LABEC M-MIA-LA - Manual (Page 89)

Ultrasonic milkanalyser
Operation manual 04.11.09 87/107
pH electrodes have junction, which allows the internal fill solution of the
measuring electrode to leak out into the solution being measured. The
junction can become clogged by contamination in the solution. If a clogged
junction is suspected it is best to clear the junction.
Heat up the diluted KCl solution to 60-80°C. Place the sensing part of the pH
electrode into the heated KCl solution for approximately 10 minutes. Allow the
electrode to cool while immersed in some unheated KCl solution.
- Protein Deposits
Prepare 1% pepsin solution in 0.1 M HCI. Allow the electrode to stand in this
solution for five to ten minutes. Rinse the electrode with de-ionized water.
2.9. Electrode activation
Generally, if the procedure of storage and maintenance had been closely
followed, the electrode can
be used immediately. However, should the electrode response become
sluggish, it may be possible that the bulb has dehydrated.
The bulb can be dehydrated by immersing the electrode in an ideal storage
solution (e.g. buffer pH 4 solution) for 1-2 hours. If this fails, the electrode
may require re-activation. If the above procedure does not reactivate the
electrode to acceptable status, try rejuvenation the electrode by following the
procedure outlined below.
2.10. Rejuvenation Procedure
Dip and stir the electrode in freon or alcohol for 5 minutes.
Leave the electrode in tap water for 15 minutes.
Dip and stir the electrode in concentrated acid (HCI, H
2
S
4
) for 5 minutes.
Leave the electrode in tap water for 15 minutes.
Dip and stir in strong base (NaOH) for 5 minutes.
Leave the electrode in tap water for 15 minutes.
Test with standard calibration solution.
Finally, test with standard calibration buffer solution to see if the electrode
yields acceptable results. You may repeat again for better response
(maximum 3 times). If the response does not improve, then the electrode has
completed its useful life. Replace with a new electrode.
2.11. Electrode Lifespan
pH electrodes have a finite lifespan due to their inherent properties. How long
a pH electrode will last will depend on how it is cared and the solution it is
used to measure. Even if an electrode is not used it still ages. Electrode
demise can usually be characterized by a sluggish response, erratic readings
or a reading, which will not change. When this occurs an electrode can no
longer be calibrated. pH electrodes are fragile and have a limited lifespan.