Acid-base titrations indirect aqueous

Sulfur dioxide (SO2) is generally measured using indirect methods. The AOAC describes a modified Monier Williams method, while the Codex standards and EC directive recommend the Tanner modified method. Both are based on similar principles, involving the distillation of the SO2 from an acidified aqueous suspension of the food. The evolved gas is subsequently trapped in hydrogen peroxide where it reacts to form sulfuric acid which is then titrated against dilute sodium hydroxide. 

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