An electrochemical sensor, its preparation method and application

Abstract

The present invention discloses an electrochemical sensor, a preparation method thereof and an application. The electrochemical sensor of the present invention comprises: a polycyclodextrin - working electrode and a counter electrode, wherein the polycyclodextrin - working electrode is composed of a working electrode and a polycyclodextrin layer formed by electro - polymerization; the cyclodextrin layer is in - situ loaded on the surface of the working electrode by cyclodextrin through an electro - polymerization reaction. The present invention also provides a preparation method of an electrochemical sensor, which comprises the following steps: placing the working electrode in a buffer solution containing cyclodextrin, performing an electro - polymerization reaction, and then placing the working electrode in a buffer solution without cyclodextrin for scanning treatment to obtain a polycyclodextrin - working electrode. The electrochemical sensor of the present invention has the advantages of a detection limit that can reach 0.006 μM, simple preparation, and low cost. Combined with the differential pulse three - step method, it can accurately detect the content of fenitrothion and is suitable for practical application and promotion.

Description

Technical Field

[0001] The present invention relates to the technical field of detection, and particularly relates to an electrochemical sensor, a preparation method thereof, and an application thereof. Background Art

[0002] Fenitrothion is an organophosphorus insecticide that is widely used in crops such as grains, cotton, and fruits. However, it has acute toxicity and can have an adverse impact on the environment and the central nervous system of organisms. Therefore, in order to avoid accidentally ingesting crops or liquids with excessive fenitrothion content, it is necessary to develop a method that can accurately and quickly detect the residual amount of fenitrothion in samples.

[0003] Electrochemical sensors, with excellent characteristics such as fast response time, high sensitivity, high speed, and low cost, have become one of the research hotspots in detection. Currently, bare working electrodes (such as glassy carbon electrodes) or electrodes modified with only one material have problems such as poor conductivity and slow electron transfer, which will lead to poor electrochemical detection performance for fenitrothion. Although modifying the electrode with a variety of improved materials can improve the detection performance of the sensor to a certain extent, the use of composite materials will undoubtedly increase the preparation cost and difficulty to a certain extent.

[0004] Therefore, it is urgent to develop and study an electrochemical sensor with good detection effect, fast speed, high sensitivity, low detection limit, accuracy, and low cost, and can also be used for the detection of fenitrothion. Summary of the Invention

[0005] In order to overcome the problems of high cost of electrode modification, weak sensitivity, and slow detection existing in the prior art, the purpose of the present invention is to provide an electrochemical sensor, a preparation method thereof, and an application thereof.

[0006] The chemical structure and electrochemical behavior of fenitrothion are as shown in A in Figure 1 ; using glassy carbon as the working electrode, saturated calomel as the reference electrode, acetic acid-sodium acetate buffer solution as the electrolyte (pH = 5.0), and platinum wire as the counter electrode, the cyclic voltammogram of the first to second cycles was measured under the conditions of a scanning rate of 50 mV / s and a test voltage range of 0.6 to -1.0 V. This cyclic voltammogram corresponds to the electrochemical behavior of fenitrothion in A in Figure 1 and is shown in B in Figure 1 .

[0007] The present invention combines Figure 1 to discuss the inventive concept and feasibility of the present invention. It can be seen from Figure 1 that in the first step, fenitrothion contains a nitro group (-NO2). The nitro group obtains electrons and protons at a certain potential and undergoes a reduction reaction to be converted into hydroxylamine (-NHOH), generating the reduced state of fenitrothion, as shown in Figure 1As shown in the reduction reaction I of A in [reference], the reduction peak of the reduction reaction I corresponds to Figure 1 the reduction peak I of B in [reference]; in the second step, the hydroxylamine in the reduced form of fenitrothion loses electrons and protons at a certain potential to undergo an oxidation reaction and is converted into nitroso (-NO), generating the oxidized form of fenitrothion, as Figure 1 shown in the oxidation reaction II of A in [reference], the oxidation peak of the oxidation reaction II corresponds to Figure 1 the oxidation peak II of B in [reference]; in the third step, the nitroso in the oxidized form of fenitrothion gains electrons and protons at a certain potential to undergo the reduction reaction II again and is restored to hydroxylamine, generating the reduced form of fenitrothion, as Figure 1 shown in the reduction reaction II of A in [reference], where the reduction peak of the reduction reaction II corresponds to Figure 1 the reduction peak II of B in [reference]. When the electrochemical reactions (i.e., reduction reaction I, reduction reaction II, and oxidation reaction II) occur, a Faraday current is generated, and the magnitude of the current is theoretically proportional to the concentration of fenitrothion. Therefore, theoretically, fenitrothion can be quantitatively analyzed based on the magnitudes of the peak currents generated by the three electrochemical reactions.

[0008] It should be noted that in the oxidation and reduction reactions of fenitrothion, the valence state of the N atom on fenitrothion mainly changes.

[0009] Meanwhile, in the present invention, by keeping the solution environment of each experiment the same or similar, it is ensured that the change in the peak current is mainly related to the content of the pesticide in the solution.

[0010] The inventive concept of the present invention is as follows: taking a glassy carbon electrode as an example, the present invention first designs to use the glassy carbon electrode as a working electrode to construct a three - electrode system, and modifies the glassy carbon electrode by an electropolymerization reaction using an electrolyte containing cyclodextrin to obtain a preliminarily electropolymerized modified glassy carbon electrode (i.e., an un - scanned poly - cyclodextrin - glassy carbon electrode, specifically referring to a poly - cyclodextrin - glassy carbon electrode that has not undergone further scanning treatment); then the poly - cyclodextrin - glassy carbon electrode is placed in an electrolyte without cyclodextrin and further reacted through scanning treatment, so as to improve the reversibility of the electrode reaction and be conducive to improving the stability for quantitative analysis, obtaining a poly - cyclodextrin - glassy carbon electrode (i.e., a scanned poly - cyclodextrin - glassy carbon electrode, an electrode modified only with cyclodextrin material); then a two - electrode system (only including a working electrode and a counter electrode) or a three - electrode system (including a working electrode, a counter electrode, and a reference electrode) is constructed using the poly - cyclodextrin - glassy carbon electrode to construct a working curve for testing the content of fenitrothion, thereby obtaining an electrochemical sensor that can be used for quantitative analysis, has a low detection limit, and high precision.

[0011] To achieve the above - mentioned purpose, the technical solution adopted by the present invention is:

[0012] In a first aspect, the present invention provides an electrochemical sensor, which comprises: a polycyclodextrin - working electrode, and the polycyclodextrin - working electrode is composed of a working electrode and a polycyclodextrin layer; the polycyclodextrin layer is formed by in - situ loading of cyclodextrin on the surface of the working electrode through an electro - polymerization reaction.

[0013] Preferably, the working electrode is selected from one of a glassy carbon electrode, a metal oxide electrode, and a metal electrode.

[0014] More preferably, the working electrode is a glassy carbon electrode.

[0015] Preferably, the cyclodextrin is selected from one or more of β - cyclodextrin, α - cyclodextrin, and γ - cyclodextrin.

[0016] More preferably, the cyclodextrin is β - cyclodextrin.

[0017] Preferably, the electrochemical sensor further comprises a reference electrode and a counter electrode.

[0018] Preferably, the reference electrode is selected from one of a calomel electrode, a silver chloride electrode, a mercurous sulfate electrode, and a mercury oxide electrode.

[0019] More preferably, the reference electrode is a calomel electrode, and the calomel electrode is a saturated calomel electrode.

[0020] Preferably, the counter electrode is selected from one of a platinum electrode and a titanium electrode.

[0021] More preferably, the counter electrode is a platinum electrode.

[0022] Preferably, the platinum electrode is a platinum wire electrode.

[0023] Specifically, the counter electrode, that is, the auxiliary electrode, can be selected from inert metal electrodes and forms an electrode system with the working electrode.

