Determination Of Pesticides Research Articles

Determination of diflufenican and azaconazole pesticides in wastewater samples by GC-MS after preconcentration with stearic acid functionalized magnetic nanoparticles-based dispersive solid-phase extraction.

This study presents the preconcentration of diflufenican and azaconazole from domestic wastewater samples by using dispersive solid-phase extraction (dSPE) for determination by gas chromatography-mass spectrometry (GC-MS). Stearic acid-coated magnetic nanoparticles were used as adsorbents for dSPE method. In order to maximize the efficiency of the extraction process, parameters such as magnetic nanoparticle (MNP) type and amount, eluent type and volume, mixing type, and mixing period were all optimized. The linear range obtained for azaconazole and diflufenican was 7.50-500ng/mL and 7.50-750ng/mL, and their limits of detection/quantification (LOD/LOQ) were calculated as 1.3/4.3ng/mL and 1.4/4.7ng/mL, respectively. By comparing the LOD values of direct GC-MS and the developed dSPE method, azaconazole and diflufenican recorded approximately 35 and 38 folds enhancement in detection power. Recovery experiments with domestic wastewater were carried out to certify the proposed method's accuracy and applicability. By using the matrix matching calibration strategy, the good percent recovery results between 98 and 105% were obtained.

Biosensors Based on Acetylcholinesterase Immobilized on Clay-Gold Nanocomposites for the Discrimination of Chlorpyrifos and Carbaryl.

This work aims at evaluating a utilization of diverse clay mineral/gold nanoparticles/acetylcholinesterase (clay/AuNPs/AChE) biosensors by using principal component analysis (PCA) for the discrimination of pesticide types and their concentration levels both in the synthetic and real samples. Applications of simple and low-cost clay/AuNP composites of different characteristics as modified-electrode materials are highlighted. Four types of clay minerals, namely, platelike kaolinite (Kaol: 1:1 aluminum phyllosilicate), globular montmorillonite (Mt: 2:1 aluminum phyllosilicate), globular bentonite (Bent: 2:1 aluminum phyllosilicate), and fibrous sepiolite (Sep: 2:1 inverted ribbons of magnesium phyllosilicate), were selected as the base materials. Due to the distinct characteristics of the selected clay, the derived clay/AuNP composites resulted in different physical morphologies, AuNP sizes and loadings, matrix hydrophobicity, and active AChE loading per electrode. These, in turn, caused divergent electrochemical responses for the pesticide determination; hence, no other enzymes apart from AChE were necessary for the fabrication of distinct biosensors. Physical and chemical characterizations of clay/AuNPs were conducted using scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy techniques. The electrochemical information was recorded by cyclic voltammetry and amperometry techniques. The enzyme inhibition results obtained from the pesticides were treated and used as input data to obtain PCA results. The four fabricated clay/AuNPs/AChE biosensors were able to discriminate chlorpyrifos and carbaryl and their concentration levels for synthetic pesticides and real samples. It was disclosed that a high enzyme inhibition and a high hydrophobic modified-electrode material affect a highly sensitive pesticide biosensor. The hydrophobic/hydrophilic character of the modified-electrode material plays a major role in discriminating the pesticide types and their concentration levels by the proposed single-enzyme sensor system. The PCA results illustrated that PC2 described the different types of pesticides, and PC1 showed the level of pesticide concentration with high first two principal components. The mixed pesticides could be identified at an especially low total concentration of 0.5 ng/mL in real samples.

Targeted and non-targeted analysis for the investigation of pesticides influence on wheat cultivated under field conditions

