Keeping your electrodes well-maintained is key for accurate, reliable measurements. If problems occur with the results of testing after you have cleaned, calibrated and stored your electrode correctly, this pH electrode troubleshooting guide covers some of the most common issues and their solutions.
If your pH readings are inconsistent between each measurement, whether they are drifting slowly or have significant variety, these issues may be the cause:
Solid and semi-solid samples can clog the function in a pH electrode, leading to unexpected changes in pH readings. Using an application-specific cleaning solution is the ideal way to resolve this issue.
If you have continual issues with the junction clogging when measuring viscous or semi-solid sample, switching to a pH electrode with an open junction design may be more suitable for your requirements.
Samples with low conductivity can cause drift and inconsistency in pH readings, as the ions from dissolved solids within the sample are a vital component in accurately measuring pH.
If you are consistently measuring samples with low conductivity you may want to choose an electrode with a high junction flow rate. Alternatively, you can add high purity potassium chloride (KCl) to your sample to increase conductivity.
Dehydration causes electrode pH readings to be inconsistent. Soaking the electrode bulb and junction in storage solution for at least one hour, but ideally overnight, is the typical solution to this problem.
To prevent dehydration from occuring in the future, using storage solution every time you complete testing with your electrode is best practice, either using a beaker for benchtop meters or by pipetting a small amount of storage solution into the cap of portable pH meter electrodes.
Noise interference from external sources such as rectifiers, motors, pumps or ballasts can affect the high impedance measuring circuit in your electrode, leading to inconsistent pH testing results.
Using an amplified electrode or matching pin electrode as a direct method is one option to prevent this issue. Taking a sample from the source and measuring elsewhere, away from the source of noise, is also a viable option.
If your electrode is providing readings that are consistently outside of the likely range of the sample, one of these issues may be the cause:
Rubbing or wiping the electrode can cause a buildup of static electricity, which interferes with the voltage reading of the electrode. In some cases, wiping may also remove the hydration layer or cause scratches that are not visible to the eye.
After cleaning the electrode, remove any excess water by blotting the surface with a lint-free paper towel to avoid damage or static buildup.
When calibrating your pH electrode, rinsing with deionised water is an important step between calibration buffers to avoid cross-contamination. Not rinsing between pH buffers can cause inaccurate readings.
Ensuring you rinse your electrodes when calibrating and checking that all buffers are in date is key to preventing inaccuracy when measuring the pH of samples after calibration.
Measuring across a wide range of temperatures can have an impact on the accuracy of results. Using a meter that has automatic temperature compensation can help to resolve this issue.
When calibrating, it’s important to note that pH buffer changes with different temperatures. These differences are listed on the buffer bottles to allow you to adjust to your environment and testing requirements..
A pH meter that displays the same reading regardless of the sample may be frozen. If the value does not change when placed in different samples and buffers after it is cleaned, calibrated and checked for other issues this may indicate a broken electrode.
If there is a crack or break in the sensing glass, a full replacement of the electrode is required.
Proper maintenance helps to prevent problems with pH electrodes. Cleaning your electrode after each use with suitable cleaning solution, ensuring you use storage solution for correct hydration and regular calibration all help to deliver accurate, reliable pH measurements.
In addition to extending the lifespan of your electrode, a maintenance routine also makes troubleshooting easier. By eliminating potential problems caused by improper maintenance you are able to find the correct solution to your issue more efficiently.
Hanna Instruments stocks a wide range of pH electrodes, accessories and solutions to suit your testing requirements. Browse our full range online today.
For more information about pH electrodes, speak to our experts directly by contacting us via email at sales@hannainstruments.co.uk or on the phone at 01525 850 855.