CN114324515A - Electrochemical sensor for detecting glyphosate based on copper porphyrin metal organic framework modified carbon paper electrode - Google Patents
Electrochemical sensor for detecting glyphosate based on copper porphyrin metal organic framework modified carbon paper electrode Download PDFInfo
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Abstract
The invention discloses an electrochemical sensor for detecting glyphosate based on a copper porphyrin metal organic framework modified carbon paper electrode, and belongs to the technical field of electrochemistry. According to the invention, the carbon paper is used as a working electrode for detecting glyphosate for the first time, and the electrochemical sensor is prepared on the basis of the copper porphyrin metal organic framework modified carbon paper electrode, and has the advantages of lower detection limit, high stability, good reproducibility and anti-interference capability. The invention provides a cheap, sensitive and stable glyphosate detection method based on the electrochemical sensor, realizes quantitative detection in the range of 0.2-120 mu M, and has a detection limit of 0.03 mu M.
Description
Technical Field
The invention relates to an electrochemical sensor for detecting glyphosate based on a copper porphyrin metal organic framework modified carbon paper electrode, and belongs to the technical field of electrochemistry.
Background
Glyphosate (GLY), which was developed in 1971 by Monsanto USA, is a broad-spectrum biocidal and systemic herbicide. Glyphosate is the most widely used herbicide in the world, and its consumption has increased dramatically in recent years, raising concerns about potential health and environmental hazards. In 2019, in 1 month, the u.s.environmental protection agency reevaluates the evidence of glyphosate carcinogenicity and draws a conclusion that glyphosate is unlikely to be carcinogenic. The french department of agriculture proposed to be at the end of 2020 in 2019, gradually stopping the use of glyphosate products. As the first large producing country and the main using country of glyphosate, the safety of China is not only related to the sustainable development of industry, but also closely related to agricultural product trade, environmental safety and human health.
Currently, more detection methods are based on mature and stable chromatography, including High Performance Liquid Chromatography (HPLC), Gas Chromatography (GC) and capillary electrophoresis. However, these methods have low efficiency, high equipment requirements and cumbersome operation. Although GC-MS/MS, HPLC-MS/MS, fluorescence, capillary electrophoresis, electrochemical sensors, etc. have all been shown to detect glyphosate and AMPA "sensitively". Also, due to the severe matrix effect, the sensitivity was reduced by 10 times even with tap water. The glyphosate and AMPA samples are difficult to pre-treat, and the main reason is that the compounds have strong polarity, are easy to dissolve in water and difficult to volatilize, are difficult to dissolve in an organic solvent, have strong complexing tendency with bivalent and trivalent metal ions, and have a large amount of complex forms in actual samples to influence the derivation and extraction efficiency of the complex forms. Therefore, the problems of low electrochemical detection sensitivity, narrow detection range, complex operation and the like existing at present are solved, and the rapid, convenient and efficient detection technology for detecting glyphosate is urgently needed.
Disclosure of Invention
The invention firstly provides a floriform porphyrin MOFs material (Cu-TCPP) as a novel sensing platform for detecting GLY, and Cu-TCPP is used as an electrode modification material for electrochemical detection of GLY. The two-dimensional layered structure of Cu-TCPP provides a large active site, and can be selectively matched with GLY to realize indirect measurement of GLY. Based on the synergistic electrocatalysis effect of Cu-TCPP and AuNPs and the larger specific surface area of carbon paper, the constructed sensor has the advantages of high analysis speed, wide linear range and high sensitivity.
The invention provides an electrochemical sensor for detecting glyphosate based on a copper porphyrin metal organic framework modified carbon paper electrode. The electrochemical sensor has the advantages of high detection speed, no need of complex pretreatment, low cost and the like, so that the research and preparation of the electrochemical sensor for detecting pesticide residues have great significance. Firstly, the carbon paper electrode is selected as the working electrode, and compared with a classical glassy carbon electrode, the carbon paper electrode has larger specific surface area and better conductivity. The carbon paper electrode is electroplated with uniform gold nanoparticles, so that the electrochemical active area of the electrode is further increased. Secondly, the flaky Cu-TCPP is selected as an electrode material, which is beneficial to the diffusion process between the material and the electrode and accelerates the reaction process. And the copper porphyrin metal organic framework is modified by adopting a dripping mode, and the gold nanoparticles and the copper porphyrin metal organic framework have synergistic effect, so that the sensitivity of electrochemical determination is improved, and the detection of GLY from non-electric activity to electric activity is realized.
