Simultaneous determination of insecticide fipronil and its metabolites in maize and soil by gas chromatography with electron capture detection.

An integrated method for the simultaneous determination of insecticide fipronil and its three metabolites, desulfinyl, sulfide, and sulfone, in maize grain, maize stem, and soil was developed. This three-step method uses liquid-solid extraction with ultrasound or mechanical grinding, followed by liquid-liquid partitioning and florisil solid-phase extraction (SPE) for cleanup. The quantification was conducted by gas chromatography-electron capture detection in triplicate for each sample. The method was validated with five replicates at three fortification concentrations, 0.002, 0.01, and 0.1 mg kg(-1), in each matrix and gave mean recoveries from 83 to 106 % with relative standard deviation ≤ 8.9 %. The limits of quantification (LOQ) were 0.002 mg kg(-1) for the compounds in all matrixes. In the field study in Beijing and Shandong 2012, fipronil-coated maize seeds were planted and the proposed method was applied for checking the possible existence of four compounds in maize and soil samples, but none of them contained residues higher than the LOQs in both application rates. Moreover, the dissipation of fipronil in soil fits first-order kinetics with half-lives 9.90 and 10.34 days in Beijing and Shandong, respectively. Combined with an adequate sample treatment, this technique offers good sensitivity and selectivity in the three complex matrixes. The results could provide guidance for the further research on pesticide distribution and safe use of fipronil as seed coat in cereals.