The basic principles of electrochemistry briefly summarised in ► Chap. 4 can also be used in the context of analysis: The potential difference between a half-cell of precisely known composition and one containing the analyte to be investigated allows conclusions to be drawn about its properties, in particular its concentration. Such investigations, which are based on the determination of electrochemical potentials, are summarised under the generic term potentiometry (► Skoog devotes the whole of Chapter 23 to potentiometry.) It should be obvious that the resulting voltage—which is the consequence of the respective potentials of the half-cells involved—depends on the concentration of the respective dissolved particles, i.e. also on the concentration of the analyte. Accordingly, Nernst’s equation (► Eqs. 4.1 and 4.2 ) comes into play here once again.