A pin-based capillary electrophoresis detection electrode and a preparation method thereof

Abstract

The application belongs to the technical field of electrochemical analysis, and particularly relates to a capillary electrophoresis detection electrode based on a large-head needle and a preparation method thereof. The electrode is composed of a nickel-plated large-head needle electrode body, a conical electrode tube, an electrode rod and an electrode lead. The large-head needle electrode body is embedded in the small opening of the conical electrode tube, and the needle cap is outside, forming the sensing part of the electrode. The electrode lead is connected with the electrode body and is led out from the wide opening of the other end of the electrode tube. In addition, gold, platinum, copper, graphene and other coatings can be modified on the surface of the needle cap electrode exposed outside the electrode tube through electrochemical deposition, coating and other methods to prepare various novel capillary electrophoresis electrochemical detection electrodes to meet the detection requirements of different substances. The capillary electrophoresis detection electrode based on the large-head needle has the characteristics of rich raw materials, low price, simple preparation and convenient use, and can be mass-produced, and has a wide application prospect in the field of electrochemical detection.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical analysis technology, specifically relating to a capillary electrophoresis detection electrode based on a pin and its preparation method. Background Technology

[0002] Capillary electrophoresis is a microfluidic analysis method that separates and analyzes samples by electrophoresis in a DC electric field within a capillary. It is characterized by microchannels and has advantages such as fast analysis speed, small sample volume, high column efficiency, and easy capillary cleaning [1]. The sample volume is only a few nanoliters, which can greatly save samples and reagents. It has been widely used in many fields such as food and drug analysis, disease diagnosis, and environmental monitoring [2,3]. Capillary electrophoresis includes conventional capillary electrophoresis using capillaries and chip capillary electrophoresis using microfluidic chips.

[0003] Due to the tiny size of the capillary channel, highly sensitive detection methods are required. Capillary electrophoresis often employs ultraviolet detectors and laser-induced fluorescence detectors. Commonly used separation capillaries typically have an inner diameter of less than 100 μm, resulting in short ultraviolet absorption path lengths and low detection sensitivity. For substances without ultraviolet absorption or that are non-fluorescent or difficult to derivatize, other detection techniques are necessary, such as electrochemical and mass spectrometry [4,5]. Electrochemical detection techniques offer advantages such as high sensitivity, good selectivity, small dead volume, low cost, and compact and easily integrated electrodes and control instruments [6,7]. These mainly include amperometric detection, potentiometric detection, and conductivity detection, with amperometric detection being the most commonly used. Detection is achieved by applying a constant potential to the detection electrode and measuring the concentration-related current signal generated by the oxidation or reduction of the analyte on the electrode. The sensitivity, selectivity, and stability of capillary electrophoresis electrochemical detection are closely related to the electrode material. Choosing the right electrode material can improve electrochemical detection performance to meet the needs of detecting different types of substances. Currently, materials such as graphite, carbon nanotubes, graphene, gold, silver, copper, and platinum have been used in the fabrication of capillary electrophoresis electrochemical detection electrodes.

[0004] A pin is a stationery and household item used to hold paper and objects in place. It gets its name from its wider end and narrower end, and consists of a tip, a body, and a cap. Currently, most pins are made by nickel-plating a steel core. Pins are commonly used as stationery to facilitate the sorting, management, and retrieval of paper documents and receipts; they are often used to clip documents to a corner of paper. They are also frequently used in the positioning and packaging of shirts and clothing. Based on length and body diameter, they are available in seven sizes, from 0 to 6. The lengths of size 0 to 6 are 20, 22, 24, 26, 28, 30, and 32 cm, respectively, and the body diameters are 0.6, 0.7, 0.7, 0.8, 0.8, 0.85, and 0.85 mm, respectively. In daily office work, size 2 pins are the most commonly used.

[0005] However, there are currently no reports on the fabrication of capillary electrophoresis electrochemical detection electrodes using commonly used laboratory nickel-plated pins and pipette tips.

[0006] References

[0007] [1] Valdes, A.; Alvarez-Rivera, G.; Socas-Rodriguez, B.; Herrero, M.; Cifuentes, A. Capillary electromigration methods for food analysis and foodomics: Advances and applications in the period February 2019-February2021. Electrophoresis, 2022, 43, 37-56.

