3.3.2. Imidacloprid

The initial deposition of imidacloprid on Clementine was 0.592 ± 0.010 mg kg−1. Imidacloprid residues dissipated 92% by harvest (42 day after spraying). The final imidacloprid residue concentration at the end of the postharvest period differed significantly from the residue level determined at harvest (Student t-test, α = 0.05). No clear conclusion can be made about the effect of cold storage on imidacloprid concentration. The higher levels of imidacloprid detected after cold storage were likely due to fruit water loss, a situation that was observed solely for the imidacloprid-treated mandarins and could be ascribed to some technical failure in the wax treatment. The dehydration of the fruit changed the level of co-extractives and, therefore, the matrix effect also changed. Changes in the matrix effect mean a different slope for the matrix-matched calibration curve, and therefore, in the residue quantitation. Our group established the presence of isobaric compounds that may have interfered with imidacloprid determination in citrus fruit that included mandarins [43]. If this interference was not compensated by the matrix-matched calibration, the imidacloprid levels would be overestimated, yielding higher concentration values for this compound.
