Determination of oxadiazon and oxyfluorfen in thyme by gas chromatography with electron-capture detection and gas chromatography/mass spectrometry

The present paper reports on an analytical method for the routine analysis of oxadiazon (5-tert-butyl-3-(2,4-dichloro-5-isopropoxyphenyl)-1,3,4-oxadiazol-2(3H)-one) and oxyfluorfen (2-chloro-α,α,α-trifluoro-p-tolyl 3-ethoxy-4-nitrophenyl ether) residues in thyme (Thymus vulgaris L. and Thymus zygis subsp. gracilis). Samples were extracted by sonication with a water-acetonitrile mixture and the herbicides were partitioned into dichloromethane. Residue levels in thyme were determined by gas chromatography with electron-capture detection (ECD). Confirmation analysis of herbicides was carried out by GC/MS in the selected ion monitoring (SIM) mode. The identification of compounds was based on retention time and on comparison of the primary and secondary ions. The average recovery by the GC-ECD method obtained for these compounds varied from 89.0 to 108.5% with a relative standard deviation between 1.9 and 6.1%. The detection limit by the GC-ECD for the pesticides studied varied from 4.9 to 13.9 µg kg−1. The proposed method was applied to thyme samples grown in the Region of Murcia (Spain). The results showed that this method provided a simple, rapid and sensitive way to analyse oxadiazon and oxyfluorfen residues in thyme.