A low frequency radio frequency glow discharge ionization device

Abstract

The invention discloses a low-frequency radio frequency glow discharge ionization device, comprising an ionization source housing with an ionization chamber, a sampling unit and an auxiliary air intake unit; the sampling unit comprises a metal sampling tube, a heating cylinder sleeved with the sampling tube, a heating rod is arranged in the heating cylinder, the sampling tube is inserted into the ionization chamber, and the end of the ionization source housing facing the sampling tube is provided with an analyte outlet for connecting with a mass spectrometer; the ionization chamber is provided with an ionization source and an electrode plate group capable of exciting an electric field, and the charged analyte ions move from the end of the sampling tube toward the analyte outlet under the guidance of the electric field; the auxiliary air intake unit comprises an air intake pipe and a heating device for heating the gas in the air intake pipe, and the air intake pipe is inserted into the ionization chamber from one end of the sampling tube. The device has the characteristics of a wide range of detection applications, high ionization efficiency, high detection sensitivity, low vacuum requirements, and the ability to detect volatile liquid samples.

Description

Technical Field

[0001] The invention relates to the field of mass spectrometry analysis and detection, and in particular to a low-frequency radio frequency glow discharge ionization device. Background Art

[0002] According to the definition of the World Health Organization, volatile organic compounds refer to a class of organic compounds that exist in the air in the form of steam at room temperature, with a saturated vapor pressure greater than 133.3 Pa and a boiling point range of 50-250°C. The main sources of volatile organic compounds are building materials, interior decoration materials, daily necessities and office supplies, outdoor industrial waste gas, automobile exhaust and photochemical smog. Many substances in volatile organic compounds are carcinogenic, teratogenic and mutagenic, posing a threat to environmental safety and human survival and reproduction. When the concentration of volatile organic compounds in indoor air is too high, it is easy to cause acute poisoning. In mild cases, symptoms such as headache, dizziness, cough, nausea and vomiting may occur, and in severe cases, convulsions, coma or memory loss may occur.

[0003] The commonly used methods for detecting volatile organic compounds in China are mainly chromatography, spectroscopy and mass spectrometry, specifically gas chromatography-flame ionization detection, Fourier transform infrared spectroscopy, photoionization detection and gas chromatography-mass spectrometry.

[0004] Gas chromatography-flame ionization detection technology responds to most volatile organic compounds and has an isocarbon response, making it suitable for monitoring the total amount of volatile organic compounds.

[0005] Fourier infrared detection technology has a wide detection spectral range and can simultaneously detect the content of multiple characteristic components of volatile organic compounds. It is fast, does not damage the sample, uses a small amount, is easy to operate, and has a high analytical sensitivity.

[0006] The photoionization detector method has a weak response to low-carbon saturated hydrocarbons and inconsistent response factors. The detector surface is easily contaminated and is not suitable for online monitoring of volatile organic compounds in pollution sources.

[0007] Gas chromatography-mass spectrometry has the advantages of high separation and resolution of gas chromatography and rapid simultaneous qualitative and quantitative analysis of mass spectrometry. It is currently the most common method for detecting volatile organic compounds.

[0008] For samples with simple matrices, a mass spectrometer can be used alone to detect volatile organic compounds for the purpose of simplifying the instrument. Currently, the commonly used ionization sources for mass spectrometers to detect volatile organic compounds are mainly electron bombardment sources and ultraviolet photoionization sources. These two ionization sources can also be used as interfaces for gas chromatography-mass spectrometry.

[0009] The electron bombardment source has high ionization efficiency and high sensitivity and can provide rich structural information, but the sample must be vaporized and is not suitable for samples that are difficult to volatilize or have poor thermal stability. The spectrum is complex and it is difficult to interpret.

[0010] The ultraviolet photoionization source can cause soft ionization of organic molecules whose ionization energy is lower than the photon energy, mainly producing molecular ions. When it is combined with a mass spectrometer, the molecular ion response signal detected is high, and basically no fragment ions are produced, which can realize real-time online monitoring and qualitative and quantitative analysis of volatile organic compounds. However, the light window material of the ultraviolet photoionization source limits the energy of the photons that can be emitted, the light flux and stability are poor, the volume is large and the cost is high.