[0008] [2]Kasicka,V.Recent developments in capillary and microchipelectroseparations of peptides(2019-Mid 2021).Electrophoresis,2022,43,82-108.

[0009] [3] Zhang, CH; Woolfork, AG; Suh, K.; Ovbude, S.; Bi, C.; Elzoeiry, M.; Hage, DSClinical and pharmaceutical applications of affinity ligands in capillaryelectrophoresis: A review. J. Pharm. Biomed. Anal., 2020, 177, 112882.

[0010] [4]Xu, MC; Zhang, HY; Tang, T.; Zhou, J.; Zhou, WH; Tan, SW; He, BSP Potential and applications of capillary electrophoresis for analyzing traditional Chinese medicine: a critical review. Analyst, 2021, 146, 4724-4736.

[0011] [5] Helena, H.; Ivona, V.; Roman, R.; Frantisek, F. Current applications of capillary electrophoresis-mass spectrometry for the analysis of biologically important analytes in urine (2017 to mid-2021): A review. J. Sep. Sci., 2022, 45, 305-324.

[0012] [6] Gao, ZT; Zhong, WWRecent(2018–2020) development in capillary electrophoresis. Anal. Bioanal. Chem., 2022, 414, 115-130.

[0013] [7] Li FR; Jiang, KM; Wu, QY; Li, ZJ; Chen, G. Fabrication of Graphene-Cuprous Oxide Hybrid Paste Electrodes for Capillary Electrophoretic Measurement of Polyhydroxy Compounds, Electroanalysis, 2023, 35(1), 206-214. Summary of the Invention

[0014] The purpose of this invention is to propose a rapid and simple method for preparing a capillary electrophoresis detection electrode based on a pin, and to obtain a novel capillary electrophoresis electrochemical detection electrode that is inexpensive, easy to manufacture, convenient to use, and has excellent performance.

[0015] The method for preparing a capillary electrophoresis detection electrode based on a pin provided by this invention includes the following steps:

[0016] (1) Heat the tip of the transparent thermoplastic conical electrode tube and insert a nickel-plated pin into the small hole at its narrow end, leaving only the pin cap exposed, as the sensing part of the electrode.

[0017] (2) Wind one end of the copper electrode lead into a spiral tube, insert it through the wide opening of the conical electrode tube, and fit the pin body inside the spiral tube.

[0018] (3) Insert one end of the hollow plastic electrode rod into the wide opening of the tapered electrode tube and fix it in place, and lead the electrode lead out from the hollow electrode rod;

[0019] (4) Insert a wedge-shaped elastomer into the end of the electrode rod, fix the electrode lead, and make the spiral tube end of the lead tightly contact the needle body of the pin to obtain a capillary electrophoresis detection electrode based on nickel-plated pin.

[0020] (5) Furthermore, a modification layer can be prepared on the exposed surface of the pin cap electrode to meet the needs of detecting different types of substances.

[0021] Furthermore:

[0022] In step (1), heating the tip of the plastic conical electrode tube involves immersing the tip of the transparent thermoplastic conical electrode tube in a water bath at 50-90°C for 1-5 minutes, or blowing it with hot air at 50-90°C for 1-5 minutes. The nickel-plated pin tip and body are then inserted into the small hole at the narrow end of the preheated plastic conical electrode tube. The diameter of the small hole should be slightly smaller than the diameter of the pin body to achieve a tight fit and seal. Preheating the tip of the conical electrode tube is to prevent cracking when the pin is inserted.

[0023] In step (2), the diameter of the copper electrode lead is 200-700μm. The method for preparing the spiral tube at one end is to use another nickel-plated pin of the same specification as a template to wind 5 to 10 turns to form a copper lead spiral tube; remove the spiral tube, insert it through the wide opening of the tapered electrode tube, and cover the pin body;

[0024] In step (3), one end of a hollow plastic electrode rod is inserted through the wide opening of the tapered electrode tube, and the electrode lead is threaded through the electrode rod. The electrode rod can extend the electrode length and facilitate operation;

[0025] In step (4), a wedge-shaped elastic body is inserted into the end of the electrode rod, and the electrode lead is fixed to the end of the electrode rod. At the same time, the thrust of the wedge-shaped elastic body can make the spiral end of the electrode lead inside the conical electrode tube in close contact with the pin body, thus obtaining a capillary electrophoresis detection electrode based on a nickel-plated pin.

