ANALYSIS OF SULFONYLUREA HERBICIDES BY GAS-LIQUID-CHROMATOGRAPHY .2. DETERMINATION OF CHLORSULFURON AND METSULFURON-METHYL IN SOIL AND WATER SAMPLES

Sulfonylureas are extracted from water samples using solid-phase extraction (SPE) with C18-silica/Teflon disks. Soil samples are extracted with 0.1 M sodium hydrogen carbonate, and the acidified extracts are processed as for water samples. The concentrated eluents are treated with diazomethane in ethyl acetate, which forms the thermally stable N,N'-dimethyl derivatives of the herbicides. Residues are screened by capillary GC using effluent splitting to electron capture and nitrogen-phosphorus detectors. Residues are confirmed by GC-MS using selected ion monitoring. Detection limits were below 0.1 mug/L for water and below 1 mug/kg for soil samples. Accuracy and precision at 0.5 and 0.l mug/L each were, respectively, for chlorsulfuron 95 +/- 2 % and 1 10 +/- 16 % and for metsulfuron-methyl 90 +/-6 % and 98 +/- 11 % At 5 and 1 mug/kg each in soil the recoveries were, respectively, for chlorsulfuron 78 +/- 20 % and 69 +/- 6 % and for metsulfuron-methyl 92 +/- 18 % and 105 +/- 17 %. The methods are superior to previous methods for these herbicides based on GC because the intact herbicides are determined rather than thermal degradation products.