Gas-chromatographic method for determination of diflufenican in soil

Decomposition in soil of the herbicide diflufenican, N-(2,4-difluorophenyl)-2-[3-(trifluoromethyl)phenoxy]-3-pyridinecarboxamide, was studied after application for weed control on Swedish railway embankments. A new sensitive method has been developed for determination of aged residues of diflufenican in soil by GC-ECD. A sample extraction using 100% methanol with "extended shake" was performed. The extract was concentrated and purified on a C-18-SPE column. Further clean-up was made by using a Silica SPE column. Minimum level of detection for diflufenican was 0.001 mu g g(-1) soil. Recovery of diflufenican over the range 0.02 mu g g(-1) to 0.2 mu g g(-1) soil by this method was generally between 94.3% and 121.2% (15 out of 15 determinations). The amounts of diflufenican found in the soil samples at various times after their application were mainly between 0.2 mu g g(-1) and level of detection.