A miniaturized device and method for continuous detection of total organic carbon in water

Abstract

The present application relates to total organic carbon analysis detection and atomic emission spectrum analysis technical field, specifically to a kind of miniaturized water body total organic carbon continuous detection device and detection method;Per sulfate solution and sample solution enter dielectric barrier discharge catalytic oxidation unit, per sulfate is used as oxidant, under the catalysis of dielectric barrier discharge microplasma in dielectric barrier discharge catalytic oxidation unit, organic carbon in sample is rapidly and efficiently converted into carbon dioxide;The gaseous product containing carbon dioxide generated is transported under the action of argon, passes through spiral coil and dryer placed in low-temperature water bath device to remove water vapor, enters tip discharge atomic emission spectrum detection unit, carries out carbon atom emission spectrum excitation, and CCD spectrum detector acquires spectrum signal through spectrum detection window, and obtains the content of TOC through data processing.The present application improves analysis sensitivity and stability, realizes the on-site continuous, rapid detection of TOC.

Description

Technical Field

[0001] This invention relates to the field of total organic carbon analysis and detection and atomic emission spectroscopy, specifically to a miniaturized device and method for continuous detection of total organic carbon in water. Technical Background

[0002] Total Organic Carbon (TOC) is a crucial parameter for assessing organic pollution. It directly reflects the total amount of organic matter in water and is independent of the chemical form and oxidation state of the organic matter, making it one of the most important environmental monitoring parameters. TOC expresses the total amount of organic matter in water by its carbon content. The measurement process typically involves two steps: first, the organic matter in the water is oxidized, converting the carbon in the organic matter into CO2; then, the CO2 content is measured, and a correlation is established between it and the TOC content, thus enabling the detection of TOC.

[0003] In existing TOC analyzers, commonly used oxidation methods include high-temperature combustion, chemical oxidation, and ultraviolet oxidation. High-temperature combustion suffers from drawbacks such as complex equipment and high energy consumption (electricity), while chemical and ultraviolet oxidation methods have low oxidation efficiency, limiting their applicability. Common detection methods include non-dispersive infrared absorption, flame ionization detectors, thermal conductivity detectors, electrical conductivity detectors, ion chromatography, gravimetric analysis, and titration analysis. Chemical analysis methods typically suffer from poor accuracy and high detection limits, while instrumental analysis methods are generally complex in structure and bulky. Furthermore, most existing TOC detection technologies and instruments are based on laboratory platforms and cannot be directly used for high-sensitivity on-site analysis. Additionally, organic carbon oxidation and CO2 detection are relatively independent, making continuous injection TOC analysis impossible. These limitations prevent them from solving the diverse problems encountered in practical work; for example, the need for rapid testing and screening, the need for on-site analysis in the event of emergencies, and the need for in-situ, real-time, continuous online analysis to avoid data distortion caused by the "sampling-delivery-testing" process of traditional laboratory analysis methods.

[0004] The key to whether a TOC analyzer can solve these problems lies in its analytical principle and instrument structure, mainly involving the sample introduction method, the organic carbon oxidation device and its subsequent CO2 detection device. These not only directly affect the overall analytical performance of the instrument, but also determine the size of the instrument, its energy consumption, the number of auxiliary devices, and whether it can achieve miniaturized on-site continuous detection applications. Therefore, the organic carbon oxidation device and its subsequent CO2 detection device have become the focus and hot topic of research in the field of TOC analysis in recent years.

[0005] Plasma, as the fourth state of matter, has a high degree of ionization and contains a large number of electrons, ions, and free radicals, thus possessing many excellent properties and finding numerous applications in the analytical field. Micro-plasma, while retaining the inherent properties of plasma, also boasts advantages such as small size, low power consumption, simple device design, and operation at atmospheric pressure. It has found widespread application in miniaturized analytical instruments, including plasma surface treatment, plasma material synthesis, plasma-induced vapor generation, and as an ion source for mass spectrometry, an atomizer for spectral analysis, and an excitation source.

[0006] Dielectric barrier discharge (DBD) is a non-equilibrium discharge in which an insulating dielectric is inserted into the discharge space. Accompanied by the generation of low-temperature micro-plasma, it contains a large number of electrons and possesses high energy. It exhibits high electron density / temperature and high excitation temperature, making it a commonly used component in miniaturized analytical instruments, such as chemical vapor generators, atomizers in atomic absorption spectrometry, and excitation sources in atomic emission spectrometry. Furthermore, DBD also possesses strong catalytic oxidation properties, making it an ideal device for the catalytic oxidation of organic carbon. Point discharge (PD) is a discharge phenomenon occurring at the sharp points of an object under a strong electric field. Therefore, it has a smaller volume and stronger, more concentrated discharge energy, resulting in higher excitation capability. It is often used as an excitation source in miniaturized atomic emission spectrometers. Because it can excite the atomic emission spectrum of carbon, it is also an ideal choice for CO2 detectors.

