Facile synthesis of a core-shell structured magnetic covalent organic framework for enrichment of organophosphorus pesticides in fruits.

A facile strategy was developed for the fabrication of a magnetic covalent organic framework (COF) via grafting of the monomers, 2,5-dihydroxyterephthalaldehyde (Dt) and 1,3,5-tris(4-aminophenyl) benzene (Tb) onto surface-modified Fe3O4 nanoparticles. The magnetic COF, named as magnetic COF-DtTb, was readily fabricated without high temperature or harsh reaction conditions. The synthesized magnetic COF-DtTb nanoparticles were fully characterized, presenting a regular core-shell spherical structure, large specific surface area, superparamagnetism, and good thermal stability. Their potential as an enrichment adsorbent was investigated to establish an efficient magnetic solid-phase extraction method for the determination of organophosphorus pesticide residues in fruits. Systematic method validation revealed good linearity in the concentration range of 1-200 µg L-1 (correlation coefficient >0.9957). The method limits of detection were in the range of 0.002-0.063 µg kg-1, the method limit of quantification was 1.00 µg kg-1 and recoveries ranged from 72.8% to 111% with RSDs lower than 12.3%. The results indicated that magnetic COF-DtTb possesses superior trace enrichment properties for organophosphorus pesticides in fruits.

Determination of coumaphos, chlorpyrifos and ethion residues in propolis tinctures by matrix solid-phase dispersion and gas chromatography coupled to flame photometric and mass spectrometric detection.

A new analytical method has been developed and successfully evaluated in routine application for the quantitative analysis of a selected group of organophosphate pesticides (coumaphos, chlorpyrifos and ethion) which can be found at trace levels in propolis tinctures (ethanolic propolis extracts); a valuable commodity used as raw material in the food and pharmaceutical industries for which there have been few attempts for pesticide residue analysis reported in the literature. The proposed methodology is based on matrix solid phase dispersion (MSPD) using aluminum sulfate anh. a novel dispersant material and subsequent column chromatography clean-up in silica gel prior to gas chromatography (GC) with both flame photometric detector (FPD) and mass spectrometry (MS) detection used for the routine quantification and identification of the residues, respectively. The limits of detection, for coumaphos, chlorpyrifos and ethion were below 26.0 µg/kg in FPD and 1.43 µg/kg for MS detection. Mean recoveries were in the range of 85-123% with RSD values below 13%, which suggests that the proposed method is fit for the purpose of analyzing pesticides in propolis tinctures containing high concentration of polyphenolics. The method has been successfully applied in our laboratory for the last 2 year in the analysis of real propolis tinctures samples.

Detection of coumaphos in honey using a screening method based on an electrochemical acetylcholinesterase bioassay.

An analytical protocol based on an electrochemical assay for the detection of acetylcholinesterase (AChE) inhibitors has been optimised for the detection of coumaphos in honey. Coumaphos is a phosphotionate insecticide requiring transformation in the corresponding oxo-form to act as an effective AChE inhibitor. The inhibition assay was based on the electrochemical detection of the product of AChE, choline, via a choline oxidase biosensors obtained using prussian-blue modified screen printed electrodes. A simple procedure for the oxidation of coumaphos via N-bromosuccinimide (NBS) and AChE inhibition was optimised. A calibration curve for coumaphos (8-1000 ng/ml) was obtained in buffer; the intra electrode CV ranged between 8 and 12% whereas the inter electrode CV was comprised between 12 and 14%. A detection limit (LOD) of 8 ng/ml was achieved, with an I(50%) of 105 ng/ml. The assay was then applied to detect coumaphos in honey samples. Despite the solubility of the samples in buffer, the assay was affected by many electrochemical interferences present in this sample matrix A simple C18 based solid phase extraction procedure has been then optimised and used for the assay. This allowed to eliminate all the electrochemical interferences with a satisfactory coumaphos recovery (around 86%) for a final LOD of 33 ng/g. The developed assay applied to detect coumaphos in different honey samples gave data well correlated with LC-MS detection.

Biodegradation of coumaphos, chlorferon, and diethylthiophosphate using bacteria immobilized in Ca-alginate gel beads.

Calcium-alginate immobilized cell systems were developed for the detoxification and biodegradation of coumaphos, an organophosphate insecticide, and its hydrolysis products, chlorferon and diethlythiophosphate (DETP). Optimum bead loadings for bioreactor operation were found to be 200 g-beads/L for chlorferon degradation and 300 g-beads/L for DETP degradation. Using waste cattle dip (UCD) solution as substrate, the degradation rate for an immobilized consortium of chlorferon-degrading bacteria was five times greater than that for freely suspended cells, and hydrolysis of coumaphos by immobilized OPH(+)Escherichia coli was 2.5 times greater. The enhanced degradation of immobilized cells was due primarily to protection of the cells from inhibitory substances present in the UCD solution. In addition, physiological changes of the cells caused by Ca-alginate immobilization may have contributed to increased reaction rates. Degradation rates for repeated operations increased for successive batches indicating that cells became better adapted to the reaction conditions over time.