Dissipation and residue determination of fluopyram and tebuconazole residues in watermelon and soil by GC-MS

A sensitive and selective method has been developed for the simultaneous determination of fluopyram and tebuconazole in watermelon and soil. The method involves an extraction procedure with acetonitrile using high-speed blender, a cleanup procedure by dispersive solid phase extraction (d-SPE) and determination using gas chromatography-mass spectrometry (GC-MS). The method has been validated for watermelon and soil samples spiked at 0.01, 0.1 and 0.5mg/kg. The average recoveries of fluopyram and tebuconazole were found in the range of 88.2-106% with relative standard deviations (RSDs) of 1.52-7.65%. A limit of quantification (LOQ) of 0.01mg/kg was obtained for both compounds. The residual levels and dissipation rates of fluopyram and tebuconazole in real watermelon and soil were determined. The half-lives of fluopyram were 6.48-6.60 days in watermelon and 15.8-24.8 days in soil. The half-lives of tebuconazole were 5.87-6.93 days in watermelon and 11.2-14.4 days in soil. The terminal residues of fluopyram and tebuconazole were all below the maximum residue limits (MRLs) value set by USA (fluopyram, 1mg/kg; tebuconazole, 0.09mg/kg). Hence it was safe for the use of the two pesticides and the results also could give a reference for MRLs setting of fluopyram and tebuconazole in watermelon in China.