Chromatographically coupled organic carbon detector and detection method

Abstract

The application discloses a kind of chromatography combined organic carbon detector and detection method, belong to chemical analysis field.The chromatography combined organic carbon detector includes microflow reagent filling unit, inorganic carbon removal unit, microfluidic electrochemical oxidation unit, microfluidic ultraviolet oxidation unit and thin film conductivity detection unit connected in sequence, by adding microfluidic electrochemical oxidation unit, when the liquid to be detected flows through the unit, electrochemical reaction occurs on the anode surface, where macromolecules or organic compounds with aromatic structure undergo chain scission or ring-opening reaction, when subsequently entering microfluidic ultraviolet oxidation unit, the effective penetration depth of ultraviolet light in the liquid to be detected is significantly improved, reducing the probability of incomplete oxidation of organic carbon due to light absorption limitation, improving the completeness of ultraviolet mineralization of organic carbon, and thus improving the accuracy and repeatability of quantitative detection results of organic carbon.

Description

Technical Field

[0001] This invention belongs to the field of chemical analysis, and more specifically, relates to a chromatography-coupled organic carbon detector and detection method. Background Technology

[0002] Natural water bodies, urban sewage, and industrial wastewater typically contain complex and diverse dissolved organic matter from various sources, exhibiting significant differences in molecular weight distribution, structural characteristics, and elemental composition. Traditional overall indicators such as chemical oxygen demand (COD), total organic carbon (TOC), and ultraviolet absorbance only reflect the total amount of organic matter or some optical characteristics, failing to reveal the distribution of different molecular weight ranges or structural components and their environmental behavior. Therefore, in water environment research, water treatment process optimization, and pollution source tracing analysis, it is urgently necessary to combine separation techniques for refined component-level characterization of organic matter.

[0003] Size exclusion chromatography (SLC) and other liquid chromatography techniques can effectively separate soluble organic compounds based on differences in molecular size or polarity, and have become important tools for analyzing the molecular weight distribution of organic compounds. By coupling the chromatographic separation unit with a detector, response signals of organic compounds in different molecular weight ranges can be obtained. However, traditional chromatographic detectors, such as ultraviolet detectors, fluorescence detectors, and refractive index detectors, mainly reflect the optical or physical properties of organic compounds. Their detection signals do not have a strict proportional relationship with the carbon content in the organic compounds, making it difficult to directly quantify the organic carbon content of each chromatographic component.

[0004] To achieve quantitative analysis at the elemental level, chromatography-coupled organic carbon detection technologies have been developed in recent years. These technologies involve completely mineralizing dissolved organic carbon in the test liquid into CO2 (which dissolves in water to form H2CO3) after chromatographic separation, followed by quantitative analysis using methods such as nitrogen stripping-infrared detection or transmembrane mass transfer-conductivity detection. Among these methods, photochemical oxidation, such as vacuum ultraviolet oxidation and ultraviolet / persulfate oxidation, is widely used due to its relatively simple structure and fast response speed. For example, Chinese invention patent CN109406705A discloses a liquid chromatography-coupled organic carbon detector and its usage method, which includes a microfluidic reagent injection module, an inorganic carbon removal module, a microfluidic ultraviolet oxidation module, and a CO2 detection subsystem. This modular structure enables continuous detection of organic carbon in the liquid chromatography effluent.

[0005] However, in practical applications, the accuracy of chromatographic-coupled organic carbon detection techniques, as described above or similar existing technologies, largely depends on the complete oxidation of organic carbon. Furthermore, UV-based oxidation is highly dependent on the physicochemical properties of the water sample. For water samples containing high levels of aromatic organic matter, humic substances, or inorganic nitrates, the UV absorbance is often high, limiting the effective penetration depth of UV light in the tested liquid. This leads to reduced oxidant activation efficiency, resulting in incomplete organic carbon mineralization and affecting the accuracy and repeatability of organic carbon quantification results. Summary of the Invention

[0006] 1. The problem to be solved To address the problem of incomplete organic carbon mineralization in existing chromatography-coupled organic carbon detection technologies, this invention provides a chromatography-coupled organic carbon detector based on photoelectric synergistic oxidation. By setting a microfluidic electrochemical oxidation unit before the microfluidic ultraviolet oxidation unit, the organic matter in the liquid to be detected is partially oxidized and its structure is destroyed in advance, thereby improving the organic carbon mineralization efficiency of the microfluidic ultraviolet oxidation unit.

[0007] 2. Technical Solution To solve the above problems, the technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a chromatography-coupled organic carbon detector, comprising a microfluidic reagent dispensing unit, an inorganic carbon removal unit, a microfluidic ultraviolet oxidation unit, and a thin-film conductivity detection unit, and further comprising a microfluidic electrochemical oxidation unit, wherein the liquid to be detected flows sequentially through the microfluidic reagent dispensing unit, the inorganic carbon removal unit, the microfluidic electrochemical oxidation unit, the microfluidic ultraviolet oxidation unit, and the thin-film conductivity detection unit.

