Fredrik Sundfors

Kinetics of electron transfer between Fe(CN)63−/4− and poly(3,4-ethylenedioxythiophene) studied by electrochemical impedance spectroscopy

The electron transfer between the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and the Fe(CN)63−/4− redox couple in aqueous solution was investigated by electrochemical impedance spectroscopy (EIS). PEDOT was electrochemically deposited on platinum from aqueous solutions containing 0.01 M 3,4-ethylenedioxythiophene (EDOT) and 0.1 M poly(sodium 4-styrenesulfonate) (NaPSS) as supporting electrolyte. Pt/PEDOT(PSS) electrodes with polymer films of different thickness were investigated at different concentrations of the redox couple in 0.1 M KCl background electrolyte solution. Impedance spectra were obtained at the dc-potential corresponding to the formal redox potential of Fe(CN)63−/4− (E°′≈220 mV) where the polymer is in the oxidized and electrically conducting state. The EIS data for the electrodes were fitted to an equivalent electrical circuit. The standard rate constant (ko) for electron-transfer between Pt/PEDOT(PSS) and Fe(CN)63−/4− was determined by calculations based on the Butler–Volmer equation. The diffusion coefficient (D) of the redox couple was also calculated from the EIS data.

Polyaniline nanoparticle-based solid-contact silicone rubber ion-selective electrodes for ultratrace measurements.

Silicone rubber (SR)-based solid-contact ion-selective electrodes (ISEs) have been prepared for the first time with an electrically conducting polymer as the solid-contact (SC) layer. The Ca(2+)- and Ag(+)-selective electrodes were based on the ionophores ETH 1001 and o-xylylenebis(N,N-diisobutyl dithiocarbamate), respectively, integrated in room temperature vulcanizing silicone rubber (RTV 3140). The SC consisted of a polyaniline nanoparticle dispersion, which was found to considerably lower the impedance of the SCISEs in comparison to the SR-based coated wire electrodes (CWE). For the CaSCISEs, the bulk membrane resistance decreased from 700 MΩ (CaCWE) to 35 MΩ. Both the Ca(2+)- and Ag(+)-selective SCISEs exhibited nanomolar detection limits with fast Nernstian responses down to 10(-8) M. The potential response of the SCISEs was not influenced by light. The selectivities of the CaSCISEs were similar and for the AgSCISE better than their plasticized PVC-based analogues. Thus, SR seems to be a viable alternative to PVC membranes in ISE applications that require low water uptake, good adhesion, and robust and fast potential responses at submicromolar sample concentrations.

FTIR-ATR Study of Water Uptake and Diffusion through Ion-Selective Membranes Based on Poly(acrylates) and Silicone Rubber

For the first time, FTIR-ATR spectroscopy was used to study the water uptake and its diffusion in ion-selective membranes (ISMs) based on poly(acrylates) (PAs) and silicone rubber (SR), which are emerging materials for the fabrication of ISMs for ultratrace analysis. Three different types of PA membranes were studied, consisting of copolymers of methyl methacrylate with n-butyl acrylate, decyl methacrylate, or isodecyl acrylate. Numerical simulations with the finite difference method showed that in most cases the water uptake of the PA and SR membranes could be described with a model consisting of two diffusion coefficients. The diffusion coefficients of the PA membranes were approximately 1 order of magnitude lower than those of plasticized poly(vinyl chloride) (PVC)-based ISMs and only slightly influenced by the membrane matrix composition. However, the simulations indicated that during longer contact times, the water uptake of PA membranes was considerably higher than that for plasticized PVC membranes. Although the diffusion coefficients of the SR and plasticized PVC membranes were similar, the SR membranes had the lowest water uptake of all membranes. This can be beneficial in preventing the formation of detrimental water layers in all-solid-state ion-selective electrodes. With FTIR-ATR, one can monitor the accumulation of different forms of water, i.e., monomeric, dimeric, clustered, and bulk water.

Procedure 4 Determination of Ca(II) in wood pulp using a calcium-selective electrode with poly(3,4-ethylenedioxythiophene) as ion-to-electron transducer

Publisher Summary This chapter presents a procedure to construct a solid-state Ca-ion selective electrodes (ISE) for the analysis of calcium in wood pulp. The stability of the solid-state Ca(II)-ISE was evaluated by immersing the electrode continuously in pulp filtrate for 9 days. The electrode was removed from the pulp filtrate only to make a three-point calibration once per day. The slope was found to be stable (27±1 mV/decade) for the whole duration of the test (9 days), and the drift of the standard potential was ca. 1 mV/day. The concentration (activity) of free Ca(II) of pulp samples determined by Ca(II)-ISEs may be significantly lower than the total Ca(II) concentration because of the complexation of Ca(II) by different components in pulp samples. This should be kept in mind when comparing results obtained by the Ca(II)-ISE with other methods, such as ICP-AES.