Storage of pH electrodes is one area which is often misunderstood, and can easily damage the electrode beyond repair if it is done incorrectly. We've taken a look at how pH electrodes should be stored to keep them in top condition.
The Structure of pH electrodes
The tip of the electrode comprises of a thin glass membrane, which is permeable to H+ ions and contains the inner buffer. Around this, a hydrated "inner gel layer" forms, and a secondary "outer gel layer" forms when the membrane comes into contact with an aqueous solution.
H+ ions diffuse in or out of the gel layer, depending on the ion concentration in the surrounding solution (this is how the electrode detects pH) - in alkaline solutions, H+ ions diffuse out, while in acidic solutions H+ ions diffuse in.
If this movement occurs too far in either direction (i.e. too many H+ ions move in or out of the gel layers), the electrode response to samples will be altered causing incorrect results.
This is why storage is important - the long periods of time that the electrode spends in storage (not in use) gives enough time for significant movement of ions.
Correct storage of pH electrodes
- NEVER store a pH electrode in water - the low ion concentration of water will cause ions to leach out of the electrode, over time this causes a slow, sluggish response time with big drifts in readings.
- NEVER store a pH electrode dry - this will cause the gel layer to dry out and disappear over time. Sometimes dry electrodes can be revived by soaking alternately in storage solution and concentrated acid, but often a dried out electrode just needs to be replaced.
- ALWAYS rinse the pH electrode before storing - to avoid contaminating the storage solution with sample carry-over, always rinse it in clean water (or a cleaning solution and then water for stubborn deposits) before going into storage solution.
- ALWAYS store a pH electrode in storage solution - to keep the membrane hydrated, and the ion levels correct, always keep your pH electrode in storage solution. This is usually 3M KCl solution, but can vary for specialist probes - check the care instructions for your specific electrode.
The TRUEscience SMART pH system incorporates a dedicated storage stand - this not only helps to keep your work bench tidy, but also ensures the electrode is always returned to a suitable storage solution.
Remember to change the storage solution regularly - roughly weekly, or sooner if you notice crystallization or discoloration.
For more information on the TRUEscience storage stand and storage solution just follow the links above, or contact us if you have any questions.