[0007] In recent years, there have been reports on the use of microplasma coupled with atomic emission spectroscopy for TOC analysis. For example, Chinese patent CN103196896A discloses a continuous flow analysis method for detecting total organic carbon in water samples. This method uses microwave-assisted sodium persulfate to oxidize TOC in the water sample to CO2, and then uses DBD microplasma to directly excite CO2 to generate characteristic carbon atom emission lines (193.0 nm), which are then quantitatively detected by a CCD spectrometer. However, the microwave-assisted oxidation device in this method is bulky and energy-intensive, making it difficult to meet the requirements for continuous on-site analysis of total organic carbon. Furthermore, the ability of DBD microplasma to excite carbon atom emission spectra is relatively weak, and the analytical sensitivity needs further improvement. For example, Li et al. (Anal. Chim. Acta, 2021) disclosed a miniaturized TOC analyzer (DBD-COVG-PD-OES), which utilizes DBD micro-plasma to catalyze the oxidation of organic carbon by persulfate to generate CO2, and excites the carbon atom emission spectrum (193.09 nm) through tip discharge micro-plasma, and then achieves quantitative detection through a CCD spectrometer. However, the sample introduction method in this scheme is a single injection, and the sample introduction and waste discharge processes rely on manual injection / waste discharge by an injection pump, which does not achieve continuous automated operation. This results in a relatively large relative standard deviation (RSD) of the analytical results. Furthermore, the specific structural parameters of the DBD reactor, the pretreatment method of gaseous products (especially the specific structure of the secondary dehydration device), and the specific size and structural parameters of the tip discharge excitation source have not been fully disclosed and optimized, resulting in room for further improvement in the overall analytical performance of the device. Summary of the Invention

[0008] The purpose of this invention is to address the problems and shortcomings of existing TOC analysis and detection technologies. In order to achieve continuous sample introduction, rapid and efficient oxidation and detection of TOC samples, further improve analytical sensitivity and stability, and miniaturize the overall instrument, this invention provides a miniaturized TOC analyzer that combines a continuous sample introduction device with a dielectric barrier discharge catalytic oxidation device and a tip discharge atomic emission spectrometry detection device, so as to achieve continuous and rapid on-site detection of TOC.

[0009] The technical solution adopted in this invention is:

[0010] A miniaturized device for continuous detection of total organic carbon in water includes a continuous automatic sampling and waste discharge unit, a dielectric barrier discharge catalytic oxidation unit, a gaseous product pretreatment unit, and a tip discharge atomic emission spectrometry detection unit.

[0011] The continuous automatic sample feeding and waste discharge unit includes a first peristaltic pump and a second peristaltic pump.

[0012] The dielectric barrier discharge catalytic oxidation unit includes a quartz outer tube with a first electrode wound around it; an inner quartz tube is located inside the outer tube, with its rear end closed and its front end open, and a second electrode located within the front opening; a first peristaltic pump is connected to the front end of the outer tube, and a second peristaltic pump is connected to the rear end; the first peristaltic pump is connected to the persulfate inlet and the sample solution inlet; the second peristaltic pump is connected to the waste liquid outlet; a gaseous product outlet is also located at the rear end of the outer tube, and a branch pipe is provided at the gaseous product outlet as a carrier gas inlet;

[0013] The gaseous product pretreatment unit includes a low-temperature water bath device and a dryer; one end of the spiral coil in the low-temperature water bath device is connected to the gaseous product outlet at the rear end of the quartz outer tube through a connecting pipe, and the other end is connected to the dryer.

[0014] The tip discharge atomic emission spectroscopy detection unit includes an electrode holder located at the dryer outlet, two opposing tip electrodes on the electrode holder, and a CCD spectral detector located outside the spectral detection window on the electrode holder.

[0015] Persulfate solution and sample solution are simultaneously introduced into the dielectric barrier discharge catalytic oxidation unit through the persulfate inlet and sample solution inlet, respectively, by a first peristaltic pump. The waste liquid after the reaction is discharged from the dielectric barrier discharge catalytic oxidation unit through the waste liquid outlet by a second peristaltic pump. Persulfate, acting as an oxidant, rapidly and efficiently converts organic carbon in the sample into carbon dioxide under the catalytic action of the dielectric barrier discharge micro-plasma in the dielectric barrier discharge catalytic oxidation unit. Argon gas enters the dielectric barrier discharge catalytic oxidation unit through the carrier gas inlet. The gaseous products containing carbon dioxide generated in the dielectric barrier discharge catalytic oxidation unit are transported by argon gas and pass through the gaseous product outlet via connecting pipes, sequentially through a spiral coil placed in a low-temperature water bath and a dryer to remove water vapor, before entering the tip discharge atomic emission spectrometry detection unit for carbon atom emission spectrum excitation. A CCD spectrometer acquires the spectral signal through the spectral detection window, and the TOC content is obtained through data processing.

