Which combined pH electrode can be used in pure water (low ionic strength water)?

Document ID

Document ID TE7199

Published Date

Published Date 03/20/2017
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Question
Which combined pH electrode can be used in pure water (low ionic strength water)?
Summary
Recommend the suitable combined pH electrode based on the characteristic of the liquid junction.
Answer
When placed in a pure water sample, pH electrodes with liquid junction providing high and continuous leak rate, will show improved response time and stability.
pH electrodes like PHC725, PHC735, PHC2401 and PHC2701 are recommended for measuring pH in low ionic strength water.
Non-refillable solid gel electrodes like PHC101 should be avoided.
 
The PHC745 with glass sleeve is also suitable for measuring pH in low ionic strength water but its use is more indicated in contaminating samples because the glass sleeve liquid junction can easily be cleaned.
 
The reason for the poorer precision and instability for low ionic strength samples is the very high resistance through the measuring chain (sample solution) which will make the measurement more sensitive to electrical noise. Another problem is that the sample has a very low buffer capacity; consequently, pH will tend to drift due to absorption of carbon dioxide from the air.
 

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