photoionization source 110 is configured to emit ionizing radiation 122 through one or more optical windows 124 inside the ionization chamber 108 to irradiate the gas sample 102 as it flows through the ionization region 118. The ionizing radiation 122 generated by the photoionization source 110 contains high-energy photons capable of ionizing one or more analytes 104 in the gas sample 102, either alone or in conjunction with the ionizing electric field 126 applied by the electric field ionization source 112. It should be understood that many types of photoionization sources are known in the art and can be used in the PID disclosed herein.

[0070] The photoionization source 110 can be configured to emit ionizing radiation 122 in the UV region of the electromagnetic spectrum, typically in the VUV sub-region, and more specifically in a wavelength range of about 150 nm to about 100 nm, which corresponds approximately to photon energies between about 8.0 eV and about 12.0 eV. This photon energy allows various analytes of interest to be ionized without, or with little or negligible, ionization of the typical carrier gas. It should be understood that while various embodiments of the present technology use ionizing radiation in the UV range, some embodiments may use ionizing radiation in other spectral ranges (e.g., the visible range).

[0071] In the illustrated embodiment, the photoionization source 110 includes a pair of UV lamps 136 positioned face-to-face on opposite sides of the chamber body 128 of the ionization chamber 108. Depending on the application, the two UV lamps 136 may be identical or different, and may be arranged symmetrically with respect to the ionization chamber 108 or may not be arranged symmetrically with respect to the ionization chamber 108. It should also be understood that, although Figures 1 to 3Two UV lamps 136 are shown, but other embodiments may alternatively include a single UV lamp or more than two UV lamps. It should also be understood that in embodiments where the photoionization source 110 includes multiple UV lamps 136, each UV lamp 136 may have its own characteristics (e.g., in terms of emission characteristics, discharge gas, and operating pressure and temperature (to name a few examples)), which may be the same as or different from the characteristics of one or more other UV lamps 136. Additionally, the characteristics of a particular UV lamp 136 may be selected based on various application-specific factors (e.g., the composition of the target analyte and chromatographic conditions (to name a few examples)). Depending on the application, these characteristics may vary or remain constant during operation. For example, the composition of the discharge gas or the operating conditions of any UV lamp 136 may be changed during operation of the PID 100, for example, to alter the emission characteristics of the UV lamp.

[0072] Each UV lamp 136 may include a lamp body 138 that encloses an internal volume defining a discharge region 140 adapted to receive a discharge gas. The lamp body 138 may be made of a dielectric material (e.g., glass, such as quartz, fused silica, or borosilicate glass). The discharge gas may be any gas or combination of gases from which a gas discharge plasma 142 accompanied by radiation (particularly UV radiation) emission can be generated. Non-limiting examples of possible discharge gases include (to name just a few): argon (Ar), xenon (Xe), krypton (Kr), neon (Ne), helium (He), hydrogen (H2), oxygen (O2), nitrogen (N2), and combinations thereof. It should be understood that the energy of the UV photons emitted by the plasma 142 depends at least in part on the composition of the discharge gas.

[0073] Each UV lamp 136 may also include at least one optical window 124 mounted to the lamp body 138. The optical window 124 may be accommodated in a corresponding opening formed in the lamp body 138, for example, in a wall of the lamp body 138 adjacent to the ionization chamber 108. In the illustrated embodiment, the optical window 124 of each UV lamp 136 is positioned in front of a corresponding opening formed in the chamber body 128 of the ionization chamber 108. Furthermore, a surface orthogonal to the optical window 124 of each UV lamp 136 is perpendicular to the longitudinal flow axis 116 along which the gas sample 102 flows in the ionization chamber 108, although other orientations may be possible in other variations. In some embodiments, the optical window 124 may be removably mounted to the lamp body 138. In this case, the optical window 124 can be removed for inspection, cleaning, repair, replacement, and / or any other suitable maintenance operations.

[0074] The optical window 124 can be made of a material with high UV transmittance in certain spectral ranges. The optical window 124 serves as a cutoff filter that determines the spectrum of ionizing radiation 122 generated in the discharge region 140, which exits the UV lamp 136 and enters the ionization chamber 108 to irradiate the gas sample 102 flowing in the ionization region 118. The optical window 124 can be characterized by a high cutoff photon energy, above which the transmittance of the optical window decreases significantly, becoming very low or negligible from a practical standpoint. Therefore, although the type of discharge gas determines the energy of the UV photons generated inside the UV lamp 136, the optical window 124 can control which of these photons are allowed to exit the UV lamp 136 and enter the ionization chamber 108.

[0075] Non-limiting examples of window materials include (to name just a few): crystalline materials (such as lithium fluoride (LiF), magnesium fluoride (MgF2), calcium fluoride (CaF2), barium fluoride (BaF2), strontium fluoride (SrF2), sodium fluoride (NaF), sapphire (Al2O3), quartz (SiO2), and combinations thereof) and any suitable current or future window materials. Since different window materials typically have different transmission spectra, the highest energy photons transmitted into the ionization chamber 108 can be controlled by selecting the window material. It should be understood that in embodiments including more than one optical window (e.g., in the case of a PID including two or more UV lamps, each of the two or more UV lamps has its corresponding optical window), the different optical windows may have or may not have the same composition. In addition to the chemical composition of the optical window, the transmittance of the optical window 124 can depend on the thickness, crystal structure and orientation, manufacturing process, surface morphology, and lifetime of the optical window. In some embodiments, the thickness of the optical window 124 is in the range of about 0.1 mm to about 1 mm, although other thicknesses may be used in other variations.

