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The Determination Of Sulphur Dioxide Concentration By The Aspiration/Oxidation Method

• This method is referred to as the aspiration/oxidation method and also referred to as the "Rankin Method".
  
  
• The method relies on sulphur dioxide (SO₂) being aspirated or drawn out of a juice or wine sample, by a stream of air bubbled through the sample (see diagram ).
  
  
• The liberated SO₂ (sulphur dioxide) is carried across, by the air flow, to a pear shaped flask containing hydrogen peroxide (H₂O₂). (see diagram)
  
  
• The SO₂ is bubbled through and reacts immediately with the H₂O₂ (hydrogen peroxide) to form sulphuric acid (H₂SO₄) as per the following equation
  
  
• The H₂SO₄ (sulphuric acid) formed is non volatile and remains in the pear shaped flask
  
  
• The amount of H₂SO₄ formed is determined by titration using a solution of sodium hydroxide (NaOH) of known concentration.
  
  
• The amount of H₂SO₄ formed is an indication of, and indirectly related to, the amount of SO₂ liberated
  
  
• Free sulphur dioxide (FSO₂), bound (BSO₂) and total (TSO₂) can all be determined using this method
  
  
• More complicated and accurate methods are available but more prone to operator error.