Meeting the Requirements of the Silver/Silver Chloride Reference Electrode

Potentiometric cells from which the pH values of standard buffer solutions are computed rely on the silver-silver chloride reference electrode which has proved to be convenient, reproducible and reliable. Of the various methods of preparation of silver-silver chloride electrodes only one concerns us here: the thermal-electrolytic type that has been used more extensively than any other form. Once prepared, the electrodes need to be equilibrated before use and between experiments. The equilibration technique must ensure voltage stability and inter-electrode, or bias, potential below 0.1 mV. In potentiometry the stability of a reference electrode is of utmost importance since an offset of 1 mV is equivalent to a deviation of about 0.02 in the pH value. A thorough study has been conducted, involving a critical assessment of the various protocols which have been developed and adopted by different research schools and have been used in the course of inter-laboratory exercises. Factors that affect the electrode performance, such as size, mass, chloridization, storage and conditioning were systematically investigated, through measurements of bias potential, leading to a set of recommended procedures that meet the requirements for high quality results. In this work, the adequacy of the optimized methodology is confirmed by means of primary pH measurements