Extraction head for detecting malathion residues in agricultural products and detection method using same

Abstract

The invention discloses an extraction head for detecting malathion residues in agricultural products and a detection method applying the extraction head, the extraction head is a composite material of poly (5-amino indole pyrrole)-ionic liquid-porous nitrogen-doped graphene, and the ionic liquid is 1-butyl-3-methylimidazolium hexafluorophosphate. The extraction head has the beneficial effects that the extraction head made of the composite material has relatively good stability and repeatability, and can be used for rapidly detecting the residue of malafos sulfur in agricultural products.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of food safety, and particularly relates to an extraction head for detecting malathion residues in agricultural products and a detection method using the same. BACKGROUND

[0002] In recent years, with the continuous improvement of people's living standards, green food and healthy food are very popular among the public. However, in order to improve the yield of crops, many farmers use pesticides for a long time and unreasonably, resulting in excessive pesticide residues. At present, in order to prevent and control the pests of agricultural products, the use of organophosphorus pesticides is still very frequent, and there are many types of organophosphorus pesticides. Malathion is an important organophosphorus pesticide, and malathion belongs to a low-toxicity insecticide. However, on October 27, 2017, the International Agency for Research on Cancer of the World Health Organization announced the preliminary reference list of carcinogens, and malathion belongs to class 2A carcinogens. Therefore, it is very important to build a high-sensitivity, accurate and rapid method for determining the content of malathion in food. SUMMARY

[0003] In order to solve the above problems, the present application provides an extraction head for detecting malathion residues in agricultural products and a detection method using the same.

[0004] According to one aspect of the present application, an extraction head for detecting malathion residues in agricultural products is provided, and the extraction head is a composite material of poly-5-aminoindole-pyrrole-ionic liquid-porous nitrogen-doped graphene, wherein the ionic liquid is 1-butyl-3-methylimidazolium hexafluorophosphate. The beneficial effect is that the extraction head of the composite material has good stability and repeatability, and can quickly detect the malathion residues in agricultural products.

[0005] In some embodiments, the method for preparing the extraction head comprises: The monomers are configured as 5-aminoindole and pyrrole, the doping agent is a mixed solution of 1-butyl-3-methylimidazolium hexafluorophosphate and porous nitrogen-doped graphene, and the electrode system is inserted into the mixed solution to prepare a composite extraction head by cyclic voltammetry. The beneficial effect is that the extraction head has stable performance, high sensitivity, and can be repeatedly used for many times, and has good extraction performance.

[0006] In some embodiments, the electrode system is: Ag / AgCl as a reference electrode; platinum wire as an auxiliary electrode; and stainless steel wire as a working electrode.

[0007] In some embodiments, the preparation method further comprises the following steps: Preparation of a sample injection device of the composite extraction head; Aging of the composite extraction head of the sample injection device, and natural air drying after aging for standby, wherein the aging comprises the following steps: After raising the temperature from 0℃ to 90℃, maintain the temperature for 30 minutes. After raising the temperature from 90℃ to 180℃, maintain the temperature for 30 minutes. The temperature was raised from 180℃ to 230℃ and then kept at that temperature for 60 minutes.

[0008] According to another aspect of this application, a method for detecting malathion residues in agricultural products is provided, characterized by comprising the following steps: The aforementioned composite extraction head was used for headspace extraction of phenolic compounds; A gas chromatography-mass spectrometry (GC-MS) model was constructed, and the extraction head was used to detect malathion sulfides.

[0009] In some embodiments, headspace extraction of phenolic compounds using a composite extraction head includes the following steps: Perform HS-SPME operation: Add saturated sodium chloride solution and malathion standard solution to the extraction flask to form the first mixture; The first mixture was heated and stirred in a water bath; Insert the injection device into the headspace extraction vial and expose the extraction head of the injection device above the extraction vial for headspace extraction. After the HS-SPME operation steps are completed, the GC-MS operation is performed: Retract the extraction head into the protective sleeve, quickly insert it into the GC-MS injection port, analyze it, and then perform GC-MS separation and detection.

