Heavy metal trace detection electrode and preparation method and application thereof

Abstract

This invention discloses a trace heavy metal detection electrode, its preparation method, and its application, belonging to the field of detection electrodes. The invention uses a copper-gold wire composite conductor as a substrate, encapsulated within a borosilicate glass capillary. An organic insulating film is formed using o-phenylenediamine to seal the micro-gaps. After activation with sulfuric acid solution, a mercury composite material is electrodeposited to obtain the detection electrode. This electrode exhibits low relative standard deviation of detection results after repeated use. After detection, only constant potential cleaning is required to effectively remove residual heavy metals and degraded films from the electrode surface. Mercury composite material is then redeposited, eliminating the need for manual polishing and fundamentally eliminating the memory effect.

Description

Technical Field

[0001] This invention relates to the field of detection electrodes, specifically to a heavy metal trace detection electrode, its preparation method, and its application. Background Technology

[0002] With the continuous advancement of industrialization, heavy metal pollution problems such as cadmium, lead, and copper have become increasingly prominent, posing a serious public health challenge to the ecological environment and human health. Due to the persistent nature of these elements, their bioaccumulation, and high toxicity, their detection limit is at the ppb level. Currently, the detection of heavy metals in water bodies mainly relies on large-scale mass spectrometry or spectroscopic instruments. While these methods can achieve high-precision detection, the equipment is expensive, making large-scale deployment difficult. Furthermore, complex pretreatment procedures are required before detection, resulting in cumbersome and time-consuming processes.

[0003] To address this issue, existing technologies have developed suspended mercury drop electrodes, which offer high sensitivity. However, mercury is highly toxic, and the electrodes have extremely poor mechanical stability, making them unsuitable for integration into portable instruments and failing to meet the needs of in-situ field testing.

[0004] CN113376231A discloses a method for fabricating a biosensor microelectrode, which includes the following steps: printing a carbon paste conductive layer, overprinting an Ag / AgCl reference electrode, overprinting an electrode insulating layer, electroplating a bismuth film on the surface, rinsing clean, drying, and packing into a sealed bag.

[0005] CN117110392A discloses an electrochemical sensor based on a copper-based multimetal microelectrode, its preparation method, and its application method. The electrochemical sensor is a three-electrode system: a platinum wire electrode as the counter electrode, a saturated calomel electrode as the reference electrode, and a copper microelectrode as the working electrode. Gold nanoparticles are deposited on the surface of the copper microelectrode using a one-step electrochemical method. The preparation of the working electrode includes the following steps: selecting or preparing a copper microelectrode; employing a three-electrode system with a platinum wire as the counter electrode, a saturated calomel electrode as the reference electrode, and the copper microelectrode as the working electrode; and depositing gold nanoparticles on the surface of the copper microelectrode using an electrochemical method.

[0006] However, existing bare gold electrodes have extremely low hydrogen evolution overpotentials. In slightly acidic water samples, when the reduction potential is relatively negative, a violent hydrogen evolution reaction occurs, generating a large number of microbubbles and extremely high cathode background current, which directly masks the leaching peak of cadmium (Cd) and affects the accuracy of detection. When detecting copper (Cu), bismuth film electrodes are prone to irreversible metallurgical interactions with copper, forming intermetallic compounds. This results in severe overlap of the leaching peaks of copper and bismuth, making it impossible to detect multiple heavy metals.

[0007] Therefore, existing detection methods and electrodes still have problems that urgently need to be solved, such as low detection sensitivity, susceptibility to interference, and severe memory effect after use. Summary of the Invention

[0008] This invention provides a heavy metal trace detection electrode, its preparation method, and its application. After coating with an organic film, electrodeposition is performed to deposit mercury and COF materials to prepare a trace / ultra-element detection electrode. The electrode does not produce a memory effect after multiple uses, has a low detection limit, and does not require manual polishing after detection, thus improving the electrode's utilization efficiency.

[0009] This invention provides a heavy metal trace detection electrode, wherein the detection limit for lead is ≤0.005 ppb and the detection limit for cadmium is ≤0.01 ppb; the relative standard deviation of the heavy metal trace detection electrode after repeated use is ≤3.92%.

[0010] The heavy metal trace detection electrode is obtained by depositing a polymer insulating film in a borosilicate glass capillary after copper and gold wires are combined, and then depositing mercury composite material through an electrochemical workstation. The mercury composite material includes mercury and COF material.

[0011] The present invention also provides a method for preparing the aforementioned heavy metal trace detection electrode, comprising the following steps: Step 1: After cleaning the borosilicate glass capillary, heat it and draw one end of the borosilicate glass capillary into an extremely fine conical tip shape with a rapidly narrowed inner diameter. Step 2: Using copper wire as the lead wire and gold wire as the working wire, the copper wire and gold wire are bonded together with nano silver glue, and then dried and cured to obtain a composite wire. Step 3: Insert the composite wire into the borosilicate glass capillary from Step 1, so that the composite wire extends from the conical tip. Heat the conical tip to melt and seal the tip of the borosilicate glass capillary with the composite wire. Connect the other end of the borosilicate glass capillary to a copper rod that matches the inner diameter of the borosilicate glass capillary. Connect the copper rod to the rear end of the copper wire to obtain the composite microelectrode precursor. Step 4: After grinding the tip of the electrode material flat to expose the gold wire end face, ultrasonically clean it, then place it in an organic electrolyte and perform cyclic voltammetry scanning. After the scanning is completed, bake and solidify to obtain the organic composite electrode material. Step 5: Place the organic composite electrode material in an activation solution and activate it using cyclic voltammetry. After activation, place the electrode in a solution containing mercury composite material for electrodeposition to obtain the heavy metal trace detection electrode.

[0012] Furthermore, the borosilicate glass capillary in step 1 has a length of 3-5 cm and an inner diameter of 0.54-0.60 mm.

[0013] Furthermore, the borosilicate glass capillary in step 1 has a purity of ≥99%, wherein the SiO2 content is 70-90%.

[0014] Furthermore, the heating temperature in step 1 is 740-780℃.

[0015] Furthermore, the inner diameter of the conical tip in step 1 is 20-50 μm.

[0016] Furthermore, the copper wire in step 2 has a length of 3-5 cm and a diameter of 0.4-0.6 mm.

[0017] Furthermore, the gold wire in step 2 has a length of 1-2 cm and a diameter of 22-28 μm.

[0018] Furthermore, the purity of the gold wire in step 2 is ≥99.9%.

[0019] Furthermore, in step 2, the silver particles in the nano-silver paste have a particle size of 20-100 nm and a silver concentration of 0.1-0.3 mg / mL.

[0020] Furthermore, the drying temperature in step 2 is 95-120℃, and the curing time is 12-20 min.

