Microextraction procedures combined with large volume injection in capillary gas chromatography for the determination of pesticide residues in environmental aqueous samples

Liquid-liquid microextraction and solid-phase extraction procedures combined with large volume on-column injection (100-150 mu l) in capillary gas chromatography with nitrogen phosphorus detector have been applied to the determination of six triazine herbicides (atrazine, simazine, terbutylazine, terbumeton, metribuzin and terbutryn) and two transformation products (deethyl and deisopropyl atrazine) in water samples. A simple and fast off-line liquid-liquid microextraction procedure (5 mi water/1 mi methyl tert butyl ether) was applied to surface water samples spiked at 0.5 mu g l(-1) level with good recoveries (> 90%) and repeatability (better than 9%) giving detection limits < 0.1 mu g l(-1). The application of a solid-phase extraction procedure (10-50 ml of water samples passed through 200 mg C-18 cartridges) allowed the quantitative recovery of all pesticides studied with coefficients of variation lower than 11%. Limits of detection for 50 ml sample volume ranged from 10 to 40 ng l(-1). Surface water samples have been analyzed using C-18 SPE (10 mi of water sample) combined with large volume injection (150 mu l) and the results compared with those obtained with conventional LLE (500 mi of water sample extracted with 2 x 50 ml dichloromethane), showing good match between them. (C) 1997 Elsevier Science B.V.