Determination of imazalil residues in lemons by gas chromatography with nitrogen-phosphorus detection

A simple and reliable method was developed for determination of imazalil residues in whole lemons. Imazalil was extracted from lemon samples with ethyl acetate under basic conditions. The ethyl acetate in the extract was evaporated, and the residue was dissolved in dichloromethane. The solution was applied to a solid-phase extraction (diol-bonded silica) cartridge. Imazalil was eluted with methanol and determined by gas chromatography (GC) with nitrogen-phosphorus detection. Recoveries at 4 fortified levels (0.1, 1.0, 2.0, and 5.0 micrograms/g) ranged from 93.3 to 97.8%, with coefficients of variation ranging from 0.2 to 3.0%. The detection limit was 0.05 microgram/g. Fifteen commercial lemon samples were analyzed for Imazalil residues; 10 were positive. Concentrations of imazalil residues ranged from 0.22 to 4.44 micrograms/g. Imazalil-positive samples were confirmed by GC with mass-selective detection (m/z 173, 215, and 217).