[0076] In some embodiments, each UV lamp 136 may include a UV mirror 144 mounted inside the lamp body 138 to guide or assist in guiding UV radiation emitted from the plasma 142 to the optical window 124. For example, in the illustrated embodiment, the UV mirror 144 is positioned on a wall of the lamp body 138 opposite to a wall of the lamp body 138 (which forms an opening for accommodating the optical window 124). For example, the UV mirror 144 may be made of a thin layer of UV-reflective material (such as an aluminum (Al) or magnesium (Mg) coating).

[0077] It should be understood that various methods can be used to excite the discharge gas inside each UV lamp 136 and generate plasma 142 that emits UV radiation. Non-limiting examples of excitation methods include (to name just a few): continuous direct current (DC) discharge, pulsed DC discharge, alternating current (AC) discharge, dielectric barrier discharge (DBD), corona discharge, radio frequency (RF) discharge, microwave (MW) discharge, hollow cathode (HC) discharge, inductively coupled plasma (ICP) discharge, and capacitively coupled plasma (CCP) discharge. It should be understood that the theory and implementation of excitation methods for UV lamps are generally known in the art and need not be described in detail herein except to facilitate understanding of the art.

[0078] For example, in Figures 1 to 3 In this configuration, UV lamps 136 are each configured to implement a DBD-based excitation method. It should be understood that, as will be apparent to those skilled in the art, Figures 1 to 3 The excitation methods shown are for illustrative purposes only and may be replaced by other excitation methods (whether DBD-based or not) to suit specific applications.

[0079] Each UV lamp 136 may include a pair of plate-shaped discharge electrodes 146a, 146b, which are spaced apart and preferably parallel to each other on opposite sides of the lamp body 138. The discharge electrodes 146a, 146b define a discharge gap in the discharge region 140 between the discharge electrodes. In some embodiments, the height of the discharge gap may range from about 0.1 mm to about 2 mm. The discharge electrodes 146a, 146b may be made of any suitable conductive material, such as various metals, metal alloys, and semiconductor materials. It should be understood that the number, size, shape, composition, structure, and arrangement of the discharge electrodes 146a, 146b may vary depending on the application.

[0080] Each UV lamp 136 may also include or be coupled to a lamp power supply 148 and associated electronic circuitry, which is connected to the pair of discharge electrodes 146a, 146b via suitable electrical connections. Alternatively, the UV lamps 136 may share a common power supply. The lamp power supply 148 is configured to apply a discharge drive signal to the discharge electrodes 146a, 146b to generate a discharge electric field 150, which is configured to generate plasma 142 emitting UV radiation in the discharge region 140 and to maintain the plasma 142 in a stable state for any desired time period. In the illustrated embodiment, the discharge electric field 150 is perpendicular to a surface orthogonal to the optical window 124, although different configurations may exist in other embodiments.

[0081] Depending on the application, the lamp power supply 148 may be voltage-controlled or current-controlled. The discharge drive signal may be a periodic time-varying voltage or current of a suitable waveform (such as a sine wave, square wave, triangular wave, or sawtooth wave). Alternatively, a pulsed DC signal may be used. In some embodiments, the discharge drive signal may be a periodic time-varying voltage with a frequency in the range of about 1 kHz to about 100 kHz and a peak-to-peak amplitude in the range of about 500 V to about 5 kV, although other values ​​may be used in other embodiments. It should be understood that the characteristics of the discharge drive signal may be selected based on the nature of the discharge and the operating conditions of the UV lamp 136 to facilitate the breakdown of the discharge gas and the generation of plasma 142. In particular, it should be understood that the peak-to-peak voltage required to generate DBD may depend on several application-specific factors, such as the ease of ionization of the discharge gas and the pressure of the discharge gas in the discharge region 140.

[0082] Each UV lamp 136 may also include one or more dielectric barriers 152a, 152b disposed in the discharge gap between the discharge electrodes 146a, 146b. For example, a pair of dielectric barriers 152a, 152b may be provided, each of which extends along and is adjacent to a corresponding one of the discharge electrodes 146a, 146b. In the illustrated embodiment, the dielectric barriers 152a, 152b may be implemented via opposing walls of the lamp body 138, which, as described above, may be made of glass or another suitable dielectric material. This allows the discharge electrodes 146a, 146b to be positioned outside the lamp body 138 that generates plasma 142. In this configuration, the discharge electrodes 146a, 146b are not exposed to the filamentary micro-discharges generated by DBD, thereby avoiding sputtering contamination and erosion of the electrode material. It should also be understood that the plasma 142 itself (i.e., the ions, electrons and other nuclides generated in the plasma 142) remains within the lamp body 138 of the UV lamp 136. Therefore, only the ionizing radiation 122 passing through the optical window 124 can enter the ionization chamber 108 to irradiate the gas sample 102.

