A highly thiocyanate-selective poly(vinyl chloride) (PVC) membrane electrode based on N,N'-ethylidene(μ-5,5-methylene-disalicylaldehyde)-acetylacetonedicopper(II) [Cu₂(II)-MDSBAE] complex as neutral carrier is reported. The electrode displays a preferential potentiometric response to thiocyanate and an anti-Hofmeister selectivity sequence in following order: SCN^－＞Sal^－＞I^－＞ClO₄^－＞NO₃^－＞Br^－＞NO₂^－＞Cl^－≈SO₃^2－＞SO₄^2－. The electrode exhibits near Nernstian potential linear range of 1.0×10^－6～1.0× 10^－1 mol/L with a detection limit of 8.1×10^－7 mol/L and a slope of －53.6 mV/decade in pH 5.0 of phosphorate buffer solution at 25 ℃. The response mechanism is discussed in view of the alternating current (A.C.) impedance technique. The coordination number and assiociation constants of axial coordination reaction of complex Cu₂(II)-MDSBAE towards SCN^－, Sal^－, I^－, ClO₄^－ and NO₃^－ were measured by means of the UV spectroscopy technique. The electrode was applied to thiocyanate ion in waste water analysis with satisfactory results.

Key words: copper(II) complex, neutral carrier, thiocyanate, ion-selective electrode