[0011] The low-frequency radio frequency glow discharge ionization source of the present invention can simultaneously detect characteristic components of multiple volatile organic compounds, organic solvents and metal ions in water, and has the characteristics of a wide range of detection applications, high ionization efficiency, high detection sensitivity, and low vacuum requirements. Compared with the commonly used discharge frequency of 13.56M for glow discharge, the discharge frequency of 1-5M of the present invention has low energy consumption, low interference, simple structure, and low price. Summary of the invention

[0012] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a low-frequency radio frequency glow discharge ionization device, which has the characteristics of wide detection application range, high ionization efficiency, high detection sensitivity and low vacuum requirement.

[0013] The technical solution adopted by the present invention is: a low-frequency radio frequency glow discharge ionization device, comprising an ionization source housing with an ionization chamber, a sample injection unit and an auxiliary gas injection unit;

[0014] The sample injection unit comprises a metal sample injection tube, a heating cylinder mounted on the sample injection tube, a heating rod arranged in the heating cylinder, the sample injection tube is inserted into the ionization chamber, and an analyte outlet for connecting to a mass spectrometer is arranged at one end of the ionization source housing facing the sample injection tube;

[0015] The ionization chamber is provided with an ionization source and an electrode plate group capable of exciting an electric field, and the charged analyte ions move from the end of the injection tube toward the analyte outlet under the guidance of the electric field;

[0016] The auxiliary air intake unit comprises an air intake pipe and a heating device for heating the gas in the air intake pipe. The air intake pipe is inserted into the ionization chamber from one end of the injection tube.

[0017] Further optimization, the ionization source includes multiple groups of cylindrical rods arranged in the ionization chamber, the cylindrical rods are arranged along the direction from the sample injection tube to the analyte outlet, and the multiple groups of cylindrical rods form a cylindrical ionization area. Each group of cylindrical rods is composed of conductive blocks and insulating sheets alternately connected in series, and adjacent conductive blocks are connected through patch capacitors and patch resistors. The conductive blocks at both ends of the cylindrical rods are connected to the radio frequency power supply and applied with different DC voltages, and the voltage of the conductive block at the sample injection tube end is higher than the voltage of the conductive block at the analyte outlet end.

[0018] Further optimization, the electrode plate group includes a positive electrode plate and a negative electrode plate that are relatively arranged, the positive electrode plate is located at one end of the sample injection tube, and the negative electrode plate is located at one end of the analyte outlet, and a DC voltage is applied to both the positive electrode plate and the negative electrode plate, and the DC voltage on the positive electrode plate is higher than the voltage of the negative electrode plate.

[0019] Further optimization, the conductive block and the insulating sheet are connected in series by insulating fixing rods, and the two ends of the insulating fixing rods are respectively connected to the positive electrode plate and the negative electrode plate.

[0020] According to further optimization, the analyte outlet is opened in the middle of the negative electrode plate, and the analyte outlet is a conical hole.

[0021] Further optimization, a vacuum exhaust port is provided on the housing of the ionization source, and a vacuum gauge is connected to the vacuum exhaust port.

[0022] Further optimized, the heating rod is a ceramic heating rod, and the ceramic heating rod is wrapped in the heating tube.

[0023] Further optimization, the heating tube is provided with a sealing sleeve outside and is fixedly connected to the ionization source housing through the sealing sleeve.

[0024] Further optimization, the air inlet pipe is made of copper material, which can effectively conduct heat. According to different test samples, it can be selected not to apply gas or to apply different gases and assist with heating to help the test sample to be effectively ionized.

[0025] In further optimization, the ionization source housing is a stainless steel body and a ground potential is applied.

[0026] Further optimization, the number of the cylindrical rods is four groups.

[0027] The low-frequency radio frequency glow discharge ionization device according to the embodiment of the present invention has at least the following beneficial effects:

[0028] 1. It has a wide detection range. It can be used as a separate glow discharge ionization source in conjunction with a mass spectrometer to detect volatile gas samples and liquid samples. It can also be used as an interface between a chromatograph and a mass spectrometer.