A comprehensive approach was applied to evaluate the effects of pesticides on the metabolism of wheat (Triticum aestivum L). The application of commercially available pesticide formulations under field cultivation conditions provided a source of metabolic data unlimited by model conditions, representing a novel approach to study the effects of pesticides on edible plants. Gas and liquid chromatography coupled to tandem mass spectrometry were employed for targeted and non-targeted analysis of wheat roots and shoots sampled six times during the six-week experiment. The applied pesticides: prothioconazole, tebuconazole, fluoxastrobin, diflufenican, florasulam, and penoxulam were found at concentrations ranging 0.0070–25.20 mg/kg and 0.0020–2.2 mg/kg in the wheat roots and shoots, respectively. The following pesticide metabolites were identified in shoots: prothioconazole-desthio (prothioconazole metabolite), 5-(4-chlorophenyl)-2,2-dimethyl-3-(1,2,4-triazol-1-ylmethyl)pentane-1,3-diol (tebuconazole metabolite), and N-(5,8-dimethoxy[1,2,4]triazolo[1,5-c]pyrimidin-2-yl)-2,4-dihydroxy-6-(trifluoromethyl)benzene sulphonamide (penoxulam metabolite). The metabolic fingerprints and profiles changed during the experiment, reflecting the cumulative response of wheat to both its growth environment and pesticides, as well as their metabolites. Approximately 15 days after the herbicide treatment no further changes in the plant metabolic profiles were observed, despite the presence of pesticide and their metabolites in both roots and shoots. This is the first study to combine the determination of pesticides and their metabolites plant tissues with the evaluation of plant metabolic responses under field conditions. This exhaustive approach contributes to broadening the knowledge of pesticide effects on edible plants, relevant to food safety.

Application of a magnetic solid-phase extraction method using a novel magnetic metal organic framework nanocomposite for extraction of malathion and diazinon pesticides from environmental water samples

Herein, a magnetic solid-phase extraction (MSPE) method using a synthesized magnetic metal-organic framework composite (Cu-MOF@Fe3O4@SiO2) was applied for the extraction of two well-known organophosphorus pesticides (Malathion and Diazinon) in several environmental water samples. After the extraction, the mentioned target analytes were measured by HPLC-UV. Under the optimal conditions obtained, acceptable linearity was observed within the concentration ranges of 10.0–500.0, and 5.0–500.0 μg/L for malathion and diazinon, respectively. The respective limits of quantification (LOQs) were determined to be 10.0 and 5.0 μg/L for malathion and diazinon. Besides, the MSPE method was successfully implemented to determine the two targets in tap water, surface water, well water, and treated waste water samples with the recoveries varying from 84.0 to 105.5 % (RSDs = 3.8–9.6 %). The obtained results indicated that the combined MOF-based MSPE/HPLC-UV method is of several valuable analytical features, such as high sensitivity, good precision, and the ease of operation and it is practically effective for the extraction and determination of organophosphorus pesticides in various water samples.

Synthesis of oil palm empty fruit bunch-based magnetic-carboxymethyl cellulose nanofiber composite for magnetic solid-phase extraction of organophosphorus pesticides in environmental water samples

This study investigated the development of a magnetic-carboxymethyl cellulose nanofiber (Fe3O4-cmCNF) composite from oil palm empty fruit bunch (OPEFB) as a promising adsorbent for the determination of organophosphorus pesticides (OPPs) in water samples via the magnetic solid-phase extraction (MSPE). The Fe3O4-cmCNF was prepared via the alkaline method and surface-modified using the carboxymethylation and sol–gel technique. The physicochemical characteristics of the Fe3O4-cmCNF were evaluated via FT-IR, VSM, SEM, TEM, XRD, TGA, and BET analysis. Diazinon, fenitrothion, and malathion were selected as the model analytes to examine the feasibility and performance of the Fe3O4-cmCNF-based MSPE to detect OPPs in real environmental water samples using gas chromatography-micro-electron capture detector (GC-µECD). Experimental parameters that affected the extraction efficiency were optimized, including the type and amount of adsorbent, extraction time, pH, type of elution solvent, and ionic strength. Based on the results, the prepared adsorbent showed a high affinity towards OPPs through hydrogen bonding as well as hydrophobic and electrostatic interaction. Under optimum conditions, the linear calibration curves were achieved for diazinon, fenitrothion, and malathion with a concentration range of 0.1–200 ng mL−1 and a suitable determination coefficient (r2) between 0.9962 and 0.9995. Furthermore, acceptable intra- and inter-day precisions were obtained between the range 1.7–4.9 % and 2.0–14.0 %, respectively. The LOD for diazinon, fenitrothion, and malathion was determined at 0.03 ng mL−1, with a satisfactory relative recovery range of 81.8–119.6 %. OPPs residues were detected in river water (0.27–0.39 ng mL−1) and wastewater (0.41–1.31 ng mL−1), indicating that the Fe3O4-cmCNF is a suitable composite for the determination of OPPs in real samples.

