Matrix-matched monitoring ion selection strategy for improving the matrix effect and qualitative accuracy in pesticide detection based on UFLC-ESI-MS/MS: A case of Chrysanthemum

Simultaneous determination of sixteen phthalic acid esters (PAEs) in soil and evaluation of matrix effect using a QuEChERS/GC/MS-internal standard method

Phthalic acid esters (PAEs) are emerging pollutants that need to be analyzed precisely. Chromatography-based determination of PAE content in soils are frequently affected by matrix effect, which may limit the quantification of different kinds of PAEs from different types of soil. Here we optimized a QuEChERS protocol combined with gas chromatography-mass spectrometry (GC-MS) for simultaneous determination of 16 PAEs in different soils. PAEs in different type of soils (fluvo-aquic soil, red soil, and black soil) were extracted with acetonitrile followed by GC-MS detection based on quantitative ion internal standard method. All 16 PAEs showed excellent linear relationships with mass peak areas (R2 > 0.99). The limits of detection (LOD) and limits of quantitation (LOQ) of all the samples were in the range of 0.91-66.97 µg/kg and 2.7-200.9 µg/kg, respectively. The accurate test at 0.5, 0.1, and 1.0 mg/kg spiking level recorded recovery rate between 80.11% and 100.99% with relative standard deviations (RSDs) ranging from 0.37 to 8.50% in tested matrices. No significant matrix effect was observed for most tested PAEs. This is a simple method with high sensitivity and strong stability, which is suitable and reproducible for quantifying large number of PAEs in different types of soil.

Constructing graphene oxide/Au nanoparticle cellulose membranes for SERS detection of mixed pesticide residues in edible chrysanthemum

Edible chrysanthemum is widely cultivated and used as an important ingredient of medicine, tea and multifunctional food. During the planting of chrysanthemum, pesticides are extensively used for preventing plant diseases and insect pests. To ensure the food safety of edible chrysanthemum, rapid detection methods are urgently needed for on-site inspection. In this study, a graphene oxide/Au nanoparticle (GO/Au NP) cellulose substrate was prepared through layer-by-layer assembly of GO and Au NPs on a mixed cellulose ester membrane. Surface-enhanced Raman spectroscopy (SERS) detection of four types of organophosphorus and organosulfur pesticides was achieved by filtering the extracting solution through the substrate and analysing SERS spectra. Qualitative and semi-quantitative detection of fenthion, phoxim, isocarbophos and thiram was accomplished with the detection limits of 38.01, 8.13, 48.97 and 8.74 ng mL-1, respectively. A spiking experiment further demonstrated the feasibility of this method for rapid and on-site detection of mixed pesticides in chrysanthemum. This study provides a new approach for rapid detection of multiple hazardous substances in flowering and herbal plants.

Food Pesticide Residues Monitoring and Health Risk Assessment

This Special Issue presents a share of the work published in the journal Foods on pesticide residue monitoring and risk assessment in food [...].

Efficient removal of phytochrome using rice straw-derived biochar: Adsorption performance, mechanisms, and practical applications

Rice straw derived biochar was fabricated and applied as a purification agent. The adsorption kinetics, isotherms, and thermodynamics for adsorbates were determined using the biochar. Adsorption kinetics and isotherms were best fitted by the pseudo-second order and Langmuir models. Biochar could effectively remove chlorophyll in 9 different solutions. Biochar was employed as a clean-up reagent for 149 pesticides detection, which revealed that biochar had a higher phytochrome removal capacity than graphitized carbon black and 123 pesticides had satisfactory recovery values. The biochar was prepared into a sample pad by electrospinning and was then used for online sample clean-up in a test strip, and it showed high ability of removing phytochrome and improving detection sensitivity. Thus, biochar could be applied as a purification agent to remove pigmentation, making it a promising candidate not only for sample pretreatment but also in the fields of food, agriculture and environment.

Deep eutectic solvent-based dispersive liquid-liquid microextraction followed by smartphone digital image colorimetry for the determination of carbofuran in water samples

A detection method of carbofuran (CBF) in water samples was reported using deep eutectic solvent (DES)-based dispersive liquid-liquid microextraction (DLLME) combined with digital image colorimetry (DIC), which was environmentally friendly, solvent-saving, rapid, and convenient. Under alkaline conditions, the green and multifunctional extractant DESs dissociated into linalool and heptanoic acid, and CBF was hydrolyzed to 2,3-dihydro-2,2-dimethyl-7-benzofuranol and further coupled with fast blue BB salt to form an azo derivative. Heptanoic acid led to the dispersion of linalool to extract the orange-red azo derivative; DIC was used for quantitative analysis using a smartphone with its associated ease of data-acquisition. This experiment optimized the types, molar ratios, and volumes of DESs and the amounts of sodium carbonate and sodium chloride. Under optimal conditions, the limits of detection (LOD) and quantitation (LOQ) were 0.024-0.032 mg L^-1 and 0.081-0.108 mg L^-1, respectively. The extraction recoveries in real samples (tap, pond, and river water) were 92.4-101.0% with a relative standard deviation below 4.6%. This method has successfully analyzed CBF in different water samples and shows prospects for the monitoring and control of CBF residues in other environmental samples.

