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The Glass and Reference Electrodes of a pH Meter

Two electrodes are involved in the measurement of pH, the glass electrode and the reference electrode.

The Glass Electrode (see diagram).


• The glass electrode can also be referred to as the sensing, measuring, indicating, working or pH electrode.
  
  
• The glass electrode is a half cell consisting of -
  
  
  • an internal silver/silver chloride (Ag/AgCl) electrode/wire
    
    
  • an internal, pH neutral (pH 7) solution of concentrated potassium chloride (KCl)
    
    
  • a sealed glass outer body with a special pH sensitive glass bulb joined at the end.
    
    This special glass bulb is able to develop an electric potential corresponding to the solutions' pH. (see explanation).
    
    
  • The reference electrode is usually incorporated into the glass/pH electrode to form a compound or combination electrode
    
    
  • Requires some care and maintinance
    
    
    
The Reference Electrode.(see diagram)


• The reference electrode is a half cell completing the pH electrode pair.
  
  
• The reference electrode -
  
  
  • consists of an internal silver/silver chloride (Ag/AgCl) electrode /wire within an inert glass tube filled with an electrolyte of saturated potassium chloride (KCL) solution.
    
    
  • completes the circuit (see diagram), with the internal electrolyte solution, (KCl), making contact with the sample solution usually via a porous glass frit (see other means)
    
    
  • provides a stable, known reference potential, against which the glass/pH electrode can be measured.
    
    
  • is usually incorporated into the glass/pH electrode to form a compound or combination electrode
    
    
  • Requires some care and maintinance
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
Temperature Probe.


• The temperature probe usually consists of a single separate thin probe that connects to your pH meter.
  
  
• It will measure the temperature of the solution and will be read by your pH meter and use the reading to calculate any compensation required for the temperature.
  
  
• It will not however, compensate for the variations of the true pH, with temperature, of the pH buffer solution, which will have to be read of your pH charts.