The technical scheme is as follows:
the invention provides a preparation method of an electrochemical sensor for detecting glyphosate, which comprises the following steps:
(1) pretreating carbon paper by using an acid solution, and then soaking the carbon paper into a tetrachloroauric acid solution for electrodeposition to obtain a gold nanoparticle AuNPs modified carbon paper electrode, which is expressed as AuNPs/CP;
(2) dispersing Cu-TCPP in a solvent to obtain Cu-TCPP dispersion liquid, then dripping the Cu-TCPP dispersion liquid on the surface of AuNPs/CP obtained in the step (1), and drying to obtain an electrochemical sensor probe which is recorded as Cu-TCPP/AuNPs/CP;
(3) and (3) forming a three-electrode system by using the electrochemical sensor probe obtained in the step (2) as a working electrode, a counter electrode and a reference electrode, and combining the three-electrode system with an electrochemical workstation to construct an electrochemical sensor.
In one embodiment of the present invention, in the step (1), the acid solution is a nitric acid solution. In particular to concentrated nitric acid (68 wt%): water, 1:1, v: v.
In one embodiment of the present invention, in step (1), the pretreatment further comprises washing and drying. Specifically, the washing is performed with acetone or ethanol. Specifically, drying was carried out at 60 ℃.
In one embodiment of the present invention, in the step (1), the chloroauric acid solution is 0.1 wt% HAuCl4·3H2O is dispersed in water.
In one embodiment of the present invention, in the step (1), the electrodeposition process is performed under a condition of-0.2V for 120 s.
In one embodiment of the present invention, in the step (2), the solvent is a mixed solution of water and 0.1% Nafion, and the volume ratio of the two is 20: 1.
In one embodiment of the present invention, in the step (2), the concentration of the Cu-TCPP dispersion is 0.7mg mL-1。
In one embodiment of the invention, a platinum wire electrode is used as a counter electrode and a saturated calomel electrode is used as a reference electrode.
The invention provides an electrochemical sensor for detecting glyphosate based on the preparation method.
The invention also provides a method for detecting glyphosate, which comprises the following steps:
immersing the three-electrode system into a series of glyphosate standard sample solutions with known concentrations, and controlling voltage to perform pre-enrichment; after pre-enrichment is finished, measuring the corresponding oxidation peak current value I and the oxidation peak current value I of a blank sample with the glyphosate concentration of 0 by a Differential Pulse Voltammetry (DPV) method0Calculating to obtain the oxidation peak current difference I-I0(Δ I); and performing linear correlation by using the obtained oxidation peak current difference value and the corresponding glyphosate concentration to obtain a quantitative detection model.
In one embodiment of the invention, the voltage of the enrichment is 0.1V.
In one embodiment of the invention, the time of enrichment is 60 s.
In one embodiment of the invention, the potential of the Differential Pulse Voltammetry (DPV) method is in the range of-0.2-0.6V.
In one embodiment of the invention, the concentration of the glyphosate standard sample ranges from 0.2 to 120. mu.M.
In one embodiment of the invention, a series of standard glyphosate samples of known concentration are prepared using 0.1M acetic acid/sodium acetate buffer (pH 6.0) as the solvent.
