REVERSED-PHASE UPLC METHOD FOR THE DETERMINATION OF MONOCROTOPHOS, THIRAM, CARBENDAZIM, CARBARYL, AND IMIDACLOPRID PESTICIDES IN MANGO AND POMEGRANATE BY QuEChERS METHOD

[Determination of thiram in wheat flour and flour improvers by high performance liquid chromatography-diode array detection]

福美双是重要的二硫代氨基甲酸酯(DTC)杀菌剂,在小麦中使用限量以1 mg/kg二硫化碳(CS₂)计。目前我国相关检测方法是针对二硫代氨基甲酸酯一类的化合物,二硫代氨基甲酸酯通过与酸反应生成CS₂,采用光谱法或色谱法测定CS₂,间接实现二硫代氨基甲酸酯测定。该方法无法特异性实现对福美双的检测,因此开展小麦粉中福美双检测方法的研究具有重要意义。研究建立了高效液相色谱-二极管阵列检测(HPLC-DAD)测定小麦粉及面粉改良剂中福美双的分析方法。小麦粉及面粉改良剂样品用乙腈溶剂提取后,经涡旋、振荡、冰水浴超声和静置后取上清液过滤,供高效液相色谱测定。采用ZORBAX plus-C18色谱柱(150 mm×4.6 mm, 5 μm)分离,以水-乙腈为流动相洗脱分析,在波长280 nm下检测。实验优化了提取溶剂及其体积、振荡超声条件、色谱柱、检测波长、流动相等条件。该方法采用保留时间和紫外光谱图定性,外标法定量。该方法在线性范围内(0.30~30.0 μg/mL)线性关系良好,相关系数(r²)为0.99999。对小麦粉及面粉改良剂进行1.5、3.0、15 mg/kg 3个水平的加标回收试验,福美双的回收率为89.6%~98.3%,相对标准偏差为1.6%~3.9%(n=6)。方法的检出限和定量限分别为0.5 mg/kg和1.5 mg/kg。该方法采用溶剂提取,操作简单,分析时间短,特异性好,具有精密度高、重复性好、检出限低等特点,适用于小麦粉及面粉改良剂中福美双快速、准确的定量检测。

Quantification of fosetyl-aluminium/phosphonic acid and other highly polar residues in pomegranates using Quick Polar Pesticides method involving liquid chromatography-tandem mass spectrometry measurement

Interest in the quantification of highly polar substances in crops has noticeably increased in the last five years. This study was designed to assess quantification of six polar residues, chlorate, ethephon, fosetly-aluminium (fosetyl-Al), glyphosate, phosphonic acid and perchlorate. A total of 2513 pomegranate samples intended for export from Turkey were analysed using the Quick Polar Pesticides (QuPPe) method. The method was in-house validated with very good performance results. The limits of quantification (LOQs) for residues were much lower than the respective EU Maximum Residue Levels (MRLs). Phosphonic acid was detected in 38.5% of pomegranate samples at quantifiable concentrations, calculated as fosetyl-Al. The concentrations ranged between 0.005 and 12.9 mg kg^-1. The 20% of pomegranate samples showed fosetyl-Al levels above the EU MRL of 2 mg kg^-1. Other polar residues were not detected in any pomegranate samples. This is the first report about highly polar pesticides in pomegranates cultivated in Turkey.

Colorimetric determination of carbendazim based on the specific recognition of aptamer and the poly-diallyldimethylammonium chloride aggregation of gold nanoparticles

This paper proposes the idea of establishing carbendazim (CBZ) colorimetric determination in spiked water samples by specific aptamers of unlabeled carbendazim (CBZ), gold nanoparticles (AuNPs) and cationic polymer poly-diallyldimethylammonium chloride (PDDA). In the absence of CBZ, the CBZ aptamer will react with the cationic polymer PDDA by electrostatic interaction to form a complex structure. Therefore, the gold nanoparticles will remain dispersed due to the lack of PDDA. However, when CBZ is added into the sensory system, the CBZ-specific aptamer can selectively capture CBZ to form a stable complex structure. Due to the consumption of the aptamer, PDDA is unable to interact with the aptamer and begins to induce aggregation of AuNPs, thereby causing the color of the solution to change from red to blue. Colorimetric determination of CBZ based on the specific recognition of aptamer and the PDDA-induced aggregation of AuNPs has a detection limit of 2.2 nM, a linear range (R = 0.9960) from 2.2 to 500 nM. The method has good sensitivity and specificity, and the average recovery of CBZ is 94.9-104.8% in the application of actual water samples. This colorimetric method is simple, time-saving and low requirements for equipment, therefore, it holds great potential for CBZ detection in the environmental water samples.

