Technical Resources

I would like to ask you a question. What could possibly be so difficult about reading the pH of pure water?

It might be neutral pH 0, and for the most part there’re no interferences, good sense says.

In practice, it can be quite difficult and often frustrating to obtain reproducible pH values in samples with low ionic strength.


This is as long as the varying junction potentials that develop across the reference junction.

Water that has very few ionic species is said to be low in alkalinity, ionic strength, or have low conductivity/high resistivity just like distilled or deionized water.

It is common to attain different pH values with new, sealed electrodes that calibrate perfectly in pH buffers when attempting to measure DI water. For instance, a fast leak rate is desirable with pure water so a pH potential can be established more quickly. Choosing a pH electrodeMore expensive doublejunction electrodes have lots of privileges over traditional singlejunction electrodes, however they are generally no better than their counterparts for pure water applications. Oftentimes sealed electrodes, usually gelfilled, have an extremely slow leak rate of the reference solution. The best choice is a refillable, ‘liquidfilled’ electrode, ideally created from low resistance glass. PH electrodes are available with a special shielded or grounded compartment, to compensate for this interference.

These static potentials may present problems in measuring pH. Electrostatic interferenceSince ultrapure water is a bad conductor, it can also be a source of static potentials.


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