Ultrasound-enhanced air-assisted liquid-liquid microextraction for the UPLC determination of organophosphorus pesticides in river water

Organophosphorus pesticide (OPP) residues in environment are harmful to ecosystem and human health. In this study, an ultrasound-enhanced air-assisted liquid–liquid microextraction (UE-AA-LLME) method was developed for ultra-high performance liquid chromatography (UPLC) determination of OPPs in water samples. The UE-AA-LLME was performed in a 1.5-mL centrifuge tube under ultrasound condition by sucking in and pushing out the mixture of aqueous solution and extraction solvent using a 2-mL syringe. After centrifugation, the sediment layer was collected and analyzed by UPLC. The parameters affecting the extraction efficiency including the type and volume of extraction solvent, pH, and extraction cycles were optimized. Under the optimized conditions, the limit of detection (LOD) of target OPPs ranged from 0.04 to 0.15 μg/L, and good linearities were acquired with correlation coefficients higher than 0.9927. The recoveries of target OPPs were evaluated to be 75.4–112.6 %, with relative standard deviations (RSDs) lower than 14.9 %. The proposed UE-AA-LLME method was successfully employed for the UPLC determination of OPPs in an urban river of Hangzhou, China. The results revealed that six OPPs were detected in the river waters at the levels of 0.06–0.54 μg/L, and the levels of OPP residues in autumn were higher than those in winter. The risk assessment suggested that there was no human health risk of OPP residues in the river water for adult and child by ingestion pathway.

Miniaturized kapok fiber-supported liquid extraction for convenient extraction of pesticide residues in vegetable oils: Determination of organochlorine pesticides as a proof-of-concept study

In this paper, a miniaturized kapok fiber-supported liquid extraction (mini-KF-SLE) method was proposed for selective extraction of pesticide residues in vegetable oils. The natural kapok fiber was used as an inert oil support material based on its hydrophobic and lipophilic properties, and the extraction device was conveniently constructed by loading 15 mg of kapok fiber at the lower middle part of a 1-mL pipette tip. The vegetable oil sample (150 mg) without any pretreatment was directly loaded, followed by the addition of 150 μL of acetonitrile (ACN) as the extractant. After static extraction for 30 min, the extractant was pipetted out with a pipettor. As the proof of concept, it was applied for extracting eight organochlorine pesticides (OCPs) from vegetable oils and the eluate was analyzed by gas chromatography-electron capture detector (GC-ECD). Under optimized conditions, the extraction recoveries of OCPs were calculated to be in ranges of 35.8–79.5%. The satisfied quantitation ability was verified by the established method with coefficients of determination (R2) being greater than 0.99. The limits of detection (LODs) were in ranges of 2.0–50.0 ng/g. The relative recoveries were in ranges of 78.3–117.0% with the inter-/intra-day relative standard deviation (RSD) both being less than 13.3%. The potential of mini-KF-SLE to extract other kinds of pesticides was further verified by the successful extracting three triazole pesticides in vegetable oils with good extraction recoveries (>41.4%). The proposed mini-KF-SLE in combination with instrument detection techniques has the great potential in the low-cost and high-throughput determination of various pesticide residues in vegetable oils.

Polyamidoamine dendrimer-functionalized silica nanocomposite with polydopamine coating for dispersive micro solid-phase extraction of benzoylurea insecticides in water samples

