EDM Today - Expert's Corner Article Published July 25th, 2017

Published Technical Articles
July 18, 2017

The Difficulties of Measuring the pH of Deionized Water - By Larry Gottlieb, Tom Smith and Jonathan Goldstein

Before we can even consider the possibilities for pH control in EDM dielectric water, we first have to determine how we can accurately measure the pH. The following treatise concerning the measurement of pH of deionized water has been prepared by the technical staff at ResinTech, Inc.

Abstract - EDMStory.jpg

Reliable pH measurement has always been difficult in pure deionized water. It is a chemical challenge. To produce reliable measurements, one must understand the theory, process, and pitfalls of pH measurement. In this article, we hope to explain some of the difficulties in the measurement of the pH of pure water.


pH is the measurement of hydrogen ion concentration in a solution. The equation for pH is pH=-log [H+]; the concentration of hydrogen ions can be calculated from the pH. pH is measured on a scale of zero to fourteen; the lower the value, the more acidic the sample or the higher concentration of hydrogen ions. Conversely, the higher the pH, the more basic the sample or lower concentration of hydrogen ions. A pH of 7 is neutral and has an equal amount of hydrogen ions and hydroxide ions.

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