Has the advantages that:
the electrochemical sensor is prepared by modifying the carbon paper electrode based on the copper porphyrin metal organic framework, the conductivity and the sensitivity of the electrode are improved by adopting a mode of electrodepositing gold nano particles, and a rapid, simple and convenient glyphosate detection method is constructed. The electrochemical sensor has lower detection limit, high stability, good reproducibility and anti-interference capability, and shows that the functional electrode modified materials MOFs have infinite potential in the field of electroanalysis. The invention adopts the carbon paper as the working electrode for detecting the glyphosate for the first time, and provides a cheap, sensitive and stable electrochemical sensor substrate, namely the throwing type carbon paper electrode can conveniently realize batch preparation and on-site rapid detection, and provides an effective analysis tool for environmental analysis and on-site monitoring of food safety.
The electrochemical sensor can realize the quantitative detection of GLY within the range of 0.2-120 mu M. Wherein the linear equation is Delta I between 0.2 mu M and 10 mu Mp＝1.0932CGLY+8.4697(R20.994); linear equation of delta I in 10-120 mu Mp＝0.0687CGLY+18.562(R20.996); the detection limit of GLY was 0.03 μ M (S/N ═ 3).
Drawings
FIG. 1 is SEM micrographs of (A) CP, (B) AuNPs/CP and (C) Cu-TCPP/AuNPs/CP; (D) FT-IR spectra of TCPP monomer and Cu-TCPP after synthesis.
FIG. 2 is a micrograph of a Cu-TCPP material (a, b are different multiples, respectively).
FIG. 3 shows different electrodes (glassy carbon electrode, conductive glass, pencil lead electrode, carbon paper electrode) in a solution of 1mmol/L [ Fe (CN) ] containing 0.2mol/L KCl6]3-/[Fe(CN)6]4-Cyclic voltammogram in solution.
FIG. 4 shows (A) bare CP and (C) Cu-TCPP/AuNPs/CP at 1.0mmol/L [ Fe (CN)6]3-/[Fe(CN)6]4-A cyclic voltammetry superposition curve with a scanning rate of 10-200 mV/s in the redox probe (containing 0.2mol/L KCl); (B) bare CP and (D) Cu-TCPP/AuNPs/CP Redox Peak Current and Scan Rate1/2A linear relationship therebetween.
FIG. 5 shows different modified electrodes at 1mmol/L [ Fe (CN) ] with 0.2mol/L KCl6]3-/[Fe(CN)6]4-Cyclic voltammetry in solution (a) and ac impedance curve (B).
FIG. 6 is a graph of acetic acid buffered water (ABS) at pH 6 and a scan rate of 50mV s-1Cyclic voltammograms of the different electrodes of (a).
FIG. 7 is a differential pulse voltammogram of different Cu-MOF modified materials for glyphosate assay.
FIG. 8 is a graph showing the change in the influence of pH on the change in oxidation peak current.
FIG. 9 is a graph showing the effect of different mass concentrations of Cu-TCPP on the change of oxidation peak current.
FIG. 10 is a graph showing the effect of different enrichment voltages on the change in oxidation peak current.
FIG. 11 is a graph showing the effect of different enrichment times on the change in oxidation peak current.
FIG. 12 is (A) a differential pulse voltammogram of a sensor for different concentrations of glyphosate solution; (B) oxidation peak current versus GLY concentration.
FIG. 13 shows (A) 10. mu. mol L of modified carbon paper electrode pairs-1Relative response of GLY solution; (B) relative response of Cu-TCPP/AuNPs/CP electrodes at different storage times.
FIG. 14 is a graph showing the peak current values measured with a Cu-TCPP/AuNPs/CP electrode containing 2. mu.M GLY (A) in the presence and absence of different zwitterions (200. mu.M) and 2. mu.M organophosphorus pesticide.
FIG. 15 is a schematic diagram of a process for preparing Cu-TCPP/AuNPs/CP modified carbon paper.
