ONLINE COMBINATION OF AUTOMATED MICROLIQUID LIQUID EXTRACTION AND CAPILLARY GAS-CHROMATOGRAPHY FOR THE DETERMINATION OF PESTICIDES IN WATER

The determination of pesticides in water is often based on liquid-liqu id extractions combined with concentration by evaporating the organic solvent followed by analysis with capillary GC. The use of selective d etection such as thermionic detection (NPD) or flame photometric detec tion (FPD) makes the use of additional clean-up unnecessary in many in stances. To obtain detection limits in the sub-ppb range with these de tectors, typically the equivalent of approximately 1 ml of sample is i njected. Hence, micro-extraction techniques, transferring the pesticid e content of 1 ml of aqueous sample to a capillary GC are feasible. In this study, micro liquid-liquid extraction with methyl tert.-butyl et her was combined with GC-FPD in a fully automated set-up, using GC sam ple introduction volumes of 500 mul which were transferred via an on-c olumn interface equipped with an early vapour exit. The organophosphor us pesticides diazinon, chlorpyriphos-methyl, malathion, chlorpyriphos -ethyl, chlorfenvinphos-cis, bromophos and azinphos-ethyl were determi ned in pond water spiked at the 0.5 mug/l level. In most cases recover ies were over 70%, while the detection limit allowed quantification at the level of the EC maximum residue limits for water intended for hum an consumption (0.1 mug/1). This communication demonstrates the practi cality of an on-line micro liquid-liquid extraction procedure which el iminates the need to use a phase separator, resulting in a set-up robu st also in the hands of relatively inexperienced personnel.