Rumors, Half-Truths, And Truths About Temperature And pH

By Mark Spencer, PhD, President of Water Analytics

A few months ago I received a call from an angry user who was using one of our differential probes and a controller. Embedded in the probe is a thermistor that measures temperature. The controller corrects for its effect on pH.  He calibrated his probe in the comfort of his control room, but when he put the probe in his warm process the pH read low by 0.2 pH units. Clearly temperature compensation was not working. He was ready to demand a refund. When I learned that his process was approximately 40°C I explained that his probe was working fine. It was his interpretation of the reading that was wrong.

Few issues are as confusing or multifaceted as the effect of temperature on pH. Most users understand that temperature changes the pH value and that temperature compensation corrects for this effect. But they're not quite sure how it works. And most don't understand that there is an effect of temperature that is very real and yet another that can cause error.

This white paper will attempt to set the record straight so that the user can get real, actionable information from his or her pH analyzer.