Determination of triazines in surface waters by membrane separation coupled on-line to a flow-injection system and partial least squares regression

A flow-injection analysis method is described intended for the determination of triazine herbicides in natural waters. The proposed flow-injection manifold incorporates a membrane separation module inserted in the sample loop of the injection valve. This module works as an extraction-preconcentration cell. Analytes are extracted from the aqueous matrix to an organic solution and are carried to the flow cell of a diode array spectrophotometric detector. A partial least squares regression method enables the simultaneous determination of both chloro- and methylthiotriazine families in mixtures without chromatographic separation. The method can therefore be used as a screening method of these classes of compounds. Optimization of the method involves study of the extraction-preconcentration process (composition of the acceptor solution, preconcentration time) as well as all the variables affecting the calibration procedure. The determination of both classes of triazines added to surface waters was satisfactory; detection limits of 4–5 μg 1−1 were achieved for the determination of binary mixtures of chloro- and methylthiotriazines added to river water samples, the relative standard deviations being < 6%.