APPLICATION OF A BIS-THIOUREA IONOPHORE FOR AN ANION-SELECTIVE ELECTRODE WITH A REMARKABLE SULFATE SELECTIVITY

Anion-selective solvent polymeric membrane electrodes based on hydroge n bond-forming, neutral ionophores with two urea or thiourea groups br idged by a m-xylylene unit are de scribed. The use of alpha,alpha'-bis (N'-phenylthioureylene)-m-xylene results in ion-selective electrodes w ith a remarkable selectivity for sulfate. An electrode with this compo und as ionophore, poly(vinyl chloride) (PVC) as polymeric matrix, 2 ni trophenyl octyl ether (o-NPOE) as plasticizer and cationic sites (50 m ol% relative to the ionophore) responds to sulfate in a Nernstian mann er in the concentration range from 10(-6) to 10(-2) M. In comparison t o conventional anion-exchanger electrodes, the interference of SCN-, N O3-, Br-, and Cl- is significantly reduced, as shown by the selectivit y coefficients determined with the matched potential method in the sul fate concentration range 1.0-10 mM (log K-sulfate,B(pot): SCN-, +2.9; NO3-, +1.6; Br-, +1.1; Cl-, -O.1). The present electrode has a higher selectivity for sulfate than any previously reported ionophore-based i on-selective electrode. No significant changes in the detection limit and response slope were observed when the electrode was stored for 28 days in an aqueous buffer solution. (C) 1998 Elsevier Science B.V.