[0016] The electrode holder is a hollow cylinder, with two pointed electrodes passing through and fixed to the electrode holder; the pointed electrodes generate discharge micro-plasma under high voltage, which excites the atomic emission spectrum of carbon, thus enabling quantitative analysis.

[0017] Furthermore, the diameter of the first electrode of the dielectric barrier discharge catalytic oxidation unit is 0.3 to 0.8 mm, and it is made of copper or a conductive material with similar ductility; the diameter of the second electrode is 1 to 3 mm, and it is made of copper or other conductive materials. The first and second electrodes are connected to a power supply, and under high voltage, discharge micro-plasma (dielectric barrier discharge) is generated.

[0018] Furthermore, the dielectric barrier discharge catalytic oxidation unit is placed horizontally or tilted; the carrier gas is argon, and the flow rate of the carrier gas is 100~400 mL / min; the persulfate oxidant solution is sodium persulfate solution or potassium persulfate solution, with a mass fraction of 10%~15%.

[0019] Furthermore, the desiccant filled inside the dryer is color-changing silica gel or anhydrous calcium chloride;

[0020] A detection method for a miniaturized device for continuous detection of total organic carbon in water includes the following steps:

[0021] Step 1: Add 10% to 15% phosphoric acid to the standard solution or sample solution and stir for 5 to 10 minutes to remove dissolved inorganic carbon;

[0022] Step 2: The 10%~15% persulfate solution and the sample solution or standard solution for removing inorganic carbon are simultaneously introduced into the dielectric barrier discharge catalytic oxidation unit through the sulfate inlet and the sample solution inlet, respectively, by the first peristaltic pump.

[0023] Step 3: Adjust the argon flow rate to 100 ~ 400 mL / min and introduce it into the dielectric barrier discharge catalytic oxidation unit through the carrier gas inlet;

[0024] Step 4: Turn on the power supply connected to the two pointed electrodes to generate tip discharge micro-plasma;

[0025] Step 5: Turn on the power supply connected to the first and second electrodes to generate dielectric barrier discharge micro-plasma.

[0026] Step 6: The waste liquid after reaction in the dielectric barrier discharge catalytic oxidation unit is discharged through the waste liquid outlet by the second peristaltic pump;

[0027] Step 7: Acquire spectral data using a CCD spectrometer and use the characteristic spectral line of carbon at 193.09 nm as the analytical line;

[0028] Step 8: After the test is completed, turn off the power supply connected to the first and second electrodes and the power supply connected to the two tip electrodes to stop the CCD spectral detector from acquiring spectral data.

[0029] Step 9: Deionized water is pumped into the dielectric barrier discharge catalytic oxidation unit through the sulfate inlet and the sample solution inlet using the first peristaltic pump to rinse the dielectric barrier discharge catalytic oxidation unit, and the rinsed liquid is discharged through the waste liquid outlet using the second peristaltic pump.

[0030] This invention provides a device and method for continuous detection of total organic carbon in water, the advantages of which are:

[0031] (1) The present invention consists of four functional units: a continuous automatic sample feeding and waste discharge unit, a dielectric barrier discharge catalytic oxidation unit, a gaseous product pretreatment unit, and a tip discharge atomic emission spectroscopy detection unit. Each unit works independently and collaboratively, with a high degree of modularity, making it easy to integrate, maintain, and carry.

[0032] (2) The present invention adopts a specific DBD device structure with a quartz outer tube and a quartz inner tube with a closed right end and an open left end, which are coaxially arranged, and are combined with a spirally wound first electrode and a second electrode extending into the inner tube. This structure can realize the integration of organic carbon oxidation and gas-liquid separation, with high oxidation efficiency, good gas-liquid separation effect, and compact structure that is easy to miniaturize.

[0033] (3) The present invention adopts a two-stage gaseous product pretreatment device that combines low-temperature water bath spiral coil cooling with dryer drying, which can effectively remove water vapor from CO2 gaseous products generated by oxidation, avoid the interference of moisture on the stability of subsequent tip discharge, and significantly improve the signal-to-noise ratio and stability of carbon atom emission spectrum signal.

