ISO 5523:1981

The determination of free sulphur dioxide consists in direkt iodometric titration of the product at a pH between 0,7 and 1, followed by blank titration of the product, freed from sulphur dioxide by boiling under reflux or by binding its free sulphur dioxide content with an exess of acetaldehyde or propioaldehyde. The bond sulphur dioxide is determined after titration of free compound, rendering of the produkt alkaline and titration of the sulphur dioxideliberated by hydrolysis with iodine in an acid medium.