Electrodes Based on Conductive Polymers SC-ISEs

Solid-contact ion-selective electrodes (SC-ISEs) are produced through direct application of a conductive polymer on an electron conductor (redox electrode) through electropolymerization, and then application of a thin film, typically a polymer (PVC) ion-selective membrane. 

The conductive polymer layer contains doping ions, which activity determines the drop in the potential at the membrane/polymer interface. If, during measurement, there is no change in the oxidation state of the polymer and in the concentration of the ion doping the polymer, the drops in the potential at the membrane/polymer and polymer/metal interfaces will also be constant. Any changes in the potential of such sensor will be determined by changes in the activity of ions in the analyzed solution, which also determine the potential at the solution/membrane interface (similar to conventional sensors) [53]. 

The selectivity of such electrode is determined only by the outer PVC membrane. Obtaining such electrodes, which lack the inner electrolyte, allows using the sensor in various positions, without the risk of the inner solution leaking out, and eliminates the need for frequent maintenance [54]. 

Some of the mentioned electrodes contain poly(pyrol) [55,57], poly(aniline) [56,58] and its derivatives poly(a-naphtylamine) [59], poly(o-phenylenediamine and poly(o-aminophenol) [60]. In the electrode [55], the conductive polymer layer was immobilized on platinum or glassy carbon. The polymer membrane sensitive to oxytetracycline hydrochloride contained various anti-ions of tetraphenylborate phosphotungstate and silicotungstate. Optimum properties were reached by the Pt/PPy/PVC (OTC-TPB) sensor containing tetraphenyl borate. It shows the Nernstial response in the concentration range of 4.0 x 10 to 5.0 x 10 mol L , very low detection limit of 1.0 x 10 mol L (0.03 ppm) and response time 25 s. The developed sensor was applied in pharmaceutical analysis. 

Another sensor based on the same polymer [57] contains glassy carbon as the substrate. In the polymer membrane sensitive to doxycycline, an association complex with tetraphenyl borate dissolved in dibutyl phthalate is located. This paper also describes the influence of different factors on the process of electropolymerization of polypyrrole. 

---