A modified electrode, its preparation method and application

Abstract

This invention discloses a modified electrode, its preparation method, and its application. The modified electrode comprises a hexabenzo[a]methyl methacrylate (HMM) layer and a working electrode, wherein the HMM layer is loaded on the surface of the working electrode. The HMM-modified material is obtained by in-situ one-step deposition on the electrode surface using electrochemical polymerization technology, thereby improving the detection performance of imidacloprid and solving the problem of poor film-forming properties caused by the poor solubility of carbon materials.

Description

Technical Field

[0001] This invention relates to the field of detection technology, and in particular to a modified electrode, its preparation method, and its application. Background Technology

[0002] Imidacloprid is a neonicotinoid pesticide widely used in agriculture. It is a nitromethylene systemic insecticide, acting as an agent of nicotinic acetylcholine receptors. It disrupts the insect's motor nervous system, causing the loss of chemical signal transduction. It does not exhibit cross-resistance issues and has multiple effects, including contact, stomach poison, and systemic action. It is used to control piercing-sucking insects and their resistant strains. Although neonicotinoid pesticides have low toxicity to higher animals, increasing research indicates that they still pose risks to the ecological environment, wildlife, and even human health. Furthermore, excessive pesticide residues can be a significant obstacle to the export of agricultural and agricultural byproducts. Therefore, developing simple, rapid, accurate, sensitive, and practical standard methods for agricultural product safety testing is of great importance to ensure public nutrition and health, mitigate the impact of excessive pesticide residues on crop quality, and improve the overall competitiveness of agricultural exports.

[0003] Electrochemical sensing technology, requiring no complex pretreatment, boasts advantages such as simplicity, speed, high sensitivity, good selectivity, and low preparation cost, making it suitable for rapid on-site detection and gradually becoming a research hotspot for pesticide residue detection. However, traditional bare working electrodes (such as glassy carbon electrodes) suffer from poor conductivity and slow electron transfer, resulting in suboptimal electrochemical detection performance for imidacloprid. Modification with functional materials can improve sensor detection performance; graphene and multi-walled carbon nanotubes are commonly used modification materials. However, graphene and other carbon materials are typically insoluble in liquids, leading to poor uniformity and stability of films formed through drop-coating methods. Summary of the Invention

[0004] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, the object of the present invention is to provide a modified electrode, its preparation method, and its application.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a modified electrode comprising a hexabenzo[a]cobalt layer and a working electrode, wherein the hexabenzo[a]cobalt layer is loaded on the surface of the working electrode.

[0007] In this invention, hexabenzo[a]benzo[b] ...

[0008] In some embodiments of the present invention, the thickness of the hexabenzo[a]cobalamin layer is 1 nm to 100 μm.

[0009] In some embodiments of the present invention, the working electrode is selected from glassy carbon electrode (GCE), metal oxide electrode, and metal electrode.

[0010] A second aspect of the present invention provides a method for preparing the modified electrode, comprising the following steps:

[0011] A hexabenzocone layer is formed on the working electrode through an electrochemical polymerization reaction.

[0012] In some embodiments of the present invention, the method for preparing the modified electrode includes the following steps: placing the working electrode in a hexaphenylbenzene solution and carrying out an electrochemical polymerization reaction to obtain the modified electrode.

[0013]

[0014] In some embodiments of the present invention, the conditions for the electropolymerization reaction are set as follows: the polymerization reaction is carried out using a constant potential method; the polymerization potential is -5V to 5V; and the polymerization time is 0 to 60 minutes.

[0015] In some embodiments of the present invention, the polymerization potential is -2V to 2V; the polymerization time is 10s to 100s.

[0016] In some embodiments of the present invention, the hexaphenylbenzene solution comprises a dichloromethane solution containing tetrabutylammonium hexafluorophosphate (Bu4NPF6) with hexaphenylbenzene.

[0017] In some embodiments of the present invention, the hexaphenylbenzene solution comprises a dichloromethane solution of 0.01 mol / L to 10 mol / L Bu4NPF6 containing 0.1 mg / mL to 100 mg / mL hexaphenylbenzene.