[0034] (4) The present invention employs a tip discharge device with specific dimensions (tungsten rod diameter 1~2 mm, conical ends facing each other, gap 1~6 mm) and a specific fixing base structure (polytetrafluoroethylene hollow cylinder, inner diameter 5~8 mm, detection window embedded in quartz plate), which can stably excite carbon atoms in CO2 to produce a characteristic emission spectrum of 193.09 nm, with high sensitivity and little spectral interference;

[0035] (5) The present invention uses a first peristaltic pump to continuously pump in persulfate solution and sample solution, and a second peristaltic pump to continuously discharge waste liquid, thereby realizing continuous injection of TOC sample solution and continuous discharge of waste liquid, which improves instrument stability. Combined with continuous oxidation and continuous spectral detection, it can quickly obtain TOC content and realize continuous online analysis.

[0036] (6) The present invention has a small overall size, low energy consumption, easy integration, few auxiliary equipment, and low cost, and can realize the miniaturization and portability of the instrument for continuous on-site analysis. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the device structure of the present invention. In the figure: 1-first peristaltic pump, 2-persulfate inlet, 3-sample solution inlet, 4-carrier gas inlet, 5-quartz outer tube, 6-first electrode, 7-second electrode, 8-quartz inner tube, 9-waste outlet, 10-second peristaltic pump, 11-gaseous product outlet, 12-connecting pipeline, 13-spiral coil, 14-low temperature water bath device, 15-dryer, 16-electrode holder, 17-tip electrode, 18-spectral detection window, 19-CCD spectrometer.

[0038] Figure 2 This is the emission spectrum of the characteristic atoms obtained in this invention. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be noted that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0040] like Figure 1 As shown, a miniaturized device for continuous detection of total organic carbon in water includes a continuous automatic sampling and waste discharge unit, a dielectric barrier discharge catalytic oxidation unit, a gaseous product pretreatment unit, and a tip discharge atomic emission spectrometry detection unit.

[0041] The continuous automatic sample feeding and waste discharge unit includes a first peristaltic pump 1 and a second peristaltic pump 10.

[0042] The dielectric barrier discharge catalytic oxidation unit includes a quartz outer tube 5, with a first electrode 6 wound around its outer surface. An inner quartz tube 8 is located inside the outer tube 5. The inner diameter of the outer tube 5 is 7-12 mm, and the outer diameter of the inner tube 8 is 3-5 mm. The inner tube 8 is closed at its rear end and open at its front end, with a second electrode 7 located within the front opening. A first peristaltic pump 1 is connected to the front end of the outer tube 5, and a second peristaltic pump 10 is connected to the rear end. The first peristaltic pump 1 is connected to a persulfate inlet 2 and a sample solution inlet 3. The second peristaltic pump 10 is connected to a waste liquid outlet 9. A gaseous product outlet 11 is also located at the rear end of the outer tube 5, and a branch pipe serves as a carrier gas inlet 4.

[0043] The first electrode 6 of the dielectric barrier discharge catalytic oxidation unit has a diameter of 0.3 to 0.8 mm and is made of copper or a conductive material with similar ductility; the second electrode 7 has a diameter of 1 to 3 mm and is made of copper or other conductive materials. The first electrode 6 and the second electrode 7 are connected to a power supply, and discharge micro-plasma (dielectric barrier discharge micro-plasma) is generated under high voltage.

[0044] The dielectric barrier discharge catalytic oxidation unit is placed horizontally or tilted; the carrier gas is argon, and the flow rate of the carrier gas is 100~400 mL / min; the persulfate oxidant solution is sodium persulfate solution or other persulfate solutions with good solubility, with a mass fraction of 10%~15%.

[0045] The gaseous product pretreatment unit includes a low-temperature water bath device 14 and a dryer 15, with a spiral coil and a dryer in the low-temperature water bath. One end of the spiral coil 13 in the low-temperature water bath device 14 is connected to the gaseous product outlet 11 at the rear end of the quartz outer tube 5 via a connecting pipe 12, and the other end is connected to the dryer 15. The desiccant filled in the dryer 15 is color-changing silica gel or anhydrous calcium chloride. The gaseous product pretreatment unit is used to cool and remove water vapor from the gaseous product. The inlet of the dryer 15 is connected to the outlet of the spiral coil 13, and the dryer 15 is filled with desiccant to further remove residual moisture from the cooled gaseous product.

[0046] The inlet of the tip discharge atomic emission spectroscopy detection unit is connected to the outlet of the dryer 15; the tip discharge atomic emission spectroscopy detection unit includes an electrode holder 16 located at the outlet of the dryer 15, two opposing tip electrodes 17 are provided on the electrode holder 16, and a CCD spectral detector 19 is provided outside the spectral detection window 18 on the electrode holder 16.