[0083] Still refer to Figures 1 to 3Each UV lamp 136 may also include one or more gas ports 154, 156 formed through the lamp body 138 to provide gas communication between the discharge region 140 and the exterior of the lamp body 138. The one or more gas ports 154, 156 may be hermetically sealed by suitable sealing components (such as plugs or valves). Depending on the application, the one or more gas ports 154, 156 may be permanently or non-permanently sealed. In the first case, the manufacturing process of the UV lamp 136 may include the following sequential steps: purging and cleaning the lamp body 138; filling the lamp body 138 with a desired type of discharge gas through the one or more gas ports 154, 156; and hermetically sealing the one or more gas ports 154, 156, and maintaining the one or more gas ports as is for the service life of the UV lamp 136. In the second case, the sealing components may be removable, for example, to purge the discharge region 140, after which the UV lamp 136 may be refilled with the same or different discharge gas under the same or different pressure and temperature conditions.

[0084] In the illustrated embodiment, one or more gas ports 154, 156 include a discharge gas inlet 154 and a discharge gas outlet 156, which may be connected to a gas flow system (not shown). The gas flow system may be configured to continuously or intermittently allow a flow of discharge gas from the discharge gas inlet 154 through the discharge region 140 to the discharge gas outlet 156. In the illustrated embodiment, the flow of discharge gas inside the UV lamp 136, the discharge electric field 150, and the surface orthogonal to the optical window 124 are perpendicular to each other. However, other embodiments may use different configurations. It should be understood that allowing the flow of discharge gas inside the UV lamp 136 during operation may, for example, be used to remove contaminants formed during plasma discharge or to remove heat from the UV lamp 136. Non-limiting examples of contaminants include sputtered deposits and other undesirable surface contaminants that may otherwise accumulate or form on the inner walls of the optical window 124 and the lamp body 138. The gas flow system may also, or alternatively, be configured to fill and purify the UV lamp 136. It should be understood that the gas flow system may include various components, including but not limited to: one or more discharge gas sources or reservoirs (e.g., gas tanks), gas lines (e.g., conduits, such as pipes or conduits for connecting to discharge gas inlet 154 and discharge gas outlet 156), flow regulators (e.g., pumps, valves, and limiters) for controlling the flow of discharge gas, etc. In some embodiments, the gas flow system may be configured to be able to select between different types of gases and gas mixtures (including doped gases) for use as discharge gas in UV lamp 136.

[0085] Still refer to Figures 1 to 3 In some embodiments, a pressure control system (not shown) may be provided to control the operating pressure inside the UV lamp 136. For example, in some embodiments, the pressure inside the UV lamp 136 may be in the range of about 10 Pa to about 200 kPa, although other pressure ranges may be used in other embodiments. Depending on the application, the pressure control system associated with the UV lamp 136 may be the same as or different from the pressure control system associated with the ionization chamber 108.

[0086] The highest photon energy levels of typical commercial PID lamps are approximately 8.4 eV (lamp window: Al₂O₃; discharge gas: Xe), 9.6 eV (lamp window: BaF₂; discharge gas: Xe), 10.0 eV (lamp window: CaF₂; discharge gas: Kr), 10.2 eV (lamp window: MgF₂; discharge gas: H₂), 10.6 eV (lamp window: MgF₂; discharge gas: Kr), and 11.7 eV (lamp window: LiF; discharge gas: Ar). These photon energies are generally sufficient to ionize a variety of VOCs of interest, but insufficient to ionize common carrier gases and major components of air, whose ionization energies are typically above 12.0 eV. High-energy lamps, whose optical windows are typically made of CaF₂, MgF₂, or LiF, can respond to a wider range of analytes. However, these high-energy lamps tend to have a limited lifespan and gradual performance degradation, which can be caused by a number of factors, including window deterioration, gas leaks, water ingress, and sputter contamination caused by electron and photon bombardment during the discharge process. In particular, PID lamp windows made of fluoride crystals (such as CaF2, MgF2, and LiF) are prone to deterioration and contamination, especially due to sunlight, water etching, window fogging, surface deposit formation, and corrosion caused by moisture. This susceptibility to deterioration and contamination typically increases with photon energy, necessitating regular, and often excessively frequent, inspection, cleaning, repair, and replacement of windows made of CaF2, MgF2, or LiF. Such frequent maintenance is generally undesirable, especially considering the relative fragility and high cost of fluoride crystal window materials, and the loss of productivity due to increased downtime.

[0087] In some embodiments, the PID 100 may include one or more optical windows 124 made of a window material whose highest energy transmitted photons have lower energies than those of common fluoride crystal materials (such as CaF2, MgF2, and LiF), yet still enable detection of analytes over a fairly wide range of ionization energies. This is because, as discussed in more detail below, in this technique, the ionization of the gas sample 102 is achieved through a combination of ionizing radiation 122 generated by the photoionization source 110 and an ionizing electric field 126 applied by the electric field ionization source 112.

