Construction of ion-selective electrodes

The unique ability of crown ethers to form stable complexes with various cations has been used to advantage in such diverse processes as isotope separations (Jepson and De Witt, 1976), the transport of ions through artificial and natural membranes (Tosteson, 1968) and the construction of ion-selective electrodes (Ryba and Petranek, 1973). On account of their lipophilic exterior, crown ether complexes are often soluble even in apolar solvents. This property has been successfully exploited in liquid-liquid and solid-liquid phase-transfer reactions. Extensive reviews deal with the synthetic aspects of the use of crown ethers as phase-transfer catalysts (Gokel and Dupont Durst, 1976 Liotta, 1978 Weber and Gokel, 1977 Starks and Liotta, 1978). Several studies have been devoted to the identification of the factors affecting the formation and stability of crown-ether complexes, and many aspects of this subject have been discussed in reviews (Christensen et al., 1971, 1974 Pedersen and Frensdorf, 1972 Izatt et al., 1973 Kappenstein, 1974). 

The process of producing an ion-sensing polymer includes the following steps (i) selection and preparation of ligand monomers, (ii) synthesis of ion complexes of the monomers or linear copolymers of the complexing monomers, (iii) preparation of cross-linked copolymers with the monomeric complexes or linear copolymer complexes, (iv) the testing of the polymers for ion selectivity, (v) optimisation of polymer ionic selectivity and (vi) the use of the polymers in the construction of ion-selective electrodes (ISEs) and optical sensors. 

Ion-selective membranes attain their permselectivity from ion-exchange, dissolution, or complexation phenomena. Different types of membranes are available for the construction of ion-selective electrodes glass and other solid state rods (crystals), liquid or polymer ion ecchangers, or dissolved ionophores. Many electrodes are commercially available with selec-tivities for different ions, mainly H, alkali metal cations, heavy metal ions, and halides or pseudohalides. Also gas-sensing electrodes may be constructed from an ion-selective electrode and a gas-permeable membrane [182]. Ion selective electrodes and gas-selective electrodes... 

Several quite different types of membrane have been used in the construction of ion-selective electrodes. Namely ... 

Figure 11.16 Common constructions of ion-selective electrodes (a) glass electrode (b) crystal or pellet membrane electrode (c) liquid membrane electrode,...

Michalska A (2006) Optimizing the analytical performance and construction of ion-selective electrodes with conducting polymer-based ion-to-electron transducers. Anal Bioanal Chem 384 391 06... 

Application of PVC in Construction of Ion-Selective Electrodes for Pharmaceutical Analysis A Review of Polymer Electrodes for Nonsteroidal,... 

Apart from PVC, other polymers are also used for construction of ion-selective electrodes. The most popular of them are hardened epoxide resins [33], soft polyurethanes [34], silicone rubber [35], poly(vinylidene chloride) [36], polysiloxanes [37] and others. 

Fig. 12.5 Common constructions of ion-selective electrodes, (a) Glass electrode, (b) Crystal or pellet-membrane electrode with internal reference electrode, (c) Pellet membrane with direct electrical contact, (d) Liquid membrane electrode.

There have also been reports on the apphcation of metal ions in the imprinting procedure. Metal ions can act either as the template (metal imprinting), like in the case of imprinted polymers designed for the construction of ion selective electrodes [61,70,91,92], or have a role in the interactions between the template and the monomers (metal-mediated imprinting) [93,94], The latter mode is less common because preparing and isolating well-defined tertiary or higher metal complexes is rather cumbersome [29]. 

Fig. 20 A-C. Possible constructions of ion-selective electrodes with solid active phases. A Direct contact of the metallic conductor with the active phase. B Contact through an inner solution and a reversible shunt element. C Contact through an inner solution and an ordinary reference electrode with salt bridge...

Fig. 28 A-D Construction of ion-selective electrodes with liquid active phases. A Home-made construction, B Orion liquid exchanger electrodes (Series 92 -), C Coming liquid exchanger electrodes, D Orion (Series 93).

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