1. Calomel Reference One of the first and most stable reference system is the mercury/calomel (Hg/Hg2Cl2; Cl-). The electrolyte which is used is saturised KCl. Advantage : very stable and reliable potential Disadvantage : Max. temperature 40°C, in power plant water formation of mercury chloride salts which can result in a precipitation in the liquid junction.
2 Silver / Silver Chloride Advantage : stable potential, can be used at high temperatures Disadvantage : Formation of soluble silver salts (precipitation in liquid junction and change of potential). This can be resolved by adding AgCl to the electrolyte or by using a silver chloride cartridge. Solutions which contain for example sulphides and hydrochloric acid can shift the potential because they can form compounds with silver. This can be resolved using a double junction bridge.
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