The Aging of the Reference Electrode

Reference electrodes do not age in principle, but their life may be considerably shortened by incorrect handling, during usage and storage.

If the reference electrode is a refillable design then it should always be topped-up with an identical electrolyte used originally by the manufacturer. Electrolytes with different KCl molarity may cause the reference potential to become unstable, the response time of the pH electrode assembly gets sluggish, and in extreme circumstances the entire conducting system may be destroyed.

The liquid junction (diaphragm), being the most critical part of the reference electrode, has to be kept clean at all times. No process liquid must enter the sensor through the diaphragm and all chemical reactions at the diaphragm must be avoided.

Reference electrodes utilizing a gel-electrolyte reduce maintenance cost as they are sealed thus don’t require refill with liquid electrolyte. Although this reference design is pressure resistant (up to 200 kPa), diffusion over the diaphragm does take place in both directions and will gradually reach the Ag-AgCl reference system, resulting in electrode poisoning. In addition the KCl concentration in the gel-electrolyte will be diluted over time by the measured media. Both of these factors result in a limited life of the reference electrode. High temperature or rapid temperature changes will also shorten the life of a gel electrode. A combination sensor with gel-electrolyte should never be used continuously in media having a temperature higher than 60°C. A reasonable pH sensor lifespan of a gel electrode is approximately 6 months if used under normal condition (pH 2 to 12 at temperatures of 25°C).

Hamilton reference electrodes utilizing the polymer electrolyte can be used in highly acidic media down to pH 0. This reference electrode is absolutely maintenance free. Although the temperature limit is raised to 130°C, it must be understood that if the electrode is continuously exposed to this high temperature the life span is drastically reduced. Under normal conditions an electrode with polymer electrolyte may easily be used up to 12 month.