Microwave plasma source and analysis method of air elements

Abstract

This invention relates to the field of microwave plasma source structure and elemental analysis methods, specifically to microwave plasma sources and methods for analyzing air elements. The microwave plasma source comprises a sealed resonant cavity consisting of an inner reflecting cavity, a resonant cavity top cover, and a lower resonant cavity. Within this resonant cavity, from the outside to the inside, are coaxially arranged an outer torch for carrying carrier gas, a middle torch for carrying air, and an inner torch for carrying carrier gas. The outer, middle, and inner torches communicate with the outside environment through corresponding interfaces. Microwave interfaces corresponding to the coaxial outer, middle, and inner torches are also provided for connecting to an external microwave source. This invention enables real-time detection and analysis of air elements without requiring air sample pretreatment, reduces the size of the detection instrument for portability, and improves air sample tolerance.

Description

Technical Field

[0001] The invention relates to the field of microwave plasma source structure and element analysis method, in particular to a microwave plasma source and an analysis method of air elements. Background Art

[0002] When analyzing elements in the air, the methods commonly used include:

[0003] 1. Direct injection method:

[0004] (1) Open carrier gas-air mixed injection system: This is the simplest injection method, in which the air sample is directly introduced through the injection tube. This method is suitable for high-concentration air samples due to its low excitation efficiency for air samples, but it is not suitable for low-concentration air samples or air samples that are easily affected by environmental pollution.

[0005] This method is to simply mix the carrier gas and air in a certain proportion and then transport them through a torch tube, and directly excite the mixed gas through microwaves. Because this method does not consider how the microwave energy is transmitted during the plasma process of single / diatomic molecules, it leads to low excitation efficiency of air samples, making it impossible to measure low-concentration elements in air samples, and can only be enriched by pretreatment, which makes it impossible to detect the element content in the air in real time. And because the microwave energy utilization rate of air samples is low, it is often necessary to use high-energy microwaves and high-flow carrier gases to excite a very small amount of air, which is not conducive to human health and the portability of instruments.

[0006] (2) Closed carrier gas-air mixed sampling system: In this method, the air sample is first sealed in a container and then gradually released into the ICP (inductively coupled plasma emission spectrometer) through a control device. This method increases the concentration of the air sample, but because it must be collected first, the detection speed is slow and the throughput is low, which is not suitable for real-time detection.

[0007] 2. Pretreatment injection method:

[0008] (1) Filtration collection: The air sample is passed through a filter to collect solid particles, then the particles in the filter are dissolved or mineralized, and finally the dissolved sample is introduced for analysis. This method requires the collection, filtration, and refinement of air samples, and has a slow detection efficiency and is not suitable for real-time detection.

[0009] (2) Cold trap collection: In this method, the air sample passes through a cold trap system where certain components (such as water vapor or volatile organic compounds) are condensed and collected. The collected substances can then be reheated and introduced. The disadvantages are the same as above, with too many steps and not suitable for real-time detection.

[0010] 3. Aerosol injection method:

[0011] (1) Aerosol generator: This device converts an air sample into an aerosol of fine droplets or solid particles, which are then introduced for analysis. This method is suitable for introducing airborne particles directly into a plasma.

[0012] (2) Nebulizer sampling: The air sample is converted into fine droplets through a nebulizer and then introduced. This requires the air sample to be liquefied first or diluted with an appropriate solvent.

[0013] Both of these require a lot of pre-processing, and too many steps are not suitable for real-time detection. Summary of the invention

[0014] The present invention provides a microwave plasma source and an analysis method for air elements, the purpose of which is to detect and analyze air elements in real time without pre-processing the air sample, reduce the size of the detection instrument, facilitate portability, and improve air sampling tolerance.

[0015] The microwave plasma source of the present invention comprises an inner reflection cavity, a resonance cavity top cover and a lower resonance cavity to form a closed resonance cavity, wherein a coaxial outer torch tube for passing a carrier gas, a middle torch tube for passing air and an inner torch tube for passing a carrier gas are arranged from outside to inside in the resonance cavity, wherein the outer torch tube, the middle torch tube and the inner torch tube are communicated with the outside through corresponding outer torch tube interfaces, middle torch tube interfaces and inner torch tube interfaces respectively, and microwave interfaces corresponding to the coaxial outer torch tube, the middle torch tube and the inner torch tube for connecting an external microwave source are also arranged.

[0016] Furthermore, the microwave interface corresponds to the outer torch tube, the middle torch tube and the inner torch tube through a resonant ring.

[0017] Furthermore, a resonant ring fixer for fixing the resonant ring is provided outside the inner reflection cavity.

[0018] Furthermore, a lower resonant cavity adjuster for adjusting the position of the lower resonant cavity is provided on the outer side of the lower resonant cavity.

[0019] Furthermore, an air conditioning device is provided in the middle torch tube and is sleeved on the outside of the inner torch tube.

