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Study Notes: Preventative Maintenance of the pH Meter Electrode

The document MTH 66 SOP: pH Measurement is mainly concerned with the calibration and use of the pH meter to measure the pH of aqueous samples but it does contain the following brief details concerning the following:

If the pH meter is found not to be operating properly, inform the Senior Technician. Under supervision from the Senior Technician carry out necessary checks on the system such as special cleaning of the electrode.

If the meter continues to malfunction, contact the supplier for advice. If a visit from a service technician is required, unplug the instrument and place an ‘Unserviceable’ tag on it. Update the Calibration Log with details of the breakdown and service.

This Study Notes will cover those activities concerning preventative maintenance to the electrode to reduce the chances of equipment failure.

Glass Electrode

  1. The special glass bulb is easily contaminated or damaged by abrasion. Care is required in its use and storage.
  2. Where appropriate the glass electrode should be filled with KCl and be kept filled.
  3. The glass electrode should never be left dry and when not in use it should be stored in a solution of 4M KCl or a concentration matching that of the KCl in the electrode. This prevents dilution of the internal solution via osmosis.
  4. The glass electrode should never be stored in deionised water for any length of time as osmosis will occur.
  5. Perform readings as quickly as possible and do not leave the electrode in the sample solution.
  6. Do not immerse the electrode in the sample so that the level of the sample is above that of the liquid in the electrode.
  7. Short term storage between samples may be done in a pH buffer closest to the pH of the samples being tested.
  8. Liquids with a high concentration of solids lead to contamination of the electrode.
  9. Rinse electrodes with distilled water between samples and prior to storage.
  10. After rinsing, dab the electrode bulb to dry with a tissue – do not wipe as this will cause abrasive damage to the bulb.
  11. Electrodes do age and have a finite useful service life. Replace the electrode when performance deteriorates and cannot be restored.

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