What is a double junction electrode and when should I use one?
A. Double junction electrodes have an extra chamber of electrolyte with a second junction between the reference electrode and the solution under test. This electrolyte is chosen to minimise transfer of ions from the solution under test which may react with the reference junction which is usually Ag/AgCl. If the solution under test contains anything which reacts with silver then a double junction is essential. Problem chemicals include halides, cyanides, proteins, tris buffers and heavy metals. The only drawback to double junction electrodes is that they tend to respond slowly and have a wider hysterisis than single junctions, otherwise all electrodes would probably be made as double junction. A new technology double junction with the accuracy and response of single junction electrodes is now available from Phoenix Electrode called the Red Rod electrode.