[0026] In step (5), the modification layer is one or more of the sensing materials selected from gold, platinum, copper, and graphene, and the modification method is electrochemical deposition or surface coating, etc., to meet the needs of detecting different types of substances and expand the range of electrochemical detection.

[0027] Preferably, in step (1), the thermoplastic conical electrode tube is made of polypropylene, polyvinyl chloride, high-density polyethylene, polyethylene terephthalate, polycarbonate, etc. Its length is 2-8m, and the inner diameter of the thin end is 0.5-0.7mm, which is slightly smaller than the diameter of the pin body (0.6-0.85mm).

[0028] Preferably, in step (3), the hollow electrode rod is made of materials selected from polyvinyl chloride, polymethyl methacrylate, polystyrene, glass fiber reinforced resin, etc. Its outer diameter is slightly smaller than the wide inner diameter of the tapered electrode tube to facilitate insertion and installation.

[0029] Preferably, in step (4), the wedge-shaped elastomer material can be silicone rubber, polyurethane, plasticized polyvinyl chloride, etc.

[0030] Preferably, in step (5), the nickel-plated pin electrode from step (4) can be placed in an aqueous solution containing 10-100mM H2AuCl4 and 10-100mM HCl, and deposited at -0.5V to -0.9V for 1-8 minutes to obtain a gold-modified capillary electrophoresis pin detection electrode.

[0031] Preferably, in step (5), the nickel-plated pin electrode from step (4) can be placed in an aqueous solution containing 2-10 mM K2PtCl4 and 20-200 mM HCl, and deposited at -0.3 V to -0.7 V for 1-6 min to obtain a platinum-modified capillary electrophoresis pin detection electrode.

[0032] Preferably, in step (5), the nickel-plated pin electrode from step (4) can be placed in a solution containing 20-80 mM copper sulfate, 1.4-1.8 M sulfuric acid and 0.5-3 mg / L of 2-mercaptobenzoimidazole, and deposited at -0.5 V to -0.8 V for 1-5 min to obtain a copper-modified capillary electrophoresis pin detection electrode.

[0033] Preferably, in step (5), after the nickel-plated pin electrode cap from step (4) is gold-plated using the method described above, it is immersed in a 0.2-1% graphene oxide aqueous solution for 2-10 seconds, then removed with the cap electrode facing down and air-dried vertically for 10-30 minutes. Then, it is baked with a 250W far-infrared lamp for 10-30 minutes to remove some of the epoxy groups from the graphene oxide, generating a conductive graphene-modified capillary electrophoresis pin detection electrode.

[0034] This invention also provides a pin-based capillary electrophoresis detection electrode prepared by the above-described method. The electrode comprises a nickel-plated pin electrode body, a tapered electrode tube, a hollow electrode rod, electrode leads, and a wedge-shaped elastomer. The pin electrode body is embedded in the tip of the tapered electrode tube, with the pin cap on the outside, forming the sensing portion of the electrode. The electrode leads are connected to the electrode body and extend from the wide opening at the other end of the electrode tube. Furthermore, various novel pin-based capillary electrophoresis electrochemical detection electrodes can be prepared by modifying the surface of the pin cap electrode exposed outside the electrode tube with coatings of gold, platinum, copper, graphene, etc., through electrochemical deposition, coating, or other methods.

[0035] Preferably, the thermoplastic conical electrode tube is made of polypropylene, polyvinyl chloride, high-density polyethylene, polyethylene terephthalate, polycarbonate, etc. Its length is 2-8m, and the inner diameter of the narrow end is 0.5-0.7mm, slightly smaller than the diameter of a pin (0.6-0.85mm).

[0036] Preferably, the hollow electrode rod is made of materials selected from polyvinyl chloride, polymethacrylate, polystyrene, glass fiber reinforced resin, etc. Its outer diameter is slightly smaller than the wide inner diameter of the tapered electrode tube to facilitate insertion and installation.

[0037] Preferably, the wedge-shaped elastomer can be made of silicone rubber, polyurethane, plasticized polyvinyl chloride, etc.