[0021] Furthermore, the length of the extension in step 3 is 1-1.5 cm.

[0022] Furthermore, the heating temperature in step 3 is 800-950℃.

[0023] Furthermore, the ultrasonic cleaning solution in step 4 is 95% ethanol and 99% acetone, and the process involves sequential cleaning.

[0024] Furthermore, in step 4, the frequency of the ultrasound is 50-60 kHz, and the cleaning time is 5-10 min.

[0025] Furthermore, the organic electrolyte in step 4 is an aqueous solution containing 0.05 mol o-phenylenediamine and 0.2 mol sulfuric acid.

[0026] Furthermore, in step 4, the voltage of the cyclic voltammetry scan is -1.6V to +1.6V, the scan speed is 10-25mV / s, and the number of scans is 30-50.

[0027] Furthermore, the baking temperature in step 4 is 120-150℃, and the curing time is 10-20 minutes.

[0028] Furthermore, the baking and curing process in step 4 is repeated 2-5 times.

[0029] Furthermore, the activation solution in step 5 is an aqueous solution containing 0.5 mol of sulfuric acid.

[0030] Furthermore, the activation voltage in step 5 is -1.6V to +1.6V.

[0031] Furthermore, in step 5, the cyclic voltammetry scanning speed is 10-25 mV / s, and the number of scans is 10-20.

[0032] Furthermore, the mercury composite material in step 5 includes mercury and COF material.

[0033] Furthermore, the concentration of the COF material in the solution containing the mercury composite material is 100-200 mg / L.

[0034] Furthermore, the concentration of mercury in the solution containing the mercury composite material is 250-300 mg / L.

[0035] Furthermore, in step 5, the deposition voltage is -0.7V and the deposition time is 20-30s.

[0036] The present invention also provides a method for applying the aforementioned heavy metal trace detection electrode, comprising the following steps: The heavy metal trace detection electrode is placed in the test solution to detect the lead and cadmium content. After the detection is completed, the heavy metal trace detection electrode is kept in the test solution, and a constant voltage is set to clean the electrode. After the mercury composite material is redeposited, the test solution is detected again.

[0037] Furthermore, the pH value of the test solution is 4.5-5.

[0038] Furthermore, the test solution contains 0.02-0.05 mol / L ascorbic acid.

[0039] Furthermore, the concentration of lead in the test solution is ≥0.001 μg / L, and the concentration of cadmium is ≥0.001 μg / L.

[0040] Furthermore, the detection voltage is -1.0V, and the enrichment time is 200-300s.

[0041] Furthermore, the constant voltage range is +0.6V to +0.7V, and the duration is 30-60s.

[0042] The beneficial effects of this invention are: This invention uses a copper and gold composite wire as a substrate, coated with an organic film, followed by activation and deposition of a mercury-COF composite material, significantly improving the sensitivity and anti-interference capability of heavy metal detection. The porous structure and high specific surface area of ​​the COF material provide uniform loading sites for the mercury film, enhancing its enrichment capacity for lead and cadmium ions, far superior to traditional bismuth film electrodes and bare gold electrodes, meeting the detection requirements for ultra-trace heavy metals. Simultaneously, the organic film coating process in this invention fills the tiny gaps between the composite wire and the capillary, improving stability and minimizing deviation during the detection process. This invention utilizes an electrochemical workstation for electrode coating (organic film), deposition (mercury composite material), and constant voltage cleaning after detection, eliminating the need for manual polishing, increasing the automation level of detection, and making it suitable for industrial production. Attached Figure Description

[0043] Figure 1 This is a differential pulse voltammetry detection diagram of lead using the heavy metal trace detection electrode described in Example 1. Figure 2 This is a differential pulse voltammetry detection diagram of cadmium using the heavy metal trace detection electrode described in Example 1. Figure 3 This is the standard curve for the detection of lead using the heavy metal trace detection electrode described in Example 1. Figure 4 This is the standard curve for cadmium detection using the heavy metal trace detection electrode described in Example 1. Figure 5 This is a detailed view of the tip of the heavy metal trace detection electrode described in Embodiment 2. Figure 6 This is a cross-sectional view of the tip of the heavy metal trace detection electrode described in Example 2. Figure 7 This is a scanning electron microscope image of the heavy metal trace detection electrode after deposition in Example 3 of this embodiment; Figure 8 This is an anti-interference test diagram of the heavy metal trace detection electrode for detecting lead described in Example 3 of this embodiment; Figure 9 This is an anti-interference test diagram of the heavy metal trace detection electrode for cadmium detection described in Example 3 of this embodiment; Figure 10 This is a test graph showing the relative standard deviation of the heavy metal trace detection electrode described in Example 3. Figure 11 This is a linear scan voltammetric test graph of the heavy metal trace detection electrode after cleaning, as described in Example 6 of this embodiment. Figure 12 The cyclic voltammetry test results for the electrodes in Comparative Example 3 and Example 1 are shown below. Figure 13 This is a test chart showing the relative standard deviation after detection by the 12 heavy metal trace detection electrodes described in this invention. Detailed Implementation

[0044] The invention will be described in detail below with reference to the embodiments: This invention provides a heavy metal trace detection electrode, its preparation method, and its application. After coating with an organic film, electrodeposition is performed to deposit mercury and COF materials to prepare a trace / ultra-element detection electrode. The electrode does not produce a memory effect after multiple uses, has a low detection limit, and does not require manual polishing after detection, thus improving the electrode's utilization efficiency.

