Synthesis and surface engineering of magnetic nanoparticles for environmental cleanup and pesticide residue analysis: A review

In recent years, water pollution and pesticide accumulation in the food chain have become a serious environmental and health hazard problem. Direct determination of these contaminants is a difficult task due to their low concentration level and the matrix interferences. Therefore, an efficient separation and preconcentration procedure is often required prior to the analysis. With the advancement in nanotechnology, various types of magnetic core–shell nanoparticles have successfully been synthesized and received considerable attention as sorbents for decontamination of diverse matrices. Magnetic core–shell nanoparticles with surface modifications have the advantages of large surface‐area‐to‐volume ratio, high number of surface active sites, no secondary pollutant, and high magnetic properties. Due to their physicochemical properties, surface‐modified magnetic core–shell nanoparticles exhibit high adsorption efficiency, high rate of removal of contaminants, and easy as well as rapid separation of adsorbent from solution via external magnetic field. Such facile separation is essential to improve the operation efficiency. In addition, reuse of nanoparticles would substantially reduce the treatment cost. In this review article, we have attempted to summarize recent studies that address the preconcentration methods of pesticide residue analysis and removal of toxic contaminants from aquatic systems using magnetic core–shell nanoparticles as adsorbents.     

Assessment of uncertainty in pesticide multiresidue analytical methods: main sources and estimation

The estimation of the uncertainty associated to analytical methods is necessary in order to establish the comparability of results. Multiresidue analytical methods lack very often of information about uncertainty of results with likely implications when results are compared with maximum residue levels (MRL) established by regulations. An adequate identification and estimation of each uncertainty source allows to laboratories to establish the accuracy of results and to balance with time-consuming and costs.     

Development of a portable biosensor for screening neurotoxic agents in water samples

A high sensitive portable biosensor system capable of determining the presence of neurotoxic agents in water has been developed. The system consists of (i) a screen-printed electrode with acetylcholinesterase (AChE) immobilized on it, (ii) a self-developed portable potentiostat with an analog to digital (A/D) converter and a serial interface for transferring data to a portable PC and (iii) an own designed software, developed with Lab-Windows CVI, used to record and process the measurements. The system has been developed to perform high precision amperometrical measurements with low drifts, low noise and a good reproducibility. In the configuration depicted, the percentage of AChE inhibition is proportional to the content of neurotoxic agents in a sample. This type of measurement is performed by the steady-state method from the first steady current (by a phosphate buffer solution) and the second steady current (by an enzymatic reaction produced by the addition of acetylthiocholine chloride to the solution). Validation was performed by analyzing spiked water samples containing pesticides. The design is specially suited for screening purposes, does not need sample preconcentration, is totally autonomous and suitable for the field detection of neurotoxic agents in water.     

Multifunctional sorbents for the extraction of pesticide multiresidues from natural waters

In this work multifunctional sorbents, based on surfactant-coated mineral oxides, are assessed for the simultaneous extraction/preconcentration of pesticide multiresidues from aqueous environmental samples. Seventeen pesticides, representative of all the common groups (triazines, phenylureas, carbamates, azols, anilides, chloroacetanilides, organophosphorous, phenoxyacids, aryloxy acids and phenols), are selected for this study. The sorbents assessed are pure sodium dodecyl sulphate (SDS) and mixed tetrabutylammonium (TBA)-SDS hemimicelles and/or admicelles adsorbed onto alumina. Because of their multifunctional character, these sorbents provide different retention mechanisms (i.e. hydrophobic, ionic and/or π-cation interactions), which highly contribute to the efficient retention of pesticides with different polarities and acidities (bases, neutrals and acids). In addition, the low volume of eluent required for complete elution of analytes (typically 1-2 mL) avoided the need of using time-consuming and tedious evaporation steps that generally are needed when cross-linked polymeric resins or carbon materials are used as sorbents. The performance of two sorbents, i.e. SDS and TBA-SDS mixed hemimicelles/admicelles, for the admicellar solid-phase extraction (ASPE) of pesticide multiresidue was comparatively investigated. The latter was selected on the basis of the higher breakthrough volumes permitted, the lower volume of eluent required and the higher sample and eluent flow rates allowed. The proposed ASPE/LC/UV approach provided detection limits lower than 100 ng L⁻¹ for the determination of the 17 pesticides tested. Recoveries from spiked (at the ng L⁻¹ level) river and underground water samples was quantitative for most of the pesticides tested.     