[0024] In a second aspect, the present invention provides a preparation method of the electrochemical sensor described in the first aspect, which comprises the following steps: placing the working electrode in a buffer solution containing cyclodextrin, performing an electro - polymerization reaction, and then placing the working electrode in a buffer solution without cyclodextrin for scanning treatment to obtain a polycyclodextrin - working electrode.

[0025] Preferably, the preparation method of the electrochemical sensor comprises the following steps:

[0026] 1) Construct an electrode system with the working electrode and the counter electrode; after the surface of the working electrode is polished, place it in a buffer solution containing cyclodextrin and perform an electro - polymerization reaction to obtain an unscanned polycyclodextrin - working electrode;

[0027] 2) Place the working electrode in a buffer solution without cyclodextrin for scanning treatment to obtain a polycyclodextrin - working electrode;

[0028] 3) Then, use the polycyclodextrin - working electrode in step 2) as the working electrode and the counter electrode to construct an electrode system to obtain an electrochemical sensor.

[0029] Preferably, the surface polishing treatment in step 1) is carried out using alumina polishing powder with a particle size of 0.01 μm to 0.1 μm as the abrasive.

[0030] Preferably, the instrument selected for the surface polishing treatment in step 1) is an electrode polishing machine.

[0031] Preferably, the electrode systems in step 1) and step 3) are two - electrode systems or three - electrode systems.

[0032] Specifically, the two - electrode system includes a working electrode and a counter electrode, the three - electrode system includes a working electrode, a counter electrode and a reference electrode, and the selection ranges of the counter electrode and the reference electrode in step 1) and step 3) are the same; the counter electrode is one of a platinum electrode and a titanium electrode; the reference electrode is one of a calomel electrode, a silver chloride electrode, a mercurous sulfate electrode and a mercury oxide electrode.

[0033] More preferably, the electrode systems in step 1) and step 3) are three - electrode systems.

[0034] Preferably, the buffer solution containing cyclodextrin in step 1) is formed by mixing cyclodextrin and a buffer solution.

[0035] Specifically, the buffer solution uses a buffer pair as the solute and deionized water or ultrapure water as the solvent.

[0036] Preferably, the buffer solutions in step 1) and step 2) are one of a phosphate buffer solution and an acetic acid - sodium acetate buffer solution.

[0037] More preferably, the buffer solutions in step 1) and step 2) are phosphate buffer solutions.

[0038] Even more preferably, the buffer solutions in step 1) and step 2) are phosphate buffer solutions with a concentration of 0.05 mol / L to 0.2 mol / L.

[0039] Preferably, the pH values of the buffer solution containing cyclodextrin in step 1) and the buffer solution without cyclodextrin in step 2) are 4.0 to 7.2.

[0040] More preferably, the pH values of the buffer solution containing cyclodextrin in step 1) and the buffer solution without cyclodextrin in step 2) are 5.0 to 7.0.

[0041] Preferably, the cyclodextrin content in the cyclodextrin-containing buffer solution in step 1) is 1 mmol / L to 20 mmol / L.

[0042] More preferably, the cyclodextrin content in the cyclodextrin-containing buffer solution in step 1) is 6 mmol / L.

[0043] Preferably, the conditions of the electropolymerization reaction in step 1) are set as follows: cyclic voltammetry is used for scanning; the polymerization potential is -5 V to 5 V; the scanning rate is 50 mV / s to 150 mV / s; the number of electropolymerization cycles is 8 to 12 cycles.

[0044] More preferably, the conditions of the electropolymerization reaction in step 1) are set as follows: cyclic voltammetry is used for scanning; the polymerization potential is -2 V to 2 V; the scanning rate is 80 mV / s to 120 mV / s; the number of electropolymerization cycles is 9 to 11 cycles.

[0045] Preferably, the conditions of the scanning process in step 2) are set as follows: cyclic voltammetry is used for scanning; the polymerization potential is -5 V to 5 V; the scanning rate is 50 mV / s to 150 mV / s; the number of scanning cycles is 2 to 5 cycles.

[0046] More preferably, the conditions of the scanning process in step 2) are set as follows: cyclic voltammetry is used for scanning; the polymerization potential is -2 V to 2 V; the scanning rate is 80 mV / s to 120 mV / s; the number of scanning cycles is 3 cycles.

[0047] Preferably, both step 1) and step 2) further include a step of drying the electrode with an inert gas, and the inert gas is nitrogen or argon.

[0048] Preferably, both step 1) and step 2) further include a step of cleaning the electrode, and the liquid used for cleaning is one or more of absolute ethanol and distilled water.

[0049] Preferably, the temperature of the drying is 20 °C to 30 °C.

[0050] In a third aspect, the present invention provides the use of the electrochemical sensor described in the first aspect or the second aspect in detecting or recovering pesticides.

[0051] Preferably, the organophosphorus pesticide is selected from one or more of parathion and fenitrothion.

[0052] More preferably, the organophosphorus pesticide is fenitrothion.

[0053] In a fourth aspect, the present invention provides a method for detecting fenitrothion, comprising the following steps:

[0054] Using the electrochemical sensor described in the first aspect, perform differential pulse three-step method on the sample to be tested. After measuring the current value of the reduction peak, quantitatively analyze the concentration of fenitrothion in the sample to be tested according to the fenitrothion standard curve.

[0055] Preferably, the detection method of fenitrothion includes the following steps:

[0056] 1) Drawing of the standard curve: Place the polycyclodextrin - working electrode in the electrochemical sensor described in the first aspect or the second aspect into fenitrothion standard solutions with different concentrations, perform scanning using the differential pulse three-step method, and use the current magnitude of the reduction peak and the concentration of the fenitrothion solution as the original data to analyze and draw the standard curve;

[0057] 2) Detecting the sample: Place the polycyclodextrin - working electrode in step 1) into the liquid sample to be tested and perform scanning using the differential pulse three-step method, measure the current magnitude of the reduction peak, and analyze and calculate the content of fenitrothion in the liquid sample to be tested according to the standard curve in step 1).

[0058] Preferably, the differential pulse three-step method includes the following steps:

[0059] S1: Under open circuit conditions, after enriching the scanned poly-β-cyclodextrin - glassy carbon electrode in the solution for 80 s to 100 s, then use the differential pulse method and set the scan from 0.6 V to -0.9 V, with the scan time consuming 55 s to 65 s, so that the nitro group on fenitrothion undergoes a reduction reaction to produce hydroxylamine;

[0060] S2: Under open circuit conditions, after enriching the scanned poly-β-cyclodextrin - glassy carbon electrode in the solution for 80 - 100 s, then use the differential pulse method and set the scan from -0.9 V to 0.6 V, with the scan duration being 55 s to 65 s, so that hydroxylamine undergoes an oxidation reaction to produce nitroso;

[0061] S3: Under open circuit conditions, after enriching the scanned poly-β-cyclodextrin - glassy carbon electrode in the solution for 55 s to 65 s, then use the differential pulse method and set the scan from 0.6 V to -0.9 V, with the scan duration being 55 s to 65 s, so that nitroso undergoes a reduction reaction to be converted into hydroxylamine, generating a reduction peak;

[0062] Among them, the differential pulse method in S1, S2, and S3 is differential pulse voltammetry, and the parameter settings are all: potential increment is 10 mV to 15 mV, pulse amplitude is 40 mV to 60 mV, pulse width is 55 ms to 65 ms, sampling width is 15 ms to 25 ms, and pulse period is 400 ms to 600 ms;

[0063] The enrichment treatment in S1, S2, and S3 specifically involves immersing the scanned poly-β-cyclodextrin-glassy carbon electrode in the sample to be tested.

[0064] Specifically, the differential pulse three-step method is designed to use stepwise scanning to enrich fenitrothion in the sample to be tested, further improving the accuracy of the detection method, reducing the detection limit of the detection method, and broadening the application range of the detection method.

[0065] Preferably, the concentration of fenitrothion in the fenitrothion standard solution in step 1) is 1 ng / mL to 5000 ng / mL.

[0066] More preferably, the concentration of fenitrothion in the fenitrothion standard solution in step 1) is 5 ng / mL to 4000 ng / mL.

