The samples you encounter in pH and titration measurements vary enormously in nature. Solution may be aqueous or non aqueous, high or low ionic strength, in sodium content or in pH value. You may need to test slurries, emulsions or suspensions of various viscosities.
Some samples will be tested at high temperatures, others at low temperatures. Biomedical samples may require special treatment to avoid contamination and assure accurate readings. Other samples are not in liquid form at all – as in the testing of agar plates and many food processing applications.
Finally, the amount of sample you have available for testing, or the container in which you must measure it, may require a special electrode for practical testing.
Look for stability and low noise in electrodes
A wide selection of pH electrodes is available commercially to suit almost any pH or titration requirement. Look for those that feature fast response, plus internal and cable shielding to minimise electrical noise and guarantee accurate, stable readings.
When selecting the right electrode(s) for the job, the following criteria should be considered:
pH sensing membrane
Many types of glass electrodes are available. Most of them are usable over the full 0 to 14 pH range, and feature exceptionally low error in samples with high sodium content. Some have very specific pH ranges, while others have very specific temperature ranges.
General Purpose Glass Electrode
These have low electrical resistance – less than 100MΩ at 25° C. They are recommended for routine pH measurements, as well as measurements at low temperatures. Their thick, rugged hemispheric membrane withstands rough handling possible in application.
NOTE: Constant immersion in solutions of very low or very high pH can reduce the effective life of this electrode type.
They have somewhat higher electrical resistance than the general purpose types, plus excellent chemical durability.
Low Resistance / Full Range pH Glass Electrodes
This glass formulation, has a much lower electrical resistance than both the general purpose or the full range / high pH glass electrodes. It is ideal for samples of limited size and for surface measurements.