Can I measure conductivity at the same time as pH or will it interfere?

Document ID

Document ID TE3223

Published Date

Published Date 27/05/2017
Question
Can I measure conductivity at the same time as pH or will it interfere?
Summary
Interference when reading Conductivity and pH simultaneously
Answer
Measuring pH and conductivity with both probes in the same solution will cause a slight interference, no matter what kind of meter or probe you have. Here is why:
Conductivity is directly proportional to the amount of salt in solution. When taking a pH reading, all of our lab pH probes will release a concentrated gel of KCl electrolyte into the solution to get a faster, more stable millivolt reading. The KCl doesn't affect the pH, but it will cause an increase in conductivity. This increase will be more noticeable if the sample has a low conductivity to begin with, if the probes are close together, and if the pH probe is left in solution for extended time.
For the most accurate readings in a small sample of low ionic strength water, you should read conductivity first, before putting the pH probe in the solution. Our Platinum series probes have a "clicker" on top, where the user directly expels the gel into the solution, and typically expels more gel than a gel filled or refillable probe would. With those probes that don't have a clicker, the gel will still slowly be sucked out of the probe, more so if the water is low ionic strength.