[0067] Specifically, the concentration of fenitrothion is 5 ng / mL to 4000 ng / mL, that is, 0.018 μM to 14.4 μM.

[0068] Preferably, the linear correlation coefficient of the standard curve in step 1) is R 2 ≥0.9988.

[0069] Preferably, the fenitrothion standard solution in step 1) is prepared by mixing fenitrothion and a buffer solution.

[0070] Preferably, the buffer solution is one of a phosphate buffer solution and an acetic acid-sodium acetate buffer solution.

[0071] More preferably, the buffer solution is an acetic acid-sodium acetate buffer solution.

[0072] Even more preferably, the buffer solution is an acetic acid-sodium acetate buffer solution with a concentration of 0.05 mol / L to 0.2 mol / L.

[0073] Preferably, the pH values of the fenitrothion standard solution in step 1) and the liquid sample to be tested in step 2) are 4.0 to 7.2.

[0074] More preferably, the pH values of the fenitrothion standard solution in step 1) and the liquid sample to be tested in step 2) are 5.0 to 6.5.

[0075] The beneficial effects of the present invention are as follows: By using a single cyclodextrin material and an electropolymerization reaction to modify the surface of the working electrode, a polycyclodextrin-working electrode is obtained, and based on this, an electrochemical sensor with good, fast, sensitive, low detection limit, accurate, and low-cost detection of fenitrothion is obtained. Specifically:

[0076] (1) The present invention provides a preparation method for an electrochemical sensor with low preparation cost, environmental friendliness, and simplicity. This method is not only suitable for batch production but also can effectively reduce the interference current signal at about 0V potential;

[0077] (2) The electrochemical sensor of the present invention has the advantages of a wide detection range for fenitrothion (range 5 ng / mL - 4000 ng / mL, i.e., 0.018 μM - 14.4 μM), low detection limit (0.006 μM), sensitive detection, rapid detection, etc., and also has the characteristic of high spike recovery rate;

[0078] (3) The present invention proposes a detection method for fenitrothion. This method uses the above-mentioned electrochemical sensor and differential pulse three-step method, which can not only obtain a standard curve with a high correlation coefficient but also quickly, accurately, and sensitively detect the content of fenitrothion in unknown samples. Description of the Drawings

[0079] Figure 1 It is the electrochemical behavior of fenitrothion and its corresponding cyclic voltammogram.

[0080] Figure 2 It is the cyclic voltammogram of the preliminarily electropolymerized poly-β-cyclodextrin-glassy carbon electrode in Example 1 when the number of electropolymerization cycles is 10.

[0081] Figure 3 It is the current signal curve graph of the reduction reaction measured in the 3rd step by the differential pulse three-step scanning method for the poly-β-cyclodextrin-glassy carbon electrode before and after scanning in acetic acid-sodium acetate buffer solution without fenitrothion in Example 2.

[0082] Figure 4 It is the cyclic voltammogram measured for the poly-β-cyclodextrin-glassy carbon electrode in Example 2 in 0.1 mol / L phosphate buffer solution without β-cyclodextrin.

[0083] Figure 5 It is the current signal curve graph of the reduction reaction measured by the differential pulse three-step scanning method for the poly-β-cyclodextrin-glassy carbon electrode of the electrochemical sensor in Example 3 in acetic acid-sodium acetate buffer solution containing 2 μg / L fenitrothion.

[0084] Figure 6 It is the current signal curve graph and the columnar graph of the current peak value of the reduction peak II measured by the differential pulse three-step scanning method for the poly-β-cyclodextrin-glassy carbon electrode prepared by electropolymerization from the 7th to the 14th cycle in Example 4.

[0085] Figure 7The current signal curve graph of the reduction reaction measured by differential pulse three-step scanning method for the poly-β-cyclodextrin-glassy carbon electrode of the electrochemical sensor in Example 5 in solution systems with different pH values, and the trend graph of the current peak value curve of reduction peak II measured under the condition of pH value ranging from 4.0 to 7.0.

[0086] Figure 8 The current signal curve graph of the reduction reaction measured by differential pulse three-step scanning method for the poly-β-cyclodextrin-glassy carbon electrode of the electrochemical sensor in Example 6 in solution systems with different fenitrothion concentrations.

[0087] Figure 9 The linear relationship graph between the current value of reduction peak II measured by the electrochemical sensor in Example 6 and the fenitrothion content. Detailed implementation manners

[0088] The content of the present invention will be further described in detail through specific examples below.

[0089] The preparation of the 0.1mol / L phosphate buffer solution used in the present invention includes the following steps: Under the condition of 20 - 25°C (room temperature), accurately weigh 4.4775g of disodium hydrogen phosphate dodecahydrate (molecular weight: 358.14g / mol) and 1.95g of sodium dihydrogen phosphate dihydrate (molecular weight: 155.96g / mol), then dissolve them with ultrapure water and make the volume up to 250mL to obtain the 0.1mol / L phosphate buffer solution, and the pH value of this liquid is about 6.8;

[0090] The preparation of the 0.1mol / L phosphate buffer solution containing 6mmol / L β-cyclodextrin used in the present invention includes the following steps: Under the condition of 20 - 25°C (room temperature), accurately weigh 4.4775g of disodium hydrogen phosphate dodecahydrate (molecular weight: 358.14g / mol), 1.95g of sodium dihydrogen phosphate dihydrate (molecular weight: 155.96g / mol) and 1.7025g of β-cyclodextrin (molecular weight: 1134.98g / mol), then dissolve them with ultrapure water and make the volume up to 250mL to obtain the 0.1mol / L phosphate buffer solution containing 6mmol / L β-cyclodextrin, and the pH value of this liquid is about 6.8;

[0091] The preparation of 0.1 mol / L acetic acid - sodium acetate buffer solution with a pH value of 5.0 in the present invention includes the following steps: Under the condition of 20 - 25 °C (room temperature), accurately weigh 1.501 g of acetic acid, and make up the volume to 250 mL with pure water to obtain an acetic acid aqueous solution with a concentration of 0.1 mol / L. Accurately weigh 2.0508 g of sodium acetate, and make up the volume to 250 mL with pure water to obtain a sodium acetate aqueous solution with a concentration of 0.1 mol / L. Then, by adjusting the mixing ratio of 0.1 mol / L acetic acid and sodium acetate, 0.1 mol / L acetic acid - sodium acetate buffer solutions with pH values of 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, and 7.0 are prepared.

[0092] Unless otherwise specified, the manufacturer of the electrochemical workstation used in the present invention is Shanghai Chenhua Instrument Co., Ltd., and the model is CHI660E; the platinum electrode used in the present invention is a platinum wire electrode, and the manufacturer is Wuhan Gaoshi Ruilian Technology Co., Ltd.; the glassy carbon electrode, platinum electrode, and saturated calomel electrode used in the present invention are all commercially available products. The reduction peak II in the present invention all refers to the current signal peak with a potential of about 0 V, and this reduction peak II corresponds to the reduction reaction II; the reduction reaction II in the present invention all refers to the reduction reaction in which the oxidized state of fenitrothion is converted into the reduced state of fenitrothion.

[0093] In the drawings of the present invention, the positive and negative of the current and potential only represent directions, and the absolute value of the current and the absolute value of the potential represent the current value or current magnitude, potential value or potential magnitude; unless otherwise specified, the current and potential in this article respectively refer to the current magnitude and potential magnitude.

[0094] Example 1

[0095] This example provides a preparation method of a preliminarily electro - polymerized poly - β - cyclodextrin - glassy carbon electrode, including the following steps:

[0096] 1) At room temperature (20 - 25 °C), attach a polishing cloth to the disk of the electrode polishing machine, and add a suspension containing abrasive made of alumina polishing powder with a particle size of 0.05 μm and ultrapure water to the polishing cloth.