[0045] Example 1 This embodiment provides a method for preparing a trace heavy metal detection electrode, including the following steps: Step 1: After cleaning a 3cm long borosilicate glass capillary (99.99% purity, 80% SiO2 content), heat it to 750℃ in a microelectrode pulling instrument to draw one end of the borosilicate glass capillary into an extremely fine conical tip shape with an inner diameter that is abruptly reduced to 50μm. Step 2: Use a 3cm long copper wire with a diameter of 0.5mm as the lead wire and a 1cm long gold wire with a diameter of 25μm (purity ≥99.9%) as the working wire. After bonding the copper wire and the gold wire with nano silver glue (silver particles with a particle size of 50nm and a silver concentration of 0.1mg / mL), place them at 100℃ for 15min to cure, and obtain a composite wire. Step 3: Insert the composite wire into the borosilicate glass capillary tube from Step 1, allowing the composite wire to extend 1 cm from the conical tip. Heat the conical tip with an oxyhydrogen flame gun to a temperature of 850°C to soften the tip of the borosilicate glass capillary tube and wrap it around the extended portion of the composite wire, thus melting and sealing the composite wire to the borosilicate glass capillary tube. Connect a copper rod with an inner diameter adapted to the borosilicate glass capillary tube to the other end of the borosilicate glass capillary tube. Connect the copper rod to the rear end of the copper wire to obtain the electrode material. Step 4: After grinding the tip of the electrode material flat to expose the gold wire end face, it is ultrasonically cleaned with 95% ethanol and 99% acetone at 50kHz for 5 minutes. Then, it is placed in 10mL of aqueous solution containing 0.05mol o-phenylenediamine and 0.2mol sulfuric acid. Cyclic voltammetry is performed at a speed of 20mV / s under a voltage of -1.6V to +1.6V, with 50 scans. After the scan, it is baked at 120℃ for 20 minutes for curing. The scanning and curing process is repeated 3 times. The polymer insulating film spontaneously undergoes anodic oxidation electropolymerization at the micro-gap of the metal edge to obtain the organic composite electrode material. Step 5: Place the organic composite electrode material in 10 mL of an aqueous solution containing 0.5 mol sulfuric acid, and perform cyclic voltammetry scanning at a rate of 20 mV / s under a voltage of -1.6 V to +1.6 V for 10 scans to activate it. Place the activated electrode in 10 mL of an aqueous solution containing 100 mg / L COF material and 300 mg / L mercury, and deposit it under a voltage of -0.7 V for 20 s to obtain the heavy metal trace detection electrode.

[0046] This embodiment also provides a method for applying the aforementioned heavy metal trace detection electrode, including the following steps: The heavy metal trace detection electrode was placed in 10 mL of pure water containing 0.02 mol / L ascorbic acid at pH 4.5. Lead solution was added dropwise to the pure water using the standard addition method, with concentrations ranging from 0.005 μg / L to 20 μg / L. Differential pulse voltammetry was used for detection during the addition process, with a constant voltage of -1.0 V and an enrichment time of 200 s. A standard curve for lead was obtained. The same method was used to obtain a standard curve for cadmium (cadmium concentrations ranging from 0.01 μg / L to 100 μg / L). The detection limits for lead and cadmium were determined to be 0.005 ppb and 0.01 ppb, respectively. After the detection is completed, the heavy metal trace detection electrode is kept in the test solution. The potential is set to +0.6V and maintained for 50 seconds to clean the electrode, remove the heavy metal impurities accumulated inside the heavy metal trace detection electrode and the degraded film on the surface. After repeating the deposition process in step 5, it can be used again.

[0047] like Figure 1 The graph shows the differential pulse voltammetry detection of lead using the heavy metal trace detection electrode described in Example 1. The lines in the graph, from bottom to top, represent the detection curves for lead concentrations ranging from 0.005 μg / L to 20 μg / L. As can be seen from the graph, the current increases with the increase of lead concentration, proving that the detection method conforms to the linear regression curve equation. Furthermore, even at a lead concentration of 0.005 μg / L, a clear dissolution peak can still be observed in the curve, and the baseline is stable, indicating low background interference. The dissolution peak positions of the lines in the graph are consistent, indicating that the detection method has good reproducibility.

[0048] like Figure 2The graph shows the differential pulse voltammetry detection of cadmium using the heavy metal trace detection electrode described in Example 1. The lines in the graph, from bottom to top, represent the detection curves for cadmium concentrations ranging from 0.01 μg / L to 100 μg / L. As can be seen from the graph, the current increases with the increase of cadmium concentration, proving that the detection method conforms to the standard curve equation. Furthermore, even at a cadmium concentration of 0.01 μg / L, a clear dissolution peak can still be observed in the curve, and the baseline is stable, indicating low background interference. The dissolution peaks of the lines in the graph are in the same position, indicating that the detection method has good reproducibility.

[0049] like Figure 3 The standard curve for lead detection using the heavy metal trace detection electrode described in Example 1 is given by I. The equation for the standard curve of lead is derived from the graph and data. p =0.0362c + 0.0558, coefficient of determination R 2 It is 0.993.

[0050] like Figure 4 The standard curve for cadmium detection using the heavy metal trace detection electrode described in Example 1 is given by I. The equation for the cadmium standard curve is derived from the graph and data. p =0.0086c + 0.0817, coefficient of determination R 2 It is 0.995.

[0051] Example 2 This embodiment provides a method for preparing a trace heavy metal detection electrode, including the following steps: Step 1: After cleaning a 3cm long borosilicate glass capillary (99.99% purity, 80% SiO2 content), heat it to 750℃ in a microelectrode pulling instrument to draw one end of the borosilicate glass capillary into an extremely fine conical tip shape with an inner diameter that is abruptly reduced to 50μm. Step 2: Use a 3cm long copper wire with a diameter of 0.5mm as the lead wire and a 1cm long gold wire with a diameter of 25μm (purity ≥99.9%) as the working wire. After bonding the copper wire and the gold wire with nano silver glue (silver particles with a particle size of 50nm and a silver concentration of 0.1mg / mL), place them at 100℃ for 15min to cure, and obtain a composite wire. Step 3: Insert the composite wire into the borosilicate glass capillary tube from Step 1, allowing the composite wire to extend 1 cm from the conical tip. Heat the conical tip with an oxyhydrogen flame gun to a temperature of 850°C to soften the tip of the borosilicate glass capillary tube and wrap it around the extended portion of the composite wire, thus melting and sealing the composite wire to the borosilicate glass capillary tube. Connect a copper rod with an inner diameter adapted to the borosilicate glass capillary tube to the other end of the borosilicate glass capillary tube. Connect the copper rod to the rear end of the copper wire to obtain the electrode material. Step 4: After grinding the tip of the electrode material flat to expose the gold wire end face, it is ultrasonically cleaned with 95% ethanol and 99% acetone at 50kHz for 5 minutes. Then, it is placed in 10mL of aqueous solution containing 0.05mol o-phenylenediamine and 0.2mol sulfuric acid. Cyclic voltammetry is performed at a speed of 20mV / s under a voltage of -1.6V to +1.6V, with 50 scans. After the scan, it is baked at 120℃ for 20 minutes for curing. The scanning and curing process is repeated 3 times. The polymer insulating film spontaneously undergoes anodic oxidation electropolymerization at the micro-gap of the metal edge to obtain the organic composite electrode material. Step 5: Place the organic composite electrode material in 10 mL of an aqueous solution containing 0.5 mol sulfuric acid, and perform cyclic voltammetry scanning at a rate of 20 mV / s under a voltage of -1.6 V to +1.6 V for 10 scans to activate it. Place the activated electrode in 10 mL of an aqueous solution containing 100 mg / L COF material and 300 mg / L mercury, and deposit it under a voltage of -0.7 V for 20 s to obtain the heavy metal trace detection electrode.

