Solid-phase microextraction of the herbicide metolachlor in runoff and tile-drainage water samples

The new rapid solid-phase microextraction (SPME) technique developed in Canada by Pawliszyn and co-workers has been used in the analysis of water for pesticide residues in laboratory studies. SPME used with gas chromatography and electron-capture detection (GC-ECD) of metolachlor in runoff water showed linear response over a wide range. The lowest concentration analyzed was 0.002 mu g/l (2 ppt), and the highest was 20 000 mu g/l (20 ppm). Over this span of seven orders of magnitude, the standard curve had an R(2) Of 0.9954 for ten data points, each of which was averaged over three or more trials. The curve below 200 mu g/l, or 0.20 ppm had a slightly different slope (R(2) 0.9996). Earlier analyses by automated SPME-GC and flame ionization detection (FID) in distilled water showed linear response over the range 180 to 180 000 mu g/l. A 100-mu m polydimethylsiloxane-coated fibre was used; metolachlor residues in the runoff water were 0.17 to 50.7 mu g/l. This is the first time, to our knowledge, that SPME has been used in the analysis of herbicide residues in runoff water.