Hail contends the meters backing the electrodes are becoming more integrated and smaller. After taking a look at what's on the market, it becomes obvious that, indeed, although hundreds of pH electrodes are available in various configurations, what usually sets them apart from one another is the applications they were designed for. To do this, however, a reference electrode is required to complete the circuit and to provide a second, unvarying potential to accurately compare with the potential produced by the measurement electrode across solution. It is important to consider what you need in a reference electrode prior to being bombarded by the battery of configurations available. Numerous liquid junction formats are available, depending on the desired flow rate.
Many companies offer combination electrodes available as either refillable or nonrefillable models.
The electrolyte may be liquid, gel, or viscolene, depending on the flow requirements. Most combination electrodes can be purchased with glass or epoxy bodies, too. Next, make sure the reference material is compatible with the sample you will be measuring. Combination electrodes are convenient, but in situations where the reference material is not compatible with the sample material, an electrode pair would be more suitable for the task. Electrodes today are made in a variety of shapes and sizes to accommodate measurements in different vessels and under varying conditions.