Interpretation of chronopotentiometric transients of ion-selective membranes with two transition times

Abstract

Passing currents through ion-selective membranes has contributed to the development of a variety of novel methods. In this work, chronopotentiometric (CP) transients with two transition times (breakpoints) are presented for the first time, with the theoretical interpretation of such voltage transients. The validity of our theory has been confirmed in experiments utilizing ETH 5294 chromoionophore-based pH sensitive membranes with and without lipophilic background electrolyte and ETH 5234 ionophore-based calcium selective membranes in which the ionophore forms 3:1 complexes with Ca 2+ ions. The conditions under which two breakpoints can be identified in the chronopotentiometric voltage transients are discussed.Spectroelectrochemical microscopy (SpECM) is used to show that the two breakpoints in the CP curves emerge approximately when the free ionophore and ion-ionophore complex concentrations approach zero at the opposite membrane-solution interfaces. The two breakpoint times can be utilized to follow simultaneously the concentration changes of the free ionophore, the ion-ionophore complex, and the mobile anionic sites in cation-selective membranes. In membranes with known composition, the time instances where breakpoints occur can be used to estimate the free ionophore and the ion-ionophore complex diffusion coefficients.

Treatment of a cyanide-free copper electroplating solution by electrodialysis: study of ion transport and evaluation of water and inputs recovery

“…This behavior may be attributed to the transport of anions with different size, molar concentrations, mobility or diffusion coefficients in the membrane matrix. A similar characteristic was observed by Zook et al (135). The authors studied the ion transport through a Ca 2+ selective membrane in contact with a solution containing an ionophore and calcium cations.…”

Chronopotentiometric study of the transport of phosphoric acid anions through an anion-exchange membrane under different pH values

“…The occurrence of several transition times in the chronopotentiograms of multicomponent solutions has also been observed by several authors. In this way, Zook et al [45], who evaluated the transport through a calcium-selective membrane submerged in a solution containing ionophore and calcium cations, found two inflection points in the chonopotentiometric curves: the first one attributed to the transport of free ionophore, and the second one assigned to the ion-ionophore complex transfer. Both inflexion points were completely separated, as a result of the difference in ion mobility and diffusion coefficient.…”

Evaluation of the transport properties of copper ions through a heterogeneous ion-exchange membrane in etidronic acid solutions by chronopotentiometry

“…[36]. The authors studied the ion transport through a Ca 2+ selective membrane in contact with a solution containing an ionophore and calcium cations.…”

“…The authors studied the ion transport through a Ca 2+ selective membrane in contact with a solution containing an ionophore and calcium cations. According to the authors, the first inflexion point was assigned to the transport of free ionophore, the second inflexion point was attributed to ion-ionophore complex transfer and both inflexion points were clearly separated from each other, indicating a difference in ion mobility and diffusion coefficient [36]. Pismenskaya et al [37] reported that pH changes on a membrane surface due to the preferential transport of hydroxyl ions may also modify the transport properties of weak electrolyte anions, depending on the membrane selectivity for each charged species.…”