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Study Notes: Care and Maintenance of the pH Meter

There are a number of important factors to consider when looking at the care and maintenance of the pH meter. This Study Notes looks at these factors but does not cover aspects such as set up, calibration and use. These aspects are more properly covered in MTH 66 SOP: pH Measurement and Study Notes: Preventative Maintenance of the pH Meter Electrode.

Positioning:
The pH meter should be positioned on the laboratory bench as follows.

  1. On a level and stable surface.
  2. Away from undue vibration and moisture.
  3. If possible at a room temperature of about 25°C to avoid extremes of temperature.
  4. In a low dust environment - cover the meter when not in use.
  5. Set up so that the pH meter is easily accessible to the operator.

The electrode should always be stored in an appropriate solution.

Cleaning of the pH meter itself:

  1. The outside case of the pH meter should be cleaned using a mild detergent or disinfectant (e.g. 70% ethanol) if required.
  2. The area around the pH meter should be kept clean and any spills of samples or reagents cleaned up immediately. Special care should be exercised when cleaning up concentrated HCl (usually) or concentrated NaOH (usually) used for adjusting the pH of solutions.
  3. Any build up of salts on the top of the electrode near the filling well (if applicable) should be cleaned using water.
  4. All wires and contacts should be cleaned to avoid corrosion.

Cleaning and Restoration:

If contamination of the glass bulb is suspected, restoration can be attempted as follows.

  1. Soak electrode in 0.1M HCl or 0.1M HNO3 for 20 minutes.
  2. Or use a more aggressive solution of 10% bleach in water for 10 minutes.
  3. Oily or greasy deposits may be removed by detergents or methanol.
  4. Protein build up may be removed by 1% pepsin in 0.1M HCl for 5 minutes.
  5. After the cleaning stage, rinse the electrode in distilled water and replace the internal filling solution (4M KCl) if appropriate.

Storage:
When not in use the pH meter should be stored in a low dust, low moisture environment.
The electrode should always be stored in an appropriate solution.


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