On-line combination of automated micro liquid-liquid extraction and capillary gas chromatography for the determination of pesticides in water

Abstract

The determination of pesticides in water is often based on liquid-liquid extractions combined with concentration by evaporating the organic solvent followed by analysis with capillary GC. The use of selective detection such as thermionic detection (NPD) or flame photometric detection (FPD) makes the use of additional clean-up unnecessary in many instances. To obtain detection limits in the sub-ppb range with these detectors, typically the equivalent of approximately 1 ml of sample is injected. Hence, micro-extraction techniques, transferring the pesticide content of 1 ml of aqueous sample to a capillary GC are feasible. In this study, micro liquid-liquid extraction with methyl tert.-butyl ether was combined with GC-FPD in a fully automated set-up, using GC sample introduction volumes of 500 μl, which were transferred via an on-column interface equipped with an early vapour exit. The organophosphorus pesticides diazinon, chlorpyriphos-methyl, malathion, chlorpyriphos- ethyl, chlorfenvinphos- cis, bromophos and azinphos-ethyl were determined in pond water spiked at the 0.5 μg/l level. In most cases recoveries were over 70%, while the detection limit allowed quantification at the level of the EC maximum residue limits for water intended for human consumption (0.1 μg/l). This communication demonstrates the practicality of an on-line micro liquid-liquid extraction procedure which eliminates the need to use a phase separator, resulting in a set-up robust also in the hands of relatively inexperienced personnel.