Fluorescent aptasensor for carbendazim detection in aqueous samples based on gold nanoparticles quenching Rhodamine B

This paper proposes a fluorescent aptasensor for the detection of carbendazim (CBZ) in aqueous solution using CBZ-specific aptamer as sensing probe, gold nanoparticles (AuNPs) and Rhodamine B (RhoB) as indicator, respectively. In the absence of CBZ, CBZ aptamer could wrap AuNPs and maintained it dispersed in NaCl solution basically. Contrarily, the aptamer could specifically combine with CBZ and form a stable aptamer-CBZ complex, leaving AuNPs exposed to be aggregated by NaCl solution. The dispersed AuNPs could efficiently quench the fluorescence of RhoB, but those aggregated AuNPs have poor capability to impair the fluorescent indicator. Thus, the concentration of CBZ could be detected quantitatively through the distinction of the fluorescence intensity. This convenient fluorescent assay for CBZ had a wide linear range from 2.33 to 800 nM and a 2.33 nM limit of detection (LOD). Furthermore, it had high selectivity over pesticides, antibiotics, metal ions and other disrupting chemicals. As for application, the method could determine CBZ in water samples with recoveries in the range of 96.3-111.2%. This fluorescent aptasensor possessed great potential application for CBZ detection in actual aquatic environment.

Recent Modifications and Validation of QuEChERS-dSPE Coupled to LC-MS and GC-MS Instruments for Determination of Pesticide/Agrochemical Residues in Fruits and Vegetables: Review

Fruits and vegetables constitute a major type of food consumed daily apart from whole grains. Unfortunately, the residual deposits of pesticides in these products are becoming a major health concern for human consumption. Consequently, the outcome of the long-term accumulation of pesticide residues has posed many health issues to both humans and animals in the environment. However, the residues have previously been determined using conventionally known techniques, which include liquid-liquid extraction, solid-phase extraction (SPE) and the recently used liquid-phase microextraction techniques. Despite the positive technological effects of these methods, their limitations include; time-consuming, operational difficulty, use of toxic organic solvents, low selective property and expensive extraction setups, with shorter lifespan of instrumental performances. Thus, the potential and maximum use of these methods for pesticides residue determination has resulted in the urgent need for better techniques that will overcome the highlighted drawbacks. Alternatively, attention has been drawn recently towards the use of quick, easy, cheap, effective, rugged and safe technique (QuEChERS) coupled with dispersive solid-phase extraction (dSPE) to overcome the setback challenges experienced by the previous technologies. Conclusively, the reviewed QuEChERS-dSPE techniques and the recent cleanup modifications justifiably prove to be reliable for routine determination and monitoring the concentration levels of pesticide residues using advanced instruments such as high-performance liquid chromatography, liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry.

Selection and Characterization of DNA Aptamers for Electrochemical Biosensing of Carbendazim

This article reports a novel aptamer-based impedimetric detection of carbendazim, a commonly used benzimidazole fungicide in agriculture. High affinity and specificity DNA aptamers against carbendazim were successfully selected using systematic evolution of ligand by exponential enrichment (SELEX). The dissociation constants (K_ds) of the selected DNA aptamers after 10 in vitro selection cycles were characterized using fluorescence-based assays showing values in the nanomolar range. The aptamer which showed the highest degree of affinity and conformation change was used to fabricate an electrochemical aptasensor via self-assembly of thiol-modified aptamer on gold electrodes. The aptasensor exploits the specific recognition of carbendazim by the aptamer immobilized on the gold surface which leads to conformational changes in the aptamer structure. This conformational change alters the access of a ferrocyanide/ferricyanide redox couple to the aptasensor surface. The aptasensor response is thus measured by following the increase in the electron transfer resistance of the redox couple using Faradaic electrochemical impedance spectroscopy. This method allowed a selective and sensitive label-free detection of carbendazim within a range of 10 pg/mL-10 ng/mL with a limit of detection of 8.2 pg/mL. The aptasensor did not show cross reactivity with other commonly used pesticides such as fenamiphos, isoproturon, atrazine, linuron, thiamethoxam, trifluralin, carbaryl, and methyl parathion. Moreover, the aptasensor has been applied in different spiked food matrixes showing high recovery percentages. We believe that the proposed aptasensor is a promising alternative to the currently used methods for carbendazim monitoring.