[0029] 2. The ionization efficiency is high, and a heating rod can be used to heat the sample to be analyzed, making it easier to decompose and ionize the sample to be analyzed, which can improve the sensitivity of the detection signal;

[0030] 3. Low vacuum requirement;

[0031] 4. It can detect volatile gas samples and liquid samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0033] Figure 1 It is a schematic diagram of the planar structure of a low-frequency radio frequency glow discharge ionization device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0035] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0036] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0037] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0038] Reference Figure 1 The schematic diagram of the planar structure of the low-frequency radio frequency glow discharge ionization device shown in the figure is characterized in that: it comprises an ionization source housing 100 having an ionization chamber 110, a sample injection unit 200 and an auxiliary gas injection unit 300;

[0039] The sample injection unit 200 includes a metal sample injection tube 210, a heating tube 220 mounted on the sample injection tube 210, a heating rod 230 is arranged in the heating tube 220, the sample injection tube 210 is inserted into the ionization chamber 110, and an analyte outlet 120 for connecting to a mass spectrometer is arranged at one end of the ionization source housing 100 facing the sample injection tube 210;

[0040] An ionization source and an electrode plate group capable of exciting an electric field are provided in the ionization chamber 110, and the charged analyte ions move from the end of the injection tube toward the analyte outlet under the guidance of the electric field;

[0041] The auxiliary air intake unit 300 includes an air intake pipe 310 and a heating device 320 for heating the gas in the air intake pipe 310. The air intake pipe 310 is inserted into the ionization chamber 110 from one end of the sample injection tube 210. The heating device 320 is a heating resistor, which is closely attached to the outside of the air intake pipe 310 and is used to heat the auxiliary gas so that the auxiliary gas can be more easily ionized. The entire auxiliary air intake unit is fixed to the ionization source housing 100 through a fixing sleeve.

[0042] When the low-frequency radio frequency glow discharge ionization device of the present application is used as a glow discharge ionization source in conjunction with a mass spectrometer to detect volatile gas samples, the volatile gas samples enter through the injection tube 210. The heat generated by the ceramic heating rod 230 is transmitted to the injection tube 210 through the stainless steel heating cylinder, so that the volatile gas samples are heated and more easily decomposed and ionized.

[0043] The heated volatile organic matter then enters the ionization chamber 110, where it is decomposed and ionized under the action of the ionization source to form charged analyte ions. The charged analyte ions are guided to the analyte outlet 120 by the electric field formed between the electrode plate groups, and enter the mass spectrometer for detection. The ceramic heating rod is used to heat the sample to be analyzed, making it easier for the sample to be analyzed to be decomposed and ionized, thereby improving the sensitivity of the detection signal.

[0044] When the low-frequency radio frequency glow discharge ionization device of the present application detects a volatile liquid sample, nitrogen or an inert gas can be introduced into the volatile liquid sample to be tested for purging, and then a hose is used to connect the outlet of the container containing the volatile liquid sample to the sample injection tube 210 of the present invention, and then the sample enters the ionization chamber 110.

[0045] The present invention can also detect certain non-volatile liquid samples. The liquid sample is directly introduced into the injection tube 210 for injection, and a DC voltage greater than 200V is applied to the injection tube 210 to help ionization.

[0046] The present invention can heat the gas sample in the tube by arranging a heating rod 220 on the sample inlet tube 210, so that the gas sample is more easily ionized when entering the ionization chamber 110, thereby improving the sensitivity of the detection signal and reducing the demand for vacuum.

[0047] In this embodiment, the ionization source includes a plurality of groups of cylindrical rods 400 arranged in the ionization chamber 110. The cylindrical rods 400 are arranged along the direction from the sample inlet tube to the analyte outlet. The plurality of groups of cylindrical rods 400 form a cylindrical ionization region. Each group of cylindrical rods 400 is formed by alternating conductive blocks 410 and insulating sheets 420 connected in series. Adjacent conductive blocks 410 are connected through chip capacitors 500 and chip resistors 600. The conductive blocks 410 at both ends of the cylindrical rods 400 are connected to a radio frequency power supply and applied with different DC voltages, and the voltage of the conductive block 410 at the end of the sample inlet tube 210 is higher than the voltage of the conductive block 410 at the end of the analyte outlet 120.

[0048] The conductive block 410 on the cylindrical rod 400 is connected to a low-frequency radio frequency power source, and the radio frequency frequency is adjustable between 1-5M. The radio frequency power between adjacent conductive blocks 410 is conducted through the chip capacitor 500.