[0038] Preferably, gold, platinum, copper, graphene, or other coatings can be applied to the exposed needle cap electrode surface using methods such as electrochemical deposition or coating to meet the needs of detecting different types of substances.

[0039] This invention also discloses the application of the pin-based capillary electrophoresis detection electrode in capillary electrophoresis electrochemical detection. For example, it can be used for the electrochemical detection of substances such as sugars and amino acids; specifically, for the capillary electrophoresis electrochemical detection of sugars in trumpet creeper flowers and synephrine and hesperidin in dried tangerine peel.

[0040] This invention inserts a pin into a conical electrode tube (such as a pipette tip), connects it to an extended electrode rod, and connects it to the needle body inside the tube via electrode leads to form a capillary electrophoresis electrochemical electrode. The pin cap is exposed outside the narrow opening of the electrode tube, serving as the sensing part. This electrode, coupled with capillary electrophoresis, can be used for the electrochemical detection of substances such as sugars and amino acids. Furthermore, gold, platinum, copper, graphene, etc., can be added to the exposed pin cap electrode tip using methods such as chemical deposition, electroplating, or coating to prepare various novel pin-based capillary electrophoresis electrochemical detection electrodes to meet the needs of detecting different types of substances. The pin-based capillary electrophoresis detection electrode developed in this invention has the advantages of abundant raw materials, low cost, simple fabrication, and convenient use. It can be mass-produced and has broad application prospects in the field of electrochemical detection.

[0041] The beneficial effects of this invention are:

[0042] 1. This invention embeds a nickel-plated pin into a small hole at the narrow end of a tapered electrode tube, with the pin cap facing outwards, serving as the sensing part of the electrode. Electrode leads are connected to the electrode body via a spiral tube and extend from the other end of the electrode tube. The nickel plating layer on the surface of the nickel-plated pin is cleverly utilized for the electrochemical catalytic oxidation of substances such as sugars, achieving high-sensitivity detection. The electrode is assembled from five components—a nickel-plated pin electrode body, a tapered electrode tube, a hollow electrode rod, electrode leads, and a wedge-shaped elastomer—through insertion and embedding. The fabrication method is simple and efficient, requiring no special equipment and significantly improving electrode manufacturing efficiency.

[0043] 2. This invention also modifies the exposed needle cap electrode surface with coatings of gold, platinum, copper, graphene, etc., by electrochemical deposition, coating and other methods to prepare a variety of novel capillary electrophoretic electrochemical detection electrodes based on pins, so as to meet the needs of detection of different kinds of substances and expand the sample detection range.

[0044] 3. The capillary electrophoresis detection electrode based on a pin, as described in this invention, is composed of five components: a nickel-plated pin electrode body, a conical electrode tube, a hollow electrode rod, electrode leads, and a wedge-shaped elastomer, which are connected and embedded together. This design eliminates the need for sealants and adhesives, allowing for quick disassembly and replacement of each component. This electrode can be used not only for electrochemical detection in conventional capillary electrophoresis, microfluidic chip capillary electrophoresis, flow injection analysis, and liquid chromatography, but also for electrochemical analyses such as voltammetry, amperometric analysis, and coulometric analysis.

[0045] 4. This invention provides a method for preparing a capillary electrophoresis detection electrode based on a pin. This method offers advantages such as simple process, high yield, low raw material cost, and the ability to be mass-produced. The prepared electrode features an overall transparent electrode tube, and the size of the pin cap electrode portion matches the size of the separating capillary. It also offers the advantage of easy alignment with capillary and microfluidic chip channels, making it a promising candidate for application in the field of capillary electrophoresis electrochemical detection.

[0046] 5. The present invention inserts a wedge-shaped elastic body into the end of the electrode rod, which not only fixes the electrode lead to the end of the electrode rod, but also the thrust of the wedge elastic body can reliably connect the spiral end of the electrode lead inside the conical electrode tube with the needle body of the pin, thus achieving electrical contact. Attached Figure Description

[0047] Figure 1 This is a schematic diagram illustrating the fabrication process of the capillary electrophoresis detection electrode based on a pin in this invention.

[0048] Figure 2 A photograph of a nickel-plated pin testing electrode.

