Residue of spirotetramat, diafenthiuron and their metabolites in fruits and vegetables by QuEChERS-ultra performance liquid chromatography-tandem mass spectrometry

A method was developed for the quantitative determination of spirotetramat, diafenthiuron and their metabolite residues (spirotetramat-enol, spirotetramat-enol-glucoside, spirotetramat-mono-hydroxy, spriotetramat-keto-hydroxy, diafenthiuron-urea, diafenthiuron-amide) by QuEChERS-ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The samples were homogenized, extracted with V (acetonitrile) : V(formic acid)=10 : 1, and cleaned-up by custom QuEChERS tubes. The separation was performed on a Shimadu Shim-pack XR-ODS column(75 mm × 2.0 mm, 1.6 μm). The compounds were identified by MS/MS in positive electrospray ionization (ESI⁺) and multiple reaction monitoring (MRM) mode, and quantified by external standard method. The linearities of diafenthiuron-urea and diafenthiuron-amide ranged from 0.001 to 0.1 mg/L. And that of the other six compounds ranged from 0.005 to 0.5 mg/L, with the correlation coeffecients higher than 0.999 3. At the fortified level from 0.001 mg/kg to 0.5 mg/kg in pear, grape, watermelon, kale, celery and leek, the average recoveries of all the eight compounds ranged from 68% to 94% with the relative standard deviations varied from 5.4% to 15%. The limits of quantification (LOQ) of the analytes were 0.001-0.005 mg/kg. The method is simple, rapid, accurate and suitable for the confirmation and quantification of those eight compounds in fruits and vegetables.