[0047] Persulfate solution and sample solution enter the dielectric barrier discharge catalytic oxidation unit simultaneously through the persulfate inlet 2 and sample solution inlet 3, respectively, under the action of the first peristaltic pump 1. The waste liquid after the reaction is discharged from the dielectric barrier discharge catalytic oxidation unit through the waste liquid outlet 9, under the action of the second peristaltic pump 10. Persulfate, acting as an oxidant, rapidly and efficiently converts organic carbon in the sample into carbon dioxide under the catalytic action of the dielectric barrier discharge micro-plasma in the dielectric barrier discharge catalytic oxidation unit. Argon gas enters the dielectric barrier discharge catalytic oxidation unit through the carrier gas inlet 4. The gaseous product containing carbon dioxide generated in the dielectric barrier discharge catalytic oxidation unit is transported by argon gas through the gaseous product outlet 11, then passes through the connecting pipe 12, sequentially through the spiral coil 13 placed in the low-temperature water bath device 14 and the dryer 15 to remove water vapor, and enters the tip discharge atomic emission spectrometry detection unit for carbon atom emission spectrum excitation. The CCD spectrometer 19 acquires the spectral signal through the spectral detection window 18, and the TOC content is obtained through data processing. Figure 2 As shown, the horizontal axis represents wavelength, and the vertical axis represents spectral intensity. Figure 2 Both 193.09 nm and 247.86 nm are characteristic atomic emission lines of carbon.

[0048] The electrode holder 16 is a hollow cylinder, and two pointed electrodes 17 are inserted through and fixed on the electrode holder 16. Under high voltage, the pointed electrodes 17 generate discharge micro-plasma, which excites the atomic emission spectrum of carbon to achieve quantitative analysis.

[0049] The tip electrodes 17 are all tungsten rod electrodes or other electrodes made of materials with good conductivity and corrosion resistance, with a diameter of 1~2 mm. The opposite ends of the electrodes are tapered tips, and the discharge gap between the two tapered tips is 1~6 mm. A quartz plate is embedded in the spectral detection window 18 on the electrode holder 16.

[0050] The electrode holder 16 is made of polytetrafluoroethylene, and the hollow inner cavity of the electrode holder 16 is a cylindrical cavity with an inner diameter of 5~8 mm; the diameter of the spectral detection window 18 is 3~5 mm.

[0051] A detection method for a miniaturized device for continuous detection of total organic carbon in water includes the following steps:

[0052] Step 1: Add 10% to 15% phosphoric acid to the standard solution or sample solution and stir for 5 to 10 minutes to remove dissolved inorganic carbon;

[0053] Step 2: The 10%~15% persulfate solution and the sample solution or standard solution for removing inorganic carbon are simultaneously introduced into the dielectric barrier discharge catalytic oxidation unit through the first peristaltic pump 1 via the sulfate inlet 2 and the sample solution inlet 3, respectively.

[0054] Step 3: Adjust the argon flow rate to 100 ~ 400 mL / min, and let it enter the dielectric barrier discharge catalytic oxidation unit through carrier gas inlet 4;

[0055] Step 4: Turn on the power supply connected to the two tip electrodes 17 to generate tip discharge micro-plasma;

[0056] Step 5: Turn on the power supply connected to the first electrode 6 and the second electrode 7 to generate dielectric barrier discharge micro-plasma.

[0057] Step 6: The waste liquid after reaction in the dielectric barrier discharge catalytic oxidation unit is discharged through the waste liquid outlet 9 by the second peristaltic pump 10;

[0058] Step 7: Acquire spectral data using CCD spectral detector 19, and use the characteristic spectral line of carbon at 193.09 nm as the analytical line;

[0059] Step 8: After the test is completed, turn off the power supply connected to the first electrode 6 and the second electrode 7 and the power supply connected to the two tip electrodes 17, and stop the CCD spectral detector 19 from acquiring spectral data.

[0060] Step 9: Deionized water is pumped into the dielectric barrier discharge catalytic oxidation unit through the first peristaltic pump 1 via the sulfate inlet 2 and the sample solution inlet 3 to rinse the dielectric barrier discharge catalytic oxidation unit, and the rinsed liquid is discharged through the waste liquid outlet 9 via the second peristaltic pump 10.

[0061] The analytical performance of this invention is compared with other methods as shown in Table 1 below:

[0062] Table 1. Comparison of analytical performance of the present invention with other methods

