Application of a bis-thiourea ionophore for an anion selective electrode with a remarkable sulfate selectivity

Anion-selective solvent polymeric membrane electrodes based on hydrogen bond-forming, neutral ionophores with two urea or thiourea groups bridged by a m-xylylene unit are de scribed. The use of alpha,alpha'-bis(N'-phenylthioureylene)-m-xylene results in ion-selective electrodes with a remarkable selectivity for sulfate. An electrode with this compound as ionophore, poly(vinyl chloride) (PVC) as polymeric matrix, 2 nitrophenyl octyl ether (o-NPOE) as plasticizer and cationic sites (50 mol% relative to the ionophore) responds to sulfate in a Nernstian manner in the concentration range from 10(-6) to 10(-2) M. In comparison to conventional anion-exchanger electrodes, the interference of SCN-, NO3-, Br-, and Cl- is significantly reduced, as shown by the selectivity coefficients determined with the matched potential method in the sulfate 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 ion-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.