The authors describe a method for the extraction of organophosphorus pesticides (OPPs) by using a magnetically separable sorbent consisting of a polyoxometalate of type BeW12O40 supported on imidazole functionalized silica-coated cobalt ferrite. The sorbent was characterized by X-ray powder diffraction, field-emission scanning electron micrographs, vibrating sample magnetometry and FT-IR. The effects of the amount of adsorbent, pH value, salt concentration, extraction time, desorption solvent nature and volume and desorption time were investigated. Under optimal conditions, the method resulted in the following figures of merit: (a) the linear parts of the calibration plots typically extend from 0.08 to 300 μg mL−1 of OPPs; (b) detection limits are between 0.02 to 0.06 ng mL−1; and (c), extraction recoveries from spiked samples vary from 70.0 to 89.2%, with relative standard deviations between 5.4 and 7.6%. The nanocomposites can be reused up to 10 times. Compared to other methods for pretreatment and preconcentration of OPPs, the new method is more rapid, sensitive, accurate and eco-friendly. The method was successfully applied to the determination of the OPP residues in water samples and fruit juices.

Keywords