EXO Calibration - Chloride ISE

EXO Calibration - Chloride ISE

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EXO Calibration - Chloride ISE

This video covers the calibration of the EXO Chloride Ion Selective Electrode in mg/L using Kor Software.

Timestamps of specific moments of the video

  • 0:00 – Overview and Required Equipment
  • 1:34 – Chloride Standard 1
  • 3:27 – Chloride Standard 2

Video Transcript

In this video, we will calibrate the EXO Chloride Ion Selective Electrode or ISE in mg/L. You can also use the EXO Handheld or the Kor Mobile app.

Before calibrating, we want to make sure our chloride sensor has been soaked overnight in 1,000 mg/L chloride standard. New sensors are shipped dry, so this step will hydrate new sensors. It is also a good idea to soak sensors that have been used in the field because this can help remove interfering ions that might have been picked up during use. After soaking, rinse and dry the sensor before proceeding with the calibration.


For best practice, make sure all the sensors, probe guards, calibration cups, and the wiper are clean. For efficiency, it may be helpful to have a dedicated probe guard and cal cup just for calibration. I also recommend removing the bottom plate from the sensor guard for ISE calibrations to minimize transfer of the solutions between standards. We will be using prepared standards for this calibration. Please check out our video on preparing the chloride standard solutions. This is a two-point calibration. We made a 10 mg/L standard for the first point and a 1,000 mg/L standard for the second point. If you expect significant temperature variation during deployment, you may choose to do a three-point calibration. You can find instructions for this in the EXO manual.

So let’s begin. Fill the cal cup up to the first line from the bottom with the 10 mg/L chloride standard. Immerse the sonde.

In Kor, we will select Chloride to calibrate. Kor Software will indicate if readings are stable in real time on this graph. Note the chloride mV value or raw sensor value from the electrode, which should be around 225 mV +/- 20 for a new sensor. An older sensor may fall outside of this mV value for the first point. But, if it has a good slope on the second point, it will provide accurate measurements.

Once the readings stabilize, we’ll click apply and proceed to the next standard. Click to add another cal point. Remove the sonde from the standard, rinse, and dry off the sensor guard and sensors.

For calibration point two, we will use the 1,000 mg/L chloride standard. Again, fill the cal cup up to the first line and immerse the sensor in the standard solution. You should see millivolt values about 80 to 130 mV below the mV value for the first calibration point. This would be a good slope for the sensor and indicate that the Ion Selective Electrode is still performing within spec.

Wait for readings to stabilize before applying the calibration. Once the readings are stable, click apply. Now you will see the calibration summary screen where you can choose to redo the calibration or complete the cal. I’ll choose to complete the calibration.

Our EXO Chloride ISE is now calibrated! Please check out our other EXO University videos, and thank you for watching.

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