Analytical determination of imidacloprid and relevant metabolite residues by LC MS/MS

A new method is described for the analytical determination of imidacloprid residues by LC MS/MS. This method allows the concurrent determination of the parent compound imidacloprid and two toxicologically relevant plant metabolites of this systemic insecticide. The method was successfully applied to examine field residue levels of these contaminants in rape and sunflower crop plants which had been seed-treated with imidacloprid. The analyzed samples included pollen, flowers, leaves, nectar, honey, wax and bees. Residues of imidacloprid and its metabolites 5-hydroxy-imidacloprid and olefin-imidacloprid are extracted with methanol/water. The extracts are subjected to liquid-liquid partition on a column filled with diatomaceous earth and subsequent solid phase extraction on a silica gel column. Quantification is performed by reversed phase HPLC with electrospray MS/MS-detection. External bracketing standards in matrix are used to compensate possible matrix effects in the ion source. The overall recoveries for imidacloprid, 5-hydroxy-imidacloprid and olefin-imidacloprid from plant matrices were between 91 and 97% with a relative standard deviation between 6.0 and 8.5%. The detector linearity and the repeatability of the method proved to be very precise. The limits of quantification were 0.005 and 0.01 mg/kg for imidacloprid and 5-hydroxy-imidacloprid, and for the olefin-metabolite, respectively. Field residue studies were conducted on seed-treated rape and sunflower crops. Small bee colonies were caged on flowering sunflower and rape plots and served as collecting devices for nectar and pollen. Flower petals, leaves, honey bees and the collected pollen and nectar samples were analysed by the new HPLC-MS/MS method. The analytical results showed no quantifiable residues in any sample material. Accordingly, honey bees will exposed to only negligible residue levels of imidacloprid when foraging on flowering seed-treated crop plants.