[0008] Preferably, the microfluidic electrochemical oxidation unit includes a microfluidic electrochemical unit housing and a microfluidic plate located inside the microfluidic electrochemical unit housing. The microfluidic plate is provided with flow paths, and the inner walls on both sides of the flow paths are respectively provided with an anode and a cathode.

[0009] More preferably, the flow path distribution shape of the microfluidic plate is S-shaped or U-shaped, the flow path width of the microfluidic plate is 0.1-1.0 mm, the flow path depth is 0.1-1.0 mm, and the flow path length is 0.5-4 m.

[0010] More preferably, the microfluidic plate is made of polyetheretherketone (PEEK).

[0011] More preferably, the anode is made of boron-doped diamond, titanium-based tin-antimony, titanium-based lead dioxide, or titanium-based titanium suboxide, and the cathode is made of boron-doped diamond, titanium, stainless steel, or platinum.

[0012] More preferably, the microfluidic electrochemical oxidation unit further includes an absorbance sensor, a current regulation circuit, and a DC power supply. The liquid to be tested flows through the absorbance sensor and then through the microfluidic plate. The absorbance sensor is used to detect the absorbance of the liquid to be tested. The current regulation circuit adjusts the output current density J of the DC power supply according to the absorbance. The current density J is proportional to the absorbance.

[0013] More preferably, the absorbance is the absorbance A of the liquid to be tested to 254nm ultraviolet light. 254 The absorbance A of the liquid to be tested to 320nm ultraviolet light 320 .

[0014] More preferably, the output current density J is: when A 254 When ≤1, J=J0+k1×A 254 ; when A 254 When J > 1, J = J0 + k2 × A 320 Where J0 is 5–30 mA / cm 2 k1 is 20-50 mA / cm 2 k2 is 40-80 mA / cm 2 The k2 is greater than the k1.

[0015] More preferably, the current density J is not greater than 100 mA / cm². 2 .

[0016] A second aspect of the present invention provides a detection method for a chromatography-coupled organic carbon detector according to any embodiment of the first aspect of the present invention, comprising the following steps: S1. The microfluidic reagent dispensing unit adds acid and oxidant to the liquid to be tested according to a set ratio and adjusts the pH value of the liquid to be tested to less than 3. S2. Use an inorganic carbon removal unit to remove inorganic carbon from the liquid to be tested; S3. When the liquid to be tested flows through the microfluidic electrochemical oxidation unit, it comes into full contact with the electrode surface in the flow path to achieve the electrochemical oxidation reaction. S4. The residual organic matter in the liquid to be tested is mineralized into CO2 by a microfluidic ultraviolet oxidation unit; S5. The liquid to be tested flows through the membrane conductivity detection unit. Under the action of the transmembrane mass transfer membrane, CO2 permeates from the sample side into the pure water on the detection side, causing a change in the conductivity of the pure water. The data processing system calculates the organic carbon content in the liquid to be tested based on the correspondence between the conductivity increment and the carbon concentration.

[0017] 3. Beneficial effects Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The chromatographic organic carbon detector provided by this invention adds a microfluidic electrochemical oxidation unit. When the liquid to be tested flows through this unit, an electrochemical reaction occurs on the anode surface, causing chain scission or ring-opening reactions in macromolecules or organic compounds with aromatic structures in the liquid to be tested, reducing the proportion of components that strongly absorb ultraviolet light in the organic system, and achieving pre-enhanced oxidation treatment of the liquid to be tested. When the liquid to be tested subsequently enters the microfluidic ultraviolet oxidation unit, the effective penetration depth of ultraviolet light in the liquid to be tested is significantly improved, the photoactivation efficiency of the oxidant is enhanced, and the active oxide species generated in the electrochemical stage are further excited or transformed into more active free radical species, significantly reducing the probability of incomplete oxidation of organic carbon due to light absorption limitation, improving the completeness of ultraviolet mineralization of organic carbon in this step, and thus improving the accuracy and repeatability of quantitative detection results of organic carbon.

[0018] (2) The chromatographic coupled organic carbon detector provided by the present invention is equipped with an absorbance sensor in the microfluidic electrochemical oxidation unit to detect the absorbance of the liquid to be tested. The current density output by the DC power supply is adjusted by the current regulation circuit so that the current density and absorbance are proportional, realizing the real-time dynamic matching between oxidation intensity and sample optical properties. This allows high absorbance or high concentration components to obtain stronger pre-oxidation, while low concentration components are protected from over-electrolysis. This solves the problem of insufficient oxidation or excessive energy consumption caused by using fixed oxidation power. It balances mineralization efficiency and system stability under different water quality conditions and extends the service life of the electrode.

