Surface studies of a chalcogenide glass ferric ion‐selective electrode Part 2: The effects of inorganic ions, organic ligands and seawater on sensor response

Abstract

AbstractX‐ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and electrochemical impedance spectroscopy (EIS) have been used to investigate the effect of inorganic ions, organic ligands and seawater on the response of the FeIII ion‐selective electrode (ISE). X‐ray photoelectron spectroscopy has shown that the formation of antimony(V) oxide/hydroxide on the chalcogenide glass membrane soaked in seawater is dictated by electrode kinetics. It has been found that selenide atoms in the chalcogenide glass are replaced by oxygen in the presence of seawater. Furthermore, EIS aging studies demonstrated that the chalcogenide glass membrane experiences a sluggish charge transfer reaction in seawater. By contrast, SIMS imaging and depth profiling on various regions of a seawater‐exposed membrane identified a phase comprising iron oxide–hydroxide–carbonate–carboxylate. Furthermore, SIMS revealed a uniform chemisorption of oxygen on the membrane surface, and adsorption does not appear to be related to specific coordination sites. X‐ray photoelectron spectroscopy failed to detect any chloride chemisorption on the membrane surface, whereas in situ EIS showed that chloride along with hydroxide ions facilitate the charge transfer process of the FeIII ISE. Moreover, the effect of humic acid on the FeIII ISE was studied using EIS. The results of this XPS, SIMS and EIS study have enabled the derivation of a response mechanism for the FeIII ISE in seawater. Copyright © 2002 John Wiley & Sons, Ltd.