[0097] Place the glassy carbon electrode vertically on the polishing cloth and the electrode polishing machine for grinding, and use the counter - clockwise drawing method for grinding. After grinding for 20 s, rinse with distilled water, ultrasonically clean with anhydrous ethanol and distilled water for 1 minute respectively, and dry with nitrogen to obtain a glassy carbon electrode with a polished surface.

[0098] 2) At room temperature (20 - 25 °C), use the polished glassy carbon electrode in step 1) as the working electrode, the platinum electrode as the counter electrode, and the saturated calomel electrode as the reference electrode to form a three - electrode system. Place the three - electrode system into a 0.1 mol / L phosphate buffer solution containing 6 mmol / L β - cyclodextrin;

[0099] Meanwhile, connect the three - electrode system to an electrochemical workstation, set to scan using cyclic voltammetry, with the scanning potential ranging from - 2.0 V to 2.0 V and the scanning rate of 100 mV / s. Set the number of electropolymerization cycles to 1 cycle, 2 cycles, 3 cycles, 4 cycles, 5 cycles, 6 cycles, 7 cycles, 8 cycles, 9 cycles, 10 cycles, 11 cycles, 12 cycles, 13 cycles, 14 cycles respectively; and collect the cyclic voltammogram when the number of electropolymerization cycles is 10 cycles, as Figure 2 shown;

[0100] After electropolymerization, purge the working electrode with nitrogen at 25 °C to obtain 14 preliminarily electropolymerized poly(β - cyclodextrin) - glassy carbon electrodes.

[0101] In Example 1, during the preparation of the preliminarily electropolymerized poly(β - cyclodextrin) - glassy carbon electrode, the real - time cyclic voltammogram of the first cycle when the number of electropolymerization cycles is 10 cycles is as shown in A of Figure 2 ; the real - time cyclic voltammograms of the first cycle to the tenth cycle when the number of electropolymerization cycles is 10 cycles are as shown in B of Figure 2 .

[0102] It can be seen from Figure 2 that: during the first - cycle forward scan (i.e., the potential is scanned from - 2.0 V to 2.0 V), the current gradually increases starting from around 1.5 V, which is due to the electropolymerization reaction between β - cyclodextrins to form a polymer deposited on the electrode surface; while during the first - cycle reverse scan (i.e., the potential is scanned from 2.0 V to - 2.0 V), oxidation peaks appear at 0.4 V and 1.1 V, which may be caused by the oxidation reaction of the β - cyclodextrin polymer deposited on the electrode upon receiving electrons. As the number of electropolymerization cycles increases, the peak current increases with the increase in the number of electropolymerization cycles (i.e., the number of cycles), indicating that the poly(β - cyclodextrin) polymer film grows stably on the surface of the glassy carbon electrode, which not only helps to enhance the conductivity of the electrode and the current signal value, but also enables the preparation of preliminarily electropolymerized poly(β - cyclodextrin) - glassy carbon electrodes.

[0103] Example 2

[0104] This example provides a method for preparing a poly(β - cyclodextrin) - glassy carbon electrode, including the following steps:

[0105] 1) At room temperature (20 - 25 °C), attach the polishing cloth to the disc of the electrode polishing machine, and add a suspension containing abrasive, which is a mixture of alumina polishing powder with a particle size of 0.05 μm and ultrapure water, to the polishing cloth.

[0106] Place the glassy carbon electrode vertically on the polishing cloth and the electrode polishing machine for grinding, and use the counterclockwise drawing method for grinding. After grinding for 20 s, rinse with distilled water, ultrasonically clean with anhydrous ethanol and distilled water for 1 minute respectively, and dry with nitrogen to obtain the glassy carbon electrode with a polished surface.

[0107] 2) At room temperature (20 - 25 °C), use the glassy carbon electrode with a polished surface in step 1) as the working electrode, the platinum electrode as the counter electrode, and the saturated calomel electrode as the reference electrode to form a three - electrode system, and place the three - electrode system in a 0.1 mol / L phosphate buffer solution containing 6 mmol / L β - cyclodextrin.

[0108] At the same time, connect the three - electrode system to the electrochemical workstation, set to scan using cyclic voltammetry, with a scanning potential of - 2.0 - 2.0 V, a scanning rate of 100 mV / s, and 10 cycles of electropolymerization; after electropolymerization, purge the working electrode with nitrogen at 25 °C to obtain the preliminarily electropolymerized poly(β - cyclodextrin) - glassy carbon electrode (i.e., the un - scanned poly(β - cyclodextrin) - glassy carbon electrode).

[0109] 3) Use the preliminarily electropolymerized poly(β - cyclodextrin) - glassy carbon electrode in step 2) as the working electrode, the platinum electrode as the counter electrode, and the saturated calomel electrode as the reference electrode to form a three - electrode system, and place the three - electrode system in a 0.1 mol / L phosphate buffer solution.

[0110] At the same time, connect the three - electrode system to the electrochemical workstation, set to scan using cyclic voltammetry, with a scanning potential of - 2.0 - 2.0 V, a scanning rate of 100 mV / s, and 3 cycles of scanning, and collect the cyclic voltammogram as Figure 4 shown; after scanning and processing, take out the working electrode, rinse it clean with ultrapure water, and purge the working electrode with nitrogen at 25 °C to obtain the poly(β - cyclodextrin) - glassy carbon electrode (i.e., the scanned poly(β - cyclodextrin) - glassy carbon electrode).

[0111] This example also provides two electrochemical sensors. These two sensors use the above - mentioned un - scanned poly(β - cyclodextrin) - glassy carbon electrode or the scanned poly(β - cyclodextrin) - glassy carbon electrode as the working electrode, and both use the platinum electrode as the counter electrode and the saturated calomel electrode as the reference electrode.

[0112] Perform electrochemical tests on these two electrochemical sensors using the differential pulse three - step scanning method (i.e., differential pulse voltammetry three - step scanning method). The specific process is as follows:

[0113] The above two three - electrode systems were immersed in a 0.1 mol / L acetic acid - sodium acetate buffer solution with a pH value of 5.0. Using the differential pulse voltammetry three - step scanning method, the current signal curves of the un - scanned poly - β - cyclodextrin - glassy carbon electrode and the scanned poly - β - cyclodextrin - glassy carbon electrode in Example 2 were measured by differential pulse voltammetry in the acetic acid - sodium acetate buffer solution, as Figure 3 shown. (For the differential pulse voltammetry three - step scanning method, refer to the description of the differential pulse voltammetry three - step scanning method in Example 3. The specific parameters of the differential pulse voltammetry three - step method are as follows: In the first step, the scanning voltage ranges from 0.6 V to - 0.9 V, the voltage increment is 13 mV, the amplitude is 50 mV, the pulse width is 60 ms, the width used is 20 ms, and the pulse period is 500 ms; in the second step, the scanning voltage ranges from - 0.9 V to 0.6 V, the voltage increment is 13 mV, the amplitude is 50 mV, the pulse width is 60 ms, the width used is 20 ms, and the pulse period is 500 ms; in the third step, the scanning voltage ranges from 0.6 V to - 0.9 V, the voltage increment is 13 mV, the amplitude is 50 mV, the pulse width is 60 ms, the width used is 20 ms, and the pulse period is 500 ms.)

[0114] It can be seen from Figure 3 that: In a 0.1 mol / L acetic acid - sodium acetate buffer solution with a pH value of 5.0, for the current signal curve measured by differential pulse voltammetry of the un - scanned poly - β - cyclodextrin - glassy carbon electrode, a very strong current signal appears at about 0 V in potential, which will cause great interference to the current of the reduction peak II of fenitrothion at 0 V. Therefore, quantitative analysis cannot be carried out. For the current signal curve measured by differential pulse voltammetry of the scanned poly - β - cyclodextrin - glassy carbon electrode, there is basically no current signal peak at 0 V in potential. Therefore, "step 3) further performing cyclic voltammetry scanning treatment in a 0.1 mol / L phosphate buffer solution without β - cyclodextrin" can better eliminate the interference current signal generated at about 0 V in potential during the detection of the poly - β - cyclodextrin film, so that the prepared poly - β - cyclodextrin - glassy carbon electrode can use the characteristic current signal peak at about 0 V in potential for quantitative analysis.