[0010] In some implementations, the extraction time is 10-35 min.

[0011] In some implementations, the stirring speed is 300 r / min-500 r / min.

[0012] In some embodiments, the extraction temperature is 45°C. o C-85 o C.

[0013] In some implementations, the salt concentration is 10%-20L; and / or the eluent time is 5 min.

[0014] This application describes the fabrication of an SPME head using poly(5-aminoindole) and pyrrole as monomers, and IL and porous N-doped graphene as dopants. The optimal headspace extraction conditions for Malathion were: stirring rate 500 r / min, saturated salt solution, GCMS elution for 5 min, and 65 °C. o C is the headspace extraction temperature. The extraction head in this application exhibits the best adsorption capacity for Malathion, resulting in the largest measured peak area. Attached Figure Description

[0015] Figure 1 The voltammetric behavior of the preparation of the polypyrrole extraction head according to one embodiment of the present invention; Figure 2 The voltammetric behavior of the preparation of the polymerized 5-aminoindole extraction head according to one embodiment of the present invention; Figure 3 The voltammetric behavior of the preparation of the polypyrrole + polymerized 5-aminoindole + ionic liquid extraction head according to one embodiment of the present invention; Figure 4 The voltammetric behavior of the polypyrrole + polymerized 5-aminoindole + porous nitrogen-doped graphene extraction head according to one embodiment of the present invention is shown. Figure 5 The voltammetric behavior of the polypyrrole + 5-aminoindole + ionic liquid + porous nitrogen-doped graphene extraction head prepared according to one embodiment of the present invention is shown. Figure 6 This is a SEM image of a polypyrrole extraction head according to an embodiment of the present invention; Figure 7 This is a SEM image of a poly5-aminoindole extraction head according to an embodiment of the present invention. Figure 8 This is a SEM image of a polypyrrole + poly5-aminoindole extraction head according to an embodiment of the present invention; Figure 9 This is a SEM image of a polypyrrole + poly5-aminoindole + porous nitrogen-doped graphene extraction head according to an embodiment of the present invention. Figures 10-11 This is a SEM image of a polypyrrole + polymerized 5-aminoindole + ionic liquid + porous nitrogen-doped graphene extraction head according to an embodiment of the present invention. Figure 12 This is a response diagram of different extraction heads of the present invention to the peak area of ​​malathion; Figure 13 This is a graph showing the effect of stirring rate on peak area in this application; Figure 14 This is a graph showing the effect of salt concentration on peak area in this application; Figure 15 This is a graph showing the effect of resolution time on peak area in this application; Figure 16 This is a graph showing the effect of extraction temperature on peak area in this application; Figure 17 This is the Malathion standard curve diagram of this application; Figure 18 This is the chromatogram of the cucumber sample in this application; Figure 19 This is the chromatogram of the tomato sample in this application; Figure 20This is the chromatogram of the lettuce sample in this application; Figure 21 This is the spiked recovery chromatogram of cucumber in this application; Figure 22 This is the chromatogram of the spiked tomato recovery in this application; Figure 23 This is the chromatogram of the spiked recovery of lettuce in this application; Detailed Implementation The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0016] I. Instrument and Reagent Instructions The main instruments and models are: gas chromatograph-mass spectrometer (Shimadzu GCMS-QP2010), vacuum tube furnace (TF1200-80), electrochemical analyzer (CHI660D), ultrasonic cleaner (KQ5200E), thermostatic magnetic stirrer (S10-3 type), and sample injector (self-made in the experiment).