[0018] A third aspect of the invention provides an electrochemical sensor comprising the modified electrode described above.

[0019] In some embodiments of the present invention, the electrochemical sensor is a two-electrode system or a three-electrode system.

[0020] In some embodiments of the present invention, the electrochemical sensor further includes a reference electrode and a counter electrode.

[0021] In some embodiments of the present invention, the reference electrode is one of a calomel electrode, a silver chloride electrode, a mercurous sulfate electrode, and a mercuric oxide electrode.

[0022] In some embodiments of the present invention, the counter electrode is one of a platinum electrode or a titanium electrode. Specifically, the counter electrode, i.e., the auxiliary electrode, can be selected from an inert metal electrode and forms an electrode system with the working electrode.

[0023] A fourth aspect of the present invention provides the application of the modified electrode described herein in the detection of electroactive nitro compounds.

[0024] In some embodiments of the present invention, the electroactive nitro compound includes imidacloprid, parathion, methyl parathion, thiamethoxam, thiamethoxam, imidacloprid, pipemidone, dinotefuran, acetamiprid, etc.

[0025] In a fifth aspect, the present invention provides a method for detecting imidacloprid, comprising using the modified electrode or the electrochemical sensor to perform voltammetry on the sample to be tested, measuring the current value of the reduction peak, and then quantitatively analyzing the imidacloprid concentration in the sample to be tested according to the imidacloprid standard curve.

[0026] In this invention, the chemical structure of imidacloprid contains an electroactive functional group—nitro (-NO2). At a certain potential, the nitro group can gain electrons and undergo a reduction reaction with protons, converting into hydroxylamine (-NHOH), thus generating the reduced state of imidacloprid and producing a significant electrochemical signal. The strength of this signal allows for quantitative analysis, and therefore, an electrochemical sensor can be used for detection.

[0027]

[0028] In some embodiments of the present invention, the voltammetry method includes any one of differential pulse voltammetry (DPV), square wave pulse voltammetry, and cyclic voltammetry (CV).

[0029] In some embodiments of the present invention, when the voltammetry is a differential pulse voltammetry, the parameters are set as follows: scan potential range of -0.7V to -1.3V, potential increment of 0.001V to 0.1V, pulse amplitude of 0.01V to 1V, pulse width of 0-60s, sampling interval of 0-10s, pulse period of 0-60s, rest time of 0-60min, and sensitivity of 1×10⁻⁶. -8 A / V ~ 1A / V.

[0030] In some embodiments of the present invention, when the voltammetry is a cyclic voltammetry, the parameters are set as follows: the scanning potential range is -0.7V to -1.3V, the scanning speed is 0.1mV / s to 5V / s, and the number of scanning cycles is 1 to 100; preferably, the parameters are set as follows: the scanning potential range is -0.7V to -1.3V, the scanning speed is 50mV / s, and the number of scanning cycles is 1.

[0031] In some embodiments of the present invention, the concentration of the sample to be tested is 0.1 nM to 1 M.

[0032] In some embodiments of the present invention, the method for detecting imidacloprid includes immersing the modified electrode in the sample to be tested; the immersion time is 1s to 360s; preferably 60s to 360s.

[0033] In some embodiments of the present invention, the method for detecting imidacloprid includes the following steps:

[0034] (1) The modified electrode in the electrochemical sensor was placed in a series of imidacloprid standard solutions, and the voltammetry method was used for detection. The current magnitude of the reduction peak and the concentration of the imidacloprid solution were used as the raw data to analyze and draw a standard curve.

[0035] (2) Place the modified electrode in the electrochemical sensor in the sample to be tested and perform voltammetry detection. After measuring the current of the reduction peak, calculate the content of imidacloprid in the liquid sample to be tested based on the standard curve in step (1).

[0036] In some embodiments of the present invention, the series of imidacloprid standard solutions and the test sample respectively include imidacloprid and a buffer solution; preferably, the buffer solution includes any one of phosphate, acetate, and citrate.