[0052] This embodiment also provides a method for applying the aforementioned heavy metal trace detection electrode, including the following steps: The heavy metal trace detection electrode was placed in 10 mL of pure water containing 0.02 mol / L ascorbic acid at pH 4.5, and detection was performed using the differential pulse voltammetry method as described in Example 1. The concentration of lead solution added was set from 0.001 μg / L to 0.005 μg / L, and the concentration of cadmium solution added was set from 0.005 μg / L to 20 μg / L. The detection limit for lead was found to be 0.004 ppb, and the detection limit for cadmium was found to be 0.005 ppb. After detection, the electrode was cleaned using the same cleaning method as in Example 1, and the mercury composite material was redeposited for continued use.

[0053] like Figure 5 This is a detailed view of the tip of the heavy metal trace detection electrode described in Embodiment 2, where the composite wire is clearly visible.

[0054] like Figure 6 This is a cross-sectional view of the tip of the heavy metal trace detection electrode described in Example 2.

[0055] Example 3 This embodiment provides a method for preparing a trace heavy metal detection electrode, including the following steps: Step 1: After cleaning a 3cm long borosilicate glass capillary (99.99% purity, 80% SiO2 content), heat it to 750℃ in a microelectrode pulling instrument to draw one end of the borosilicate glass capillary into an extremely fine conical tip shape with an inner diameter that is abruptly reduced to 50μm. Step 2: Use a 3cm long copper wire with a diameter of 0.5mm as the lead wire and a 1cm long gold wire with a diameter of 25μm (purity ≥99.9%) as the working wire. After bonding the copper wire and the gold wire with nano silver glue (silver particles with a particle size of 50nm and a silver concentration of 0.1mg / mL), place them at 100℃ for 15min to cure, and obtain a composite wire. Step 3: Insert the composite wire into the borosilicate glass capillary tube from Step 1, allowing the composite wire to extend 1 cm from the conical tip. Heat the conical tip with an oxyhydrogen flame gun to a temperature of 850°C to soften the tip of the borosilicate glass capillary tube and wrap it around the extended portion of the composite wire, thus melting and sealing the composite wire to the borosilicate glass capillary tube. Connect a copper rod with an inner diameter adapted to the borosilicate glass capillary tube to the other end of the borosilicate glass capillary tube. Connect the copper rod to the rear end of the copper wire to obtain the electrode material. Step 4: After grinding the tip of the electrode material flat to expose the gold wire end face, it is ultrasonically cleaned with 95% ethanol and 99% acetone at 50kHz for 5 minutes. Then, it is placed in 10mL of aqueous solution containing 0.05mol o-phenylenediamine and 0.2mol sulfuric acid. Cyclic voltammetry is performed at a speed of 20mV / s under a voltage of -1.6V to +1.6V, with 50 scans. After the scan, it is baked at 120℃ for 20 minutes for curing. The scanning and curing process is repeated 3 times. The polymer insulating film spontaneously undergoes anodic oxidation electropolymerization at the micro-gap of the metal edge to obtain the organic composite electrode material. Step 5: Place the organic composite electrode material in 10 mL of an aqueous solution containing 0.5 mol sulfuric acid, and perform cyclic voltammetry scanning at a rate of 20 mV / s under a voltage of -1.6 V to +1.6 V for 10 scans to activate it. Place the activated electrode in 10 mL of an aqueous solution containing 100 mg / L COF material and 300 mg / L mercury, and deposit it under a voltage of -0.7 V for 20 s to obtain the heavy metal trace detection electrode.

[0056] This embodiment also provides a method for applying the aforementioned heavy metal trace detection electrode, including the following steps: The heavy metal trace detection electrode was placed in 10 mL of a test solution containing 0.02 mol / L ascorbic acid at pH 4.5. The test solution contained 10 μg / L lead and 10 μg / L cadmium. The voltage was set to -1.0 V and the enrichment time was 200 s. The lead and cadmium content was detected. After the detection, the heavy metal trace detection electrode was kept in the test solution. The potential was set to +0.6 V and maintained for 60 s to clean the electrode, removing heavy metal impurities accumulated inside the electrode and the degraded film on the surface. The deposition process in step 5 was repeated, and the test solution was tested again. After repeating 20 times, the relative standard deviation of the heavy metal trace detection electrode was calculated to be 3.6%.

[0057] like Figure 7 This is a scanning electron microscope image of the heavy metal trace detection electrode after deposition in Example 3. The adsorbed COF material is clearly visible on the electrode surface in the image.

[0058] like Figure 8 This is an anti-interference test diagram of the heavy metal trace detection electrode for lead detection described in Example 3, with 100 times the concentration of Zn added. 2+ Mg 2+ Cu 2+ Ca 2+ Cd 2+ And 50 times the concentration of Bi 3+ It has no significant effect on lead determination (response current change is less than 5%).

[0059] like Figure 9 This is an anti-interference test diagram of the heavy metal trace detection electrode for cadmium detection described in Example 3, with 100 times the concentration of Zn added. 2+ Mg 2+ Cu 2+ Ca 2+ Pb 2+ And 50 times the concentration of Bi 3+ It has no significant effect on the determination of cadmium (response current change is less than 5%).

[0060] like Figure 10 The graph shows the relative standard deviation (RSD) of the heavy metal trace detection electrode described in Example 3. The RSD obtained after 20 consecutive tests with the same electrode is 3.6%.

[0061] Example 4 This embodiment provides a method for preparing a trace heavy metal detection electrode, including the following steps: Step 1: After cleaning a 3cm long borosilicate glass capillary (99.99% purity, 80% SiO2 content), heat it to 750℃ in a microelectrode pulling instrument to draw one end of the borosilicate glass capillary into an extremely fine conical tip shape with an inner diameter that is abruptly reduced to 50μm. Step 2: Use a 3cm long copper wire with a diameter of 0.5mm as the lead wire and a 1cm long gold wire with a diameter of 25μm (purity ≥99.9%) as the working wire. After bonding the copper wire and the gold wire with nano silver glue (silver particles with a particle size of 50nm and a silver concentration of 0.1mg / mL), place them at 100℃ for 15min to cure, and obtain a composite wire. Step 3: Insert the composite wire into the borosilicate glass capillary tube from Step 1, allowing the composite wire to extend 1 cm from the conical tip. Heat the conical tip with an oxyhydrogen flame gun to a temperature of 850°C to soften the tip of the borosilicate glass capillary tube and wrap it around the extended portion of the composite wire, thus melting and sealing the composite wire to the borosilicate glass capillary tube. Connect a copper rod with an inner diameter adapted to the borosilicate glass capillary tube to the other end of the borosilicate glass capillary tube. Connect the copper rod to the rear end of the copper wire to obtain the electrode material. Step 4: After grinding the tip of the electrode material flat to expose the gold wire end face, it is ultrasonically cleaned with 95% ethanol and 99% acetone at 50kHz for 5 minutes. Then, it is placed in 10mL of aqueous solution containing 0.05mol o-phenylenediamine and 0.2mol sulfuric acid. Cyclic voltammetry is performed at a speed of 20mV / s under a voltage of -1.6V to +1.6V, with 50 scans. After the scan, it is baked at 120℃ for 20 minutes for curing. The scanning and curing process is repeated 3 times. The polymer insulating film spontaneously undergoes anodic oxidation electropolymerization at the micro-gap of the metal edge to obtain the organic composite electrode material. Step 5: Place the organic composite electrode material in 10 mL of an aqueous solution containing 0.5 mol sulfuric acid, and perform cyclic voltammetry scanning at a rate of 20 mV / s under a voltage of -1.6 V to +1.6 V for 10 scans to activate it. Place the activated electrode in 10 mL of an aqueous solution containing 100 mg / L COF material and 300 mg / L mercury, and deposit it under a voltage of -0.7 V for 20 s to obtain the heavy metal trace detection electrode.

