Let’s start by defining some terms here.
An Electrode is a device used to connect the metal part of a circuit to the nonmetallic part of a circuit — most often liquid, vacuum, or semiconductor.
A Reference Electrode is an electrode that has a specific, known amount of electrode potential — that is to say, an electrode where the amount of electricity that moves through the electrode is a predetermined quantity. This is important, because with a reference electrode, you can pump a specific amount of electricity into the nonmetallic part of the circuit, and test the other end of that part of the circuit to find out what the resistance of that part is.
This is very useful in several fields where the resistance of the nonmetallic part of the circuit varies for specific reasons. For example, in the biomedical field, there are any number of human body parts that you may want to measure the resistance of for various reasons. The galvanic skin response, for example, is a measure of the resistance of your skin as taken by a reference electrode, using your skin as the nonmetallic part of the circuit. It can help you determine your stress level, and is used in guided biofeedback, polygraph machines, and more.
The most common reference electrode in the biotech field is the silver/silver chloride electrode. That simply means that the electrode is composed of a core of pure silver wire that is either dipped in or electroplated with a thin layer of silver chloride. The silver/silver chloride electrode is characterized by fast electrode kinetics, meaning that once you reach a sufficiently high level of current, the electrode’s own resistance drops to zero and is passes 100% of the electricity put in. This makes it an excellent reference electrode because the amount of energy going into the nonmetallic part of the circuit is equal to the amount of energy going into the electrode itself, which is easily controllable.
In the next part of this brief look at the silver/silver chloride electrode, we’ll talk about the many uses of this top tier bit of biomedical machinery.