[0037] In some embodiments of the present invention, the concentration of the series of imidacloprid standard solutions is 5 μmol / L to 1000 μmol / L; preferably 5 μmol / L to 850 μmol / L.

[0038] In some embodiments of the present invention, when the concentration of the series of imidacloprid standard solutions is 5 μmol / L to 100 μmol / L, the linear correlation coefficient of the corresponding standard curve is R. 2 ≥0.99988.

[0039] In some embodiments of the present invention, when the concentration of the series of imidacloprid standard solutions is 100 μmol / L to 850 μmol / L, the linear correlation coefficient of the corresponding standard curve is R. 2 ≥0.99602.

[0040] In some embodiments of the present invention, the pH of the series of imidacloprid standard solutions is 5.00 to 8.00; the pH of the sample to be tested is 5.00 to 8.00; preferably 6.40 to 7.60.

[0041] In some embodiments of the present invention, the voltammetric detection includes the following steps:

[0042] Under open-circuit conditions, the modified electrode after scanning is enriched in solution, and then voltammetry is used, with the scanning range set from -0.7V to -1.3V, to reduce the nitro group on imidacloprid to produce hydroxylamine.

[0043] In some embodiments of the present invention, the enrichment process specifically involves immersing the modified electrode in the sample to be tested.

[0044] In some embodiments of the present invention, the enrichment process takes 0 to 360 seconds; preferably 60 to 360 seconds; and more preferably 240 to 360 seconds.

[0045] The beneficial effects of this invention are: by using electrochemical polymerization technology to deposit hexabenzo[a]methyl methacrylate modified material on the electrode surface in situ in a one-step manner, the detection performance of imidacloprid is improved, and the problem of poor film-forming properties caused by poor solubility of carbon materials is solved. Attached Figure Description

[0046] Figure 1 This is a cyclic voltammetric scan of the blank GCE electrode and the HBC / GCE electrode in imidacloprid phosphate buffer in Example 3 of the present invention.

[0047] Figure 2 The electrochemical behavior of imidacloprid was tested using the CV method and the DPV method in Examples 3 and 4 of this invention.

[0048] Figure 3 The images show DPV scans (a) of HBC / GCE electrodes with different polymerization times in imidacloprid phosphate buffer and (b) of peak current values ​​of the corresponding electrodes at different polymerization times in Example 5 of this invention.

[0049] Figure 4 The figures shown in Example 6 of this invention are DPV scans of the HBC / GCE electrode in imidacloprid phosphate buffer solutions at different pH values ​​(a) and the relationship between the imidacloprid phosphate buffer solutions at different pH values ​​and their corresponding DPV peak current values ​​(b).

[0050] Figure 5 The images show DPV scans (a) and (b) of different enrichment times and their corresponding DPV peak current values ​​for the HBC / GCE electrode enriched in imidacloprid phosphate buffer in Example 7 of this invention.

[0051] Figure 6 The graph shows the DPV electrochemical response (a) of the HBC / GCE electrode in phosphate buffer solutions with different imidacloprid concentrations in Example 8 of the present invention, and the linear relationship between different imidacloprid concentrations and their corresponding DPV peak current values ​​(b).

[0052] Figure 7 This is a graph showing the peak current values ​​of 10 identical HBC / GCE electrodes in imidacloprid phosphate buffer in Example 9 of the present invention.

[0053] Figure 8 This is a graph showing the relationship between different interfering substances added in Embodiment 10 of the present invention and their corresponding peak current values. Detailed Implementation

[0054] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments and comparative examples are all available from conventional commercial sources or can be obtained by existing technical methods. Unless otherwise specified, the test or experimental methods are conventional methods in the art.

[0055] In this invention, the pretreatment method for the GCE electrode is as follows: At room temperature, a polishing cloth is attached to the disc of an electrode polishing machine. A certain amount of alumina polishing powder with a particle size of 0.05 μm is added to the polishing cloth, and a few drops of ultrapure water are added to the polishing powder to form a suspension. The GCE electrode is then polished perpendicular to the polishing cloth and the electrode polishing machine, using a counterclockwise drawing method for 20 seconds, while keeping the electrode polishing machine stable. After polishing, the suspension on the electrode surface is cleaned with distilled water. Then, it is ultrasonically cleaned with anhydrous ethanol for 1 minute and dried with nitrogen gas.