[0063] Analytical methods Injection volume Analysis time Detection limit Linear range RSD Remark Titration - Approximately 30 minutes 0.05% - - It is low in cost and does not rely on expensive equipment, but its analytical sensitivity is relatively low. Combustion oxidation - non-dispersive infrared absorption method - Approximately 30 minutes <![CDATA[0.1 mg L -1 ]]> - 6.3% It ensures thorough oxidation and accurate results, but the instrument is bulky and consumes a lot of energy, so it is generally used for laboratory analysis. UV-ECD Continuous injection Approximately 15 minutes <![CDATA[0.002 mg L -1 ]]> <![CDATA[0.002 - 4 mg L -1 ]]> - It has a low detection limit, but limited oxidation capacity and a small linear range, limiting its application scenarios. It is mainly suitable for clean water samples with low concentration, low salinity, and low particulate matter. HTC-IC 1000 mL Approximately 30 minutes <![CDATA[0.002 mg L -1 ]]> <![CDATA[0.01 - 2.5 mg L -1 ]]> - It provides thorough oxidation and accurate results, but has a narrow linear range, a large instrument size, high energy consumption, and high maintenance costs, and is generally used for laboratory analysis. Direct ICP-AES - - <![CDATA[0.07 mg L -1 ]]> - 2.2% It is susceptible to interference from carbon compounds in the air, which can lead to significant errors in the analytical results. MVOG-DBD-AES Continuous injection Continuous analysis <![CDATA[0.01 mg L -1 ]]> <![CDATA[0.1 - 20 mg L -1 ]]> 6.5% The detection limit is low, but the device is large and consumes a lot of energy, making it difficult to apply to continuous on-site analysis. DBD-COVG-PD-OES 1 mL Approximately 6 minutes <![CDATA[0.02 mg L -1 ]]> <![CDATA[0.1 - 200 mg L -1 ]]> 3.9% The device is small in size and consumes little energy, but manual discontinuous injection and the stability and detection limit of the analytical results need further improvement. This invention Continuous injection Continuous analysis <![CDATA[0.01mg L -1 ]]> <![CDATA[00.05-200mg L -1 ]]> 1.1% The device is small in size, consumes little energy, provides continuous automatic sample injection, has good stability, and has a low detection limit.

[0064] Data sources for the analysis methods in the table:

[0065] (1) Titration method, data sourced from the literature: Guo Yingchao, Liu Wei, Gu Zhoulei. Comparative determination of organic carbon in soil by titration and high frequency infrared spectroscopy. Xinjiang Nonferrous Metals, 2023, 46 (1): 15-16.

[0066] (2) Combustion oxidation-non-dispersive infrared absorption method, data sourced from the literature: National Environmental Protection Standard of the People's Republic of China HJ 501-2009 "Determination of total organic carbon in water by combustion oxidation-non-dispersive infrared absorption method".

[0067] (3) UV-ECD: UV oxidation-conductivity detector method, data sourced from the literature Federer, U.; Kaufmann, PR; Hutterli, MA; Schüpbach, S.; Stocker, TF, Continuous Flow Analysis of Total Organic Carbon in Polar Ice Cores. Environmental Science & Technology 2008, 42, (21), 8039-8043.

[0068] (4) HTC-IC: High-temperature combustion-ion chromatography, data sourced from Fung, YS; Wu, Z.; Dao, KL, Determination of Total Organic Carbon in Water by Thermal Combustion-Ion Chromatography. Analytical Chemistry 1996, 68, (13), 2186-2190.

[0069] (5) Direct ICP-OES: Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-OES) method. Data sourced from the literature: Maestre, SE; Mora, J.; Hernandis, V.; Todolí, JL, A System for the Direct Determination of the Nonvolatile Organic Carbon, Dissolved Organic Carbon, and Inorganic Carbon in Water Samples through Inductively Coupled Plasma Atomic Emission Spectrometry. Analytical Chemistry 2003, 75, (1), 111-117.

[0070] (6) MVOG-DBD-AES: Microwave-assisted oxidation vapor generation-dielectric barrier discharge atomic emission spectrometry, data sourced from the literature: Han, B.; Jiang, X.; Hou, X.; Zheng, C., Miniaturized DielectricBarrier Discharge Carbon Atomic Emission Spectrometry with Online Microwave-Assisted Oxidation for Determination of Total Organic Carbon. Analytical Chemistry 2014, 86, (13), 6214-6219.

[0071] (7) DBD-COVG-PD-OES: Dielectric barrier discharge-catalytic oxidation vapor generation-point discharge atomic emission spectrometry, data source: Li, K.; Chen, Z.; He, L.; Hou, X.; Jiang, X., MiniaturizedTOC analyzer using dielectric barrier discharge for catalytic oxidation vapor generation and point discharge optical emission spectrometry. AnalyticaChimica Acta, 2021, 1172: 338683.

