Comparison of simplified methods for pesticide residue analysis -: Use of large-volume injection in capillary gas chromatography

The combination of manual and automated extraction procedures using low sample volumes (5-50 ml) with large-volume oncolumn injection (LVI) (200 mu l) in capillary gas chromatography with flame photometric detection (GC-FPD) has allowed the determination of 16 organophosphorus pesticides in clean water samples at the low ng l(-1) level with an important simplification in the sample preparation step. A simple and fast offline liquid-liquid microextraction procedure (2-5 ml water/1 ml methyl tert.-butyl ether) has been applied to spiked groundwater samples (containing 0.5 ng of each pesticide) with good recoveries lover 80%) and precision (better than 10%), giving detection limits between 5 and 100 ng l(-1) using 200 mu l injections in the GC-FPD system. The application of an inline automated Liquid-Liquid microextraction-LVI-GC procedure (2 ml water/2 ml methyl tert.-butyl ether: injection of 200 mu l in GC-FPD) using the autosampler ASPEC XL led to lower recoveries (>50%) as a result of the low efficiency for mixing organic and aqueous phases, although with very satisfactory coefficients of variation (lower than 78) and detection Limits between 20 and 200 ng l(-1). Manual and automated solid-phase extraction procedures using the well known C-18 cartridges and the new Oasis HLB have been applied to groundwater samples (5-50 ml) spiked with 1 ng of each pesticide. Results obtained for both the manual and the automated procedures were satisfactory (recoveries over 80%) and the limits of detection for 50 ml sample volume ranged from 1 to 6 ng l(-1). (C) 1998 Elsevier Science B.V. All rights reserved.