[0115] During the preparation of the scanned poly - β - cyclodextrin - glassy carbon electrode in Example 2, the cyclic voltammetry curve collected in a 0.1 mol / L phosphate buffer solution without β - cyclodextrin in step 3) is as Figure 4 shown.

[0116] It can be seen from Figure 4It can be seen that as the number of scanning cycles increases, the current on the working electrode gradually decreases and finally stabilizes, indicating that the poly-β-cyclodextrin film on the un-scanned poly-β-cyclodextrin-glassy carbon electrode is doped with β-cyclodextrin monomers and unreduced cations. In this embodiment, the design is to place the un-scanned poly-β-cyclodextrin-glassy carbon electrode (working electrode) in a 0.1 mol / L phosphate buffer solution without cyclodextrin and perform scanning treatment by using multiple cyclic voltammetry. The current signals of the working electrode at about 0 V and about 1.5 V of the potential basically disappear (that is, the β-cyclodextrin monomers and unreduced cations basically all react completely), thereby eliminating the interference of the poly-β-cyclodextrin-glassy carbon electrode (working electrode) on the current signals at about 0 V and 1.5 V of the potential, and further laying a foundation for being able to use the current signals at about 0 V and 1.5 V of the potential as quantitative analysis signals.

[0117] Example 3

[0118] This embodiment provides a poly-β-cyclodextrin-glassy carbon electrode (i.e., the scanned poly-β-cyclodextrin-glassy carbon electrode), and its preparation method is the same as that of Example 2.

[0119] This embodiment provides an electrochemical sensor including the above poly-β-cyclodextrin-glassy carbon electrode, a platinum electrode, and a saturated calomel electrode.

[0120] This embodiment provides an analytical test method, including the following steps:

[0121] 1) Under the condition of room temperature (20 - 25 °C), use the scanned poly-β-cyclodextrin-glassy carbon electrode as the working electrode, the saturated calomel electrode as the reference electrode, and the platinum wire electrode as the counter electrode to form a three-electrode system, and insert it into an acetic acid-sodium acetate solution with a pH of 5.0 containing 2 μg / mL fenitrothion.

[0122] 2) Test by differential pulse three-step method:

[0123] Step 1, under open-circuit conditions, after enriching the scanned poly-β-cyclodextrin-glassy carbon electrode in the solution for 90 s, then use differential pulse voltammetry and set the scan from 0.6 V to -0.9 V, and the scan takes 58 s to cause the nitro group on fenitrothion to undergo a reduction reaction to produce hydroxylamine.

[0124] Step 2, under open-circuit conditions, after enriching the scanned poly-β-cyclodextrin-glassy carbon electrode in the solution for 90 s, then use differential pulse voltammetry and set the scan from -0.9 V to 0.6 V, and the scan duration is 58 s to cause hydroxylamine to undergo an oxidation reaction to form nitroso.

[0125] Step 3: Under open circuit conditions, after the scanned poly-β-cyclodextrin-glassy carbon electrode is enriched in the solution for 60 s, differential pulse voltammetry is then used, and the scanning is set from 0.6 V to -0.9 V with a scanning duration of 58 s, so that the nitroso group undergoes a reduction reaction to be converted into hydroxylamine, generating a reduction peak;

[0126] Among them, the parameter settings of differential pulse voltammetry in Step 1, Step 2, and Step 3 are all: the potential increment is 13 mV, the pulse amplitude is 50 mV, the pulse width is 60 ms, the sampling width is 20 ms, and the pulse period is 500 ms;

[0127] The enrichment treatment in Step 1, Step 2, and Step 3 is specifically carried out by the method of static immersion.

[0128] Meanwhile, the fenitrothion in the solution can be quantitatively analyzed according to the magnitude of the peak current of the reduction peak II around 0 V in the curve obtained by scanning in Step 3 and the working curve measured in Example 6.

[0129] The measured current signal curve of the reduction reaction II is as Figure 5 shown.

[0130] As Figure 5 can be seen: When the poly-β-cyclodextrin-glassy carbon electrode after scanning treatment is tested by the differential pulse three-step method in the acetic acid-sodium acetate buffer solution containing fenitrothion, in Step 3, the half-peak width of the signal peak around the potential of 0 V in the measured curve is relatively narrow, the peak current is high, and the symmetry of the peak is good. This signal peak belongs to the reduction peak II, corresponding to the reduction reaction II of fenitrothion in the electrochemical behavior (see Figure 1 ), which indicates that the peak current value of the reduction peak II can be selected for quantitative analysis.

[0131] Example 4

[0132] This example provides a preparation method of a poly-β-cyclodextrin-glassy carbon electrode, including the following steps:

[0133] 1) At room temperature (20 - 25 °C), attach a polishing cloth to the disc of an electrode polishing machine, and add a suspension containing abrasive, which is a mixture of alumina polishing powder with a particle size of 0.05 μm and ultrapure water, to the polishing cloth;

[0134] Vertically place the glassy carbon electrode on the polishing cloth and the electrode polishing machine for grinding, and use the counterclockwise drawing method for grinding. After grinding for 20 s, rinse with distilled water, ultrasonically clean with absolute ethanol and distilled water for 1 minute respectively, and dry with nitrogen to obtain a glassy carbon electrode with a polished surface;

[0135] 2) At room temperature (20 - 25 °C), use the polished glassy carbon electrode in step 1) as the working electrode, the platinum electrode as the counter electrode, and the saturated calomel electrode as the reference electrode to form a three - electrode system. Then place the three - electrode system into a 0.1 mol / L phosphate buffer solution containing 6 mmol / L β - cyclodextrin;

[0136] At the same time, connect the three - electrode system to an electrochemical workstation. Set the cyclic voltammetry scan with a scan potential of - 2.0 - 2.0 V and a scan rate of 100 mV / s. The number of electropolymerization cycles is 7, 8, 9, 10, 11, 12, 13, and 14 cycles respectively. After electropolymerization, purge the working electrode with nitrogen at 25 °C to obtain 8 preliminarily electropolymerized poly(β - cyclodextrin) - glassy carbon electrodes (i.e., poly(β - cyclodextrin) - glassy carbon electrodes without scanning);

[0137] 3) Use each of the 8 preliminarily electropolymerized poly(β - cyclodextrin) - glassy carbon electrodes in step 2) as the working electrode alone, and form a three - electrode system with the platinum electrode as the counter electrode and the saturated calomel electrode as the reference electrode. Then place the three - electrode system in a 0.1 mol / L phosphate buffer solution;

[0138] At the same time, connect the three - electrode system to an electrochemical workstation. Set the cyclic voltammetry scan with a scan potential of - 2.0 - 2.0 V and a scan rate of 100 mV / s, and the number of scan cycles is 3. Then collect the cyclic voltammogram. After scanning and processing, take out the working electrode, rinse it thoroughly with ultrapure water, and purge the working electrode with nitrogen at 25 °C to obtain 8 poly(β - cyclodextrin) - glassy carbon electrodes (i.e., poly(β - cyclodextrin) - glassy carbon electrodes after scanning).

[0139] This example provides an electrochemical sensor, including the poly(β - cyclodextrin) - glassy carbon electrode, platinum electrode, and saturated calomel electrode provided above. This electrochemical sensor still uses the poly(β - cyclodextrin) - glassy carbon electrode as the working electrode, the platinum electrode as the counter electrode, and the saturated calomel electrode as the reference electrode.