[0072] Before sample injection, a certain amount of phosphoric acid is added to the standard solution or sample solution. After stirring for a few minutes, dissolved inorganic carbon is removed, ensuring that the carbon content obtained in the analysis is the total organic carbon content. The persulfate solution and the sample solution are automatically and continuously pumped into the dielectric barrier discharge catalytic oxidation unit via a peristaltic pump. Under the catalytic action of the dielectric barrier discharge micro-plasma, organic carbon can be rapidly and efficiently converted into carbon dioxide. After removing water vapor from the gaseous products through a spiral coil low-temperature water bath and a dryer, the carbon enters the tip discharge micro-plasma and is excited. Quantitative analysis is achieved through the spectral response at the characteristic spectral line of carbon at 193.09 nm. The reaction waste liquid is automatically discharged via a peristaltic pump. When there is no spiral coil cooling, under the same experimental conditions, the atomic emission spectral signal intensity of carbon is only 1 / 3 of that with spiral coil cooling; when there is no dryer, under the same experimental conditions, the atomic emission spectral signal intensity of carbon is only 1 / 5 of that with a dryer. According to experimental research, the concentric coaxial quartz tube DBD structure (quartz outer tube + quartz inner tube) in this invention improves the TOC oxidation rate by more than 50% compared with the conventional planar DBD structure. The micro-plasma excitation capability is strongest when the distance between the two pointed electrodes of the tip discharge is 3 mm; when the electrode distances are 1 mm, 2 mm, 4 mm, 5 mm, and 6 mm, the intensity of the excited 193.09 nm spectral line is 2 / 5, 4 / 5, 3 / 5, 1 / 2, and 1 / 3 of that at a 3 mm distance, respectively.

[0073] Mechanistic studies show that persulfate, under the action of DBD micro-plasma, generates a large number of sulfate radicals and hydroxyl radicals, which have strong oxidizing properties and can rapidly and efficiently oxidize various organic carbons to CO2. However, the presence of persulfate or DBD micro-plasma alone is insufficient for the effective and rapid oxidation of organic carbons. The role of DBD is primarily catalytic, not oxidative. After gaseous CO2 enters the tip discharge micro-plasma, high-energy electrons in the micro-plasma first interact with CO2 molecules through inelastic collisions. This interaction occurs via direct electron excitation dissociation, vibrational excitation dissociation, and Penning dissociation, dissociating the CO2 molecules into fragments such as CO and O. Subsequently, CO molecules further break CO bonds under high-energy electron or high-temperature conditions, completing the atomization of carbon atoms. Finally, the atomized ground-state carbon atoms collide with high-energy electrons and are excited to the excited state. When the excited-state carbon atoms spontaneously return to the ground state, they emit characteristic atomic emission spectra (with the 193.09 nm spectral line as the analytical line), thus enabling the quantitative detection of CO2. This process relies on the unique advantage of tip discharge, which concentrates energy input and generates high-density, high-energy electrons within a tiny space. It can efficiently drive the entire physicochemical process from molecular dissociation to atomic excitation, making it an ideal miniaturized excitation source for atomic emission spectroscopy. Tip discharge microplasma, with its strong localized electric field generated within a tiny space by its electrode tip structure, can highly concentrate energy, exhibiting significant advantages in excitation capability and efficiency. Therefore, compared to direct excitation by DBD microplasma, it can obtain a stronger carbon atom emission spectrum signal intensity. Simultaneously, the excitation region of tip discharge is concentrated near the tip, resulting in a stable plasma state less affected by external factors such as carrier gas flow rate and voltage fluctuations, thus demonstrating superior signal stability. In contrast, DBD microplasma has a larger discharge region and dispersed energy, resulting in relatively limited excitation capability required to generate atomic emission spectra. Furthermore, the plasma state is easily affected by various experimental conditions, leading to relatively insufficient stability. Therefore, tip discharge microplasma outperforms direct DBD microplasma excitation in both signal intensity and stability, making it a more ideal miniaturized excitation source for carbon atom emission spectroscopy.

[0074] This device has the advantages of simple and compact structure, small size, low energy consumption, few auxiliary equipment, convenient operation, high oxidation efficiency, and high sensitivity. It is expected to be developed into a miniaturized or even portable TOC continuous analysis instrument, creating new applications for on-site analysis.