[0056] In this invention, the preparation method of a 0.1 mol / L Bu4NPF6 dichloromethane solution containing 1 mg / mL HBC is as follows: At room temperature, accurately weigh 0.01 g of hexaphenylbenzene and 0.38743 g of Bu4NPF6 and dissolve them together in 10 mL of dichloromethane to obtain a 0.1 mol / L Bu4NPF6 dichloromethane solution containing 1 mg / mL HBC. The Bu4NPF6 is pre-dried at 120°C for 6–8 h, and the dried Bu4NPF6 is then sealed and stored at room temperature.

[0057] In this invention, the method for preparing the phosphate buffer solution is as follows: At room temperature, accurately weigh 4.4775 g of disodium hydrogen phosphate dodecahydrate and 1.95 g of sodium dihydrogen phosphate dihydrate using an electronic balance, dissolve them together in ultrapure water, and prepare them in a 250 mL volumetric flask to obtain a 0.1 mol / L phosphate buffer solution. Then, adjust the pH of the buffer solution by adding 0.1 mol / L hydrochloric acid solution or 0.1 mol / L sodium hydroxide solution to prepare a phosphate buffer solution with the required pH.

[0058] Example 1

[0059] This embodiment prepares a modified GCE electrode, and the specific process is as follows:

[0060] At room temperature, clean GCE electrodes, platinum wire electrodes, and Ag / Ag were used. + The electrodes were placed in a 0.1 mol / L dichloromethane solution containing 1 mg / mL hexaphenylbenzene (Bu4NPF6), ensuring all electrodes were completely submerged. HBC molecules were deposited on the surface of the bare GCE electrode using a potentiostatic method. The parameters were set as follows: initial potential 1.65 V, sampling interval 0.001 s, and scan time 70 s. After deposition, the electrodes were cleaned with dichloromethane and allowed to air dry, yielding the modified GCE electrode (HBC / GCE electrode).

[0061] Example 2

[0062] In this embodiment, GCE electrodes modified with different HBC polymer film thicknesses are prepared. The specific process is as follows:

[0063] At room temperature, using a clean GCE electrode as the working electrode, Ag / Ag + Using the reference electrode and the platinum wire electrode as the counter electrode, HBC / GCE electrodes were electropolymerized for 10 s, 30 s, 50 s, 70 s, and 90 s respectively in a dichloromethane solution containing 1 mg / mL hexaphenylbenzene in 0.1 mol / L Bu4NPF6 using a potentiostatic method (potential of 1.65 V and sampling interval of 0.001 s). The electrodes were then cleaned with dichloromethane and air-dried for later use, resulting in HBC / GCE electrodes with different polymerization times.

[0064] Example 3

[0065] A method for detecting imidacloprid, the specific process of which is as follows:

[0066] At room temperature, a blank GCE electrode and the HBC / GCE electrode prepared in Example 1 were used as working electrodes, respectively, with a saturated calomel electrode as the reference electrode and a platinum wire electrode as the counter electrode. A 1×10⁻⁶ electrode was inserted into the electrode. -4The imidacloprid phosphate buffer solution (pH = 6.80) was analyzed using the CV method. The scanning potential range was -0.7V to -1.3V, the scan rate was 50mV / s, and the number of scans was one revolution. The results are as follows: Figure 1 As shown.

[0067] from Figure 1 It can be seen that the reduction peak of the GCE electrode at around -1.006 V is relatively small, with a peak current of only 0.836E-5 A, while the HBC / GCE electrode shows a reduction peak at -1.062 V, and the peak current of the reduction peak is 3.856E-5 A, which is 4.6 times higher than that of the GCE electrode. Therefore, under the same conditions, the HBC / GCE electrode has better detection performance for imidacloprid than the GCE electrode. This is mainly because the HBC polymer film has a catalytic effect on the electrochemical reaction of imidacloprid, increasing the electrocatalytic active area of ​​the electrode, accelerating electron transfer, and resulting in a rapid electrochemical reaction. Therefore, compared with the GCE electrode, the peak current value of the reduction peak of the HBC / GCE electrode is significantly higher, indicating that the use of hexabenzo[a]methyl methacrylate (HCM)-modified electrode is beneficial for enhancing the imidacloprid reduction peak signal.

