Applications of voltammetric ion selective electrodes to complex matrices

Abstract

The practical application of two different voltammetric ion selective electrodes (VISE) to measure ion activity in complex solutions has been explored. 7,7,8, and tetrathiafulvalene (TTF) microcrystals adhered to an electrode surface act as a low selectivity voltammetric ion sensor. Resistance drop effects and pH artifacts were minimised by the addition of an "innocent" supporting electrolyte (buffer) to the analyte solution. In this format, addition of an ionophore to improve selectivity resulted in a reduction in current magnitude, due to competition for the ion. In contrast, voltammetry of a thin film containing a redox active species, electrolyte, ionophore and membrane solvent provides a highly selective ion sensor. Choice of ionophore was shown to affect the upper concentration detection limit. Use of ionic liquids as a combined membrane solvent and electrolyte was demonstrated. Methods to attach both VISE types to low-cost screen-printed electrodes have been explored. Various potential referencing techniques were also investigated. Both the microcrystal and thin film VISEs could be used to determine ion activity in complex solutions, as demonstrated in seawater, beverages, plasma and whole blood. Dissolved oxygen does not need to be removed, as it does not affect the response. However calibration methods are important for sensor accuracy and issues relating to electrode fouling must be addressed. The practical application of two different voltammetric ion selective electrodes (VISE) to measure ion activity in complex solutions has been explored. 7,7,8, and tetrathiafulvalene (TTF) microcrystals adhered to an electrode surface act as a low selectivity voltammetric ion sensor. Resistance drop effects and pH artifacts were minimised by the addition of an "innocent" supporting electrolyte (buffer) to the analyte solution. In this format, addition of an ionophore to improve selectivity resulted in a reduction in current magnitude, due to competition for the ion. In contrast, voltammetry of a thin film containing a redox active species, electrolyte, ionophoreand membrane solvent provides a highly selective ion sensor. Choice of ionophore was shown to affect the upper concentration detection limit. Use of ionic liquids as a combined membrane solvent and electrolyte was demonstrated. Methods to attach both VISE types to low-cost screen-printed electrodes have been explored. Various potential referencing techniques were also investigated. Both the microcrystal and thin film VISEs could be used to determine ion activity in complex solutions, as demonstrated in seawater, beverages, plasma and whole blood. Dissolved oxygen does not need to be removed, as it does not affect the response. However calibration methods are important for sensor accuracy and issues relating to electrode fouling must be addressed.

Optical and Electrochemical Methods for Determining the Effective Area and Charge Density of Conducting Polymer Modified Electrodes for Neural Stimulation

“…In this case, a simple phosphate buffer was chosen, but an argument could be made to use a more complex testing solution 27,28 . In particular, placement of the electrode into the body results in rapid fouling by proteins, which affect the charge measured from cyclic voltammetry 20 .…”

Improved Nitrate Sensing Using Solid Contact Ion Selective Electrodes Based on TTF and Its Radical Salt

“…Figure 2 shows exemplary cyclic voltammograms obtained at a scan rate of 0.1 Vs −1 over the potential range of +0.40 V and −0.30 V with the GCD/TTF electrode when placed in 0.1 M KNO 3 solution. According to, 31 TTF is oxidized to the TTF + and NO 3 − anions are incorporated into the crystal lattice.…”

Voltammetric Characterization of Ion–Ionophore Complexation Using Thin Polymeric Membranes: Asymmetric Thin-Layer Responses

“…Noticeably, no effect of the complexation stoichiometry was considered in recent voltammetric studies with thin ionophore-doped polymeric membranes. 26,27 Experimentally, we demonstrate a novel application of voltammetric ion-selective electrodes based on double polymeric membranes 28 to characterize the complexation of three cation-selective ionophores (Figure 1). With this electrode setup, a ∼1.6 μm thick plasticized poly(vinyl chloride) (PVC) membrane is doped with an ionophore and spin-coated onto a gold electrode modified with decyl-substituted poly(3,4-(ethylenedioxy)thiophene) (PEDOT-C 10 ) as an efficient voltammetric cation-to-electron transducer.…”