Homogeneous solid-state membrane electrodes

More recent investigations of C. Harzdorf [84] have shown that thick layers electrolytically deposited on silver (for example anodized for one hour at 1 mA/cm in 1 M KQ, KBr, 0.1 M K1 solution and finally clearly polished with a soft rag) are completely equivalent to the homogeneous solid-state membrane electrodes. 

The operational characteristics of homogeneous solid-state membrane electrodes are generally quite similar. As long as the inner shunt system is not an easily polarizable solid-solid contact [4], these electrodes can handle relatively high measuring circuit currents without deviating from Nernstian response (after correcting for the i R potential drop). 

As a rule, the homogeneous solid-state membrane electrodes do not need to be conditioned. They can be stored dry and are immediately ready for use. Cleaning (sanding and polishing) is only necessary if the electrode has been poisoned by contacting a solution containing an ion which forms a less soluble precipitate with the measured ion than does the corresponding electrode counter ion. 

Table 2. Homogeneous solid-state membrane electrodes... 

Due to its large compressibility, silver sulfide serves, for many manufacturers, as a basis material for halide as well as metal electrodes. In this case only about 30% of the corresponding silver halide is used relative to silver sulfide, and the mixture is compressed at higher pressures and temperatures. It is, strictly speaking, no longer a homogeneous solid-state membrane. 

Since they operate in the same fashion, the electric and electrochemical properties of the heterogeneous solid-state membrane electrodes on the market today resemble those of the homogeneous precipitate membrane electrodes in many ways. The most important data are summarized in Table 3. By the same principles outlined in the previous chapter, the heterogeneous iodide electrode can also detect cyanide. In contrast to the homogeneous membranes, those which include silicone rubber as a support ma-... 

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.

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