[0019] (3) The thin-film conductivity detection unit in the chromatography-coupled organic carbon detector provided by this invention has an adjustable pure water flow rate on the detection side, which can change the dilution degree and renewal rate of carbon dioxide in the detection side liquid. Using a lower flow rate when detecting low-concentration samples is beneficial to improving the conductivity response intensity and reducing the detection limit; using a higher flow rate when detecting high-concentration samples is beneficial to avoiding signal saturation, accelerating baseline recovery and widening the detection range, thereby improving the adaptability of the device to samples of different concentrations. Attached Figure Description

[0020] Figure 1 This is a functional framework diagram of the chromatography-coupled organic carbon detector in this invention; Figure 2 This is a schematic diagram of the structure of the chromatography-coupled organic carbon detector in Embodiment 1 of the present invention; Figure 3 The results of the detection of the molecular weight distribution of organic carbon in landfill leachate by the chromatography-coupled organic carbon detector in Example 1 of the present invention; Figure 4 The results of the detection of the molecular weight distribution of organic carbon in the secondary sedimentation tank effluent of a municipal wastewater treatment plant using a chromatography-coupled organic carbon detector in Example 2 of the present invention. Figure 5 This is a functional framework diagram of the chromatography-coupled organic carbon detector in Comparative Example 1 of the present invention; Figure 6 This is a schematic diagram of the structure of the chromatography-coupled organic carbon detector in Comparative Example 1 of the present invention; Figure 7 The results of the detection of the molecular weight distribution of organic carbon in landfill leachate by the chromatography-coupled organic carbon detector in Comparative Example 1 of the present invention are shown. Figure 8 This is a functional framework diagram of the chromatography-coupled organic carbon detector in Comparative Example 2 of the present invention; Figure 9 This is a schematic diagram of the structure of the chromatography-coupled organic carbon detector in Comparative Example 2 of the present invention; Figure 10 The results of the detection of the molecular weight distribution of organic carbon in landfill leachate by the chromatography-coupled organic carbon detector in Comparative Example 2 of the present invention are shown. Figure 11 This is a schematic diagram of the structure of the chromatography-coupled organic carbon detector in Comparative Examples 3 and 4 of the present invention; Figure 12 The results of the detection of the molecular weight distribution of organic carbon in landfill leachate by the chromatography-coupled organic carbon detector in Comparative Example 3 of the present invention are shown. Figure 13 The results of the detection of the molecular weight distribution of organic carbon in landfill leachate using a chromatography-coupled organic carbon detector in Comparative Example 4 of this invention are shown.

[0021] In the diagram: 1. Microfluidic reagent dispensing unit; 101. Acid microfluidic injection pump; 102. Acid storage box; 103. Oxidant microfluidic injection pump; 104. Oxidant storage box; 105. Mixer; 2. Inorganic carbon removal unit; 201. Degassing coil; 202. Degassing unit housing; 203. Vacuum sensor; 204. Speed ​​control circuit; 205. Miniature vacuum pump; 206. CO2 absorption tube; 3. Microfluidic electrochemical oxidation unit; 301. Absorbance sensor; 302. Current control circuit; 303. DC power supply; 304. Microfluidic electrochemical unit housing; 305. Microfluidic plate; 306. Anode; 307. Cathode; 4. Microfluidic UV oxidation unit; 401. Microfluidic UV oxidation unit housing; 402. Microfluidic flow path; 403. UV lamp; 404. UV lamp power supply; 5. Thin-film conductivity detection unit; 501. Transmembrane mass transfer unit housing; 502. Transmembrane mass transfer membrane; 503. Miniature conductivity detector; 504. Pure water storage box; 505. Constant flow water pump. Detailed Implementation

[0022] It should be noted that when a component is referred to as being "mounted" on another component, it can be directly on the other component or the two components can be integrated as one unit; when a component is referred to as being "connected" to another component, it can be directly connected to the other component or the two components can be integrated as one unit. Furthermore, terms such as "upper," "lower," "left," "right," and "middle" used in this specification are merely for clarity of description and are not intended to limit the scope of implementation. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0024] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0025] As used herein, “adjacent” means that two structures or elements are close to each other. Specifically, elements identified as “adjacent” may be adjacent or connected. Such elements may also be close to or near each other without necessarily touching. In some cases, the precision of proximity may depend on the specific context.

[0026] Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as "less than about 4.5," which should be interpreted to include all the values ​​and ranges described above. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0027] Figure 1 The functional framework diagram of the chromatography-coupled organic carbon detector provided by the present invention includes a microfluidic reagent dispensing unit 1, an inorganic carbon removal unit 2, a microfluidic electrochemical oxidation unit 3, a microfluidic ultraviolet oxidation unit 4, and a thin-film conductivity detection unit 5 through which the liquid to be detected flows sequentially. As a preferred embodiment, the units are detachably connected.

[0028] Example 1 Figure 2 This is a structural diagram of the chromatography-coupled organic carbon detector provided in Embodiment 1 of the present invention.

