SOLID-PHASE EXTRACTION OF POLAR PESTICIDES FROM ENVIRONMENTAL WATER SAMPLES ON GRAPHITIZED CARBON AND EMPORE-ACTIVATED CARBON DISKS AND ONLINE COUPLING TO OCTADECYL-BONDED SILICA ANALYTICAL COLUMNS

The suitability of Empore-activated carbon disks (EACD), Envi-Carb gra phitized carbon black (GCB) and CPP-50 graphitized carbon for the trac e enrichment of polar pesticides from water samples was studied by mea ns of off-line and on-line solid-phase extraction (SPE). In the off-li ne procedure, 0.5-2 1 samples spiked with a test mixture of oxamyl, me thomyl and aldicarb sulfoxide were enriched on EnviCarb SPE cartridges or 47 mm diameter EACD and eluted with dichloromethane-methanol. Afte r evaporation, a sample was injected onto a C-18-bonded silica column and analysed by liquid chromatography with ultraviolet (LC-UV) detecti on. EACD performed better than EnviCarb cartridges in terms of breakth rough volumes (>2 1 for all test analytes), reproducibility (R.S.D. of recoveries, 4-8%, n=3) and sampling speed (100 ml/min); detection lim its in drinking water were 0.05-0.16 mu g/l. In the on-line experiment s, 4.6 mm diameter pieces cut from original EACD and stacked onto each other in a 9 mm long precolumn, and EnviCarb and CPP-50 packed in 10x 2.0 mm I.D. precolumn, were tested, and 50-200 ml spiked water samples were preconcentrated. Because of the peak broadening caused by the st rong sorption of the analytes on carbon, the carbon-packed precolumns were eluted by a separate stream of 0.1 ml/min acetonitrile which was mixed with the gradient LC eluent in front of the C-18 analytical colu mn. The final on-line procedure was also applied for the less polar pr opoxur, carbaryl and methiocarb. EnviCarb could not be used due to its poor pressure resistance. CPP-50 provided less peak broadening than E ACD: peak widths were 0.1-0.3 min and R.S.D. of peak heights 4-14% (n= 3). In terms of analyte trapping efficiency on-line SPE-LC-UV with a C PP-50 precolumn also showed better performance than when Bondesil C-18 /OH or polymeric PLRP-S was used, but chromatographic resolution was s imilar. With the CPP-50-based system, detection limits of the test com pounds were 0.05-1 mu g/l in surface water.