Magnetic graphene oxide-based solid-phase extraction combined with dispersive liquid-liquid microextraction for the simultaneous preconcentration of four typical pesticide residues in fruit juice and pulp

In the present work, magnetic graphene oxide-based solid-phase extraction combined with dispersive liquid-liquid microextraction has been developed for the extraction and preconcentration of some widely used pesticide residues in juice and pulp of fruits before their determination with gas chromatography-flame ionization detection. In this method, an appropriate weight of a synthetic magnetic graphene oxide is added into fruit pulp and homogenized for a specified time. Then, the magnetic graphene oxide containing the adsorbed pesticides is separated from pulp using a magnet and the pesticides are desorbed using an appropriate volume of a water-miscible organic solvent. In the following, the eluent is mixed with a low water-soluble extraction solvent (at a microliter level) and rapidly dispersed into the fruit juice. The optimum conditions were found to be 150 mg of magnetic graphene oxide, 4.0 min for extraction time, 1.0 mL of acetonitrile as the eluent, 4.0 min for adsorption time, and 105 mu L of chloroform as an extraction solvent. An excellent linearity was achieved in the range of 3.5-10,000 mu g kg(-1) (r(2) >= 0.997). The limits of detection and quantification ranged from 1.0-6.0 mu g kg(-1) and 3.5-20 mu g kg(-1), respectively. A good repeatability was obtained with the relative standard deviation <= 9%. Furthermore, extraction recoveries and enrichment factors were in the range of 69-81% and 340-399, respectively.