19 Nov, 2014  |  Written by  |  under Sensors

By Jill Jermain

Our Customer Service Tech, Paul Lim, has received customer calls regarding a common issue that happens during the shipping and storing of pH sensors and thought we should share this information. It’s a standard industry practice to ship pH sensors with a protective potassium chloride-filled rubber boot, but sometimes crystals form on the rubber boot. This causes some customers to assume that the sensor is defective and order an immediate replacement, but this is not the case.

RAIblogThe potassium chloride helps keep the sensor hydrated and ready for immediate use, while the rubber boot prevents damage, such as cracking or scratching, to the glass bulb during shipment. Crystals can sometimes form on the rubber boot of new, unopened pH sensors. However, what most customers don’t realize is that the potassium chloride solution in the rubber boot tends to creep out and crystallize over time. This is a completely natural phenomenon. White crystals of potassium chloride form due to the evaporation of the solution, and will appear around the cap and tape as shown in the photographs. In order to remove these crystals, one should simply rinse off the outside of the sensor before removing the tape.

It’s also essential to check whether the potassium chloride solution completely evaporated out of the rubber boot. If this occurs, then the sensor should be soaked in either pH 4 or 7 buffer or in tap water for several hours to restore response. One should note that it’s never acceptable to use deionized water for soaking as it will damage the special glass membrane and shorten the operating life of the sensor. After conditioning is completed, the pH sensor is now ready for calibration and prepared to measure the process liquid.

In summary, the potassium chloride salt crystallization is not destructive to the electrode, nor does it hinder the electrode’s performance if treated properly. Customers can save valuable time and money by avoiding the risk of delaying a critical process measurement due to the misperception that the electrode is not functional because of the potassium chloride crystallization present on the sensor.