[0017] Main reagents and specifications: Methanol (AR, Fengchuan Chemical Reagent Technology Co., Ltd.); Nitrogen-doped graphene purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd. (Nanjing, China), porous nitrogen-doped graphene obtained by nitric acid oxidation; N,N-dimethylformamide (DMF), anhydrous ethanol (AR); 1-Butyl-3-methylimidazolium hexafluorophosphate (99%, purchased from Jiuding Chemical); Tetrabutylammonium perchlorate (99%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.); 5-aminoindole (98%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.); Pyrrole (99%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.); Malathion (AR, 100%, purchased from Beijing Bailingwei Technology Co., Ltd.); Acetonitrile (GR, Tianjin Kemeiou Chemical Reagent Co., Ltd.), Sodium chloride (AR, Nanhui Pengzhen Yingfang Chemical Plant); Watson's drinking water (professionally distilled); Polyamide resin and epoxy resin.

[0018] II. Implementation (a) Operating conditions of the electrochemical instrument Parameter settings: Cyclic voltammetry for polypyrrole is between 0 and 1.5 V; scan rate: 0.05 mV / s; number of scans: 100. Cyclic voltammetry for 5-aminoindole is between 0.2 and 1.8 V; scan rate: 0.05 mV / s; number of scans: 100. Electrodeposition polymerization is carried out under these conditions.

[0019] (II) Preparation of composite SPME head First, a three-electrode system was assembled in a DMF solution containing 0.05 mol / L 5-Aminoindole and PY, 0.1 mol / L tetrabutylammonium perchlorate, 10 μL / mL IL, and 0.05 mg / mL porous Nitrogen-doped graphene. The system used a stainless steel wire as the working electrode, a platinum wire as the counter electrode, and silver and silver chloride (Ag-AgCl) as reference electrodes. Then, the system was immersed in the prepared solution, and CV scanning was performed to prepare the extraction head. This process was repeated by changing the electrolyte composition to prepare other extraction heads. The final prepared extraction heads included: polypyrrole; polymerized 5-aminoindole; polymerized polypyrrole + polymerized 5-aminoindole; polymerized polypyrrole + polymerized 5-aminoindole + porous nitrogen-doped graphene; and polymerized polypyrrole + polymerized 5-aminoindole + porous nitrogen-doped graphene + ionic liquid.

[0020] The prepared extraction head was aged in a vacuum tube furnace. Then, epoxy resin and polyamide resin were mixed in a 1:1 ratio and used to fix the extraction head into a self-made sample injector. After drying, different extraction coating sample injector devices were prepared.

[0021] (iii) Aging Place the extraction head in a ceramic dish lined with aluminum foil, then place it in a vacuum tube furnace. Set the aging program to 90°C. o C, aging, after 30 minutes, the temperature rises to 180°C. o C, continue aging for 30 minutes, temperature increased to 230°C o C, age for 60 minutes, and set aside for later use after aging.

[0022] (iv) Headspace Extraction Add 7 mL of saturated sodium chloride solution to a 20 mL extraction flask, add a magnetic stir bar, then add the prepared malathion standard solution. Seal the flask with raw rubber tape, replace the cap with a cleaned rubber stopper, and seal it with an aluminum cap. Adjust the thermostatic magnetic stirrer to maintain a constant temperature of 65°C. o C. Place the extraction flask in a water bath. Then, insert the homemade sampler into the extraction flask, push the handle to expose the extraction head to the headspace of the solution, and perform headspace extraction under magnetic stirring at 500 r / min. After 50 min, retract the extraction head into the protective sleeve and quickly insert it into the GC-MS for analysis and detection.

[0023] (v) GC-MS operation Using a DB-5ms column as the separation column, the column oven temperature was 80°C. o C; Inlet temperature 230 oC, splitless injection mode; injection time 1 min; flow control mode: pressure; pressure 65.2 kPa; total flow rate 40.0 mL / min; column flow rate 1.0 mL / min; linear velocity 36.8 cm / sec; purge flow rate 3.0 mL / min; column oven temperature program setting: 80 o C is maintained for 1 minute, at 10 o Heat to 250 °C / min o Maintain temperature at C for 5 minutes. Ion source temperature 200°C. o C; Interface temperature 250 o C; solvent delay 1 min. The characteristic ion peaks of malathion are shown in Table 2-1.

