Response of the Iron Chalcogenide Glass Membrane Ion‐Selective Electrode in a Seawater Ligand Mimetic Calibration Buffer

Abstract

As a continuation of recent mechanistic studies into the influence of seawater ligands on the surface chemistry of the iron chalcogenide glass membrane ion-selective electrode (ISE), the present study has investigated the response of the iron(III) ISE in a seawater ligand mimetic system to examine its suitability as a calibration medium for the electroanalysis of raw or natural seawater. Significantly, dip method calibrations of the ISE in a mixture of salicylate, ethylene diamine tetraacetic acid (EDTA), ethylene diamine and minor amounts of dissolved iron(III) and copper(II) yielded the expected Nernstian response of 30 mV/decade according to the known ion-exchange/electron transfer response mechanism of this ISE. Furthermore, ideal Nernstian response of the electrode is also obtained in a continuous flow analysis (CFA) mode, noting that this provides scope for using a hydrodynamic flow regime to minimize the electrode release of iron and the concomitant detection limit of the ISE. Ultimately, repetitive CFA analyses of free iron(III) in raw or natural seawater yielded a free iron(III) level commensurate with the expected inorganic and organic speciation of iron(III) in seawater.

Response of a copper(II) and iron(III) ion-selective electrode bielectrode array in saline media

“…The EIS/SR-GIXRD data revealed a destruction of the surface layer of the ISE in organic-free or artificial seawater due to a complete removal of all surface crystalline phases, while raw seawater comprising natural organic ligands and a seawater ligand mimetic system containing en, salicylate, EDTA along with millimolar and sub-millimolar amounts of iron and copper is capable of protecting the iron(III) ISE's surface against this destructive dissolution process. In later research by the authors[34], it was demonstrated that this seawater ligand mimetic was capable of averting the seawater ligand interference on the chalcogenide glass membrane iron(III) ISE allowing reliable determinations of free iron(III) in seawater, and this is the reason for its selection as the calibration buffer in the present study.Table 1lists the equilibria and major species that are implicated in the MINTEQA2 V3.11 calculations of the metal speciation in the calibration buffer system. The MINTEQA2 V3.11 software uses its database of equilibrium constants, K, at zero ionic strength, I, and utilizes a socalled ion association model to correct to K(I) taking account of the variation in activity coefficients, γ, as a function of I, viz.…”

“…A combined copper-iron buffer was prepared using 10 -4 M FeCl 3 , 10 [30,34] is presented in Figure 3.…”