[0049] Figure 3The images are: (a) a photograph of the head of the pin detection electrode, (b) a microscopic photograph of the electrode sensing part of the pin cap, (c) a microscopic photograph of the connection between the electrode lead spiral tube and the pin body inside the conical electrode tube, and (d) a microscopic photograph of the narrow tip of a 200 μm pipette tip.

[0050] Figure 4 Microscopic photograph of the surface of the electrode body of the nickel-plated pin inspection electrode head.

[0051] Figure 5 Cyclic voltammetry curves of a nickel-plated pin detection electrode in (a) 75 mM NaOH aqueous solution and (b) 75 mM NaOH aqueous solution containing 10 mM glucose. Scan rate: 100 mV / s.

[0052] Figure 6 Capillary electrophoresis patterns of a mixed solution of 0.5 mM mannitol (a), sucrose (b), lactose (c), glucose (d), and fructose (e) were obtained using a nickel-plated pin electrode.

[0053] Figure 7 Electrophoretic patterns of carbohydrate compounds in water extracts of trumpet vine flower samples were obtained using a nickel-plated pin electrode. a represents mannitol, b represents sucrose, d represents glucose, and e represents fructose.

[0054] Figure 8 Scanning electron microscope image of graphene modified on the detection surface of a pin electrode.

[0055] Figure 9 Capillary electrophoresis patterns of (a) synephrine and (b) hesperidin in tangerine peel extract were obtained using a graphene-modified pin electrode.

[0056] In the diagram, the markings are: 1 is a pin; 2 is a conical electrode tube; 3 is an electrode lead; 4 is an electrode lead spiral tube; 5 is an electrode rod; and 6 is a wedge-shaped elastic body. Detailed Implementation

[0057] The present invention will be further described below with reference to embodiments and accompanying drawings.

[0058] Example 1: Fabrication of a capillary electrophoresis detection electrode based on nickel-plated pins and its application in the detection of carbohydrates.

[0059] A schematic diagram of the fabrication process of the nickel-plated pin detection electrode is shown below. Figure 1It mainly consists of a No. 2 steel core nickel-plated pin 1 (24mm long, 1mm cap diameter, 0.7mm body diameter), a 200μL polypropylene pipette tip 2 (50mm long, 0.55mm narrow diameter, 6mm wide diameter), a 0.5mm diameter copper lead 3, and an electrode rod 5 (10mm long, 5mm outer diameter, 3mm inner diameter). One end of the electrode lead 3 is wound 7 to 8 times using the other pin body as a template to form a copper lead spiral tube 4. The narrow end of the 200μL pipette tip is immersed in a water bath at 70-80℃ for 3 minutes. The tip and body of the nickel-plated pin 1 are then inserted into the preheated small hole at the narrow end of the pipette tip. The hole diameter should be slightly smaller than the pin body diameter to ensure a tight fit and seal. The preheating of the narrow end of the tapered electrode tube is to prevent cracking when the pin is inserted. Next, one end of the copper electrode lead spiral tube 4 is inserted through the wide opening of the pipette tip and covers the pin body. One end of the rigid PVC hollow electrode rod 5 is then inserted through the wide opening of the pipette tip, ensuring the electrode lead 3 passes through the electrode rod 5. Next, a wedge-shaped silicone rubber sheet 6 is inserted into the end of the electrode rod 5 to fix the electrode lead 3 to the end of the electrode rod 5. Simultaneously, the thrust of the wedge-shaped silicone rubber sheet 6 ensures close contact between the electrode spiral tube end inside the pipette tip 2 and the pin body, thus obtaining a capillary electrophoresis detection electrode based on a nickel-plated pin. Figure 2 and Figure 3 Photo a shows the actual nickel-plated pin detection electrode. As can be seen, the electrode tube is entirely transparent, which facilitates alignment between the detection electrode and the outlet of the separating capillary, and reduces the difficulty of positioning operations.