[0062] This embodiment also provides a method for applying the aforementioned heavy metal trace detection electrode, including the following steps: The heavy metal trace detection electrode was placed in 10 mL of a test solution containing 0.05 mol / L ascorbic acid at pH 4.5. The test solution contained 10 μg / L lead and 10 μg / L cadmium. The voltage was set to -1.0 V and the enrichment time was 200 s. The lead and cadmium content was detected. After the detection, the heavy metal trace detection electrode was kept in the test solution. The potential was set to +0.6 V and maintained for 60 s to clean the electrode, removing heavy metal impurities accumulated inside the electrode and the degraded film on the surface. The deposition process in step 5 was repeated, and the test solution was tested again. After repeating 20 times, the relative standard deviation of the heavy metal trace detection electrode was calculated to be 3.33%.

[0063] Example 5 This embodiment provides a method for preparing a trace heavy metal detection electrode, including the following steps: Step 1: After cleaning a 3cm long borosilicate glass capillary (purity 99.99%, SiO2 content 80%) with an inner diameter of 0.60mm, heat it to 780℃ in a microelectrode pulling instrument to draw one end of the borosilicate glass capillary into an extremely fine conical tip shape with an inner diameter that is abruptly reduced to 50μm. Step 2: Use a 3cm long copper wire with a diameter of 0.6mm as the lead wire and a 1cm long gold wire with a diameter of 28μm (purity ≥99.9%) as the working wire. After bonding the copper wire and the gold wire with nano silver glue (silver particles with a particle size of 50nm and a silver concentration of 0.1mg / mL), place them at 120℃ for 12min to cure, and obtain a composite wire. Step 3: Insert the composite wire into the borosilicate glass capillary tube from Step 1, allowing the composite wire to extend 1.5 cm from the conical tip. Heat the conical tip with an oxyhydrogen flame gun to a temperature of 950°C to soften the tip of the borosilicate glass capillary tube and wrap it around the extended portion of the composite wire, thus melting and sealing the composite wire to the borosilicate glass capillary tube. Connect a copper rod with an inner diameter adapted to the borosilicate glass capillary tube to the other end of the borosilicate glass capillary tube. Connect the copper rod to the rear end of the copper wire to obtain the electrode material. Step 4: After grinding the tip of the electrode material flat to expose the gold wire end face, it is ultrasonically cleaned with 95% ethanol and 99% acetone at 50kHz for 5 minutes. Then, it is placed in 10mL of aqueous solution containing 0.04mol o-phenylenediamine and 0.25mol sulfuric acid. Cyclic voltammetry is performed at a speed of 20mV / s under a voltage of -1.6V to +1.6V, with 50 scans. After the scan, it is baked at 120℃ for 20 minutes for curing. The scanning and curing process is repeated 3 times. The polymer insulating film spontaneously undergoes anodic oxidation electropolymerization at the micro-gap of the metal edge to obtain the organic composite electrode material. Step 5: Place the organic composite electrode material in 10 mL of an aqueous solution containing 0.5 mol sulfuric acid, and perform cyclic voltammetry scanning at a rate of 20 mV / s under a voltage of -1.6 V to +1.6 V for 10 scans to activate it. Place the activated electrode in 10 mL of an aqueous solution containing 150 mg / L COF material and 250 mg / L mercury, and deposit it at a voltage of -0.7 V for 30 s to obtain the heavy metal trace detection electrode.

[0064] This embodiment also provides a method for applying the aforementioned heavy metal trace detection electrode, including the following steps: The heavy metal trace detection electrode was placed in 10 mL of a test solution containing 0.02 mol / L ascorbic acid at pH 4.5. The test solution contained 10 μg / L lead and 10 μg / L cadmium. The voltage was set to -1.0 V and the enrichment time was 200 s. The lead and cadmium content was detected. After the detection, the heavy metal trace detection electrode was kept in the test solution. The potential was set to +0.6 V and maintained for 60 s to clean the electrode, removing heavy metal impurities accumulated inside the electrode and the degraded film on the surface. The deposition process in step 5 was repeated, and the test solution was tested again. After repeating 20 times, the relative standard deviation of the heavy metal trace detection electrode was calculated to be 3.92%.

[0065] Example 6 This embodiment provides a method for preparing a trace heavy metal detection electrode, including the following steps: Step 1: After cleaning a 3cm long borosilicate glass capillary (99.99% purity, 80% SiO2 content), heat it to 740℃ in a microelectrode pulling instrument to draw one end of the borosilicate glass capillary into an extremely fine conical tip shape with an inner diameter that is abruptly reduced to 20μm. Step 2: Use a 3cm long copper wire with a diameter of 0.4mm as the lead wire and a 1cm long gold wire with a diameter of 22μm (purity ≥99.9%) as the working wire. After bonding the copper wire and the gold wire with nano silver glue (silver particles with a particle size of 50nm and a silver concentration of 0.1mg / mL), place them at 95℃ for 20min to cure, and obtain a composite wire. Step 3: Insert the composite wire into the borosilicate glass capillary tube from Step 1, allowing the composite wire to extend 1 cm from the conical tip. Heat the conical tip with an oxyhydrogen flame gun at 800°C to soften the tip of the borosilicate glass capillary tube and wrap it around the extended portion of the composite wire, thus melting and sealing the composite wire to the borosilicate glass capillary tube. Connect a copper rod with an inner diameter adapted to the borosilicate glass capillary tube to the other end of the borosilicate glass capillary tube. Connect the copper rod to the rear end of the copper wire to obtain the electrode material. Step 4: After grinding the tip of the electrode material flat to expose the gold wire end face, it is ultrasonically cleaned with 95% ethanol and 99% acetone at 50kHz for 5 minutes. Then, it is placed in 10mL of aqueous solution containing 0.04mol o-phenylenediamine and 0.25mol sulfuric acid. Cyclic voltammetry is performed at a speed of 20mV / s under a voltage of -1.6V to +1.6V, with 50 scans. After the scan, it is baked at 140℃ for 15 minutes for curing. The scanning and curing process is repeated 3 times. The polymer insulating film spontaneously undergoes anodic oxidation electropolymerization at the micro-gap of the metal edge to obtain the organic composite electrode material. Step 5: Place the organic composite electrode material in 10 mL of an aqueous solution containing 0.5 mol sulfuric acid, and perform cyclic voltammetry scanning at a rate of 20 mV / s under a voltage of -1.6 V to +1.6 V for 10 scans to activate it. Place the activated electrode in 10 mL of an aqueous solution containing 200 mg / L COF material and 300 mg / L mercury, and deposit it at a voltage of -0.7 V for 30 s to obtain the heavy metal trace detection electrode.

