The reference electrodes most commonly employed are the silver/silver chloride electrode and the saturated calomel electrode. The voltammetry cell is connected to an electrical circuit, the basic form of which is shown in figure 15.

The power for the circuit is supplied by a programmable voltage supply one side of which is connected to the counter electrode and also often to electrical earth. This electrical supply can provide linear or other types of voltage programs with respect to time. The other output of the supply passes through a milliammeter to the working electrode that measures the current from the working electrode. The milliammeter must be isolated from earth (and/or the counter electrode). A high impedance input voltmeter is connected between the working electrode and the reference electrode and must also be isolated from earth (and/or the counter electrode). The voltage of the working electrode at any time is taken as the voltage, as measured by the voltmeter, minus the reference voltage of the reference electrode. Modern instrumentation takes advantage of the very high impedance FET operational amplifiers that renders the electronic circuitry relatively simple and very compact and, in particular simplifies the design of the programmable voltage supply.

Figure 15. The Basic Circuit Employed with a Voltammetry Cell

Most cells are also fitted with a helium or nitrogen sparging line and also with fairly efficient stirrers. Neither of these facilities is always employed and their use will depend on the type of analysis or investigation being carried out. The helium or nitrogen sparging (the former is the most effective sparging gas) is used to remove traces of dissolved oxygen from the air that can sometimes interfere with the electrode reactions that are taking place. The stirrer is sometimes used to investigate hydrodynamic conditions of electrolysis (a subject that will be discussed in due course). However, the study of hydrodynamic effects is often better examined by using a rotating disk electrode (RDE).