Detailed Description
Materials and reagents: glyphosate, aminomethylphosphonic acid, Aladdin reagent (Shanghai) Co., Ltd; carbon paper (thickness)0.19mm), shanghai hesen; tetrachloroauric acid, trihydrate, Shanghai Tantake Technology, Inc.; meso-tetra (4-carboxyphenyl) porphine (97%), Beijing YinoKai science, Inc.; nafion (5% w/w), Bailingwei (Shanghai) science and technology, Inc.; organophosphorus pesticides, Shanghai Michelin Biochemical technology, Inc.; trifluoroacetic acid, copper nitrate, trihydrate (Cu (NO)3)2·3H2O, 99%), polyvinylpyrrolidone, trifluoroacetic acid, potassium chloride, anhydrous sodium sulfate, anhydrous magnesium sulfate, iron sulfate heptahydrate, calcium chloride dihydrate, cadmium chloride 2.5 water, lead acetate trihydrate, anhydrous sodium acetate, glacial acetic acid, anhydrous ethanol, national reagent (shanghai) ltd; .
Instruments and equipment: CHI660C electrochemical workstation, saturated calomel electrode, platinum electrode, shanghai chenhua instruments; KQ-100DB type digital control ultrasonic cleaner, Kunshan ultrasonic instruments ltd; SHA-B constant temperature oscillator, china corporation, usa; model SU8100 scanning electron microscope, ri zhu. Model IS10 fourier transform infrared (FT-IR) spectrometer, Nicolet, usa. Model T9 double-beam uv-vis spectrophotometer, beijing pros general instruments ltd.
EXAMPLE 1 preparation of electrochemical sensor
(1) Preparation of Cu-TCPP:
synthesizing a Cu-TCPP modified material by adopting a solvothermal method: 3.6mg of Cu (NO)3)2·3H2O, 10 μ L of trifluoroacetic acid (1M), 10mg of polyvinylpyrrolidone PVP was dissolved in 12mL of a mixed solvent of DMF and ethanol (V: V ═ 3:1) to obtain a mixed solution a; weighing 4mg of TCPP, and dissolving the TCPP in 4mL of mixed solvent of DMF and ethanol (V: V ═ 3:1) to obtain mixed solution B; dropwise adding the mixed solution B into the mixed solution A (under stirring), performing ultrasonic treatment for 10min, pouring into a polytetrafluoroethylene reaction tube, sealing the polytetrafluoroethylene reaction tube in a stainless steel reaction kettle, heating to 80 ℃, and reacting for 20 h; after the reaction is finished, cooling to room temperature, washing the Cu-TCPP for 3 times at 8000rpm for 10min by using absolute ethyl alcohol, and removing monomers which do not participate in the reaction; and centrifuging, collecting the precipitate, drying at 50 ℃ in vacuum, and standing overnight to finally obtain the Cu-TCPP.
(2) AuNPs deposition modified carbon paper electrode (preparation of AuNPs/CP):
before modifying the electrode, pretreating the carbon paper: ultrasonic cleaning in nitric acid (68 wt% concentrated nitric acid: water, 1:1, v: v), acetone, and ethanol sequentially for 30min, and oven drying at 60 deg.C. Immersing the pretreated carbon paper electrode into HAuCl4·3H2And depositing for 120s in O (0.1%) solution under the condition of-0.2V, and correspondingly obtaining the AuNPs deposition modified carbon paper electrode which is expressed as AuNPs/CP.
(3) Preparation of Cu-TCPP/AuNPs/CP:
dispersing a Cu-TCPP nano material in a mixed solution (20:1, v: v) of water and 0.1% Nafion to obtain a Cu-TCPP dispersion liquid, and controlling the concentration of the Cu-TCPP dispersion liquid to be 0.7mg mL-1. And (3) dripping 30 mu LCu-TCPP dispersion liquid on the surface of an AuNPs/CP electrode, drying at 60 ℃ to obtain an electrochemical sensor probe, and recording the electrochemical sensor probe as Cu-TCPP/AuNPs/CP.
(4) Constructing an electrochemical sensor:
establishing a three-electrode system by taking the obtained electrochemical sensor probe as a positive electrode, a platinum wire electrode as a counter electrode and a saturated calomel electrode as a reference electrode; and used in conjunction with an electrochemical workstation to construct an electrochemical sensor.