[0060] Figure 3 Microscopic images are shown of the pin detection electrode head, the pin cap sensing electrode body, the connection point between the lead-wire spiral tube and the pin detection electrode tube, and the narrow opening of a 200 μL pipette tip. The results show that the pin body is embedded in the narrow opening of the pipette tip, and the tip tip is not ruptured by the pin body. Furthermore, the nickel-plated pin detection electrode cap has a bright and rounded surface, approximately 1 mm in diameter and 0.5 mm in height, matching the dimensions of the capillary tube. Figure 3 As can be seen, the copper spiral tube can achieve good contact between the electrode lead and the pin body, and can be pulled out, which facilitates the assembly, disassembly and replacement of the electrode. Figure 3 c indicates that the diameter of the pipette tip orifice for a 200μL pipette is approximately 0.55mm, which is slightly smaller than the diameter of the pin body (0.7mm), thus effectively securing the pin body.

[0061] Microscopic images of the nickel-plated pin detection electrode head, cap, and electrode body were also observed using a microscope. Figure 4As can be seen, the electrode surface is covered with pits, which greatly increases the surface roughness and improves detection sensitivity. Furthermore, the numerous micron-sized protrusions can be considered as a micron-array electrode, further enhancing detection sensitivity.

[0062] Figure 5 Cyclic voltammetry curves of the nickel-plated pin detection electrode in 75 mM NaOH aqueous solution and 75 mM NaOH aqueous solution containing 10 mM glucose were obtained at a scan rate of 100 mV / s. In the 75 mM NaOH aqueous solution without glucose, a pair of Ni(III) / Ni(II) redox peaks appeared in the cyclic voltammetry curve of the nickel-plated pin detection electrode. After adding glucose to the 75 mM NaOH aqueous solution, the anodic peak current increased significantly, while the cathode peak current decreased, indicating that the nickel-plated pin detection electrode has a catalytic effect on the electrochemical oxidation of glucose. The anodic and cathode peaks in the cyclic voltammetry curve of glucose on the nickel-plated pin electrode correspond to the processes of Ni(OH)₂ oxidation to NiOOH and NiOOH reduction to Ni(OH)₂. In this process, electrogenerated Ni(III) can catalyze the oxidation of carbohydrates.

[0063] To verify the performance of the nickel-plated pin detection electrode, it was coupled with a capillary zone to separate and detect mannitol, sucrose, lactose, glucose, and fructose. Figure 6 The capillary electrophoresis pattern of a 0.5 mM standard mixed solution of mannitol, sucrose, lactose, glucose, and fructose was obtained using a nickel-plated pin electrode. The results show that the five sugars were completely separated within 10 minutes, with good peak shapes and high sensitivity, indicating that the nickel-plated pin electrode can be used as a capillary electrophoresis electrochemical detection electrode with a good response to sugars.

[0064] Under the selected capillary electrophoretic separation and detection conditions for mannitol, sucrose, lactose, glucose, and fructose, standard mixed solutions of these five sugar compounds (all at a concentration of 0.5 mM) were repeatedly injected nine times, and the electrophoretic peak current was measured to study the stability and reproducibility of the electrode. Each detection time was 20 min. The relative standard deviations of the measured peak currents for mannitol, sucrose, lactose, glucose, and fructose were 2.8%, 3.1%, 3.5%, 2.6%, and 3.3%, respectively. This indicates that the developed nickel-plated pin detection electrode exhibits good reproducibility and stability, which is related to the electrocatalytic activity of the nickel plating on the electrode surface.

[0065] The nickel-plated pin detection electrode prepared in Example 1 was coupled with capillary electrophoresis to analyze the contents of mannitol, sucrose, glucose, and fructose in *Campsis grandiflora* flower samples under selected separation and detection conditions to examine the performance of the developed electrode in actual sample analysis. Each sample was measured in triplicate. The capillary electrophoresis separation capillary was a 40 cm long fused silica capillary (inner diameter 25 μm, outer diameter 360 μm). The separation and injection voltage was 12 kV, the injection time was 6 s, the detection potential was 0.6 V, and the electrophoretic separation solution was a 75 mM NaOH aqueous solution. Figure 7 Electrophoretic patterns of carbohydrate compounds in the water extract of *Campsis grandiflora* were obtained using a nickel-plated pin electrode. Mannitol, sucrose, glucose, and fructose were detected, but lactose was not. The measured values ​​were 11.71, 13.52, 47.84, and 55.12 mg / g, with corresponding relative standard deviations of 3.7%, 3.0%, 3.3%, and 2.7%, respectively, which are satisfactory. The electrochemical detection technique used is selective, responding only to electrochemically active substances, thus simplifying the electrophoretic pattern. Since traditional Chinese medicine is a complex multi-component sample system with numerous interfering substances, the selectivity and detection range can be improved by selecting the electrode and detection potential.

