Determination of Total Sulfur Dioxide (SO₂) in wine

The sulfur dioxide contained in a wine is made to react with an organic disulphide in order to form a colored compound, whose intensity, measured at 420 nm in end-point, is directly proportional to the concentration of total sulfur dioxide in the sample.

Sulfur dioxide (SO₂) is used in oenology mainly as preservative, but also for other purposes (for example for antiseptic, antioxidant, antioxidasic, solubilizing, combining and clarifying functions). Part of the SO₂ that is added as potassium metabisulfite to musts and wines undergoes a series of reactions. Therefore, after a short period of time, most of the sulfur dioxide reacts with some of the substances present, binds with them and forms addition compounds (combined sulfur dioxide) that are unable to express the typical properties of unbound molecules. Therefore, only the part that does not combine (free sulfur dioxide) plays an important role in preserving wine from oxidizing alterations and from some micro-organisms. This test can be used to determine the total content of SO₂ in wine, which is the sum of the free and combined sulfur dioxide fractions.

The calibration curve of CDR WineLab^®, obtained using reference methods.