Validation of a Multi-Residue Analysis Method for 287 Pesticides in Citrus Fruits Mandarin Orange and Grapefruit Using Liquid Chromatography-Tandem Mass Spectrometry

Since the introduction of the positive list system (PLS) for agricultural products in the Republic of Korea, the demand for a quick, easy multi-residue analysis method increased continuously. Herein, the quick, easy, cheap, effective, rugged, and safe (QuEChERS) technique combined with liquid chromatography−tandem mass spectrometry was employed to optimize a method for the multi-residue analysis of 287 pesticide residues in mandarin orange and grapefruit. Method validation was conducted in terms of selectivity, limit of quantitation (LOQ), linearity, accuracy, precision, and matrix effect. All the compounds at low spiking levels (1, 2.5, 5, or 10 mg/kg) could be quantified at LOQs lower than 0.01 mg/kg (PLS level). The linearity of the matrix-matched calibration curve for each compound is in the range 0.5−50 μg/L, and its coefficient of determination (R2) is >0.990. Satisfactory recovery values of 70−120% with a relative standard deviation of ≤20% are obtained for all compounds in the mandarin orange and grapefruit samples. A negligible matrix effect (−20−20%) is observed for more than 94.8% and 85.4% of the pesticides in mandarin orange and grapefruit, respectively. Therefore, this analytical method can contribute to pesticide residue analyses of citrus fruits for routine laboratory testing.

Rapid screening of imidacloprid residue in grains and medicinal herbs: A newly designed hapten and monoclonal antibody

Three different imidacloprid hapten structures were designed to conjugate with proteins (bovine serum albumin, BSA; ovalbumin, OVA; keyhole limpet hemocyanin, KLH) for screening the optimal immunogen and coating antigen. Among these, an unreported antigen (hapten 6-KLH) was selected as the optimal immunogen and coating antigen. In addition, an imidacloprid-specific and high titer monoclonal antibody (IMIB7C3) was obtained by using the above-selected immunogen. A sensitive ic-ELISA (indirect competitive enzyme-linked immunosorbent assay) with a half-maximal inhibitory concentration (IC₅₀) of 1.3 ng mL^-1 was established by using the IMIB7C3 antibody (only 1.2 ng per well) to detect the residues of imidacloprid in grains (wheat and maize) and different herbs (Notoginseng radix et rhizoma, Dioscoreae rhizoma, Lonicerae japonicae flos, Astragali radix, Jujubae fructus). The detection results of real samples by the developed immunoassay were confirmed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), which proved the accuracy and reliability of the established ic-ELISA. These results indicate that the proposed ic-ELISA method is suitable for rapid and high-throughput detection of imidacloprid residues in agricultural products and medicinal herbs. Furthermore, a quantitative risk assessment was conducted for Lonicerae japonicae flos based on the detection results, which indicates an acceptable risk to human health after the intake of Lonicerae japonicae flos polluted by imidacloprid.

Luminescent determination of propineb fungicide by using a carbon quantum dots-europium ions system

We propose a modification of lanthanide-sensitized luminescence (LSL) to increase the selectivity and sensitivity of analytical methods based on this detection. LSL consists in the formation of complexes of lanthanide ions and organic compounds. Then, an intramolecular energy transfer occurs from the excited state of the ligand (organic analyte) to the emitting level of the lanthanide. The utilization of luminescent nanoparticles (carbon quantum dots, CQDs) in LSL systems can enhance their sensitivity and selectivity. CQDs can react with lanthanide ions through their carboxylic groups. These systems can thus be used as time-resolved luminescent probes. Propineb (PPN), a well-known dithiocarbamate fungicide, has been selected as the target analyte to show the advantages of using CQDs in LSL systems. The method proposed is based on the quenching produced by PPN in europium-CQDs luminescence, obtaining a detection limit of 0.03 μg mL^-1 PPN and a method detection limit of 3 mg kg^-1 in capers (bud and fruit), fulfilling the maximum residue limit in these samples (25 mg kg^-1). The results showed that the use of nanoparticles in LSL systems may provide novel and simple analytical methods for the screening of contaminants in the agri-food sector.