[0029] like Figure 2 As shown, the microfluidic reagent dispensing unit 1 includes an acid microfluidic injection pump 101, an acid storage box 102, an oxidant microfluidic injection pump 103, an oxidant storage box 104, a mixer 105, and connecting tubing. The acid microfluidic injection pump 101 and the oxidant microfluidic injection pump 103 are connected to the acid storage box 102 and the oxidant storage box 104, respectively, to extract the acid and oxidant from the storage boxes and inject them into the mixer 105 to mix with the liquid to be tested. The acid microfluidic injection pump 101 and the oxidant microfluidic injection pump 103 drive a micro-injector via a precision stepper motor-driven screw, achieving continuous quantitative delivery of the acid and oxidant, which adjusts the pH of the liquid to be tested to less than 3. The injection flow rate of the acid and oxidant is 0.2–8 μL / min. The acid is 10%–50% phosphoric acid (volume fraction), and the oxidant is 1%–10% persulfate solution (mass concentration). In this embodiment, the injection flow rate of the acid and oxidant is 2 μL / min, the acid is 30% phosphoric acid by volume, and the oxidant is 5% potassium persulfate solution by mass.

[0030] like Figure 2As shown, the inorganic carbon removal unit 2 includes a degassing coil 201, a degassing unit housing 202, a vacuum sensor 203, a speed control circuit 204, a miniature vacuum pump 205, a CO2 absorption tube 206, and connecting pipes. This unit is used to remove the original inorganic carbon in the liquid to be tested, avoiding background interference to the subsequent quantification of organic carbon. The degassing coil 201 is located inside the degassing unit housing 202. When the liquid to be tested flows through the degassing coil 201, under negative pressure, outside air enters the housing after removing CO2 through the CO2 absorption tube 206, purging the outer wall of the degassing coil 201 and forming a CO2 concentration difference inside and outside the capillary, thereby promoting the outward diffusion of dissolved CO2 in the liquid to be tested and achieving efficient removal. As a preferred embodiment, the degassing coil 201 can be made of a breathable but waterproof capillary wound into a spiral structure. The capillary material is Teflon AF2400 or polydimethylsiloxane (PDMS), with an inner diameter of 0.2–1.0 mm, an outer diameter of 1.0–3.0 mm, and a length of 1–10 m. In this embodiment, the capillary material is Teflon AF2400, the inner diameter is 0.5 mm, the outer diameter is 2.0 mm, and the length is 5 m. The vacuum sensor 203 is connected to the pipeline between the one-way valve and the degassing unit housing 202 via a three-way structure, used to monitor the internal pressure of the housing in real time and transmit the pressure signal to the speed control circuit 204. The speed control circuit 204 automatically adjusts the operating frequency or start / stop state of the miniature vacuum pump 205 based on the difference between the real-time pressure value detected by the vacuum sensor 203 and the preset target vacuum level, forming a closed-loop control system to maintain a stable negative pressure environment inside the degassing unit housing 202. The miniature vacuum pump 205 is connected to the degassing unit housing 202 through a one-way valve and is used to evacuate the inside of the housing. As a preferred embodiment, the relative vacuum level inside the housing is not greater than -80 kPa. In this embodiment, the relative vacuum level inside the degassing unit housing 202 is maintained at less than -85 kPa.

[0031] like Figure 2 As shown, the microfluidic electrochemical oxidation unit 3 includes an absorbance sensor 301, a current control circuit 302, a DC power supply 303, a microfluidic electrochemical unit housing 304, a microfluidic plate 305, an anode 306, a cathode 307, and connecting pipes.

[0032] A microfluidic plate 305 is disposed inside the housing 304 of the microfluidic electrochemical unit. The microfluidic plate 305 has flow paths, and an anode 306 and a cathode 307 are respectively disposed on the inner walls of opposite sides of the flow paths. Both the anode 306 and the cathode 307 are connected to a DC power supply 303. As a preferred embodiment, the anode 306 is made of boron-doped diamond, titanium-based tin-antimony, titanium-based lead dioxide, or titanium-based titanium suboxide, and the cathode 307 is made of boron-doped diamond, titanium, stainless steel, or platinum. In this embodiment, the anode 306 is made of boron-doped diamond, and the cathode 307 is made of titanium.

[0033] The liquid to be tested enters the flow path on the microfluidic plate 305 through a connecting pipe, and is output to the downstream unit after electrochemical oxidation. As a preferred embodiment, the flow path distribution shape of the microfluidic plate 305 is processed into an S-shape or a U-shape using etching technology. The flow path width of the microfluidic plate 305 is 0.1–1.0 mm, the flow path depth is 0.1–1.0 mm, and the flow path length is 0.5–4 m, to increase the electrode contact area and reaction residence time. As a preferred embodiment, the microfluidic plate 305 is made of polyetheretherketone (PEEK). In this embodiment, the microfluidic plate 305 uses a PEEK plate with an etched S-shaped flow path structure, a flow path width of 0.5 mm, a depth of 0.5 mm, and a total length of 2 m.