[0140] Figure 6Testing methods and conditions for the data: Place the eight poly-β-cyclodextrin-glassy carbon electrodes provided in this example into an acetic acid-sodium acetate buffer solution with a pH of 5.3 containing 5 μg / mL fenitrothion, use a platinum electrode as the counter electrode, and a saturated calomel electrode as the reference electrode, and select the methods and conditions of the differential pulse three-step method in Example 3 for testing (that is, the parameters of the differential pulse voltammetry three-step method are as follows: In the first step, the scanning voltage is from 0.6 to -0.9 V, the voltage increment is 13 mV, the amplitude is 50 mV, the pulse width is 60 ms, the width is 20 ms, and the pulse period is 500 ms; in the second step, the scanning voltage is from -0.9 to 0.6 V, the voltage increment is 13 mV, the amplitude is 50 mV, the pulse width is 60 ms, the width is 20 ms, and the pulse period is 500 ms; in the third step, the scanning voltage is from 0.6 to -0.9 V, the voltage increment is 13 mV, the amplitude is 50 mV, the pulse width is 60 ms, the width is 20 ms, and the pulse period is 500 ms).

[0141] The current signal curve graph measured by the differential pulse three-step method for the poly-β-cyclodextrin-glassy carbon electrode prepared by electro-polymerization from the 7th to the 14th cycle in Example 4 is as Figure 6 shown in A of Figure 6 . Read the current peak value (the current peak value of the reduction peak II) at the potential of 0 V in A of Figure 6 , and the bar graph organized and drawn is as Figure 6 shown in B of

[0142] . The number of cycles in Figure 6 represents the number of electro-polymerization cycles during preparation.

[0143] Example 5

[0144] This example provides a preparation method for a poly-β-cyclodextrin-glassy carbon electrode, including the following steps:

[0145] 1) At room temperature (20 - 25 °C), attach the polishing cloth to the disc of the electrode polishing machine, and add a suspension containing abrasive, which is a mixture of alumina polishing powder with a particle size of 0.05 μm and ultrapure water, to the polishing cloth.

[0146] Place the glassy carbon electrode vertically on the polishing cloth and the electrode polishing machine for grinding, and use the counterclockwise drawing method for grinding. After grinding for 20 s, rinse with distilled water, ultrasonically clean with anhydrous ethanol and distilled water for 1 minute respectively, and dry with nitrogen to obtain the glassy carbon electrode with a polished surface.

[0147] 2) At room temperature (20 - 25 °C), use the glassy carbon electrode with a polished surface in step 1) as the working electrode, the platinum electrode as the counter electrode, and the saturated calomel electrode as the reference electrode to form a three - electrode system, and place the three - electrode system in a 0.1 mol / L phosphate buffer solution containing 6 mmol / L β - cyclodextrin.

[0148] At the same time, connect the three - electrode system to an electrochemical workstation, set to perform cyclic voltammetry scanning, with a scanning potential of - 2.0 - 2.0 V, a scanning rate of 100 mV / s, and 10 cycles of electro - polymerization; after electro - polymerization, purge the working electrode with nitrogen at 25 °C to obtain the preliminarily electro - polymerized poly(β - cyclodextrin) - glassy carbon electrode (i.e., the un - scanned poly(β - cyclodextrin) - glassy carbon electrode).

[0149] 3) Use the preliminarily electro - polymerized poly(β - cyclodextrin) - glassy carbon electrode in step 2) as the working electrode separately, and form a three - electrode system with the platinum electrode as the counter electrode and the saturated calomel electrode as the reference electrode, and place the three - electrode system in a 0.1 mol / L phosphate buffer solution.

[0150] At the same time, connect the three - electrode system to an electrochemical workstation, set to perform cyclic voltammetry scanning, with a scanning potential of - 2.0 - 2.0 V, a scanning rate of 100 mV / s, and 3 scanning cycles, and collect the cyclic voltammogram; after scanning and processing, take out the working electrode, rinse it clean with ultrapure water, and purge the working electrode with nitrogen at 25 °C to obtain the poly(β - cyclodextrin) - glassy carbon electrode (i.e., the scanned poly(β - cyclodextrin) - glassy carbon electrode).

[0151] This example provides an electrochemical sensor, including the poly(β - cyclodextrin) - glassy carbon electrode, platinum electrode, and saturated calomel electrode provided above; this electrochemical sensor still uses the poly(β - cyclodextrin) - glassy carbon electrode as the working electrode, the platinum electrode as the counter electrode, and the saturated calomel electrode as the reference electrode.

[0152] Test the electrochemical sensor of this example, and the specific process is as follows:

[0153] 1) Mix acetic acid solution and sodium acetate solution in a certain proportion to prepare acetic acid-sodium acetate buffer solutions with the same addition amount of fenitrothion (i.e., the concentration of fenitrothion is 2 μg / L), and pH values of 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, and 7.0 respectively.

[0154] Place the poly-β-cyclodextrin-glassy carbon electrode in the electrochemical sensor provided in Example 5 into the acetic acid-sodium acetate buffer solutions with pH values of 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, and 7.0.

[0155] 2) Use the method and test conditions of the differential pulse three-step method in Example 3 for testing.

[0156] 3) Collect the current signal curve graph obtained from the test ( Figure 7 ).

[0157] Since fenitrothion will undergo hydrolysis under alkaline conditions, in this example, only acidic conditions are selected to analyze the more preferred conditions for detecting fenitrothion in acetic acid-sodium acetate buffer solutions.

[0158] The current signal curve graph of the reduction reaction II measured by the differential pulse three-step method for the poly-β-cyclodextrin-glassy carbon electrode of the electrochemical sensor in Example 5 in different pH value solution systems is as shown in Figure 7 A; Select the peak current of the reduction peak II (i.e., the absolute value of the current, also known as the current peak value) measured under the conditions of pH value from 4.0 to 7.0, and plot it as a curve change trend graph, as shown in Figure 7 B.

[0159] It can be seen from Figure 7 that within the range of the pH value of the detection solution system from 4.0 to 7.0, the peak current value of the reduction peak II first increases and then decreases with the increase of the pH value, and the peak current value of the reduction peak II reaches the maximum value when the pH value of the detection solution system is 5.0, which indicates that the pH value of the solution system has an obvious influence on the detection results of the electrochemical sensor.

[0160] Further analysis shows that when the pH value of the detection solution system is greater than 5.5, its acidity is too low, resulting in the hydrolysis of fenitrothion and causing the peak current value of the reduction peak II to decrease; when the pH value of the detection solution system is less than 5.0, the acidity is too high, and the redox reaction of fenitrothion is difficult to occur. Therefore, the pH value of the acetic acid-sodium acetate buffer solution for the detection solution being 5.0 - 5.5 is one of the preferred conditions for detecting fenitrothion, and subsequently, this is used as the condition for detecting and analyzing the solution containing fenitrothion.

[0161] Meanwhile, within the range of 4.0 to 7.0 for the pH value of the detection solution system, although the peak current value shifts with the change of the pH value of the detection solution system, the absolute value of the peak value of the reduction peak II is selected for data analysis, and standard curves can be plotted with different pH values, and this is used as the basis for the electrochemical sensor of the present invention to quantitatively analyze fenitrothion. Therefore, the implementation mode of the present invention is not limited by the above embodiments.

[0162] Example 6

[0163] This example provides a preparation method of a poly-β-cyclodextrin-glassy carbon electrode, including the following steps:

[0164] 1) At room temperature (20 - 25 °C), attach the polishing cloth to the disc of the electrode polishing machine, and add a suspension containing abrasive, which is a mixture of alumina polishing powder with a particle size of 0.05 μm and ultrapure water, to the polishing cloth.

[0165] Place the glassy carbon electrode vertically on the polishing cloth and the electrode polishing machine for grinding, and use the counterclockwise drawing method for grinding. After grinding for 20 s, rinse with distilled water, ultrasonically clean with absolute ethanol and distilled water for 1 minute respectively, and dry with nitrogen to obtain the surface-ground glassy carbon electrode.

[0166] 2) At room temperature (20 - 25 °C), use the surface-ground glassy carbon electrode in step 1) as the working electrode, the platinum electrode as the counter electrode, and the saturated calomel electrode as the reference electrode to form a three-electrode system, and place the three-electrode system in a 0.1 mol / L phosphate buffer solution containing 6 mmol / L β-cyclodextrin.

