In this video, we'll be replacing the EXO Ion Selective Electrode, or ISE, sensor module.
EXO Ion Selective Electrodes feature convenient, replaceable modules, so you don’t have to worry about dealing with a refill solution. New ISE modules are shipped dry in a protective storage bottle. These modules typically last 3 to 6 months, depending on use conditions. There are three ISEs available, including Ammonium, Chloride, and Nitrate. Here we will be replacing an Ammonium sensor module, but these instructions may be used for any EXO ISE.
To start, let’s remove the sensor from the EXO Sonde. If the sensors are wet, be sure to dry them prior to removing them. I’m also going to tilt the sonde down a little to ensure no water droplets enter the port. Next, we are going to remove and discard the old sticker from the sensor.
With the sticker removed, you will see that there is a rubber plug positioned in the plastic ring at the base of the sensor module; this keeps the locking mechanism in place. We’ll carefully remove this plug with a flat-head screwdriver. With the plug removed, we can now squeeze the plastic ring so that it compresses the gap left by the rubber plug. Next, we’ll pull the sensor module straight back from the sensor body. You may need to wiggle it slightly to get it out and it may require a bit of effort.
Note that the act of removing the module damages its o-rings, so DO NOT try to reuse the old o-rings. Once the old module is removed, inspect the port for any debris. You can use a kimwipe to clean the port of old o-ring grease. Use compressed air to remove any moisture if present.
Next, we’ll take our new sensor module and check the o-rings to make sure they are seated and in good condition. This is a new module, so everything looks good!
We also want to make sure that they are lubricated prior to installation. New modules should already be lubricated, but it is always good to check. Additionally, avoid using too much grease, as this may compromise the seal. The sensor module is keyed to fit in only one orientation. Make sure to line up the prongs with the gaps inside the port. You’ll notice a small one and a large one. With the sensor lined up, firmly press until the module clicks into place. Wipe away any excess o-ring grease that may be present on the sensor. Every new module includes a sticker where you can write the install date with a permanent marker. We’ll wrap the seam where the module meets the sensor with this sticker. With that, our ISE module is installed.
Before use, the sensor must be soaked in its high-concentration calibration standard. For Ammonium, we are using a 100 mg/L standard solution. We recommend soaking overnight. Then the sensor must be calibrated.
For short-term storage, you can keep Ion Selective Electrodes in a humid air environment, such as the sealed EXO cup with a small amount of tap water, filling just 1 cm from the bottom. We don’t want the sensor tip to be submerged. Never store an ISE in distilled or deionized water, as this will shorten the life of the module. For long-term storage, the sensor should be stored dry. It can be left installed in the EXO Sonde or uninstalled in its protective bottle. The sensor must then be rehydrated before use by soaking overnight in its high-concentration calibration standard. After soaking, rinse the sensor and proceed with calibration.
Please be sure to check out our other EXO University videos, and thanks for watching!