Coulometric response characteristics of solid contact ion-selective electrodes for divalent cations
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ORIGINAL PAPER
Coulometric response characteristics of solid contact ion-selective electrodes for divalent cations Tingting Han 1 & Zekra Mousavi 1
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Ulriika Mattinen 1
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Johan Bobacka 1
Received: 23 April 2020 / Revised: 6 June 2020 / Accepted: 7 June 2020 # The Author(s) 2020
Abstract The chronoamperometric and coulometric response of solid contact ion-selective electrodes (SCISEs) for the detection of divalent cations was investigated in order to provide a more complete description of the mechanism of the recently introduced coulometric transduction method for SCISEs. The coulometric transduction method has earlier been employed only for SCISEs that were selective to monovalent ions. The SCISEs utilized poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrene sulfonate) (PSS−) as the solid contact (ion-to-electron transducer). PEDOT(PSS) was electrodeposited on glassy carbon and covered with plasticized PVC-based ion-selective membranes (ISMs) that were selective towards divalent cations (Ca2+, Pb2+). In contrast to earlier studies, the results obtained in this work show that the coulometric response for the Pb2+-SCISE was limited mainly by ion transport in the PEDOT(PSS) layer, which was not the case for the Ca2+-SCISE, nor was it observed earlier for the monovalent ions. The exceptional behavior of the Pb2+-SCISE was explored further by electrochemical impedance spectroscopy, and it was shown that the effective redox capacitance of PEDOT(PSS) was significantly higher for the Pb2+-SCISE than for the Ca2+-SCISE although the polymerization charge of PEDOT(PSS) was the same. The slow transport of Pb2+ in PEDOT(PSS) was tentatively related to complexation between Pb2+ and PEDOT(PSS). Keywords Solid contact ISE . Divalent cations . Coulometric transduction . Charge transfer . Impedance
Introduction Ion-selective electrodes (ISEs) are important analytical tools that are widely used in many fields related to our daily life, such as clinical diagnostics, environmental monitoring, agriculture, and food industry [1–5]. Thus, there is a great demand for durable, easy-to-use, and less-frequently calibrated ISEs. Over the years, the performance of ISEs has been significantly improved. The detection limit of polymeric membrane-based ISEs was lowered to ca. 10−11 M by adjusting the internal filling solution in the traditional design [6]. The so-called solid contact ion-selective electrodes (SCISEs) were developed in order to overcome limitations of the internal filling solution, i.e., to obtain more durable sensors that are easy to manufacture, can be miniaturized, and Wishing Professor Fritz Scholz a happy 65th birthday! * Johan Bobacka [email protected] 1
Johan Gadolin Process Chemistry Centre, Laboratory of Molecular Science and Engineering, Åbo Akademi University, Biskopsgatan 8, FI-20500 Åbo, Finland
require little maintenance. Among various solid contact materials in SCISEs, conducting polymers proved to be useful as their mixed ion-electron conductivity and high redox (pseudo) capacitance improved
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