Reference Electrodes for Non-Aqueous Solutions

The reference electrodes used in non-aqueous systems can be classified into two types. One type uses, in constructing a reference electrode, the same solvent as that of the solution under study. The other type is an aqueous reference electrode, usually an aqueous Ag/AgCl electrode or SCE. Some reference electrodes are listed in Table 6.2 and are briefly discussed below. For other types of reference electrodes used in non-aqueous solutions, see Ref. [4], 

G good for general use F applicable under limited conditions (see text). 

Reference Electrodes That Use the Same Solvent as the Solution Under Study 

Silver-Silver Ion Electrode This is the most popular reference electrode used in non-aqueous solutions. Since Pleskov employed it in acetonitrile (AN) in 1948, it has been used in a variety of solvents. It has a structure as shown in Fig. 6.1(a) and is easy to construct. Its potential is usually reproducible within 5 mV, if it is prepared freshly using pure solvent and electrolyte. The stability of the potential, however, is not always good enough. The potential is stable in AN, because Ag+ is strongly solvated in it. In propylene carbonate (PC) and nitromethane (NM), however, Ag+ is solvated only weakly and the potential is easily influenced by the presence of trace water and other impurities. In dimethylformamide (DMF), on the other hand, Ag+ is slowly reduced to Ag°, causing a gradual potential shift to the negative direction.2) This shift can reach several tens of millivolts after a few days. 

2) DMF works as a reducing agent (2Ag++ HC0NMe2+H20 - 2Ag°+Me2NCOOH+2H+). The reduction process has been used to produce monolayers and stable colloids of silver nanoparticles (Pastoriza-Santos, I., Liz-Mar-zin, L.M. Pure Appl. Chem. 2000, 72, 83). 

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