[0066] This embodiment also provides a method for applying the aforementioned heavy metal trace detection electrode, including the following steps: The heavy metal trace detection electrode was placed in 10 mL of a test solution containing 0.03 mol / L ascorbic acid at pH 5. The test solution contained 10 μg / L lead and 10 μg / L cadmium. The voltage was set to -1.0 V and the enrichment time was 200 s. The lead and cadmium content was detected. After the detection, the heavy metal trace detection electrode was kept in the test solution. The potential was set to +0.6 V and maintained for 60 s to clean the electrode, removing heavy metal impurities accumulated inside the electrode and the degraded film on the surface. The deposition process in step 5 was repeated, and the test solution was tested again. After repeating 20 times, the relative standard deviation of the heavy metal trace detection electrode was calculated to be 2.56%.

[0067] like Figure 11 The figure shows the linear scanning voltammetry test results of the heavy metal trace detection electrode after cleaning in Example 6. The right figure is the response curve in Example 6, and the left figure is the response curve obtained by manual polishing instead of constant voltage cleaning. As can be seen from the figure, the curves are similar, and the curve in Example 6 has no other impurities, which is sufficient to show that the constant voltage cleaning method in Example 6 can completely replace the existing manual polishing method.

[0068] Example 7 This embodiment provides a method for preparing the COF materials in Examples 1-6 and Comparative Examples 1 and 3, including the following steps: Step 1: 14.16 mg (0.04 mmol) of 1,3,5-tris(4-aminophenyl)benzene and 11.12 mg (0.06 mmol) of 2,5-divinyl-1,4-phenylenedialdehyde were dispersed in 5 mL of acetonitrile by stirring at 300 rpm for 10 min. 0.3 mL of acetic acid and 0.024 mL of aniline were added. After sonication for 5 min, the mixture was heated to 30 °C and reacted for 72 h. After the reaction was completed, the solid product was separated by centrifugation. The solid product was washed three times with tetrahydrofuran and ethanol, respectively, and then dried at 60 °C and -0.1 MPa for 12 h to obtain a flower-like covalent organic framework material. Step 2: 0.12g of the flower-like covalent organic framework material, 0.14g of 2,3-dimercaptosuccinic acid, and 0.015g of azobisisobutyronitrile were dispersed in 10mL of N,N-dimethylformamide under a stirring at 300rpm for 10min. The mixture was then placed under a nitrogen atmosphere and heated to 80℃. The mixture was stirred at 300rpm for 2d to carry out the reaction. After the reaction was completed, the solid product II was separated by centrifugation. The solid product II was washed three times with acetone and ethanol, respectively, and then dried at 60℃ and -0.1MPa for 12h to obtain the carboxyl flower-like covalent organic framework material. Step 3: Disperse 0.1g of the carboxyl flower-like covalent organic framework material in 52.5mL of tetrahydrofuran by stirring at 300rpm for 10min. Add 3.75mL of 0.1wt% tetrachloroauric acid solution. After mechanical shaking for 3h in the dark, add 15mL of 13.3mg / L sodium borohydride solution (solvent: tetrahydrofuran). Continue shaking for another 3h in the dark at a frequency of 60 times / min. Wash three times with acetone and ethanol respectively, and dry at 60℃ and -0.1MPa for 12h to obtain the COF material. (e.g., patent CN121338716A) Comparative Example 1 This comparative example provides a method for preparing a trace heavy metal detection electrode, comprising the following steps: Step 1: After cleaning a 3cm long borosilicate glass capillary (99.99% purity, 80% SiO2 content), heat it to 750℃ in a microelectrode pulling instrument to draw one end of the borosilicate glass capillary into an extremely fine conical tip shape with an inner diameter that is abruptly reduced to 50μm. Step 2: Use a 3cm long copper wire with a diameter of 0.5mm as the lead wire and a 1cm long gold wire with a diameter of 25μm (purity ≥99.9%) as the working wire. After bonding the copper wire and the gold wire with nano silver glue (silver particles with a particle size of 50nm and a silver concentration of 0.1mg / mL), place them at 100℃ for 15min to cure, and obtain a composite wire. Step 3: Insert the composite wire into the borosilicate glass capillary tube from Step 1, allowing the composite wire to extend 1 cm from the conical tip. Heat the conical tip with an oxyhydrogen flame gun to a temperature of 850°C to soften the tip of the borosilicate glass capillary tube and wrap it around the extended portion of the composite wire, thus melting and sealing the composite wire to the borosilicate glass capillary tube. Connect a copper rod with an inner diameter adapted to the borosilicate glass capillary tube to the other end of the borosilicate glass capillary tube. Connect the copper rod to the rear end of the copper wire to obtain the electrode material. Step 4: After grinding the tip of the electrode material flat to expose the gold wire end face, it is ultrasonically cleaned with 95% ethanol and 99% acetone at 50kHz for 5 minutes. Then, it is placed in 10mL of aqueous solution containing 0.05mol o-phenylenediamine and 0.2mol sulfuric acid. Cyclic voltammetry is performed at a speed of 20mV / s under a voltage of -1.6V to +1.6V, with 50 scans. After the scan, it is baked at 120℃ for 20 minutes for curing. The scanning and curing process is repeated 3 times. The polymer insulating film spontaneously undergoes anodic oxidation electropolymerization at the micro-gap of the metal edge to obtain the organic composite electrode material. Step 5: Place the organic composite electrode material in 10 mL of an aqueous solution containing 0.5 mol sulfuric acid, and perform cyclic voltammetry scanning at a rate of 20 mV / s under a voltage of -1.6 V to +1.6 V for 10 scans to activate it. Place the activated electrode in 10 mL of an aqueous solution containing 100 mg / L COF material and 300 mg / L mercury, and deposit it under a voltage of -0.7 V for 20 s to obtain the heavy metal trace detection electrode.

