Capacitive Model for Coulometric Readout of Ion-Selective Electrodes

We present here a capacitive model for the coulometric signal transduction readout of solid-contact ion-selective membrane electrodes (SC-ISE) with a conducting polymer (CP) as an intermediate layer for the detection of anions. The capacitive model correlates well with experimental data obtained for chloride-selective SC-ISEs utilizing poly­(3,4-ethylenedioxythiophene) (PEDOT) doped with chloride as the ion-to-electron transducer. Additionally, Prussian blue is used as a simple sodium capacitor to further demonstrate the role of the transduction layer. The influence of different thicknesses of PEDOT as a conducting polymer transducer, different thicknesses of the overlaying ion-selective membranes deposited by drop casting and spin coating, and different compositions of the chloride-selective membrane are explored. The responses are evaluated in terms of current–time, charge–time, and charge–chloride activity relationships. The utility of the sensor with coulometric readout is illustrated by the monitoring of very small concentration changes in solution

Solid-Contact Ion-Selective Electrodes with Highly Selective Thioamide Derivatives of <i>p</i>-<i>tert</i>-Butylcalix[4]arene for the Determination of Lead(II) in Environmental Samples

Thioamide derivatives of <i>p</i>-<i>tert</i>-butylcalix­[4]­arene were used as ionophores in the development of solid-contact ion-selective electrodes based on conducting polymer poly­(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT/PSS) which was synthesized by electrodeposition on the glassy carbon electrodes. The typical ion-selective membranes with optionally two different plasticizers [bis­(2-ethylhexyl)­sebacate (DOS) and 2-nitrophenyl octyl ether (NPOE)] were investigated. The potentiometric selectivity coefficients were determined by separate solution method (SSM) for Pb²⁺ over Cu²⁺, Cd²⁺, Ca²⁺, Na⁺, and K⁺. High selectivity toward Pb²⁺ was obtained. By applying two conditioning protocols, a low detection limit log­(<i>a</i>_DL) ≈ −9 was achieved. The fabricated ion-selective electrodes were used to determine Pb²⁺ concentration in environmental samples. The obtained results were compared to analysis done by inductively coupled plasma mass spectrometry (ICPMS)

Reduced Graphene Oxide Films as Solid Transducers in Potentiometric All-Solid-State Ion-Selective Electrodes

The development of ion-selective electrodes (ISEs) using solid-state transducer materials is of great interest for advanced potentiometric detection systems. At present, conducting polymers are the most used solid-state transducing materials. However, their reliability is strongly related to their chemical stability and the formation of internal water films. Here we report on the use of reduced graphene oxide (RGO) films of different thicknesses as transducer materials in potentiometric all-solid-state ISEs. First, the transduction mechanism is fully analyzed, revealing that RGO films act as asymmetric capacitors where their electron density is in contact with ions of the electrolyte solution, creating a capacitance due to the constant phase elements present in the system. Second, as a proof of concept, RGO films are used in a calcium ISE showing highly reproducible sensing responses and outstanding increased signal-to-noise ratios with drifts of only 10 μV/h. These performance parameters are among the best compared to those of other ISE transducer materials so far. With its ease of fabrication and processing into reproducible films of controlled thickness and ease for further tailoring chemical composition and tailoring electrical properties, RGO offers great promise as a reliable high-performance transducer material for solid-state ISE sensors