[0034] The DC power supply 303 is electrically connected to the anode 306 and cathode 307 respectively through the current regulation circuit 302, and is used to provide an adjustable DC current to the electrodes. The current density can be calculated based on the electrode area, so the current density is also adjustable. The output current range of the DC power supply 303 is 0 to 1000 mA, and the output voltage range is 0 to 30 V, to adapt to the electrochemical reaction requirements under different electrode materials and different flow rate conditions.

[0035] An absorbance sensor 301 is located at the inlet side of the microfluidic electrochemical unit housing 304. The liquid to be tested flows through the absorbance sensor 301 and then through the microfluidic plate 305. It is used to perform real-time absorbance detection of the liquid entering the electrochemical reaction channel. The sensor includes an ultraviolet light source, a flow-through detection cell, and a photodiode detector. In this embodiment, LEDs emitting 254±5nm and 320±5nm ultraviolet light are used as the ultraviolet light source. Before entering the electrochemical reaction zone, the liquid to be tested passes through the flow-through detection cell. The detected absorbance signal is transmitted to the current control circuit 302, and two gallium nitride-based photodiodes are used to detect the intensity of ultraviolet light at the corresponding wavelengths, thereby determining the absorbance A of the liquid to 254nm ultraviolet light. 254 and absorbance A to 320nm ultraviolet light 320The absorbance of 254nm ultraviolet light is an important indicator for characterizing common low-concentration organic matter in water. For high-concentration organic matter, the absorbance value of the above wavelength is too high, so the absorbance of 320nm ultraviolet light is used.

[0036] The current regulation circuit 302, based on its signal conditioning and acquisition unit, performs transimpedance amplification, filtering, and analog-to-digital conversion on the absorbance signal to obtain a stable digital detection signal. It then adjusts the current density J output by the DC power supply 303 according to a preset current density control strategy. The output current density J is: Current density J is based on the absorbance sensor 301 detecting A... 254 With A 320 Perform piecewise calculations when A 254 When ≤1, the current density J is calculated according to the formula J=J0+k1×A 254 Perform calculations; when A 254 When the current density J is greater than 1, the formula is J = J0 + k2 × A. 320 Calculations are performed, where J0 is the base current density, and k1 and k2 are proportionality coefficients, with k2 being greater than k1. As a preferred option, J0 is 5–30 mA / cm². 2 k1 is 20-50 mA / cm 2 k2 is 40-80 mA / cm 2 In this embodiment, J0 is set to 20 mA / cm. 2 k1 is taken as 20mA / cm 2 k2 is taken as 40mA / cm 2 To avoid electrode overload and enhanced side reactions, the current density J should not exceed the preset maximum current density of 100 mA / cm². 2 Therefore, the calculated value of the current density J needs to be compared with the preset maximum current density. When the calculated value exceeds the maximum current density, the maximum current density is used as the final output. Through this closed-loop control strategy, the electrochemical oxidation intensity can be dynamically matched with the changes in the concentration of different components during chromatographic separation, achieving adaptive pre-oxidation.

[0037] The microfluidic ultraviolet oxidation unit 4 includes a microfluidic ultraviolet oxidation unit housing 401, a microfluidic flow path 402, an ultraviolet lamp 403, an ultraviolet lamp power supply 404, and connecting pipes. The microfluidic flow path 402 is located inside the microfluidic ultraviolet oxidation unit housing 401 and connects to the outlet of the upstream microfluidic electrochemical oxidation unit 3. It is used to receive the liquid to be tested after electrochemical pre-oxidation treatment and to carry out further oxidation under ultraviolet light irradiation. The microfluidic flow path 402 is a spiral tube wound from a capillary quartz tube, and the ultraviolet lamp 403 is placed at the center of the capillary quartz spiral tube. As a preferred embodiment, the inner diameter of the microfluidic flow path 402 is set to 0.1–1.0 mm, and the channel length is set to 0.5–4 m to increase the light path length and liquid residence time, thereby improving mineralization efficiency. In this embodiment, the microfluidic flow path 402 has an inner diameter of 0.5 mm, an outer diameter of 2.0 mm, and a channel length of 2 m, and is connected to an external pipeline via a PEEK connector. The UV lamp power supply 404 provides a stable operating voltage and current to the UV lamp 403 to ensure the stability of the light output intensity. As a preferred embodiment, the interior of the microfluidic UV oxidation unit housing 401 can be equipped with a reflective layer or optical reflective structure to improve UV light utilization. Simultaneously, the housing structure is a sealed structure to prevent UV leakage and ensure operational safety. In this embodiment, the UV lamp 403 is a 185 nm wavelength vacuum UV lamp.

