A multiresidue method with mobile on-site sampling based on SPE for ultratrace analysis of plant protectants in environmental waters

A new multiclass/multiresidue method for monitoring plant protectant residu es in raw- and drinking waters with on-site sampling using a mobile, self-c ontained sampling unit based on SPE was developed and validated. 38 active compounds with widely varying chemical and physicochemical properties (acid -base properties, polarities, vapor pressures, solubilities) are measured f rom just one sample and work-up. 100 mt water, acidified with acetic acid, are drawn through a cartridge filled with Amberchrom resins by means of a c alibrated 100 mt syringe driven by servo motors, control circuit and rechar geable battery. Volumetric flow is high, quantitative extraction of acidic, neutral and weak basic substances is accomplished in a few minutes and loa ded cartridges are transported into the laboratory. Further work-up, i.e. e lution, drying, concentration and solvent change, is designed strictly non- selectively and produces 250 mu L of an "extract", which is the starting po int of two GC measurement lines, GC-NPD and GC-ECD. Chlorinated herbicide a cids are derivatised into perfluorinated benzyl esters employing reaction c onditions so smooth that the organochlorine hydrocarbons are not destroyed at all and both substance classes can be chromatographed in one GC run. ECD -chromatograms from derivatised solutions are rather complex, therefore the flow is split after injection onto two columns with different polarities a nd two EC-detectors in order to resolve all analytes and matrix interferent s. Short-chain carbonic acids added to the water prior to preconcentration are adsorbed on the hydrophobic surface in a reversible process and impart the Amberchrom resins with a partially hydrophilic character. Method perfor mance was ascertained using tap water fortified at the 0.2 mu g L-1 level: Mean recoveries were between 70 and 115% and method detection limits (MDLs) below 0.08 mu g L-1. Waters from different sources did not affect the reco veries, loaded cartridges are stable for two weeks' storage when cooled.