FULLY AUTOMATED WATER ANALYZER BASED ON ONLINE SOLID-PHASE EXTRACTIONGAS-CHROMATOGRAPHY

An automated procedure for the analysis of aqueous samples by membrane disk extraction coupled on-line to capillary gas chromatography (GC) is presented. Organophosphorus pesticides are preconcentrated from aqu eous samples on three 0.5 mm thick, 4.0 mm diameter XAD-2 membrane ext raction disks which are mounted in a polymer holder for use in a PROSP EKT sample processor. The layers are dried by a stream of nitrogen (30 min at ambient temperature). Desorption of the analytes is carried ou t with ethyl acetate which is directly introduced into a retention gap under partially concurrent solvent evaporation conditions, using an e arly solvent vapor exit. The method is a fully software-controlled aut omated system, and includes sample preparation, sample transfer and GC analysis. The final analysis is carried out by GC with nitrogen-phosp horus (NPD) or mass-selective detection. The technique is applied to t he determination of a series of organophosphorus pesticides in tap wat er and water from European rivers. With a sample volume of only 2.5 mL , the detection limits achieved with the NPD were 20-50 ng L-1 in tap water and 20-100 ng L-1 in river water.