2.5. IFU 7a
The IFU 7a method is a modified version of the Monier-Williams distillation, designed for the analysis of fruit juices. In a Lieb–Zacherl apparatus, 15mL of phosphoric acid was added to 50mL of the sample. The flask was heated to boiling temperature, so bound sulfites were released and gaseous sulfur dioxide was distilled into the receiver flask, which was equipped with 3mL of hydrogen peroxide solution (c = 0.3%), where SO2 was oxidized to sulfate. The resulting sulfuric acid was quantified by titration with sodium hydroxide solution (c = 0.01mol/L).