And (3) Cu-TCPP characterization: the chemical bond of Cu-TCPP was characterized by fourier spectroscopy (as shown in fig. 1D). FTIR spectra of TCPP and Cu-TCPP at 716, 1000cm-1Shows the characteristic absorption peak of the macrocyclic skeleton. Located at about 1400cm-1The peak at (a) corresponds to the stretching vibration of the C ═ N bond of the pyrrole ring. 1108 and 1607cm-1The absorption peak of (a) is the skeletal vibration of the outer benzene ring, 1660cm-1The peak of (A) is a C ═ O peak oscillation at the carboxyl group of 772cm-1The peak of (1) is a characteristic peak of benzene ring substitution. 1108 and 1607cm-1The absorption peak of (2) is the skeletal oscillation of the outer benzene ring. Compared with TCPP, 1270cm in the Cu-TCPP nano material-1The peak intensity was significantly reduced because hydrogen on-OH was replaced by metal ions to form Cu-O bonds, indicating that Cu2+Successfully harmonized with the carboxyl group in TCPP. 1000cm-1The characteristic peak is attributed to N-Cu bond stretching vibration absorption, which shows that the metal ion Cu in the synthesized metalloporphyrin derivative2+Has been coordinated with a porphyrin ringA compound (I) is provided.
Characterization of the Cu-TCPP/AuNPs/CP modified electrode: and the surface morphologies of the Cu-TCPP MOFs and the Cu-TCPP/AuNPs are characterized by utilizing a scanning electron microscope. Cu-TCPP MOFs show three-dimensional flower-like structures composed of ultrathin nanoflakes (fig. 2). It provides a larger specific surface area and an efficient pi-electron system at the electrode surface. Fig. 1A is a bare CP image, which consists of carbon fibers in a porous structure. After electrodeposition, the gold nanoparticles are uniformly distributed on the surface of the carbon paper. (FIG. 1C) SEM image of the synthesized Cu-TCPP/AuNPs nanocomposite. Many gold nanoparticles are uniformly deposited on the surface.
Characterization of Cu-TCPP/AuNPs/CP electrochemical Properties: firstly, the electrochemical active area of the modified electrode is inspected in the redox probe by adopting a CV method at different scanning rates, and the set voltage is-0.2-0.6V. As shown in FIG. 4, the redox peak current of the modified electrode increases linearly with the increase of sweep rate in the range of 10-200 mV/s. Redox peak current and v of CP electrode1/2The linear equations of (a) are: i ispa(μA)＝41.735ν1/2+39.806(R2＝0.998)，Ipc(μA)＝42.469ν1/2+39.328(R20.991). Redox peak current and v of Cu-TCPP/AuNPs/CP modified electrode1/2The linear equations of (a) are: i ispa(μA)＝783.607ν1/2-22.107(R2＝0.998)，Ipc(μA)＝754.426ν1/2+21.456(R20.999). According to Randles-sevick equation[42]Calculating the electrical activity area of the Cu-TCPP/AuNPs/CP: i isp＝268600n3/2AD1/2Cν1/2，
Wherein Ip, n, A, C and v represent the peak anode current, the electron transfer number of the redox reaction, and the electroactive area, [ Fe (CN) ]6]3-/[Fe(CN)6]4-Concentration and scan rate. The diffusion coefficient of D is 7.60X 10-6cm2 s-1. We found that the electroactive area of the electrode modified by Cu-TCPP and AuNPs is significantly increased, and is increased by 18.8 times compared with that of a bare CP electrode.
By Cyclic Voltammetry (CV) at 1mmol L-1[Fe(CN)6]3-/[Fe(CN)6]4-In the Redox probe (containing 0.2mol L)-1KCl) at 100mV s-1The electrochemical properties of the different electrodes were investigated (fig. 5A). The redox peak current on the Cu-TCPP/AuNPs/CP and AuNPs/CP electrodes is obviously higher than that of a bare CP electrode, and the AuNPs have good conductivity. The Cu-TCPP/AuNPs/CP modified carbon paper electrode presents a pair of reversible redox peaks, wherein the potential difference of the redox peaks is 77mV, the peak currents are-223.5 muA and 206.5 muA respectively, and compared with the AuNPs/CP electrode, the conductivity is improved to a certain extent.
