Comparison of gas chromatography and immunoassay methods in quantifying fenitrothion residues in grape juice processed into alcoholic drinks.

Wine and Arak, the national alcoholic drink in Lebanon, were prepared from grape juice fortified with fenitrothion to a concentration of 20ppm. Samples of the 11 fractions produced by the fermentation and distillation steps were analyzed for fenitrothion residues using gas chromatography (GC) and enzyme-linked immunosorbent assay (ELISA). Results of residue analyses showed that the two techniques were highly correlated (r = 0.978) and indicated that fenitrothion was stable during the fermentation steps but not during distillation. The clarified wine 35 days later contained about 85% (15.3 ppm) of the fenitrothion concentration found in the juice as determined by GC analysis. Arak was prepared by a two-steps distillation of the clarified wine. The alcohol distillate and undistilled fraction from the first distillation contained 2.5 ppm and 5.8 ppm of fenitrothion, respectively. No fenitrothion residues were detected by both techniques in the four fractions collected from the second distillation step.