[0069] This comparative example also provides a method for applying the aforementioned heavy metal trace detection electrode, including the following steps: The heavy metal trace detection electrode was placed in 10 mL of a test solution with a pH of 4.5, containing 10 μg / L lead and 10 μg / L cadmium. The voltage was set to -1.0 V, and the enrichment time was 200 s. The lead and cadmium content was detected. After the detection, the heavy metal trace detection electrode was kept in the test solution, and the potential was set to +0.6 V for 60 s to clean the electrode, removing heavy metal impurities accumulated inside the electrode and the degraded film on the surface. The test solution was then tested again. After repeating the test 20 times, the relative standard deviation of the heavy metal trace detection electrode was calculated to be 5.04%.

[0070] Comparative Example 2 This comparative example provides a method for preparing a trace heavy metal detection electrode, comprising the following steps: Step 1: After cleaning a 3cm long borosilicate glass capillary (99.99% purity, 80% SiO2 content), heat it to 750℃ in a microelectrode pulling instrument to draw one end of the borosilicate glass capillary into an extremely fine conical tip shape with an inner diameter that is abruptly reduced to 50μm. Step 2: Use a 3cm long copper wire with a diameter of 0.5mm as the lead wire and a 1cm long gold wire with a diameter of 25μm (purity ≥99.9%) as the working wire. After bonding the copper wire and the gold wire with nano silver glue (silver particles with a particle size of 50nm and a silver concentration of 0.1mg / mL), place them at 100℃ for 15min to cure, and obtain a composite wire. Step 3: Insert the composite wire into the borosilicate glass capillary tube from Step 1, allowing the composite wire to extend 1 cm from the conical tip. Heat the conical tip with an oxyhydrogen flame gun to a temperature of 850°C to soften the tip of the borosilicate glass capillary tube and wrap it around the extended portion of the composite wire, thus melting and sealing the composite wire to the borosilicate glass capillary tube. Connect a copper rod with an inner diameter adapted to the borosilicate glass capillary tube to the other end of the borosilicate glass capillary tube. Connect the copper rod to the rear end of the copper wire to obtain the electrode material. Step 4: After grinding the tip of the electrode material flat to expose the gold wire end face, it is ultrasonically cleaned with 95% ethanol and 99% acetone at 50kHz for 5 minutes. Then, it is placed in 10mL of aqueous solution containing 0.05mol o-phenylenediamine and 0.2mol sulfuric acid. Cyclic voltammetry is performed at a speed of 20mV / s under a voltage of -1.6V to +1.6V, with 50 scans. After the scan, it is baked at 120℃ for 20 minutes for curing. The scanning and curing process is repeated 3 times. The polymer insulating film spontaneously undergoes anodic oxidation electropolymerization at the micro-gap of the metal edge to obtain the organic composite electrode material. Step 5: Place the organic composite electrode material in 10 mL of an aqueous solution containing 0.5 mol sulfuric acid, and perform cyclic voltammetry scanning at a rate of 20 mV / s under a voltage of -1.6 V to +1.6 V for 10 scans to activate it. Place the activated electrode in 10 mL of an aqueous solution containing 300 mg / L mercury and deposit it at a voltage of -0.7 V for 20 s to obtain the heavy metal trace detection electrode.

[0071] This comparative example also provides a method for applying the aforementioned heavy metal trace detection electrode, including the following steps: The differential pulse voltammetry method described in Example 1 was used for detection. The concentration of lead solution added was set to be 0.005 μg / L to 10 μg / L, and the concentration of cadmium solution added was set to be 0.005 μg / L to 10 μg / L. The detection limit for lead was found to be 0.01 ppb, and the detection limit for cadmium was found to be 0.015 ppb. After the detection was completed, the same cleaning method as in Example 1 was used for cleaning and deposition of mercury composite material. Subsequently, the heavy metal trace detection electrode was placed in 10 mL of a test solution containing 0.02 mol / L ascorbic acid at pH 4.5. The test solution contained 10 μg / L lead and 10 μg / L cadmium. The voltage was set to -1.0 V and the enrichment time to 200 s. The lead and cadmium content was detected. After the detection, the heavy metal trace detection electrode was kept in the test solution. The potential was set to +0.6 V and maintained for 60 s to clean the electrode, removing heavy metal impurities accumulated inside the electrode and the degraded film on the surface. The deposition process in step 5 was repeated, and the test solution was tested again. After repeating this process 20 times, the relative standard deviation of the heavy metal trace detection electrode was calculated to be 5.82%.

[0072] Comparative Example 3 This comparative example provides a method for preparing a trace heavy metal detection electrode, comprising the following steps: Step 1: After cleaning a 3cm long borosilicate glass capillary (99.99% purity, 80% SiO2 content), heat it to 750℃ in a microelectrode pulling instrument to draw one end of the borosilicate glass capillary into an extremely fine conical tip shape with an inner diameter that is abruptly reduced to 50μm. Step 2: Use a 3cm long copper wire with a diameter of 0.5mm as the lead wire and a 1cm long gold wire with a diameter of 25μm (purity ≥99.9%) as the working wire. After bonding the copper wire and the gold wire with nano silver glue (silver particles with a particle size of 50nm and a silver concentration of 0.1mg / mL), place them at 100℃ for 15min to cure, and obtain a composite wire. Step 3: Insert the composite wire into the borosilicate glass capillary tube from Step 1, allowing the composite wire to extend 1 cm from the conical tip. Heat the conical tip with an oxyhydrogen flame gun to a temperature of 850°C to soften the tip of the borosilicate glass capillary tube and wrap it around the extended portion of the composite wire, thus melting and sealing the composite wire to the borosilicate glass capillary tube. Connect a copper rod with an inner diameter adapted to the borosilicate glass capillary tube to the other end of the borosilicate glass capillary tube. Connect the copper rod to the rear end of the copper wire to obtain the electrode material. Step 4: After grinding the tip of the electrode material flat to expose the gold wire end face, it is ultrasonically cleaned with 95% ethanol and 99% acetone at 50kHz for 5 minutes. Then, it is placed in 10mL of aqueous solution containing 0.5mol sulfuric acid and cyclic voltammetry is performed at a speed of 20mV / s under a voltage of -1.6V to +1.6V for 10 cycles to activate the electrode. The activated electrode is then placed in 10mL of aqueous solution containing 100mg / L COF material and 300mg / L mercury and deposited at -0.7V for 20s to obtain the heavy metal trace detection electrode.