[0066] Example 2: Preparation of gold-modified capillary electrophoresis pin detection electrode

[0067] Example 2: Based on the nickel-plated pin detection electrode of Example 1, a gold-modified capillary electrophoretic pin detection electrode was prepared. Specifically, the nickel-plated pin electrode was placed in an aqueous solution containing 50 mM H₂AuCl₄ and 50 mM HCl, and deposition was carried out at a potential of -0.7 V for 6 min to obtain the gold-modified capillary electrophoretic pin detection electrode. The gold electrode exhibits a catalytic effect on the electrochemical oxidation of compounds such as thiol groups, demonstrating a good electrochemical response.

[0068] Example 3: Preparation and application of graphene-modified capillary electrophoresis pin detection electrode

[0069] The gold-modified capillary electrophoresis pin detection electrode prepared in Example 2 was immersed in a 0.5% graphene oxide aqueous solution for 8 seconds, then removed and air-dried vertically with the pin cap facing down for 20 minutes. Next, it was baked under a 250W far-infrared lamp for 20 minutes, with a distance of 20 cm between the electrode surface and the lamp surface. Far-infrared radiation causes some oxygen-containing groups to be removed from the graphene oxide, generating a conductive graphene-modified capillary electrophoresis pin detection electrode. Figure 8 A scanning electron microscope image of graphene modified on the detection surface of a pin electrode, showing typical graphene wrinkled morphology.

[0070] Figure 9Capillary electrophoresis patterns of (a) synephrine and (b) hesperidin in the methanol extract of dried tangerine peel were detected using a graphene-modified pin electrode. Synephrine and hesperidin were identified by spiking. The capillary for separation was a 40 cm long fused silica capillary (25 μm inner diameter, 360 μm outer diameter). The separation and injection voltage was 9 kV, the injection time was 6 s, the detection potential was 0.8 V, and the electrophoresis solution was 50 mM borate buffer (pH 9.2). It is evident that synephrine and hesperidin are present in high concentrations in dried tangerine peel and are markers for evaluating its quality.

[0071] Example 4: Preparation of platinum-modified capillary electrophoresis pin detection electrode

[0072] The nickel-plated pin electrode prepared in Example 1 was placed in an aqueous solution containing 5 mM K2PtCl4 and 100 mM HCl and deposited at a potential of -0.6 V for 5 min to obtain a platinum-modified capillary electrophoretic pin detection electrode, which can be used for capillary electrophoretic electrochemical detection of substances such as hydrazine and aromatic amines that have good response on platinum electrodes.

[0073] Example 5: Copper-modified capillary electrophoresis pin detection electrode

[0074] The nickel-plated pin electrode prepared in Example 1 was placed in a solution containing 50 mM copper sulfate, 1.6 M sulfuric acid and 0.5-3 mg / L 2-mercaptobenzoimidazole, and deposited at -0.5 V to -0.8 V for 1-5 min to obtain a copper-modified capillary electrophoresis pin detection electrode, which can be used for capillary electrophoretic electrochemical detection of substances such as sugars, amino acids, polyhydroxy compounds, and glycosides that have a good response to copper electrodes.

[0075] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a capillary electrophoresis detection electrode based on a pin, characterized in that, The specific steps are as follows: (1) Heat the tip of the transparent thermoplastic conical electrode tube and insert a nickel-plated pin into the small hole at its narrow end, leaving only the pin cap exposed, as the sensing part of the electrode. (2) Wind one end of the copper electrode lead into a spiral tube, insert it through the wide opening of the conical electrode tube, and fit the pin body inside the spiral tube. (3) Insert one end of the hollow plastic electrode rod into the wide opening of the tapered electrode tube and fix it, and lead the electrode lead out from the hollow electrode rod; (4) Insert a wedge-shaped elastomer into the end of the electrode rod, fix the electrode lead, and make the spiral end of the lead tightly contact the pin body to obtain a capillary electrophoresis detection electrode based on nickel-plated pin. (5) Prepare a modification layer on the exposed surface of the pin cap electrode to meet the needs of detecting different types of substances.