[0088] For example, in Figures 1 to 3 In the PID 100, the optical window 124 of each UV lamp 136 can be made of sapphire. Sapphire optical windows exhibit high mechanical strength, high chemical resistance, and high thermal stability. These properties make sapphire optical windows advantageous in a variety of applications considering lifespan, stability, ease of handling, and / or resistance to mechanical, chemical, and / or thermal abrasion. Because sapphire is the second hardest natural material on Earth after diamond, sapphire optical windows can be made thinner than other common window materials, thereby increasing optical transmittance. Furthermore, UV-grade sapphire is highly resistant to UV damage from sunlight and other sources. However, because the transmittance of UV-grade sapphire exhibits a sharp decrease above approximately 8.5 eV, PID lamps with sapphire windows will not ionize analytes with ionization energies higher than this level. Therefore, the range of detectable analytes associated with lamp windows made of sapphire may be significantly reduced compared to the range associated with lamp windows made of fluoride crystals such as CaF2, MgF2, and LiF. In some applications, this reduced detection range may be undesirable or unacceptable.

[0089] However, in the illustrated embodiment, the gas sample 102 is not ionized solely by photoionization, but by field-assisted photoionization, due to the ionizing electric field 126 applied by the electric field ionization source 112 in the ionization region 118. This means that, with the assistance of the ionizing electric field 126, a target analyte 104 having an ionization energy of, for example, 10 eV, becomes ionizable and subsequently detectable, which would otherwise not be possible by photoionization using only the sapphire lamp window 124, since sapphire cannot transmit or can only weakly transmit photon energies above 8.5 eV. Therefore, by using field-assisted photoionization, the PID 100 can benefit from the enhanced mechanical, chemical, and thermal robustness and durability of the sapphire window compared to a conventional fluoride crystal window, without being or minimally limited by the typically narrow range of detectable analytes of the sapphire window.

[0090] Still refer to Figures 1 to 3 An electric field ionization source 112 is configured to apply an ionizing electric field 126 inside the ionization chamber 108 to intersect with the flow of gas sample 102 in the ionization region 118. The ionizing electric field 126 is combined with ionizing radiation 122 emitted by the photoionization source to ionize the gas sample 102.

[0091] The electric field ionization source 112 may include a pair of plate-shaped ionization electrodes 158a, 158b, which are positioned on opposite sides of the ionization chamber 108 in a spaced-apart and preferably parallel relationship. In the illustrated embodiment, the ionization electrodes 158a, 158b are positioned outside the ionization chamber 108. The ionization electrodes 158a, 158b may be located at substantially the same longitudinal position as the UV lamp 136 relative to the ionization chamber 108 along the sample flow path 134. This ensures, or helps to ensure, that the ionizing radiation 122 and the ionizing electric field 126 simultaneously interact with the flowing gas sample 102 and have an appropriate degree of spatial overlap, thereby enabling the gas sample 102 to undergo effective field-assisted photoionization. The ionization electrodes 158a, 158b may be made of any suitable conductive material, such as various metals, metal alloys, and semiconductor materials. It should be understood that the number, size, shape, composition, structure, and arrangement of the ionization electrodes 158a, 158b may vary depending on the application.

[0092] The electric field ionization source 112 may also include or be coupled to the ionization power supply 160 and associated electronic circuitry, which is connected to the ionization electrodes 158a, 158b via suitable electrical connections. The ionization power supply 160 is configured to apply an ionization drive signal to the ionization electrodes 158a, 158b to generate an ionizing electric field 126 in the ionization region 118. Depending on the application, the ionization power supply 160 may be voltage-controlled or current-controlled. In the illustrated embodiment, the ionizing electric field 126, the surface orthogonal to the optical window 124, and the longitudinal flow axis 116 are perpendicular to each other. However, other embodiments may use different configurations.

[0093] In some embodiments, the ionization drive signal may be a direct current (DC) signal. In this specification, the term "direct current" refers to an electrical signal characterized by a unidirectional flow of charge without a change in polarity, as opposed to the term "alternating current," which refers to an electrical signal characterized by a bidirectional flow of charge with a change in polarity. The term "direct current" includes continuous direct current and pulsed direct current. Specifically, the DC signal may have a constant amplitude or may change abruptly (e.g., square waveform) or gradually (e.g., ramp waveform) over time, making various types of DC waveforms possible, including fully rectified and partially rectified waveforms. However, in other embodiments, low-frequency AC signals (e.g., in the range of about 100 Hz to about 10 kHz, although other ranges may be used) may also be used to generate the ionizing electric field 126.

[0094] The ionization drive signal applied to the ionization electrodes 158a and 158b can have a sufficiently high amplitude to generate an ionization electric field 126 that is strong enough to meaningfully assist photoionization. In some embodiments, the amplitude of the ionization electric field 126 can be approximately 10. 5V / m to approximately 5×10 7 Within the range of V / m, although other field strength values ​​may be used in other embodiments. It should be understood that the strength of the ionizing electric field 126 can be controlled by the configuration of the ionizing electrodes 158a, 158b (e.g., the size, shape, composition, structure, and arrangement of the ionizing electrodes) and the characteristics of the ionization drive signal applied to the ionizing electrodes 158a, 158b by the ionization power supply 160 (e.g., the amplitude and waveform of the ionization drive signal). Depending on the application, the ionizing electric field 126 may be spatially uniform or non-spatially uniform in the ionization region 118, and the strength of the ionizing electric field can be selected based on various operating conditions (such as the gas pressure inside the ionization chamber 108).

