DETERMINATION OF TOTAL IMIDACLOPRID RESIDUES IN COFFEE BY GAS CHROMATOGRAPHY–MASS SPECTROMETRY

ABSTRACT

The insecticide imidacloprid and its metabolites in green beans, roasted beans, and freeze–dried coffee were extracted with a mixture of methanol and 1% H₂SO₄ (1/3, v/v). The cleanup procedure involved hexane partitioning and XAD-4 resin cleanup eluted with methanol. Imidacloprid and its metabolites in the 5-hydroxy-, olefin-, and desnitro-forms in the extracts were oxidized with KMnO₄ (pH 14) to 6-chloronicotinic acid which was then recovered with methyl t-butyl ether (MTBE). The residue was dissolved in acetonitrile after the evaporation of MTBE, and 6-chloronicotinic acid was derivatized with methyl trimethylsilyl trifluoroacetamide for gas chromatography-mass spectrometric quantification. Recoveries of total imidacloprid residues ranged from 90 to 110% at different fortification levels. The method was applied to the analysis of coffee samples collected from trees that received five foliar applications of the insecticide. All treated samples of green and roasted beans, and freeze–dried coffee were found to contain imidacloprid residues.

Keywords:

• Imidacloprid
• Insecticide
• Coffee

ACKNOWLEDGMENTS

This work was supported in part by funds from USDA IR-4 and a grant from State of Hawaii Department of Agriculture. The authors thank Julia Coughlin for preparing the coffee samples, Karl Yanagihara for reviewing the manuscript and technical assistance, and Bayer Corp. for donating the standards.