Development of an improved ligand mimetic calibration system for the analysis of iron(Ⅲ) in seawater using the iron(Ⅲ) chalcogenide glass ion selective electrode: A combined mechanistic and analytical study

摘要

Further to previous work on a seawater ligand mimetic calibration system for the electroanalysis of iron(Ⅲ) in seawater using the iron chalcogenide glass ion-selective electrode (ISE), this study utilized alternative blends of synthetic ligands, in order to fine-tune and optimize the calibration response characteristics of this sensor for the electroanalysis of free iron(Ⅲ) in seawater. Herein, an alternative calibration system (ACS) was derived using a mixture of 10~(-4)M iron(Ⅲ) chloride, 10~(-4)M ethylenedi-aminetetraacetic acid (EDTA), 10~(-3) M copper(Ⅱ) sulphate, 5 × 10~(-3) M ethylenediamine (EN) and 0.60M sodium chloride yielding a Nernstian response of about 30 mV decade~(-1). The electroanalysis of free iron(Ⅲ) in seawater using the ACS generated a free iron(Ⅲ) level commensurate with the predicted organic and inorganic speciation of iron(Ⅲ) in seawater. Furthermore, electrochemical impedance spec-troscopy (EIS), synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy have demonstrated that the surface reaction processes of this membrane in the ACS are comparable to those experienced in a natural seawater matrix. Ultimately, this study demonstrated that the ACS can mimic the surface chemistry and concomitant potentiomet-ric response characteristics of the iron(Ⅲ) sensor in seawater, enabling reliable electroanalyses of free iron(Ⅲ) in seawater.