Graphene oxide dispersed with ferrite nano-particles as magnetic solid phase extraction adsorbent for chlorpyrifos and diazinon

Abstract

Magnetic graphene oxide, Fe₃O_4-GO has been synthesized through oxidation of graphite via modified Hummer’s method followed by a one step co-precipitation method. Fe₃O₄-GO was used in the extraction of two organophosphorus pesticides (OPPs), namely chlorpyrifos and diazinon using magnetic solid phase extraction (MSPE) technique. The GO and Fe₃O₄-GO synthesised was characterized using Fourier transform infrared spectroscopy (FT-IR), and field emission scanning electron microscopy (FESEM). Optimum conditions obtained from the optimization process were as follows: 80 mL sample volume, 50 mg of adsorbent, 10 min extraction time followed by desorption process using 500 μL of acetonitrile. Under the optimum conditions, Fe₃O₄-GO MSPE method showed excellent linearity in the range of 0.1-10 μg L^-1 with coefficient of determination (R²) of 0.9997 for both OPPs. Precision studies found that the repeatability of this Fe₃O₄-GO MSPE method (RSD, n = 3) were 9.95% and 9.05% for chlorpyrifos and diazinon respectively. Meanwhile the reproducibility (RSD, n = 9) observed was 11.45% for chlorpyrifos and 13.35% for diazinon. The limit of detection (LOD = 3 S/N) for chlorpyrifos was 0.034 μg L^-1 and 0.40 μg L^-1 for diazinon. Lake water sample was spiked with 0.5 μg L^-1 of each of the OPPs after confirming the non-detection in the sample using gas chromatography-electron capture detector (GC-ECD). Percentage recoveries of the two OPPs from lake water samples were found to be 57.71% for chlorpyrifos and 73.86% for diazinon. The Fe₃O₄-GO MSPE method was found to be susceptible to matrix effect from the lake water sample analysed.  The Fe₃O_4-GO MSPE method was also applied to the determination of the two OPPs from tomato sample using matrix-matched calibration curve in the range of 1-50 μg L^-1.  Good coefficient of determination (R²) value of 0.9963 and 0.9897 for chlorpyrifos and diazinon respectively was observed. Both OPPs were found to be present in the tomato sample analysed (0.19 μg L^-1 of chlorpyrifos and 7.88 μg L^-1 of diazinon).