[0095] The characteristics of the ionization drive signal can be selected based on several specific application factors, such as the range of ionization energies of the analyte 104 in the gas sample 102. In some embodiments, the ionization electric field 126 can be strong enough to increase the upper limit of the range of ionization energies of analytes that the PID 100 can detect by about 1 eV to about 4 eV, although values ​​outside this range are possible in other embodiments. For example, a conventional PID including a UV lamp with a sapphire window can use photoionization alone to detect analytes with ionization energies up to about 8.5 eV. Conversely, a PID such as those disclosed herein and including the same or similar sapphire UV lamp can use field-assisted photoionization to detect analytes with ionization energies up to about 12.5 eV. This is because the ionization electric field is configured to supplement the missing energy for ionizing analytes with higher ionization energies that would otherwise not be ionized by UV radiation generated by the sapphire UV lamp alone.

[0096] It should be understood that by using field-assisted photoionization, the disclosed PID can use more durable but lower-energy UV lamps (such as UV lamps with sapphire windows) while responding to compounds with an ionization energy range comparable to that provided by higher-energy but less durable UV lamps (such as UV lamps based on CaF2, MgF2, LiF and other fluoride crystals).

[0097] It should also be understood that the selectivity of the disclosed PID can be adjusted according to various application-specific factors, such as the range of ionization energies of the target analyte, by varying the strength of the ionizing electric field during or between operations. This selectivity typically changes inversely with the electric field strength. Such control of selectivity is generally not easily achieved in conventional PIDs that rely solely on photoionization for ionization.

[0098] In some embodiments, the disclosed PID may include a UV lamp having a window made of fluoride crystal, but configured to operate at a lower photon energy level than a conventional PID in an attempt to extend the UV lamp's lifetime. In this case, the impact of the reduction in the highest photon energy on the range of detectable analytes can be mitigated or even eliminated by applying an ionizing electric field to provide field-assisted photoionization. In some embodiments, the highest photon energy can be reduced by selecting the discharge gas; in some cases, this may involve adding one or more doping gases to the selected discharge gas. For example, in some embodiments, the discharge gas formed from helium may be doped with small amounts of argon, krypton, nitrogen, or combinations thereof to reduce the energy of the emitted photons.

[0099] In some embodiments, the disclosed PID may include multiple optical windows, not all of which have the same composition. In one variation, the PID may include a pair of UV lamps, with the respective optical windows of the pair made of different materials. For example, the optical window of one UV lamp may be made of sapphire, while the optical window of the other UV lamp may be made of fluoride crystals (such as CaF2, MgF2, and LiF). Depending on the application, the two UV lamps may be activated simultaneously or at different times during the operation of the PID. For example, in some cases, a fluoride crystal UV lamp may be activated only when it is needed or particularly useful, thereby helping to effectively extend the lifespan of the fluoride crystal UV lamp.

[0100] In some implementations, the intensity of photon emission can be reduced by increasing the pressure of the discharge gas in the discharge region. This is because increasing pressure tends to reduce the mean free path of electrons, thereby reducing electron drift velocity, which in turn reduces the number of emitted photons. Reducing the intensity of photon emission can extend or help extend the lifespan of the PID lamp.

[0101] Still refer to Figures 1 to 3An ion detector 114 is configured to measure the ionization current generated by the ionized gas sample 102 in a detection region 120. The ion detector 114 may include a pair of detection electrodes 162a, 162b disposed in the detection region 120. In the illustrated embodiment, the detection electrodes 162a, 162b are plate-shaped and disposed in a spaced-apart parallel relationship inside the ionization chamber 108. The detection electrodes 162a, 162b may be made of any suitable conductive material, such as various metals, metal alloys, and semiconductor materials. It should be understood that, as will be apparent to those skilled in the art, the number, size, shape, composition, structure, and arrangement of the detection electrodes 162a, 162b may vary depending on the application. The detection electrodes 162a, 162b have a bias voltage applied between them, which generates a detection electric field 164 in the detection region 120. In the illustrated embodiment, the detection electric field 164, the surface orthogonal to the optical window 124, and the longitudinal flow axis 116 are perpendicular to each other. However, other embodiments may use different configurations.

[0102] The ion detector 114 may also include or be coupled to a detection power supply 166 and associated electronic circuitry, which is connected to the detection electrodes 162a, 162b via suitable electrical connections. The detection power supply 166 is configured to establish and maintain a bias voltage between the detection electrodes 162a, 162b to generate a detection electric field 164 in the detection region 120. In some embodiments, the bias voltage may be a DC voltage with an amplitude ranging from about 50V to about 150V, although values ​​outside this range may be used in other embodiments. The detection electric field 164 deflects and separates ions and electrons in the stream of ionized gas sample 102, such that one detection electrode collects ions while the other collects electrons.