[0049] A DC voltage of about 150V is applied to the rightmost conductive block 410 on the cylindrical rod 400 , and a DC voltage of about 80V is applied to the leftmost conductive block 410 on the rod. The DC current between adjacent conductive blocks is conducted through the chip resistor 600 .

[0050] The sample is ionized in a cylindrical region surrounded by multiple groups of cylindrical rods 400. Compared with the common discharge frequency of 13.56M for glow discharge, the discharge frequency of 1-5M in the present invention has low energy consumption, and the low radio frequency can reduce the interference of the ionization source to the outside world, reduce impurity peaks and consume less energy.

[0051] In this embodiment, the electrode plate group includes two relatively arranged positive electrode plates 710 and negative electrode plates 720. The positive electrode plate 710 is located at one end of the sample injection tube, and the negative electrode plate 720 is located at one end of the analyte outlet. A DC voltage is applied to both the positive electrode plate 710 and the negative electrode plate 720, and the DC voltage on the positive electrode plate 710 is higher than the voltage on the negative electrode plate 720.

[0052] Among them, the positive electrode plate 710 applies a DC voltage of about 200V, and the negative electrode plate 720 applies a DC voltage of about 50V, which is lower than the voltage on the positive electrode plate 710. An electric field is formed between the positive electrode plate 710 and the negative electrode plate 720. Under the guidance of the electric field, the ions to be analyzed are transmitted from one end of the injection tube to one end of the analyte outlet, and enter the mass spectrometer for analysis and detection.

[0053] In this embodiment, the electrode plate 710 and the negative electrode plate 720 are both stainless steel plates, and the two stainless steel plates are fixed to the ionization source housing 100 by a polytetrafluoroethylene fixing block.

[0054] The conductive block 410 and the insulating sheet 420 are connected in series by an insulating fixing rod 430 , and both ends of the insulating fixing rod 430 are connected to the positive electrode plate 710 and the negative electrode plate 720 respectively.

[0055] In this embodiment, the conductive block 410 and the insulating sheet 420 are connected in series by polytetrafluoroethylene fixed rods. There are six cylindrical rods 400, four groups in total, forming a cylindrical area. Both ends of the cylindrical rods 400 are connected to the stainless steel plate, and the connection is provided with an insulating sheet 420 to achieve the effect of insulating connection.

[0056] In this embodiment, the analyte outlet 120 is opened in the middle of the negative electrode plate 720, and the analyte outlet 120 is a conical hole. The conical hole is located in the middle of the negative electrode plate 720 and is located in the ionization area surrounded by four groups of cylindrical rods 400. The ionized analyte enters the mass spectrometer from the conical hole for analysis.

[0057] The ionization source housing 100 is provided with a vacuum pumping port 130, and the vacuum pumping port 130 is connected to a vacuum gauge 131. The ionization source housing 100 is provided with a vacuum pumping port 130, so that the air pressure of the entire ionization chamber 110 is maintained at about 50 Pa. The vacuum pumping port 130 is also connected to a vacuum gauge 131 for measuring low vacuum, which is used to monitor the air pressure in the ionization chamber in real time.

[0058] Among them, for volatile gas samples, the vacuum degree is maintained at about 1-60Pa, and the ionization efficiency is better. For liquid samples, the vacuum degree is maintained at about 100Pa, and the ionization efficiency is better.

[0059] The heating tube 220 is provided with a sealing sleeve 240 outside and is fixedly connected to the ionization source housing 100 through the sealing sleeve 240. The sealing sleeve 240 is made of polytetrafluoroethylene insulation material, which can effectively insulate heat and shield external interference.

[0060] The injection tube 210 is made of stainless steel and is used to introduce the sample to be tested. According to the different samples to be tested, the injection tube can also apply a voltage higher than 200V to help ionize the liquid sample.

[0061] The ionization source housing 100 is a stainless steel body and is applied with a ground potential. In order to improve the sensitivity of detection and reduce the quenching of the analysis ions due to collision with the background gas, the entire ionization chamber 110 is sealed with the ionization source housing 100 .

[0062] The ionization source housing 100 is used to seal the ionization chamber 110 and shield the interference of the outside world on the radio frequency discharge in the ionization chamber 110. The material of the ionization source housing 100 is stainless steel and a ground potential is applied.

