Column switching liquid chromatography and post-column photochemically fluorescence detection to determine imidacloprid and 6-chloronicotinic acid in honeybees

The determination of imidacloprid and its main metabolite (6-chloronicotinic acid) in honeybees was performed by liquid chromatography with post-column photochemical derivatisation in alkaline medium and fluorescence detection. The compounds were extracted from honeybees with acetone under ultrasound conditions prior to liquid–liquid partition with dichloromethane. The separation of extract components was performed using a 50 mm × 4.6 mm i.d. short column packed with 5 μm Aquasil C18 using an acetonitrile:water gradient program as mobile phase. Injection of samples in 0.1 mol L−1 H3PO4/KH2PO4 buffer solution (pH 3) improved the chromatographic separation between the most polar components of matrix and the 6-chloronicotinic acid. Matrix components were removed to waste using an on-line clean-up method previously to post-column reaction. Limits of quantification were 0.3 and 5.0 μg L−1 (corresponding to 1.2 and 20.0 μg kg−1 in the honeybee sample) for imidacloprid and 6-chloronicotinic acid, respectively. The recovery was ranged from 80.2 to 91.7% with a relative standard deviation lower than 9.0%.