[0024] Table 1 Characteristic Selective Ions of Malathion

[0025] III. Effect Characterization 1. Voltammetric behavior of extraction head prepared by electropolymerization The CV curves of the electrochemically prepared extraction head were recorded in the experiment.

[0026] Figure 1 The graph uses PPY as the monomer. Compared with other graphs, the voltammetric curves are more chaotic. This is because the polymerization is carried out in a neutral environment with a lack of electrolyte, which leads to slower electron transfer during pyrrole polymerization.

[0027] Figure 2 The CV curve for 5-Aminoindole monomer shows two oxidation potentials, approximately 1.1 V and 1.4 V, with the amino and indole polymerization sites respectively. The amino group is the primary polymerization site. The presence of two oxidation potentials is related to the structure of 5-NH2-IAA. Figure 3 It is a Poly-5-Aminoindole-PPY ionic liquid. Figure 4 It is Poly-5-Aminoindole-PPY-porous nitrogen-doped graphene. When Poly-5-Aminoindole-PPY are common monomers, the peak current gradually increases with the increase of the number of polymerization cycles and the growth of polymerization time (the oxidation potential of amino increases from 1.1 V to 1.6 V; the oxidation potential of indole increases from 1.4 V to 1.8 V), indicating that the synergistic effect of the two is obvious. Figure 5This is the CV curve of Poly-5-Aminoindole-PY-IL-N-doped graphene. The oxidation potential is approximately 0.8 V, at which a distinct oxidation peak appears. Simultaneously, a peroxide peak appears when the voltage increases to 1.1 V, with a maximum peak current of -0.0007 A. The peak current gradually increases with the increase of the number of polymerization cycles and polymerization time, indicating that this composite polymer coating has good conductivity. Compared with the curve using PPY and 5-Aminoindole as monomers, this curve clearly shows that the peak current and oxidation potential gradually increase with the increase of the number of polymerization cycles and polymerization time.

[0028] 2. Characterization of the microstructure of the extraction head 2.1 Comparison of the microstructure of the extraction head at lower magnifications The microstructure of the extraction heads for PPY, Poly-5-Aminoindole, PPY+Poly-5-Aminoindole, PPY+Poly-5-Aminoindole-N-doped graphene, and Poly-5-Aminoindole-PY-IL-N-doped graphene was characterized using SEM. Figure 6 It can be seen that the obtained Poly-PY adheres well to the stainless steel wire and simultaneously exhibits a typical cauliflower-like structure. From Figure 7 It can be seen that Poly-5-Aminoindole is evenly and tightly coated on stainless steel wire, with a consistent texture and a raised-and-low structure.

[0029] from Figure 8 The image shows a SEM image of PPY+Poly-5-Aminoindole. The synergistic effect of the two results in a denser and more regular coating, which can effectively improve the microstructure of the coating, and will be very beneficial to the improvement of coating performance. Figure 9 SEM images of the Poly-PY-5-Aminoindole-N-doped graphene extraction head. Figures 10-11 As can be seen from Poly-5-Aminoindole and PPY, the addition of IL and N-doped graphene makes them more readily apparent and denser, which is more conducive to the adsorption of the substances we need. Figures 10-11The preparation conditions for Poly-PY-5-Aminoindole-IL-N-doped graphene shown are: pyrrole 0.1 mol / L, 5-aminoindole 0.05 mol / L, IL 10 μL / mL, and N-doped porous graphene 0.05 mg / mL. The cross-sectional characterization diagram of the Poly-PY-5-Aminoindole-IL-N-doped graphene extraction head shows that during coating on the electrochemical workstation, the polymerization of 5-aminoindole-pyrrole-ionic liquid-nitrogen-doped graphene proceeds from the inside out of the stainless steel wire in concentric rings over time, forming a relatively dense structure. This polymerization method can increase the number of times the extraction head can be used.

