Superparamagnetic core-shells anchored onto graphene oxide grafted with phenylethyl amine as a nano-adsorbent for extraction and enrichment of organophosphorus pesticides from fruit, vegetable and water samples

A novel adsorbent composed of silica coated magnetic microparticles (Fe3O4@SiO2) and graphene oxide (GO) functionalized with phenylethyl amine (PEA) was synthesized and characterized using Fourier transform-infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), and CHN elemental analysis techniques. The adsorbent (Fe3O4SiO2@GO-PEA) was then used in a magnetic solid phase extraction (MSPE) of six organophosphorous pesticides (OPPs) including methyl parathion, fenitrothion, methidathion, ethion, methyl azinphos and coumaphos prior to gas chromatography-nitrogen phosphorus detection (GC-NPD). The fabricated adsorbent combines the advantages of superior adsorption capability of modified GO and magnetic separability of magnetite microparticles to provide high adsorption capacity, and easy isolation from sample solutions. The main experimental parameters affecting the extraction recovery of OPPs including extraction time, pH, adsorbent dosage, salt concentration, and desorption conditions were investigated and optimized. Under the optimal conditions, linear responses were obtained in the concentration range of 0.06-200 mu g L-1 with the determination coefficients (R-2) between 0.9945 and 0.9996. The limits of detection were from 0.02 to 0.1 mu g L-1 and the intraday and inter-day relative standard deviations (RSDs) were less than 4.8 and 6.4%, respectively. The method was successfully applied for determination of the OPPs in apple, grape, pear, bell pepper, celery and water samples. The obtained recoveries were in the range of 90.4-108.0% (RSDs = 1.9-6.6%, n = 3) for fruits and vegetables, and 94.6-104.2% (RSDs = 2.0-4.8%, n = 3) for water samples. The excellent extraction performance of the adsorbent can be attributed to its structure characteristics where the phenyl rings of PEA grafted on the GO nanosheets are accessible to interact effectively with OPPs via delocalized pi-electron system. (C) 2015 Elsevier B.V. All rights reserved.