Traditional glass pH electrodes are very delicate and need regular care to keep them in good working order.
If your electrode has been damaged by exposure to incompatible chemicals such as proteins, heavy metals or sulphides, you may be able to clean and revive it using specialized cleaning solutions…
pH electrodes that have a single junction are particularly susceptible to damage, and can become blocked and stop working if they come into contact with samples that contain proteins, heavy metals or sulphides.
While ideally you should choose a specialized electrode for your samples (see our previous blog posts on this topic here or our Quick Guide here) you may be able to clean and revive damaged electrodes with specialized cleaning solutions.
Contact with Proteins
If an electrode has become blocked by protein contamination, soak it in a Pepsin and Hydrochloric Acid (5% Pepsin and 0.1 mol/L HCl) solution for 1 hour.
Contact with Sulphides
When an electrode has an electrolyte that contains Silver ions, these can react with Sulphides in samples to cause a junction blockage of Silver Sulphide (Ag2S). For this type of blockage a Thiourea solution should be used, soak until the discolouration disappears.
Poor storage or maintenance
For electrodes that have not been properly stored in storage solution, or which have been scratched, a regeneration solution could provide further life.
This solution contains Hydrofluoric Acid (HF) which etches away a top layer of the glass to expose a new one.
HF is highly hazardous so observe strict safety cautions when using this solution – only use the minimum volume needed and wear full PPE of goggles, gloves, and a lab coat. Ensure the vessel you use is resistant to HF as most chemicals, including glass, are not!
Only allow the sensor tip to touch the liquid – if the regeneration solution touches the main shaft it will corrode it.
A 1 minute treatment time should be enough – after this rinse thoroughly with water and then leave to soak in pH 7 buffer for 1 hour. After this the sensor should rest overnight in the reference electrolyte solution specific to the sensor.
Points to remember!
Whichever cleaning method you use, remember the golden rules;
- Do not rub or wipe the electrode – this will scratch the glass and create an electrostatic charge which makes the signal unstable.
- When using or cleaning the electrode just gently swirl it in the solution, taking care not to knock the container
- Rinse with water between samples and after use
- Store in storage solution when not in use – usually 3 molar KCl
- Choose a specialized electrode where possible to ensure the best results
If all else fails…
Remember that electrodes are considered to be a consumable part of the pH meter – like the tyres on a car they do degrade over time and will need to be replaced.
If cleaning methods have not worked then look at replacing your electrode.
Even very carefully stored and maintained electrodes are only expected to last for between 1 and 3 years.