Advanced Cleaning: Relationship Between Conductivity, Surface Tension and pH

Q: I am doing a conductivity study using Alconox detergent. As I test different lots, I am seeing that the pH and Surface Tension listed on the certificate of analysis differs between lots. Do you think these variables affect conductivity enough to alter my results?

A: Great question! First, let us say that when running tests on AlconoxⓇ Powdered Precision Cleaner, we encourage engineers and scientists to use 10g or more of Alconox solution for a representative sample.

Here’s the short answer… Surface tension does not have any interactive relationship with conductivity; pH has a very small, essentially negligible interaction with conductivity; and concentration and temperature are much bigger causes of change in conductivity.

And now the long answer to explain why… Conductivity results from conductive ions, dissolved solids and aggregations of molecules in solution. Surface tension does not change any of these factors.  

The changes in pH largely derive from the variations in the completeness of neutralization of the sodium alkylbenzene sulfonate and sodium EDTA.  Slightly under-neutralized material will have some alkylbenzene sulfonic acid or Na3EDTAH being present which tends to give a slightly lower pH. Slightly over neutralized material will have some excess sodium hydroxide which will give a slightly higher pH.

And while slightly more or less ions present in a solution would cause lower or higher conductivity, in comparison to all the other ingredients in Alconox detergent powder the contribution to conductivity by these materials is extremely small.

In internal conductivity studies we have done, conductivity did not correlate with pH.

We are happy to discuss this further any time.

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