[0020] Specifically, the air conditioning device is an eight-channel control valve.

[0021] The present invention also provides an analysis method for air elements, wherein carrier gas, air and carrier gas are respectively input into the corresponding outer torch tube, middle torch tube and inner torch tube through the outer torch tube interface, middle torch tube interface and inner torch tube interface of the above-mentioned microwave plasma source, and then the microwave source excites the electrons of the carrier gas in the outer torch tube and the inner torch tube through the microwave interface to produce ionization to form an electron avalanche, and then the electrons of the electron avalanche are used to excite the air in the middle torch tube, and then the air elements in the middle torch tube are analyzed.

[0022] Furthermore, when the microwave source is working, the signal strength of the microwave resonant frequency is enhanced through the resonant ring, thereby improving the output power and efficiency of the microwave source.

[0023] Furthermore, the stability of the air introduced into the middle torch tube is controlled by an air conditioning device arranged in the middle torch tube.

[0024] Furthermore, the air conditioning device is an eight-channel regulating valve.

[0025] The beneficial effects of the present invention include:

[0026] 1. Through experiments, it is known that the air injection tolerance (that is, the ratio of air to carrier gas-air) of the microwave plasma source of the present invention is improved from less than 0.1% of the prior art to 20%. Due to the use of a coaxial multi-channel torch tube structure in a sandwich form, the porous flow mixing of the inert maintenance gas (carrier gas) and air is better, the air excitation efficiency is higher, and under the same carrier gas amount, more air can be excited, thereby making the air injection tolerance of the microwave plasma source higher.

[0027] 2. Higher safety. Since air has a high utilization rate for microwave energy, the microwave power can be lower when exciting the same amount of air, meeting the requirement of 10 -10 g / cm 3 Sodium detection only requires a 150W microwave source. At the same power, the existing ICP (inductively coupled plasma emission spectrometer) cannot even ignite the air. And because the microwave source has low energy, it is also safer for the human body.

[0028] 3. The volume of the microwave plasma source is smaller. Since the carrier gas volume requirement is smaller and the microwave source requires lower power, the volume of the microwave plasma source made using the sample injection device can be smaller and can be suitable for use as a portable instrument.

[0029] 4. Real-time detection can be achieved. Due to the higher excitation efficiency, there is no need for pre-treatment of air samples, so the detection speed is faster and can be detected in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a structural cross-sectional view of the microwave plasma source of the present invention. DETAILED DESCRIPTION

[0031] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application usually described and shown in the drawings here can be arranged and designed in various configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0032] like Figure 1 As shown, the microwave plasma source of the present invention is composed of an inner reflection cavity 1, a resonant cavity top cover 8 and a lower resonant cavity 7 to form a closed resonant cavity, wherein the inner reflection cavity 1 is used to reflect microwaves, and the lower resonant cavity 7 is an adjustable resonant cavity, which cooperates with the inner reflection cavity 1 and the resonant cavity top cover 8 to form a closed resonant cavity, and also plays the role of resonant frequency selection. In the resonant cavity, a coaxial outer torch tube 3 for passing a carrier gas (argon is used in this embodiment), a middle torch tube 4 for passing air and an inner torch tube 5 for passing a carrier gas (argon is used in this embodiment) are arranged from outside to inside, and the outer torch tube 3, the middle torch tube 4 and the inner torch tube 5 are communicated with the outside world through the corresponding outer torch tube interface 31, the middle torch tube interface 41 and the inner torch tube interface 51 respectively. The outer torch tube 3, the middle torch tube 4 and the inner torch tube 5 form a sandwich-type coaxial multi-channel torch tube structure, thereby achieving better porous flow mixing of argon and air, higher excitation efficiency of air, and more air can be excited under the same argon amount, so that the air injection tolerance of the microwave plasma source is higher. A microwave interface 11 corresponding to the coaxial outer torch tube 3, the middle torch tube 4 and the inner torch tube 5 for connecting to an external microwave source is also provided.

[0033] The microwave interface 11 corresponds to the outer torch tube 3, the middle torch tube 4 and the inner torch tube 5 through the resonant ring 2, and a resonant ring fixture 9 for fixing the resonant ring 2 is provided on the outer side of the inner reflection cavity 1. The resonant ring 2 is used to enhance the signal strength of the microwave frequency. When the microwave source works at the resonant frequency, the resonant ring 2 can enhance the electromagnetic field strength of this frequency, thereby improving the output power and efficiency of the microwave source.

[0034] A lower resonant cavity adjuster 6 for adjusting the position of the lower resonant cavity 7 is provided outside the lower resonant cavity 7. The lower resonant cavity adjuster 6 can adjust the position of the lower resonant cavity 7 to enhance the output power of the microwave source.