[0068] Example 4

[0069] A method for detecting imidacloprid, the specific process of which is as follows:

[0070] At room temperature, using the HBC / GCE electrode prepared in Example 1 as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire electrode as the counter electrode, a 1×10⁻⁶ electrode was inserted. -4 The following parameters were used: mol / L imidacloprid phosphate buffer (pH = 6.80), and the DPV method was employed: scanning potential range -0.7V to -1.3V, potential increment 0.004V, amplitude 0.05V, pulse width 0.06s, sampling interval 0.02s, pulse period 0.5s, settling time 2s, and sensitivity 1×10⁻⁶. -4 A / V. The result is as follows: Figure 2 As shown.

[0071] from Figure 2 It can be seen that the peak current of the irreversible reduction peak is significantly greater when using the CV method than when using the DPV method. However, the peak current of the DPV method is more uniform and stable, and the background current is smaller. Therefore, the DPV method is selected for experimental condition optimization, linear range experiments, repeatability experiments, stability experiments, and spike recovery experiments.

[0072] Example 5

[0073] A method for detecting imidacloprid, the specific process of which is as follows:

[0074] Following the method of Example 4, HBC / GCE electrodes with different polymer times prepared in Example 2 were used to test 1×10⁻¹⁰ HBC / GCE electrodes using the DPV method. -4 The test results for the mol / L imidacloprid phosphate buffer (pH = 6.80) are as follows: Figure 3 As shown in (a), to better compare the peak current at different polymerization times, a dotted line graph was plotted between the peak current and polymerization time, as follows: Figure 3 As shown in (b).

[0075] from Figure 3 It can be seen that the peak current increases with increasing polymerization time, reaching its highest point at 70 seconds. Further increases in polymerization time lead to a decrease in peak current. When the polymerization time is less than 70 seconds, the film thickness increases continuously with increasing polymerization time, resulting in an increase in the amount of HBC deposited on the electrode and thus enhancing the catalytic effect. When the polymerization time is greater than 70 seconds, the polymer film thickness increases, conductivity decreases, and resistance to electron transfer increases, affecting the electron transfer rate, thus causing a decrease in peak current. Therefore, a polymerization time of 70 seconds yields a working electrode with excellent electrochemical catalytic activity and the highest peak current. Thus, the reduction peak current is highest at a polymerization time of 70 seconds, indicating that the HBC polymer film thickness is just right, resulting in excellent electrochemical catalytic activity of the electrode.

[0076] Example 6

[0077] A method for detecting imidacloprid, the specific process of which is as follows:

[0078] At room temperature, a 0.1 mol / L phosphate buffer solution was prepared, and the pH was adjusted to 5.60, 6.00, 6.40, 6.80, 7.20, 7.60, and 8.00 by adding 0.1 mol / L hydrochloric acid solution or 0.1 mol / L sodium hydroxide solution. Using the HBC / GCE electrode prepared in Example 1 as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire electrode as the counter electrode, the DPV method was used to test 1×10⁻⁶ different pH values ​​according to the method in Example 4. -4 The test results for the mol / L imidacloprid phosphate buffer are as follows: Figure 4 As shown in (a), to make the comparison more intuitive, the peak current is plotted against the pH value. Figure 4 (b)

[0079] from Figure 4It can be seen that within the pH range of 5.60–8.00, the peak current value first increases and then decreases with increasing pH, reaching its maximum at pH 6.80. Under acidic conditions, the working electrode surface is less prone to reaction, and the lower the pH, the smaller the current response. Under alkaline conditions, imidacloprid is highly unstable, reducing the amount of imidacloprid reacting on the electrode surface and significantly decreasing the peak current. At pH 6.80, it exhibits excellent electrochemical catalytic activity towards the analyte. Therefore, the electrochemical signal and peak current are both maximum at pH 6.80.

