SOLID-PHASE EXTRACTION OF PESTICIDE-RESIDUES FROM GROUND-WATER - COMPARISON BETWEEN EXTRACTION CARTRIDGES AND EXTRACTION DISKS

Octadecyl (C18) bonded porous silica sorbent cartridges and Empore membrane extraction discs were evaluated for the solid-phase extraction (SPE) of organochlorine (lindane, dicofol, chlorfenson and tetradifon) and organophosphorus pesticides (dimethoate, fenitrothion and methidathion) from ground water. The 500-mg C18 cartridges quantitatively adsorbed these pesticides, including the most polar (dimethoate), with recoveries ranging from 68 to 113% for a ground water sample spiked at the 0.1 mug l-1 level. SPE with 500-mg C18 Empore discs also quantitatively adsorbed the pesticides with recoveries between 73 and 115% for the 0.1 mug l-1 level, but only after eluting with 15 ml of ethyl acetate compared with 4 ml using cartridges and a longer analysis time per sample. After elution with ethyl acetate, the extract was concentrated to an appropriate volume, between 100 and 500 mul, under a gentle stream of nitrogen. Detection limits were lower than 0.1 mug l-1, which is currently the maximum level allowed by the EEC for pesticide residues in drinking water. Determination was effected by capillary gas chromatography using electron-capture and nitrogen-phosphorus detectors.