2. The method for preparing a capillary electrophoresis detection electrode according to claim 1, characterized in that: In step (1), the tip of the plastic conical electrode tube is heated by immersing the tip of the transparent thermoplastic conical electrode tube in a water bath at 50-90°C for 1-5 minutes, or by blowing it with hot air at 50-90°C for 1-5 minutes; the tip and body of the nickel-plated pin are inserted into the small hole at the narrow end of the preheated plastic conical electrode tube, the diameter of the small hole being slightly smaller than the diameter of the pin body, to achieve a tight fit and seal of the pin body; In step (2), the diameter of the copper electrode lead is 200-700μm, and the method for preparing one end of the spiral tube is as follows: use another nickel-plated pin of the same specification as a template to wind 5 to 10 turns to form a copper lead spiral tube; remove the spiral tube, insert it through the wide opening of the tapered electrode tube, and cover the pin body; In step (3), one end of the hollow plastic electrode rod is inserted through the wide opening of the tapered electrode tube, and the electrode lead is threaded through the electrode rod; the electrode rod can extend the electrode length. In step (4), a wedge-shaped elastic body is inserted into the end of the electrode rod, and the electrode lead is fixed to the end of the electrode rod. At the same time, the thrust of the wedge elastic body makes the spiral end of the electrode lead in the conical electrode tube come into close contact with the needle body, thus obtaining a capillary electrophoresis detection electrode based on a nickel-plated needle. In step (5), the modification layer is one or more of the following: gold, platinum, copper, and graphene sensing materials, and the modification method is electrochemical deposition or surface coating.

3. The method for preparing a capillary electrophoresis detection electrode according to claim 1, characterized in that, In step (3), the hollow electrode rod material is selected from polyvinyl chloride, polymethyl methacrylate, polystyrene, and glass fiber reinforced resin; its outer diameter is slightly smaller than the wide inner diameter of the tapered electrode tube so as to facilitate insertion and installation.

4. The method for preparing a capillary electrophoresis detection electrode according to claim 1, characterized in that, In step (4), the material of the wedge-shaped elastomer is selected from silicone rubber, polyurethane, and plasticized polyvinyl chloride.

5. The method for preparing a capillary electrophoresis detection electrode according to claim 1, characterized in that, In step (5): The nickel-plated pin electrode from step (4) is placed in an aqueous solution containing 10-100 mM H2AuCl4 and 10-100 mM HCl, and deposited at -0.5 V to -0.9 V for 1-8 min to obtain a gold-modified capillary electrophoresis pin detection electrode; or The nickel-plated pin electrode from step (4) is placed in an aqueous solution containing 2-10 mM K2PtCl4 and 20-200 mM HCl, and deposited at -0.3 V to -0.7 V for 1-6 min to obtain a platinum-modified capillary electrophoresis pin detection electrode; or The nickel-plated pin electrode from step (4) is placed in a solution containing 20-80 mM copper sulfate, 1.4-1.8M sulfuric acid, and 0.5-3 mg / L of 2-mercaptobenzoimidazole, and deposited at -0.5V to -0.8V for 1-5 min to obtain a copper-modified capillary electrophoresis pin detection electrode; or After the cap portion of the nickel-plated pin electrode in step (4) is gold-plated as described above, it is immersed in a 0.2-1% graphene oxide aqueous solution for 2-10 seconds and then removed with the cap electrode facing down. It is then air-dried vertically in the air for 10-30 minutes. Then, it is baked with a 250W far-infrared lamp for 10-30 minutes to remove some of the epoxy groups from the graphene oxide, thereby generating a conductive graphene-modified capillary electrophoresis pin detection electrode.

6. A capillary electrophoresis detection electrode obtained by the preparation method according to any one of claims 1-5.

7. The use of the capillary electrophoresis detection electrode as described in claim 6 in capillary electrophoresis electrochemical detection.

8. The use of the capillary electrophoresis detection electrode as described in claim 7 in capillary electrophoresis electrochemical detection, wherein the capillary electrophoresis electrochemical detection is the electrochemical detection of sugars or amino acids.

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