What is the difference between refillable and non-refillable pH combination electrodes?
pH combination electrodes have either plastic or glass housings. A refillable pH combination electrode is equipped with a filling hole on the electrode housing. When the external reference solution of the electrode is depleted, the filling hole can be opened to refill KCl solution. In contrast, a non-refillable pH combination electrode contains gelled KCl inside, which is not easy to leak and has no filling hole.
Refillable pH combination electrodes feature a relatively high permeation rate of the reference solution, stable and reproducible liquid junction potential, and high measurement accuracy. Moreover, KCl solution can be refilled or replaced when the reference solution is depleted or contaminated. Its drawback is relatively cumbersome operation. When using a refillable pH combination electrode, the filling hole shall be opened to increase liquid pressure and speed up electrode response. When the electrolyte level is 2 cm below the filling hole, fresh electrolyte shall be replenished in a timely manner.
Non-refillable pH combination electrodes are easy to maintain and operate, so they are widely used. However, for laboratory pH electrodes under long-term continuous use, the KCl concentration at the liquid junction will decrease, affecting measurement accuracy. Therefore, non-refillable pH combination electrodes shall be immersed in electrode soaking solution when not in use to maintain good performance for the next measurement. Most laboratory pH electrodes are not used for long-term continuous testing, so the impact of this structure on accuracy is relatively minor. Industrial pH combination electrodes have lower requirements for measurement accuracy, so ease of use becomes the primary consideration.
