Investigation of carbofuran and its metabolites by gas-liquid chromatography in green and dry hops

Abstract

Processed hop cones (Humulus americanus) are an important flavoring component in beer, and it is possible that carbofuran and its metabolites could be found in treated hops and thus in beer. Hop cones were treated with 1.12 kg/ha active ingredient carbofuran (2, 3-dihydro-2, 2-dimethyl-7-benzofuranyl-N-methyl carbamate) for the control of root weevils (Otiorhynchus sulcatus, O. ovatus). The carbamates in the cones were determined using gas-liquid chromatography (GLC) and a thermionic specific detector. The percent recoveries for the carbamates ranged from 88.7 ± 5.3 to 95.3 ± 6.3% (green hops) and from 88.6 ± 12.3 to 98.0 ± 5.0% (dry hops). The phenolic metabolites were analyzed as their 2, 4-dinitrophenol ether derivatives, using GLC with an electron capture detector. The percent recoveries ranged from 85.0 ± 5.8 to 88.3 ± 8.5% (green hops) and from 80.3 ± 4.4 to 95.3 ± 3.0% (dry hops). The GLC procedure was sensitive to 0.05 ppm. Control samples in all cases contained less than 0.05 ppm and green, treated hop cones had residues of less than 0.05 ppm. Dry treated hop cones contained less than 0.05 ppm of all chemicals, except 3-keto-7-phenol (0.12 ppm) and the 3,7-diol (0.07 ppm). Although the U.S. Environmental Protection Agency (EPA) has not established tolerance levels for carbofuran and its metabolites in hop cones, the present investigation shows that residue levels on green and dry hop cones are well below the EPA's tolerances for carbofuran in other commodities.