TY - JOUR T1 - Determination of Molecular and “Truly” Free Sulfur Dioxide in Wine: A Comparison of Headspace and Conventional Methods JF - American Journal of Enology and Viticulture JO - Am J Enol Vitic. DO - 10.5344/ajev.2020.19052 SP - ajev.2020.19052 AU - Todd W. Jenkins AU - Patricia A. Howe AU - Gavin L. Sacks AU - Andrew L. Waterhouse Y1 - 2020/03/13 UR - http://www.ajevonline.org/content/early/2020/03/05/ajev.2020.19052.abstract N2 - 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 (<5%) and low limits of detection (0.033 mg/L molecular SO2, or approximately 1 mg/L free SO2 in wine at pH 3.5). When A-O, Ripper, HS-GC-SCD, and HS-GDT methods were compared on a diverse set of wine samples, the HS-GC method correlates to the HS-GDT method (r2 = 0.92) and achieves higher precision (RSD = 3.7), whereas HS-GC correlates well with A-O on white wines (r2 = 0.85, slope = 0.90) but was found to have a weaker correlation for red wines (r2 = 0.71, slope = 0.44). The GC’s flexibility for other procedures, stability, and low operating costs per sample make it attractive, and headspace methods have been shown to be better at predicting microbial stability in red wines. ER -