[0038] like Figure 2 As shown, the thin-film conductivity detection unit 5 includes a transmembrane mass transfer unit housing 501, a transmembrane mass transfer membrane 502, a micro conductivity detector 503, a pure water storage box 504, a constant flow water pump 505, and connecting pipelines. The transmembrane mass transfer membrane 502 is disposed inside the transmembrane mass transfer unit housing 501 and is used to transfer CO2 generated after UV oxidation from the sample side to the pure water on the detection side, achieving selective gas permeation. Fluid on the sample side flows along one side of the membrane, while the detection side is a pure water channel. CO2 permeates through the membrane into the pure water under the drive of the concentration gradient, forming HCO3. - CO3 2-Plasma is used to alter the conductivity of the solution on the detection side. The transmembrane mass transfer membrane 502 is a hydrophobic membrane material that is permeable to air but impermeable to liquid, and can be selected from Teflon AF2400 membrane or PDMS membrane, with a thickness of 50–200 μm. In this embodiment, the transmembrane mass transfer membrane 502 is a Teflon AF2400 membrane with a thickness of 75 μm. A miniature conductivity detector 503 is disposed on the flow path on the detection side to detect changes in the conductivity of pure water in real time and outputs the conductivity signal to the data processing system to calculate the organic carbon content in the sample based on the conductivity increment. A pure water storage box 504 is used to store pure water on the detection side, and a constant flow water pump 505 is used to drive pure water to form a stable flow on the detection side to ensure that the concentration gradient in the transmembrane mass transfer process continues and improves the mass transfer efficiency. The constant flow pump 505 is a flow-adjustable constant flow driven pump with an output flow rate of 0.02–2.0 mL / min, preferably 0.05–1.0 mL / min, which can be adjusted according to the concentration range of the sample to be tested or the intensity of the detection signal. As a preferred embodiment, a lower flow rate of 0.02–0.20 mL / min is used for low-concentration sample detection to reduce the dilution effect of the detection-side liquid on the permeated components and improve the conductivity response intensity; a higher flow rate of 0.20–2.0 mL / min is used for high-concentration sample detection to reduce the risk of signal saturation, accelerate the replenishment of the detection-side liquid, and expand the detection linear range. In this embodiment, the output flow rate of the constant flow pump 505 is 0.5 mL / min.

[0039] The method of using the chromatography-coupled organic carbon detector provided in this embodiment is as follows: The microfluidic reagent dispensing unit 1 simultaneously adds an acid and an oxidant to the liquid to be tested according to a set ratio, making the pH value of the liquid to be tested <3; the original inorganic carbon in the sample is removed in the inorganic carbon removal unit 2; the fluid after inorganic carbon removal enters the microfluidic electrochemical oxidation unit 3, where, under real-time monitoring by the absorbance sensor 301, the output of the DC power supply 303 is dynamically adjusted according to a preset current density control strategy, causing the organic matter to undergo an electrochemical oxidation reaction on the surface of the anode 306, reducing the sample absorbance and generating a certain amount of active species; the liquid to be tested after electrochemical pre-oxidation enters the microfluidic ultraviolet oxidation unit 4, where, under the irradiation of the ultraviolet lamp 403, the oxidant and the electrochemically generated active species are fully activated for deep oxidation, allowing the residual organic matter to be fully mineralized to generate CO2; the liquid to be tested enters the membrane conductivity detection unit 5, where, under the action of the transmembrane mass transfer membrane 502, CO2 permeates from the sample side into the pure water on the detection side, forming HCO3 on the detection side. - CO3 2- Plasma causes changes in the conductivity of pure water; a micro conductivity detector 503 detects the conductivity change signal of the solution on the detection side in real time, and the data processing system calculates the organic carbon content in the sample based on the correspondence between the conductivity increment and the carbon concentration.

[0040] The chromatographic organic carbon detector provided in this embodiment was coupled with a size exclusion liquid chromatography (HPLC) system. The size exclusion HPLC system was manufactured by Agilent Technologies, Inc., and included a quaternary pump, autosampler, column oven, and size exclusion column (model HW-50S). The mobile phase was phosphate buffer solution, and the flow rate was 1 mL / min. The analyzed water sample was leachate from a landfill treated with a 0.45 μm filter membrane; the injection volume was 500 μL. The molecular weight distribution of organic carbon was determined as follows: Figure 3 As shown, organic compounds with elution times between 15 and 22 min are defined as macromolecular protein-like biological components, organic compounds with elution times between 22 and 37 min are defined as humic acids, organic compounds with elution times between 37 and 42 min are defined as fulvic acids, organic compounds with elution times between 42 and 49 min are defined as building block-type substances, and substances with elution times after 49 min are defined as small molecule substances.

[0041] Furthermore, the current density control system used in this embodiment results in low overall energy consumption, with each batch of samples consuming approximately 6 watt-hours. The adaptive current density control system avoids excessive oxidation and side reaction deposition on the electrode surface, effectively reducing electrode surface wear and extending electrode lifespan. The entire instrument requires no electrode replacement or complex maintenance within 12 months of operation.