[0030] 2.3 Comparison of peak areas of malathion with different extraction heads The experiment investigated the effect of different extraction heads on the peak area of ​​Malathion, the target analyte. From... Figure 12 It was found that Poly-PY-PY-5-Aminoindole-IL-Nitrogen-doped graphene has a good adsorption effect on Malathion, and the performance of the extraction coating is improved by ionic liquid and graphene doping.

[0031] III. Condition Optimization Implementation Examples 3.1 Stirring rate The stirring rate is closely related to the extraction performance, so the stirring rate was optimized in this experiment, such as... Figure 13 As shown, when the stirring rate is 300 r / min-500 r / min, the peak area increases, and when it exceeds 500 r / min, the peak area decreases. Therefore, under these GC-MS conditions, 500 r / min yields the best results.

[0032] 3.2 Salt solution concentration In the experiment, a single-factor experiment was conducted to consider the effect of salt solution concentration on the peak area of ​​Malathion, such as... Figure 14 As shown, when the salt concentration is 10%-20%, the extracted peak area is relatively small. As the salt concentration gradually increases, the extracted peak area becomes larger, and the extraction effect is optimal when the salt solution reaches saturation. Therefore, this experiment uses a saturated salt solution for headspace extraction.

[0033] 3.3 Resolution Time The desorption time is closely related to whether the adsorbed substances can fully volatilize. Therefore, the experiment also recorded the effect of different desorption times on the Malathion peak area, as shown in the curve relationship. Figure 15As can be seen, the peak area gradually increases with the increase of the extraction time. When the time reaches 5 min, the peak area is the largest. After 5 min, the peak area decreases. Therefore, the optimal extraction time is 5 min.

[0034] 3.4 Temperature The experiment also explored the T of headspace extraction, such as Figure 16 As shown, from 45 o C-85 o C. As the extraction temperature (T) increases, the peak area of ​​the extracted Malathion peak continuously increases. When T reaches 65°C... o The extraction effect is optimal at temperature C. If the temperature is further increased, the volatility of Malathion is suppressed, and the peak area decreases accordingly. Therefore, the optimal temperature for headspace extraction under GCMS conditions is 65°C. o C.

[0035] IV. Performance Analysis Under optimized experimental conditions, different concentrations of Malathion were analyzed. Figure 17 As can be seen, the peak area increases with increasing Malathion concentration, exhibiting a good linear relationship. The linear equation is y = -258.95972 + 2581.16C (μg / mL), R0 2 =0.99608, the detection limit is 0.007 μg / mL. At the same time, three parallel determinations of the same concentration of Malathion were performed using one extraction head, and the relative standard deviation was 3.3%, indicating that the extraction head has good stability.

[0036] V. Testing of actual samples The test was to detect the presence of malathion in agricultural products. Therefore, the actual samples used were cucumbers, lettuce, and tomatoes randomly purchased from the market. The specific operating steps were as follows: 25 g of crushed cucumber, lettuce, and tomato samples were weighed separately, and 50 mL of methanol solution was added for dissolution and extraction. The samples were homogenized thoroughly for 2 minutes using a high-speed homogenizer. Excess residue was then filtered through filter paper. The filtered liquid was added to a 0.06% NaCl solution and vortexed thoroughly for 2 minutes. After removal, the mixture was allowed to stand at room temperature for 20 minutes until the solution separated into layers. 10 mL of the methanol layer from the separated liquid phases was collected in a beaker and heated at 40°C. o Evaporate the solution in a constant-temperature water bath until 1 mL remains. Then, add 1 mL of the sample solution to 6 mL of saturated salt solution in an extraction flask, seal, perform headspace extraction, and GC-MS detection. No malathion residue was detected, indicating that the cucumbers, tomatoes, and lettuce in this market are free of malathion residue. See sample chromatogram below. Figures 18-20In addition, to evaluate the above detection method, samples were spiked for recovery, with recoveries ranging from 97.56% to 116.25% and RSDs (n=3) from 2.7% to 10.1%, indicating that this method can be used for the detection of real samples. The spiked recovery chromatogram is shown below. Figures 21-23 .