近年来,由农药残留导致的环境污染问题已引起社会的广泛关注,开发便捷高效的分析方法对农药残留进行检测和监测十分必要。研究设计并成功制备了聚多巴胺涂敷的聚酰胺-胺树状分子功能化的二氧化硅复合材料(SiO2-PAMAM-PDA),并采用透射电镜对其进行表征。开发了以此复合材料为吸附剂的分散微固相萃取方法(D-μ-SPE),并结合高效液相色谱对水基质中的4种苯甲酰脲类杀虫剂(BUs)残留进行了富集检测。多巴胺结构中含有丰富的苯环、氨基及羟基,可与目标物形成氢键、π-π相互作用,从而增强了材料对苯甲酰脲的萃取能力。对吸附剂用量、萃取时间等可能影响萃取效率的条件进行了单因素优化。在最优条件下,该方法的线性范围在10~500 μg/L之间,根据3倍信噪比(S/N)计算所得的检出限(LOD)为1.1~2.1 μg/L,回收率为82.8%~94.1%,相对标准偏差(RSD)为2.1%~8.0%。将建立的方法与已报道的以苯甲酰脲作为目标物的方法进行了对比,发现方法样品用量及萃取剂用量均较少,且所需前处理时间较短,有机溶剂消耗也较少,为苯甲酰脲类农药的检测提供了更快速、绿色的选择。为评估所开发方法的实际样品适用性,将其应用于3种河水样品中4种苯甲酰脲类杀虫剂的分析检测,所得回收率及RSD分别为69.5%~99.4%和0.2%~9.5%,表明此方法在实际样品中同样具有较高的准确性和精密度。

Optimization of a Multi-Residue Analytical Method during Determination of Pesticides in Meat Products by GC-MS/MS.

In this study, a multi-residue analysis was developed for 32 compounds, including pesticides and metabolites, in five meat products using gas chromatography-tandem mass spectrometry (GC-MS/MS). The validation of the developed analytical method was also evaluated in accordance with Codex Alimentarius guidelines. Aminopropyl (NH2), C18, and florisil solid phase extraction (SPE) cartridges were used to evaluate and optimize the cleanup procedure of the tested samples prior to GC-MS/MS analysis. Based on the analytical performance, the C18 SPE cartridge was deemed to be the most suitable among the examined SPE cartridges. The optimized method demonstrated that 29 out of 32 tested compounds acquired good linearity (R2 ≥ 0.99), and 25 tested compounds displayed the method limit of quantification (MLOQ) ≤ 0.01 mg/kg. Out of the 32 tested compounds, only 21 compounds met the acceptable analytical criteria for the lard and tallow samples, compared to 27 compounds in the beef, pork, and chicken samples that falls within the acceptable standards for recovery (70–120%) and analytical precision (relative standard deviation RSD ≤ 20%). The average matrix effect was widely varied (20.1–64.8%) in the studied meat samples that were affected by either ion enhancement or suppression. In particular, in the lard sample, 13 compounds showed poor recovery and analytical precision due to ion suppression. Thus, the matrix effect (ME) was considered a critical factor during multi-residue pesticide analysis in different meat products. In conclusion, this developed analytical method can be used as a routine monitoring system for residual pesticide analysis in livestock products with acceptable analytical standards. Further meticulous analytical studies should be optimized and validated for multi-residue pesticide analysis in diversified meat products.

Application of the QuEChERS method for the determination of pesticides, PAHs and PCBs in fish in Senegal

Pollution of water by persistent organic pollutants is well described; however, little is known about the accumulation of these pollutants by aquatic organisms. For this reason, a method based on QuEChERS extraction and gas chromatography coupled to tandem mass spectrometry (GC-MS/MS) was developed for the determination of pesticides, polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in the muscles of five fish species from the bay of Soumbedioune (Dakar, Senegal). This method shows good recoveries of extraction (68.2-98.1% for pesticides, 83.87-98.10% for PAHs and 81.30-98.15% for PCBs), precision (% RSD ≤ 1%), sensitivity (LODs between 0.001 and 0.079 ng g−1), linearity (R2 ≥ 0.99) and repeatability and reproducibility, evaluated for three concentration levels (10 ng g−1, 200 ng g−1 and 500 ng g−1), ≤ 15% for the majority of pollutants under study except for alachlor, atrazine, acetochlor, dicofol, deltamethrin and dichlorvos where a RSD ≥ 20% was determined for the 10 ng g−1 concentration. Organic pollutants have been detected in fish from the Soumbedioune coast demonstrating the necessity of a regular survey of water and fish in order to protect the populations.

