ABSTRACT
This chapter describes how electrodes work, giving examples of how to use them. It also describes advice on how to select the best electrodes for a given application, and how to maintain them for optimum performance. A pH electrode built into the probe senses the change in pH, which is directly proportional to the ammonium ion content of the sample. pH, chloride, fluoride, sodium, and most other ion-selective electrodes sense the ion "directly." Ion-selective electrodes are potentiometric sensors; their electrode potential when placed in a solution is related to the activity of a selected ion in that solution. Membrane electrodes have membranes which are selectively permeable to a particular ion. The ammonia diffuses through a gas-permeable membrane at the tip of the probe and dissolves in an internal filling solution, thereby changing the pH. Like membrane electrodes, solid-state electrodes can become coated with impermeable precipitates.