[0037] As shown above, this experiment used PY and 5-Aminoindole as monomers and IL and N-doped graphene as dopants to prepare various SPME heads. To find the optimal conditions for headspace extraction of Malathion, after multiple experiments, the optimal conditions were determined to be: stirring rate 500 r / min, saturated salt solution, GCMS resolution for 5 min, and 65°C. o C is the headspace extraction temperature. The linear equation for the determination of the standard is y = -258.95972 + 2581.16C, R 2 =0.99608, linear range 0.010 μg / mL-0.140 μg / mL, limit of detection 0.007 μg / mL. Spiked samples were recovered, with recoveries between 97.56% and 116.25% and RSDs (n=3) between 2.7% and 10.1%.

[0038] The Poly-5-Aminoindole-PY-IL-N-doped graphene extraction head proposed in this application shows great promise for the detection of organophosphate residues in agricultural products.

[0039] The above descriptions are merely some embodiments of the present invention. It should be noted that those skilled in the art can make other modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. An extraction head for detecting malathion residues in agricultural products, characterized in that, The extraction head is a composite material of poly5-aminoindole-pyrrole-ionic liquid-porous nitrogen-doped graphene, wherein the ionic liquid is 1-butyl-3-methylimidazolium hexafluorophosphate.

2. The extraction head according to claim 1, characterized in that, The method for preparing the extraction head includes: The monomers were 5-aminoindole and pyrrole, and the dopant was a mixed solution of 1-butyl-3-methylimidazolium hexafluorophosphate and porous nitrogen-doped graphene. The solvent was N,N-dimethylformamide, and the electrolyte was tetrabutylammonium perchlorate. The electrode system was inserted into the mixed solution, and a composite extraction head was prepared by cyclic voltammetry.

3. The extraction head according to claim 2, characterized in that, The electrode system consists of: Ag / AgCl as the reference electrode; platinum wire as the auxiliary electrode; and stainless steel wire as the working electrode.

4. The extraction head according to claim 2, characterized in that, The preparation method further includes the following steps: A sample introduction device for preparing a composite extraction head; The composite extraction head of the sample introduction device is aged, and after aging, it is air-dried for later use. The aging process includes the following steps: After raising the temperature from 0℃ to 90℃, maintain the temperature for 30 minutes. After raising the temperature from 90℃ to 180℃, maintain the temperature for 30 minutes. The temperature was raised from 180℃ to 230℃ and then kept at that temperature for 60 minutes.

5. A method for detecting malathion residues in agricultural products, characterized in that, Includes the following steps: The composite extraction head-head extraction of malathion sulfide as described in claims 1-4; A gas chromatography-mass spectrometry (GC-MS) model was constructed, and the extraction head was used to detect malathion sulfides.

6. The detection method according to claim 5, characterized in that, The headspace extraction of phenolic compounds using the composite extraction head includes the following steps: Perform HS-SPME operation: Add saturated sodium chloride solution and malathion standard solution to the extraction flask to form the first mixture; The first mixture was heated and stirred in a water bath; Insert the injection device into the headspace extraction vial and expose the extraction head of the injection device above the extraction vial for headspace extraction. After the HS-SPME operation steps are completed, the GC-MS operation is performed: Retract the extraction head into the protective sleeve, quickly insert it into the GC-MS injection port, analyze it, and then perform GC-MS separation and detection.

7. The detection method according to claim 6, characterized in that, Extraction time is 10-35 min.

8. The detection method according to claim 6, characterized in that, The stirring speed is 300 r / min-500 r / min.

9. The detection method according to claim 6, characterized in that, The extraction temperature is 45 °C - 85 °C.

10. The detection method according to claim 6, characterized in that, Salt concentration is 10%-20L; And / or the parsing time is 5 minutes.

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