A method for on-line matrix elimination to enable selective quantification of ultraviolet absorbing analytes by a flow-injection analysis procedure is described. Selectivity is achieved by electric field driven extraction across a polymer inclusion membrane. The method was demonstrated on the example of the determination of naproxen from spiked human urine. Membranes of 10 µm thickness were employed which consisted of 7.5 mg cellulose triacetate as base polymer, 5 mg of o-nitrophenyl octyl

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... as plasticizer and 7.5 mg of Aliquat 336 as cationic carrier. Ten µL of sample was introduced into a continuous stream of background solution consisting of 100 µM aqueous NaClO 4 with a flow rate of 2 µL/min while applying a voltage of 150 V to the extraction cell. The target ion was electrokinetically transported across the membrane and enriched in 1.5 µL of a stagnant acceptor solution. This was subsequently pumped past a flow-through UV detector for quantification. The method showed a linear range from 5 to 200 µM with a correlation coefficient of 0.9978 and a reproducibility of typically 7% (n = 8). The detection limit of the method for naproxen was 2 µM.