Determination of Molecular and “Truly” Free Sulfur Dioxide in Wine: A Comparison of Headspace and Conventional Methods

Conventional methods such as the Ripper titration and Aeration-Oxidation (A-O) are employed widely for the analysis of sulfur dioxide (SO2) in wine. However, the free SO2 reported by these procedures is overestimated due to dissociation of weakly bound SO2 forms during the analysis, particularly from anthocyanin-bisulfite complexes. “Truly” free SO2 in wine can be determined from the headspace SO2 concentration of an equilibrated wine sample. A headspace SO2 method based on gas detection tubes (HS-GDT) was recently described but is not readily automated. While SPME gave poor precision in our hands, our new method, based on static headspace gas chromatography and sulfur chemiluminescence detection (HS-GC-SCD), is readily automated, and achieves high precision (