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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.