Improvement of the silver/silver chloride reference electrode and its application to pH measurement

When a silver/silver chloride (Ag/AgCl) reference electrode was used continuously in a low conductivity solution or reductive solution, it was often observed that stability of the liquid junction potential was lost. This phenomenon was remarkable with a Ag/AgCl reference electrode compared to a calomel reference electrode. We found that 340 mg l(-1) of silver was dissolved in 3 M potassium chloride (KCI) internal solution as silver complex ions (AgClx-(x-1)) for x = 2 or 3. However, only 1.93 mg l(-1) of silver chloride (AgCl) can theoretically be dissolved in water. The complex ion that effused into the sample solution through the liquid junction clogged the liquid junction (e.g. porous ceramic) as AgCl, or as metallic silver (Ag) in reducing solution. Therefore, the constant effusion of KCl internal solution was inhibited, and the liquid junction potential became unstable or fluctuating. A new reference electrode was developed, which can eliminate AgClx-(x-1) in 3 M KCl internal solution by the use of chelating resins. A combination of this reference electrode with a pH electrode made long-term stable pH measurements possible.