Coated-wire electrodes development

Selig reported a potentiometric titration method for the analysis of procaine and some other organic cations precipitated by tetraphenylborate [67]. The development of ion selective coated-wire electrodes, and their application in the titration of procaine and other pharmaceutically important substances, was reported [68]. 

Symmetrical placement of the ion-selective membrane is typical for the conventional ISE. It helped us to define the operating principles of these sensors and most important, to highlight the importance of the interfaces. Although such electrodes are fundamentally sound and proven to be useful in practice, the future belongs to the miniaturized ion sensors. The reason for this is basic there is neither surface area nor size restriction implied in the Nernst or in the Nikolskij-Eisenman equations. Moreover, multivariate analysis (Chapter 10) enhances the information content in chemical sensing. It is predicated by the miniaturization of individual sensors. The miniaturization has led to the development of potentiometric sensors with solid internal contact. They include Coated Wire Electrodes (CWE), hybrid ion sensors, and ion-sensitive field-effect transistors. The internal contact can be a conductor, semiconductor, or even an insulator. The price to be paid for the convenience of these sensors is in the more restrictive design parameters. These must be followed in order to obtain sensors with performance comparable to the conventional symmetrical ion-selective electrodes. 

In our laboratory, these disadvantages have been overcome with the development of the coated wire electrode (CWE). This sensor, having response characteristics equal to and occasionally better than conventional types, is only 1-2 mm in diameter (further size reduction can be easily achieved), can be used at any angle, and costs only a few pennies to make. Indeed, they can be considered "disposable", though with proper handling lifetimes of over six... 

The integration of chemically sensitive membranes with solid-state electronics has led to the evolution of miniaturized, mass-produced potentiometric probes known as ion-selective field effect transistors (ISFETs). The development of ISFETs is considered as a logical extension of coated-wire electrodes (described in Section 5.2.4). The construction of ISFETs is based on the tech-... 

The multiple coated wire type catheters developed at General Electric have also been evaluated in vivo. For example, the pH-sensing device was implanted in the femoral artery of beagle dogs for up to 6 hours (L3). Over that time span, the pH of the blood as measured by the in vivo coated wire electrode was nearly identical to that measured in vitro with conventional glass electrode instrumentation. In addition, the same catheter also has been used percutaneously to measure the muscle pH of dogs in shock (K14). The... 

PPy is known to exhibit anionic or cationic potentiometric responses depending on the doping ion. PPy films doped with mobile inorganic anions show anionic sensitivity, while PPy films doped with anions of low mobility such as sulfate, large organic anions, or polyanions show cationic sensitivity. This bifunctionality of ionic and redox sensitivity makes PPy apphcable as an all-sohd-state, ion-selective electrode. All-solid-state, potentiometric PPy sensors were developed for potassium and sodium sensing, which showed better response time, selectivity and most importantly long-term stabihty than the coated wire electrode [130]. 

The general trend to miniaturize chemical sensors and to make them cheap and easier for handling has led to the development of potentiometric sensors with solid internal contact. This class of sensors includes different types of solid-state electrodes, solid-state contact, and coated wire electrodes as well as ion-selective field-effect transistors (FETs). 

Ba " ", Cs, NH4", Ag" ") and anions (NOi j Cl , HCOi ). Solid-state ISEs (coated wire electrodes) have also been developed in which the sensitive membrane is coated directly onto a metal wire, usually a silver-silver halide. While these have the advantage of being small and easy to fabricate, they have been noted for their unpredictable properties and suffer from lifetime and stability problems. More sophisticated approaches involve the use of semiconductor planar fabrication technologies to deposit ion-sensitive layers onto semiconductor substrates to produce ion-selective field-effect transistors. These are conceptually very attractive but it has proven very difficult to produce devices as good as the equivalent ISE. 

Coated wire electrodes, CWE Coated-wire ion-selective electrodes, CWISE (CWE), have been developed to overcome some of the disadvantages of i.s.e.s, namely their large size, the need for an upright position in some types, and their high cost. 

The increased interest in using ISEs has led to the development of new sensor materials that show high selectivity for a variety of anions and cations and new approaches for electrode constraction. Several attempts have been made to eliminate the internal reference electrode resulting in a solid-state sensor design. Examples of these types of sensors include coated wire electrodes, graphite rods, graphite-based electrodes, and ion-selective field-effect transistors (ISFETs). 

Cottrell was the first who used a PVC-coated wire electrode for the determination of low concentrations of surfactants. Extensive articles and excellent overviews on CWEs for the determination of surfactants were published by Vytras s group, who were very active in developing simple coated wire electrodes for cationic and ampholytic surfactants especially during the... 

Coated wire ion selective electrodes were first developed in 1971, and comprise a film of PVC or other suitable polymeric matrix substrate containing a dissolved electro-active species, coated on a conducting substrate (generally a metal, although any material whose conductivity is substantially higher than that of the film can be used.) Electrodes of this sort are simple, inexpensive, durable and capable of... 

The development of the reductive mode LCEC technique has been slow because of difficulties in preparing convenient and reliable working electrodes for use with a high efficiency chromatographic separation. In addition, problems are encountered with dissolved oxygen and heavy metals. Solid electrodes have been used with limited success for reductive LCEC. Mercury pool electrodes (44-47), the DME (48-53), and platinum wire electrodes coated with mercury (49) are generally not satis-... 

Glass electrode An electrode consisting of an AgCl-coated silver wire in contact with an HCl solution of known standard concentration (usually 1.00 M) in a thin-walled glass bulb when immersed in a solution, this electrode develops a potential that is sensitive to the relative [H ] concentrations (and hence to pH differences) of the internal standard solution and the outside solution. 

One of the first portable instruments for CE coupled to ECD was developed in 1998 by Kappes and Hauser [185]. The instrument included a 30-W HVPS module capable of providing 30 kV DC, a signal amplifier and an ADC. Potentiometric detection was carried out using a coated-wire-ion-selective electrode. The system was powered by two 12 V lead-acid batteries and was contained in a PVC case 340 x 175 x 175 mm (Ixwxh) size with a total... 

Janmngroatsakul, W, C. Lertvachirapaiboon, W. Ngeontae, W. Aeungmaitrepirom, O. ChailapakuL S. Ekgasit, and T. Tuntulani. 2013. Development of coated-wire silver ion selective electrodes on paper using conductive films of silver nanoparticles. Analyst 138 6786-6792. 

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