[0167] At the same time, connect the three-electrode system to an electrochemical workstation, set cyclic voltammetry for scanning, the scanning potential is -2.0 to 2.0 V, the scanning rate is 100 mV / s, and the number of electropolymerization cycles is 10; after electropolymerization, purge the working electrode with nitrogen at 25 °C to obtain a preliminarily electropolymerized poly-β-cyclodextrin-glassy carbon electrode (i.e., the un-scanned poly-β-cyclodextrin-glassy carbon electrode).

[0168] 3) Use the preliminarily electropolymerized poly-β-cyclodextrin-glassy carbon electrode in step 2) as the working electrode separately, and form a three-electrode system with the platinum electrode as the counter electrode and the saturated calomel electrode as the reference electrode, and place the three-electrode system in a 0.1 mol / L phosphate buffer solution.

[0169] Meanwhile, connect the three-electrode system to an electrochemical workstation, set the cyclic voltammetry for scanning, with the scanning potential ranging from -2.0 V to 2.0 V, the scanning rate of 100 mV / s, and the number of scanning cycles of 3, and collect the cyclic voltammogram curve; after scanning and processing, take out the working electrode, rinse it thoroughly with ultrapure water, and purge the working electrode with nitrogen under the condition of 25 °C to obtain a poly-β-cyclodextrin-glassy carbon electrode (i.e., the scanned poly-β-cyclodextrin-glassy carbon electrode).

[0170] This embodiment provides an electrochemical sensor, including the poly-β-cyclodextrin-glassy carbon electrode, platinum electrode, and saturated calomel electrode provided above; this electrochemical sensor still uses the poly-β-cyclodextrin-glassy carbon electrode as the working electrode, the platinum electrode as the counter electrode, and the saturated calomel electrode as the reference electrode.

[0171] This embodiment also provides a quantitative detection method for fenitrothion, and the specific process is as follows:

[0172] 1) At room temperature, use the poly-β-cyclodextrin-glassy carbon electrode after scanning and processing as the working electrode, the saturated calomel electrode as the reference electrode, and the platinum wire electrode as the counter electrode to form a three-electrode system, and insert it into an acetic acid-sodium acetate solution with pH = 5.0 containing fenitrothion, and connect it to the electrochemical workstation;

[0173] 2) Drawing of the standard curve: At room temperature (20 - 25 °C), prepare 0.1 mol / L sodium acetate solution and 0.1 mol / L acetic acid solution, and adjust the pH value by adjusting the mixing ratio of the two solutions to obtain an acetic acid-sodium acetate buffer solution with a pH value of 5.0 - 5.5

[0174] Dilute the fenitrothion standard solution with a concentration of 10 mg / mL with an acetic acid-sodium acetate buffer solution with a pH value of 5.3 into standard solutions with concentrations of 5 ng / mL, 10 ng / mL, 50 ng / mL, 75 ng / mL, 100 ng / mL, 200 ng / mL, 500 ng / mL, 750 ng / mL, 1000 ng / mL, 1250 ng / mL, 1500 ng / mL, 1750 ng / mL, 3000 ng / mL, and 4000 ng / mL respectively;

[0175] Adopt the test conditions and methods of the differential pulse three-step method in Example 3 for testing, and according to the original data graph measured by the 3rd step scanning of the differential pulse three-step method; accordingly, plot the magnitude of the peak current of the reduction peak II around 0 V (i.e., the absolute value of the peak value of the reduction peak II) against the concentration of fenitrothion in the standard solution to draw a standard curve;

[0176] Obtain the standard curve through data analysis, and require the linear correlation coefficient R 2 ≥0.998;

[0177] 3) Quantitative analysis and testing of fenitrothion was carried out using differential pulse three-step scanning method: adjust the pH value of the solution to be tested to 5.3, record the volume change of the solution, and then use the three-electrode system in step 1) after cleaning and drying, insert it into the solution to be tested, and perform three-step scanning using the same test conditions and methods of differential pulse three-step method as in step 2). According to the magnitude of the peak current of the reduction peak II around 0 V measured in the third-step scanning, data analysis was carried out to obtain the content in the solution to be tested.

[0178] In Example 6, the current signal curve of the third-step reduction reaction II measured by differential pulse voltammetry scanning method for the poly-β-cyclodextrin-glassy carbon electrode of the electrochemical sensor in a solution system with different fenitrothion concentrations is as Figure 8 shown. The linear relationship diagram between the current value of the reduction peak II measured by the electrochemical sensor in Example 6 and the fenitrothion content is as Figure 9 shown.

[0179] From Figure 8 and Figure 9 it can be seen that in the concentration range of 5 - 140 ng / mL, the linear equation between the peak current magnitude (referring to the absolute value) of the reduction peak II and the fenitrothion concentration is: I1(A) = 5.093e -9 ×c(ng / mL) + 1.819e -7 , the linear correlation coefficient: R 2 = 0.99889; in the concentration range of 140 - 4000 ng / mL, the linear equation between the peak current and the fenitrothion concentration is: I2(A) = 2.247e -9 ×c(ng / mL) + 6.107e -7 , the linear correlation coefficient: R 2 = 0.99985; where c represents the concentration of fenitrothion in the solution, the linear equation is obtained by analyzing with computer Origin software, e represents the meaning of 10, for example, the meaning of e -9 is 10 -9 .

[0180] The linear range of the above two standard curves (i.e., linear equations) for fenitrothion detection is 5 - 4000 ng / mL (i.e., 0.018 - 14.4 μM), and the detection limit calculated using three times the signal-to-noise ratio is 0.006 μM.

[0181] Example 7

[0182] In this example, at room temperature (20 °C - 25 °C), Chinese cabbage juice was selected and analyzed by the standard addition method using the poly-β-cyclodextrin-glassy carbon electrode after scanning in Example 6. The specific process is as follows:

[0183] 1) Grind and mash Chinese cabbage with a mortar, and filter to obtain Chinese cabbage juice;

[0184] 2) Take 1 mL of the above Chinese cabbage juice, add a certain amount of fenitrothion, and dilute it to 10 mL with pH = 5.0, 0.1 mol / L acetic acid - sodium acetate buffer solution, so that the concentrations of fenitrothion added are 5 ng / mL, 1000 ng / mL, and 2000 ng / mL respectively;

[0185] 3) Use a polycyclodextrin - glassy carbon electrode as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire as the counter electrode, and perform tests using the differential pulse voltammetry three - step scanning method in Example 3, and record the peak current of the reduction peak II at about 0 V obtained in the third step of scanning;

[0186] 4) Substitute the peak current of the reduction peak II into the standard curve, calculate the theoretical concentration of fenitrothion, and the ratio of the theoretical concentration to the actually added concentration is the recovery rate; the test and analysis results are shown in Table 1.

[0187] Table 1 Detection results of the standard addition recovery experiment

[0188]

[0189] Note: The calculation method of the recovery rate in Table 1 is as follows: Take Chinese cabbage juice as the base solution for preparing the fenitrothion solution, quantitatively add fenitrothion, then detect using the same method, and substitute the magnitude of the peak current of the reduction peak II at about 0 V obtained in the third step of scanning into the standard curve and calculate the theoretical concentration of fenitrothion. The ratio of the theoretical concentration of fenitrothion to the actual concentration of fenitrothion added is the recovery rate.

[0190] As can be seen from Table 1: The recovery rate of this test method for fenitrothion is between 99.4% - 117.0% (although there are deviations in data processing, it does not affect its technical effect of achieving a high recovery rate).

[0191] Comparative Example 1

[0192] This comparative example provides an electrochemical sensor including an activated multi - walled carbon nanotube - glassy carbon electrode (working electrode), a platinum wire electrode (counter electrode), and a saturated Ag / AgCl electrode (reference electrode). In this comparative example, carbon nanotubes are selected to modify the glassy carbon electrode to improve its conductivity, aiming to compare with the technical solution (i.e., the example) proposed in the present invention.

