SUPPORTED LIQUID MEMBRANE TECHNIQUE FOR TIME-INTEGRATING FIELD SAMPLING OF ACIDIC HERBICIDES AT SUB PARTS-PER-BILLION LEVEL IN NATURAL-WATERS

A method for continuous sampling of acidic herbicides in natural waters based on supported liquid membrane extractions has been developed. A porous PTFE membrane was impregnated with an organic solvent, ensuring only uncharged molecules passed through the membrane. Selecting the pH in the donor and acceptor phases selectively enriched acidic substances on the acceptor side. The herbicides (bentazon, 2,4-D, dicamba, dichlorprop, MCPA, and mecoprop) were continuously sampled during 24 h. After collection, the samples were taken to the laboratory for quantification using liquid chromatography with UV detection. The extraction efficiences for the herbicides were ca. 0.70, resulting in detection limits of ca. 40 ng/L, sample volumes of 1 L (24-h sampling), in clean aqueous samples. The detection limits in natural waters are somewhat higher and are estimated to ca. 0.1 mug/L. Changes in both air and water temperatures had no significant effect on the extraction efficiencies.