Optimization and Validation of a Method Using GC–MS and QuEChERS for Pesticide Determination in Banana Pulp

Optimization and Validation of a Method Using GC–MS and QuEChERS for Pesticide Determination in Banana Pulp

A ratiometric supramolecular fluorescent probe for on-site determination of cyfluthrin in real food samples

The massive use of cyfluthrin pesticide in agriculture has brought growing concerns on the food safety due to its chemical stability, easy-to-accumulation, and several harmful effects on human health. Design of a rapid, reliable and portable analytical method for on-site monitoring cyfluthrin is of great significance. Although reported assays showed high sensitivity and selectivity to cyfluthrin, these intensity-based outputs suffered from the interference from a variety of analyte-independent factors, i.e. the instrumental parameters, which often led to the poor accuracy and repeatability of detection results. In this work, we reported a novel host–guest supramolecular probe by using albumin as the host and solvatofluorochromic flavonoid as the guest, for the first time, successfully realizing ratiometric determination of cyfluthrin. This probe was capable of detecting cyfluthrin with the fast response (10 s), high sensitivity (LOD ∼70 ppb) and selectivity, good anti-interference performance, and remarkably distinct emission color change from orange to green. Moreover, the portable paper-based test strips could be facilely obtained and utilized for ratiometric determination cyfluthrin pesticide in food samples, such as apple, tomato, cucumber. The signal outputs could be captured and analyzed by using a smartphone, demonstrating the application potential of this probe in on-site food analysis. We expected this work may open up a novel avenue for on-site determination of pesticides with the simple testing apparatuses.

The RP-HPLC method development and validation for simultaneous determination of oryzalin and ethofumesate pesticides in soil and water

Abstract A sensitive and reliable method for simultaneous determination of oryzalin and ethofumesate residues in pantnagar soil and water was validated. The compounds were extracted by LLE with dichloromethane from water, and acetone:methanol mixture from soil followed by SPE cleanup. Detection and quantification was done by RP-HPLC using mobile phase methanol:water (70:30, v/v) at 280 nm. The developed method showed satisfactory validation results with linearity (0.99), relative standard deviations (1.55 and 1.73%), and limit of quantification (0.002 μg g−1 and 0.005 μg g−1) for ethofumesate and oryzalin, respectively. Recoveries ranged for oryzalin and ethofumesate from 79.80–90.52, 75.58–86.04% (soil) and 83.50–95.92, 82.28–94.60% (water), respectively. The method could be used for routine high-throughput detection and determination of these compounds.

Comparison of Polyacrylonitrile-and Polypyrrole-based Electrochemical Sensors for Detection of Propamocarb in Food Samples

Food safety is a crucial issue; all countries have struggled against pesticides for years. In this study, Polypyrrole (PPy)- and Polyacrylonitrile (PAN)-based non-enzymatic electrochemical sensors were investigated to detect the pesticide propamocarb (PM) in food samples. Under the experimental conditions, the proposed strategy exhibited a high selectivity of the disposable PPy-based and PAN-based sensors for the determination of propamocarb pesticide in the concentration of 1 μM with a rapid detection within 1 min at pH 7.4 and 25 °C. We demonstrated the detection of PM residues on cucumber and tomato samples with good electrochemical performances towards the real-time usability on real food samples. PAN-based non-enzymatic electrochemical sensor has good sensitivity, higher selectivity, and stability than PPy-based non-enzymatic electrochemical sensor. The prepared PAN-based non-enzymatic electrochemical sensor is a potential candidate to be used in devices which perform food safety in agricultural products.

H-beta zeolite-based dispersive solid-phase strategy for the multi-residue determination of pesticides

In this work, electrostatic interactions, hydrogen bonding and other interactions between a variety of pesticides and H-beta zeolite are discussed based on thermodynamics (Gibbs free energy, enthalpy, and entropy). Combined with the physical properties of the target compounds (octanol-water partition coefficient and molar volume), the characteristics of the physical adsorption on the synthetic zeolite were analyzed, the results of H-beta zeolite adsorption showed that the adsorption rate had a nonlinear relationship with the physical properties, and the adsorption reaction was dominated by the adsorption on the surface and in the pores of the H-beta zeolite. Based on the principle of zeolite adsorption, the parameters of absorbent amount, adsorption time, sample pH, ion strength, sample volume and desorption solvent were optimized, a vortex-assisted dispersive solid-phase extraction procedure coupled with liquid chromatography-tandem mass spectrometry was developed for the analysis of multiple pesticides in surface water. The sample was adjusted by phosphate buffer or hydrochloric acid to pH 4, then adsorbed by 50 mg of zeolite within 10 min, adding 2% (g/v) sodium chloride to the solution. The absorbent was eluted with a mixture of acetonitrile-methanol containing 0.5% formic acid after separation, then filtered prior to analysis. The optimized vortex-assisted dispersive solid-phase extraction method simultaneously achieved a low adsorbent dosage, a high enrichment factor of 25, rapid pre-concentration for 30 min, a low solvent usage of 2 mL and multi-target simultaneous analysis. Method performance in terms of accuracy, precision, limit of detection, and limit of quantitation was performed to validate the reliability of the procedure. The proposed protocol achieved acceptable accuracy (recoveries between 62% and 107%), and precision (relative standard deviation < 20%). The limit of detection of the method was below 0.1 μg/L, and the limit of quantitation was 0.08 μg/L or 0.2 μg/L. The results indicated that zeolite is a promising adsorbent with high adsorption capacity. It has the advantages of being a fast, simple, green and economical method for determining residual pesticides in water.

