Solid contact ISEs

In polymer-based ISEs, electrical contact between the membrane and inner reference electrode is made via an inner filling electrolyte. This type of ISE is the most common and they are usually referred to as liquid contact ISEs or very often simply ISEs. On the other hand, the contact can be obtained by the substitution of the aqueous inner solution with another polymeric material, to produce so-called solid-contact ISEs Table 2.1 provides current achievements in trace level... 

Solid-contact ISEs with conducting polymers as ion-to-electron transducers and plasticized PVC-based sensing membranes may be applied... 

Conducting polymers have been studied as potentiometric ion sensors for almost two decades and new sensors are continuously developed. The analytical performance of solid-state ion sensors with conducting polymers as ion-to-electron transducer (solid-contact ISEs) has been significantly improved over the last few years. Of particular interest is the large improvement of the detection limit of such solid-contact ISEs down to the nanomolar level. Further optimization of the solid contacts as well as the ion-selective membranes will most certainly extend the range of practical applications. 

Ionophore-based solvent polymeric membranes are widely used as sensing membranes in ion-selective electrodes (ISEs) [24,25]. This type of potentiometric sensor has attracted great interest in the last decade due to the extraordinary improvement in the detection limit down to picomolar (10-12 M) levels [26,27], Furthermore, solid-contact ISEs have been developed by using various conducting polymers, including PEDOT, as the ion-to-electron transducer [28-31],... 

Infrared synchrotron micro-spectroscopy is also an appropriate method for identifying and visualizing the existence of localized water at buried interfaces, particularly between multilayers of polymers. It was recently shown that water inclusions can be imaged at the buried interface of solid-contact-ion-selective electrodes (SC-ISEs) [22]. In this study a poly(methyl metha-crylate)-poly(decyl methacyrlate) [PMMA-PDMA] copolymer was used. Since the PMMA-PDMA copolymer is known to be water repellent and unsuitable for water sorption at measurable levels in the bulk membrane, the detection (or non-detection) of water by reflectance SR-FTIR is symbolic of the presence (or absence) of localized zones of water at the buried interface of a solid-contact ISE employing PMMA-PDMA as the sensing membrane. In fact, SR-FTIR revealed the presence of micrometer-sized inclusions of water at the gold-to-membrane interface, whereas coupling a hydrophobic solid contact of poly(3-octylthiophene 2,5-diyl) (POT) prevented the accumulation of water at the buried interface (Fig. 2) [22]. 

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