[0103] The ion detector 114 may also include a detection circuit 168 electrically connected to the detection electrodes 162a, 162b via suitable electrical connections. The detection circuit 168 is configured to measure the ionization current generated by ions and electrons collected by the detection electrodes 162a, 162b, and output a detection signal representing the measured ionization current. Depending on the application, it will be apparent to those skilled in the art that the detection circuit 168 can have various configurations. Non-limiting examples of these configurations include (to name just a few): transimpedance amplifier configuration, current integrating amplifier configuration, and logarithmic amplifier configuration.

[0104] Still refer to Figures 1 to 3The PID 100 may also include a control and processing unit 170. The control and processing unit 170 may be configured to control, monitor, and / or coordinate the function and operation of various components of the PID 100 (e.g., ionization chamber 108, photoionization source 110, electric field ionization source 112, and ion detector 114) and various pressure, temperature, and flow rate conditions. The control and processing unit 170 may also be configured to analyze the detection signal received from the detection circuit 168 to derive, for example, information about the presence and concentration of analyte 104 in the gas sample 102 based on calibration with known standard gases. In GC applications, the control and processing unit 170 may process the detection signal into a chromatogram. It should be understood that the basic principles of processing chromatographic data to derive analytical information about the test sample are generally well known in the art and need not be described in detail herein except to facilitate understanding of the art.

[0105] The control and processing unit 170 may be implemented in hardware, software, firmware, or any combination thereof, and is connected to various components of the PID 100 via wired and / or wireless communication links to send and / or receive various types of electrical signals, such as timing and control signals, measurement signals, and data signals. The control and processing unit 170 may be controlled by direct user input and / or programming instructions, and may include an operating system configured to control and manage various functions of the PID 100. Depending on the application, the control and processing unit 170 may be fully or partially integrated with or physically separated from other hardware components of the PID 100. In the illustrated embodiment, the control and processing unit 170 typically includes a processor 172 and a memory 174.

[0106] Processor 172 may include or be a subset of the following components: a computer; a microprocessor; a microcontroller; a coprocessor; a central processing unit (CPU); an image signal processor (ISP); a digital signal processor (DSP) running on a system-on-a-chip (SoC); a single-board computer (SBC); a dedicated graphics processing unit (GPU); a dedicated programmable logic device embodied in a hardware device, such as a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC); a digital processor; an analog processor; digital circuits designed to process information; analog circuits designed to process information; a state machine; and / or other mechanisms configured to process information electronically and operate collaboratively as a processor. Depending on the application, processor 172 may include a single processing unit or multiple processing units. Multiple processing units may be physically located within the same device, or processor 172 may represent the processing functions of multiple devices operating collaboratively.

[0107] The memory 174, also referred to as a computer-readable storage medium, is capable of storing computer programs and other data to be retrieved by the processor 172. In this specification, the terms "computer-readable storage medium" and "computer-readable memory" are intended to refer to a non-transitory and tangible computer product that can store and transmit executable instructions for implementing the various steps of the methods disclosed herein. A computer-readable memory can be any computer data storage device or component of such a device, including: random access memory (RAM); dynamic RAM; read-only memory (ROM); magnetic storage devices such as hard disk drives, solid-state drives, floppy disks, and magnetic tapes; optical storage devices such as optical discs (e.g., CDs and CD-ROMs), digital video discs (DVDs), and Blu-ray discs. TM Optical discs; flash memory drives; and / or other non-transitory memory technologies. As those skilled in the art will understand, multiple such storage devices may be provided. A computer-readable storage device may be associated with, coupled to, or included in a computer or processor configured to execute instructions contained in a computer program stored in the computer-readable storage device and relating to various functions associated with the computer or processor.

[0108] Reference Figure 4 A flowchart of an embodiment of a method 200 for analyzing a gas sample is provided. Method 200 can be implemented using a PID (such as...) Figures 1 to 3The method 200 is implemented using either a PID (as shown) or another PID. Method 200 includes step 202: flowing a gas sample through an ionization chamber comprising an ionization region and a detection region. Method 200 further includes step 204: subjecting the gas sample to ionizing radiation (e.g., UV radiation) and an ionizing electric field in the ionization region to ionize the gas sample into an ionized gas sample. Method 200 further includes step 206: detecting an ionizing current generated by the ionized gas sample in the detection region to generate a detection signal conveying information about the gas sample. In some embodiments, the method may include the steps of generating ionizing radiation and supplying ionizing radiation to the ionization region. For example, ionizing radiation can be generated by exciting a discharge gas into a plasma and generating ionizing radiation from the plasma. The plasma may be a dielectric barrier discharge plasma. In some embodiments, generating ionizing radiation may include operating a pair of UV lamps arranged relative to the ionization chamber. In some embodiments, supplying ionizing radiation to the ionization region may include transmitting the ionizing radiation through an optical window. As described above, the optical window can be made of window materials including lithium fluoride (LiF), magnesium fluoride (MgF2), calcium fluoride (CaF2), barium fluoride (BaF2), strontium fluoride (SrF2), sodium fluoride (NaF), sapphire (Al2O3), or quartz (SiO2), or combinations thereof.

