pH / ORP Sensor Storage and Regeneration

How to store a pH sensor?  How long can the sensor sit dry?  How can the sensor be regenerated?  Learn more in this article.

pH Sensor Storage

Your new pH or ORP sensor will ship with a small cap over the tip of the sensor. This cap will contain an electrolyte-based storage solution designed to keep the pH-sensitive glass membrane and porous diaphragm hydrated. This cap is referred to as a “watering cap” and should be saved for future usage.

When inspecting a new pH sensor, the watering cap should have visible liquid present. There may be salt crystals around the cap seal. These crystals are non-toxic (Potassium Chloride) and are completely normal. The cap should be hand-tightened, and any excess salt can rinse off with tap water.

Example of a pH watering cap which is shipped with all pH sensors

Exposing the pH Glass Membrane to Air

The glass membrane on the pH sensor has a thin gel layer that must remain hydrated in order to keep the pH sensor functional. If the gel layer is allowed to dry out, then the sensor response to changing pH will become slow or potentially non-existent. Typically, 24 to 48 hours will create a notable effect in response; however, any prolonged loss of hydration should be avoided. If drying out has occurred, then test the sensor response in pH buffer solutions. A sensor should respond to a 3pH change (say from 4 to 7pH) in < 30 seconds. Alternatively, if the sensor cannot pass calibration, we should question it.
 

The response of the pH sensor can sometimes be improved through alternating exposure to strong bases and acids. The procedure is as follows:

Immerse the sensor in 0.1 – 1 M NaOH for 10 min, then in 0.1 – 1 M HCl for 10 min. After regeneration, place the sensor in storage solution for a further 15 min.

When the sensor is not in use, keep the sensor tip hydrated in Hamilton storage solution (Ref 238931) or 3M KCl. Storage in acidic or basic solutions should be avoided.
 

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