[0080] Example 7

[0081] A method for detecting imidacloprid, the specific process of which is as follows:

[0082] Following the method of Example 4, the HBC / GCE electrode prepared in Example 1 was inserted as the working electrode into a 1×10 - 4 After enriching in mol / L imidacloprid phosphate buffer (pH = 6.80) for 60s, 120s, 180s, 240s, 300s, and 360s respectively, the DPV method was used for testing according to the method in Example 4. The test results are as follows: Figure 5 As shown in (a), the relationship between peak current value and enrichment time is plotted. Figure 5 (b)

[0083] Analysis of the two figures reveals that as the enrichment time increases, the peak current of imidacloprid continuously increases. However, once a certain enrichment time is reached, the peak current stops increasing, indicating that imidacloprid reaches adsorption saturation on the working electrode surface. After reaching saturation, extending the enrichment time does not further increase the peak current; instead, it tends to decrease. The oxidation peak current is highest at 300 seconds of enrichment. In other embodiments, the enrichment time was set to 300 seconds.

[0084] Example 8

[0085] A method for detecting imidacloprid, the specific process of which is as follows:

[0086] (1) At room temperature, prepare 0.1 mol / L hydrochloric acid solution and 0.1 mol / L sodium hydroxide solution, and adjust the pH to 6.80 by adjusting the mixing ratio of the two solutions. Dilute the prepared imidacloprid standard solution with pH=6.80 phosphate buffer solution to prepare imidacloprid standard solutions with concentrations of 5 μmol / L, 7.5 μmol / L, 10 μmol / L, 25 μmol / L, 50 μmol / L, 75 μmol / L, 100 μmol / L, 200 μmol / L, 400 μmol / L, 550 μmol / L, 750 μmol / L and 850 μmol / L.

[0087] (2) At room temperature, the HBC / GCE electrode prepared in Example 1 was used as the working electrode, the saturated calomel electrode as the reference electrode, and the platinum wire electrode as the counter electrode. They were inserted into the imidacloprid standard solution prepared in (1) and tested using the DPV method according to the method in Example 4. A standard curve was plotted based on the peak current value of the reduction peak and the corresponding imidacloprid concentration.

[0088] Figure 6 (a) The DPV electrochemical response of the hexabenzo[a]oxa]oxa electrode in 0.1 mol / L phosphate buffer at pH 6.80 with different imidacloprid concentrations is shown. A distinct reduction peak is observed near -0.992 V, and the peak current response increases with increasing imidacloprid concentration. The peak current versus concentration curve is shown below. Figure 6 As shown in (b), by fitting the curve, it was found that the peak current and its concentration showed a good linear relationship in the two concentration ranges of 5μM~100μM and 100μM~850μM.

[0089] The linear regression equation is: I1(A) = 0.01416c(μmol / L) + 0.30237(R) 2 =0.99988)

[0090] I2(A)=0.00287c(μmol / L)+1.457(R 2 =0.99602)

[0091] The detection limit calculated using a signal-to-noise ratio of three is 1.67 μM.

[0092] Example 9

[0093] A method for detecting imidacloprid, the specific process of which is as follows:

[0094] Ten identical HBC / GCE electrodes prepared in Example 1 were used as working electrodes, a saturated calomel electrode as a reference electrode, and a platinum wire electrode as a counter electrode. These electrodes were then inserted into a 1×10... -4 In mol / L imidacloprid phosphate buffer (pH = 6.80), following the method in Example 4, 10 sets of tests were performed using the DPV method. Bar graphs were created showing the different electrodes and peak currents, as follows: Figure 7 As shown.

[0095] from Figure 7 It can be observed that the peak current measured by the 10 HBC / GCE electrodes is around 1.8E-5A, indicating good repeatability.

