Amperometric sensors coated-membrane

Amperometric sensors as well as most electrocatalytic and battery electrodes operate under diffusion-controlled conditions, and thus their response depends on the flux of electroactive solutes (or their transformation products) to the conductive electrode surface, be it a film-coated electrode or the three-dimensional conductive network of porous electrodes. In order to examine the qualitative factors that influence the flux to such electrodes, it is valuable to examine a simple conceptual model. We examine here the diffusion-limited current to a test case planar electrode of area. A, coated by a thin flhn of thickness, d. Diffusion-limited conditions frequently accompany a high overpotential operation such that the concentration of the key analyte is negligible at the surface of the electrode. Under these conditions, the concentration drop across the membrane determines the faradaic current ... 

This applies to another possible way of non-electrolytic accumuladcm, based on spontaneous transfer and distribution of a species between two liquid phases, typically from an aqueous solution into a non-polar medium, when the role of exchanged species can be attributed to neutral molecules or ion associates with compensated charge. This is accompUshed with the liquid binder in carlxMi paste mixtures or by liquid membranes coating the tips of potentiometric or amperometric sensors. In both cases, extraction (Eq. 5.12a) and the reverse process, re-extraction, take place in the electrode bulk ( ELB ) before the release from the interior to the aqueous phase ( AQ ) and the final disintegration during detection (Eq. 5.12b) ... 

Wang, R., Okajima, T., Kitamura, R, and Ohsaka, T., A novel amperometric O2 gas sensor based on supported room-temperature ionic liquid porous polyethylene membrane-coated electrodes, Electroanalysis, 16, 66-72, 2004. 

Efforts to produce a phosphate-selective ISE have been hindered by its diverse spe-ciation and lability in biological samples a recent review describes various potentiometric and amperometric approaches to this problem [22]. Of the potentiometric approaches, selectivity is most often achieved using inorganic or organometal-lic extracting agents such as organotin compounds in liquid-membrane ISEs, cobalt complexes or metallic cobalt in coated-wire and metallic electrodes, respectively. Nickel phosphate, silver phosphate, and mixtures of lead precipitates have also been used in phosphate ISEs. All of these sensors suffer from limited selectivity. Enzyme-based sensors for phosphate have also been a topic of research as yet, however, no commercial phosphate sensor exists [22]. 

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