Comparative evaluation of different methods of determining pesticide residues in plant product

Abstract

Pesticides have played an important role in improving the crop yield and eliminating the pests and diseases in modern agricultural production. However, the improper use of pesticides often leads to the excessive pesticide residues, which cause serious harm to human health and ecological environment. As we all known, leafy vegetables have obvious seasonality and economy, and the planting scale is not as large as that of grain crops, and their growth cycle is short, so the requirements for external environmental conditions are stricter. Therefore, the differences and laws of pesticide absorption and transport of leafy vegetables are studied, which are important for pesticide pollution control. Additionally, it is particularly urgent to develop a simple, efficient, and low-cost detection technology for analysing the pesticide residues to strictly control the excessive pesticide residues. Compared with traditional detection methods, the electrochemical sensing analysis technology has several advantages such as high efficiency, simple analysis operation, and inexpensive measurement equipment. In this work, the differences of pesticide absorption and transfer in different leaf vegetables were studied, and the dynamic absorption and accumulation rules were explored in hydroponic lettuce. Otherwise, a series of electrochemical sensor by using several nanocomposite materials as modification materials of sensing electrodes were proposed for the pesticide detection. Under the optimal conditions, the fabricated electrochemical sensors showed highly sensitive pesticide detection performance with satisfactory recovery rates and low limit of detection (LOD) values. The good repeatability, reproducibility, stability, and anti-interference can be achieved at the fabricated sensors. Moreover, the accurate and sensitive quantitative analysis performance can be obtained at the fabricated sensor for the detection of pesticide residues in real samples. The main research contents are as follows: (1) IMI was taken as the test pesticide, and Lettuce, pakchoi-Shanghaiqing, pakchoi-Jimaocai, GaoGeng Cabbage and Greengrocery were taken as the experimental objects, focusing on the differences of IMI pesticide absorption and transfection in different leafy vegetables, and exploring the dynamic absorption and accumulation law. The results showed that the roots of vegetable could absorb pesticides in culture water, and then transfer to stem, leaves, old leaves, new leaves and other parts. The residue of IMI in different parts of lettuce was different. With the increase of days, IMI was continually accumulated in the leaves, and the residual concentration of IMI in the leaves was gradually higher than that in other parts, and the concentration of old leaves was higher than that in new leaves. (2) Carboxylated multi-walled carbon nanotubes (MWCNT-COOH) showed high electrical conductivity and good dispersing property due to the one-dimensional hollow conductive carbon structure and carboxyl functionalization. MWCNT-COOH was used to modify the glassy carbon electrode (GCE) for the fabrication of MWCNT-COOH/GCE sensor towards carbendazim (CBZ). The presence of carboxyl group improved the dispersion degree of carbon nanotubes to a certain extent, which could realize the uniform distribution of carbon material, and the one-dimensional hollow conductive carbon structure contributes to the efficient charge transport on the sensing electrode surface, which could enhance the electrochemical response. Under the optimal conditions, the fabricated MWCNT-COOH/GCE sensor exhibited good CBZ detection performance with low LOD value (6.7nm). The good practical feasibility can be obtained at the fabricated sensor for the detection of CBZ in cabbage, cucumber and potato samples with low RSD from 1.95% to 4.78% and good recoveries from 93.6 to 104.4%, and then the results are evaluated by using HPLC to confirm the accuracy of CBZ electrochemical detection. (3) Biomass-derived porous carbon possessed abundant low-cost biomass carbon source. Soybean-derived porous carbon (SDPC) with three-dimensional (3D) interconnected porous structure was prepared by using the expired soybean as carbon source through a high-temperature carbonization process. SDPC was used to modify the glassy carbon electrode (GCE) for the fabrication of SDPC/GCE sensor towards imidacloprid (IMI). The 3D interconnected porous structure of SDPC significantly improved the electrical conductivity and good absorption capability for IMI due to the interconnected carbon conductive network and large specific surface area. Under the optimal conditions, the fabricated SDPC/GCE sensor exhibited a low LOD value (5.18 nM) in wide IMI linear concentration range of 0.3-75 μM. The good practical feasibility can be obtained at the fabricated sensor for the detection of IMI in tomato and cucumber samples, and then the results are evaluated by using HPLC to confirm the accuracy of IMI electrochemical detection. (4) The pesticide electrochemical detection performance can be improved based on the synergistic effect of nanocomposite sensitizer. The multifunctional nanocomposite of superconductive carbon black (SCB) and ZrO2 was prepared by a simple and efficient ultrasound-assisted strategy. The SCB@ZrO2 nanocomposite was used to modify the glassy carbon electrode (GCE) for the fabrication of SCB@ZrO2/GCE sensor towards methyl parathion (MP). SCB nanoparticles showed high electrical conductivity, which promoted the efficient charge transport, and ZrO2 nanoparticles possessed strong affinity towards the phosphorus groups of MP, which enhanced the accumulation ability of MP. Under the optimal conditions, the fabricated SCB@ZrO2/GCE sensor exhibited a low LOD value (0.045 μM) in MP linear concentration range of 0.03-10 μM. The good practical feasibility can be obtained at the fabricated sensor for the detection of MP in lettuce, cucumber and tomato samples, and then the results are evaluated by using HPLC to confirm the accuracy of MP electrochemical detection. (5) The expired sugarcane juice (SJ)-derived porous carbon spheres (PCS) were prepared by hydrothermal method and furhter modified with β-cyclodextrin (β-CD). The SJPCS@β-CD nanocomposite was used to modify the glassy carbon electrode (GCE) for the fabrication of SJPCS@β-CD/GCE sensor towards methyl parathion (MP). SJPCS with interconnected porous structure exhibits excellent electrical conductivity, strong adsorption property, and high specific surface area, while β-CD with molecular recognition property achieves the uniform dispersion of SJPCS and promotes the recognition and adsorption of MP molecules. Thanks to the synergistic combination of SJPCS and β-CD, the SJPCS@β-CD/GCE sensor exhibited respectable MP determination performance with low limit of detection of 5.87 nM in the MP concentration range of 0.01-10 μM. For the MP detection in vegetables (onion, cabbage, spinach), the fabricated sensor showed good practicability with adequate relative standard deviation of 1.06% to 4.25% and satisfactory recoveries of 96.5 to 100.5%, and then the results are evaluate by using HPLC to confirm the accuracy of IMI electrochemical detection. A promising strategy for the rapid determination of methyl parathion in food products was developed.