Anion-selective liquid-membrane electrodes preparation

In order to improve the practical application of potentiometric sensors, much effort must be devoted to developing membrane materials whose selectivity deviates fi-om the Hofmeister series. Chloride- and nitrite-selective electrodes based on lipophylic vitamin B12 derivatives have been reported by Simon.xhese electrodes were the first anion-selective electrodes of which selectivity sequence did not obey the Hofmeister series. Since then, a number of anion-selective liquid-membrane electrodes have been developed using a variety of hosts metallocenes, diphosphonium dication salts, diquartemary ammonium dication salts, bisthiourea derivatives, metalloporphyrins, lipophylic macrocyclic polyamines, cytosine-dependent triamine and metallophtalocyamines. " " Among this large variety of compounds studied, the metalloporphyrins seem to be the most promising for the preparation of effective ion-selective potentiometric sensors. " - ... 

Ion-selective electrodes (ISEs) are relatively simple membrane-based po-tentiometric devices which are capable of accurately measuring the activity of ions in solution. Selectivity of these transducers for one ion over another is determined by the nature and composition of the membrane materials used to fabricate the electrode. While many scientists are quite familiar with the glass membrane pH electrode first described by Cremer (CIO), most are for less aware of the other types of ISEs which may be prepared with crystalline, liquid, and polymer membranes and which allow for the selective measurement of a wide variety of cations and anions (e.g., Na" ", K" ", Ca ", Ag" ", Cl, Br , F , and organic ions). Moreover, in recent years, the range of measurable species has been further extended to include dissolved gases and... 

Free-standing films of desirable thickness and/or porosity have been prepared and developed for gas-gas separations and as ion sieves [438-40]. In this case, by appropriate selection of the dopant anion, electrode-posited PPy films can be made to pass some ions several decades more efficient than other methods. Another possibility to construct polypyrrole-based membranes is to combine them with a second conventional membrane to improve performance. Thus PPy films have been deposited on an alumina or polycarbonate substrate to form durable permeselective membranes for gas and liquid separation [441,442]. 

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