[0096] Example 10

[0097] A method for detecting imidacloprid, the specific process of which is as follows:

[0098] In a phosphate buffer solution (pH = 6.80) containing imidacloprid, sodium hydroxide solution with a concentration 10 times that of imidacloprid was added. + K + Zn 2+ Inorganic ions, malathion, and fenitrothion were used. The HBC / GCE electrode prepared in Example 1 was used as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire electrode as the counter electrode. Following the method in Example 4, the DPV method was used for testing, and bar charts showing the addition of different substances and peak current values ​​were obtained. Figure 8 As shown.

[0099] from Figure 8 As can be seen from the experimental results, the peak current value of imidacloprid detection did not change significantly after the addition of different substances, remaining around 1.75E-5A. This indicates that these substances have little effect on the electrochemical reaction signal for imidacloprid detection, meaning that the hexabenzo[a] ...

[0100] Example 11

[0101] A method for detecting imidacloprid, the specific process of which is as follows:

[0102] At room temperature, the pear was ground and crushed in a mortar and pestle, and filtered to obtain pear juice. 1 mL of pear juice was taken, and a certain amount of imidacloprid was added. The mixture was diluted to 10 mL with a pH of 6.80 and a concentration of 0.1 mol / L phosphate buffer, resulting in imidacloprid concentrations of 50 ng / mL and 100 ng / mL, respectively. Using the HBC / GCE electrode prepared in Example 1 as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire as the counter electrode, the DPV method was used for testing according to the method in Example 4, and the peak current of the reduction peak was recorded. The peak current of the reduction peak was substituted into the standard curve to calculate the theoretical concentration of imidacloprid. The ratio of the theoretical concentration to the actual added concentration was the recovery rate. The test and analysis results are shown in Table 1, with the imidacloprid recovery rate ranging from 102.03% to 105.1%.

[0103] Table 1 Spike Recovery Experiment

[0104]

[0105] Comparative Example

[0106] This comparative example demonstrates the preparation of an electrochemical sensor and its detection of imidacloprid. The specific process is as follows:

[0107] (1) Pretreatment of GCE electrode: At room temperature, a polishing cloth is attached to the disc of an electrode polishing machine. A certain amount of alumina polishing powder with a particle size of 0.05μm is added to the polishing cloth, and a few drops of ultrapure water are added to the polishing powder to form a suspension. The GCE electrode is then polished perpendicular to the polishing cloth and the electrode polishing machine, using a counterclockwise drawing method for 20 seconds, while keeping the electrode polishing machine stable. After polishing, the suspension on the electrode surface is cleaned with distilled water. Then, it is ultrasonically cleaned with anhydrous ethanol for 1 minute and dried with nitrogen.

[0108] (2) Add 0.05 mg of graphene oxide (GO) powder to 1 mL of ultrapure water and sonicate in an ultrasonic instrument for 1 h to obtain a GO dispersion with a concentration of 0.05 mg / mL. Use a pipette to take 4 μL of the 0.05 mg / mL GO dispersion and drop it onto the clean surface of a GCE electrode. Let it dry naturally at room temperature to obtain a graphene oxide / glassy carbon electrode (GO / GCE). The GO film formed on the GO / GCE surface is visibly uneven, indicating that there are differences in detection sensitivity and other properties at different positions on the electrode, which affects the overall detection performance.

[0109] (3) Prepare imidacloprid standard solutions with concentrations of 5 μM, 10 μM, 25 μM, 50 μM, 75 μM, 100 μM, 250 μM, 500 μM, 750 μM and 1000 μM respectively using 0.1 M phosphate buffer solution with pH 6.80.

[0110] (4) Using the GO / GCE electrode prepared in (2) as the working electrode, the calomel electrode as the reference electrode, and the platinum wire electrode as the counter electrode, they were inserted into imidacloprid standard solutions of different concentrations prepared in (3). The standard solutions were tested using the DPV method. The test parameters were as follows: scanning potential range of -0.6V to -1.2V, potential increment of 0.004V, amplitude of 0.05V, pulse width of 0.06s, sampling interval of 0.02s, pulse period of 0.5s, settling time of 2s, and sensitivity of 1×10⁻⁶. -4 A / V. After the test, it was found that the GO film on the GO / GCE electrode would detach and fall into the solution, indicating that the GO film is not firmly bonded to the GCE electrode, is easily detached, and cannot be recycled. A standard curve was plotted based on the peak current value of the reduction peak and the corresponding imidacloprid concentration. The sensor's detection range for imidacloprid is 5μM~140μM and 140μM~750μM, with a detection limit of 1.7μM.

