Marine Chemistry, 10 (1981) 249--255 249 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netheralands Short Note A NOTE ON THE POLAROGRAPHIC BEHAVIOR OF THE CU(II) ION SELECTIVE ELECTRODE IN SEAWATER ALBERTO ZIRINO and PETER F. SELIGMAN Marine Environment Branch, Naval Ocean Systems Center, San Diego, CA 92152 (U.S.A.) (Received April 23, 1980; revision accepted December 1, 1980) ABSTRACT Zirino, A. and Seligman, P.F., 1981 A note on the polarographic behavior of the Cu(II) ion-selective electrode in seawater. Mar. Chem., 10: 249--255. The non-Nernstian behavior of a solid-state cupric ion-selective electrode in seawater isattributed to a reduction of Cu 2+ at the surface in accordance with a suggestion made in the literature.This 'polarographic' behaviour was demonstrated by showing that the elec- trode potential is affected by molecular oxygen in solution. INTRODUCTION Jasinski et al. (1974) proposed that Cu in seawater may be measurable with a commercial Cu(II) ion-selective electrode (ISE). The CuS-Ag2 S mem- brane system used in this electrode has been shown to respond in seawater to sub-micro-molar additions of Cu 2+ and to changes in Cu 2+ activity resulting from changes in the concentrations of organic and inorganic ligands which have an affinity for Cu 2+, (Jasinksi et al., 1974; Williams and Baldwin, 1976; Rosen and Williams, 1978). Williams and Baldwin (1976) determined the steady-state ISE potentials of several samples after immersion in natural sea- water. They observed that water from a polluted environment generated more positive potential (indicative of higher levels of Cu 2+) than water from open-ocean areas. Similarly, for a deep station occupied off the coast of Southern California, deep samples produced potentials more positive than surface ones. This is in accordance with recent observations which indicate possible biogenic depletion of Cu in oceanic surface waters (Boyle and Ed- mond, 1975). Despite the agreement between recorded potentials and other significant observations, the determination of Cu concentrations and/or activities in seawater with ISE's remains speculative for the following reasons: in C1- media, the electrode response is decidedly non-Nernstian, reaching 40--60mV per decade (Jasinski et al., 1974; Williams and Baldwin, 1976; Oglesby et al., 1977), Hg 2+ and Ag + interfere substantially and the measured potential is dependent upon the rate of flow (or rate of stirring) of the solution past the membrane surface (Jasinski et al., 1974; Rice and Jasin- ski, 1976). 0304-4203/81/0000---0000/$02.50 © 1981 Elsevier Scientific Publishing Company.