[0042] Example 2 This embodiment is basically the same as Embodiment 1, except that the water sample analyzed is the effluent from the secondary sedimentation tank of a municipal wastewater treatment plant that has been treated with a 0.45 μm filter membrane. The molecular weight distribution of organic carbon is as follows: Figure 4 As shown, organic matter with a peak elution time of 15–24 min is defined as macromolecular protein-like biological components; organic matter with a peak elution time of 24–36 min is defined as humic acid; organic matter with a peak elution time of 36–41 min is defined as fulvic acid; organic matter with a peak elution time of 41–48 min is defined as building block-like substances; and substances with a peak elution time after 48 min are defined as small molecule substances. The landfill leachate used in Example 1 had a higher concentration, while the effluent from the secondary sedimentation tank used in this example had a lower concentration. Therefore, the chromatographically coupled organic carbon detector used in Example 1 showed good detection results for both high and low concentration samples.

[0043] Comparative Example 1 This comparative example provides a chromatography-coupled organic carbon detection system, whose overall structure, operating parameters and operating conditions are basically the same as those in Example 1. The only difference is that the microfluidic electrochemical oxidation unit 3 is not set up, and the liquid to be detected directly enters the microfluidic ultraviolet oxidation unit 4 after the inorganic carbon removal unit 2.

[0044] Figure 5and Figure 6 These are the functional framework diagram and structural schematic diagram of the chromatography-coupled organic carbon detector used in this comparative example. Figure 5 and Figure 6 As shown, after the liquid to be tested is added with acid and oxidant through the microfluidic reagent dispensing unit 1, it first enters the inorganic carbon removal unit 2 to remove the original inorganic carbon. Then, it directly enters the microfluidic ultraviolet oxidation unit 4 through the connecting pipeline for oxidation treatment under ultraviolet lamp 403 irradiation. The CO2 generated after ultraviolet oxidation enters the thin-film conductivity detection unit 5 for detection. The detection results of its organic carbon molecular weight distribution are shown below. Figure 7 As shown. By Figure 7 It can be seen that the chromatographic peak area obtained in this comparative example is significantly lower than that obtained in Example 1, indicating that the organic carbon mineralization is incomplete. This is because without electrochemical oxidation, the water sample has a high UV absorbance, and the conductivity response produced by UV oxidation alone is weak.

[0045] Comparative Example 2 This comparative example provides a chromatography-coupled organic carbon detection system, whose overall structure, operating parameters and operating conditions are basically the same as those in Example 1. The only difference is that the microfluidic ultraviolet oxidation unit 4 is not set up, and the liquid to be detected directly enters the thin film conductivity detection unit 5 after flowing through the microfluidic electrochemical oxidation unit 3.

[0046] Figure 8 and Figure 9 These are the functional framework diagram and structural schematic diagram of the chromatography-coupled organic carbon detector used in this comparative example. Figure 8 and Figure 9 As shown, after the liquid to be tested is fed with acid and oxidant through the microfluidic reagent dispensing unit 1, it first enters the inorganic carbon removal unit 2 to remove the original inorganic carbon. Then it enters the microfluidic electrochemical oxidation unit 3 for pre-oxidation under electrochemical oxidation conditions. After electrochemical oxidation, the liquid to be tested is no longer subjected to deep UV oxidation, but instead directly enters the thin-film conductivity detection unit 5 through a connecting pipe for detection. The detection results of its organic carbon molecular weight distribution are shown below. Figure 10 As shown. By Figure 10It can be seen that the chromatographic peak area obtained in this comparative example is significantly lower than that obtained in Example 1, indicating that the organic carbon mineralization is incomplete. This is because the degree of mineralization is limited when electrochemical oxidation is used alone. Furthermore, a significant abnormal response peak was observed at a retention time of approximately 60–70 min, which did not correspond to the chromatographically separated components. Analysis shows that under chlorinated water conditions, free chlorine and other oxidizing substances may be generated during electrochemical oxidation. These substances can permeate through the transmembrane mass transfer membrane 502 into the detection side, causing changes in conductivity signals and interfering with the accuracy and stability of the organic carbon detection results. In contrast, Example 1, by setting up a microfluidic ultraviolet oxidation unit 4 after electrochemical pre-oxidation, further transforms or decomposes the aforementioned oxidizing substances, effectively eliminating the abnormal response peak and improving the accuracy and repeatability of the detection results.

[0047] Comparative Example 3 This comparative example provides a chromatography-coupled organic carbon detection system, whose overall structure, operating parameters, and operating conditions are basically the same as those in Example 1, except that the absorbance sensor 301 and the current control circuit 302 are not included (e.g., ...). Figure 11 As shown), the current density is fixed at 20 mA / cm². 2 When the same sample is analyzed under the same chromatographic conditions, the molecular weight distribution of organic carbon is as follows: Figure 12 As shown. By Figure 12 It is evident that the conductivity response of the system treated with a fixed lower current density is significantly lower than that of Example 1, and the obtained chromatographic peak area is smaller, indicating that the organic carbon was not completely mineralized. When processing recalcitrant or large molecular organic compounds, the effect of electrochemical oxidation at low current densities is limited, resulting in low chromatographic peaks and affecting the accuracy and repeatability of quantitative results.