[0111] (5) At room temperature, wash the corn sample thoroughly, grind it, and filter it through a funnel to obtain corn juice. Take 1 mL of corn juice and dilute it 100 times with pH=6.80 phosphate buffer. Weigh a certain amount of imidacloprid and use it to prepare a solution with a concentration of 5×10⁻⁶. -5mol / L, 1×10 -4 mol / L imidacloprid corn sample solution. Using the method in (3), the DPV method was used to treat 5×10 mol / L imidacloprid corn sample solution. -5 mol / L, 1×10 -4 The mol / L imidacloprid corn sample solution was tested, and the peak current of the reduction peak was recorded. The peak current of the reduction peak was substituted into the standard curve to calculate the theoretical concentration of imidacloprid. The recovery rates were calculated by comparing the theoretical concentration with the actual concentration added, which were 100.4% and 101.4%, respectively.

[0112] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for detecting imidacloprid, characterized in that: The method includes using an electrochemical sensor for detecting imidacloprid to perform voltammetric analysis on the sample, measuring the current value of the reduction peak, and then quantitatively analyzing the imidacloprid concentration in the sample according to the imidacloprid standard curve. The electrochemical sensor for detecting imidacloprid includes a modified electrode, a reference electrode, and a counter electrode. The modified electrode includes a hexabenzo[a]methyl methacrylate (HMM) layer and a working electrode, with the HMM layer loaded on the surface of the working electrode. The electrochemical sensor for detecting imidacloprid detects the electrochemical signal generated by imidacloprid under voltammetric analysis.

2. The method for detecting imidacloprid according to claim 1, characterized in that: The thickness of the hexabenzo[a]cobala layer is 1 nm to 100 μm.

3. The method for detecting imidacloprid according to claim 1, characterized in that: The method for preparing the modified electrode includes the following steps: A hexabenzocone layer is formed on the working electrode through an electrochemical polymerization reaction.

4. The method for detecting imidacloprid according to claim 3, characterized in that: The method for preparing the modified electrode includes the following steps: placing the working electrode in a hexaphenylbenzene solution and carrying out an electrochemical polymerization reaction to obtain the modified electrode.

5. The method for detecting imidacloprid according to claim 4, characterized in that: The conditions for the electrochemical polymerization reaction are set as follows: the polymerization reaction is carried out by constant potential method; the polymerization potential is -5V to 5V; the polymerization time is 0 to 60 min.

6. The method for detecting imidacloprid according to claim 1, characterized in that: The method for detecting imidacloprid includes immersing a modified electrode in the sample to be tested; the immersion time is 1s to 360s.

7. The method for detecting imidacloprid according to claim 1, characterized in that: The pH of the sample to be tested is 5.0~8.

0.

8. The method for detecting imidacloprid according to claim 1, characterized in that: When the voltammetry method is differential pulse voltammetry, the parameters are set as follows: scan potential range of -0.7V to -1.3V, potential increment of 0.001V to 0.1V, pulse amplitude of 0.01V to 1V, pulse width of 0-60s, sampling interval of 0-10s, pulse period of 0-60s, rest time of 0-60min, and sensitivity of 1×10⁻⁶. -8 A / V ~ 1A / V.

9. The method for detecting imidacloprid according to claim 1, characterized in that: When the voltammetry is a cyclic voltammetry, the parameters are set as follows: the scanning potential range is -0.7V to -1.3V, the scanning speed is 0.1mV / s to 5V / s, and the number of scanning cycles is 1 to 100.

10. The method for detecting imidacloprid according to claim 9, characterized in that: The parameters were set as follows: scanning potential range of -0.7V to -1.3V, scanning speed of 50mV / s, and number of scans of 1.

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