What pH sensor options are available for continuous measurement in low ionic-strength water?

Document ID

Document ID TE12899

Published Date

Published Date 05/06/2021
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Question
What pH sensor options are available for continuous measurement in low ionic-strength water?
Summary
online pH probe options for low ionic-strength water
Answer
Measuring pH in low-ionic strength water is a challenge.  See the following article for why measuring pH is challenging in low conductivity water. 
The online measurement options will vary depending on the conductivity range of the water.  Standard pH probes (both combination pH and differential pH sensors) may start to show issues when installed in water having conductivity values around or below ~250uS/cm. 
 
Option 1: Differential style pH sensor, 6028P4
This sensor has a special glass electrode and a low conductivity preamp designed to yield better results in lower conductivity waters.  This sensor may be a good fit if the water has a conductivity value above 50-100uS/cm. 
 
Option 2: High purity style sensor, 8362sc
This sensor is specifically designed to measure pH in very low conductivity water.  The specially designed flow chamber and electrode allow for accurate results in ultra-pure water.  If the water's conductivity is around or below 50uS/cm, or the above mentioned options are not working, this sensor is may be the best choice.
 
Please note, all of the above mentioned conductivity ranges are estimates.  The exact function of a specific style of pH sensor will need to be assessed for each individual type of water as more than one factor will influence the function of each sensor style. 

See the following articles for more information on conductivity and pH measurement in high purity water

Is the low conductivity of my process water causing issues with my pH probe?
What is the minimum conductivity recommended for installing a pHD probe?
Conductivity Resources

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