[0193] This comparative example provides a preparation method of an electrochemical sensor, including the following steps:

[0194] 1) Polish the surface of the glassy carbon electrode with alumina slurry, perform ultrasonic cleaning with ethanol and water, and air - dry at room temperature

[0195] 2) The carbon nanotubes were dispersed in absolute ethanol for functionalization to obtain a uniformly dispersed 0.5 mg / mL carbon nanotube-ethanol dispersion (the content of carbon nanotubes was 0.5 mg / mL).

[0196] 3) 20 μL of the 0.5 mg / mL carbon nanotube-ethanol dispersion in step 2) was drop-coated on the surface of the polished glassy carbon electrode and air-dried to obtain a multi-walled carbon nanotube-glassy carbon electrode.

[0197] 4) The multi-walled carbon nanotube-glassy carbon electrode in step 3) was immersed in an acetic acid-sodium acetate buffer solution with a pH value of 5.0, and a three-electrode system was constructed with a platinum wire electrode as the counter electrode and a saturated Ag / AgCl electrode as the reference electrode. After connecting it to an electrochemical workstation, continuous potential scanning was used for activation (cyclic voltammetry was used for activation, and the scanning potential was set to 0.1 - 1.2 V, and the scanning rate was 100 mV / s) to obtain an activated multi-walled carbon nanotube-glassy carbon electrode.

[0198] 5) Using the activated multi-walled carbon nanotube-glassy carbon electrode in step 4) as the working electrode, a platinum wire electrode as the counter electrode, and a saturated Ag / AgCl electrode as the reference electrode, a three-electrode system was constructed to obtain an electrochemical sensor containing the activated multi-walled carbon nanotube-glassy carbon electrode.

[0199] The working curve of fenitrothion was measured using the electrochemical sensor prepared in this example, which specifically included the following process:

[0200] 1) Standard fenitrothion solutions with concentrations of 0.2 - 60 μM were prepared using a 0.2 M acetic acid-sodium acetate buffer solution with a pH of 5.0.

[0201] 2) The multi-walled carbon nanotube-glassy carbon electrode was used as the working electrode, the saturated Ag / AgCl was used as the reference electrode, and the platinum wire electrode was used as the counter electrode. They were respectively inserted into the fenitrothion standard solutions with different concentrations in step 1). First, the electrode was pretreated with a potential of -0.7 V (vs. Ag / AgCl) for 25 s.

[0202] After that, square wave voltammetry was used to test the standard solutions, and the test voltage range was -0.3 V to 0.35 V.

[0203] Among them, the parameter settings of square wave voltammetry were: potential increment of 6 mV, pulse amplitude of 25 mV, and frequency of 150 Hz; finally, the data obtained from the test was analyzed.

[0204] After the above tests, the detection range of this electrochemical sensor was 0.2 - 60 μM, and through analysis, the detection limit of fenitrothion was 0.08 μM.

[0205] It can be known through testing that the recovery rate of the spiked recovery experiment of the electrochemical sensor provided in this comparative example in river water is 97.2%-104%.

[0206] For the electrochemical sensor and its performance testing method of this comparative example, reference can be specifically made to the journal: Electrochemical study of fenitrothion and bifenox and their simultaneous determination using multiwalled carbon nanotube modified glassy carbon electrode. Journal of Electroanalytical Chemistry, 2016, 767: 188–194. In particular, the paragraphs of "2.2 Dispersion and functionalization of CNTs and modification of GCE", "3.6 Optimization of parameters for simultaneous determination of FT and BF" and "3.8 Analytical features" in this journal.

[0207] By comparing Example 6, Example 7 and Comparative Example 1, it can be found that the electrochemical sensor prepared by the present invention has a lower detection limit (0.006 μM) for the detection of fenitrothion, and the testing method of the present invention has a higher recovery rate.

[0208] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A detection method for fenitrothion, characterized in that It includes the following steps: Use an electrochemical sensor to perform differential pulse three-step method on the sample to be tested. After measuring the current value of the reduction peak, quantitatively analyze the concentration of fenitrothion in the sample to be tested according to the fenitrothion standard curve; The differential pulse three-step method includes the following steps: S1: Under open circuit conditions, after enriching the scanned poly-β-cyclodextrin-glassy carbon electrode in the solution for 80 s to 100 s, then use differential pulse method to scan from 0.6 V to -0.9 V, and the scanning time is 55 s to 65 s; S2: Under open circuit conditions, after enriching the scanned poly-β-cyclodextrin-glassy carbon electrode in the solution for 80 s to 100 s, then use differential pulse method to set the scan from -0.9 V to 0.6 V, and the scanning duration is 55 s to 65 s; S3: Under open circuit conditions, after enriching the scanned poly-β-cyclodextrin-glassy carbon electrode in the solution for 80 s to 100 s, then use differential pulse method to set the scan from 0.6 V to -0.9 V, and the scanning duration is 55 s to 65 s; Among them, the differential pulse method in S1, S2, and S3 is differential pulse voltammetry; the parameter settings in S1, S2, and S3 are all: the potential increment is 10 mV to 15 mV, the pulse amplitude is 40 mV to 60 mV, the pulse width is 55 ms to 65 ms, the sampling width is 15 ms to 25 ms, and the pulse period is 400 ms to 600 ms; the enrichment treatment in S1, S2, and S3 is specifically to immerse the scanned poly-β-cyclodextrin-glassy carbon electrode in the sample to be tested; The electrochemical sensor is provided with a polycyclodextrin-working electrode, and the polycyclodextrin-working electrode is composed of a working electrode and a polycyclodextrin layer; the polycyclodextrin layer is that cyclodextrin is in-situ loaded on the surface of the working electrode through electropolymerization reaction; The preparation method of the electrochemical sensor includes the following steps: Place the working electrode in a buffer solution containing cyclodextrin, after electropolymerization reaction, then place the working electrode in a buffer solution without cyclodextrin for scanning treatment to obtain a polycyclodextrin-working electrode.

2. The detection method of fenitrothion according to claim 1, characterized in that, The working electrode is selected from one of a glassy carbon electrode, a metal oxide electrode, and a metal electrode; the cyclodextrin is selected from one or more of β-cyclodextrin, α-cyclodextrin, and γ-cyclodextrin.

3. The detection method of fenitrothion according to claim 1, characterized in that, The electrochemical sensor further includes a reference electrode and a counter electrode; the reference electrode is one of a calomel electrode, a silver chloride electrode, a mercurous sulfate electrode, and a mercury oxide electrode.

4. The detection method of fenitrothion according to claim 1, characterized in that: The preparation method of the electrochemical sensor includes the following steps: 1) Construct an electrode system with the working electrode and the counter electrode; after the surface of the working electrode is polished, then place it in a buffer solution containing cyclodextrin for electropolymerization reaction to obtain an unscanned polycyclodextrin-working electrode; 2) Place the working electrode in a buffer solution without cyclodextrin for scanning treatment to obtain a polycyclodextrin-working electrode; 3) Then use the polycyclodextrin-working electrode in step 2) as the working electrode and the counter electrode to construct an electrode system to obtain an electrochemical sensor.

5. The detection method of fenitrothion according to claim 4, characterized in that, The buffer solution in Step 1) and Step 2) is one of phosphate buffer solution and acetic acid-sodium acetate buffer solution; the pH values of the cyclodextrin-containing buffer solution in Step 1) and the cyclodextrin-free buffer solution in Step 2) are 4.0 to 7.2; the cyclodextrin content of the cyclodextrin-containing buffer solution in Step 1) is 1 mmol / L to 20 mmol / L.

6. The detection method of fenitrothion according to claim 4, characterized in that, The conditions of the electro-polymerization reaction in Step 1) are set as follows: cyclic voltammetry is used for scanning; the polymerization potential is -5 V to 5 V; the scanning rate is 50 mV / s to 150 mV / s; the number of electro-polymerization cycles is 8 to 12; the conditions of the scanning treatment in Step 2) are set as follows: cyclic voltammetry is used for scanning; the polymerization potential is -5 V to 5 V; the scanning rate is 50 mV / s to 150 mV / s; the number of scanning cycles is 2 to 5.

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