User manual

4.8 Cleaning the pH electrode

Note: The pH electrode has a limited lifetime and should be replaced

every six months, or when the response time is slow or the slope is

out of range (<80%).

Use one of the following procedures to clean the electrode to

improve the response:

• Salt deposits: Dissolve the deposit by immersing the electrode

first in 0.1 M HCl, then in 0.1 M NaOH, and again in 0.1 M

HCl. Each immersion is for a 5 minute period. Rinse the

electrode tip in distilled water.

• Oil or grease films: Wash the electrode tip in a liquid detergent

and water. If the film is known to be soluble in a particular

organic solvent, wash with this solvent. Rinse the electrode tip

in distilled water.

• Protein deposits: Dissolve the deposit by immersing the

electrode in a 1% pepsin solution in 0.1 M HCl for five

minutes, followed by thorough rinsing with distilled water.

If these procedures fail to rejuvenate the electrode, the problem is

most likely a clogged liquid junction.

1 Heat a 1 M KNO

solution to 60 - 80 °C.

2 Place the electrode tip in the heated KNO

solution.

3 Allow the electrode to cool while immersed in the KNO

solution before re-testing.

If these steps fail to improve the electrode response, replace the

electrode.

WARNING! HCl and NaOH are injurious to health.

Avoid spillage.

Monitor UPC-900

User Manual 18-1125-55 Edition AE

Maintenance 4