We have characterized iron chalcogenide glass ion‐selective electrode (ISE) membranes sourced from several different laboratories (viz., two prepared by Nanolytical in the present study, one sourced from Curtin University from two decades ago, and another sourced from the Chemical Sensors Group at St Petersburg University, Russia) using synchrotron radiation X‐ray photoelectron spectroscopy (SR XPS), near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy and field emission scanning electron microscopy (FESEM). It has been found that the surface speciation and surface composition of membranes are comparable to previously characterized ones within the bounds of experimental uncertainty, confirming the uniformity and integrity of ISE membranes prepared using a similar method. The FESEM morphology of membranes revealed the nanoscale porosity of a 10 nm thick modified surface layer (MSL) on the iron chalcogenide glass ISE, with Fe L3 edge NEXAFS depth profiling of membranes exposed to very low levels of Fe 3+ in buffered media, as well as higher concentrations in unbuffered solutions, revealing that ion‐exchange occurs over the entirety of the ISE membrane MSL. Furthermore, in accordance with observations of an “Fe suctioning” effect in unbuffered and buffered Fe standards at low levels of Fe 3+ , we revealed declines in Fe L3 edge NEXAFS signals in the depth profiles of Fe‐treated membranes compared to a polished ISE membrane. Accordingly, similarly prepared ISE membranes can provide repeatable and internally consistent membrane characteristics.
Marco et al. (Fri,) studied this question.