In this study, a method for extraction and preconcentration trace amounts of two organophosphorus pesticides (oxadiazon and profenofos) in environmental water was developed by using magnetic solid phase extraction followed by high performance liquid chromatography-ultraviolet detection. The Fe3O4@SiO2–C18 nanoparticles were synthesized by the chemical coprecipitation method and characterized by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, and vibrating sample magnetometer. The Fe3O4@SiO2–C18 nanoparticles were also easily separated via an external magnetic field during extraction process of oxadiazon and profenofos from environmental water. The influence of several variables including the pH of sample, sorption time, sorbent amount, eluent solvent and its volume and salt concentration in the extraction process was investigated. For this purpose, a multivariate strategy based on central composite design and desirability function was applied in order to optimize the significant variables. Under the optimum conditions, detection limits were 0.05 and 0.07 ng mL−1 for profenofos and oxadiazon, respectively. Linear dynamic ranges were achieved in the range of 0.5–10 ng mL−1 for two analytes. The relative recoveries (RR%) along with relative standard deviation (RSD%) (n = 5) were obtained to be 90 % (RSD = 9.2 %) and 86 % (RSD = 9.8 %) for oxadiazon and profenofos, respectively.