[0048] Comparative Example 4 This comparative example provides a chromatography-coupled organic carbon detection system, whose overall structure, operating parameters, and operating conditions are basically the same as those in Example 1, except that the absorbance sensor 301 and the current control circuit 302 are not included (e.g., ...). Figure 11 As shown), the current density is fixed at 60 mA / cm². 2 When the same sample is analyzed under the same chromatographic conditions, the molecular weight distribution of organic carbon is as follows: Figure 13 As shown. By Figure 13 It is evident that while the system with a fixed high current density achieved a strong conductivity response, its overall energy consumption was high, approximately 10 watt-hours per batch of samples. Furthermore, the prolonged high current density resulted in severe oxidation deposition on the electrode surface, leading to a short electrode lifespan and requiring electrode replacement and system maintenance every four months, thus affecting the stability of long-term detection.

[0049] The above description provides an illustrative overview of the present invention and its embodiments. This description is not restrictive, and the embodiments shown are merely one example of the invention's implementation. Actual implementations are not limited to these examples. Therefore, if those skilled in the art are inspired by this description and design similar implementations and examples without departing from the spirit of the invention, such designs should fall within the scope of protection of the present invention.

Claims

1. A chromatography-coupled organic carbon detector, comprising a microfluidic reagent dispensing unit (1), an inorganic carbon removal unit (2), a microfluidic ultraviolet oxidation unit (4), and a thin-film conductivity detection unit (5), characterized in that: It also includes a microfluidic electrochemical oxidation unit (3), and the liquid to be tested flows sequentially through a microfluidic reagent dispensing unit (1), an inorganic carbon removal unit (2), a microfluidic electrochemical oxidation unit (3), a microfluidic ultraviolet oxidation unit (4), and a thin film conductivity detection unit (5). The liquid to be tested contains macromolecules or organic compounds with aromatic structures. The microfluidic electrochemical oxidation unit (3) includes a microfluidic electrochemical unit housing (304) and a microfluidic plate (305) located inside the microfluidic electrochemical unit housing (304). The microfluidic plate (305) is provided with flow paths, and the inner walls on both sides of the flow paths are respectively provided with an anode (306) and a cathode (307). The microfluidic electrochemical oxidation unit (3) further includes an absorbance sensor (301), a current regulation circuit (302), and a DC power supply (303). The DC power supply (303) is electrically connected to the anode (306) and the cathode (307). The liquid to be tested flows through the absorbance sensor (301) and then through the microfluidic plate (305). The absorbance sensor (301) is used to detect the absorbance of the liquid to be tested. The current regulation circuit (302) adjusts the output current density J of the DC power supply (303) according to the absorbance. The absorbance is the absorbance A of the liquid to be tested for 254nm ultraviolet light. 254 The absorbance A of the liquid to be tested to 320nm ultraviolet light 320 The output current density J is: when A 254 When ≤1, J=J0+k1×A 254 ; when A 254 When J > 1, J = J0 + k2 × A 320 Where J0 is 5–30 mA / cm 2 k1 is 20-50 mA / cm 2 k2 is 40-80 mA / cm 2 The k2 is greater than the k1.

2. The chromatographic coupled organic carbon detector according to claim 1, characterized in that: The flow path distribution shape of the microfluidic plate (305) is S-shaped or U-shaped. The flow path width of the microfluidic plate (305) is 0.1-1.0 mm, the flow path depth is 0.1-1.0 mm, and the flow path length is 0.5-4 m.

3. The chromatographic coupled organic carbon detector according to claim 1, characterized in that: The microfluidic plate (305) is made of polyetheretherketone.

4. The chromatographic coupled organic carbon detector according to claim 1, characterized in that: The anode (306) is made of boron-doped diamond, titanium-based tin-antimony, titanium-based lead dioxide, or titanium-based titanium suboxide, and the cathode (307) is made of boron-doped diamond, titanium, stainless steel, or platinum.

5. The chromatographic coupled organic carbon detector according to any one of claims 1 to 4, characterized in that: The current density J is not greater than 100 mA / cm² 2 .

6. The detection method of the chromatographic coupled organic carbon detector according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1, Microfluidic reagent dispensing unit (1) adds acid and oxidant to the liquid to be tested according to the set ratio, and adjusts the pH value of the liquid to be tested to less than 3; S2. Use inorganic carbon removal unit (2) to remove inorganic carbon from the liquid to be tested; S3. When the liquid to be tested flows through the microfluidic electrochemical oxidation unit (3), it comes into full contact with the electrode surface in the flow path to achieve the electrochemical oxidation reaction. S4. The residual organic matter in the liquid to be tested is mineralized into CO2 by the microfluidic ultraviolet oxidation unit (4); S5. The liquid to be tested flows through the membrane conductivity detection unit (5). Under the action of the transmembrane mass transfer membrane (502), CO2 passes through the membrane from the sample side into the pure water on the detection side, causing a change in the conductivity of the pure water. The data processing system calculates the organic carbon content in the liquid to be tested based on the correspondence between the conductivity increment and the carbon concentration.

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