Other Details of Electrode Design

The electrodes described in this section are commercially available. The body of these electrodes may be either glass or epoxy plastic, as we have discussed. Epoxy plastic electrodes are unbreakable. Some electrodes are gel-filled electrodes and are sealed. This means that the KC1 solution has a gelatin mixed with it. There is no vent hole, they cannot be refilled with saturated KC1, and solid KC1 cannot be added. 

Some electrodes are double-junction electrodes. Such electrodes are encased in another glass tube and therefore have two junctions, or porous plugs. The purpose of such a design is to prevent contamination—the contamination of the electrode solution with the analyte solution, the contamination of the analyte solution with the electrode solution, or both, by the diffusion of either solution through the porous tip or plug. See the next section for tips concerning these problems. 

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