Analysis of phenylurea herbicides from plants by GC/MS

Seven phenylurea herbicides (chlorbromuron, fluometuron, diuron, linuron, metobromuron, monolinuron, monuron) were isolated from weed plant materials by extraction with acidic aqueous solutions—the aqueous extract preconcentrated and cleaned-up by using a continuous SPE module. Elution with ethyl acetate resulted in >95% recovery of the herbicides from the LiChrolut-EN sorbent column. Separation of the seven herbicides was easily achieved working under fixed gas-chromatographic conditions and, although other peaks were also detected (corresponding to isocyanate degradation products), they showed different retention times and lower intensity than the parent compounds; in addition, as reproducible chromatograms in terms of herbicide-to-isocyanate product peak areas ratio were obtained, no derivatization was required. The analytical figures of merit of the GC/MS method in the selective ion monitoring mode are as follows: limits of detection from 0.5 to 5.0 ng ml−1; precision (R.S.D.) ≈7.0%; and preconcentration factor 100 (using 10 ml of sample extract). The proposed GC/MS method offers better resolution and selectivity than the conventional LC-UV method.