Trace analysis of organophosphorus pesticide residues in fruit juices and vegetables by an electrochemically fabricated solid-phase microextraction fiber coated with a layer-by-layer graphenized graphite/graphene oxide/polyaniline nanocomposite.

Herein, a solid-phase microextraction pencil lead fiber coated with a layer-by-layer graphenized graphite/graphene oxide/polyaniline nanocomposite (GG/GO/PANI) was fabricated by an in situ electrochemical technique for the trace analysis of organophosphorus pesticide residues in packed grape and apple juice and also fresh tomato samples. The effects of various parameters, including the type of desorption solvent, adsorption time, desorption time, pH, salt addition, and stirring rate, on the extraction efficiency of the studied pesticides were investigated and accordingly, these parameters were optimized. The proposed fiber demonstrated desirable linear ranges (0.01-300 μg L-1) with good correlation coefficients (R2 ≥ 0.996) as well as low limits of detection (0.003-0.03 μg L-1) for the studied pesticides. The relative standard deviations (n = 5) for the extraction of 50 μg L-1 of each analyte were less than 7 and 11.5% for inter and intra-day precisions, respectively. This fast, facile, and repeatable electrochemical fabrication method produced a porous and homogeneous coating. The proposed fiber demonstrated good extraction efficiency, high stability, and long life-time despite being low cost. The successful application of the proposed fiber for the trace determination of pesticides in complex food matrices was proven by the satisfactory relative recoveries of 80.7-116.5%.