How To Select The Right Ph Buffers

By Author: Tom Young
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When considering which pH buffers to use it's important to remember that the purity and make up of the buffers is consistent with the pH controller that you choose to use.
The standard sequence for pH calibration is to take three points of reference to ensure that the calibration occurs across a suitable number of deciles to ensure a proper reading can be taken.
Assuming that the electrode to be calibrated is located within a process or effluent chemical then the electrode will need to be cleaned. Using a strong acid like Hydrochloric Acid should be enough to ensure that the electrode is cleaned should ensure that the reference of the electrode is working as the controller should record a change in pH value.
With the instrument in calibration mode normally you will be required to insert the ph electrode into a high or low buffer. The high value on older meters can be a value of 9.2pH, but ...
... for newer meters this is normally a value of 9 or 10.
Before inserting the electrode into the buffer solution available or corresponding to the instrument it's important that the hydrochloric acid is removed from the electrode. This should be done with demineralized water to prevent a shock to the electrode but standard tap water can be used too. A small amount of pressure can be used to remove and debris from the electrode.
The electrode should then be inserted into the initial calibration solution - whether the high or low value is used first depends entirely on the meter. Either way the electrode should be relatively dry to prevent contamination of the buffer.
When the electrode is inserted into the solution - we recommend waiting for 10 - 15 minutes to ensure that the correct reading is registered. Older electrodes may take longer to adjust and depending on personal feeling - this can be a sign that the electrode will need to replaced or at least monitored for inconsistencies.
When you're happy with the reading ensure that the setpoint is stored into the pH meter, and once again clean the electrode using water (demin or otherwise). Follow this with the low value of pH. The lower value of the normally has a value of 4.Again wait 10 - 15 minutes before ensuring that the setpoint is stored.
It's important to ensure that all the readings take place at a temperature correlating to the pH meter. Most meters use a temperature standard of 25 degrees centigrade but can also allow a manual offset. The pH Temperature scale follows the nernst equation E = E0 - kT·pH. So for example - at a temperature of 75 degrees centigrade - our pH buffer solution would read a value of 4.5 pH - a significant drift.
Modern pH Meters will take into account the temperature using a temperature compensator. If this is installed ensure the temperature compensator is in the buffer solution when calibrating.
When calibration is complete we would recommend that you display the electrode degradation screen if available. This is visible on most modern pH meters and should show the value of pH that the instrument expects, the value that it is showing and the percentage difference. Anything outside of 10 - 15% could suggest either extrusions within the connecting cable, degradation of the electrode, or connectivity issues with the instrument.
When the calibration is complete - ensure that the electrode is clean and take a sample reading from a neutral (pH 7.0) solution to ensure accuracy.

awe offer a range of chemical dosing pumps and other equipment and controllers for use in water treatment, effluent treatment and processing. We offer a range of ph Buffer Solution as well as calibration solution for redox electodes and conductivity cells.