[0073] This comparative example also provides a method for applying the aforementioned heavy metal trace detection electrode, including the following steps: The differential pulse voltammetry method described in Example 1 was used for detection. The concentration of lead solution added was set to be 0.005 μg / L to 10 μg / L, and the concentration of cadmium solution added was set to be 0.005 μg / L to 10 μg / L. The detection limit for lead was found to be 0.03 ppb, and the detection limit for cadmium was found to be 0.03 ppb. After the detection was completed, the same cleaning method as in Example 1 was used for cleaning and depositing mercury composite material. Subsequently, the heavy metal trace detection electrode was placed in 10 mL of a test solution containing 0.02 mol / L ascorbic acid at pH 4.5. The test solution contained 10 μg / L lead and 10 μg / L cadmium. The voltage was set to -1.0 V and the enrichment time to 200 s. The lead and cadmium content was detected. After the detection, the heavy metal trace detection electrode was kept in the test solution. The potential was set to +0.6 V and maintained for 60 s to clean the electrode, removing heavy metal impurities accumulated inside the electrode and the degraded film on the surface. The deposition process in step 5 was repeated, and the test solution was tested again. After repeating this process 20 times, the relative standard deviation of the heavy metal trace detection electrode was calculated to be 10.05%.

[0074] like Figure 12 The figures show the cyclic voltammetry test results of the electrodes in Comparative Example 3 and Example 1. Comparative Example 3, without the organic film, exhibited a higher background current and a larger redox peak response during the test, indicating that there may be micro-gaps between the metal wire and the glass capillary, which cause additional charging current and interfacial reactions after electrolyte seepage. In Example 1, after being covered with the organic film, the overall current response of the cyclic voltammetry curve was significantly reduced, the peak current decreased, and the curve enclosed area shrank, indicating that the organic film effectively blocked the micro-gaps at the electrode edge, reduced background current interference, and improved the stability of the electrode interface. The test electrolyte was an acetic acid solution with a pH of 4.5.

[0075] like Figure 13The graph shows the relative standard deviation (RSD) test results of the 12 heavy metal trace detection electrodes described in this invention. After testing multiple electrodes, the RSD is 1.49%, which is sufficient to demonstrate that the electrode material prepared by the method in this invention meets the standard production requirements for industrialization.

[0076] Table 1 shows the relative standard deviation of the heavy metal trace detection electrodes described in this embodiment and the comparative example.

[0077] As shown in the table above, the heavy metal trace detection electrode in this embodiment not only has a low detection limit, but also maintains a relative standard deviation of <5% after multiple uses. This standard deviation is superior to that of existing detection electrodes, demonstrating excellent stability. In Comparative Example 1, the absence of ascorbic acid during detection causes oxidation of the test solution during repeated testing, leading to an increase in the relative standard deviation. In Comparative Example 2, only a mercury film was deposited without the addition of COF material, preventing the electrodes from working synergistically, resulting in a relatively lower detection limit and a relatively higher relative standard deviation. In Comparative Example 3, the lack of organic film coating resulted in micro-gaps between the composite wire and the capillary. The redeposition of the mercury composite material led to instability during electrode detection, significantly increasing the relative standard deviation.

[0078] In this invention, all electrochemical-related tests and experiments use a three-electrode system, where the counter electrode is a platinum sheet and the reference electrode is an Ag / AgCl electrode.

[0079] As can be seen from the above, the heavy metal trace detection electrode of the present invention has a wide range of applications, low cost, and a very high market prospect.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a trace heavy metal detection electrode, characterized in that, Includes the following steps: Step 1: After cleaning the borosilicate glass capillary, heat it and draw one end of the borosilicate glass capillary into an extremely fine conical tip shape with a rapidly narrowed inner diameter. Step 2: Using copper wire as the lead wire and gold wire as the working wire, the copper wire and gold wire are bonded together with nano silver glue, and then dried and cured to obtain a composite wire. Step 3: Insert the composite wire into the borosilicate glass capillary tube in Step 1, so that the composite wire extends from the conical tip. Heat the conical tip to melt and seal the tip of the borosilicate glass capillary tube with the composite wire. Connect the other end of the borosilicate glass capillary tube to a copper rod that matches the inner diameter of the borosilicate glass capillary tube. Connect the copper rod to the rear end of the copper wire to obtain the electrode material. Step 4: After grinding the tip of the electrode material flat to expose the gold wire end face, ultrasonically clean it, then place it in an organic electrolyte and perform cyclic voltammetry scanning. After the scanning is completed, bake and solidify to obtain the organic composite electrode material. Step 5: Place the organic composite electrode material in an activation solution and activate it using cyclic voltammetry. After activation, place the electrode in a solution containing mercury composite material for electrodeposition to obtain the heavy metal trace detection electrode. The organic electrolyte in step 4 is an aqueous solution containing 0.05 mol o-phenylenediamine and 0.2 mol sulfuric acid; The mercury composite material in step 5 includes mercury and COF material.

2. The preparation method according to claim 1, characterized in that, In step 4, the voltage for the cyclic voltammetry scan is -1.6V to +1.6V, the scan speed is 10-25mV / s, and the number of scans is 30-50.

3. The preparation method according to claim 1, characterized in that, The activation solution in step 5 is an aqueous solution containing 0.5 mol of sulfuric acid.

4. The preparation method according to claim 1, characterized in that, The scanning speed of the cyclic voltammetry in step 5 is 10-25 mV / s, and the number of scans is 10-20.

5. The preparation method according to claim 1, characterized in that, The deposition voltage in step 5 is -0.7V, and the deposition time is 20-30s.

6. A heavy metal trace detection electrode prepared by the method according to any one of claims 1-5, characterized in that, The detection limit for lead metal by the heavy metal trace detection electrode is ≤0.005 ppb, and the detection limit for cadmium metal is ≤0.01 ppb; the relative standard deviation of the heavy metal trace detection electrode after repeated use is ≤3.92%. The heavy metal trace detection electrode is obtained by depositing a polymer insulating film in a borosilicate glass capillary after copper and gold wires are combined, and then depositing mercury composite material through an electrochemical workstation. The mercury composite material includes mercury and COF material.

7. A method for applying the heavy metal trace detection electrode according to claim 6, characterized in that, Includes the following steps: The heavy metal trace detection electrode is placed in the test solution to detect the lead and cadmium content. After the detection is completed, the heavy metal trace detection electrode is kept in the test solution, and a constant voltage is set to clean the electrode. After the mercury composite material is redeposited, the test solution is detected again.

8. The application method according to claim 7, characterized in that, The pH value of the test solution is 4.5-5.

9. The application method according to claim 7, characterized in that, The test solution contains 0.02-0.05 mol / L ascorbic acid.

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