TY - JOUR T1 - A Headspace Gas Detection Tube Method for Measurement of SO2 in Wine without Disruption of Sulfur Dioxide Equilibria JF - American Journal of Enology and Viticulture JO - Am. J. Enol. Vitic. DO - 10.5344/ajev.2015.14125 SP - ajev.2015.14125 AU - Jussara M. Coelho AU - Patricia A. Howe AU - Gavin L. Sacks Y1 - 2015/04/23 UR - http://www.ajevonline.org/content/early/2015/04/24/ajev.2015.14125.abstract N2 - The headspace gas detection tube (HS-GDT) method for measurement of molecular and free sulfur dioxide (SO2) in wine is a simple and low cost procedure using commercial industrial safety colorimetric tubes. A syringe is used to sample a wine and to create a closed headspace, which is expelled through the GDT after equilibrium is obtained. The vapor-phase concentration of SO2 (PSO2) is determined from the manufacturer’s printed markings, and then related to the molecular SO2 concentration based on Henry’s law coefficients or, more accurately, on calibration curves. Typical wine ethanol concentrations had a significant effect on the pKa of SO2, as has been previously reported, but no effect on Henry’s law coefficients; calibration curves in model wine and aqueous buffer yielded indistinguishable results when appropriate pKa values were used. Best results for calibration curves were achieved with 200 mL headspace of model wines (5–40 mg/L free SO2, equivalent to 0.14 to 1.12 mg/L molecular SO2), which yielded satisfactory linearity (r2 = .99), reproducibility (mean CV = 8% for molecular SO2 > 0.4 mg/L), and detection limits (0.21 mg/L molecular SO2). Molecular SO2 measured by HS-GDT and by aeration-oxidation (A-O) showed a strong correlation between methods for white and blush wines (r2 = 0.97) and a poor correlation for red wines (r2 = 0.72). A-O values averaged 2-fold higher than HS-GDT values in red wines. The difference in molecular SO2 values by A-O and HS-GDT was well correlated with estimated molecular SO2 decrease due to anthocyanin-bisulfite adduct formation (r2 = 0.936), supporting the hypothesis that dissociation of anthocyanin-bisulfite adducts occurs during A-O analysis. By not perturbing this equilibrium, HS-GDT accurately reports free and molecular SO2 values. ER -