[0109] In some embodiments, method 200 may include the following steps: providing a pair of ionizing electrodes and applying an ionization drive signal to the ionizing electrodes to generate an ionizing electric field in the ionization region.

[0110] In some embodiments, step 206 of detecting the ionization current may include: providing a pair of detection electrodes; biasing the detection electrodes to generate a detection electric field in a detection region to deflect ions and electrons in the ionized gas sample onto a corresponding one of the detection electrodes for collection by the detection electrode; and measuring the ionization current based on the ions and electrons collected by the detection electrode.

[0111] Of course, various modifications can be made to the above embodiments without departing from the scope of the appended claims.

Claims

1. A photoionization detector (PID), comprising: An ionization chamber configured such that a flow of gas sample can pass through the ionization chamber, the ionization chamber defining an ionization region and a detection region; A photoionization source configured to generate ionizing radiation for irradiating a stream of gas sample in the ionization region; An electric field ionization source is configured to apply an ionizing electric field inside the ionization chamber to intersect with the flow of the gas sample in the ionization region, wherein the ionizing electric field is configured to combine with the ionizing radiation to ionize the gas sample into an ionized gas sample. as well as An ion detector configured to detect ionization current generated by the ionized gas sample in the detection region.

2. The photoionization detector according to claim 1, wherein, The ionization chamber includes a chamber body, a sample inlet configured to receive the gas sample into the chamber body, and a sample outlet configured to discharge the gas sample from the chamber body.

3. The photoionization detector according to claim 1, wherein, The photoionization source is configured to emit ionizing radiation in the ultraviolet (UV) region.

4. The photoionization detector according to claim 3, wherein, The photoionization source is configured to emit ionizing radiation in a wavelength range between 150 nm and 100 nm.

5. The photoionization detector according to claim 3, wherein, The photoionization source includes a UV lamp, and the UV lamp includes: A lamp body that encloses a discharge area, the discharge area being configured to receive discharge gas. A lamp power supply, configured to excite the discharge gas inside the discharge region into plasma that generates the ionizing radiation; and An optical window is mounted to the lamp body and configured such that at least a portion of the ionizing radiation generated inside the discharge region can pass through the optical window and enter the ionization chamber.

6. The photoionization detector according to claim 5, wherein, The UV lamp is configured to operate according to an excitation method based on dielectric barrier discharge.

7. The photoionization detector according to claim 6, wherein, The UV lamp includes: A pair of discharge electrodes, positioned at a distance from each other on opposite sides of the lamp body, to define a discharge gap in the discharge region; and A pair of dielectric barrier portions are disposed in the discharge gap, each dielectric barrier portion extending along and adjacent to a corresponding one of the discharge electrodes. The lamp power supply is configured to excite the discharge gas into plasma by applying a discharge drive signal to the discharge electrode, thereby generating a discharge electric field across the discharge gap.

8. The photoionization detector according to claim 7, wherein, The lamp body includes a pair of opposing sidewalls providing the pair of medium blocking portions.

9. The photoionization detector according to any one of claims 5 to 8, wherein, The flow of the gas sample, the ionization electric field, and the surface orthogonal to the optical window are perpendicular to each other.

10. The photoionization detector according to any one of claims 5 to 8, wherein, The UV lamp includes a discharge gas inlet and a discharge gas outlet, the discharge gas inlet being configured to receive the discharge gas into the discharge region, and the discharge gas outlet being configured to discharge the discharge gas from the discharge region.

11. The photoionization detector according to claim 10, wherein, The discharge gas inlet and the discharge gas outlet are configured to be connected to a gas flow system, which is configured to allow the discharge gas to flow from the discharge gas inlet through the discharge region to the discharge gas outlet.

12. The photoionization detector according to any one of claims 5 to 8, wherein, The discharge gas includes: argon (Ar), xenon (Xe), krypton (Kr), neon (Ne), helium (He), hydrogen (H2), oxygen (O2), nitrogen (N2), or combinations thereof.

13. The photoionization detector according to any one of claims 5 to 8, wherein, The UV lamps include a pair of UV lamps positioned on opposite sides of the ionization chamber.

14. The photoionization detector according to any one of claims 5 to 8, wherein, The optical window is made of a window material including lithium fluoride (LiF), magnesium fluoride (MgF2), calcium fluoride (CaF2), barium fluoride (BaF2), strontium fluoride (SrF2), sodium fluoride (NaF), sapphire (Al2O3), or quartz (SiO2), or a combination thereof.

15. The photoionization detector according to any one of claims 1 to 4, further comprising an optical window configured such that at least a portion of the ionizing radiation can pass through the optical window before entering the ionization region.

16. The photoionization detector according to claim 15, wherein, The optical window is made of a window material including lithium fluoride (LiF), magnesium fluoride (MgF2), calcium fluoride (CaF2), barium fluoride (BaF2), strontium fluoride (SrF2), sodium fluoride (NaF), sapphire (Al2O3), or quartz (SiO2), or a combination thereof.

