Solid State Electrodes with Electroactive Coatings

It is up to the interested and innovative experimenter to test other association complexes for their usefulness as specific electrode phases. 

4 Solid State Electrodes with Electroactive Coatings 

A similar construction has been described by Ansaldi and Epstein [160]. They fixed a 0.5 mm thick calcium-selective PVC membrane (preparation see Sec. 3.3.4) on the surface of a graphite electrode (used for spectroscopy), and obtained a solid-state calcium electrode which exhibited the characteristics of the fluid membrane type. 

Morf and Pretsch [161] discuss solid-state microelectrodes consisting of ion-selective PVC membranes for Ca , Ba, Li , Na and mounted on a silver surface which has been pre-treated with tetraphenylborate. These electrodes have lifetimes of a year and more. The EMF stabilities were excellent, and lacking a fluid/ fluid phase boundary, the electrodes were less pressure-sensitive. 

Before measuring any of the ions listed in Table 5, the organic exchanger phase must first be saturated with the appropriate measured ion, in order to achieve suffi- 

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Figure 2 Basic types of ISE (A) glass electrode (B) electrode with a solid homogeneous or heterogeneous membrane (C) classical liquid membrane electrode (D) electrode without internal solution (all-solid-state electrode) (E) coated-wire electrode. 1, Internal standard solution 2, internal reference electrode (Ag/AgCI) 3, membrane 4, glass or plastic body of the electrode 5, reservoir of the electroactive substance solution 6, solid-state contact and 7, metal wire.

PPY is a very well known conducting polymer used in numerous works as the electroactive component of an all-solid-state ISE. Most of the papers dealt with a PPY-coated PVC electrode where PPY is doped with different anions, inorganic such as chloride or organic such as dodecyl sulphate. Several techniques were used to characterize these devices. Potentiometric measurements represent a method allowing thermodynamic characterization. AC electrogravimetry was also used to characterize ion and solvent motions at the PVC/electrolyte interface to imderstand how the electroactive film (Prussian blue, conducting polymer, etc.) ensures the mediation between the membrane and the electrode. ... 

A new kind of all solid-state sensors was first reported by Cattrall and Preiser in 1971 in which the internal reference element was in direct contact with the sensing membrane and thus contained no aqueous solution. The first group of such simplified sensors was those of the so-called coated wire construction type (CWE). In this approach, a metal wire was dipped with a solution of PVC in THF containing also a suitable electroactive material. During evaporation of the solvent, a PVC film on the metal wire surface was formed. Although different materials such as platinum, silver or sliver chloride, and aluminum could serve as central conductors, the nature of the wire support had no substantial influence on the electrode performance if it did not react with the membrane components. ... 

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