Abstract:

A method using capillary gas chromatography was presented for the determination of allyl isothiocyanate (AITC) residue in agro-products fumigated with it. Samples were extracted with dichloromethane. A capillary gas chromatography system equipped with flame ionization detector (FID) was used. Mean recoveries of AITC in a sample spiked at the levels of 1, 5 and 25 mg/kg ranged between 70.6% and 92.3%, with relative standard deviations (RSDs) within the range of 3.6%－9.3%. The presented method exhibited a limit of determination of 0.1 mg/kg. The degradation of AITC in fumigated agro-products including rice seeds, wheat seeds, commercial rice, Chinese date and Jew's-ear, as a result of enzymolysis, hydrolysis or photolysis, complied with first-order kinetic equations, with half-life periods ranging from 28 to 75 d. After 112 d storage, the AITC residues in fumigated rice seeds, wheat seeds, rice, Chinese date and Jew s-ear were 11.8, 150.7, 2.8, 77.5, 3.3 mg/kg and 8.2 mg/kg at the treatment level of 25 mg/L and 5.6, 189.2, 3.6, 26.9, 1.2 mg/kg and 10.2 mg/kg at the treatment level of 100 mg/L. Therefore, the dosage of 20% dichloromethane solution of AITC should be set at the level of 25 mg/L. After 2 d sealed AITC fumigation, at least 14 d air exposure of agro-products is required for the degradation of most AITC residue.

Key words: allyl isothiocyanate, fumigation, residual analysis, degradation kenetics