[0063] The present invention not only expands the application scope of the glow discharge ionization source, but also the detection method thereof in combination with a mass spectrometer can simultaneously detect characteristic components of multiple volatile organic compounds, and has the characteristics of wide detection application scope, low energy consumption, small interference, low vacuum requirement, high sensitivity, simple structure and low price. The ionization source can be used to detect volatile organic liquid samples and directly detect metal ions in certain non-volatile liquid samples by purging.

[0064] Of course, the present invention is not limited to the above-mentioned embodiments, and those skilled in the art may make equivalent modifications or substitutions without violating the spirit of the present invention, and these equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A low frequency radio frequency glow discharge ionization device, characterized in that: It comprises an ionization source housing (100) having an ionization chamber (110), a sample injection unit (200) and an auxiliary gas injection unit (300); The sample injection unit (200) comprises a metal sample injection tube (210), a heating tube (220) mounted on the sample injection tube (210), a heating rod (230) being arranged in the heating tube (220), the sample injection tube (210) being inserted into the ionization chamber (110), and an analyte outlet (120) for connecting to a mass spectrometer is arranged at one end of the ionization source housing (100) facing the sample injection tube (210); An ionization source and an electrode plate group capable of exciting an electric field are provided in the ionization chamber (110), and the charged analyte ions move from the end of the injection tube toward the analyte outlet under the guidance of the electric field; The auxiliary air intake unit (300) comprises an air intake pipe (310) and a heating device (320) for heating the gas in the air intake pipe (310); the air intake pipe (310) is inserted into the ionization chamber (110) from one end of the injection tube (210); The ionization source comprises a plurality of groups of cylindrical rods (400) arranged in the ionization chamber (110), the cylindrical rods (400) being arranged along a direction from a sample injection tube to an analyte outlet, the plurality of groups of cylindrical rods (400) forming a cylindrical ionization region, each group of cylindrical rods (400) being formed by alternating series connection of conductive blocks (410) and insulating sheets (420), adjacent conductive blocks (410) being connected via patch capacitors (500) and patch resistors (600), the conductive blocks (410) at both ends of the cylindrical rods (400) being connected to a radio frequency power supply and being applied with different direct current voltages, and the voltage of the conductive block (410) at the sample injection tube end being higher than the voltage of the conductive block (410) at the analyte outlet end; The ionization source housing (100) is provided with a vacuum pumping port (130), and the vacuum pumping port (130) is connected to a vacuum gauge (131); The number of the cylindrical rods (400) is four groups.

2. The low frequency radio frequency glow discharge ionization device according to claim 1, characterized in that: The electrode plate group comprises a positive electrode plate (710) and a negative electrode plate (720) arranged opposite to each other, wherein the positive electrode plate (710) is located at one end of the sample injection tube, and the negative electrode plate (720) is located at one end of the analyte outlet. A direct current voltage is applied to both the positive electrode plate (710) and the negative electrode plate (720), and the direct current voltage on the positive electrode plate (710) is higher than the voltage on the negative electrode plate (720).

3. The low frequency radio frequency glow discharge ionization device according to claim 2, characterized in that: The conductive block (410) and the insulating sheet (420) are connected in series by an insulating fixing rod (430), and the two ends of the insulating fixing rod (430) are respectively insulated and connected to the positive electrode plate (710) and the negative electrode plate (720).

4. The low frequency radio frequency glow discharge ionization device according to claim 2 or 3, characterized in that: The analyte outlet (120) is opened in the middle of the negative electrode plate (720), and the analyte outlet (120) is a conical hole.

5. The low-frequency radio frequency glow discharge ionization device according to any one of claims 1 to 3, characterized in that: The heating rod (230) is a ceramic heating rod, and the ceramic heating rod is wrapped in the heating cylinder (220).

6. The low frequency radio frequency glow discharge ionization device according to any one of claims 1 to 3, characterized in that: The heating tube (220) is provided with a sealing sleeve (240) outside and is fixedly connected to the ionization source housing (100) via the sealing sleeve (240).

7. The low frequency radio frequency glow discharge ionization device according to any one of claims 1 to 3, characterized in that: The ionization source housing (100) is a stainless steel body and is applied with a ground potential.

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