In addition, the EIS can represent the surface characteristics of the electrode, and further examine the electron transfer efficiency of the electrode in a solution so as to research the conductivity of the electrode modification material. In the range of 0.1-105The measurement was carried out with an amplitude of 5mV in the frequency range of Hertz. Each EIS diagram has two regions: a semicircular region and a linear region. The semi-circle is associated with an electron transfer resistance (Ret), which is coupled to the dielectric and insulating properties of the electrode/electrolyte junction. In the EIS diagram, the smaller the semi-circle diameter, the smaller the impedance, i.e., the faster the electron transfer rate. As shown in FIG. 5B, the impedance of Cu-TCPP/CP is greatest because 2D MOF materials have poor conductivity and a high stacking tendency, resulting in a reduction of exposed active sites and a limitation of electron transfer. The impedance of the Cu-TCPP/AuNPs/CP modified electrode is remarkably reduced because the electric active area of the CP is increased by introducing the AuNPs, and the conductivity of the electrode is greatly improved.
Example 2 detection of Glyphosate based on electrochemical sensor
And (3) electrochemical detection process:
the electrochemical sensor prepared in example 1 was used as a positive electrode, a platinum wire electrode was used as a counter electrode, and a saturated calomel electrode was used as a reference electrode, and a three-electrode system was established.
A series of glyphosate standard samples with known concentrations (0 mu M, 1 mu M, 3 mu M, 5 mu M, 7 mu M, 10 mu M, 20 mu M, 40 mu M, 60 mu M, 80 mu M, 100 mu M and 120 mu M) are prepared by dissolving different dosages of glyphosate in an equal volume of 0.1M acetic acid/sodium acetate buffer (pH 6.0).
Immersing the three-electrode system in the prepared glyphosate standard sample solution with a series of concentrations, enriching for 60s under the voltage of 0.1V, and measuring the corresponding oxidation peak current value I and the oxidation peak current value I of a blank sample with the glyphosate concentration of 0 by adopting a Differential Pulse Voltammetry (DPV) method within the potential range of-0.2-0.6V0Calculating to obtain the oxidation peak current difference I-I0(ii) a And performing linear correlation by using the obtained oxidation peak current difference and the corresponding glyphosate concentration to obtain a quantitative detection model.
The results are shown in FIG. 12, where (A) the differential pulse voltammogram of the sensor versus glyphosate and (B) the oxidation peak current versus GLY concentration. In the concentration range of 0.2-120. mu.M, the oxidation peak current decreases with increasing GLY concentration, in two linear steps: the linear equation is delta I in the range of 0.2-10 mu Mp＝1.0932CGLY+8.4697(R20.994). Linear equation of Delta I between 1.0 and 120 mu Mp＝0.0687CGLY+18.562(R20.996), the detection limit of GLY was 0.03 μ M (S/N — 3).
EXAMPLE 3 optimization of working electrodes for electrochemical Sensors
(one) influence of differently modified electrodes
Glassy carbon electrodes, conductive glass, pencil lead electrodes, and carbon paper electrodes were selected for comparison, and their peak currents were 14.2 μ a, 75.8 μ a, 43.7 μ a, and 182.2 μ a, respectively. The electrode has a large specific surface area compared to a conventional electrode, as shown in fig. 3. Compared with a bare CP electrode, the electrochemical active area of the Cu-TCPP/AuNPs/CP modified electrode is remarkably increased by 18.8 times, as shown in figure 4. Comparing the electrochemical effects of different modified electrodes by cyclic voltammetry and alternating current impedance method, the method can find that AuNPs and Cu-TCPP have good synergistic interaction, improve the surface performance of the electrode and accelerate the electron transfer rate, as shown in FIG. 5. The synthesized copper porphyrin metal organic framework material generates an oxidation peak of copper ions at 0.192V, after GLY is added, the oxidation peak is inhibited, and the reduced current value and the glyphosate concentration show a linear trend, which indicates that the invention can be applied to the detection of GLY, and is shown in figure 6.