[0035] An air conditioning device 10 with an eight-channel regulating valve structure is provided in the middle torch tube 4 and is sleeved outside the inner torch tube 5. The air conditioning device 10 with an eight-channel regulating valve structure is the key to maintaining the stability of the air in the middle torch tube 4. According to aerodynamic theory and experiments, the eight-channel regulating valve can improve the structural stability of the carrier gas-air-carrier gas. If only a coaxial torch tube structure is used, the sandwich structure formed cannot exist stably and is easily disturbed.

[0036] The principle of the microwave plasma source of the present invention for detecting elements in the air is to first use microwaves to excite the easily ionized carrier gas, ionize the electrons in the carrier gas to form an electron avalanche, and then use the electrons of the electron avalanche to excite the air. If it is a traditional carrier gas-air mixed structure, due to the atomic cluster effect of the carrier gas and the air, the same monoatomic / diatomic gas has a tendency to agglomerate, so the air and the carrier gas are in pieces, and many electrons generated by the carrier gas do not excite the air, resulting in a very small proportion of air that can be ionized. The coaxial structure of the carrier gas-air-carrier gas sandwich form of the present invention will form electron avalanches on both sides of the air, and most of the electrons generated by the carrier gas are used to excite the air, so that the excitation efficiency of the air is improved, thereby improving the sensitivity of the detection and the air tolerance of the microwave plasma source.

[0037] The present invention also provides an analysis method for air elements. Through the outer torch tube interface 31, the middle torch tube interface 41 and the inner torch tube interface 51 of the microwave plasma source described in this embodiment, the carrier gas, air and carrier gas are respectively input into the corresponding outer torch tube 3, the middle torch tube 4 and the inner torch tube 5, and then the external microwave source is started to work, and the signal strength of the microwave resonant frequency is enhanced through the resonant ring 2, thereby improving the output power and efficiency of the microwave source. The microwave source excites the electrons of the argon gas in the outer torch tube 3 and the inner torch tube 5 through the microwave interface 11 to produce ionization, forming an electron avalanche, and then the electrons of the electron avalanche are used to excite the air in the middle torch tube 4, and then the air elements in the middle torch tube 4 are analyzed. During the operation of the microwave plasma source, the air conditioning device 10 with an eight-channel regulating valve structure set in the middle torch tube 4 controls the stability of the air entering the middle torch tube 4.

[0038] The above-mentioned embodiments only express the specific implementation methods of the present application, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the protection scope of the present application. It should be pointed out that for ordinary technicians in this field, relevant deformations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A microwave plasma source, characterized by: The invention relates to a closed resonant cavity body formed by an inner reflection cavity (1), a resonant cavity top cover (8) and a lower resonant cavity (7). In the resonant cavity body, a coaxial outer torch tube (3) for passing a carrier gas, a middle torch tube (4) for passing air and an inner torch tube (5) for passing a carrier gas are arranged from outside to inside. The outer torch tube (3), the middle torch tube (4) and the inner torch tube (5) are respectively connected to the outside through corresponding outer torch tube interfaces (31), middle torch tube interfaces (41) and inner torch tube interfaces (51). A microwave interface (11) corresponding to the coaxial outer torch tube (3), middle torch tube (4) and inner torch tube (5) for connecting to an external microwave source is also arranged. An air conditioning device (10) which is sleeved on the outside of the inner torch tube (5) is arranged in the middle torch tube (4). The air conditioning device (10) is an eight-channel regulating valve. A lower resonant cavity regulator (6) for adjusting the position of the lower resonant cavity (7) is arranged on the outside of the lower resonant cavity (7).

2. The microwave plasma source according to claim 1, characterized in that: The microwave interface (11) corresponds to the outer torch tube (3), the middle torch tube (4) and the inner torch tube (5) through the resonant ring (2).

3. The microwave plasma source according to claim 2, characterized in that: A resonant ring fixer (9) for fixing the resonant ring (2) is provided outside the inner reflection cavity (1).

4. The analysis method of air elements is characterized by: Through the outer torch tube interface, middle torch tube interface and inner torch tube interface of the microwave plasma source according to any one of claims 1 to 3, the carrier gas, air and carrier gas are respectively input into the corresponding outer torch tube, middle torch tube and inner torch tube, and then the microwave source excites the electrons of the carrier gas in the outer torch tube and the inner torch tube through the microwave interface to produce ionization to form an electron avalanche, and then the electrons of the electron avalanche are used to excite the air in the middle torch tube, and then the air elements in the middle torch tube are analyzed.

5. The method for analyzing air elements as claimed in claim 4, characterized in that: When the microwave source is working, the signal strength of the microwave resonant frequency is enhanced through the resonant ring, thereby improving the output power and efficiency of the microwave source.

6. The method for analyzing air elements as claimed in claim 4, characterized in that: The stability of the air introduced into the middle torch is controlled by an air regulating device arranged in the middle torch.

7. The method for analyzing air elements as claimed in claim 4, characterized in that: The air conditioning device is an eight-channel regulating valve.

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