Trace enrichment and sample preparation of alkylthio-s-triazine herbicides in environmental waters using a supported liquid membrane technique in combination with high-performance liquid chromatography

Abstract

Sample pre-treatment and enrichment using the supported liquid membrane (SLM) technique for the determination of alkylthio-s-triazine herbicides in river water samples was investigated. The uncharged herbicide molecules from the flowing aqueous donor solution diffuse through a porous poly(tetrafluoroethylene) membrane, which is immobilized with a water-immiscible organic solvent, and are trapped in a stagnant acidic acceptor phase since they become protonated. Using undecane as a membrane solvent, the SLM methodology was successfully used for the enrichment and separation of seven alkylthio-s-triazine herbicides in environmental waters with extraction efficiencies of 60% or better. The LC results obtained on spiking the pesticides in river water samples further confirmed the selectivity of the method. The influence of the various SLM extraction parameters on the extraction efficiency was studied. In this system, the partition coefficient, K_p, between the donor and the membrane phases is large, and effects due to carry over and membrane memory are very small. Detection limits of about 0.03 µg l^–1 were obtained by extraction of 1.0 µg l^–1 samples in both reagent and river water at a donor flow rate of 7.0 ml min^–1 for about 70 min. Further advantages of the procedure are the reduced analysis time and an increase in the sample accumulation rate in the acceptor phase.