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Flow rate

• During FSO₂ determinations
  
  
  • The flow rate of one litre per minute (1 L/min.) is important as too high a flow rate will result in some of the BSO₂ (bound sulphur dioxide), in equilibrium with the FSO₂ (free sulphur dioxide), to be liberated as FSO₂.
    
    This will result in high, false readings.
    
    
  • A flow rate significantly faster then 1L/min, may result in a insufficient time being made available for the SO₂ aspirated to be able to react with the H₂O₂ (see equation).
    
    
  • Too low a flow rate can result in low, false readings due to the failure of all of the FSO₂ to be aspirated across.
    
    
  • The flow rate can be determined with a soap bubble flow meter.
    
    NOTE: the flow rate as well the 15 minute aspiration time are important for the above reasons.
    
    
    
• During BSO₂ and TSO₂ determinations
  
  
  • Too high a flow rate will not matter significantly as once all the SO₂ has been liberated, readings should stay static.
    
    
  • Too low a flow rate can result in low, false readings due to the possible failure of all of the SO₂ being aspirated across.