USA 
Europe Glass pH sensors have a porous ceramic junction that allows the reference electrolyte (a KCl solution) to contact the measured solution. During extended dry storage, the reference electrolyte may slowly leak from the junction by design, forming a visible drop of liquid inside the bellows.
- This electrolyte is non-cytotoxic (data available on request) and diffuses very slowly into the process fluid under normal conditions, as with any glass pH sensor.
- The presence of a small amount of liquid in the bellows is normal and does not indicate any damage to the sensor or create any additional exposure of the process to new materials.