Cyclic voltammograms of different modified electrodes were investigated and compared as shown in figure 5. The bare CP electrode was found to be absent of reversible redox peaks, and it should be that the target GLY rarely exhibits the desired electrochemical activity at accessible potentials. The target substance is measured by adopting the Cu-TCPP/AuNPs/CP composite modified electrode, and an obvious anode peak is generated at 0.192V, which shows that Cu+Oxidized Cu2+Copper was completely reduced at-0.6V. The anodic peak current for copper ions decreased after the addition of 20. mu.M GLY. GLY can be indicated by a change in the current signal.
(II) Effect of different Cu-MOF modified materials
The Cu-TCPP is selected as an electrode modification material, so that not only is the complexation between metal ions and GLY provided and the indirect determination of a target object realized, but also two unstable peaks are generated by combining gold nanoparticles compared with other Cu-MOF materials such as Cu-BTC, and due to the excellent catalytic performance of the Cu-TCPP, the Cu-TCPP has better cooperative catalytic performance with the gold nanoparticles and better sensitivity, as shown in figure 7.
(III) Effect of different Cu-TCPP Material concentrations
The content of the metal organic framework material Cu-TCPP on the surface of the electrode plays an important role in the electrocatalytic behavior of the sensor. And (3) researching the influence of the content of Cu-TCPP on the surface of the electrode on electrochemical sensing by adopting a DPV method. As can be seen from FIG. 9, when the Cu-TCPP content was 0.7mg mL-1Of Ti2+The maximum oxidation peak current occurs and as the material concentration increases, the current response decreases, possibly due to agglomeration of the material stack affecting the electron transfer process between the target and the electrode surface. So we chose 0.7mg mL-1The optimal concentration of the Cu-TCPP modified electrode surface is obtained.
Example 4 optimization of assay conditions
Influence of (A) pH
The pH of the acetic acid/sodium Acetate (ABS) buffer solution has a significant effect on the acid-base dissociation of GLY, which can lead to its oxidative chargeThe bit and oxidation currents change. Therefore, the effect of pH on electrochemical oxidation of GLY was first investigated using DPV (fig. 8). The results show that as the pH increases, Cu2+The response peak current of (2) is gradually increased, which indicates that protons participate in the reaction process between Cu-TCPP/AuNPs/CP and GLY. The peak current of both targets then levels off at higher pH values. Comprehensively considering the influence of the pH value on the electrochemical oxidation current of the target, and finally selecting the ABS buffer solution with the pH value of 6 as an optimal system for detecting GLY.
(II) Effect of enrichment Voltage
To obtain the best sensitivity, we optimized the enrichment potential of GLY on Cu-TCPP/AuNPs/CP surface (fig. 10) to obtain the best sensitivity. Under acidic conditions, GLY is negatively charged, and the application of positive voltage can drive GLY to be enriched to the surface of the electrode, so that the peak current value is increased in the stage of-0.1V to 0.1V. Due to Cu+/Cu2+Is in the vicinity of 0.192V, and when copper is completely oxidized, copper ions on the surface of the electrode are saturated and partially dissolved, resulting in a drop in current. We chose 0.1V as the optimal enrichment potential.
(III) Effect of enrichment time
At 0.1mol L-1In the ABS buffer (pH 6) system, the effect of deposition time on copper ion oxidation was studied. As shown in fig. 11. This is probably due to the saturation of glyphosate loading at the active sites of the electrode surface due to the enrichment of glyphosate on the electrode surface. Delta IPIncreasing with deposition time. After 60 seconds, the current tended to drop, and in this study, 60 seconds was selected as the optimal deposition time.
Example 5 reproducibility and interference verification of electrochemical detection of sensor
The reproducibility, interference and stability of the electrodes were investigated under optimal conditions. In order to examine the reproducibility of the sensor, 6 carbon paper electrodes were prepared by the same modification method, and glyphosate solutions of the same concentration were tested. As shown in fig. 13, the relative standard deviation of the obtained response current was 2.5%, indicating that the sensor had good reproducibility. The peak current signal of the prepared sensor remained 82.2% of the original value after being stored at 4 ℃ for 1 month. The result shows that the prepared sensor has good stability and reproducibility and can be used for detecting GLY.
