Potentiometric sensors electrode process

By using different membranes, it is possible to obtain potentiometric sensors for gases such as sulfur dioxide or nitrogen dioxide. Such sensors employ similar (acid-base) or other equilibrium processes. These devices, along with their equilibrium processes and internal electrodes, are summarized in Table 6-2. Membrane coverage... 

A. Ivanov, G. Evtugyn, L.V. Lukachova, E.E. Karyakina, HC. Budnikov, S.G. Kiseleva, A.V. Orlov, G.P. Karpacheva, and A.A. Karyakin, Cholinesterase potentiometric sensor based on graphite screen-printed electrode modified with processed polyaniline. IEEE Sensors J. 3, 333-340 (2003). 

The disadvantages described above in terms of the irreversibility of the polyion response stimulated further research efforts in the area of polyion-selective sensors. Recently, a new detection technique was proposed utilizing electrochemically controlled, reversible ion extraction into polymeric membranes in an alternating galvanostatic/potentiostatic mode [51]. The solvent polymeric membrane of this novel class of sensors contained a highly lipophilic electrolyte and, therefore, did not possess ion exchange properties in contrast to potentiometric polyion electrodes. Indeed, the process of ion extraction was here induced electrochemically by applying a constant current pulse. 

Electrode modification by the attachment of various types of biocomponents holds considerable promise as a novel approach for electrochemical (potentiometric, conductometric, and amperometric) biosensors. Potentiometric sensors based on coupled biochemical processes have already demonstrated considerable analytical success [26,27]. More recently, amperometric biosensors have received increasing attention [27,28] partially as a result of advances made in the chemical modification of electrode surfaces. Systems based on... 

Ion selective electrodes (ISEs) or, in a wider sense, potentiometric sensors have demonstrated its usefulness to yield information of chemical species in automated and autonomous operation. This feature has fostered their use in the monitoring of numerous processes, in the industrial, clinical and environmental fields, among others. Current practice with these devices relies on sensors with high selectivity only in this way, a simple determination of a single ion is possible in presence of its interferents. Some reluctances on the broadening of their use are surely due to the fact that ISEs are not specific but show high selectivity towards a reduced number of ions. 

Although the basic principles of type III potentiometric sensors are apphcable for gaseous oxide detection, this should not obscure the fact that these sensors still require further development. This is especially true in view of the kinetics of equilibria and charged species transport across the solid electrolyte/electrode interfaces where auxiliary phases exist. Real life situations have shown that, in practice, gas sensors rarely work under ideal equilibrium conditions. The transient response of a sensor, after a change in the measured gas partial pressure, is in essence a non-equilibrium process at the working electrode. Consequently, although this kind of sensor has been studied for almost 20 years, practical problems still exist and prevent its commercialization. These problems include slow response, lack of sensitivity at low concentrations, and lack of long-term stability. " It has been reported " that the auxiliary phases were the main cause for sensor drift, and that preparation techniques for electrodes with auxiliary phases were very important to sensor performance. ... 

Improvement of the geometric structure of the working electrode by a well-controlled PEVD process benefits the performance of a CO sensor in many ways. To optimize kinetic behavior, the response and recovery times of CO potentiometric sensors were studied at various auxiliary phase coverages. This was realized by a unique experimental arrangement to deposit the Na COj auxiliary phase in-situ at the working electrode of type III potentiometric CO sensors by PEVD in a step-wise fashion. Since the current and flux of solid-state transported material in a series of PEVD processes can be easily moiutoredto control the amount of deposit... 

Typical construction and its output characteristics of ZrO -based sensors are shown in Fig. 2.7. The cell in oxygen sensors is usually shaped like a test tube where the inner and outer surfaces are each coated with ultrathin layers of porous platinum which act as the cathode and anode electrodes. The output of this potentiometric sensor is due to the combined effect of chemical and electrical processes. At high temperatures >650 °C, zirconium dioxide exhibits two mechanisms (Park et al. 2009) (1) ZrO partly dissociates to produce oxygen ions, which can be transported through the material when a voltage is applied and (2) ZrO behaves like a solid eleetrolyte for oxygen. 

Shankenberg et al. [46] in their work on the novel potentiometric sensor for medical devices developed a novel evaporation process for the deposition of an Ag I AgCl I Ag layer combination serving as a thin-film reference electrode. 

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