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 electr on-capture and flame photometric detection. The calibration equation f or 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 o bserved for fenthion, deltamethrin and trifluralin, but the proposed m ethod was suitable for other pesticides studied. The limits of detecti on 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.