顺应时代发展,创新农药化学课程教学

顺应时代发展对农药化学教学的要求,依据现代教学论的基本原则,对农药化学课程教学进行了课堂教学-学生实验-生产实践"三位一体"的改革与实践,形成了理论学习-实验-理论学习-实践-理论学习的良性教学模式。实践表明,该模式能全面有效地提高学生创新能力和综合素质。     

Sensitive Electrochemical Determination of Trifluralin at a Disposable Pencil Graphite Electrode

A sensitive differential pulse (DP) voltammetric method has been proposed for the determination of trifluralin (TFA) based on both its reduction and oxidation at a disposable pencil graphite electrode (PGE). DP voltammograms recorded under optimized conditions show that oxidation and reduction peak currents increased linearly in the range from 1.0 to 75.0 μM and from 0.50 to 100.0 μM TFA, respectively. LOD and sensitivity values have been determined as 0.39 μM and 11170 μA mM⁻¹ cm⁻² for oxidation and as 0.20 μM and 22167 μA mM⁻¹ cm⁻² for reduction. The acceptable recovery values (95.2–104.8 %) were obtained from real water samples.     

纳米银修饰的超疏水界面用于农药的超灵敏检测

采用化学还原法,在具有不同微观结构的规整的不锈钢网和聚纤维素酯薄膜表面合成了银纳米颗粒.利用氟化试剂对复合界面进行处理,形成超疏水性能的界面,能有效地浓缩目标分子.以罗丹明6G(R 6G)为分析物,纳米银修饰聚纤维素酯薄膜为基底,采用表面增强拉曼散射(SERS)分析了氟化处理前后基底对目标分子的检测能力.实验结果表明,具有超疏水性能的复合基底对R 6G分子的检出限为1 ×10-16 mol/L.以纳米银修饰的不锈钢网和聚纤维素酯两种复合材料为基底,对常用杀虫剂敌百虫的检出限分别为1×10-15 mol/L和1×10-16 mol/L.     

Development and validation of a multiresidue method for the determination of 323 pesticide residues in dry herbs using QuEChERS method and LC-ESI-MS/MS

A multiresidue method was studied for determination of 323 pesticides representing a wide range of physicochemical properties in dry herbs (chamomile and parsley) based on QuEChERS method and LC-ESI-MS/MS analysis. In the current study, three different parameters were optimised for a higher accuracy and a lower matrix effects: extraction procedures, cleanup and matrix effect. Optimum extraction efficiency was obtained at sample hydration of 10 mL water on 2 g dry herbs and soaking time for 10 min. Use of different extraction techniques supported the use of mechanical shaker in comparison with ultrasound and handed shaking. As a way to remove interfering components from final extract, different cleanup techniques were studied: three dispersive solid phase extraction (D-SPE) (C₁₈, primary secondary amine and graphitised carbon black) have been investigated; matrix effect was reduced, but several pesticides were lost during the cleanup process. Unlike the SPE (hydrophilic lipophilic balanced polymer) produced a good recovery with all substances without expected reduction in matrix effect. Moreover, sample dilution and LC-MS/MS injection volume were studied, 3 µL injection volume was found to be the best sensitive condition without sample dilution. The developed method was validated by performing recovery tests at 0.01, 0.05 and 0.1 mg/kg, the average recoveries ranged from 70% to 120%. The reproducibility expressed as relative standard deviation (RSD %) was ≤ 20%.     

固相萃取-气相色谱-质谱法测定果蔬中36种农药残留

采用气相色谱-质谱法测定果蔬中36种农药残留。果蔬试样经丙酮-水匀质,二氯甲烷液-液萃取,然后过石墨化炭黑固相萃取柱净化,浓缩定容后在DB-5毛细管色谱柱(30 m×0.25 mm,0.25μm)分离,质谱中选择电喷雾离子源-选择离子监测模式。36种农药残留的质量浓度在一定范围内与其峰面积呈线性关系,检出限(3S/N)均不高于15μg·kg-1。加标回收率在75.3%~115%之间,测定值的相对标准偏差(n=6)在0.6%~7.8%之间。