Nano eco-friendly voltammetric determination of pesticide, imidacloprid and its residues in thyme and guava leaves

Imidacloprid is a pesticide that belongs to neonicotinoids group that is commonly used in agriculture. Use of imidacloprid may lead to contamination of plants with its residues. In this work, a carbon paste electrode modified with synthesized chitosan nanoparticles and aluminum silicate was prepared as a new sensor for detection of imidacloprid residues in thyme and guava leaves. Upon modification of the carbon paste electrode, a linear response of imidacloprid was obtained and it was found to cover a wide range of 2 × 10−8 to 1 × 10−4 mol L−1 with good correlation coefficient (0.999). Limit of detection (LOD) was found to be 1.5 × 10−9 mol L−1 and limit of quantification (LOQ) was found to be 4.5 × 10−9 mol L−1. Modification of electrodes enhanced the method sensitivity, reproducibility, and increased linearity range of the method for determination of imidacloprid residues in thyme and guava leaves to monitor the suitable pre-harvest intervals.

Determination of multiple pesticides in Eucommia ulmoides followed by gas chromatography mass spectrometry based on a solid-phase extraction method.

Eucommia ulmoides, a precious Chinese herbal medicine, lack of studies on the detection of its pesticide residues. A simple sample preparation based on the solid-phase extraction (SPE) procedure was established for the analysis of 16 kinds of pesticides in Eucommia ulmoides by gas chromatography mass spectrometry (GC-MS) with selective ion monitoring mode. Here, the type and volume of extraction solvent and eluent, the kinds of sorbents in SPE Cleanert column, were optimized. Under the optimal conditions, a good linear relationship was obtained in the range of 0.005 to 5.0mg/L with correlation coefficient (r) higher than 0.9990, and the average recoveries (AR) of 16 pesticides ranged from 79.6 to 109.2% at the spiking levels of 0.01, 0.1, and 0.5mg/kg. The relative standard deviations (RSD) were 0.78 to 9.56% (n = 6). The results show that the established method can not only fully meet the analytical requirements of various pesticides in Eucommia ulmoides, but also have the potential to be applied in the detection of pesticide residues in others Chinese herbal medicine.

Quantitative screening of pesticides and their metabolites in human matrices: Are we ready to switch to high resolution mass spectrometry?

