Influence of the solid-phase extraction process on calibration and performance parameters for the determination of pesticide residues in water by gas chromatography

Twenty-six organophosphorus, organochlorine and other electron-capture detection-sensitive pesticides were extracted from water in a single step using a C-18 solid-phase extraction cartridge, eluted with ethyl acetate and isooctane and determined by gas chromatography with electron-capture and flame photometric detection. The calibration equation for the extraction method was calculated for a twentyfold concentration range, including the EC limit of 0.1 mu g/l. The linearity, precision, sensitivity and detection limit of the method were studied, applying the statistical model of linear regression. A lack of linearity was observed for fenthion, deltamethrin and trifluralin, but the proposed method was suitable for other pesticides studied. The limits of detection range from 20 to 120 ng II applying the calibration graph and from 1 to 40 ng/l based on a signal-to-noise ratio of 3:1.