Isotope-labeled internal standards and grouping scheme for determination of neonicotinoid insecticides and their metabolites in fruits, vegetables and cereals - A compensation of matrix effects.

Neonicotinoid insecticides (NIs) are widely used. However they produce high levels of residues and are toxic to non-target organisms, especially when their metabolites exhibit comparable or elevated toxicities. In this study, we established a multi-residue analytical method for analyzing 20 compounds - 8 NIs and their 11 major toxic metabolites. QuEChERS pretreatment and ultra-high-performance liquid chromatography-tandem mass spectrometry were used to detect residues in fruits, vegetables and cereals. Determination time was shortened to 6 min. Average recoveries of all compounds were in the range of 90.1-105.5%, with relative standard deviations lower than 15.0% and the limit of quantitation being 10 µg kg. For the first time, 8 NIs and 11 major toxic metabolites were grouped simultaneously, such that the matrix effect of analytes was satisfactorily corrected using their own isotopically labeled molecules; other NIs and metabolites in the same group were also corrected. This is the first report that simultaneously quantified multiple metabolites of eight NIs in multiple matrices.