Despite increasing debates about their potential side effects on human health, data on the risks and impacts associated with pesticides is scarce and fragmented. There is a need for analytical tools for the measurement of most pesticides and/or their metabolites to which the population might be exposed. In this study, we present both untargeted and targeted Liquid Chromatography High Resolution Mass Spectrometry (LC-HRMS) screenings, suitable for the determination of pesticides in serum. We included 205 pesticides and metabolites of interest, comprising among others carbamates, dithiocarbamates, neonicotinoids, organochlorines, organophosphates and pyrethroids. A QuEChERS salt extraction was applied and chromatographic separation was performed in a biphenyl 2.7 μm (100 × 2.1 mm I.D.) column. For the HRMS acquisition, a Q-TOF (LCMS-9030®, Shimadzu) was used. Data was acquired either with an untargeted (Data independant acquisition, DIA), or targeted acquisition mode (HR-MS/MS). For each molecule, we determined the limit of detection (LOD) in a calibration range between 0.05 and 10 ng/mL. The procedure was applied to 62 patient serum samples. Results were then compared with those of a classical Multiple reaction Monitoring (MRM) LC-MS/MS screening method based on a low resolution acquisition (triple quadrupole; LCMS-8060®, Shimadzu). Six calibration curves (on 6 different days) revealed that about 99% of the compounds exhibited a LOD≤5 ng/mL for both targeted and untargeted screenings. For about 2 thirds of the molecules (66% and 68%, respectively), LOD was ≤0.5 ng/mL. For about one quarter of them (22% and 26%, respectively) LOD≤0.1 ng/mL. Out of the 62 serum samples, 79 compounds (22 different pesticides and metabolites) were detected by LC-HRMS. At very low LOD (<0.05 ng/mL), only 7 additional compounds could be detected using the low resolution approach. We developed highly sensitive LC-HRMS screening methods allowing the detection of a large panel of pesticides considered responsible for environmental and occupational exposure. Some compounds however remain inaccessible to LC and require GC analysis demonstrating the need to combine analytical techniques to gain a better understanding of population exposure to pesticides.

Ultrasound-assisted one-step reduction and self-assembly of carbon dots-reduced graphene oxide: Mechanism investigation and solid phase microextraction of ultra-trace organochlorine pesticides

In this work, carbon dots-reduction graphene oxide (CDs/RGO) composite was synthesized by a facile and green strategy with one-step reduction and self-assembly of GO and CDs under ultrasonic treatment. CDs was successfully applied to reduce GO to RGO, and anchored on the surface of RGO simultaneously under ultrasonic treatment within 20 min. The reduction mechanism was demonstrated by density functional theory calculations, which confirmed the electron transfer from CDs to GO and supplemented the reduction mechanism of GO by CDs. Characterizations results showed that the as-prepared CDs/RGO composite exhibited lamellar spacing and wrinkled structures, and abundant chemical groups in comparison to RGO reduced by sodium borohydride. In view of excellent morphology and chemical structures, the CDs/RGO composite was used for the first time in extraction and determination of ultra-trace organochlorine pesticides (OCPs) from water by means of solid phase microextraction (SPME) coupled with gas chromatography-mass spectrometry. The CDs/RGO coating presented superior extraction capacities for OCPs compared with commercial SPME coatings and sodium borohydride reduced RGO. The proposed analytical method exhibited high sensitivity with detection limit of 0.003–0.051 ng/L, excellent linearity in concentration range of 0.050–2500 ng/L, and satisfactory precision for seven OCPs. The excellent performances made the proposed method to be applied in determination of ultra-trace OCPs in real water successfully. This work proposed a green approach to synthesize CDs/RGO composite and a potential coating sorbent for SPME.

Novel colorimetric aptasensor based on MOF-derived materials and its applications for organophosphorus pesticides determination

For the visual detection of four organophosphorus pesticides (OPs), a colorimetric aptasensor was developed based on aptamer-mediated bimetallic metal-organic frameworks (MOFs) nano-polymers. Fe-Co magnetic nanoparticles (MNPs) and Fe-N-C nanozymes were prepared based on pyrolytic reaction, and were labeled with broad spectrum aptamers and complementary chains of organophosphorus pesticides respectively. The hybridization of aptamers and complementary chains led to the formation of nano-polymers. In the presence of target pesticides, they competed with complementary chains for aptamers on Fe-Co MNPs, resulting in a large number of Fe-N-C nanozymes signal labels being released into the supernatant. Fe-N-C nanozymes showed similar activity to peroxidase and catalyzed the 3,3′,5,5′-tetramethylbenzidine-hydrogen peroxide (TMB-H2O2) color system to turn the solution blue-green under mild conditions. The magnetic probes had good selectivity and sensitivity, and were easily separated by magnetic absorption. The sensor functioned well under optimal conditions, demonstrating good stability and specificity for four pesticides: phorate, profenofos, isocarbophos and omethoate, and the detection limits of four pesticides were as low as 0.16 ng/mL, 0.16 ng/mL, 0.03 ng/mL and 1.6 ng/mL respectively, and the recovery rate of OPs residue in vegetable samples was satisfactory. The work described here provided a simple, rapid and sensitive way to construct a biosensor.