Response Characteristics of Electrochemical Sensors
As can be seen from Figure 3.1, the potential is not dependent on the activ ity, a of the ion, but on -log a. The same type of function can be deducted from the Nemst equation:
Usually, the ionic strength is kept constant by the addition of a strong elec trolyte to each solution (e.g., NaCl, KC1), or by buffering the solution with a buffer that can also maintain the ionic strength at a constant value. By maintaining the ionic strength at a constant value, the activity can be substituted with the concen tration, and further more for an ion Mz+, pM = -log cMz+ is used. The electrode function is given by:
The most utilized electrode function is E = f(pH) for the H+-selective mem brane electrode (e.g., glass electrode), when the concentration of H30 + ions has to be determined in solution.