17. The photoionization detector according to any one of claims 1 to 8, wherein, The electric field ionization source includes: A pair of ionizing electrodes, the pair of ionizing electrodes being arranged relative to the ionizing region; and An ionization power source configured to apply an ionization drive signal to the ionization electrode to generate the ionization electric field in the ionization region.

18. The photoionization detector according to claim 17, wherein, The ionization power supply is configured to generate the ionization drive signal as a direct current (DC) signal.

19. The photoionization detector according to claim 17, wherein, The ionization power source is configured to control the amplitude of the ionization electric field to increase the upper limit of the range of ionization energies of detectable analytes in the gas sample by an amount from 1 eV to 4 eV.

20. The photoionization detector according to any one of claims 1 to 8, wherein, The ion detector includes: A pair of detection electrodes, the pair of detection electrodes being arranged relative to the detection region; A detection power supply configured to apply a voltage between the detection electrodes to generate a detection electric field in the detection region, wherein the detection electric field is configured to deflect ions and electrons in the ionized gas sample to a corresponding one of the detection electrodes for collection by the detection electrode; and A detection circuit configured to measure the ionization current based on the ions and electrons collected by the detection electrode.

21. The photoionization detector according to any one of claims 1 to 8, further comprising a control and processing unit, said control and processing unit being configured to: Receive a detection signal representing the ionization current from the ion detector; and Analyte information about the analytes in the gas sample is determined based on the detection signal.

22. The photoionization detector according to claim 21, wherein, The analyte information includes the presence or absence of the analyte in the gas sample, or the amount of the analyte in the gas sample.

23. A photoionization detector, comprising: An ionization chamber configured to receive a gas sample, the ionization chamber defining an ionization region and a detection region; A UV radiation source configured to generate UV radiation, the UV radiation source including an optical window configured to transmit at least a portion of the UV radiation into the ionization chamber to irradiate the gas sample in the ionization region, wherein the optical window is made of a window material including sapphire (Al2O3). An electric field ionization source configured to apply an ionizing electric field to the gas sample in the ionization region, wherein the ionizing electric field is configured to combine with transmitted UV radiation to ionize the gas sample into an ionized gas sample; and An ion detector configured to detect ionization current generated by the ionized gas sample in the detection region.

24. The photoionization detector according to claim 23, wherein, The optical window is configured to substantially prevent the transmission of UV photons with photon energies greater than 8.5 eV, and wherein the transmitted UV radiation and the ionizing electric field are configured to ionize analytes in the gas sample with ionization energies greater than 10 eV.

25. The photoionization detector according to claim 23, wherein, The UV radiation source is configured to generate dielectric barrier discharge plasma and to generate the UV radiation from the dielectric barrier discharge plasma.

26. The photoionization detector according to any one of claims 23 to 25, wherein, The electric field ionization source includes: A pair of ionization electrodes, positioned spaced apart on opposite sides of the ionization chamber outside the chamber; and An ionization power source configured to apply an ionization drive signal to the ionization electrode to generate the ionization electric field in the ionization region.

27. A method for analyzing a gas sample, comprising: The gas sample is passed through an ionization chamber that includes an ionization region and a detection region; The gas sample is subjected to ionizing radiation and an ionizing electric field in the ionization region, wherein the ionizing radiation and the ionizing electric field combine to ionize the gas sample into an ionized gas sample. as well as The ionization current generated by the ionized gas sample is detected in the detection area to generate a detection signal that transmits information about the gas sample.

28. The method according to claim 27, wherein, The ionizing radiation includes UV radiation.

29. The method of claim 27, further comprising: The ionizing radiation is generated; as well as The ionizing radiation is supplied to the ionizing region.

30. The method according to claim 29, wherein, The generation of the ionizing radiation includes: Excite the discharge gas into plasma; and The ionizing radiation is generated from the plasma.

31. The method according to claim 30, wherein, The plasma is a dielectric barrier discharge plasma.

32. The method according to any one of claims 29 to 31, wherein, Generating the ionizing radiation includes operating a pair of UV lamps arranged relative to the ionization chamber.

33. The method according to any one of claims 29 to 31, wherein, Supplying the ionizing radiation into the ionizing region includes: transmitting the ionizing radiation through an optical window.

34. The method according to claim 33, wherein, The optical window is made of a window material including lithium fluoride (LiF), magnesium fluoride (MgF2), calcium fluoride (CaF2), barium fluoride (BaF2), strontium fluoride (SrF2), sodium fluoride (NaF), sapphire (Al2O3), or quartz (SiO2), or a combination thereof.

35. The method according to any one of claims 27 to 31, further comprising: Provide a pair of ionization electrodes; as well as An ionization drive signal is applied to the ionization electrode to generate the ionization electric field in the ionization region.

36. The method according to any one of claims 27 to 31, wherein, Detecting the ionization current includes: Provide a pair of detection electrodes; The detection electrode is biased to generate a detection electric field in the detection region, causing ions and electrons in the ionized gas sample to be deflected onto a corresponding one of the detection electrodes for collection by the detection electrode; and The ionization current is measured based on the ions and electrons collected by the detection electrode.

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