Abstract: A solid-phase extraction (SPE)-reversed-phase high performance liquid chromatographic (RP-HPLC) method for the determination of phoxim and diazinon in oranges has been developed. The analytical procedure involved in the ultrasonic extraction with methanol, the purification using a C18 SPE column, and the separation on a liquid chromatography column by the isocratic elution with acetonitrile-water (85∶15, v/v) at the flow rate of 0.7 mL/min and the ultraviolet wavelength of 254 nm. The results demonstrated that the linear ranges of phoxim and diazinon were 0.1-10.0 mg/L and 0.4-10.0 mg/L, and the detection limits of 4.1 and 6.7 μg/L, respectively. The average recoveries ranged from 87.3% to 102.7% with the relative standard deviations of 0.9%-4.9% at the spiking levels of 0.10 and 0.5 mg/kg in orange samples. The analytical results obtained by SPE were compared with those of the matrix solid-phase dispersion (MSPD) cleanup method. The recovery of diazinon using the SPE cleanup method was better, but the MSPD cleanup method was much suitable for phoxim. The lower background can be obtained via each cleanup method.

Key words: high performance liquid chromatography (HPLC), matrix solid-phase dispersion (MSPD), oranges , organophosphorous pesticides, solid-phase extraction (SPE)