In addition, the selectivity of the developed sensor was evaluated by introducing cations and anions at 100 times higher concentrations than the analyte and an organic substance at the same amount as the analyte. This study analyzed two interfering substances: one group is GLY metabolites and organophosphorus pesticides. The other is the anion (Na) commonly found in the sample+，K+，Pb2+，Cd2+，Ca2+，Fe2+，Cl-，SO4 2-) They can be GLY coordinated, interference measurement. The experimental results show that these interfering substances have little interfering effect (FIG. 14).
EXAMPLE 6 actual sample testing
Food samples (soybean, wheat, carrot, drinking water) were purchased from local supermarkets and treated according to standard methods (national standard of the people's republic of china GB/T23750-. Food samples were pretreated by adding GLY standard solutions at various concentrations (1, 5. mu.M) and analyzed using the method. The results are shown in Table 1.
TABLE 1 content of GLY in the actual samples
The practical application of Cu-TCPP/AuNPs/CP is verified by detecting the concentration of glycine in real samples of soybean, carrot, wheat, water and the like in the table 1. Glycine is detected from the soybeans, the content of the glycine is 6.35 mu M, and the soybean protein meets the limit requirements of national standards. The recovery test was performed by a standard addition method, and the accuracy of the fabricated sensor was evaluated. When 4 food samples are loaded, the recovery rate of GLY is 97.5-110.7% (RSD is less than 10.0%).
Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. A preparation method of an electrochemical sensor for detecting glyphosate is characterized by comprising the following steps:
(1) pretreating carbon paper by using an acid solution, and then soaking the carbon paper into a tetrachloroauric acid solution for electrodeposition to obtain a gold nanoparticle AuNPs modified carbon paper electrode, which is expressed as AuNPs/CP;
(2) dispersing Cu-TCPP in a solvent to obtain Cu-TCPP dispersion liquid, then dripping the Cu-TCPP dispersion liquid on the surface of AuNPs/CP obtained in the step (1), and drying to obtain an electrochemical sensor probe which is recorded as Cu-TCPP/AuNPs/CP;
(3) and (3) forming a three-electrode system by using the electrochemical sensor probe obtained in the step (2) as a working electrode, a counter electrode and a reference electrode, and combining the three-electrode system with an electrochemical workstation to construct an electrochemical sensor.
2. The method according to claim 1, wherein in the step (2), the concentration of the Cu-TCPP dispersion is 0.7mg mL-1。
3. The method of claim 1, wherein the electrodeposition process is carried out at-0.2V for 120 s.
4. The method according to claim 1, wherein the solvent in step (2) is a mixture of water and 0.1% Nafion at a volume ratio of 20: 1.
5. An electrochemical sensor for detecting glyphosate obtained by the preparation method of any one of claims 1-4.
6. A method for detecting glyphosate is characterized by comprising the following steps:
immersing the three-electrode system obtained in claim 1 in a series of standard glyphosate sample solutions of known concentration, and controlling the voltage to perform pre-enrichment; after pre-enrichment is over, the difference is passedMeasuring corresponding oxidation peak current value I and oxidation peak current value I of a blank sample with the glyphosate concentration of 0 by pulse voltammetry0Calculating to obtain the oxidation peak current difference I-I0(ii) a And performing linear correlation by using the obtained oxidation peak current difference value and the corresponding glyphosate concentration to obtain a quantitative detection model.
7. The method of claim 6, wherein the enriched voltage is 0.1V.
8. The method of claim 6, wherein the time for enrichment is 60 s.
9. The method of claim 6, wherein the concentration of the glyphosate standard sample is in the range of 0.2-120 μ M.
10. A method according to any of claims 6-9, characterized in that the potential of the differential pulse voltammetry is in the range-0.2-0.6V.
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