Resumen de A Headspace Gas Detection Tube Method to Measure SO2 in Wine without Disrupting SO2 Equilibria

Jussara M. Coelho, Patricia A. Howe, Gavin L. Sacks

• The headspace gas detection tube (HS-GDT) method to measure molecular and free sulfur dioxide (SO2) in wine is a simple and inexpensive 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 in the wine 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 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 to 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 double the HS-GDT values in red wines. The difference in molecular SO2 values by A-O and HS-GDT correlated well with the estimated molecular SO2 decrease due to formation of anthocyanin-bisulfite adduct (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.