Werner E MORF

On the basis of previously reported correlations between the lipophilicity of membrane components, their partition coefficient between the membrane and the sample, and the lifetime of corresponding neutral-carrier-based sensors, the lipophilicities of ionophores and plasticizers in analytically relevant ion-selective electrodes, ISFETs, and optodes are analyzed and reported. Equations for the estimation of the lifetimes of liquid membranes in continuous-flow systems are presented, and ...

A unified and comparative treatment of traditional potentiometric and amperometric enzyme electrodes and of enzyme reactors is presented. Exact theoretical descriptions are given for limiting cases, and relatively simple approaches for general cases. The latter approximations are obtained from the respective solutions for a two-segmented membrane model. They allow an explicit description and a full characterization of the response curves by only two kinetic parameters, which are the ...

The fabrication and characterization of a combined pO2, pCO2 and pH chemical sensor, designed for blood-gas monitoring, are discussed. Classical electrochemical principles are used in a miniaturized planar-type structure. Both amperometric (pO2) and potentiometric devices (pCO2 pH) are integrated on a 10 mm × 10 mm chip. The transducer part of the chip is realized using standard silicon technology. Polyacrylamide and polysiloxane layers, which are used as hydrogel and gas-permeable ...

The time-dependent behavior of sensor systems based on enzyme membranes is treated theoretically. The comparative treatment covers traditional potentiometric and amperometric enzyme electrodes as well as enzyme reactors. Theoretical solutions are derived by the method of Laplace transforms. The relationships refer to the analytically useful range of relatively low substrate concentrations where the response signal is a function of the sample concentration. Numerical simulations using ...

New mercury organic compounds with 1–3 metal centers and different substituants were synthesized as anion-selective ionophores. They were incorporated into solvent polymeric membranes, and the selectivity, slope of response, response time, emf repeatability, and the signal stability of the corresponding ion-selective electrodes (ISEs) were studied. Ortho-dimercury aromatic compounds were found to induce an adequate chloride-selectivity for physiological measurements. The anion ...

A theoretical approach to the steady-state limiting current response behavior of multiple microelectrode arrays, consisting of spherical, hemispherical, disk-shaped, or hemicylindrical electrode units, is presented. An approximative treatment is given for realistic arrays that contain microelectrodes of finite size and a rigorous description is offered for hypothetical arrays of point or line electrodes. The theories account for convection influences in the sample solution by restricting ...

A novel electrochemiluminescence (ECL) detector is presented in this article. The detector is applied for micellar electrokinetic chromatographic separation of dichlorotris(2,2'-bipyridyl)ruthenium(II) hydrate [Ru-(bpy)] and dichlorotris(1,10-phenanthroline)ruthenium-(II) hydrate [Ru(phen)] on a microfabricated glass device. It consists of a microfabricated "U"-shape floating platinum electrode placed across the separation channel. The legs of the U function respectively as working and ...

The sum of the concentrations of calcium and magnesium in water samples can be determined directly with a neutral carrier-based Mg2+/Ca2+-selective electrode (divalent ion-selective electrode), without addition of any auxiliary complexing agent such as acetylacetone. This approach works well, even in situations where calcium-selective electrodes do not detect the second inflection point because the calcium/magnesium concentration ratio is too high ([Ca2+]:[Mg2+] ⪢5:1) or the sodium ...

Based on A theoretical treatment of neutral carrier liquid-membrane electrodes, propositions are derived to reduce the interference of the cation response by lipid-soluble anions in the sample solution. The performance of such electrodes is shown to be improved by incorporating lipophilic anions, such as tetraphenylborate, into the membrane. There is A quantitative agreement between the theoretical predictions and the results thus obtained for carrier based calcium- and ...

Selectivities were measured for membrane electrodes containing a given amount of a neutral carrier (ETH 1692) and varying amounts of the additive potassium tetrakis(p-chlorophenyl)borate. The pronounced selectivity changes induced by the additive agreed with a theoretical model. Both theory and experiment confirmed that an optimum composition of the membrane exists. Ideally, sensors for monovalent cations should contain only small amounts of the additive, whereas sensors for divalent ...

A new micro total analysis system (μTAS) designed for volumetric nanotitrations, integrating two electroosmotically driven nanopumps and a sensor unit, is presented. The unique feature of the integrated electroosmotic pumps is their ability to pump widely different solutions, independent of intrinsic characteristics such as pH or ionic strength, with the exception of viscosity. Typical flow rates achieved are in the range of 2–65nl/s, depending on the number of microchannels connected in ...

A thin aqueous layer is formed between the polymeric ion-selective membrane and an inner gold electrode. Its composition can be altered upon sample changes, which leads to drifting potentials. It is shown by theory and experiment that interfering ions enter the inner layer much faster than primary ones. Measurement protocols with equal contact times for the sample and the reconditioning solution can therefore not eliminate the effect of changes in the composition of the inner solution. ...

Zero-current ion transport through polymeric membranes of ion-selective electrodes (ISEs) alters the composition of the inner solution of these sensors. This causes long-term drifts of the electromotive force that are relevant for miniaturized ISEs as well as for most solid-contacted ISEs in which a thin aqueous layer is formed between the membrane and the metal electrode during conditioning. By a similar mechanism, the composition of the sample can be significantly altered during the ...

Results of voltammetric, potentiometric, chronoamperometric, ion transport, and extraction studies on neutral carrier based, plasticized poly(vinyl chloride) membranes are summarized. They unambiguously confirm that such bulk membranes dispose of immobile anionic sites. These fixed sites lead to a Donnan exclusion of other anions from the membrane and thus to a permselectivity for cations. The results are in perfect agreement with the predictions of earlier membrane models. A rigorous ...