[0075] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A miniaturized device for continuous detection of total organic carbon in water, characterized in that, It includes a continuous automatic sample feeding and waste discharge unit, a dielectric barrier discharge catalytic oxidation unit, a gaseous product pretreatment unit, and a tip discharge atomic emission spectroscopy detection unit; The continuous automatic sample feeding and waste discharge unit includes a first peristaltic pump (1) and a second peristaltic pump (10); The dielectric barrier discharge catalytic oxidation unit includes a quartz outer tube (5), with a first electrode (6) wound around the outside of the quartz outer tube (5); a quartz inner tube (8) is provided inside the quartz outer tube (5), with the rear end of the quartz inner tube (8) closed and the front end open, and a second electrode (7) is provided in the front end opening; the front end of the quartz outer tube (5) is connected to a first peristaltic pump (1), and the rear end is connected to a second peristaltic pump (10), the first peristaltic pump (1) is connected to a persulfate inlet (2) and a sample solution inlet (3); the second peristaltic pump (10) is connected to a waste liquid outlet (9); the rear end of the quartz outer tube (5) is also provided with a gaseous product outlet (11), and the gaseous product outlet (11) is also provided with a branch pipe as a carrier gas inlet (4); The gaseous product pretreatment unit includes a low-temperature water bath device (14) and a dryer (15). One end of the spiral coil (13) in the low-temperature water bath device (14) is connected to the gaseous product outlet (11) at the rear end of the quartz outer tube (5) through a connecting pipe (12), and the other end is connected to the dryer (15). The tip discharge atomic emission spectroscopy detection unit includes an electrode holder (16) located at the outlet of the dryer (15), two opposing tip electrodes (17) are provided on the electrode holder (16), and a CCD spectroscopy detector (19) is provided outside the spectral detection window (18) on the electrode holder (16). Under the action of the first peristaltic pump (1), the persulfate solution and the sample solution enter the dielectric barrier discharge catalytic oxidation unit simultaneously through the persulfate inlet (2) and the sample solution inlet (3), respectively. The waste liquid after the reaction is discharged from the dielectric barrier discharge catalytic oxidation unit through the waste liquid outlet (9) under the action of the second peristaltic pump (10). Persulfate, as an oxidant, rapidly and efficiently converts the organic carbon in the sample into carbon dioxide under the catalytic action of the dielectric barrier discharge micro-plasma in the dielectric barrier discharge catalytic oxidation unit. Argon enters the dielectric barrier discharge catalytic oxidation unit through the carrier gas inlet (4). The gaseous products containing carbon dioxide generated in the dielectric barrier discharge catalytic oxidation unit are transported by argon through the gaseous product outlet (11) and through the connecting pipe (12) through the spiral coil (13) and the dryer (15) placed in the low temperature water bath device (14) to remove water vapor. It then enters the tip discharge atomic emission spectroscopy detection unit to excite the carbon atom emission spectrum. The CCD spectrometer (19) collects the spectral signal through the spectral detection window (18) and obtains the TOC content through data processing.

2. The miniaturized device for continuous detection of total organic carbon in water as described in claim 1, characterized in that, The electrode holder (16) is a hollow cylinder, with two pointed electrodes (17) passing through and fixed on the electrode holder (16); the pointed electrodes (17) generate discharge micro-plasma under high voltage, which excites the atomic emission spectrum of carbon and realizes quantitative analysis.

3. The miniaturized device for continuous detection of total organic carbon in water as described in claim 1, characterized in that, The first electrode (6) and the second electrode (7) of the dielectric barrier discharge catalytic oxidation unit are made of conductive materials. The first electrode (6) and the second electrode (7) are connected to a power supply. Under high voltage, discharge micro-plasma, namely dielectric barrier discharge micro-plasma, is generated.

4. The miniaturized device for continuous detection of total organic carbon in water as described in claim 1, characterized in that, The persulfate oxidant solution is a sodium persulfate solution or a potassium persulfate solution, with a mass fraction of 10% to 15%.

5. A miniaturized method for continuous detection of total organic carbon in water, characterized in that, The apparatus for continuous detection of total organic carbon in water as described in any one of claims 1 to 4 includes the following steps: Step 1: Add 10% to 15% phosphoric acid to the standard solution or sample solution and stir for 5 to 10 minutes to remove dissolved inorganic carbon; Step 2: The 10%~15% persulfate solution and the sample solution or standard solution for removing inorganic carbon are simultaneously introduced into the dielectric barrier discharge catalytic oxidation unit through the sulfate inlet (2) and the sample solution inlet (3) respectively by the first peristaltic pump (1); Step 3: Adjust the argon flow rate to 100 ~ 400 mL / min and enter the dielectric barrier discharge catalytic oxidation unit through the carrier gas inlet (4); Step 4: Turn on the power supply connected to the two pointed electrodes (17) to generate tip discharge micro-plasma; Step 5: Turn on the power supply connected to the first electrode (6) and the second electrode (7) to generate dielectric barrier discharge micro-plasma; Step 6: The waste liquid after reaction in the dielectric barrier discharge catalytic oxidation unit is discharged through the waste liquid outlet 9 by the second peristaltic pump (10); Step 7: Acquire spectral data using a CCD spectral detector (19) and use the characteristic spectral line of carbon at 193.09 nm as the analytical line; Step 8: After the test is completed, turn off the power supply connected to the first electrode (6) and the second electrode (7) and the power supply connected to the two tip electrodes (17) to stop the CCD spectral detector (19) from collecting spectral data. Step 9: Deionized water is pumped into the dielectric barrier discharge catalytic oxidation unit through the sulfate inlet (2) and the sample solution inlet (3) by the first peristaltic pump (1) to rinse the dielectric barrier discharge catalytic oxidation unit, and the rinsed liquid is discharged through the waste liquid outlet (9) by the second peristaltic pump (10).

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